Rectisol system

Abstract

The present application discloses a Rectisol system, comprising a first heat exchanger, an inlet gas separator tank, a feed gas scrubber, a medium-pressure flash column, a CO2 stripper, an H2S concentration column, a thermal regeneration column, a methanol-water separation column, and a tail gas scrubber, which are connected in sequence. A five-section feed gas scrubber is used, one section is used for sulfide removal, and four sections are used for CO2 removal. Decarbonization sections undergo three inter-stage heat exchanges, thereby reducing the circulation amount of lean methanol. In addition, no semi-lean liquid is used during scrubbing, simplifying the process, and making the tail gas emission index easy to guarantee. A CO2 recovery system is optimized, and a two-stage flash column and sulfur-free methanol are used to perform low-pressure flashing to produce a CO2 product gas, ensuring that the yield of CO2 meets production requirements.

Description

A low-temperature methanol washing system Technical Field

[0001] This application relates to a low-temperature methanol washing system, belonging to the field of methanol washing technology. Background Technology

[0002] Low-temperature methanol washing technology typically uses cold methanol as the absorbent solvent, leveraging methanol's high solubility for acidic gases at low temperatures to remove them from the feed gas. The process generally includes an absorption tower and several desorption towers. The absorption tower absorbs the acidic gases, while the desorption towers desorb the acidic gases and return the lean methanol solution to the absorption tower for methanol recycling.

[0003] However, the existing low-temperature methanol washing systems have large circulation volumes, complex processes, and mostly use semi-lean liquor, making it difficult to guarantee exhaust gas emission standards.

[0004] Summary of the Invention

[0005] To address the problems of existing low-temperature methanol washing systems having large circulation volumes, complex processes, and often using semi-lean solutions, making it difficult to guarantee tail gas emission standards, according to one aspect of this application, a low-temperature methanol washing system is provided, comprising a first heat exchanger, an inlet gas separator, a raw material gas scrubbing tower, a medium-pressure flash evaporator, a CO2 desorption tower, an H2S concentration tower, a thermal regeneration tower, a methanol-water separator, and a tail gas scrubbing tower connected in sequence.

[0006] The raw gas scrubbing tower consists of interconnected sections A, B, C, D, and E from bottom to top.

[0007] The bottom of section B of the raw gas scrubbing tower is connected to the top of section A of the raw gas scrubbing tower through the seventeenth heat exchanger.

[0008] The medium-pressure flash tower includes sections A and B, and the two sections are isolated from each other. The top outlet of section B of the medium-pressure flash tower is connected to section A of the medium-pressure flash tower through an external passage.

[0009] The bottom of section B of the raw gas scrubbing tower is connected to section B of the medium-pressure flash evaporator in sequence through the seventh heat exchanger and the fourth heat exchanger.

[0010] The bottom outlet of section A of the raw gas scrubbing tower is connected to section A of the medium-pressure flash evaporator in sequence through the seventh heat exchanger, the nineteenth heat exchanger, and the third heat exchanger.

[0011] The ammonia synthesis process uses coal as raw material, and adopts pulverized coal gasification to produce crude coal gas. After being pressurized, it is sent to the shift process to convert CO into H2, and then input into the low-temperature methanol washing system of this application. After the shift gas is washed by low-temperature methanol and purified, it becomes fresh gas that meets the requirements of ammonia synthesis. The fresh gas is pressurized by the synthesis gas compressor and sent to the low-pressure ammonia synthesis process to produce the intermediate product ammonia.

[0012] Optionally, the top of section E of the raw gas scrubbing tower is connected to the purified gas to liquid nitrogen scrubbing passage;

[0013] The bottom of section E of the raw gas scrubbing tower is connected to the top of section D of the raw gas scrubbing tower via a fifth heat exchanger.

[0014] The bottom of section D and the bottom of section C of the raw gas scrubbing tower are connected to the top of section C and the top of section B of the raw gas scrubbing tower respectively through a sixth heat exchanger.

[0015] Preferably, the A section of the medium-pressure flash evaporator is connected to the inlet of the first heat exchanger via a circulating gas compressor and a second heat exchanger in sequence.

[0016] The fifth and sixth heat exchangers are installed to reduce the temperature of the rich absorbent solution and improve the absorption capacity.

[0017] Optionally, the CO2 desorption tower includes sections A and B that are connected within the tower;

[0018] The bottom outlets of sections A and B of the medium-pressure flash evaporator are both connected to section B of the CO2 desorption tower.

[0019] The top output gas of section B of the CO2 desorption tower passes through the nineteenth heat exchanger and the first heat exchanger in sequence before being output.

[0020] Optionally, the H2S concentration tower includes sections A, B, and C, wherein section A of the H2S concentration tower is internally connected to section B of the H2S concentration tower, and section C of the H2S concentration tower is located above section B of the H2S concentration tower and the two are internally isolated.

[0021] The bottom of section C of the H2S concentration tower is connected to the top of section B of the H2S concentration tower via an external passage.

[0022] The gas output from the top of section C of the H2S concentration tower passes sequentially through the nineteenth heat exchanger and the first heat exchanger before being output.

[0023] The bottom outlet of section B of the medium-pressure flash evaporator is also connected to section C of the H2S concentration tower.

