A hydrogen-based vertical shaft furnace reducing gas circulation system and method based on CO2 capture

Abstract

The application discloses a hydrogen-based shaft furnace reduction gas recycling system and method based on CO2 capture, which comprises a hydrogen-based shaft furnace, a dehydration and dust removal device, a CO2 adsorption device, a dry reforming device, a gas mixing device and a heating furnace; the hydrogen-based shaft furnace is connected with the dehydration and dust removal device through a pipeline at a top gas outlet, the dehydration and dust removal device is connected with the CO2 adsorption device through a pipeline at a gas outlet, the CO2 adsorption device is connected with the dry reforming device through a conveying device at a discharge port, the gas outlet of the dry reforming device and the gas outlet of the CO2 adsorption device are connected with the gas mixing device through pipelines at a gas inlet, the mixer gas outlet of the gas mixing device is connected with the heating furnace through a pipeline at a gas inlet, and the gas outlet of the heating furnace is connected with the hydrogen-based shaft furnace through a pipeline at a gas inlet; and the gas inlet of the dry reforming device is also connected with a reduction gas pipeline. The system has simple overall equipment structure, and the CO2 recovery efficiency can reach more than 95%, and the reduction gas recovery rate is high.

Description

Technical Field

[0001] This invention relates to a hydrogen metallurgical system, and more particularly to a hydrogen-based vertical shaft furnace reducing gas circulation system and method based on CO2 capture. Background Technology

[0002] In the current low-carbon context, hydrogen metallurgy is receiving increasing attention in the steel industry, with hydrogen-based vertical shaft furnaces becoming a hot topic. Under current conditions in my country, the main obstacle to the widespread adoption of hydrogen-based vertical shaft furnaces lies in the high cost of reducing gas. While Xuan Steel and Zhongjin Taihang have proposed using coke oven gas as the reducing gas to reduce costs, a large amount of this gas needs to be used as a heat source inside the furnace. Therefore, a significant amount of unreacted reducing gas remains after the reduction reaction, requiring a recirculation system to re-enter the furnace to ensure efficient gas utilization.

[0003] Although the top gas contains a large amount of unreacted gas, it also contains reduced CO2 and H2O. If this is recirculated into the hydrogen-based shaft furnace system, it will severely impact the reduction efficiency and negatively affect the system itself. Therefore, the top gas of a hydrogen-based shaft furnace is typically pre-dehydrated and dust-removed, while also removing CO2, before being recirculated back into the furnace. Currently, the main processes for CO2 removal are pressure swing adsorption (PSA) and alkaline leaching. After CO2 treatment, it is recovered for other uses, but CO2 is discharged from the hydrogen-based shaft furnace system during these processes, resulting in significant storage, transportation, and subsequent processing costs. If CO2 could be efficiently removed from the top gas and converted into reducing gas, allowing the top gas to circulate completely within the system, the gas utilization efficiency of the hydrogen-based shaft furnace system would be significantly improved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hydrogen-based vertical shaft furnace reducing gas circulation system based on CO2 capture, so as to effectively utilize CO2 in the furnace top gas and improve the reduction efficiency; the present invention also provides a hydrogen-based vertical shaft furnace reducing gas circulation method based on CO2 capture.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the system of the present invention is as follows: it includes a hydrogen-based vertical shaft furnace, a dehydration and dust removal device, a CO2 adsorption device, a dry reforming device, a gas mixing device, and a heating furnace; the gas outlet at the top of the hydrogen-based vertical shaft furnace is connected to the inlet of the dehydration and dust removal device via a pipeline, the outlet of the dehydration and dust removal device is connected to the inlet of the CO2 adsorption device via a pipeline, the outlet of the CO2 adsorption device is connected to the inlet of the dry reforming device via a conveying device, and the outlets of both the dry reforming device and the CO2 adsorption device are connected to the inlet of the gas mixing device via pipelines; the outlet of the mixer of the gas mixing device is connected to the inlet of the heating furnace via a pipeline, and the outlet of the heating furnace is connected to the gas inlet of the hydrogen-based vertical shaft furnace via a pipeline; the inlet of the dry reforming device is also connected to a reducing gas pipeline.

