Combined Cycle Gas Turbine Startup Emissions

摘要

Gas turbine (GT) startup (SU) emissions limits are included in nearly all air permits. This was not always the case, but over the past decade or so as NO_x, and especially CO, analyzers became more accurate at measuring the wide range of emissions during a gas turbine startup (CO can range from < 1 to several thousand parts per million), air regulators have required quantification and of course, limits. Historically, GT combined cycle (CC) SU emissions have been categorized as 'Cold', 'Warm', and 'Hot', based on the number of hours since the previous shutdown, and the steam turbine rotor and/or inlet temperatures. However in reality, these categories have proven themselves to be fluid, vague and quite frankly, the wrong way to qualify CC SU emissions. Based on operational data from several large-frame (e.g. 'F' and H' GT), Siemens is promoting a more logical approach, based on oxidation (aka 'CO') and SCR catalyst temperatures, which are the true differentiators between startup types. This paper is an update to last year's, prepared due to the collection and analysis of numerous GT CC startups, which indicate that (1) our original characterization of the types of startup was correct, and (2) we needed to further refine said characterization to take not only time since previous shutdown into account, but actual initial catalyst temperature. Hence, new and additional data will be presented to support the methodology of quantifying GT CC SU as either 'Cold' or 'Non-Cold', defining each, as well as permitting strategies when estimating emissions for regulatory agencies. We continue to strive for industry and regulatory understanding and acceptance of this new, belter way of looking at GT CC SU, one that makes technical sense as well as allows more operational flexibility while maintaining emissions as low as practical.