A system and method for co-production of syngas, nitrogen and lng from raw coal gas

Abstract

The present application relates to a kind of raw coal gas co-production LNG, synthesis gas and nitrogen system and method.The system includes main heat exchanger, nitrogen removal tower evaporator, nitrogen removal tower condenser, dehydrogenation tower evaporator, dehydrogenation tower condenser, stripping tower condenser, nitrogen compressor after-cooler, refrigerant compressor first-stage cooler, refrigerant compressor second-stage cooler, nitrogen removal tower, dehydrogenation tower, stripping tower, first separation tank, second separation tank, nitrogen buffer tank, refrigerant first-stage separation tank, refrigerant second-stage separation tank, nitrogen compressor, refrigerant compressor first-stage, refrigerant compressor second-stage and several pipelines.The present application is applicable to high nitrogen content raw coal gas, can simultaneously efficiently produce LNG, synthesis gas and higher purity nitrogen product etc..

Description

Technical Field

[0001] This invention relates to the field of cryogenic separation in the chemical industry, specifically to a system and method for the combined production of LNG, syngas, and nitrogen from raw coal gas. Background Technology

[0002] Raw coal gas is a byproduct of coal pyrolysis, a waste product of the coal chemical industry. Due to its high nitrogen content, low levels of effective gaseous components such as H2 and CH4, and complex impurities, it has historically been difficult to process and utilize comprehensively. While some manufacturers use it as fuel for power generation, most still burn it in open flames, releasing it into the air. This not only wastes resources but also severely impacts the environment.

[0003] How to utilize waste coal gas efficiently, energy-savingly, and environmentally in a way that achieves both economic and environmental benefits, thereby promoting the healthy development of the coal chemical industry, is a new issue that urgently needs to be addressed within the industry.

[0004] Currently, the technologies commonly used in the industry to produce LNG and syngas or hydrogen-rich products from coal chemical tail gas, such as coke oven tail gas, are mostly suitable for gases with low nitrogen content (below 10%) and high hydrogen content. However, raw coal gas has a high nitrogen content and low hydrogen content. If existing technologies are still used, the hydrogen extraction rate will be relatively low, and the nitrogen component in the raw coal gas will not be effectively extracted and utilized. The upstream coal chemical and raw coal gas front-end processing processes require a large amount of nitrogen, which usually needs to be supplied by a separate air separation unit, increasing not only equipment investment costs but also the energy consumption of the air separation unit.

[0005] Based on the above, this invention proposes a system and method for the joint production of LNG, syngas and nitrogen from raw coal gas. The purified raw coal gas can be used to simultaneously produce LNG, syngas and nitrogen through this system and method. Summary of the Invention

[0006] This invention addresses the aforementioned problems in existing technologies by providing a system and method for the co-production of LNG, syngas, and nitrogen from raw coal gas. This technology efficiently extracts the effective components CH4 and H2 from raw coal gas after washing, shift conversion, low-temperature methanol washing, methanation, and deep dehydration processes to produce high-value LNG and syngas products. Simultaneously, it effectively extracts the nitrogen component to produce high-purity nitrogen, providing the necessary nitrogen source for upstream coal chemical plants and raw coal gas treatment processes. Except for a small amount of nitrogen needed for plant start-up, the large quantities of nitrogen required for normal operation of coal chemical plants and raw coal gas treatment processes do not need to be prepared separately. This technology achieves a nitrogen production rate of [missing information - likely Nm³ / s]. 3 Nitrogen production energy consumption is only about 0.05 kWh, far lower than that of air separation units per Nm³.3 The production energy consumption of nitrogen is approximately 0.2 kWh, which greatly reduces the investment in equipment and the energy consumption of operation.

[0007] The objective of this invention is primarily achieved through the following approach:

[0008] A system for co-producing LNG, syngas, and nitrogen from raw coal gas is disclosed. The raw coal gas is processed by a purification module to obtain purified gas. The system includes a main heat exchanger, a denitrification tower evaporator, a denitrification tower condenser, a dehydrogenation tower evaporator, a dehydrogenation tower condenser, a stripping tower condenser, a nitrogen compressor aftercooler, a refrigerant compressor primary cooler, a refrigerant compressor secondary cooler, a denitrification tower, a dehydrogenation tower, a stripping tower, a first separation tank, a second separation tank, a nitrogen buffer tank, a refrigerant primary separation tank, and a refrigerant secondary separation tank. The system includes a nitrogen compressor, a primary refrigerant compressor, a secondary refrigerant compressor, and several pipelines. The denitrification tower condenser and evaporator are located at the top and bottom of the denitrification tower, respectively. The dehydrogenation tower condenser and evaporator are also located at the top and bottom of the dehydrogenation tower, respectively. The stripping tower condenser is located at the top of the stripping tower. The purified gas flows sequentially through the main heat exchanger, the denitrification tower evaporator, the dehydrogenation tower evaporator, the main heat exchanger, and the middle section of the dehydrogenation tower via pipelines. The gas phase outlet at the top of the dehydrogenation tower is connected to the main heat exchanger via a pipeline. The gas phase outlet from the main heat exchanger, after passing through the ninth flow limiting valve, yields syngas. The liquid phase outlet at the bottom of the dehydrogenation tower connects to the middle of the denitrification tower via a pipeline through the first throttle valve. The liquid phase outlet at the bottom of the denitrification tower, after passing through the main heat exchanger and the second throttle valve, yields LNG. The gas phase outlet at the top of the denitrification tower is divided into three branches via a pipeline. The first branch, after passing through the main heat exchanger and the sixth flow limiting valve, yields sludge gas. The second branch, after passing through the seventh throttle valve and the main heat exchanger, yields nitrogen-rich tail gas. The third branch... After passing through the third throttling valve, the gas enters the bottom of the stripping tower. The liquid phase outlet at the bottom of the stripping tower is divided into two paths through pipelines. One path, after passing through the fifth throttling valve, yields liquid nitrogen product, while the other path, after passing through the main heat exchanger and the fourth flow limiting valve, yields nitrogen product. The gas phase outlet at the top of the stripping tower, after passing through the main heat exchanger and the eighth flow limiting valve through pipelines, yields hydrogen-rich tail gas. The low-temperature cold source for the denitrification tower condenser, the dehydrogenation tower condenser, and the stripping tower condenser is provided by nitrogen circulation. The cooling capacity of the main heat exchanger is provided by mixed refrigerant circulation.

