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COOLfuel™ [Patented] Case Study 117
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| TXU Electric-Collin Station power plant | |
As part of its State Implementation Plan (SIP) to comply with Federal Clean Air Act requirements, the Texas Commission on Environmental Quality (TCEQ) recently enacted stringent air quality regulations for power generators in Texas. For utilities located in designated ozone non-attainment areas, such as Dallas-Fort Worth (DFW), they must reduce total NOx emissions by approximately 88% by May 2005.
TXU Electric initially developed a compliance plan for their DFW-area generating units that included using combustion and post combustion NOx control technologies. Large units, which were expected to operate the most, would receive both combustion and post combustion technologies to achieve about 95% reduction in their NOx emission rates. Other units, which were expected to operate less and, therefore, have less potential to emit NOx, would receive conventional combustion-based technologies that were expected to achieve about 50% reduction in NOx emissions.
TXU recognized that an opportunity existed to reduce their total NOx reduction costs if they could incorporate an advanced combustion-based technology with a higher NOx-reduction capability than conventional combustion technologies. To determine the extent to which these advanced combustion modifications could be made to reduce NOx, TXU Electric and the TODD® Combustion Group of John Zink Company joined forces and expertise to apply COOLfuel™ gas-conditioning technology at the Collin Station Power Plant. This technology had been successfully applied to a wide variety of boiler applications since the early nineties but had not previously been implemented on a utility boiler.
The Collin Station power plant is a 160 MWe facility, placed into service in 1955, that uses a Combustion Engineering tangentially fired boiler to supply 1,200,000 lb/hr of superheated steam to its electric turbines. The boiler has 40 tilting, natural gas fired burners with ten burners arranged in a single column in each corner of the furnace. The plant is a peaking unit in TXU's power generating system that is normally run in automatic mode five days a week and is shutdown during the weekends.
An initial survey of baseline NOx emissions indicated that the boiler had NOx emission levels of 0.16 lb/MMBtu of fuel burned, equivalent to about 132 ppm corrected to 3% O2, and CO levels ranging from 100 to 400 ppm.
The patented and patent-pending COOLfuel™ system is based on a unique principle applied within the fuel supply to the boiler. Boiler flue gases are induced, using available fuel pressure as the motive force, and mixed with the existing natural gas fuel to generate a low BTU gas that results in substantially reduced emissions. This technology allows the use of flue gases for NOx control without requiring modification, replacement or addition of fans.
A COOLfuel system was designed for the Collin unit with the goal of demonstrating NOx emissions levels of less than 0.042 lb/MMBtu or 35 ppm. The engineers installed a COOLfuel mixing device in the gas piping immediately upstream of each of the burners and modified the existing burner nozzles to accommodate the higher volumetric flow of the COOLfuel gases.
The project was conducted on a very fast schedule to accommodate a scheduled boiler outage. Final design, fabrication, delivery and installation were completed on time, and the unit was brought back on line, on schedule in June 2000. With the availability of this unit being subject to the demands of the electrical supply grid, a critical part of the project was ensuring that the installation, start-up, and optimization of the system did not result in any unscheduled lack of availability for the unit.
The NOx reduction levels demonstrated at the TXU Collin plant as a result of the COOLfuel installation exceeded the proposed NOx-reduction goals of the project, without negative impact to the operation of the unit after more than three years of service. NOx emission rates achieved during testing are shown in Table 1, with CO levels remaining below 300 ppm. COOLflow modeling results were used to further optimize the combustion air system, reducing pressure drop and lowering operating O2 levels, which compensated for the added pressure drop in the furnace due to the additional flue gas flow. This modification allowed the unit to operate at the same generating capacity as before the retrofit.
The project results validate the effectiveness of COOLfuel gas conditioning to substantially reduce NOx on gas-fired utility boiler systems, without sacrificing the operating capacity of the units. To date, COOLfuel systems have been used to successfully reduce NOx from boilers and other combustion applications with heat inputs ranging in size from less than 1 million Btu/hr to more than 1.6 billion BTU/hr.
Table 1
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| MWe Rate | NOx (lb/MMBtu) | NOx (ppm) | |
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| < 100 0.0 | 0.025 - 0.030 | 20 - 25 | |
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| 100 - 140 | 0.030 - 0.035 | 25 - 29 | |
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| 140 - 160 | 0.035 - 0.040 | 29 - 33 | |
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