Исследование степени выгорания пылеугольного топлива при обеспечении предварительного контакта с горячим воздухом

Abstract

A situation in which unburned carbon remains after combustion of pulverized coal in the furnaces of power-generating boilers is due to the fact that large particles do not have enough time to burn out completely during their dwelling in the furnace space. Typically, the high-density coal-air mixture conduits (HDCC) used at coal-fired thermal power plants are directly connected to the main burners and cut in the vertical hot air ducts. This connection arrangement has a number of drawbacks; in particular, pulsations of pulverized coal-air mixture pressure arise in the pulverized coal conduits, and it is impossible to secure early ignition of pulverized coal due to its being insufficiently heated upstream of the burner. For solving this problem (i.e., making sure that pulverized coal more promptly comes in contact with hot primary air) under the conditions of the Starobeshevo thermal power plant, a new pulverized coal feeding arrangement was tried out in 2010, according to which the HDCC is cut into the primary air channel near the pulverized coal bunker. With this arrangement put in use, it became possible to completely avoid the need to support the pulverized coal flame with gas at a load of 130 MW and to decrease the amount of unburned carbon by about 1%. The pulverized coal fuel transformations in the course of its being in contact with hot air upstream of the burner inlet were investigated. To this end, fuel samples were taken directly under the pulverized coal bunker and upstream of the burners located at different distances from the bunker. It has been determined that in the course of fuel being in contact with hot air for a period from 0.5 to 0.9 s, the total moisture content in it decreased by 4...48%, and the content of volatiles decreased by 6...25%. Simplest numerical assessments have shown that the release of such amounts of volatiles and their combustion immediately after entering the furnace yield a heat release sufficient for heating the fuel and primary air by several hundred degrees. The revealed regularity explains the physical nature of the results in terms of decreasing the amount of unburned carbon that have been achieved after re-cutting the pulverized coal conduits and taking measures for pulverized coal to more promptly come in contact with hot air.