A coal gasification and fuel cell coupled combined heat and power system and method for papermaking

Abstract

The application provides a coal gasification and fuel cell coupled combined heat and power system and method for papermaking, which is composed of a pulping unit, a bleaching unit, a drying unit, an acidification unit, a carbonization unit, an alkalization unit, an activation unit, a primary gasification unit, a secondary gasification unit, a water-gas shift unit and a fuel cell. Black liquor generated by the pulping and bleaching unit is converted into crude carbon through the acidification and carbonization units, part of the crude carbon is converted into activated carbon through the alkalization and activation units and is used as an adsorbent of the carbonization unit, and part of the crude carbon and coal are converted into CO through two-stage gasification and are converted into hydrogen through a water-gas shift, and the hydrogen is used as raw material of the fuel cell to generate electric energy. The system further comprises multiple heat exchange units and heat transfer units, high-grade energy of H2, CO and H2O is maximally utilized, and through fine energy management and gradient utilization strategies, efficient heat and electric energy production is realized, and stable and efficient energy supply is provided for the whole system.

Description

Technical Field

[0001] This invention belongs to the field of pulp and paper technology, specifically relating to a combined heat and power system and method for papermaking that couples coal gasification with fuel cells. Background Technology

[0002] The paper industry is an energy-intensive sector, requiring significant amounts of heat and electricity to power various equipment and processes. China's paper production capacity has continuously expanded, now ranking first in the world. Furthermore, the demand for paper products continues to grow in both production and daily life. To fully meet market demand, pulp and paper companies are continuously expanding their production scale and increasing capacity.

[0003] As production scale expands and capacity increases, the heat and electricity required by paper mills gradually increase. To meet this demand, large enterprises generally adopt self-generation for energy supply. These enterprises often own their own power plants, using coal-fired power generation to ensure production efficiency. Although this method is low-cost, the limited availability of coal resources and low energy utilization efficiency have become bottlenecks restricting its sustainable development. In addition, coal-fired power generation generates large amounts of pollutants such as CO2, SO2, and NOx, which have serious negative impacts on the environment.

[0004] Most enterprise-owned power plants currently employ combined heat and power (CHP) technology. Through energy grading and separate heat and power production, the chemical energy of coal is converted into steam energy, which drives a steam turbine to perform work. The exhaust steam from the turbine is then used in paper production. Most plants utilize coal-fired boilers capable of generating high-temperature, high-pressure steam, as well as boilers that provide heat to the paper production line, ensuring the normal operation of the steam turbine generator sets and meeting the plant's electricity needs. Because the standby boilers operate on a hot standby basis, the overall operating load is low, and the capacity of some equipment cannot be fully utilized, resulting in low operating efficiency. If one boiler fails, the remaining boilers cannot quickly increase their operating load to meet steam demand, thus affecting the stable, reliable, and safe operation of the entire production line.

[0005] The pulp production process generates a large amount of wastewater containing high concentrations of pollutants. This wastewater has a complex composition, and direct discharge into water bodies would cause serious pollution. It also contains many recyclable substances; without treatment, it would be a waste of resources. Currently, the most widely used method for treating this wastewater is the combustion-based alkali recovery process. This process converts the wastewater into solid products, primarily sodium ferrite, through steps such as evaporation, concentration, combustion, and causticization. These solid products, after hydrolysis, produce sodium hydroxide alkali and iron oxide. Sodium hydroxide can be used in industrial alkali production or the cooking stage in papermaking, while iron oxide can be recycled. This process can achieve an alkali recovery rate of over 90% and recovers heat energy during calcination, making it a relatively mature wastewater treatment method. However, this method only recovers alkali; a large amount of lignin remains in the wastewater and is burned for heat. Furthermore, this method requires large-scale equipment such as multi-stage evaporators and combustion furnaces, resulting in significant initial investment, and is therefore only suitable for large-scale paper mills.

[0006] Traditional coal-fired power generation is inefficient, consumes a lot of energy, and causes environmental pollution; combined heat and power (CHP) has insufficient heating capacity, limited heating range, and poor economic efficiency; the waste liquid treatment efficiency of the alkali recovery process is limited, and the investment cost is high. This invention proposes a CHP system with waste liquid treatment capabilities. Summary of the Invention

[0007] In view of this, the present invention proposes a combined heat and power system and method for papermaking that couples coal gasification with fuel cells. The system can prepare activated carbon by hydrothermal carbonization of the waste liquid generated in the papermaking process. The crude carbon generated during carbonization is then converted into CO by staged coal gasification, and then H2 is produced by water-gas shift reaction. This H2 is used to provide power for mechanical pulping and fan heat exchange in a high-temperature fuel cell. Multiple heat exchange units and heat transfer units are interspersed to achieve gradient utilization of energy and efficient heat and power generation.

