Natural gas cracking and tail gas utilization system

Abstract

The natural gas cracking and tail gas utilization system comprises a three-phase separator, a compressor unit, a decarburization device, a dehydration device, a mercury removal device, a refrigerant compressor unit, a nitrogen compressor unit, a cold box, a methane cracking furnace, a helium purification device, a hydrogen purification device, a liquefied natural gas storage tank and a carbon dioxide liquefaction device. According to the components of the natural gas, through three-phase separation, precise filtration, pressurization, decarburization, dehydration, demercuration, liquefaction, reheating gasification, catalytic pyrolysis, helium purification, hydrogen purification and carbon dioxide liquefaction, efficient utilization of the carbon nanotubes prepared from the natural gas and pyrolysis tail gas is achieved, and the device has the advantages of being high in efficiency, small in energy consumption and the like; the utilization value of the natural gas can be effectively improved.

Description

Technical Field

[0001] This application belongs to the technical field of new energy, and particularly relates to a natural gas cracking and tail gas utilization system. Background Art

[0002] In recent years, with the continuous development of urban construction and the continuous increase of population, the air pollution in cities has become increasingly serious, and the environmental pollution situation is very severe. As a high-quality clean energy, natural gas has broad application prospects and is also one of the powerful means to solve environmental problems. With the rapid development of science and technology, carbon nanotubes, as a new material in the field of nanotechnology, have attracted extensive attention worldwide.

[0003] The new technology of producing carbon nanotubes from natural gas uses natural gas or pure methane as raw materials and produces carbon nanotubes that meet the requirements of lithium battery factories under a relatively high catalyst ratio. During the production process of producing carbon nanotubes from natural gas, a large amount of tail gas will be generated, including: hydrogen, methane, carbon dioxide, helium, etc. These gases all have high commercial value, and how to make efficient use of them is a problem that needs attention and solution. Utility Model Content

[0004] The technical problem to be solved by this utility model is: to solve the deficiency of low utilization efficiency of natural gas in the prior art, and thus provide a natural gas cracking and tail gas utilization system.

[0005] Principle of high-temperature cracking of natural gas:

[0006] The principle of high-temperature catalytic cracking of natural gas is that methane molecules crack into carbon atoms and hydrogen molecules at a high temperature of 500 - 800 °C and under the action of nickel-based, iron-based, and molybdenum-based catalysts. The carbon atoms form a nanoscale tubular hollow structure on the surface of the catalyst. The cracking equation is:

[0007] CH 4 →C + 2H 2 +Q

[0008] Methane cracks under the action of a catalyst. Among them, 20 - 30% of methane cracks to generate hydrogen, and the main components of the cracking tail gas are methane and hydrogen.

[0009] Since hydrogen and helium are extremely difficult to separate, in order to extract helium from natural gas, the low-temperature method principle is first used to extract helium from natural gas, and then the liquefied natural gas cold energy after helium extraction is absorbed by the cracking tail gas to achieve cold energy exchange. The reheated gaseous methane enters the methane cracking furnace for cracking, and the cracked tail gas after pre-cooling and temperature reduction is separated into methane and hydrogen by the low-temperature rectification method, and the methane cools down to become liquefied natural gas.

[0010] The technical solution adopted by the utility model to solve its technical problems is as follows: A natural gas cracking and tail gas utilization system includes a three-phase separator, a compressor unit, a decarbonization device, a dehydration device, a mercury removal device, a refrigerant compressor unit, a nitrogen compressor unit, a cold box, a methane cracking furnace, a regenerator, a helium purification device, a hydrogen purification device, a liquefied natural gas storage tank, and a carbon dioxide liquefaction device. The three-phase separator, the compressor unit, the decarbonization device, the dehydration device, the mercury removal device, the cold box, and the liquefied natural gas storage tank are connected in sequence through pipelines; the refrigerant compressor unit compresses the mixed refrigerant and conveys the cold quantity to the cold box through the pipeline. The nitrogen compressor unit compresses nitrogen and conveys the cold quantity to the cold box through the pipeline. The methane cracking furnace catalytically cracks the high-purity gaseous methane from the cold box. The helium purification device purifies the flashed natural gas from the cold box and the liquefied natural gas storage tank. The hydrogen purification device purifies the hydrogen from the rectification tower of the cold box. The carbon dioxide liquefaction device compresses, dries, removes hydrocarbons, liquefies, rectifies, stores, and transports the vent gas from the decarbonization device to produce high-purity liquid carbon dioxide.