[0024] The bottom of section B of the CO2 desorption tower is connected to section B of the H2S concentration tower via a ninth liquid pump.

[0025] The bottom of section A of the CO2 desorption tower is connected to section A of the H2S concentration tower in sequence via a second liquid pump and a seventh heat exchanger.

[0026] The H2S concentration tower section B is connected to the tail gas scrubbing tower via the twenty-first heat exchanger and the first heat exchanger in sequence.

[0027] The H2S concentration tower section B is connected to the CO2 desorption tower section A in sequence via the first liquid pump, the eighth heat exchanger, and the sixth heat exchanger.

[0028] The bottom of section A of the H2S concentration tower is connected to the nitrogen stripping tower in sequence via a third liquid pump, a second filter, and a ninth heat exchanger.

[0029] The top of the raw gas scrubbing tower is connected to a liquid nitrogen scrubbing device, which is also connected to section A of the H2S concentration tower.

[0030] Preferably, the top of the nitrogen stripping tower is connected to section A of the H2S concentration tower, and the bottom is connected to the thermal regeneration tower in sequence through an eighth liquid pump, a third filter, and a tenth heat exchanger.

[0031] The nitrogen stripping tower has a nitrogen inlet at the bottom for nitrogen to be introduced.

[0032] Optionally, the top of the thermal regeneration tower is connected to the reflux tank via a twelfth heat exchanger;

[0033] The top of the reflux tank is connected to the H2S gas separator via the fourteenth heat exchanger and the thirteenth heat exchanger in sequence.

[0034] The top of the H2S gas separator is connected to the sulfur recovery passage via the fourteenth heat exchanger;

[0035] The top and bottom of the H2S gas separator are also connected to section A of the H2S concentration tower, respectively.

[0036] The bottom of the reflux tank is connected to the thermal regeneration tower via a sixth liquid pump.

[0037] Optionally, the bottom of the thermal regeneration tower is sequentially connected to the tenth heat exchanger, the lean methanol tank, the fourth liquid pump, and the eighteenth heat exchanger;

[0038] The outlet of the eighteenth heat exchanger is divided into two paths. One path is connected to the first heat exchanger, and the other path is connected to the raw gas scrubbing tower section E in sequence through the ninth heat exchanger, the twenty-first heat exchanger, and the eighth heat exchanger.

[0039] The bottom of the thermal regeneration tower is also connected in sequence to a fifth liquid pump and a first filter;

[0040] The outlet of the first filter is divided into two paths: one path is connected to the tenth heat exchanger, and the other path is connected to the methanol-water separation tower through the sixteenth heat exchanger.

[0041] Preferably, an eleventh heat exchanger is also provided at the bottom of the thermal regeneration tower.

[0042] Optionally, the inlet gas separator is connected to the CO2 / methanol separator via the sixteenth heat exchanger;

[0043] The top of the CO2 / methanol separator is connected to section B of the CO2 desorption tower;

[0044] The bottom of the CO2 / methanol separator is connected to the methanol-water separator.

[0045] Optionally, the top of the methanol-water separator is connected to the thermal regeneration tower;

[0046] The bottom of the methanol-water separator is connected to the tail gas scrubbing tower via the twentieth heat exchanger.

[0047] Preferably, a fifteenth heat exchanger is also provided at the bottom of the methanol-water separation tower.

[0048] Optionally, the top of the exhaust gas scrubbing tower is connected to the exhaust gas output passage;

[0049] The bottom of the tail gas scrubbing tower is connected to the methanol-water separation tower in sequence via the seventh liquid pump and the twentieth heat exchanger.

[0050] The exhaust gas scrubbing tower is also equipped with a demineralized water inlet.

[0051] Optionally, the twentieth heat exchanger is also connected to a wastewater output passage.

[0052] The process of low-temperature methanol washing of raw gas in this system mainly includes:

[0053] 1. Raw material gas scrubbing

[0054] The feed gas entering the low-temperature methanol washing system is mixed with the circulating flash vapor after exiting the circulating gas compressor and the second heat exchanger. A small amount of anti-icing methanol can be injected into it here. After being cooled by heat exchange with the synthesis gas, CO2 gas and tail gas through the first heat exchanger, and after the water is separated in the inlet gas separator, it enters the feed gas washing tower.

[0055] The raw gas scrubbing tower is divided into five sections. Section A of the raw gas scrubbing tower is the desulfurization section, and the four sections above it are the decarbonization sections.

[0056] Sulfides in the feed gas are removed in section A of the feed gas scrubbing tower. The feed gas is scrubbed with a portion of CO2-rich methanol liquid from the decarbonization section to remove sulfides such as H2S and some components such as CO2 before entering the decarbonization section. At this point, the gas entering the decarbonization section no longer contains sulfur.

[0057] The CO2 in the raw gas is removed to the specified level in sections B, C, D, and E of the raw gas scrubbing tower. The raw gas is then scrubbed with a lean methanol solution in the upper part of section E of the raw gas scrubbing tower to remove CO2 until the purification requirements are met.

[0058] The purified gas is drawn from the top of the raw material gas scrubbing tower and sent to the liquid nitrogen scrubbing device. The liquid nitrogen scrubbing device returns a portion of the synthesis gas, which is then sent back to the liquid nitrogen scrubbing device after exchanging heat with the seventeenth heat exchanger and the first heat exchanger in sequence with the rich methanol and the raw material gas to recover the cold energy.