[0008] The technical solution adopted by this invention to solve the technical problem is: A combined heat and power system for papermaking, coupling coal gasification and a fuel cell, characterized in that it comprises a pulping unit, a bleaching unit, a drying unit, an acidification unit, a carbonization unit, an alkalization unit, an activation unit, a flow control unit, a primary gasification unit, a secondary gasification unit, a combustion unit, a fan heat exchange unit, a heat exchange unit, a heat transfer unit, a water-gas shift unit, a separation unit, and a fuel cell, wherein: The pulping unit is used to prepare pulp by effectively dissociating fibers from wood or other raw materials using mechanical pulping, chemical pulping or biological pulping techniques. The bleaching unit is used to bleach the pulp to give it a corresponding whiteness. Both the pulping unit and the bleaching unit will produce waste liquid containing fibers, organic matter, inorganic salts and pigments. The drying unit is used to remove moisture from the paper web during the pulp-to-paper web production process. The heat source for drying and dehydration is high-temperature air generated by the fan heat exchange unit. The acidification unit is used to acidify lignin in the waste liquid to precipitate it. The acidification process uses CO2 as the acidifying agent, and the reaction temperature is between 150 and 200°C. In a closed environment, the introduced CO2 reacts with the lignin in the waste liquid, causing the lignin to be converted into acidified lignin precipitate. At the same time, the sodium salt in the waste liquid is converted into NaHCO3, enriching and separating the sodium element. Inorganic silicon salts are also converted into SiO2 precipitate, which enters the carbonization unit together with the acidified lignin. Since the temperature of the waste liquid generated by the pulping unit and the bleaching unit is between 80 and 120°C, the acidification and carbonization processes both require heat transfer and mass transfer units to provide heat. The carbonization unit is used to decompose the acidified lignin precipitated by the acidification unit into small molecule organic matter and then into crude carbon in a hydrothermal environment. The crude carbon is fed into the alkalization unit and the secondary gasification unit through the flow control unit I to prepare activated carbon and staged gasification of coal. Since SiO2 in the crude carbon does not affect the secondary gasification process, the crude carbon participating in the staged gasification of coal does not need to go through the alkalization unit, but is directly fed into the secondary gasification unit through the flow control unit I. The alkalization unit uses dilute alkali solution to wash away SiO2 contained in the crude carbon produced by the carbonization unit and produce coke. By purifying the crude carbon, the quality of the activated carbon is improved, so as to achieve better adsorption in the acidification process. The activation unit is used to produce activated carbon. The process uses steam to physically activate coke to prepare activated carbon, which can be used in the acidification unit to adsorb organic matter. The flow control unit includes flow control unit I, flow control unit II, flow control unit III, and flow control unit IV, used to adjust the proportion of different streams according to actual production conditions. Flow control unit I adjusts the proportion of the crude carbon mixture produced by the carbonization unit flowing to the alkalization unit and the secondary gasification unit, with a proportion range of 0-100%. 0% represents all the crude carbon mixture from the carbonization unit flowing to the secondary gasification unit for staged coal gasification, while 100% represents all the crude carbon mixture from the carbonization unit flowing to the alkalization unit for activated carbon preparation. Since the acidification unit only requires a small amount of activated carbon to achieve good adsorption, excess coke can be fed to the secondary gasification unit. Flow control unit II adjusts the proportion of CO2 separated by the separation unit flowing to the acidification unit and the secondary gasification unit, with a proportion range of 0-100%. 0% represents 0% of the CO2 flowing to the acidification unit compared to the CO2 separated by the separation unit, while 100% represents 100% of the CO2 flowing to the acidification unit compared to the CO2 separated by the separation unit. This allows for flexible adjustment based on the amount of wastewater to be treated. Flow control unit III adjusts the proportion of CO2 flowing to the fuel cell. The proportion of H2O produced and sent to the fan heat exchange unit and the heat and mass transfer unit ranges from 0% to 100%. 0% means that the proportion of H2O sent to the fan heat exchange unit is 0% of the proportion of H2O produced by the fuel cell, and 100% means that the proportion of H2O sent to the fan heat exchange unit is 100% of the proportion of H2O produced by the fuel cell. If the original temperature of H2O is low or the amount of waste liquid to be treated is large, H2O is directly fed into the heat and mass transfer unit without passing through the fan heat exchange unit. The flow control unit IV is used to adjust the proportion of CO produced by the secondary gasification unit sent to the fan heat exchange unit and the heat exchange unit, which also ranges from 0% to 100%. 0% means that the proportion of CO sent to the fan heat exchange unit is 0% of the proportion of CO produced by the secondary gasification unit, and 100% means that the proportion of CO sent to the fan heat exchange unit is 100% of the proportion of CO produced by the secondary gasification unit. If the temperature of H2O produced by the fuel cell is high enough or the heat required by the drying unit is relatively small, CO is directly fed into the heat exchange unit without passing through the fan heat exchange unit. The primary and secondary gasification units are used to convert coal into coke and then into CO. The reaction temperature of the secondary gasification units is between 800 and 1200℃. The primary gasification unit decomposes coal at high temperature under air-isolated conditions to produce coke and coke oven gas. The coke oven gas converts chemical energy into thermal energy through the combustion unit. The high-temperature flue gas produced can supply heat to the secondary gasification unit through heat transfer unit I. The secondary gasification unit uses CO2 as a gasifying agent to gasify coke and produce CO. The combustion unit is used to burn coke oven gas to produce high-temperature flue gas, converting the chemical energy of the coke oven gas into thermal energy. The fan heat exchange unit is used to utilize the high-grade energy of H2O and CO. The water temperature produced by the fuel cell is between 500 and 1000°C, and the CO temperature produced by the secondary gasification unit is between 800 and 1200°C. This unit uses a fan to blow hot air through a heat exchange tube coil with a large contact area of ​​high-temperature H2O and CO, and the generated hot air is supplied to the drying unit. The electrical energy consumed is provided by the fuel cell. The heat exchange unit is used to exchange heat between the CO stream generated by the secondary gasification unit and the H2 stream separated from the separation unit, while simultaneously heating O2. Since the temperature of the CO generated by the secondary gasification unit is between 800 and 1200°C, and the temperature of the H2 generated by the water-gas shift unit is between 200 and 300°C, a portion of the CO's energy is utilized through a fan heat exchange before the CO is introduced into the heat exchange unit to bring the H2 and O2 to the 500-1000°C required for the fuel cell. The heat transfer unit includes a heat transfer unit I and a heat and mass transfer unit, used to recover and utilize the high-grade energy of the high-temperature gas stream generated by the device to provide heat for devices that require heat consumption. Heat transfer unit I is a heat transfer partition that uses the heat from the high-temperature flue gas generated by coke oven gas combustion to heat the primary and secondary gasification units. The heat and mass transfer unit is a single unit that separates H2O (after heat exchange by the fan) and CO (after convective heat exchange with H2) into heat transfer streams and mass transfer streams. The heat transfer streams transfer the heat from H2O and CO to the acidification and carbonization units, respectively, where the reaction temperature is between 150 and 200°C. The mass transfer streams then transport H2O and CO to the water-gas shift unit for water-gas shift reaction. The water-gas shift unit is used to perform the water-gas shift reaction. The reaction temperature is between 200 and 300°C. CO and H2O react to provide sufficient CO2 for the acidification unit and the secondary gasification unit, while the generated H2 can be used to power the hydrogen fuel cell. The separation unit is used to separate H2 and CO2 generated by the water-gas shift unit and discharge unreacted CO and H2O. CO2 is divided into two streams by the flow control unit II. One stream is fed into the acidification unit as an acidifying agent to precipitate lignin, and the other stream is fed into the secondary gasification unit to react with coke to generate CO. H2 is fed into the high-temperature fuel cell to generate electricity after reaching the required temperature through the heat exchange unit.

