Dimethyl ether-electricity co-production process for biomass gasification coupling alkaline electrolytic cell hydrogen production

Abstract

The invention discloses a dimethyl ether-electricity co-production process for biomass gasification coupled alkaline electrolytic cell hydrogen production, which is characterized in that a gasification furnace takes steam and oxygen as gasification agents, and corn straws are converted into crude synthesis gas Syngas; the heat of the crude synthesis gas can heat the gasifying agent water vapor through the heat exchanger, and the redundant heat of the synthesis gas is transferred to the CO2 in the supercritical state through the heat exchanger for cyclic power generation. As H2S is contained in the synthesis gas and can interfere with the subsequent synthesis of methanol, a separator is arranged to remove H2S in Syngas 2. The synthesis gas Syngas 3 subjected to waste heat utilization and purification cannot meet the requirement of methanol synthesis, and hydrogen generated by the alkaline electrolyzed water unit is mixed with the synthesis gas Syngas 3, so that the SN of the synthesis gas reaches 2.03, and the requirement of methanol synthesis is met. And the gas Syngas 4 is cooled and compressed and then enters a methanol synthesis reactor to generate methanol and other gases. Methanol enters a DME synthesis reactor after being heated and compressed. The material flow at the outlet of the reactor is cooled and then enters a distillation tower, and DME is separated out. And the material flow at the bottom outlet of the distillation tower enters the distillation tower to separate methanol from water, wherein the methanol is circulated back to the R-DME. According to the system, the alkaline water electrolysis hydrogen production unit and the S-CO2 Brayton cycle unit are innovatively coupled, and corn straw biomass can be efficiently converted into DME and electric power.

Description

[Technical field]

[0001] The invention relates to the field of biomass gasification to produce biofuels, and in particular to a system for producing dimethyl ether by using biomass as raw materials and corn stalk gasification-alkaline water electrolysis. [Background technology]

[0002] Burning corn straw produces a large amount of greenhouse gases, harmful gases, smoke and dust, posing a threat to the environment and public health. Landfill is another common and simple way to deal with corn straw, but because corn straw mainly contains non-biodegradable lignocellulosic biomass, which is slowly degraded by microorganisms, leachate containing toxic heavy metals and harmful chemicals will be produced over time, and it may also cause groundwater contamination. In addition, the release of methane gas from landfills has caused concerns about site safety and global warming. In recent years, thermochemical and biochemical conversion technologies have been gradually applied. Biological processes mainly include fermentation, anaerobic digestion and aerobic composting, which can convert corn straw into biofuels (such as bioethanol and biogas) and bioresources (compost and biofertilizer). Thermochemical treatment methods mainly include pyrolysis, gasification and liquefaction, which can convert organic matter in corn straw into bio-oil, syngas and biochar, realizing the resource utilization of corn straw. Among various thermochemical conversion technologies, gasification is currently recognized as an advanced and efficient method. As an important fuel, dimethyl ether has similar properties to liquefied petroleum gas. It can be synthesized from conventional raw materials such as coal and crude oil, as well as renewable raw materials such as biomass and waste. Dimethyl ether can be used as a substitute for diesel because its cetane number is 55-60, which exceeds the cetane number of fossil diesel. Compared with traditional diesel, the combustion of dimethyl ether produces less NO X 、SO X The study showed that DME has a low replacement cost as an alternative fuel, is more energy efficient and produces less CO2 emissions than other liquid biofuels.

[0003] Currently, the most advanced method for producing dimethyl ether is through methanol dehydration. Therefore, the present invention proposes a corn straw gasification-alkaline water electrolysis system for producing dimethyl ether. First, the corn straw is gasified into synthesis gas, and the synthesis gas is coupled with an alkaline water electrolysis hydrogen production unit to make it meet the needs of methanol synthesis, and methanol is further synthesized. Then, methanol is dehydrated to produce dimethyl ether. [Summary of the invention]

[0004] [Technical issues to be solved]

[0005] The present invention provides a method of using coal and biomass as mixed raw materials, steam and oxygen as gasification agents, and innovatively coupling an alkaline water electrolysis hydrogen production unit and an S-CO2 Brayton cycle unit to efficiently convert corn straw biomass into DME and electricity. It can reduce the threat to the environment and public health caused by the large amount of greenhouse gases, harmful gases, smoke and dust produced by straw burning, and convert organic matter in corn straw into bio-oil, synthesis gas and biochar, realizing the resource utilization of corn straw.

[0006] [Technical solution]

[0007] In view of the environmental pollution caused by straw burning and the low energy conversion rate of biomass hydrogen production, the present invention proposes a process for preparing dimethyl ether by an alkaline water electrolysis hydrogen production unit and an S-CO2 Brayton cycle unit using coal and biomass as raw materials and steam and oxygen as gasification agents, which can improve the conversion rate of low-level energy while reducing pollutant emissions.

