In the past year 35 years, Lehigh's Energy Research Center (ERC)
has developed a variety of technologies and solutions that improve
the operating efficiency of power plants while reducing emissions of
toxic substances and greenhouse gases.
One ERC technology has achieved a 70-percent reduction in mercury
emissions from coal-fired power plants by modifying the physical
conditions of boilers. A second promotes the capture of toxic acids,
and the capture and reuse of water, by condensing water and acid
vapors in separate heat exchangers. A third limits costly slagging
on boiler tubes by integrating optical technologies and artificial
intelligence.
And Boiler OP, a combustion optimization technology developed at
the ERC in the mid-1990s, has been implemented at more than two
dozen U.S. power plants, a coal-powered plant in China, and an
oil-fired plant in Mexico.
Recently, the ERC was awarded a grant from the U.S. Department of
Energy (DOE) to develop methods of recovering and reusing the heat
that would be generated by the carbon-dioxide (CO2) compression
process in a carbon capture system. Carbon capture, which involves
the removal of CO2 from power-plant flue gas, would make it possible
to generate electric power from coal while avoiding significant
emissions of CO2 to the atmosphere.
The 30-month grant is being awarded through DOE's National Energy
Technology Laboratory (NETL). The funding was provided by the
American Recovery and Reinvestment Act of 2009, the economic
stimulus package passed by Congress in February.
The goal of the research project, says ERC director Edward Levy,
is to facilitate carbon capture and sequestration, or storage (CCS),
and thus limit the amount of CO2, a greenhouse gas, emitted into the
atmosphere by coal-fired power plants.
Towards that end, the ERC will use the DOE grant to train
graduate students to develop computational models of the methods
that are used to capture and compress CO2 and to estimate the
increases in efficiency that will result from each method.
The benefits of reusing captured heat
Coal-fired power plants produce half the electricity in the U.S.
and account for about 75 percent of total power generation in China,
which leads the world in coal consumption. At a coal-fired plant,
finely ground coal is mixed with air and burned in a boiler, or
furnace, where it heats water in the boiler pipes into steam that
spins turbines to generate electric current. Meanwhile, carbon from
the coal reacts with oxygen in the air to form CO2, which exits the
power plant with the flue gas and enters the atmosphere.
CCS technologies separate CO2 from the flue gas and then compress
the CO2 to high pressure. Compressed CO2 can be transported by
pipeline and is currently used to help extract oil from underground
reservoirs in a process known as enhanced oil recovery. Scientists
are also evaluating the feasibility of injecting compressed CO2 one
or two miles below the earth's surface into saline aquifers whose
geological features would sequester the CO2 underground.
The goal of the current ERC project, says Levy, is to recover
heat that is generated when CO2 is compressed and to use that heat
to improve the efficiency of the power plant's operation.
"It requires a tremendous amount of pressure, about 2,200 pounds
per square inch or close to 150 atmospheres, to compress CO2 to a
supercritical state," says Levy. "In the compression process, CO2
heats up, creating the potential for heat to be recovered and used
beneficially within the power plant.
"All carbon capture schemes reduce power plant efficiency and
increase the cost of generating electricity. We're trying to
mitigate this. We're looking at different types of compressors to
see how much heat can be recovered and what we can do with this heat
to improve power plant efficiency."
The ERC has conducted other research projects that promoted the
reduction of carbon emissions. One project involved the recovery of
water from flue gas and another removed water from high-moisture
coals. Both resulted in improvements in power plant efficiency and
reduction in the rates of CO2 formation.
In the new project, students will use a software tool called
ASPEN, which is used widely to help engineers model chemical
processes.
SOURCE: Lehigh University