Compound for flue gas deoxidation and flue gas deoxidation method

Abstract

The invention discloses a compound for flue gas deoxidation and a flue gas deoxidation method, and relates to the technical field of flue gas treatment for preventing spontaneous combustion injection of residual coal in a goaf. The compound comprises coal semicoke and a composite metal oxide which are mixed, wherein the composite metal oxide comprises CoO and CuO in a mass ratio of 7: (2.5-3.5); the compound is combusted through a fixed bed, and flue gas generated by combustion is deoxidized; when the coal semicoke is used for catalytic combustion deoxidation, CoO and CuO in a certain proportion are added, so that the oxygen consumption rate is high, the CO generation amount and the CO concentration are low, the ignition point is reduced, and the comprehensive effect is good; the problem that the concentration of O2 and the concentration of CO in the flue gas are too high when the flue gas is injected into an underground goaf is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of fire prevention and extinguishing in mine goafs, and relates to flue gas treatment for preventing and controlling spontaneous combustion of residual coal in goafs, and specifically relates to a composite material for flue gas deoxidation and a flue gas deoxidation method. Background Art

[0002] The coal industry and coal-fired power plants are crucial for achieving my country's "dual carbon" goals. Reducing carbon emissions is a key area of focus for the coal sector in the future. Previously, the coal industry typically used pressure swing adsorption (PSA) to generate inert gas for underground fire prevention and extinguishing. While this method is currently the most technologically mature and automated, its low sample recovery rate and high energy consumption have led to economic constraints that have hindered the industry's development. Flue gas from coal-fired power plants is my country's largest centralized carbon emitter, accounting for the majority of carbon emissions. Flue gas from coal-fired power plants primarily consists of nitrogen (68%-74%), carbon dioxide (11%-16%), and oxygen (4%-10%), with other pollutants at ppm levels. This is essentially a low-oxygen waste gas rich in inert gases. If it could be treated and utilized instead of traditional inert gas for goaf storage, it could not only achieve goaf fire prevention and extinguishing, reduce carbon emissions, but also offer significant economic benefits.

[0003] According to early monitoring data, a large number of thermal power plants are unable to operate at full capacity, and the oxygen content of their flue gas emissions is between 5% and 10%. This has brought unavoidable technical and economic problems to underground flue gas fire prevention and extinguishing (existing research shows that the best effect is achieved when the oxygen content is below 3%). Due to the high concentration of O2 in the flue gas, direct use may have the opposite effect. How to solve the above problems economically and effectively to achieve the goal of energy conservation and emission reduction is the focus of current research.

[0004] Currently, common gas deoxygenation technologies are mainly divided into three categories: physical deoxygenation technology, biological deoxygenation technology, and chemical deoxygenation technology. Physical deoxygenation technology mainly separates oxygen based on the physical properties of the gas, such as pressure swing adsorption and temperature swing adsorption. However, the flue gas composition of power plants is complex, and traditional physical methods are not only complex but also costly. Biological deoxygenation technology mainly relies on the metabolism of microorganisms to consume oxygen, but the metabolism of microorganisms is affected by many factors, with long startup times and high maintenance costs. Traditional chemical deoxygenation technology mainly utilizes the combustion catalysis of coal, but direct combustion will produce more polluting gases, which runs counter to the purpose of flue gas deoxygenation. However, this method has the characteristics of high efficiency, wide application range, high economic benefits, and customization in actual use.

[0005] In view of this, there is a need for a method to treat O2 in power plant flue gas to achieve the above-mentioned energy-saving, economical and emission-reducing flue gas deoxygenation goals without generating more additional products to cause secondary pollution to the flue gas. Summary of the Invention

[0006] The present invention overcomes the shortcomings of the existing technology and proposes a composite material for flue gas deoxygenation and a flue gas deoxygenation method; coal semi-coke is used, which is a material with less pollution, better economic benefits, higher combustion rate and more stable combustion than raw coal, and deoxygenation is achieved by catalyzing the combustion of the coal semi-coke by adding metal oxides and compound metal oxide catalysts; the problem of excessive O2 concentration and CO concentration in the flue gas when injected into the underground goaf is solved.