[0009] A method for cogeneration of coal gasification and fuel cells in papermaking, the method comprising: The acidification unit treats the wastewater generated from the pulping and bleaching units. In a closed system, the acidifying agent CO2 reacts with lignin, converting it into acidified lignin that precipitates and enters the carbonization unit, simultaneously enriching and separating sodium. Under hydrothermal conditions, the carbonization unit decomposes the acidified lignin precipitated from the acidification unit into small-molecule organic matter, which is then further decomposed into carbon powder, participating in the staged gasification of coal and the preparation of activated carbon. Flow control unit I adjusts the ratio of the crude carbon mixture generated by the carbonization unit to the alkalization unit and the secondary gasification unit. The acidification unit requires only a small amount of activated carbon to achieve good adsorption, while most of the coke is fed into the secondary gasification unit. The alkalization unit uses dilute alkali. Liquid washing removes SiO2 impurities from the coke produced in the carbonization unit, and the cleaned coke is then fed into the activation unit. The activation unit uses steam to physically activate the coke to prepare activated carbon, which is used to adsorb organic matter in the acidification unit. Under air-isolated conditions, the primary gasification unit decomposes coal at high temperatures to produce coke and coke oven gas. The coke continues to be fed into the secondary gasification unit, where CO2 gasifies the coke and produces CO. The coke oven gas then enters the combustion unit, where the high-temperature flue gas heats the secondary gasification unit through the heat transfer layer of heat transfer unit I. The CO produced in the secondary gasification unit and the H2O produced by the fuel cell contain high-grade energy. The fan heat exchange unit uses a fan to purge the high-temperature flue gas. The heat exchange coils, with a large contact area, are used to exchange H2O and CO. The hot air generated is supplied to the drying unit, while the electrical energy consumed is provided by the fuel cell. The CO produced in the secondary gasification unit may or may not pass through a fan heat exchanger depending on actual production needs. If the temperature of the H2O produced by the fuel cell is high enough or the drying unit requires relatively little heat, it is directly fed into the heat exchanger without passing through the fan heat exchanger. The flow control unit IV adjusts the ratio of CO flowing to the fan heat exchanger and the main heat exchanger. The H2O produced by the fuel cell also needs to be fed through a fan heat exchanger depending on the actual situation. If the original temperature of the H2O is low or the amount of waste liquid to be treated is large, it is directly fed into the heat and mass transfer unit without passing through the fan heat exchanger. The fan heat exchange unit uses flow control unit III to regulate the ratio of H2O flowing to the fan heat exchange unit and the heat and mass transfer unit. In the heat exchange unit, the CO stream after fan heat exchange exchanges heat with the H2 stream separated from the water-gas shift unit, while simultaneously heating O2. The heat and mass transfer unit separates the H2O after fan heat exchange and the CO after convective heat exchange with H2 into heat transfer streams and mass transfer streams. The heat transfer streams transfer their heat to the acidification and carbonization units to provide heat for the acidification and carbonization processes, while the mass transfer streams transfer H2O and CO to the water-gas shift unit for water-gas shift reaction. CO and H2O react to produce H2 and CO2, which are then separated and discharged by the separation unit, along with any unreacted CO and H2O.CO2 is split into two streams by the flow control unit II, serving as the acidifying agent in the acidification unit and the gasifying agent in the secondary gasification unit, respectively. The flow control unit II can flexibly adjust the ratio of CO2 flowing to the acidification unit and the secondary gasification unit according to the amount of waste liquid to be treated. H2, after reaching a suitable temperature through the heat exchange unit, is used for high-temperature fuel cell power generation.

[0010] The beneficial effects of this invention are: (1) Through efficient technologies such as acidification and carbonization units, recyclable substances such as NaHCO3 and lignin are precisely extracted and converted from waste liquid, and the crude carbon generated from the waste liquid conversion is used as raw material to participate in coal graded gasification, which significantly improves the comprehensive utilization efficiency and resource value of the substances.

[0011] (2) By adopting a staged conversion strategy, coal is converted into coke oven gas, carbon monoxide and other products. The coke oven gas generates heat through combustion, thus providing a stable energy supply for the gasification process. Carbon monoxide is converted into hydrogen through water gas conversion, which is used as fuel for fuel cells. This not only improves the overall energy utilization efficiency, but also effectively reduces the environmental burden by reducing the generation of carbon dioxide and other pollutants.

[0012] (3) Multiple heat exchange units and heat transfer units were designed to maximize the use of high-grade energy such as H2, CO, and H2O. Through refined energy management and gradient utilization strategies, efficient heat and electricity generation was achieved, providing a stable and efficient energy supply for the entire system.

[0013] (4) The reaction temperature of high-temperature fuel cells and coal staged gasification is close, and the hydrogen produced by the conversion of carbon monoxide, a product of coal gasification, contains a small amount of carbon monoxide impurities. High-temperature fuel cells are less sensitive to carbon monoxide. Therefore, coupling coal staged gasification with high-temperature hydrogen fuel cells can not only reduce energy loss, but also ignore the negative impact of carbon monoxide impurities in hydrogen on high-temperature fuel cells, thereby realizing the efficient operation mode of cogeneration in the papermaking process and further improving the energy utilization efficiency and environmental performance of the whole process. Attached Figure Description

[0014] Figure 1 A schematic diagram of a combined heat and power system for papermaking, which couples coal gasification with a fuel cell, provided by the present invention; Figure 2 A flowchart of a cogeneration method for papermaking coal gasification coupled with fuel cells provided by the present invention; Among them, 1-pulping unit, 2-bleaching unit, 3-drying unit, 4-acidification unit, 5-carbonization unit, 6-flow control unit I, 7-alkalization unit, 8-activation unit, 9-primary gasification unit, 10-secondary gasification unit, 11-combustion unit, 12-heat transfer unit I, 13-fan heat exchange unit, 14-flow control unit IV, 15-flow control unit III, 16-heat exchange unit, 17-heat and mass transfer unit, 18-water-gas conversion unit, 19-separation unit, 20-flow control unit II, 21-fuel cell. Detailed Implementation

