A system and process for purifying raw gas under pressure

Abstract

The invention discloses a system and process for purifying raw coal gas under pressure, including a compression separation system, a water washing deammonification system, a methanol washing benzene dehydration system, a low-temperature methanol washing desulfurization system and a purified gas expansion energy recovery system. The raw coal gas after rough purification enters the compression separation system, and after pressurization, enters the water washing deammonification system for deammonification. The raw coal gas treated with deammonification enters the methanol washing benzene dehydration system for debenzenization. The raw coal gas after methanol washing enters the low-temperature methanol washing desulfurization system for desulfurization. The purified gas after low-temperature methanol washing enters the purified gas expansion energy recovery system for energy recovery. The invention has high precision in deammonification, debenzenization and desulfurization. After deammonification, the ammonia in the raw coal gas is less than 5PPM, the recovered ammonia water concentration is high, and the added value is high. After debenzenization, the benzene in the raw coal gas is less than 5PPM, the benzene recovery rate is high, and the subsequent debenzenization investment and cost are reduced. After desulfurization, the total sulfur in the raw coal gas is less than 1PPM, and the subsequent desulfurization investment and cost are reduced. At the same time, the recovered acid gas sulfide concentration is high and the added value is high.

Description

Technical Field

[0001] The invention belongs to the technical field of purification of coke oven gas or cracking furnace gas in chemical equipment, and particularly relates to a system and process for purifying raw gas under pressure. Background Art

[0002] At present, the deamination, desulfurization and debenzenization of coke oven gas or cracking furnace gas are all carried out under low pressure. Most of the deamination processes use sulfuric acid and ammonia to generate sulfur ammonia, and a small part of the deamination process uses phosphoric acid to absorb ammonia, and then distills it to generate liquid ammonia or ammonia water. These two processes require large investments and high production costs, and the deamination accuracy is not high. After deamination, the raw gas still contains 50 mg / cubic ammonia; the debenzening process uses an oil washing debenzening process, which requires large investments, high energy consumption, and low debenzening accuracy. After debenzening, the raw gas still contains 2 g / cubic benzene; the desulfurization process uses a wet method, the raw gas is dirty, the by-product sulfur is of poor quality and low value, and the wet desulfurization inevitably produces secondary salts, which has high processing costs. At the same time, the wet desulfurization cannot remove organic sulfur, and the inorganic sulfur can only be removed to 20 mg / cubic. After desulfurization, part of the gas is used as fuel, and the flue gas needs to be desulfurized after combustion. The flue gas desulfurization investment is large and the cost is high. If the desulfurized gas is used for other purposes, it is also necessary to convert the organic sulfur into inorganic sulfur for removal, which requires large investment and high cost. Summary of the invention

[0003] The purpose of the present invention is to provide a raw gas pressure purification system and process for the above-mentioned problems, which can effectively solve the problems of high investment, high cost and poor removal effect existing in the low-pressure purification treatment method used in the prior art.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A raw gas pressure purification system, characterized by comprising a compression separation system, a methanol elution benzene dehydration system and a low-temperature methanol elution desulfurization system;

[0006] The compression and separation system includes at least one compressor and a gas-liquid separator corresponding to the compressor. The raw coal gas enters the methanol elution benzene dehydration system after being pressurized and water separated by the compression and separation system;

[0007] The methanol elution benzene dehydration system is composed of a methanol washing tower and a de-heavy dehydration regeneration system. The pressurized raw gas enters the methanol washing tower for washing and de-benzening. The methanol washing tower is connected to the de-heavy dehydration regeneration system to form a circulation loop. The non-condensable gas separated by the de-heavy dehydration regeneration system is returned to the inlet end of the compression separation system through a pipeline and mixed with the raw gas.

[0008] The low-temperature methanol washing and desulfurization system includes a low-temperature methanol washing tower, a rich liquid gas-liquid separator and a low-temperature methanol washing regeneration system. The raw coal gas after methanol washing enters the low-temperature methanol washing tower after heat exchange, the methanol liquid after desulfurization is pressurized by a pressure pump at the bottom of the low-temperature methanol washing tower and enters the rich liquid gas-liquid separator after heat exchange, and the purified gas at the top of the low-temperature methanol washing tower returns to the front of the low-temperature methanol washing and desulfurization system for circulation, and the rich liquid gas-liquid separator is connected to the low-temperature methanol washing regeneration system.

[0009] The raw gas pressure purification system described in the present invention also includes a purified gas expansion energy recovery system, which includes an expansion compressor and an expansion gas cooling recovery heat exchanger. The purified gas after washing in the low-temperature methanol washing tower enters the expansion compressor, and after expansion and pressure reduction, the cooling energy is recovered by the expansion gas cooling recovery heat exchanger and then goes to the purified gas low-pressure pipeline network.

[0010] The raw gas pressure purification system described in the present invention, wherein the low-temperature methanol washing regeneration system comprises a regeneration tower, a regeneration tower reflux tank and a cryogenic separator, the rich liquid gas-liquid separator is connected to the regeneration tower, the top of the regeneration tower is connected to the regeneration tower reflux tank and the cryogenic separator in sequence, the liquid phase at the bottom of the regeneration tower reflux tank returns to the regeneration tower, and the liquid phase at the bottom of the cryogenic separator enters the rich liquid gas-liquid separator.

[0011] The raw gas pressure purification system described in the present invention also includes a water washing and deammoniation system, which includes a water washing tower and an ammonia evaporation tower. The pressurized raw gas enters the water washing tower, and the gas at the top of the water washing tower enters the methanol washing tower. The bottom of the water washing tower is connected to a classifier, and ammonia is evaporated from the top of the ammonia evaporation tower to obtain concentrated ammonia water. The non-condensable gas returns to the inlet of the compression and separation system and mixes with the raw gas. The lean liquid after ammonia is removed from the kettle of the ammonia evaporation tower is heat exchanged with the dilute ammonia water entering the ammonia evaporation tower. Most of it is further cooled by a cooler and used as a circulating absorption liquid for the water washing tower, and a small part is further treated as a sewage discharge and sewage delivery device.

[0012] The raw gas pressure purification system described in the present invention adopts a multi-stage compression structure, and the compression and separation system thereof adopts a multi-stage compression structure. The outlet of each compressor of the multi-stage compression is connected to the corresponding gas-liquid separator, and the gas treated by the gas-liquid separator is sent to the inlet of the next compressor, and the gas treated by the gas-liquid separator corresponding to the last compressor is directly sent to the methanol washing tower of the methanol elution benzene dehydration system.

[0013] The raw gas pressure purification system described in the present invention adopts a multi-stage compression structure, and the compression and separation system thereof adopts a multi-stage compression structure. The outlet of each compressor of the multi-stage compression is connected to the corresponding gas-liquid separator, and the gas treated by the gas-liquid separator is sent to the inlet of the next compressor, and the outlet of the last compressor is connected to the water washing tower of the water washing and deammonification system.

[0014] The raw gas pressure purification system described in the present invention adopts a single-stage compression structure in its compression and separation system. The pressurized raw gas is indirectly cooled by a water cooler and then sent to the methanol washing tower of the methanol elution and benzene dehydration system.

[0015] The raw gas pressure purification system described in the present invention adopts a single-stage compression structure in its compression and separation system. The pressurized raw gas is indirectly cooled by a water cooler and then sent to a water washing tower of a water washing and deammonification system.

[0016] In the raw coal gas pressure purification system described in the present invention, the outlet gas of each compressor of the multi-stage compression is cooled by indirect cooling or direct contact cooling, and the direct contact cooling circulating water comes from the gas-liquid separator of each stage, that is, the bottom outlet of the gas-liquid separator of each stage passes through the corresponding interstage water cooling pump, and after being cooled by the cooler, it circulates to the outlet of the gas-liquid separator of the corresponding stage.

[0017] The raw coal gas pressure purification system described in the present invention has the bottom of the water washing tower connected to the stratifier, the upper part of the stratifier is connected to the de-weighting and dehydration regeneration system, the lower part of the stratifier is divided into two paths of dilute ammonia water, one of which is connected to the outlet end of the compressor of the last stage and is used for direct contact cooling of the cooling water of the outlet gas of the compressor of this stage, and the other is connected to the ammonia evaporation tower.