[0008] A dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer is characterized in that the device used in the process comprises the following parts: a gasification and synthesis gas purification unit, an S-CO2 Brayton cycle unit, an alkaline water electrolysis unit, a methanol synthesis unit and a DME synthesis unit. The specific implementation steps are as follows:

[0009] At 800℃, the gasifier uses steam and oxygen as gasifiers to convert corn stalks into crude syngas. The temperature of the crude syngas is 800℃, and this part of the heat can be used to heat the gasifier water vapor through the heat exchanger. The temperature of the syngas at the heat exchanger outlet is 742℃. The excess heat of the syngas is transferred to the CO2 in the supercritical state through the heat exchanger for cyclic power generation, which will obtain an electrical energy output of 67.09kW. CO2 with higher temperature and pressure will drive the turbine to generate electricity with a power generation capacity of 129.66kW. The CO2 discharged from the CT is heat exchanged in the heat exchanger to heat the CO2 with a lower temperature. The CO2 flow with a lower temperature is cooled in the heat exchanger, and the CO2 is compressed in the compressor with a final pressure of 20MPa, which will consume 62.57kW of electricity. Since the syngas contains H2S, it will interfere with the subsequent synthesis of methanol, so a separator is set to remove H2S from Syngas 2.

[0010] The SN of the syngas Syngas 3 after waste heat utilization and purification is only 0.85, which cannot meet the requirements of methanol synthesis. The alkaline water electrolysis unit can convert water into hydrogen and oxygen. Part of the oxygen produced is used as the gasification agent required for corn straw gasification, and the rest is sold. The hydrogen produced by the alkaline water electrolysis hydrogen production unit is mixed with the syngas Syngas 3 to make the SN of the syngas reach 2.03, which meets the requirements of methanol synthesis. After cooling and compression, the temperature of the gas Syngas 4 becomes 170°C and the pressure becomes 50bar, and it enters the methanol synthesis reactor to produce methanol and other gases.

[0011] After being cooled by the cooler, the logistics enters the flash tank to separate the condensable products from the non-condensable reactants, and the non-condensable reactants are recycled. The condensed components enter the distillation tower to separate the light fraction LIGHTS. The separated logistics enter the distillation tower, methanol is obtained at the top of the tower, and water is obtained at the bottom of the tower. Methanol enters the DME synthesis reactor after heating and compression. The temperature of the reactor inlet logistics is 279.62℃ and the pressure is 10bar. After being cooled, the reactor outlet logistics enters the distillation tower DIS-3 to separate DME. The bottom outlet logistics of the distillation tower DIS-3 enters the distillation tower to separate methanol and water, and the methanol is recycled back to R-DME.

[0012] According to a preferred embodiment of the present invention, it is characterized in that: S-CO2 Brayton cycle power generation technology is a power generation technology using S-CO2 as a working fluid. Compared with organic Rankine cycle power generation, S-CO2 Brayton cycle power generation has significant advantages because CO2 is chemically stable, non-toxic and non-flammable at high temperatures. In addition, the critical temperature of CO2 is relatively low, about 31°C, and it is easy to reach a supercritical state. S-CO2 Brayton cycle power generation has the advantages of high efficiency, low cost, and flexibility, and can efficiently convert the heat of the syngas produced by gasification into electricity.

[0013] [Beneficial Effects]

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) Rationally handle the problem of corn straw burning and reduce the threat to the environment and public health caused by the large amount of greenhouse gases, harmful gases, smoke and dust produced by straw burning.

[0016] (2) S-CO2 Brayton cycle power generation has the advantages of high efficiency, low cost and flexibility, and can efficiently convert the heat of the synthesis gas produced by gasification into electricity.

Brief Description of the Drawings

[0017] Attached Figure 1 The invention discloses a dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with an alkaline electrolyzer.

[0018] In the figure, 1-biomass, 2-oxygen, 3-steam for biomass preheating, 4-slag, (1)-gasification and synthesis gas purification unit, 5-high-temperature gaseous products after biomass gasification, 6-Syngas 1, 7-Syngas 2, 8-CO2, 9-electricity, (2)-alkaline water electrolysis unit, (3)-S-CO2 Brayton cycle unit, 10-Syngas3, 11-cooling water, 12-H2O, 13-H2, 14-Syngas 4, 15-non-condensable reactants, 16-Syngas4 rich stream, 17-condensate, (4)-methanol synthesis unit, 18-methanol, 19-H2O, (5) R-DEM reactor, 20-methanol, (6)-dimethyl ether synthesis unit, 21-methanol, 22-dimethyl ether, 23-H2O, 24-methanol. [Specific implementation method]

[0019] Embodiment 1:

[0020] The biomass feed 1 is 1000 kg / h, and the feed amount of the gasification agent 2 is 130 kg / h. The operating pressure of the gasification unit (5) is 1 atm, and the operating temperature is 800°C; the supercritical carbon dioxide Brayton cycle unit (3) has a carbon dioxide compressor discharge pressure of 20 MPa, a turbine pressure ratio of 0.44, an isentropic efficiency of 85%, and a mechanical efficiency of 98%; the alkaline electrolyzer hydrogen production unit (2) has an operating temperature of 72.75°C, an operating pressure of 7 bar, an electrolyte concentration of 35% KOH, and an effective electrode area of ​​1000 cm 2 The methanol synthesis unit reactor temperature is 250°C and the pressure is 50 bar. The dimethyl ether synthesis unit uses an adiabatic reactor with a reactor temperature of 279.62°C and a pressure of 10 bar. The purity of the obtained product is 99%.

