Method and device for recycling effective gas of low-temperature methanol washing device

Abstract

The invention provides an effective gas recovery method and device for a low-temperature methanol washing device, and the method comprises the following steps: raw material gas and lean methanol are subjected to desulfurization and decarburization in a shift gas washing tower, qualified purified gas is obtained at the top of the shift gas washing tower, and methanol without hydrogen sulfide is obtained at the middle part of the shift gas washing tower; methanol containing hydrogen sulfide is obtained from a tower kettle of the shift gas washing tower; and the hydrogen sulfide-free methanol and the hydrogen sulfide-containing methanol are respectively subjected to gas stripping operation through high-pressure nitrogen, effective gases of hydrogen and carbon monoxide are recovered, and the obtained recycle gas is returned to the raw material gas. A high-pressure nitrogen gas stripping mode is adopted to replace a medium-pressure flash evaporation mode to recycle effective gas, the concentration of the effective gas in the circulation gas generated in the process is increased by about one time, the pressure of the obtained circulation gas is close to that of raw gas, the compression ratio of a compressor is greatly reduced, and the energy consumption is reduced. By adopting high-pressure nitrogen gas stripping, the flow of circulating gas can be greatly reduced, and the power consumption of the compressor is reduced.

Description

Technical Field

[0001] The invention belongs to the field of low-temperature methanol washing, and in particular relates to a method and a device for effective gas recovery of a low-temperature methanol washing device. Background Art

[0002] In the existing low-temperature methanol washing process, the rich methanol coming out of the washing tower enters the medium-pressure flash tank for reduced-pressure flash evaporation to recover the effective gases H2 and CO dissolved in the rich methanol. In order to ensure that the recovery rate of the effective gas is greater than 99.6%, the general flash pressure is about 1 / 3 of the operating pressure of the raw gas. At this flash pressure, a large amount of CO2 is also desorbed, resulting in more than half of the circulating gas being composed of CO2, resulting in large equipment investment and operating energy consumption of the circulating gas compressor. In addition, these circulating gases with high CO2 content return to the raw gas to participate in the absorption process again, resulting in a waste of cooling capacity. Invention content

[0003] In view of this, the present invention aims to propose a method and device for effective gas recovery of a low-temperature methanol washing device to solve at least one technical problem in the background technology.

[0004] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0005] The present invention provides a method for effective gas recovery of a low-temperature methanol washing device, comprising the following steps:

[0006] The raw gas and lean methanol are desulfurized and decarbonized in the shift gas scrubber, and qualified purified gas is obtained at the top of the shift gas scrubber, and methanol without hydrogen sulfide is obtained in the middle of the shift gas scrubber;

[0007] The bottom of the conversion gas scrubber obtains methanol containing hydrogen sulfide;

[0008] Methanol without hydrogen sulfide and methanol containing hydrogen sulfide are respectively subjected to gas stripping operation by high-pressure nitrogen to recover effective hydrogen and carbon monoxide, and the obtained circulating gas is returned to the raw gas.

[0009] Furthermore, the methanol without hydrogen sulfide and the methanol containing hydrogen sulfide coming out of the conversion gas scrubber are sent to the high-pressure nitrogen stripping tower after cooling.

[0010] Methanol without hydrogen sulfide and methanol containing hydrogen sulfide enter the upper part of the high-pressure nitrogen stripping tower, and high-pressure nitrogen enters the lower part of the stripping tower;

[0011] The high-pressure nitrogen stripping tower is fed with high-pressure nitrogen to strip methanol without hydrogen sulfide and methanol containing hydrogen sulfide;

[0012] The circulating gas obtained from the top of the high-pressure nitrogen stripping tower is pressurized by a compressor and mixed with the raw gas.

[0013] Further, the high-pressure nitrogen stripping tower includes a first high-pressure nitrogen stripping tower and a second high-pressure nitrogen stripping tower;

[0014] The first high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the first high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0015] And / or, the second high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the second high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0016] Furthermore, the pressure range of the high-pressure nitrogen stripping tower is 3.0-6.0 MPaG.

[0017] Furthermore, methanol without hydrogen sulfide and methanol containing hydrogen sulfide are subjected to gas stripping operation by high-pressure nitrogen, and then pass through a medium-pressure flash evaporation system to flash out a portion of flash gas with high nitrogen content and send it to an H2S concentration tower for use as gas stripping nitrogen. The methanol without hydrogen sulfide and methanol containing hydrogen sulfide coming out of the medium-pressure flash evaporation system enter the CO2 analysis tower and the H2S concentration system in turn.

