Grayson Station applies technology to burn landfill gas, reduce Nox
The City of Glendale, Calif., took an innovative approach to NOx reduction compliance when retrofitting its Grayson Generating Station. Glendale contracted Western Environmental Equipment Corp. to supply low-NOx burners, flue gas recirculation (FGR), burner management and combustion control systems, and turnkey supply and construction.
Low NOx levels were achieved with the plant?s 20-MW and 45-MW boilers, which burn a combination of natural gas and landfill gas. The project was driven by requirements to comply with strict NOx emission regulations and the desire to utilize municipal waste-generated landfill gas for power generation.
A new flue gas recirculation system was designed and installed, capable of recirculating up to 25 percent of the boiler flue gases to the combustion air for NOx reduction. New microprocessor-based burner management and combustion control systems were supplied with a PC man-machine interface and custom Windows graphics for burner and boiler control.
NOx levels of less than 29 ppm were achieved on Unit 3 and 38 ppm on Unit 4. These emission levels were achieved with combustion air preheat temperatures exceeding 500 F. Even lower emissions were achieved with landfill gas. Boiler controls were automated to maximize landfill gas usage. The control system automatically maximizes landfill gas fuel and modulates the support fuel to carry the balance of the required load. The FGR rate is controlled as a function of boiler load to achieve minimum NOx emissions throughout the operating range.
The recovered landfill gas is expected to provide electricity for 30,000 homes and save the city and its residents $26 million dollars over the next 20 years. Based on the success of this project, the city plans to expand the automatic control system to include other boiler subsystems such as steam temperature and pressure, furnace pressure and CO trim. The city also plans to apply the technology to Unit 5 to allow firing of landfill gas on a third unit.