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CN-121513737-B - Carbon dioxide hydrogenation methane synthesizing system adapting to fluctuation of hydrogen source

CN121513737BCN 121513737 BCN121513737 BCN 121513737BCN-121513737-B

Abstract

The invention discloses a carbon dioxide hydrogenation methane synthesizing system adapting to fluctuation of a hydrogen source, and solves the technical problems that the existing methanation reaction system relies on a hydrogen storage buffer device to stabilize fluctuation of the hydrogen source, so that equipment investment is large, occupied area is large and potential safety hazards exist. The device comprises a raw material supply unit, a preheating unit, a reaction unit, a waste heat recovery unit, a cooling separation unit, a circulation unit and a control unit, wherein a flow detection device is arranged on a hydrogen feed pipe line of the raw material supply unit, a raw material preheater of the preheating unit performs primary preheating on mixed raw material gas, an electric heater performs secondary heat supplement, the reaction unit comprises a primary adiabatic reactor and a secondary adiabatic reactor, the waste heat recovery unit comprises a primary steam generator and a secondary steam generator, a main outlet pipeline connected with a gas phase outlet of a water separator of the cooling separation unit is divided into an outer conveying pipeline and a circulation pipeline, and the control unit uses fresh hydrogen flow as a feedforward variable to perform cooperative regulation.

Inventors

  • LIU YIHUA
  • YANG ZHIGANG
  • WANG PEI
  • MA YIYUN
  • HE ZHI

Assignees

  • 四川思源创达环保科技有限公司

Dates

Publication Date
20260508
Application Date
20260108

Claims (8)