[0006] Furthermore, the outlet of the CO2 adsorption device is also connected to the fuel inlet of the heating furnace via a pipeline.

[0007] The method of the present invention uses the above-described apparatus and comprises the following steps:

[0008] (1) The top gas discharged from the hydrogen-based vertical furnace is pretreated by a dehydration and dust removal device to remove water vapor and furnace dust; then it is carbonized and absorbed by a CO2 adsorption device using an absorbent.

[0009] (2) The remaining gas from the top gas that is not adsorbed by the CO2 adsorption device enters the gas mixing device as one gas stream.

[0010] (3) The carbonized absorbent enters the dry reforming unit and the reducing gas is introduced into the unit. The methane in the reducing gas undergoes dry reforming with the absorbent to generate a mixed gas of CO and H2, which, together with the reducing gas, enters the gas mixing unit as a second gas.

[0011] (4) The first gas and the second gas are mixed in the gas mixing device to form a mixed reducing gas. After being heated by the heating furnace, the mixed reducing gas is introduced into the hydrogen-based vertical furnace as the process gas for hydrogen-based reduction.

[0012] Furthermore, in step (2), a portion of the top gas is used as fuel for the heating furnace.

[0013] Furthermore, in step (4), the proportion of N2 in the mixed reducing gas meets the requirements of the process gas.

[0014] Furthermore, in step (4), the process gas contains (CH4+CO+H2) > 75%, H2 / CO ≥ 2.5, and the process gas flow rate is 150,000–190,000 m³ / h. 3 / h.

[0015] The beneficial effects of adopting the above technical solution are as follows: This invention recovers CO2 from the top gas and circulates it in the overall hydrogen-based vertical furnace process, converting CO2 into CO and H2 through dry reforming reaction, effectively utilizing the CO2 in the top gas, which is conducive to the efficient utilization of the current hydrogen-based vertical furnace process. At the same time, the proportion of reducing gas in the process gas is increased after treatment, which can further improve the reduction efficiency.

[0016] The system of this invention has a simple overall structure, no CO2 emission during the reduction gas circulation process, and a CO2 recovery efficiency of over 95%. The overall process system has a high reduction gas recovery rate, the system conversion process is easy to operate, and the proportion of reducing gas in the process gas is further increased after circulation, which can effectively improve the reduction efficiency. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a schematic diagram of the system structure of the present invention. Detailed Implementation

[0019] Figure 1 As shown, this hydrogen-based vertical shaft furnace reducing gas circulation system based on CO2 capture includes a hydrogen-based vertical shaft furnace, a dehydration and dust removal device, a CO2 adsorption device, a dry reforming device, a gas mixing device, and a heating furnace. The top gas outlet of the hydrogen-based vertical shaft furnace is connected to the inlet of the dehydration and dust removal device via a pipeline. Thus, the gas after the reduction reaction, i.e., the top gas, is discharged from the top gas outlet of the hydrogen-based vertical shaft furnace and enters the dehydration and dust removal device to remove water vapor and furnace dust and other impurities. The outlet of the dehydration and dust removal device is connected to the inlet of the CO2 adsorption device via a pipeline; thus, the CO2 adsorption device uses an absorbent to carbonate and absorb the CO2 in the dehydrated and dust-removed top gas. The outlet of the CO2 adsorption unit is connected to the inlet of the dry reforming unit via a conveying device. The inlet of the dry reforming unit is also connected to the reducing gas pipeline. Thus, the carbonated absorbent is fed into the dry reforming unit, calcined to form CO2, and reacts with the methane in the reducing gas fed into the dry reforming unit to form a reaction gas mainly composed of CO and H2. The outlets of both the dry reforming unit and the CO2 adsorption unit are connected to the inlet of a gas mixing unit via pipelines. Thus, the remaining top gas after CO2 adsorption by the CO2 adsorption unit enters the gas mixing unit as one gas path, and the reaction gas generated from calcining the dry reforming unit enters the gas mixing unit as a second gas path. The two gas paths are mixed to obtain a mixed reducing gas. The outlet of the mixer in the gas mixing unit is connected to the inlet of the heating furnace via a pipeline, and the outlet of the heating furnace is connected to the gas inlet of the hydrogen-based vertical shaft furnace via a pipeline. Thus, the mixed reducing gas, after being heated in the heating furnace, re-enters the hydrogen-based vertical shaft furnace as a reducing gas for smelting. The outlet of the CO2 adsorption device is also connected to the fuel inlet of the heating furnace through a pipeline. A small amount of gas remaining in the furnace top gas after CO2 adsorption by the CO2 adsorption device is introduced into the heating furnace and used as fuel to balance the N2 ratio in the system.