[0015] The objectives and technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and embodiments; like Figure 1 As shown, Figure 1 This is a schematic diagram of a combined heat and power system (CHP) for papermaking, which couples coal gasification with a fuel cell. The system includes: a pulping unit 1, a bleaching unit 2, a drying unit 3, an acidification unit 4, a carbonization unit 5, a flow control unit I 6, an alkalization unit 7, an activation unit 8, a primary gasification unit 9, a secondary gasification unit 10, a combustion unit 11, a heat transfer unit I 12, a fan heat exchange unit 13, a flow control unit IV 14, a flow control unit III 15, a heat exchange unit 16, a heat and mass transfer unit 17, a water-gas shift unit 18, a separation unit 19, a flow control unit II 20, and a fuel cell 21. Pulping unit 1 is used to prepare pulp by effectively dissociating fibers from wood or other raw materials using mechanical pulping, chemical pulping or biological pulping techniques. Bleaching unit 2 is used to bleach the pulp to give it the corresponding whiteness. Both pulping unit 1 and bleaching unit 2 will produce waste liquid containing fibers, organic matter, inorganic salts and pigments. The drying unit 3 is used to remove moisture from the paper web during the pulp-to-paper web process. The heat source for drying and dehydration is the high-temperature air generated by the fan heat exchange unit 13. Acidification unit 4 is used to acidify lignin in waste liquid to precipitate it. In a closed system, the acidifying agent CO2 reacts with the lignin in the waste liquid, causing the lignin to be converted into acidified lignin precipitate. At the same time, the sodium salt in the waste liquid is converted into NaHCO3, enriching and separating the sodium element. Inorganic silicon salt is also converted into SiO2 precipitate, which enters carbonization unit 5 together with acidified lignin. Both acidification unit 4 and carbonization unit 5 are heated by heat transfer and mass transfer unit 17. In a hydrothermal environment, carbonization unit 5 decomposes the acidified lignin produced by acidification unit 4 into small molecule organic matter, which is then decomposed into crude carbon containing SiO2 impurities. The flow control unit I6 is used to pass the crude carbon produced by the carbonization unit 5 into the alkalization unit 7 and the secondary gasification unit 10 respectively. A portion of the crude carbon enters the alkalization unit 7 through the flow control unit I6 and is converted into carbon powder. The carbon powder enters the activation unit 8 as a raw material for preparing activated carbon, and a portion enters the secondary gasification unit 10 as a gasification raw material to react with carbon dioxide to produce carbon monoxide. The alkalization unit 7 uses a dilute alkali solution to wash away SiO2 from the crude carbon produced by the carbonization unit 5, thereby producing carbon powder. The carbon powder is then introduced into the activation unit 8 as a raw material for preparing activated carbon. Activation unit 8 is used to produce activated carbon. Activated carbon is prepared by physical activation of carbon powder through water vapor. The activated carbon is then passed into acidification unit 4 to adsorb organic matter in waste liquid. The primary gasification unit 9 is used to decompose coal at high temperature under air-isolated conditions to produce coke and coke oven gas. The coke is fed into the secondary gasification unit 10 to participate in the reaction. The coke oven gas is converted from chemical energy to thermal energy through the combustion unit 11. The generated high-temperature flue gas is heated by the heat transfer unit I 12 to supply heat to the primary gasification unit 9 and the secondary gasification unit 10. The secondary gasification unit 10 uses CO2 as a gasification agent to react with the coke produced by the primary gasification unit 9 and the crude carbon produced by the carbonization unit 5 to produce CO. After heat recovery and utilization, the CO is introduced into the water-gas shift unit 18 to participate in the reaction. The fan heat exchange unit 13 is used to recover heat from the H2O generated by the fuel cell 21 and the CO generated by the secondary gasification unit 10. It includes a fan a and a heat exchange tube plate b. The heat exchange tube plate b has at least two inlets and two outlets. One inlet is connected to an H2O outlet of the flow control unit III 15, and the other inlet is connected to a CO outlet of the flow control unit IV 14. The H2O outlet is connected to the H2O inlet of the heat transfer and mass transfer unit 17, and the CO outlet is connected to the CO inlet of the heat transfer and mass transfer unit 17. The high-temperature H2O generated by the fuel cell 21 enters the heat exchange tube plate b of the fan heat exchange unit 13 through the flow control unit III 15, and the CO generated by the secondary gasification unit 10 enters the heat exchange tube plate b of the fan heat exchange unit 13 through the flow control unit IV 14. The fan a blows the heat exchange tube plate b containing high-temperature H2O and CO, recovers the heat of H2O and CO, and generates high-temperature air. The generated high-temperature air is used as a heat source to supply the drying unit 3. The electrical energy consumed by the fan a is provided by the fuel cell 21. The flow control unit Ⅳ14 is used to feed the CO generated by the secondary gasification unit 10 into the fan heat exchange unit 13 and the heat exchange unit 16 respectively. The CO stream flowing into the fan heat exchange unit 13 is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit 3. The CO stream flowing into the heat exchange unit 16 exchanges heat with the H2 separated by the separation unit 19 and the newly added O2 to recover heat. The flow control unit Ⅲ15 is used to feed the H2O generated by the fuel cell 21 into the fan heat exchange unit 13 and the heat and mass transfer unit 17 respectively. The H2O stream flowing into the fan heat exchange unit 13 is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit 3. After passing through the fan heat exchange unit 13, it flows into the heat and mass transfer unit 17. Part of the H2O stream first undergoes heat recovery through the fan heat exchange unit 13 and then undergoes secondary heat recovery through the heat and mass transfer unit 17. Part of the stream undergoes heat recovery directly through the heat and mass transfer unit 17. The heat exchange unit 16 is used to exchange heat between the CO generated by the secondary gasification unit 10 and the H2 separated from the separation unit 19, and at the same time preheat the O2. The heat and mass transfer unit 17 is used to perform secondary heat recovery on the H2O stream and CO stream after heat recovery. The H2O and CO streams flowing out from the outlet of the fan heat exchange unit 13 and the CO streams flowing out from the outlet of the heat exchange unit 16 are divided into heat transfer streams and mass transfer streams through the heat and mass transfer unit 17. The heat transfer streams transfer the heat of H2O and CO to the acidification unit 4 and the carbonization unit 5, respectively, while the mass transfer streams transfer H2O and CO to the water-gas conversion unit 18 for water-gas conversion reaction. In the water-gas shift unit 18, CO and H2O undergo a water-gas shift reaction, providing sufficient CO2 for the acidification unit 4 and the secondary gasification unit 10, while the generated H2 serves as the feedstock for the fuel cell 21. The separation unit 19 is used to separate H2 and CO2 generated by the water-gas conversion unit 18 and discharge unreacted CO and H2O. CO2 is divided into two streams by the flow control unit II 20. One stream is fed into the acidification unit 4 as an acidifying agent to precipitate lignin, and the other stream is fed into the secondary gasification unit 10 to react with coke to generate CO. H2 is heated by the heat exchange unit 16 and then fed into the fuel cell 21 to generate electricity. The flow control unit II 20 is used to pass the CO2 separated by the separation unit 19 into the acidification unit 4 and the secondary gasification unit 10 respectively. Part of the CO2 enters the acidification unit 4 as an acidifying agent and reacts with the lignin in the waste liquid to produce acidified lignin precipitate. Part of the CO2 enters the secondary gasification unit 10 as a gasification agent. Fuel cell 21 is used to convert the chemical energy in H2 into electrical energy. It includes a hydrogen inlet, an oxygen inlet, and a water outlet. Hydrogen and oxygen generate electrical energy through fuel cell 21, accompanied by a high-temperature H2O stream. The generated electrical energy is used to power fan a of fan heat exchange unit 13.

