The behaviour of waxy compounds in the drying system of a peat power plant

Abstract

In peat drying processes organic compounds are liberated or formed from peat and may contribute to the forming of deposits in off-gas streams. The waxy compounds constitute one such major group. To investigate their role the amount and composition of peat extracts in dust and deposit samples taken from various sites in a peat power plant of 250 MW t were analyzed. The power plant employs an indirect combustion system, i.e. gases from the dryer are separately fed to the stack. The dust samples were taken from the dryer gas flow and from the flue gas flow in the stack using both suction- and deposit-type probes, as well as from the fly ash. The deposit samples were taken from the drying mill, the particle separator and the flue gas blower. The lipid composition of the extracts was analyzed by gas chromatography. All samples contained lipid components typical of peat, such as long-chain fatty acids, hydroxy acids and fatty alcohols. The lipids and most clearly the fatty acids were enriched in the samples compared to the fuel peat samples. The amounts of lipids and fatty acids were on average 3- and 5-fold, respectively, in the dust samples from the dryer gas flow, 12- and nearly 20-fold in those from the flue gas flow, and 3- and 4-fold in the deposit samples from the drying mill and the flue gas blower compared to those measured for the peat samples. Both increasing the drying temperature and increasing the lipid content of the fuel peat increased the amount of lipids in the dust samples. The amount of lipids carried in the gas flows indicates that the deposits may partly result from combination, in the gas streams, of the lipids with peat and ash dust.