[0020] Figure 1 As shown, the hydrogen-based vertical shaft furnace reducing gas recycling method based on CO2 capture adopts the following steps:

[0021] 1) The hydrogen-based vertical shaft furnace reduces iron-containing furnace charge with thermal reducing gas. The reducing gas, heated by the heating furnace, enters from the middle of the vertical shaft furnace, and the furnace top gas after the reduction reaction is discharged from the furnace top gas outlet.

[0022] 2) The top gas discharged from the hydrogen-based vertical furnace enters the dehydration and dust removal device, which pre-treats the gas to remove water vapor and furnace dust and other impurities.

[0023] 3) After dehydration and dust removal, the coal gas enters the CO2 adsorption unit, where the CO2 in the coal gas is absorbed by carbonation using an absorbent. The main components of the remaining gas after CO2 absorption are CH4, CO, H2, N2, and incompletely captured CO2. Most of this remaining gas is sent as a separate flow to the gas mixing unit, with a flow rate of 80,000–110,000 m³ / h. 3 / h, H2 / CO ≥ 2.5 volume ratio, temperature 300~500℃; a small portion of the remaining gas is used as fuel gas in the heating furnace to balance the N2 ratio in the system. The proportion of the gas introduced into the mixing device is adjusted according to the N2 ratio in the process gas composition to ensure that the reduced gas after mixing is equivalent to the process gas. The reaction temperature of the CO2 adsorption device is 500~680℃, and the CO2 reacts with the absorbent M. X O reacts with M X O + CO2 = M X CO3, where M is Ca, Mg, Na or K, meaning the absorbent is CaO, MgO, Na2O or K2O.

[0024] 4) The carbonated absorbent in the CO2 adsorption device is fed into a calcination dry reforming unit, where it is calcined and converted into CO2. CO2 then undergoes a dry reforming reaction with the methane introduced into the calcination dry reforming unit, converting it into a reaction gas whose main components are CO and H2. This reaction gas is then fed into a gas mixing unit as a secondary gas stream, with a flow rate of 40,000–90,000 m³ / h. 3 / h, H2 / CO ≥ 1 volume ratio, temperature 500–700℃. The reaction temperature of the calcined dry reforming unit is 720–900℃, and the absorbent M after carbonation. X CO3 undergoes a calcination reaction M X CO3=M X O+CO2 releases CO2, which reacts with the added methane in a dry reforming reaction: CH4+CO2=CO+H2. Based on the mass of CO2 converted from the increase in weight of the absorbent before and after the reaction, the required amount of methane gas is added to ensure complete conversion of CO2.

[0025] 5) The flow rate of the second gas is further supplemented after the first gas is introduced into the gas mixing device, so that the flow rate of process gas introduced into the hydrogen-based vertical furnace in each cycle is equal. The two gases are mixed to form a mixed reducing gas, and the N2 ratio in the mixed reducing gas meets the requirements of the process gas.