[0018] Further, the medium-pressure flash system is a medium-pressure flash tank or a flash tower;

[0019] And / or, the medium-pressure flash system operates within a specific pressure range of 1.0 to 6.0 MPaG and a temperature range of -10 to -50°C.

[0020] The device used in the method for effective gas recovery of the low-temperature methanol washing device includes a shift gas washing tower, a first high-pressure nitrogen gas stripping tower, and a second high-pressure nitrogen gas stripping tower;

[0021] The lower part of the shift gas washing tower is provided with a shift raw gas inlet, and the top of the shift gas washing tower discharges purified gas;

[0022] The middle part of the shift gas washing tower is connected to the first high-pressure nitrogen stripping tower through a pipeline;

[0023] The lower part of the shift gas washing tower is connected to the second high-pressure nitrogen stripping tower through a pipeline;

[0024] The top circulating gas of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower is compressed by the circulating gas compressor and then connected to the raw gas;

[0025] The lower parts of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower are both connected to high-pressure nitrogen;

[0026] Product gas is discharged from the bottom of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower.

[0027] Furthermore, the lower part of the shift gas washing tower is connected to the shift raw gas inlet through a pipeline, and the pipeline between the shift raw gas inlet and the shift gas washing tower is provided with a first lean methanol inlet pipeline, a first heat exchanger, and a methanol-water separator in sequence;

[0028] The methanol-water separator is connected to the methanol-water separation tower, and the top of the methanol-water separator is connected to the conversion gas washing tower;

[0029] And / or, a circulating gas compressor is provided on the pipeline connecting the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower with the raw gas;

[0030] And / or, a second lean methanol inlet pipeline is provided at the upper part of the shift gas scrubber;

[0031] And / or, a plurality of heat exchange pipes are provided on the upper part of the shift gas washing tower, both ends of the heat exchange pipes are respectively connected to the shift gas washing tower, and a second heat exchanger is provided on the heat exchange pipes;

[0032] And / or, a third heat exchanger and a first valve are provided on the pipeline connecting the middle part of the shift gas washing tower with the first high-pressure nitrogen stripping tower;

[0033] A branch pipe is provided on the pipeline connected to the first high-pressure nitrogen stripping tower in the middle of the shift gas washing tower, the branch pipe is connected to the shift gas washing tower, and a second valve is provided on the branch pipe;

[0034] And / or, a fourth heat exchanger and a third valve are provided on the pipeline connecting the bottom of the shift gas scrubber with the second high-pressure nitrogen stripping tower;

[0035] And / or, the tops of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower are both connected to the feed gas.

[0036] Further, the flash system includes a first methanol-rich medium-pressure flash device and a second methanol-rich medium-pressure flash device;

[0037] The bottom of the first high-pressure nitrogen stripping tower is connected to the first methanol-rich medium-pressure flash device, and a fourth valve is provided on the pipeline between the first high-pressure nitrogen stripping tower and the first methanol-rich medium-pressure flash device;

[0038] The bottom of the second high-pressure nitrogen stripping tower is connected to the second methanol-rich medium-pressure flash device, and a fifth valve is provided on the pipeline between the second high-pressure nitrogen stripping tower and the second methanol-rich medium-pressure flash device;

[0039] And / or, the tops of the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are connected to the H2S concentration tower;

[0040] And / or, the bottoms of the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are connected to the CO2 analysis tower;

[0041] And / or, the top of the CO2 analysis tower outputs product gas, and the middle and bottom of the CO2 analysis tower are connected to the H2S concentration tower.

[0042] The rich methanol from the kettle of the high-pressure nitrogen stripping tower passes through the medium-pressure flash system, and a portion of the flash gas with high nitrogen content is sent to the H2S concentration tower for use as stripping nitrogen, and it can also increase the concentration of CO2 product gas in the downstream low-pressure flash system. The rich methanol from the medium-pressure flash system enters the subsequent low-pressure flash and H2S concentration system for desorption of CO2 and concentration of H2S.

