The AZEP (Advanced Zero Emissions Power Plant) project addresses the development of a novel “zero emissions,” gas turbine-based, power generation process to reduce CO2 emissions. Preliminary calculations indicate the attractiveness of this concept in comparison to conventional tail-end CO2 capture. Key to achieving the AZEP project targets is the development of a combustion system to burn natural gas with nearly stoichiometric amounts of oxygen and high levels of exhaust gas dilution. Within the first part of this study the fundamental combustion properties of AZEP gas mixtures are quantitatively determined. Significant inhibition results from the high level of exhaust gas dilution. In the second part a staged, rich–lean combustion concept, proposed to improve combustion stability, is investigated. It was shown that significant levels of hydrogen could be produced by a first stage, partial catalytic oxidation (PCO) of methane. Furthermore, it is shown that the addition of this produced hydrogen improves the stability of the downstream, second stage burnout zone. It was demonstrated that the produced syngas could act to reduce the blowout limit by ca. 100 K as compared to homogeneous gas phase combustion.
Concerning the efforts in reducing the impact of fossil fuel combustion on climate change for power production utilizing gas turbine engines Flue Gas Recirculation (FGR) in combination with post combustion carbon capture and storage (CCS) is one promising approach. In this technique part of the flue gas is recirculated and introduced back into the compressor inlet reducing the flue gas flow (to the CCS) and increasing CO2 concentrations. Therefore FGR has a direct impact on the efficiency and size of the CO2 capture plant, with significant impact on the total cost. However, operating a GT under depleted O2 and increased CO2 conditions extends the range of normal combustor experience into a new regime. High pressure combustion tests were performed on a full scale single burner reheat combustor high-pressure test rig. The impact of FGR on NOx and CO emissions is analyzed and discussed in this paper. While NOx emissions are reduced by FGR, CO emissions increase due to decreasing O2 content although the SEV reheat combustor could be operated without problem over a wide range of operating conditions and FGR. A mechanism uncommon for GTs is identified whereby CO emissions increase at very high FGR ratios as stoichiometric conditions are approached. The feasibility to operate Alstom’s reheat engine (GT24/GT26) under FGR conditions up to high FGR ratios is demonstrated. FGR can be seen as continuation of the sequential combustion system which already uses a combustor operating in vitiated air conditions. Particularly promising is the increased flexibility of the sequential combustion system allowing to address the limiting factors for FGR operation (stability and CO emissions) through separated combustion chambers.
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