[0059] 2. Medium-pressure flash evaporation recovery of effective gases from methanol-rich products

[0060] After being absorbed by H2S and CO2, the sulfur-rich methanol that comes out of section A of the raw gas scrubbing tower is heated by the seventh heat exchanger and the nineteenth heat exchanger, and then cooled by the third heat exchanger. After being depressurized, dissolved H2, CO gas and a small amount of H2S, CO2 and other gases are flashed out in section A of the medium-pressure flash tower.

[0061] Similarly, the sulfur-free methanol liquid from the decarbonization section of the raw gas scrubbing tower is heated by the seventh heat exchanger and cooled by the fourth heat exchanger. After depressurization, dissolved H2, CO gas and a small amount of CO2 gas are flashed out in section B of the medium-pressure flash tower.

[0062] The flash gas from the medium-pressure flash tower and the recycled hydrogen returned after being washed with liquid nitrogen are pressurized by the recycled gas compressor and returned to the raw material gas to recover useful gases.

[0063] 3. Methanol-rich low-pressure flash evaporation and stripping

[0064] The sulfur-containing methanol exiting from section A of the CO2 desorption tower is depressurized and sent to the middle of section B of the CO2 desorption tower, where dissolved CO2 is flashed out, and some of the dissolved H2S is also flashed out at the same time.

[0065] A portion of the sulfur-free methanol liquid exiting from section B of the CO2 desorption tower enters the top of section B of the CO2 desorption tower, where dissolved CO2 gas is flashed out under low pressure. At the same time, H2S in the sulfur-containing methanol flash vapor is washed away. CO2 product gas is obtained at the top of the CO2 desorption tower. This product gas is sent out of the system as high-purity CO2 product gas after exchanging heat with the methanol-rich gas and the feed gas through the nineteenth heat exchanger and the first heat exchanger.

[0066] When CO2 product gas is not needed, this gas is combined with the tail gas and sent to the tail gas scrubbing tower for water washing before being released into the atmosphere.

[0067] The sulfur-containing methanol exiting from section B of the CO2 desorption tower enters the middle of section B of the H2S concentration tower, where it continues to flash evaporate dissolved CO2 under low pressure.

[0068] A portion of the sulfur-free methanol liquid exiting from section B of the medium-pressure flash distillation tower enters section C of the H2S concentration tower. After CO2 gas is flashed out under reduced pressure, it enters the upper part of section B of the H2S concentration tower to wash the sulfides in the tail gas. The CO2 gas obtained from section C of the H2S concentration tower is combined with the CO2 gas at the top of the CO2 desorption tower.

[0069] The tail gas obtained from the B section of the H2S concentration tower has qualified sulfur content. After heat exchange in the 21st heat exchanger and the 1st heat exchanger, it enters the tail gas scrubbing tower and is scrubbed with demineralized water. The tail gas that meets the emission standards after water washing is released into the air through a tall chimney. The scrubbing water containing a small amount of methanol at the bottom of the tail gas scrubbing tower is sent to the methanol-water separation tower to recover methanol after heat exchange in the 20th heat exchanger.

[0070] The sulfur-containing methanol solution exiting from the lower part of section B of the H2S concentration tower serves as the cold source with the lowest solution temperature in the system. It exchanges heat with lean methanol solution in the eighth heat exchanger, and then enters section A of the CO2 desorption tower after heat exchange in the sixth heat exchanger. After flash evaporation of CO2 product gas, the liquid is pressurized by the second liquid pump, and then enters section A of the H2S concentration tower after heat exchange in the seventh heat exchanger with the rich liquid at the bottom of the feed gas scrubbing tower. To fully desorb the dissolved CO2 in the rich methanol liquid, low-pressure nitrogen is introduced for gas stripping. After gas stripping, the bottom of the H2S concentration tower yields methanol liquid with low CO2 content and low temperature. This methanol liquid contains a small amount of CO2 and basically all the sulfides in the feed gas. It is pressurized by the third liquid pump, filtered through the second filter, and heated by the ninth heat exchanger before entering the nitrogen stripping tower. A small amount of nitrogen is used for gas stripping at room temperature to fully desorb the CO2. The gas from the nitrogen stripping tower is fed into section A of the H2S concentration tower; the rich methanol at the bottom of the nitrogen stripping tower is pressurized by the eighth liquid pump, filtered by the third filter, and after exchanging heat with the lean methanol from the thermal regeneration tower in the tenth heat exchanger, it enters the thermal regeneration tower for thermal regeneration.

[0071] 4. Methanol-rich thermal regeneration

[0072] The thermal regeneration tower produces lean methanol at the bottom and H2S-rich gas at the top. After exiting the bottom of the thermal regeneration tower, the lean methanol is cooled by the tenth heat exchanger and enters the lean methanol tank. It is then pumped out and pressurized by the fourth liquid pump, and subsequently cooled by the eighteenth, ninth, twenty-first, and eighth heat exchangers before being sent to the top of the feed gas scrubbing tower, completing the methanol cycle.

[0073] The gas with a high H2S concentration obtained at the top of the thermal regeneration tower is cooled and then separated into sulfur-containing methanol liquid.