[0009] Preferably, the main heat exchanger, denitrification tower evaporator, denitrification tower condenser, dehydrogenation tower evaporator, dehydrogenation tower condenser, stripping tower condenser, denitrification tower, dehydrogenation tower, stripping tower, first separation tank, and second separation tank are all housed in a low-temperature insulation box.

[0010] Preferably, the low-pressure circulating nitrogen gas passes through a nitrogen compressor, a nitrogen compressor aftercooler, and a nitrogen buffer tank in sequence via pipelines before entering the main heat exchanger to be cooled into subcooled liquid nitrogen. Then, it is divided into three branches through pipelines. The fourth branch is sent to the denitrification tower condenser after passing through the eleventh throttle valve, the fifth branch is sent to the dehydrogenation tower condenser after passing through the tenth throttle valve, and the sixth branch is sent to the stripping tower condenser after passing through the twelfth throttle valve. The low-pressure circulating nitrogen gas evaporated from the denitrification tower condenser, the dehydrogenation tower condenser, and the stripping tower condenser is sent to the nitrogen compressor for recirculation and pressurization after passing through the main heat exchanger.

[0011] Preferably, the mixed refrigerant is piped sequentially through a refrigerant compressor stage one, a refrigerant stage one cooler, a refrigerant stage one separator, a refrigerant compressor stage two, a refrigerant stage two cooler, and a refrigerant stage two separator to obtain two branches of mixed refrigerant. The liquid mixed refrigerant of the seventh branch returns to the main heat exchanger after passing through the main heat exchanger, the thirteenth throttle valve, and the first separator, and is then sent to the refrigerant compressor stage one for cyclic compression. The gaseous mixed refrigerant of the eighth branch returns to the main heat exchanger after passing through the main heat exchanger, the fourteenth throttle valve, and the second separator, and is then sent to the refrigerant compressor stage one for cyclic compression.

[0012] Preferably, the denitrification tower, dehydrogenation tower, and stripping tower are all packed towers.

[0013] Another object of the present invention is to provide a method for co-producing LNG, syngas and nitrogen using the above-described system of raw coal gas, the steps of which are as follows:

[0014] 1) The purified gas obtained after the raw coal gas purification process enters the main heat exchanger for pre-cooling and then enters the hot flow channel of the denitrification tower evaporator. After being cooled in the denitrification tower evaporator, it enters the hot flow channel of the dehydrogenation tower evaporator. After being cooled in the dehydrogenation tower evaporator, it enters the main heat exchanger for further cooling and is then drawn from the bottom of the main heat exchanger and sent to the middle of the dehydrogenation tower. Under the action of heat and mass exchange, the hydrogen component in the gas phase at the top of the dehydrogenation tower increases, while most of the methane and nitrogen are enriched in the liquid phase at the bottom of the dehydrogenation tower. The gas at the top of the dehydrogenation tower enters the dehydrogenation tower condenser and is partially condensed. Among them, the methane and most of the nitrogen become liquid and return to the top of the dehydrogenation tower as reflux liquid. Most of the hydrogen component and some of the nitrogen component remain in the gas phase and are drawn from the top of the dehydrogenation tower to obtain hydrogen-nitrogen synthesis gas. This synthesis gas is then sent to the main heat exchanger for reheating to room temperature and then sent to the downstream ammonia synthesis unit or hydrogen extraction unit for use.

[0015] 2) Under the heating effect of the heat source of the dehydrogenation tower evaporator, most of the hydrogen components, carrying a small amount of nitrogen components, are evaporated into gas and become the rising gas at the bottom of the dehydrogenation tower. Most of the remaining methane and nitrogen components are retained in the liquid at the bottom of the dehydrogenation tower. This part of the liquid is sent to the denitrification tower. Under the heat and mass exchange, the methane content in the liquid phase at the bottom of the denitrification tower increases. Under the heating effect of the heat source of the denitrification tower evaporator, most of the nitrogen components are evaporated into gas and become the rising gas at the bottom of the denitrification tower. Most of the remaining methane and trace amounts of nitrogen components are retained in the liquid at the bottom of the denitrification tower. LNG product is obtained at the bottom of the denitrification tower. This part of the LNG product is subcooled in the main heat exchanger and then sent to the downstream LNG storage tank for storage.

