Combustion kinetics of sewage sludge and combustible wastes |
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Authors: | Ho-Soo Lee Sung-Keun Bae |
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Institution: | (1) School of Chemistry, University of Science and Technology of China, Hefei, Anhui, 230026, China; |
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Abstract: | This study estimated the kinetics of the mono- and co-combustion of sewage sludge pellets and combustible wastes such as municipal
solid waste (MSW) and refuse-derived fuel (RDF). Sewage sludge was manufactured into pellets with a diameter of 8, 12, or
16 mm and a length of 30 mm. The RDF was composed of paper and plastics and was formed into pellets with a diameter of 8 mm
and a length of 30 mm. MSW samples were synthesized using combustible wastes such as garbage, paper, plastics, and wood. The
MSW was adjusted to have a moisture content of around 40% after shredding to under 10 mm. A laboratory-scale batch type stoker
incinerator was used for the combustion and the gas composition of the flue gas was measured. The activation energy was calculated
using the experimental results, and then the relation of the decomposition rate and reaction time was evaluated using the
shrinking core model. The decomposition rate of the sludge pellets decreased as their diameter and moisture content increased,
and the co-combustion of sludge pellets and combustible waste was affected by the amount of combustible waste. The individual
combustion rates of the cylindrical sludge pellets or RDF were mainly controlled by the chemical reaction, but in the case
of shredded MSW it was mostly influenced by gas diffusion. The rate for the co-combustion of sludge pellets and combustible
wastes was mainly determined by the combustion rate of the combustible waste. The activation energy of the 8-mm-diameter sludge
pellets was between 6.70 and 10.0 kcal/mol, according to the moisture content, but it was lower for MSW and RDF. In the case
of MSW co-combustion, the reaction rate accelerated as the moisture content of the sludge pellets decreased, but it was markedly
increased by the addition of RDF, regardless of the sludge moisture content. |
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