System for preparing liquefied natural gas by hydrogen supplementing of coal gas in medium-low temperature pyrolysis

Abstract

The application discloses a system for preparing liquefied natural gas by hydrogen supplementing of coal gas in medium-low temperature pyrolysis, which comprises a water electrolysis hydrogen production device, a methane synthesis device, a coal pyrolysis furnace, a coal gas reforming device, a pressure swing adsorption hydrogen extraction device and a deep cooling liquefaction device; the water electrolysis hydrogen production device is connected with an inlet of the methane synthesis device; a pyrolysis gas outlet and a semi-coke outlet of the coal pyrolysis furnace are connected with an inlet of the coal gas reforming device, and an outlet of the coal gas reforming device is connected with an inlet of the methane synthesis device; an outlet of the methane synthesis device is connected with an inlet of the pressure swing adsorption hydrogen extraction device, and the pressure swing adsorption hydrogen extraction device is connected with the deep cooling liquefaction device. The application realizes the collaborative conversion and integrated innovation of the medium-low temperature coal pyrolysis process and the water electrolysis hydrogen production process, develops and enriches product types and additional values, and has no technical barriers in equipment or devices, and is convenient for industrialization or large-scale application.

Description

A system for producing liquefied natural gas from medium- and low-temperature pyrolysis coal gas with hydrogen supplementation Technical Field

[0001] This invention belongs to the field of medium- and low-temperature pyrolysis gas conversion and utilization, specifically relating to a system for preparing liquefied natural gas by supplementing hydrogen from medium- and low-temperature pyrolysis gas. Background Technology

[0002] my country's energy structure, characterized by "abundant coal, scarce oil, and limited gas," dictates the crucial role of coal in the country's energy utilization, acting as a "ballast" or "stabilizer" for energy security. Low-rank coal accounts for approximately half of my country's coal reserves, and the medium-to-low temperature pyrolysis of low-rank coal is a potential pathway to achieve graded and differentiated coal conversion and clean, efficient utilization. This not only helps extract oil and gas resources from coal, reducing my country's dependence on imported oil and gas, but also yields semi-coke products with high carbon content and high calorific value (relative to raw coal).

[0003] Medium- and low-temperature pyrolysis gas is an important product of coal thermal decomposition (or dry distillation) at medium- and low temperatures (usually 500–700℃) (yield reaching 5%–15% of the dry coal mass). After purification processes such as deoiling and desulfurization, its main components are CH4 (approximately 23%–37% of the volume of medium- and low-temperature pyrolysis gas), CO2 (approximately 5%–34%), H2 (approximately 12%–29%), and CO (approximately 10%–18%), with small amounts of C2-C4 hydrocarbons (Coal Chemical Industry, 2012, 158:1-5; Coal Conversion, 2020, 43:12-19; ​​Clean Coal Technology, 2021, 27:157-163). Some coal pyrolysis processes, by using combustion flue gas as the heat carrier, introduce impurities such as N2 into the medium- and low-temperature pyrolysis gas, further reducing its quality and increasing the difficulty of separation. Currently, the commercially available vertical furnace coal pyrolysis process suffers from problems such as resource waste and environmental pollution because the pyrolysis gas produced is difficult to utilize centrally due to the small scale of individual furnaces and their dispersed construction. Most of the gas is treated crudely by burning for heating or by simply "lighting up the skylight".

[0004] There is limited research, both domestically and internationally, on the production of natural gas from medium- and low-temperature pyrolysis gas using hydrogen supplementation, while there are numerous reports on the technical design and application of natural gas or LNG production from coke oven gas. However, the composition of coke oven gas differs significantly from that of medium- and low-temperature pyrolysis gas. The main components of coke oven gas are: H2 (approximately 55%–63%), CH4 (approximately 22%–27%), CO (approximately 5%–8%), CO2 (approximately 1.5%–3%), N2 (approximately 3%–5%), O2 (approximately 0.3%–0.5%), and other hydrocarbons (C). m H n(Approximately 2%–3%) (Natural Gas Industry, 2020, 40: 112-117; Chemical Engineering, 2021, 49: 73-78.). Market research indicates that some coke oven gas-to-natural gas projects already in operation in China frequently experience problems such as catalyst deactivation, reaction tower explosions, and compressor malfunctions in terms of process flow, catalysts, and equipment reliability (Natural Gas Industry, 2020, 40: 112-117; Chemical Engineering, 2021, 49: 73-78.).