  1. 1. A carbon dioxide hydrogenation methane synthesizing system adapting to fluctuation of a hydrogen source is characterized by comprising the following components: The raw material supply unit comprises a carbon dioxide feed line and a hydrogen feed line, wherein the hydrogen feed line is provided with a flow detection device, the carbon dioxide feed line and the hydrogen feed line are combined to form a total feed line, and the total feed line is used for conveying mixed raw material gas consisting of carbon dioxide, hydrogen and circulating gas; The preheating unit comprises a raw material preheater and an electric heater, wherein the raw material preheater is provided with a cold side channel and a hot side channel, an inlet of the cold side channel is connected with the main feeding pipeline and used for introducing the mixed raw material gas, an outlet of the cold side channel is connected with an inlet of the electric heater and used for outputting the mixed raw material gas after primary preheating, an inlet of the hot side channel is used for introducing a system reaction product to primary preheat the mixed raw material gas in the cold side channel, an outlet of the hot side channel is used for outputting the system reaction product after heat exchange and cooling, the electric heater is used for carrying out secondary heat supplement on the mixed raw material gas after primary preheating, and an outlet of the electric heater is used for outputting the mixed raw material gas after secondary heat supplement; The reaction unit comprises a first-stage adiabatic reactor and a second-stage adiabatic reactor, wherein an inlet of the first-stage adiabatic reactor is connected with an outlet of the electric heater and is used for receiving mixed raw material gas subjected to second-stage heat supplement, an outlet of the first-stage adiabatic reactor is used for outputting first-stage reaction product gas, an inlet of the second-stage adiabatic reactor is used for receiving first-stage reaction product gas cooled by the first-stage steam generator, and an outlet of the second-stage adiabatic reactor is used for outputting second-stage reaction product gas; The waste heat recovery unit comprises a primary steam generator and a secondary steam generator, wherein a material inlet of the primary steam generator is connected with an outlet of the primary adiabatic reactor and is used for receiving the primary reaction product gas, a material outlet of the primary steam generator is connected with an inlet of the secondary adiabatic reactor and is used for outputting the cooled primary reaction product gas, a material inlet of the secondary steam generator is connected with an outlet of the secondary adiabatic reactor and is used for receiving the secondary reaction product gas, and a material outlet of the secondary steam generator is connected with a hot side channel inlet of the raw material preheater and is used for outputting the cooled secondary reaction product gas as a system reaction product; The cooling separation unit comprises a water cooler and a water separator, wherein an inlet of the water cooler is connected with a hot side channel outlet of the raw material preheater and is used for receiving reaction products subjected to heat exchange and temperature reduction, an outlet of the water cooler is connected with an inlet of the water separator and is used for outputting reaction products subjected to deep cooling, the water separator is used for carrying out gas-liquid separation on the reaction products subjected to deep cooling, a liquid phase outlet of the water separator is used for discharging condensed water, a gas phase outlet of the water separator is connected with a main outlet pipeline for outputting methane-rich gas, the main outlet pipeline is divided into an outer conveying pipeline and a circulating pipeline, the outer conveying pipeline is used for conveying methane-rich synthetic gas to the outside, and a pressure regulating device is arranged on the outer conveying pipeline which is used for refluxing part of the methane-rich gas as circulating gas; The circulating unit comprises a circulating compressor, an inlet of the circulating compressor is connected with the circulating pipeline and used for receiving the circulating gas, and an outlet of the circulating compressor is combined with the main feeding pipeline and used for mixing the pressurized circulating gas with fresh carbon dioxide and hydrogen; The control unit is in signal connection with the flow detection device, the circulating compressor and the pressure regulating device; The control unit is configured to cooperatively adjust the operating frequency of the circulating compressor and the opening of the pressure adjusting device by taking the fresh hydrogen flow detected by the flow detecting device as a feedforward variable, so that the gas mass flow in the primary adiabatic reactor and the gas mass flow in the secondary adiabatic reactor are maintained within a preset range; when the fresh hydrogen flow rate is reduced, the control unit reduces the opening degree of the pressure regulating device to increase the flow resistance of the outgoing line, so that more methane-rich gas flows back through the circulating line, and simultaneously increases the operating frequency of the circulating compressor to increase the circulating gas flow rate, thereby compensating for the reduction of the fresh feed rate; When the fresh hydrogen flow rate is increased, the control unit increases the opening degree of the pressure regulating device and reduces the operating frequency of the recycle compressor so as to reduce the recycle gas flow rate and increase the delivery ratio; the primary steam generator comprises a shell, a heat exchange tube bundle