阅读说明：本技术 一种烯烃聚合物生产中兼顾树脂输送、脱气和排放气回收的装置和方法 (Device and method for simultaneously achieving resin conveying, degassing and exhaust gas recovery in olefin polymer production ) 是由 阳永荣 林渠成 廖祖维 董轩 黄正梁 包崇龙 孙婧元 杨遥 张浩淼 王靖岱 蒋斌 于 2020-12-04 设计创作，主要内容包括：本发明公开了一种烯烃聚合物生产中兼顾树脂输送、脱气和排放气回收的装置和方法。该装置包括：树脂输送和脱气机构,其用于将树脂产品从反应器输送到脱气仓,用于在脱气仓中脱除树脂中的烃类物质；排放气回收机构,其用于接收来自所述脱气机构的排放气流,并回收其中的烃类物质和氮气。本发明的装置和方法不仅能够回收排放气中的乙烯等烃类物质和氮气,而且可以回收不同压力等级的高纯度氮气,实现更高水平的输送和脱气效果。(The invention discloses a device and a method for simultaneously realizing resin conveying, degassing and exhaust gas recovery in olefin polymer production. The device includes: a resin transfer and degassing mechanism for transferring the resin product from the reactor to a degassing bin for removing hydrocarbon species from the resin in the degassing bin; and the exhaust gas recovery mechanism is used for receiving the exhaust gas flow from the degassing mechanism and recovering hydrocarbon substances and nitrogen in the exhaust gas flow. The device and the method can recover hydrocarbon substances such as ethylene and the like and nitrogen in the exhaust gas, and can recover high-purity nitrogen with different pressure grades, thereby realizing higher-level conveying and degassing effects.)

1. An apparatus for achieving resin transfer, degassing and vent gas recovery in olefin polymer production, comprising:

a conveying mechanism for conveying the resin product from the reactor to the degassing bin; the resin conveying mechanism adopts at least one strand of nitrogen from an exhaust gas recovery mechanism;

the degassing mechanism is used for removing hydrocarbon substances in the resin in the degassing bin; the resin degassing mechanism adopts at least one strand of nitrogen from an exhaust gas recovery mechanism;

and the exhaust gas recovery mechanism is used for receiving the exhaust gas flow from the degassing mechanism, recovering hydrocarbon substances in the exhaust gas flow and obtaining high-purity nitrogen with multiple pressure grades.

2. The apparatus according to claim 1, wherein the conveying means uses nitrogen gas from the exhaust gas recovery means at a higher pressure level than the degassing means uses nitrogen gas from the exhaust gas recovery means.

3. The apparatus of claim 1, wherein the vent gas recovery mechanism recovers high purity nitrogen gas having a nitrogen purity of between 85 mol% and 98 mol%.

4. The apparatus of claim 1, wherein the high purity pressure stages of the multiple pressure stages of the exhaust gas recovery mechanism comprise at least a pre-turboexpansion pressure and a post-turboexpansion pressure.

5. The apparatus of claim 1, wherein said delivery mechanism comprises:

a discharge tank for receiving resin pellets obtained by the production of the olefin polymer, receiving high-pressure fresh nitrogen and high-purity nitrogen from the vent gas recovery mechanism as a transport gas, and transporting the resin pellets to the degassing mechanism by the transport gas.

6. The apparatus of claim 1, wherein said degassing mechanism comprises:

and the degassing bin is used for receiving the conveying gas carrying the resin particles from the conveying mechanism, receiving fresh nitrogen and high-purity nitrogen from the exhaust gas recovery mechanism as the purge gas, degassing hydrocarbon impurities and unreacted olefin monomers in the resin particles under the action of the purge gas and outputting the exhaust gas containing olefin, alkane impurities and nitrogen.

7. The apparatus of claim 1, wherein the exhaust gas recovery mechanism comprises:

a multi-stage compressor for compressing the discharge gas from the de-aeration tank;

a cooler for cooling a multi-stage compressor outlet stream, outputting a first gas-liquid mixture;

the first stage of gas-liquid separators are used for receiving the first gas-liquid mixture from the cooler, carrying out phase separation and outputting a first liquid phase component rich in heavy components and a first gas phase component rich in light components; when the multistage gas-liquid separator is included, the Nth stage gas-liquid separator receives the gas-phase component of the upper stage gas-liquid separator, cools the gas-phase component to obtain a gas-liquid mixture, performs phase separation, and outputs an Nth liquid-phase component and an Nth gas-phase component;

at least one turbine for receiving the gas phase components of the gas-liquid separator to produce high pressure high purity nitrogen gas in multiple pressure stages; the temperature of the stream is reduced after the stream is expanded through a turbine, and cold energy is provided;

and the multi-flow-strand heat exchanger is used for realizing the heat exchange process among the streams in the exhaust gas recovery mechanism.