[0011] Further, the cold box is composed of a first-stage plate heat exchanger, a second-stage plate heat exchanger, a cryogenic pump, a third-stage plate heat exchanger, a high-pressure rectification tower, a low-pressure rectification tower, and a liquefied natural gas subcooler connected in sequence through pipelines. The mercury removal device is connected to the first-stage plate heat exchanger through a pipeline. The input end of the refrigerant compressor unit is connected to the second-stage plate heat exchanger through a pipeline, and the output end is connected to the first-stage plate heat exchanger through a pipeline. The input end of the nitrogen compressor unit is connected to the high-pressure rectification tower and the low-pressure rectification tower through pipelines. The output end of the refrigerant compressor unit is connected to the first-stage plate heat exchanger through a pipeline. The input end of the hydrogen purification device is connected to the high-pressure rectification tower and the low-pressure rectification tower through pipelines. The input end of the liquefied natural gas storage tank is connected to the liquefied natural gas subcooler through a pipeline. The cold box uses a third-stage plate heat exchanger and a rectification tower to realize the liquefaction of natural gas, the reheating and gasification of the pyrolysis feed gas, and the liquefaction separation of the pyrolysis tail gas, generating liquefied natural gas, high-purity gaseous methane, and hydrogen.

[0012] Further, the nitrogen compressor unit uses a screw compressor or a piston compressor to compress nitrogen, mainly compressing the nitrogen for refrigeration coming out of the cold box, cooling it through a circulating nitrogen compressor, and then entering the cold box for refrigeration.

[0013] Further, the methane cracking furnace is a catalytic pyrolysis furnace, and the catalytic pyrolysis furnace is used to catalytically crack the high-purity gaseous methane from the cold box, generating carbon nanotubes and a pyrolysis tail gas containing hydrogen and methane.

[0014] Further, the helium purification device uses pressure swing adsorption to purify the flashed natural gas from the cold box and the liquefied natural gas storage tank, generating high-purity helium.

[0015] Further, the hydrogen purification device uses pressure swing adsorption to purify the hydrogen from the rectification tower of the cold box, generating high-purity hydrogen.

[0016] The beneficial effects of the present utility model are as follows:

[0017] By providing a three-phase separator, a compressor unit, a decarbonization device, a dehydration device, a mercury removal device, a refrigerant compressor unit, a nitrogen compressor unit, a cold box, a methane cracking furnace, a recuperator, a helium purification device, a hydrogen purification device, a liquefied natural gas storage tank, and a carbon dioxide liquefaction device, such as the three-phase separator, the compressor unit, the decarbonization device, the dehydration device, the mercury removal device, and the cold box, according to the components of natural gas, through processes of three-phase separation, precision filtration, pressurization, decarbonization, dehydration, mercury removal, liquefaction, reheating and vaporization, catalytic pyrolysis, helium purification, hydrogen purification, and carbon dioxide liquefaction, the present utility model realizes the efficient utilization of natural gas to produce carbon nanotubes and the pyrolysis tail gas, and can effectively improve the utilization value of natural gas. Description of the Drawings

[0018] The technical solutions of the present application will be further described below with reference to the drawings and embodiments.

[0019] Figure 1 is the overall structural schematic diagram of the embodiment of the present application;

[0020] Figure 2 is the structural schematic diagram of the cold box of the embodiment of the present application;

[0021] The reference numerals in the drawings are as follows:

[0022] 01, three-phase separator; 02, compressor unit; 03, decarbonization device; 04, dehydration device; 05, mercury removal device; 06, refrigerant compressor unit; 07, nitrogen compressor unit; 08, cold box; 09, methane cracking furnace; 10, recuperator; 11, liquefied natural gas storage tank; 12, helium purification device; 13, hydrogen purification device; 14, carbon dioxide liquefaction device; 0801, first-stage plate heat exchanger; 0802, second-stage plate heat exchanger; 0803, cryogenic pump; 0804, third-stage plate heat exchanger; 0805, high-pressure rectification tower; 0806, low-pressure rectification tower; 0807, liquefied natural gas subcooler; A, natural gas feed line; B, mixed refrigerant line; C, nitrogen line; D, liquid methane line; E, high-purity methane gas line; F, carbon nanotube line; G, pyrolysis tail gas; H, high-purity helium gas line; I, high-purity hydrogen gas line; J, high-purity liquid carbon dioxide line. Detailed Embodiments

