| A computer program was developed to model the combustion behavior in stoker fired boilers. The model is applicable to coal, bark, and refuse furnaces. A Bragg stirred reactor volume is followed by a series of slices representing a plug flow volume. Combustion was modeled as a second order reaction proportional to fuel and oxygen concentrations. Arrhenius rate constant was included to study the effects of frequency factor and activation energy. A by-pass factor was theorized; this factor accounted for fuel residence time distribution and mixing behavior. The radiation heat transfer was modeled as a function of concentrations of H(,2)O, CO(,2), and particulates (flame blackening).; Variables studied were: frequency factor, activation energy, stirred reactor height, bypass, air/fuel ratio, and blackening. It was not possible to distinguish between the effects of frequency factor and activation energy; high frequency factor or low activation energy produced rapid burning, while opposite values retarded and even stopped burning. Increasing air/fuel ratio increased combustion efficiency, but reduced furnace temperatures and boiler efficiency. As the stirred reactor volume was increased the combustion efficiency, peak furnace temperature, and boiler efficiency decreased. Also, the peak temperature shifted to higher in the furnace. Increasing bypass produced results similar to those due to larger stirred reactor volumes, except that peak temperature was not necessarily reduced.; It was postulated that a relationship between stirred reactor volume and bypass existed. It was assumed that as the volume increased the bypass would decrease. A function of these variables was developed and tested. As the volume was increased and the bypass reduced, the peak temperature dropped and shifted higher in the furnace. The effects on combustion and boiler efficiency were inconclusive, but indicate the two variables cancel each other (producing constant values).; Blackening reduces combustion efficiency and temperature but increases boiler efficiency. No peak temperature shift occurred. |
