Systematic homogenization of heterogenous biomass batches – Industrial-scale production of solid biofuels in two case studies

Biomass is a heterogeneous material with respect to its chemical composition due to different plant species and components as well as the potential content of impurities. Especially in the production of large fuel batches heterogeneous chemical compositions are a challenge with respect to the required compliance with fuel standards and emission thresholds during utilization. This can be avoided by fuel pre-treatment and systematic homogenization during fuel production. For this reason, the study analyses the effects of biomass leaching in combination with homogenization of biomass batches on industrial-scale. Within two case studies, low-quality herbaceous biomasses, i.e. foliage and wheat straw were pretreated and homogenized in quantities ranging from 8 to 51 tons. In the first case study, foliage was first leached, then mixed with sawdust and homogenized by separating batch parts with high ash content, followed by systematic recombination of the batches. In the second case study, homogenization of straw pellets (untreated and leached) was attempted by a layering approach during bagging. Both case studies (i) confirm earlier findings that critical fuel components can be substantially reduced by leaching (i.e. reduction of ash content MV by 45 w-%) but indicate that material agitation during leaching is necessary; (ii) underscore that systematic homogenization is necessary for fuel batches consisting of materials from different origins and reduce i.e.-the ash content RSD by 48%, and (iii) demonstrate that even low-quality fuels from herbaceous biomass assortments can comply with the requirements of fuel standards if dedicated fuel pretreatment is employed.