A method and system for upgrading low-carbon coal gas based on a carbon dioxide cycle in a steel joint production

Abstract

This invention belongs to the field of iron and steel metallurgy and comprehensive energy utilization technology, specifically disclosing a method and system for upgrading low-carbon coal gas in integrated iron and steel production based on carbon dioxide recycling. This invention captures and purifies high-purity CO2 from blast furnace gas, completely replacing nitrogen used for converter slag splashing and bottom blowing. It utilizes the sensible heat of the high-temperature flue gas in the converter to drive a reduction reaction between pulverized coal and CO2, generating high-concentration CO, thus upgrading and improving the efficiency of converter gas. The upgraded gas is then recovered for power generation, industrial furnace fuel, or chemical raw materials. The CO2 produced during combustion is captured and recycled again, forming a closed-loop carbon cycle within the plant: capture-conversion-utilization-recapture. This invention can increase the CO volume fraction of converter gas to over 85%, increase the calorific value by 20%–50%, and reduce carbon emission intensity per ton of steel by 8%–10%, achieving carbon emission reduction, energy saving and cost reduction, and energy value-added effects. The process is compact, adaptable to existing production lines, and has strong industrial feasibility.

Description

Technical Field

[0001] This invention relates to the fields of iron and steel metallurgy and comprehensive energy utilization technology, and in particular to a method and system for upgrading low-carbon coal gas in iron and steel co-production based on carbon dioxide recycling. Background Technology

[0002] The steel industry is a typical energy-intensive industry, with long-process smelting producing large amounts of blast furnace gas and converter gas as byproducts. Blast furnace gas contains 18-25% CO2, and existing capture technologies such as amine process and pressure swing adsorption are mature, but the high-value utilization pathways for CO2 are limited and the economics are insufficient. Converter steelmaking produces high-temperature flue gas at 1400-1600℃, containing 10-20% CO2. Its high-quality sensible heat is mostly used to produce low-grade steam, and its chemical energy is not fully utilized.

[0003] Traditional converters use nitrogen as the carrier gas for slag splashing and bottom blowing agitation. Nitrogen production relies on air separation units, resulting in high energy consumption. Furthermore, nitrogen only plays a physical role and does not participate in chemical reactions or contribute chemical energy. Existing related technologies are mostly isolated improvements that do not systematically couple blast furnace gas CO2, converter high-temperature waste heat, and inherent energy-consuming processes within the steel plant, thus failing to form a closed-loop carbon cycle and energy-added system.

[0004] To address the aforementioned technical deficiencies, this invention provides a method and system for upgrading low-carbon coal gas in steel co-production based on CO2 cycle, achieving carbon resource utilization, energy efficiency, and low operating costs. Summary of the Invention

[0005] The purpose of this invention is to provide a compact and economically efficient method for carbon recycling and energy upgrading in steel plants. It deeply integrates CO2 captured from blast furnace gas into the converter process, completely replacing nitrogen to save air separation energy consumption. It utilizes the high temperature of the converter to convert CO2 and pulverized coal into high-value CO, improving the quality and calorific value of the gas, constructing a closed-loop carbon resource cycle within the plant, and achieving improved system energy efficiency and a significant reduction in carbon emission intensity.

[0006] To achieve the above objectives, the basic solution provided by this invention is: a method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide cycle, comprising the following steps: S1: Carbon dioxide capture and supply: CO2 gas with a purity of >95% is captured and purified from the blast furnace gas produced in the blast furnace ironmaking process through gas separation technology, and then stored under pressure to form a stable and adjustable pressure gas source. S2: Carbon dioxide completely replaces nitrogen in converters: In the converter steelmaking process, nitrogen is no longer used, and high-purity CO2 is used for slag splashing, furnace protection, top blowing, and bottom blowing agitation to complete the physical process function and participate in the molten pool reaction as a reaction raw material. S3: Converter blowing coupled with pulverized coal injection and high-temperature CO2 reduction for upgrading: During the desiliconization, dephosphorization, decarburization and slag splashing protection stages of the converter, a mixture of pulverized coal and CO2 is injected at a position where the flue gas temperature is ≥900℃. The endothermic reactions C+CO2→2CO and 2C+O2→2CO occur, and the sensible heat of the flue gas is used to convert CO2 and pulverized coal into CO, thereby upgrading the coal gas. Specifically, during the converter blowing stage and before the oxygen blowing ends, pulverized coal injection is started when the volume concentration of O2 in the flue gas is ≥1.0%. The injected pulverized coal reacts with excess O2 and CO2 to generate CO, converting the coal gas that was originally forced to be released due to the O2 concentration ≥1.6% into recoverable high-calorific-value coal gas. S4: High-quality coal gas recovery and recycling: After upgrading, the coal gas is recovered for power generation, industrial furnace fuel or chemical raw materials. The CO2 produced by combustion is returned to step S1 for capture again, forming a closed carbon cycle.

