A system and method for coupling pyrolysis and gasification to treat CO2 and phenolic wastewater

Abstract

The present invention discloses a system and method for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater, which relates to the technical field of hierarchical utilization of coal pyrolysis and gasification. The system includes a downer pyrolysis furnace and a fixed-bed gasification furnace connected to each other, as well as a gas-liquid separator, a low-temperature methanol washing device, and an oil-water separator. The treatment process is as follows: lump coal raw materials are in counter-current contact with high-temperature gasified coal gas in the downer pyrolysis furnace for pyrolysis. The semicoke produced by pyrolysis enters the fixed-bed gasification furnace for gasification reaction. The high-temperature gasified coal gas produced by the gasification reaction is returned to the downer pyrolysis furnace as the heat source and pyrolysis medium required for pyrolysis. The phenolic wastewater and carbon dioxide produced after pyrolysis can be returned to the fixed-bed gasification furnace as gasification agents to participate in the gasification reaction at the same time. The present invention improves the heat transfer efficiency of the pyrolysis-gasification process, realizes the process of comprehensively treating carbon dioxide and phenolic wastewater, improves the overall carbon conversion rate, and realizes product diversification.

Description

Technical Field

[0001] The present invention relates to the technical field of coal pyrolysis and gasification hierarchical utilization technology, and particularly relates to a system for coupling pyrolysis and gasification to treat CO2 and phenolic wastewater. Background Art

[0002] Coal chemical industry is a coal processing and conversion industry that uses coal as the main raw material and aims to produce clean energy and chemical products. Based on the characteristics of China's lack of oil and gas resources and relatively rich coal resources, modern coal chemical industry relies on technological innovation to achieve the supplement and partial substitution of oil and natural gas resources, which is an important part of the national energy production and consumption revolution.

[0003] Coal gasification technology is known as the leader of the modern coal chemical industry. It can convert coal into simple and stable inorganic small molecules such as CO, H2, and CO2. However, it inevitably has problems such as a large amount of carbon dioxide emissions, high energy consumption levels, and low energy utilization efficiency.

[0004] Coal pyrolysis technology is the core technology for efficient conversion of modern coal by quality. It has various problems such as low tar yield, low energy utilization efficiency of the reaction system, serious coking, difficult conversion and utilization of semi-coke, and difficult treatment of phenolic wastewater.

[0005] To solve the problems existing in coal gasification and coal pyrolysis, the invention patent CN201710946347 proposes a downer-fixed bed pyrolysis-gasification integration method. This method uses a downer bed pyrolysis and a fixed bed gasification process, and uses high-temperature coal gas as the pyrolysis medium to improve the heat transfer efficiency. However, since the gasified coal gas and pulverized coal are in a co-current contact mode, the heat transfer efficiency is not maximized, and the phenolic wastewater generated during the reaction process is difficult to treat, and the carbon dioxide emissions are large.

[0006] Although the existing pyrolysis-gasification technology has solved the disadvantages of the traditional coal conversion technology that cannot effectively and cleanly utilize coal to a certain extent, due to the limitations of its process flow, problems such as large carbon dioxide emissions, large wastewater emissions, high energy consumption levels, and low energy utilization efficiency have emerged.

[0007] Therefore, how to more reasonably improve the heat transfer efficiency of the pyrolysis-gasification process and reduce the emissions of carbon dioxide and wastewater is the key to the development of truly low-carbon and green hierarchical utilization of pyrolysis-gasification. Summary of the Invention

[0008] To solve the above technical problems, the present invention discloses a system and method for coupling pyrolysis and gasification to treat CO2 and phenolic wastewater. The system reasonably couples pyrolysis and gasification into one. The lump coal raw material contacts countercurrently with the high-temperature gasified coal gas in the downer pyrolysis furnace for pyrolysis. The semicoke produced by pyrolysis enters the fixed-bed gasification furnace for gasification reaction. The high-temperature gasified coal gas produced by the gasification reaction is returned to the downer pyrolysis furnace as the heat source and pyrolysis medium required for pyrolysis. The phenolic wastewater and carbon dioxide produced after pyrolysis can be simultaneously returned to the fixed-bed gasification furnace as gasifying agents to participate in the gasification reaction. The present invention realizes the co-production of syngas and tar and achieves the purpose of comprehensively treating carbon dioxide and phenolic wastewater.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A system for coupling pyrolysis and gasification to treat CO2 and phenolic wastewater includes a connected downer pyrolysis furnace and a fixed-bed gasification furnace, and also includes a gas-liquid separator, a low-temperature methanol washing device, and an oil-water separator;

