A tail gas recycling and purification system for hydrogen-based direct reduction of iron production process

Abstract

This invention relates to a tail gas recycling and purification system for hydrogen-based direct reduction of iron, belonging to the fields of hydrogen metallurgy and carbon capture technology. The system includes: a green hydrogen preparation unit (100) that outputs hydrogen for reduction; a hydrogen-based direct reduction unit (200) having a reduction reactor and a furnace top tail gas outlet; and a tail gas recycling and purification unit consisting of a dust removal module (310), a condensation and dehydration module (320), a CO₂ capture and purification module (330), and a hydrogen pressurization and reinjection module (340) arranged sequentially along the airflow direction. The dust removal module separates and recovers iron oxide dust; the condensation and dehydration module recovers the water generated in the reaction and returns it to the electrolytic cell for water replenishment via a condensate recovery pipeline (L1); the CO₂ capture and purification module enriches and purifies the low concentration of CO₂ in the tail gas to ≥99.5% as the product outflow; and the hydrogen pressurization and reinjection module pressurizes the decarbonized hydrogen and reinjects it into the reducing gas inlet via a reducing gas return pipeline (L2) to combine with fresh hydrogen. The system integrates reducing gas circulation, water closed-loop, and CO₂ purification to reduce net consumption of reducing agent and external water consumption, while also ensuring stable operation under the fluctuation of renewable energy.

Description

Technical Field

[0001] This invention relates to the fields of hydrogen metallurgy and carbon capture and utilization technology, specifically to a tail gas recycling and purification system for hydrogen-based direct reduction iron production, and more particularly to an integrated system for reducing gas recycling, reaction-generated water recovery, and carbon dioxide capture and purification based on renewable energy-based water electrolysis for hydrogen production. Background Technology

[0002] The traditional blast furnace-converter long process in the steel industry has high carbon emission intensity. The hydrogen-based direct reduction iron process uses hydrogen instead of carbonaceous reducing agents, and the main reaction produces water, which has the potential to significantly reduce CO2 emissions during the process.

[0003] In the direct hydrogen reduction process, the exhaust gas from the reduction reactor typically contains unreacted hydrogen, water vapor generated during the reaction, a small amount of CO2 derived from associated carbonates or impurities in the iron ore, and trace amounts of iron oxide dust. Existing engineering approaches often suffer from the following shortcomings:

[0004] (1) The unreacted hydrogen recovery rate is low, and the hydrogen in the tail gas is often partially released or simply burned, resulting in high consumption of reducing agent.

[0005] (2) The separation of water vapor and CO2 in the exhaust gas is energy-intensive and lacks a dedicated integrated purification process for the characteristics of "high hydrogen concentration and low CO2 concentration".

[0006] (3) CO2 is often only stored or emitted at low value, without forming a usable product chain with the front-end green hydrogen system;

[0007] (4) There is a matching problem between the fluctuation of renewable energy power generation output and the continuous and stable operation of the reduction unit. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a tail gas recycling and purification system for direct reduction of iron with hydrogen, which achieves efficient hydrogen circulation, closed-loop recovery of reaction-generated water and enrichment and purification of CO2 through the orderly integration of dust removal, cascade condensation and dehydration, CO2 capture and purification and hydrogen pressurization and reinjection, and is compatible with stable operation under the fluctuation of renewable energy power.

[0009] To solve the above problems, the present invention adopts the following technical solution:

[0010] A tail gas recycling and purification system for hydrogen-based direct reduction of iron includes: a green hydrogen production unit configured to generate electricity using renewable energy and produce hydrogen through water electrolysis, outputting hydrogen for reduction; a hydrogen-based direct reduction unit having a reduction reactor, a reducing gas inlet, and a tail gas outlet at the top of the furnace; and a tail gas recycling and purification unit, which sequentially includes a dust removal module, a condensation and dehydration module, a CO2 capture and purification module, and a hydrogen pressurization and reinjection module along the airflow direction of the tail gas outlet at the top of the furnace; wherein, the condensate outlet of the condensation and dehydration module is returned to the green hydrogen production unit for water replenishment via a condensate recovery pipeline; the lean CO2 tail gas outlet of the CO2 capture and purification module is connected to the inlet of the hydrogen pressurization and reinjection module, and the outlet of the hydrogen pressurization and reinjection module is returned to the reducing gas inlet via a reducing gas return pipeline and merged with fresh hydrogen.

[0011] In the preferred embodiment, the green hydrogen production unit uses an alkaline electrolyzer or a proton exchange membrane electrolyzer and is equipped with a hydrogen storage buffer tank; the reduction reactor is a vertical furnace or a fluidized bed reactor with an operating temperature of 800℃~1050℃; the dust removal module uses a high-temperature ceramic filter or a cyclone separator and performs magnetic separation to recover the separated dust; the condensation and dehydration module uses a multi-stage indirect condenser for stepped cooling; the CO2 capture and purification module uses pressure swing adsorption coupled with cryogenic distillation to improve the CO2 purity to ≥99.5%; the system can also be equipped with a waste heat recovery heat exchanger to preheat the return gas or combustion air, and can be connected to an external CO2 resource utilization module to produce green methanol / synthetic fuel or for enhanced oil recovery and mineralization storage.

