A Catalytic Combustor for High-Temperature Gas Turbines

Catalytic combustion has been the subject of thorough research work for over two decades, mainly in the U.S. and Japan. However, severe material problems in the ceramic or metallic monolith prevented regular operation in most cases. Still, during these two decades, turbine inlet temperatures were raised remarkably, and lean premix combustors have become standard in stationary gas turbines. In view of these facts, a simple “monolith-in-tube” concept of a catalytic combustor was adapted for the use in high-temperature gas turbines. Its essential feature is the fact that a considerable portion of the homogeneous gas phase reaction is shifted to the thermal reactor, thus lowering the catalyst temperature. This is achieved by the employment of very short catalyst segments. The viability of this concept has been demonstrated for a variety of pure hydrocarbons, alcohols as well as common liquid fuels. Extensive experimental investigations of the atmospheric combustor led to the assessment of parameters such as reference velocity, fuel-to-air ratio, and fuel properties. The maximum combustor exit temperature was 1673 K with a corresponding catalyst temperature of less than 1300 K for diesel fuel. Boundary conditions were in all cases combustion efficiency (over 99.9 percent) and pressure loss (less than 6 percent). Additionally, a model has been developed to predict the characteristic values of the catalytic combustor such as necessary catalyst length, combustor volume, and emission characteristics. The homogeneous reaction in the thermal reactor can be calculated by a one-dimensional reacting flow model.