[0018] The raw coal gas pressure purification system of the present invention, when the purified gas is fully depressurized for use or part of the purified gas is depressurized for use while the other part of the purified gas is neither depressurized nor pressurized for use, the top of the low-temperature methanol washing tower is connected to the expansion compressor, and the purified gas that needs to be depressurized enters the expansion end of the expansion compressor to expand to the pressure of the purified gas low-pressure pipeline network, and then absorbs methanol and sulfur-containing tail gas with the low-temperature methanol washing regeneration system for heat exchange and recovery of cold energy before going to the low-pressure pipeline network, the expansion work of the expansion compressor is recovered from the raw raw coal gas, and for the single-stage compression structure of the raw coal gas, the insufficient compression work of the raw coal gas is provided by other energy sources; for the multi-stage compression structure of the raw coal gas, its expansion compression is replaced by a first-stage compressor with similar power in the compression separation system;

[0019] When only a part of the purified gas is needed for pressure reduction and the other part of the purified gas needs to be pressurized, the purified gas at the top of the low-temperature methanol washing tower is divided into two parts: one part enters the expansion end of the expansion compressor to expand to the pressure of the purified gas low-pressure pipeline network, and then absorbs methanol and sulfur-containing tail gas with the low-temperature methanol washing regeneration system to exchange heat and recover cold energy before going to the purified gas low-pressure pipeline network; the other part of the purified gas enters the compression section of the expansion compressor to recover expansion work.

[0020] A process for purifying raw coal gas under pressure, characterized in that it specifically comprises the following process steps:

[0021] Step 1: The crude coal gas after rough purification enters the compression and separation system, which includes at least one compressor and a gas-liquid separator corresponding to the compressor. The pressure after single-stage or multi-stage compression is 0.2-0.8MPaG;

[0022] Step 2: the pressurized raw gas enters a methanol elution benzene dehydration system, which is composed of a methanol washing tower and a de-heavy dehydration regeneration system. In the methanol washing tower, regenerated circulating methanol is used to remove water, benzene and naphthalene components in the raw gas, and then the crude benzene and naphthalene heavy components are regenerated by the de-heavy dehydration regeneration system, and water in the methanol liquid is removed;

[0023] Step 3: The raw gas after methanol washing enters the low-temperature methanol washing and desulfurization system, which includes a low-temperature methanol washing tower, a rich liquid gas-liquid separator, a regeneration tower, a regeneration tower reflux tank and a cryogenic separator. The raw gas after debenzenization is first heat-exchanged with the purified gas at the top outlet of the low-temperature methanol washing tower for cooling, and then enters the low-temperature methanol washing tower. In the low-temperature methanol washing tower, the regenerated circulating low-temperature methanol is used to remove the sulfide and part of the carbon dioxide in the raw gas. The methanol liquid after absorbing the sulfide and part of the carbon dioxide is pressurized by a booster pump and then heat-exchanged with the methanol liquid at the bottom outlet of the regeneration tower for heating, and then enters the rich liquid gas-liquid separator, and the gas returns to the low-temperature methanol washing and desulfurization system. In the previous cycle of the system, methanol liquid enters the regeneration tower, sulfuric acid gas is extracted from the top of the regeneration tower, and then enters the regeneration tower reflux tank after passing through the regeneration tower condenser. The gas phase of the regeneration tower reflux tank goes to the tail gas deep cold heat exchanger, and its liquid phase returns to the regeneration tower. The sulfide tail gas is further condensed into methanol by the tail gas deep cold heat exchanger and then enters the deep cold separator. The liquid phase of the separator enters the rich liquid gas-liquid separator, and the gas phase sulfide tail gas is sent to the sulfur recovery system; the methanol without sulfide comes out from the bottom of the regeneration tower, first heat-exchanges and cools down with the methanol coming out of the low-temperature methanol washing tower, and then heat-exchanges and cools down with the expanded low-temperature and low-pressure purified gas, and finally returns to the low-temperature methanol washing tower after cooling by the refrigerant to circulate and absorb sulfide;

[0024] Step 4. The purified gas after washing with low-temperature methanol enters an expansion energy recovery system. The purified gas expansion energy recovery system includes an expansion compressor and an expansion gas cold recovery heat exchanger. The purified gas that needs to be reduced in pressure enters the expansion section of the expansion compressor to expand and reduce the pressure to the purified gas low-pressure pipeline pressure. The expansion work is recovered by the compression end of the expansion compressor. The expansion work of the expansion compressor is recovered by compressing raw coal gas or purified gas. After expansion, the low-temperature purified gas exchanges heat with the low-temperature methanol washing and desulfurization regeneration system to recover cold and then goes to the purified gas low-pressure pipeline.

[0025] The process for purifying raw coal gas under pressure described in the present invention comprises the following steps: in step 1, the pressurized raw coal gas enters a water washing and deammonification system, and the water washing and deammonification system comprises a water washing tower and an ammonia evaporation tower. In the water washing tower, ammonia in the raw coal gas is absorbed by regenerated circulating water to become dilute ammonia water, and then enters the ammonia evaporation tower to obtain concentrated ammonia water. The non-condensable gas returns to the compressor inlet and mixes with the raw coal gas. The lean liquid after ammonia is removed from the kettle of the ammonia evaporation tower is heat-exchanged with the dilute ammonia water entering the ammonia evaporation tower. Most of it is further cooled in a cooler and used as circulating absorption liquid for the water washing tower, and a small part is further treated as sewage discharge and sewage delivery device.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention has high deammoniation accuracy. After deammoniation, the ammonia content in the raw gas is less than 5 PPM. The recovered ammonia water has a high concentration and high added value.

[0028] (2) The present invention has high debenzenization accuracy. After debenzenization, the benzene content in the raw gas is less than 5 PPM, the benzene recovery rate is high, and the subsequent debenzenization investment and cost are reduced.

[0029] (3) The present invention has high desulfurization accuracy. The total sulfur in the raw coal gas after desulfurization is less than 1 PPM, which reduces the subsequent desulfurization investment and costs. At the same time, the recovered acid gas has a high sulfide concentration and high added value.

[0030] (4) The size of the equipment and pipelines of the present invention is reduced, and the investment is reduced.

[0031] The invention effectively solves the problems of high investment, high cost, low value of by-products, increased subsequent processing costs and environmental pollution caused by incomplete removal in the current low-pressure deamination, debenzenization and desulfurization processes of raw coal gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be described by way of specific embodiments with reference to the accompanying drawings, in which

[0033] Figure 1 It is a schematic diagram of the process flow of Example 1 of the present invention.

[0034] Figure 2 It is a schematic diagram of the process flow of Example 2 of the present invention.

[0035] Figure 3 It is a schematic diagram of the process flow of Example 3 of the present invention.

[0036] Figure 4 It is a schematic diagram of the process flow of Example 4 of the present invention.

[0037] Figure 5 It is a system schematic diagram of the present invention.

[0038] Markings in the figure: 1 is a compression separation system, 2 is a methanol elution benzene dehydration system, 3 is a low-temperature methanol elution desulfurization system, 4 is a purified gas expansion energy recovery system, 5 is a water washing deammonification system, C1 is a first-stage centrifugal compressor or a first-stage reciprocating compressor, C2 is a second-stage centrifugal compressor or a second-stage reciprocating compressor, C3 is a third-stage centrifugal compressor, C4 is a water-sprayed screw compressor, C5 is an expansion compressor, V1 is a first-stage gas-liquid separator, V2 is a second-stage gas-liquid separator, V3 is a stratifier, V4 is a rich liquid gas-liquid separator, V5 is a regeneration tower reflux tank, V6 is a deep cold separator, E1 is a first cooler, E 2 is the second cooler, E3 is the water cooler, E4 is the lean and rich liquid heat exchanger, E5 is the third cooler, E6 is the first heat exchanger, E7 is the second heat exchanger, E8 is the third heat exchanger, E9 is the regeneration tower condenser, E10 is the expansion gas cooling recovery heat exchanger, E11 is the fourth heat exchanger, E12 is the tail gas deep cooling heat exchanger, P1 is the first interstage water cooling pump, P2 is the second interstage water cooling pump, P3 is the circulation pump, P4 is the ammonia still kettle pump, P5 is the booster pump, M1 is the de-weighting and dehydration regeneration system, T1 is the water washing tower, T2 is the ammonia still tower, T3 is the methanol washing tower, T4 is the low-temperature methanol washing tower, and T5 is the regeneration tower. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0040] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0042] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0043] In the description of the embodiments of the present invention, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the invention product is usually placed when in use, or the orientation or positional relationship commonly understood by those skilled in the art, or the orientation or positional relationship in which the invention product is usually placed when in use, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0044] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "setting" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances; the drawings in the embodiments are used to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations.

[0045] Embodiment 1:

[0046] like Figure 1 and 5 As shown, a system for purifying raw gas under pressure includes a compression and separation system 1, a water washing and deammonification system 5, a methanol elution and benzene dehydration system 2, a low-temperature methanol elution and desulfurization system 3 and a purified gas expansion energy recovery system 4. The raw gas after rough purification enters the compression and separation system, and after pressurization, enters the water washing and deammonification system for deammonification. The raw gas after deammonification treatment enters the methanol elution and benzene dehydration system for debenzene. The raw gas after methanol washing enters the low-temperature methanol elution and desulfurization system for desulfurization. The purified gas after low-temperature methanol washing enters the purified gas expansion energy recovery system to recover energy.

