Experimental Investigations of Catalytic Combustion for High-Pressure Gas Turbine Applications

Abstract

Catalytic combustion has proven to be a suitable alternative to conventional flame combustion in gas turbines for achieving Ultra-Low Emission levels (ULE). In the process of catalytic combustion, it is possible to achieve a stable combustion of lean fuel/air mixtures which results in reduced combustion temperature in the combustor. The ultimate result is that almost no thermal-NOx is formed and the emissions of carbon monoxide and hydrocarbon emissions are reduced to single-digit limits. Successful development of catalytic combustion technology would lead to reducing pollutant emissions in gas turbines to ultra-low levels at lower operating costs. Since the catalytic combustion prevents the pollutant formations in the combustion there is no need for costly emission cleaning systems. High-quality experimental data of combustion catalyst operations at gas turbine working conditions and validated numerical models are essential tools for the design and development of catalytic gas turbine combustors. The prime objective of the work presented in this paper was to obtain catalytic operational data under said conditions. Experimental investigations were carried out to determine the operational data on different types of combustion catalysts against different fuel types at gas turbine operational conditions. A pilot-scale 100 k W high-pressure combustion test facility was used for the experimental investigations of catalytic combustion under real gas turbine conditions. Combustor pressure can be maintained at any desired level between 1 to 35 bars. The maximum combustion air supply is 100 g/s, which can be electrically preheated up to 600°C and humidified up to 30% of weight as required by test conditions. Catalysts used in the test facility are highly active noble metal catalysts for ignition purposes and thermally stable metal oxide catalysts for continuing reactions. Tests are conducted as the testing of single catalyst segments or combinations of several segments. The measurements taken are flow rates (air/fuel ratio) temperatures (inlet, surface and the outlet of each catalyst segment), pressure (combustor) and emissions of NOx, CO and UHC. This paper presents the design of the high-pressure catalytic combustion test facility and an experimental comparison of methane combustion over Pd on alumina and Pd/Pt (bi-metal) on alumina catalysts at varying pressure levels up to 20 bars. The catalysts concerned were cylindrical shaped (35 mm in diameter and 20 mm in height) honeycomb type fully coated catalysts. The results showed that the Pt/Pd on alumina catalysts is better in low temperature ignition and combustion stability over the Pd on alumina catalysts. Emission measurements showed that the fuel conversion over the tested Pt/Pd on alumina catalyst was around 10% while fuel conversion over a similar Pd on alumina catalyst (geometry and capacity) was only 4%. Fuel conversion rates showed the tendency to be further reduced (over the same catalysts) against increasing pressure.