Combustion characteristics of the various solid fuel have been investigated in two fluidized bed combustors(FBC) of laboratory and pilot scales. Fraction and reactivity of the volatile in a solid fuel are important parameters to determine the combustion characteristics in FBC. In this point of view, refuse derived fuel(RDF) and high density poly ethylene(HDPE), with high volatile content and local anthracite coal, with high char content were chosen for investigation of the co-combustion characteristics of the mixed fuel. $O_2$, $CO_2$. CO and hydrocarbon concentrations and temperature distributions were measured in the batch and continuous type of FBC for HDPE, coal and mixture of the two.
Fraction of the volatile burnt in the freeboard was calculated quantitatively by means of the heat balance calculation. The results showed that the fraction of the combustible burnt in the freeboard was small for the coal, while that of HDPE and RDF was noticeably higher and increase with the decrease of the oxygen concentration in the bed. It was reasoned that the most of the volatile was burnt in bed due to the sufficient availability of the combustion air, stay in the bed of fuel and high bed temperature. The results showed that the co-combustion was an effective method for improving the stability of the combustion process and the efficiency, and for achieving on effective distribution of the heat release in the bed and the freeboard.
