阅读说明：本技术 通过Claus尾气的部分或完全催化氧化来生产单质硫的方法 (Process for the production of elemental sulphur by partial or complete catalytic oxidation of a Claus tail gas ) 是由 M·特莱夫森 M·莫勒霍杰 M·利克 于 2020-05-06 设计创作，主要内容包括：本发明涉及一种用于由包含H<Sub>2</Sub>S的原料气和硫酸的料流生产单质硫的方法和工艺设备。所述方法和工艺设备允许设计和操作Claus尾气硫酸设备,大大减少了辅助燃料的消耗,并减少了用于SO<Sub>2</Sub>氧化和硫酸冷凝步骤的设备尺寸和成本。(The invention relates to a catalyst for synthesis of alpha-olefins from alpha-olefins 2 A process and a plant for the production of elemental sulphur from a feed gas of S and a stream of sulphuric acid. The method and process equipment allowThe Claus tail gas sulfuric acid equipment is designed and operated, SO that the consumption of auxiliary fuel is greatly reduced, and the consumption of SO 2 The equipment size and cost of the oxidation and sulfuric acid condensation steps.)

1. A catalyst for the treatment of a mammal comprising from 15 vol%, 20 vol%, 30 vol%, 40 vol% or 50 vol% to 99 vol% or 100 vol% H₂A process for the production of elemental sulphur from a feed gas of S and a stream of sulphuric acid, the process comprising the steps of:

a. providing a Claus reaction furnace feed stream comprising an amount of said feed gas, an amount of sulfuric acid, an amount of oxygen, and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric with respect to the Claus reaction;

b. directing the Claus reactor feed stream to a reactor operating at an elevated temperature, e.g., greater than 900 ℃, providing a Claus converter feed gas;

c. cooling the Claus converter feed gas to provide a cooled Claus converter feed gas and optionally withdrawing elemental sulfur from the gas;

d. directing the cooled Claus converter feed gas into contact with a material that is catalytically active in a Claus reaction;

e. optionally withdrawing a Claus tail gas and elemental sulphur by cooling the effluent from said material catalytically active in the Claus reaction;

f. directing a stream comprising the Claus tail gas, oxygen, and optionally a fuel as a feed gas to a plant for sulfur oxidation to provide SO₂Converter feed gas;

g. directing the SO₂Converter feed gas and in-situ SO₂By oxidation to SO₃In contact with catalytically active materials to provide an SO-rich atmosphere₃The gas of (4);

h. by reacting SO₃Absorption into sulfuric acid or SO₃Hydrating said SO-enriched mixture₃Is converted into concentrated sulfuric acid and cooledAnd condensing the sulfuric acid;

i. recycling at least a portion of the sulfuric acid produced to the Claus reaction furnace,

characterized in that a quantity of combustible material present in the Claus tail gas is oxidized at an inlet temperature below 400 ℃ in the presence of a material having catalytic activity in the oxidation of sulphur.

2. The method of claim 1, wherein the concentrated sulfuric acid has a concentration of at least 80 w/w% or 90 w/w% of H₂SO₄。

3. The process according to claim 1 or 2, wherein the amount of sulphur in the stream of concentrated sulphuric acid is higher than 1%, 3% or 5% of the total amount of elemental sulphur withdrawn from the process and lower than 17%, 21% or 25% of the total amount of elemental sulphur withdrawn from the process.

4. The method of claim 1, 2, or 3, wherein an amount, such as less than 40% or 50%, of the Claus tail gas is directed to an incinerator, thereby providing a combusted Claus tail gas that is combined with an additional amount of Claus tail gas, such as a remaining amount of Claus tail gas.

5. The process of claim 4, wherein the combined combusted Claus tail gas and the additional amount of Claus tail gas are at least 2 vol% O₂Is conducted to a homogeneous reaction zone having a temperature in excess of 400 ℃ and provides a residence time of at least 0.5 seconds.

6. The process of claim 5, wherein a turbulizer is installed in the homogeneous reaction zone.

7. The process according to claims 5 and 6, wherein a steam generating heat exchanger is provided at the outlet of the homogeneous reaction zone.

8. The method of claim 4, 5, 6 or 7 wherein the amount of Claus tail gas directed to the incinerator is controlled such that the temperature rise of the oxidation of the remaining combustibles in the Claus tail gas from the catalytic section of the plant for sulfur oxidation is maintained below 100 ℃, 150 ℃ or 200 ℃.

9. The process of claim 1, 2, or 3 wherein the Claus tail gas is not directed to a non-catalytic oxidation unit.

10. The method of claim 9 wherein a quantity of fuel and oxidant are directed to an incinerator, wherein the method can be reconfigured during operation to direct all of the Claus tail gas to an incinerator.

11. The process of claim 9 or 10 wherein the temperature rise in the Claus tail gas catalytic oxidation reactor is maintained below 100 ℃, 150 ℃ or 200 ℃ by diluting the Claus tail gas catalytic oxidation reactor feed gas with an amount of recycled oxidized Claus tail gas and/or an amount of oxidant.

12. The process of claim 10 or 11 wherein one or both of the Claus tail gas catalytic oxidation reactors is an internally cooled reactor.

13. The process of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 wherein the oxidant and optionally the volume of process gas are added to the Claus tail gas in a ratio such that the mixture of Claus tail gas, optional volume of process gas, and oxidant is below the Lower Flammability Level (LFL) of the mixture.

14. The process of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 wherein the oxidizing agent is added to the Claus tail gas in two or more stages in a ratio such that the mixture of Claus tail gas, optional process gas volume, and oxidizing agent is below the Limiting Oxygen Concentration (LOC) of the mixture.

15. A process apparatus, comprising: a Claus reaction furnace, a Claus waste heat boiler, a Claus conversion section, a device for sulfur oxidation and a sulfuric acid section;

wherein the Claus reaction furnace has a feedstock inlet, a sulfuric acid inlet, and an outlet;

the Claus waste heat boiler has a gas inlet, a gas outlet, and an elemental sulfur outlet;

the Claus conversion section is provided with a gas inlet, a gas outlet and an elemental sulfur outlet;

said means for sulfur oxidation comprises a material that is catalytically active in sulfur oxidation and has an inlet and an outlet; and is

The sulfuric acid working section is provided with a gas inlet, a gas outlet and a sulfuric acid outlet;

and wherein the feedstock inlet of the reaction furnace is configured to receive a feedstock gas and an oxidant;

wherein the outlet of the Claus reaction furnace is configured to be in fluid communication with the gas inlet of the Claus waste heat boiler;

wherein a gas outlet of a Claus waste heat boiler is configured to be in fluid communication with a gas inlet of the Claus conversion section;

wherein the inlet of the means for sulfur oxidation is configured to be in fluid communication with the gas outlet of the Claus conversion section;

and wherein the outlet of the device for sulphur oxidation is configured to be in fluid communication with a gas inlet of a sulphuric acid section,

characterized in that the sulfuric acid outlet of the sulfuric acid section is in fluid communication with the sulfuric acid inlet of the Claus reaction furnace.

16. The process plant of claim 15 wherein the reaction furnace is divided into a Claus reaction zone having a feed gas inlet, O and a sulfuric acid evaporation zone₂An inlet, an optional fuel inlet, and an exhaust gas outlet; and the sulfuric acid evaporation zone has an off-gas inlet, a sulfuric acid inlet, and an outlet, and wherein the off-gas outlet of the Claus reaction furnace zone is configured to be in fluid communication with the off-gas inlet of the sulfuric acid evaporation zone.

17. The process unit of claim 16 wherein the Claus reaction zone and/or the sulfuric acid evaporation zone comprises a turbulizer.

18. Process equipment according to claim 16 or 17, wherein the sulphuric acid evaporation zone comprises impingement means, such as impingement walls or chambers filled with inert material.

19. The process unit according to any one of claims 16 to 18, wherein the sulfuric acid evaporation zone comprises a two-phase nozzle or a pressure nozzle using compressed air.

20. The process unit according to any one of claims 15 to 19, wherein the means for sulphur oxidation is an incinerator, a catalytic plant or a combination thereof.

21. The process plant according to any one of claims 15 to 20, wherein the sulfuric acid section comprises a section configured to subject SO₂Oxidation to SO₃Followed by a catalytic section configured to hydrate the SO by condensation₃To provide sulfuric acid, or by passing SO₃An absorber for absorption in sulfuric acid to provide sulfuric acid.

22. The process unit according to claim 15, wherein said means for sulphur oxidation is an incinerator and said process unit further comprises a bypass connecting the gas outlet of said Claus conversion section with the outlet of said incinerator.

23. The process plant of claim 22 further comprising a homogeneous reaction zone downstream of said incinerator and said bypass.

24. The process unit according to claim 23, wherein a turbulizer is installed in the homogeneous reaction zone.

25. A process unit according to claim 23 or 24 wherein a steam generating heat exchanger is provided at the outlet of the homogeneous reaction zone.

26. A process unit according to claim 15, wherein an intermediate storage tank is provided between the sulfuric acid outlet of the sulfuric acid section and the sulfuric acid inlet of the Claus reaction furnace.

27. A process plant according to any one of claims 15 to 26, wherein the sulphuric acid section comprises SO₂A converter and a sulfuric acid condenser.

Technical Field

The invention relates to a device for sealingH₂A process for the conversion of S to elemental sulphur and sulphuric acid, optionally with an adjustable ratio between elemental sulphur and sulphuric acid.

Background

H₂S is a common by-product of many processes including hydrodesulfurization of refinery streams, natural gas processing, and viscose production. It is desirable to use H₂S is converted before being discharged into the atmosphere, since H₂S is highly toxic, odorous and poses a challenge to the environment.

In refinery processes, in addition to producing the well-known high concentrations of H₂Outside the S gas, it is also generally possible to generate a so-called sour water stripper, which contains almost equal amounts of H₂S、H₂O and NH₃。

Especially in refineries, for H reduction₂The process of choice for S has been the Claus process, which has been widely known and optimized over the last eighty years. Claus Process by H₂Substoichiometric combustion of S in a Claus reactor to form SO₂To provide a Claus converter feed gas. The subsequent Claus process will convert H₂S and SO₂Converted to form elemental sulphur, which can be condensed and withdrawn.

Typically, the removal efficiency of the Claus process is 95% to 98%, which is insufficient to meet environmental requirements. Therefore, it is common practice to carry out tail gas treatment after the Claus process to reduce the sulfur by more than 99%. The tail gas treatment is typically a sulfuric acid plant, which introduces the requirements for treating sulfuric acid.

It has now been determined that sulfuric acid can be recycled to the Claus reaction furnace where sulfur formation can be promoted, and in addition, provides the opportunity to optimize the size and operating costs of the Claus reaction and Claus tail gas processing equipment. It has also been determined that configurations of sulfuric acid plants having at least some amount of catalytic oxidation of the Claus tail gas have additional benefits in terms of energy consumption.

In WO 2012/152919A 1, a sulfuric acid process for treating Claus tail gas is proposed, wherein H in Claus tail gas is described₂S to H₂SO₄Transformation of (2). The method comprises the following steps:

1. sub-stoichiometric oxidation

Claus transformation

3. Reduced sulfur species (H) in Claus tail gas at 400-₂S) oxidation

4.SO₂Catalytic oxidation to SO₃

5. Condensation of sulphuric acid

It has been recognized that H₂SO₄The product is not always desirable and it is recommended that the sulfuric acid be recycled to the upstream Claus reaction furnace or H as described above₂And S oxidation step. However, the recycling of sulfuric acid is only considered as a reduction of sulfuric acid and H has not been evaluated yet₂SO₄The consequence of recycling on the wet sulfuric acid or Claus process, i.e. H is not recognized₂SO₄Recycle requires a reduction in O directed to the Claus reactor₂In amounts, the advantageous effects on the Claus process and the sulfuric acid process are not achieved.

It is also recognized in WO 2012/152919A 1 that in a Claus reaction furnace and H₂Auxiliary fuels may be required in both S oxidation steps to achieve the desired operating temperature without realizing the use of feed gas as H in a sulfuric acid process₂The beneficial effect of S-oxidized auxiliary fuel.

Thus, H₂SO₄The proposal for recycle to the Claus reactor does not itself provide a process that can be performed, but requires other process modifications.

