The influence of heat transfer conditions on the parameters characterizing the ignition of coal-water fuel particles

Abstract

The future of thermal power engineering both in Russia and abroad will depend in many respects on the use of coal as main fuel for generating heat and electricity. In this connection, matters concerned with development and introduction of new environmentally friendly and energy efficient coal firing technologies are becoming of much importance. Firing coal in the form of coal-water fuel is one of the most promising solutions. However, despite a rather long history of its development (more than 40 years), this technology has not found wide use as yet, which in all likelihood is due to lack of full mathematical and physicochemical models describing the processes that take place when a coal-water fuel particle undergoes thermal treatment and ignition. The article presents the results obtained from numerical solution of the coal-water fuel particle ignition problem taking into account simultaneously occurring main thermal treatment processes (thermal conductivity, water evaporation, filtration heat and mass transfer, thermal decomposition of the fuel organic part, and thermochemical interaction between water vapor and coke carbon). The ignition problem is solved using the finite difference method. For calculating the evaporation process taking into account nonequilibrium nature of the parameters at the interface boundary of the initial “coal-water fuel—dry coal” system, the method of capturing the phase transition front at the difference mesh node was used. The results obtained from numerical modeling were used for determining the conditions and parameters characterizing the ignition of coal-water fuel particles under the conditions typically existing in the furnace space of boiler units. The extent to which radiant heat transfer influences the ignition delay time is determined. It is shown that radiant heat transfer plays a determining role in the thermal preparation of fuel for ignition.