[0016] The CO generated by the secondary gasification unit 10 flows into the fan heat exchange unit 13 and the heat exchange unit 16 respectively through the flow control unit IV 14. The CO stream flowing into the fan heat exchange unit 13 is cooled by the fan and generates high-temperature air, which serves as the heat source for the drying unit 3. The CO stream flowing into the heat exchange unit 16 undergoes heat recovery by exchanging heat with the H2 separated by the separation unit 19 and the newly added O2. After undergoing primary heat recovery through the fan heat exchange unit 13 and the heat exchange unit 16, the CO is fed into the heat and mass transfer unit 17 for secondary heat recovery. The recovered heat is used to heat the acidification unit 4 and the carbonization unit 5. After passing through the heat and mass transfer unit 17, CO enters the water-gas conversion unit 18 to participate in the reaction. The flow control unit IV 14 is used to adjust the proportion of CO flowing into the fan heat exchange unit 13 and the heat exchange unit 16 respectively. The proportion adjustment range is 0-100%. 0% means that all the CO produced by the secondary gasification unit 10 flows into the heat exchange unit 16 through the flow control unit IV 14, and 100% means that all the CO produced by the secondary gasification unit 10 flows into the fan heat exchange unit 13 through the flow control unit IV 14.

[0017] The H2O generated by fuel cell 21 flows into fan heat exchange unit 13 and heat and mass transfer unit 17 respectively through flow control unit III 15. The H2O stream flowing into fan heat exchange unit 13 is cooled by fan blowing and generates high-temperature air. The high-temperature air serves as the heat source for drying unit 3. After passing through fan heat exchange unit 13, it flows into heat and mass transfer unit 17. Part of the H2O undergoes heat recovery first through fan heat exchange unit 13 and then undergoes secondary heat recovery through heat and mass transfer unit 17. The other part undergoes heat recovery directly through heat and mass transfer unit 17. Flow control unit III 15 adjusts the ratio of the two H2O flow directions according to the heat required by drying unit 3, acidification unit 4, and carbonization unit 5. The ratio adjustment range is 0-100%. 0% means that all H2O generated by fuel cell 21 enters heat and mass transfer unit 17 through flow control unit III 15. 100% means that all H2O generated by fuel cell 21 enters fan heat exchange unit 13 through flow control unit III 15.

[0018] The flow control unit I6 is used to adjust the ratio of the crude carbon produced by the carbonization unit 5 to the alkalization unit 7 and the secondary gasification unit 10 respectively. The adjustment range is 0-100%. 0% means that all the crude carbon produced by the carbonization unit 5 is fed into the secondary gasification unit 10 through the flow control unit I6, and 100% means that all the crude carbon produced by the carbonization unit 5 is fed into the alkalization unit 7 through the flow control unit I6.

[0019] The flow control unit II 20 is used to adjust the ratio of CO2 separated by the separation unit 19 to the acidification unit 4 and the secondary gasification unit 10 respectively. The adjustment range is 0-100%. 0% means that all the CO2 separated by the separation unit 19 flows into the secondary gasification unit 10 through the flow control unit II 20, and 100% means that all the CO2 separated by the separation unit 19 flows into the acidification unit 4 through the flow control unit II 20.

[0020] The heat exchanger coil b of the fan heat exchanger unit 13 is made of finned tubes and has two forms: single coil and multi-coil.

[0021] An example is applied to the aforementioned cogeneration method for papermaking coal gasification coupled with a fuel cell, the method comprising: The pulping unit 1 and bleaching unit 2 produce wastewater containing fiber, organic matter, inorganic salts, and pigments. This wastewater enters the acidification unit 4 and reacts with the acidifying agent CO2. After adsorption by activated carbon, it is converted into acidified lignin precipitate, simultaneously producing SiO2 precipitate. The acidified lignin precipitate and SiO2 precipitate then enter the carbonization unit 5, where they are converted into crude carbon under a hydrothermal environment. The crude carbon is then directed to the alkalization unit 7 and the secondary gasification unit 10 via a flow control unit I6, which regulates the ratio of the two flow directions. In the alkalization unit 7, the crude carbon reacts with a dilute alkali solution to remove SiO2. Impurities are removed, producing carbon powder. The carbon powder is then fed into activation unit 8 for physical activation with steam to prepare activated carbon. The activated carbon is then fed into acidification unit 4 to adsorb organic matter in the waste liquid. The crude carbon reacts with CO2 in secondary gasification unit 10 to produce CO. Coal is fed into primary gasification unit 9 and decomposes at high temperature in a closed environment to produce coke and coke oven gas. The coke is then fed into secondary gasification unit 10 to react with CO2 to produce CO. The coke oven gas enters combustion unit 11, and the high-temperature flue gas produced by combustion supplies heat to primary gasification unit 9 and secondary gasification unit 10 through heat transfer unit I 12. The CO produced by the secondary gasification unit 10 and the H2O produced by the fuel cell 21 contain high-grade energy. The CO produced by the secondary gasification unit 10 flows into the fan heat exchange unit 13 and the heat exchange unit 16 respectively through the flow control unit IV 14. The CO stream flowing into the fan heat exchange unit 13 is cooled by the fan and generates high-temperature air, which serves as the heat source for the drying unit 3. The CO stream flowing into the heat exchange unit 16 undergoes heat recovery by exchanging heat with the H2 separated by the separation unit 19 and the newly added O2. After undergoing primary heat recovery through the fan heat exchange unit 13 and the heat exchange unit 16, the CO is fed into the heat and mass transfer unit 17 for secondary heat recovery. The recovered heat is used to heat the acidification unit 4 and the carbonization unit 5. After passing through the heat and mass transfer unit 17, CO enters the water-gas shift unit 18 to participate in the reaction. The H2O generated by the fuel cell 21 flows into the fan heat exchange unit 13 and the heat and mass transfer unit 17 respectively through the flow control unit Ⅲ 15. The H2O stream flowing into the fan heat exchange unit 13 is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit 3. After passing through the fan heat exchange unit 13, it flows into the heat and mass transfer unit 17. Part of the H2O undergoes heat recovery first through the fan heat exchange unit 13 and then undergoes secondary heat recovery through the heat and mass transfer unit 17. The part of the H2O is directly recovered through the heat and mass transfer unit 17. The ratio of the two H2O flow directions is adjusted according to the heat required by the drying unit 3, acidification unit 4, and carbonization unit 5. After heat recovery, H2O and CO are separated into heat transfer streams and mass transfer streams through heat and mass transfer unit 17. The heat transfer streams transfer the heat of H2O and CO to acidification unit 4 and carbonization unit 5, respectively, while the mass transfer streams transfer H2O and CO to water-gas shift unit 18 for water-gas shift reaction. CO and H2O react in water-gas shift unit 18 to produce H2 and CO2. Separation unit 19 separates H2 and CO2 and discharges unreacted CO and H2O. CO2 is divided into two streams through flow control unit II 20, which serve as acidifying agent in acidification unit 4 and gasifying agent in secondary gasification unit 10, respectively. Flow control unit II 20 adjusts the ratio of CO2 flowing to acidification unit 4 and secondary gasification unit 10 according to the amount of waste liquid to be treated. H2 is fed into fuel cell 21 after reaching the reaction temperature through heat exchange unit 16 to convert chemical energy into electrical energy.