[0007] The present invention is achieved through the following technical solutions: A composite for flue gas deoxidation comprises mixed coal semi-coke and composite metal oxides, wherein the composite metal oxides account for 9-12% of the composite by mass; the composite metal oxides comprise CoO and CuO in a mass ratio of 7:2.5-3.5.

[0008] Preferably, the mass percentage of the composite metal oxide in the composite is 10%.

[0009] More preferably, the mass ratio of CoO to CuO is 7:3.

[0010] A flue gas deoxidation method comprises the following steps: burning a composite material for flue gas deoxidation in a fixed bed to deoxidize the flue gas generated by the combustion.

[0011] Preferably, the coal semi-coke of the composite species is obtained by low-temperature dry distillation of coal.

[0012] Preferably, after the coal is dried, it is dry distilled at 550-650° C. for 2-3 hours under a nitrogen atmosphere.

[0013] Preferably, the coal is 60-80 mesh.

[0014] Preferably, the drying is carried out in a vacuum drying oven at 60° C. for 24 hours.

[0015] Preferably, the nitrogen flow rate is 100 ml / min.

[0016] Preferably, during fixed bed combustion, the mass of the composite is 0.5-0.8 g, and the flue gas flow rate is 100-110 ml / min.

[0017] The beneficial effects of the present invention compared to the prior art are: (1) The combustion product of coal semi-coke catalyzed by metal oxides is flue gas, which will not cause other pollution. In addition, it also undergoes desulfurization and denitrification processes before being injected into the well, which will not bring additional economic burden.

[0018] (2) The oxygen concentration of power plant flue gas is not high, ranging from 4% to 10%. The proximity of thermal power plants to coal mines facilitates the flow of treated flue gas into goafs for fire prevention and extinguishing. Coal is readily available and low-cost. Using non-precious metals for catalytic combustion offers both good catalytic effects and higher economic benefits.

[0019] (3) Compared with direct combustion and deoxidation of raw coal, the use of coal semi-coke can effectively improve resource utilization, reduce pollution, and improve economic benefits, and the deoxidation and combustion effects are more stable.

[0020] (4) In the deoxidation of coal semi-coke catalyzed by metal oxides, when the metal oxide catalyst is added in the form of 7% CoO + 3% CuO, the deoxidation efficiency can be improved while the ignition temperature is reduced, and less CO is produced.

[0021] (5) The residual O2 and the generated CO can be used as raw materials for CO catalysis in the subsequent process to catalytically oxidize CO to generate CO2, which is suitable for injection into the goaf; O2 can be reduced to within the safety line. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention. The technical solutions of the present invention will be described in detail below with reference to the embodiments, but the scope of protection is not limited thereto.

[0023] Reasons for choosing coal semi-coke: Bituminous coal has a high volatile content, making it easy to ignite. However, excessive volatiles lead to unstable combustion, generating a large amount of flue gas during combustion, which in turn produces other impurities. This makes its use as a flue gas deoxygenator meaningless. Furthermore, directly using coal for deoxygenation has low economic value and results in a waste of resources. On the other hand, bituminous coal semi-coke's extremely low water content and inherent structure make it easy to ignite. Its low volatile content also makes it smokeless during combustion, eliminating the generation of other impurities. Pre-treatment involves dry distillation and pyrolysis of the coal. The pyrolysis process can convert the hydrogen-rich components in the coal into coal gas and coal tar for reuse. The large amount of semi-coke produced can also be used for combustion and other purposes, improving the comprehensive utilization rate of coal resources and generating higher economic benefits.

[0024] After carbonization, the structure of coal semi-coke becomes brittle and porous, with a higher specific surface area, which makes it more reactive during catalytic combustion. When mixed with metal oxide catalysts, the catalytic effect will be more obvious.