[0016] 3) The gas at the top of the denitrification tower enters the denitrification tower condenser and is partially condensed. Methane and a small amount of nitrogen become liquid and return to the top of the denitrification tower as reflux liquid. Most of the remaining nitrogen components remain in the gas phase and are extracted from the top of the denitrification tower to obtain nitrogen-rich tail gas. This nitrogen-rich tail gas is divided into three parts. One part of the nitrogen-rich tail gas is reheated in the main heat exchanger and sent to the upstream low-temperature methanol washing section as stripping gas as waste nitrogen product. Another part of the nitrogen-rich tail gas is reheated in the main heat exchanger and sent to the upstream dehydration section as regeneration gas. The last part of the nitrogen-rich tail gas is sent to the bottom of the stripping tower as raw material as stripping gas.

[0017] 4) The stripping gas entering the stripping tower strips the hydrogen component in the top reflux liquid into the gas phase. Part of the liquid nitrogen at the bottom of the stripping tower is sent to the liquid nitrogen storage tank as liquid nitrogen product. The remaining liquid nitrogen is vaporized and reheated in the main heat exchanger and sent upstream as nitrogen product to supplement nitrogen consumption. The gas at the top of the stripping tower is partially condensed in the stripping tower condenser. Most of the nitrogen becomes liquid and returns to the top of the stripping tower as reflux liquid. Most of the hydrogen component carries part of the nitrogen component and is extracted from the top of the stripping tower. This part of the gas is reheated in the main heat exchanger and sent upstream for recycling or directly to the flare network.

[0018] Preferably, the purified gas comprises N2, H2 and CH4.

[0019] Preferably, the purified gas contains 40-80% N2, 1-20% H2, and 1-30% CH4.

[0020] Preferably, the pressure setting range of the purified gas is 1.5 to 3.0 MPa.

[0021] Therefore, the present invention has the following advantages:

[0022] (1) This invention is applicable to raw coal gas with high nitrogen content and can simultaneously and efficiently produce LNG, syngas and nitrogen with high purity.

[0023] (2) The hydrogen-nitrogen ratio in the hydrogen-rich gas product obtained by this method can be effectively controlled at 3:1, which can be directly used as the feed gas for downstream ammonia synthesis. The nitrogen components in the synthesis gas all come from the nitrogen in the original gas, which effectively utilizes the high nitrogen content in the feed gas and does not require external nitrogen to be consumed for nitrogen preparation.

[0024] (3) The recovery rate of hydrogen in the syngas product obtained by this method can be controlled within the range of 90-99%, achieving efficient recovery and utilization of hydrogen. At the same time, it also provides favorable conditions for the high purity of the nitrogen-rich gas at the top of the denitrification tower. The purity of this nitrogen-rich gas can reach more than 97% and can be directly used for stripping gas in the upstream low-temperature methanol washing section, etc.

[0025] (4) This method effectively utilizes the high nitrogen content of raw coal gas to extract nitrogen products. The nitrogen purity can reach over 99.8%, providing necessary nitrogen for upstream coal chemical and raw coal gas purification processes. It also provides necessary supplementary nitrogen for the nitrogen circulation system and refrigerant circulation system of the cryogenic separation process. After the system is in normal operation, no external nitrogen consumption is required, which is far lower than the production energy consumption of external liquid nitrogen devices. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the present invention.

[0027] Diagram description: E01 - Main heat exchanger, E02 - Denitrification tower evaporator, E03 - Denitrification tower condenser, E04 - Dehydrogenation tower evaporator, E05 - Dehydrogenation tower condenser, E06 - Stripping tower condenser, E07 - Nitrogen compressor aftercooler, E08 - Refrigerant compressor primary cooler, E09 - Refrigerant compressor secondary cooler;

[0028] T01 - Denitrification tower, T02 - Dehydrogenation tower, T03 - Stripping tower;

[0029] D01 - First Separator, D02 - Second Separator, D03 - Nitrogen Buffer Tank, D04 - First-Stage Refrigerant Separator, D05 - Second-Stage Refrigerant Separator;

[0030] CO1 - Nitrogen compressor, CO2 - Refrigerant compressor stage 1, CO3 - Refrigerant compressor stage 2;

[0031] V01 - First throttle valve, V02 - Second throttle valve, V03 - Third throttle valve, V04 - Fourth flow limiting valve, V05 - Fifth throttle valve, V06 - Sixth flow limiting valve, V07 - Seventh throttle valve, V08 - Eighth flow limiting valve, V09 - Ninth flow limiting valve, V10 - Tenth throttle valve, V11 - Eleventh throttle valve, V12 - Twelfth throttle valve, V13 - Thirteenth throttle valve, V14 - Fourteenth throttle valve;

[0032] 01-First tributary, 02-Second tributary, 03-Third tributary, 04-Fourth tributary, 05-Fifth tributary, 06-Sixth tributary, 07-Seventh tributary, 08-Eighth tributary, 11-Purified gas;

[0033] X01 - Purification module, X02 - Low-temperature cold storage box. Detailed Implementation

[0034] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0035] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art. Unless otherwise specified, the components or equipment in the following embodiments are general standard parts or components known to those skilled in the art, and their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0036] Example:

