Functional mapping of torrefied product characteristics with index of torrefaction

Abstract

Torrefaction converts raw biomass into a product with higher energy density, higher fixed carbon, better grindability, HHV and longer shelf life. The extent of improvement in these and other properties can be governed by appropriately regulating the reactor operating conditions for a specified biomass. The industrial applications ranging from biofuels to chemicals have different priorities for the specific characteristics of the torrefied biomass. Some of the earlier studies on torrefaction have quantified the overall process performance by defining a parameter or index for the degree or severity of torrefaction. However, very few attempts have been made to relate the torrefaction severity to the properties of the torrefied biomass. In this paper, we have simplified the reference condition for earlier proposed definition of index of torrefaction (Basu et al. [1]) and showed that there exists a quantifiable functional relationship between the defined index and the characteristics of the torrefied biomass. The mapping co-relations depend on the type of biomass feedstock, and the index informs the type of biomass appropriate for a specific application. While this paper focuses only on classical torrefaction characteristics such as energy density, proximate and elemental analyses, and batch and continuous grindability, this analysis can be generalized to quantify other non-classical characteristics such as densification, cooking fuel characteristics, and biochar-soil interactions. © 2020 Elsevier B.V.