Method for reducing oxygen content of flue gas using modified carbon-based fuel and deoxidizing material

Abstract

The application aims to provide a method for reducing oxygen content of flue gas by using modified carbon-based fuel and a deoxidizing material, and belongs to the technical field of flue gas purification of coal-fired power plants, coal gangue solid waste resource utilization and disaster prevention and control of coal mining goaf. A water solution containing a transition metal salt is loaded on coal and / or coal gangue, and after drying, a modified carbon-based fuel is obtained; the modified carbon-based fuel is subjected to in-situ catalytic combustion deoxidization in oxygen-containing flue gas, oxygen in the flue gas is consumed, and ash containing transition metal oxides is generated; the ash is leached by using an acid solution, and a transition metal salt solution is recovered; the recovered solution is returned to be used for preparing a modified solution, and circulation of active components is realized. In the application, a highly dispersed catalyst is generated by in-situ pyrolysis of the transition metal salt, the ignition point of the carbon-based fuel in a low-oxygen flue gas atmosphere is reduced, CO generation is greatly inhibited, and meanwhile, resource recycling of the transition metal is realized, and the application has the characteristics of high deoxidization efficiency, low operation cost and strong raw material adaptability.

Description

Technical Field

[0001] This invention belongs to the technical fields of flue gas purification in coal-fired power plants, resource utilization of coal gangue solid waste, and disaster prevention and control in coal mine goaf areas. Specifically, it relates to a method for reducing the oxygen content of flue gas using modified carbon-based fuels and deoxygenation materials. Background Technology

[0002] Against the backdrop of China's "dual carbon" strategic goals, carbon emission control from coal-fired power plants, solid waste disposal in coal mining areas, and disaster prevention and control in mining subsidence areas have become three major challenges that the energy industry urgently needs to address collaboratively.

[0003] On the one hand, coal mine goaf areas pose serious safety hazards. With the continuous mining of coal resources, large areas of goaf have formed underground. The residual coal left in these goaf areas is highly susceptible to spontaneous combustion under leaky air and oxygen supply conditions. Currently, the commonly used prevention and control method in coal mines is nitrogen injection fire suppression technology, which involves injecting high-purity nitrogen into the goaf area to inertize the internal atmosphere and reduce the oxygen content, thereby inhibiting spontaneous combustion of the residual coal. However, nitrogen injection requires dedicated nitrogen generators, which involve large equipment investments, high energy consumption, and no environmental benefits.

[0004] On the other hand, coal-fired power plants emit large amounts of flue gas during operation. In addition to inert components such as CO2 and N2, the flue gas also contains a certain proportion of residual O2. While existing carbon capture, utilization, and storage (CCUS) technologies can capture CO2 from flue gas, they generally suffer from complex processes, high capture costs, and high energy consumption, limiting their large-scale application. Furthermore, the large quantities of coal gangue generated during coal mining and washing, when stored in the open for extended periods, not only occupy significant land resources but also pose a risk of spontaneous combustion due to heat accumulation within the gangue piles, releasing toxic and harmful gases such as sulfur dioxide and hydrogen sulfide, causing severe air and soil pollution.

[0005] Based on the geographical proximity of coal-fired power plants at mine mouths and coal mine goaf areas, researchers have proposed a technical concept of using power plant flue gas to replace pure nitrogen gas for atmosphere replacement in coal mine goaf areas. This approach aims to use the inert components abundant in the flue gas to replace the existing pure nitrogen gas, which can both achieve inerting and disaster prevention in goaf areas and find a low-cost, large-scale disposal method for power plant flue gas.

[0006] However, directly injecting flue gas from coal-fired power plants into goaf areas presents a core constraint: excessively high residual oxygen content in the flue gas. The oxygen content in the flue gas from ordinary coal-fired power plants is typically 6%-12% or even higher. Injecting flue gas with this oxygen content directly into goaf areas would not only fail to inhibit spontaneous combustion of residual coal, but could also provide oxygen-rich conditions for its oxidation, accelerating the spontaneous combustion process and even posing a fire risk. Therefore, how to effectively and economically reduce the oxygen content in flue gas has become a key bottleneck for the practical implementation of this technology.