Disclosure of Invention

According to the invention, a catalyst is provided with increased conversion and thermal efficiency₂A process for the conversion of S to elemental sulphur, wherein the Claus process is combined with a sulphuric acid process. According to the method, sulfuric acid produced in a sulfuric acid process for treating a Claus tail gas is recycled to the Claus reaction furnace for decomposition and elemental sulfur production.

In broad terms, the invention relates to a composition for the treatment of a mammal comprising from 15 vol%, 20 vol%, 30 vol%, 40 vol% or 50 vol% to 99 vol% or 100 vol% H₂Feed gas of S and stream of sulfuric acid to produce monoA process for producing elemental sulfur, the process comprising the steps of:

a. providing a Claus reaction furnace feed stream comprising an amount of said feed gas, an amount of sulfuric acid, an amount of oxygen, and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric with respect to the Claus reaction;

b. directing the Claus reactor feed stream to a reactor operating at an elevated temperature, e.g., greater than 900 ℃, providing a Claus converter feed gas;

c. cooling the Claus converter feed gas to provide a cooled Claus converter feed gas and optionally withdrawing elemental sulfur from the gas;

d. directing the cooled Claus converter feed gas into contact with a material that is catalytically active in a Claus reaction;

e. optionally withdrawing a Claus tail gas and elemental sulphur by cooling the effluent from said material catalytically active in the Claus reaction;

f. directing a stream comprising the Claus tail gas, oxygen, and optionally a fuel as a feed gas to a plant for sulfur oxidation, providing SO₂Converter feed gas;

g. directing the SO₂Converter feed gas and in-situ SO₂By oxidation to SO₃In contact with catalytically active materials to provide an SO-rich atmosphere₃The gas of (4);

h. by reacting SO₃Absorption into sulfuric acid or SO₃Hydrating said SO-enriched mixture₃The gas is converted into concentrated sulfuric acid, and the sulfuric acid is cooled and condensed;

i. recycling at least a portion of the sulfuric acid produced to the Claus reaction furnace,

characterized in that an amount of combustible material in the Claus tail gas is oxidized at an inlet temperature below 400 ℃ in the presence of a material that is catalytically active in the sulfur oxidation, with the associated benefits of allowing the design and operation of Claus tail gas sulfuric acid plants, greatly reducing the consumption of auxiliary fuels, and reducing the amount of material used for SO oxidation₂The equipment size and cost of the oxidation and sulfuric acid condensation steps.

Another aspect relates toA process apparatus, comprising: a Claus reaction furnace, a Claus waste heat boiler, a Claus conversion section, a device for sulfur oxidation and a sulfuric acid section, wherein the Claus reaction furnace has a feedstock inlet, a sulfuric acid inlet and an outlet; the Claus waste heat boiler is provided with a gas inlet, a gas outlet and an elemental sulfur outlet; the Claus conversion section is provided with a gas inlet, a gas outlet and an elemental sulfur outlet; the apparatus for sulfur oxidation comprises a material having catalytic activity in sulfur oxidation and having an inlet and an outlet; the sulfuric acid working section is provided with a gas inlet, a gas outlet and a sulfuric acid outlet; and wherein the feed inlet of the reaction furnace is configured to receive a feed gas and an oxidant; wherein the outlet of the Claus reaction furnace is configured to be in fluid communication with the inlet of the Claus waste heat boiler; wherein the outlet of the Claus waste heat boiler is configured to be in fluid communication with an inlet of a Claus conversion section; wherein the inlet of the means for sulfur oxidation is configured to be in fluid communication with the gas outlet of the Claus conversion section; and wherein the outlet of the means for sulphur oxidation is arranged in fluid communication with the inlet of a sulphuric acid section, characterized in that the sulphuric acid outlet of the sulphuric acid section is in fluid communication with the sulphuric acid inlet of said Claus reaction furnace, with the associated benefits of allowing the design and operation of a Claus tail gas sulphuric acid plant, substantially reducing the consumption of auxiliary fuels, and reducing the use of SO for SO₂The equipment size and cost of the oxidation and sulfuric acid condensation steps; and such process equipment has high thermal efficiency and low auxiliary fuel consumption due to the catalytic oxidation of the Claus tail gas at low temperatures.

Brief description of the drawings

FIG. 1 depicts a Claus plant layout comprising a sulfuric acid tail gas plant, incineration of the Claus tail gas, and recycling of acid to the Claus reaction furnace.

FIG. 2 depicts a Claus plant layout that includes a partial catalytic sulfuric acid tail gas plant and the recycle of acid to the Claus reaction furnace.

FIG. 3 depicts a Claus plant layout that includes a fully catalytic sulfuric acid tail gas plant and the recycle of acid to the Claus reaction furnace.

Detailed Description

For the purposes of this application, it should be derived in the hypothesis of the feed gasN, H, C, S and the product of O is N₂、H₂O、CO₂And SO₂The stoichiometric amount of oxygen is defined in the case of (2). If less than the stoichiometric amount of oxygen (also referred to as sub-stoichiometric) is present, this means that not all feed components are fully oxidized. For Claus gas feed, this means that after sub-stoichiometric combustion/reaction, the process gas may contain unconverted H from the feed stream₂S、NH₃And hydrocarbons and in O₂H formed in deficient environment₂CO, COS and CS₂。

For the purposes of this application, fuel shall be defined as a composition which when treated with O₂Will form N when oxidized₂、H₂O、CO₂And SO₂As a reaction product and releases a large amount of energy by reaction. Hydrocarbons (e.g. natural gas, which contains CH)₄And C₂H₆) And H₂The mixture of S is typically a fuel gas, but the fuel gas may also contain CO, NH₃And H₂。

For the purposes of this application, oxygen (O)₂) Is understood to comprise O₂Such as air, high oxygen air and pure oxygen, but may also be a stream comprising O₂The process gas of (1).

For the purposes of this application, a device for sulfur oxidation should be understood to be any device that receives a reduced sulfur compound (e.g., H)₂S, COS and CS₂) Or elemental sulphur and converting it to SO₂The process equipment of (1). Such means for sulfur oxidation may be an incinerator, a catalytic device, or a combination thereof.

For the purposes of this application, combustible is to be understood as reduced sulfur compounds, elemental sulfur or fuels which can be oxidized to H in the presence of excess oxygen in the flame₂O、CO₂Or SO₂Is composed of H₂S，COS、CS₂、CH₄、NH₃CO and H₂。

For the purposes of this application, a sulfuric acid section is understood to be intended to contain SO₂To sulfuric acid. Can be combined withThe sulfuric acid section is implemented by SO₂Oxidation to SO₃Then SO hydrated by condensation₃To provide sulfuric acid, or by passing SO₃An absorber for providing sulfuric acid by absorption in sulfuric acid, but for removing SO from the gas₂Other plants for producing sulphuric acid (e.g. H)₂O₂Scrubbers) are also known to those skilled in the art.

For the purposes of this application, a sulfuric acid plant is understood to be a plant for sulfur oxidation and a subsequent sulfuric acid section for receiving sulfur compounds (e.g. H)₂S、SO₂COS and CS₂) Or elemental sulfur and converting it to sulfuric acid.

For the purposes of this application, a Claus reaction furnace can be described as comprising two zones: a reaction furnace zone and a sulfuric acid evaporation zone. The names of these zones are merely the names of the individual zones and are not exclusive descriptions of the chemical reactions that take place therein.

For the purposes of this application, a homogeneous reaction zone may be described as a space or compartment in which the temperature, O₂The combination of the concentration and the residence time of the process gas passing through the space or compartment allows a conversion of more than 80% of part or all of the one or more reactive compounds comprised in the process gas.

In broad terms, the invention relates to a composition for the treatment of a mammal comprising from 15 vol%, 20 vol%, 30 vol%, 40 vol% or 50 vol% to 99 vol% or 100 vol% H₂A process for producing elemental sulfur from a feed gas of S and a stream of sulfuric acid, the process comprising the steps of:

a. providing a Claus reaction furnace feed stream comprising an amount of said feed gas, an amount of sulfuric acid, an amount of oxygen, and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric with respect to the Claus reaction;

b. directing the Claus reactor feed stream to a reactor operating at an elevated temperature, e.g., greater than 900 ℃, providing a Claus converter feed gas;

c. cooling the Claus converter feed gas to provide a cooled Claus converter feed gas and optionally withdrawing elemental sulfur from the gas;

d. directing the cooled Claus converter feed gas into contact with a material that is catalytically active in a Claus reaction;

e. optionally withdrawing a Claus tail gas and elemental sulphur by cooling the effluent from said material catalytically active in the Claus reaction;

f. directing a stream comprising the Claus tail gas, oxygen, and optionally a fuel as a feed gas to a plant for sulfur oxidation, providing SO₂Converter feed gas;

g. directing the SO₂Converter feed gas and in-situ SO₂By oxidation to SO₃In contact with catalytically active materials to provide an SO-rich atmosphere₃The gas of (4);

h. by reacting SO₃Absorption into sulfuric acid or SO₃Hydrating said SO-enriched mixture₃The gas is converted into concentrated sulfuric acid, and the sulfuric acid is cooled and condensed;

i. recycling at least a portion of the sulfuric acid produced to the Claus reaction furnace,

characterized in that an amount of combustible material in the Claus tail gas is oxidized at an inlet temperature below 400 ℃ in the presence of a material that is catalytically active in the sulfur oxidation, with the associated benefits of allowing the design and operation of Claus tail gas sulfuric acid plants, greatly reducing the consumption of auxiliary fuels, and reducing the amount of material used for SO oxidation₂The equipment size and cost of the oxidation and sulfuric acid condensation steps.

In another embodiment, the concentrated sulfuric acid has a concentration of at least 80 w/w% or 90 w/w% H₂SO₄With the associated benefit that this concentrated sulfuric acid provides O for the Claus reaction₂While avoiding excessive evaporation of water due to the use of lower concentrations of sulfuric acid.

In another embodiment, the amount of sulfur in the stream of concentrated sulfuric acid is above 1%, 3% or 5% and below 17%, 21% or 25% of the total amount of elemental sulfur withdrawn from the process, with the associated benefit that this amount of concentrated sulfuric acid provides O for the Claus reaction₂While avoiding the excessive heat required for the evaporation of sulfuric acidAmount of the compound (A).

In another embodiment, a quantity (e.g., less than 40% or 50%) of the Claus tail gas is directed to an incinerator, thereby providing a combusted Claus tail gas, which is combined with an additional quantity of Claus tail gas (e.g., a remaining quantity of Claus tail gas), with the associated benefit of providing a more stable hot Claus tail gas oxidation for incinerators that are not operational at the sulfuric acid plant, and a substantially reduced quantity of auxiliary fuel.

In another embodiment, the combined combusted Claus tail gas and the additional amount of Claus tail gas are at least 2 vol% O₂Is conducted to a homogeneous reaction zone having a temperature in excess of 400 ℃ and provides a residence time of at least 0.5 seconds, with the associated benefit of energy efficient oxidation of a quantity of Claus tail gas at moderate temperatures, thereby reducing the volume of catalytically active material required and increasing the temperature in the reactor containing the catalytically active material.

In another embodiment, a turbulizer is installed in the homogeneous reaction zone with the associated benefit of increasing the conversion in the homogeneous reaction zone.

In another embodiment, providing a steam generating heat exchanger at the outlet of the homogeneous reaction zone has the associated benefit of providing high thermal efficiency of the overall process and stable process gas temperatures for the downstream sulfuric acid section.

In another embodiment, controlling the amount of Claus tail gas directed to the incinerator such that the temperature rise of the oxidation of the remaining combustibles in the Claus tail gas from the catalytic section of the plant for sulfur oxidation remains below 100 ℃, 150 ℃ or 200 ℃, has the associated benefit of ensuring that the catalyst operates efficiently and for a long period of time.

In another embodiment, not directing the Claus tail gas to the non-catalytic oxidation unit has the associated benefit of avoiding operation of the Claus tail gas incinerator, thereby avoiding the need to overheat the Claus tail gas prior to oxidation in the incinerator by, for example, adding a secondary fuel (which would increase operating costs and increase equipment costs due to higher flow rates).