8. The apparatus of claim 7, wherein the plurality of stages of gas-liquid separators comprise:

a first gas-liquid separator for receiving the first gas-liquid mixture from the cooler and separating phases to output a first liquid phase component rich in C4+ higher hydrocarbon impurities and a first gas phase component rich in nitrogen and C2+ lower hydrocarbon impurities;

a second gas-liquid separator for receiving a second gas-liquid mixture obtained by cooling the first gas-phase component, separating phases, and outputting a second liquid-phase component rich in C4+ high-carbon hydrocarbon impurities and a second gas-phase component rich in nitrogen and C2+ low-carbon hydrocarbon impurities;

and the third gas-liquid separator is used for receiving a third gas-liquid mixture obtained by cooling the second gas-phase component, performing phase separation and outputting a third liquid-phase component rich in C2+ low-carbon hydrocarbon impurities and a third gas-phase component of high-purity nitrogen.

9. A method for achieving resin transfer, degassing and vent gas recovery in olefin polymer production, comprising the steps of:

conveying the resin product from the discharge tank to a degassing mechanism using fresh nitrogen and at least one stream of nitrogen from an exhaust gas recovery mechanism;

fresh nitrogen and at least one stream of nitrogen from an exhaust gas recovery mechanism are adopted to remove hydrocarbon substances in the resin in a degassing mechanism;

receiving the discharge gas flow from the degassing mechanism, recovering hydrocarbon substances in the discharge gas flow, and obtaining high-purity nitrogen with multiple pressure grades.

10. The method of claim 9, wherein the nitrogen from the vent gas recovery mechanism for delivery is at a higher pressure level than the nitrogen from the vent gas recovery mechanism for degassing.

Technical Field

The invention belongs to the field of tail gas recovery, and particularly relates to a device and a process for recovering exhaust gas from a polyolefin device.

Background

In the production process of olefin polymers, unreacted polymerization monomers such as ethylene, propylene, butene, hexene and the like, and condensing agents and solvents such as isopentane, hexane and the like, which are dissolved in polyolefin resin, must be removed to ensure the safety of downstream production and transportation processes and to meet the standard of environmental protection. Therefore, the polymerization process has high devolatilization requirements for polyolefin resins and strict product indexes. In order to meet the product quality requirement, fresh nitrogen is often used for conveying, blowing and removing resin particles in production. The removal process has high requirement on the purity of nitrogen and large consumption, and the generated exhaust gas also needs to be separated and recycled.

There are many separation schemes for recovering the exhaust gas, such as compression condensation, pressure swing adsorption, membrane separation, and cryogenic cooling. These separation schemes allow for partial recovery of comonomer and condensing agent. Because the boiling points of nitrogen and ethylene in the exhaust gas are low, the nitrogen and ethylene are difficult to be completely separated and recycled. Patent CN103520946B adopts a cryogenic separation process to recover nitrogen, and all low-pressure nitrogen obtained after expansion is used for purging and degassing a degassing bin. WO2017023433A1 adopts a two-stage membrane separation process to separate exhaust gas, and high-pressure nitrogen with lower purity is used for purging and degassing a degassing bin. Patent CN102389643A uses the compressed and condensed exhaust gas as the transport gas to transport the resin particles from the reactor to the degassing bin.

The above methods, while achieving nitrogen recycle, are not satisfactorily integrated with the devolatilization process of polyolefin processes. In order to realize the efficient removal of hydrocarbon substances in the resin particles, nitrogen which is as pure as possible is used for purging removal, but the purity of the exhaust gas after compression and condensation cannot meet the requirement. The resin devolatilization process also has certain requirements on the pressure of nitrogen. On the one hand, the degassing bin is operated at a low pressure and does not require a high pressure nitrogen purge. On the other hand, high pressure nitrogen stream delivery is required due to the height difference of the resin particles from the reactor to the degassing bin. It can be seen that to minimize nitrogen consumption, both high purity high pressure and low pressure nitrogen are recovered. However, none of the current separation processes involving membrane separation or cryogenic separation or pressure swing adsorption can simultaneously obtain two pressure levels of high purity nitrogen. The reason is that the membrane separation and the pressure swing adsorption both need pressure difference driving, the streams have different pressure grades and different purities, and the cryogenic separation needs to utilize high-pressure nitrogen stream expansion refrigeration and only obtains low-pressure high-purity low-pressure nitrogen streams.

Therefore, the polyolefin exhaust gas recovery device and the method for effectively recovering high-purity nitrogen at different pressure levels have great economic benefits and practical significance.

Disclosure of Invention

It is an object of the present invention to provide an apparatus for efficiently recovering components of an exhaust gas in the production of an olefin polymer. Which comprises a resin conveying and degassing mechanism and an exhaust gas recovery mechanism. The device provided by the invention realizes more efficient removal of hydrocarbon substances in resin particles and saves the nitrogen consumption and pressure energy through the cooperative work of the two mechanisms.

The invention comprises a resin conveying step, a resin degassing step and an exhaust gas recovery step.

The device of the invention comprises:

a resin transfer and degassing mechanism for transferring the resin product from the reactor to a degassing bin for removing hydrocarbon species from the resin in the degassing bin;

and the exhaust gas recovery mechanism is used for receiving the exhaust gas flow from the resin degassing mechanism and recovering hydrocarbon substances and nitrogen in the exhaust gas flow.

