Control of Primary Zone Soot Formation in a Semi-Closed Cycle Gas Turbine

Abstract

Spectroscopic measurements were made on the primary zone flame of a constant speed, semi-closed cycle, and recuperated gas turbine. This was undertaken at various loads while introducing cooled exhaust gas into the combustor reactant stream as a diluent. Operating conditions included primary reaction zone equivalence ratios from 0.42 to 0.64 and reactant oxygen concentration from 15.4 to 20.7% at an average combustion pressure of 34.8 psia. The results demonstrated a power relationship between soot volume fraction and the oxygen concentration in the reactant gas mixture. Soot formation was reduced by an order of magnitude when oxygen concentration was reduced to 17.5%. Two predictive models, based on data regression analysis, were developed for soot temperature as a function of combustion pressure and oxygen concentration and for soot volume fraction, normalized to the maximum observed, as a function of equivalence ratio, oxygen concentration, soot temperature and combustion pressure. The models demonstrate a close agreement with data and predict both soot temperature and soot volume fraction will increase with primary zone oxygen concentration.