[0037] like Figure 1 The system shown is a co-production system for LNG, syngas, and nitrogen from raw coal gas. The raw coal gas is processed by purification module X01 to obtain purified gas 11. The system mainly includes a main heat exchanger E01, a denitrification tower evaporator E02, a denitrification tower condenser E03, a dehydrogenation tower evaporator E04, a dehydrogenation tower condenser E05, a stripping tower condenser E06, a nitrogen compressor aftercooler E07, a refrigerant compressor primary cooler E08, a refrigerant compressor secondary cooler E09, a denitrification tower T01, a dehydrogenation tower T02, a stripping tower T03, and a first separation tank. The system includes D01, second separator D02, nitrogen buffer tank D03, refrigerant primary separator D04, refrigerant secondary separator D05, nitrogen compressor CO1, refrigerant compressor primary CO2, refrigerant compressor secondary CO3, and several pipelines. The denitrification tower condenser E03 and denitrification tower evaporator E02 are located at the top and bottom of the denitrification tower T01, respectively. The dehydrogenation tower condenser E05 and dehydrogenation tower evaporator E04 are located at the top and bottom of the dehydrogenation tower T02, respectively. The stripping tower condenser E06 is located at the top of the stripping tower T03.

[0038] The aforementioned raw coal gas undergoes washing, conversion, low-temperature methanol washing, methanation, and deep dehydration processes in purification module X01 to obtain purified gas 11. This purification module X01 is mainly used to remove impurities from the raw coal gas and convert CO and CO2 to CH4 to the greatest extent possible. Purified gas 11 is then sent into the system. It should be noted that the raw coal gas purification process is a relatively complete technology in the prior art, and will not be described in detail here. This invention mainly utilizes the purified gas 11 after the raw coal gas purification to prepare LNG, syngas, and nitrogen. The typical composition of the purified gas 11 entering the system after being processed by purification module X01 is: N2: 40-80%, H2: 1-20%, CH4: 1-30%, and the typical pressure is 1.5-3.0 MPa.

[0039] Purified gas 11 flows sequentially through pipelines to the main heat exchanger E01, the denitrification tower evaporator E02, the dehydrogenation tower evaporator E04, the main heat exchanger E01, and the middle of the dehydrogenation tower T02. The gas phase outlet at the top of the dehydrogenation tower T02 is connected to the main heat exchanger E01 via a pipeline. After exiting the main heat exchanger E01, it passes through the ninth flow limiting valve V09 to obtain syngas product. The liquid phase outlet at the bottom of the dehydrogenation tower T02 is connected to the middle of the denitrification tower T01 via a pipeline through the first throttle valve V01. The liquid phase outlet at the bottom of the denitrification tower T01 is connected to the main heat exchanger E01 and the second throttle valve V02 via a pipeline to obtain LNG product. The gas phase outlet at the top of the denitrification tower T01 is distributed via pipelines... The system consists of three branches. The first branch, 01, passes through the main heat exchanger E01 and the sixth flow limiting valve V06 to produce sludge nitrogen. The second branch, 02, passes through the seventh throttle valve V07 and the main heat exchanger E01 to produce nitrogen-rich tail gas. The third branch, 03, passes through the third throttle valve V03 and enters the bottom of the stripping tower T03. The liquid phase outlet at the bottom of the stripping tower T03 is divided into two paths through a pipeline. One path passes through the fifth throttle valve V05 to produce liquid nitrogen, and the other path passes through the main heat exchanger E01 and the fourth flow limiting valve V04 to produce nitrogen. The gas phase outlet at the top of the stripping tower T03 passes through the main heat exchanger E01 and the eighth flow limiting valve V08 through a pipeline to produce hydrogen-rich tail gas.

[0040] The low-temperature cold source for the denitrification tower condenser E03, the dehydrogenation tower condenser E05, and the stripping tower condenser E06 is provided by nitrogen circulation; the cooling capacity of the main heat exchanger E01 is provided by mixed refrigerant circulation.

[0041] The aforementioned main heat exchanger E01, denitrification tower evaporator E02, denitrification tower condenser E03, dehydrogenation tower evaporator E04, dehydrogenation tower condenser E05, stripping tower condenser E06, denitrification tower T01, dehydrogenation tower T02, stripping tower T03, first separation tank D01, and second separation tank D02 are all housed in a low-temperature cold storage box X02.

[0042] Specifically, low-pressure circulating nitrogen passes through a pipeline sequentially through nitrogen compressor C01, nitrogen compressor aftercooler E07, and nitrogen buffer tank D03 before entering the main heat exchanger E01 to be cooled into subcooled liquid nitrogen. Then, it is divided into three branches through a pipeline. The fourth branch 04 is sent to the denitrification tower condenser E03 after passing through the eleventh throttle valve V11. The fifth branch 05 is sent to the dehydrogenation tower condenser E05 after passing through the tenth throttle valve V10. The sixth branch 06 is sent to the stripping tower condenser E06 after passing through the twelfth throttle valve V12. The low-pressure circulating nitrogen after evaporation from the denitrification tower condenser E03, dehydrogenation tower condenser E05, and stripping tower condenser E06 is sent to the nitrogen compressor C01 for recirculation and pressurization after passing through the main heat exchanger E01.

