Method for separating dry gas of light and heavy refinery plant, device and application thereof
阅读说明：本技术 分离轻重炼厂干气的方法及其装置与应用 (Method for separating dry gas of light and heavy refinery plant, device and application thereof ) 是由 邵华伟 张敬升 邹弋 李东风 叶杰铭 罗淑娟 过良 于 2020-06-03 设计创作，主要内容包括：本发明涉及废气回收领域,公开了一种分离轻重炼厂干气的方法及其装置与应用。所述方法包括以下步骤：轻炼厂干气一段压缩；轻炼厂干气精制；重炼厂干气压缩；将重炼厂压缩干气进行冷却、气液分相,得到第一液相和第一气相；将轻炼厂精制干气和第一气相进行混合,得到混合干气,并对混合干气进行升压、冷却,得到冷却干气；将冷却干气送入吸收塔的中部,与来自吸收塔的顶部的吸收剂逆流接触,塔顶得到第二气相,塔釜得到第二液相；将第二液相送入解吸塔的中部,进行解吸,塔顶得到的第三气相与第一液相合并,得到提浓气送出界区；塔釜得到贫吸收剂。所述方法能够同时对轻重炼厂干气中的碳二及更重组分进行分离,并能够降低吸收剂的用量以及能耗。(The invention relates to the field of waste gas recovery, and discloses a method for separating dry gas of a light and heavy refinery plant, a device and application thereof. The method comprises the following steps: first-stage compression of dry gas of a light refinery; refining dry gas of a light refinery; compressing the dry gas of the heavy refinery; cooling the compressed dry gas in the heavy refinery, and performing gas-liquid phase separation to obtain a first liquid phase and a first gas phase; mixing the refined dry gas of the light refinery with the first gas phase to obtain mixed dry gas, and boosting and cooling the mixed dry gas to obtain cooled dry gas; feeding the cooled dry gas into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower to obtain a second gas phase at the tower top and obtain a second liquid phase at the tower kettle; feeding the second liquid phase into the middle part of a desorption tower for desorption, combining a third gas phase obtained at the top of the tower with the first liquid phase to obtain a concentrated gas, and feeding the concentrated gas out of a boundary region; and obtaining the lean absorbent at the tower bottom. The method can simultaneously separate the carbon dioxide and heavier components in the dry gas of the light and heavy refinery, and can reduce the consumption of the absorbent and the energy consumption.)
1. A method for separating dry gas from light and heavy refineries, characterized in that the method comprises the following steps:
(1) first-stage compression of dry gas of a light refinery;
(2) refining dry gas of a light refinery: decarbonizing and drying the light refinery compressed dry gas obtained in the step (1) to obtain light refinery refined dry gas;
(3) compressing the dry gas of the heavy refinery;
(4) cooling and phase splitting of dry gas in heavy refineries: cooling the heavy refinery compressed dry gas obtained in the step (3), and performing gas-liquid phase separation to obtain a first liquid phase and a first gas phase;
(5) and (3) secondary compression of dry gas of the light refinery: mixing the refined dry gas obtained in the step (2) with the first gas phase obtained in the step (4) to obtain mixed dry gas, and boosting and cooling the mixed dry gas to obtain cooled dry gas;
(6) and (3) absorbing the intercooled oil: feeding the cooled dry gas obtained in the step (5) into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower to obtain a second gas phase at the tower top and obtain a second liquid phase at the tower bottom;
(7) desorbing: feeding the second liquid phase obtained in the step (6) into the middle part of a desorption tower for desorption, combining a third gas phase obtained at the top of the tower with the first liquid phase obtained in the step (4) to obtain a concentrated gas, and feeding the concentrated gas out of a boundary region; and obtaining the lean absorbent at the tower bottom.
2. The method of claim 1, wherein the light refinery dry gas comprises hydrogen, methane, carbon dioxide, hydrogen sulfide, oxygen, nitrogen, a carbon two component, a carbon three component, a carbon four component, and heavier components;
more preferably, the content of the carbon two component is 10-20 vol%, the content of the carbon three component is 0-20 vol%, the content of the carbon four and heavier components is 0-10 vol%, the sum of the content of the hydrogen and the methane is 30-75 vol%, the content of the carbon dioxide is 0-20 vol%, and the content of the hydrogen sulfide is 0-20% based on the total volume of the light refinery dry gas;
preferably, the heavy refinery dry gas comprises hydrogen, methane, a carbon two component, a carbon three component, a carbon four component and heavier components;
more preferably, the sum of the contents of hydrogen and methane is 5 to 40 vol%, the sum of the contents of the carbon two components is 20 to 80 vol%, and the sum of the contents of the carbon three, the carbon four and heavier components is 5 to 80 vol%, based on the total volume of the heavy refinery dry gas.
3. The process according to claim 1 or 2, wherein in step (1) the pressure of the light refinery dry gas is increased to 1-2.2MPaG, preferably 1-1.6 MPaG;
preferably, the one-stage compression is a one-stage compression or a two-stage compression.
4. The method according to any one of claims 1-3, wherein in step (2), the decarbonizing comprises the steps of: and (3) sending the compressed dry gas of the light refinery into the bottom of a decarbonizing tower to contact with a decarbonizing agent from the top of the decarbonizing tower, thus obtaining decarbonized dry gas at the tower top and obtaining a rich decarbonizing agent at the tower bottom.
5. The method of claim 4, wherein in step (2), the drying process comprises: sending the decarbonized dry gas into a drying tower to contact with a dehydrating agent;
preferably, the dehydrating agent is selected from molecular sieves and/or activated carbon.
6. The process according to any one of claims 1 to 5, wherein in step (3) the pressure of the heavy refinery dry gas is increased to 1-2MPaG, preferably 1.3-1.7 MPaG;
preferably, the compression is one-stage compression or two-stage compression.
7. The method according to any one of claims 1 to 6, wherein in step (4), the temperature of the re-refinery compressed dry gas after cooling is-15 ℃ to 15 ℃, preferably-10 ℃ to 10 ℃;
preferably, the conditions of the gas-liquid phase separation are such that: the volume ratio of carbon dioxide and heavier components in the first liquid phase to carbon dioxide and heavier components in the refinery dry gas is greater than 3: 10, preferably 5: 10-7: 10.
8. the process according to any one of claims 1 to 7, wherein in step (5), the pressure of the mixed dry gas is increased to 2.5 to 3.5MPaG, preferably 2.5 to 3 MPaG;
preferably, in the step (5), the temperature of the mixed dry gas after cooling is-20 ℃ to-40 ℃, and preferably-30 ℃ to-35 ℃.
9. A process according to any one of claims 1 to 8, wherein the absorbent is a carbon trisection, preferably a liquefied gas and/or refinery propane;
preferably, the theoretical plate number of the absorption tower is 25 to 50, preferably 25 to 30;
preferably, the operating pressure of the absorption column is from 2.5 to 3.5MPaG, preferably from 2.5 to 3 MPaG;
preferably, the overhead temperature of the absorber is from-20 ℃ to-40 ℃, preferably from-25 ℃ to 35 ℃;
preferably, the temperature of the tower kettle of the absorption tower is 40-100 ℃, preferably 50-70 ℃;
preferably, the number of theoretical plates of the desorption tower is 20-50, preferably 20-30;
preferably, the operating pressure of the desorber is from 1 to 3MPaG, preferably from 1.2 to 2.5 MPaG;
the top temperature of the desorption tower is preferably-10 ℃ to 50 ℃, and is preferably-5 ℃ to 20 ℃;
the temperature of the bottom of the desorption tower is 60-120 ℃, and preferably 60-100 ℃.