The device of the invention adopts purer high-pressure recycled nitrogen to convey the resin particles, so that the residue of a discharging system is effectively reduced, the starting time period is prolonged, a certain degassing function is realized while conveying, a better resin devolatilization effect can be obtained, the residual amount of hydrocarbons in the particles is effectively reduced, and the influence of the residue on the product quality and the subsequent transportation safety are prevented.

According to a particular embodiment of the invention, the conveying and degassing mechanism comprises: the mixer is used for receiving the sixth gas phase flow and the fresh nitrogen from the exhaust gas recovery mechanism, and the sixth gas phase flow and the fresh nitrogen are mixed and then input into the discharge tank as conveying gas; the discharge tank is used for receiving resin particles obtained by olefin polymer production and conveying the resin particles to the degassing bin through pressurized conveying gas; and the degassing bin is used for receiving the conveying gas carrying the resin particles, degassing hydrocarbon impurities and unreacted olefin monomers in the resin particles under the action of the purging gas and outputting exhaust gas containing olefin, alkane impurities and nitrogen.

According to an embodiment of the invention, the pressurized conveying gas is nitrogen from the exhaust gas recovery unit, the pressure of the nitrogen is 10-30 bar, preferably 15-25 bar, and the purity of the nitrogen is 85-98 mol%, preferably 90-97 mol%. The total flow of the pressurized transport gas is controlled by additional fresh high pressure nitrogen.

According to one embodiment of the invention, the resin particles in the degassing bin are in reverse contact with the purge gas, the resin particles are in contact with at least one stream of nitrogen gas which is from an exhaust gas recovery mechanism and has higher purity in the upper half section of the degassing bin to realize the removal of high-carbon hydrocarbon impurities, and the resin particles are in contact with fresh nitrogen gas in the lower half section to finish the removal of low-carbon hydrocarbon impurities.

According to an embodiment of the present invention, the exhaust gas recovery mechanism includes:

a multi-stage compressor for compressing the discharge gas from the de-aeration tank;

a cooler for cooling a multi-stage compressor outlet stream, outputting a first gas-liquid mixture;

the first stage of gas-liquid separators are used for receiving the first gas-liquid mixture from the cooler, carrying out phase separation and outputting a first liquid phase component rich in heavy components and a first gas phase component rich in light components; when the multistage gas-liquid separator is included, the Nth stage gas-liquid separator receives the gas-phase component of the upper stage gas-liquid separator, cools the gas-phase component to obtain a gas-liquid mixture, performs phase separation, and outputs an Nth liquid-phase component and an Nth gas-phase component;

at least one turbine for generating high pressure high purity nitrogen at multiple pressure levels; the temperature of the stream is reduced after the stream is expanded through a turbine, and cold energy is provided;

at least one multi-stream heat exchanger for effecting a heat exchange process between the streams in the exhaust gas recovery mechanism.

According to a specific embodiment of the present invention, the several stages of gas-liquid separators comprise:

a first gas-liquid separator for receiving the first gas-liquid mixture from the cooler and separating phases to output a first liquid phase component rich in C4+ higher hydrocarbon impurities and a first gas phase component rich in nitrogen and C2+ lower hydrocarbon impurities;

a second gas-liquid separator for receiving a second gas-liquid mixture obtained by cooling the first gas-phase component, separating phases, and outputting a second liquid-phase component rich in C4+ high-carbon hydrocarbon impurities and a second gas-phase component rich in nitrogen and C2+ low-carbon hydrocarbon impurities;

and the third gas-liquid separator is used for receiving a third gas-liquid mixture obtained by cooling the second gas-phase component, performing phase separation and outputting a third liquid-phase component rich in C2+ low-carbon hydrocarbon impurities and a third gas-phase component of high-purity nitrogen.

According to one embodiment of the invention, the cooler cools the multi-stage compressor outlet stream to as low a temperature as possible with an inexpensive cooling medium, such as circulating cooling water, to save energy consumption of the subsequent plant.

According to an embodiment of the invention, the first liquid phase component output after the phase separation by the first gas-liquid separator is rich in C4+ higher hydrocarbon impurities.

According to a specific embodiment of the invention, the temperature of the first gas phase flow is reduced to-20 to-60 ℃ after being cooled by the first multi-flow heat exchanger, preferably-45 to-55 ℃, and the second liquid phase component output after phase separation by the second gas-liquid separator mainly comprises C4+ high-carbon hydrocarbon impurities, and contains a small amount of C2+ low-carbon hydrocarbon impurities and nitrogen.

According to a specific embodiment of the invention, the temperature of the second gas-phase component output by the second gas-liquid separator is reduced to-150 to-100 ℃ after being cooled by the second multi-stream heat exchanger, preferably-130 to-110 ℃, and the third liquid-phase component output after being subjected to phase separation by the third gas-liquid separator is mainly C2+ low-carbon hydrocarbon impurities.

