Coal chemical gasification process for reducing fine slag residual carbon content

Abstract

A coal chemical gasification process for reducing the residual carbon content of fine slag includes: a gasifier vertically designed from top to bottom as a combustion chamber, a Boudouar reaction chamber, a downcomer, and a quench chamber; molten slag drips directly from the combustion chamber into the quench chamber via the downcomer, without passing through the Boudouar reaction chamber; high-temperature syngas from the combustion chamber directly enters the Boudouar reaction chamber from its lower side wall outlet; a portion of the CO2 removed by the purification unit is preheated and pressurized before being injected into the Boudouar reaction chamber; during the process of the high-temperature syngas entering the Boudouar reaction chamber, the residual carbon in the high-temperature syngas is fully stirred and comes into full contact with CO2, resulting in a Boudouar reaction; after entering the Boudouar reaction chamber, it undergoes another Boudouar reaction with the injected CO2; the high-temperature syngas after the reaction in the Boudouar reaction chamber enters the downcomer from the bottom outlet, and then enters the quench chamber for rapid cooling and dust removal. This process significantly improves carbon conversion rate and effective gas production rate without affecting the stability of liquid slag discharge from the gasifier, and reduces CO2 emissions. It has the advantages of low energy consumption, high gasification efficiency, good system stability, significant environmental benefits, and minimal investment increase.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical technology, specifically relating to a coal chemical gasification process for reducing the carbon content of fine slag, and particularly to a coal chemical gasification process that utilizes the high-temperature sensible heat of syngas to drive the Boudouar reaction to improve carbon conversion and reduce the carbon content of fine slag without affecting the stable operation of the gasifier. Background Technology

[0002] Coal gasification technology is a chemical technology that converts coal / carbon into combustible gases such as carbon monoxide and hydrogen through high-temperature reactions. It is a leading technology in the coal chemical industry. Fluidized bed gasification technology, due to its large production capacity and high carbon conversion rate, has become the preferred process for modern large-scale coal chemical projects. In fluidized bed gasification, the syngas temperature at the gasifier outlet is high, typically reaching 1250-1600℃, and is rich in sensible heat and unreacted carbon particles (residual carbon). How to handle and utilize this high-temperature syngas is crucial to determining the process's energy efficiency and economic viability.

[0003] Existing processes are mainly divided into two categories: quenching process and waste heat recovery (waste boiler) process. That is, the syngas is cooled down by quenching or by recovering heat through a waste heat boiler before entering the water washing / purification unit.

[0004] Quenching Process: CN1900234A discloses a quenching process for pressurized dry pulverized coal gasification, comprising five parts: pressurized dry pulverized coal gasification, water spray quenching, quenching chamber quenching, ash and slag discharge, and ash and water treatment. This process directly cools the high-temperature crude coal gas using water quenching. While this process can rapidly cool the gas and increase the water-to-gas ratio, it wastes most of the high-temperature sensible heat of the crude coal gas and also reduces the reactivity of the residual char at high temperatures.

[0005] Waste heat recovery process: CN110684562A discloses a gasifier with radiant heat exchange, which recovers part of the high-temperature sensible heat by-product steam through a radiant waste boiler. However, this process involves large equipment investment, complex structure, and risks of slagging and ash accumulation on the heat exchange surface and short operating cycle, especially with extremely stringent requirements for coal quality (such as ash melting point and viscosity-temperature characteristics).

[0006] To address the above issues, some existing technologies attempt to couple cooling with chemical reactions. For example: CN105154140A proposes a multi-stage fluidized bed coal gasification method coupled with high-temperature shift conversion. A "high-temperature shift section" is set up in the gasifier, and hydrogen production is increased by injecting water or steam to utilize the sensible heat of the coal gas to undergo a water-gas shift reaction (CO + H2O → CO2 + H2). This method utilizes sensible heat to convert CO into H2 and CO2, but it does not involve the resource utilization of CO2. Furthermore, directly injecting water into the gasifier will lower the reaction temperature inside the furnace, affecting liquid slag discharge.

[0007] CN105925313A proposes a carbon dioxide / coke gasification method involving a three-stage gasification process. Steam, pure oxygen, and dry pulverized coal are injected into the first furnace to generate syngas. Steam, carbon dioxide, and coke powder are injected into the second furnace. In the third furnace, coke blocks are used to react counter-currently with the syngas to induce the Boudouar reaction (C + CO2 ≒ 2CO). This scheme has significant drawbacks: firstly, the syngas temperature in the second furnace is significantly lower, which is unfavorable for the forward Boudouar reaction; secondly, a large amount of coke needs to be added to the third furnace instead of utilizing the residual coke carried by the syngas itself, leading to a complex process and increased energy consumption; and thirdly, temperature and reaction control within the counter-current moving bed reactor are difficult, making side reactions more likely.

