Experimental Studies And Numerical Simulation Of Induction-heating Multi-stage Free-oil Ignition Of Pulverized Coal

It is well known that coal is the mail fuel n most of boilers in China. Although oil is used only in the case of ignition and low load operation, the amount is very great. In order to save the precious and expensive oil, a novel technology, induction-heating multi-stage free-oil ignition technology of pulverized coal (MFIT), is brought forward in this thesis. Based on the study of ignition mechanism of coal, ignition criterion, heating method and ignition theory of pulverized coal (PC), MFIT integrates hot-wall ignition technology, induction heating technology and multi-stage ignition technology. A series of research work is carried out to study IMFIT in this thesis.Experiments on the measurement of temperature with thermocouple in alternating electromagnetic field are conducted. The effects of factors on the measurement result are studied, such as position, integral time, environment temperature, power supply, heating power and encapsulation mode of thermocouple. Effective measures are obtained to decrease the negative effect of alternating magnetic field, which ensure that accurate measurement will be acquired in the following experiments.A lot of experiments have been done on the induction-heating single-stage free-oil ignition of PC with direct inlet mode and swirl inlet mode. The results of different inlet mode are compared with each other. Test results show that the ignition process of PC in ignition chamber includes three stages. The effects of velocity, PC concentration and wall temperature on the ignition of PC are studied. Through experiments of excess air coefficient on the PC combustion in stove, it is concluded that it is no use to add too much air at the beginning of free-oil ignition of PC.Experiments of feeding PC simultaneously are carried out for the first time in multi-stage free-oil ignition technology of PC. The result shows that it is feasible to puff all coal-air mixtures simultaneously in EVIFIT. It is discovered that the combustion condition of the second stage PC is up to the outlet temperature of the first stage PC and the content of combustible gases in first stage flue also plays positive effect on the ignition of second stage PC. The effects of parameters of two coal-air mixture, wall temperature of first ignition chamber and annular filling air on IMFIT are studied experimentally in this thesis.In this thesis, the numerical simulations of ignition and combustion of PC in IMFIT are conducted. The ignition processes of two stages PC are studied. The influence of particle diameter distribution, parameters of two coal-air mixture, wall temperature of first ignition chamber is investigated. From the distribution of velocity and temperature in ignition chamber for second PC, why the ignition of second PC is delayed by annular filling air is discovered. The numerical simulation provides a quick way for the research work of EVIFIT and decreases the cost of experiments greatly.The industrial burner using the induction-heating free-oil ignition technology of PC is designed and constructed in this thesis. The experimental study is carried out on a boiler and the coal-air mixture is ignited successfully for the first time in plant. Theindustrial experiments provide valuable experience for the application of the new technology.Finally, some problems met in the induction-heating free-oil ignition technology of PC, such as cokeability and ignition of low volatile coal, are analyzed and discussed. This broadens the way for further research.