Catalytic combustion design

In the catalytic combustion design, the sensor consists of a measuring and a reference cell, with a filament in each. The measuring filament is provided... 

Kolodziej A, Lojewska J. Short-channel structured reactor for catalytic combustion Design and evaluation. Chemical Engineering and Processing Process Intensification 2007 46 637-648. 

PGM catalyst technology can also be appHed to the control of emissions from stationary internal combustion engines and gas turbines. Catalysts have been designed to treat carbon monoxide, unbumed hydrocarbons, and nitrogen oxides in the exhaust, which arise as a result of incomplete combustion. To reduce or prevent the formation of NO in the first place, catalytic combustion technology based on platinum or palladium has been developed, which is particularly suitable for appHcation in gas turbines. Environmental legislation enacted in many parts of the world has promoted, and is expected to continue to promote, the use of PGMs in these appHcations. 

Dutta, P., Cowell, L.H., Yee, D.K., and Dalla Betta, R.A., Design and Evaluation of a Single-Can Full Scale Catalytic Combustion System for Ultra-Low Emissions Industrial Gas Turbines, ASME 97-GT-292. 

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

Different design concepts have been proposed to match the severe requirements of catalytic combustors. A main classification criterion is based on fuel/air stoichiometry in the catalyst section, which has a dominant effect on the selection of catalytic materials and on the operating characteristics of the combustor. In this section, only configurations based on lean catalytic combustion will be described. The peculiar characteristics of rich catalytic combustion will be described in a separate section. 

The first design concept tried to exploit fully the potential of catalytic combustion by completing the process in a single catalyst section. In such a configuration, a... 

Early studies in this field [35, 36] indicated that a high surface-to-volume ratio, which represents a hurdle for gas-phase combustion, is instead an advantage for catalytic combustion. In fact the small scale enhances considerably the rate of gas-solid mass transfer, which favors the kinetics of the combustion process and compensates for the short residence time. Also, as is well established for large-scale systems, the presence of a catalytic phase allows for stable combustion at significantly lower temperature than traditional homogeneous burners [55, 56]. This makes the design and operation of microcombustors more fiexible. Several recent studies have explored the potential of catalytic microcombustors using H2 [37, 38, 50], methane [37], propane [52,53,57] and mixtures of H2 with propane [57], butane [38,47,52] and dimethyl ether [52]. 

It can be concluded from the previous sections that the p>erfect combustion catalyst has not been found yet, and it is most likely very hard to develop. Hence, reaction engineering must help to circumvent the inherent compromise between activity and stability and the limitations of material science as of today. In this section, the principles of the most promising approaches are outlined. Figure 9 shows schematically the three currently most promising approaches in catalytic combustor design. 

The second issue is the improvement of the low-temperature performance of combustion catalysts, i.e., the activity at combustor inlet conditions. All the proposed catalytic combustor designs available today need a pilot flame, or a heat exchanger in the case of recuperative gas turbines, to heat the compressed combustion air to a temperature sufficient for ignition of the catalyst. The possibility of avoiding this pilot flame is considered very important, since it would further reduce NO emissions. The catalyst surface area and washcoat loading are very important for the low-tempcraturc activity. 

R.A. Dalla Betta, J.C. Schlatter, M. Chow, D.K. Yee, and T. Shoji, Catalytic combustion technology to achieve ultra low NO. emissions Catalyst design and performance characteristics, Proc. 2nd Int. Workshop Catalytic Combustion, 18-20 April, Tokyo (H. Arai, ed.). Catalysis Society of Japan, Tokyo, 1994, p. 154. 

J.R Kesselring, W.V Krill, H.L. Atkins, R.M. Kendall, and J.T. Kelly, Design Criteria for Stationary Source Catalytic Combustion Systems Report EPA-600/7-79-181, pp. 7-71 (1979). 

The problems encountered in developing catalysts for fully catalytic combustion have led to the development of various design approaches in which the catalyst temperature stays below the combustor outlet temperature. These approaches are described in the following sections. 

Fig. 7. Three systems engineering solutions for high-temperature catalytic combustion. A multiple monolith catalyst design B partial catalytic combustion C hybrid (catalytic + thermal) combustion LGC Lean gas-phase combustion.

The first innovative systems engineering approach is of Osaka Gas Company in Japan. They developed a multiple monolith catalyst design for the gas-turbine combustion of methane. In this design, different materials are used to fulfil different functions within the catalyst. A palladium catalyst is placed at the entrance of the catalyst system to ignite the catalytic combustion reaction and to raise the temperature. This temperature is then enough... 

The same group [2.354] has also recently reported on the performance of a membrane reactor with separate feed of reactants for the catalytic combustion of methane. In this membrane reactor methane and air streams are fed at opposite sides of a Pt/y-A Os-activated porous membrane, which also acts as catalyst for their reaction. In their study Neomagus et al. [2.354] assessed the effect of a number of operating parameters (temperature, methane feed concentration, pressure difference applied over the membrane, type and amount of catalyst, time of operation) on the attainable conversion and possible slip of unconverted methane to the air-feed side. The maximum specific heat power load, which could be attained with the most active membrane, in the absence of methane slip, was approximately 15 kW m with virtually no NO emissions. These authors report that this performance will likely be exceeded with a properly designed membrane, tailored for the purpose of energy production. 

Today, combustion catalysts that can operate up to 900-1000 °C have been developed and studied in both laboratory- and pilot-scales. Still, two catalyst features have not been fully developed. To begin with, a catalyst system that can operate above 1000 °C for one year of operation or more. Secondly, a catalyst system that can ignite natural gas at compressor outlet temperatures of approximately 200-400 °C. However, several combustion chamber designs have been proposed that utilize the features of catalytic combustion, but which operate the catalyst module at approximately 500-1000 °C. Here, a homogeneous zone is used to increase the temperature of the gas to the final maximum temperature. These designs are described in detail in Section 5 of this review. 

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