Figure 5. Propane mole fraction profiles along the fluid centerline of the gas turbine combustor under different fluid velocity conditions.
The homogeneous reaction rate profiles along the fluid centerline of the gas turbine combustor are presented in Figure 6 under different fluid velocity conditions. In a gas turbine engine, inlet air is continuously compressed, mixed with fuel in an inflammable proportion, and then contacted with an ignition source to ignite the mixture which will then continue to burn [71, 72]. The heat energy thus released then flows in the combustion gases to a turbine where it is converted to rotary energy for driving equipment such as an electrical generator [73, 74]. The channels through the unitary body or skeletal structure can be of any shape and size consistent with the desired superficial surface and should be large enough to permit relatively free passage of the gas mixture. The channels may be parallel, or generally parallel, and extend through the support from one side to an opposite side, such channels being separated from one another by preferably thin walls. The channels may also be multi-directional and may even communicate with one or more adjacent channels. The channel inlet openings can be distributed across essentially the entire face or cross-section of the support subject to initial contact with the gas to be oxidized. The unitary, skeletal structure support type of oxidation catalyst can be characterized by having a plurality of flow channels or paths extending therethrough in the general direction of gas flow. The flow channels need not pass straight through the catalyst structure and may contain flow diverters or spoilers. The skeletal structure support is preferably constructed of a substantially chemically inert, rigid, solid material capable of maintaining its shape and strength at high temperatures. The support may have a low thermal coefficient of expansion and low thermal conductivity. Often, the skeletal support is porous but its surface may be relatively non-porous, and it may be desirable to roughen its surface so that it holds the catalyst coating better, especially if the support is relatively non-porous. The support may be metallic or ceramic in nature or a combination thereof. The combustion gases are exhausted to atmosphere after giving up some of their remaining heat to the incoming air provided from the compressor. Operating the combustion process in a very lean condition is one of the simplest ways of achieving lower temperatures and hence lower nitrogen oxides emissions. Very lean ignition and combustion, however, inevitably result in incomplete combustion and the attendant emissions which result therefrom. In addition, combustion processes cannot be sustained at these extremely lean operating conditions. In a catalytic combustor, fuel is burned at relatively low temperatures. While emissions can be reduced by combustion at these temperatures, the utilization of catalytic combustion is limited by the amount of catalytic surface required to achieve the desired reaction and the attendant undesirable pressure drop across the catalytic surface. Also, the time to bring the catalytic combustor up to operating temperature continues to be of concern. In conventional thermal combustion systems, a fuel and air in flammable proportions are contacted with an ignition source to ignite the mixture which will then continue to burn. Flammable mixtures of most fuels are normally burned at relatively high temperatures, which inherently results in the formation of substantial emissions of nitrogen oxides. In the case of gas turbine combustors, the formation of nitrogen oxides can be decreased by limiting the residence time of the combustion products in the combustion zone. However, even under these circumstances, undesirable quantities of nitrogen oxides are nevertheless produced. In combustion systems utilizing a catalyst, there is little or no nitrogen oxides formed in a system which burns the fuel at relatively low temperatures. Such combustion heretofore has been generally regarded as having limited practicality in providing a source of power as a consequence of the need to employ amounts of catalyst so large as to make a system unduly large and cumbersome. Consequently, combustion utilizing a catalyst has been limited generally to such operations as treating tail gas streams of nitric acid plants. The catalytically supported thermal combustion involves essentially adiabatic combustion of a mixture of fuel and air or fuel, air, and inert gases in the presence of a solid oxidation catalyst operating at a temperature substantially above the instantaneous auto-ignition temperature of the mixture, but below a temperature which would result in any substantial formation of oxides of nitrogen under the conditions existing in the catalyst.