[0023] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0024] In the description of the present application, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as limiting the protection scope of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present utility model, unless otherwise stated, the meaning of "a plurality" is two or more.

[0025] In the description of the present application, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", "connected to" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood through specific circumstances.

[0026] The technical solution of the present application will be described in detail below with reference to the drawings and in conjunction with the embodiments. Embodiment

[0027] This embodiment provides a natural gas cracking and tail gas utilization system, including a three-phase separator 01, a compressor unit 02, a decarbonization device 03, a dehydration device 04, a mercury removal device 05, a refrigerant compressor unit 06, a nitrogen compressor unit 07, a cold box 08, a methane cracking furnace 09, a recuperator 10, a liquefied natural gas storage tank 11, a helium purification device 12, a hydrogen purification device 13, and a carbon dioxide liquefaction device 14, which are connected by pipelines.

[0028] First, the raw materials in the natural gas raw material pipeline A enter the three-phase separator 01. The three-phase separator 01 uses a three-phase separator and a precision filter to separate and purify the liquid and solid in the natural gas.

[0029] Then it enters the compressor unit 02. The compressor unit 02 uses a screw compressor to boost the pressure of the natural gas to 4.0 MPaG.

[0030] Then it enters the decarbonization device 03. The decarbonization device 03 uses the amine solution absorption method to remove carbon dioxide from the natural gas, and then regenerates the amine solution by high temperature.

[0031] Then it enters the dehydration device 04 and the mercury removal device 05. The dehydration device 04 uses the temperature swing adsorption method to adsorb the moisture in the natural gas through the adsorbent, and then regenerates the adsorbent through high temperature. The mercury removal device 05 uses activated carbon adsorbent to remove mercury in the natural gas, and finally enters the cold box 08.

[0032] Refrigerant compressor unit 06 uses a screw compressor to compress the mixed refrigerant to 3.2MPaG and deliver the cold to the cold box. The refrigerant in the mixed refrigerant refrigeration cycle is mainly a mixture of nitrogen, methane, ethylene, propane, isopentane and other substances in a certain proportion. The mixed refrigerant with a good ratio is compressed by the compressor, and after cooling, it enters the separator at the compressor outlet to separate the liquid condensed due to pressurization and temperature reduction.

[0033] Nitrogen compressor unit 07 uses a screw compressor to compress nitrogen to 2.0MPaG and deliver the cold to the cold box. It mainly compresses and cools the nitrogen coming out of the cold box before entering the cold box for refrigeration. Nitrogen is pre-cooled to a certain temperature in the plate heat exchanger, then throttled and depressurized, and returns to the main heat exchanger for reheating after providing cold to the distillation tower. The reheated nitrogen enters the nitrogen compressor unit and is compressed to 2.0MPaG, and the cycle repeats.

[0034] Cold box 08 is composed of a first-stage plate heat exchanger 0801, a second-stage plate heat exchanger 0802, a cryogenic pump 0803, a third-stage plate heat exchanger 0804, a high-pressure distillation tower 0805, a low-pressure distillation tower 0806 and a liquefied natural gas subcooler 0807, which realizes the liquefaction of natural gas, the reheating and gasification of pyrolysis raw gas and the liquefaction and separation of pyrolysis tail gas to generate liquefied natural gas, high-purity gaseous methane and hydrogen.

[0035] The methane cracking furnace 09 uses a catalytic pyrolysis furnace to catalytically crack the high-purity gaseous methane from the cold box 08 to generate carbon nanotubes and pyrolysis tail gas containing hydrogen and methane.

[0036] The liquefied natural gas storage tank 11 uses a storage tank to store liquefied natural gas.