[0074] The sulfur-containing methanol liquid obtained during the H2S separation process is returned to the bottom of the H2S concentration tower, while acidic gas with a high H2S concentration is separated and sent to sulfur recovery as an acidic gas product; if necessary, part of the H2S gas is recycled back into the H2S concentration tower to increase the H2S concentration in the acidic gas product.

[0075] 5. Methanol-water separation

[0076] The aqueous methanol separated from the inlet gas separator also contains CO2. After heat exchange in the sixteenth heat exchanger, it enters the CO2 / methanol separator for flash evaporation. The flashed gas phase is sent to the CO2 desorption tower, and the liquid phase is sent to the middle section of the methanol-water separator.

[0077] The aqueous solution containing a small amount of methanol that comes out from the bottom of the tail gas scrubbing tower also enters the middle part of the methanol-water separation tower; the small amount of lean methanol that comes out from the bottom of the thermal regeneration tower is used as reflux in the methanol-water separation tower after heat exchange through the sixteenth heat exchanger.

[0078] The methanol vapor at the top of the methanol-water separator is returned to the middle of the thermal regeneration tower, and water with a methanol content meeting the emission standards is obtained at the bottom of the methanol-water separator. After heat exchange and cooling, the water is discharged from the system.

[0079] The system consists of a heat exchange network of more than 20 heat exchangers to recover cold energy and ensure excellent process conditions.

[0080] The beneficial effects that this application can produce include:

[0081] The low-temperature methanol washing system provided in this application adopts a five-stage feed gas washing tower and an upper three-stage heat exchange, which saves the circulation volume and eliminates the need for semi-lean liquor, simplifying the process and making it easier to ensure the exhaust gas emission indicators.

[0082] Meanwhile, the CO2 recovery system was optimized by using a two-stage flash tower with sulfur-free methanol for low-pressure flash evaporation, which ensured the CO2 production. Attached Figure Description

[0083] Figure 1 is a schematic diagram of a low-temperature methanol washing system provided in one embodiment of this application.

[0084] List of components and reference numerals: Detailed Implementation

[0085] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0086] Unless otherwise specified, the raw materials and catalysts used in the embodiments of this application were all purchased commercially.

[0087] According to one embodiment of this application, a low-temperature methanol washing system is provided, comprising a first heat exchanger E-101, an inlet gas separator V-101, a raw material gas scrubbing tower C-101, a medium-pressure flash evaporator C-108, a CO2 desorption tower C-102, an H2S concentration tower C-103, a thermal regeneration tower C-104, a methanol-water separation tower C-105, and a tail gas scrubbing tower C-106 connected in sequence.

[0088] The raw gas scrubbing tower C-101 includes sections A, B, C, D, and E that are interconnected inside the tower, from bottom to top.

[0089] The bottom of section C-101B of the raw gas scrubbing tower is connected to the top of section C-101A of the raw gas scrubbing tower through the seventeenth heat exchanger E-117;

[0090] The medium-pressure flash evaporator C-108 includes sections A and B, and the two sections are isolated from each other. The top outlet of section B of the medium-pressure flash evaporator C-108 is connected to section A of the medium-pressure flash evaporator C-108 through an external passage.

[0091] The bottom of section C-101B of the raw gas scrubbing tower is connected to section C-108B of the medium-pressure flash evaporator via the seventh heat exchanger E-107 and the fourth heat exchanger E-104 in sequence.

[0092] The bottom outlet of section C-101A of the raw gas scrubbing tower is connected to section C-108A of the medium-pressure flash evaporator via the seventh heat exchanger E-107, the nineteenth heat exchanger E-119, and the third heat exchanger E-103 in sequence.

[0093] The ammonia synthesis process uses coal as raw material, and adopts pulverized coal gasification to produce crude coal gas. After being pressurized, it is sent to the shift process to convert CO into H2, and then input into the low-temperature methanol washing system of this application. After the shift gas is washed by low-temperature methanol and purified, it becomes fresh gas that meets the requirements of ammonia synthesis. The fresh gas is pressurized by the synthesis gas compressor and sent to the low-pressure ammonia synthesis process to produce the intermediate product ammonia.

[0094] The top of section C-101E of the raw gas scrubbing tower is connected to the purified gas to liquid nitrogen scrubbing passage;

[0095] The bottom of section C-101E of the raw gas scrubbing tower is connected to the top of section C-101D of the raw gas scrubbing tower through the fifth heat exchanger E-105.

[0096] The bottom of section C-101D and the bottom of section C-101C of the raw gas scrubbing tower are connected to the top of section C-101C and the top of section C-101B of the raw gas scrubbing tower respectively through the sixth heat exchanger E-106.

[0097] The medium-pressure flash tower C-108A section is connected to the inlet of the first heat exchanger E-101 via a circulating gas compressor K-101 and a second heat exchanger E-102.

[0098] The fifth heat exchanger E-105 and the sixth heat exchanger E-106 are installed to reduce the temperature of the rich absorbent solution and improve the absorption capacity.

[0099] The CO2 desorption tower C-102 includes sections A and B that are connected inside the tower;

[0100] The bottom outlets of sections C-108A and B of the medium-pressure flash evaporator are respectively connected to section C-102B of the CO2 desorption tower;

[0101] The top output gas of section C-102B of the CO2 desorption tower passes sequentially through the nineteenth heat exchanger E-119 and the first heat exchanger E-101 before being output.