[0007] Furthermore, the gas separation technology described in step S1 is chemical absorption or pressure swing adsorption.

[0008] Furthermore, the temperature of the flue gas at the injection point in step S3 is 1000℃-1600℃.

[0009] Furthermore, in step S3, the coal powder particle size is ≤0.2mm, the 200-mesh sieve passing rate is ≥90%, and the fixed carbon content is ≥80%.

[0010] Furthermore, the CO volume fraction in the converter gas after upgrading in step S3 is 85%-95%; the calorific value is 10000-11000 kJ / Nm³. 3 .

[0011] Furthermore, the pulverized coal injection flow rate is 5-10 kg / min, and the gas-solid mass ratio of pulverized coal to CO2 is 1:1 to 1:2.

[0012] A low-carbon gas upgrading system for steel co-production based on carbon dioxide cycle, comprising: CO2 capture and storage unit: used to capture, purify, and pressurize CO2 from blast furnace gas for storage; Converter gas substitution unit: CO2 is introduced into the converter top blowing slag splashing system and bottom blowing agitation system to replace nitrogen; Converter active fume hood injection unit: includes injection guns, pulverized coal supply system, CO2 conveying system and closed-loop control system; Gas purification and recovery unit: purifies, transports, and utilizes the upgraded coal gas; Carbon cycle unit: The CO2 generated after the utilization of coal gas is sent back to the CO2 capture and storage unit.

[0013] Furthermore, the spray gun is a water-cooled double-layered sleeve type, with an outer layer of high-temperature resistant alloy steel cooling water channel and an inner layer of wear-resistant steel liner, the inner tube diameter being... Outer diameter of the outer tube Wall thickness 5mm; nozzle is an outlet contraction type, orifice diameter... The material is silicon carbide ceramic, with a temperature resistance of ≥1600℃; the cooling water flow rate is ≥10m³ / h. 3 / h, inlet and outlet water temperature difference ≤15℃.

[0014] Furthermore, the closed-loop control system includes an online infrared gas analyzer, a control mechanism, and an actuator. It automatically adjusts the pulverized coal injection rate based on the CO2 concentration of the coal gas using a PID algorithm, and sets the CO2 control target to 4%-6%. The control mechanism is a DCS or PLC control system.

[0015] Furthermore, it also includes a safety interlock, the triggering conditions of which are: when the converter tilt angle is greater than ±10°, the speed of the primary dust removal fan is less than 1100 rpm, or the O2 content of the gas is greater than 1.6%, or the cooling water is abnormal, the blowing will automatically stop.

[0016] Compared with the prior art, the advantages of this invention are: 1. Construct a closed-loop carbon cycle within the plant, reducing carbon emission intensity per ton of steel by 8% to 10%, and realizing the resource utilization of CO2 from waste to carbon carrier; 2. Completely replaces nitrogen, saving electricity consumption in air separation nitrogen production; increases the calorific value of coal gas by 20%~50%, resulting in significant benefits in power generation and fuel substitution; 3. Upgrade the utilization of the high-temperature waste heat of the converter at 1400-1700℃ from low-grade steam to drive high-value-added chemical reactions; 4. It is highly compatible with existing production lines. The new equipment is mature and reliable, with low modification costs, and does not affect the main production rhythm. It is safe and controllable. Detailed Implementation