10. The method according to any one of claims 1-9, wherein the method further comprises: boosting the pressure of the lean absorbent obtained in the step (7), cooling and returning to the absorption tower;
preferably, the cooling is water cooling and propylene cooling in sequence;
more preferably, the lean absorbent is cooled to-20 ℃ to-40 ℃, preferably to-25 ℃ to-35 ℃.
11. The method according to any one of claims 1-10, wherein the method further comprises:
a step of subjecting the second gas phase obtained in the step (6) to post-treatment to recover the absorbent in the second gas phase;
preferably, the post-processing step comprises: sending the second gas phase into a primary cold box-expander system for treatment;
or the second gas phase is sent to a secondary cold box-expander system for treatment;
or the second gas phase is sent to an expander-cold box system for treatment;
preferably, the process stream minimum temperature in the cold box-expander system is from-70 to-110 ℃, preferably from-90 to-110 ℃;
more preferably, the post-processing step comprises: sending the second gas phase into a cold box for cooling, and sending the cooled second gas phase into a second liquid separation tank to obtain a fourth gas phase and a fourth liquid phase;
more preferably, the fourth gas phase is sent to an expansion system for refrigeration, and the obtained refrigeration gas is sent to a cold box for cooling the second gas phase; the fourth liquid phase is returned to the top of the absorption column.
12. The method of any of claims 1-11, wherein the concentrate gas comprises hydrogen, methane, a carbon two component, a carbon three component, and a carbon four or more component;
more preferably, the hydrogen is present in an amount of 0 to 5 vol%, preferably 0 to 1 vol%, based on the total volume of the concentrate gas; the content of the methane is 0-5 vol%, preferably 0-3 vol%; the content of the carbon dioxide component is 60-90 vol%, preferably 70-85 vol%; the content of the carbon three components is 5-20 vol%, preferably 10-20 vol%; the content of the carbon four or more component is 0 to 20 vol%, preferably 0 to 5 vol%.
13. An apparatus for separating dry gas from light and heavy refinery plants, said apparatus comprising: the system comprises a first compressor, a decarbonization tower, a drying tower, a second compressor, a third compressor, a first liquid separation tank, a compressor inter-stage tank, a first cooler, a second liquid separation tank, an absorption tower and a desorption tower;
the first compressor is used for compressing the light refinery dry gas and is communicated with the decarbonization tower;
the bottom of the decarbonization tower is communicated with a first compressor and is used for contacting the light refinery compressed dry gas from the first compressor with a decarbonizing agent, and the top of the decarbonization tower and the tower kettle respectively discharge decarbonized dry gas and a rich decarbonizing agent;
the drying tower is communicated with the top of the decarburization tower and is used for drying the decarburization dry gas to obtain refined dry gas of a light refinery;
the third compressor, the first cooler and the first liquid separation tank are communicated in sequence and are used for compressing and cooling the dry gas of the heavy refinery and separating the gas and the liquid phases;
the compressor inter-stage tank is respectively communicated with the drying tower and the top of the first liquid separation tank and is used for mixing the refined dry gas of the light refinery from the drying tower with the first gas phase from the top of the first liquid separation tank to obtain mixed dry gas;
the second compressor is respectively communicated with the compressor inter-segment tank and the second cooler and is used for compressing and cooling the mixed dry gas to obtain cooled dry gas;
the second cooler, the absorption tower and the desorption tower are communicated in sequence;
the middle part of the absorption tower is communicated with a second cooler and is used for enabling the cooled dry gas to be in countercurrent contact with an absorbent, and a second gas phase and a second liquid phase are respectively discharged from the tower top and the tower kettle of the absorption tower;
the middle part of the desorption tower is communicated with the bottom of the absorption tower, the top of the desorption tower is communicated with the bottom of the first liquid separation tank, and the desorption tower is used for desorbing the second liquid phase discharged from the bottom of the absorption tower, and the top of the desorption tower obtains a third gas phase which is combined with the first liquid phase from the first liquid separation tank and is sent out of the boundary zone as a concentrated gas; and obtaining the lean absorbent from the tower bottom of the desorption tower.
14. The apparatus of claim 13, wherein the apparatus further comprises an absorbent circulation pump, an absorbent water cooler, and an absorbent propylene cooler;
the absorbent circulating pump, the absorbent water cooler and the absorbent propylene cooler are communicated with the desorption tower and the absorption tower and are used for feeding the lean absorbent from the tower kettle of the desorption tower into the top of the absorption tower after boosting and cooling the lean absorbent;
preferably, the device further comprises a cold box, a second separation liquid tank and an expansion machine;
the cold box is used for cooling the second gas phase from the top of the absorption tower;
and the second liquid separation tank is respectively communicated with the cold box and the expander and is used for separating the cooled second gas phase from the cold box, the obtained fourth gas phase is sent into the cold box and is used for cooling the second gas phase, and the obtained fourth liquid phase returns to the top of the absorption tower.
15. Use of the method of any one of claims 1 to 12 or the apparatus of claim 13 or 14 in refinery dry gas separation.
Technical Field
The invention relates to the field of waste gas recovery, in particular to a method for separating dry gas of a light and heavy refinery plant, a device and application thereof.
Background
The refinery dry gas from the oil refining chemical plant, such as catalytic cracking dry gas, delayed coking dry gas, PSA (pressure swing adsorption) gas, hydrocracking dry gas, PX (para-xylene) disproportionation fuel gas, PX isomerization fuel gas, reforming dry gas and the like, usually contains more carbon dioxide and heavier components, and if the carbon dioxide and the heavier components in the dry gas are recovered and sent to an ethylene plant cracking furnace or a subsequent separation unit to be used as raw materials, the economic benefit is remarkable. The refinery dry gas represented by catalytic dry gas, coking dry gas, PSA desorption gas and the like has a large content of light components such as hydrogen, methane, nitrogen and the like, and has a carbon content of about 10-20% vol, which is hereinafter referred to as light refinery dry gas. The refinery dry gas represented by the cracking dry gas, the aromatic dry gas (including PX disproportionation fuel gas, PX isomerization fuel gas and the like) and the like has higher content of carbon and above components, for example, the content of ethane in the PX disproportionation fuel gas can reach 25-70% vol when the molar content is higher, and the sum of the three components of carbon and carbon in the hydrocracking dry gas can exceed 50% vol, which is collectively referred to as heavy refinery dry gas.
At present, methods for recovering carbon dioxide and heavier components from refinery dry gas mainly comprise a cryogenic separation method, a pressure swing adsorption method, an oil absorption method and the like, and various methods have various characteristics. The cryogenic separation method has mature process, high ethylene recovery rate and purity, but large investment, and higher energy consumption for recovering the dilute ethylene; the pressure swing adsorption method has simple operation, low energy consumption, low product purity, low ethylene recovery rate and large occupied area.
