Mathematical modeling of combustion in a grate-fired boiler burning straw and effect of operating conditions under air- and oxygen-enriched atmospheres

A three-dimensional mathematical model has been developed as a tool for furnace structure design and operation conditions optimization when the straw combustion is in oxygen-enriched or conventional air atmospheres. Mathematical methods have been used based on a combination of FLIC (A fluid Dynamic Incinerator Code) code for the in-bed incineration and commercial software FLUENT for the over-bed combustion. Oxygen-enriched atmospheres promote the destruction of most pollutants due to the high oxygen partial pressures and temperatures, which is reflected by very low residual amounts of organic combustion by-products in the bottom ash and flue gas of the straw-fired boiler unit. The predictions indicated that the maximum combustion temperature is around 1500K, CO emission is 201vppm and O2 concentration is about 6.9vol% at furnace exit, and it is shown that mathematical models can serve as a reliable tool for detailed analysis of straw combustion processes in the packed-bed furnace when compared with literature measurement data. In comparison to traditional straw combustion, the deviation of flue gas CO and NO is 27.5% and 62.1%, respectively. The numerical simulation results showed that combustion under the oxygen-enriched atmosphere excelled combustion under conventional air.