[0005] Therefore, in the design of processes for producing natural gas from medium- and low-temperature pyrolysis coal gas, although existing technologies and applications for producing natural gas from coke oven gas or liquefied natural gas (LNG) can be referenced and learned from, the significant differences in the composition of the two raw materials necessitate the organic integration of the production process with the design, manufacturing, construction, and use of the equipment. This is crucial to effectively avoid or resolve various problems that may arise during production. Furthermore, the production of natural gas from medium- and low-temperature pyrolysis coal gas is a complex system engineering project. During actual project operation, the control of process parameters in each stage must be considered to ensure seamless integration of each stage and the safe and stable operation of the entire system. Summary of the Invention

[0006] To fill the current technological gap in the production of liquefied natural gas from medium- and low-temperature pyrolysis coal gas by adding hydrogen, this invention provides a system for producing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by adding hydrogen.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A system for producing liquefied natural gas by supplementing hydrogen from medium- and low-temperature pyrolysis coal gas includes an electrolytic water hydrogen production unit, a methane synthesis unit, a coal pyrolysis furnace, a coal gas reforming unit, a pressure swing adsorption hydrogen extraction unit, and a cryogenic liquefaction unit.

[0009] The water electrolysis hydrogen production unit is connected to the inlet of the methane synthesis unit;

[0010] The pyrolysis gas outlet and semi-coke outlet of the coal pyrolysis furnace are connected to the inlet of the coal gas reforming unit, and the outlet of the coal gas reforming unit is connected to the inlet of the methane synthesis unit.

[0011] The outlet of the methane synthesis unit is connected to the inlet of the pressure swing adsorption (PSA) hydrogen extraction unit, which is in turn connected to the cryogenic liquefaction unit.

[0012] Furthermore, the water electrolysis hydrogen production unit is connected to a generator set.

[0013] Furthermore, the water electrolysis hydrogen production device is equipped with a water feed port and a product oxygen output port.

[0014] Furthermore, the water electrolysis hydrogen production unit is connected to the methane synthesis unit via a hydrogen storage tank.

[0015] Furthermore, the hydrogen storage tank is equipped with a circulating gas compression device.

[0016] Furthermore, the pyrolysis gas outlet of the coal pyrolysis furnace is connected to a purification treatment device, a gas storage tank, and a gas reforming device.

[0017] Furthermore, the semi-coke outlet of the coal pyrolysis furnace is connected to the gas reforming unit via a stirring and mixing device. The outlet of the gas reforming unit is also connected to the inlet of the solid separation and treatment device, and the outlet of the solid separation and treatment device is connected to the catalyst feeding port on the stirring and mixing device.

[0018] Furthermore, the mixing device is also equipped with a catalyst feeding port.

[0019] Furthermore, the methane synthesis unit is equipped with a saturated steam outlet.

[0020] Furthermore, the outlet of the pressure swing adsorption hydrogen extraction unit is also connected to the inlet of the methane synthesis unit.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Compared to existing coal gas to liquefied natural gas (LNG) plants (including traditional coke oven gas to LNG plants), this invention effectively couples the water electrolysis to hydrogen production process by setting up an electrolysis to hydrogen production device. It can utilize the surplus electricity generated during peak periods of clean and renewable energy generation such as wind and solar power to achieve water electrolysis to produce hydrogen (green hydrogen) and convert the produced hydrogen into natural gas. In other words, it realizes the on-site conversion of surplus electricity generated during peak periods of wind and solar power generation into chemical energy (used for hydrogen supplementation from medium- and low-temperature pyrolysis coal gas to LNG), which is more convenient for energy storage and transportation.