The oil absorption method mainly separates gas mixture by utilizing different solubility of absorbent to each component in gas, generally, heavy components above C2 and C2 are absorbed by the absorbent firstly, noncondensable gases such as methane, hydrogen and the like are separated, and then each component in the absorbent is separated by a rectification method. The intercooled oil absorption method is one of the common processes. The method has the characteristics of low investment cost, high carbon recovery rate, strong adaptability to raw material gas and the like. However, the conventional intercooling oil absorption process does not generally distinguish raw material dry gas, and if the raw material contains light refinery dry gas and heavy refinery dry gas, the light refinery dry gas and the heavy refinery dry gas are mixed together and sent into the main absorption tower after being pressurized and cooled by the compressor. The carbon dioxide and heavier components in the heavy refinery dry gas are also subjected to an absorption-desorption process, and finally are sent out of the battery limit area from the top gas phase of the desorption tower or the extracted absorbent. In the process, the circulating absorbent has more dosage, the load of the desorption tower is larger, the low-temperature propylene cold quantity required for cooling the circulating absorbent is more, and the energy consumption of the device is larger. Meanwhile, because the intercooled absorption temperature is below 0 ℃, in order to avoid freezing and blocking the pipeline of the equipment, all feed gases need to be subjected to CO removal2And dehydration treatment, the investment of the device is large.
US5502971 discloses a low-pressure low-temperature process for recovering C2 and heavier hydrocarbons, which is suitable for recovering refinery dry gas. The process eliminates the traditional high pressure scheme and adopts a low pressure technology instead, so that the recovery temperature can be kept above the temperature of the generated nitric acid resin, the potential possibility of danger is avoided, and simultaneously, the higher olefin yield can be kept. Although the process adopts a low-pressure scheme, the temperature is still as low as-100 ℃, and the process still belongs to a cryogenic separation process, so the investment is large and the energy consumption is high.
CN101063048A discloses a method for separating refinery dry gas by adopting an intercooled oil absorption method, which comprises the steps of compression, acid gas removal, drying and purification, absorption, desorption, cold quantity recovery, rough separation and the like, and has the advantages of low absorbent cost, low loss and the like. However, when the dry raw gas contains both light refinery dry gas and heavy refinery dry gas, the two dry gases (possibly multiple strands of raw gas) need to be mixed at the inlet or between the stages of the compressor. C2+ components in the heavy refinery dry gas are diluted and then sent to an absorption tower and a desorption tower for concentration. The circulating absorbent has more dosage, the load of the desorption tower is larger, and the propylene cold quantity required for cooling the circulating absorbent is more.
CN102382680A discloses a combined process of catalytic cracking absorption stabilization system and cold oil absorption in carbon three. The process cancels a desorption tower of an absorption stabilizing system, and dry gas at the tops of a stabilizing tower and a reabsorption tower is sent into an intercooling carbon three-oil absorption tower after being compressed, amine-washed, alkali-washed and dried. After the absorption of the intermediate cooling oil, the carbon-rich three absorbent is sent to a demethanizer of the ethylene plant for treatment. In the process, the raw material treated by the cold oil absorption part is dry gas from an absorption stabilizing system, and the content of C2+ components in the dry gas is low. And the desorption process of the carbon-rich triple absorbent is carried out in the demethanizer of the ethylene device outside the battery limits, and if the consumption of the carbon-rich triple absorbent is increased, the energy consumption of the demethanizer, the deethanizer and other separation units of the ethylene device is increased.
In summary, when the raw dry gas contains both light refinery dry gas (containing less carbon dioxide and heavier components) and heavy refinery dry gas (containing more carbon dioxide and heavier components) during the recovery of the carbon dioxide and heavier components in the refinery dry gas, the conventional intercooled oil absorption process mixes the light refinery dry gas and the heavy refinery dry gas in the gas compression stage, and most of the C2+ components in the heavy refinery dry gas are diluted and still undergo the subsequent absorption-desorption process. The circulating absorbent has more dosage, the load of a reboiler at the tower bottom of the desorption tower is larger, the propylene cold quantity required for cooling the circulating absorbent is more, and the energy consumption of the system is larger. And all light and heavy refinery dry gases need to be subjected to decarburization and dehydration treatment, so that the investment of the device is large.
Disclosure of Invention
The invention aims to solve the problems of high energy consumption of a separation system and high absorbent consumption caused by the mixing of light and heavy refinery dry gases in the prior art when the refinery dry gases are separated, and provides a method for separating the light and heavy refinery dry gases, and a device and application thereof. The method can simultaneously separate carbon dioxide and heavier components in light refinery dry gas represented by catalytic dry gas, coking dry gas, PSA desorption gas and the like and heavy refinery dry gas represented by aromatic hydrocarbon dry gas, cracking dry gas and the like, and can reduce the consumption of an absorbent and save the energy consumption required by a separation system.
In order to achieve the above object, a first aspect of the present invention provides a method for separating dry gas of a light and heavy refinery, characterized in that the method comprises the following steps:
(1) first-stage compression of dry gas of a light refinery;
(2) refining dry gas of a light refinery: decarbonizing and drying the light refinery compressed dry gas obtained in the step (1) to obtain light refinery refined dry gas;
(3) compressing the dry gas of the heavy refinery;
(4) cooling and phase splitting of dry gas in heavy refineries: cooling the heavy refinery compressed dry gas obtained in the step (3), and performing gas-liquid phase separation to obtain a first liquid phase and a first gas phase;
(5) and (3) secondary compression of dry gas of the light refinery: mixing the refined dry gas obtained in the step (2) with the first gas phase obtained in the step (4) to obtain mixed dry gas, and boosting and cooling the mixed dry gas to obtain cooled dry gas;
(6) and (3) absorbing the intercooled oil: feeding the cooled dry gas obtained in the step (5) into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower to obtain a second gas phase at the tower top and obtain a second liquid phase at the tower bottom;
(7) desorbing: feeding the second liquid phase obtained in the step (6) into the middle part of a desorption tower for desorption, combining a third gas phase obtained at the top of the tower with the first liquid phase obtained in the step (4) to obtain a concentrated gas, and feeding the concentrated gas out of a boundary region; and obtaining the lean absorbent at the tower bottom.
The invention provides a device for separating dry gas of light and heavy refineries, which is characterized by comprising the following components: the system comprises a first compressor, a decarbonization tower, a drying tower, a second compressor, a third compressor, a first liquid separation tank, a compressor inter-stage tank, a first cooler, a second liquid separation tank, an absorption tower and a desorption tower;
the first compressor is used for compressing the light refinery dry gas and is communicated with the decarbonization tower;
the bottom of the decarbonization tower is communicated with a first compressor and is used for contacting the light refinery compressed dry gas from the first compressor with a decarbonizing agent, and the top of the decarbonization tower and the tower kettle respectively discharge decarbonized dry gas and a rich decarbonizing agent;
the drying tower is communicated with the top of the decarburization tower and is used for drying the decarburization dry gas to obtain refined dry gas of a light refinery;
the third compressor, the first cooler and the first liquid separation tank are communicated in sequence and are used for compressing and cooling the dry gas of the heavy refinery and separating the gas and the liquid phases;
the compressor inter-stage tank is respectively communicated with the drying tower and the top of the first liquid separation tank and is used for mixing the refined dry gas of the light refinery from the drying tower with the first gas phase from the top of the first liquid separation tank to obtain mixed dry gas;
the second compressor is respectively communicated with the compressor inter-segment tank and the second cooler and is used for compressing and cooling the mixed dry gas to obtain cooled dry gas;
the second cooler, the absorption tower and the desorption tower are communicated in sequence;
the middle part of the absorption tower is communicated with a second cooler and is used for enabling the cooled dry gas to be in countercurrent contact with an absorbent, and a second gas phase and a second liquid phase are respectively discharged from the tower top and the tower kettle of the absorption tower;
the middle part of the desorption tower is communicated with the bottom of the absorption tower, the top of the desorption tower is communicated with the bottom of the first liquid separation tank, and the desorption tower is used for desorbing the second liquid phase discharged from the bottom of the absorption tower, and the top of the desorption tower obtains a third gas phase which is combined with the first liquid phase from the first liquid separation tank and is sent out of the boundary zone as a concentrated gas; and obtaining the lean absorbent from the tower bottom of the desorption tower.