[0011] The top of the downer pyrolysis furnace is provided with a lump coal inlet, the bottom is provided with a semicoke outlet, one side of the upper part is provided with a pyrolysis gas mixture outlet, and one side of the lower part is provided with a gasified coal gas inlet;

[0012] The top of the fixed-bed gasification furnace is provided with a semicoke inlet, one side of the upper part is provided with a gasified coal gas outlet, the bottom is provided with a gasification residue outlet, and an oxygen inlet, a phenolic wastewater inlet, and a carbon dioxide inlet are also provided in the lower part of the fixed-bed gasification furnace;

[0013] The pyrolysis gas mixture outlet on the downer pyrolysis furnace is connected to the inlet of the cooler, the outlet of the cooler is connected to the middle inlet of the gas-liquid separator, the gas-phase outlet at the top of the gas-liquid separator is connected to the inlet of the low-temperature methanol washing device, the carbon dioxide outlet on the low-temperature methanol washing device is connected to the carbon dioxide inlet on the fixed-bed gasification furnace, the oil-water mixture outlet at the bottom of the gas-liquid separator is connected to the oil-water mixture inlet at the top of the oil-water separator, and a phenolic wastewater outlet is provided on one side of the upper part of the oil-water separator. The phenolic wastewater outlet is connected to the phenolic wastewater inlet on the fixed-bed gasification furnace;

[0014] The semicoke outlet on the downer pyrolysis furnace is connected to the semicoke inlet on the fixed-bed gasification furnace, and the gasified coal gas outlet on the fixed-bed gasification furnace is connected to the gasified coal gas inlet on the downer pyrolysis furnace.

[0015] As a further aspect of the present invention, a purified gas outlet is also provided on the low-temperature methanol washing device.

[0016] As a further aspect of the present invention, a heavy oil outlet is also provided at the bottom of the oil-water separator, and the discharged heavy oil is a coal tar product.

[0017] Further, in the present invention, the gasification residue outlet on the fixed bed gasifier is communicated with the inlet of the slag hopper.

[0018] The present invention also discloses a method for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater, which uses the above-mentioned system for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater. The specific process is as follows:

[0019] Lump coal raw materials with a particle size of 10-50 mm enter the downer pyrolysis furnace through the lump coal inlet and contact the high-temperature gasified coal gas from the fixed bed gasifier in a countercurrent manner. The lump coal is heated to 550-700 °C by the high-temperature gasified coal gas, and a rapid pyrolysis reaction can occur under normal pressure. While pyrolyzing and releasing volatile components, semicoke is also generated.

[0020] The pyrolysis gas mixture discharged from the upper part of the downer pyrolysis furnace enters the cooler and is cooled to 60-80 °C. After cooling, it enters the gas-liquid separator for gas-liquid separation. Most of the water and coal tar vapor are cooled into a liquid oil-water mixture, and the gas phase enters the low-temperature methanol washing unit to further remove the acidic gases therein.

[0021] The CO2 generated after the acid removal treatment in the low-temperature methanol washing unit enters the fixed bed gasifier as a gasification agent for the gasification reaction. The purified gas after removing the acidic gases can be directly used as a raw material for the downstream process.

[0022] The oil-water mixture discharged from the bottom of the gas-liquid separator is sent into the oil-water separator. The heavy oil therein is discharged from the heavy oil outlet of the oil-water separator, and the phenolic wastewater enters the fixed bed gasifier to participate in the gasification reaction.

[0023] The semicoke obtained after the rapid pyrolysis reaction is sent into the fixed bed gasifier and contacts the gasification agents O2, CO2, and phenolic wastewater entering from the lower part of the fixed bed gasifier. Under the conditions of 2.5-4 MPa and 1000-1250 °C, a gasification reaction occurs to generate high-temperature gasified coal gas and gasification residue. The high-temperature gasified coal gas is sent into the downer pyrolysis furnace to participate in the pyrolysis reaction, and the gasification residue falls into the slag hopper under the action of gravity for collection.

[0024] Further, in the present invention, the high-temperature gasified coal gas discharged from the upper part of the fixed bed gasifier contains CO, H2, CO2, and H2O, and the temperature of the high-temperature gasified coal gas is: 1000-1250 °C.

[0025] Further, in the present invention, the pyrolysis gas mixture discharged from the upper part of the downer pyrolysis furnace includes gasified coal gas, CH4, H2, CO, CO2, H2O, tar vapor, and phenols.

[0026] Further, in the present invention, the acidic gases entering the low-temperature methanol washing unit contain CO2, H2S, and COS.

