Torrefaction and Densification of Wood Sawdust for Bioenergy Applications

Peyman Alizadeh,Edmund Mupondwa,Bagher Emadi,Duncan Cree,Phani K Adapa,Lope G Tabil

doi:10.3390/fuels3010010

Abstract

In this study, wood sawdust as waste residue from wood processing mills was pretreated using torrefaction to improve fuel properties and densified to facilitate transportation. Sawdust was torrefied in a fixed bed reactor using inside temperatures (IT) of 230, 260 and 290 °C for 15, 30 and 45 min, residence time. Due to the low calorific value of the treatments, the outside temperature (OT) of the fixed bed reactor was used instead for a fixed duration of 45 min, which resulted in an increase in energy value by 40% for the most severe conditions. The mechanical strength of the pellets was enhanced by adding 20% binder (steam-treated spruce sawdust) to biochar, which improved the pellet tensile strength by 50%. Liquid by-products from the torrefaction process contained furfural and acetic acid, which can be separated for commercial uses. Thermochemical analysis showed better fuel properties of OT torrefied samples such as high fixed carbon (52%), low volatiles (41%) and lower oxygen contents (27%) compared to IT torrefied samples (18, 77 and 43%, respectively). Low moisture uptake of torrefied pellets compared to raw pellets, along with other attributes such as renewability, make them competent substitutes to fossil-based energy carriers such as coal.

Highlights

Due to a rising worldwide demand to gradually phase out fossil fuels and become carbon neutral by 2050 [1], renewable energy sources such as biomass are becoming increasingly important [2]
The particle density of torrefied samples decreased slightly with no visible pattern related to the severity of treatment; according to Wang et al [52], this quality can be improved after torrefaction of sawdust
The higher heating value of torrefied samples using outside temperature (OT) was considerably larger than inside temperatures (IT) samples in comparable conditions, for example, the differences were 15, 16 and 30% corresponding to torrefaction at 230, 260 and 290 ◦ C for 45 min

Summary

Introduction

Due to a rising worldwide demand to gradually phase out fossil fuels and become carbon neutral by 2050 [1], renewable energy sources such as biomass are becoming increasingly important [2]. Provincial governments in Canada have introduced laws requiring coal-fired power plants to shut down to curb greenhouse gas emissions [3]. The Ontario government, for instance, was the first in North America to phase out coal-fired electricity generation plants [4]. Atikokan Generating Station, with a capacity of 205 MW, is currently the top bioenergy plant in North America, and utilizes only biomass as feedstock [3]. Consistent, highly accessible (especially in Canada) and desirable fuel source [5] that has growth potential and can be utilized at a moderate thermoecologic cost [6,7]. Biomass usage for energy generation has expanded in many countries with the target of reducing global warming, improving employment and ensuring a reliable energy supply [9]

Methods

Results

Conclusion