Experimental Research On Briquette Used In Lime Vertical Kiln And Numerical Simulation Of Briquette's Drying Process

Briquette can be used as a substitute fuel of coke in lime vertical kiln, which can relieves the contradiction between supply and requirement of fuel effectively and enhances economical efficiency of lime production. The drying of briquette is one of essential steps in the process of briquetting, it is of significant meanings to study the drying behaviors of briquette in the optimization of the drying process of briquetting and energy conservation.The Jinzhunshan anthracite of Hunan was used as the raw coal, based on the basic function of binder, a compound binder was adopted in the orthogonal experiment of briquette used in lime vertical kiln. There are eight factors including magnesium base binder, magnesium base activator, biomass fiber, water reducing agent, mixture ration of bituminous coal , briquetting pressure, briquetting water and the size-composition of anthracite were examined in the orthogonal experiment, six indexes of briquette including original compressive strength, original drop shatter strength, cold compressive strength, cold drop shatter strength, hot compressive strength and the thermal stability were evaluated. Test results were analyzed systematically utilizing the way of the breakdown formula evaluation for considering all the indexes. Based on the range analysis and variance analysis of synthetic evaluation results, the optimal compound binder and briquetting technical parameters were obtained. Through validation and cost valuation, the result indicates that the anthracite briquette prepared according to the optimal scheme obtained in this experiment can meet the demand of the industrial production of lime vertical kiln and it also has good economical efficiency. Then the function of binder and optimal briquetting technical parameters were analyzed simply.Briquette is a typical porous media. Based on the basic theory of heat and mass transfer in porous media, primary mechanisms of transportation for liquid and gas in drying process of porous media were analyzed. Assume phase transformation, heat and mass transfer in every mass point of briquette in local thermodynamics equilibrium and based on volume-averaging theory, the mathematical model of drying process of briquette was established using the three state-variable: saturation of liquid S, temperature T and pressure of mixture gas P_g, which is composed of the conservation equation and the energy conservation equation of porous media, including solid, liquid, vapor and air. After discretization of governing equations and boundary conditions with fully implicit finite difference technique, the distributions of the state-variable including saturation of liquid S, temperature T and pressure of mixture gas P_g were obtained during the drying process of briquette at every node by solving interactive equations. Some conclusions were achieved by analyzing the results of numerical simulation: the drying rate will be faster by heightening the drying temperature and coefficient of heat transfer, or reducing the thickness of briquette.Some original work is as follows: Test results were analyzed systematically utilizing the way of the breakdown formula evaluation, which brings on good overall performance of the developed briquette. The drying process of briquette was simulated based on the basic theory of heat and mass transfer in porous media, the distributions of the state-variable during the drying process of briquette were obtained, and the numerical results are very useful for the optimization of the drying process of briquette.