| OCR Text |
Show temperature is achieved [3]. It was shown [2] that the rates of oxidation reactions of methane can be enhanced very significantly through the homogeneous mixing with the reactants, of small proportions of the uncooled products. Such mixing does not only lead to a slight preheating of the reactive mixture, hence speeding up somewhat the reaction, but may also provide a small amount of badly needed radicals and other active species leading to enhancement of the rates of the early stages of the reaction. The extent of this enhancement to the rates would depend largely on the composition of the mixture, temperature and the mass of recirculated gases employed. What is also significant is that such improvements appear to be achievable even for fuel mixtures containing a very substantial amount of diluents such as carbon dioxide. ADIABATIC CONSTANT PRESSURE REACTION INITIAL TEMPERATURE-IOCOK EQUIVALENCE RATI0(*)»I.0 CHC4H+4C 02 20% RATIOS 20 30 40 50 RESIDENCE TIME (IDS) 7.5 Equ.R-IJnrtT-IOOOK, CH4+CQ2+Air o.o» C O peak adiab.constP reactor *-©-f H2peak -&- COequiU 4 H2equfl. CO2*10 COnOinit 10 20 30 40 SO 60 70 60 90 100 CH4 concentration (% by volume) Fig. 3 Variations in the concentrations of methane with time during a constant pressure adiabatic combustion process for various fuel mixtures of methane and carbon dioxide in stoichiometric proportion with air. The initial temperature is 1000 K and atmospheric pressure Fig. 4 Typical variations in the peak and equilibrium concentrations of CO, H ^ and C 0 2 during adiabatic combustion at constant atmospheric pressure of various fuel mixtures of methane and carbon dioxide for stoichiometric mixtures with initial temperature of 1000K. Considerations of some combustion characteristics The flammability limits of methane with oxygen or oxygenated air are much wider than the corresponding values in air and would tolerate significantly greater amounts of carbon dioxide. Moderate changes in pressure do not influence markedly the lean limit and thus would not increase the tolerance to the presence of carbon dioxide with the methane. However, the rich limit is extended significantly with the increase in pressure indicating that fuel rich mixtures containing greater amounts of carbon dioxide in methane can be burnt at higher pressures [4]. 5 |