[0043] Further, the high-pressure nitrogen stripping tower includes a first high-pressure nitrogen stripping tower and a second high-pressure nitrogen stripping tower;

[0044] The first high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the first high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0045] And / or, the second high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the second high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0046] And / or, the pressure range of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower is 3.0-6.0 MPaG.

[0047] The new process of effective gas recovery of the low-temperature methanol washing device of the present invention is characterized in that the effective gas is recovered by high-pressure nitrogen gas stripping operation instead of reduced pressure flash evaporation. Under the high-pressure nitrogen gas stripping operation, the desorption degree of H2 and CO is higher than that of CO2, so the circulating gas with a higher effective gas concentration can be obtained. The specific pressure range of the high-pressure nitrogen gas stripping operation is 3.0-6.0MPaG, and the temperature range is -10--50°C. Because N2 will also dissolve partly under high pressure, if the downstream has requirements for CO2 concentration, it is necessary to increase the medium-pressure flash evaporation system to discharge part of the flash gas with high nitrogen content and increase the concentration of CO2 product gas. If the downstream has no requirements for CO2 concentration, the medium-pressure flash evaporation system can be cancelled.

[0048] And / or, the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are medium-pressure flash tanks or desorption towers;

[0049] And / or, the pressure range of the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are both 1.0 to 6.0 MPaG, and the temperature range is -10 to -50°C.

[0050] Compared with the prior art, the method and device for effective gas recovery of the low-temperature methanol washing device created by the present invention have the following advantages:

[0051] 1. The present invention proposes a new process for effective gas recovery of a low-temperature methanol washing device. In this new process, high-pressure nitrogen gas stripping operation is used to recover effective gas, and a medium-pressure flash evaporation system is also prepared to adjust the concentration of the downstream CO2 product gas. The conversion raw gas from the boundary area enters the conversion gas washing tower for desulfurization and decarbonization, and the H2S and CO2 qualified purified gas obtained at the top of the tower is sent to the downstream. The rich methanol that has absorbed the acid gas also dissolves some H2 and CO, so effective gas recovery is required; the rich methanol coming out of the tower bottom and the middle of the tower enters the upper part of the high-pressure nitrogen gas stripping tower, and the tower bottom is introduced with high-pressure nitrogen for gas stripping operation. The circulating gas obtained at the top of the tower is pressurized by the compressor and returned to the raw gas to ensure that the recovery rate of H2+CO is not less than 99.6%.

[0052] 2. The new process for recovering effective gas from the low-temperature methanol washing device described in the present invention. The medium-pressure flash evaporation method is replaced by the high-pressure nitrogen stripping method to recover effective gas. The concentration of effective gas in the circulating gas generated by the process is increased by about one time, and the pressure of the circulating gas is close to the pressure of the raw gas, which greatly reduces the flow rate of the circulating gas and the compression ratio of the compressor, and can greatly reduce the power consumption of the circulating gas compressor. The new process for recovering effective gas from the low-temperature methanol washing device of the present invention, the rich methanol from the washing tower is sent to the high-pressure nitrogen stripping tower after cooling, without a decompression process in the middle, the tower kettle is introduced with high-pressure nitrogen to strip the rich methanol, the circulating gas obtained at the top of the tower is pressurized by the compressor and sent to the raw gas inlet, the rich methanol from the high-pressure nitrogen stripping tower is sent to the medium-pressure flash tank, the setting of the medium-pressure flash tank can adjust the concentration of the CO2 product gas, and a part of the flash gas with high nitrogen content is flashed and sent to the downstream H2S concentration tower as stripping nitrogen, and the rich methanol from the medium-pressure flash tank is sent to the subsequent low-pressure flash evaporation and H2S concentration system. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0054] Figure 1 A schematic diagram of an effective gas recovery device for a low-temperature methanol washing device according to an embodiment of the present invention;

[0055] Figure 2 A schematic diagram of the pipeline name of the effective gas recovery device of the low-temperature methanol washing device described in the embodiment of the present invention;

[0056] Figure 3 The material balance data table of the main positions of the improved low-temperature methanol washing process described in the embodiment of the present invention;

[0057] Figure 4 It is a material balance data table for the main positions of the low-temperature methanol washing process described in the embodiment of the invention.