[0102] The H2S concentration tower C-103 includes sections A, B and C. Section A of H2S concentration tower C-103 is connected to section B of H2S concentration tower C-103, and section C of H2S concentration tower C-103 is located above section B of H2S concentration tower C-103 and the two are isolated from each other inside the tower.

[0103] The bottom of section C-103C of the H2S concentration tower is connected to the top of section C-103B of the H2S concentration tower via an external passage;

[0104] The gas output from the top of section C-103C of the H2S concentration tower passes sequentially through the nineteenth heat exchanger E-119 and the first heat exchanger E-101 before being output.

[0105] The bottom outlet of the medium-pressure flash distillation tower C-108B section is also connected to the H2S concentration tower C-103C section.

[0106] The bottom of the CO2 desorption tower C-102B section is connected to the H2S concentration tower C-103B section via the ninth liquid pump P-109.

[0107] The bottom of the CO2 desorption tower C-102A section is connected to the H2S concentration tower C-103A section in sequence via the second liquid pump P-102 and the seventh heat exchanger E-107.

[0108] The H2S concentration tower C-103B section is connected to the tail gas scrubbing tower C-106 via the twenty-first heat exchanger E-121 and the first heat exchanger E-101 in sequence.

[0109] The H2S concentration tower C-103B section is connected to the CO2 desorption tower C-102A section in sequence through the first liquid pump P-101, the eighth heat exchanger E-108, and the sixth heat exchanger E-106.

[0110] The bottom of the H2S concentration tower C-103A section is connected to the nitrogen stripping tower C-107 via the third liquid pump P-103, the second filter S-102, and the ninth heat exchanger E-109 in sequence.

[0111] The top of the raw gas scrubbing tower C-101 is connected to a liquid nitrogen scrubbing device, which is also connected to section C-103A of the H2S concentration tower.

[0112] The top of the nitrogen stripping tower C-107 is connected to the H2S concentration tower C-103A section, and the bottom is connected to the thermal regeneration tower C-104 in sequence through the eighth liquid pump P-108, the third filter S-103, and the tenth heat exchanger E-110.

[0113] The nitrogen stripping tower C-107 has a nitrogen inlet at its bottom for nitrogen to be introduced.

[0114] The top of the thermal regeneration tower C-104 is connected to the reflux tank V-106 via the twelfth heat exchanger E-112;

[0115] The top of the reflux tank V-106 is connected to the H2S gas separator V-105 via the fourteenth heat exchanger E-114 and the thirteenth heat exchanger E-113 in sequence.

[0116] The top of the H2S gas separator V-105 is connected to the sulfur recovery passage via the fourteenth heat exchanger E-114.

[0117] The top and bottom of the H2S gas separator V-105 are also connected to section C-103A of the H2S concentration tower, respectively.

[0118] The bottom of the reflux tank V-106 is connected to the thermal regeneration tower C-104 via a sixth liquid pump P-106.

[0119] The bottom of the thermal regeneration tower C-104 is sequentially connected to the tenth heat exchanger E-110, the lean methanol tank V-104, the fourth liquid pump P-104, and the eighteenth heat exchanger E-118.

[0120] The outlet of the eighteenth heat exchanger E-118 is divided into two paths. One path is connected to the first heat exchanger E-101, and the other path is connected to the raw material gas scrubbing tower C-101E section in sequence through the ninth heat exchanger E-109, the twenty-first heat exchanger E-121, and the eighth heat exchanger E-108.

[0121] The bottom of the thermal regeneration tower C-104 is also connected in sequence to a fifth liquid pump P-105 and a first filter S-101;

[0122] The outlet of the first filter S-101 is divided into two paths: one path is connected to the tenth heat exchanger E-110, and the other path is connected to the methanol-water separation tower C-105 through the sixteenth heat exchanger E-116.

[0123] The bottom of the thermal regeneration tower C-104 is also equipped with an eleventh heat exchanger E-111.

[0124] The inlet gas separator V-101 is connected to the CO2 / methanol separator V-108 via the sixteenth heat exchanger E-116;

[0125] The top of the CO2 / methanol separator V-108 is connected to section C-102B of the CO2 desorption tower.

[0126] The bottom of the CO2 / methanol separator V-108 is connected to the methanol-water separator C-105.

[0127] The top of the methanol-water separation tower C-105 is connected to the thermal regeneration tower C-104;

[0128] The bottom of the methanol-water separator C-105 is connected to the tail gas scrubbing tower C-106 via the twentieth heat exchanger E-120.

[0129] The bottom of the methanol-water separator C-105 is also equipped with a fifteenth heat exchanger E-115.

[0130] The top of the exhaust gas scrubbing tower C-106 is connected to the exhaust gas output passage.

[0131] The bottom of the tail gas scrubbing tower C-106 is connected to the methanol-water separation tower C-105 via the seventh liquid pump P-107 and the twentieth heat exchanger E-120 in sequence.

[0132] The exhaust gas scrubbing tower C-106 is also equipped with a demineralized water inlet.

[0133] The twentieth heat exchanger E-120 is also connected to the wastewater output passage.