Aiming at the defects of the prior art, the invention provides a device and a method for efficiently conveying resin products, degassing and recovering components of exhaust gas in olefin polymer production, which have the following outstanding advantages: the synchronous recycling of the high-pressure high-purity nitrogen and the normal-pressure high-purity nitrogen is realized; the high-pressure high-purity nitrogen is used as conveying gas, so that pressure recovery is realized, and residues of a discharging system are effectively reduced, so that the driving time is prolonged, and a certain degassing function is attached; the exhaust gas recovery mechanism can realize the recovery of the exhaust gas without a coolant except circulating cooling water, and has the advantages of low energy consumption, low investment cost, high economic benefit, environmental protection and no pollution.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings briefly described below are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 shows a schematic process flow diagram of example 1 of the present invention.

FIG. 2 shows a schematic process flow diagram of example 2 of the present invention.

In the drawings, like components are denoted by like reference numerals. The figures are not drawn to scale.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings of the present invention. It is to be understood that the described embodiments are merely exemplary of some, but not necessarily all, embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

As shown in FIG. 1, the present invention provides a recovery apparatus of polyolefin vent gas capable of simultaneously preparing high-pressure and low-pressure high-purity nitrogen gas, comprising:

the resin conveying and degassing mechanism X is used for receiving a resin product output by the polyolefin fluidized bed reactor, conveying the resin product to a degassing bin from a discharge tank through conveying gas obtained by mixing high-pressure high-purity nitrogen gas flow and fresh high-pressure nitrogen gas, and outputting discharge gas after two-stage purging and degassing of low-pressure high-purity nitrogen gas and low-pressure fresh nitrogen gas;

an off-gas recovery means Y for receiving off-gas from the resin conveying and degassing means X and recovering therein C4+ higher hydrocarbon streams b1 and a11, C2+ lower hydrocarbon stream a12, high pressure high purity nitrogen stream a6, low pressure high purity nitrogen stream a14, a portion of the nitrogen being sent to the flare as the remaining off-gas stream a13 in order to prevent accumulation of hydrogen or lower alkanes in the system;

in this embodiment, the resin transfer and degassing mechanism X includes a mixer, a discharge tank, and a degassing bin. The first inlet T2 of the mixer is connected with high-pressure fresh nitrogen, the second inlet T3 is connected with the first outlet T46 of the first splitter in the exhaust gas recovery mechanism Y, the outlet T4 is connected with the first inlet T5 of the discharge tank, the second inlet T6 of the discharge tank is connected with the outlet T1 of the fluidized bed reactor, the outlet T7 of the discharge tank is connected with the first inlet T8 of the degassing bin, the second inlet T9 of the degassing bin is connected with low-pressure fresh nitrogen, the third inlet T10 of the degassing bin is connected with the second outlet T52 of the second splitter in the exhaust gas recovery mechanism Y, and the outlet T11 of the degassing bin is connected with the inlet T12 of the multistage compressor in the exhaust gas recovery mechanism Y.

In this example, high-pressure fresh nitrogen (pure nitrogen in this example) and high-pressure high-purity nitrogen stream a6 were mixed in a mixer and output as a conveying gas to a discharge tank, and the resin product was pneumatically conveyed to a degassing bin. Wherein the pressure of the high-pressure high-purity nitrogen a6 is 10-30 bar, preferably 15-25 bar, and the purity of the nitrogen is 85-98 mol%, preferably 90-97 mol%, which accounts for 0.4-1, preferably 0.8-1 of the total conveying gas flow ratio; the pressure of the high pressure fresh nitrogen gas was kept in agreement with the pressure of the high pressure high purity nitrogen gas a 6. Due to the recycling of the high-pressure high-purity nitrogen, compared with a method using high-pressure fresh nitrogen for conveying, the method greatly reduces the consumption of the fresh nitrogen; compared with a method of using a compressed and condensed gas phase stream as conveying gas, the method greatly improves the purity of nitrogen, thereby effectively reducing the residue of a discharging system, prolonging the driving time and having a certain degassing function.

In the embodiment, the resin particles are subjected to two-stage purging in a degassing bin by low-pressure fresh nitrogen (pure nitrogen in the embodiment) and low-pressure high-purity nitrogen a14, and C4+ high-carbon hydrocarbon impurities in the resin particles are removed in the upper stage by low-pressure high-purity nitrogen a14, wherein the pressure of the low-pressure high-purity nitrogen a14 is 1.5-5 bar, preferably 2-4 bar, and the nitrogen purity is 90-99 mol%, preferably 95-98 mol%; c2+ low-carbon hydrocarbon impurities are removed from the lower section through low-pressure fresh nitrogen, the pressure of the low-pressure fresh nitrogen is consistent with that of normal-pressure high-purity nitrogen a14, and the output exhaust gas mainly comprises C2+ low-carbon hydrocarbon impurities, C4+ high-carbon hydrocarbon impurities and nitrogen. Due to the recycling of low-pressure high-purity nitrogen, the consumption of fresh nitrogen is greatly reduced compared with a method using fresh nitrogen for purging.