[0008] In summary, existing technologies still have significant shortcomings in efficiently utilizing the high-temperature sensible heat of syngas while simultaneously achieving resource utilization of its inherent residual carbon and synergistically converting carbon dioxide to increase the production of usable gas. Developing a coal chemical gasification process that efficiently couples energy and materials without reducing the gasifier's thermal efficiency or interfering with stable ash discharge is a pressing technical challenge in this field. Summary of the Invention

[0009] This invention aims to overcome the shortcomings of existing technologies and provide a coal chemical gasification process that reduces the residual carbon content in fine slag. Without injecting any cold material into the combustion chamber of the gasifier or affecting its high-temperature liquid slag discharge stability, the sensible heat of the syngas itself is used to reinject the carbon dioxide removed by the purification unit from the upper part of the Boudouar reaction chamber of the gasifier, which further reacts with the residual carbon in the syngas to increase the yield of effective gas (CO) in the syngas, reduce CO2 emissions, and lower the residual carbon content in the fine slag.

[0010] This invention provides a coal chemical gasification process for reducing the residual carbon content of fine slag, comprising the following steps: Step 1: Direct delivery of high-temperature synthesis gas: The high-temperature syngas generated by the gasifier is directly transferred from the combustion chamber to the Boudouar reaction chamber without cooling, maintaining its temperature in the high-temperature zone required for the Boudouar reaction. Step 2, CO2 injection: The CO2 gas removed by the downstream purification unit is injected into the Boudouar reaction chamber; Step 3, the Boudouar reaction in the Boudouar reaction chamber: In the Boudouar reaction chamber, the residual carbon in the high-temperature syngas is fully mixed with CO2. The high-temperature sensible heat of the syngas drives the Boudouar reaction: C + CO2 ≒ 2CO, so that the residual carbon entrained in the syngas reacts with CO2 to generate CO. Step four, cooling and separation in the quench chamber: The syngas after the reaction in step three is transferred to a quench chamber for quenching to freeze the reaction and separate solid particles, resulting in cooled crude syngas.

[0011] Furthermore, the gasifier is vertically designed from top to bottom as a combustion chamber, a Boudouar reaction chamber, a downcomer, and a quench chamber.

[0012] Furthermore, step five involves removing and reusing CO2: The crude syngas from step four is purified and CO2 is removed, with at least a portion of the removed CO2 being returned to the Boudouar reaction chamber.

[0013] Furthermore, step six involves the treatment of the slag: The molten slag drips directly from the funnel at the bottom of the combustion chamber into the quench chamber via the downcomer, without passing through the Boudouar reaction chamber.

[0014] Furthermore, in step one, the high-temperature syngas from the combustion chamber of the gasifier is directly exported from the outlet on the lower side wall of the combustion chamber into the Boudouar reaction chamber of the gasifier.

[0015] Further, in step two, the CO2 removed by the purification unit is preheated, pressurized by a compressor, and then injected from the top of the Boudouar reaction chamber of the gasifier.

[0016] Furthermore, the high-temperature synthesis gas after the reaction in the Boudouar reaction chamber enters the downcomer from the bottom outlet of the reaction chamber, and then enters the quench chamber for rapid cooling and dust removal.

[0017] Furthermore, CO2 is not directly injected into the combustion chamber of the gasifier to avoid affecting the reaction temperature and slag discharge inside the gasifier.

[0018] Furthermore, the CO2 removal portion described in step five is returned to the Boudouar reaction chamber, while the remaining portion is discharged or stored.

[0019] Furthermore, in the Boudouar reaction in step three, the reactants mainly utilize the residual carbon carried by the synthesis gas itself, rather than additional coke or carbon-containing materials.

[0020] Furthermore, during the process of the high-temperature syngas entering the Boudouar reaction chamber, the residual carbon in the high-temperature syngas is fully stirred and comes into full contact with CO2, resulting in the Boudouar reaction. After entering the Boudouar reaction chamber, it undergoes another Boudouar reaction with the injected CO2.

[0021] Furthermore, in step one, the temperature of the high-temperature zone required for the Boudouar reaction is not lower than 850°C, or not lower than 900°C or 1000°C.