[0058] Description of reference numerals:

[0059] 1. Shift gas washing tower; 2. First high-pressure nitrogen stripping tower; 3. Second high-pressure nitrogen stripping tower; 4. First lean methanol inlet pipeline; 5. First heat exchanger; 6. Second lean methanol inlet pipeline; 7. Second heat exchanger; 8. Third heat exchanger; 9. First valve; 10. Second valve; 11. Third valve; 12. First methanol-rich medium-pressure flash device; 13. Second methanol-rich medium-pressure flash device; 14. Fourth valve; 15. Fifth valve; 16. Methanol-water separator; 17. Fourth heat exchanger; 18. Circulating gas compressor; 19. CO2 analysis tower. DETAILED DESCRIPTION

[0060] 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.

[0061] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0062] Example 1

[0063] The method for recovering effective gas from a low-temperature methanol washing device comprises the following steps: raw gas and lean methanol are desulfurized and decarbonized in a conversion gas washing tower 1, qualified purified gas is obtained at the top of the conversion gas washing tower 1, methanol without hydrogen sulfide is obtained in the middle of the conversion gas washing tower 1; methanol containing hydrogen sulfide is obtained at the bottom of the conversion gas washing tower 1; methanol without hydrogen sulfide and methanol containing hydrogen sulfide are respectively stripped by high-pressure nitrogen to recover effective gas hydrogen and carbon monoxide, and the obtained circulating gas is returned to the raw gas.

[0064] The methanol without hydrogen sulfide and the methanol containing hydrogen sulfide coming out of the conversion gas washing tower 1 are sent to the high-pressure nitrogen stripping tower after cooling, and the methanol without hydrogen sulfide and the methanol containing hydrogen sulfide enter the upper part of the high-pressure nitrogen stripping tower, and the high-pressure nitrogen is introduced into the lower part of the stripping tower; the high-pressure nitrogen stripping tower is introduced with high-pressure nitrogen to strip the methanol without hydrogen sulfide and the methanol containing hydrogen sulfide; the circulating gas obtained at the top of the high-pressure nitrogen stripping tower is pressurized by a compressor and mixed with the raw gas.

[0065] The high-pressure nitrogen gas stripping tower includes a first high-pressure nitrogen gas stripping tower 2 and a second high-pressure nitrogen gas stripping tower 3;

[0066] The first high-pressure nitrogen stripping tower 2 is two tower bodies connected in series end to end, or the first high-pressure nitrogen stripping tower 2 is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0067] And / or, the second high-pressure nitrogen stripping tower 3 is two tower bodies connected in series end to end, or the second high-pressure nitrogen stripping tower 3 is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0068] The pressure range of the first high-pressure nitrogen stripping tower 2 and the second high-pressure nitrogen stripping tower 3 is 3.0-6.0 MPaG.

[0069] Example 2

[0070] The above-mentioned embodiment 1 includes a shift gas washing tower 1, a first high-pressure nitrogen gas stripping tower 2, and a second high-pressure nitrogen gas stripping tower 3; the lower part of the shift gas washing tower 1 is provided with a shift raw gas inlet, and the top of the shift gas washing tower 1 discharges purified gas; the middle part of the shift gas washing tower 1 is connected to the first high-pressure nitrogen gas stripping tower 2 through a pipeline; the lower part of the shift gas washing tower 1 is connected to the second high-pressure nitrogen gas stripping tower 3 through a pipeline; the top circulating gas of the first high-pressure nitrogen gas stripping tower 2 and the second high-pressure nitrogen gas stripping tower 3 is compressed by the circulating gas compressor 18 and then communicated with the raw gas;

[0071] The lower parts of the first high-pressure nitrogen stripping tower 2 and the second high-pressure nitrogen stripping tower 3 are both connected to high-pressure nitrogen; the product gas is discharged from the bottom of the first high-pressure nitrogen stripping tower 2 and the second high-pressure nitrogen stripping tower 3.

