Oxy-fuel Circulating Fluidized Bed Combustion
Circulating fluidized bed combustion (CFBC) is a clean energy technology that can utilize a variety of opportunity fuels for producing steam and electrical power. This technology is now available in both subcritical and supercritical forms.
CFBC uses a high-velocity fluidizing gas to entrain fuel particles and maintain a fluidized bed of fuel, ash, and a sulphur capture sorbent. The technology is particularly suited to oxygen-enhanced combustion for the purposes of increasing energy efficiencies and providing near zero-emissions power production. All the established advantages of circulating fluidized bed combustion are transferable to oxy-fuel CFBC.
Compared to oxy-fuel PC boilers, oxy-fuel CFBC has several unique advantages:
- Oxy-fuel CFBC requires significantly less recycled flue gas to control boiler temperature due to the re-circulating solids that effectively act as a heat moderator. This permits the use of a much higher oxygen concentration in the combustor, and allows the economics of oxy-fuel CFBC to be significantly improved over PC firing through a reduction of the size of the CFBC boiler island by as much as 50%. From the point of view of CFBC technology this is an important factor given that scaling up of FBC units much above 300 MWe thermal was not considered practical.
- Oxy-fuel CFBC does not require sophisticated burner systems and, since the bulk of the heat transfer is accomplished with solids, it does not require any significant re-arrangement of heat exchange as is required in oxy-fuel PC boilers. Along with its ability for in-situ SOx removal, oxy-fuel CFBC is an attractive solution in a retrofit scenario.
- In addition, oxy-fuel CFBC systems can co-fire biomass at any level, making it possible to offer net reductions of anthropogenic CO2 emissions.
CanmetENERGY has two facilities at Ottawa for conducting research in oxy-fired CFBC. The first is a small-scale mini-CFB, while the other is a pilot-scale 0.8 MWth CFB unit. Both units are capable of producing high flue gas CO2 concentrations: 85-90% for the mini-CFB; and 80-85% for the pilot-scale unit. Research activities include studying combustion behaviour of various fuels (coal, petroleum coke, biomass and blends), including emissions characteristics, heat transfer, effect of recycle strategies (wet or dry) and oxygen concentration.
CanmetENERGY is currently conducting a joint research project on oxy-fuel CFBC with Foster Wheeler North America and Foster Wheeler Finland using the pilot-scale unit. This project aims to help Foster Wheeler acheive its goal of building a 30 MWth technology demonstration plant in Ciuden, Spain. The ultimate goal of the project is to demonstrate a carbon capture and storage (CCS) facility fully integrated in an approximately 300 MWe power plant employing oxy-fuel-CFBC boiler technology. Other partners in this project include Vattenfall of Sweden, and Endesa Generación S.A. (ENDESA) and La Fundación Ciudad de la Energía (CIUDEN) of Spain.
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