Research On Reductive Behavior Of Oxidized Pellets Under Microwave Irradiation

On traditional heating, the reaction rate of the direct reduction which the oxidized pellet reduced by coal is slow, and the thermal efficiency is low. Different from traditional heating, material can be heated faster with microwave heating. It can improve the reaction speed and short the reaction time. Microwave radiation has not only thermal effect and it is possible has "non-thermal effect". Research on the apparent activation energy and the reductive behavior of the oxidized pellets reduced by coal under microwave heating from the dynamics and the microscope has important significance to develop the technology that reduce oxidized pellet by coal with microwave heating.In this paper, temperature rising characteristics of the pellets and the reduction process of the mixture under microwave have been studied. The results show that the temperature rising fastest when the microwave power for 1300w, the size of oxidized pellets for 12mm-16mm, and quality of 120g. Warming performance of the mixture is similar as single oxidized pellets. The effective of the reduction is better when the microwave power is larger and the end temperature is higher. Increasing anthracite coal could not influence reduction obviously. When microwave power for 1300w, oxidized pellets for 120g, C/Fe for 0.375 and the end temperature for 1050℃, the reaction ratio is largest for 73.92%.The reductive kinetics of the oxidized pellets reduced by coal was studied. The results show that the reaction mechanism obeys diffusion-controlled model when microwave power for 1300w and the temperature between 550℃and 800℃. The apparent activation energy is found to be 75.31kJ/mol. In the second stage, i.e., between 850℃and 1050℃, the reaction mechanism also obeys diffusion-controlled model. And the apparent activation energy is found to be 53.17kJ/mol. During temperature of 850℃and 1050℃, reaction process belongs to diffusion-controlled model with conventional heating, and the apparent activation energy is 205.1kJ/mol that is higher more than the apparent activation energy under microwave heating. It shows that, microwave heating have "non-thermal effect" which can reduce activation energy and promote reduction reaction.The reductive behavior of the oxidized pellet by coal under microwave and the micro structure evolution of the reduced pellets were studied. The results show that gasification reaction of anthracite start and the quality of anthracite decrease rapidly when the end temperature about 650℃. At that time, the compressive strength of the reduced pellet reach lowest, and then it increase fast as the temperature rising. Reduction is proceed from high state iron oxides to low state iron oxides successive. Reaction obeys the un-reacted core model. The process is controlled by the microwave heating model and gas-solid reaction model. Microwave heating model can create good dynamic condition for the reduction.