In the present embodiment, the exhaust gas recovery mechanism Y includes a multistage compressor, a cooler, a turbine, two multi-stream heat exchangers, two throttle valves, two splitters, and three gas-liquid separators. Wherein the multistage compressor inlet T12 is connected to the degassing silo outlet T11 of the resin conveying and degassing apparatus X, the multistage compressor outlet T13 is connected to the cooler inlet T14, the cooler outlet T15 is connected to the first gas-liquid separator inlet T16, the first gas-liquid separator first outlet T17 is connected to the first stream inlet T19 of the first multi-stream heat exchanger, the second outlet T18 of the first gas-liquid separator outputs C4+ the higher hydrocarbon stream b1, the first stream outlet T20 of the first multi-stream heat exchanger is connected to the second gas-liquid separator inlet T29, the second gas-liquid separator first outlet T30 is connected to the first stream inlet T34 of the second multi-stream heat exchanger, the first stream outlet T35 of the second multi-stream heat exchanger is connected to the third gas-liquid separator inlet T42, the third gas-liquid separator first outlet T43 is connected to the second stream inlet T36 of the second multi-stream heat exchanger, the second stream outlet T35 of the second multi-stream heat exchanger is connected to the second multi-stream heat exchanger T27, a fifth stream outlet T28 of the first multi-stream heat exchanger is connected to a first splitter inlet T45, a first outlet T46 of the first splitter is connected to a first mixer inlet T3 of the resin transfer and degassing unit X, a second outlet T47 of the first splitter is connected to a turbine inlet T48, a turbine outlet T49 is connected to a fourth stream inlet T40 of the second multi-stream heat exchanger, a fourth stream outlet T41 of the second multi-stream heat exchanger is connected to a fourth stream inlet T25 of the first multi-stream heat exchanger, a fourth stream outlet T26 of the first multi-stream heat exchanger is connected to an inlet T50 of the second splitter, a first outlet T51 of the second splitter delivers a discharge stream a13 to a flare, a second outlet T52 of the second splitter is connected to a third inlet T10 of the degassing unit X of the resin transfer and degassing unit X, a second outlet T6 of the second gas separator is connected to an inlet T32 of the first throttle valve, a second outlet T33 of the first throttle valve is connected to an inlet T21 of the first multi-stream heat exchanger, a second stream outlet T22 of the first multi-stream heat exchanger outputs a C4+ high-carbon hydrocarbon material stream a11, a second outlet T44 of the third gas-liquid separator is connected with an inlet T45 of a second throttling valve, a second throttling valve outlet T46 is connected with a third stream inlet T38 of the second multi-stream heat exchanger, a third stream outlet T39 of the second multi-stream heat exchanger is connected with a third stream inlet T23 of the first multi-stream heat exchanger, and a third stream outlet T24 of the first multi-stream heat exchanger outputs a C2+ low-carbon hydrocarbon material stream a 12.

In this example, the multistage compressor is a centrifugal compressor, 2 stages of compression, with an outlet pressure of 20bar, and the discharge gas is cooled to 40 ℃ interstage by circulating cooling water.

In this example, the cooler is a tubular heat exchanger and cools the compressed exhaust gas to 40 ℃.

In this embodiment, the first multi-stream heat exchanger and the second multi-stream heat exchanger are both plate heat exchangers, the temperature of the first outlet T20 of the first multi-stream heat exchanger is-20 to-60 ℃, preferably-45 to-55 ℃, and the temperature of the first outlet T35 of the second multi-stream heat exchanger is-150 to-100 ℃, preferably-130 to-110 ℃.

In the embodiment, the second outlets of the first gas-liquid separator and the second gas-liquid separator output C4+ high-carbon hydrocarbon liquid streams, the liquid phase stream output by the second gas-liquid separator is expanded to the temperature of-50 to-60 ℃ of the liquid phase component b3 after passing through the first throttling valve, and the temperature of the gas phase component a11 after cold recovery in the first multi-stream heat exchanger is 25 to 35 ℃.

In the embodiment, a second outlet T44 of the third gas-liquid separator outputs a C2+ low-carbon hydrocarbon liquid material flow, the temperature of a liquid-phase component b5 is between 135 ℃ and 115 ℃ after the liquid-phase component is expanded to the normal pressure through a second throttle valve, the temperature of a gas-liquid mixture C4 is between 70 ℃ and 50 ℃ after cold is recovered in a second multi-stream heat exchanger, and the temperature of a gas-phase component a12 is between 20 ℃ and 40 ℃ after the cold is recovered in a first multi-stream heat exchanger.