[0022] In one embodiment, the presence of the flow control unit Ⅲ15 can adjust the ratio of H2O generated by the fuel cell 21 to the fan heat exchange unit 13 and the heat and mass transfer unit 17. H2O first passes through the fan heat exchange unit 13 to generate hot air, and then enters the heat and mass transfer unit 17 to provide heat. However, if the original temperature of H2O is relatively low or the amount of waste liquid to be treated is large, H2O can be directly introduced into the heat and mass transfer unit 17 without passing through the fan heat exchange unit 13.

[0023] In another embodiment, the presence of the flow control unit IV 14 can adjust the ratio of CO generated by the secondary gasification unit 10 to the fan heat exchange unit 13 and the heat exchange unit 16. CO first passes through the fan heat exchange unit 13 to generate hot air, and then passes through the heat exchange unit 16 to exchange heat with H2 via convection; however, if the temperature of H2O generated by the fuel cell 21 is high enough or the heat required by the drying unit 3 is relatively small, CO can be directly introduced into the heat exchange unit 16 without passing through the fan heat exchange unit 13.

[0024] In another embodiment, a portion of the coal enters the primary gasification unit 9 for staged gasification, while a portion enters the combustion unit 11 for combustion to generate high-temperature flue gas for heating.

[0025] Therefore, those skilled in the art should understand that the description of specific embodiments in this invention is not intended to limit the concept and scope of the invention. Any modifications and improvements to the technical solutions made without departing from the technical solutions of this invention will still fall within the protection scope of this invention.

