A Multi Fuelled Cyclone Combustor

Abstract

The paper outlines a series of tests carried out on a prototype 1.5 MW vertical cyclone combustor with integral ash removal which removes in excess of 80% of the ash. For high calorific value fuels such as coal the system is run fuel rich to avoid slagging. The low calorific value exhaust gases are passed via a transfer duct into an inverted swirl burner/furnace arrangement where final burnout of the gasified products occur.

The sytem, designed to utilise a wide range of solid fuels was evaluated for a range of biomass materials and coal. The coal work investigated the effects of crushed (d_m ≃ 250 μm) and pulverised (d_m ≃ 70–80 μm) bituminous coals on system performance whilst biomass trials investigated the effects of chopped straw, chicken litter, shredded paper and refuse derived fuels.

The fuel and air were premixed and fired tangentially in all cases into the primary combustor. The combustor was operated over a range of mixture ratios (φ) from fuel rich (φ = 0.5) to fuel lean (φ = 2.0) with temperatures in the order of 1250°C, hence operated in a non-slagging mode. The whole system was operated with a minimum of secondary air, required only to burn the gasified products from the primary chamber.

The trials included monitoring of exhaust gases for a range of emissions. In addition, isokinetic sampling of the exhaust gases was carried out to determine particulate emission levels.

Results show that best fuel burnout is achieved with biomass material levels better than 99% being achieved. Satisfactory performance was achieved with coal, (ash retention emissions) with fuel burnout in the order of 80%. Ash retention values for the biomass materials was in excess of 80% up to 98%. Coal ash retention levels were lower when analysed on a mass balance basis but of the same order when considering particulate emissions.