In a third aspect, the invention provides a use of the above method or apparatus in refinery dry gas separation
Through the technical scheme, the method for separating the dry gas of the light and heavy refinery, the device and the application thereof provided by the invention have the following beneficial effects:
(1) in the invention, the light and heavy refinery dry gases are respectively compressed and cooled, most of the carbon dioxide and heavier components in the heavy refinery dry gases enter the liquid phase of the liquid separation tank and are directly combined into the concentrated gas product without undergoing an absorption-desorption process, the absorption dosage of circulating carbon three is reduced on the basis of ensuring the recovery rate of the carbon dioxide, the propylene cold quantity required by a reboiler of a desorption tower and a cooling circulating absorbent is saved, and the energy consumption of the device is reduced.
(2) In the invention, most of light components such as hydrogen, methane, nitrogen and the like in the heavy refinery dry gas are compressed and then sent into the absorption tower, and are separated from the carbon two components in the absorption-desorption process, so that the content requirement of the light components in the final product concentrated gas is ensured.
(3) In the invention, because the content of water, carbon dioxide and hydrogen sulfide in the dry gas of the heavy refinery is low, after compression, cooling and phase splitting, light components such as hydrogen, methane, nitrogen and the like in the dry gas of the heavy refinery are directly merged with the refined dry gas of the light refinery, thereby reducing the load of the refined part (a decarbonizing tower, a drier and the like) of the dry gas.
(4) In the preferred embodiment of the invention, the carbon three-fraction is used as the absorbent, the carbon in the dry gas is absorbed in the absorption tower, and the raw material of the absorbent is easy to obtain and has low cost.
(5) In the preferred embodiment of the invention, a cold box and an expander system are adopted, and the self pressure of the tail gas is utilized for expansion refrigeration, so that the loss of the carbon three absorbent is reduced.
(6) In the preferred embodiment of the invention, the lowest temperature of the operations of compression cooling, absorption and rectification in the process flow is above-40 ℃, an ethylene-propylene binary refrigeration system is not needed, and the method has less investment, simple operation and low energy consumption compared with a cryogenic separation process;
(7) according to the invention, the method can obviously improve the separation efficiency of the refinery dry gas, the recovery rate of the carbon two component in the concentrated gas is more than 92%, and the carbon two component can be used as the raw material of the ethylene device.
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention for separating carbon dioxide and heavier components from light and heavy refinery dry gas.
Description of the reference numerals
1, light refinery dry gas; 2 a first compressor; 3a second compressor; 4, heavy refinery dry gas; 5 a third compressor; 6 a first cooler; 7 a first liquid separation tank; 8 compressor inter-stage tank; 9, a decarbonizing tower; 10 drying tower; 11 a second cooler; 12 a decarbonizing agent; 13, a rich decarbonizer; 14 an absorption column; 15 a desorber; 16 an absorbent circulation pump; 17 absorbent water cooler; 18 absorbent propylene coolers; 19-cycle carbon three absorbent; 20, a cold box; 21 a second liquid separation tank; 22 an expander; 23 tail gas; and 24, concentrating the gas.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a method for separating dry gas of light and heavy refineries, which is characterized by comprising the following steps:
(1) first-stage compression of dry gas of a light refinery;
(2) refining dry gas of a light refinery: decarbonizing and drying the light refinery compressed dry gas obtained in the step (1) to obtain light refinery refined dry gas;
(3) compressing the dry gas of the heavy refinery;
(4) cooling and phase splitting of dry gas in heavy refineries: cooling the heavy refinery compressed dry gas obtained in the step (3), and performing gas-liquid phase separation to obtain a first liquid phase and a first gas phase;
(5) and (3) secondary compression of dry gas of the light refinery: mixing the refined dry gas obtained in the step (2) with the first gas phase obtained in the step (4) to obtain mixed dry gas, and boosting and cooling the mixed dry gas to obtain cooled dry gas;
(6) and (3) absorbing the intercooled oil: feeding the cooled dry gas obtained in the step (5) into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower to obtain a second gas phase at the tower top and obtain a second liquid phase at the tower bottom;
(7) desorbing: feeding the second liquid phase obtained in the step (6) into the middle part of a desorption tower for desorption, combining a third gas phase obtained at the top of the tower with the first liquid phase obtained in the step (4) to obtain a concentrated gas, and feeding the concentrated gas out of a boundary region; and obtaining the lean absorbent at the tower bottom.
According to the invention, the dry gas of the light refinery and the dry gas of the heavy refinery are compressed and pressurized respectively, the dry gas of the heavy refinery is compressed and then is cooled and subjected to gas-liquid phase separation treatment, the gas phase of a liquid separating tank is sent into an intersegmental tank of a dry gas compressor of the light refinery, the separated gas is combined with the dry gas of the light refinery, and then is further compressed and cooled and then is sent into a downstream absorption tower for absorption-desorption treatment, and the dry gas refining links of decarburization, drying and the like of the dry gas of the light refinery are carried out before the dry gas refining links are merged with the gas phase of the liquid separating tank of the dry gas of the heavy refinery; the liquid phase of the liquid separating tank at the outlet of the dry gas compressor of the heavy refinery is directly merged into the concentrated gas product and is sent out of the battery limits.
According to the invention, the light and heavy refinery dry gases are respectively treated, so that the carbon dioxide and heavier components in the heavy refinery dry gas are prevented from being diluted, the carbon dioxide recovery rate is ensured, the circulating absorption dose, the load of a reboiler of a desorption tower and the low-temperature propylene cold quantity required by cooling a circulating absorbent are reduced, the loads of refining units such as decarbonization and dehydration of raw material gas are reduced, the energy consumption of the device is saved, and an ethylene-propylene binary refrigeration system is not required.
In the present invention, the pressure is a gauge pressure unless otherwise specified.
According to the invention, the light refinery dry gas comprises hydrogen, methane, carbon dioxide, hydrogen sulphide, oxygen, nitrogen, a carbon two component, a carbon three component, a carbon four component and heavier components.
Preferably, the content of the carbon two component is 10-20 vol%, the content of the carbon three component is 0-20 vol%, the content of the carbon four and heavier components is 0-10 vol%, the sum of the content of the hydrogen and the methane is 30-75 vol%, the content of the carbon dioxide is 0-20 vol%, and the content of the hydrogen sulfide is 0-20 vol% based on the total volume of the light refinery dry gas.
According to the invention, the heavy refinery dry gas comprises hydrogen, methane, a carbon two component, a carbon three component, a carbon four component and heavier components.