In another embodiment, a quantity of fuel and oxidant is directed to the incinerator, wherein the process can be reconfigured during operation to direct all of the Claus tail gas to the incinerator, with the associated benefit of being able to continue operation with the sulfuric acid section of the Claus tail gas treatment plant forced shut down.

In another embodiment, by diluting the Claus tail gas catalytic oxidation reactor feed gas with an amount of recycled oxidized Claus tail gas and/or an amount of oxidant, the temperature rise in the Claus tail gas catalytic oxidation reactor is maintained below 150 ℃ to 200 ℃, with the associated benefit of ensuring effective and long term operation of the catalyst.

In another embodiment, one or both of the Claus tail gas catalytic oxidation reactors are internally cooled reactors, with the associated benefit of simplifying the control scheme, especially for feedstocks with high variability.

In another embodiment, the oxidant and optional process gas volume are added to the Claus tail gas in a ratio such that the mixture of Claus tail gas, optional process gas volume, and oxidant is below the Lower Flammability Level (LFL) of the mixture, with the associated benefit of safe operation at high efficiency.

In another embodiment, the oxidant is added to the Claus tail gas in two or more stages in a ratio such that the mixture of Claus tail gas, optional process gas volume, and oxidant is below the Limiting Oxygen Concentration (LOC) of the mixture, with the associated benefit of safe operation at high efficiency.

Another aspect relates to a process apparatus comprising: a Claus reaction furnace, a Claus waste heat boiler, a Claus conversion section, a device for sulfur oxidation and a sulfuric acid section, wherein the Claus reaction furnace has a feedstock inlet, a sulfuric acid inlet and an outlet; the Claus waste heat boiler is provided with a gas inlet, a gas outlet and an elemental sulfur outlet; the Claus conversion section is provided with a gas inlet, a gas outlet and an elemental sulfur outlet; the apparatus for sulfur oxidation comprises a material having catalytic activity in sulfur oxidation and having an inlet and an outlet; sulfuric acid working section toolA gas inlet, a gas outlet and a sulfuric acid outlet are arranged; and wherein the feed inlet of the reaction furnace is configured to receive a feed gas and an oxidant; wherein the outlet of the Claus reaction furnace is configured to be in fluid communication with the inlet of the Claus waste heat boiler; wherein the outlet of the Claus waste heat boiler is configured to be in fluid communication with an inlet of a Claus conversion section; wherein the inlet of the means for sulfur oxidation is configured to be in fluid communication with the gas outlet of the Claus conversion section; and wherein the outlet of the means for sulphur oxidation is arranged in fluid communication with the inlet of a sulphuric acid section, characterized in that the sulphuric acid outlet of the sulphuric acid section is in fluid communication with the sulphuric acid inlet of said Claus reaction furnace, with the associated benefits of allowing the design and operation of a Claus tail gas sulphuric acid plant, substantially reducing the consumption of auxiliary fuels, and reducing the use of SO for SO₂The equipment size and cost of the oxidation and sulfuric acid condensation steps; and such process equipment has high thermal efficiency and low auxiliary fuel consumption due to the catalytic oxidation of the Claus tail gas at low temperatures.

In another embodiment, the Claus reaction furnace is divided into a Claus reaction furnace zone and a sulfuric acid vaporization zone, wherein a quantity of feed gas, a quantity of O, and a quantity of oxygen are introduced into the Claus reaction furnace zone₂And optionally a quantity of fuel to the Claus reaction furnace zone, providing a Claus reaction furnace zone off-gas, and directing the Claus reaction furnace zone off-gas and a quantity of sulfuric acid to a sulfuric acid evaporation zone, has the associated benefits that the process involves injecting sulfuric acid in a separate sulfuric acid evaporation zone, allowing high temperature combustion of the feed gas (including impurities) without cooling due to vaporization and decomposition of the sulfuric acid, and providing an energy efficient combination of Claus and Claus tail gas plants.

In another embodiment, the temperature in the outlet of the reaction furnace zone is 50-500 ℃, preferably 50-200 ℃ higher than the temperature at the outlet of said sulfuric acid evaporation zone, with the associated benefits of providing energy efficient cooling and less need for heat exchange equipment.

In another embodiment, the split of the feed gas into a reactor zone feed directed to the reactor zone and a sulfuric acid evaporation zone feed directed to the sulfuric acid evaporation zone has the associated benefit of enabling independent control of the temperature of the reactor zone and the sulfuric acid evaporation zone.

In another embodiment, the ratio between the above-described furnace zone feed and sulfuric acid vaporization zone feed is controlled to maximize the thermal destruction of impurities present in the furnace zone, typically by maximizing the temperature in the furnace zone.

In another embodiment, the average process gas residence time in the Claus reaction furnace is less than 5 seconds, more preferably less than 2 seconds, with the associated benefit that such a reaction furnace is of suitable size while having sufficient time to vaporize sulfuric acid, and desirably to convert H₂Conversion of S to SO₂Partial chemical conversion and destruction of impurities.

In another embodiment, the reactor zone and/or the sulfuric acid evaporation zone comprises a turbulizer, with the associated benefit of narrowing the residence time distribution in the reactor zone and the sulfuric acid evaporation zone.

In another embodiment, the sulfuric acid evaporation zone comprises impingement means, such as impingement walls or chambers filled with inert material, with the associated benefit of breaking down the droplets by collision to ensure that no liquid H is present in the Claus converter feed₂SO₄。

In an alternative process, steps (d) and (e) are carried out 2-5 times in sequence, with the associated benefit that higher conversions can be achieved in the process.

In another embodiment, the material that is catalytically active in the Claus reaction comprises an activated aluminum (III) oxide or titanium (IV) oxide, with the associated benefit that such material provides an efficient process for producing elemental sulfur.

In another embodiment, step (d) is carried out at a pressure of from 200mbarg to 700mbarg, a temperature of from 200 ℃ to 350 ℃ and 800Nm³/h/m³To 3000Nm³/h/m³With the associated benefit that such conditions are effective for the production of elemental sulphur.

In another embodiment, step (d) is carried out at a temperature of from 100 ℃ to 150 ℃, and step (e) comprises the steps of: periodically heating said catalytically active in the Claus reactionMaterials to allow removal of condensed elemental sulfur in either the liquid or vapor phase have the associated benefit that low temperatures favor SO₂And H₂The very high conversion of S to sulphur, not only because of the low temperature, but also because the reaction products have been removed, thus providing even better conditions for high conversion.

In another embodiment, the reducing is performed with SO₂Conversion to SO₃Wherein the catalytically active material comprises vanadium, has the associated benefit that such material provides an efficient process for the production of sulphuric acid.

In another embodiment, said step (g) is carried out at a pressure of 50mbar g to 200mbar g, a temperature of 380 ℃ to 520 ℃ and 800Nm per catalyst bed³/h/m³To 1500Nm³/h/m³With the associated benefit that such conditions are conducive to the conversion of SO₂Oxidation to form SO₃Is effective.

In another embodiment, the amount of sulfur in the recycle stream of sulfuric acid is greater than 1%, 3%, or 5% and less than 17%, 21%, or 25% of the total amount of elemental sulfur withdrawn from the process. A recycle above the lower limit has the benefit of providing a reduction in the volume of process gas, while a recycle below the upper limit avoids the situation where additional fuel must be added to the reactor zone, resulting in additional process volume and operating costs.

In another embodiment, the sulfuric acid in the recycle stream of sulfuric acid is atomized in the sulfuric acid evaporation zone in a two-phase nozzle or pressure nozzle using compressed air, and wherein the residence time in the sulfuric acid evaporation zone is at least 0.5 seconds, 1 second, or 1.5 seconds, with the associated benefit that such residence time is sufficient to completely evaporate the sulfuric acid droplets.

In another embodiment, the residence time in the Claus reactor zone is at least 0.5 seconds or 1 second, with the associated benefit of allowing for destruction of, for example, hydrocarbons or NH at elevated temperatures₃And ensures that the downstream Claus catalytic reactor and the sulfur condenser operate without problems.

In another embodiment, the directing isMolar ratio H of the components to the reaction furnace zone₂S:O₂At least 2.5, with the associated benefit of being due to the presence of hydrogen from H₂SO₄Such low oxygen feed is capable of achieving H₂S to SO₂Partial conversion of the sub-stoichiometry of (a) with addition of the remaining O₂To obtain the desired H of 2.0 in the Claus tail gas₂S:SO₂And (4) the ratio.

In another embodiment, cooling and directing a quantity of gas in the process to an upstream location to control the process temperature has the associated benefit of enabling active control of the temperature of the highly exothermic process.

In another embodiment, preheating one or more streams directed to the Claus reaction furnace by heat exchange with a hot process stream has the associated benefit of minimizing or eliminating the need for auxiliary fuel to reach the desired temperature for vaporizing sulfuric acid and feedstock conversion.

In another embodiment, preheating one or more streams directed to the means for sulfur oxidation by heat exchange with a hot process stream has the associated benefit of minimizing or avoiding convection to the stream for oxidation of sulfur compounds to SO₂Then adding SO₂Oxidation to SO₃The desired temperature of the auxiliary fuel.

In another embodiment, the means for sulfur oxidation is a combination of thermal oxidation and catalytic oxidation processes, with the associated benefit that Claus tail gas oxidation has significantly reduced auxiliary fuel consumption and oxidized Claus tail gas flow while being robust to variations in the concentration of combustibles in the Claus tail gas.

In another embodiment, the cooling for SO is by heat exchange (e.g., inter-bed heat exchange or internally cooled catalytic reactor)₂Oxidation to SO₃Or H is₂The oxidation of at least one of the catalytically active materials of S to elemental sulphur and/or at least one product taken from one of the catalytically active materials has the associated advantage of being able to pass through an inter-bed heat exchange or with a tubular or hot plate cooling circuitInternally cooled catalytic reactors (e.g., boiling water reactors) enable active control of the temperature of highly exothermic processes.

The present invention describes a combination of the Claus process and the sulfuric acid process that can efficiently produce the amount of sulfuric acid required by the process equipment, or even avoid the production of sulfuric acid and convert excess sulfuric acid to elemental sulfur, which can be transported to other locations.

To achieve maximum conversion to elemental sulfur, 1/3H must be added₂Conversion of S to SO₂。

H₂S+1.5O₂->SO₂+H₂O (1)

H is controlled by controlling the amount of oxygen in the reaction furnace zone₂S and SO₂The stoichiometric ratio therebetween. The oxygen is usually supplied from the atmosphere, but may also be highly oxygenated air, even pure O₂。

The oxygen added to the reactor zone must also take into account the NH in the feed stream₃、CO、H₂And the amount of hydrocarbons.

If the combustion temperature in the reactor zone is below 1100 deg.C, for example NH₃The transformation of (a) may not be complete. As a result, Claus converter feed gas may form ammonium salts (e.g., (NH) that may plug the Claus condenser₄)₂SO₄And (NH)₄)₂S₂O₃)。

The partially oxidized Claus converter feed gas is then converted to elemental sulfur in the presence of a catalytically active material, such as activated alumina (III) or titania (IV), typically at a temperature above 200 ℃, by the following reaction:

2H₂S+SO₂->3/8S₈+2H₂O (2)

typically 2-4 Claus converters are operated in series to maximize conversion, which increases the cost of the Claus plant.

Temperature control in the Claus process is important to ensure that the elemental sulfur formed in the catalytic converter remains in the gaseous state, so that the sulfur is only condensed at the desired process location. A further limitation is related to the fact that: since the Claus process is exothermic, it is beneficial to operate at low temperatures.

An alternative to the above-described process is the so-called sub-dew point Claus process, in which the catalytically active material is operated at a temperature at which the elemental sulphur is not in the gas phase. Such a sub-dew point Claus process would require an appropriate scheme to remove the condensed sulfur, for example by pulsing the temperature and purging the elemental sulfur with an inert gas.

Even with 3-4 Claus converters/condensers/reheaters in series, sulfur recovery cannot reach above about 98%, which is not sufficient to meet most environmental regulations. Thus, Claus plants are usually equipped with a so-called Claus tail gas solution, of which the above-mentioned sub-dew point process is an example. There are many off-gas processes with different characteristics. To achieve very high removal efficiencies, these Claus tail gas plants become complex and cost close to the Claus plant itself.