[0023] This invention, by setting up a coal pyrolysis furnace, a coal gas reforming unit, and a methane synthesis unit, successfully achieves the synergistic conversion and integrated innovation of medium-low temperature coal pyrolysis technology and water electrolysis for hydrogen production, thus developing and enriching product types and added value. This invention connects the semi-coke outlet of the coal pyrolysis furnace to the coal gas reforming unit via a stirring and mixing device. The semi-coke from coal pyrolysis, mixed with a certain amount of catalyst, is first used in the coal gas reforming unit for the reforming of medium-low temperature pyrolysis gas. Then, the gas from the reforming reaction is used in the methane synthesis unit for methane synthesis. Its key advantages are: firstly, under the action of a catalyst, the semi-coke from coal pyrolysis can react with the CO2 component in the medium-low temperature pyrolysis gas (C... 半焦The process involves converting CO2 in the medium-low temperature pyrolysis gas into CO, thereby consuming the CO2 component and simultaneously converting the semi-coke from coal decomposition into porous carbon products. Secondly, it eliminates the "decarbonization" step in the traditional coke oven gas to liquefied natural gas process, simplifying the process and improving economic efficiency. Thirdly, converting the CO2 component in the medium-low temperature pyrolysis gas into CO before the methane synthesis reaction helps save hydrogen consumption (according to the equations CO + 3H2 = CH4 + H2O and CO2 + 4H2 = CH4 + 2H2O, it can be seen that to produce one unit volume of methane (the main component of natural gas), using CO as a raw material can save 25% of hydrogen consumption compared to using CO2). This invention provides a potential pathway for the high-value utilization of medium-low temperature pyrolysis gas. The main equipment in the system proposed in this invention can all adopt traditional equipment already in commercial production, and there are no technical barriers in terms of equipment, facilitating large-scale production or market promotion.

[0024] Furthermore, this invention can not only realize the conversion of medium- and low-temperature pyrolysis coal gas and hydrogen into liquefied natural gas on-site, but also partially convert coal pyrolysis semi-coke in the coal gas reforming unit to produce porous carbon (whose value is far higher than that of coal pyrolysis semi-coke). The water electrolysis process also outputs high-purity oxygen to the outside of the system. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the system for preparing liquefied natural gas by hydrogen supplementation from medium- and low-temperature pyrolysis coal gas provided by the present invention.

[0026] Among them, 1-generator set; 2-hydrogen production unit by water electrolysis; 3-hydrogen storage tank; 4-circulating gas compression unit; 5-methane synthesis unit; 6-coal pyrolysis furnace; 7-purification treatment unit; 8-coal gas storage tank; 9-coal gas reforming unit; 10-stirring and mixing unit; 11-solid separation treatment unit; 12-pressure swing adsorption hydrogen extraction unit; 13-cryogenic liquefaction unit. Detailed Implementation

[0027] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0028] In addition, the element in this invention is referred to as "fixed to" or "set on" another element, indicating that it can be directly mounted on another element or directly connected to the body of another element.

[0029] Referring to Figure 1, the system for producing liquefied natural gas from medium- and low-temperature pyrolysis coal gas provided by the present invention mainly includes thirteen main pieces of equipment: a generator set 1, an electrolysis water hydrogen production device 2, a hydrogen storage tank 3, a circulating gas compression device 4, a methane synthesis device 5, a coal pyrolysis furnace 6, a purification treatment device 7, a coal gas storage tank 8, a coal gas reforming device 9, a stirring and mixing device 10, a solid separation treatment device 11, a pressure swing adsorption hydrogen extraction device 12, and a cryogenic liquefaction device 13.

