Processing of low-density waste in fluidized bed made out of lightweight expanded clay aggregate

Abstract

The main aim of the study is to obtain a new, innovative method for the organization of combustion processes in fluidized bed reactors. A key aspect of the change in the organization of the fluidized bed combustion process is the creation of a fluidized bed made out of lightweight expanded clay aggregate (LECA). The new fluidized bed has a density of 0.5 g/cm3, therefore, allowing for thermal processing of low-density solid and liquid industrial wastes, as well as waste biomass. Polyolefins (polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, and polypropylene homopolymer) were selected as examples of low-density solid wastes. The use of an innovative fluidized bed for liquid waste degradation was studied on the example of glycerol combustion. Waste wood chips were chosen to represent low-density biomass. Thermal degradation of selected materials in the fluidized bed made out of LECA was carried out at a temperature range of 500–900 °C with an interval of 100 °C. Video analysis of the fluidized bed surface proved the sinking of waste materials into the bed and significant elimination of diffusion flames in the freeboard. Qualitative and quantitative flue gas analysis was carried out using the FTIR spectrometer. More than 95% conversion of the carbon contained in the polyolefins to CO2 was achieved already at 700 °C. At 500 °C, more than 30% of the polymeric carbon left the reactor as aromatic compounds. To avoid the emission of harmful aldehydes during the thermal processing of glycerol, the bed should be heated to at least 800 °C. Waste wood chips as an alternative fuel can be thermally incinerated in the fluidized bed made out of LECA. The disappearance of volatile organic compounds and CO emissions occurred at 700 °C and 800 °C.