Claims

1. A combined heat and power system coupling coal gasification and fuel cells for papermaking, characterized in that, The system includes a pulping unit (1), a bleaching unit (2), a drying unit (3), an acidification unit (4), a carbonization unit (5), a flow control unit I (6), an alkalization unit (7), an activation unit (8), a primary gasification unit (9), a secondary gasification unit (10), a combustion unit (11), a heat transfer unit I (12), a fan heat exchange unit (13), a flow control unit IV (14), a flow control unit III (15), a heat exchange unit (16), a heat and mass transfer unit (17), a water-gas conversion unit (18), a separation unit (19), a flow control unit II (20), and a fuel cell (21). The pulping unit (1) is used to prepare pulp by effectively dissociating fibers from wood or other raw materials using mechanical pulping, chemical pulping or biological pulping techniques. The bleaching unit (2) is used to bleach the pulp to give it the corresponding whiteness. Both the pulping unit (1) and the bleaching unit (2) will produce waste liquid containing fibers, organic matter, inorganic salts and pigments. The drying unit (3) is used to remove moisture from the paper web during the pulp-to-paper web process. The heat source for drying and dehydration is the high-temperature air generated by the fan heat exchange unit (13). The acidification unit (4) is used to acidify the lignin in the waste liquid to precipitate it. In the closed system, the acidifying agent CO2 introduced reacts with the lignin in the waste liquid, causing the lignin to be converted into acidified lignin precipitate. At the same time, the sodium salt in the waste liquid is converted into NaHCO3, enriching and separating the sodium element. The inorganic silicon salt is also converted into SiO2 precipitate, which enters the carbonization unit (5) together with the acidified lignin. Both the acidification unit (4) and the carbonization unit (5) are heated by the heat transfer and mass transfer unit (17). The carbonization unit (5) decomposes the acidified lignin produced by the acidification unit (4) into small molecule organic matter and then into crude carbon containing SiO2 impurities in a hydrothermal environment. The flow control unit I (6) is used to pass the crude carbon produced by the carbonization unit (5) into the alkalization unit (7) and the secondary gasification unit (10) respectively. A portion of the crude carbon enters the alkalization unit (7) through the flow control unit I (6) and is converted into carbon powder. The carbon powder enters the activation unit (8) as a raw material for preparing activated carbon, and a portion enters the secondary gasification unit (10) as a gasification raw material to react with carbon dioxide to produce carbon monoxide. The alkalization unit (7) washes away SiO2 from the crude carbon produced by the carbonization unit (5) with dilute alkali solution to produce carbon powder, which is then introduced into the activation unit (8) as a raw material for preparing activated carbon. The activation unit (8) is used to produce activated carbon. The carbon powder is physically activated by water vapor to prepare activated carbon. The activated carbon is then passed into the acidification unit (4) to adsorb organic matter in the waste liquid. The primary gasification unit (9) is used to decompose coal at high temperature under isolated air conditions to produce coke and coke oven gas. The coke is fed into the secondary gasification unit (10) to participate in the reaction. The coke oven gas is converted from chemical energy to thermal energy through the combustion unit (11). The generated high-temperature flue gas is heated by the heat transfer unit I (12) to supply heat to the primary gasification unit (9) and the secondary gasification unit (10). The secondary gasification unit (10) uses CO2 as a gasifying agent to react with the coke produced by the primary gasification unit (9) and the crude carbon produced by the carbonization unit (5) to produce CO. After the CO is heat-recovered and utilized, it is fed into the water-gas shift unit (18) to participate in the reaction. The fan heat exchange unit (13) is used to recover heat from the H2O generated by the fuel cell (21) and the CO generated by the secondary gasification unit (10). It includes a fan (a) and a heat exchange coil (b). The heat exchange coil (b) has at least two inlets and two outlets. One inlet is connected to an H2O outlet of the flow control unit III (15), and the other inlet is connected to a CO outlet of the flow control unit IV (14). The H2O outlet is connected to the H2O inlet of the heat and mass transfer unit (17), and the CO outlet is connected to the CO inlet of the heat and mass transfer unit (17). The high-temperature H2O generated by the fuel cell (21) enters the heat exchange tube coil (b) of the fan heat exchange unit (13) through the flow control unit III (15), and the CO generated by the secondary gasification unit (10) enters the heat exchange tube coil (b) of the fan heat exchange unit (13) through the flow control unit IV (14). The fan (a) blows the heat exchange tube coil (b) containing high-temperature H2O and CO, recovers the heat of H2O and CO and generates high-temperature air. The generated high-temperature air is used as a heat source to supply the drying unit (3). The electrical energy consumed by the fan (a) is provided by the fuel cell (21). The flow control unit Ⅳ (14) is used to pass the CO generated by the secondary gasification unit (10) into the fan heat exchange unit (13) and the heat exchange unit (16) respectively. The CO stream flowing into the fan heat exchange unit (13) is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit (3). The CO stream flowing into the heat exchange unit (16) is heat recovered by exchanging heat with the H2 separated by the separation unit (19) and the newly added O2. The flow control unit Ⅲ (15) is used to pass the H2O generated by the fuel cell (21) into the fan heat exchange unit (13) and the heat transfer and mass transfer unit (17) respectively. The H2O stream flowing into the fan heat exchange unit (13) is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit (3). After passing through the fan heat exchange unit (13), it flows into the heat transfer and mass transfer unit (17). Part of the H2O stream first undergoes heat recovery through the fan heat exchange unit (13) and then undergoes secondary heat recovery through the heat transfer and mass transfer unit (17). Part of the stream undergoes heat recovery directly through the heat transfer and mass transfer unit (17). The heat exchange unit (16) is used to exchange heat between the CO generated by the secondary gasification unit (10) and the H2 separated from the separation unit (19), and at the same time preheat the O2; The heat and mass transfer unit (17) is used to perform secondary heat recovery on the H2O stream and CO stream after heat recovery. The H2O and CO streams flowing out from the outlet of the fan heat exchange unit (13) and the CO streams flowing out from the outlet of the heat exchange unit (16) are divided into heat transfer streams and mass transfer streams through the heat and mass transfer unit (17). The heat transfer streams transfer the heat of H2O and CO to the acidification unit (4) and the carbonization unit (5) respectively, while the mass transfer streams transfer H2O and CO to the water-gas conversion unit (18) for water-gas conversion reaction. In the water-gas shift unit (18), CO and H2O undergo a water-gas shift reaction, providing sufficient CO2 for the acidification unit (4) and the secondary gasification unit (10), while the generated H2 serves as a feedstock for the fuel cell (21). The separation unit (19) is used to separate H2 and CO2 generated by the water-gas conversion unit (18) and discharge unreacted CO and H2O. CO2 is divided into two streams by the flow control unit II (20). One stream is fed into the acidification unit (4) as an acidifying agent to precipitate lignin, and the other stream is fed into the secondary gasification unit (10) to react with coke to generate CO. H2 is heated by the heat exchange unit (16) and then fed into the fuel cell (21) to generate electricity. The flow control unit II (20) is used to pass the CO2 separated by the separation unit (19) into the acidification unit (4) and the secondary gasification unit (10) respectively. Part of the CO2 enters the acidification unit (4) as an acidifying agent and reacts with the lignin in the waste liquid to produce acidified lignin precipitate. Part of the CO2 enters the secondary gasification unit (10) as a gasifying agent. The fuel cell (21) is used to convert the chemical energy in H2 into electrical energy. It includes a hydrogen inlet, an oxygen inlet and a water outlet. Hydrogen and oxygen generate electrical energy through the fuel cell (21) and are accompanied by a high-temperature H2O stream. The generated electrical energy is used to power the fan (a) of the fan heat exchange unit (13).

2. The combined heat and power system for papermaking gasification coupled with a fuel cell, as described in claim 1, is characterized in that, The CO generated by the secondary gasification unit (10) is utilized in a cascade manner. The CO generated by the secondary gasification unit (10) flows into the fan heat exchange unit (13) and the heat exchange unit (16) respectively through the flow control unit IV (14). The CO stream flowing into the fan heat exchange unit (13) is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit (3). The CO stream flowing into the heat exchange unit (16) is heat recovered by exchanging heat with the H2 separated by the separation unit (19) and the newly added O2. After the CO has undergone one heat recovery through the fan heat exchange unit (13) and the heat exchange unit (16), it is fed into the heat and mass transfer unit ( ). 17) Secondary heat recovery is performed, and the recovered heat is used to heat the acidification unit (4) and the carbonization unit (5). After passing through the heat and mass transfer unit (17), CO enters the water-gas conversion unit (18) to participate in the reaction. The flow control unit IV (14) is used to adjust the proportion of CO flowing into the fan heat exchange unit (13) and the heat exchange unit (16) respectively. The proportion adjustment range is 0-100%. 0% means that all the CO generated by the secondary gasification unit (10) flows into the heat exchange unit (16) through the flow control unit IV (14). 100% means that all the CO generated by the secondary gasification unit (10) flows into the fan heat exchange unit (13) through the flow control unit IV (14).

