Abstract
Microwave (MW)-assisted torrefaction and pelleting could enhance biomass fuel properties and energy applications. Plastic wastes are considered as a replacement source binder in pellets to minimize their effect on the environment as pollutants. High-density polyethylene (HDPE), an extractable plastic from recycling waste, was investigated as a binder for torrefied wheat and barley straw pellets. Fuel pellet characteristics, such as durability, density, tensile strength, and water absorption, were used to evaluate the pellets produced from a single pelleting test. The results showed that the addition of HDPE as a binder significantly increased the pellet quality in terms of density (686.12–982.93 kg/m3), tensile strength (3.68 and 4.53 MPa) for wheat and barley straw, and reduced ash content of the pellet from 10.34 to 4.59% for barley straw pellet and 10.66 to 3.88% for wheat straw pellets. The higher heating value (HHV) increased with increasing biochar mix and HDPE binder blend. The highest HHV value observed for barley straw was 28.34 MJ/kg, while wheat straw was 29.78 MJ/kg. The study further indicated that MW torrefaction of biomass-biochar mix with HDPE binder reduced the moisture adsorption of wheat and barley straw pellets, which can significantly improve their storage capability in humid locations. The moisture uptake ratio for MW-torrefied barley straw pellets was 0.10–0.25 and wheat straw pellets 0.11–0.25 against a moisture uptake ratio of 1.0 for untreated biomass. MW torrefaction of wheat and barley straw with biochar and HDPE binder addition during pelleting is a promising technique to improve biomass fuel pellet properties.
Highlights
Herbaceous biomass is estimated to contribute between 10 and 14% of the world’s energy supply (Liu et al, 2014), and energy demand prediction is globally expected to grow more than 50% by 2025 due to increasing demand from rapidly developing countries (Ragauskas et al, 2006)
The torrefied barleybiochar mix has slightly smaller particle sizes compared to the torrefied wheat straw-biochar mix
Biochar mixed with biomass during MW torrefaction treatment improved the bulk density and particle density and reduced the moisture content of the biomass after torrefaction
Summary
Herbaceous biomass is estimated to contribute between 10 and 14% of the world’s energy supply (Liu et al, 2014), and energy demand prediction is globally expected to grow more than 50% by 2025 due to increasing demand from rapidly developing countries (Ragauskas et al, 2006). Commercial production of wood-based pellets is done globally in large scale compared to agricultural biomassbased pellets, which have limited production Canadian biomass magazine (2017) reported that global wood pellets for heating and industrial applications had shown continuous growth in the past decade compared to agricultural biomass-based pellets. Agricultural biomass-based pellets are mostly produced through torrefaction, and there would be triple production growth from 2020. The adoption of Torrefaction and Pelleting Wheat/Barley Straw agricultural biomass-based fuel pellets is influenced by government/private policy and financial incentives (Agu, 2018). Reducing fossil fuel prices in the future will increase productivity in an increasingly competitive biomass pellet market (Canadian biomass magazine, 2012)
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