[0037] The helium purification device 12 uses pressure swing adsorption to purify the flash natural gas in the cold box 08 and the liquefied natural gas storage tank 11 to generate high-purity helium.

[0038] The hydrogen purification device 13 uses pressure swing adsorption to purify the hydrogen in the distillation tower of the cold box 08 to generate high-purity hydrogen.

[0039] The carbon dioxide liquefaction device 14 compresses, dries, decarbonizes, liquefies, distills, and stores and transports the purge gas from the decarbonization device 03 to generate high-purity liquid carbon dioxide.

[0040] In an implementable solution of the present utility model, the raw natural gas containing methane, light hydrocarbons, carbon dioxide, helium, nitrogen, water, mercury, etc. enters a three-phase separator 01 to remove liquid water, liquid oil droplets and solid particle impurities in the natural gas. The pre-purified natural gas enters a compressor unit 02 and is compressed to 4.0 MPaG. The pressurized natural gas enters a decarbonization device 03. The decarbonization device absorbs carbon dioxide in the natural gas through amine solution, and then desorbs and discharges the carbon dioxide by heating and regenerating the amine solution, and sends it to a carbon dioxide liquefaction device 14. The natural gas after decarbonization enters a drying tower of a dehydration device 04 to remove the water in the natural gas. The natural gas after dehydration enters a mercury removal device 05, and the mercury in the natural gas is adsorbed by a mercury removal agent.

[0041] The mixed refrigerant is composed of methane, ethylene, propane, isopentane, nitrogen, etc. Due to the different boiling points of each component, it condenses and subcools in each heat exchanger, is decompressed through a J-T valve and enters the return refrigerant, and sequentially cools the methane-rich gas and the forward refrigerant in different temperature zones. After being reheated, the return refrigerant exits the cold box 08 and enters a mixed refrigerant compressor unit 06 and is cyclically compressed to 3.2 MPaG.

[0042] The circulating nitrogen is compressed by a nitrogen compressor unit 07 and then enters a first-stage plate heat exchanger 0801 and a second-stage plate heat exchanger 0802 of the cold box 08, is cooled into a liquid, and then throttles into a high-pressure rectification tower 0805 and a low-pressure rectification tower 0806 respectively. After absorbing heat and vaporizing, it enters the nitrogen compressor unit 07 and is cyclically compressed to 2.0 MPaG.

[0043] The methane-rich gas containing methane, light hydrocarbons, nitrogen and helium enters a first-stage plate heat exchanger 0801 and a second-stage plate heat exchanger 0802 of the cold box 08, and exchanges heat with the mixed refrigerant from a refrigerant compressor unit 06. Methane and light hydrocarbons in the natural gas are cooled to below -162 °C and become liquid-phase output. The unliquefied nitrogen, helium and flashed methane mixed gas is transported to a helium purification device 12, and high-pressure helium with a purity of more than 99.999% is generated through processes such as compression, purification, cryogenic separation, adsorption, de-hydrogenation, purification, compression and storage.

[0044] The liquefied natural gas output from the second-stage plate heat exchanger 0802 is transported to a third-stage plate heat exchanger 0804 through a cryogenic pump 0803, exchanges heat with the methane and hydrogen mixed gas generated by a methane cracking furnace 09 to generate methane gas, and enters the catalytic pyrolysis furnace of the methane cracking furnace 09. After methane fully contacts a nickel-based catalyst, about 30% of the methane gas undergoes a cracking reaction to generate carbon atoms and hydrogen molecules, and the carbon atoms accumulate to form carbon nanotubes.

[0045] After being precooled by the three-stage plate heat exchanger 0804, the mixed gas of methane and hydrogen after pyrolysis passes through the second-stage plate heat exchanger 0802 and the first-stage plate heat exchanger 0801, exchanges heat with the mixed refrigerant from the refrigerant compressor unit 06, and the generated gas-liquid mixture enters the high-pressure rectification column 0805 partly, and the other part enters the reboiler at the bottom of the low-pressure rectification column 0806 for heat exchange and then enters the high-pressure rectification column 0805 for rectification. The hydrogen-rich gas at the top of the column goes to the hydrogen purification device 13. The methane-rich liquid is obtained at the bottom of the high-pressure rectification column 0805, throttled and then enters the middle of the low-pressure rectification column 0806 for rectification. The liquefied natural gas is obtained at the bottom of the low-pressure rectification column 0806, subcooled by the liquefied natural gas subcooler 0807 and then sent to the storage tank of the liquefied natural gas storage tank 11 for storage.

