Physicochemical upgrading of agroresidues as feedstocks for energy production via thermochemical conversion methods

Ash-related problems including deposition, slagging, fouling, sintering, and agglomeration, caused during the operation of biomass gasifiers and combustors using various agroresidues, e.g., wheat straw, olive residue, corn cobs, as feedstocks constitute the limiting factor for a broad use of this kind of biomass materials for energy production via thermochemical conversion methods. Ash content minimization and simultaneous removal of a number of so-called troublesome elements, e.g., potassium, sodium, chlorine, sulfur, from the ash fraction of these materials were performed by two different pretreatment techniques, fractionation and leaching. Fractionation appeared to remove in all cases a large amount of the materialʹs inherent ash fraction but resulted in a deterioration of the quality of the remaining ash. On the other hand, leaching resulted in both removal of a large portion of the materialʹs inorganic fraction and an improvement of the quality of the remaining ash by removing to a large extent the so-called troublesome elements causing problems during the thermochemical conversion of biomass. Furthermore, ash thermal behavior of various untreated and pretreated samples using sintering tests performed in a laboratory muffle furnace in combination with SEM-EDX elemental analyses of the thermally treated ash samples was studied. In most cases, the results from the thermal treatment technique appeared to be in good agreement with the results obtained from the ash elemental analyses of the tested samples.