Advanced Application of Excess Enthalpy Combustion Technology to Boiler Systems

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Based on our findings we recommend the following guidelines for obtaining uniform heat flux profile using the concept of excess enthalpy flame in the combustion chamber: a) Mechanical shift of the burner. b) Alternate firing using 2 or more burners. c) Change the flame temperature profile using controlled fuel-air mixing. Stable combustion may be obtained through the use of some combination of on-off control and/or through the use of delayed mixing. High temperature excess enthalpy combustion, which employs the high temperature air, has many advantages including wider stability limits than that obtained under traditional operational conditions. The lean llammablility limits of various fuel and air mixture is shown in Fig. 2.5. The lean flammablility limits of methane is 5.2% of fuel in the mixture (equivalence ratio = 0.52) for standard temperature and pressure conditions. This lean limit extends down to 1.5% (equivalence ratio = 0.145) at a temperature of 1000° C. This suggests that a stable flame can be maintained even in 3.5 times more dilute mixture as compared to the mixture under standard conditions. The various methods to control the distribution of heat flux that can be selected are given in Fig. 2.6. 1400 1200 p 1000 | 800 I 600 | 400 r* 200 h 0 -200 - v^\ C-iHio i Flammable Region \ \CH4 y \C2H6 \ * CJHS\ \ 1 1 1 1 0 1 2 3 4 5 6 Fuel Concentration |vol%l Fig. 2.5 Lean Flammability Limts of Hydrocarbon Fuels [21 along the axis or the along t h c \ ^ c h ; | m b e r circumference of the chamber ^ * > N > * C-l l> 7T/2 JT 3/4 K 27T b-2 c-2 nil n 3/4 K in 0 nil n 3/4 K in a-4 l>-4 ON-OFF • 0 TT/2 n 3/4 n in Fig. 2.6 Methods to Control the Heat Flux Distribution 3 118