The elemental sulfur produced is generally not directly produced to contain H₂S waste streams, but elemental sulphur is easily transported to other locations and can be stored for long periods.

A common alternative to the Claus process is the reaction of H, for example by the so-called wet sulfuric acid process₂S is converted to sulfuric acid. The sulfuric acid produced can be used in other chemical processes of the plant. The wet sulfuric acid process may also constitute a tail gas clean-up of the Claus process plant. A similar dry sulfuric acid process can also be used in this connection.

Sulfuric acid process of reaction of H₂Oxidation of S to SO₂Introducing SO₂By oxidation to SO₃Followed by SO₃The latter is achieved by reaction with water in the gas phase in a so-called wet sulfuric acid process or by absorption in concentrated sulfuric acid in a so-called contact or dry process. SO in the presence of a catalytically active material, usually comprising vanadium₂Oxidation to SO₃The reaction temperature during this period will be in the range of 370 ℃ and 630 ℃. Typically, wet sulfuric acid processes produce sulfuric acid at concentrations ranging from 92% to 98%, while dry sulfuric acid processes can also produce sulfuric acid at concentrations in excess of 98%.

Furthermore, it is attractive to collect high pressure steam in the range of from 30 to 80barg from a highly exothermic sulfuric acid process, whereas the Claus process can only provide low pressure and significantly less steam.

However, even if sulfuric acid is commercially available, the production of large quantities of sulfuric acid may not be attractive because the transportation of sulfuric acid is complex and regulated.

The reactions that take place in the sulfuric acid process (dry and wet) are:

H₂S+1.5O₂->SO₂+H₂O (3)

SO₂+0.5O₂->SO₃(4)

SO₃+H₂O->H₂SO₄(5)

these three reactions are exothermic and release 3-4 times more energy than the Claus reactions (1) and (2).

The overall reaction of the sulfuric acid process can be described as follows:

H₂S+2O₂->H₂SO₄(6)

the wet sulfuric acid process, as a common Claus tail gas solution, provides a solution that meets environmental regulatory requirements at lower capital investment and operating costs than alternatives. The only disadvantage of the wet sulfuric acid process to date is that the sulfuric acid product is not always desirable.

It has now been recognized that the integration of the Claus process and the sulfuric acid process can also be carried out by recycling all or substantially all of the sulfuric acid produced to the Claus reaction furnace. With the new invention, the integration of the Claus/wet sulfuric acid process will eliminate the inconvenient drawbacks of sulfuric acid products while reducing the equipment size of the Claus process and the wet sulfuric acid process and improving the thermal efficiency of the integrated process.

The combustion of sulfuric acid is known from the regeneration of spent sulfuric acid in wet sulfuric acid plants, but has not been carried out in the reaction furnace of the Claus process or under the Claus process conditions.

Upon injection of sulfuric acid into the sulfuric acid evaporation zone, the following overall reaction will occur:

H₂SO₄+3H₂S→2S₂+4H₂O (7)

to accomplish this overall reaction, the following reactions must be accomplished:

H₂SO₄(liquid) → H₂SO₄(gas) (8)

H₂SO₄(gas) → H₂O (gas) + SO₃(gas) (9)

SO₃(gas) → SO₂(gas) +0.5O₂(gas) (10)

Reaction (8) is a common evaporation reaction, wherein the energy required for heating the liquid and evaporating the water and sulfuric acid is provided by the surrounding hot process gas. The effect of the complete evaporation of the sulfuric acid is that gaseous H₂SO₄Is much less corrosive than liquid H₂SO₄A droplet.

Reaction (9) is an endothermic dissociation reaction, which occurs almost instantaneously at temperatures above 600 ℃. At this time, some SO₃Will start with H₂S reacts to form SO₂、H₂O and elemental sulfur.

Reaction (10) is an endothermic decomposition reaction, which is rapid at temperatures above 900 ℃. In an oxygen-rich atmosphere, chemical equilibrium prevents complete dissociation, but in a reducing atmosphere, O₂Removal of product (by reaction with H)₂S reaction) will allow complete decomposition. At these elevated temperatures, H₂S and O₂The reaction between them is very fast.

Since the residence time in the sulfuric acid evaporation zone is typically 1-2 seconds, it must be ensured that reactions 8, 9, 10 and 1 are completed within this time. When the process gas is cooled (i.e., in a Claus waste heat boiler), the reaction rate drops dramatically and further conversion will be negligible.

In the downstream Claus reactor, O is present in the process gas which is contacted with the catalyst₂And/or SO₃Will result in catalyst deactivation by a "sulfation" reaction in which the catalytically active alumina or titania is converted to non-catalyticActive aluminium or titanium sulphates are thus oxidised and the formation of sulphur in these reactors will be reduced, resulting in an increase in unconverted sulphur species going to the downstream tail gas sulphuric acid plant and increased emissions to the atmosphere.

Furthermore, SO in the process gas₃May combine with water and condense during passage through the sulfur condensation unit and form sulfuric acid in the elemental sulfur product, which can lead to corrosion of process equipment.

In order to eliminate any unconverted SO from the sulphuric acid evaporation zone₃The risk of causing operational problems in the Claus converter and the elemental sulphur condenser, it may be preferred to install a catalytic reactor between the outlet of the waste heat boiler and the first sulphur condenser or the first Claus catalytic reactor. The catalyst can effectively pass through H existing in the waste gas of the reaction furnace₂S and H₂Adding SO₃Reduction to harmless SO₂And/or elemental sulfur.

The Claus tail gas sulfuric acid process can be operated if all of the sulfuric acid produced in the Claus process is directed to the sulfuric acid evaporation zone, wherein H₂The reduction of S takes advantage of the very high removal and thermal efficiency of the sulfuric acid plant and the only product therein is elemental sulfur, which is easy to handle and transport.

Furthermore, by recycling of sulfuric acid, by H₂SO₄Decomposition of (2) releases O₂Thus, the amount of oxidant added to the combustion will be reduced, with the benefit of greatly reducing the volume of the process if the oxidant is atmospheric, since atmospheric air contains nearly 80% inert N₂I.e. O per volume₂Having 4 volumes of N₂。

The overall Claus reaction is based on air as oxygen carrier to the Claus reaction furnace:

4H₂S+2O₂+8N₂→2S₂+4H₂O+8N₂(11)

similarly, based on H₂SO₄As O to a Claus reaction furnace₂Support, overall Claus reaction:

3H₂S+H₂SO₄→2S₂+4H₂O (12)

comparing these two reactions, it is clear that H₂SO₄Is excellent in O₂Support and has the (theoretical) potential to reduce the Claus tail gas volumetric flow by 67% compared to atmospheric air.

Considering H₂The reaction of S (reactions 1 and 2) is generally considered to be rapid and not a rate-determining reaction.

As a rule of thumb, temperatures of 1000-. Similarly, 1200-1250 ℃ is required to ensure NH in the reaction furnace₃Is correctly destroyed.

To achieve such high temperatures, especially in the case of feed gases having low calorific values, it may be necessary to select feed gas preheating, oxygen enrichment, acid gas fractionation and/or fuel gas co-combustion.

With the introduction of sulfuric acid, the correct design and operation of the Claus burner and the reaction furnace will become more important, since the overall effect of injecting sulfuric acid into the Claus reaction furnace is a reduction in temperature, the exact value depending on the heating value of the feed gas and the relative amount of sulfuric acid directed to the reaction furnace. Considering that the sulfuric acid form provides about 5% of the total sulfur production, the total temperature drop in the Claus reactor will typically be 50-100 ℃.

The simplest arrangement is to configure the Claus burner to accept all the feed and adjust the temperature in the Claus reactor by adding fuel gas and/or utilizing, for example, feed gas preheating and oxygen enrichment.

However, in some cases, this may increase the fuel gas consumption, the combustion air flow and the total process gas flow significantly to such an extent: the Claus and Claus tail gas plant will become too large resulting in a less competitive solution. Furthermore, increased fuel consumption will increase operating costs.

It has been recognized that the catalyst has a lower O content than the corresponding Claus reaction₂High temperatures are established in the stoichiometric reactor zone and the sulfuric acid is directed to a downstream sulfuric acid evaporation zone (which passes through the endothermic heat associated with the evaporation, dehydration and dissociation of sulfuric acid)Reaction to cool the process gas), there may be destruction of hydrocarbons and NH₃Providing the necessary temperature while retaining the O of the sulfuric acid₂The benefit of the enrichment properties. This is achieved by the following recognition: as long as hydrocarbons and NH are destroyed in the high temperature reactor zone₃The same high temperature is not required in the sulfuric acid evaporation zone containing the sulfuric acid injection, since it is the same as H₂SO₄Related reactions (7-10) and direct reactions with H₂S-related reactions (1-2) will occur at these lower temperatures. Lower temperatures will result in H₂S and SO₂The equilibrium conversion to elemental sulphur is lower, but the downstream catalytic converter can compensate for this slightly lower yield of elemental sulphur in the reaction furnace.

O injected with sulfuric acid₂The enrichment and process gas cooling effect results in a smaller process gas flow to the waste heat boiler and a lower process gas temperature, so that a smaller, cheaper waste heat boiler can be used.

In one embodiment, the Claus reaction furnace is configured such that the high temperature reaction furnace zone comprising the Claus burner receives the entire amount of combustion air, containing NH₃And the sulfuric acid vaporization zone is configured to receive a total amount of sulfuric acid and optionally a portion of the acid gas. The cooling effect due to the sulfuric acid injection is delayed to NH₃This will enable destruction of NH without co-combustion of fuel gas before it is destroyed₃。

The Claus reaction furnace is configured to receive a feed gas, an oxidant, an optional fuel, and sulfuric acid in a single zone, thereby reducing the length of the reaction furnace chamber. This arrangement would be suitable for feed gases having a sufficiently high heating value so that the temperature of the reaction furnace is high enough to destroy impurities, even in view of the temperature drop caused by the evaporation and dissociation of sulfuric acid. This may also be a preferred arrangement when the sulfuric acid flow rate is low and does not significantly reduce the reactor temperature.

The reactor zone is operated under very fuel-rich conditions, i.e. O₂Input lower than complete conversion of all combustibles to CO₂、SO₂And H₂The amount of O required. For Claus reaction furnaceThis is a conventional operation, as there is typically only about 1/3H₂S and O₂And (4) reacting. However, as the sulfuric acid is injected into the sulfuric acid vaporization zone, the reactor zone is operated with even lower oxygen input because of the substantial amount of O₂Is through H₂SO₄Supplied, with a lesser amount being provided by the atomizing medium in the sulfuric acid evaporation zone. Heat and O generated in the reactor zone₂The input is directly related and the process gas temperature is directly related to the amount of heat and process gas generated in the reactor zone. To increase the temperature in the reactor zone, the total amount of process gas can be reduced by bypassing a portion of the acid gas to the sulfuric acid vaporization zone. The amount of acid gas that can be bypassed depends on several factors, such as the heating value of the inlet stream, the degree of preheating of the feed stream, the desired reactor zone temperature, the presence of impurities in the acid gas, and the sulfuric acid vaporization zone temperature.

In refineries, for example, there will usually be concentrated acid gases (>80vol％H₂S) and containing NH₃And H₂S gas (sour water stripper (SWS) gas), where the majority of the sulfur input is present in the sour gas. The reactor zone may then be configured to receive the entire amount of SWS gas and combustion air and an amount of acid gas such that the temperature of the reactor zone is about 1200 to 1250 ℃, and complete NH is achieved before the sulfuric acid vaporization zone₃Destruction, in which sulfuric acid, any atomizing medium and remaining acid gas are injected. With this arrangement, the temperature in the sulfuric acid evaporation zone will be of minor importance, since the acid gas contains a low concentration of impurities (e.g., hydrocarbons) that would otherwise require a certain temperature to completely destroy it.

In a natural gas processing plant, the feed gas to a Claus plant will contain a lower concentration of H₂S (in general)<60 vol%) and will contain hydrocarbons, which require temperatures above 1000-. In this case, the preferred choice is most likely to be to direct the entire amount of acid gas into the reactor zone.

