Catalytic combustion chamber

Catalyst monoliths may laos be employed as catalytic combustion chambers preceding aircraft and stationary gas turbines. As shown diagramatically in Fig. 16, a catalytic combustor comprises a preheat region, a catalyst monolith unit and a thermal region. In the preheat region, a small fuel-rich flame burner is employed to preheat the fuel-air mixture before the hot gases reach the monolith unit. Additional fuel is then injected into the hot gas stream prior to entry to the monolith where... 

The anode exhaust gas is mixed with air, and the nonoxidized components are totally oxidized in a catalytic combustion chamber. Because air is fed in excess, the exhaust gas from the burner still contains a significant amount of oxygen. This gas is then fed to the cathode channel where the electrochemical reduction of oxygen takes place. There, new carbonate ions are produced from carbon dioxide and oxygen according to the backward direction of the following cathode reaction ... 

For the calculation of the electrochemical reaction rates the cathode gas composition is required. Considering the MCFC as a black box, the anode feed gas is completely oxidized with air which is fed into the catalytic combustion chamber, either electro-chemically or in an ordinary combustion reaction. With this, the amount and composition of the exhaust gas is independent of the electric cell performance and can be calculated directly from the conditions of the anode feed and the air feed. According to the assumption of spatially concentrated conditions inside the cathode channel, the exhaust conditions correspond to the conditions in the cathode gas channel. Thus, the cathode gas composition is determined from a combustion calculus. 

Figure 5 Designs of catalytic combustion chambers for gas turbine applications...

The mechanism of poisoning automobile exhaust catalysts has been identified (71). Upon combustion in the cylinder tetraethyllead (TEL) produces lead oxide which would accumulate in the combustion chamber except that ethylene dibromide [106-93-4] or other similar haUde compounds were added to the gasoline along with TEL to form volatile lead haUde compounds. Thus lead deposits in the cylinder and on the spark plugs are minimized. Volatile lead hahdes (bromides or chlorides) would then exit the combustion chamber, and such volatile compounds would diffuse to catalyst surfaces by the same mechanisms as do carbon monoxide compounds. When adsorbed on the precious metal catalyst site, lead haUde renders the catalytic site inactive. 

Further oxidation of the pollutants outside the combustion chamber. This oxidation may be either by normal combustion or by catalytic oxidation. These systems require the addition of air into the exhaust manifold at a point downstream from the exhaust valve. An air pump is employed to provide this air. Figure 31-2 illustrates an engine with an air pump and distribution manifold for the oxidation of CO and hydrocarbons (HC) outside the engine. 

A recent innovation includes use of a catalytic combustor. Several tests with large turbines indicate that this alternative can reduce NO, emission to less than 5 ppmv. The catalyst inside the combustion chamber actually causes a portion of the fuel to bum without the presence of a flame. This significantly reduces combustion temperature. 

Effect of Additives. One of the first attempts to solve the preignition problem by additives was the use of tributyl phosphite, claimed in a patent by Campbell (14) This compound inhibited the catalytic activity of lead compounds in promoting the glowing of carbon. A later patent issued to Withrow claimed that trimethyl phosphate and trimethyl phosphite also are effective as fuel additives in inhibiting surface ignition due to leaded deposits (94). Street, in 1952, ran tests with tricresyl phosphate as an additive in leaded fuel and reported that the phosphorus compound affected the occurrence of lead compounds in the end-gas region of the combustion chamber (80). 

Catalytic Ignition(Rocketry). A method of igniting the main propints in a rocket combustion chamber by utilizing a solid or a liq catalyst to initiate chem decompn or breakdown of one of the proplnts and thereby to generate ignition temp and pressure Ref Rocket Encycl(1959), 73... 

Tanaka et al. [73] developed another MEMS system for the catalytic combustion of butane. It is composed of a combustion chamber 8 mm wide, 14 mm long and 150 pm deep which was prepared by anisotropic wet etching of a silicon substrate. The substrate was then covered with Pyrex glass applying anodic bonding. Combustion was performed on a platinum/titania catalyst... 

Recent concepts to achieve NOx purification from lean exhaust gas are emerging. In the NSR system, the material favors the reactive adsorption of NO to N02 which is stored as a nitrate complex in 02 rich atmosphere. The exhaust gas is then switched to a stoichiometric or HC rich environment in which the nitrate is thermodynamically unstable. The stored NOx is then released and catalytically reacts with excess HC species in the exhaust gas to form N2. In the SNR system, the NOx are temporarily stored on an adsorbent and periodically recirculated to the combustion chamber to be decomposed in the combustion process. In these processes the key point is the adsorption/desorption of N02 which has been... 

---