In this embodiment, the first outlet T43 of the third gas-liquid separator outputs high-pressure high-purity nitrogen, the temperature of the gas-phase component a4 after heat recovery in the second multi-stream heat exchanger is-70 to-50 ℃, the temperature of the gas-phase component a5 after cold recovery in the first multi-stream heat exchanger is 20 to 40 ℃, the gas-phase component a6 is split in the first splitter, a part of the gas-phase component a6 is used as conveying gas, the split ratio thereof is 0 to 1, preferably 0.4 to 0.6, and the gas-phase component a6 is output to a mixer in the resin conveying and degassing mechanism X through the first outlet T46 of the first splitter; the other part of the gas-phase component a7 is output to a turbine through a second outlet T47 of the first flow divider, the temperature of the expanded gas-phase component a8 is-130 to-150 ℃ after the turbine is expanded and cooled, the temperature of the gas-phase component a9 is-50 to-70 ℃ after cold is recovered by the second multi-strand heat exchanger, the temperature of the gas-phase component a10 is 20 to 40 ℃ after cold is recovered by the first multi-strand heat exchanger, the split ratio of the split part of the gas-phase component a14 is 0.5 to 0.95 as purge gas, the purge gas is output to a degassing bin in the resin conveying and degassing mechanism X through a second outlet T52 of the second flow divider, and the other part of the gas-phase component a13 is used as residual discharge gas.

Example 2

As shown in FIG. 2, the present invention provides a recovery apparatus of polyolefin vent gas capable of simultaneously preparing high-pressure, medium-pressure and low-pressure high-purity nitrogen gas, comprising:

the resin conveying and degassing mechanism X is used for receiving a resin product output by the polyolefin fluidized bed reactor, conveying the resin product to a degassing bin from a discharge tank through conveying gas obtained by mixing high-pressure high-purity nitrogen gas flow and fresh high-pressure nitrogen gas, and outputting discharge gas after two-stage purging and degassing of low-pressure high-purity nitrogen gas and low-pressure fresh nitrogen gas;

an off-gas recovery means Y for receiving off-gas from the resin conveying and degassing means X and recovering therein C4+ high hydrocarbon stream b1, C2+ low hydrocarbon stream a21, high pressure high purity nitrogen stream a6, medium pressure high purity nitrogen a13, low pressure high purity nitrogen stream a18, a portion of the nitrogen being sent to a flare as a remaining off-gas stream a19 in order to prevent accumulation of hydrogen or low carbon alkanes in the system;

compared with the embodiment 1 shown in the attached drawing 1, a turbine is added in the embodiment 2 shown in the attached drawing 2, a first turbine outlet stream a10 is divided after cold energy is recovered in a second multi-flow heat exchanger to obtain a gas phase component a12, a medium-pressure high-purity nitrogen stream a13 is obtained after cold energy is recovered in the first multi-flow heat exchanger continuously, and the nitrogen stream is output to a middle inlet T8 of a discharge tank outlet pipeline of a resin conveying and degassing mechanism X for relay conveying, so that a better resin conveying effect is realized; in addition, after cold energy is recovered in the first multi-flow heat exchanger, the second outlet liquid-phase component b2 of the second gas-liquid separator is mixed with the conveying gas and enters the inlet T17 of the multistage compressor again, so that the composition of C4+ high-carbon hydrocarbons in the second outlet liquid-phase component b1 of the first gas-liquid separator is improved, and a better separation effect is achieved.

In this embodiment, the resin transfer and degassing mechanism X includes a mixer, a discharge tank, and a degassing bin. The first inlet T2 of the first mixer is connected to high pressure fresh nitrogen, the second inlet T3 is connected to the first outlet T60 of the first splitter in the exhaust gas recovery mechanism Y, the outlet T4 is connected to the first inlet T5 of the discharge tank, the second inlet T6 of the discharge tank is connected to the outlet T1 of the fluidized bed reactor, the outlet T7 of the discharge tank is connected to the first inlet T9 of the degassing bin, the intermediate inlet T8 of the outlet line of the discharge tank is connected to the fourth stream outlet T30 of the first multi-stream heat exchanger in the exhaust gas recovery mechanism Y, the second inlet T10 of the degassing bin is connected to low pressure fresh nitrogen, the third inlet T11 of the degassing bin is connected to the second outlet T71 of the third splitter in the exhaust gas recovery mechanism Y, and the outlet T12 of the degassing bin is connected to the inlet T13 of the multi-stage compressor in the exhaust gas recovery mechanism Y.

In this example, high pressure fresh nitrogen (pure nitrogen in this example) and high pressure high purity nitrogen stream a6 were mixed in a mixer and delivered to a discharge tank as a transport gas, and due to a pressure drop between the discharge tank and the degassing chamber, medium pressure high purity nitrogen stream a13 was delivered as a transport gas into a relay delivery at intermediate inlet T8 of the outlet line of the discharge tank to pneumatically transport the resin product to the degassing chamber. Wherein the pressure of the high-pressure high-purity nitrogen a6 is 10-30 bar, preferably 15-25 bar, and the purity of the nitrogen is 85-98 mol%, preferably 90-97 mol%, which accounts for 0.3-1, preferably 0.6-0.8 of the total conveying gas flow ratio; the pressure of the high-pressure fresh nitrogen is consistent with that of the high-pressure high-purity nitrogen a 6; the pressure of the medium-pressure high-purity nitrogen a13 is 5-15 bar, preferably 5-10 bar, the nitrogen purity is consistent with that of the high-pressure high-purity nitrogen a6, and the nitrogen purity accounts for 0.1-0.5, preferably 0.1-0.3 of the total conveying gas flow rate. Because of the recycling of the high-pressure high-purity nitrogen and the medium-pressure high-purity nitrogen, compared with the method using high-pressure fresh nitrogen for conveying, the method greatly reduces the consumption of fresh nitrogen; compared with a method of using a compressed and condensed gas phase stream as conveying gas, the method greatly improves the purity of nitrogen, thereby effectively reducing the residue of a discharging system, prolonging the driving time and having a certain degassing function.