Both the reactor zone and the sulfuric acid vaporization zone may be equipped with turbulizers to accomplish efficient mixing of the process gas from the reactor zone with the sulfuric acid and optionally a portion of the acid gas as quickly as possible. The turbulizers may be, for example, choke rings (choke rings), vector walls, tangential inlets, etc., which will provide a narrower residence time distribution for the process gas, enhance mixing, increase evaporation of sulfuric acid droplets, and reduce the likelihood that droplets experience much lower than average residence times.

The sulphuric acid evaporation zone may also be equipped with an impingement device to reduce the amount of large droplets which, due to their large inertia, will not follow the streamlines of the gas which are redirected in the impingement device when approaching obstacles. In contrast, large droplets will continue to travel forward and collide with the obstacle and evaporate from the obstacle surface. As a result, unreacted SO is reduced₃The risk of processes being entrained downstream of the waste heat boiler of the Claus reaction furnace, thus avoiding the condensation of sulfuric acid in the sulfur condenser and/or the deactivation of the catalyst by sulfation in the Claus catalytic converter. Such a percussion device may be a checkered wall, a tripwire wall, a vector wall, a maze wall and a compartment of (inert) packing material.

The integrated processes according to the present disclosure may also benefit from the use of high oxygen air or substantially pure oxygen in the reactor zone. The use of high oxygen air has the benefit of reducing the inert nitrogen content of the process gas, thereby reducing the volume of the process gas and hence the size of the equipment. The absence of dilution by nitrogen also has the effect of increasing the combustion temperature, which may be beneficial if there are impurities that require complete conversion, particularly because the amount of oxygen in the Claus furnace is sub-stoichiometric. Since Claus catalysts are sensitive to the presence of impurities such as light hydrocarbons, it is often advantageous to operate the Claus reaction furnace with high oxygen air to reach elevated temperatures to fully oxidize the impurities. This has the additional benefit of enabling an initial homogeneous non-catalytic Claus conversion, which can be carried out at temperatures above 900 ℃.

However, from a thermal efficiency perspective, high combustion temperatures may be limited by the choice of materials of construction in the Claus reaction furnace and downstream waste heat boiler. For high concentration of H₂S feed gas, oxygen richThe assembly raises the process gas temperature above the design temperature of the material. However, H₂SO₄The combination of recycling (cooling of the process gas by evaporation and acid decomposition) will make it possible to utilize the enriched oxygen in this arrangement.

The apparatus for sulfur oxidation in a Claus tail gas plant may typically be an incinerator with atmospheric air as O₂Source operation, moreover, it may also be beneficial to direct gases having low concentrations of sulfur species to an incinerator because complete combustion of the sulfur species releases significantly more energy than the partial oxidation occurring in the Claus reaction furnace. Such an arrangement will reduce the consumption of auxiliary fuel and make the thermal efficiency of the tail gas sulfuric acid plant higher. One possible disadvantage is that the additional sulfuric acid produced cannot be directed into the Claus reaction furnace without the need for auxiliary fuel in the Claus reaction furnace to provide energy for the evaporation and dissociation of the sulfuric acid. In a two-zone reactor in which sulfuric acid is injected into the sulfuric acid evaporation zone, the injection capacity of sulfuric acid is significantly improved as compared to a single-zone Claus reactor.

As a result, it may be beneficial to include a high concentration of H₂The feed gas of S is led to a Claus plant, while the feed gas having a lower concentration and comprising NH is led₃By-passing the raw gas to a Claus tail gas incinerator.

If the Claus tail gas incinerator receives only a limited amount of H₂The Claus tail gas of the S has too low a calorific value to maintain stable combustion. In that case, auxiliary fuel needs to be added. Such auxiliary fuel may be H₂S, SWS gas or hydrocarbon feed, but preferably a quantity of existing feed gas to an integrated Claus and sulfuric acid plant is used. If auxiliary fuel is not readily available, or the increased sulfuric acid product cannot be processed or exported in the Claus reactor, the catalytic scheme for Claus tail gas oxidation can be selected for use.

The integration between the Claus process and the sulfuric acid process has integration advantages. These include the possibility of reducing the volume flow in the Claus process by providing the oxidizing agent in the form of sulfuric acid, which can replace the atmosphere. In addition, the use of the feed gas can be optimized such that it will contain para-sulfurIs directed to the Claus process while the heat energy and non-reactive products (e.g., CO) are directed₂) The contributing feed gas is directed to the sulfuric acid process. When the process is designed to recycle an excessive amount of sulfuric acid, additional fuel may be required to provide the heat required for the evaporation and dissociation of the sulfuric acid.

In a preferred embodiment, the sulfuric acid produced in the Claus tail gas sulfuric acid plant is cooled and directed to an intermediate storage tank. In principle, the sulfuric acid storage tank can be omitted, since the Claus reaction furnace is designed to receive the entire sulfuric acid product from the sulfuric acid plant. However, in order to ensure high reliability of the whole plant, the installation of the tank allows the Claus plant to be operated (for a short time) without sulphuric acid injection while the sulphuric acid plant is still operating. This can occur during start-up and shut-down and if maintenance of the sulfuric acid lance/nozzle is required. The tank also enables the withdrawal of sulfuric acid product if sulfuric acid is the desired product, and also allows for the input of sulfuric acid from other sources.

The tank capacity for 4-120 hours of sulfuric acid production is a good compromise between tank cost and flexibility of the Claus + Claus tail gas sulfuric acid plant.

In another embodiment, the sulfuric acid produced in the Claus tail gas sulfuric acid plant is further concentrated in an acid concentrator before being recycled to the Claus reaction furnace. The operation of such a concentration plant will require energy to evaporate water from the sulfuric acid, but then most of this energy is saved in the sulfuric acid evaporation zone. The benefit of this embodiment is the lower reduction in process gas temperature in the sulfuric acid vaporization zone, and the reduction in process gas flow through the Claus plant and Claus tail gas plant.

The integration of these two processes also enables the implementation of a method: wherein operation of the Claus process can be performed at low conversion (e.g., 90% or 95%) because additional conversion in the sulfuric acid process can be less expensive than adding an additional Claus converter stage.

Standard Claus plant layout requires H in the feed gas₂S>50 vol% to achieve thermal self-sustaining in a Claus reactor. At a lower levelH₂At S concentrations, feed gas preheating and so-called split configurations are required. Claus plant treatments with less than 10-20 vol% H are rarely seen₂S as raw material gas. On the other hand, the sulfuric acid process is very efficient in treating these so-called H-lean₂S gas, thereby producing concentrated sulfuric acid. The sulfuric acid product is highly concentrated with respect to sulfur and oxygen.

Treating lean H₂Sulfuric acid plant and process for treating H-rich gas with S (and/or other sulfur compound) gas₂The combination of a Claus plant receiving the gas of S and the acid from the sulfuric acid plant would be an advantageous installation, since the feed streams to the Claus plant and the sulfuric acid plant are optimal in terms of conversion efficiency, thermal efficiency and plant size/cost.

The coupling between the Claus process and the sulfuric acid process can also be used to optimize the treatment of the feed. The sulfuric acid process, especially the wet sulfuric acid process, has the advantage of being well suited for contaminated feeds, including the ammonia-containing SWS gas discussed above, "dirty sulfur" containing organic and moderate amounts of inorganic impurities, dilute H₂S、SO₂And other sulfur compound containing streams, including flue gas from the combustor and FCC gas. Similarly, in contrast, H is enriched₂The gas of S, which has to be diluted before being treated in the wet sulfuric acid plant, can be used directly in the Claus process.

One common device for sulfur oxidation in Claus tail gas is a thermal incinerator, which treats the entire flow of Claus tail gas. In a Claus tail gas incinerator all sulphur compounds will be oxidized to SO₂And a few percent of SO₂Will be further oxidized to SO₃. To ensure CO and H₂The incinerator temperature is typically 850-. The addition of fuel gas is required because the heating value of the Claus tail gas is too low to maintain a stable flame. The fuel gas is typically hydrocarbon-based (e.g. natural gas), but may also be a feed gas to an upstream Claus plant, e.g. containing H₂S gas and further containing NH₃So-called sour water stripping. Using sour water stripper as fuel will produce NO_xOf the NO_xCan be effectively removed in an SCR reactorThe reactor can be located in SO₂Upstream of the converter. NH for SCR reactions₃May be supplied from an external storage facility or may be obtained from the sour water stripper.

Since the Claus tail gas does not contain O₂Therefore, O must be added₂Usually in atmospheric form.

The off-gas from the Claus tail gas incinerator is cooled in one or two steps to a temperature of 370 ℃ and 450 ℃, which is SO₂Typical inlet temperature of the converter, in SO₂In the converter, SO is present in the presence of a catalytically active material comprising vanadium oxide₂Through reaction with O₂Catalytically converted to SO by reaction₃。

In SO₂Upstream of the converter, it may be necessary to add O in atmospheric form₂Incinerators are usually designed to have a low excess of O in the exhaust gas₂And additional air is added to the incinerator to increase O₂The concentration may not be feasible because it increases fuel consumption.

In SO₂In the converter, 1-3 catalyst layers are installed with integrated cooling, usually by means of heat exchangers located below each layer, to remove the heat of reaction and control the inlet temperature of the next catalyst layer. These interbed heat exchangers typically use high pressure steam as a cooling medium, but high pressure water, molten heat transfer salts, process gases, and air may also be used. SO (SO)₂The oxidation catalyst is vanadium based. SO (SO)₂SO in the converter₂Conversion efficiencies are typically above 99% to ensure that greater than 99.9% of the total sulfur is removed from the feed gas.

Adding SO₂The converter off-gas is cooled and led to a sulfuric acid condenser where the gas, SO, is further cooled₃And H₂Reaction of O to form H₂SO₄And condensed in the form of concentrated sulfuric acid having a concentration of 90-98% w/w. Hot concentrated sulfuric acid is withdrawn from the condenser, cooled in a recirculation loop, and then pumped to storage. From there it can be transferred to a Claus plant and injected into a Claus reaction furnace to be evaporated, decomposed and form elemental sulphur.

The cooled gas leaving the sulfuric acid condenser is substantially free of sulfuric acid and may be directed to a stack or unit to further reduce sulfuric acid mist and/or SO₂。

The cooling medium in the sulfuric acid condenser is atmospheric air, which receives heat indirectly from the process gas by heat exchange through the glass walls, usually tubes. The cooling air may be inside or outside the tubes and will exit the condenser at a temperature of 180 ℃ to 270 ℃. Part of the hot air may be used as combustion air in incinerators, and/or in SO₂Upstream addition of the converter to provide for SO₂To SO₃Oxidized O of₂。

Incinerators operating at 850-. Auxiliary fuel is a typical energy source, but combustion of auxiliary fuel requires addition of O₂(in the form of air) this results in an increased flow of process gas out of the incinerator, thereby increasing the size and cost of downstream equipment. In addition, the auxiliary fuel may be expensive or may even be unavailable. A common measure for reducing the energy input to the incinerator in the form of auxiliary fuel is for example preheating of the Claus tail gas and/or combustion air.

In wet sulfuric acid plants, up to 90% -100% of the energy released can be recovered as high pressure steam, which may justify the use of auxiliary fuels. However, if the steam is of low value or of limited use, the layout of the sulfuric acid plant can be optimized to minimize auxiliary fuel consumption. The best way to achieve this is to lower the oxidation temperature of the sulfur compounds in the Claus tail gas, for which purpose a sulfuric acid plant layout with semi-catalytic or fully catalytic Claus tail gas oxidation has been invented.

It has been recognized that significant auxiliary fuel savings can be realized by combining the thermal incineration of a minor portion of the Claus tail gas with a catalytic oxidation step to provide a semi-catalytic Claus tail gas oxidation unit. Such a semi-catalytic oxidation unit would have the same characteristics as the thermal unit for Claus tail gas oxidation, but consume less than 50% of the auxiliary fuel and reduce the SO going downstream₂Oxidation and sulfuric acid coolingThe process gas flow rate of the condensing step significantly reduces operational and capital costs.

In a semi-catalytic oxidation layout, the Claus tail gas is preferably preheated and split immediately upstream of the thermal incinerator: the smaller fraction is directed to an incinerator for sulfur-containing compounds (and H)₂And CO), the greater part bypassing the incinerator and mixing with the hot incinerator exhaust gases.

