A flue gas desulfurization and iodine-sulfur cycle hydrogen production coupling system and method based on ammonium sulfite circulation

Abstract

This invention discloses a coupled system and method for flue gas desulfurization and iodine-sulfur cycle hydrogen production based on ammonium sulfite cycling. The system consists of an ammonium sulfite cycling desulfurization unit and a semi-open-ring iodine-sulfur cycle hydrogen production unit. The ammonium sulfite cycle achieves efficient capture and enrichment of SO₂ from flue gas, with zero ammonia consumption and no escape. It constructs a closed-ring iodine and open-ring / semi-open-ring iodine-sulfur hydrogen production system, using flue gas SO₂ as the external sulfur source. The traditional 850℃ high-temperature decomposition step of iodine-sulfur with sulfuric acid is eliminated; hydrogen is produced only by decomposing hydrogen iodide at 300–450℃. Iodine is recycled in a closed-ring manner, with sulfuric acid as a byproduct. This invention simultaneously achieves deep flue gas desulfurization, sulfur resource utilization, and low-cost hydrogen production, significantly reducing energy consumption and operating costs. It possesses excellent environmental and economic benefits and is applicable to sulfur-containing flue gas treatment and hydrogen co-production scenarios in thermal power, steel, coking, and chemical industries.

Description

Technical Field

[0001] This invention belongs to the field of flue gas desulfurization and hydrogen production technology, specifically involving a system and method that uses ammonium sulfite to circulate and absorb and enrich sulfur dioxide in flue gas, and constructs an iodine closed-loop and sulfur open-loop semi-open-loop iodine-sulfur hydrogen production system from exogenous SO2, thereby achieving the coupling of flue gas desulfurization and low-cost hydrogen production. Background Technology

[0002] Ammonia desulfurization is one of the mainstream desulfurization technologies for industrial flue gas. Its core process involves ammonia water absorbing sulfur dioxide to produce ammonium sulfite / ammonium bisulfite, which is then oxidized to obtain ammonium sulfate as a byproduct. Traditional ammonia desulfurization suffers from problems such as severe ammonia slip, high ammonia consumption, low value of byproducts, and poor economic efficiency. Iodine-sulfur cycle hydrogen production is a classic thermochemical water splitting technology, with the core being the Bunsen reaction: SO2 + I2 + 2H2O → H2SO4 + 2HI. The traditional iodine-sulfur cycle is a closed-loop system of sulfur and iodine, which requires sulfuric acid to be decomposed and regenerated into SO2 at a high temperature of 850℃. This places extremely high demands on the heat source and consumes a huge amount of energy, becoming a core bottleneck for commercialization. In existing technologies, flue gas desulfurization and iodine-sulfur hydrogen production are mostly independent processes. There is no semi-open-ring coupling scheme that uses ammonium sulfite to enrich flue gas SO2 as an external sulfur source and constructs an iodine-closed-ring sulfur-open-ring. This cannot simultaneously solve the problems of ammonia consumption and low by-product value in ammonia desulfurization, as well as the high-temperature sulfuric acid decomposition bottleneck in traditional iodine-sulfur cycles. Therefore, there is an urgent need for a technical solution that can efficiently couple flue gas desulfurization with hydrogen production processes to achieve the utilization of sulfur resources, reduce hydrogen production energy consumption, and improve system economy. Summary of the Invention