[0007] Utilizing carbon-based materials (such as coal or coal gangue) near coal mines to undergo a redox reaction with residual O2 in flue gas is, in principle, a simple, economical method with a large deoxygenation capacity. The basic idea is to use carbon to combine with O2 at high temperatures to generate CO2 or CO, thereby converting the O2 in the flue gas into carbon oxides, achieving "recombustion" deoxygenation of the flue gas.

[0008] However, directly using coal or coal gangue for combustion and deoxygenation in a low-oxygen flue gas atmosphere presents significant technical obstacles. On the one hand, since the oxygen content of flue gas is typically around 6%-12%, far lower than that of conventional air, the ignition temperature of coal or coal gangue increases significantly under this low-oxygen, high-inert-gas environment, while the combustion rate slows down. This results in enormous energy consumption required to maintain stable combustion, leading to poor economic efficiency. On the other hand, incomplete combustion under low-oxygen conditions significantly exacerbates the generation and release of CO. As a highly toxic and flammable gas, CO, if injected into the goaf of a coal mine along with the treated flue gas, will introduce new and significant safety hazards and violate relevant environmental emission standards.

[0009] Researchers have explored technical pathways for deoxygenating power plant flue gas using catalysts. For example, patent CN120424692A discloses a composite material and method for flue gas deoxygenation, which mixes coal semi-coke with a composite metal oxide of CoO and CuO and achieves flue gas deoxygenation through fixed-bed combustion. However, this technology still has the following shortcomings in practical applications: First, the added CoO / CuO composite metal oxide is only physically mixed with the coal semi-coke, resulting in insufficient contact between the catalyst and the carbon matrix, limiting catalytic efficiency under low-oxygen conditions and requiring further improvement in deoxygenation effect. Second, during combustion, the uneven distribution of the catalyst in the physically mixed system leads to incomplete combustion of carbon in some areas, resulting in high CO production and posing a safety hazard to subsequent goaf gas injection. Third, as an added catalyst, CoO / CuO is discharged with the ash after the reaction, and the active components cannot be recovered, resulting in high operating costs and waste of metal resources.

[0010] Based on the above analysis, to achieve large-scale industrial applications of reducing flue gas oxygen content using coal or coal gangue, neither direct combustion nor physical mixing with external catalysts is sufficient. Modifying coal and coal gangue to improve their catalytic combustion efficiency in low-oxygen flue gas environments and suppress the formation of toxic byproducts such as CO is a necessary prerequisite for safe and efficient flue gas deoxygenation. However, there are currently few reports on specialized technologies for modified catalytic combustion of coal-based materials under low-oxygen flue gas environments, especially those with active component recycling characteristics. Summary of the Invention