[0026] 6) The mixed reducing gas from the gas mixing device enters the heating furnace, which heats the mixed reducing gas to 900–1050°C and then introduces it into the hydrogen-based vertical shaft furnace as process gas. The hydrogen-based vertical shaft furnace requires that the volume percentage of reducing gas (CH4+CO+H2) in the process gas be >75%, the H2 / CO ratio be ≥2.5, and the process gas flow rate be 150,000–190,000 m³ / h. 3 / h.

[0027] Example: The method for circulating hydrogen-based vertical shaft furnace reducing gas based on CO2 capture is as follows.

[0028] This embodiment is based on a hydrogen-based vertical shaft furnace system with an annual production capacity of 500,000 tons, using process gas with a composition of H2+CO+CH4=76%, H2 / CO=7, and a process gas flow rate of 155,000 m³ / h. 3 / h, after being heated to 1020℃ in a heating furnace, the iron-containing furnace charge is introduced into a hydrogen-based vertical furnace system to reduce the iron-containing furnace charge;

[0029] After reduction, the top gas is discharged from the top of the hydrogen-based vertical shaft furnace, with the remaining reducing gas still accounting for 55%, and the top gas flow rate is 175,500 m³ / h. 3 / h, the top gas enters the dehydration and dust removal device, and the water vapor and dust in the top gas are completely removed;

[0030] After dehydration and dust removal, the top gas from the furnace enters the CO2 adsorption unit. CaO particles are selected as the adsorbent. The unit is heated to 580℃, where CaO reacts with CO2 to form CaCO3. The CO2 removal rate in the gas reaches 97%. After CO2 removal, the remaining gas is discharged from the unit. After being balanced with N2 by the circulating gas, a small amount of the gas is fed into the heating furnace as fuel gas to balance the N2 content in the system. The remaining gas is used as one stream in the mixed gas system, with a flow rate of 85,000 m³ / h. 3 / h, H2 / CO = 7.7, CaCO3 particles are transferred to the dry reforming unit;

[0031] The dry reforming unit is controlled at 850℃. CaCO3 transferred to the dry reforming unit undergoes a decomposition reaction, converting to CaO + CO2. Based on the law of conservation of mass during the reaction process, CH4 is added to react with the released CO2, undergoing a reforming reaction that converts the gas to H2 + CO. This converted gas then enters the mixed gas system as a secondary gas stream. The CaO particles after the reaction are processed and then collected for reuse. The secondary gas flow rate is 70,000 m³ / s. 3 / h, H2 / CO = 2;

[0032] After the first and second gas supply lines are used for circulation, the total process gas flow rate is maintained at 155,000 m³ / h. 3 / h, the reducing gas is mixed by the mixing system and the proportion of reducing gas reaches 83%, and the hydrogen-carbon ratio is reduced to 3.5. After mixing, the reducing gas is fed into the heating furnace and heated to 1020℃ before being fed into the hydrogen-based vertical furnace. Due to the increase in the proportion of reducing gas, the reduction efficiency of the hydrogen-based vertical furnace is further improved.

[0033] To more clearly illustrate the dynamics of various gas streams in the process, the gas flow conditions of each unit in the case implementation scheme are listed below:

[0034] The process gas first enters the heater and is heated to 1020℃, with H2 + CO + CH4 = 76%, H2 / CO = 7, and a flow rate of 155,000 m³ / h. 3 / h, then enters a hydrogen-based vertical furnace for reduction;

[0035] After reduction, the gas is discharged from the top of the furnace, with H2 + CO + CH4 = 55%, H2 / CO = 7.7, and the gas flow rate at the top of the furnace is 175,500 m³ / h. 3 / h, temperature is 400℃;

[0036] The blast furnace top gas enters the dehydration and dust removal device, with H2 + CO + CH4 = 72%, H2 / CO = 7.7, and a flow rate of 135,000 m³ / h. 3 / h, temperature 80℃;

