COMBUSTION PERFORMANCE AND RESIDUE ANALYSIS OF TRIAL BURNS IN A PILOT SCALE SLAG TAP FURNACE WITH COALS AND WASTE FUELS

摘要

Experiments to evaluate the suitability of different fuels (coals, sewage sludges and biomass) as single fuelrnand co-combusted were carried out in a 300 kWth cyclone slag-tap furnace test facility with regard to combustionrnperformance and residue composition. A description of the test facility and the experimental settings is presented.rnExperiments were carried out with the fuels using different thermal load and fuel shares. Generally the operationrnwas not problematic, with stable flames, early ignition, high burnout, low CO-emissions and high ash capture ratesrnin the furnace. Characteristic trends of SO_2- and NO_x-emissions for the different fuels and blends were measured.rnFocus of the investigations was on ash-forming constituents, volatilisation of inorganic components and slag properties.rnThe ash forming constituents behave selectively and form different slag, deposit and ash compositions.rnDuring the combustion of alkali rich fuels, like some brown coal types or residuary straw, sodium and potassiumrnare volatilised. The decrease of these components in the slag results in a change of slag viscosity in the furnace andrnan increase of alkali-sulfate and alkali-chloride deposits at lower temperatures in the flue gas path. Formation ofrnsulfates and chlorides depends on fuel contents and the presence of sulfur in the flue gas. In sewage sludge combustion,rnin addition to above mentioned enrichments of alkali, the compounds Zinc and Pb strongly concentrated inrnthe fine ashes and deposits in the flue gas path. In co-combustion experiments these effects were less pronounced.rnDue to the available sulfur originating from coal in moderate co-combustion (i.e. low ash shares of the secondaryrnfuel) no alkali chlorides were found. Due to dilution of ash in co-combustion fewer alkali sulfates were detected,rnand due to the combined slag composition slag flow was ensured.