Process for directly synthesizing dimethyl ether through hydrogenation of carbon dioxide by efficiently utilizing waste

Abstract

The invention discloses a process for directly synthesizing dimethyl ether (DME) by taking urban organic wastes as raw materials, preparing synthesis gas (H2, CO and CO2) through gasification and efficiently utilizing residual heat and components. The synthesis gas firstly passes through a Kalina cycle system to recover waste heat and generate power, then the hydrogen content is increased through water vapor shift, and CO2 is captured through a chemical adsorption method to obtain high-purity hydrogen. And the captured CO2 and hydrogen are mixed, preheated and compressed, and then enter a reactor to generate DME, methanol and water under the action of a catalyst. After the reaction product is cooled and subjected to gas-liquid separation, unreacted gas is recycled; and rectifying the liquid-phase product to obtain a DME product, and recycling methanol for reproduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of urban solid waste gasification for automobile fuel, in particular to the direct synthesis of dimethyl ether from carbon dioxide hydrogenation using hydrogen-rich synthesis gas produced by a downdraft gasifier with urban solid waste as raw material. BACKGROUND

[0002] The production of bioenergy has a wide range of raw materials, including forest, agricultural and livestock waste, energy crops, and organic components of urban solid waste. These biomass raw materials can be directly used for power generation or heating through different routes, or can be converted into gaseous, liquid or solid fuels. Among the diversified utilization paths of biomass energy, thermochemical conversion technology is considered as a key technology to break through the bottleneck of large-scale application of biomass energy due to its high energy conversion efficiency and flexible product regulation characteristics. Pyrolysis and gasification are considered as the most attractive method among various waste energy technologies. Gasification technology not only helps to improve waste management efficiency, but also provides a broad prospect for clean energy production with low carbon emissions. Through the gasification process, biomass is converted into synthesis gas, which can not only be used for the production of heat and electricity, but also can further generate other high-value-added products. Dimethyl ether has significant application potential due to its high cetane number and low emission characteristics, and is considered as a high-quality alternative fuel for diesel, especially suitable for heavy transportation and industrial combustion scenarios.

[0003] The most common method of producing dimethyl ether at present is to first produce methanol and then perform a dehydration reaction, but it is limited by the carbon-hydrogen ratio of the biomass raw material, and additional purification of impurities generated in the gasification process is required. In contrast, the path of first preparing hydrogen and then reacting with carbon dioxide can accurately regulate the hydrogen-carbon ratio, improve the yield and selectivity of methanol and dimethyl ether, and enhance the flexibility of carbon sources by externally capturing carbon dioxide. This study innovatively proposes an integrated system for producing dimethyl ether based on urban solid waste, which produces hydrogen-rich synthesis gas through advanced gasification technology, and innovatively couples the Kalina cycle to realize waste heat power generation, effectively improving the energy cascade utilization rate of the system. The system integrates carbon capture and storage technology, and uses the captured CO2 and externally supplemented CO2 as carbon sources together in the catalytic reactor to synthesize dimethyl ether with hydrogen. SUMMARY

[0004] [PROBLEMS TO BE SOLVED]

[0005] The traditional urban solid waste treatment method has the bottlenecks of low energy conversion efficiency and high risk of secondary pollution, and the existing dimethyl ether preparation technology depends on fossil fuel raw materials, so that the carbon footprint in the production process is high. The present application proposes a direct synthesis process path, by integrating a Kalina cycle waste heat recovery system and a carbon capture technology, a new type of synergistic process with negative carbon emission characteristics is developed. Compared with the production method of adjusting the stoichiometric number (H2 / CO ratio) of synthesis gas after traditional organic solid waste gasification, the present system adopts a carbon dioxide hydrogenation technology route, which effectively utilizes additional carbon dioxide resources and significantly improves the product yield.

[0006] [Technical scheme]

[0007] The present application proposes a process method for preparing dimethyl ether by using coal and biomass as raw materials, steam and oxygen as gasifying agents, an alkaline electrolytic water hydrogen production unit and an S-CO2 Brayton cycle unit, which can reduce pollutant emissions and improve the conversion rate of low-grade energy.