[0047] Specifically, the compression and separation system 1 includes a three-stage compressor and a three-stage gas-liquid separator corresponding to the three-stage compressor. The compressor adopts a reciprocating compressor or a centrifugal compressor. The outlet of each compressor of the three-stage compression is connected to the corresponding gas-liquid separator. The gas treated by the gas-liquid separator is sent to the inlet of the next compressor. The outlet of the last compressor is connected to the water washing tower T1 of the water washing and deammonification system 5. The raw coal gas after three-stage compression and gas-liquid separation enters the water washing tower for deammonification treatment.

[0048] Among them, the outlet gas cooling of each compressor of the three-stage compression adopts indirect cooling or direct contact cooling. The gas temperature after cooling is ~40°C. The direct contact cooling circulating water comes from the gas-liquid separator of each stage, that is, the bottom outlet of the gas-liquid separator of each stage passes through the corresponding interstage water cooling pump, and after being cooled by the cooler, it circulates to the outlet of the corresponding gas-liquid separator. The direct contact cooling circulating water of the last stage of compression comes from the stratifier at the bottom of the water washing tower. The oil-containing condensed water condensed between the stages of the three-stage compression is sent to the stratifier at the bottom of the water washing tower.

[0049] Specifically, the water washing and deammonification system 5 includes a water washing tower T1 and an ammonia evaporation tower T2. The pressurized raw gas enters the water washing tower T1, and the gas at the top of the water washing tower T1 enters the methanol washing tower T3. The bottom of the water washing tower T1 is connected to a stratifier V3. The upper part of the stratifier V3 is connected to a de-weighting and dehydration regeneration system M1 for treating the oil phases such as benzene and naphthalene at the upper part of the stratifier. The lower part of the stratifier V3 is divided into two paths, one of which is pressurized by a pump and cooled and then connected to the outlet of the compressor of the last stage. , used as direct contact cooling of the cooling water of the last stage compressor outlet gas, and the other part is heat exchanged with the water coming out of the bottom of the ammonia evaporation tower and enters the ammonia evaporation tower T2. Ammonia is evaporated from the top of the ammonia evaporation tower T2 to obtain concentrated ammonia water. The non-condensable gas returns to the inlet of the compression separation system 1 and mixes with the raw coal gas. The lean liquid after ammonia is removed from the bottom of the ammonia evaporation tower T2 is heat exchanged with the dilute ammonia water entering the ammonia evaporation tower T2. Most of it is further cooled and cooled in the cooler and then used as the circulating absorption liquid of the water washing tower T1, and a small part is used as the sewage discharge and sewage delivery device for further treatment.

[0050] Specifically, the methanol elution benzene dehydration system 2 is composed of a methanol washing tower T3 and a de-heavy dehydration regeneration system M1. The pressurized raw gas enters the methanol washing tower T3 for washing and de-benzening treatment. The methanol washing tower T3 is connected to the de-heavy dehydration regeneration system M1 to form a circulation loop. The non-condensable gas separated by the de-heavy dehydration regeneration system M1 is returned to the inlet end of the compression separation system 1 through a pipeline and mixed with the raw gas. The outlet temperature of the raw gas of the methanol washing tower is 10-40°C, which is controlled by the circulating methanol temperature and flow rate; the methanol-rich liquid that absorbs water and benzene and the oil phase separated by the water washing and de-ammonia stratifier are separated in the de-heavy dehydration regeneration system, the separated non-condensable gas is returned to the compressor inlet and mixed with the raw gas, the separated water is sent to the bottom stratifier of the water washing tower or sent out for further treatment, the separated crude benzene is used as a crude product, and the separated naphthalene, tar and other components are sent out for further recovery. The regenerated methanol obtained after separation is used as the circulating methanol absorption liquid of the methanol washing tower.

[0051] Preferably, the methanol washing tower adopts a multi-layer spray empty tower or a plate tower or a packed tower or a combination of a multi-layer spray empty tower and a plate tower or a multi-layer spray empty tower and a packed tower. The number of plates in the methanol washing tower and the amount of circulating methanol absorbed are adjusted according to the requirements for water and benzene content in the outlet gas of the methanol washing tower.

[0052] Specifically, the low-temperature methanol washing and desulfurization system 3 includes a low-temperature methanol washing tower T4, a rich liquid gas-liquid separator V4, a regeneration tower T5, a regeneration tower reflux tank V5 and a deep cold separator V6. The raw coal gas after methanol washing enters the low-temperature methanol washing tower T4 after heat exchange. The desulfurized methanol liquid is pressurized by a pressure pump P5 at the bottom of the low-temperature methanol washing tower T4 and enters the rich liquid gas-liquid separator V4 after heat exchange. The gas at the top of the low-temperature methanol washing tower T4 returns to the front circulation of the low-temperature methanol washing and desulfurization system 3. The rich liquid gas-liquid separator V4 is connected to the regeneration tower T5. The sulfur content of methanol after regeneration is controlled by the regeneration tower, and the circulation amount and temperature of the absorbed methanol are adjusted at the same time, so that the sulfide in the purified gas after low-temperature methanol washing meets the sulfide requirements for fuel gas or gas for other purposes. The top of the regeneration tower T5 is connected to the regeneration tower reflux tank V5 and the cryogenic separator V6 in sequence. The regeneration tower T5, the regeneration tower reflux tank V5 and the cryogenic separator V6 constitute a low-temperature methanol washing regeneration system. The liquid phase at the bottom of the regeneration tower reflux tank V5 returns to the regeneration tower T5, and the liquid phase at the bottom of the cryogenic separator V6 enters the rich liquid gas-liquid separator V4.

[0053] Specifically, the purified gas expansion energy recovery system 4 includes an expansion compressor C5 and an expansion gas cooling recovery heat exchanger E10. The purified gas after washing by the low-temperature methanol washing tower T4 enters the expansion compressor C5, and after expansion and pressure reduction, it recovers cooling energy through the expansion gas cooling recovery heat exchanger E10 and then goes to the purified gas low-pressure pipeline network.

[0054] Among them, only a part of the purified gas is needed for pressure reduction while the other part of the purified gas needs to be pressurized. The purified gas at the top of the low-temperature methanol washing tower T4 is divided into two parts: one part enters the expansion end of the expansion compressor C5 to expand to the pressure of the purified gas low-pressure pipeline network, and then absorbs methanol and sulfur-containing tail gas with the low-temperature methanol washing regeneration system to exchange heat and recover cold energy before going to the purified gas low-pressure pipeline network; the other part of the purified gas enters the compression section of the expansion compressor C5 to recover expansion work.

[0055] like Figure 1 and 5 As shown, a process for purifying raw gas under pressure, wherein the raw gas includes coke oven gas, cracking furnace gas, pyrolysis gas and other coal gas containing benzene, ammonia and sulfur obtained from coal as raw materials, specifically includes the following process steps:

[0056] Step 1, the raw coal gas after rough purification enters the compression and separation system, which includes a three-stage compressor and a three-stage gas-liquid separator corresponding to the three-stage compressor. The pressure after three-stage compression is 0.2-0.8MPaG, and the pressure after compression is preferably 0.3-0.5MPaG; the raw coal gas after pressurization and cooling to ~40°C enters the water washing and deammonification system, and the temperature of the raw coal gas at the top of the water washing tower is about 10-40°C, which is controlled by the temperature and flow rate of the circulating absorption water at the top of the tower; specifically, the water washing and deammonification system includes a water washing tower and an ammonia still, in which the ammonia in the raw coal gas is absorbed by regenerated circulating water to become dilute ammonia water, and then enters the ammonia still to obtain concentrated ammonia water, and the non-condensable gas returns to the compressor inlet to mix with the raw coal gas, and the lean liquid after ammonia removal in the kettle of the ammonia still is heat-exchanged with the dilute ammonia water entering the ammonia still, and most of it is further cooled and cooled by the cooler as the circulating absorption liquid of the water washing tower, and a small part is further treated as the sewage discharge and sewage delivery device.

[0057] Specifically, the temperature of the crude gas after rough purification is 30-60°C, the pressure is 0.003-0.01MPaG, and the molar composition is 40-60% hydrogen, 6-20% carbon monoxide, 1-7% carbon dioxide, 18-30% methane, 0-6% nitrogen, 1-7% water, 0.2-1.2% oxygen, and 0.6-3% polycarbons. 3 The raw coal gas contains 0.1-0.8 g of tar, 0.05-0.6 g of naphthalene, 4-8 g of H2S, 0.05-0.5 g of organic sulfur, 3-8 g of ammonia, 0.5-2 g of hydrogen cyanide, and 20-40 g of crude benzene.

