Commissioning of a 0.8 MWth CFBC for oxy-fuel combustion

Abstract Oxy-fuel FBC technology is a new technology being developed for power production from carbonaceous fuels which also produces a near pure steam of CO2 ready for sequestration or storage. Unlike oxy-fuel pulverized fuel combustion technology, oxy-fuel FBC offers the possibility of using poor quality coals, hydrocarbon residues and a range of other materials including biomass. In western Canada, pitches, tars and bottoms in particular are available in large quantities, and this technology offers an opportunity to use many of these waste feedstocks in an environmentally benign manner. In addition, oxy-fuel CFBC can be fired at lower flue gas recycle ratio than its pulverized fuel equivalent, offering potentially smaller plants for any given power output. Finally, like air fired systems it also offers in situ sulphur capture. CanmetENERGY has operated a 50 kW oxy-fuel CFBC with full flue gas recycle since 2006. Initial results were very encouraging and to further study oxy-fuel FBC technology, a 0.8 MWth CFBC unit has also been retrofitted for oxy-fuel research. The facility is used to simulate commercial oxy-fuel CFBC performance and to do this it has been extensively modified, by adding an oxygen supply, flue gas recycle train, an air tight fly ash discharge system, a flue gas compressor for bag house pulsing and system purge, etc., as well as upgrading the control and instrumentation for oxy-firing. The most major challenge has been to properly seal the entire CFBC unit to prevent air ingress. Fuels fired during the commissioning phase included bituminous coal from the US, petroleum coke, and lignite from Canada. Combustion under oxy-fuel conditions has proved to be very stable and the transitions from air to the oxy-fuel firing mode and the reverse transition are rapid and present little or no operational difficulties. This work has also demonstrated that the retrofitted oxy-fuel CFBC produces a stream of flue gas containing 80–90% of CO2, while NOx emissions have been shown to be significantly lower compared to air firing when operating with the same fuel. Finally, SO2 capture was in the range of 70–75%, but the limestone utilization is lower than in air-firing mode, and research is on-going to better understand sulphation performance under oxy-firing conditions.