arranged in the shell and a steam drum communicated with the shell; The heat exchange tube bundle is provided with a tube side inlet and a tube side outlet, the tube side inlet is connected with the outlet of the primary adiabatic reactor and used for receiving the primary reaction product gas, and the tube side outlet is connected with the inlet of the secondary adiabatic reactor and used for outputting the cooled primary reaction product gas; The shell side of the shell is provided with a medium inlet for introducing boiler feed water or low-pressure steam as a heat exchange medium, the heat exchange medium is in a boiling state with coexisting vapor-liquid two phases after absorbing heat of primary reaction product gas in the tube side and generates steam, and the steam enters the steam drum to carry out steam-water separation; the steam pressure in the steam drum determines the saturation temperature of a heat exchange medium in the shell side, and further determines the heat transfer temperature difference between primary reaction product gas in the tube side and the heat exchange medium in the shell side; The control unit is in signal connection with the first steam regulating valve and is configured to regulate the opening degree of the first steam regulating valve according to an inlet temperature detection signal of the secondary adiabatic reactor so as to maintain the inlet temperature of the secondary adiabatic reactor within a range of 250 ℃ to 280 ℃; When the temperature of the primary reaction product gas is reduced due to the decrease of the fresh hydrogen flow, the control unit increases the opening of the first steam regulating valve to increase the steam external discharge capacity, reduces the steam pressure in the steam drum, thereby reducing the saturation temperature of the heat exchange medium, reducing the heat transfer temperature difference and reducing the heat exchange quantity, and maintaining the inlet temperature of the secondary adiabatic reactor within the range of 250-280 ℃; when the temperature of the primary reaction product gas is increased due to the increase of the fresh hydrogen flow, the control unit reduces the opening of the first steam regulating valve to reduce the steam external discharge capacity, and improves the steam pressure in the steam drum, so that the saturation temperature of the heat exchange medium is improved, the heat transfer temperature difference is maintained, the heat exchange amount is increased, and the inlet temperature of the secondary adiabatic reactor is maintained within the range of 250-280 ℃; the structure of the secondary steam generator is the same as that of the primary steam generator, and the secondary steam generator comprises a shell, a heat exchange tube bundle arranged in the shell and a steam drum communicated with the shell, wherein a tube side inlet of the heat exchange tube bundle of the secondary steam generator is connected with an outlet of the secondary adiabatic reactor and is used for receiving the secondary reaction product gas, and a tube side outlet of the heat exchange tube bundle of the secondary steam generator is connected with a hot side channel inlet of the raw material preheater; the top of the steam drum of the secondary steam generator is provided with a second steam outlet pipeline, the second steam outlet pipeline is provided with a second steam regulating valve, and the steam external discharge capacity of the secondary steam generator is controlled by regulating the opening of the second steam regulating valve, so that the steam pressure in the steam drum of the secondary steam generator and the saturation temperature of a heat exchange medium in the shell pass of the steam drum of the secondary steam generator are regulated; the steam outlet pipeline of the primary steam generator and the second steam outlet pipeline are converged to form a medium-pressure steam header pipe, and the medium-pressure steam header pipe is communicated with a medium-pressure steam pipeline arranged between the cold side channel outlet of the raw material preheater and the inlet of the electric heater, so that medium-pressure steam generated by the primary steam generator and the secondary steam generator is conveyed into the mixed raw material gas after primary preheating for heat compensation; A first pressure detection device and a first flow detection device are sequentially arranged on a steam outlet pipeline of the primary steam generator along the steam flow direction, and a second pressure detection device and a second flow detection device are sequentially arranged on a second steam outlet pipeline along the steam flow direction; pressure safety valves are respectively arranged on the steam drum of the primary steam generator and the steam drum of the secondary steam generator; The control unit is in signal connection with the second steam regulating valve, the first pressure detection device, the first flow detection device, the second pressure detection device and the second flow detection device, and is configured to regulate the opening degree of the second steam regulating valve according to a hot side channel inlet temperature detection signal of the raw material preheater; When the flow rate of the fresh hydrogen is increased and the operating frequency of the circulating compressor is reduced to reduce the flow rate of the circulating gas, the temperatures of the first-stage reaction product gas and the second-stage reaction product gas are increased, the opening degree of the first steam regulating valve and the second steam regulating valve is reduced by the control unit to improve the steam pressure in each steam drum, at the moment, the steam yield of the first-stage steam generator and the second-stage steam generator is correspondingly