CHARACTERISTICS

Fluidized bed combustion (FBC) is a well-established power generation technology. In the combustor, a "bed" of crushed coal mixed with limestone is suspended on jets of air, tumbling in a manner that resembles a boiling liquid, hence the name "fluidized". The limestone in the mixture acts as a chemical sponge, capturing more than 90% of the sulfur before it escapes the boiler. The resulting waste is removed with the ash, in the form of a benign solid easily disposed of or used in agricultural and construction applications. The lower combustion temperature needed in the process prevents the formation of 70-80% of the nitrogen oxides typically emitted by conventional pulverized coal boilers. FBC systems also have the ability to use high-ash coals. Compared to conventional sub-critical pulverized coal steam plants, FBC provides a high sulfur capture rate without degrading thermal efficiency.

There are two types of FBC systems, atmospheric (AFBC) and pressurized (PFBC), which operates at pressures 6 to 16 times higher than normal atmospheric pressure. PFBC systems can achieve higher thermal efficiencies than AFBC systems. The increased energy in the high pressure gases exiting the PBFC boiler can drive both a gas and steam turbine, known as a combined cycle system. Also, the higher thermal efficiencies of PFBC systems result in lower carbon-containing coal fuel requirements when compared to current conventional pulverized coal steam plants. This results in lower emissions of greenhouse gases.

Currently, AFBC is commercially available in the U.S.; PFBC has been demonstrated but is not in widespread commercial operations. Based on operating performance, future plants are expected to have significantly reduced capital costs.

SIZE:
10 to 100 MW equivalent for industrial boilers, 75 to 350 MW for electric utility applications.

FEATURES:
New baseload generation capacity or repowering of older conventional coal-fired plants. Can burn a wide variety of low-quality coals and municipal wastes. Repowering with PFBC increases plant efficiency and can raise plant capacity by 20-25%.

COST:
AFBC (200 MW): $1,500-2,000/kW
AFBC (repowering): $500-$1,000/kW
PFBC (demonstration): $1,900-$3,200/kW
PFBC (commercial): $1,000-$1,500/kW (expected)

CURRENT USAGE:
Approximately 300 AFBC units supply heat to industrial processes, municipalities, oil producers, and farms in the U.S. and Europe. One 70 MW PFBC demonstration project has operated in the U.S., with a second 145 MW_e demonstration project scheduled to begin operations in 2002. A 135 MW_e plus 224 MW heat PFBC operates in Stockholm Sweden. Single PBFC plants are also in operation in Spain (79 MW Escatron project) and Japan.

POTENTIAL USAGE:
Older conventional coal-fired plants considering life extension or retirement could be repowered using FBC technology. In the U.S. alone, over 100 GWs of capacity are already greater than 30 years old, and are therefore potential candidates. Demand for new coal-fired generation capacity, where controls on sulfur and nitrogen oxide emissions must be included, are also candidates for FBC technology.

CLIMATE CHANGE IMPACT

EMISSION EFFECT:
    

CONDITIONS FOR EMISSIONS MITIGATION:

• AFBC efficiencies reduce carbon emission by approximately 3% compared to conventional steam coal plants.
• Near-term PFBCs that achieve efficiencies of 40-45% will reduce carbon emissions by 17-27% when compared to conventional steam coal plants with efficiencies of 33%. In the longer term, PBFC is expected to achieve 50% efficiency; carbon emissions will be reduced by 34% compared to conventional steam coal plants currently in operation.

EMISSION ESTIMATE:
PFBC—reduce C emissions by 17-34% of current emissions
AFBC—reduce C emissions by 3% of current emissions

COST-EFFECTIVENESS:
The capital costs of these systems are high. However, they inherently reduce CO₂ emissions.

SECONDARY EFFECTS:
Higher efficiencies will also reduce associated air pollutant emissions from burning fossil fuels.

ISSUES ASSOCIATED WITH IMPLEMENTING ACTION

• PFBCs are currently being demonstrated, but are not yet commercially deployed.
• These technologies have a high capital cost relative to new, natural-gas combined cycle technologies. Therefore, to be competitive, they must use low and negative cost fuels (e.g., wastes).

RESOURCES

• United States Department of Energy, 1998, Clean Coal Technology Demonstration Program Project Fact Sheets 1997.
• International Energy Agency, 1993, Electric Power Technologies: Environmental Challenges and Opportunities.
• United States Department of Energy, Office of Fossil Energy, 1997, Sustainable Development with Clean Coal.

CONTACTS

American Electric Power Service Corp.
Mario Marrocco
Columbus, OH
Tel: (614) 223-2460
Fax: (614) 223-3204
http://www.aep.com

Lakeland Electric & Water Utilities
Alfred M. Dodd
Project Manager
Lakeland, FL
Tel: (941) 499-6461
Fax: (941) 499-6344

U.S. Department of Energy
Donald Bonk
Federal Energy Technology Center
Morgantown, WV
Tel: (304) 285-4889
dbonk@fetc.doe.gov
http://www.fetc.doe.gov

U.S. Department of Energy
Donald W. Geiling
Federal Energy Technology Center
Tel: (304) 285-4784
dgeili@fetc.doe.gov
http://www.fetc.doe.gov