A method for producing low-carbon olefins from coal

Abstract

The application discloses a method and system for producing low-carbon olefins by taking coal as raw material, and can improve carbon utilization rate of the process of producing low-carbon olefins from coal, reduce carbon dioxide emission of the process, shorten the process flow, and realize clean, efficient and green utilization of coal according to local conditions. The application directly synthesizes olefins from synthesis gas, and does not need to produce methanol from synthesis gas and then produce olefins from the methanol, so that the process is short and construction investment is low.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical industry, specifically relating to a system and process for producing low-carbon olefins from coal. Background Technology

[0002] Low-carbon olefins generally refer to olefins with 2-4 carbon atoms, mainly including ethylene, propylene and butene. They are the most important chemical products and synthetic material monomers in the petrochemical industry and occupy a pivotal position in the national economy.

[0003] In recent years, my country's coal chemical industry has developed rapidly, and coal-to-olefins technology, as one of the important routes for olefin production, has developed rapidly and now occupies a significant proportion of domestic olefin production capacity. The routes for producing low-carbon olefins from coal are mainly divided into two categories: one is the indirect route, which involves coal to methanol via syngas, followed by methanol-to-olefins (MTO); the other is the direct route, which involves coal to low-carbon olefins in a single step via syngas. The former has been successfully implemented industrially. This route mainly consists of air separation, coal gasification, shift conversion, syngas to methanol, and methanol-to-olefins. However, this route is relatively long, and because the hydrogen-to-carbon ratio in the crude syngas from coal gasification cannot meet the requirements for subsequent methanol synthesis, the crude syngas needs to enter a shift conversion unit to convert some of the carbon monoxide into hydrogen and carbon dioxide to meet the hydrogen-to-carbon ratio required for methanol synthesis. Therefore, this reduces carbon utilization and increases carbon dioxide emissions. Furthermore, this route generates a large amount of wastewater in the methanol-to-olefins section, resulting in relatively high water consumption. In recent years, direct coal-to-olefins from syngas has received continuous attention due to its advantages of a shorter route and lower water consumption.

[0004] Patent document CN108017480A discloses an apparatus and method for directly producing low-carbon olefins from coal via syngas. This apparatus includes a coal gasification unit, a syngas purification unit, a reaction-to-olefins unit, and a gas recovery and olefin separation unit. A syngas mixer is installed between the syngas purification unit and the reaction-to-olefins unit. This patent eliminates the water-gas shift conversion unit, achieving the required hydrogen-to-carbon ratio for the olefins-to-olefins unit by fully recovering unconverted syngas from the reaction outlet gas. However, this method is only applicable to water-coal slurry gasification technology and cannot be applied to pulverized coal gasification technology, which produces crude syngas with an even lower hydrogen-to-carbon ratio. Summary of the Invention

[0005] This invention provides a method and system for producing low-carbon olefins from coal. This method and system can improve the carbon utilization rate of the coal-to-low-carbon olefins process, reduce carbon dioxide emissions, shorten the process flow, and achieve efficient, clean and green utilization of coal.

[0006] To achieve the above objectives, the present invention provides a method for producing low-carbon olefins from coal, specifically:

[0007] A method for producing low-carbon olefins from coal, characterized in that:

[0008] 1) The electricity generated by the renewable energy power generation system is sent to the water electrolysis hydrogen production system to obtain hydrogen and oxygen through water electrolysis;

[0009] 2) The oxygen produced in step 1) is sent to the coal gasification system to undergo a partial oxidation reaction to obtain crude syngas;

[0010] 3) The crude syngas is sent to the crude syngas purification system to remove impurities and obtain purified syngas that meets the requirements for syngas to olefins.

[0011] 4) After the purified syngas is mixed with the first cycle syngas produced in step 7) and the second cycle syngas produced in step 9), the hydrogen produced in step 1) is added to adjust the hydrogen-to-carbon ratio in the syngas to meet the requirements of the syngas to olefins system.

[0012] 5) In the syngas-to-olefins system, the mixed syngas reacts under the action of a catalyst to produce C1-C10 hydrocarbons. The outlet reactant gas of the syngas-to-olefins system is a mixture of C1-C10 hydrocarbons and unconverted syngas.

[0013] 6) The syngas-to-olefins output reaction gas enters the reaction gas purification system to remove impurities and obtain purified reaction gas;

[0014] 7) The purified reaction gas enters the reaction gas roughing system to separate and obtain the first cycle syngas and hydrocarbon-rich reaction gas. The first cycle syngas is pressurized and recycled back to the syngas to olefins system, and the hydrocarbon-rich reaction gas enters the reaction gas pressurization and drying system.

