Comprehensive Utilization Of Waste Coke Powder Preparation Of High-ash Carbonaceous Reductant

In the dissertation, the technology and fundamentals of the demineralization processing to prepare carbon reductants from high-ash waste coke breeze by pressure-leaching method are systematically studied.This dissertation firstly introduces the situations of silicon metal and calcium carbide industries and the carbon reductants used in silicon metal and calcium carbide production, and points out the contradiction between the rapid development of silicon metal and calcium carbide industries and the shortage of carbon reductants. Meanwhile, the history of coke using as a reductant and the source and usage status quo of high-ash coke breeze are also be introduced. On the basis of the over view of the domestic and international research results about demineralization techniques and the application status of these techniques, the direction in studies of the demineralization processing for carbon reductants from high-ash waste coke breeze are proposed. Thereby, significance and main contents of this resreach are put forward explicitly.The research chooses coke breeze from the coking plant in Yunnan as study object. According to the existing form of ash minerals in coke breeze and the thermodynamics analysis results of demineralization by pressure-leaching method, the technical route of pressure alkali leaching followed by acid leaching at atmospheric on coke breeze demineralization is put forward, and the theory foundation on demineralization are inveatigated.(1) The element categories and contents, the phase composition and distribution characteristics of ash in coke breeze are analysed with modern analysis and testing technology. The main ash elements in coke breeze are Si, Al, Fe, Ca, Ti and S, which exist generally as the oxidate. The main phase compositions of ash minerals are quartz, cristobalite, mullite, hematite, and anhydride. The mostly mineral particles are mixed with coke particles, and a few fine minerals particles are intimately associated with the coke matrix. It is difficult to separate minerals particles from coke particles by the physical method. The chemical leaching is more suitable for demineralization of coke breeze.(2) The thermodynamics laws of pressure leaching of coke breeze are analysed. The Igα-pH diagrams of Si, Al, Fe, Ca, Ti and Mg, the (p-pH diagram of Al-Si-H2O system at different temperature, the Ig(c)-pH diagrams of Si-H2O system, AI-H2O system and Al-Si-H2O system are construted respectively.(3) The effects of leaching agents, initial concentration, particle size, temperature, leaching duration, liquid-to-solid ratio, ect. on the degree of demineralization are examined from the technological angle. The reasonable technological conditions obtained by factor experiments are that alkali leaching; particle size<75μm, temperature180～200℃, NaOH solution concentration15wt.%, leaching duration30min, liquid-to-solid ratio4:1～8:1, self-pressure; acid leaching:temperature90℃, H2SO4solution concentration12wt.%, leaching duration30min, liquid-to-solid ratio6:1. The results of the extensive experiment conducted under the reasonable conditions prove the feasibility and applicability of the proposed demineralization method. The degree of demineralization is more than85%, the content of ash is less than4.5%, the degrees of the removal of Si, Al and Mg is more than85%, the degree of Ca removal is more than97%, and the degree of Fe removal is more than70%.(4)Under the determind conditions, the kinetics of coke breeze demineralization are studied. The original "kinetic model of Crank-Ginstling-Brounshtein" for liquid-solid reaction is used to obtain the kinetic equation for the removal of Si and Al in ash and investigate the controlled step of Si and Al removal. The results show that the Si and Al minerals removal reaction activation energy is27.635kJ/mol and36.041kJ/mol respectively, and the process of the Si and Al removal are both controlled by the interior diffusion. The kinetic equationfor the effect of alkali leaching temperature on the degree of Si and Al minerals removal are: In k’si=0.51792+3.3239×103×T/1In k’al=-1.13402+4.33495×103×T/1(5) The physical and chemical properties of coke breeze are studied before and after demineralization. Through the comparison with the reductant used in silicon metal and calcium carbide production, and the application mode of the de-ash coke breeze is put forward. The possibility of using de-ash coke breeze as reductant for silicon metal and calcium carbide production is proved by the analysis of physical and chemical property of de-ash coke breeze and the reduction experiments.(6) The environmental and economical evaluation of the process are made. The cost of the reductant from de-ash coke breeze is￥1855.25/t, lower than the price of carbon reductant for silicon metal and calcium carbide, which has considerable economic benefit. The results of environmental evaluation show that wastewater and dregs produced by the reductant production can be recycled, the productive process has low effect of environment. The results of the environmental and economical evaluation indicate that the process is feasible.(7) The reductant production from de-ash coke breeze increases the added value of high-ash coke breeze, which can solve the environmental treathens from waste piling, and it provides a new reductant resourse for silicon metal and calcium carbide production, and then to realize the comprehensive utilization of the coking coal.