ARCHIVED REPORTS LEC APPLICATION FOR CERTIFICATION

Home Browse Search

5AC:EVALUATION OF BEST AVAILABLE CONTROL TECHNOLOGY 5.1 C.1 BACT for the CTGIHRSG: Normal Operations 5.1C.1.1 NOx Emissions 5.1C.1.1.1 Achievable Controlled Levels and Available Control Options The most recent NOx BACT listings for combined-cycle combustion turbines in this size range are summarized in Table 5.1C-1. The most stringent NOx limit in these recent BACT determinations is a 2.0 ppml limit averaged over a 1-hour averaging period,excluding startups and shutdowns. This level is achieved using DLN combustors and SCR. The Elk Hills project was given the option of using SCONOx instead of SCR,with a NOx limit of 2.5 ppm. The SJVAPCD adopted Rule 4703 (Stationary Gas Turbines) to limit NOx emissions from these devices. Rule 4703 specifies an enhanced Tier II NOx emission limit of 3 ppmv @ 15% O2 for natural gas-fired combustion gas turbines rated at no less than 10 MW and equipped with SCR (April 30,2008 deadline). SCONOx is a NOx reduction system produced by Goal Line Environmental Technologies. It is now distributed by EmeraChem as EMx. This system uses a single catalyst to oxidize both NOx and CO and then a regeneration system to convert the NO2 to N2 and water vapor. The system does not use ammonia as a reagent.The EMx process has been demonstrated in practice on much smaller gas turbines,including Redding Electric Utility's (REU) Unit 5,a 43-MW Alstom GTX100 combined-cycle gas turbine. While the technology has never been demonstrated on a gas turbine the size of the 7FA,the technology is considered by the manufacturer to be scalable. The SCR system uses ammonia injection to reduce NOx emissions. SCR systems have been widely used in combined-cycle gas turbine applications of all sizes,including the 7FA and the larger H-class. The SCR process involves the injection of ammonia into the flue gas stream via an ammonia injection grid upstream of a reducing catalyst. The ammonia reacts with the NOx in the exhaust stream to form N2 and water vapor. The catalyst does not require regeneration,but must be replaced periodically—approximately every 3 years. Either SCR or SCONOx technology,in combination with dry low-NOx (DLN) combustion, will achieve a NOx emission level of 2.0 ppmvd@ 15% 02. 5.1C.1.1.1.1 Environmental Impacts The use of SCR will result in ammonia emissions due to an allowable ammonia slip limit of 10 ppmvd @ 15% 02. A health risk screening analysis of the proposed project using air dispersion modeling showed the acute hazard index and a chronic hazard index each to be much less than 1,based on an ammonia slip limit of 10 ppmv @ 15% 02. In accordance with the District's Integrated Air Toxics program and currently accepted practice, a hazard index below 1.0 is not considered significant. Therefore,the toxic impact of the ammonia slip resulting from the use of SCR is deemed to be not significant and is not a sufficient reason to eliminate SCR as a control alternative. 1 All turbine/HRSG exhaust emissions concentrations shown are corrected to 15% 02. 5.1C 2 SAC/371322/082330016(LEC_5.1 C_APPENDIX.DOC)