[0015] 8) The hydrocarbon-rich reaction gas is pressurized and dried in the reaction gas pressurization and drying system before entering the olefin separation system;

[0016] 9) The hydrocarbon-rich reaction gas is separated in the olefin separation system to obtain the product and the remaining unconverted syngas. The remaining unconverted syngas is used as the second circulating syngas and then recirculated back to the syngas to olefin system after being pressurized.

[0017] The present invention discloses a method for producing low-carbon olefins from coal, further characterized in that the method mainly comprises a renewable energy power generation system, an electrolysis water hydrogen production system, a coal gasification system, a crude syngas purification system, a syngas olefin production system, a reaction gas purification system, a reaction gas crude separation system, a reaction gas pressurization and drying system, and an olefin separation system.

[0018] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the renewable energy power generation system includes one or more combined power generation systems such as solar power generation, wind power generation, concentrated solar power (CSP), and geothermal power generation. Preferably, the renewable energy power generation system consists of solar power generation facilities and wind power generation facilities, wherein the solar power generation facilities include photovoltaic modules, inverters, and photovoltaic transformers; and the wind power generation facilities include wind turbines and wind transformers.

[0019] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the water electrolysis hydrogen production system includes one or more combinations of alkaline water electrolysis hydrogen production systems, proton exchange membrane hydrogen production systems, anion exchange membrane hydrogen production systems, and high-temperature solid oxide hydrogen production systems. Preferably, the water electrolysis hydrogen production system is an alkaline water electrolysis hydrogen production system, which consists of an electrolysis section, a gas-liquid separation section, and a hydrogen purification section. The electrolysis section mainly includes an electrolytic cell, a transformer, and a rectifier; the gas-liquid separation section mainly includes a gas-liquid separator, a washing cooler, an alkaline cooler, and an alkaline circulating pump; and the hydrogen purification section mainly includes a deoxygenator, a dryer, and a cooler.

[0020] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the coal gasification system can employ a coal-water slurry gasification process or a pulverized coal gasification process. The coal gasification reaction temperature is 1100–1600℃, the pressure is 4.0–8.0 MPa, preferably 4.0–6.5 MPa, and the hydrogen-to-carbon molar ratio of the crude syngas produced is (0.4–1):1, preferably (0.4–0.8):1.

[0021] The present invention provides a method for producing low-carbon olefins from coal, further characterized in that: the crude syngas produced by the coal gasification system does not require water-gas conversion and can be directly entered into the crude syngas purification system.

[0022] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the crude syngas purification system employs an absorbent to physically absorb and remove acidic gases such as CO2, H2S, and COS from the crude syngas. The absorbent includes methanol, sulfolane, polyethylene glycol dimethyl ether, and alkanolamines, preferably methanol.

[0023] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: after mixing purified syngas with first-cycle syngas and second-cycle syngas, at least a portion of hydrogen produced by a water electrolysis hydrogen production system is added. The hydrogen-to-carbon ratio in the syngas entering the syngas-to-olefins system is adjusted by adding hydrogen produced from the water electrolysis hydrogen production system. The hydrogen-to-carbon molar ratio of the mixed syngas at the inlet of the syngas-to-olefins system is (1.0–3):1, preferably (2.0–2.5):1.

[0024] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the reaction conditions of the syngas-to-olefins system are a reaction temperature of 300–500°C and a reaction pressure of 2.0–7.0 MPa.G, preferably 380–420°C and 4.0–6.0 MPa.G. The syngas-to-olefins system employs a bifunctional catalyst composed of oxides and molecular sieves. The syngas-to-olefins system can employ one or more of a fixed-bed reactor, a moving-bed reactor, and a fluidized-bed reactor; as a preferred embodiment, a fixed-bed reactor is used.

[0025] This invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the reaction gas purification system is mainly used to remove oxygen-containing compounds, heavy hydrocarbons, and acidic gases from the reaction gas. The oxygen-containing compounds include one or more of methanol, dimethyl ether, ethanol, propionaldehyde, and acetone. The acidic gas is mainly CO2 generated by the syngas to olefins system reaction. The oxygen-containing compounds and heavy hydrocarbons can be removed by physical adsorption or absorption using an adsorbent. Preferably, the oxygen-containing compounds and heavy hydrocarbons in the reaction gas are removed by water washing in a water washing tower. The acidic gas can be removed by physical absorption using an adsorbent or by chemical reaction using an alkaline substance. Preferably, the acidic gas in the reaction gas is removed by a 5wt%–20wt% alkaline solution.