[0017] The present invention will be further described in detail below through specific embodiments: A method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide cycle includes the following steps: S1: Carbon dioxide capture and supply: CO2 gas with a purity >95% is captured and purified from blast furnace gas produced in the blast furnace ironmaking process through gas separation technology, and then stored under pressure to form a stable and adjustable pressure gas source; the gas separation technology is chemical absorption or pressure swing adsorption. S2: Carbon dioxide completely replaces nitrogen in converters: In the converter steelmaking process, nitrogen is no longer used, and high-purity CO2 is used for slag splashing, furnace protection, top blowing, and bottom blowing agitation to complete the physical process function and participate in the molten pool reaction as a reaction raw material. S3: Converter blowing coupled with pulverized coal injection and high-temperature CO2 reduction upgrading: During the converter desiliconization, dephosphorization, decarburization, and slag splashing furnace protection stages, a mixture of pulverized coal and CO2 is injected at a location with a flue gas temperature ≥900℃. This results in endothermic reactions C+CO2→2CO and 2C+O2→2CO, utilizing the sensible heat of the flue gas to convert CO2 and pulverized coal into CO, thus upgrading the coal gas. The flue gas temperature at the injection point is 1000℃-1600℃, the pulverized coal particle size is ≤0.2mm, the 200-mesh sieve pass rate is ≥90%, and the fixed carbon content is ≥80%. The CO volume fraction in the upgraded converter gas is 85%-95%, and the calorific value is 10000-11000kJ / Nm³. 3 ; During the initial blowing phase of the converter (first 2-3 minutes) and the last 1-2 minutes before the oxygen blowing ends, the CO concentration in the flue gas is low and the O2 and CO2 concentrations are high due to the low temperature of the molten pool or incomplete carbon-oxygen reaction. Under normal circumstances, when the O2 volume concentration in the gas reaches 1.6%, the gas is switched off and released to prevent the risk of electrostatic precipitator explosion, resulting in energy waste.

[0018] In this scheme, the pulverized coal injection system is activated in advance during the aforementioned time period. When the online O2 analyzer detects an O2 volume concentration ≥1.0%, pulverized coal is automatically injected at a relatively low flow rate (3–5 kg / min). The pulverized coal reacts with O2 in the flue gas in the reaction 2C + O2 → 2CO, and simultaneously reacts with CO2 in the reaction C + CO2 → 2CO. This rapidly consumes excess O2 and generates CO, reducing the O2 concentration in the flue gas to below 1.0%, thereby recovering all the previously released flue gas. Calculations show that each heat of steel in a 120-ton converter can recover an additional 500–800 Nm³ of flue gas. 3 This increases the calorific value by the equivalent of 10-15 kgce / t steel.

[0019] S4: High-quality coal gas recovery and recycling: The upgraded coal gas is recovered for power generation, industrial furnace fuel or chemical raw materials. The CO2 produced by combustion is returned to step S1 for capture again, forming a closed-loop carbon cycle. The coal powder injection flow rate is 5-10 kg / min, and the gas-solid mass ratio of coal powder to CO2 is 1:1-1:2.

[0020] A low-carbon gas upgrading system for steel co-production based on carbon dioxide cycle, comprising: CO2 capture and storage unit: used to capture, purify, and pressurize CO2 from blast furnace gas for storage; Converter gas substitution unit: CO2 is introduced into the converter top blowing slag splashing system and bottom blowing agitation system to replace nitrogen; The converter's active fume hood injection unit includes injection guns, a pulverized coal supply system, a CO2 conveying system, and a closed-loop control system. The injection guns are water-cooled, double-layered, with an outer layer of high-temperature alloy steel cooling water channels and an inner layer of wear-resistant steel lining. The inner tube diameter... Outer diameter of the outer tube Wall thickness 5mm; nozzle is an outlet contraction type, orifice diameter... The material is silicon carbide ceramic, with a temperature resistance of ≥1600℃; the cooling water flow rate is ≥10m³ / h. 3 / h, inlet and outlet water temperature difference ≤15℃; the closed-loop control system includes an online infrared gas analyzer, a control mechanism and an actuator, and automatically adjusts the coal powder injection rate based on the coal gas CO2 concentration using a PID algorithm, with the CO2 control target set at 4%-6%, and the control mechanism is a DCS or PLC control system. Gas purification and recovery unit: purifies, transports, and utilizes the upgraded coal gas; Carbon cycle unit: The CO2 generated after the utilization of coal gas is sent back to the CO2 capture and storage unit; Safety Interlock: The safety interlock is triggered when the converter tilt angle is greater than ±10°, the speed of the primary dust removal fan is less than 1100 rpm, the O2 content of the gas is greater than 1.6%, or the cooling water is abnormal. The injection will stop automatically.

[0021] Implementing this plan requires a top-and-bottom combined blowing converter with a capacity of at least 120 tons. The specific operation is as follows: S1: CO2 capture: The hydrogen-rich carbon circulating blast furnace gas (CO2 content 25-35%) in the plant is purified by pressure swing adsorption (PSA) to obtain carbon dioxide with a purity of over 95%, removing nitrogen, water vapor, sulfides and other impurities; CO2 gas at a pressure of 1.2MPa, with sufficient carbon dioxide supply, is stored in a buffer tank.