[0012] Compared with the prior art, the present invention has at least the following beneficial effects:

[0013] By establishing an orderly loop of "dust removal → dehydration → decarbonization → hydrogen reinjection", the comprehensive utilization rate of hydrogen is improved and the net consumption of reducing agent is reduced.

[0014] The water generated in the reaction is condensed, recovered, and purified before being used as makeup water for the electrolyzer, reducing external water consumption and forming a closed water loop.

[0015] It can still obtain a high-purity CO2 product stream under low CO2 concentration background, creating conditions for the value-added utilization of carbon resources or low-leakage storage.

[0016] The configuration of hydrogen storage buffer tanks and electrolyzers helps to mitigate the impact of curtailment of solar and wind power on the operating conditions of the reduction unit. Attached Figure Description

[0017] Figure 1 The overall process flow diagram of the system provided in the embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the segmented tail gas recirculation of the two-stage reduction process provided in an embodiment of the present invention.

[0019] The markings in the attached diagram mean: 100 - Green hydrogen preparation unit; 200 - Hydrogen-based direct reduction unit (reduction reactor); 310 - Dust removal module; 320 - Condensation and dehydration module; 330 - CO2 capture and purification module (330a Pressure Swing Adsorption Section / 330b Low Temperature Distillation Section); 340 - Hydrogen pressurization and reinjection module; 350 - CO2 resource utilization module; 360 - Waste heat recovery heat exchanger; L1 - Condensate recovery pipeline; L2 - Reducing gas reflux pipeline. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings. It should be understood that the following embodiments are merely illustrative of the technical concept of the present invention and are not intended to limit the scope of protection of the present invention.

[0021] like Figure 1 As shown, one embodiment of the system includes: a renewable energy power generation device, a water electrolysis hydrogen production device (alkaline electrolyzer or PEM electrolyzer) (100), a hydrogen purification and storage buffer tank, a hydrogen-based vertical shaft furnace / fluidized bed reduction reactor (200), a high-temperature ceramic filter (310), a multi-stage indirect condenser (320), a vacuum pressure swing adsorption device (VSA / PSA) (330a), a low-temperature distillation column (330b), a hydrogen compressor / pressurization reinjection module (340), and corresponding pipelines, valves, and automatic control instruments.

[0022] High-purity hydrogen from the water electrolysis hydrogen production unit is buffered and stabilized before entering the reduction reactor (200) as a reducing gas. In the reduction reactor, hydrogen reacts with iron oxide (such as Fe2O3 / Fe3O4) to generate metallic iron powder and water vapor. The temperature of the tail gas at the top of the furnace can be on the order of 800℃ to 900℃. The components include, for example, H2, H2O, a small amount of CO2 and dust.

[0023] The exhaust gas from the furnace top first enters the dust removal module (310) to remove iron oxide dust. The collected dust is then magnetically separated and sold as a high-grade Fe2O3 product or returned to the feed. After dust removal, the exhaust gas enters the condensation and dehydration module (320) for staged cooling, causing water vapor to condense into liquid water. The condensate is then purified by filtration / ion exchange and returned to the electrolytic cell water inlet through the condensate recovery pipeline L1, achieving a closed-loop water system.

[0024] After dehydration, the tail gas enters the CO2 capture and purification module: first, the CO2 is enriched from about 1% to 5% to about 60% to 80% by vacuum pressure swing adsorption, and then enters the low temperature distillation column to obtain liquid CO2 product with a purity of ≥99.5% under the conditions of about -50℃ to -20℃ and 1.5MPa to 3.0MPa; the main gas after CO2 removal is hydrogen, which is pressurized to 0.8MPa to 2.5MPa by the hydrogen pressurization and reinjection module (340), and then mixed with fresh hydrogen through the reducing gas reflux pipeline L2 before entering the reduction reactor.

[0025] A waste heat recovery heat exchanger (360) can be installed between the condensation and dehydration module and the CO2 capture and purification module to preheat the return hydrogen or combustion air using the waste heat of the tail gas to reduce overall energy consumption.

[0026] For high-grade iron ore, a two-stage reduction reactor can also be used (pre-reduction stage 600℃~750℃ / final reduction stage 900℃~1050℃). The tail gas from the two stages can be configured with relatively independent dust removal-dehydration-decarburization-reinjection sub-loops (see...). Figure 2 This reduces energy loss caused by mixing high and low temperature airflows and improves system energy efficiency.