[0026] The present invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the reaction gas coarse separation system adopts one or more of the following technologies: pressure swing adsorption separation, membrane separation, and solvent absorption. As a preferred embodiment, pressure swing adsorption separation separates most of the unconverted syngas from C1 to C10 hydrocarbons.

[0027] The present invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the proportion of the first circulating syngas obtained by the reaction gas coarse separation system to the unconverted syngas in the purified reaction gas (i.e., the syngas recovery rate) is 80-99.9%, preferably 95-99%.

[0028] The present invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the olefin separation system adopts a cryogenic separation method, which can be one of a pre-propane removal process, a pre-ethane removal process, or a sequential separation process, and mainly consists of a demethanizer, a deethaner, an ethylene distillation column, a depropanizer, a propylene distillation column, a debutanizer, and a refrigerant compressor.

[0029] The present invention discloses a method for producing low-carbon olefins from coal, further characterized in that: the remaining unconverted syngas obtained from the olefin separation system is used as a second circulating syngas, pressurized, and then recycled back to the syngas-to-olefins system.

[0030] The present invention has the following beneficial effects:

[0031] 1. This invention uses syngas to directly produce olefins, eliminating the need to produce methanol from syngas and then olefins from methanol, which has the advantages of a shorter process and lower construction investment.

[0032] 2. This invention uses renewable energy to generate electricity, electrolyzes water to produce hydrogen and oxygen, provides the oxygen required for gasification in the coal gasification system, and provides the hydrogen required for the hydrogen-to-carbon ratio in the syngas-to-olefins system. At the same time, it realizes the consumption of green electricity, reduces the scale of air separation in existing technologies, and greatly reduces carbon emissions in the coal utilization process.

[0033] 3. This invention eliminates the water-gas conversion process, reducing carbon emissions during coal utilization while improving carbon utilization efficiency. Furthermore, this invention adjusts the hydrogen-to-carbon ratio in the syngas by adding green hydrogen, adapting to the carbon-to-hydrogen ratio of the syngas output from different coal gasification technologies.

[0034] 4. This invention separates most of the unconverted syngas first through the reaction gas coarse separation system, which greatly reduces the load on the subsequent olefin separation system and has the advantages of low energy consumption and low equipment investment. Attached Figure Description

[0035] Appendix Figure 1 This invention provides a schematic flowchart of a method for producing low-carbon olefins from coal.

[0036] The attached diagram is labeled as follows: 1-Wind power generation system, 2-Photovoltaic power generation system, 3-Water electrolysis hydrogen production system, 4-Pulverized coal gasification system, 5-Air separation system, 6-Low-temperature methanol washing system, 7-Syngas to olefins system, 8-Syngas water washing tower, 9-Alkali washing tower, 10-Pressure swing adsorption separation system, 11-Rich hydrocarbon reaction gas compressor, 12-Rich hydrocarbon reaction gas dryer, 13-Olefin separation system, S1-Electricity generated by the wind power generation system, S2-Electricity generated by the photovoltaic power generation system. S3 - Oxygen produced by the water electrolysis hydrogen production system; S4 - Hydrogen produced by the water electrolysis hydrogen production system; S5 - Oxygen produced by air separation; S6 - Crude syngas; S7 - Purified syngas; S8 - Mixed syngas; S9 - Outlet reaction gas from the syngas to olefins system; S10 - Reaction gas after water washing; S11 - Reaction gas after alkali washing; S12 - First cycle syngas; S13 - Hydrocarbon-rich reaction gas; S14 - Hydrocarbon-rich reaction gas after pressurization; S15 - Hydrocarbon-rich reaction gas after drying; S16 - Second cycle syngas. Detailed Implementation

[0037] The implementation of the technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0038] To better understand the technical solution of the present invention, the following embodiments further illustrate the content of the present invention.

[0039] like Figure 1 As shown, this embodiment is equipped with a wind power generation system 1 and a photovoltaic power generation system 2. The generated electricity is sent to a water electrolysis hydrogen production system 3, where oxygen and hydrogen are produced through electrolysis. To improve the carbon utilization rate of coal and reduce the water consumption in the coal gasification process, this embodiment adopts a pulverized coal gasification process.