Preferably, the sum of the contents of hydrogen and methane is 5-40 vol%, the content of the carbon two component is 20-80 vol%, and the sum of the contents of carbon three, carbon four and heavier components is 5-80 vol%, based on the total volume of the heavy refinery dry gas.
In the present invention, the carbon two component is a component having 2 carbon atoms, such as ethane and/or ethylene; the carbon three component refers to a component with 3 carbon atoms, such as propane and/or propylene; the carbon four component refers to a component having 4 or more carbon atoms, such as butane and/or butene.
According to the invention, in step (1), the pressure of the light refinery dry gas is increased to 1-2.2MPaG, preferably 1-1.6 MPaG.
According to the invention, the one-stage compression is a one-stage compression or a two-stage compression.
In the invention, the carbon dioxide, hydrogen sulfide and water in the raw material light refinery dry gas are removed by decarbonizing and drying the light refinery compressed dry gas.
According to the invention, in step (2), the decarburization comprises the steps of: and (3) sending the compressed dry gas of the light refinery into the bottom of a decarbonizing tower to contact with a decarbonizing agent from the top of the decarbonizing tower, thus obtaining decarbonized dry gas at the tower top and obtaining a rich decarbonizing agent at the tower bottom.
In the invention, the compressed dry gas of the light refinery is contacted with the decarbonizer to remove the dioxide tower and the hydrogen sulfide in the compressed dry gas of the light refinery.
In the present invention, the amount of the decarbonizing agent is not particularly limited, and can be determined by those skilled in the art based on the general knowledge of the prior art. The decarbonizing column is a typical absorption column, and there is no particular requirement for the number of theoretical plates and the operating pressure, and those skilled in the art can determine the number of the theoretical plates and the operating pressure based on the general knowledge of the prior art.
In the present invention, the decarbonizer may be a decarbonizer which is conventional in the art, for example, MDEA decarbonizer.
According to the invention, in step (2), the drying treatment comprises: and (3) feeding the decarbonized dry gas into a drying tower to contact with a dehydrating agent.
Preferably, the dehydrating agent is selected from molecular sieves and/or activated carbon.
Furthermore, according to the specification of the dry gas raw material and the requirements of downstream devices on products, organic sulfur removal treatment, arsenic removal treatment, mercury removal treatment and the like can be added after drying treatment so as to remove organic sulfur, arsenic and mercury in the raw material gas.
In the invention, in order to ensure that more carbon and the above components in the heavy refinery dry gas enter the first liquid phase in the step (4) so as to reduce the total energy consumption of the device; meanwhile, less light components such as hydrogen, methane and nitrogen in the dry gas of the heavy refinery enter the first liquid phase in the step (4) to avoid the reduction of the content of the light components in the concentrated gas of the final recovered product, and the inventor researches the lifting pressure of the dry gas of the heavy refinery in the step (2), and the research shows that the requirements can be simultaneously met when the pressure of the dry gas of the heavy refinery is increased to 1-2 MPaG.
Furthermore, when the pressure of the dry gas of the heavy refinery is increased to 1.3-1.7MPaG, the comprehensive effect is more excellent.
According to the invention, in step (3), the compression is one-stage compression or two-stage compression.
In the present invention, in the step (4), the gas-liquid separation may be performed in an apparatus capable of achieving gas-liquid separation which is conventional in the art, for example, the gas-liquid separation is performed in the first liquid-separation tank described in the present invention.
In the present invention, in step (4), in order to ensure that the gas-liquid phase has an appropriate gas-liquid ratio and methane has an appropriate portion in the gas-liquid two-phase, the inventors have studied the temperature of the heavy refinery compressed dry gas after cooling in step (4), and have found that the above requirements can be satisfied simultaneously when the temperature of the heavy refinery compressed dry gas after cooling is-15 ℃ to 15 ℃.
Furthermore, when the temperature of the heavy refinery dry gas after cooling is-10 ℃ to 10 ℃, the comprehensive effect is more excellent.
According to the invention, the conditions of the gas-liquid phase separation are such that: the volume ratio of carbon dioxide and heavier components in the first liquid phase to carbon dioxide and heavier components in the refinery dry gas is greater than 3: 10, preferably 5: 10-7: 10.
according to the present invention, in the step (5), the pressure of the mixed dry gas is increased to 2.5 to 3.5MPaG, preferably 2.5 to 3 MPaG.
In the present invention, in the step (5), the number of compression stages in the pressure raising step is not particularly limited, and one-stage compression is preferably employed.
According to the present invention, in the step (5), the temperature of the mixed dry gas after cooling is from-20 ℃ to-40 ℃, preferably from-30 ℃ to-35 ℃.
In the present invention, the refrigerant used for cooling may be a refrigerant conventional in the art, such as propylene refrigeration.
According to the invention, the absorbent is a carbon-three fraction, preferably liquefied gas and/or refinery propane.
According to the invention, the number of theoretical plates of the absorption column can be 25 to 50, preferably 25 to 30.
According to the invention, the operating pressure of the absorption column can be between 2.5 and 3.5MPaG, preferably between 2.5 and 3 MPaG.
According to the present invention, the overhead temperature of the absorption column may be-20 ℃ to-40 ℃, preferably-25 ℃ to-35 ℃.
According to the present invention, the bottom temperature of the absorption column may be 40 to 100 ℃, preferably 50 to 70 ℃.
According to the invention, the number of theoretical plates of the desorber may be between 20 and 50, preferably between 20 and 30.
According to the present invention, the operating pressure of the desorption column may be 1 to 3MPaG, preferably 1.2 to 2.5 MPaG.
According to the present invention, the top temperature of the desorption column may be-10 ℃ to 50 ℃, preferably-5 ℃ to 20 ℃.
According to the present invention, the temperature of the bottom of the desorption column may be 60 to 120 ℃, preferably 60 to 100 ℃.
According to the invention, the method further comprises: and (4) boosting the pressure of the lean absorbent obtained in the step (7), cooling and returning to the absorption tower.
According to the invention, the cooling is water cooling and propylene cooling in sequence.
Preferably, the lean absorbent is cooled to-20 ℃ to-40 ℃, more preferably to-25 ℃ to-35 ℃.
According to the invention, the method further comprises: a step of subjecting the second gas phase obtained in the step (6) to a post-treatment to recover the absorbent in the second gas phase.
According to the invention, the step of post-processing comprises: sending the second gas phase into a primary cold box-expander system for treatment;
or the second gas phase is sent to a secondary cold box-expander system for treatment;
alternatively, the second gaseous phase is sent to an expander-cold box system for processing.
According to the invention, the temperature of the process stream in the cold box-expander system may be in the range of-70 ℃ to-110 ℃, preferably in the range of-90 ℃ to-110 ℃.
In the present invention, the process stream refers to the stream coming from and going between the cold box and the expander. In particular, it refers to the stream exiting expander 22.
According to the invention, the step of post-processing comprises: and (3) sending the second gas phase into a cold box for cooling, and sending the cooled second gas phase into a second liquid separation tank to obtain a fourth gas phase and a fourth liquid phase.
Further, the fourth gas phase is sent to an expansion system for refrigeration, and the obtained refrigeration gas is sent to a cold box for cooling the second gas phase; the fourth liquid phase is returned to the top of the absorption column.