[0022] Furthermore, in step two, CO2 preheating and injection: CO2 gas removed from the downstream purification unit is first sent to a heat exchanger to exchange heat with the high-temperature stream in subsequent steps (such as, but not limited to, the syngas at the outlet of the quench chamber). The preheated CO2 is then injected into the Boudouar reaction chamber of the gasifier.

[0023] This process does not directly inject the CO2 into the combustion chamber of the gasifier to avoid affecting the reaction temperature and slag discharge in the gasifier.

[0024] Furthermore, in step two, the heat source for preheating the injected CO2 comes from the syngas exiting the quench tower in step four or the hot stream in the process.

[0025] Furthermore, in step three, the Boudouar reaction in the Boudouar reaction chamber of the gasifier... The syngas produced by the fluidized bed gasifier contains CO, H2, CO2, H2O, CH4, and unreacted carbon particles. Without passing through any waste heat boiler, radiant heat exchanger, or quench unit, it is directly discharged from the lower side outlet of the gasifier combustion chamber into the Boudouar reaction chamber of the gasifier to carry out the Boudouar reaction: Under high temperature conditions, carbon dioxide reacts with the residual carbon entrained in the syngas in the Boudouar reaction: C + CO2 ≒ 2CO. This reaction is a strongly endothermic reaction, which fully utilizes the sensible heat of the syngas to provide the heat of reaction. After the reaction, the solid residual carbon and carbon dioxide are consumed, generating CO with twice the volume. The temperature of the gas at the outlet of the Boudouar reaction chamber decreases due to the endothermic reaction, but it is still maintained above the effective reaction temperature (not lower than 850℃, or not lower than 900℃, 1000℃).

[0026] Further, step four: cooling and separation in the quench chamber. After the reaction in step three, the high-temperature syngas enters from the top of the downcomer at the bottom of the Boudouar reaction chamber of the gasifier. It then enters the quench chamber of the gasifier and its temperature drops to around the saturation temperature, instantly "freezing" the reaction and preventing the reverse reaction (2CO→C+CO2) from occurring. During the quenching process, the remaining fly ash and a small amount of unreacted fine carbon particles in the syngas are wetted by water, agglomerated, and settled, forming black water that is discharged. The temperature and dust content of the syngas after quenching meet the requirements for entering the downstream purification unit (including conversion, desulfurization, and decarbonization processes).

[0027] Furthermore, the gasification process does not inject CO2 or water vapor into the combustion chamber of the gasifier to avoid affecting the temperature of the liquid slag discharge inside the gasifier.

[0028] Furthermore, the residual carbon content in the syngas exiting the Dual reactor is less than 10 g / Nm³. 3 Syngas, or less than 8 g / Nm 3 Syngas, or less than 6 g / Nm 3 Synthesis gas.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. Reduce the content of fine slag residue and improve carbon conversion rate and gasification efficiency: It subverts the traditional practice of directly cooling the syngas in the quench or waste boiler process. It utilizes the originally wasted residue to react with CO2 to generate CO, reducing the content of fine slag residue and significantly improving the total carbon conversion rate and CO yield.

[0030] 2. Reduce CO2 emissions and realize resource utilization: Convert CO2, which originally required high energy consumption for compression and storage or direct emission, into valuable CO, realize the resource utilization of carbon, and have significant environmental and economic benefits.

[0031] 3. Significantly reduced energy consumption: This invention does not consume any external heat source, but fully utilizes the high sensible heat of the syngas itself to drive the endothermic Boudouar reaction. Compared with other processes that require additional heat or coke, the energy consumption advantage is extremely significant.

[0032] 4. Ensuring continuous and stable system operation: The relevant reactions of this invention are carried out in the Boudouar reaction chamber of the gasifier, without injecting any low-temperature materials (such as carbon dioxide, water or steam) into the combustion chamber of the gasifier. This completely avoids the high-temperature liquid slag discharge conditions in the gasifier, fundamentally avoiding the risks of slag discharge difficulties and slag blockage caused by injecting gas / liquid into the furnace in the prior art, and ensuring the long-term stable operation of the gasification device.

[0033] 5. Simple process and easy to operate: This process only requires adding a syngas outlet to the lower side of the existing gasifier combustion chamber and adding a Boudouar reaction chamber vertically below the gasifier combustion chamber, and adding a syngas inlet to the upper part of the downcomer.

