US Department of Energy`s high-temperature and high-pressure particulate cleanup for advanced coal-based power systems Page: 4 of 13
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where the significant parameters affected are filtration temperature, gas chemistry, char or dust morphology,
and system material requirements.
PFBC Power System
In a PFBC system, jets of air suspend a mixture of coal and sorbent (limestone or dolomite) during
combustion, converting it into a suspension of red-hot particles that flow like a fluid. The sorbent captures
sulfur oxides that are released by the burning coal. By pressurizing the combustor, a combined cycle system
can be created which increases power production. To realize this increased power production, the HTHP
PFBC exhaust products must be cleaned of particulate matter. The HTHP filtered gas stream from the
combusted coal is used to drive a gas turbine. Heat recovered from the exhaust of the gas turbine and the
steam generated from the fluidized-bed drives a steam turbine.
To further improve PFBC plant efficiency, a partial gasification reactor (carbonizer) is added with an
accompanying filter system. In this approach the production of a fuel gas permits topping combustion with
the vitiated PFBC exhaust gas, thereby raising gas turbine inlet temperatures. Integrating combustion and
gasification processes in this way results in a advanced PFBC system with more than 50 percent efficiency.
Particulate Removal Performance Goals for High-Temperature and High Pressure-Particulate
New Source Performance Standards (NSPS) mandated by the Clean Air Act requires stationary power
sources, greater than 70 MWe, to control particulate emissions to stringent levels. This level of particulate
control will limit the emissions of particulate matter to below 0.03 pound of particulate emitted per million
Btu of fuel consumed (0.03 lb/MMBtu, higher heating value). This level of cleanup can be attained with
fabric bag-type filters and electrostatic precipitators presently deployed on conventional coal-fired power
plants. Future regulations presently under consideration by the Environmental Protection Agency may tighten
the present NSPS by a factor of ten. It is the intent of these particulate emission standards to have a positive
effect on the environment. By most estimates, limitations on gas turbine inlet particulate concentrations are
more stringent than existing NSPS and possibly future NSPS.
Gas turbine manufacturers are concerned with particulate inlet concentrations caused by deposition and
erosion of gas turbine blades. Due to the uncertainty associated with the deposition and erosion mechanisms,
particular turbine manufacturers tend to specify a range of particulate concentrations and particle size limits.
Furthermore, the different manufacturers provide different specifications or ranges. In general, erosion limits
stipulate that there should be no particles greater than 10 microns in diameter, 10 percent between 10 and
5 microns in diameter, and 90 percent less than 5 microns in diameter. Particle deposition appears to be a
concern for concentrations greater than 100 ppm . Figure 1 illustrates both the turbine inlet and
environmental limitations for particulate matter. Particulate removal requirements for gas turbines essentially
determine the performance goals for particulate cleanup systems in the PFBC and IGCC coal-based power
Meeting particulate concentration and size limitations for gas turbines will also provide other benefits. One
benefit is the lack of fouling of post-turbine heat recovery steam generators. Furthermore, due to the absence
of particulate matter, denser tube spacing with higher throughputs can be achieved, producing more efficient
and compact heat transfer equipment. Additionally, conventional post-process particulate cleanup would no
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Dennis, R.A. US Department of Energy`s high-temperature and high-pressure particulate cleanup for advanced coal-based power systems, article, May 1, 1997; United States. (digital.library.unt.edu/ark:/67531/metadc677771/m1/4/: accessed December 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.