The exhaust gas from the incinerator at 850-₂S、S₈、COS、CS₂CO and H₂But is substantially free of H₂S、S₈、COS、CS₂CO and H₂The hot incinerator flue gases of (a) are combined, which has a lower concentration and a higher temperature. The mixing temperature is generally in the range of 400-750 ℃ and at this temperature, provided that there is sufficient O₂Residence time and effective gas mixing, H₂S and CS₂Can be easily oxidized by a homogeneous gas phase reaction. To reduce size and fuel gas consumption, excess O in the incinerator tail gas is typically 2-4 vol%₂The incinerator was operated. The by-passed Claus tail gas is O-free₂It may therefore be necessary to add additional (preheated) air in the mixing zone. Since effective mixing of 2-3 streams is important, means for enhancing mixing are preferred. Such a device can be simple, as a tangential inlet flow of smaller streams into incinerator flue gases, or consist of internal structures in the process gas duct (e.g. deflector plates, choke rings and vector walls). To provide the time required for mixing and homogeneous gas phase reaction, the homogeneous reaction zone may be an extension of the incinerator furnace combustion chamber with a residence time of 0.5 to 2 seconds. The brick lining of the combustion chamber will easily maintain the temperature of the process gas before and after the homogeneous reaction, but metal pipes are also possible.

The combustible gas associated with homogeneous oxidation in the Claus tail gas is H₂S and CS₂. At temperatures above 400 ℃ H₂S will be readily oxidized to SO₂And H₂O；CS₂Will be oxidized into COS and SO₂。H₂And CO requires temperatures above 600-. COS can be oxidized at temperatures in the range of 500-.

COS, CO, and H remaining after completion of the homogeneous reaction₂Catalytic oxidation will be required and therefore this semi-oxidised process gas must be cooled to the optimum oxidation catalyst temperature. Gas cooling may be performed using, for example, a waste heat boiler that generates steam, a steam superheater, a gas/gas heat exchanger, or any other heat exchanger, alone or in combination. It would be advantageous to include a waste heat boiler generating steam immediately downstream of the homogeneous reaction zone, since the waste heat boiler is very robust to fluctuations in the inlet temperature, thereby significantly reducing the outlet temperature fluctuations of the waste heat boiler. H in Claus tail gas in case of excursion of the Claus plant₂This is advantageous when the S concentration increases suddenly, thereby increasing the temperature at the outlet of the homogeneous reaction zone. The temperature rise of the waste heat boiler is greatly reduced, so that the operation of downstream equipment is close to normal operation parameters.

H₂、COS、CS₂The catalytic oxidation reaction with CO is carried out using a noble metal-doped catalyst, which must be resistant to sulfur compounds. Such catalysts are described, for example, in EP2878358, which typically comprises V, Ti and Pd or Pt, and will typically be structured catalysts, such as monoliths. Typically, such catalysts are useful for H above 200-320 deg.C₂、COS、CS₂、H₂The oxidation of S and CO is active but may be damaged by long term operation above 500 ℃.

The temperature increase in the catalytic oxidation reactor will preferably bring the process gas temperature to the downstream SO₂Converter and SO₂The expected value for the oxidation catalyst is typically in the range of 370 ℃ and 450 ℃. The temperature rise in the catalytic oxidation reactor can be controlled by the fraction of Claus tail gas that bypasses the incinerator and/or the degree of heat removal in the heat exchanger between the incinerator outlet and the catalytic oxidation reactor inlet.

The oxidation catalyst has an operating temperature interval characterized by virtually no catalytic activity at temperatures below the minimum (inlet) temperature and by the risk of catalyst degradation (chemical and/or mechanical) at temperatures above the maximum allowable (outlet) temperature. The temperature range is specific to each catalyst and compound to be oxidized.

In SO₂In the converter, one or more catalyst layers are installed to ensure the required SO₂To SO₃Thereby, the emission target can be achieved. Due to SO₂The oxidation reaction is exothermic and reversible, SO heat must be removed to achieve SO₂The optimal thermodynamic conditions for the conversion. Typically, a steam generator, steam superheater and/or gas/gas heat exchanger are used to extract heat in the heat exchanger installed between the catalyst layers while ensuring that the cooling medium is always maintained above the sulfuric acid dew point temperature in the process gas.

In an incinerator, homogeneous reaction zone, catalytic oxidation reactor and SO₂Consumption in converter O₂And O is₂As atmosphere or enriched in O₂Is supplied to the incinerator and/or is added at a location between the incinerator outlet and the catalytic reactor inlet. In order to reduce fuel consumption in incinerators and to reduce heat exchanger costs, as much air as possible is added immediately upstream of the catalytic oxidation reactor. In principle, the air can be introduced into the catalytic oxidation reactor and SO₂Further division between converters, but the increased complexity of the plant due to the two air management systems, likely outweighs the benefit of a slightly lower process gas flow through the catalytic oxidation reactor.

Another meaning of supplying oxygen to the Claus tail gas is to ensure that the mixture of Claus tail gas (including combustible gases), incinerator flue gas and air (including oxygen) formed does not form an explosive mixture with the attendant risk of causing uncontrolled oxidation (explosion) in the plant. By ensuring that the concentration of combustible gas is safely below the so-called lower level of flammability LFL or O₂Is below the so-called limit oxygen concentration LOC to avoid this. LFL requirement to be kept below that of the mixtureExcess amount of process gas from incinerator and/or containing O₂To dilute the Claus tail gas, typically air. To O kept below LOC requirement of the mixture₂Is well controlled so that it does not exceed a safe value. Avoiding explosive mixtures by operating below the LOC value generally requires the addition of O-containing compounds in one or more stages₂The gas of (2).

The best strategy choice is made based on knowledge about the composition of the Claus tail gas and the level of fluctuation of possible/allowable combustibles in the Claus tail gas. An abnormal state of the upstream Claus plant may lead to an increase in the combustible concentration, for example H₂S will increase the heating value of the gas and thus increase the energy release in the process, thereby increasing the temperature of the process gas. Care must be taken to design the equipment robust enough that the equipment and catalyst can withstand a given additional temperature rise. This is for oxidizing H₂S、H₂、CO、CS₂CO and S_xAre particularly important. The layout of the semi-catalytic sulfuric acid plant is robust to such fluctuations, since most of the combustible gas is oxidized in the incinerator and in the homogeneous reaction zone upstream of the process gas cooling in the waste heat boiler. The waste heat boiler is robust to an increase in the inlet temperature. After thorough mixing of the process gas (including the by-passed Claus tail gas and incinerator flue gas) and excess O₂In, for practical purposes, H₂S and CS₂The homogeneous oxidation (conversion to COS) of (c) will occur at a temperature of 400 c or higher. Temperatures well above 600-700 ℃ are required to enable H₂And homogeneous oxidation of CO is of industrial interest.

Leaving SO₂SO of converter₃The gas being substantially free of S₈、H₂S、COS、CS₂、H₂And CO. SO (SO)₃Will react with H in the process gas₂O is combined to form H₂SO₄The steam, which will then be condensed to concentrated sulfuric acid in an indirectly cooled sulfuric acid condenser. H of condensed sulfuric acid₂SO₄The concentration ranges from 90 to 98.5% w/w, depending on the H in the process gas₂O and SO₃The ratio of (a) to (b). Claus tail gas generally hasHigh H₂Concentration of O: (>20 vol% H₂O), thus 90-94% w/w of H₂SO₄Is the expected acid concentration. And taking out concentrated sulfuric acid from the sulfuric acid condenser, cooling and sending the concentrated sulfuric acid into a sulfuric acid storage tank.

Concentrated sulfuric acid may even be further concentrated before being sent to a storage tank for storage at a concentration of 96-98.5% w/w, if desired. There would be little benefit in reducing the water injection into the Claus reaction furnace from the lower concentration of sulfuric acid, but since the acid concentration is very energy consuming, the overall energy consumption of the plant as a whole is likely to increase.

The concentration of sulfuric acid from the sulfuric acid condenser can also be reduced by reducing the H in the process gas₂The O concentration is increased. The Claus tail gas typically comprises 25 to 30 vol% H₂O and reduction of H₂The O concentration not only increases the sulfuric acid concentration but also significantly reduces the process gas flow in the sulfuric acid plant. However, the cost of reducing the water concentration in the process gas is very high, since the process gas temperature should be reduced to below 50-60 ℃ to condense most of the water, which is also contaminated with elemental sulphur, H₂S、SO₂And/or H₂SO₄Contamination and therefore further processing is required.

The cooled gas leaving the sulfuric acid condenser is substantially free of SO₃And H₂SO₄And thus may be directed to a chimney. In some cases, it may be desirable to remove SO₂And additional units for acid mist, e.g. SO₂A scrubber tower and a wet electrostatic filter.

Atmospheric air is usually used as cooling medium in the sulfuric acid condenser, whereas SO is removed₃Most of the heat recovered in gas cooling and acid condensation is used in the sulfuric acid plant, for example as heated combustion and oxidation air, and for preheating boiler feed water or Claus tail gas.

The concentrated sulfuric acid produced in the sulfuric acid condenser is pumped from the sulfuric acid storage tank to the Claus reaction furnace where sulfuric acid is sprayed into the furnace in the form of a fine mist, whereby a rapid evaporation of the liquid is achieved and the well-known Claus reaction can be started. The smallest droplets are obtained by using a two-phase (pneumatic) nozzleIs achieved by using compressed air, N₂Steam or any other gas "cuts" the sulfuric acid into very fine droplets. Hydraulic (pressure) nozzles can also be used, but the droplets are slightly larger and will require a longer evaporation time.

Safe shutdown of SO if operating conditions are out of range (trip)₂A converter or a sulfuric acid condenser, it is possible to bypass the process gas directly from the catalytic oxidation reactor to the chimney, so that the incinerator and therefore the Claus plant can be kept operational. Process gas upstream of the catalytic oxidation reactor may be bypassed to the stack if allowed by the restrictions on (temporary) emissions.

It has been recognized that by recycling and staging O two catalytic reactors including different oxidation catalysts with different properties with process gas₂By adding the combination, the Claus tail gas can be oxidized without thermal incineration (and therefore without the use of auxiliary fuel), thereby greatly reducing the operating cost of Claus tail gas treatment equipment.

The layout of the complete catalytic Claus tail gas sulfuric acid oxidation plant will enable Claus tail gas treatment without the use of an incinerator. However, it may be desirable to have the incinerator operate in a hot standby mode so that if the sulfuric acid plant is forced to an unplanned shutdown, the Claus tail gas can be quickly directed to the incinerator. Under normal operation, the incinerator can be operated with minimal fuel gas consumption under hot standby operation, thus saving fuel compared to the Claus process layout under normal operation, where the entire Claus tail gas is directed to the incinerator to be heated to 800-.

In most cases, a fully catalytic Claus tail gas sulfuric acid oxidation plant will be able to operate without consuming auxiliary fuels because the H in the Claus tail gas is oxidized at 200 ℃ to 500 ℃₂、CO、H₂S、COS、CS₂And S₈Catalytic oxidation to H₂O、CO₂And SO₂And adding SO₂Catalytic oxidation to SO₃Sufficient energy is released. The primary contributor to the heating value of the Claus tail gas is H₂S、H₂And CO. If the heating value of the Claus tail gas becomes too low, a small portion of the feed gas to the Claus tail gas plant can be directed to the Claus tail gas plant and in this way the heating value is increased. Another way to increase the heating value of the Claus tail gas is to deliberately reduce the conversion of the Claus plant. This can be achieved, for example, by increasing H₂S/SO₂And/or by operating the Claus catalytic reactor at a non-optimal temperature (which would normally increase the inlet temperature).

With natural gas (CH)₄) Or other light hydrocarbons, is not a good solution because especially CH₄The molecules are very stable and oxidation does not typically occur at foreseeable operating temperatures and catalyst types. Suitable auxiliary fuels will be those containing H₂CO and/or H₂S, which are already present in the Claus tail gas and are readily oxidized by the foreseeable catalyst.

A complete catalytic oxidation sulfuric acid plant will be equipped with a heater for starting up the plant, which is normally not used during normal operation. However, these heaters can be operated if the heating value of the Claus tail gas becomes too low. The heater may be a burner (using, for example, natural gas), an electric heater, and/or a heat exchanger that receives energy from an external device.