[0008] The present process system uses municipal organic waste as raw material to prepare high-temperature synthesis gas (main components are H2, CO and CO2) through gasification reaction. For the heat recovery of high-temperature synthesis gas, a multi-stage waste heat utilization system is innovatively constructed: the synthesis gas is first heated by the heat exchanger and the Kalina cycle system arranged in parallel, and the heat is transferred to the ammonia-water binary working medium. The heated Kalina working medium is separated into gas and liquid phases in the separator, the ammonia-rich gas phase working medium drives the turbine expander to generate power, and the ammonia-lean liquid phase working medium is pressurized after condensation and returned to the system for reheating, thereby forming a closed thermodynamic cycle. The synthesis gas after waste heat utilization enters the water-gas shift section to undergo a water-gas shift reaction to increase the hydrogen content in the synthesis gas. The hydrogen-rich synthesis gas then enters the carbon capture system based on the chemical absorption method, and the CO2 is selectively adsorbed by the amino solvent to obtain a high-purity hydrogen source. The captured carbon dioxide is used as part of the carbon source for the subsequent reaction. After mixing, the CO2 and hydrogen are preheated by the heat exchanger and pressurized by the compressor, and then enter the reactor to directly generate DME, methanol and water under the action of the catalyst. The reaction products are cooled by the heat exchanger and then separated into gas and liquid phases in the separator, and the unreacted gas is recycled. Subsequently, the liquid products enter the rectifying column to separate DME as the main product, and the remaining liquid is further separated, wherein the methanol is recovered at the top of the column and recycled to the reactor to produce dimethyl ether.

[0009] According to the preferred embodiment of the application, the core feature of the Kalina cycle is that, for the temperature gradient characteristics of the gasification waste heat, the ammonia-water mixed working medium is used to realize high-efficiency recovery of the medium and low temperature waste heat (80-300 DEG C), and the temperature glide is matched through the non-azeotropic characteristics of the working medium, so that the waste heat power generation efficiency is improved; at the same time, the heat exchange network needs to be optimized and the working medium separation device needs to be added to adapt to the wide temperature range heat source, and if necessary, a composite cycle can be constructed, and the total power generation capacity of the system can be increased by 15-20%. In addition, through the isolation type heat exchange design, the ammonia working medium is avoided to cross the carbon capture process, while the carbon source utilization rate is taken into account, the incremental cost is exchanged for long-term low-carbon benefits, and energy-carbon synergistic effect is realized.

[0010] [Advantages]

[0011] Compared with the prior art, the application has the following advantages:

[0012] (1) By coupling the direct hydrogenation catalysis of CO2 in the gasification synthesis gas and the external supplemented CO2, the conversion of CO2 to dimethyl ether (DME) is realized in a single reactor, the intermediate link of methanol synthesis and dehydration in the traditional indirect process is omitted, the equipment investment and operation complexity are effectively reduced, and the carbon loss in the reaction process is reduced.

[0013] (2) The Kalina cycle is used to recover the medium and low temperature waste heat generated by the gasification system in stages, and heat energy is provided for the solvent regeneration and hydrogen compression of the CO2 capture unit, which significantly reduces the demand for external energy of the system.

[0014] (3) By integrating the biomass source MSW gasification and the recycling of captured CO2, the direct synthesis process realizes part of the carbon neutral input at the raw material end, and the process carbon emission is constrained by combining the carbon capture and storage technology, forming a technical closed loop of "waste resourceization-carbon directional conversion-negative carbon emission". [BRIEF DESCRIPTION OF DRAWINGS]

[0015] Attachment Figure 1 The application is a kind of waste efficient utilization of carbon dioxide hydrogenation direct synthesis dimethyl ether process.