[0058] Step 2: The raw coal gas after deammoniation enters the methanol elution benzene dehydration system, which is composed of a methanol washing tower and a de-heavy dehydration regeneration system. Regenerated circulating methanol is used in the methanol washing tower to remove water, benzene and naphthalene components in the raw coal gas, and then the crude benzene and naphthalene heavy components are regenerated through the de-heavy dehydration regeneration system, and the water in the methanol liquid is removed.

[0059] Step 3: The raw gas after methanol washing enters the low-temperature methanol washing and desulfurization system, which includes a low-temperature methanol washing tower, a rich liquid gas-liquid separator, a regeneration tower, a regeneration tower reflux tank and a cryogenic separator. The raw gas after debenzenization is first heat-exchanged with the purified gas at the top outlet of the low-temperature methanol washing tower for cooling, and then enters the low-temperature methanol washing tower. In the low-temperature methanol washing tower, the regenerated circulating low-temperature methanol is used to remove the sulfide and part of the carbon dioxide in the raw gas. The methanol liquid after absorbing the sulfide and part of the carbon dioxide is pressurized by a booster pump and then heat-exchanged with the methanol liquid at the bottom outlet of the regeneration tower for heating, and then enters the rich liquid gas-liquid separator, and the gas returns to the low-temperature methanol washing and desulfurization system. In the previous cycle of the system, methanol liquid enters the regeneration tower, and sulfuric acid gas is extracted from the top of the regeneration tower, and then enters the regeneration tower reflux tank after passing through the regeneration tower condenser. The gas phase of the regeneration tower reflux tank goes to the tail gas deep cold heat exchanger, and its liquid phase returns to the regeneration tower. The sulfide tail gas is further condensed into methanol by the tail gas deep cold heat exchanger and then enters the deep cold separator. The liquid phase of the separator enters the rich liquid gas-liquid separator, and the gas phase sulfide tail gas is sent to the sulfur recovery system; the methanol without sulfide comes out from the bottom of the regeneration tower, firstly exchanges heat with the methanol coming out of the low-temperature methanol washing tower for cooling, and then exchanges heat with the expanded low-temperature and low-pressure purified gas for cooling, and finally returns to the low-temperature methanol washing tower for circulation to absorb sulfide after cooling by the refrigerant.

[0060] Furthermore, the circulation amount and temperature of the absorbed methanol can be adjusted so that the sulfide in the purified gas after washing with low-temperature methanol meets the sulfide requirements for use as fuel gas or as gas for other purposes.

[0061] Furthermore, the regenerated sulfuric acid gas can be further processed for sulfur recovery.

[0062] Step 4. The purified gas after washing with low-temperature methanol enters an expansion energy recovery system. The purified gas expansion energy recovery system includes an expansion compressor and an expansion gas cold recovery heat exchanger. The purified gas that needs to be reduced in pressure enters the expansion section of the expansion compressor to expand and reduce the pressure to the purified gas low-pressure pipeline pressure. The expansion work is recovered by the compression end of the expansion compressor. The expansion work of the expansion compressor is recovered by compressing raw coal gas or purified gas. After expansion, the low-temperature purified gas exchanges heat with the low-temperature methanol washing and desulfurization regeneration system to recover cold and then goes to the purified gas low-pressure pipeline.

[0063] The process of this embodiment 1 is specifically described below with reference to specific examples:

[0064] After rough purification, the coke oven gas has a gas volume of 96010Nm 3 / h, temperature is 40℃, pressure is 0.01MPaG, molar composition is 54.44% hydrogen, 5.82% carbon monoxide, 2.06% carbon dioxide, 24.40% methane, 4.22% nitrogen, 4.070% water, 0.56% oxygen, 2.2% polycarbons. 3Coke oven gas contains 0.6 g tar, 0.5 g naphthalene, 5 g H 2 S, 0.5 g organic sulfur, 7 g ammonia, 1.5 g hydrogen cyanide, 34 g crude benzene.

[0065] The above-mentioned coke oven gas first enters the three-stage centrifugal compressors C1~C3, is compressed to 0.12MPaG and 122℃ by the first-stage centrifugal compressor C1, is cooled to 40℃ by direct contact with circulating cooling water, and enters the first-stage gas-liquid separator V1. The liquid at the bottom of the first-stage gas-liquid separator V1 is pressurized to 0.3MPaG by the first interstage water-cooling pump P1, and then is cooled to 35℃ by the first cooler E1 and circulated to the inlet of the first-stage centrifugal compressor C1. The circulating water flow rate is ~540t / h. The raw coal gas coming out of the first-stage gas-liquid separator V1 is compressed to 0.33MPaG and 121℃ by the second-stage centrifugal compressor C2, and is cooled to 40℃ by direct contact with circulating cooling water before entering the second-stage gas-liquid separator V2. The liquid at the bottom of the second-stage gas-liquid separator V2 is pressurized to 0.45MPaG by the second interstage water-cooling pump P2, and then cooled to 35℃ by the second cooler E2, and circulated to the outlet of the second-stage centrifugal compressor C2. The circulating water flow rate is ~560t / h. The raw coal gas coming out of the second-stage gas-liquid separator V2 is compressed to 0.74MPaG and 121℃ by the third-stage centrifugal compressor C3, and then cooled to 40℃ by direct contact with circulating cooling water before entering the water washing tower T1. The circulating coolant comes from the stratifier V3 at the bottom of the water washing tower T1. The circulating liquid is pressurized to 0.85MPaG by the circulating pump P3, and then cooled to 35℃ by the water cooler E3, and circulated to the outlet of the third-stage centrifugal compressor C3. The circulating water flow rate is ~560t / h.

[0066] The ammonia content of the coke oven gas coming out from the top of the water washing tower T1 is ≤5ppm, the temperature is 36℃, and it enters the downstream methanol washing tower T3.

[0067] The bottom of the water washing tower T1 is connected to the stratifier V3. The oil phases such as benzene and naphthalene in the upper part of the stratifier V3 are sent to the de-weighting and dehydration regeneration system M1. Part of the dilute ammonia water in the lower part of the stratifier V3 is used as the cooling water for the outlet gas of the third-stage centrifugal compressor C3; part of it enters the ammonia evaporation tower T2, with a flow rate of ~53.3t / h.

[0068] Ammonia evaporation can be carried out by atmospheric pressure or medium pressure. In this example, atmospheric pressure ammonia evaporation process is adopted. The lean liquid coming out of the kettle of ammonia evaporation tower T2 is heated to 85°C by the lean-rich liquid heat exchanger E4 and then enters the ammonia evaporation tower T2.

[0069] Ammonia is evaporated from the top of the ammonia still T2 to obtain ~4.47t / h of ammonia water with a mass concentration of ~15%. The non-condensable gas at the top of the tower returns to the inlet of the first-stage centrifugal compressor C1 and mixes with the raw coke oven gas. The bottom of the ammonia still T2 is used to remove ammonia water with a flow rate of ~48.8t / h. It is heat-exchanged with the dilute ammonia water entering the ammonia still T2 through the ammonia still T2 bottom pump P4 and mixed with 1.2t / h of supplementary ammonia washing desalted water. It is then further cooled to 35℃ by the third cooler E5 and used as circulating absorption water for the water washing tower. The sewage is discharged regularly.

[0070] The coke oven gas with ammonia removed enters the methanol washing tower T3, where it is circulated and washed with 10°C regenerated methanol at ~30t / h. The coke oven gas after dehydration and debenzenization has benzene ≤5ppm and water ≤1ppm, and the temperature is 24°C.

[0071] The methanol-rich liquid that absorbs water and benzene enters the re-heavy dehydration and regeneration system M1 together with the oil phase separated by the water washing and deammonification separator V3. The non-condensable gas separated by the heavy dehydration and regeneration system M1 is returned to the compressor inlet and mixed with the coke oven gas. The separated water is sent to the sewage treatment system for treatment. The separated crude benzene is used as the crude product, and the separated naphthalene, tar and other components are sent out for further recovery. The regenerated methanol obtained after separation is used as the circulating methanol absorption liquid of the methanol washing tower T3.

[0072] The coke oven gas from the methanol washing tower T3 and the coke oven gas at the top outlet of the low-temperature methanol washing tower T4 are cooled to -30°C through the first heat exchanger E6 and the second heat exchanger E7, and then enter the low-temperature methanol washing tower T4. In the low-temperature methanol washing tower T4, -45°C regenerated low-temperature methanol ~ 135t / h is used for circulating washing. The total sulfur content of the coke oven gas after desulfurization is ≤1ppm, and the temperature is -43°C.