[0043] Specifically, the mixed refrigerant passes through pipelines sequentially through the first stage CO2 of the refrigerant compressor, the first stage refrigerant cooler E08, the first stage refrigerant separator D04, the second stage CO3 of the refrigerant compressor, the second stage refrigerant cooler E09, and the second stage refrigerant separator D05 to obtain two branches of mixed refrigerant. The liquid mixed refrigerant in the seventh branch 07 passes through the main heat exchanger E01, the thirteenth throttle valve V13, and the first separator D01 before returning to the main heat exchanger E01, and then is sent to the first stage CO2 of the refrigerant compressor for cyclic compression. The gaseous mixed refrigerant in the eighth branch 08 passes through the main heat exchanger E01, the fourteenth throttle valve V14, and the second separator D02 before returning to the main heat exchanger E01, and then is sent to the first stage CO2 of the refrigerant compressor for cyclic compression.

[0044] In this embodiment, the denitrification tower T01, the dehydrogenation tower T02, and the stripping tower T03 are all packed towers.

[0045] The method for co-producing LNG, syngas, and nitrogen from raw coal gas based on the above system comprises the following steps:

[0046] 1) The purified gas 11 obtained after the raw coal gas purification process enters the main heat exchanger E01 for pre-cooling and then enters the hot flow channel of the denitrification tower evaporator E02. After being cooled in the denitrification tower evaporator E02, it continues to enter the hot flow channel of the dehydrogenation tower evaporator E04 for further cooling. After cooling, it continues to enter the main heat exchanger E01 for further cooling and is then drawn from the bottom of the main heat exchanger E01 and sent to the middle of the dehydrogenation tower T02. Under the action of heat and mass exchange, the hydrogen content in the gas phase at the top of the tower increases, while almost all of the methane and most of the nitrogen are enriched in the liquid phase at the bottom of the tower. The gas at the top of the dehydrogenation tower T02 enters... In the dehydrogenation tower condenser E05, some of the methane and a large amount of nitrogen are condensed and returned to the top of the dehydrogenation tower T02 as reflux liquid. Almost all of the hydrogen components and some of the nitrogen components remain in the gas phase and are extracted from the top of the dehydrogenation tower T02 to obtain hydrogen-nitrogen synthesis gas. By reasonably controlling the load of the dehydrogenation tower top condenser E05, the hydrogen-nitrogen ratio in this gas stream can be effectively controlled at about 3:1, which is beneficial to the production of downstream ammonia synthesis unit. This synthesis gas is then sent to the main heat exchanger E01 for reheating to room temperature before being sent to the downstream ammonia synthesis unit or hydrogen extraction unit for use.

[0047] 2) The liquid phase at the bottom of the dehydrogenation tower T02, rich in nitrogen and methane, is heated by the heat source E04 in the dehydrogenation tower evaporator. Most of the hydrogen components, carrying a small amount of nitrogen, are evaporated into gas and become the rising gas at the bottom of the tower. Almost all the methane and most of the nitrogen components are retained in the liquid at the bottom of the tower. This portion of liquid is depressurized and flow-limited by the first throttling valve V01 and then sent to the denitrification tower T01. Under the action of heat and mass exchange, the methane content in the liquid phase at the bottom of the denitrification tower T01 increases, and the rising gas in the denitrification tower evaporator E04... Under the heating action of heat source 02, most of the nitrogen components contained therein are evaporated into gas and become the rising gas at the bottom of the denitrification tower T01. This also ensures the purity of the LNG product at the bottom of the tower. Almost all of the remaining methane and trace amounts of nitrogen components are retained in the liquid at the bottom of the tower. The bottom of the denitrification tower T01 yields LNG product with a purity of ≤1% for non-condensable gases such as nitrogen. This part of the LNG product enters the main heat exchanger E01 for further subcooling, and then passes through the second throttle valve V02 to reduce pressure and limit flow before being sent to the downstream LNG storage tank for storage.

[0048] 3) The nitrogen content in the gas phase at the top of the denitrification tower T01 increases. The gas from the top of the tower enters the denitrification tower condenser E03 and is partially condensed. Methane and a small amount of nitrogen become liquid and return to the top of the denitrification tower T01 as reflux liquid. The remaining large amount of nitrogen remains in the gas phase and is extracted from the top of the denitrification tower T01 to obtain nitrogen-rich tail gas with high nitrogen purity (approximately 97% or higher). By reasonably controlling the load of the denitrification tower top condenser E03, the methane content in this gas stream can be effectively controlled within a low range to ensure LNG production. With a high recovery rate of methane components in the product, the nitrogen-rich tail gas was subsequently divided into three parts for utilization: the nitrogen-rich gas from the first branch 01 was reheated in the main heat exchanger E01 and then flow-limited by the sixth flow-limiting valve V06 before being sent as waste nitrogen product to the upstream low-temperature methanol washing section as stripping gas; the nitrogen-rich gas from the second branch 02 was depressurized and flow-limited by the seventh throttle valve V07 before entering the main heat exchanger E01 for reheating, and finally sent to the upstream dehydration section as regeneration gas; the nitrogen-rich gas from the third branch 03 was sent as raw material to the bottom of the stripping tower T03 as stripping gas.

[0049] 4) In step 3), the stripping gas entering stripping tower T03 strips the hydrogen component in the top reflux liquid into the gas phase, thereby obtaining liquid nitrogen with a purity of over 99.8% at the bottom of stripping tower T03. Part of the liquid nitrogen is extracted, depressurized and flow-limited by the fifth throttle valve V05, and sent to the liquid nitrogen storage tank as liquid nitrogen product. The remaining liquid nitrogen is vaporized and reheated in the main heat exchanger E01, and then flow-limited by the fourth flow-limiting valve V04, and sent upstream as nitrogen product to supplement nitrogen consumption. The gas with a slightly higher hydrogen content at the top of stripping tower T03 is partially condensed in the stripping tower condenser E06. A large amount of nitrogen becomes liquid and returns to the top of stripping tower T03 as reflux liquid. Almost all of the remaining hydrogen component, carrying some nitrogen component, is extracted from the top of stripping tower T03 as gas. This part of the gas is reheated in the main heat exchanger E01, and then flow-limited by the eighth flow-limiting valve V08 before being sent upstream for recycling or directly to the flare network.

