THE FORMATION OF SUBMICRON AEROSOL-PARTICLES, HCL AND SO2 IN STRAW-FIRED BOILERS

The concentration of submicron particles, HCl and SO2 in the flue gas from the combustion of straw from wheat, barley and oil seed rape was studied by field measurements on two utility boilers. The concentratio n of submicron particles varies from 75-2000 mg Nm(-3 ) and the mean d iameter in the range from 0.2 to 0.6 mu m. The principal constituents of the submicron particles are potassium sulfhate and chloride. The co ncentration and composition of the submicron particles depend on the c ontent of K, Cl and S in the straw. These elements are to a great exte nt volatilized in the combustion zone. A theoretical analysis indicate s that the gas to particle conversion occurs during the cooling of the flue gas by the homogeneous nucleation of K2SO4 particles, which act as condensation nuclei for the subsequent condensation of KCl. It is f ound that the kinetics of the oxidation of SO2, which is slow below 80 0 degrees C, is important for the chemical changes of the flue gas. Th e composition of the submicron particles and the concentration of SO2 and HCl can be approximately predicted from the assumption that the fl ue gas composition is determined by a chemical equilibrium for the sul fation reaction at 812 +/- 10 degrees C. (C) 1998 Elsevier Science Ltd . All rights reserved.