Environmental Engineering Reference
from the gasifier turn a gas turbine. Hot exhaust from the gas turbine is
then fed into a conventional steam turbine, producing a second source of
power. This dual, or combined cycle arrangement of turbines is not pos-
sible with conventional coal combustion. It offers major improvements in
power plant efficiencies.
Conventional combustion plants are about 35% efficient (fuel-to-
electricity). Coal gasification could boost efficiencies to 50% in the near
term and to 60% with technology improvements. Higher efficiencies mean
better economics and reduced greenhouse gases.
Compared to conventional combustion, carbon dioxide exits a coal
gasifier in a concentrated stream instead of a diluted flue gas. This allows
the carbon dioxide to be captured more easily and used for commercial
purposes or sequestered.
Historically, the use of gasification has been to produce fuels, chemi-
cals and fertilizers in refineries and chemical plants. DOE's Clean Coal
Technology Program allowed utilities to build and operate two coal gas-
ification power plants; Tampa, Florida, and West Terre Haute, Indiana. A
Clean Coal Technology gasification project is also operating at Kingsport,
Tennessee, producing coal gas that is chemically recombined into indus-
trial grade methanol and other chemicals. Gasification power plants are
estimated to cost about $1200 per kilowatt, compared to conventional coal
plants at around $900 per kilowatt.
The Vision 21 program is focused on new concepts for coal-based en-
ergy production where modular plants could be configured to produce a
variety of fuels and chemicals depending on market needs with virtually
no environmental impact outside the plant's footprint. Membranes would
be used to separate oxygen from air for the gasification process and to
separate hydrogen and carbon dioxide from coal gas.
Improved gasifier designs would be more durable and capable of
handling a variety of carbon-based feedstocks. Advanced gas cleaning
technologies would capture virtually all of the ash particles, sulfur, nitro-
gen, alkali, chlorine and hazardous air pollutants.
The Clean Coal Power Initiative would spend $2 billion over the next
10 years for these high-potential, but still high-risk, technologies. Targets
are an efficiency greater than 52% with emissions of NO x = 0.06, lb/mil-
lion Btu and SO 2 = 0.06 lb/million Btu and a cost of less than $1,000/kW.
Estimates for producing and delivering coal-generated hydrogen
range from $4.50 to $5.60/kg, which is getting close to the cost of U.S. gas-
oline on an equivalent energy basis.