[0022] S2: CO2 completely replaces nitrogen: After tapping from the converter, the slag splashing and furnace protection stage begins. The original nitrogen valves are closed, and the system is switched to CO2. CO2 is supplied at a rate of 40,000 Nm³. 3 A flow rate of [flow rate] / h and a pressure of 1.6 MPa are blown into the furnace through the top lance for approximately 3–5 minutes. Simultaneously, throughout the converter's blowing process, the bottom-blowing agitator gas source is switched from N2 to CO2, with the flow rate adjusted according to the smelting process requirements. The slag is effectively splashed up and adheres to the furnace lining, achieving the required furnace protection effect; the bottom-blowing CO2 provides excellent agitation.

[0023] S3: Converter active hood injection for upgrading during the blowing process: During the peak period of decarburization in the converter blowing process and the subsequent slag splashing stage, the pulverized coal injection system is started.

[0024] Spray gun: A single water-cooled spray gun extends into the furnace opening from the side wall of the converter's movable smoke hood, with a depth of 20-25cm.

[0025] The flue gas temperature measuring device is installed on the flue.

[0026] Injected material: Anthracite powder (85% fixed carbon, particle size <200 mesh).

[0027] Operating parameters: The system is designed based on a gas-to-solid ratio of 1:1 (mass ratio). The initial system setting is a pulverized coal feed rate of 8 kg / min, corresponding to a CO2 flow rate of 4 Nm³. 3 / min (approximately 8 kg / min mass flow rate). In actual operation, the gas-solid ratio can be adjusted between 1:1 and 1:2, at which point the CO2 flow rate will be 4–8 Nm³. 3 The pulverized coal injection rate varies within a range of / min. The final pulverized coal injection rate is automatically adjusted by the control system based on real-time monitoring of the CO2 content in the coal gas, and the set value is implemented to control the CO2 content in the coal gas at 5%.

[0028] Reaction process: After the pulverized coal and CO2 mixture is injected into the high-temperature flue gas, a rapid gasification and reduction reaction occurs. Analysis at the fan room inlet line shows that the control system fine-tunes the pulverized coal injection rate based on CO2 concentration feedback, ensuring that the CO2 concentration in the rear part of the flue gas duct remains stable within the target range, while the CO concentration rises synchronously and steadily.

[0029] S4: Gas recovery: Upgraded converter gas enters the LT system for purification.

[0030] The upgraded converter gas has a CO volume fraction of 88% and a calorific value of 10,500 kJ / Nm³. 3 Compared to the conventional level (approximately 7500 kJ / Nm³), 3 (40% increase)

[0031] S5: Gas Recycling: This high-calorific-value gas is preferentially supplied to the plant's gas-steam combined cycle generator set as fuel. Due to the increased fuel calorific value and improved combustion characteristics, the generator set efficiency increases by approximately 2 percentage points year-on-year, resulting in an annual increase in power generation benefits of tens of millions of yuan. Surplus gas is used in steel rolling furnaces for baking alloys, scrap steel, and other raw materials, replacing some of the purchased natural gas. The flue gas generated after these gas utilization processes, rich in CO2, eventually flows into the plant's gas system along with boiler flue gas or furnace exhaust gas, with some re-entering the blast furnace gas network, where it can be captured again by the capture system in step S1 and participate in the next cycle.

[0032] Operational Results Evaluation: This system achieves resource utilization of CO2 by completely replacing nitrogen used for converter slag splashing and bottom blowing agitation with CO2, and utilizing residual heat for pulverized coal reduction at the converter inlet. Calculations show that CO2 can replace 24-26 Nm³ of nitrogen per ton of steel. 3 If 80% of the CO2 is reduced, the CO2 consumed in place of nitrogen is reduced to approximately 38–42 Nm³ of CO. 3 / t; however, the increase in CO due to the release of coal gas through pulverized coal injection during the start-up and end-of-blowing stages of converter smelting is not included in this value.

[0033] It can also produce corresponding high-calorific-value coal gas. By constructing an in-plant carbon cycle, the dependence on external fossil fuels is significantly reduced. The carbon emission intensity per ton of steel is reduced by about 8-10% throughout the process. At the same time, through saving nitrogen production electricity consumption, improving power generation efficiency or fuel substitution due to improved coal gas quality, the production cost per ton of steel is significantly reduced, resulting in both economic and environmental benefits.

