Numerical Simulation Of Heat Transfer For Cr（OH）₃ Calcination Rotary Kiln

Cr2O3 is widely used in various industries,including ceramic,refractory material,pigment.China is one of the major producing country of Cr2O3.In 2017,13.84 million ton chromite ore has been imported to China,ratio of import dependence was 95%and value of import was the first in the world.The main method to produce Cr2O3 is hydrometallurgy process,using rotary kilns as calcination facility.Rotary kilns had problems as calcination unevenly,and waste of energy.According to the relationship of three variables in kiln,heat transfer and flow process existed in kiln influence energy consumption and calcination quality.Take this into consideration,research of heat transfer process is the way to increase the quality of product and decrease energy consumption.Currently,no research of Cr(OH)3 calcination rotary kiln has been reported.Other research of bulk material calcination/roasting rotary kiln was referenced,and one dimensional heat transfer model of Cr(OH)3 calcination rotary kiln was built using Matlab.Based on the model,drawbacks of two dimensional and three dimensional model,like lacking comprehensiveness,non-convergence and wasting time,was overcome,and two dimensional heat transfer model was built,using results of one dimensional model as definite condition.Thus research of thermal process in kiln was conducted.The main research contents,conclusions and innovations are shown as below.(1)Based on mechanisms of heat transfer in Cr(OH)3 calcination rotary kiln,one dimension model of heat transfer process in rotary kiln was established using Matlab.Results of one dimension model were translated in UDF,and were utilized as definite conditions of two dimension model,thus two dimension model was established.(2)Convection and radiation are dominated heat transfer mechanisms in kiln.From kiln inlet to outlet,convection heat transfer percent decrease from 58.9%to 8.9%;radiation heat transfer percent increase from 7.3%to 91.1%.Convection is dominated mechanism in preheating zone,preheating zone take 13.3%whole kiln length,material is heated form 300 K to 630K.Dominated heat transfer mechanism transfer from convection to radiation in heating zone,heating zone take 45.4%whole kiln length,material is heated form 630 K to 1000K.Radiation is dominated mechanism in reacting zone,reacting zone take 41.3%whole length,material is heated form 1000 K to 1438K.(3)Both gas and inner wall heat material in rotary kiln,and gas is dominated part.With material move from inlet to outlet,heat gas transferred to material increase from 71.5%to 100%.Heat inner wall transferred to material decrease from 28.5%to 0%(4)The major factors affecting temperature distribution in kiln are fuel quantity,throughput and combustion air quantity.When fuel quantity increase by 5%,temperature of material increase 77 K,increase by 5.35%.When throughput increase by 5%,temperature of material decrease 56 K,increase by 3.89%,When combustion air quantity increase by 5%,temperature of material decrease 36 K,increase by 2.51%.(5)Based on mechanisms of heat transfer in Cr(OH)3 calcination rotary kiln,appropriate operating parameters were found.Maximal throughput is 3634t/A,increase by 10.4%,decrease 15.6×104 kgce annually.Natural gas input decrease by 7%,decrease 11.2×104 kgce annually.