[0027] Further, in the present invention, the oil-water mixture discharged from the bottom of the gas-liquid separator contains phenols, water, and coal tar.

[0028] The beneficial effects of the present invention are as follows compared with the prior art:

[0029] (1) Returning the carbon dioxide generated in the cold methanol wash unit to the fixed bed gasifier as one of the gasifying agents for the gasification reaction effectively reduces the carbon dioxide emissions and improves the carbon conversion rate.

[0030] (2) Returning the phenol-containing wastewater separated by the oil-water separator to the fixed bed gasifier as one of the gasifying agents for the gasification reaction effectively reduces the wastewater discharge. Additionally, the phenols in the wastewater can be decomposed into effective gases such as CO and H2 by the high-temperature gasification reaction.

[0031] (3) The heat source required for the pyrolysis reaction in the downer bed pyrolyzer is provided by the high-temperature gasified coal gas, eliminating the need for an additional pyrolysis heat source. Moreover, a countercurrent heat exchange is formed between the high-temperature gasified coal gas and the lump coal raw material in the downer bed pyrolyzer, greatly improving the heat exchange efficiency. At the same time, the high-temperature semi-coke in the downer bed pyrolyzer can directly enter the fixed bed gasifier for gasification without coke quenching.

[0032] The present invention reasonably couples the pyrolysis process and the gasification process into one, solving the technical problem of large carbon dioxide emissions in the existing pyrolysis-gasification technology, effectively reducing carbon emissions, improving the overall carbon conversion rate, and achieving product diversification; reducing the wastewater discharge and effectively treating the phenol-containing wastewater; reducing energy consumption and improving energy utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic process flow diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] A system for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater disclosed by the present invention, as shown in the figure, includes a downer-bed pyrolysis furnace and a fixed-bed gasification furnace connected to each other, as well as a gas-liquid separator, a low-temperature methanol washing device, and an oil-water separator. The pyrolysis process is completed in the downer-bed pyrolysis furnace, and the gasification process is completed in the fixed-bed gasification furnace. The gas-liquid separator is used to separate the cooled gas phase and liquid phase. The low-temperature methanol washing device is used to remove acidic gases, and the oil-water separator realizes the separation of heavy oil and phenolic wastewater.

[0036] At the top of the downer-bed pyrolysis furnace, there is a lump coal inlet, and the lump coal raw material for pyrolysis is fed into the downer-bed pyrolysis furnace through this inlet. At the bottom of the downer-bed pyrolysis furnace, there is a semicoke outlet for discharging the high-temperature semicoke generated during the pyrolysis process. On one side of the upper part of the downer-bed pyrolysis furnace, there is a pyrolysis gas mixture outlet for discharging the pyrolysis gas mixture obtained from the pyrolysis reaction in the downer-bed pyrolysis furnace. On one side of the lower part of the downer-bed pyrolysis furnace, there is a gasification gas inlet, and the high-temperature gasification gas generated by the gasification reaction in the fixed-bed gasification furnace enters the downer-bed pyrolysis furnace through this inlet to participate in the pyrolysis reaction.

[0037] At the top of the fixed-bed gasification furnace, there is a semicoke inlet, and the high-temperature semicoke obtained from the pyrolysis reaction enters the fixed-bed gasification furnace through this semicoke inlet. On one side of the upper part of the fixed-bed gasification furnace, there is a gasification gas outlet for discharging the high-temperature gasification gas generated by the gasification reaction from the fixed-bed gasification furnace. At the bottom of the fixed-bed gasification furnace, there is a gasification residue outlet. At the lower part of the fixed-bed gasification furnace, there are also an oxygen inlet, a phenolic wastewater inlet, and a carbon dioxide inlet, which are respectively used to introduce O2, phenolic wastewater, and CO2 into the fixed-bed gasification furnace.

[0038] In this system, the pyrolysis gas mixture outlet on the downer-bed pyrolysis furnace is connected to the inlet of the cooler, the outlet of the cooler is connected to the middle inlet of the gas-liquid separator, the gas phase outlet at the top of the gas-liquid separator is connected to the inlet of the low-temperature methanol washing device, the carbon dioxide outlet on the low-temperature methanol washing device is connected to the carbon dioxide inlet on the fixed-bed gasification furnace, the oil-water mixture outlet at the bottom of the gas-liquid separator is connected to the oil-water mixture inlet at the top of the oil-water separator, and on one side of the upper part of the oil-water separator, there is a phenolic wastewater outlet, and the phenolic wastewater outlet is connected to the phenolic wastewater inlet on the fixed-bed gasification furnace.

