Yewen Tan

Effect of Operating Conditions on SO2 and NOx Emissions in Oxy-Fuel Mini-CFB Combustion Tests

Anthropogenic CO2 production is caused primarily by fossil fuel combustion. In consequence, it is increasingly necessary to find ways to reduce these emissions when fossil fuel is used. CO2 capture and storage (CCS) appears to be among the most promising. All of the CCS technologies involve producing a pure stream of CO2 either by concentrating it from the flue gases, or by using pure oxygen as the combustion gas. The latter option, oxy-fuel combustion, has now been well studied for pulverized coal combustion, but hasreceived relatively little attention to date in the case of oxy-fuel circulating fluidized bed combustion. Recently, oxy-fuel CFBC hasbeen examined ina 100 kW pilot plant operating with flue gas recycle at CanmetEnergy. The results strongly support the view that this technology offers all of the advantages of air-fired FBC, with one possible exception. Emissions such as CO or NOx are lower or comparable to air firing. It is possible to switch from air-firing to oxy-firing mode easily, with oxygen concentrations as high as 60–70%, and flue gas recycle levels of 50–60%. Only sulphur capture is poorer. However, this result is not in good agreement with other studies, and the reasons for this discrepancy need further exploration. Here, longer tests have confirmed previous findings from CanmetEnergy with two coals and a petroleum coke. It also appears that changing from direct to indirect sulphation with the petroleum coke improves sulphur capture efficiency, although a similar effect could not be confirmed with coal from these results.

Oxy-fuel coal burner design: From CFD modeling to pilot scale testing

Publisher Summary This chapter focuses on a sequence of combustion tests performed on the Vertical Combustor Research Facility of the CANMET Energy Technology Centre to calculate the performance of a burner design optimized for oxy-fuel combustion of coal. In addition, the chapter evaluates burner and combustor design concepts for lower NOx during O2 firing based on recommendations made by CFD modeling. The tests are carried out with a high volatile lignite coal at a heat input of 0.21 MWth, with both air firing and oxygen firing. The flue gas compositions are monitored during the tests and extensive flame probing is conducted. All tests are executed using a high volatile lignite coal. Extensive flame sampling, including temperature and major species, is conducted and radial and axial measurements are performed. As a result, the new burner emitted considerably lower NOx compared to previous ones. This test made it possible to bring NOx emissions to below 0.15 lb/MBTU while firing in O2/RFG mode. Results confirmed the superiority of the current design by considerably decreasing NOx formation during oxygen firing of the coal while maintaining excellent fuel burnout.