[0021] Embodiment 2:

[0022] The biomass feed 1 is 800 kg / h, and the feed amount of the gasification agent 2 is 110 kg / h. The operating pressure of the gasification unit (5) is 1 atm, and the operating temperature is 800°C; the supercritical carbon dioxide Brayton cycle unit (3) has a carbon dioxide compressor discharge pressure of 18 MPa, a turbine pressure ratio of 0.42, an isentropic efficiency of 87%, and a mechanical efficiency of 99%; the alkaline electrolyzer hydrogen production unit (2) has an operating temperature of 70°C, an operating pressure of 7 bar, an electrolyte concentration of 35% KOH, and an effective electrode area of ​​1000 cm 2 The methanol synthesis unit reactor temperature is 250°C and the pressure is 50 bar. The dimethyl ether synthesis unit uses an adiabatic reactor with a reactor temperature of 279.62°C and a pressure of 10 bar. The purity of the obtained product is 99%.

Claims

1. A dimethyl ether-electricity cogeneration process for hydrogen production by biomass gasification coupled with alkaline electrolyzer, which is mainly characterized by The device used in the process comprises the following parts: a gasification and synthesis gas purification unit (1), an alkaline water electrolysis unit (2), an S-CO2 Brayton cycle unit (3), a methanol synthesis unit (4), and a DME synthesis unit (6); wherein the synthesis gas generated by the gasification and synthesis gas purification unit (1) is mainly composed of CO and H2; the S-CO2 Brayton cycle unit (3) is located after the gasification and synthesis gas purification unit ①, and is used to efficiently convert the heat of the synthesis gas generated by gasification into electricity. The S-CO2 Brayton cycle power generation has the advantages of high efficiency, low cost, and flexibility; The methanol synthesis unit (4) is located after the alkaline water electrolysis unit (2). The hydrogen produced by the alkaline water electrolysis unit is mixed with the synthesis gas Syngas 3 to make the SN of the synthesis gas reach 2.03, meeting the requirements of methanol synthesis; finally, methanol is dehydrated to synthesize dimethyl ether. The dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer mainly comprises the following steps: (1) Coal and biomass are used as mixed raw materials (1), steam and oxygen are used as gasifying agents (2), and enter the gasification and synthesis gas purification unit (1), and the organic components in the raw materials undergo a series of gasification reactions to obtain high-temperature gaseous products rich in crude synthesis gas Syngas, CO2 and H2 (5), and the inorganic components are converted into inert slag (4); (2) The obtained high temperature gaseous product (5) enters the S-CO2 Brayton cycle unit (3) to efficiently convert the heat of the synthesis gas produced by gasification into electricity; (3) an alkaline water electrolysis unit (2) to convert water into hydrogen (13) and oxygen (2). The alkaline water electrolysis unit produces hydrogen that is mixed with synthesis gas (Syngas) (10) to meet the demand for methanol synthesis; (4) After being cooled and compressed, the gas Syngas (14) has a temperature of 170°C and a pressure of 50 bar and enters the methanol synthesis reactor to produce methanol (18) and other gases; (5) Methanol (18) is heated and compressed before entering the DME synthesis reactor. Methanol (18) and water are separated, with methanol being recycled back to R-DME.

2. A dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer according to claim 1, characterized in that Corn stover biomass can be efficiently converted into DME and electricity.

3. The dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer according to claim 1, characterized in that: Corn straw is converted into crude syngas, the temperature of which is 800°C. This heat can be used to heat the gasifying agent water vapor through a heat exchanger.

4. The dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer according to claim 1, characterized in that: The excess heat of the synthesis gas is transferred to the supercritical CO2 to generate electricity in a cycle.

5. The dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer according to claim 1, characterized in that: The alkaline water electrolysis unit (2) can convert water into hydrogen (13) and oxygen (2), wherein a part of the generated oxygen (2) is used as a gasification agent required for corn stover gasification, and the rest is sold.

6. The dimethyl ether-electricity cogeneration process for producing hydrogen by coupling biomass gasification with alkaline electrolyzer according to claim 1, characterized in that: The alkaline water electrolysis unit (2) generates hydrogen (13) which is mixed with the synthesis gas (Syngas) (10) to make the SN of the synthesis gas reach 1.90-2.10 to meet the requirements of methanol synthesis. The methanol (18) is heated and compressed before entering the DME synthesis reactor to generate dimethyl ether (22).

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