Although generally high enough for a fully catalytic Claus tail gas oxidation sulfuric acid plant, the heating value of the Claus tail gas is still considered low, thus requiring a very thermally efficient layout of the sulfuric acid plant, i.e., from the reduced species (H) in the Claus tail gas₂、CO、H₂S、COS、CS₂) Oxidation of (SO), SO₂Oxidation and SO of₃A significant portion of the heat released for conversion to concentrated sulfuric acid must be used to heat the Claus tail gas and the air required for the oxidation reaction.

The Claus tail gas and optional pit vent gas (pit vent gas) are preheated by excess heat from the sulfuric acid plant, preferably in the form of high pressure steam or hot cooling air from the sulfuric acid condenser. Because the Claus tail gas does not contain O₂Therefore, in order to cause the oxidation reaction to proceed, it is necessary to supply O to the off-gas₂. Preferably, atmospheric air is used as O₂Support, but rich in O from sulphuric acid plant₂Air and/or recycled process gas of (a) is also an option.

Adding air to the Claus tail gas is not a simple task, since explosive mixtures may form, and this risk must be minimized/eliminated. Especially H₂And H₂The amount of S is related to the formation of explosive mixtures because the Lower Flammability Limit (LFL) of these compounds, at room temperature, is reduced to 3-4 vol% at 4-5 vol% when the Claus tail gas is heated to 200 ℃. The general rule states that the concentration of combustibles must not exceed 25% of the lower flammability limit, i.e. after mixing with air, CO, H₂And H₂The sum of the S concentrations should not exceed 0.7-1 vol%. In certain industries, it is permissible to operate at concentrations not exceeding 50% of the LFL. Dilution of the Claus tail gas results in a large air addition, which increases the process gas flow, thereby making all parts of the sulfuric acid plant large. Furthermore, the energy balance will be compromised as the added dilution air will require energy for heating, and therefore may require the addition of auxiliary fuel or energy from an external source. Another option would be to dilute the Claus tail gas with process gas recycled from a location downstream of the catalytic oxidation reactor. This option effectively dilutes the process gas below the LFL limit while limiting the increase in process gas volume to a small portion of the plant compared to the entire plant resulting from dilution with atmospheric air. Furthermore, since energy remains within the device, the energy balance is not compromised.

Another energy-efficient method is to stage the oxygen addition to the Claus tail gas so that the oxygen concentration can always be kept below the so-called limiting oxygen concentration LOC. Less than O₂The concentration, the mixed gas will be non-combustible, independent of the concentration of the combustible. By using staged addition of oxygen, the oxidation reaction of the reducing species in the Claus tail gas can be carried out with minimal addition of oxygen, thereby minimizing equipment size and eliminating the need for external energy supplies such as supplemental fuel additions and (electric) heaters. The method also has the advantage of simple control, since onlyIt is necessary to control the amount of oxygen-containing gas so that operation below LOC can be achieved at all times. Dilution with gas to remain below the LFL will depend on the concentration of the combustibles, which may fluctuate or may drift over time, rapidly increasing the concentration of the combustibles. At room temperature, H₂S, CO and H₂LOC values of (A) are 6.5 vol%, 5.0 vol% and 4.5 vol%, respectively. As the temperature increases, the LOC value will decrease. The usual operation is at O₂Operating at concentrations 2-3 vol% lower than LOC, the limit depending on whether O is measured or calculated only₂And (4) concentration. In case of a drift of the combustible concentration increase, there is a consumption of all O₂And the risk of forming a reducing atmosphere. In a reducing atmosphere, there is a risk of elemental sulphur being formed, which may condense in undesired locations, and of deactivating the oxidation catalyst.

For optimal operation of the catalytic oxidation step, the operating temperature must also be tightly controlled so that the inlet temperature is above the light-off temperature of the catalyst and the outlet temperature is below the maximum design temperature of the catalyst (e.g., to avoid mechanical damage or chemical deactivation). In order to control these temperatures, it is possible to utilize recirculation of the process gas which has already been converted. In principle, the temperature can also be controlled by simple air dilution, but the addition of air is also limited by flammability limits. Furthermore, recirculation is preferred over simple dilution because simple dilution increases the process gas flow in all process equipment, while recirculation of process gas limits the increase in process gas flow to a limited number of process equipment. Examples of ignition temperatures and maximum operating temperatures can be found in, for example, EP 2878358.

In a preferred arrangement, the preheated Claus tail gas and sulfur pit vent gas are mixed with preheated atmosphere such that O₂The concentration is below the limiting oxygen concentration limit and then directed to the first catalytic oxidation reactor. The catalyst is characterized by the absence of precious metals and therefore only partially oxidizes combustible compounds in the process gas. Catalyst H₂Oxidation of S to SO₂And H₂O, and mixing with CS₂Oxidation to COS and SO₂And COS, CO and H₂Passed over the catalyst with little reaction. The advantage of this catalyst is that its light-off temperature is significantly lower than that of noble metal-based oxidation catalysts (see EP 2878358). The heat evolved in the first oxidation reactor raises the process gas temperature to such an extent that it is above the light-off temperature of the second oxidation catalyst, which will remove all reducing species (mainly COS, CO and H)₂) Complete conversion to SO₂、H₂O and CO₂. The second oxidation catalyst is characterized by comprising a noble metal, such as Pd and Pt. The distribution of the reaction over both catalysts also provides the benefit of distributing the heat released over a higher volume. The heat generated by the oxidation of all combustibles in the Claus tail gas will generally result in a temperature increase that is too high for the individual catalyst, i.e. likely to exceed the maximum catalyst outlet temperature.

It may be necessary to supply additional O upstream of the second oxidation reactor₂Which may be staged to add O₂The concentration is kept below the LOC value or by dilution to keep the combustible concentration well below the LFL. In Claus Tail gas H₂In the case where the S concentration is high, the heat evolved in the first oxidation reactor may cause the outlet temperature to be too high to fit the inlet of the second oxidation reactor, and therefore it may be necessary to install a heat exchanger between the first and second oxidation reactors.

In order to control the outlet temperature of the second catalytic reactor, a process gas recirculation loop is preferably applied, which loop may be equipped with a temperature control device (heat exchanger), so that the temperature at the inlet of the second oxidation reactor may be controlled simultaneously. A blower is required in the recirculation loop.

EP2878358 describes a flow-through catalyst system without a heat exchanger for O-rich, containing lower concentrations of combustible compounds than Claus tail gas₂The oxygen addition and temperature control between catalysts are designed as a specific catalyst system.

US 4,171,347 describes a catalyst and process for the preparation of a catalyst which also contains H₂And CO from the process gas₂S selective oxygenTo SO₂I.e. not oxidizing H₂And CO. To reduce H₂The temperature of the process gas during or after S-oxidation is suggested to be cooled by cold air addition in the catalytic reactor, recirculation of the converted process gas and dilution with air. However, the patent is unaware of the effects of homogeneous reactions occurring and does not take into account the risk of explosive mixtures forming when diluting the feed gas with air. In addition, the inclusion of CO and H for the conversion is not considered₂And is substantially free of H₂And (4) further processing the process gas of S.

Downstream of the second oxidation reactor, all the sulfur species are SO₂In the form of a few percent conversion to SO₃. SO is then optionally adjusted by passing the process gas through a heat exchanger and adding preheated air₂Temperature and/or O of gas₂In a concentration SO as to be in SO₂To reach the desired temperature and O at the inlet of the converter₂/SO₂And (4) the ratio. The process gas temperature can also be adjusted by preheating the air temperature so that no heat exchanger need be used on the process gas stream-such layout optimization will depend on the combustible concentration in the Claus tail gas and the air added to the upstream catalytic reactor. If the air preheating involves heat exchange with the partially or fully converted process gas, it must be ensured that the air temperature is above the sulfuric acid dew point temperature in the process gas. Otherwise, there is a risk that sulfuric acid condenses on the air heater surfaces, causing corrosion of the heat exchanger material and possible leakage, possibly increasing emissions through the stack.

In SO₂In the converter, SO is converted by means of a vanadium-based catalyst arranged in one or more catalyst layers with a heat exchanger arranged between the layers₂Oxidation to SO₃. The required conversion efficiency determines the number of catalyst layers, but typically 1-3 layers are required. Leaving SO₂SO of converter₃The gas is passed to a sulphuric acid condenser where the process gas is cooled indirectly by the atmosphere, sulphuric acid is condensed and taken off, and the clean process gas is led to a stack. The hot cooling air from the sulfuric acid condenser is used as O in the sulfuric acid plant₂The source, thereby utilizing the heat removed in the condenser of the sulfuric acid plant.

The sulfuric acid is cooled and pumped to a sulfuric acid storage tank from which it is pumped to a Claus reaction furnace for decomposition and reformation to elemental sulfur in a Claus plant.

An alternative to a two-stage catalytic oxidation reactor with staged addition of air, mixing and heat exchange between the reactors is a cooled reactor, where both catalysts are located in the cooled reactor and internal cooling ensures that the catalyst operates in a range between the minimum and maximum temperatures.

If it is difficult to keep below LFL and/or LOC in this cooled reactor, it is an option to use two reactors in series and cool at least one of them. The first catalytic reactor is most suitable for cooling, since the heat evolved is usually highest and fluctuations in the heating value are usually derived from H₂S，H₂S will be oxidized in the first catalytic reactor and it is therefore possible to reduce the risk of overheating the catalyst in the second catalytic reactor.

Since the heating value of the Claus tail gas is relatively low, the internal recovery of the reaction energy released within the sulfuric acid plant is very important, and therefore, the optimum combination of air staging, air dilution, process gas recycle, and heat exchanger location will depend on the exact amount of combustibles in the Claus tail gas. In addition, any deviation in the heating value of the Claus tail gas must be considered, as such deviation can alter the temperature and oxygen distribution in the sulfuric acid plant. It is possible that a non-optimal design for normal Claus tail gas composition may be preferred so that the sulfuric acid plant can still be operated safely in case of a sudden increase in the heating value, for example caused by a change in the composition of the feed gas to the Claus plant or poor oxygen control of the Claus plant. Such designs typically involve greater than necessary process gas recirculation because this is an effective way to suppress temperature increases in the catalytic oxidation reactor to protect the catalyst from overheating.

When the Claus tail gas incinerator is decoupled from the fully catalytic sulfuric acid plant, it will be necessary to activate the heater to heat the process gas to the desired temperature of 200-. The heater may be a fired heater, a heat exchanger with a thermal medium from an external source, or an electric heater. The location of the start-up heater is preferably upstream of the second catalytic oxidation reactor, but may also be upstream of the first catalytic oxidation reactor or in the process gas recirculation loop.