[0050] This embodiment also provides the working principle of low-pressure circulating nitrogen and mixed refrigerant:

[0051] Low-pressure circulating nitrogen is pressurized by nitrogen compressor C01, cooled by nitrogen compressor aftercooler E07, buffered by buffer tank D03, and then cooled by main heat exchanger E01 until it becomes subcooled liquid nitrogen before being extracted. This portion of liquid nitrogen is divided into three streams: fourth branch 04, fifth branch 05, and sixth branch 06. The liquid nitrogen from the fourth branch 04 is depressurized and flow-limited by the eleventh throttle valve V11 and sent to the denitrification tower condenser E03 to partially condense the gas at the top of the denitrification tower T01 to obtain the necessary reflux liquid and high-purity nitrogen-rich gas at the top of the tower. The liquid nitrogen from the fifth branch 05 is depressurized and flow-limited by the tenth throttle valve V10. The gas is then fed into the dehydrogenation tower condenser E05 to partially condense the gas at the top of the dehydrogenation tower T02 to obtain the necessary reflux liquid and synthesis gas with a hydrogen-to-nitrogen ratio of 3:1. The liquid nitrogen from the sixth branch 06 is sent to the stripping tower condenser E06 after being depressurized and flow-limited by the twelfth throttle valve V12 to partially condense the gas at the top of the stripping tower T03 to obtain the necessary reflux liquid. The low-pressure circulating nitrogen gas evaporated from the denitrification tower condenser E03, the dehydrogenation tower condenser E05, and the stripping tower condenser E06 is reheated to room temperature by the main heat exchanger E01 and then sent to the nitrogen compressor C01 for cyclic pressurization, and the cycle is repeated.

[0052] The low-pressure, ambient-temperature mixed refrigerant is pressurized by CO2 in the first stage of the refrigerant compressor, cooled by E08 in the first stage of the refrigerant cooler, separated by D04 in the first stage of the refrigerant separator, pressurized by CO3 in the second stage of the refrigerant compressor, cooled by E09 in the second stage of the refrigerant cooler, and separated by D05 in the second stage of the refrigerant separator, resulting in two mixed refrigerant streams in two branches: a gaseous mixed refrigerant in the eighth branch 08 and a liquid mixed refrigerant in the seventh branch 07. The liquid mixed refrigerant in the seventh branch 07 is subcooled in the main heat exchanger E01 and then extracted. After passing through the thirteenth throttle valve V13 and the first separator D01, the refrigerant returns to the main heat exchanger E01, where it is reheated to room temperature before returning to the first stage CO2 of the refrigerant compressor for recirculation and compression. The gaseous mixed refrigerant of the eighth branch 08 is cooled to subcooled in the main heat exchanger E01, then extracted and returned to the main heat exchanger E01 after passing through the fourteenth throttle valve V14 and the second separator D02. After being reheated to room temperature in the heat exchanger E01, it returns to the first stage CO2 of the refrigerant compressor for recirculation and compression.

[0053] This invention provides a system and method for co-producing LNG, syngas, and nitrogen from raw coal gas. It is suitable for raw coal gas with high nitrogen content and can simultaneously and efficiently produce LNG, syngas (or hydrogen-rich gas), and nitrogen with high purity.

[0054] The hydrogen-nitrogen ratio in the hydrogen-rich gas product obtained by this cryogenic separation method can be effectively controlled at 3:1, and it can be directly used as feed gas for downstream ammonia synthesis. The nitrogen components in the synthesis gas all come from the nitrogen in the original gas, effectively utilizing the high nitrogen content in the feed gas, and eliminating the need for external nitrogen to be consumed for nitrogen preparation.

[0055] The hydrogen recovery rate of the syngas (or hydrogen-rich gas) product obtained by this cryogenic separation method can be controlled within the range of 90-99%, achieving efficient hydrogen recovery and utilization. At the same time, it also provides favorable conditions for the high purity of the nitrogen-rich gas at the top of the denitrification tower. The purity of this nitrogen-rich gas can reach more than 97% and can be directly used for stripping gas in the upstream low-temperature methanol washing section, etc.

[0056] This cryogenic separation method effectively utilizes the high nitrogen content of raw coal gas to extract nitrogen products with a purity of over 99.8%. This provides necessary nitrogen for upstream coal chemical and raw coal gas purification processes, and also provides necessary supplementary nitrogen for the nitrogen circulation system and refrigerant circulation system of the cryogenic separation process. Once the system is running normally, no external nitrogen consumption is required.

[0057] The energy consumption for nitrogen product production in this invention is only 0.05 kW·h / Nm³. 3 The nitrogen output is approximately 0.2 kW·h / Nm³, significantly lower than that of an external nitrogen generator under the same product pressure. 3The energy consumption of nitrogen production equipment is significantly reduced, minimizing investment and energy consumption. Simultaneously, this technology can flexibly produce liquid nitrogen as backup nitrogen for upstream and downstream coal chemical plants, based on their specific needs. The energy consumption for liquid nitrogen production is only 0.4 kW·h / Nm³. 3 The energy consumption of liquid nitrogen is much lower than that of external liquid nitrogen equipment, resulting in extremely high economic benefits.