[0025] Step 2: Selection of metal oxide catalyst: Metal oxide additives transfer oxygen atoms to carbon atoms, accelerating oxygen diffusion and facilitating coal combustion. They exhibit a significant catalytic effect during coal pyrolysis and combustion, accelerating the combustion of fixed carbon. Furthermore, they mitigate environmental pollution from coal combustion and exhibit excellent desulfurization and denitrification properties.

[0026] This embodiment uses coal semi-coke as the raw material for catalytic combustion flue gas deoxidation. By optimizing metal oxides and compounding metal oxides, a formula with relatively excellent effects is found to achieve more efficient removal of O2 from flue gas at a lower temperature level, producing more CO2 and less CO.

[0027] Due to the variability of coal masses, the inlet flue gas flow rate is not fixed and should be adjusted based on actual conditions such as outlet oxygen concentration and oxidizer energy consumption. The oxidizer temperature should be selected based on actual deoxidation and CO production. A fixed-bed experiment was conducted in the laboratory using 0.6g of coal semi-coke at a flue gas flow rate of 100ml / min.

[0028] Regarding the selection of metal oxides, common non-precious metal oxides were selected for comparison, and the grinding method was used to add the metal oxides in the experiment. The metal oxides with higher addition amounts were given priority for preliminary screening. The maximum oxygen consumption rate of O2, the maximum average oxygen consumption rate, the amount of CO generated and the highest point of CO concentration when different metal oxides were added were compared. The combustion data of different metal oxides are shown in Table 1.

[0029] Analysis of the data in the table above indicates that the best overall effect is achieved when CoO, Al₂O₃, and CuO are added. Coal char with these three metal oxides exhibits higher oxygen consumption rates, with CoO exhibiting the highest and average oxygen consumption rates. While CuO exhibits a lower oxygen consumption rate, it significantly reduces CO formation, which has a positive impact on subsequent CO treatment and its use as an inert gas in goafs. The other eight metal oxides lack a strong catalytic effect on the combustion of bituminous coal char and are ineffective in suppressing CO formation. Therefore, CoO, Al₂O₃, and CuO were selected as catalysts for bituminous coal char, and the optimal formulation was achieved by combining the advantages of these different catalysts.

[0030] After semi-coke combustion, the O2 concentration in flue gas can be reduced to approximately 2.5%, while a relatively high amount of CO is produced. While increasing the oxygen consumption rate, it is also important to consider reducing CO generation. Adding suitable metal oxide catalysts can effectively increase the oxygen consumption rate of semi-coke combustion and reduce the CO generation rate. Among these, CoO, a single metal oxide, can increase the oxygen consumption rate of bituminous coal semi-coke by nearly 40%. CuO can reduce the CO generation rate of bituminous coal semi-coke by 37.91%, and Al2O3 can reduce the combustion temperature of bituminous coal semi-coke to a certain extent. Mixing these three metal oxides in a certain proportion can combine their respective advantages.

[0031] Step 3: Selection of metal oxide addition ratio In previous studies, the addition ratio of metal oxide catalysts to raw coal samples typically ranged from 1% wt% to 10% wt%, a range that covers the requirements for testing the catalytic effect of coal spontaneous combustion in most studies. Considering the need for large-scale field application of experimental formulations, in addition to experimental validity, ease of operation and cost-effectiveness were also important considerations. The grinding method (physical mixing) for adding metal oxides is simple to operate, requires minimal additional processing, is low-cost, requires no complex equipment, and is less destructive to the original structure of the coal sample, making it more suitable for field application. Semi-coke, as a porous carbon-based material, has physical limits on the amount of metal oxides it can support on its surface and within its pores. Literature indicates that the critical loading level for bituminous coal semi-coke is approximately 10-15 wt%. Above this value, metal particles cannot effectively disperse and aggregate, clogging the pores. Therefore, the metal oxide loading level should be controlled below 10% wt. The optimal loading level was determined through gradient experiments (3%, 5%, and 10%), observing oxygen consumption rates, CO concentrations, and production. The experimental data are shown in Table 2.