[0011] This invention addresses the shortcomings of existing direct combustion deoxygenation technologies, such as difficulty in ignition under low-oxygen atmospheres, high energy consumption, numerous CO byproducts, and high single-use cost of active components. It provides a method and deoxygenation material for reducing flue gas oxygen content using modified carbon-based fuels. This method aims to achieve high process integration, low operating costs, and establish an internal circulation mechanism for the active components.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: A method for reducing the oxygen content of flue gas using modified carbon-based fuels is based on the following core concept: directly loading deoxidizing active components onto the fuel itself, enabling the catalytic combustion deoxidation reaction and the fuel's own conversion process to occur in situ in synergistic manner; and further recovering the active components from the ash residue after the reaction using hydrometallurgical methods, achieving the circulation of the active components within the system; specifically including the following steps: S1. Mix an aqueous solution containing at least one transition metal salt with carbon-based fuel, and then dry it to obtain modified carbon-based fuel; S2. The modified carbon-based fuel is fed into the reaction device, and oxygen-containing flue gas to be deoxygenated is introduced. Under heating conditions, the modified carbon-based fuel reacts with the oxygen in the oxygen-containing flue gas, consuming the oxygen in the oxygen-containing flue gas and generating solid ash slag rich in transition metal oxides. During the heating process, the transition metal salts loaded on the carbon-based fuel undergo thermal decomposition before the carbon-based fuel reaches its ignition point, generating highly dispersed transition metal oxide particles in situ. The transition metal oxide particles act as a catalyst, lowering the ignition point of carbon-based fuels and catalyzing the oxidation reaction of carbon-based fuels with oxygen, enabling the reaction to proceed efficiently at a temperature lower than that required for conventional direct combustion, consuming O2 in the flue gas, and simultaneously inhibiting the formation of CO. S3. Collect the solid ash residue generated in step S2, and leach the solid ash residue with acid to convert the transition metal oxides into soluble transition metal salts that enter the liquid phase. After solid-liquid separation, obtain a recovery liquid rich in transition metal salts. S4. All or part of the recovered liquid obtained in step S3 is returned to step S1 for use in preparing the aqueous solution containing the transition metal salt.

[0013] Furthermore, in S1, the carbon-based fuel includes one or both of coal and coal gangue.

[0014] Furthermore, the coal includes one or both of low-rank and high-rank coal.

[0015] Furthermore, the low-rank coal includes at least one of lignite, peat, long-flame coal, and gas coal; the high-rank coal includes at least one of lean coal, poor coal, and anthracite.

[0016] Furthermore, the combustible component of the coal gangue is not less than 15 wt%, preferably not less than 20 wt%.

[0017] Furthermore, in S1, the transition metal salt is a transition metal nitrate.

[0018] Furthermore, the transition metal in the transition metal salt includes at least one of iron, copper, manganese, cobalt, and nickel.

[0019] Furthermore, the loading method includes spraying, soaking, or mixing.

[0020] Furthermore, in S3, the acid solution is a nitric acid solution, and the leaching process is carried out at room temperature; if efficiency is to be improved, the temperature can be increased to 60°C.

[0021] Furthermore, after step S3 and before step S4, the method further includes a step of purifying and / or adjusting the concentration of the recovered liquid.

[0022] Furthermore, the purification includes chemical precipitation for impurity removal and / or filtration; the concentration adjustment includes evaporation concentration and / or replenishment with fresh transition metal salts.

[0023] In a second aspect, the present invention provides a modified carbon-based deoxygenating material for flue gas deoxygenation, wherein the deoxygenating material is prepared by the method of step S1 in the first aspect described above, and the catalytically active component contained in the deoxygenating material is at least partially derived from the recycling and reuse of the reaction ash residue from step S2 within the system.

[0024] The beneficial effects of this invention are as follows: This invention generates a highly dispersed catalyst through in-situ pyrolysis of transition metal salts, which lowers the ignition point of carbon-based fuels in a low-oxygen flue gas atmosphere, significantly suppresses CO generation, and simultaneously realizes the resource recovery and utilization of transition metals. It features high deoxygenation efficiency, low operating cost, and strong raw material adaptability. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art, inspired by the concept of this invention, can adapt the process parameters in each step according to the actual characteristics of the raw materials, on-site conditions, and economic requirements.

[0026] This invention provides a method for reducing the oxygen content of flue gas using modified carbon-based materials. The core of the method is as follows: an aqueous solution containing transition metal salts (preferably transition metal nitrates) is loaded onto carbon-based fuel (coal and / or coal gangue), and the modified carbon-based fuel is obtained after drying; the modified carbon-based fuel is subjected to in-situ catalytic combustion deoxygenation in oxygen-containing flue gas; after the reaction is completed, the ash residue is collected, and the transition metal is recovered by leaching with acid (preferably nitric acid), and the recovered liquid is reused in the front-end modification step to achieve the recycling of active components.

