Combustion Tests on a Blend of Liquid Refinery Residues and Coal: CFBC Operation Behaviour and Emissions Characteristics With Special Emphasis on the Intermediate Species C_xH_y, HCN and NH₃

Investigations on the combustion of a blend of liquid refinery residues and a hard coal are presented in the current paper. The experiments were done in an atmospheric circulating fluidized bed combustor (CFBC) with a thermal capacity of 100 kW. The operation behaviour and pollutant formation characteristics are determined using axial profile measurements at 19 different ports along the combustion chamber. The measurement campaign included the variation of the primary to secondary air ratio, the global air to fuel ratio, the residence time in the primary zone, the overall temperature of the combustion chamber and the Ca/S ratio. The current paper concentrates on results obtained at primary air ratio of 0.65, an overall air ratio of 1.1, a mean combustion temperature of 850°C and a Ca/S-ratio of 0. Measurement of the flue gas components O₂, C_xH_y, CO, CO₂, H₂, NO_x, N₂O, NH₃ and SO₂ are made by standard gas analysing techniques. In order to detect the specific hydrocarbon species produced and oxidized during the combustion process a Fourier Transformation Infrared Spectrometer (FTIR) extends the existing gas analysis system. The gas species measured by FTIR-Spectroscopy are CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆ and C₃H₈. Also the important precursors for the NO_x-Formation HCN and NH₃ are examined with the FTIR-Spectrometer in the primary and secondary zone. The current experiments are compared with results obtained by burning liquid refinery residues only, with special regard to the consumption of the nitrogenous intermediates HCN and NH₃.