reduced, and the amount of complementary heat steam conveyed into the mixed raw gas after primary preheating through the medium-pressure steam main pipe and the medium-pressure steam pipeline is correspondingly reduced; When the fresh hydrogen flow is reduced and the operating frequency of the circulating compressor is increased to increase the circulating gas flow, the temperatures of the first-stage reaction product gas and the second-stage reaction product gas are reduced, the control unit increases the opening degree of the first steam regulating valve and the second steam regulating valve to reduce the steam pressure in each steam pocket, at the moment, the steam yield of the first-stage steam generator and the second-stage steam generator is correspondingly increased, the heat supplementing steam quantity conveyed to the mixed raw gas after primary preheating through the medium-pressure steam header pipe and the medium-pressure steam pipeline is correspondingly increased, meanwhile, the reaction heat release quantity is reduced due to the reduction of the fresh hydrogen flow, the heat carried by the reaction product in a hot side channel of the raw material preheater is correspondingly reduced, and the increased heat supplementing steam quantity compensates the deficiency of the first-stage preheating quantity.
  2. 2. The carbon dioxide hydro-synthesis methane system that accommodates fluctuations in hydrogen source as defined in claim 1 wherein a ratio of the flow of recycle gas to the flow of fresh hydrogen is maintained in a range of 3:1 to 8:1.
  3. 3. The system for synthesizing methane by hydrogenating carbon dioxide, which adapts to fluctuation of a hydrogen source, according to claim 1, wherein the electric heater is controlled by adopting a silicon controlled rectifier to regulate power, and the power regulation range is 10-100% of rated power; The control unit is in signal connection with the electric heater and is configured to adjust the power output of the electric heater according to an inlet temperature detection signal of the primary adiabatic reactor, so that the inlet temperature of the primary adiabatic reactor is maintained within a light-off temperature range.
  4. 4. The system for synthesizing methane by hydrogenating carbon dioxide, which adapts to fluctuation of a hydrogen source, according to claim 1, wherein the cooling separation unit is further provided with a nitrogen interface, and the nitrogen interface is communicated with the circulating pipeline; The control unit is configured to switch the circulation pipeline to a nitrogen circulation mode after receiving a shutdown instruction, introduce nitrogen through the nitrogen interface, and reduce the bed temperatures of the primary adiabatic reactor and the secondary adiabatic reactor to below 100 ℃ at a set cooling rate by utilizing the water cooler.
  5. 5. The system for synthesizing methane by hydrogenating carbon dioxide, which adapts to fluctuation of a hydrogen source, as set forth in claim 4, wherein the set cooling rate is 5 ℃ per minute to 15 ℃ per minute; the control unit is configured to adjust the cooling water flow rate of the water cooler according to the bed temperature detection signals of the primary adiabatic reactor and the secondary adiabatic reactor in a nitrogen circulation mode, so that the bed cooling rate is maintained within the set cooling rate range.
  6. 6. The system for synthesizing methane by hydrogenating carbon dioxide, which adapts to fluctuation of a hydrogen source, as set forth in claim 1, wherein the primary steam generator and the secondary steam generator are controlled by three impulse levels, wherein the three impulses comprise a drum liquid level signal, a steam outlet flow signal and a water supply flow signal; the control unit takes the drum liquid level signal as a main control signal and the steam outlet flow signal as a feedforward signal, and when the steam outlet flow suddenly increases, the control unit increases the water supply supplement quantity in advance according to the feedforward signal so as to counteract false liquid level drop generated by vaporization aggravation.
  7. 7. The system for synthesizing methane by hydrogenating carbon dioxide, which adapts to fluctuation of a hydrogen source, according to claim 1, wherein the circulating compressor is driven by variable frequency, and the ratio of the circulating air flow to the fresh hydrogen flow corresponding to the rotating speed adjusting range is adjusted to be 2:1-8:1; When the fresh hydrogen flow rate is reduced to below 50% of the rated flow rate, the control unit increases the operating frequency of the circulating compressor to enable the ratio of the circulating air flow rate to the fresh hydrogen flow rate to be above 5:1, and when the fresh hydrogen flow rate is reduced to below 30% of the rated flow rate, the control unit increases the operating frequency of the circulating compressor to enable the ratio of the circulating air flow rate to the fresh hydrogen flow rate to be above 7:1.
  8. 8. The system for synthesizing methane by hydrogenating carbon dioxide, which is suitable for fluctuation of a hydrogen source, as set forth in claim 1, wherein the hydrogen source connected with the hydrogen feeding pipeline is a renewable energy source, namely a water electrolysis hydrogen production device, and the renewable energy source comprises wind energy, solar energy or wind-solar complementary energy; The fluctuation of the hydrogen source is represented by that the flow rate of the fresh hydrogen reaches 80-100% of the rated flow rate in the peak period of renewable energy power generation and the flow rate of the fresh hydrogen is reduced to 20-50% of the rated flow rate in the valley period of renewable energy power generation.