[0037] After the coal gas enters the CO2 adsorption unit, one stream is fed into the mixing system, where H2 + CO + CH4 = 72%, H2 / CO = 7.7, and the flow rate is 85,000 m³ / h. 3 / h, temperature is 400℃;

[0038] After conversion by the dry reforming unit, the gas is fed into the mixing unit as a secondary gas, with a flow rate of 70,000 m³ / h. 3 / h, H2 / CO=2, temperature is 650℃;

[0039] The mixed reducing gas enters the heating furnace, with H2 + CO + CH4 = 83%, H2 / CO = 3.5, and a total flow rate of 155,000 m³. 3 / h, maintain the balance of the total system's process gas flow into the furnace, and heat the gas to 1020℃ before it enters the furnace for production.

Claims

1. A hydrogen-based vertical shaft furnace reducing gas circulation system based on CO2 capture, characterized in that: It includes a hydrogen-based vertical shaft furnace, a dehydration and dust removal device, a CO2 adsorption device, a dry reforming device, a gas mixing device, and a heating furnace. The gas outlet at the top of the hydrogen-based vertical shaft furnace is connected to the inlet of the dehydration and dust removal device via a pipeline. The outlet of the dehydration and dust removal device is connected to the inlet of the CO2 adsorption device via a pipeline. The outlet of the CO2 adsorption device is connected to the inlet of the dry reforming device via a conveying device. The outlets of both the dry reforming device and the CO2 adsorption device are connected to the inlet of the gas mixing device via pipelines. The outlet of the mixer of the gas mixing device is connected to the inlet of the heating furnace via a pipeline. The outlet of the heating furnace is connected to the gas inlet of the hydrogen-based vertical shaft furnace via a pipeline. The inlet of the dry reforming device is also connected to a reducing gas pipeline. The outlet of the CO2 adsorption device is also connected to the fuel inlet of the heating furnace via a pipeline. The absorbent of the CO2 adsorption device is CaO, MgO, Na2O, or K2O.

2. A method for circulating reducing gas in a hydrogen-based vertical shaft furnace based on CO2 capture, using the system described in claim 1, characterized in that, The following steps are to be taken: (1) The top gas discharged from the hydrogen-based vertical furnace is pretreated by a dehydration and dust removal device to remove water vapor and furnace dust; then it is carbonized and absorbed by a CO2 adsorption device using an absorbent. (2) The remaining gas in the top gas that is not adsorbed by the CO2 adsorption device enters the gas mixing device as a gas stream, and a portion of the top gas is used as fuel for the heating furnace; the proportion of the gas stream entering the gas mixing device is adjusted according to the N2 ratio in the process gas composition so that the reduced gas mixed by the gas mixing device is equivalent to the process gas. (3) The carbonized absorbent enters the dry reforming unit and the reducing gas is introduced into the unit. The methane in the reducing gas undergoes dry reforming with the absorbent to generate a mixed gas of CO and H2, which, together with the reducing gas, enters the gas mixing unit as a second gas. (4) The first gas and the second gas are mixed in the gas mixing device to form a mixed reducing gas. After being heated by the heating furnace, the mixed reducing gas is introduced into the hydrogen-based vertical furnace as the process gas for hydrogen-based reduction.

3. The method for circulating reducing gas in a hydrogen-based vertical shaft furnace based on CO2 capture according to claim 2, characterized in that: In step (4), the proportion of N2 in the mixed reducing gas meets the requirements of the process gas.

4. A method for circulating reducing gas in a hydrogen-based vertical shaft furnace based on CO2 capture, as described in claim 2 or 3, characterized in that: In step (4), the process gas contains (CH4+CO+H2) > 75%, H2 / CO ≥ 2.5, and the process gas flow rate is 150,000–190,000 m³ / h. 3 / h.

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