[0027] In step S1, the selection of carbon-based fuel has high on-site adaptability. For coal gangue-rich mining areas, coal gangue is preferred as the carbon-based fuel, which can both dispose of solid waste and reduce raw material costs; for coal gangue-scarce mining areas, low-rank or high-rank coal can be used as substitutes. The particle size of the carbon-based fuel is usually controlled within the range of 80-200 mesh to ensure sufficient reaction surface area and bed permeability. The concentration of the transition metal nitrate solution can be flexibly adjusted according to the target loading, generally controlling the metal element mass to account for 1%-20% of the carbon-based fuel mass, preferably 5%-15%. The loading method can be spraying, soaking, or mechanical blending. After loading, drying at 60℃-120℃ for 1h-24h yields the modified carbon-based fuel.

[0028] In step S2, modified carbon-based fuel is loaded into a fixed-bed reactor or a fluidized-bed reactor, and flue gas from a coal-fired power plant to be treated is introduced. The oxygen content in the flue gas is typically between 6% and 12%, and the reaction temperature is generally controlled between 350℃ and 650℃, depending on the type of carbon-based fuel and the catalyst loading. During the heating process, the transition metal nitrates loaded on the surface of the carbon-based fuel undergo thermal decomposition in the range of approximately 200℃ to 300℃, generating highly dispersed transition metal oxide particles in situ. These particles adhere tightly to the carbon matrix surface, significantly reducing the ignition point of the carbon-based fuel during subsequent heating and catalyzing the complete oxidation reaction of carbon with O2. Compared with the direct combustion of unmodified carbon-based fuel, the modified catalytic combustion not only has a lower ignition temperature but also a more complete combustion process, resulting in a significant reduction in CO production.

[0029] In step S3, the solid ash residue discharged in step S2 is collected and leached with nitric acid solution under heating. The transition metal oxides in the ash residue react with nitric acid to form soluble transition metal nitrates. After pressure filtration or centrifugation, a recovered leachate rich in transition metal nitrates is obtained. As needed, the recovered leachate can be purified (e.g., adjusting pH to precipitate and remove impurity ions) and its concentration adjusted (e.g., evaporation concentration or addition of fresh metal salts) to ensure its reuse performance meets the requirements of step S1.

[0030] In step S4, the recovered liquid obtained in step S3 is used to replace all or part of the freshly prepared transition metal salt solution and is returned to step S1 for the modification treatment of the next batch of carbon-based fuel, thereby realizing the circulation of transition metal ions within the system.

[0031] Example 1 In this embodiment, coal gangue with a combustible component of approximately 15 wt% was used as the carbon-based fuel. The effects of different types of transition metal nitrates and different loading amounts on the catalytic deoxygenation effect were investigated. The peak concentration of CO in the reaction tail gas was monitored as the evaluation index. The lower the CO peak value, the more complete the catalytic combustion, and the better the safety and environmental friendliness of the deoxygenation process.

[0032] Coal gangue was crushed to a particle size of 80-200 mesh, and aqueous solutions of transition metal nitrates of different concentrations were prepared. Modified coal gangue samples were prepared with loadings of 5% Fe (ferric nitrate), 5% Ce (cerium nitrate), 5% Cu (copper nitrate), 10% Cu, 15% Cu, 5% Co (cobalt nitrate), 10% Co, and 15% Co, based on the percentage of metal element mass in the solution relative to the coal gangue mass. The loading method was equal-volume impregnation. After impregnation, the samples were dried at 60℃ for 24 hours to obtain the modified coal gangue samples.

[0033] Each time, 1.5g of the modified coal gangue sample was weighed and placed in a fixed-bed reactor. Simulated flue gas from a coal-fired power plant (O2 9 vol%, CO2 12 vol%, the remainder being N2, flow rate 100 mL / min) was introduced, and the temperature was increased from room temperature to 450℃ at a rate of 5℃ / min. The peak CO concentration during the reaction process was recorded as the evaluation criterion. The experimental results are shown in Table 1 below.

