Ash deposition mechanism of shoe manufacturing waste combustion in a full-scale CFB boiler

Abstract

China is the largest shoe production country and the disposal of large amounts of shoe manufacturing waste (SMW) has become a rising problem. Incineration is regarded as a promising route for the utilization of SMW, since there exist considerable amounts of carbonaceous compounds in SMW. However, there are still some challenges for SMW incineration plant, such as corrosion, ash deposition, and pollution issues. This work investigated the ash deposition behavior in a full-scale SMW CFB boiler with 576 t/d treatment capability. Results suggest that submicron particles and uncooled inorganic vapors are the deposit precursors during initial deposition stage, and they are normally rich in alkali chlorides. Therefore, inner ash deposit layer contains a high concentration of alkali chlorides, even though alkali content in original fuel is negligible. The alkali chlorides in initial deposits can further aggravate tube surface corrosion and cause Fe enrichment in the initial layer. In contrast with inner layer deposits, the outer deposit layer shows relatively uniform characteristics and is mainly composed of Ca-rich minerals since raw ash in SMW is dominated by CaO. Overall, the ash deposition rate in SMW combustion is fairly high compared to other solid waste and biomass, and the deposition propensity increases when the flue gas temperature increases. The ash deposits are observed to have high compressive strength and hard to be removed through soot-blowing during operation. This work sheds the light on the ash deposition behavior of SMW during circulating fluidized bed combustion, which facilitates the design and optimization of industrial boilers.