Claims

1. A system for recycling and purifying tail gas from the direct reduction of iron with hydrogen, characterized in that, include: The green hydrogen production unit (100) is configured to generate electricity using renewable energy and produce hydrogen through water electrolysis, outputting hydrogen for reduction. The hydrogen-based direct reduction unit (200) has a reduction reactor, a reducing gas inlet and a furnace top tail gas outlet, wherein the reduction reactor is configured to reduce iron oxide to metallic iron powder using hydrogen as the reducing gas. as well as The exhaust gas recycling and purification unit (300) is connected sequentially along the airflow direction of the exhaust gas outlet at the top of the furnace: The dust removal module (310) has its inlet connected to the tail gas outlet at the top of the furnace and is used to separate and recover iron oxide dust in the tail gas. The condensation and dehydration module (320) has its inlet connected to the outlet of the dust removal module and is used to condense water vapor in the exhaust gas into liquid water. The condensate recovery pipeline (L1) connects the condensate outlet of the condensate dehydration module (320) back to the water inlet of the green hydrogen preparation unit (100); The CO2 capture and purification module (330) is connected to the exhaust outlet of the condensation and dehydration module (320) and is configured to enrich and purify CO2 in the exhaust gas and output a high-purity CO2 product stream. The hydrogen pressurization and reinjection module (340) is connected to the lean CO2 tail gas outlet of the CO2 capture and purification module (330) and is configured to pressurize the purified hydrogen and send it back to the reducing gas inlet via the reducing gas return pipeline (L2), and then merge it with the fresh hydrogen output from the green hydrogen preparation unit (100) and enter the reduction reactor.

2. The system according to claim 1, characterized in that, The green hydrogen preparation unit (100) adopts an alkaline electrolyzer or a proton exchange membrane electrolyzer, and a hydrogen purification device and a hydrogen storage buffer tank are set downstream of the electrolyzer. The hydrogen storage buffer tank is used to smooth out gas supply fluctuations caused by renewable energy power fluctuations.

3. The system according to claim 1, characterized in that, The reduction reactor is a vertical furnace or a fluidized bed reactor, with an operating temperature range of 800℃ to 1050℃.

4. The system according to claim 1, characterized in that, The dust removal module (310) adopts a high-temperature ceramic filter or a cyclone separator; the separated iron oxide dust is magnetically separated and sold as ferric oxide product, or returned to the feed end of the reduction reactor for reuse.

5. The system according to claim 1, characterized in that, The condensation and dehydration module (320) adopts a multi-stage indirect condenser, which condenses water vapor into liquid water through stepped cooling; the condensate recovery pipeline (L1) is also equipped with a purification unit, which includes a filtration and ion exchange device, and the purified condensate is recycled as makeup water for the electrolytic cell.

6. The system according to claim 1, characterized in that, The CO2 capture and purification module (330) adopts a coupled process of pressure swing adsorption and cryogenic distillation: the pressure swing adsorption section enriches the CO2 concentration from 1% to 5% to 60% to 80%; the cryogenic distillation section increases the CO2 purity to ≥99.5%; the pressure swing adsorption adopts vacuum pressure swing adsorption, and the adsorbent includes molecular sieves or activated carbon; the operating temperature range of the cryogenic distillation is -50℃ to -20℃, and the operating pressure is 1.5MPa to 3.0MPa.

7. The system according to claim 1, characterized in that, It also includes a CO2 resource utilization module (350), which is connected to the high-purity CO2 product outlet of the CO2 capture and purification module (330). It is used to synthesize green fuel from high-purity CO2 and green hydrogen provided by the green hydrogen preparation unit (100) through methanol synthesis or Fischer-Tropsch synthesis, or to use high-purity CO2 for enhanced oil recovery, mineralization and storage, or as an industrial raw material for sale.

8. The system according to claim 1, characterized in that, The hydrogen-based direct reduction unit (200) adopts a two-stage reduction process, including a pre-reduction section and a final reduction section. The temperature of the pre-reduction section is 600℃~750℃, and the temperature of the final reduction section is 900℃~1050℃. The pre-reduction section and the final reduction section are respectively equipped with a relatively independent dust removal module, a condensation and dehydration module, a CO2 capture and purification module, and a hydrogen pressurization and reinjection module, forming a segmented circulation loop.

9. The system according to claim 1, characterized in that, A waste heat recovery heat exchanger (360) is provided between the condensation and dehydration module (320) and the CO2 capture and purification module (330) to preheat the reflux hydrogen or combustion air entering the reducing gas inlet using the waste heat of the tail gas after dehydration.

10. The system according to claim 1, characterized in that, The hydrogen pressurization and reinjection module (340) pressurizes the purified hydrogen to 0.8MPa to 2.5MPa, and then sends it to the reducing gas inlet after it is combined with fresh hydrogen through the reducing gas return pipeline (L2).

Images