Evaluation of  Ultra Low NOx PC Burner Flame

The goal of this project is to develop a cost-effective NOx control system that can be deployed in coal-burning power plants by the year 2002, and achieve a NOx level below 0.15 lbs/million Btu for a wide range of coals. The project is scheduled for completion in September 2001. Since the first retrofit of a double-register burner (DRB) in 1973 produced a 50% reduction in NOx, these burners have been installed in 70 boilers with a combined capacity exceeding 40,000 MW. The next major advance, the DRB-XCL™, yielded reductions of NOx in the 50-70% range without over-fire air (OFA). To date, the XCL™ has been installed in 86 boilers, with and without OFA, for more than 23,000 MW total. The most recent burner, the ultra low NOx DRB-4ZTM, was developed during the period 1993-1997, in DOE’s Low Emissions Boiler System program. NOx levels below 0.20 lbs/MM Btu were recorded with Illinois #6 coal. To simplify retrofits, MTI recently tested an equally successful, small throat (plug-in) version of the DRB-4Z™, in a project supported by DOE and the Ohio Coal Development Office.

The current project will optimize and test the plug-in burner with SNCR in the 100 MM Btu/hr Clean Environment Development Facility at Alliance, Ohio. This will provide data for a single burner in the capacity range of utility applications under well-controlled and commercially representative conditions. The effects of coal rank will be examined by firing three coals: a Powder River Basin subbituminous (Spring Creek), a high-volatile bituminous (Illinois #6) and a medium-volatile bituminous (Pennsylvania Middle Kittanning). No staging will be employed; a stoichiometric ratio range from 1.10 to 1.28 will be tested, with 17% excess air being the target at full load. Coal will be pulverized as common boiler grind, 70 to 75% through 200 mesh.

MTI recognizes that commercial boilers could produce higher levels of NOx than indicated for similar conditions in the CEDF, owing to burner flame interactions, coal property variations, etc. Therefore, the target in the CEDF has been set at 0.125 lbs/MM Btu, to provide confidence for the 0.15 lbs/MM Btu figure in commercial installations. In addition to the NOx work, MTI will perform some tests to investigate the influence of the ULNB on the fate of mercury during coal combustion. Mercury has been a subject of intense research for a decade, with reference to its partitioning into gas and particulate phases and speciation in the gas phase. The ULNB introduces a new factor, however, since attempts to reach very low levels of NOx have been associated with an increase in unburned carbon. This carbon generally is weighted to the smaller size fraction of the fly ash, providing active sites for reaction with mercury.