A Comprehensive Review on Biomass Torrefaction

Abstract

Biomass is a versatile energy resource that could be used as a sustainable energy resource in solid, liquid and gaseous form of energy sources. Torrefaction is an emerging thermal biomass pretreatment method that has an ability to reduce the major limitations of biomass such as heterogeneity, lower bulk density, lower energy density, hygroscopic behavior, and fibrous nature. Torrefaction, aiming to produce high quality solid biomass products, is carried out at 200-300 °C in an inert environment at an atmospheric pressure. The removal of volatiles through different decomposition reactions is the basic principle behind the torrefaction process. Torrefaction upgrades biomass quality and alters the combustion behavior, which can be efficiently used in the co-firing power plant. This paper presents a comprehensive review on torrefaction of biomass and their characteristics. Despite of the number of advantages, torrefaction is motivated mainly for thermochemical conversion process because of its ability to increase hydrophobicity, grindability and energy density of biomass. In addition to this, torrefied biomass could be used to replace coal in the metallurgical process, and promoted as an alternative of charcoal.

An Index for Quantifying the Degree of Torrefaction

“…Torrefied biomass is thus considered a potential substituent for coal in pulverized coal-power plants. This process is performed within a narrow temperature range of 200 to 300 °C at a low heating rate and in a non-oxidizing environment (Tumuluru et al 2010;Nhuchhen et al 2014). Conventional pyrolysis that is carried out at a higher temperature range primarily produces liquid fuels, whereas the torrefaction process mainly produces a solid product (Tumuluru et al 2010;Nhuchhen et al 2014).…”

“…Much work has been done to understand the process of torrefaction and to study the effects of different operating parameters (temperature, residence time, size, presence of oxygen) on the yield and qualities of torrefied products from various biomasses (Nhuchhen et al 2014;Chen et al 2015). However, little attention has been directed towards defining a numerical representation of the quality of the torrefied product.…”

Comparison of solid biofuels produced from olive pomace with two different conversion methods: torrefaction and hydrothermal carbonization

“…Among all the sustainable energies, biomass energy has the broad availability worldwide and this makes it an interesting option [2]. On the other hand, as an energy resource, biomass has its disadvantages such as structural heterogeneity, nonuniform physical properties, low energy density, hygroscopic nature, and low bulk density [3]. These characteristics prevent the use of biomass instead of fossil fuels.…”

Assessment of the Influence of Torrefied Biomass Physical Characteristics, Design and Operating Variables on Gasification Efficiency

“…The reason for the high calorific value obtained may be attributed to alteration in chemical properties caused by torrefaction, especially with regards to the reduced oxygen-carbon and hydrogen-carbon ratios. Low oxygen-carbon and hydrogen-carbon ratios of biomass will increase calorific value and will lead to improved gasification characteristics of the biomass in terms of efficiency [21,22].…”