[0016] In the figure, G01-gasifier, H01-heat exchanger 1, H02-heat exchanger 2, S01-flash tank 1, T01-turbine 1, H03-heat exchanger 3, H04-heat exchanger 4, R01-reactor 1, H05-heat exchanger 5, R02-reactor 2, H06-heat exchanger 6, S02-flash tank 2, C01-distillation column 1, H07-heat exchanger 7, C02-distillation column 2, S03-flash tank 3, H08-heat exchanger 8, R03-reactor 3, H09-heat exchanger 9, C03-distillation column 3, C04-distillation column 4. [DETAILED DESCRIPTION]

[0017] Example 1:

[0018] With 1000 kg / h municipal organic waste as raw material, high-temperature synthesis gas (containing H2 40-45%, CO 30-35%, CO2 15-20%) is generated in a gasification furnace (G01) at 800°C. The synthesis gas then enters a multi-stage waste heat recovery system: through the parallel arrangement of heat exchangers and a Kalina cycle system (ammonia-water working medium, mass ratio 70:30, initial pressure 2.5 MPa) for efficient heat exchange, the synthesis gas temperature is reduced to 200°C, and the working medium is heated and then enters a separator (S01) to realize phase separation; the ammonia-rich gas phase working medium (ammonia content >90%) drives a turbine expander (T01, isentropic efficiency 85%) to generate power, and the ammonia-lean liquid phase working medium (ammonia content <30%) is returned to the cycle after reheating by a condenser (H01, cooled to 40°C) and a booster pump (P01, pressure restored to 2.5 MPa), forming a closed thermodynamic cycle. The synthesis gas after waste heat recovery enters the water-gas shift section (reaction temperature 250°C, pressure 1.8 MPa), and the hydrogen content is increased to 55-60% by the action of the catalyst; the hydrogen-rich synthesis gas then enters the carbon capture system (amino solvent absorption tower C01, operating temperature 30°C, pressure 1.0 MPa), selectively adsorbs CO2 (capture rate >95%), and obtains high-purity hydrogen (purity >99%); the captured CO2 (purity >90%) is mixed with hydrogen at a molar ratio of 1:3 as a carbon source, preheated by a preheater (H02, heated to 300°C) and compressed by a compressor (K01, pressurized to 5.0 MPa) into a fixed-bed reactor (R01, catalyst Cu-Zn-Al, reaction temperature 280°C), and DME, methanol and water are synthesized. The reaction product is cooled by a cooler (H03, cooled to 50°C) and then enters a gas-liquid separator (S02), and the unreacted gas (containing H2, CO2) is recycled to the reaction section; the liquid phase product enters a rectifying column (C02, top temperature 65°C, bottom temperature 150°C), and 500 kg / h DME is separated as the main product, and the recovered methanol at the top is returned to the reactor (R01) to recycle and dehydrate to produce DME.

[0019] Example 2:

[0020] With 1000 kg / h municipal organic waste as raw material, high-temperature synthesis gas (containing H2 45-50%, CO 25-30%, CO2 15-20%) is generated in a gasifier (G01) at 850℃. The synthesis gas then enters a multi-stage waste heat recovery system: through the parallel arrangement of heat exchangers and a Kalina cycle system (ammonia-water working medium, mass ratio 70:30, initial pressure 2.5 MPa) for efficient heat exchange, the synthesis gas temperature is reduced to 200℃, and the working medium is separated into gas and liquid phases in a separator (S01). The ammonia-rich gas phase working medium (ammonia content >90%) drives a turbine expander (T01, isentropic efficiency 85%) to generate power, and the ammonia-lean liquid phase working medium (ammonia content <30%) is condensed in a condenser (H01, cooled to 40℃) and pressurized by a booster pump (P01, pressure restored to 2.5 MPa) before returning to the cycle for reheating, forming a closed thermodynamic cycle. The synthesis gas after waste heat recovery enters a water-gas shift section (reaction temperature 250℃, pressure 1.8 MPa), and the hydrogen content is increased to 55-60% through the action of a catalyst. The hydrogen-rich synthesis gas then enters a carbon capture system (amino solvent absorption tower C01, operating temperature 30℃, pressure 1.0 MPa), selectively adsorbs CO2 (capture rate >95%), and obtains high-purity hydrogen (purity >99%). The captured CO2 (purity >90%) is mixed with hydrogen at a molar ratio of 1:3 as a carbon source, preheated by a preheater (H02, heated to 300℃), and pressurized by a compressor (K01, pressurized to 5.0 MPa) before entering a fixed-bed reactor (R01, catalyst Cu-Zn-Al, reaction temperature 280℃). DME, methanol, and water are synthesized. The reaction products are cooled by a cooler (H03, cooled to 50℃) and then enter a gas-liquid separator (S02), and the unreacted gas (containing H2 and CO2) is recycled to the reaction section. The liquid phase product enters a rectifying column (C02, top temperature 65℃, bottom temperature 150℃), and 520 kg / h DME is separated as the main product. The recovered methanol at the top of the column is returned to the reactor (R01) for dehydration and DME production.