[0134] The process of low-temperature methanol washing of raw gas in this system mainly includes:

[0135] 1. Raw material gas scrubbing

[0136] The feed gas entering the low-temperature methanol washing system is mixed with the circulating flash vapor after exiting the circulating gas compressor K-101. A small amount of anti-icing methanol can be injected into it here. After being cooled by heat exchange with the synthesis gas, CO2 gas and tail gas through the first heat exchanger E-101, and after the water is separated in the inlet gas separator V-101, it enters the feed gas washing tower C-101.

[0137] The raw gas scrubbing tower C-101 is divided into five sections. Section A of the raw gas scrubbing tower C-101 is the desulfurization section, and the four sections above it are the decarbonization sections.

[0138] Sulfides in the raw gas are removed in section C-101A of the raw gas scrubbing tower. The raw gas is scrubbed with a portion of CO2-rich methanol liquid from the decarbonization section to remove sulfides such as H2S and some components such as CO2 before entering the decarbonization section. At this point, the gas entering the decarbonization section no longer contains sulfur.

[0139] The CO2 in the raw gas is removed to the specified level in sections C-101B, C, D, and E of the raw gas scrubbing tower. The raw gas is then scrubbed with a lean methanol solution in the upper part of section C-101E of the raw gas scrubbing tower to remove CO2 until the purification requirements are met.

[0140] The purified gas is drawn from the top of the raw material gas scrubbing tower C-101 and sent to the liquid nitrogen scrubbing device. The liquid nitrogen scrubbing device returns a portion of the synthesis gas, which is then sent back to the liquid nitrogen scrubbing device after exchanging heat with the rich methanol and raw material gas in sequence through the seventeenth heat exchanger E-117 and the first heat exchanger E-101 to recover the cold energy.

[0141] 2. Medium-pressure flash evaporation recovery of effective gases from methanol-rich products

[0142] After being absorbed by H2S and CO2, the sulfur-rich methanol that comes out of section C-101A of the raw gas scrubbing tower is heated by the seventh heat exchanger E-107 and the nineteenth heat exchanger E-119, and then cooled by the third heat exchanger E-103. After depressurization, it is flashed in section C-108A of the medium-pressure flash tower to release dissolved H2, CO gas and a small amount of H2S, CO2 and other gases.

[0143] Similarly, the sulfur-free methanol liquid from the decarbonization section of the raw gas scrubbing tower C-101 is heat-exchanged by the seventh heat exchanger E-107 and cooled by the fourth heat exchanger E-104. After depressurization, dissolved H2, CO gas and a small amount of CO2 gas are flashed out in the C-108B section of the medium-pressure flash tower.

[0144] The flash gas exiting the medium-pressure flash tower C-108 and the circulating hydrogen returned after being washed with liquid nitrogen are pressurized by the circulating gas compressor K-101 and returned to the raw material gas to recover useful gases.

[0145] 3. Methanol-rich low-pressure flash evaporation and stripping

[0146] The sulfur-containing methanol exiting from section C-102A of the CO2 desorption tower is depressurized and sent to the middle of section C-102B of the CO2 desorption tower, where dissolved CO2 is flashed out, and some of the dissolved H2S is also flashed out at the same time.

[0147] A portion of the sulfur-free methanol liquid exiting from section C-102B of the CO2 desorption tower enters the top of section C-102B of the CO2 desorption tower, where dissolved CO2 gas is flashed out under low pressure. At the same time, H2S in the sulfur-containing methanol flash vapor is washed away. CO2 product gas is obtained at the top of the CO2 desorption tower C-102. This product gas is sent out of the system as high-purity CO2 product gas after exchanging heat with rich methanol and raw material gas through the nineteenth heat exchanger E-119 and the first heat exchanger E-101.

[0148] When CO2 product gas is not needed, this gas is combined with the tail gas and sent to the tail gas scrubbing tower C-106 for water washing before being released into the atmosphere.

[0149] The sulfur-containing methanol exiting from section C-102B of the CO2 desorption tower enters the middle of section C-103B of the H2S concentration tower, where it continues to flash evaporate dissolved CO2 under low pressure.

[0150] A portion of the sulfur-free methanol liquid exiting from section C-108B of the medium-pressure flash distillation tower enters section C-103C of the H2S concentration tower. After CO2 gas is flashed out under reduced pressure, it enters the upper part of section C-103B of the H2S concentration tower to wash the sulfides in the tail gas. The CO2 gas obtained from section C-103C of the H2S concentration tower is combined with the CO2 gas at the top of the CO2 desorption tower C-102.

[0151] The tail gas obtained from the H2S concentration tower C-103B section has qualified sulfur content. After heat exchange in the 21st heat exchanger E-121 and the first heat exchanger E-101, it enters the tail gas scrubbing tower C-106 and is scrubbed with demineralized water. The tail gas that meets the emission standards after water washing is vented through a tall chimney. The wash water containing a small amount of methanol at the bottom of the tail gas scrubbing tower C-106 is sent to the methanol-water separation tower C-105 after heat exchange in the 20th heat exchanger E-120 to recover methanol.

