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5.1C:EVALUATION OF BEST AVAILABLE CONTROL TECHNOLOGY <br /> cannot be effectively reduced. Therefore,the pound per hour NOx, CO,and VOC limits <br /> proposed by the applicant for startup and shutdown periods represent achievable emissions <br /> limits based on experience with other, similar turbine projects and are considered BACT for <br /> startup and shutdown. <br /> Since the emission rates cannot be reduced,startup emissions must be addressed by <br /> minimizing the amount of time the gas turbine and HRSG spend in startup. Efforts have <br /> been made by turbine and HRSG manufacturers to develop ways of reducing the time <br /> required to ramp up the CTG load to where the DLN combustors will be effective and <br /> exhaust temperatures will allow the control devices to be effective. LEC is proposing to <br /> utilize a new Rapid Response process for this project. Rapid Response includes the <br /> following project features: <br /> • HRSG design: The HRSG will be designed to optimize heat transfer to the tubes,which <br /> will allow the HRSG to heat up more quickly. This will reduce gas turbine hold time at <br /> low load, especially during cold startups. <br /> • Auxiliary boiler: The proposed project includes an auxiliary steam boiler that will <br /> provide steam during startup. The auxiliary boiler steam will preheat the CTG fuel and <br /> provide steam turbine sealing steam prior to CTG startup,thereby allowing the <br /> condenser vacuum to be established and the condenser to be in a condition ready to <br /> accept steam earlier in the startup cycle. <br /> Both of these project design features are expected to reduce hold times for the gas turbine <br /> and therefore to allow the gas turbine/HRSG to reduce startup times,especially for cold <br /> and warm startups. Because this Rapid Response process has not yet been demonstrated on <br /> an operating gas turbine plant,LEC cannot assume the risk that the process will not operate <br /> as advertised by GE. Therefore,the NOx, CO, and VOC emissions limits proposed for the <br /> project assume that, as a worst case,the Rapid Response process does not allow a significant <br /> reduction in startup times. <br /> In summary,LEC is proposing to go beyond BACT for startup and shutdown emissions by <br /> installing the Rapid Response system,but the applicant is not taking credit for the expected <br /> effectiveness of the Rapid Response system in reducing startup emissions. <br /> 5.1 C.3 BACT for the Auxiliary Boiler <br /> 5.1C.3.1 NOx Emissions <br /> 5.1C.3.1.1 Achievable Controlled Levels and Available Control Options <br /> NOx is formed during combustion through two mechanisms: (1) thermal NOx,which is the <br /> oxidation of elemental nitrogen in combustion air;and (2) fuel NOx,which is the oxidation <br /> of fuel-bound nitrogen.Since natural gas is relatively free of fuel-bound nitrogen,the <br /> contribution of this second mechanism to the formation of NOx emissions in natural gas- <br /> fired equipment is minimal and thermal NOx is the chief source of NOx emissions.Thermal <br /> NOx formation is a function of residence time, oxygen level, and flame temperature, and <br /> can be minimized by controlling these elements in the design of the combustion equipment. <br /> SAC/371322/082330016(LEC_5.1C_APPENDIX.DOC) 5.1C 15 <br />