[0040] Oxygen S5 produced by air separation system 5 and oxygen S3 produced by water electrolysis hydrogen production system are sent together to pulverized coal gasification system 4, where partial oxidation reaction occurs to produce crude syngas S6. The crude syngas enters low-temperature methanol washing system 6 directly without conversion to remove acidic gases such as CO2, H2S, and COS from the crude syngas S6, thereby obtaining purified syngas S7.

[0041] Purified syngas S7 is mixed with first-cycle syngas S12 and second-cycle syngas S16, and then a portion of hydrogen S4 produced by the water electrolysis hydrogen production system 3 is added, thus ensuring that the hydrogen-to-carbon ratio in the mixed syngas S8 meets the requirements of the syngas-to-olefins system 7. Within the syngas-to-olefins system 7, the mixed syngas, under the action of the catalyst bed in the reactor, generates C1-C10 hydrocarbons, while also producing byproducts such as methanol, dimethyl ether, aldehydes, and ketones. Since the CO conversion rate in the syngas is approximately 50%, the outlet reaction gas S9 of the syngas-to-olefins system consists of unreacted syngas, the generated C1-C10 hydrocarbons, and a small amount of byproducts.

[0042] In the syngas to olefins system 7, the reactor outlet material is cooled to 40°C after heat recovery and sent to the syngas water scrubbing tower 8. In the syngas water scrubbing tower 8, oxygen-containing compounds such as methanol, dimethyl ether, aldehydes, and ketones, as well as a small amount of heavy hydrocarbons, are removed from the syngas to olefins system outlet reaction gas S9 by water scrubbing. After water scrubbing, the reaction gas S10 is sent to the alkaline scrubbing tower 9 to remove CO2 before being sent to the pressure swing adsorption (PSA) separation system 10. In the PSA separation system 10, unreacted syngas in the alkaline-scrubbed reaction gas S11 is separated by PSA and used as the first circulating syngas S12, which is then pressurized and sent back to the syngas to olefins system 7.

[0043] The CO recovery rate in the first cycle synthesis gas S12 is approximately 95%, and the H2 recovery rate is approximately 99%. The desorbed gas from the pressure swing adsorption separation system 10 is the hydrocarbon-rich reaction gas S13. The hydrocarbon-rich reaction gas S13 is at approximately 35°C and a pressure of approximately 0.02 MPa. After being pressurized to 2.0–4.5 MPa by the hydrocarbon-rich reaction gas compressor 11, it enters the hydrocarbon-rich reaction gas dryer 12 to remove the water content in the pressurized hydrocarbon-rich reaction gas S14 to 0.5–10 ppmw, and then it is sent to the olefin separation system 13.

[0044] The olefin separation system 13 employs a cryogenic separation technology sequential separation process, consisting of a demethanizer, a deethaner, an ethylene distillation column, a depropanizer, a propylene distillation column, a debutanizer, and a refrigerant compressor. The dried hydrocarbon-rich reaction gas S15 is separated within the olefin separation system 13 to obtain methane, ethane, polymer-grade ethylene, polymer-grade propylene, mixed C4 and C5+ products. Simultaneously, the remaining syngas is used as a second-cycle syngas S16, which is pressurized and returned to the syngas-to-olefins system 7 for recycling.

[0045] The above are merely typical embodiments of the present invention. It should be noted that those skilled in the art can make several improvements or substitutions without departing from the principles described in the present invention, and these improvements or substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing low-carbon olefins from coal, characterized in that: 1) The electricity generated by the renewable energy power generation system is sent to the water electrolysis hydrogen production system to obtain hydrogen and oxygen through water electrolysis; 2) The oxygen produced in step 1) is sent to the coal gasification system to undergo a partial oxidation reaction to obtain crude syngas; 3) The crude syngas is sent to the crude syngas purification system to remove impurities and obtain purified syngas that meets the requirements for syngas to olefins. 4) After the purified syngas is mixed with the first cycle syngas produced in step 7) and the second cycle syngas produced in step 9), the hydrogen-to-carbon ratio in the syngas is adjusted by adding the hydrogen produced in step 1) to meet the requirements of the syngas to olefins system. 5) In the syngas-to-olefins system, mixed syngas reacts under the action of a catalyst to produce C1-C10 hydrocarbons. The outlet reactant gas of the syngas-to-olefins system is a mixture of C1-C10 hydrocarbons and unconverted syngas. 6) The syngas-to-olefins output reaction gas enters the reaction gas purification system to remove impurities and obtain purified reaction gas; 7) The purified reaction gas enters the reaction gas roughing system to separate and obtain the first cycle syngas and hydrocarbon-rich reaction gas. The first cycle syngas is pressurized and recycled back to the syngas to olefins system, and the hydrocarbon-rich reaction gas enters the reaction gas pressurization and drying system. 8) The hydrocarbon-rich reaction gas is pressurized and dried in the reaction gas pressurization and drying system before entering the olefin separation system; 9) The hydrocarbon-rich reaction gas is separated in the olefin separation system to obtain the product and the remaining unconverted syngas. The remaining unconverted syngas is used as the second circulating syngas and then recirculated back to the syngas to olefin system after being pressurized.

2. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The method mainly consists of a renewable energy power generation system, an electrolysis water hydrogen production system, a coal gasification system, a crude syngas purification system, a syngas olefin production system, a reaction gas purification system, a reaction gas crude separation system, a reaction gas pressurization and drying system, and an olefin separation system.

3. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The renewable energy power generation system includes one or more of the following combined power generation systems: solar power generation system, wind power generation system, concentrated solar power generation system, and geothermal power generation system.

4. The method for producing low-carbon olefins from coal according to claim 3, characterized in that: The renewable energy power generation system consists of solar power generation facilities and wind power generation facilities, wherein the solar power generation facilities include photovoltaic modules, inverters and photovoltaic power generation transformers; and the wind power generation facilities include wind turbines and wind power generation transformers.

5. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The water electrolysis hydrogen production system includes one or more combinations of alkaline water electrolysis hydrogen production system, proton exchange membrane hydrogen production system, anion exchange membrane hydrogen production system, and high-temperature solid oxide hydrogen production system.

6. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The coal gasification system adopts a coal-water slurry gasification process or a pulverized coal gasification process; the coal gasification reaction temperature is 1100-1600℃, the pressure is 4.0-8.0MPa, and the hydrogen-carbon molar ratio of the crude syngas produced is (0.4-1):

1.

7. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The crude syngas purification system uses an absorbent to physically absorb and remove CO2, H2S, and COS acidic gases from the crude syngas; the absorbent includes methanol, sulfolane, polyethylene glycol dimethyl ether, and alkanolamines.

8. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: After the purified syngas is mixed with the first and second cycle syngas, at least a portion of the hydrogen produced by the water electrolysis hydrogen production system is added. The hydrogen-to-carbon ratio in the syngas entering the syngas to olefins system is adjusted by adding the hydrogen produced by the water electrolysis hydrogen production system. The hydrogen-to-carbon molar ratio of the mixed syngas at the inlet of the syngas to olefins system is (1.0 to 3):

1.

9. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The reaction conditions for the syngas-to-olefins system are a reaction temperature of 300–500 °C and a reaction pressure of 2.0–7.0 MPa.G.

10. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The syngas-to-olefins system employs a bifunctional catalyst composed of oxides and molecular sieves; the syngas-to-olefins system employs one or more combinations of fixed-bed reactors, moving-bed reactors, and fluidized-bed reactors.

11. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The reaction gas purification system is mainly used to remove oxygen-containing compounds, heavy hydrocarbons, and acidic gases from the reaction gas; the oxygen-containing compounds include one or more of methanol, dimethyl ether, ethanol, propionaldehyde, and acetone; the acidic gases are mainly CO2 generated by the syngas to olefins system; the oxygen-containing compounds and heavy hydrocarbons can be removed by physical adsorption with adsorbents or by physical absorption with absorbents.

12. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The reaction gas rough separation system employs one or more of the following technologies: pressure swing adsorption separation, membrane separation, and solvent absorption, to separate most of the unconverted syngas from C1 to C10 hydrocarbons.

13. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The proportion of the first-cycle syngas obtained from the separation of the reaction gas coarse separation system to the unconverted syngas in the purified reaction gas (i.e., the syngas recovery rate) is 80-99.9%.

14. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The olefin separation system employs a cryogenic separation method, which can be one of the following: a pre-propane removal process, a pre-ethane removal process, or a sequential separation process. It mainly consists of a demethanizer, a deethaner, an ethylene distillation column, a depropanizer, a propylene distillation column, a debutanizer, and a refrigerant compressor.

15. The method for producing low-carbon olefins from coal according to claim 1, characterized in that: The remaining unconverted syngas obtained from the olefin separation system is used as the second circulating syngas, pressurized, and then recycled back to the syngas-to-olefins system.

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