Research On Construction Of A Universal Prediction Model Of The Char Combustion Rate

Char combustion rate prediction models are important to the design of industrial boilers. Classic models of coal chars proposed by other researchers are accurate and universal, but there is no universal prediction model of the char combustion rate that is applicable for both coals and biomass. Considering the differences on physical and chemical properties and the actual combustion condition between biomass chars and coal chars, this thesis tried building a universal prediction model of the char combustion rate based on a classic model of coal chars, by changing the carbon oxidation reaction order n and the intrinsic activation energy E_b.First, we proposed the method of determining n by a micro-fluidized bed(MFB) and verified the accuracy of it, and the result was directly used to modify the classic model of coal chars mentioned above. The result shows that the accuracy of the original model is improved, which means that this determination method has a broader application potential.Next, we checked the accuracy of the modified model when predicting the combustion rates of different coal chars at different combustion states. E_b was set as 180kJ/mol and n was determined by MFB or set according to other researchers' work. The result shows that the modified model is still applicable for predicting the combustion rates of coal chars.Finally, we determined the intrinsic activation energy of the combustion of biomass chars using the temperature-programmed thermogravimetric analysis(TGA), and the selection of E_b was investigated. Besides, the reasons why the E_b of biomass chars is lower than that of coal chars were also investigated. The result shows that the E_b of biomass chars is affected by the type of biomass(110-160kJ/mol). Thus, a data base is needed for the selection of the E_b of biomass chars. The phenomenon that the E_b of biomass chars is lower than that of coal chars may be caused by the catalysis of K, more active groups, and the higher proportion of the disordered carbon.