[0152] The sulfur-containing methanol solution exiting from the lower part of section C-103B of the H2S concentration tower serves as the cold source with the lowest solution temperature in the system. It exchanges heat with lean methanol in the eighth heat exchanger E-108, and then with the sixth heat exchanger E-106 before entering section C-102A of the CO2 desorption tower. After flash evaporation of the CO2 product gas, the liquid is pressurized by the second liquid pump P-102, and after exchanging heat with the rich liquid at the bottom of the feed gas scrubbing tower C-101 in the seventh heat exchanger E-107, it enters section C-103A of the H2S concentration tower. To fully desorb the dissolved CO2 from the methanol-rich liquid, low-pressure nitrogen is introduced for stripping. After stripping, the bottom of the H2S concentration tower C-103 yields a methanol liquid with low CO2 content and low temperature. This methanol liquid contains a small amount of CO2 and virtually all the sulfides in the raw gas. It is pressurized by the third liquid pump P-103, filtered through the second filter S-102, and heated by the ninth heat exchanger E-109 before entering the nitrogen stripping tower C-107. A small amount of nitrogen is used for stripping at room temperature to fully desorb the CO2. The gas from the nitrogen stripping tower C-107 is fed into section A of the H2S concentration tower C-103; the rich methanol at the bottom of the nitrogen stripping tower C-107 is pressurized by the eighth liquid pump P-108, filtered through the third filter S-103, and after exchanging heat with the lean methanol from the thermal regeneration tower C-104 in the tenth heat exchanger E-110, it enters the thermal regeneration tower C-104 for thermal regeneration.

[0153] 4. Methanol-rich thermal regeneration

[0154] Lean methanol is obtained at the bottom of the thermal regeneration tower C-104, and H2S-rich gas is obtained at the top. After exiting the bottom of the thermal regeneration tower C-104, the lean methanol is cooled by the tenth heat exchanger E-110 and then enters the lean methanol tank V-104. After being drawn out and pressurized by the fourth liquid pump P-104, it is sequentially cooled by heat exchangers E-118, E-109, E-121, and E-108 before being sent to the top of the feed gas scrubbing tower C-101, completing the methanol cycle.

[0155] The gas with a high H2S concentration obtained at the top of the thermal regeneration tower C-104 is cooled and then separated into sulfur-containing methanol liquid.

[0156] The sulfur-containing methanol liquid obtained during the H2S separation process is returned to the bottom of the H2S concentration tower C-103, while acidic gas with a high H2S concentration is separated and sent to sulfur recovery as an acidic gas product. If necessary, part of the H2S gas is recycled back into the H2S concentration tower C-103 to increase the H2S concentration in the acidic gas product.

[0157] 5. Methanol-water separation

[0158] The aqueous methanol separated from the inlet gas separator V-101 also contains CO2. After heat exchange in the sixteenth heat exchanger E-116, it enters the CO2 / methanol separator V-108 for flash evaporation. The flashed gas phase is sent to the CO2 desorption tower C-102, and the liquid phase is sent to the middle part of the methanol-water separator C-105.

[0159] The aqueous solution containing a small amount of methanol that comes out from the bottom of the tail gas scrubbing tower C-106 also enters the middle of the methanol-water separation tower C-105; the small amount of lean methanol that comes out from the bottom of the thermal regeneration tower C-104 is refluxed into the methanol-water separation tower C-105 after heat exchange in the sixteenth heat exchanger E-116.

[0160] The methanol vapor at the top of the methanol-water separator C-105 returns to the middle of the thermal regeneration tower C-104, and the bottom of the methanol-water separator C-105 yields water with a methanol content that meets the emission standards. After heat exchange and cooling, the water is discharged from the system.

[0161] The system consists of a heat exchange network of more than 20 heat exchangers to recover cold energy and ensure excellent process conditions.

[0162] The above description is only a part of the embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A low-temperature methanol washing system, characterized in that, It includes a first heat exchanger, an inlet gas separator, a feed gas scrubbing tower, a medium-pressure flash evaporator, a CO2 desorption tower, an H2S concentration tower, a thermal regeneration tower, a methanol-water separator, and a tail gas scrubbing tower connected in sequence. The raw gas scrubbing tower consists of interconnected sections A, B, C, D, and E from bottom to top. The bottom of section B of the raw gas scrubbing tower is connected to the top of section A of the raw gas scrubbing tower through the seventeenth heat exchanger. The medium-pressure flash tower includes sections A and B, and the two sections are isolated from each other. The top outlet of section B of the medium-pressure flash tower is connected to section A of the medium-pressure flash tower through an external passage. The bottom of section B of the raw gas scrubbing tower is connected to section B of the medium-pressure flash evaporator in sequence through the seventh heat exchanger and the fourth heat exchanger. The bottom outlet of section A of the raw gas scrubbing tower is connected to section A of the medium-pressure flash evaporator in sequence through the seventh heat exchanger, the nineteenth heat exchanger, and the third heat exchanger.

2. The low-temperature methanol washing system according to claim 1, characterized in that, The top of section E of the raw gas scrubbing tower is connected to the purified gas to liquid nitrogen scrubbing passage; The bottom of section E of the raw gas scrubbing tower is connected to the top of section D of the raw gas scrubbing tower through a fifth heat exchanger. The bottom of section D and the bottom of section C of the raw gas scrubbing tower are connected to the top of section C and the top of section B of the raw gas scrubbing tower, respectively, through a sixth heat exchanger.