[0046] The hydrogen-rich tail gas from the cold box 08 enters the hydrogen purification device 13, and adopts a one-stage 8-1-4 flushing process flow, that is, 1 of the 8 adsorption towers in the device is always in the state of feeding and adsorption. Its adsorption and regeneration process consists of adsorption, continuous 4 times of equal pressure reduction, reverse release, flushing, continuous 4 times of equal pressure boost and final hydrogen boost, and becomes high-pressure hydrogen with a purity of more than 99.99%.

[0047] The regenerated purge gas from the decarbonization device 03 enters the carbon dioxide liquefaction device 14, is compressed to 2.5 MPa, and then adopts a temperature swing adsorption process to remove moisture, hydrocarbons and alcohols in the gas. The purified carbon dioxide gas becomes liquid carbon dioxide with a purity of more than 99.99% through condensation and rectification.

[0048] Inspired by the ideal embodiments according to the present application above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this application. The technical scope of this application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A natural gas cracking and tail gas utilization system, characterized in that: The invention comprises a three-phase separator, a compressor unit, a decarbonization device, a dehydration device, a demercuration device, a refrigerant compressor unit, a nitrogen compressor unit, a cold box, a methane cracking furnace, a regenerator, a helium purification device, a hydrogen purification device, a liquefied natural gas storage tank and a carbon dioxide liquefaction device. The three-phase separator, the compressor unit, the decarbonization device, the dehydration device, the demercuration device, the cold box and the liquefied natural gas storage tank are connected in sequence through pipelines; the refrigerant compressor unit compresses the mixed refrigerant and transmits the cold energy to the cold box through management; the nitrogen compressor unit compresses the nitrogen and transmits the cold energy to the cold box through pipelines; the methane cracking furnace catalytically cracks the high-purity gaseous methane from the cold box; the helium purification device purifies the flash natural gas from the cold box and the liquefied natural gas storage tank; the hydrogen purification device purifies the hydrogen from the distillation tower of the cold box; the carbon dioxide liquefaction device compresses, dries, dehydrocarbonizes, liquefies, distills and stores and transports the vented air from the decarbonization device to generate high-purity liquid carbon dioxide.

2. A natural gas cracking and tail gas utilization system according to claim 1, characterized in that: The cold box includes a first-stage plate heat exchanger, a second-stage plate heat exchanger, a cryogenic pump, a third-stage plate heat exchanger, a high-pressure distillation tower, a low-pressure distillation tower and a liquefied natural gas supercooler connected in sequence through pipelines. The mercury removal device is connected to the first-stage plate heat exchanger through a pipeline. The input end of the refrigerant compressor unit is connected to the second-stage plate heat exchanger through a pipeline, and the output end is connected to the first-stage plate heat exchanger through a pipeline. The input end of the nitrogen compressor unit is connected to the high-pressure distillation tower and the low-pressure distillation tower through a pipeline, and the output end of the refrigerant compressor unit is connected to the first-stage plate heat exchanger through a pipeline. The input end of the hydrogen purification device is connected to the high-pressure distillation tower and the low-pressure distillation tower through a pipeline, and the input end of the liquefied natural gas storage tank is connected to the liquefied natural gas supercooler through a pipeline.

3. A natural gas cracking and tail gas utilization system according to claim 2, characterized in that: The nitrogen compressor unit uses a screw compressor or a piston compressor to compress the nitrogen.

4. A natural gas cracking and tail gas utilization system according to claim 1, characterized in that: The methane cracking furnace is a catalytic pyrolysis furnace.

5. A natural gas cracking and tail gas utilization system according to claim 1, characterized in that: The helium purification device uses pressure swing adsorption to purify flash natural gas in cold boxes and liquefied natural gas storage tanks.

6. A natural gas cracking and tail gas utilization system according to claim 1, characterized in that: The hydrogen purification device uses pressure swing adsorption to purify hydrogen in a cold box distillation tower.

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