EXPERIMENTS IN A ONCE-THROUGH FURNACE SIMULATING DIFFERENT EXTENTS OF RECYCLE GAS CLEANING IN COAL-FIRED OXY-FUEL COMBUSTION: CONVERSION OF SO_2 TO SO_3

摘要

The SO_x concentrations during oxy-fuel combustion are generally higher compared to conventional air firing. The higher SO_x concentrations, particularly SO_3 in combination with high concentration of water in the recycled stream, increase the acid dew point temperature of the system, thereby increasing allowable flue gas temperatures and reducing the thermal efficiency of a power plant. This paper presents results on experiments carried out at a 20 kW once-through combustion rig of Institute of Combustion and Power Plant Technology (IFK) of the University of Stuttgart. At this rig a novel methodology to investigate oxy-fuel process configurations was employed, for which impurities were injected on purpose to the oxidant gas of the once-through reactor to simulate different extents of oxy-fuel recycle gas treatment. Three Australian coals, which have previously been tested in the Aioi furnace of IHI, were used in the experiments. The SO_x emissions and conversion of SO_2 to SO_3 were measured and compared with existing literature, finding good agreement. The capture of SO_x in a baghouse filter was also evaluated. Acid dew point temperatures (ADPs) for the flue gas were calculated for the various firing conditions. The ADP temperatures increased by up to 50 K when changing from air to oxy-firing with full recycling of H_2O and SO_2. Considerable differences in the ADPs were found for different extents of oxy-fuel recycle gas treatment. The SO_3 capture by the fly ash in the bag filter has been found to reduce the ADP temperature by as much as 16 K.