Ongoing Development of a Low Emission Industrial Gas Turbine Combustion Chamber

Abstract

Experiments were performed in laboratory-and full-scale combustors to test the feasibility of meeting proposed EPA emission standards. It was found that by uniformly mixing gaseous fuel and primary zone air prior to combustion and burning fuel leanly (equivalence ratio <1.0), it was possible to meet the proposed emission standards in an industrial gas turbine. The characteristic narrow range of flame stability obtained with lean premix combustion necessitated the use of fuel staging or variable geometry to handle the operational range of the engine. Fuel staging was selected for its relative simplicity. Consequently, EPA proposed emission standards were met only over a narrow range covering the engine operation at and near the design point. Experiments on small scale models of various sizes operated with gaseous and liquid fuels showed that, contrary to expectation, NOx production from a lean premix combustion system is independent of the system pressure in the pressure range investigated (1 atm to 16 atm). The desirability of high combustor inlet temperature and pressure for premixing was indicated. Despite the complexities of premixing fuel and air, such a combustion system, in addition to meeting the proposed emission standards, offers advantages such as easing of combustor wall cooling problems, improved combustor exit temperature distribution, and freedom from exhaust and primary zone smoke.