Agglomeration Potential of Tropical Residual Biomass - Investigation on the Interactions between Ash Elements and Quartz Sand

In agro-industrial countries, residual biomass may have a significant technical potential for use in productive chains and in the energy sector. The use of residual biomass in thermochemical conversion processes entails some challenges, mainly derived from the variability of physical properties and the presence of specific chemical elements. Fluidized bed combustors are a convenient alternative for the conversion of biomass due to their flexibility and high conversion efficiency. However, agglomeration can occur due to the interaction between the biomass ashes and the bed material. The literature identifies temperature and concentration of some chemical elements (Si, Ca, Cl, and K) as the parameters with highest impact on the agglomeration potential. Likewise, melt-induced, and coating-induced has been identified as the most important agglomeration mechanisms in biomass combustion.

This work presents an experimental study of the interaction between biomass ashes and quartz sand at different temperatures under fixed bed conditions, for three selected tropical biomasses: oil palm kernel, oil palm rachis and coffee husk. A first assessment of the agglomeration potential was done through agglomeration indexes available in literature and based on the ash composition found for each biomass. Thereafter, quartz sand and biomass ash mixtures in a mass relation 90:10 were heated up (at a rate of 10 K/min). The final temperature and time in the oven were varied: 700, 800 and 900 °C and 2, 4, 6 and 8 hours, respectively. The product obtained from each experiment was analyzed using stereomicroscopy, X-ray fluorescence (XRF), scanning electron microscopy and energy dispersive X-ray analysis (SEM-EDX). Agglomeration indexes and experimental results on SEM-EDX and XRF allow a better understanding of the agglomeration mechanisms.