In the invention, the method also comprises the step of heating the concentrated gas to the normal temperature (25-30 ℃) by adopting a heater and then sending the concentrated gas out of the boundary area.
According to the invention, the concentrate gas comprises hydrogen, methane, a carbon two component, a carbon three component and a carbon four or more component.
Preferably, the hydrogen is present in an amount of 0 to 5 vol%, preferably 0 to 1 vol%, based on the total volume of the concentrate gas; the content of the methane is 0-5 vol%, preferably 0-3 vol%; the content of the carbon dioxide component is 60-90 vol%, preferably 70-85 vol%; the content of the carbon three components is 5-20 vol%, preferably 10-20 vol%; the content of the carbon four or more component is 0 to 20 vol%, preferably 0 to 5 vol%.
In a second aspect, the present invention provides an apparatus for separating dry gas from light and heavy refinery plants, comprising: the system comprises a first compressor, a decarbonization tower, a drying tower, a second compressor, a third compressor, a first liquid separation tank, a compressor inter-stage tank, a first cooler, a second liquid separation tank, an absorption tower and a desorption tower;
the first compressor is used for compressing the light refinery dry gas and is communicated with the decarbonization tower;
the bottom of the decarbonization tower is communicated with a first compressor and is used for contacting the light refinery compressed dry gas from the first compressor with a decarbonizing agent, and the top of the decarbonization tower and the tower kettle respectively discharge decarbonized dry gas and a rich decarbonizing agent;
the drying tower is communicated with the top of the decarburization tower and is used for drying the decarburization dry gas to obtain refined dry gas of a light refinery;
the third compressor, the first cooler and the first liquid separation tank are communicated in sequence and are used for compressing and cooling the dry gas of the heavy refinery and separating the gas and the liquid phases;
the compressor inter-stage tank is respectively communicated with the drying tower and the top of the first liquid separation tank and is used for mixing the refined dry gas of the light refinery from the drying tower with the first gas phase from the top of the first liquid separation tank to obtain mixed dry gas;
the second compressor is respectively communicated with the compressor inter-segment tank and the second cooler and is used for compressing and cooling the mixed dry gas to obtain cooled dry gas;
the second cooler, the absorption tower and the desorption tower are communicated in sequence;
the middle part of the absorption tower is communicated with a second cooler and is used for enabling the cooled dry gas to be in countercurrent contact with an absorbent, and a second gas phase and a second liquid phase are respectively discharged from the tower top and the tower kettle of the absorption tower;
the middle part of the desorption tower is communicated with the bottom of the absorption tower, the top of the desorption tower is communicated with the bottom of the first liquid separation tank, and the desorption tower is used for desorbing the second liquid phase discharged from the bottom of the absorption tower, and the top of the desorption tower obtains a third gas phase which is combined with the first liquid phase from the first liquid separation tank and is sent out of the boundary zone as a concentrated gas; and obtaining the lean absorbent from the tower bottom of the desorption tower.
According to the invention, the apparatus also comprises an absorbent circulation pump, an absorbent water cooler and an absorbent propylene cooler.
In the invention, the absorbent circulating pump, the absorbent water cooler and the absorbent propylene cooler are communicated with the desorption tower and the absorption tower and are used for feeding the lean absorbent from the tower kettle of the desorption tower into the top of the absorption tower after boosting and cooling the lean absorbent;
according to the invention, the device also comprises a cold box, a second separation tank and an expansion machine.
In the present invention, the cold box is used to cool the second gas phase from the top of the absorption tower.
In the invention, the second liquid separation tank is respectively communicated with the cold box and the expander and is used for separating the cooled second gas phase from the cold box, the obtained fourth gas phase is sent into the cold box and is used for cooling the second gas phase, and the obtained fourth liquid phase returns to the top of the absorption tower.
In a third aspect the invention provides the use of the above method or apparatus for refinery dry gas separation.
The method and apparatus of the present invention are further described with reference to fig. 1.
The pressure of the light refinery dry gas 1 is increased to 1-2.2MPaG by a first compressor 2, and the compressed dry gas is sent to a decarbonizing tower 9;
the light refinery compressed dry gas from the first compressor 2 enters the bottom of the decarbonizing tower 9, the decarbonizing agent 12 is injected from the top of the decarbonizing tower to remove carbon dioxide and hydrogen sulfide in the light refinery compressed dry gas, and the decarbonized dry gas at the top of the decarbonizing tower is sent to the drying tower 10; a molecular sieve dehydrating agent is arranged in the drying tower 10, saturated water in the decarbonized dry gas is removed to obtain refined dry gas, and the refined dry gas is sent to a compressor intersegmental tank 8;
the pressure of the dry gas 4 of the heavy refinery is increased to 1-2MPaG through a second compressor 5, the dry gas is cooled to-15 ℃ to 15 ℃ in a first cooler 6, the dry gas is sent into a first liquid separation tank 7 for gas-liquid phase separation, the first gas phase at the top of the first liquid separation tank is sent into a compressor intersegment tank 8, and the first liquid phase at the bottom of the first liquid separation tank is merged into a concentrated gas 24;
the pressure of the mixed dry gas discharged from the top of the compressor inter-stage tank 8 is increased to 2.5-3.5MPaG through the third compressor 3, and is cooled to-20 ℃ to-40 ℃ through the second cooler 11 to obtain cooled dry gas which is sent to the middle part of the absorption tower 14;
in the absorption tower 14, a carbon three-fraction is used as an absorbent 19 and is sprayed from the top of the absorption tower to absorb a carbon two-fraction and heavier components in the dry gas, a second gas phase which is not absorbed at the top of the absorption tower is sent to a cold box 20, and a second liquid phase at the bottom of the absorption tower is sent to a desorption tower 15 for treatment;
the second gas phase from the top of the absorption tower 14 is cooled in the cold box 20 by the refrigerant gas from the expander 22, and the cooled gas is sent to the second separation tank 21 to be subjected to gas-liquid separation. In the second liquid separation tank, the carbon-carbon absorbent entrained in the gas phase is condensed, and returns to the top of the absorption tower 14 along with the fourth liquid phase at the bottom of the second liquid separation tank for recycling. The fourth gas phase at the top of the second liquid separation tank expands in an expander 22 to do work and refrigerate, the obtained refrigerating gas is sent into a cold box 20 to cool the second gas phase from the top of the absorption tower 14, and the tail gas 23 containing methane and hydrogen obtained after heat exchange is discharged into a fuel gas pipe network or used by others.
The second liquid phase from the tower bottom of the absorption tower 14 enters the middle part of a desorption tower 15, and the third gas phase at the tower top of the desorption tower and the first liquid phase at the bottom of the first liquid separation tank 7 are combined to be used as a concentrated gas 24 product which is sent to an ethylene device to be used as a raw material. And the third liquid phase at the bottom of the desorption tower is pressurized by an absorbent circulating pump 16, cooled by an absorbent water cooler 17, cooled to the temperature of between 20 ℃ below zero and 40 ℃ below zero by an absorbent propylene cooler 18, and returned to the absorption tower 14 for recycling.
The present invention will be described in detail below by way of examples. In the following examples of the present invention,
the carbon dioxide recovery is calculated by the formula: x 100% of (ethane + ethylene) in the concentrated gas, (ethane + ethylene) in the light refinery dry gas and (ethane + ethylene) in the heavy refinery dry gas); the calculation formula of the carbon recovery rate is as follows: the x is 100% of (propane + propylene) in the concentrated gas, (propane + propylene) in the light refinery dry gas and (propane + propylene) in the heavy refinery dry gas).