[0034] This process significantly improves carbon conversion rate and effective gas production rate without affecting the stability of liquid slag discharge from the gasifier, and reduces carbon dioxide emissions. It has the advantages of low energy consumption, high gasification efficiency, good system stability, significant environmental benefits, and minimal investment increase. Attached Figure Description

[0035] Figure 1 Process flow diagram of this process Detailed Implementation

[0036] The present invention will be further illustrated by specific embodiments below, but the scope of protection of the present invention is not limited thereto.

[0037] The detection equipment used in this process includes an elemental analyzer and a gas chromatograph.

[0038] Elemental analyzers are used to determine the carbon, hydrogen, and nitrogen content of organic materials. The sample is converted into carbon dioxide, water vapor, and nitrogen at high temperature in a catalytic oxidation (or cracking)-reduction tube. The mixed gas is then separated into individual components by a chromatographic column, and the response value of each component is measured separately using a thermal conductivity detector. Based on the response value of each component and the sensitivity of the corresponding element, the content of each element in the sample is calculated. The entire determination process is completed automatically and rapidly according to the operating procedures and preset sample data specified by the instrument system.

[0039] Gas chromatographs are used to analyze the content of gases such as carbon dioxide, hydrogen, carbon monoxide, and methane.

[0040] Example 1 A coal-water slurry gasifier is used, which is vertically designed from top to bottom as a combustion chamber, a Boudouar reaction chamber, a downcomer, and a quench chamber.

[0041] Water-coal slurry and oxygen are injected into the combustion chamber of the gasifier. The gasification pressure in the gasifier is 6.25 MPa and the gasification temperature is 1250℃.

[0042] In the gasifier combustion chamber, coal-water slurry and oxygen react to generate high-temperature syngas. The composition (volume ratio) of the syngas at the combustion chamber outlet is: carbon monoxide 41%, hydrogen 36%, carbon dioxide 19%, water 3%, methane 0.25%, and residual carbon 15.6 g / Nm³. 3 Syngas, along with other unavoidable impurity gases, is introduced directly into the Budur reaction chamber of the gasifier at a temperature of approximately 1250°C without any cooling equipment.

[0043] Carbon dioxide (purity ≥99%) removed from the downstream purification unit (low-temperature methanol cleaning unit) is pressurized to 6.5 MPa by a compressor, preheated to 200°C, and then injected into the Boudouar reaction chamber.

[0044] High-temperature synthesis gas (1250℃) and preheated carbon dioxide were mixed at a volume ratio of approximately 10% and then introduced into the Boudouar reaction chamber of the gasifier, where a vigorous Boudouar reaction occurred, causing the outlet gas temperature to drop to approximately 980℃. Analysis revealed that the outlet gas contained 42.46% carbon monoxide, 32.04% hydrogen, and 23.72% carbon dioxide, with the residual carbon content reduced to 3 g / Nm³. 3 Synthesis gas, and other unavoidable impurity gases.

[0045] The gas then enters from the bottom of the Budur reaction chamber of the gasifier and from the top of the downcomer. The gas enters the gasifier quench chamber through the downcomer and its temperature drops to around the saturation temperature, instantly "freezing" the reaction and preventing the reverse reaction (2CO→C+CO2) from occurring. During the quenching process, the remaining fly ash and a small amount of unreacted fine carbon particles in the syngas are wetted by water, agglomerated, and settled, forming black water that is discharged. The temperature and dust content of the syngas after quenching meet the requirements for entering the downstream purification unit.

[0046] The molten slag produced in the combustion chamber drips from the funnel at the bottom of the combustion chamber, passes through the Boudouar reaction chamber, and enters the quench chamber through the downcomer.

[0047] Compared with the traditional quench process without carbon dioxide reinjection, the effective carbon monoxide production in this embodiment is increased by about 11%, carbon dioxide emissions are reduced by about 12.3%, and the fine slag carbon content is reduced by 80.8%.

[0048] Example 2 The difference from Example 1 is that carbon dioxide is mixed into the Budur reaction chamber of the gasifier at a volume ratio of about 8%.

[0049] Testing revealed that the outlet gas contained 42.70% carbon monoxide, 32.73% hydrogen, and 22.75% carbon dioxide, with the residual carbon content reduced to 5 g / Nm³. 3 Synthesis gas, and other unavoidable impurity gases.

[0050] The outlet temperature of the Budur reaction chamber in the gasifier is 1020℃. Ultimately, the effective carbon monoxide production increases by approximately 9.2%, carbon dioxide emissions decrease by approximately 10.4%, and fine slag residue is reduced by 68%.

