Low Load Operation Range Extension by Autothermal On-Board Syngas Generation

Abstract

The increasing amount of volatile renewable energy sources drives the necessity of flexible conventional power plants to compensate for fluctuations of the power supply. Gas turbines in a combined cycle power plant (CCPP) adjust the power output quickly but a sudden increase of CO and UHC emissions limit their turn-down ratio. To extend the turn-down ratio, part of the fuel can be processed to syngas, which exerts a higher reactivity. An autothermal on-board syngas generator in combination with two different burner concepts for natural gas and syngas mixtures are presented in this study. A mixture of natural gas, water vapor and air reacts catalytically in an autothermal reactor test rig to form syngas. At atmospheric pressure, the fuel processor generates syngas with a hydrogen content of ∼30 vol% and a temperature of 800 K within a residence time of 200 ms. One concept for the combustion of natural gas and syngas mixtures comprises a generic swirl stage with a central lance injector for the syngas. The second concept includes a central swirl stage with an outer ring of jets. The combustion is analyzed for both concepts by OH*-chemiluminescence, lean blow out (LBO) limit and gaseous emissions. The central lance concept with syngas injection exhibits an LBO adiabatic flame temperature that is 150 K lower than in premixed natural gas operation. For the second concept an extension of almost 200 K with low CO emission levels can be reached. This study shows that autothermal on-board syngas generation is feasible and efficient in terms of turn-down ratio extension and CO burn-out.