Experimental Study On Enhanced Mineralization Of High Concentration CO₂ By Coal Thermoelectric Solid Waste

The’double carbon’strategic goal is a solemn commitment made by China to cope with global climate change.CCUS（Carbon Capture,Utilization and Storage）is a necessary technical means for carbon emission reduction.A large amount of coal thermal power solid waste is produced in the process of coal thermal power generation.Coal fly ash and desulfurization gypsum are typical bulk coal thermoelectric solid wastes.The calcium and magnesium substances contained in the coal thermoelectric solid waste can mineralize with the carbonate produced by the dissolution of CO₂ in the medium to form a stable carbonate,thereby achieving carbon emission reduction.Modern coal chemical industry is an important way for clean and efficient utilization of coal,but its production process will discharge saline wastewater.Studies have shown that saline wastewater can be used as a mineralization reaction medium.Using coal thermoelectric solid waste to mineralize high concentration CO₂（coal-to-hydrogen enterprises,≥98%）,on the one hand,it can open up new ways for the resource utilization of coal thermoelectric solid waste,on the other hand,it is of great significance for the industrial application of CCUS technology.Taking coal thermoelectric solid waste as the research object,the experimental study on carbon fixation of coal thermoelectric solid waste was carried out by using coal chemical salty wastewater instead of aqueous solution as the wet mineralization reaction medium.The main research are as follows:（1）Coal thermoelectric solid waste has the basic mineralogical conditions for mineralization and storage of CO₂.The average content of Ca O in coal fly ash is 6.81%.The main mineral phases are silica（Si O₂）and mullite(Al₆Si₂O₁₃).The particle size range is 30～110μm,the average specific surface area is 1.5184 m²/g,and the average pore volume is 0.0394 cm³/g.The average content of Ca O in desulfurization gypsum is more than 40%.The main mineral phase is calcium sulfate dihydrate（Ca SO₄·2H₂O）.The particle size range is 10～100μm,the average specific surface area is 11.7662 m²/g,and the average pore volume is 0.3164 cm³/g.The desulfurized gypsum has larger specific surface area and pore volume,better adsorption performance,and can provide more reactive sites for CO₂ mineralization.（2）Find out the dissolution characteristics of calcium and magnesium salts in coal thermoelectric solid waste.The dissolution medium,dissolution time,temperature,reactant particle size and liquid-solid ratio will affect the dissolution of calcium and magnesium salts in coal thermoelectric solid waste to varying degrees.The dissolution effect of calcium and magnesium ions in ammonium chloride medium is better than that in saline wastewater medium.Considering the experimental effect and economy,under the conditions of solid waste particle size 75～120μm,dissolution time 1 h,temperature60°C,liquid-solid ratio 5 m L/g and ammonium chloride concentration 25 g/L,the dissolution concentrations of calcium and magnesium ions in coal fly ash were 392.10mg/L and 23.55 mg/L,respectively.The dissolution concentrations of calcium and magnesium ions in desulfurization gypsum were 1862.75 mg/L and 487.52 mg/L,respectively.（3）The CO₂ mineralization performance of different coal thermoelectric solid wastes in the reaction medium was evaluated,and the CO₂ mineralization reaction law of coal thermoelectric solid wastes was revealed.Due to the different chemical composition and physical properties of coal fly ash and desulfurization gypsum,the amount of carbon fixation varies greatly.In saline wastewater,0.9523 mol CO₂ and 6.4064 mol CO₂ can be fixed per kilogram of coal fly ash and desulfurized gypsum,respectively.The amount of carbon fixation of coaland desulfurized gypsum in the medium is:pure water<ammonium chloride<saline wastewater.The chemical reaction process of CO₂ direct wet mineralization of coal thermoelectric solid waste includes the dissolution of calcium and magnesium ions,the dissolution of CO₂ and the formation of Ca CO₃.The crystal forms of mineralization products of coal fly ash and desulfurization gypsum in different media are also different.In saline wastewater,the crystal form of coal fly ash mineralization product is massive calcite,and the desulfurization gypsum mineralization product is calcite and vaterite.In the ammonium chloride medium,the crystal form of the coal fly ash mineralization product is aragonite,and the desulfurization gypsum mineralization product is calcite.（4）The influence of various parameter conditions on carbon sequestration was discussed,and the optimized parameters of enhanced CO₂ mineralization technology of coal thermoelectric solid waste combined with saline wastewater were obtained.The reaction equilibrium time of CO₂ mineralization of coal fly ash is 120 min,the optimum initial CO₂ pressure is 1 MPa,the optimum mineralization temperature is 65°C,and the amount of ammonia added is 5 m L.The results of response surface modeling show that the order of the influence of each parameter on the carbon sequestration of coal fly ash is:initial CO₂ pressure>mineralization time>mineralization temperature.The maximum carbon sequestration of coal fly ash optimized by the model is 0.95 mol/kg,and the parameter conditions are t_c=150 min,T_c=66°C,P=1.25 MPa.The reaction equilibrium time of CO₂ mineralization by desulfurized gypsum is 60 min,the optimal initial CO₂pressure is 1.5 MPa,the optimal mineralization temperature is 65°C,and the amount of ammonia added is 10 m L.In the response surface model,the order of the influence of each parameter on the carbon sequestration of desulfurized gypsum is:mineralization temperature>initial CO₂ pressure>mineralization time.The maximum carbon sequestration of the model was 6.70 mol/kg,and the parameter conditions were t_c=71min,T_c=73°C and P=1.9 MPa.Figure[28]Table[16]Reference[116]...