Plasma assisted power coal combustion in the furnace of utility boiler: Numerical modeling and full-scale test

Abstract

This work presents modern plasma technology for solid fuel ignition and combustion. It promotes more effective and environmentally friendly low-rank coal incineration. To implement this technology at coal fired thermal power plants plasma-fuel systems (PFSs) were developed. PFS is a pulverized coal burner equipped with arc plasmatron producing high temperature air stream of 4000–6000°C. Basis of technology PFS is plasma thermo-chemical preparation of coal for burning. It consists in plasma heating of air–coal mixture up to temperature of coal volatiles release and char carbon partial gasification. In PFS air–coal mixture is deficient in oxygen therefore carbon is oxidized mainly to carbon monoxide. As a result, at the PFS exit a highly reactive mixture is formed of combustible gases and partially burned char particles, together with products of combustion, while the temperature of the mixture is around 1050°C. Further mixing with air promotes intensive ignition and combustion of the prepared in the PFS fuel.PFS have been tested for boilers start up and pulverized coal flame stabilization at 30 power boilers of 75–950t/h steam productivity. The boilers were equipped with different types of pulverized coal burners: direct flow, muffle and swirl burners. At tests of the PFS power coals of all ranks (lignite, bituminous, anthracite and their mixtures) were incinerated. Volatile content of them was in range of 4–50%, ash varied from 15% to 48% and heat of combustion was from 6690 to 25100kJ/kg.To show advantages of the plasma technology of coal combustion before conventional one numerical investigation of plasma ignition, gasification and thermo-chemical preparation of air–coal mixture for incineration in a power boiler was fulfilled. The numerical modeling was performed for low-rank bituminous coal of 40% ash content incinerated at a boiler of 420t/h steam productivity. Both analysis of the numerical modeling and experience of PFS industrial use showed ecological efficiency of the plasma technology. When plasmatrons operate in the regime of plasma stabilization of pulverized coal flame, NOX emission is reduced twice and amount of unburned carbon is reduced four times. The PFSs reduce the temperature at the exit of the furnace. Tests of the PFS for the boiler BKZ-420 of Almaty TPP-2 cold startup confirmed the possibility of high-ash Ekibastuz coal ignition in the cold furnace without heating of primary air.