In the embodiment, the resin particles are subjected to two-stage purging in a degassing bin by using low-pressure fresh nitrogen (pure nitrogen in the embodiment) and low-pressure high-purity nitrogen a18, and C4+ high-carbon hydrocarbon impurities in the resin particles are removed in the upper stage by using low-pressure high-purity nitrogen a18, wherein the pressure of the low-pressure high-purity nitrogen a14 is 1.5-5 bar, preferably 2-4 bar, and the nitrogen purity is 90-99 mol%, preferably 95-98 mol%; c2+ low-carbon hydrocarbon impurities are removed from the lower section through low-pressure fresh nitrogen, the pressure of the low-pressure fresh nitrogen is consistent with that of normal-pressure high-purity nitrogen a18, and the output exhaust gas mainly comprises C2+ low-carbon hydrocarbon impurities, C4+ high-carbon hydrocarbon impurities and nitrogen. Due to the recycling of low-pressure high-purity nitrogen, the consumption of fresh nitrogen is greatly reduced compared with a method using fresh nitrogen for purging.

In the present embodiment, the exhaust gas recovery mechanism Y includes a mixer, a multistage compressor, a cooler, two turbines, two multi-stream heat exchangers, two throttle valves, three splitters, and three gas-liquid separators. Wherein the first inlet T13 of the second mixer is connected to the degassing silo outlet T12 of the resin conveying and degassing mechanism X, the second inlet T14 of the second mixer is connected to the second stream outlet T26 of the first multi-stream heat exchanger, the second mixer outlet T15 is connected to the multistage compressor inlet T16, the multistage compressor outlet T17 is connected to the cooler inlet T18, the cooler outlet T19 is connected to the first gas-liquid separator inlet T20, the first gas-liquid separator first outlet T21 is connected to the first stream inlet T23 of the first multi-stream heat exchanger, the second outlet T22 of the first gas-liquid separator outputs C4+ higher hydrocarbon stream b1, the first stream outlet T24 of the first multi-stream heat exchanger is connected to the second gas-liquid separator inlet T37, the second gas-liquid separator first outlet T38 is connected to the first stream inlet T42 of the second multi-stream heat exchanger, the first stream outlet T43 of the second multi-stream heat exchanger is connected to the third gas-liquid separator inlet T54, the third gas-liquid separator first outlet T55 is connected to the second stream inlet T44 of the second multi-stream heat exchanger, the second stream outlet T45 of the second multi-stream heat exchanger is connected to the sixth stream inlet T33 of the first multi-stream heat exchanger, the sixth stream outlet T34 of the first multi-stream heat exchanger is connected to the first splitter inlet T59, the first outlet T60 of the first splitter is connected to the first mixer inlet T3 of the resin transfer and degasification mechanism X, the second outlet T61 of the first splitter is connected to the seventh stream inlet T35 of the first multi-stream heat exchanger, the seventh stream outlet T36 of the first multi-stream heat exchanger is connected to the third stream inlet T46 of the second multi-stream heat exchanger, the third stream outlet T47 of the second multi-stream heat exchanger is connected to the first turbine inlet T62, the first turbine outlet T63 is connected to the fifth stream inlet T50 of the second multi-stream heat exchanger, the fifth stream outlet T64 of the second multi-stream heat exchanger is connected to the stream inlet T51 of the first multi-stream heat exchanger, a second splitter first outlet T65 is connected to a first multi-stream heat exchanger fourth stream inlet T29, a first multi-stream heat exchanger fourth stream outlet T30 is connected to an outlet line intermediate inlet T8 of a discharge tank in resin transfer and degassing mechanism X, a second splitter second outlet T66 is connected to a second turbine inlet T67, a second turbine outlet T68 is connected to a second multi-stream heat exchanger sixth stream inlet T52, a second multi-stream heat exchanger sixth stream outlet T53 is connected to a first multi-stream heat exchanger fifth stream inlet T31, a first multi-stream heat exchanger fifth stream outlet T32 is connected to a third splitter inlet T69, a third splitter first outlet T70 outputs a discharge stream a19 for flare, a third splitter second outlet T71 is connected to a third inlet T11 in resin transfer and degassing mechanism X, a second outlet T39 of a second gas separator is connected to an inlet T40 of a first throttle valve, an outlet T41 of the first throttling valve is connected to a second stream inlet T25 of the first multi-stream heat exchanger, a second stream outlet T26 of the first multi-stream heat exchanger is connected to a second inlet T14 of the second mixer, C4+ high carbon hydrocarbon stream a20 is recycled, a second outlet T56 of the third gas-liquid separator is connected to an inlet T57 of the second throttling valve, a second throttling valve outlet T58 is connected to a fourth stream inlet T48 of the second multi-stream heat exchanger, a fourth stream outlet T49 of the second multi-stream heat exchanger is connected to a third stream inlet T27 of the first multi-stream heat exchanger, and a third stream outlet T28 of the first multi-stream heat exchanger outputs C2+ low carbon hydrocarbon stream a 21.

