Search for Alternative Raw Materials for Pellet Production – a Preliminary Study

A preliminary study for a selection of local alternative raw materials and their possible applicability in pellet production was done. 13 alternative biomass sources available in Riga, Latvia were tested: pine mix pellets (PMP); pellets of a mix of wood shavings, synthetic and textile waste (SSK); hogweed (Heracleum sosnowsky, HW); the full plant of Solidago canadensis L. (SC); the full plant of Solidago canadensis L. outgrown (SCO); mowed grass from the municipality (MGM); mowed grass from the garden (MGG); chamomile full plant without stems (Matricaria chamomilla, CF); hemp without roots (Cannabis sativa L., HWR); hemp stems (Cannabis sativa L., HS); hemp leaves with seeds (Cannabis sativa L., HLS); spent grain (SG); damaged spent grain (DSG). The determined quality parameters were the moisture content, the ash content, the calorific value and ash melting temperature. A comparison was made with the quality parameters defined in ENplus certification for B-class wood pellets in requirements for producers. Additional determination of chemical composition using XRD (X-ray diffraction) and SEM-EDX (scanning electron microscopy – energy dispersive X-ray spectroscopy) for the ash of two selected materials – SC and HLS – was performed to determine possible issues. The main issues highlighted by the results is the high ash content of alternative materials, up to 11.27 wt% while it is below 2.00 wt% for B-class wood pellets, and the low ash deformation temperature, below 1100 °C for 5 of the studied materials. Considering this, a calculation was made to determine the optimal proportion of alternative material to be used in a raw material mix for pellets to achieve a quality corresponding to B-class wood pellets. The aim of the study is to evaluate a set of locally available biomass materials, determining the values of their characteristic parameters, thus identifying alternative resources to wood for the production of pellets. This kind of promoting the diversification of energy resources, increasing energy independence and strengthening energy security.