Analysis of the rate of combustion of biomass char in a fluidised bed of CLOU particles

Combustion of Biomass in Fluidized Beds: A Review of Key Phenomena and Future Perspectives

“…The rate is then controlled by the transfer of oxygen from the bulk. These three situations are often referred to as Regime I (kinetic control), Regime II (intraparticle diffusion control), and Regime III (interparticle diffusion control); although, for combustion, Regime II can also indicate a situation where the reaction takes place in a thin external shell within the char particle, so that the observed rate is influenced by both internal and external transport.…”

“…Reaction is more exothermic than ; therefore, if the CO/CO 2 ratio is low, meaning CO 2 is the primary product of char combustion, then the released heat is significant, causing an increase in the char temperature and consequently faster combustion. Research on the CO/CO 2 ratio has been primarily carried out for coal char, with only a few studies reporting on the CO/CO 2 ratio in biomass combustion . This is quite a significant gap in research because biomass chars are frequently described as more reactive, which should directly connect to the distribution in the combustion products.…”

“…The char was prepared in a fluidized bed, but the combustion experiment was carried out in a thermogravimetric analyzer. Kwong et al demonstrated that the birch char combusted with a CO/CO 2 ratio between 0 to 4.0, changing with the experimental temperature between 700 and 900 °C.…”

“…For a variety of chars (mainly coal chars and graphites), Smith performed a meta-analysis of results gathered from other researchers, coming up with the order of reaction and a set of intrinsic kinetic parameters, giving the values of n , A i , and E i to be 1, 470 T p , and 179.4 kJ mol –1 , respectively. Because of the lack of similar studies gathering information on biomass chars, Kwong et al successfully applied Smith’s intrinsic kinetics when analyzing the combustion of birch char in a fluidized bed, in the presence of active bed materials that release O 2(g) in chemical looping oxygen uncoupling experiments . Applying the kinetics of coal char in modeling the combustion of biomass is debatable, as biomass chars are more reactive than high-rank coal chars; the difference in the combustion rates reaches up to 5 orders of magnitude .…”

“…Here, again, the two reactions are interconnected. Kwong et al demonstrated that the presence of a CLOU-type OC enhances the rate of combustion of birch char, significantly exceeding the rates observed in an analogous (the same p O 2 ) experiment but with inert bed material . The authors provided an analytical model for predicting the time of complete combustion in CLOU and, thus, the means of estimating the expected enhancement in the combustion rate.…”