[0032] Based on the data in the table above, it can be analyzed that, for single metal oxide additives, a 10% addition of CoO results in the highest oxygen consumption rate, significantly higher than 3% and 5% additions, and reduces CO generation by 24.6% and 22.9% compared to 3% and 5%, respectively. This results in the best overall performance, which significantly improves with increasing additive dosage, making it suitable as a core component for enhancing oxygen consumption. Its optimal addition level is 5% to 10%. While the oxygen consumption rate decreases significantly with increasing CuO additive level, CO generation also decreases significantly, but remains minimal overall. Therefore, for optimal overall effectiveness, the CuO dosage should be around 3% of the additive. When formulating multiple components, CoO should be the primary component due to its highest oxygen consumption rate and excellent CO control capabilities. Low levels of CuO can synergistically enhance catalytic oxygen consumption and minimize CO generation, complementing CoO. Al2O3 can serve as a secondary component to enhance stability. To facilitate subsequent formulations with multiple metal oxides, a 10% addition level is optimal.

[0033] Example 1 This embodiment proposes a flue gas deoxygenation method based on the combustion of semi-coke catalyzed by metal oxides: Take flue gas with an oxygen concentration of 9%, CO2 of 12% and the remaining gas being N2 as an example.

[0034] Step 1: Preparation of coal semi-coke: Take a 60-mesh coal sample and dry it in a vacuum drying oven at 60°C for 24 hours, then let it stand and cool to room temperature for 24 hours. Then take 20g of the cooled coal sample each time and distill it at 600°C for 2 hours in a nitrogen atmosphere with a nitrogen flow rate of 100ml / min. The solid sample obtained after distillation is coal semi-coke.

[0035] Step 2, Compounding: Three equal parts of coal semi-coke are ground and mixed with different weight ratios of compounded metal oxides to produce three coal samples. The total weight of the added metal oxides in the coal sample is 10% by weight. The single metal oxides in the metal oxide catalyst are CuO, Al2O3, and CoO. These three metal oxides are mixed in ratios of 5:5, 7:3, and 3:7, respectively, to produce compounded metal oxides, which are then mixed with the coal semi-coke to produce the coal sample.

[0036] Step 3, coal sample combustion: fixed bed combustion, with the mass of each coal sample being 0.6 g and the flue gas flow rate being 100 ml / min, a curve of oxygen variation with temperature was obtained. The oxygen consumption rate curve was calculated using the oxygen consumption rate formula. The experimental results of coal flue gas deoxygenation for each coal sample are shown in Table 3, and the CO generation amount is shown in Table 4.

[0037] Step 3: Thermogravimetric experiment was performed to study the change in ignition point temperature when metal oxides were added. TG and DTG curves were obtained through thermogravimetric experiments, and the ignition point was obtained through the tangent method, as shown in Table 5.

[0038] Experimental data show that when a single metal oxide is added as a catalyst, all three additives have a certain catalytic effect on the oxygen consumption of coal char. CoO has the highest oxygen consumption rate, but the ignition temperature does not change significantly. CuO has the lowest CO production, but the oxygen consumption capacity does not increase significantly. Al2O3 has a less significant improvement in oxygen consumption, and CO production increases, but the ignition point decreases somewhat. Each of the three catalysts has advantages and disadvantages in catalyzing coal char combustion. Considering the combination of the three catalysts and their synergistic effects.

[0039] In the orthogonal experiment, adding 5% Al2O3+5%CoO has the lowest ignition temperature. However, considering the three points comprehensively, when adding 7%CoO+3%CuO, it has a higher oxygen consumption rate, less CO generation and a lower ignition point, which is the best overall.