[0039] In addition, the semicoke outlet on the downer-bed pyrolysis furnace is connected to the semicoke inlet on the fixed-bed gasification furnace, and the gasification gas outlet on the fixed-bed gasification furnace is connected to the gasification gas inlet on the downer-bed pyrolysis furnace.

[0040] Particularly, a purified gas outlet is also provided on the above-mentioned low-temperature methanol washing device, and the obtained purified gas can be directly sent to the downstream reaction device as a raw material.

[0041] Specifically, a heavy oil outlet is further provided at the bottom of the above oil-water separator, and the discharged heavy oil becomes coal tar products.

[0042] Specifically, the gasification residue outlet on the above fixed bed gasifier is connected to the slag hopper inlet. The gasification residue obtained after the gasification reaction aggregates into ash in the slag hopper due to gravity and is discharged from the ash outlet at the bottom of the slag hopper.

[0043] A method for pyrolysis-gasification coupling treatment of CO2 and phenol-containing wastewater disclosed by the present invention specifically includes the following processes:

[0044] (1) Pyrolysis reaction

[0045] Lump coal raw materials with a particle size of 10 - 50 mm enter the downward moving bed pyrolysis furnace through the lump coal inlet and contact countercurrently with the high-temperature gasification gas from the fixed bed gasifier. In the downward moving bed pyrolysis furnace, the lump coal is rapidly heated to 550 - 700 °C by the high-temperature gasification gas, and a rapid pyrolysis reaction can occur under normal pressure. While pyrolyzing and releasing volatile components, semi-coke is also generated.

[0046] After the pyrolysis reaction, the pyrolysis gas mixture discharged from the upper part of the downward moving bed pyrolysis furnace includes gasification gas, CH4, H2, CO, CO2, H2O, tar vapor, phenols, etc.

[0047] (2) Cooling and gas-liquid separation

[0048] The pyrolysis gas mixture discharged from the upper part of the downward moving bed pyrolysis furnace enters the cooler and is cooled to 60 - 80 °C by the cooling medium. After cooling, it enters the gas-liquid separator for gas-liquid separation. At this time, most of the water and coal tar are cooled into a liquid-phase oil-water mixture, and the gas phase enters the low-temperature methanol washing unit to further remove the acidic gases therein.

[0049] (3) Gasification reaction

[0050] The acidic gases entering the low-temperature methanol washing unit contain CO2, H2S, and COS. The CO2 generated after the acid removal treatment in the low-temperature methanol washing unit enters the fixed bed gasifier as a gasification agent for the gasification reaction, and the purified gas after removing the acidic gases can be directly used as a raw material for the downstream process.

[0051] The oil-water mixture discharged from the bottom of the gas-liquid separator is sent into the oil-water separator. The heavy oil therein is discharged from the heavy oil outlet of the oil-water separator, and the phenol-containing wastewater will enter the fixed bed gasifier to participate in the gasification reaction.

[0052] The char obtained after fast pyrolysis reaction is fed into a fixed-bed gasifier, where it comes into contact with the gasifying agents O2, CO2 and phenolic wastewater entering from the lower part of the fixed-bed gasifier. Under the conditions of 2.5 - 4 MPa and 1000 - 1250 °C, a gasification reaction occurs to generate high-temperature gasified coal gas and gasification residue. The high-temperature gasified coal gas is fed into a downer pyrolysis furnace to participate in the pyrolysis reaction, and the gasification residue falls into a slag hopper for collection under the action of gravity.

[0053] The high-temperature gasified coal gas discharged from the upper part of the fixed-bed gasifier contains CO, H2, CO2 and H2O.

[0054] The oil-water mixture discharged from the bottom of the gas-liquid separator contains phenols, water and coal tar.

[0055] The present invention combines pyrolysis with gasification to achieve the co-production of syngas and tar, with the characteristics of high energy utilization rate, low carbon dioxide emission and low phenolic wastewater discharge, greatly reducing the production cost, being low-carbon and environmentally friendly, and having good application prospects.