[0073] The rich liquid in the bottom of the low-temperature methanol washing tower T4 is pressurized to 1.0MPaG by the booster pump P5, and then heated to 130°C by the third heat exchanger E8 before entering the rich liquid gas-liquid separator V4. The gas phase of the separator returns to the inlet of the first heat exchanger E6, and the liquid phase enters the regeneration tower T5. The sulfuric acid gas is desorbed by the regeneration tower T5, and the sulfuric acid gas enters the regeneration tower condenser E9 and is cooled to 40°C and enters the regeneration tower reflux tank V5. The gas phase of the reflux tank goes to the tail gas deep cooling heat exchanger E12, and the liquid phase returns to the regeneration tower T5. The sulfide tail gas is cooled to -15°C by the tail gas cryogenic heat exchanger E12, and then enters the cryogenic separator V6 after further condensing methanol. The liquid phase of the separator is circulated back to the rich liquid gas-liquid separator V4, and the gaseous sulfide tail gas is sent to the sulfur recovery system. The methanol-lean liquid is cooled to -45°C by the third heat exchanger E8, the expansion gas cooling recovery heat exchanger E10, and the fourth heat exchanger E11, and then sent to the low-temperature methanol washing tower T4 for cyclic washing.

[0074] The purified gas volume from the top of the low-temperature methanol scrubber T4 is ~89377Nm 3 / h, the pressure is ~0.64MPaG, the molar composition is 58.46% hydrogen, 6.23% carbon monoxide, 1.91% carbon dioxide, 26.12% methane, 4.53% nitrogen, 0.6% oxygen, 2.12% polycarbons, 0.02% methanol, and enters the expansion energy recovery system. The expansion energy recovery system consists of an expansion compressor C5 and an expansion gas cooling recovery heat exchanger E10. The purified gas is divided into two parts, one for decompression and the other for boosting. The purified gas used for decompression is ~40220Nm 3 / h enters the expansion compressor C5 expansion section to expand and reduce pressure ~15kPaG, and then recovers the cold energy through the expansion gas cold energy recovery heat exchanger E10 and goes to the purified gas low-pressure pipeline network. The expansion work is recovered by the compression end of the expansion compressor, and ~49157Nm 3 / h purified gas pressure is increased to 1.19MPaG.

[0075] Embodiment 2:

[0076] Example 2 is basically the same as Example 1, and the difference is mainly as follows: Figure 2 As shown, since the raw coal gas after rough purification does not contain ammonia or contains trace amounts of ammonia, it is not necessary to add a water washing and deammonification system. That is, the gas treated by the gas-liquid separator corresponding to the last-stage compressor of the compression and separation system is directly sent to the methanol washing tower T3 of the methanol elution and benzene dehydration system 2 for debenzene treatment.

[0077] The process of this embodiment 2 is specifically described below with reference to specific examples:

[0078] The cracked coal gas after rough purification has a gas volume of 52893Nm 3 / h, temperature is 40℃, pressure is 0.01MPaG, and the molar composition is 45.73% hydrogen, 13.64% carbon monoxide, 6.87% carbon dioxide, 24.97% methane, 4.08% water, and 2.24% polycarbons. 3 The cracked coal gas contains 0.5g tar, 0.4g naphthalene, 6g H 2 S, 0.5g organic sulfur, 0.01g ammonia, 1g hydrogen cyanide, 35g crude benzene.

[0079] The above cracked coal gas first enters the two-stage reciprocating compressors C1 and C2, and is compressed to 0.14MPaG and 130℃ by the first-stage reciprocating compressor C1. It is directly contacted with circulating cooling water and cooled to 40℃ before entering the first-stage gas-liquid separator V1. The liquid at the bottom of the first-stage gas-liquid separator V1 is pressurized to 0.25MPaG by the first interstage water-cooling pump P1, and then cooled to 35℃ by the first cooler E1, and circulated to the outlet of the first-stage reciprocating compressor C1. The circulating water flow rate is ~500t / h. The cracked coal gas from the first-stage gas-liquid separator V1 is compressed to 0.42MPaG and 129℃ by the second-stage reciprocating compressor C2, and then directly contacts with the circulating cooling water and is cooled to 20℃ before entering the second-stage gas-liquid separator V2. The circulating cooling water comes from the bottom of the second-stage gas-liquid separator V2. The circulating liquid is pressurized to 0.6MPaG by the second interstage water-cooling pump P2, and then cooled to 15℃ by the second cooler E2, and circulated to the outlet of the second-stage reciprocating compressor C2. The circulating water flow rate is ~500,000t / h.

[0080] The purified gas coming out from the top of the second-stage gas-liquid separator V2 has a temperature of 20°C and enters the downstream methanol washing tower T3, wherein the second-stage gas-liquid separator V2 is equipped with a stratifier.

[0081] The benzene, naphthalene and other oil phases in the upper part of the stratifier of the second-stage gas-liquid separator V2 are sent to the de-weighting and dehydration regeneration system M1, and part of the water in the lower part of the stratifier is used as cooling water for the outlet gas of the second-stage reciprocating compressor C2; ~1.6t / h is sent as sewage to the sewage treatment device for further treatment.

[0082] The cracked coal gas coming out of the top of the second-stage gas-liquid separator V2 enters the methanol washing tower T3, where it is circulated and washed with 10°C regenerated methanol ~8t / h. The cracked coal gas after dehydration and debenzenization has benzene ≤5ppm, water ≤1ppm, and temperature 16°C.

[0083] The methanol-rich liquid that absorbs water and benzene enters the de-weighting and dehydration regeneration system M1 together with the oil phase separated by the second-stage gas-liquid separator V2. The non-condensable gas separated by the de-weighting and dehydration regeneration system M1 is returned to the inlet of the first-stage reciprocating compressor C1 to mix with the cracked coal gas. The separated water is sent to the sewage treatment system for treatment. The separated crude benzene is used as the crude product, and the separated naphthalene, tar and other components are sent out for further recovery. The regenerated methanol obtained after separation is used as the circulating methanol absorption liquid of the methanol washing tower T3.

[0084] The coke oven gas from the methanol washing tower T3 and the coke oven gas at the top outlet of the low-temperature methanol washing tower T4 are cooled to -30°C through the first heat exchanger E6 and the second heat exchanger E7, and then enter the low-temperature methanol washing tower T4. In the low-temperature methanol washing tower T4, -45°C regenerated low-temperature methanol ~122t / h is used for circulating washing. The total sulfur content of the coke oven gas after desulfurization is ≤1ppm, and the temperature is -42°C.

[0085] The rich liquid in the bottom of the low-temperature methanol washing tower T4 is pressurized to 1.0MPaG by the booster pump P5, and then heated to 118°C by the third heat exchanger E8 before entering the rich liquid gas-liquid separator V4. The gas phase of the separator returns to the inlet of the first heat exchanger E6, and the liquid phase enters the regeneration tower T5. The sulfuric acid gas is desorbed by the regeneration tower T5, and the sulfuric acid gas enters the regeneration tower condenser and is cooled to 40°C and enters the regeneration tower reflux tank V5. The gas phase of the reflux tank goes to the tail gas deep cooling heat exchanger E12, and the liquid phase returns to the regeneration tower T5. The sulfide tail gas is cooled to -20°C by the tail gas cryogenic heat exchanger E12, and then enters the cryogenic separator V6 after further condensing methanol. The liquid phase of the separator is circulated back to the rich liquid gas-liquid separator V4, and the gaseous sulfide tail gas is sent to the sulfur recovery system. The methanol-lean liquid is cooled to -45°C by the third heat exchanger E8, the expansion gas cooling recovery heat exchanger E10, and the fourth heat exchanger E11, and then sent to the low-temperature methanol washing tower T4 for cyclic washing.

[0086] The purified gas volume from the top of the low-temperature methanol scrubber T4 is ~49307Nm 3 / h, the pressure is ~0.35MPaG, the molar composition is 49.43% hydrogen, 14.73% carbon monoxide, 6.51% carbon dioxide, 26.93% methane, 1.94% polycarbons, 0.04% methanol, and enters the expansion energy recovery system. The expansion energy recovery system consists of an expansion compressor C5 and an expansion gas cooling recovery heat exchanger E10. The purified gas is divided into two parts, one for decompression and the other for boosting. The purified gas used for decompression is ~22188Nm 3 / h enters the expansion compressor C5 expansion section to expand and reduce pressure ~15kPaG, and then recovers the cold energy through the expansion gas cold energy recovery heat exchanger E10 and goes to the purified gas low-pressure pipeline network. The expansion work is recovered by the compression end of the expansion compressor, and ~27119Nm 3 / h purified gas pressure is increased to 0.6MPaG.

[0087] Embodiment 3:

[0088] Example 3 is basically the same as Example 1, and the main difference is that: Figure 3 and 5 As shown, the compression and separation system 1 adopts a single-stage compression structure. The pressurized raw coal gas is sent to the water washing tower T1 of the water washing and deammonification system 5 after being indirectly cooled by the water cooler E3 or directly contact cooled. The gas temperature after cooling is ~40°C, and the direct contact cooling circulating water comes from the water phase of the stratifier at the bottom of the water washing tower. The compressor adopts a water-spraying screw compressor C4. When the water-spraying screw pressurization scheme is adopted, the stratifier increases the diversion of a part of the dilute ammonia water as the circulating spray water of the water-spraying screw; when the compressed outlet gas adopts direct contact cooling, an additional diversion part is used as the compressor outlet gas cooling water, which is directly contacted with the compressor outlet gas after being pressurized and cooled by a pump.

