ARCHIVED REPORTS LEC APPLICATION FOR CERTIFICATION

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5AC:EVALUATION OF BEST AVAILABLE CONTROL TECHNOLOGY There are two basic means of controlling NOx emissions from boilers: combustion controls and post-combustion controls. Combustion controls act to reduce the formation of NOx during the combustion process,while post-combustion controls remove NCIx from the exhaust stream. Combustion control technologies for this type of boiler application include low-NOx burners,flue gas recirculation and staged combustion. Post-combustion controls include SCR and selective non-catalytic reduction(SNCR). These are discussed below in order of most effective to least effective. Selective Catalytic Reduction. The effectiveness of an SCR system requires the catalyst,and thus the treated exhaust stream,to be within a certain temperature range for the NOx reduction reaction to take place. The auxiliary boiler will be operated to support the Rapid Response turbine startup process and will be operated only up to 468 hours per year. The boiler is designed to provide 45,000 lb/hr of steam,with a minimum load of approximately 20,000 lb/hr to provide steam for steam turbine seals and sparging and the remaining 25,000 lb/hr for fuel gas heating. The majority of boiler operations are expected to be at low load, where the exhaust gas temperature is expected to be below the minimum needed for effective SCR control. While the boiler will operate at full load periodically,the length of time at which it will operate is expected to be so short that the SCR system could rarely,if ever,be used effectively. Therefore,this technology is not considered technically feasible for the auxiliary boiler in this application. Selective Noncatalytic Reduction (SNCR).SNCR involves injection of ammonia or urea with proprietary conditions into the exhaust gas stream without a catalyst. SNCR technology requires gas temperatures in the range of 1200 to 2000°F. The exhaust temperature for the proposed auxiliary boiler is 375°F,well below the minimum SNCR operating temperature. Therefore,SNCR is not technically feasible for this application. Ultra-Low NOx Burners with Flue Gas Recirculation (FGR).Low-NOx burners with FGR are commonly used on industrial-sized package boilers such as the LEC auxiliary boiler. These burners minimize the formation of thermal NOx and FGR reduces the oxygen in the combustion zone to further reduce NOx formation. Ultra-low NOx burners with FGR can achieve NOx emission rates of 7 to 9 ppmvd @ 3% 02 without post-combustion controls. A 9 ppm emission rate was recently accepted as BACT for the Colusa Generating Station auxiliary boiler and was considered the lowest technologically feasible emission rate for that particular application. A summary of the permitted emissions limits for other,similar boilers is provided in Table 5.1C-5 below. 5.1C.3.1.1.1 District BACT Determinations The SJVAPCD's BACT determination for boilers in this size range with variable loads shows that less than 15 ppmc is considered achieved in practice while 9 ppm is considered technically feasible. The BAAQMD has determined that 9 ppmc is achieved in practice while 7 ppmc is considered technologically feasible. However,the BAAQMD BACT guideline indicates that SCR is needed to achieve 7 ppmc,and, as discussed above,SCR is not feasible for this application. 5.1C 16 SAC/371322/082330016(LEC_5.1C_APPENDIX.DOC)