Detailed description of the drawings

In FIG. 1, the wet sulfuric acid plant is a Claus tail gas plant characterized in that at least a portion of the sulfuric acid produced is recycled to the Claus reaction furnace. Claus equipment receives the feed containing H₂S, which is combusted in a Claus reactor (6) with atmospheric air or high oxygen air (4). The optional fuel gas (3) can also be conducted to the Claus reaction furnace. In a Claus reaction furnace, H₂S is partially oxidized to SO₂And sulfur is formed. Any amount of NH in the feed gas₃And/or the decomposition of hydrocarbons to N, respectively₂And H₂O and CO₂And H₂And O. The temperature of the Claus reaction furnace is usually 1,000-1,400 ℃ and the residence time is 1-2 seconds. The Claus reaction furnace gas is typically cooled to about 300 ℃ in a waste heat boiler located at the furnace exit, and the off-gas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser off-gas (12) is reheated in a heat exchanger (14) or by an in-line burner and the reheated process gas (16) enters a first Claus reactor (18) filled with a catalyst comprising activated alumina or titania to effect H₂S and SO₂Reacting to form elemental sulfur. The reactor off-gas (20) is directed to another sulfur condenser (22) where the elemental sulfur is condensed and discharged via line 62 to a sulfur pit (66). The process gas (24) then passes through another catalytic Claus stage via a process gas reheater (26), Claus reactor (30) and sulfur condenser (34) connected by lines 28 and 32. The condensed sulfur is discharged via line 64 to a sulfur pit (66). The tail gas (36) is heated in a heat exchanger (37), preferably using excess heat from the sulphuric acid plant (typically in the form of high pressure steam). Heated Claus tail gas (39) Is directed to an incinerator (42) where it is mixed with hot air (100), auxiliary fuel (44) and pit exhaust gas (72) from a downstream sulfuric acid plant. Pit vent gas is formed by flushing/purging the sulfur pit with atmospheric air supplied via line 70. The pit exhaust gas mainly has a small amount of H₂S and SO₂Is present in the air. Pit vent gas (72) may also be directed to the Claus reaction furnace (6). The temperature and residence time in the incinerator 42 are high enough to allow complete conversion of all sulfur-containing species to SO₂SO of a few percent₂Is further oxidized into SO₃. The incinerator flue gas is cooled in a waste heat boiler (which is typically an integral part of the incinerator) and directed via line 74 to a heat exchanger (75) for further cooling to SO₂Desired temperature at the inlet of the converter (84). In SO₂In the converter, 1-3 layers of SO containing vanadium oxide are installed₂Oxidation catalyst, each layer being separated by a heat exchanger to remove the heat of reaction. To fully convert SO₂The converter off-gas (86) is directed to a sulfuric acid condenser (88) where the sulfuric acid is condensed, concentrated and separated from the process gas, exits through line 104 at the bottom of the condenser, and is cooled and pumped to a sulfuric acid storage tank (106). The cleaned condenser off-gas (90) is directed to a stack (50). The sulfuric acid condenser (88) uses indirect air cooling, where cold cooling air (92) enters the top and hot air (94) exits at the bottom. At least a portion of the heated air may be further heated in a heat exchanger (75) and the further heated air 96 is directed to the incinerator via line 100 and a portion of the further heated air (98) is added to the cooled incinerator flue gas (80) to ensure at SO₂Sufficient oxygen in the reformer feed gas (82) is available for SO₂SO in the converter (84)₂And (4) oxidizing. Further heated air (98) may also be added to the process gas (74) upstream of the air heater (75).

If SO₂If the converter (84) or sulfuric acid condenser (88) is somehow forced to an unplanned shutdown, the incinerator flue gas (74) can be directed to a stack (not shown) to keep the Claus plant running, which will ensure a 94-97% reduction in sulfur during the failure.

Sulfuric acid from the sulfuric acid storage tank (106) is directed to the Claus reaction furnace (6) by a pump and through line 108. The sulfuric acid is atomized into the furnace by means of hydraulic nozzles or preferably by means of pneumatic (two-phase) nozzles.

FIG. 2 shows a sulfuric acid plant as a Claus tail gas plant in which a portion of the sulfur compounds in the Claus tail gas (36) are catalytically oxidized.

Claus equipment receives the feed containing H₂S, which is combusted in a Claus reactor (6) with atmospheric air or high oxygen air (4). In a Claus reaction furnace, H₂S is partially oxidized to SO₂And sulfur is formed. Any amount of NH in the feed gas₃And/or the decomposition of hydrocarbons to N, respectively₂And H₂O and CO₂And H₂And O. The temperature of the Claus reaction furnace is usually 1,000-1,400 ℃ and the residence time is 1-2 seconds. The Claus reaction furnace gas is typically cooled to about 300 ℃ in a waste heat boiler located at the furnace exit, and the off-gas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser off-gas (12) is reheated in a heat exchanger (14) or by an in-line burner and the reheated process gas (16) enters a first Claus reactor (18) filled with a catalyst comprising activated alumina or titania to effect H₂S and SO₂Reacting to form elemental sulfur. The reactor off-gas (20) is directed to another sulfur condenser (22) where the elemental sulfur is condensed and discharged via line 62 to a sulfur pit (66). The process gas (24) then passes through another catalytic Claus stage via a process gas reheater (26), Claus reactor (30) and sulfur condenser (34) connected by lines 28 and 32. The condensed sulfur is discharged via line 64 to a sulfur pit (66).

The Claus tail gas (36) is heated in a heat exchanger (37), preferably using excess energy from the sulfuric acid plant, preferably in the form of high pressure steam. Downstream of the tail gas heater (37), the preheated Claus tail gas (39) is split into two portions: a portion (41) is directed to an incinerator (42) and a portion is directed by a line 43 to a location immediately downstream of the incinerator (42). Incinerator(42) Receives oxygen in hot air (128) from a sulfuric acid plant, auxiliary fuel (44), and optionally pit exhaust gas (72) from a sulfur pit (66), and all sulfur compounds are oxidized to SO₂. The hot process gas (45) from the incinerator is mixed with a by-pass portion (43) of the Claus tail gas and optionally an amount of preheated air via line 129 to form a mixed process gas (110) characterized by a content of Claus tail gas compounds. The mixed process gases are allowed time to react by a homogeneous gas phase reaction and then the homogeneous reaction zone off-gas (110) is cooled in one or two steps via a waste heat boiler (112) and/or a gas/air heat exchanger (116) to achieve the desired inlet temperature for the catalytic oxidation reactor (120). A specific zone can be allocated for the homogeneous reaction of the mixed process gases, for example an extension of the incinerator furnace, with a residence time of typically 0.5 to 2 seconds, but also metal pipes. (120) The catalyst(s) in (a) converts all Claus tail gas compounds (e.g., H)₂S、COS、CS₂、H₂、S₈And CO) to SO₂、H₂O and CO₂. The catalyst may be of a single type or of two types, as described in EP 2878358. The oxidized process gas (122) is then directed to SO₂A converter (84) in which SO is introduced₂Oxidation to SO₃. The air/gas heat exchanger (116) may also be located downstream of the catalytic reactor (120), depending on the exact composition of the Claus tail gas (36) and the need for air preheating.

SO₂The converter (84) contains 1-3 for SO₂Oxidized catalyst layers with coolers installed between the layers to remove the heat of reaction. The converted and cooled process gas (86) is directed to a sulfuric acid condenser (88), where concentrated sulfuric acid is withdrawn via line 104 and directed to a sulfuric acid storage tank (106), and the cleaned process gas (90) is directed to a stack (50). Cooling air for the indirectly cooled condenser (88) is supplied via line 92 and hot cooling air is withdrawn via line 94. Optionally, at least a portion of the heated cooling air (94) is further heated in a gas/air heat exchanger 116, and the further heated cooling isAir (126) is directed to the incinerator via line 128, a portion of the air may be directed to a location immediately downstream of the incinerator (42) via line 129, or to the catalytic oxidation reactor (120) and SO via line 130₂Position between the converter feed gases (124) is SO₂SO in the converter (84)₂Oxidation provides sufficient oxygen. Further heated air (130) may also be added upstream of the catalytic oxidation reactor (120).

Sulfuric acid from sulfuric acid storage tank (106) is directed to Claus reaction furnace (6) by means of a pump and through line 108. The sulfuric acid is atomized into the furnace by means of hydraulic nozzles or preferably by means of pneumatic (two-phase) nozzles.

In SO₂In the event that the converter (84) and sulfuric acid condenser (88) are forced down, the oxidized Claus tail gas (122) or the partially oxidized tail gas (110, not shown) can be directed to the stack (50) for a limited time to keep the Claus plant operational.

FIG. 3 shows a sulfuric acid Claus tail gas plant in which the Claus tail gas is oxidized by catalytic means only.

Claus equipment receives the feed containing H₂S, which is combusted in a Claus reactor (6) with atmospheric air or high oxygen air (4). In a Claus reaction furnace, H₂S is partially oxidized to SO₂And sulfur is formed. Any amount of NH in the feed gas₃And/or the decomposition of hydrocarbons to N, respectively₂And H₂O and CO₂And H₂And O. The temperature of the Claus reaction furnace is usually 1,000-1,400 ℃ and the residence time is 1-2 seconds. The Claus reaction furnace gas is typically cooled to about 300 ℃ in a waste heat boiler located at the furnace exit, and the off-gas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser off-gas (12) is reheated in a heat exchanger (14) or by an in-line burner and the reheated process gas (16) enters a first Claus reactor (18) filled with a catalyst comprising activated alumina or titania to effect H₂S and SO₂Reacting to form elemental sulfur. The reactor off-gas (20) is directed to another sulfur condenser(22) Where the elemental sulfur is condensed and discharged via line 62 to a sulfur pit (66). The process gas (24) then passes through another catalytic Claus stage via a process gas reheater (26), Claus reactor (30) and sulfur condenser (34) connected by lines 28 and 32. The condensed sulfur is discharged via line 64 to a sulfur pit (66).

The tail gas (36) from the Claus plant is heated in a heat exchanger (37) by means of the surplus heat from the sulphuric acid plant. The heated tail gas (39) is mixed with pit vent gas (72) and hot air (166) and optionally an amount of recycled process gas (162). The mixed process gas (134) is directed to a first catalytic reactor (136) where some compounds in the mixed process gas are oxidized while others are not. The partially converted process gas (138) is then optionally cooled in a heat exchanger (e.g., a boiler) (not shown), mixed with an amount of recycled process gas (160) and/or an optional amount of hot air (168) to produce and direct a partially converted process gas (140) to a second catalytic reactor (142) where all combustible compounds (e.g., H) are introduced₂CO, COs) is completely oxidized to CO₂，H₂O and SO₂. The reactor off-gas (144) is then split into a recycle portion (154) and a portion (146), and the portion (146) is directed to a process gas cooler (148) and further to SO₂A converter (84). The recirculated process gas (154) is optionally cooled in heat exchanger 156 and the cooled recycle gas (158) is directed via line 160 to a location upstream of the second catalytic reactor (142) and optionally via line 162 to a location upstream of the first catalytic reactor (136). The process gas recycle blower will overcome the pressure differential of the process gas, recycle stream and control damper (not shown). The purpose of recycling the oxidized process gas is to moderate the temperature in the catalytic converters 136 and 142. From SO₂The converted process gas at any stage in the converter (84) may also be used as recycle gas.

Optionally mixing the cooled converted process gas (150) from the process gas cooler (148) with hot air (174) to pass to the SO₂Transformation ofThe process gas of the vessel (152) is at a suitable temperature and contains sufficient oxygen for the SO₂And (4) carrying out oxidation reaction. The process gas (152) is then directed to SO₂A converter (84) in which SO is introduced₂Oxidation to SO₃. The converter contains 1-3 catalyst layers with coolers installed between the layers to remove the heat of reaction. The converted and cooled process gas (86) is directed to a sulfuric acid condenser (88), where concentrated sulfuric acid is withdrawn via line 104 and directed to a sulfuric acid storage tank (106), and the cleaned process gas (90) is directed to a stack (50). Cooling air for the indirectly cooled condenser (88) is supplied via line 92 and hot cooling air is withdrawn via line 94. A portion of the hot cooling air (94) may be supplied to one or more locations in the sulfuric acid plant: upstream of the first catalytic reactor 136 via line 166, between the outlet of the first catalytic reactor (136) and the inlet of the second catalytic reactor (142) via line 168, and/or to SO via line 174₂Upstream of the converter (84). Either the entire hot air stream (94) or the individual streams (164, 168, 166, 170) may be further heated in a heat exchanger, such as for passage to SO₂The hot air (170) of the reformer is shown as being further heated in a heat exchanger 172 prior to mixing with the process gas 150, preferably by heat exchange with superheated steam or hot process gas.

Sulfuric acid from the sulfuric acid storage tank (106) is directed to the Claus reaction furnace (6) by a pump and through line 108. The sulfuric acid is atomized into the furnace by means of hydraulic nozzles or preferably by means of pneumatic (two-phase) nozzles.

In the event that the sulfuric acid plant is forced to a shutdown, the heated Claus tail gas (39) can be diverted to the thermal incinerator (42) via line 131. Fuel (44) and combustion air (46) are supplied to ensure that the heating value and oxygen can fully oxidize combustible materials in the Claus tail gas. The incinerator flue gas is optionally cooled in a waste heat boiler and directed to a stack (50) via line 48.

Since the temperature of the Claus tail gas is not sufficient to initiate catalytic H₂S oxidation, therefore a heater (not shown) needs to be started up to start up the sulfuric acid plant, and it is preferable to start it upIs placed immediately upstream of the second catalytic reactor (142). The heater may be an electric heater, a fuel gas fired heater, or receive a heating medium from other process equipment.