Catalytic Combustion for Gas Turbines

J2.2 Lean Catalytic Combustion for Gas Turbines 365 Table 12.1 Design criteria and operating conditions of GT combustors. 

Catalytic combustion for gas turbines has received much attention in recent years in view of its unique capability of simultaneous control of NOX) CO, and unbumed hydrocarbon emissions.1 One of the major challenges to be faced in the development of industrial devices is associated with the severe requirements on catalytic materials posed by extreme operating conditions of gas turbine combustors. The catalytic combustor has to ignite the mixture of fuel (typically natural gas) and air at low temperature, preferably at the compressor outlet temperature (about 350 °C), guarantee complete combustion in few milliseconds, and withstand strong thermal stresses arising from long-term operation at temperatures above 1000°C and rapid temperature transients. 

However, most of the following discussion will deal with catalytic combustion for gas turbine applications. Figure 4 shows a schematic view of an open-cycle gas turbine unit with a catalytic combustor (cf. a conventional unit in Fig. 2.). 

Catalytic combustion for gas turbines is an area that has developed rapidly during the last two decades. Several novel approaches for catalytic combustors have shown high potential often as a result of combined materials science and reaction engineering. However, a substantial effort is still needed before commercial gas turbines with catalytic combustors become available on the market. 

This problem can be circumvented in a fuel-rich approach to catalytic combustion for gas turbines recently proposed. In this method fuel is mixed with air to form a fuel-rich mixture that is reacted over the catalyst to produce both partial and total oxidation products. The reaction products are then mixed with excess air and burned in a homogenous flame. Because the gases exiting the catalyst are fuel-rich, they cannot sustain combustion in the event of a homogenous flame backup. The promise of this method needs to be confirmed in full-scale turbine tests. 

Forzatti, P. Status and perspectives of catalytic combustion for gas turbines. Catalysis Today 2003, 83, 3-18. 

Catalytic combustion for gas turbines is an important tool for lowering NO emissions from gas turbines. Multistage catalytic reactors for gas turbines have shown ultralow emissions, namely 0.5 ppm NO.v, 0.8 ppm CO, and 1.7 ppm un-bumed hydrocarbons from natural gas fuel [145]. 

E. M. Johansson, D. Papadias, P.O. Thevenin, A.G. Ersson, R. Gabrielsson, P.G. Menon, P.H. Bjornbom and S.G. Jaras, in Catalytic Combustion for Gas Turbine Applications, Catalysis-Specialist Periodical Reports, Volume 14, Royal Society of Chemistry, Cambridge 2001... 

In this section, recent development of high temperature stable support materials as well as washcoat and active materials is reviewed. Some of the most promising materials to be used as supports in catalytic combustion for gas turbine applications are summarized in Table 1. These monolithic support materials, such as alumina or zirconia, could also be used as washcoat materials with another preparation method. Typical light-off temperatures and specific surface areas for some of the interesting catalyst compositions are summarized in Table 2. 

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