Effect Of Microwave Radiation On Char Microstructure And Char-NO Reactions

The green, lowcost, high-efficiency emission reduction of NO_x in the field of industrial coal combustion has become a focus. In recent years, the reduction of NO by char has become a hot research topic, and the technology of ―mixture fuel of char and pulverized coal‖ in foreign metallurgical industry has achieved some results. However, with the increase of heat treatment temperature and time, the char gradually shows a trend of graphitization degree, which decreases the reduction ability of char obviously. Recycle char’s NO_x reduction ratio will be improved significantly if we can achieve the activation and improve microstructure characteristics in the char at low temperature(20~800℃)outside the reactor. In this paper, the microwave-thermogravimetry-infrared reactor system is designed. The paper regards Shuozhou bituminous coal and synthetic coal char as the experimental subject. By exploring the variational rules about microstructure and reactivity of char-NO under the different microwave conditions, the optimum conditions of microwave activating char and activation mechanism are being determined. It can provide a reference to the development of denitrification technology in industrial boiler.The nano powder, sucrose, deionized water and ethanol are as raw materials to prepare synthetic coal char according to a certain proportion. Shuozhou bituminous coal char and synthetic coal char are prepared in Muffle furnace. The carbonization temperature is 800 ℃ and 900 ℃. Shuozhou bituminous coal char and synthetic coal char are modified by different microwave power and time in the microwavethermogravimetry-infrared reactor system. Pore structure, degree of graphitization, lattice defect and the variation rule of oxygen functional groups in char before and after microwave irradiation are obtained by different analytical methods, including pressure mercury, XRD, Raman and XPS test etc. The results show that the power and time of microwave treatment have a certain effect on the microstructure of char. With the increase of power and the prolongation of time, specific surface area and pore volume of Shuozhou bituminous coal char and synthetic coal char show a trend of firstly increasing and then decreasing. After microwave treatment, the relative content of C-O, C=O, O=C-O in coal char decreases; The degree of graphite structure in the Shuozhou bituminous coal char doesn’t show obvious regularity but the degree of graphite structure in the synthetic coal char firstly decreases and then increases.Firstly, the reactivity of microwave modification of large particles Shuozhou bituminous char-NO is explored on the condition of 800 ℃ and 900 ℃ in the large particle thermogravimetric reactor system. Secondly, synthetic coal char is modified by microwave at room temperature and 800℃ respectively. Then the reactivity of modified synthetic coal char-NO is investigated in the vertical and horizontal tube furnace experimental system with programmed temperature method. Thirdly, the reactivity of synthetic coal char-NO is investigated at 800℃ under the condition of intermittent microwave treatment in microwave-thermogravimetryinfrared reactor system. The results show that the reactivities of Shuozhou bituminous char-NO and synthetic coal char-NO firstly both increase and then decrease with the increase of microwave power and time. The optimum microwave power and time of Shuozhou bituminous char are respectively 640 W and 90 s. The optimum microwave power and time of synthetic coal char are respectively 480W(or 640W) and 90s; When microwave is applied, the efficiency of NO reduction in synthetic coal char increases rapidly, which is determined by the microwave thermal effect and non-thermal effect; The reactivity of synthetic coal char-NO, which is modified at room temperature, is better than modified at 800℃. The changes of pore structure, the degree of graphitization and the oxygen functional groups of char before and after microwave treatment have an important effect on the reactivities of Shuozhou bituminous char-NO and synthetic coal char-NO under the condition of high temperature.