Ongoing Development of a Gas Turbine Combustion System for Gaseous Fuels With a Wide Range of Wobbe Index Values

Abstract

Development of a combustion system at the author’s Company was carried out at atmospheric pressure to achieve successful operation of a 5500-hp (Type H) gas turbine on gaseous fuels covering a wide range of Wobbe Index (WI) values from 48.04 MJ/nm3 (1220 Btu/scf) for natural gas to 18.90 MJ/nm3 (480 Btu/scf) for natural gas and carbon dioxide mixtures. Mixtures with the latter composition have direct applications for gas turbine engines burning fuels derived from sanitary landfills and liquid sewage. Wide-range operational capability offers the flexibility to fire gas turbines with either pipeline quality natural gas or medium-heating-value fuel, depending on availability. For such applications, if a fuel injector is designed to operate satisfactorily on natural gas fuel, it will have unacceptably high pressure drops when operating on fuels with WI values towards the lower end of the range. On the other hand, if the fuel injector is designed to operate properly on fuels with WI values on the lower end of the range, it will have unacceptably low pressure drops when operating on fuels with WI values towards the higher end of the range, which causes combustion-driven pressure oscillation feedback into the fuel-injection system. This feedback usually increases the amplitude of combustion-driven pressure oscillation and can cause significant damage to the gas turbine in a relatively short time. This paper describes the design and development work carried out to resolve these problems.