Brief Description of Project:
AmerenEnergy Generating (AEG) Company's Hutsonville power generation Unit #4 (Boiler #6) will be retrofitted with ClearStack Combustion (ClearStack) Corporation's multi-pollutant reduction Ashworth Combustor. The purpose of the project is to demonstrate the strong potential of this technology to reduce multiple pollutants, at a cost lower than currently-available technologies, and to accelerate commercialization. The host site is in Hutsonville, IL. EPRI through a Tailored Collaboration project ($200,000) with AEG and three other major electric utilities; Dynegy, DTE Energy and Tennessee Valley Authority (TVA) will be part of the project team. Further, the Illinois Department of Economic Opportunity (DCEO) has committed to contribute $5 million to the project.

The patented Ashworth Combustor^TM is a three-stage pulverized coal molten slag bath gasification/combustion technique that reduces the major air pollutants (Nitrogen Oxides, Sulfur Dioxide, Mercury, other metal air toxics and particulate) associated with coal combustion. A 40 million Btu/hr Ashworth Combustor was retrofitted and successfully tested on a coal-fired stoker at the Lincoln Developmental Center in Lincoln, Illinois in 2003. Below is a summary of those test results.

• Nitrogen Oxide (NO_X) emissions as low as 0.095 lb/106 Btu
• Sulfur Dioxide (SO₂) Reduction of 72% at a Calcium/Sulfur ratio of 0.85, achieving 85% calcium utilization
• 99 wt% Carbon Conversion
• Carbon Monoxide (CO) emissions of 15 to 30 ppmvd @ 3% O₂
• Mercury (Hg) capture in slag/fly ash of 93 to 100 wt%
• Leach tests of slag and fly ash yielded 0 mg Hg/L of leachate
• Near 100% capture of Sb, As, Ba, Be, Cd, Cr, Co, Cu, Pb, Mo, Ni, Se, Ag, Tl, V, Zn & 80% Mn with slag and fly ash. TCLP tests showed the concentrations of Ag, As, Ba, Cd, Pb, and Se in the leachate were all well below the EPA regulatory limit for both the fly ash and slag samples
• 26% Fluorine and 14% Chlorine capture by ash (Ca/S ratio of 0.85)
• Potential for Carbon Dioxide reduction by co-firing biomass with coal
• In addition, a 65% reduction in particulate emissions from the boiler is projected when applied to the Hutsonville pulverized coal-fired unit

The Lincoln Demonstration provided clear results and clarification of the process, which indicates that similar or greater environmental performance approaching performance targets in the Clean Coal Program Roadmap will be achieved with the retrofit of Hutsonville Unit #4.

The major equipment additions/modifications required to retrofit the technology will be; addition of limestone bin(s) with feeders, replacement of coal burners with combustors, installation of a slag quench and sluice system and installation of an overfire air (OFA) system.

Unit #4 is named after the GE turbine to which it supplies steam and gets its steam from a Combustion Engineering (nominally 80MWe) tangentially fired boiler (Unit #6). It produces 1500 psig/1005^oF superheated steam. The boiler has both superheat and reheat, with a gross heat rate of around 10,800 Btu/kWhr. There are three Raymond Pulverizers and pulverized coal is air swept to three burner levels located on the four corners of the boiler furnace. There is also a sulfur trioxide (SO₃) flue gas conditioning system on the boiler.

In this project, coal feed rates to the pulverizers will be recorded and controlled. Airflows to all three stages of combustion will be measured and controlled. Oxygen sensor(s) on the unit will be used to trim the airflows to obtain the desired air:fuel stoichiometries for the three stages of coal oxidation. The unit will be equipped to record and trend data and using an existing Continuous Emissions Monitoring System (CEMS). The project includes an 18-month test program firing Illinois bituminous coal, using nearby limestone for fluxing the ash and for capturing sulfur, mercury and other metal air toxics.

Based on a comparison for an 80 MWe retrofit, the capital cost of the Ashworth Combustor system is about 40% of the cost of a Selective Catalytic Reduction (SCR) plus Wet Limestone Scrubber system. The operating cost is only 35% of the combined SCR plus Wet Limestone Scrubber. Further, this gives no credit for the removal of mercury, other metal air toxics and halides. The low cost Ashworth Combustor is attributable to the capability of this technology to seamlessly integrate with existing or new hardware and to reduce multiple pollutants using simple, scientifically-based gasification/combustion techniques with low-cost limestone. Because a chemical plant is not required on the backend of the power plant, saleable, solid combustion by-products are produced and cost is further reduced.

In the near term, this technique will provide the electric utility industry with a low cost solution to reduce NOx, SO₂, and mercury emissions from smaller coal-fired units (200 MWe and less). The installation of Selective Catalytic Reduction plus Wet Scrubbers is uneconomic for the smaller electric utility boilers and if low cost multi-pollutant technologies like the Ashworth Combustor are not developed; many of these smaller power plants will be shut down in the not-too-distant future. In the long term, this combustion technology has the real potential to be the Best Available Control Technique (BACT) for coal combustion on new coal-fired power plants. In future development, this technology could also be pressurized and fired with oxygen under pressure to provide a cleaner coal gasifier for integrated gas combined cycle (IGCC) systems.