Examples and comparative examples the compositions of the light and heavy refinery dry gases are shown in table 1. The gas composition was measured using the standard ASTM D1945.
TABLE 1 Dry gas flowrate composition of refinery
Light refinery dry gas
Heavy refinery dry gas
Temperature, C
40.0
40.0
Pressure, MPaG
0.60
0.30
Mass flow, t/h
50.0
20.0
Composition in mol%
H2
40.80
6.99
H2S
0.06
0.00
CO
0.75
0.00
CO2
0.57
0.00
O2
0.83
0.00
N2
11.12
0.00
CH4
20.15
3.94
C2H6
16.43
60.12
C2H4
0.25
0.00
C3H8
5.11
19.01
C3H6
0.05
0.00
C4H10
2.50
6.21
C4H8
0.02
0.00
C5+
1.27
3.72
H2O
0.07
0.00
Example 1
The method for separating the carbon and heavier components in the dry gas of the light and heavy refineries by adopting the intercooled oil absorption method is adopted to separate the dry gas of the refineries.
The specific process comprises the following steps:
the light refinery dry gas, with the composition shown in table 1 and pressure of 0.6MPaG, enters the first compressor, and the pressure is increased to 1.5MPaG, and is sent to the bottom of the decarbonization tower.
In the decarbonizing tower, MDEA decarbonizing agent (the flow rate of the decarbonizing agent is about 100t/h) is injected from the top of the decarbonizing tower to absorb carbon dioxide and hydrogen sulfide in the compressed dry gas of the light refinery. And sending the decarbonized dry gas at the top of the decarbonization tower into a drying tower. A3A type molecular sieve dehydrating agent is arranged in the drying tower, saturated water in the decarbonized dry gas is removed, and the obtained refined dry gas is sent into a compressor intersegmental tank.
The heavy refinery dry gas, with the composition shown in table 1, was fed to the second compressor at a pressure of 0.3MPaG, increasing the pressure to 1.5 MPaG. And (3) after the pressurized compressed dry gas is cooled to 0 ℃ in a first cooler, sending the compressed dry gas into a first liquid separation tank for gas-liquid phase separation, sending a first gas phase at the top of the first liquid separation tank into a compressor inter-stage tank, combining a first liquid phase at the bottom of the first liquid separation tank into a concentrated gas product, and sending the concentrated gas product out of a boundary area. Wherein the volume ratio of the carbon dioxide and heavier components in the first liquid phase to the carbon dioxide and heavier components in the refinery dry gas is 5.2: 10.
the mixed dry gas discharged from the top of the compressor inter-stage tank is compressed to 3MPaG by a third compressor, cooled to-35 ℃, and sent to the middle part of the absorption tower.
In the absorption tower, liquefied gas (specifically comprising 45 vol% of propane, 33 vol% of butane and 22 vol% of pentane) is used as an absorbent (the circulation amount of the absorbent is 70t/h), and the liquefied gas is sprayed from the top of the tower to absorb the carbon dioxide fraction and heavier components in the dry gas. The number of theoretical plates of the absorption tower is preferably 30, the operation pressure is 3MPaG, the tower top temperature is-30 ℃, and the tower bottom temperature is 64 ℃. The tower kettle of the absorption tower is heated by low-pressure steam, the second gas phase which is not absorbed at the tower top is sent to a cold box, and the third liquid phase at the tower kettle is sent to a desorption tower for treatment.
And the second gas phase from the top of the absorption tower enters a cold box, is cooled to minus 50 ℃ by the refrigerating gas from the expander, and is sent to a second liquid separation tank for gas-liquid phase separation. And returning the fourth liquid phase at the bottom of the second separation liquid tank to the top of the absorption tower. And the fourth gas phase at the top of the second liquid separation tank enters an expander to do work and refrigerate, the refrigerating gas (with the temperature of-105 ℃) obtained at the outlet of the expander enters the second gas phase at the top of the cooling absorption tower of the cold box, and the tail gas obtained after heat exchange is discharged into a fuel gas pipe network.
The second liquid phase from the bottom of the absorption tower enters the middle part of the desorption tower. The theoretical plate number of the desorption tower is 30, the operation pressure is 2.5MPaG, the tower top temperature is 20 ℃, and the tower kettle temperature is 95 ℃. The desorption tower is heated by low-pressure steam, and after the third gas phase at the top of the tower and the first liquid phase at the bottom of the first liquid separation tank are combined, the third gas phase is heated to 45 ℃ and is taken as a concentrated gas product to be sent out of a boundary zone and sent to an ethylene device to be used as a raw material. And the third liquid phase at the tower bottom of the desorption tower is pressurized by an absorbent circulating pump, is cooled to 40 ℃ by circulating water in an absorbent water cooler, is cooled to-35 ℃ by a-40 ℃ propylene refrigerant in an absorbent propylene cooler, and then returns to the absorption tower for recycling.
In this example, the composition of the enriched gas is shown in table 2, in which the carbon recovery rate is 95.2%.
TABLE 2
Concentration gas
Temperature, C
45.4
Pressure, MPaG
2.46
Mass flow, t/h
33.85
Composition in mol%
H2
0.05
CH4
2.23
C2H6
77.48
C2H4
0.60
C3H8
14.73
C3H6
0.08
C4H10
3.02
C5+
1.81
Example 2
In comparison with example 1, the second gas phase obtained at the top of the absorption column was not worked up.
The light refinery dry gas, with the composition shown in table 1 and pressure of 0.6MPaG, enters the first compressor, and the pressure is increased to 1.5MPaG, and is sent to the bottom of the decarbonization tower.
In the decarbonizing tower, MDEA decarbonizing agent (the flow rate of the decarbonizing agent is about 100t/h) is injected from the top of the decarbonizing tower to absorb carbon dioxide and hydrogen sulfide in the compressed dry gas of the light refinery. And sending the decarbonized dry gas at the top of the decarbonization tower into a drying tower. A3A type molecular sieve dehydrating agent is arranged in the drying tower, saturated water in the decarbonized dry gas is removed, and the obtained refined dry gas is sent into a compressor intersegmental tank.
The heavy refinery dry gas, with a composition as shown in table 2, was fed to the second compressor at a pressure of 0.3MPaG, increasing the pressure to 1.5 MPaG. And (3) after the pressurized compressed dry gas is cooled to 0 ℃ in a first cooler, sending the compressed dry gas into a first liquid separation tank for gas-liquid phase separation, sending a first gas phase at the top of the first liquid separation tank into a compressor inter-stage tank, combining a first liquid phase at the bottom of the first liquid separation tank into a concentrated gas product, and sending the concentrated gas product out of a boundary area. Wherein the volume ratio of the carbon dioxide and heavier components in the first liquid phase to the carbon dioxide and heavier components in the refinery dry gas is 6.2: 10.
the mixed dry gas discharged from the top of the compressor inter-stage tank is compressed to 3MPaG by a third compressor, cooled to-35 ℃, and sent to the middle part of the absorption tower.