Claims

1. A process for direct synthesis of dimethyl ether from carbon dioxide and hydrogen by efficient utilization of waste, the process is mainly characterized by The device used in the process comprises the following parts: G01-gasifier, H01-heat exchanger 1, H02-heat exchanger 2, S01-flash tank 1, T01-turbine 1, H03-heat exchanger 3, H04-heat exchanger 4, R01-reactor 1, H05-heat exchanger 5, R02-reactor 2, H06-heat exchanger 6, S02-flash tank 2, C01-distillation column 1, H07-heat exchanger 7, C02-distillation column 2, S03-flash tank 3, H08-heat exchanger 8, R03-reactor 3, H09-heat exchanger 9, C03-distillation column 3, C04-distillation column 4. The process for directly synthesizing dimethyl ether from carbon dioxide and hydrogen by efficient utilization of waste mainly comprises the following steps: (1) using urban organic waste as raw material, high-temperature synthesis gas (main components are H2, CO and CO2) is generated through gasification reaction; (2) the high-temperature synthesis gas is heat-exchanged with the Kalina cycle system through parallel heat exchangers, and the ammonia-water working medium is separated into rich ammonia gas phase and lean ammonia liquid phase after heat absorption; the rich ammonia gas phase drives the turbine to generate power, and the liquid phase returns to the system after condensation and pressure increase to form a closed thermodynamic cycle; (3) the synthesis gas after waste heat recovery enters the water-gas shift section, and the hydrogen content is increased through the water-gas shift reaction to generate hydrogen-rich synthesis gas; (4) the hydrogen-rich synthesis gas is selectively adsorbed by the amino solvent chemical absorption method to obtain high-purity hydrogen, and the captured CO2 is stored as a subsequent carbon source; (5) the CO2 and hydrogen are preheated and pressurized after mixing, and react to generate dimethyl ether (DME), methanol and water under the action of a catalyst; (6) the reaction products are separated after cooling, and the unreacted gas part is returned to the reactor for recycling; (7) the liquid phase products are separated by a distillation column to obtain DME as the main product, and the remaining liquid is further separated to recover methanol, which is recycled to the reactor for DME production.

2. The process for direct synthesis of dimethyl ether from carbon dioxide and hydrogen by hydrogenation for efficient use of waste according to claim 1, characterized in that The urban solid waste can be efficiently converted into dimethyl ether and electric energy.

3. The process for direct synthesis of dimethyl ether from carbon dioxide and hydrogen by hydrogenation for efficient use of waste according to claim 1, characterized by, The urban solid waste is used as synthesis gas, and the temperature of the crude synthesis gas is relatively high, so the heat can be used to generate power through the Kalina cycle.

4. The process for direct synthesis of dimethyl ether from carbon dioxide and hydrogen by hydrogenation for efficient use of waste according to claim 1, characterized by, The captured carbon dioxide is used as part of the raw material through carbon capture technology.

5. The process for direct synthesis of dimethyl ether from carbon dioxide and hydrogen by hydrogenation for efficient use of waste according to claim 1, characterized by, The hydrogen-rich synthesis gas after water-gas shift and carbon capture is used for direct synthesis of dimethyl ether from carbon dioxide and hydrogen.

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