In this example, the multistage compressor is a centrifugal compressor, 2 stages of compression, with an outlet pressure of 20bar, and the discharge gas is cooled to 40 ℃ interstage by circulating cooling water.

In this example, the cooler is a tubular heat exchanger and cools the compressed exhaust gas to 40 ℃.

In this embodiment, the first multi-stream heat exchanger and the second multi-stream heat exchanger are both plate heat exchangers, the temperature of the first outlet T20 of the first multi-stream heat exchanger is-20 to-60 ℃, preferably-45 to-55 ℃, and the temperature of the first outlet T35 of the second multi-stream heat exchanger is-150 to-100 ℃, preferably-130 to-110 ℃.

In the embodiment, the second outlet of the first gas-liquid separator outputs a C4+ high-carbon hydrocarbon liquid stream, the liquid phase stream output by the second gas-liquid separator passes through the first throttling valve and is expanded to the temperature of-50 to-60 ℃ of the liquid phase component b3 after the normal pressure is reached, and the temperature of the gas phase component a20 after cold energy recovery in the first multi-stream heat exchanger is 25 to 35 ℃.

In the embodiment, a second outlet T56 of the third gas-liquid separator outputs a C2+ low-carbon hydrocarbon liquid material flow, the temperature of a liquid-phase component b5 is between 135 ℃ and 115 ℃ after the liquid-phase component is expanded to the normal pressure through a second throttle valve, the temperature of a gas-liquid mixture C4 is between 50 ℃ and 70 ℃ after cold is recovered in a second multi-stream heat exchanger, and the temperature of a gas-phase component a12 is between 20 ℃ and 40 ℃ after the cold is recovered in a first multi-stream heat exchanger.

In this embodiment, the first outlet T55 of the third gas-liquid separator outputs high-pressure high-purity nitrogen, the temperature of the gas-phase component a4 after heat recovery in the second multi-stream heat exchanger is-70 to-50 ℃, the temperature of the gas-phase component a5 after cold recovery in the first multi-stream heat exchanger is 20 to 40 ℃, the gas-phase component a6 is split in the first splitter, a part of the gas-phase component a6 is used as conveying gas, the split ratio thereof is 0 to 1, preferably 0.3 to 0.5, and the gas-phase component a6 is output to a mixer in the resin conveying and degassing mechanism X through the first outlet T60 of the first splitter; the other part of the gas-phase component a7 is cooled again by the first multi-flow heat exchanger to obtain a gas-phase component a8 with the temperature of minus 60 ℃ to minus 40 ℃, and then is cooled by the second multi-flow heat exchanger to obtain a gas-phase component a9 with the temperature of minus 110 ℃ to minus 90 ℃, the pressure of the gas-phase component a10 expanded by the first turbine is 5-10 bar, the temperature is-140 to-120 ℃, the temperature of the gas-phase component a11 is between-125 and-105 ℃ after the cold energy is recovered by the second multi-stream heat exchanger, the gas is divided in a second flow divider, part of the gas phase component a12 is recovered in a first multi-flow heat exchanger to obtain a gas phase component a13 with the temperature of 20-40 ℃ and is used as conveying gas, the split flow ratio is 0-0.4, preferably 0-0.2, and the waste water is output to a middle inlet T8 of an outlet pipeline of a discharge tank in a resin conveying and degassing mechanism X through a fourth stream outlet T30 of the first multi-stream heat exchanger; and the gas-phase component a14 at the second outlet of the second flow divider enters a second turbine for expansion and temperature reduction, the pressure of the gas-phase component a15 is 2-4 bar, the temperature is-130-150 ℃, the temperature of the gas-phase component a16 after cold recovery in the second multi-flow heat exchanger is-70-50 ℃, the temperature of the gas-phase component a17 after cold recovery in the first multi-flow heat exchanger is 20-40 ℃, the split ratio of a part of the gas-phase component a18 is 0.5-0.95, the gas-phase component a is output to a degassing bin in a resin conveying and degassing mechanism X through a second outlet T71 of the third flow divider, and the other part of the gas-phase component a19 is used as residual discharge gas and sent to a torch.

According to the embodiment provided by the invention, the exhaust gas recovery mechanism can realize the recovery of the exhaust gas without a coolant except circulating cooling water, and has the advantages of low energy consumption, low investment cost, high economic benefit, environmental protection and no pollution.

It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.