OCR Text |
Show LIM SIMULATIONS OF GAS INJECTION AND REBURNING IN TWO COAL-FIRED UTILITY BOILERS Richard D. Frederiksen and Werner J.A. Dahm NGB Technologies, Inc. 2600 Roseland, Suite 100 Ann Arbor, MI 48103-2135 USA John Pratapas and Robert V. Serauskas Gas Research Institute 8600 West Bryn Mawr Avenue Chicago, IL 60631-3505 USA William Bartok William Bartok, Inc. 956 Wyandotte Trail Westfield, NJ 07090 USA Results are presented from LIM-based simulations of fuel-lean gas reburning (FLGR) in two different types of coal-fired utility boilers to assess the capabilities of such simulations for supporting gas reburning system development. In the first of these boilers - a 112 MWe roof-fired pulverized coal unit (Duquesne Light Company's Elrama Unit 2 - the simulations were able to identify the origins of several unexpected factors that limited the NOx reduction attainable with the original reburn system design. The simulations also indicated specific changes in the gas injection system to achieve higher levels of NOx reduction at lower levels of gas input. In the second boiler - a 327 MWe cyclone fired unit (Commonwealth Edison's Joliet Unit 6 - the simulations were conducted in advance of any field data from the unit. Results correctly predicted all aspects of the reburn system performance subsequently measured under full load conditions without steam injection. These include quantitative predictions of the reduction in NOx emissions and increase in CO emissions. These results indicate that LIM-based simulations provide an effective way of obtaining accurate a priori assessment of the performance of gas reburning systems in a wide range of coal-fired utility boilers. 1. INTRODUCTION In large installations such as utility boilers and waste incinerators, as well as high temperature industrial processes such as glass and metal processing furnaces, natural gas reburning can play an essential role in reducing emissions to meet regulatory levels. The chemical kinetic basis for gas reburning is largely understood, stemming from the original experiments by Wendt in 1973 that showed NOx reduction by secondary fuel injection. Natural gas injected into hot furnace gases forms hydrocarbon radicals (primarily CH) which react with N O to form HCN. The HCN then undergoes a further series of reactions involving NO to form N2. However, if the HCN instead reacts with 02 it can reform NO. Consequently, effective removal of NO can be accomplished via gas injection in a reburn zone to promote CH radical |