Research On Spout-fluidized Gas-solid-state Decarburizaiton Kinetics Of High-carbon Ferrochrome Powders By Microwave Heationg

Medium and low carbon ferrochrome is the main raw material to producestainless steel and tool steel, low carbon alloy steel, the demand for medium andlow carbon ferrochrome is also growing. The gas-solid-state reaction process formedium and low carbon ferrochrome production can not only avoiddisadvantages of harmful metallurgical chrome slag produced in liquid-phasedecarburization of high-carbon ferrochrome, but make the use of the advantagesof good heat and mass transfer in gas-solid-state reactions. It can also improvethe reaction ability of powder material, strengthen gas-solid-statedecarburization reaction, improve reaction kinetics condition and realizedecarburization of high carbon ferrochrome powder in low temperature. So thegas-solid-state decarburization of high-carbon ferrochrome powder gainsincreasing attention.In this study, the High-carbon ferrochrome powders were decarburized ingas-solid-state spout-fluidized bed by microwave heating and the cold spoutedfluidized characteristics of the decarburized materials were investigated. Heatingtemperature goes up from700℃to1000℃and holding time ranges from0to 180min, respectively, the temperature changes of the sample were recorded toexplore the temperature rising characteristics of the sample. The particle sizes,carbon content and the phenomenon of agglomeration were analyzed after thedecarburization materials cooled to25℃. The main conclusion of this study is asfollow:(1)The result shows that bed materials appears a spout-fluid bedcharacteristic when the initial static bed heights of high-carbon ferrochromepowders are higher than the maximum spouted bed height by theoreticalcalculations.(2)The particle size and density are the main factors that affect spoutedfluidizing quality. The maximum spouting pressure drop progressively increaseswith static bed height and particle density and tends to increase with particlediameter. The minimum spout-fluidizing velocities grows with static bed heightand particle diameter. The bed voidage goes up with the superficial gas velocityincreases. The material mass has a more remarkable influence on the bedvoidage of coarse particles than of the finer particles.(3)In spouted fluidized bed under microwave heating, heating characteristicof high carbon ferrochrome powder is better, showing a two-stage temperatureincrease, the average heating rate of the first phase is36℃·min-1, the averageheating rate of the second phase from is down to7℃·min-1.(4)Spouted fluidized bed under microwave heating can achieve effectivedecarburization for high carbon ferrochrome powder. Respectively, high-carbon ferrochrome powder is heated to700℃,800℃,900℃,1000℃and preservedheating for0min,60min,120min,180min. After that, carbon content ofhigh-carbon ferrochrome powder decreases. With the increase of temperatureand holding time, the decarburization percentage of high-carbon ferrochromepowder significantly increases. When the decarburization temperature is1000℃and holding time is180min, the carbon content of high-carbon ferrochromepowder is reducing to4.109%, decarburization percentage is up to49.64%.(5)During the experiment, no defluidization happens in high-carbonferrochrome powder, after that, the size of decarburized material is significantlydifferent than that before the reaction. The mass fraction of finer particles hassignificantly reduced and the mass fraction of coarse particles has increased.(6)By thermodynamic calculation and kinetics analysis, microwave heatingspouted fluidized bed can achieve decarburization of high carbon ferrochromedecarburization at low temperature, using the unreacted core model, thecalculated apparent activation energy of decarburization reaction is88.47kJ·mol-1.The diffusion of gases becomes the restrictive step for decarburizationreaction.(7)Microwave heating can affect the path of chemical reactions andimprove the dynamic conditions of gas-solid decarburization. It can alsoaccelerate gas-solid decarburization, promoting the diffusion of carbon in carbonferrochrome powder and reducing the reaction activation energy ofdecarburization.