3. A low-temperature methanol washing system according to any one of claims 1-2, characterized in that, The medium-pressure flash tower section A is connected to the inlet of the first heat exchanger via a circulating gas compressor and a second heat exchanger.

4. A low-temperature methanol washing system according to any one of claims 1-3, characterized in that, The CO2 desorption tower includes sections A and B that are connected within the tower; The bottom outlets of sections A and B of the medium-pressure flash evaporator are both connected to section B of the CO2 desorption tower. The top output gas of section B of the CO2 desorption tower passes through the nineteenth heat exchanger and the first heat exchanger in sequence before being output.

5. A low-temperature methanol washing system according to any one of claims 1-4, characterized in that, The H2S concentration tower includes sections A, B, and C. Section A of the H2S concentration tower is internally connected to section B of the H2S concentration tower, and section C of the H2S concentration tower is located above section B of the H2S concentration tower and the two are internally isolated. The bottom of section C of the H2S concentration tower is connected to the top of section B of the H2S concentration tower via an external passage. The gas output from the top of section C of the H2S concentration tower passes sequentially through the nineteenth heat exchanger and the first heat exchanger before being output. The bottom outlet of section B of the medium-pressure flash evaporator is also connected to section C of the H2S concentration tower. The bottom of section B of the CO2 desorption tower is connected to section B of the H2S concentration tower via a ninth liquid pump. The bottom of section A of the CO2 desorption tower is connected to section A of the H2S concentration tower in sequence via a second liquid pump and a seventh heat exchanger. The H2S concentration tower section B is connected to the tail gas scrubbing tower via the twenty-first heat exchanger and the first heat exchanger in sequence. The H2S concentration tower section B is connected to the CO2 desorption tower section A in sequence via the first liquid pump, the eighth heat exchanger, and the sixth heat exchanger. The bottom of section A of the H2S concentration tower is connected to the nitrogen stripping tower in sequence via a third liquid pump, a second filter, and a ninth heat exchanger. The top of the raw gas scrubbing tower is connected to a liquid nitrogen scrubbing device, which is also connected to section A of the H2S concentration tower.

6. A low-temperature methanol washing system according to any one of claims 1-5, characterized in that, The top of the nitrogen stripping tower is connected to section A of the H2S concentration tower, and the bottom is connected to the thermal regeneration tower via the eighth liquid pump, the third filter, and the tenth heat exchanger in sequence. The nitrogen stripping tower has a nitrogen inlet at the bottom for nitrogen to be introduced.

7. A low-temperature methanol washing system according to any one of claims 1-6, characterized in that, The top of the thermal regeneration tower is connected to the reflux tank via the twelfth heat exchanger; The top of the reflux tank is connected to the H2S gas separator via the fourteenth heat exchanger and the thirteenth heat exchanger in sequence. The top of the H2S gas separator is connected to the sulfur recovery passage via the fourteenth heat exchanger; The top and bottom of the H2S gas separator are also connected to section A of the H2S concentration tower, respectively. The bottom of the reflux tank is connected to the thermal regeneration tower via a sixth liquid pump.

8. A low-temperature methanol washing system according to any one of claims 1-7, characterized in that, The bottom of the thermal regeneration tower is sequentially connected to the tenth heat exchanger, the lean methanol tank, the fourth liquid pump, and the eighteenth heat exchanger. The outlet of the eighteenth heat exchanger is divided into two paths. One path is connected to the first heat exchanger, and the other path is connected to the raw gas scrubbing tower section E in sequence through the ninth heat exchanger, the twenty-first heat exchanger, and the eighth heat exchanger. The bottom of the thermal regeneration tower is also connected in sequence to a fifth liquid pump and a first filter; The outlet of the first filter is divided into two paths: one path is connected to the tenth heat exchanger, and the other path is connected to the methanol-water separation tower through the sixteenth heat exchanger.

9. A low-temperature methanol washing system according to any one of claims 1-8, characterized in that, The bottom of the thermal regeneration tower is also equipped with an eleventh heat exchanger.

10. A low-temperature methanol washing system according to any one of claims 1-9, characterized in that, The inlet gas separator is connected to the CO2 / methanol separator via the sixteenth heat exchanger; The top of the CO2 / methanol separator is connected to section B of the CO2 desorption tower; The bottom of the CO2 / methanol separator is connected to the methanol-water separator.

11. A low-temperature methanol washing system according to any one of claims 1-10, characterized in that, The top of the methanol-water separator is connected to the thermal regeneration tower; The bottom of the methanol-water separator is connected to the tail gas scrubbing tower via the twentieth heat exchanger.

12. A low-temperature methanol washing system according to any one of claims 1-11, characterized in that, The methanol-water separator is also equipped with a fifteenth heat exchanger at the bottom.

13. A low-temperature methanol washing system according to any one of claims 11-12, characterized in that, The top of the exhaust gas scrubbing tower is connected to the exhaust gas output passage; The bottom of the tail gas scrubbing tower is connected to the methanol-water separation tower in sequence via the seventh liquid pump and the twentieth heat exchanger. The exhaust gas scrubbing tower is also equipped with a demineralized water inlet.

14. A low-temperature methanol washing system according to any one of claims 11-13, characterized in that, The twentieth heat exchanger is also connected to the wastewater output passage.

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