[0072] The lower part of the shift gas washing tower 1 is connected to the shift raw gas inlet through a pipeline, and the first lean methanol inlet pipeline 4, the first heat exchanger 5, and the methanol-water separator 16 are sequentially arranged on the pipeline between the shift raw gas inlet and the shift gas washing tower 1; the methanol-water separator 16 is connected to the methanol-water separation tower, and the top of the methanol-water separator 16 is connected to the shift gas washing tower 1;

[0073] A circulating gas compressor 18 is provided on the pipelines connecting the first high-pressure nitrogen stripping tower 2 and the second high-pressure nitrogen stripping tower 3 with the raw gas; a second lean methanol inlet pipeline 6 is provided on the upper part of the shift gas scrubber 1; a plurality of heat exchange pipelines are provided on the upper part of the shift gas scrubber 1, and both ends of the heat exchange pipelines are respectively connected to the shift gas scrubber 1, and a second heat exchanger 7 is provided on the heat exchange pipeline;

[0074] A third heat exchanger 8 and a first valve 9 are provided on the pipeline connecting the middle of the shift gas scrubber 1 with the first high-pressure nitrogen stripping tower 2; a branch pipe is provided on the pipeline connecting the middle of the shift gas scrubber 1 with the first high-pressure nitrogen stripping tower 2, the branch pipe is connected to the shift gas scrubber 1, and a second valve 10 is provided on the branch pipe; a fourth heat exchanger 17 and a third valve 11 are provided on the pipeline connecting the bottom of the shift gas scrubber 1 with the second high-pressure nitrogen stripping tower 3;

[0075] The tops of the first high-pressure nitrogen stripping tower 2 and the second high-pressure nitrogen stripping tower 3 are both connected to the feed gas. The flash system includes a first methanol-rich medium-pressure flash device 12 and a second methanol-rich medium-pressure flash device 13; the bottom of the first high-pressure nitrogen stripping tower 2 is connected to the first methanol-rich medium-pressure flash device 12, and a fourth valve 14 is provided on the pipeline between the first high-pressure nitrogen stripping tower 2 and the first methanol-rich medium-pressure flash device 12; the bottom of the second high-pressure nitrogen stripping tower 3 is connected to the second methanol-rich medium-pressure flash device 13, and a fifth valve 15 is provided on the pipeline between the second high-pressure nitrogen stripping tower 3 and the second methanol-rich medium-pressure flash device 13;

[0076] The tops of the first methanol-rich medium-pressure flash device 12 and the second methanol-rich medium-pressure flash device 13 are connected to the H2S concentration tower; the bottoms of the first methanol-rich medium-pressure flash device 12 and the second methanol-rich medium-pressure flash device 13 are connected to the CO2 decomposition tower 19; the top of the CO2 decomposition tower 19 outputs product gas, and the middle and bottom of the CO2 decomposition tower 19 are connected to the H2S concentration tower.

[0077] The rich methanol from the kettle of the high-pressure nitrogen stripping tower passes through the medium-pressure flash system, and a portion of the flash gas with high nitrogen content is sent to the H2S concentration tower for use as stripping nitrogen, and it can also increase the concentration of CO2 product gas in the downstream low-pressure flash system. The rich methanol from the medium-pressure flash system enters the subsequent low-pressure flash and H2S concentration system for desorption of CO2 and concentration of H2S.

[0078] The high-pressure nitrogen gas stripping tower includes a first high-pressure nitrogen gas stripping tower 2 and a second high-pressure nitrogen gas stripping tower 3;

[0079] The first high-pressure nitrogen stripping tower 2 is two tower bodies connected in series end to end, or the first high-pressure nitrogen stripping tower 2 is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0080] And / or, the second high-pressure nitrogen stripping tower 3 is two tower bodies connected in series end to end, or the second high-pressure nitrogen stripping tower 3 is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

[0081] The pressure range of the first high-pressure nitrogen stripping tower 2 and the second high-pressure nitrogen stripping tower 3 is 3.0-6.0 MPaG. The first methanol-rich medium-pressure flash device 12 and the second methanol-rich medium-pressure flash device 13 are medium-pressure flash tanks or desorption towers; the pressure range of the first methanol-rich medium-pressure flash device 12 and the second methanol-rich medium-pressure flash device 13 are both 1.0-6.0 MPaG, and the temperature range is -10--50°C.

[0082] Table 1 Composition of conversion feed gas

[0083]

[0084] The V11 version of ASPEN PLUS was used for the effect verification of the specific implementation part of the present invention.

[0085] The selection of physical property method has a huge impact on the simulation results, mainly because each physical property method has a certain scope of application. According to the physical property method selection program that comes with the ASPEN PLUS software, the prior art shows that the PSRK equation has a small deviation in the full-process simulation calculation of low-temperature methanol, which is closer to the actual data of the factory. Therefore, in this embodiment, the PSRK equation is selected for simulation calculation.