[0030] The generator set 1 is connected to the water electrolysis hydrogen production unit 2. Generator set 1 generates electricity using wind and / or solar power, providing power to the water electrolysis hydrogen production unit 2. The water electrolysis hydrogen production unit 2 is equipped with a water inlet and a product oxygen outlet. The water electrolysis hydrogen production unit 2 is connected to the hydrogen inlet of the hydrogen storage tank 3. The hydrogen produced by the water electrolysis hydrogen production unit 2 is temporarily stored in the hydrogen storage tank 3, while the product oxygen can be directly output to the outside of the system. The hydrogen outlet of the hydrogen storage tank 3 is connected to the inlet of the methane synthesis unit 5, providing a relatively stable hydrogen feedstock for the methane synthesis unit 5. The hydrogen storage tank is equipped with an outlet for connection to the circulating gas compression device 4. Connecting the hydrogen storage tank 3 to the circulating gas compression device 4 facilitates the compression and storage of hydrogen, which is beneficial for increasing the hydrogen storage capacity within a given capacity of the hydrogen storage tank 3. The methane synthesis unit 5 is equipped with two material outlets. One outlet is used for the output of saturated steam, and the other outlet is connected to the inlet of the pressure swing adsorption hydrogen extraction unit 12. The hydrogen outlet of the pressure swing adsorption hydrogen extraction unit 12 is connected to the methane synthesis unit 5 to transport the recovered hydrogen to the methane synthesis unit 5. The tail gas outlet of the pressure swing adsorption hydrogen extraction unit 12 is connected to the cryogenic liquefaction unit 13 to output LNG (liquefied natural gas).

[0031] The coal pyrolysis furnace 6 is equipped with a coal feeding port, a pyrolysis gas outlet, a semi-coke outlet, and a tar outlet. The pyrolysis gas outlet of the coal pyrolysis furnace 6 is connected to the inlet of the purification treatment device 7, and the outlet of the purification treatment device 7 is connected to the gas storage tank 8. The semi-coke outlet of the coal pyrolysis furnace 6 is divided into two paths: one path is connected to the inlet of the stirring and mixing device 10, and the outlet of the stirring and mixing device 10 is connected to the inlet of the gas reforming device 9. The outlet of the gas reforming device 9 is divided into two paths: one path is connected to the inlet of the methane synthesis device 5, outputting the reacted gas to the methane synthesis device; the other path is connected to the solid separation treatment device 11, outputting the reacted solids to the solid separation treatment device. The solid separation treatment device 11 has two outlets: one directly outputs porous carbon products, and the other outlet is connected to the stirring and mixing device 10, conveying the recovered catalyst to the catalyst material.

[0032] After coal undergoes pyrolysis in the coal pyrolysis furnace 6, the resulting pyrolysis gas is transported to the purification treatment unit 7 for dust removal, desulfurization, and other purification treatments. One path of the coal pyrolysis semi-coke produced by the coal pyrolysis furnace 6 is directly discharged outside the system; the other path is transported to the stirring and mixing unit 10 for mixing with the catalyst, and then the mixture of coal pyrolysis semi-coke and catalyst is transported to the gas reforming unit 9. After being processed by the purification treatment unit 7, the pyrolysis gas is temporarily stored in the gas storage tank 8. The stirring and mixing unit 10 is also equipped with a catalyst feeding port.

[0033] The gas storage tank 8 is equipped with a connection port for the circulating gas compression device 4, which facilitates the compression and storage of gas and helps to increase the gas storage capacity when the capacity of the gas storage tank 8 is fixed. The gas storage tank 8 is also connected to the gas reforming unit 9 to provide a stable gas source for the gas reforming unit 9.

[0034] In the coal pyrolysis semi-coke and catalyst mixture, the pyrolysis gas undergoes catalytic reforming in the coal gas reforming unit 9. The resulting material is output in two paths: one path is used for the gas output, which is transported to the methane synthesis unit 5 as feed gas; the other path is used for the solid output, connected to the solid separation and treatment unit 11. The solid material from the coal gas reforming unit 9 is separated in the solid separation and treatment unit 11. On one hand, porous carbon products are output outside the system; on the other hand, the recovered catalyst is transported to the catalyst material to achieve catalyst recycling.