[0058] It should be understood that this embodiment is for illustrative purposes only and is not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A system for co-producing LNG, syngas, and nitrogen from raw coal gas, wherein the raw coal gas is processed by a purification module (X01) to obtain purified gas (11), characterized in that: The system includes a main heat exchanger (E01), a denitrification tower evaporator (E02), a denitrification tower condenser (E03), a dehydrogenation tower evaporator (E04), a dehydrogenation tower condenser (E05), a stripping tower condenser (E06), a nitrogen compressor aftercooler (E07), a refrigerant compressor primary cooler (E08), a refrigerant compressor secondary cooler (E09), a denitrification tower (T01), a dehydrogenation tower (T02), a stripping tower (T03), a first separation tank (D01), a second separation tank (D02), a nitrogen buffer tank (D03), and a cooling tower. The system includes a primary refrigerant separator (D04), a secondary refrigerant separator (D05), a nitrogen compressor (C01), a primary refrigerant compressor (C02), a secondary refrigerant compressor (C03), and several pipelines. The denitrification tower condenser (E03) and denitrification tower evaporator (E02) are located at the top and bottom of the denitrification tower (T01), respectively. The dehydrogenation tower condenser (E05) and dehydrogenation tower evaporator (E04) are located at the top and bottom of the dehydrogenation tower (T02), respectively. The stripping tower condenser (E06) is located at the top of the stripping tower (T03). Purified gas (11) flows sequentially through the main heat exchanger (E01), denitrification tower evaporator (E02), dehydrogenation tower evaporator (E04), main heat exchanger (E01) and the middle of dehydrogenation tower (T02) via pipeline. The gas phase outlet at the top of the dehydrogenation tower (T02) is connected to the main heat exchanger (E01) via pipeline. After exiting the main heat exchanger (E01), it passes through the ninth flow limiting valve (V09) to obtain the synthesis gas product. The liquid phase outlet at the bottom of the dehydrogenation tower (T02) is connected to the middle of the denitrification tower (T01) via pipeline through the first throttle valve (V01). The liquid phase outlet at the bottom of the denitrification tower (T01) is connected to the main heat exchanger (E01) and the second throttle valve (V02) via a pipeline to obtain LNG product. The gas phase outlet at the top of the denitrification tower (T01) is divided into three branches via a pipeline. The first branch (01) is connected to the main heat exchanger (E01) and the sixth flow limiting valve (V06) to obtain waste nitrogen product. The second branch (02) is connected to the main heat exchanger (E01) and the seventh throttle valve (V07) to obtain nitrogen-rich tail gas product. The third branch (03) is connected to the bottom of the stripping tower (T03) via the third throttle valve (V03). The liquid phase outlet at the bottom of the stripping tower (T03) is divided into two paths through pipelines. One path leads to liquid nitrogen product after passing through the fifth throttle valve (V05), and the other path leads to nitrogen product after passing through the main heat exchanger (E01) and the fourth flow limiting valve (V04). The gas phase outlet at the top of the stripping tower (T03) leads to hydrogen-rich tail gas after passing through the main heat exchanger (E01) and the eighth flow limiting valve (V08) through pipelines. The low-temperature cold source for the denitrification tower condenser (E03), the dehydrogenation tower condenser (E05), and the stripping tower condenser (E06) is provided by nitrogen circulation; The cooling capacity of the main heat exchanger (E01) is provided by a mixed refrigerant cycle.

2. The system for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 1, characterized in that: The main heat exchanger (E01), denitrification tower evaporator (E02), denitrification tower condenser (E03), dehydrogenation tower evaporator (E04), dehydrogenation tower condenser (E05), stripping tower condenser (E06), denitrification tower (T01), dehydrogenation tower (T02), stripping tower (T03), first separation tank (D01), and second separation tank (D02) are all installed in a low-temperature cold storage box (X02).

3. A system for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 2, characterized in that: Low-pressure circulating nitrogen passes through a pipeline sequentially through a nitrogen compressor (C01), a nitrogen compressor aftercooler (E07), and a nitrogen buffer tank (D03) before entering the main heat exchanger (E01) to be cooled into subcooled liquid nitrogen. Then, it is divided into three branches through a pipeline. The fourth branch (04) is sent to the denitrification tower condenser (E03) after passing through the eleventh throttle valve (V11), the fifth branch (05) is sent to the dehydrogenation tower condenser (E05) after passing through the tenth throttle valve (V10), and the sixth branch (06) is sent to the stripping tower condenser (E06) after passing through the twelfth throttle valve (V12). The low-pressure circulating nitrogen after evaporation from the denitrification tower condenser (E03), the dehydrogenation tower condenser (E05), and the stripping tower condenser (E06) is sent to the nitrogen compressor (C01) for recirculation and pressurization after passing through the main heat exchanger (E01).