[0086] Comparative Example 1

[0087] This comparative example adopts the conventional medium-pressure flash evaporation method. According to the calculation results of ASPEN PLUS, the molar fraction of H2 in the circulating gas (stream No. 305) produced by the medium-pressure (1.6MpaA) flash evaporation method of the conventional process is only 33%, and more than 65% of the gas is CO2. This result is close to the data of actual industrial operation. The circulating gas flow rate produced by the medium-pressure flash evaporation process is 280kmol / h, and the calculated H2 recovery rate is 99.8%.

[0088] Example 3

[0089] This embodiment adopts the method and device described in Examples 1 and 2. According to the calculation results of ASPEN PLUS, the molar fraction of H2 in the circulating gas produced by high-pressure nitrogen stripping is about 60%, and the molar fraction of CO2 is reduced to 26%. The circulating gas composition also contains 13% N2. For synthetic ammonia, N2 is also a raw gas, so the proportion of synthetic ammonia raw gas in the circulating gas reaches more than 70%, which is much higher than the circulating gas produced by the medium-pressure flash evaporation method. In addition, to ensure that the recovery rate of hydrogen is greater than 99.6%, it is necessary to combine the flow rate of the circulating gas. The flow rate of the circulating gas produced by the high-pressure nitrogen stripping method is 168kmol / h, and the calculated recovery rate of H2 is 99.9%, which can meet the requirements of the hydrogen recovery rate, and the flow rate of the circulating gas in the process described in this embodiment is reduced by about 40% compared with the traditional process.

[0090] The circulating gas pressure generated by the high-pressure nitrogen stripping solution is close to the pressure of the raw gas, so the circulating gas only needs to be pressurized by about 0.5Mpa to return to the raw gas inlet.

[0091] Comparative Example 2

[0092] This comparative example is the same as comparative example 1. In the conventional medium-pressure flash evaporation method, since the pressure of the circulating gas drops to 1.6MpaA, it needs to be pressurized by about 4.4Mpa before returning to the raw gas inlet.

[0093] By comparing the above embodiments and comparative examples, it can be seen that:

[0094] (1) Based on the circulating gas flow rate and the required inlet and outlet pressures, and assuming a compressor efficiency of 80%, the shaft powers of the circulating gas compressor 18 required by these two methods are 8.5 kW and 275 kW respectively, which is a difference of about 30 times.

[0095] (2) From the perspective of equipment investment, the high-pressure nitrogen gas stripping solution requires the addition of two high-pressure nitrogen gas stripping towers (which can also be combined into one device, divided into two sections, upper and lower) compared to the traditional medium-pressure flash evaporation process. According to preliminary estimates, the additional investment required is approximately RMB 5.7 million. However, due to the reduction in gas volume and compression ratio of the circulating gas compressor 18, the investment cost can be reduced to half of that of the circulating gas compressor 18 in the traditional process, saving approximately RMB 1.5 million in investment.

[0096] (3) From the perspective of operating costs, considering a certain degree of operating flexibility, according to the compressor selection scheme fed back by the manufacturer, the motor power of the circulating gas compressor 18 of the traditional medium-pressure flash evaporation scheme is about 500KW, and the motor power of the circulating gas compressor 18 of the high-pressure nitrogen scheme is about 37KW. The difference in operating costs between the two in one year is about 1.8 million (calculated based on an operating time of 8,000 hours and an electricity fee of 0.5 yuan / kW·h). Considering the comprehensive equipment investment and operating costs, when the operation cycle of the device exceeds 2.5 years, the high-pressure nitrogen stripping scheme has obvious economic benefits, which is conducive to reducing the total cost of the low-temperature methanol washing device.