[0003] This invention aims to solve the above problems and provides a coupled system and method for flue gas desulfurization and iodine-sulfur cycle hydrogen production based on ammonium sulfite cycle. The core innovation is the ammonium sulfite cycle capture of SO2 + iodine in a closed-loop and sulfur-open-loop semi-open-loop iodine-sulfur hydrogen production process, which eliminates the traditional 850℃ high-temperature sulfuric acid decomposition step of iodine-sulfur, and only retains the medium- and low-temperature hydrogen iodide decomposition, thus realizing the synergistic effect of desulfurization, hydrogen production and sulfur resource utilization. Technical solution A coupled flue gas desulfurization and iodine-sulfur cycle hydrogen production system based on ammonium sulfite cycle includes: Ammonium sulfite circulating desulfurization unit: used to absorb sulfur dioxide in flue gas, regenerate ammonium sulfite by heating and decomposing ammonium bisulfite, realize closed-loop zero consumption of ammonia, and release high concentration of sulfur dioxide gas at the same time; Semi-open-loop iodine-sulfur cycle hydrogen production unit: Receives sulfur dioxide output from the ammonium sulfite cycle desulfurization unit, uses flue gas SO2 as an external sulfur source, and reacts with iodine and water to produce sulfuric acid and hydrogen iodide. Hydrogen iodide is decomposed to produce hydrogen. Iodine element is in closed-loop cycle, and sulfur element is supplied in an open loop, eliminating the need for high-temperature decomposition of sulfuric acid to regenerate SO2. Preferably, the ammonium sulfite circulating desulfurization unit comprises: Absorption tower: Ammonium sulfite solution comes into countercurrent contact with flue gas to absorb SO2 and generate ammonium bisulfite solution; Heating decomposer: The ammonium bisulfite solution is heated to 80–100°C and decomposed into ammonium bisulfite solution and high-concentration SO2 gas; Circulation pipeline: Regenerated ammonium sulfite is returned to the absorption tower, and ammonium bisulfite is sent to the heating decomposer. Preferably, the semi-open-ring iodine-sulfur cycle hydrogen production unit comprises: Bunsen reactor: SO2 reacts with aqueous iodine solution to produce sulfuric acid and hydrogen iodide; Hydrogen iodide decomposer: Hydrogen iodide is heated to 300–450℃ and decomposes into hydrogen and iodine; Iodine circulation pipeline: Iodine is returned to the Bunsen reactor for closed-loop use. Preferably, the heat source for the heating decomposer is waste heat from flue gas at 120–150°C. Preferably, the absorption tower operates at a temperature of 45–55°C and a pH of 5–6. Preferably, the operating temperature of the heating decomposer is 90–100°C, and the decomposition conversion rate of ammonium bisulfite is 50%–85%. Preferably, the SO2 gas produced by decomposition is directly introduced into the Bunsen reactor without the need for drying. A method for coupling flue gas desulfurization and iodine-sulfur cycle hydrogen production based on ammonium sulfite cycle includes the following steps: Inside the absorption tower, ammonium sulfite solution absorbs SO2 from flue gas to generate ammonium bisulfite solution; Ammonium bisulfite is fed into a heating decomposer, where it decomposes into ammonium sulfite and SO2 at 80–100°C. The ammonium sulfite is then returned to the absorption tower for recycling. The SO2 is introduced into the Bunsen reactor and reacts with iodine water to produce sulfuric acid and hydrogen iodide. The hydrogen iodide decomposes into hydrogen and iodine at 300–450°C, with the iodine being returned to the Bunsen reactor for recycling. Beneficial effects Zero-loss closed-loop ammonia system: Ammonium sulfite is recycled and regenerated, eliminating ammonia escape and the need for continuous ammonia replenishment, thus significantly reducing operating costs; High-value utilization of sulfur: enriching low-concentration flue gas SO2 into high-concentration SO2 to realize the resource utilization of waste gas; Breaking through the iodine-sulfur bottleneck: By adopting a closed-ring iodine and open-ring semi-open-ring sulfur structure, the high-temperature decomposition of sulfuric acid at 850℃ is eliminated, and hydrogen iodide is only decomposed at 300–450℃, significantly reducing the energy consumption for hydrogen production. Excellent economic performance: High-value sulfuric acid is produced as a byproduct, and hydrogen is produced simultaneously, turning the system from an environmental cost item into a revenue item; High-efficiency utilization of waste heat: using the low-temperature waste heat of flue gas to drive decomposition, and making high-value utilization of low-grade heat energy. High desulfurization efficiency: SO2 absorption efficiency ≥99%, stably meeting ultra-low emission requirements. Attached Figure Description Figure 1. Flowchart of ammonium sulfite desulfurization cycle Figure 2. Flowchart of semi-open-ring iodine-sulfur cycle hydrogen production Detailed Implementation Example 1 The flue gas volume is 300,000 Nm³ / h, and the SO2 concentration is 2000 mg / Nm³. Absorption tower: temperature 50℃, pH 5.5, ammonium sulfite solution concentration 15%, desulfurization efficiency ≥99%; Heating decomposer: The waste heat of the flue gas is 130℃, which is heated to 90℃-100℃ and held for 10-20 minutes, with a decomposition conversion rate of about 70%-80%; Hydrogen production unit: Bunsen reaction at 120°C, hydrogen iodide decomposition at 400°C, iodine closed-loop recycling. Annual benefits: Recovers approximately 4,800 tons of SO2, produces approximately 7,300 tons of sulfuric acid as a byproduct, and generates approximately 150 tons of hydrogen; reduces operating costs by more than 70% compared to traditional ammonia desulfurization and reduces energy consumption by more than 40% compared to traditional iodine-sulfur hydrogen production.