4. A system for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 2, characterized in that: The mixed refrigerant passes through pipelines sequentially through the first stage of the refrigerant compressor (CO2), the first stage refrigerant cooler (E08), the first stage refrigerant separator (D04), the second stage of the refrigerant compressor (CO3), the second stage refrigerant cooler (E09), and the second stage refrigerant separator (D05) to obtain two branches of mixed refrigerant. The liquid mixed refrigerant of the seventh branch (07) passes through the main heat exchanger (E01), the thirteenth throttle valve (V13), and the first separator (D01) before returning to the main heat exchanger (E01) and then being sent to the first stage of the refrigerant compressor (CO2) for cyclic compression. The gaseous mixed refrigerant of the eighth branch (08) passes through the main heat exchanger (E01), the fourteenth throttle valve (V14), and the second separator (D02) before returning to the main heat exchanger (E01) and then being sent to the first stage of the refrigerant compressor (CO2) for cyclic compression.

5. A system for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 1, characterized in that: The denitrification tower (T01), dehydrogenation tower (T02), and stripping tower (T03) are all packed towers.

6. A method for co-producing LNG, syngas, and nitrogen from raw coal gas using the system described in any one of claims 1-5, characterized in that: The method includes the following steps: 1) The purified gas (11) obtained after the purification treatment of raw coal gas enters the main heat exchanger (E01) for pre-cooling and then enters the hot flow channel of the denitrification tower evaporator (E02). After being cooled in the denitrification tower evaporator (E02), it enters the hot flow channel of the dehydrogenation tower evaporator (E04). After being cooled in the dehydrogenation tower evaporator (E04), it enters the main heat exchanger (E01) for further cooling and is drawn from the bottom of the main heat exchanger (E01) and sent to the middle of the dehydrogenation tower (T02). Under the action of heat and mass exchange, the hydrogen group in the gas phase at the top of the dehydrogenation tower (T02) is reduced. As the concentration rises, most of the methane and nitrogen are enriched in the liquid phase at the bottom of the dehydrogenation tower (T02). The gas at the top of the dehydrogenation tower (T02) enters the dehydrogenation tower condenser (E05) and is partially condensed. The methane and most of the nitrogen become liquid and return to the top of the dehydrogenation tower (T02) as reflux liquid. Most of the hydrogen components and some nitrogen components remain in the gas phase and are extracted from the top of the dehydrogenation tower (T02) to obtain hydrogen-nitrogen synthesis gas. This synthesis gas is then sent to the main heat exchanger (E01) for reheating to room temperature before being sent to the downstream ammonia synthesis unit or hydrogen extraction unit for use. 2) Under the heating effect of the heat source of the dehydrogenation tower evaporator (E04), most of the hydrogen components, carrying a small amount of nitrogen components, are evaporated into gas and become the rising gas at the bottom of the dehydrogenation tower (T02). Most of the remaining methane and nitrogen components are retained in the liquid at the bottom of the dehydrogenation tower (T02). This part of the liquid is sent to the denitrification tower (T01). Under the heat and mass exchange, the methane content in the liquid phase at the bottom of the denitrification tower (T01) increases. Under the heating effect of the heat source of the denitrification tower evaporator (E02), most of the nitrogen components are evaporated into gas and become the rising gas at the bottom of the denitrification tower (T01). Most of the remaining methane and trace amounts of nitrogen components are retained in the liquid at the bottom of the denitrification tower (T01). LNG product is obtained at the bottom of the denitrification tower (T01). This part of the LNG product is subcooled in the main heat exchanger (E01) and then sent to the downstream LNG storage tank for storage. 3) The gas at the top of the denitrification tower (T01) enters the denitrification tower condenser (E03) and is partially condensed. Methane and a small amount of nitrogen become liquid and return to the top of the denitrification tower (T01) as reflux liquid. Most of the remaining nitrogen components remain in the gas phase and are extracted from the top of the denitrification tower (T01) to obtain nitrogen-rich tail gas. This nitrogen-rich tail gas is divided into three parts. One part of the nitrogen-rich tail gas is reheated in the main heat exchanger (E01) and sent to the upstream low-temperature methanol washing section as stripping gas as waste nitrogen product. Another part of the nitrogen-rich tail gas is reheated in the main heat exchanger (E01) and sent to the upstream dehydration section as regeneration gas. The last part of the nitrogen-rich tail gas is sent to the bottom of the stripping tower (T03) as stripping gas as raw material. 4) The stripping gas entering the stripping tower (T03) strips the hydrogen component in the top reflux liquid into the gas phase. Part of the liquid nitrogen at the bottom of the stripping tower (T03) is sent to the liquid nitrogen storage tank as liquid nitrogen product. The remaining liquid nitrogen is vaporized and reheated in the main heat exchanger (E01) and sent upstream as nitrogen product to supplement nitrogen consumption. The gas at the top of the stripping tower (T03) is partially condensed in the stripping tower condenser (E06). Most of the nitrogen becomes liquid and returns to the top of the stripping tower (T03) as reflux liquid. Most of the hydrogen component carries part of the nitrogen component and is extracted from the top of the stripping tower (T03). This part of the gas is reheated in the main heat exchanger (E01) and sent upstream for recycling or directly to the flare network.

7. A method for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 6, characterized in that: The purified gas (11) consists of N2, H2 and CH4.

8. A method for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 7, characterized in that: The purified gas (11) contains 40-80% N2, 1-20% H2, and 1-30% CH4.

9. A method for co-producing LNG, syngas, and nitrogen from raw coal gas according to claim 8, characterized in that: The pressure setting range of the purified gas (11) is 1.5 to 3.0 MPa.

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