[0097] In addition, combined with the analysis of the three logistics data of 305 / 501 / 502, it can be seen that about 88% of the gas-lift nitrogen is dissolved in the methanol-rich solution, so a methanol-rich medium-pressure flash system is also added to this process. The main purpose is to reduce the concentration of N2 and H2 in the CO2 product gas. The pressure of the medium-pressure flash system is set to 2.2MpaA. From the 405 logistics data, it can be seen that the concentration of CO2 in the obtained CO2 product gas is >97.5%, and the concentration of H2 is <1000ppm, which can meet the requirements of downstream such as coal transportation and synthetic soda ash. From the 401 / 402 logistics data, it can be obtained that the total amount of flash gas generated is about 280kmol / h, and 44% of the flash gas is N2, which can be sent to the downstream H2S concentration tower as gas-lift nitrogen. For projects that do not require the use of CO2, such as water-coal slurry gasification process, the downstream product is only ammonia, and the methanol-rich medium-pressure flash system can be cancelled. At this time, the CO2 concentration in the CO2 product gas obtained by the low-pressure flash system is about 92%, and the tail gas from the H2S concentration tower is washed with water and discharged into the atmosphere through the vent tube. This process has an obvious feature, which can centrally recover the pressure difference energy from the high-pressure gas stripping system to the low-pressure flash system (about 5.5MpaA at the inlet and about 0.9MpaA at the outlet). For traditional processes, generally only the pressure difference energy from high-pressure to medium-pressure flash can be recovered (about 5.7MpaA at the inlet and about 1.7MpaA at the outlet).

[0098] The high-pressure nitrogen gas stripping method is used to recover the effective gas in the low-temperature methanol washing process. This process has the following two characteristics: first, it can realize the recovery of high-concentration hydrogen. The concentration of hydrogen in the circulating gas can reach 60%, which reduces the circulating gas flow rate while ensuring the effective gas recovery rate; second, the operating pressure of the high-pressure gas stripping tower is close to the operating pressure of the washing tower, which reduces the compression ratio of the circulating gas compressor 18. The improved solution process can effectively reduce the operating cost of the low-temperature methanol washing device and achieve the goal of energy conservation and emission reduction.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for recovering effective gas from a low-temperature methanol washing device, characterized in that: The steps include: The raw gas and lean methanol are desulfurized and decarbonized in the shift gas scrubber, and qualified purified gas is obtained at the top of the shift gas scrubber, and methanol without hydrogen sulfide is obtained in the middle of the shift gas scrubber; The bottom of the conversion gas scrubber obtains methanol containing hydrogen sulfide; Methanol without hydrogen sulfide and methanol containing hydrogen sulfide are respectively subjected to gas stripping operation by high-pressure nitrogen to recover effective hydrogen and carbon monoxide, and the obtained circulating gas is returned to the raw gas.

2. The method for recovering effective gas from a low-temperature methanol washing device according to claim 1, characterized in that: The methanol without hydrogen sulfide and the methanol containing hydrogen sulfide coming out of the conversion gas scrubber are sent to the high-pressure nitrogen stripping tower after cooling. Methanol without hydrogen sulfide and methanol containing hydrogen sulfide enter the upper part of the high-pressure nitrogen stripping tower, and high-pressure nitrogen enters the lower part of the stripping tower; The high-pressure nitrogen stripping tower is fed with high-pressure nitrogen to strip methanol without hydrogen sulfide and methanol containing hydrogen sulfide; The circulating gas obtained from the top of the high-pressure nitrogen stripping tower is pressurized by a compressor and mixed with the raw gas.

3. The method for recovering effective gas from a low-temperature methanol washing device according to claim 3, characterized in that: The high-pressure nitrogen stripping tower includes a first high-pressure nitrogen stripping tower and a second high-pressure nitrogen stripping tower; The first high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the first high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head; And / or, the second high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the second high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head.

4. The method for recovering effective gas from a low-temperature methanol washing device according to claim 3, characterized in that: The pressure range of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower is 3.0-6.0 MPaG.

5. The method for effective gas recovery of a low-temperature methanol washing device according to claim 1, characterized in that: Methanol without hydrogen sulfide and methanol containing hydrogen sulfide are stripped by high-pressure nitrogen, and then pass through a medium-pressure flash evaporation system to flash out a portion of flash gas with high nitrogen content and send it to the H2S concentration tower for use as stripping nitrogen. The methanol without hydrogen sulfide and methanol containing hydrogen sulfide coming out of the medium-pressure flash evaporation system enter the CO2 analysis tower and the H2S concentration system in turn.

6. The method for recovering effective gas from a low-temperature methanol washing device according to claim 5, characterized in that: The medium-pressure flash system is a medium-pressure flash tank or flash tower; And / or, the pressure range of the first methanol-rich medium-pressure flash unit and the second methanol-rich medium-pressure flash unit is 1.0 to 6.0 MPaG, and the temperature range is -10 to -50°C.