3. A combined heat and power system for papermaking coal gasification coupled with a fuel cell, as described in claim 1, is characterized in that, The H2O generated by the fuel cell (21) is utilized in a cascade manner. The H2O generated by the fuel cell (21) flows into the fan heat exchange unit (13) and the heat transfer and mass transfer unit (17) respectively through the flow control unit III (15). The H2O stream flowing into the fan heat exchange unit (13) is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit (3). After passing through the fan heat exchange unit (13), it flows into the heat transfer and mass transfer unit (17). A portion of the H2O is first heat recovered through the fan heat exchange unit (13) and then further heat-recovered through the heat transfer and mass transfer unit (17). Secondary heat recovery is performed, with a portion of the heat being recovered directly through the heat and mass transfer unit (17). The flow control unit III (15) adjusts the ratio of the two flow directions of H2O according to the heat required by the drying unit (3), acidification unit (4), and carbonization unit (5). The ratio adjustment range is 0-100%. 0% means that all the H2O generated by the fuel cell (21) enters the heat and mass transfer unit (17) through the flow control unit III (15), and 100% means that all the H2O generated by the fuel cell (21) enters the fan heat exchange unit (13) through the flow control unit III (15).

4. A combined heat and power system for papermaking, coupling coal gasification and fuel cells, as described in claim 1, characterized in that, The flow control unit I (6) is used to adjust the proportion of crude carbon produced by the carbonization unit (5) being fed into the alkalization unit (7) and the secondary gasification unit (10), respectively. The adjustment range is 0-100%. 0% means that all the crude carbon produced by the carbonization unit (5) is fed into the secondary gasification unit (10) through the flow control unit I (6), and 100% means that all the crude carbon produced by the carbonization unit (5) is fed into the alkalization unit (7) through the flow control unit I (6).

5. A combined heat and power system for papermaking coal gasification coupled with a fuel cell, as described in claim 1, is characterized in that, The flow control unit II (20) is used to adjust the ratio of CO2 separated by the separation unit (19) to the acidification unit (4) and the secondary gasification unit (10). The adjustment range is 0-100%. 0% means that all CO2 separated by the separation unit (19) flows into the secondary gasification unit (10) through the flow control unit II (20), and 100% means that all CO2 separated by the separation unit (19) flows into the acidification unit (4) through the flow control unit II (20).

6. A combined heat and power system for papermaking, coupling coal gasification and fuel cells, as described in claim 1, characterized in that, The heat exchange coil (b) of the fan heat exchange unit (13) is made of finned tubes and has two forms: single coil and multi-coil.

7. A method for cogeneration of coal gasification and fuel cell in papermaking, applied to the system according to any one of claims 1-6, characterized in that, The method includes: The pulping unit (1) and bleaching unit (2) produce waste liquid containing fiber, organic matter, inorganic salts, and pigments. The waste liquid enters the acidification unit (4) and reacts with the acidifying agent CO2. After being adsorbed by activated carbon, it is converted into acidified lignin precipitate, and SiO2 precipitate is produced at the same time. The acidified lignin precipitate and SiO2 precipitate enter the carbonization unit (5) and are converted into crude carbon in a hydrothermal environment. The crude carbon is connected to the alkalization unit (7) and the secondary gasification unit (10) through the flow control unit I (6). The flow control unit I (6) can adjust the ratio of the two flow directions of the crude carbon. The crude carbon reacts with dilute alkali solution in the alkalization unit (7) to remove SiO2. Impurities are generated to produce carbon powder. The carbon powder is fed into the activation unit (8) and activated carbon is prepared by physical activation with water vapor. The activated carbon is fed into the acidification unit (4) to adsorb organic matter in the waste liquid. The crude carbon reacts with CO2 in the secondary gasification unit (10) to produce CO. Coal is fed into the primary gasification unit (9) and decomposes at high temperature in a closed environment to produce coke and coke oven gas. The coke is fed into the secondary gasification unit (10) and reacts with CO2 to produce CO. The coke oven gas enters the combustion unit (11). The high-temperature flue gas generated by combustion is heated by the heat transfer unit I (12) to heat the primary gasification unit (9) and the secondary gasification unit (10). The CO produced by the secondary gasification unit (10) and the H2O produced by the fuel cell (21) contain high-grade energy. The CO produced by the secondary gasification unit (10) flows into the fan heat exchange unit (13) and the heat exchange unit (16) respectively through the flow control unit IV (14). The CO stream flowing into the fan heat exchange unit (13) is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit (3). The CO stream flowing into the heat exchange unit (16) undergoes heat recovery by exchanging heat with the H2 separated by the separation unit (19) and the newly added O2. After the CO undergoes primary heat recovery through the fan heat exchange unit (13) and the heat exchange unit (16), it is fed into the heat and mass transfer unit (17) for secondary heat recovery. The recovered heat is used to heat the acidification unit (4) and the carbonization unit (5). After passing through the heat and mass transfer unit (17), H2O enters the water-gas conversion unit (18) to participate in the reaction. The H2O generated by the fuel cell (21) flows into the fan heat exchange unit (13) and the heat and mass transfer unit (17) respectively through the flow control unit III (15). The H2O stream flowing into the fan heat exchange unit (13) is cooled by the fan and generates high-temperature air. The high-temperature air serves as the heat source for the drying unit (3). After passing through the fan heat exchange unit (13), it flows into the heat and mass transfer unit (17). Part of the H2O is first heat recovered through the fan heat exchange unit (13) and then heat recovered again through the heat and mass transfer unit (17). Part of the H2O is directly heat recovered through the heat and mass transfer unit (17). The ratio of the two flow directions of H2O is adjusted according to the heat required by the drying unit (3), acidification unit (4) and carbonization unit (5). After heat recovery, H2O and CO are divided into heat transfer streams and mass transfer streams through the heat transfer and mass transfer unit (17). The heat transfer streams transfer the heat of H2O and CO to the acidification unit (4) and the carbonization unit (5), respectively. The mass transfer streams transfer H2O and CO to the water-gas conversion unit (18) for water-gas conversion reaction. CO and H2O react in the water-gas conversion unit (18) to produce H2 and CO2. The separation unit (19) separates H2 and CO2 and discharges the unreacted CO and H2O. CO2 is divided into two streams through the flow control unit II (20), which serve as the acidifying agent of the acidification unit (4) and the gasifying agent of the secondary gasification unit (10), respectively. The flow control unit II (20) adjusts the ratio of CO2 to the acidification unit (4) and the secondary gasification unit (10) according to the amount of waste liquid to be treated. H2 is fed into the fuel cell (21) after reaching the reaction temperature through the heat exchange unit (16) to convert chemical energy into electrical energy.

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