In the absorption tower, liquefied gas (specifically comprising 36 vol% of propane, 36 vol% of butane and 28 vol% of pentane) is used as an absorbent (the circulation amount of the absorbent is 70t/h), and the liquefied gas is sprayed from the top of the tower to absorb the carbon dioxide fraction and heavier components in the dry gas. The number of theoretical plates of the absorption tower is preferably 30, the operation pressure is 3MPaG, the tower top temperature is-26 ℃, and the tower bottom temperature is 65 ℃. The tower kettle of the absorption tower is heated by low-pressure steam, the unabsorbed second gas phase at the tower top is sent out of a boundary area, and the third liquid phase at the tower kettle is sent into a desorption tower for treatment.
The second liquid phase from the bottom of the absorption tower enters the middle part of the desorption tower. The theoretical plate number of the desorption tower is 30, the operation pressure is 2.5MPaG, the tower top temperature is 18 ℃, and the tower bottom temperature is 101 ℃. The desorption tower is heated by low-pressure steam, and after the third gas phase at the top of the tower and the first liquid phase at the bottom of the first liquid separation tank are combined, the third gas phase is heated to 45 ℃ and is taken as a concentrated gas product to be sent out of a boundary zone and sent to an ethylene device to be used as a raw material. And the third liquid phase at the tower bottom of the desorption tower is pressurized by an absorbent circulating pump, is cooled to 40 ℃ by circulating water in an absorbent water cooler, is cooled to-35 ℃ by a-40 ℃ propylene refrigerant in an absorbent propylene cooler, and then returns to the absorption tower for recycling. Since the second gas phase was not post-treated by the cold box expander, the propane content in the recovered tail gas was reduced, ultimately resulting in a reduction in propane content in the recycled absorbent relative to example 1.
In this example, the composition of the enriched gas is shown in table 3, in which the carbon recovery rate is 93%.
TABLE 3
Example 3
The method for separating the carbon and heavier components in the dry gas of the light and heavy refineries by adopting the intercooled oil absorption method is adopted to separate the dry gas of the refineries.
The specific process comprises the following steps:
the light refinery dry gas, gas composition as shown in table 1, pressure 0.6MPaG, enters the first compressor, increases pressure to 1.0MPaG, and is sent to the bottom of the decarbonization tower.
In the decarbonizing tower, MDEA decarbonizing agent (decarbonizing agent flow rate is about 110t/h) is injected from the top of the decarbonizing tower to absorb carbon dioxide and hydrogen sulfide in the compressed dry gas of the light refinery. And sending the decarbonized dry gas at the top of the decarbonization tower into a drying tower. A3A type molecular sieve dehydrating agent is arranged in the drying tower, saturated water in the decarbonized dry gas is removed, and the obtained refined dry gas is sent into a compressor intersegmental tank.
The heavy refinery dry gas, gas composition as shown in table 1, at a pressure of 0.3MPaG, was fed to the second compressor to increase the pressure to 1 MPaG. And (3) cooling the pressurized compressed dry gas to-10 ℃ in a first cooler, then sending the compressed dry gas into a first liquid separation tank for gas-liquid phase separation, sending a first gas phase at the top of the first liquid separation tank into a compressor inter-stage tank, combining a first liquid phase at the bottom of the first liquid separation tank into a concentrated gas product, and sending the concentrated gas product out of a boundary area. Wherein the volume ratio of the carbon dioxide and heavier components in the first liquid phase to the carbon dioxide and heavier components in the refinery dry gas is 4.4: 10.
the mixed dry gas discharged from the top of the compressor inter-stage tank is compressed by a third compressor to 2.5MPaG, cooled to-30 ℃, and sent to the middle part of the absorption tower.
In the absorption tower, liquefied gas (specifically comprising 46 vol% of propane, 32 vol% of butane and 22 vol% of pentane) is used as an absorbent (the circulation amount of the absorbent is 75t/h), and the liquefied gas is sprayed from the top of the tower to absorb the carbon dioxide fraction and heavier components in the dry gas. The number of theoretical plates of the absorption tower is preferably 25, the operating pressure is 2.5MPaG, the temperature at the top of the tower is-21 ℃, and the temperature at the bottom of the tower is 54 ℃. The tower kettle of the absorption tower is heated by low-pressure steam, the second gas phase which is not absorbed at the tower top is sent to a cold box, and the third liquid phase at the tower kettle is sent to a desorption tower for treatment.
And the second gas phase from the top of the absorption tower enters a cold box, is cooled to minus 50 ℃ by the refrigerating gas from the expander, and is sent to a second liquid separation tank for gas-liquid phase separation. And returning the fourth liquid phase at the bottom of the second separation liquid tank to the top of the absorption tower. And the fourth gas phase at the top of the second liquid separation tank enters an expander to do work and refrigerate, the refrigerating gas (with the temperature of-98 ℃) obtained at the outlet of the expander enters the second gas phase at the top of the cooling absorption tower of the cold box, and the tail gas obtained after heat exchange is discharged into a fuel gas pipe network.
The second liquid phase from the bottom of the absorption tower enters the middle part of the desorption tower. The theoretical plate number of the desorption tower is 20, the operation pressure is 1.2MPaG, the tower top temperature is-1 ℃, and the tower kettle temperature is 57 ℃. The desorption tower is heated by low-pressure steam, and after the third gas phase at the top of the tower and the first liquid phase at the bottom of the first liquid separation tank are combined, the third gas phase is heated to 45 ℃ and is taken as a concentrated gas product to be sent out of a boundary zone and sent to an ethylene device to be used as a raw material. And the third liquid phase at the tower bottom of the desorption tower is pressurized by an absorbent circulating pump, is cooled to 40 ℃ by circulating water in an absorbent water cooler, is cooled to-25 ℃ by a-40 ℃ propylene refrigerant in an absorbent propylene cooler, and then returns to the absorption tower for recycling.
In this example, the composition of the enriched gas is shown in Table 4, in which the carbon recovery rate is 92.4%.
TABLE 4
Comparative example 1
The dry gas shown in table 1 was recovered according to a typical cold oil absorption process scheme of CN101063048A, wherein the feed conditions and carbon dioxide recovery rate were the same as in example 1, and the resulting enriched gas product had the composition shown in table 5 and the process conditions and energy consumption shown in table 6.
Comparative example 2
Compared with the example 1, the method does not contain the step of refining the light refinery dry gas. Because the temperature of the absorption tower is below 0 ℃, water or carbon dioxide is carried in the material flow, and the material flow can be frozen at a low-temperature position, so that the equipment or the pipeline is frozen and blocked, and the separation of refinery dry gas cannot be realized.
TABLE 5
Concentration gas
Composition in mol%
CH4
2.71
C2H6
86.11
C2H4
0.72
C3H8
10.38
C3H6
0.08
TABLE 6
From tables 2 to 6, compared with the conventional intercooling oil absorption process, the process has the advantages that the light and heavy refinery dry gas is respectively compressed and cooled, most of the carbon dioxide and the heavy components in the heavy refinery dry gas are directly merged into concentrated gas products along with a compression condensate, the circulating carbon three absorbent dosage, the load of a reboiler of a desorption tower and the load of an absorbent propylene cooler are reduced, the low-pressure steam consumption of the device and the consumption of the refrigeration capacity of propylene at the temperature of minus 40 ℃ are reduced, and the energy consumption of the device is low. The dry gas of the heavy refinery which does not contain water basically does not enter the decarbonization and dehydration units, thereby reducing the investment of the device.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.