Chemical Characteristics of Ash Formed from the Combustion of Shoe Manufacturing Waste in a 2.5 MWth Circulating Fluidized Bed Combustor
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The ash formation behaviour and associated compositional characteristics of the combustion of shoe manufacturing waste (SMW) in a 2.5 MWth pilot-scale circulating fluidized bed combustor (CFBC) were investigated to better understand the combustion behaviour and to find effective management strategy for the disposal of the ash streams produced. The compositional characterisations for the ashes produced from the pilot demonstrations showed the presence of a variety of trace heavy metals both in the fly ash and bottom ash. A pronounced uneven partitioning behaviour was observed on the distribution of these heavy metals between the fly ash and bottom ash, and it was found that all the heavy metals except chromium were preferentially enriched in the fly ash, with the contents of lead and cadmium in the fly ash being over 11 and 6 times higher than in the bottom ash. Leaching tests demonstrated that the concentrations of most of the aforementioned metals present in the leachates from the fly ash and bottom ash could meet the permissible limits for landfill disposal but with lead as an exception with its concentration in the fly ash leachates being over 2 times higher than the limit. The total PCDD and PCDF contents both in the fly ash and bottom ash were also much below the legal limit. To further understand the ash behaviour, the slagging and fouling tendency during SMW combustion in the CFBC was examined by use of the characterisation of the ash mineralogy and the results indicated that the SMW ash likely had low tendencies for slagging and fouling. The best two valorization routes for the SMW bottom ash and fly ash were recommended, one being to use them to produce colloidal silica medium to obtain safe inert filler and the other being to use them as the raw materials in the cement industry.
KeywordsShoe manufacturing waste Ash Heavy metals PCDD and PCDF Ash fusion temperature
The authors gratefully acknowledge the support from the National Key R&D Program of China (2018YFB0605102), National Natural Science Foundation of China (No. 51676040), Jiangsu Natural Science Foundation of China (BK20181281), the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (17KJB470007), the Scientific Foundation of Nanjing Institute of Technology (YKJ201609) and the Key Research and Development Program of Zhenjiang (SH2018014). The authors would also like to acknowledge the provision of a scholarship to Mr. Changqi Liu by the China Scholarship Council (CSC) which enables him to be able to complete part of the reported work at the University of Nottingham.
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