7. The device used in the method for recovering effective gas from a low-temperature methanol washing device according to any one of claims 1 to 6, characterized in that: It includes a shift gas scrubber, a first high-pressure nitrogen stripping tower, and a second high-pressure nitrogen stripping tower; The lower part of the shift gas washing tower is provided with a shift raw gas inlet, and the top of the shift gas washing tower discharges purified gas; The middle part of the shift gas washing tower is connected to the first high-pressure nitrogen stripping tower through a pipeline; The lower part of the shift gas washing tower is connected to the second high-pressure nitrogen stripping tower through a pipeline; The top circulating gas of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower is compressed by the circulating gas compressor and then connected to the raw gas; The lower parts of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower are both connected to high-pressure nitrogen; Product gas is discharged from the bottom of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower.

8. The device used in the method for recovering effective gas from a low-temperature methanol washing device according to claim 7, characterized in that: The lower part of the conversion gas washing tower is connected to the conversion raw gas inlet through a pipeline, and the pipeline between the conversion raw gas inlet and the conversion gas washing tower is provided with a first lean methanol inlet pipeline, a first heat exchanger, and a methanol-water separator in sequence; The methanol-water separator is connected to the methanol-water separation tower, and the top of the methanol-water separator is connected to the conversion gas washing tower; And / or, a circulating gas compressor is provided on the pipeline connecting the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower with the raw gas; And / or, a second lean methanol inlet pipeline is provided at the upper part of the shift gas scrubber; And / or, a plurality of heat exchange pipes are provided on the upper part of the shift gas washing tower, both ends of the heat exchange pipes are respectively connected to the shift gas washing tower, and a second heat exchanger is provided on the heat exchange pipes; And / or, a third heat exchanger and a first valve are provided on the pipeline connecting the middle part of the shift gas washing tower with the first high-pressure nitrogen stripping tower; A branch pipe is provided on the pipeline connected to the first high-pressure nitrogen stripping tower in the middle of the conversion gas washing tower, and the branch pipe is connected to the conversion gas washing tower, and a second valve is provided on the branch pipe; And / or, a fourth heat exchanger and a third valve are provided on the pipeline connecting the bottom of the shift gas scrubber with the second high-pressure nitrogen stripping tower; And / or, the tops of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower are both connected to the feed gas.

9. The device used in the method for recovering effective gas from a low-temperature methanol washing device according to claim 7, characterized in that: The flash evaporation system comprises a first methanol-rich medium-pressure flash evaporation device and a second methanol-rich medium-pressure flash evaporation device; The bottom of the first high-pressure nitrogen stripping tower is connected to the first methanol-rich medium-pressure flash device, and a fourth valve is provided on the pipeline between the first high-pressure nitrogen stripping tower and the first methanol-rich medium-pressure flash device; The bottom of the second high-pressure nitrogen stripping tower is connected to the second methanol-rich medium-pressure flash device, and a fifth valve is provided on the pipeline between the second high-pressure nitrogen stripping tower and the second methanol-rich medium-pressure flash device; And / or, the tops of the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are connected to the H2S concentration tower; And / or, the bottoms of the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are connected to the CO2 analysis tower; And / or, the top of the CO2 analysis tower outputs product gas, and the middle and bottom of the CO2 analysis tower are connected to the H2S concentration tower.

10. The device used in the method for recovering effective gas from a low-temperature methanol washing device according to claim 7, characterized in that: The high-pressure nitrogen stripping tower includes a first high-pressure nitrogen stripping tower and a second high-pressure nitrogen stripping tower; The first high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the first high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head; And / or, the second high-pressure nitrogen stripping tower is two tower bodies connected in series end to end, or the second high-pressure nitrogen stripping tower is one tower body, and the tower body is divided into an upper tower body and a lower tower body by a head; And / or, the pressure range of the first high-pressure nitrogen stripping tower and the second high-pressure nitrogen stripping tower is 3.0-6.0 MPaG; And / or, the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are medium-pressure flash tanks or desorption towers; And / or, the pressure range of the first methanol-rich medium-pressure flash device and the second methanol-rich medium-pressure flash device are both 1.0 to 6.0 MPaG, and the temperature range is -10 to -50°C.

Images