Claims

1. A coupled system and method for flue gas desulfurization and iodine-sulfur cycle hydrogen production based on ammonium sulfite cycle, characterized in that, include: The ammonium sulfite circulating desulfurization unit is used to absorb sulfur dioxide in flue gas, regenerate ammonium sulfite by heating and decomposing ammonium bisulfite, and release high concentrations of sulfur dioxide gas at the same time. The semi-open-ring iodine-sulfur cycle hydrogen production unit is used to receive the sulfur dioxide gas, construct an iodine closed-loop and sulfur open-loop semi-open-ring system with flue gas SO2 as an external sulfur source, react with iodine and water to generate sulfuric acid and hydrogen iodide, decompose hydrogen iodide to produce hydrogen, and reuse iodine in a closed loop, without the need for high-temperature decomposition of sulfuric acid to regenerate SO2.

2. The system according to claim 1, characterized in that, The ammonium sulfite circulating desulfurization unit includes: In the absorption tower, ammonium sulfite solution contacts the flue gas to absorb SO2, generating ammonium bisulfite solution; The heating decomposer heats the ammonium bisulfite solution to 80–100°C, decomposing it into ammonium bisulfite solution and SO2 gas. The circulating pipeline returns the regenerated ammonium sulfite to the absorption tower, while the ammonium bisulfite is sent to the heating decomposer.

3. The system according to claim 1, characterized in that, The semi-open-ring iodine-sulfur cycle hydrogen production unit includes: In the Bunsen reactor, SO2 reacts with an aqueous iodine solution to produce sulfuric acid and hydrogen iodide. The hydrogen iodide decomposer heats hydrogen iodide to 300–450°C and decomposes it into hydrogen and iodine. The iodine circulation pipeline returns iodine to the Bunsen reactor.

4. The system according to claim 2, characterized in that, The heat source for the heating decomposer is the waste heat from the flue gas at 120–150℃. When the waste heat from the flue gas is insufficient, an external heat source is connected.

5. The system according to claim 2, characterized in that, The absorption tower operates at a temperature of 45–55℃ and a pH value of 5–6.

6. The system according to claim 2, characterized in that, The heating decomposer operates at a temperature of 90–100℃, with an ammonium bisulfite decomposition conversion rate of 50%–85%.

7. The system according to claim 1, characterized in that, The SO2 gas produced by decomposition is directly fed into the Bunsen reactor without the need for drying.

8. A method for coupling flue gas desulfurization and iodine-sulfur cycle hydrogen production based on ammonium sulfite cycle, characterized in that, include: Step 1: Inside the absorption tower, ammonium sulfite solution absorbs SO2 from flue gas to generate ammonium bisulfite; Step 2: Ammonium bisulfite decomposes at 80–100℃, regenerating ammonium bisulfite for recycling and releasing SO2. Step 3: The SO2 is introduced into the Bunsen reactor and reacts with iodine water to produce sulfuric acid and hydrogen iodide; Step four: The hydrogen iodide is decomposed at 300–450°C to produce hydrogen, and the iodine is recycled in a closed loop.

9. The method according to claim 8, characterized in that, In step two, the conversion rate of ammonium bisulfite is 50%–85%, and the undecomposed portion is returned to the absorption tower with the regenerated liquid.

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