[0034] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide recycling, characterized in that, Includes the following steps: S1: Carbon dioxide capture and supply: CO2 gas with a purity of >95% is captured and purified from the blast furnace gas produced in the blast furnace ironmaking process through gas separation technology, and then stored under pressure to form a stable and adjustable pressure gas source. S2: Carbon dioxide completely replaces nitrogen in converters: In the converter steelmaking process, nitrogen is no longer used, and high-purity CO2 is used for slag splashing, furnace protection, top blowing, and bottom blowing agitation to complete the physical process function and participate in the molten pool reaction as a reaction raw material. S3: Converter blowing coupled with pulverized coal injection and high-temperature CO2 reduction for upgrading: During the desiliconization, dephosphorization, decarburization and slag splashing protection stages of the converter, a mixture of pulverized coal and CO2 is injected at a position where the flue gas temperature is ≥900℃. The endothermic reactions C+CO2→2CO and 2C+O2→2CO occur, and the sensible heat of the flue gas is used to convert CO2 and pulverized coal into CO, thereby upgrading the coal gas. Specifically, during the converter blowing stage and before the oxygen blowing ends, pulverized coal injection is started when the volume concentration of O2 in the flue gas is ≥1.0%. The injected pulverized coal reacts with excess O2 and CO2 to generate CO, converting the coal gas that was originally forced to be released due to the O2 concentration ≥1.6% into recoverable high-calorific-value coal gas. S4: High-quality coal gas recovery and recycling: After upgrading, the coal gas is recovered for power generation, industrial furnace fuel or chemical raw materials. The CO2 produced by combustion is returned to step S1 for capture again, forming a closed carbon cycle.

2. The method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide recycling according to claim 1, characterized in that, The gas separation technology mentioned in step S1 is chemical absorption or pressure swing adsorption.

3. The method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide cycle according to claim 1, characterized in that, The temperature of the flue gas at the injection point in step S3 is 1000℃-1600℃.

4. The method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide cycle according to claim 1, characterized in that, The coal powder in step S3 has a particle size ≤ 0.2 mm, a 200-mesh sieve pass rate ≥ 90%, and a fixed carbon content ≥ 80%.

5. The method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide cycle according to claim 1, characterized in that, The converter gas after upgrading in step S3 has a CO volume fraction of 85%-95% and a calorific value of 10000-11000 kJ / Nm³. 3 .

6. The method for upgrading low-carbon coal gas in steel co-production based on carbon dioxide cycle according to claim 1, characterized in that, The pulverized coal injection flow rate is 5-10 kg / min, and the gas-solid mass ratio of pulverized coal to CO2 is 1:1 to 1:

2.

7. A low-carbon coal gas upgrading system for steel co-production based on carbon dioxide cycle, characterized in that, include: CO2 capture and storage unit: used to capture, purify, and pressurize CO2 from blast furnace gas for storage; Converter gas substitution unit: CO2 is introduced into the converter top blowing slag splashing system and bottom blowing agitation system to replace nitrogen; Converter active fume hood injection unit: includes injection guns, pulverized coal supply system, CO2 conveying system and closed-loop control system; Gas purification and recovery unit: purifies, transports, and utilizes the upgraded coal gas; Carbon cycle unit: The CO2 generated after the utilization of coal gas is sent back to the CO2 capture and storage unit.

8. A low-carbon coal gas upgrading system for steel co-production based on carbon dioxide recycling as described in claim 7, characterized in that, The spray gun is a water-cooled double-layered sleeve type, with an outer layer of high-temperature resistant alloy steel cooling water channel and an inner layer of wear-resistant steel liner. The inner tube diameter is... Outer diameter of the outer tube Wall thickness 5mm; nozzle is an outlet contraction type, orifice diameter... The material is silicon carbide ceramic, with a temperature resistance of ≥1600℃; the cooling water flow rate is ≥10m³ / h. 3 / h, inlet and outlet water temperature difference ≤15℃.

9. A low-carbon coal gas upgrading system for steel co-production based on carbon dioxide recycling as described in claim 7, characterized in that, The closed-loop control system includes an online infrared gas analyzer, a control mechanism, and an actuator. It automatically adjusts the pulverized coal injection rate based on the CO2 concentration of the coal gas using a PID algorithm, with the CO2 control target set at 4%-6%. The control mechanism is a DCS or PLC control system.

10. A low-carbon coal gas upgrading system for steel co-production based on carbon dioxide recycling according to claim 7, characterized in that, It also includes a safety interlock, the triggering conditions of which are: when the converter tilt angle is greater than ±10°, the speed of the primary dust removal fan is less than 1100 rpm, or the O2 content of the gas is greater than 1.6%, or the cooling water is abnormal, the blowing will automatically stop.

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