[0089] The process of this embodiment 3 is specifically described below with reference to specific examples:

[0090] After rough purification, the raw gas volume is 95486Nm 3 / h, temperature is 40℃, pressure is 0.01MPaG, molar composition is 50.90% hydrogen, 9.43% carbon monoxide, 2.83% carbon dioxide, 23.56% methane, 4.71% nitrogen, 4.08% water, 0.94% oxygen, 1.88% polycarbons. 3 The raw gas contains 0.6g tar, 0.5g naphthalene, 5g H 2 S, 0.5 g organic sulfur, 7 g ammonia, 1.5 g hydrogen cyanide, 34 g crude benzene.

[0091] The above-mentioned raw coal gas first enters the water-sprayed screw compressor C4, is compressed to 0.5MPaG by the water-sprayed screw compressor C4, is indirectly cooled to 40°C by the water cooler E3, and enters the water washing tower T1.

[0092] The purified gas coming out from the top of the water scrubber T1 has an ammonia content of ≤5ppm and a temperature of 40°C, and enters the downstream methanol scrubber T3.

[0093] The bottom of the water washing tower T1 is connected to the classifier V3. The oil phases such as benzene and naphthalene in the upper part of the classifier V3 are sent to the de-weighting and dehydration regeneration system M1. Part of the dilute ammonia water in the lower part of the classifier V3 is used as cooling water for the water-spraying screw compressor C4; part of it enters the ammonia evaporation tower T2, with a flow rate of ~27.6t / h.

[0094] Ammonia evaporation can be carried out by atmospheric pressure or medium pressure. In this example, atmospheric pressure ammonia evaporation process is adopted. The lean liquid coming out of the kettle of ammonia evaporation tower T2 is heated to 85°C by the lean-rich liquid heat exchanger E4 and then enters the ammonia evaporation tower T2.

[0095] Ammonia is evaporated from the top of the ammonia evaporation tower T2 to obtain ~3t / h of ammonia water with a mass concentration of ~16%. The non-condensable gas at the top of the tower returns to the inlet of the water-spraying screw compressor C4 and mixes with the raw material waste gas. The ammonia evaporation tower T2 kettle is used to remove ammonia water with a flow rate of ~24.6t / h. It is heat-exchanged with the dilute ammonia water entering the ammonia evaporation tower T2 through the ammonia evaporation tower kettle pump P4 and mixed with 0.4t / h of supplementary ammonia washing desalted water. It is then further cooled to 35℃ by the third cooler E5 and used as circulating absorption water for the water washing tower. The sewage is discharged regularly.

[0096] The raw gas from which ammonia has been removed enters the methanol washing tower T3, where it is washed in a circulating manner with 10°C regenerated methanol (25 t / h). After dehydration and benzene removal, the raw gas has benzene ≤5 ppm and water ≤1 ppm, and the temperature is 25°C.

[0097] The methanol-rich liquid that absorbs water and benzene enters the de-weighting and dehydration regeneration system 1 together with the oil phase separated by the water washing and deammonification stratifier V3. The non-condensable gas separated by the de-weighting and dehydration regeneration system M1 is returned to the compressor inlet and mixed with the raw coal gas. The separated water is sent to the sewage treatment system for treatment, the separated crude benzene is used as the crude product, and the separated naphthalene, tar and other components are sent out for further recovery. The regenerated methanol obtained after separation is used as the circulating methanol absorption liquid of the methanol washing tower T3.

[0098] The coke oven gas from the methanol washing tower T3 and the coke oven gas at the top outlet of the low-temperature methanol washing tower T4 are cooled to -30°C through the first heat exchanger E6 and the second heat exchanger E7, and then enter the low-temperature methanol washing tower T4. In the low-temperature methanol washing tower T4, -45°C regenerated low-temperature methanol ~190t / h is used for circulating washing. The total sulfur content of the coke oven gas after desulfurization is ≤1ppm, and the temperature is -43°C.

[0099] The rich liquid in the bottom of the low-temperature methanol washing tower T4 is pressurized to 1.0MPaG by the booster pump P5, and then heated to 116°C by the third heat exchanger E8 before entering the rich liquid gas-liquid separator V4. The gas phase of the separator returns to the inlet of the first heat exchanger E6, and the liquid phase enters the regeneration tower T5. The sulfuric acid gas is desorbed by the regeneration tower T5, and the sulfuric acid gas enters the regeneration tower condenser and is cooled to 40°C and enters the regeneration tower reflux tank V5. The gas phase of the reflux tank goes to the tail gas deep cooling heat exchanger E12, and the liquid phase returns to the regeneration tower T5. The sulfide tail gas is cooled to -10°C by the tail gas cryogenic heat exchanger E12, and then enters the cryogenic separator V6 after further condensing methanol. The liquid phase of the separator is circulated back to the rich liquid gas-liquid separator V4, and the gaseous sulfide tail gas is sent to the sulfur recovery system. The methanol-lean liquid is cooled to -45°C by the third heat exchanger E8, the expansion gas cooling recovery heat exchanger E10, and the fourth heat exchanger E11, and then sent to the low-temperature methanol washing tower T4 for cyclic washing.

[0100] The purified gas volume from the top of the low-temperature methanol scrubber T4 is ~89277Nm 3 / h, the pressure is ~0.42MPaG, the molar composition is 54.43% hydrogen, 10.06% carbon monoxide, 2.69% carbon dioxide, 25.14% methane, 5.03% nitrogen, 1.0% oxygen, 1.6% polycarbons, 0.03% methanol, and enters the expansion energy recovery system. The expansion energy recovery system consists of an expansion compressor C5 and an expansion gas cooling recovery heat exchanger E10. The purified gas is divided into two parts, one part is used for pressure reduction, and the other part is used for pressure increase. The purified gas used for pressure reduction ~40175Nm3 / h enters the expansion section of the expansion compressor C5 for expansion and pressure reduction ~15kPaG, and then recovers the cooling capacity through the expansion gas cooling recovery heat exchanger E10 to go to the purified gas low-pressure pipeline network, and the expansion work is recovered by the compression end of the expansion compressor, and ~49102Nm 3 / h purified gas pressure is increased to 0.74MPaG.

[0101] Embodiment 4:

[0102] Example 4 is basically the same as Example 1, and the difference is mainly as follows: Figure 4 and 5 As shown, the purified gas at the top outlet of the low-temperature methanol washing tower T4 is all depressurized for use, or part of the purified gas is depressurized for use, while the other part of the purified gas is neither depressurized nor pressurized for use. The top of the low-temperature methanol washing tower T4 is connected to the expansion compressor C5, and the purified gas that needs to be depressurized enters the expansion end of the expansion compressor C5 to expand to the pressure of the purified gas low-pressure pipeline network, and then absorbs methanol and sulfur-containing tail gas with the low-temperature methanol washing regeneration system for heat exchange and recovers cold energy before going to the low-pressure pipeline network. The expansion work of the expansion compressor C5 is recovered from the raw raw coal gas. For the single-stage compression structure of the raw coal gas, the insufficient part of the compression work of the raw coal gas is provided by other energy sources; for the multi-stage compression structure of the raw coal gas, as in this embodiment, its expansion compression is replaced by the third-stage centrifugal compressor C3 with similar power in the compression separation system 1.

[0103] The process of this embodiment 4 is specifically described below with reference to specific examples:

[0104] After rough purification, the raw gas volume is 106440Nm 3 / h, temperature is 40℃, pressure is 0.01MPaG, molar composition is 54.56% hydrogen, 5.83% carbon monoxide, 2.07% carbon dioxide, 24.46% methane, 4.23% nitrogen, 4.07% water, 0.56% oxygen, 2.23% polycarbons. 3 The raw gas contains 0.6g tar, 0.5g naphthalene, 5g H 2 S, 0.5 g organic sulfur, 7 g ammonia, 1.5 g hydrogen cyanide, 34 g crude benzene.

