An anlysis of the behaviour of non-slagging, coal fired, cyclone combustors using a phenomenological model

Abstract

A phenomenological model has been used to analyse the behaviour of the internal aerodynamic processes and particulate motion occurring in non-slagging coal fired cyclone combustors. The model includes boundary layer effect on the outer, top and bottom walls, a shrinking core/fragmentation model of coal combustion and momentum coupling between flow and particle dynamics. A non-slagging cyclone combustor operates normally fuel rich at a mixture ratio of about 0.7 to maintain cyclone chamber gas temperatures below 1300°C and wall temperatures about 1100°C. With a crushed coal of size range m=≈200–400 μm 90%<1 mm, having a high ash fusion temperature, good fuel burnout and retention of particles larger than 30 μm in the cyclone chamber has been demonstrated. The long residence times of material in the outer regions of the cyclone chamber causes a large slip velocity between that of the inlet and the main vortex in cyclone chamber and this factor affects the design of the tangential inlet. Burnout of the gasified products of combustion was achieved in a secondary combustor. Low NOx emissions derive from the low operating temperature of the primary cyclone chamber.