Combustion of Apple Juice Wastes in a Cyclone Combustor for Thermal Energy Generation

Abstract

The thermal conversion of biomass fuels using different combustion technologies has increased worldwidely in the latest years due to the energetic exploitation potential of wastes as well as to the strong increase of environmental consciousness in the industrial sector. In this work the bagasse obtained from the apple juice industry (AB) was characterized and the gaseous emissions resulting from its combustion in a pilot scale cyclone combustor were measured and compared to limits imposed by Brazilian and international current legislations. Wood and wood-based materials are extensively used as fuel for thermal energy generation particularly in the Brazilian food industry, which demands large amounts of steam. Considering that, sawdust (SD) was also characterized, burned in the same conditions and the gaseous emissions analyzed for comparison purposes. Sampling for the volatile organic compounds benzene, toluene, ethyl-benzene and xylene (BTEX, expressed as total organic carbon, TOC) and polycyclic aromatic hydrocarbons (PAH) were performed and the samples analyzed by gaseous chromatography-mass spectrometry (GC-MS). Chemical properties showed that the volatile matter value of AB is high (85.36 wt%, daf) what indicates that the solid burn rapidly. The absence of sulfur in its composition represents an advantage in relation to fossil fuels because its combustion does not release sulfur derived compounds. The lower heating value is 21.09 MJ.kg−1 (daf), 26.9% higher than the heating value of SD (16.62 MJ.kg−1). The effect of the N fuel content found in AB composition was clearly noticed through the high NOx concentration in the flue gas resulted from its burning. Comparing the properties and the burning profiles of SD and AB, it can be stated that this industrial waste obtained from the apple juice industry is suitable for direct combustion, constituting a renewable energy source for this industrial sector, however, measures as air staging and staged addition of fuel, or flue gas cleaning technologies would be required for reducing the NOx emission. Concerning the presence of toxic compounds as PAH, they were not detected once the operation conditions applied resulted in controlled gaseous emissions and temperature profile. Also, TOC concentrations remained below the regulations limits considered.