[0056] Certainly, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A system for coupling pyrolysis and gasification to treat CO2 and phenolic wastewater, comprising a downer pyrolysis furnace and a fixed-bed gasification furnace connected to each other, characterized in that, It also includes a gas-liquid separator, a low-temperature methanol washing unit, and an oil-water separator; The top of the downer pyrolysis furnace is provided with a lump coal inlet, the bottom is provided with a semi-coke outlet, the upper side is provided with a pyrolysis gas mixture outlet, and the lower side is provided with a gasification gas inlet; The top of the fixed-bed gasifier is provided with a semi-coke inlet, the upper side is provided with a gasification gas outlet, the bottom is provided with a gasification residue outlet, and an oxygen inlet, a phenol-containing wastewater inlet, and a carbon dioxide inlet are also provided at the lower part of the fixed-bed gasifier; The pyrolysis gas mixture outlet on the downer pyrolysis furnace is connected to the inlet of the cooler, the outlet of the cooler is connected to the middle inlet of the gas-liquid separator, the gas-phase outlet at the top of the gas-liquid separator is connected to the inlet of the low-temperature methanol washing unit, the carbon dioxide outlet on the low-temperature methanol washing unit is connected to the carbon dioxide inlet on the fixed-bed gasifier, the oil-water mixture outlet at the bottom of the gas-liquid separator is connected to the oil-water mixture inlet at the top of the oil-water separator, a phenol-containing wastewater outlet is provided on the upper side of the oil-water separator, and the phenol-containing wastewater outlet is connected to the phenol-containing wastewater inlet on the fixed-bed gasifier; The semi-coke outlet on the downer pyrolysis furnace is connected to the semi-coke inlet on the fixed-bed gasifier, and the gasification gas outlet on the fixed-bed gasifier is connected to the gasification gas inlet on the downer pyrolysis furnace.

2. The pyrolysis-gasification coupling system for treating CO2 and phenolic wastewater according to claim 1, wherein A purified gas outlet is also provided on the low-temperature methanol washing unit.

3. The pyrolysis-gasification coupling system for treating CO2 and phenolic wastewater according to claim 1, wherein A heavy oil outlet is also provided at the bottom of the oil-water separator, and the discharged heavy oil is a coal tar product.

4. The pyrolysis-vaporization coupling system for treating CO2 and phenolic wastewater according to claim 1, wherein The gasification residue outlet on the fixed-bed gasifier is connected to the inlet of the slag hopper.

5. A method for coupling pyrolysis and gasification to treat CO2 and phenolic wastewater, using the device described in any one of claims 1-4, characterized in that, Specific process: Lump coal raw materials with a particle size of 10-50 mm enter the downer pyrolysis furnace through the lump coal inlet, and are in countercurrent contact with the high-temperature gasification gas from the fixed-bed gasifier. The lump coal is heated to 550-700 °C by the high-temperature gasification gas, and rapid pyrolysis reaction can occur under normal pressure. While pyrolyzing and releasing volatile components, semi-coke is also generated; The pyrolysis gas mixture discharged from the upper part of the downer pyrolysis furnace enters the cooler and is cooled to 60-80 °C. After cooling, it enters the gas-liquid separator for gas-liquid separation. Most of the water and coal tar steam are cooled into a liquid-phase oil-water mixture, and the gas phase enters the low-temperature methanol washing unit to further remove the acidic gases therein; The CO2 generated after the acid removal treatment in the low-temperature methanol washing unit enters the fixed-bed gasifier as a gasification agent for the gasification reaction, and the purified gas after removing the acidic gases can be directly used as a raw material for the downstream process; The oil-water mixture discharged from the bottom of the gas-liquid separator is sent into the oil-water separator. The heavy oil therein is discharged from the heavy oil outlet of the oil-water separator, and the phenol-containing wastewater will enter the fixed-bed gasifier to participate in the gasification reaction; The semi-coke obtained after the rapid pyrolysis reaction is sent into the fixed-bed gasifier, and is in contact with the gasification agents O2, CO2, and phenol-containing wastewater entering from the lower part of the fixed-bed gasifier. Under the conditions of 2.5-4 MPa and 1000-1250 °C, a gasification reaction occurs to generate high-temperature gasification gas and gasification residue. The high-temperature gasification gas is sent into the downer pyrolysis furnace to participate in the pyrolysis reaction, and the gasification residue falls into the slag hopper under the action of gravity for collection.

6. The method for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater according to claim 5, characterized in that, The high-temperature gasified coal gas discharged from the upper part of the fixed-bed gasifier contains CO, H2, CO2, and H2O, and the temperature of the high-temperature gasified coal gas is 1000 - 1250 °C.

7. The method for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater according to claim 5, wherein The pyrolysis gas mixture discharged from the upper part of the downer pyrolyzer includes gasified coal gas, CH4, H2, CO, CO2, H2O, tar vapor, and phenols.

8. The method for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater according to claim 5, characterized in that, The acid gas entering the low-temperature methanol washing unit contains CO2, H2S, and COS.

9. The method for pyrolysis-gasification coupling treatment of CO2 and phenolic wastewater according to claim 5, wherein, The oil-water mixture discharged from the bottom of the gas-liquid separator contains phenols, water, and coal tar.

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