[0051] Example 3 The difference from Example 1 is that carbon dioxide is mixed into the Budur reaction chamber of the gasifier at a volume ratio of about 6%.

[0052] Testing revealed that the outlet gas contained 43.08% carbon monoxide, 33.43% hydrogen, and 21.64% carbon dioxide, with the residual carbon content reduced to 6.5 g / Nm³. 3 Synthesis gas, and other unavoidable impurity gases.

[0053] The outlet temperature of the Budur reaction chamber in the gasifier is 1050℃. Ultimately, the effective carbon monoxide production increases by approximately 7.8%, carbon dioxide emissions decrease by approximately 8.9%, and residual carbon is reduced by 58.3%.

[0054] Example 4 The difference from Example 1 is that carbon dioxide is mixed into the Budur reaction chamber of the gasifier at a volume ratio of about 4%.

[0055] Testing revealed that the outlet gas contained 43.31% carbon monoxide, 34.18% hydrogen, and 20.60% carbon dioxide, with the residual carbon content reduced to 8.6 g / Nm³.3 Synthesis gas, and other unavoidable impurity gases.

[0056] The outlet temperature of the Budur reaction chamber in the gasifier is 1120℃. Ultimately, the effective carbon monoxide production increases by approximately 6%, carbon dioxide emissions decrease by approximately 6.9%, and residual carbon is reduced by 44.8%.

[0057] This process significantly improves carbon conversion rate and effective gas production rate without affecting the stability of liquid slag discharge from the gasifier, and reduces carbon dioxide emissions. It has the advantages of low energy consumption, high gasification efficiency, good system stability, significant environmental benefits, and minimal investment increase.

Claims

1. A coal chemical gasification process for reducing the residual carbon content of fine slag, comprising the following steps: Step 1: Direct delivery of high-temperature synthesis gas: The high-temperature syngas generated by the gasifier is directly transferred from the combustion chamber to the Boudouar reaction chamber without cooling, maintaining its temperature in the high-temperature zone required for the Boudouar reaction. Step 2, CO2 injection: The CO2 gas removed by the downstream purification unit is injected into the Boudouar reaction chamber; Step 3, the Boudouar reaction in the Boudouar reaction chamber: In the Boudouar reaction chamber, the residual carbon in the high-temperature syngas is fully mixed with CO2. The high-temperature sensible heat of the syngas drives the Boudouar reaction: C + CO2 ≒ 2CO, so that the residual carbon entrained in the syngas reacts with CO2 to generate CO. Step four, cooling and separation in the quench chamber: The syngas after the reaction in step three is transferred to a quench chamber for quenching to freeze the reaction and separate solid particles, resulting in cooled crude syngas.

2. The coal chemical gasification process according to claim 1, characterized in that, Including step five, removing and reusing CO2: The crude syngas from step four is purified and CO2 is removed, with at least a portion of the removed CO2 being returned to the Boudouar reaction chamber.

3. The coal chemical gasification process according to claim 2, characterized in that, Including step six, slag treatment: The molten slag drips directly from the funnel at the bottom of the combustion chamber into the quench chamber via the downcomer, without passing through the Boudouar reaction chamber.

4. The coal chemical gasification process according to claim 1, characterized in that, Step 1: The high-temperature syngas from the combustion chamber of the gasifier is directly exported from the outlet on the lower side wall of the combustion chamber into the Boudouar reaction chamber of the gasifier.

5. The coal chemical gasification process according to claim 1, characterized in that, Step two: The CO2 removed by the purification unit is preheated, pressurized by the compressor, and then injected from the top of the Boudouar reaction chamber of the gasifier.

6. The coal chemical gasification process according to claim 1, characterized in that, The high-temperature synthesis gas after the reaction in the Boudouar reaction chamber enters the downcomer from the bottom outlet of the reaction chamber, and then enters the quench chamber for rapid cooling and dust removal.

7. The coal chemical gasification process according to claim 1, characterized in that, CO2 is not directly injected into the combustion chamber of the gasifier to avoid affecting the reaction temperature and slag discharge inside the gasifier.

8. The coal chemical gasification process according to claim 1, characterized in that, The CO2 removed in step five is partially returned to the Boudouar reaction chamber, while the remaining portion is discharged or stored.

9. The coal chemical gasification process according to claim 1, characterized in that, The Boudouar reaction in step three utilizes the residual carbon carried by the syngas itself as reactants, rather than additional coke or carbon-containing materials.

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