[0105] The above-mentioned raw coal gas first enters the three-stage centrifugal compressors C1~C3, is compressed to 0.11MPaG and 117℃ by the first-stage centrifugal compressor C1, is cooled to 40℃ by direct contact with circulating cooling water, and enters the first-stage gas-liquid separator V1. The liquid at the bottom of the first-stage gas-liquid separator V1 is pressurized to 0.2MPaG by the first interstage water-cooling pump P1, and then is cooled to 35℃ by the first cooler E1, and circulated to the outlet of the first-stage centrifugal compressor C1. The circulating water flow rate is ~600t / h. The raw coal gas coming out of the first-stage gas-liquid separator V1 is compressed to 0.3MPaG and 117℃ by the second-stage centrifugal compressor C2, and is cooled to 40~45℃ by direct contact with circulating cooling water before entering the second-stage gas-liquid separator V2. The liquid at the bottom of the second-stage gas-liquid separator V2 is pressurized to 0.4MPaG by the second interstage water-cooling pump P2, and then cooled to 35~45℃ by the second cooler E2, and circulated to the outlet of the second-stage centrifugal compressor C2, with a circulating water flow rate of ~560t / h. The raw coal gas from the second-stage gas-liquid separator V2 is compressed to 0.5MPaG and 90℃ at the compression end of the expansion compressor C5, and is cooled to 40℃ by direct contact with circulating cooling water before entering the water washing tower T1. The circulating cooling water comes from the classifier V3 at the bottom of the water washing tower T1. The circulating water is pressurized to 0.6MPaG by the circulating pump P3, and then cooled to 35℃ by the water cooler E3, and circulated to the compression end outlet of the expansion compressor C5. The circulating water flow rate is ~600t / h.

[0106] The purified gas coming out from the top of the water scrubber T1 has an ammonia content of ≤5ppm and a temperature of 46°C, and enters the downstream methanol scrubber T3.

[0107] The bottom of the water washing tower T1 is connected to the stratifier V3. The oil phases such as benzene and naphthalene in the upper part of the stratifier V3 are sent to the de-weighting and dehydration regeneration system M1. Part of the dilute ammonia water in the lower part of the stratifier V3 is used as the cooling water for the outlet gas of the third-stage centrifugal compressor C3; part of it enters the ammonia evaporation tower T2, with a flow rate of ~44.7t / h.

[0108] Ammonia evaporation can be carried out by atmospheric pressure or medium pressure. In this example, atmospheric pressure ammonia evaporation process is adopted. The lean liquid coming out of the kettle of ammonia evaporation tower T2 is heated to 85°C by the lean-rich liquid heat exchanger E4 and then enters the ammonia evaporation tower T2.

[0109] Ammonia is evaporated from the top of the ammonia still T2 to obtain ~4.3t / h of ammonia water with a mass concentration of ~15%. The non-condensable gas at the top of the tower returns to the inlet of the first-stage centrifugal compressor C1 and mixes with the raw material waste gas. The bottom of the ammonia still T2 tower is used to remove ammonia water, with a flow rate of ~40.3t / h. It is heat-exchanged with the dilute ammonia water entering the ammonia still T2 through the ammonia still T2 tower pump P4 and mixed with 1.7t / h of supplementary ammonia washing desalted water. It is then further cooled to 35℃ by the third cooler E5 and used as circulating absorption water for the water washing tower. The sewage is discharged regularly.

[0110] The raw gas from which ammonia has been removed enters the methanol washing tower T3, where it is circulated and washed with 10°C regenerated methanol (35 t / h). After dehydration and debenzenization, the raw gas has benzene ≤5 ppm, water ≤1 ppm, and the temperature is 28°C.

[0111] The methanol-rich liquid that absorbs water and benzene enters the de-weighting and dehydration regeneration system M1 together with the oil phase separated by the water washing and deammonification separator V3. The non-condensable gas separated by the de-weighting and dehydration regeneration system M1 is returned to the compressor inlet to mix with the raw coal gas. The separated water is sent to the bottom separator of the water washing tower or the sewage treatment system for treatment. The separated crude benzene is used as the crude product, and the separated naphthalene, tar and other components are sent out for further recovery. The regenerated methanol obtained after separation is used as the circulating methanol absorption liquid of the methanol washing tower T3.

[0112] The coke oven gas from the methanol washing tower T3 and the coke oven gas at the top outlet of the low-temperature methanol washing tower T4 are cooled to -30°C through the first heat exchanger E6 and the second heat exchanger E7, and then enter the low-temperature methanol washing tower T4. In the low-temperature methanol washing tower T4, -45°C regenerated low-temperature methanol ~ 210t / h is used for circulating washing. The total sulfur content of the coke oven gas after desulfurization is ≤1ppm, and the temperature is -43°C.

[0113] The rich liquid in the bottom of the low-temperature methanol washing tower T4 is pressurized to 1.0MPaG by the booster pump P5, and then heated to 121°C by the third heat exchanger E8 before entering the rich liquid gas-liquid separator V4. The gas phase of the separator returns to the inlet of the first heat exchanger E6, and the liquid phase enters the regeneration tower T5. The sulfuric acid gas is desorbed by the regeneration tower T5, and the sulfuric acid gas enters the regeneration tower condenser and is cooled to 40°C and enters the regeneration tower reflux tank V5. The gas phase of the reflux tank goes to the tail gas deep cooling heat exchanger E12, and the liquid phase returns to the regeneration tower T5. The sulfide tail gas is cooled to -15°C by the tail gas cryogenic heat exchanger E12, and then enters the cryogenic separator V6 after further condensing methanol. The liquid phase of the separator is circulated back to the rich liquid gas-liquid separator V4, and the gaseous sulfide tail gas is sent to the sulfur recovery system. The methanol-lean liquid is cooled to -45°C by the third heat exchanger E8, the expansion gas cooling recovery heat exchanger E10, and the fourth heat exchanger E11, and then sent to the low-temperature methanol washing tower T4 for cyclic washing.

[0114] The purified gas volume from the top of the low-temperature methanol scrubber T4 is ~99187Nm 3 / h, the pressure is 0.4MPaG, the molar composition is 58.53% hydrogen, 6.25% carbon monoxide, 1.84% carbon dioxide, 26.14% methane, 4.53% nitrogen, 0.6% oxygen, 2.06% polycarbons, and 0.03% methanol, and then enters the expansion energy recovery system. The expansion energy recovery system is composed of an expansion compressor C5 and an expansion gas cooling recovery heat exchanger E10. All the purified gas enters the expansion section of the expansion compressor C5 to expand and reduce the pressure by 15kPa, and then exchanges heat with the low-temperature methanol washing regeneration system to recover cooling energy before going to the purified gas low-pressure pipeline network. The expansion work is recovered by the compression end of the expansion compressor C5 as the source of the third-stage compression energy of the raw gas.

[0115] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A system for purifying raw gas under pressure, characterized in that: It comprises a compression separation system (1), a methanol elution benzene dehydration system (2) and a low-temperature methanol elution desulfurization system (3); The compression separation system (1) comprises at least one compressor and a gas-liquid separator corresponding to the compressor. The raw coal gas enters the methanol elution benzene dehydration system (2) after being pressurized and subjected to water separation treatment in the compression separation system (1); The methanol elution benzene dehydration system (2) is composed of a methanol washing tower (T3) and a de-heavy dehydration regeneration system (M1). The pressurized raw gas enters the methanol washing tower (T3) for washing and de-benzening. The methanol washing tower (T3) is connected to the de-heavy dehydration regeneration system (M1) to form a circulation loop. The non-condensable gas separated by the de-heavy dehydration regeneration system (M1) is returned to the inlet end of the compression separation system (1) through a pipeline and mixed with the raw gas. The low-temperature methanol washing and desulfurization system (3) comprises a low-temperature methanol washing tower (T4), a rich liquid gas-liquid separator (V4) and a low-temperature methanol washing regeneration system. The raw coal gas after methanol washing enters the low-temperature methanol washing tower (T4) after heat exchange. The methanol liquid after desulfurization is pressurized by a pressure pump (P5) from the bottom of the low-temperature methanol washing tower (T4) and enters the rich liquid gas-liquid separator (V4) after heat exchange. The purified gas at the top of the low-temperature methanol washing tower (T4) returns to the front circulation of the low-temperature methanol washing and desulfurization system (3). The rich liquid gas-liquid separator (V4) is connected to the low-temperature methanol washing regeneration system. The raw gas pressure purification system further comprises a purified gas expansion energy recovery system (4), wherein the purified gas expansion energy recovery system (4) comprises an expansion compressor (C5) and an expanded gas cold recovery heat exchanger (E10), wherein the purified gas after being washed by the low-temperature methanol washing tower (T4) enters the expansion compressor (C5), is expanded and depressurized, and then is sent to the purified gas low-pressure pipeline network after recovering cold through the expanded gas cold recovery heat exchanger (E10); The low-temperature methanol washing regeneration system comprises a regeneration tower (T5), a regeneration tower reflux tank (V5) and a cryogenic separator (V6); the rich liquid gas-liquid separator (V4) is connected to the regeneration tower (T5); the top of the regeneration tower (T5) is connected to the regeneration tower reflux tank (V5) and the cryogenic separator (V6) in sequence; the bottom liquid phase of the regeneration tower reflux tank (V5) returns to the regeneration tower (T5); the bottom liquid phase of the cryogenic separator (V6) enters the rich liquid gas-liquid separator (V4); the raw gas pressure purification system also comprises a water washing deammoniation system (5); the water washing deammoniation system (5) comprises a water washing tower (T5); 1) and an ammonia evaporation tower (T2), the pressurized raw gas enters a water scrubber (T1), the gas at the top of the water scrubber (T1) enters a methanol scrubber (T3), the bottom of the water scrubber (T1) is connected to a stratifier (V3), ammonia is evaporated from the top of the ammonia evaporation tower (T2) to obtain concentrated ammonia water, and the non-condensable gas returns to the inlet of the compression separation system (1) to mix with the raw gas, and the lean liquid after ammonia removal from the bottom of the ammonia evaporation tower (T2) exchanges heat with the dilute ammonia water entering the ammonia evaporation tower (T2), most of which is further cooled by a cooler and used as circulating absorption liquid for the water scrubber (T1), and a small part is used as a sewage discharge and sewage device for further treatment.