[0040] Experimental example: formula confirmation and comparison In the formula of 7%CoO+3%CuO, if CoO is replaced with Al2O3, it can be found that its oxygen consumption rate is significantly reduced, and the amount of CO generated is also significantly increased; if CoO is replaced with Fe2O3 and MnO2, although the amount and rate of CO generated are reduced to a certain extent, the oxygen consumption rate is significantly reduced, which will affect the reduction of oxygen removal rate. Replacing CuO with Al2O3 and CaO can be found that its oxygen consumption rate is significantly reduced, and the amount of CO generated is also significantly increased; although the maximum oxygen consumption rate is increased by 6% when CuO is replaced by Fe2O3, its maximum average oxygen consumption rate is reduced, and the amount of CO generated is greatly increased, and the highest point of CO concentration is increased by 32%; it can be seen that there is a synergistic effect between CoO and CuO. These two metal oxides are added to bituminous coal semi-coke in a ratio of 7:3, which can effectively remove oxygen from flue gas and produce less CO. They cannot be separated or their components transformed.

[0041] While maintaining the total addition amount of CoO and CuO, the ratio of the two is varied. It is found that decreasing the CoO ratio significantly decreases the oxygen consumption rate and the maximum average oxygen consumption rate. While CO generation decreases, the decrease is small. Taking all factors into consideration, a change in the ratio degrades the catalyst's effectiveness and makes it unsuitable. CoO increases the oxygen consumption rate, while CuO reduces CO generation. A 7:3 ratio achieves an optimal balance between their effects. This ratio achieves the best trade-off between combustion efficiency (oxygen consumption rate), environmental friendliness (CO generation), and combustion completeness (O2 demand). Adjusting the ratio would result in an imbalance in performance indicators, failing to meet the dual requirements of efficient and clean combustion. Therefore, this ratio cannot be changed.

[0042] In summary, when using coal semi-coke for catalytic combustion deoxygenation and subsequent treatment in flue gas deoxygenation and subsequent filling into goafs, a total catalyst mass ratio of 10 wt% and a CoO:CuO ratio of 7:3 achieves a high oxygen consumption rate, an 11.53% increase in deoxygenation compared to no addition, and a low CO generation and concentration, along with a reduced ignition point, resulting in the best overall performance. Furthermore, the two metal oxides cannot be separated, and their ratio cannot be changed.

[0043] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be considered that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, they can make several simple deductions or substitutions without departing from the present invention, which should be regarded as belonging to the scope of patent protection determined by the submitted claims of the present invention.

Claims

1. A composite for flue gas deoxidation, characterized in that: The invention comprises mixed coal semi-coke and composite metal oxides, wherein the composite metal oxides account for 9-12% of the composite material by mass; the composite metal oxides comprise CoO and CuO in a mass ratio of 7:2.5-3.

5.

2. The composite for flue gas deoxidation according to claim 1, characterized in that: The mass percentage of the composite metal oxide in the composite is 10%.

3. The composite for flue gas deoxidation according to claim 2, characterized in that: The mass ratio of CoO to CuO is 7:

3.

4. A flue gas deoxygenation method, characterized in that: The method comprises the following steps: burning the composite material for flue gas deoxidation according to any one of claims 1 to 3 in a fixed bed to deoxidize the flue gas generated by the combustion.

5. A flue gas deoxygenation method according to claim 4, characterized in that: The coal semi-coke of the composite species is obtained by low-temperature dry distillation of coal.

6. A flue gas deoxygenation method according to claim 5, characterized in that: After the coal is dried, it is dry distilled at 550-650°C for 2-3 hours under a nitrogen atmosphere.

7. A flue gas deoxygenation method according to claim 6, characterized in that: The coal is 60-80 mesh.

8. A flue gas deoxygenation method according to claim 6, characterized in that: The drying step is to dry the mixture in a vacuum drying oven at 60° C. for 24 h.

9. A flue gas deoxygenation method according to claim 6, characterized in that: The nitrogen flow rate was 100 ml / min.

10. A flue gas deoxygenation method according to claim 4, characterized in that: During fixed bed combustion, the mass of the composite is 0.5~0.8g and the flue gas flow rate is 100~110 ml / min.

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