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

Abstract

Volatile renewable energy sources induce power supply fluctuations. These need to be compensated by flexible conventional power plants. Gas turbines in combined cycle power plants adjust the power output quickly but their turn-down ratio is limited by the slow reaction kinetics, which leads to CO and unburned hydrocarbon emissions. To extend the turn-down ratio, part of the fuel can be converted to syngas, which exhibits a higher reactivity. By an increasing fraction of syngas in the fuel, the reactivity of the mixture is increased and total fuel mass flow and the power output can be reduced. An autothermal on-board syngas generator in combination with two different burner concepts for natural gas (NG)/syngas mixtures was presented in a previous study (Baumgärtner, M. H., and Sattelmayer, T., 2017, “Low Load Operation Range Extension by Autothermal On-Board Syngas Generation,” ASME J. Eng. Gas Turbines Power, 140(4), p. 041505). The study at hand shows a mass-flow variation of the reforming process with mass flows, which allow for pure syngas combustion and further improvements of the two burner concepts which result in a more application-oriented operation. The first of the two burner concepts comprises a generic swirl stage with a central lance for syngas injection. Syngas is injected with swirl to avoid a negative impact on the total swirl intensity and nonswirled. The second concept includes a central swirl stage with an outer ring of jets. For this burner, syngas is injected in both stages to avoid NOx emissions from the swirl stage. Increased NOx emissions produced by NG combustion of the swirl pilot were reported in last year's paper. For both burners, combustion performance is analyzed by OH*-chemiluminescence and gaseous emissions. The lowest possible adiabatic flame temperature without a significant increase of CO emissions was 170–210 K lower for the syngas compared to low load pure NG combustion. This corresponds to a decrease of 15–20% in terms of thermal power.