2. The raw gas pressure purification system according to claim 1 is characterized by: The compression separation system (1) adopts a multi-stage compression structure. The outlet of each compressor of the multi-stage compression is connected to the corresponding gas-liquid separator. The gas treated by the gas-liquid separator is sent to the inlet of the next compressor. The gas treated by the gas-liquid separator corresponding to the last compressor is directly sent to the methanol washing tower (T3) of the methanol elution benzene dehydration system (2).

3. The raw gas pressure purification system according to claim 1 is characterized by: The compression separation system (1) adopts a multi-stage compression structure. The outlet of each compressor of the multi-stage compression is connected to the corresponding gas-liquid separator, and the gas treated by the gas-liquid separator is sent to the inlet of the next compressor. The outlet of the last compressor is connected to the water washing tower (T1) of the water washing and deammonification system (5).

4. The raw gas pressure purification system according to claim 1 is characterized in that: The compression separation system (1) adopts a single-stage compression structure. The pressurized raw gas is indirectly cooled by a water cooler (E3) and then sent to the methanol washing tower (T3) of the methanol elution benzene dehydration system (2).

5. The raw gas pressure purification system according to claim 1 is characterized by: The compression separation system (1) adopts a single-stage compression structure. The pressurized raw gas is indirectly cooled by a water cooler (E3) and then sent to a water washing tower (T1) of a water washing and deammonification system (5).

6. The raw gas pressure purification system according to claim 2 or 3, characterized in that: The outlet gas of each compressor of the multi-stage compression is cooled by indirect cooling or direct contact cooling. The direct contact cooling circulating water comes from the gas-liquid separator of each stage, that is, the bottom outlet of the gas-liquid separator of each stage passes through the corresponding interstage water cooling pump, and after being cooled by the cooler, it circulates to the outlet of the gas-liquid separator of the corresponding stage.

7. The system for purifying raw gas under pressure according to claim 1, 3 or 5, characterized in that: The bottom of the water washing tower (T1) is connected to a stratifier (V3), the upper part of the stratifier (V3) is connected to a deweighting and dehydrating regeneration system (M1), and the lower part of the stratifier (V3) is divided into two paths, one of which is connected to the outlet end of the compressor of the last stage and is used for direct contact cooling of the cooling water of the outlet gas of the compressor of this stage, and the other is connected to the ammonia evaporation tower (T2).

8. The raw gas pressure purification system according to claim 1 is characterized by: When the purified gas is fully depressurized for use or part of the purified gas is depressurized for use while the other part of the purified gas is neither depressurized nor pressurized for use, the top of the low-temperature methanol washing tower (T4) is connected to the expansion compressor (C5), and the purified gas to be depressurized enters the expansion end of the expansion compressor (C5) and expands to the pressure of the purified gas low-pressure pipeline network, and then absorbs methanol and sulfur-containing tail gas with the low-temperature methanol washing regeneration system to exchange heat and recover cold energy before going to the low-pressure pipeline network. The expansion work of the expansion compressor (C5) is recovered from the raw raw coal gas. For the single-stage compression structure of the raw coal gas, the insufficient compression work of the raw coal gas is provided by other energy sources; for the multi-stage compression structure of the raw coal gas, its expansion compression is replaced by a first-stage compressor with similar power in the compression separation system (1); When only a part of the purified gas is needed for pressure reduction and the other part of the purified gas needs to be pressurized, the purified gas at the top of the low-temperature methanol washing tower (T4) is divided into two parts: one part enters the expansion end of the expansion compressor (C5) to expand to the pressure of the purified gas low-pressure pipeline network, and then absorbs methanol and sulfur-containing tail gas with the low-temperature methanol washing regeneration system to exchange heat and recover cold energy before going to the purified gas low-pressure pipeline network; the other part of the purified gas enters the compression section of the expansion compressor (C5) to recover expansion work.

9. A process for purifying raw coal gas under pressure, characterized in that: The raw gas pressure purification system according to claim 1 specifically comprises the following process steps: Step 1: The crude coal gas after rough purification enters the compression and separation system, which includes at least one compressor and a gas-liquid separator corresponding to the compressor. The pressure after single-stage or multi-stage compression is 0.2-0.8MPaG; Step 2: the pressurized raw gas enters a methanol elution benzene dehydration system, which is composed of a methanol washing tower and a de-heavy dehydration regeneration system. In the methanol washing tower, regenerated circulating methanol is used to remove water, benzene and naphthalene components in the raw gas, and then the crude benzene and naphthalene heavy components are regenerated by the de-heavy dehydration regeneration system, and water in the methanol liquid is removed; Step 3: The raw gas after methanol washing enters the low-temperature methanol washing and desulfurization system, which includes a low-temperature methanol washing tower, a rich liquid gas-liquid separator, a regeneration tower, a regeneration tower reflux tank and a cryogenic separator. The raw gas after debenzenization is first heat-exchanged with the purified gas at the top outlet of the low-temperature methanol washing tower for cooling, and then enters the low-temperature methanol washing tower. In the low-temperature methanol washing tower, the regenerated circulating low-temperature methanol is used to remove the sulfide and part of the carbon dioxide in the raw gas. The methanol liquid after absorbing the sulfide and part of the carbon dioxide is pressurized by a booster pump and then heat-exchanged with the methanol liquid at the bottom outlet of the regeneration tower for heating, and then enters the rich liquid gas-liquid separator, and the gas returns to the low-temperature methanol washing and desulfurization system. In the previous cycle of the system, methanol liquid enters the regeneration tower, sulfuric acid gas is extracted from the top of the regeneration tower, and then enters the regeneration tower reflux tank after passing through the regeneration tower condenser. The gas phase of the regeneration tower reflux tank goes to the tail gas deep cold heat exchanger, and its liquid phase returns to the regeneration tower. The sulfide tail gas is further condensed into methanol by the tail gas deep cold heat exchanger and then enters the deep cold separator. The liquid phase of the separator enters the rich liquid gas-liquid separator, and the gas phase sulfide tail gas is sent to the sulfur recovery system; the methanol without sulfide comes out from the bottom of the regeneration tower, first heat-exchanges and cools down with the methanol coming out of the low-temperature methanol washing tower, and then heat-exchanges and cools down with the expanded low-temperature and low-pressure purified gas, and finally returns to the low-temperature methanol washing tower after cooling by the refrigerant to circulate and absorb sulfide; Step 4. The purified gas after washing with low-temperature methanol enters an expansion energy recovery system. The purified gas expansion energy recovery system includes an expansion compressor and an expansion gas cold recovery heat exchanger. The purified gas that needs to be reduced in pressure enters the expansion section of the expansion compressor to expand and reduce the pressure to the purified gas low-pressure pipeline pressure. The expansion work is recovered by the compression end of the expansion compressor. The expansion work of the expansion compressor is recovered by compressing raw coal gas or purified gas. After expansion, the low-temperature purified gas exchanges heat with the low-temperature methanol washing and desulfurization regeneration system to recover cold and then goes to the purified gas low-pressure pipeline.

10. The process for purifying raw coal gas under pressure according to claim 9, characterized in that: In the step 1, the pressurized raw gas enters the water washing and deammonification system, which includes a water washing tower and an ammonia evaporation tower. In the water washing tower, the ammonia in the raw gas is absorbed by regenerated circulating water to become dilute ammonia water, and then enters the ammonia evaporation tower to obtain concentrated ammonia water. The non-condensable gas returns to the compressor inlet and mixes with the raw gas. The lean liquid after ammonia is removed from the kettle of the ammonia evaporation tower is heat-exchanged with the dilute ammonia water entering the ammonia evaporation tower. Most of it is further cooled by the cooler and used as the circulating absorption liquid of the water washing tower, and a small part is further treated as the sewage discharge device.

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