[0034] Table 1 Peak CO concentration in the reaction tail gas under different modification conditions As shown in Table 1, the peak CO concentration in the reaction tail gas was significantly controlled after modifying coal gangue with transition metal nitrates. Co(NO3)2 showed particularly strong performance; when the loading reached 15%, the peak CO concentration was only 0.095%, far lower than the typical peak CO concentration when unmodified coal gangue was directly burned. This indicates that the method of this invention, through in-situ catalysis, greatly promotes the complete oxidation of carbon and effectively inhibits the formation of the toxic byproduct CO. Meanwhile, copper nitrate also showed good CO inhibition effects and can be flexibly selected based on the availability of metal resources and cost factors.

[0035] It should be noted that the key operating parameters of each step in the process of this invention can be adaptively adjusted within a wide range according to the characteristics of the raw materials. For example, the concentration, application amount, drying conditions, reaction temperature, flue gas flow rate, and concentration and temperature of the leaching acid can all be determined by those skilled in the art through conventional optimization experiments based on actual working conditions, without departing from the protection scope of this invention.

[0036] The above description is merely a preferred embodiment of the present invention and does not limit the scope of the patent. Any equivalent structural transformations made based on the inventive concept of the present invention and the content of this specification, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A method for reducing the oxygen content of flue gas using modified carbon-based fuels, characterized in that: The deoxidizing active components are directly loaded onto the fuel body, enabling the catalytic combustion deoxidation reaction and the fuel's own conversion process to occur in situ in synergistic manner; furthermore, the active components are recovered from the ash residue after the reaction using hydrometallurgical methods, realizing the circulation of the active components within the system; specifically, the following steps are included: S1. Mix an aqueous solution containing at least one transition metal salt with carbon-based fuel, and then dry it to obtain modified carbon-based fuel; S2. The modified carbon-based fuel is fed into the reaction device, and oxygen-containing flue gas to be deoxygenated is introduced. Under heating conditions, the modified carbon-based fuel reacts with the oxygen in the oxygen-containing flue gas, consuming the oxygen in the oxygen-containing flue gas and generating solid ash slag rich in transition metal oxides. S3. Collect the solid ash residue generated in step S2, and leach the solid ash residue with acid to convert the transition metal oxides into soluble transition metal salts that enter the liquid phase. After solid-liquid separation, obtain a recovery liquid rich in transition metal salts. S4. All or part of the recovered liquid obtained in step S3 is returned to step S1 for use in preparing the aqueous solution containing the transition metal salt.

2. The method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 1, characterized in that: In S1, the carbon-based fuel includes one or both of coal and coal gangue.

3. The method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 2, characterized in that: The coal includes one or both of low-rank and high-rank coal; the combustible component of the coal gangue is not less than 15 wt%.

4. The method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 3, characterized in that: The low-rank coal includes at least one of lignite, peat, long-flame coal, and gas coal; the high-rank coal includes at least one of lean coal, poor coal, and anthracite.

5. The method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 1, characterized in that: In S1, the transition metal salt is a transition metal nitrate.

6. A method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 5, characterized in that: The transition metal in the transition metal salt includes at least one of iron, copper, manganese, cobalt, and nickel.

7. The method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 1, characterized in that: The loading method includes spraying, soaking, or mixing.

8. The method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 1, characterized in that: In S3, the acid solution is a nitric acid solution, and the leaching process is carried out at room temperature or 60°C.

9. A method for reducing the oxygen content of flue gas using modified carbon-based fuel according to claim 1, characterized in that: After step S3 and before step S4, the method further includes a step of purifying and / or adjusting the concentration of the recovered liquid. The purification process includes chemical precipitation for impurity removal and / or filtration; the concentration adjustment includes evaporation concentration and / or replenishment with fresh transition metal salts.

10. A deoxidizing material for reducing the oxygen content of flue gas using modified carbon-based fuels, characterized in that, The deoxidizing material is prepared by step S1 of the method according to any one of claims 1 to 9.

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