Description

Carbon dioxide hydrogenation methane synthesizing system adapting to fluctuation of hydrogen source Technical Field The invention relates to the technical field of carbon capture utilization and renewable energy consumption, in particular to a carbon dioxide hydrogenation methane synthesis system adapting to fluctuation of a hydrogen source. Background The technology for synthesizing methane by hydrogenating carbon dioxide can not only consume carbon dioxide but also produce clean fuel by reacting the carbon dioxide trapped in industry with hydrogen under the action of a catalyst to generate methane. When hydrogen is sourced from renewable energy sources for water electrolysis to prepare hydrogen, the technology can also convert intermittent renewable energy sources such as wind energy, solar energy and the like into chemical energy convenient for storage and transportation, and realize energy conversion of electric-gas coupling. Existing methanation reaction systems generally include a raw material supply unit, a preheating unit, a reaction unit, a waste heat recovery unit, and a cooling separation unit. The method comprises the steps of mixing carbon dioxide and hydrogen to form mixed raw material gas by a raw material supply unit, preheating the mixed raw material gas by a raw material preheater by utilizing waste heat of reaction products of a system, supplementing heat by an electric heater, enabling the carbon dioxide and the hydrogen to react under the action of a catalyst to generate methane and water by a reaction unit, recovering the heat of the reaction products by a steam generator to generate steam by a waste heat recovery unit, cooling the reaction products by a cooling separation unit, separating condensed water, and sending the methane-enriched gas. The raw material supply unit is provided with a large number of hydrogen storage tanks serving as hydrogen storage buffer devices, and hydrogen is stored in the high-pressure hydrogen storage tanks and then is output at a stable flow rate. The hydrogen storage tank needs to bear higher storage pressure, and has large equipment investment, large occupied area and potential safety hazard. In addition, the hydrogen storage link increases the complexity and operation and maintenance cost of the system, and reduces the overall economy. Disclosure of Invention The inventor notices that renewable energy power generation has obvious fluctuation and intermittent characteristics, wind power generation is influenced by wind speed to show daily and seasonal fluctuation, photovoltaic power generation is changed along with sunlight intensity change, the yield of hydrogen production by electrolysis of water also fluctuates, and if the carbon dioxide hydrogenation methane synthesizing system per se has the capability of adapting to fluctuation of a hydrogen source, a hydrogen storage buffer device can be omitted or simplified, and investment and operation cost are reduced. Therefore, the invention aims to provide a carbon dioxide hydrogenation methane synthesizing system adapting to fluctuation of a hydrogen source, and solve the technical problems that the existing methanation reaction system relies on a hydrogen storage buffer device to stabilize fluctuation of the hydrogen source, so that equipment investment is large, occupied area is large and potential safety hazards exist. The invention provides a carbon dioxide hydrogenation methane synthesizing system adapting to fluctuation of a hydrogen source, which comprises a raw material supply unit, a methane synthesizing unit and a methane synthesizing unit, wherein the raw material supply unit comprises a carbon dioxide feed pipeline and a hydrogen feed pipeline, a flow detection device is arranged on the hydrogen feed pipeline, the carbon dioxide feed pipeline and the hydrogen feed pipeline are combined to form a total feed pipeline, and the total feed pipeline is used for conveying carbon dioxide, A mixed raw material gas composed of hydrogen and circulating gas; the preheating unit comprises a raw material preheater and an electric heater, wherein the raw material preheater is provided with a cold side channel and a hot side channel, an inlet of the cold side channel is connected with the main feeding pipeline and used for introducing the mixed raw material gas, an outlet of the cold side channel is connected with an inlet of the electric heater and used for outputting the mixed raw material gas after primary preheating, an inlet of the hot side channel is used for introducing a system reaction product so as to carry out primary preheating on the mixed raw material gas in the cold side channel, an outlet of the hot side channel is used for outputting a system reaction product after heat exchange and cooling, an outlet of the electric heater is used for carrying out secondary heat compensation on the mixed raw material gas after primary preheating, an outlet of the electric heater is used for outputting the