Multi-mode combustion facility for thermal treatment studies of wastes and biomass

Abstract

This article describes newly built Multi-Mode Combustion Facility (MCF) used for investigating thermal destruction of industrial wastes and combustion of biomass. A flexible, refractory-lined combustion chamber consists of individual sections of various heights and diameter of 0.5 m. The MCF can be used either as a fluidized bed combustor (FBC) to study the combustion of solid residues or as a single-burner furnace (SBF) to study cofiring of biomass and natural gas. The facility is designed such that the outer wall temperature should not exceed 327 K with the use of water-cooling system and refractory materials. The inner temperature of each section is independent of the rest of the sections and controlled individually. This arrangement allows for the combustion process to be carried out in a multizone manner called low–high–low (LHL) temperature approach. The LHL approach means that the waste/biomass is initially fed into a low temperature zone (<1060 K) and then subjected to the high temperature treatment (∼1500 K) that is followed by another low temperature zone (<1160 K). The LHL setup allows for heavy metals encapsulation and immobilization within the fly ash particles. The facility has 25 openings for sampling of solids and gases at different stages of the combustion process, as well as in situ observation. Experiments reported in this article were performed in the bubbling FBC mode with the purpose of testing the leachability of heavy metals (Cd, Cr, and Pb) from fly ash generated during two different combustion approaches: (1) multi-zone LHL treatment, and (2) no-LHL. Baseline fluidization properties of different bed materials were tested. Axial profiles of temperature and gas concentration (CO2, NO, and NOx) were compared. The results show that the leachability of the heavy metals (Cd, Cr, and Pb) contained in the LHL-generated ash particles was negligible (0.14, 0.061, and 1.55 ppm, respectively), while the leachability data from the no-LHL technique were 30.7, 14.3, and 0.647 ppm, respectively. It was concluded that the MCF facility is easy to operate, flexible, and useful for studies of various waste-to-energy options. Our results also show an improvement in heavy metals leachability when using the LHL combustion technique.