[0035] The reformed coal gas from the coal gas reforming unit 9 and the hydrogen produced by the water electrolysis hydrogen production unit 2 undergo a methanation reaction in the methane synthesis unit 5. The reacted material in the methane synthesis unit 5 is divided into two output devices: one for saturated steam output and the other for pressure swing adsorption (PSA) hydrogen extraction unit 12. After hydrogen extraction from the tail gas in the PSA unit 12, it is sent to the methane synthesis unit 5 for hydrogen recovery and utilization. After hydrogen extraction in the PSA unit 12, the remaining tail gas is sent to the cryogenic liquefaction unit 13 to liquefy the methane-rich gas into liquefied natural gas (LNG) before being output from the system.

[0036] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used in this specification are well known to those skilled in the art. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" includes any combination of one or more of the associated listed items.

Claims

1. A system for producing liquefied natural gas by supplementing hydrogen from medium- and low-temperature pyrolysis coal gas, characterized in that, It includes an electrolytic water hydrogen production unit (2), a methane synthesis unit (5), a coal pyrolysis furnace (6), a coal gas reforming unit (9), a pressure swing adsorption hydrogen extraction unit (12), and a cryogenic liquefaction unit (13); wherein, the electrolytic water hydrogen production unit (2) is connected to the inlet of the methane synthesis unit (5); the pyrolysis gas outlet and semi-coke outlet of the coal pyrolysis furnace (6) are connected to the inlet of the coal gas reforming unit (9), the outlet of the coal gas reforming unit (9) is connected to the inlet of the methane synthesis unit (5); the outlet of the methane synthesis unit (5) is connected to the inlet of the pressure swing adsorption hydrogen extraction unit (12), and the pressure swing adsorption hydrogen extraction unit (12) is connected to the cryogenic liquefaction unit (13).

2. The system for preparing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by hydrogen supplementation according to claim 1, characterized in that, The water electrolysis hydrogen production unit (2) is connected to a generator set (1).

3. The system for preparing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by hydrogen supplementation according to claim 1, characterized in that, The water electrolysis hydrogen production device (2) is equipped with a water feed port and a product oxygen output port.

4. The system for producing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by hydrogen supplementation according to claim 1, characterized in that, The water electrolysis hydrogen production unit (2) is connected to the methane synthesis unit (5) via a hydrogen storage tank (3).

5. The system for producing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by hydrogen supplementation according to claim 1, characterized in that, A circulating gas compression device (4) is installed on the hydrogen storage tank (3).

6. The system for preparing liquefied natural gas by supplementing hydrogen from medium- and low-temperature pyrolysis coal gas according to claim 1, characterized in that, The pyrolysis gas outlet of the coal pyrolysis furnace (6) is connected to the gas reforming unit (9) via the purification treatment device (7), the gas storage tank (8).

7. The system for preparing liquefied natural gas by hydrogen supplementation from medium- and low-temperature pyrolysis coal gas according to claim 1, characterized in that, The semi-coke outlet of the coal pyrolysis furnace (6) is connected to the gas reforming unit (9) via the stirring and mixing device (10). The outlet of the gas reforming unit (9) is also connected to the inlet of the solid separation and treatment device (11). The outlet of the solid separation and treatment device (11) is connected to the catalyst feeding port on the stirring and mixing device (10).

8. The system for preparing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by hydrogen supplementation according to claim 7, characterized in that, The mixing device (10) is also equipped with a catalyst feeding port.

9. The system for preparing liquefied natural gas by hydrogen supplementation from medium- and low-temperature pyrolysis coal gas according to claim 1, characterized in that, The methane synthesis unit (5) is equipped with a saturated steam outlet.

10. The system for preparing liquefied natural gas from medium- and low-temperature pyrolysis coal gas by hydrogen supplementation according to claim 1, characterized in that, The outlet of the pressure swing adsorption hydrogen extraction unit (12) is also connected to the inlet of the methane synthesis unit (5).

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