An assessment of the torrefaction of North American pine and life cycle greenhouse gas emissions

P Mcnamee,P.W.R Adams,M.C Mcmanus,B Dooley,L.I Darvell,A Williams,J.M Jones

doi:10.1016/j.enconman.2016.01.006

P Mcnamee, P.W.R Adams + Show 5 more

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https://doi.org/10.1016/j.enconman.2016.01.006

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Journal: Energy Conversion	Publication Date: Feb 7, 2016
Citations: 72	License type: cc-by

Affiliation: University of Leeds, University of Bath

Abstract

Bioenergy is increasingly being used to meet EU objectives for renewable energy generation and reducing greenhouse gas (GHG) emissions. Problems with using biomass however include high moisture contents, lower calorific value and poor grindability when compared to fossil fuels. Torrefaction is a pre-treatment process that aims to address these issues. In this paper four torrefaction treatments of pine were performed and a mass–energy balance calculated. Using experimental data, a pellet production supply chain incorporating torrefaction was modelled and compared to an existing wood pellet system to determine life-cycle GHG emissions. Two utility fuels, wood chips and natural gas, were considered to provide process heat in addition to volatile gases released during torrefaction (torgas). Experimental results show that torrefaction reduces the moisture content and increases the calorific value of the fuels. Increasing torrefaction temperature and residence time results in lower mass and energy yields. GHG emissions reduce with increasing torrefaction severity. Emissions from drying & torrefaction and shipping are the highest GHG contributors to the supply chain. All 4 torrefaction conditions assessed outperformed traditional wood pellet supply chain emissions but more land is required which increases with temperature and residence time. Sensitivity analysis results show that emissions increase significantly where natural gas is used for utility fuel and no torgas is utilised.

Highlights

Several EU countries are endeavouring to increase the use of renewable energy and reduce greenhouse gas emissions by 2020 with further targets set for 2030 [1,2]
This decreasing yield is mainly attributed to loss of moisture and volatile material from the parent fuel through devolatilisation of the hemicellulose fractions which can become extensive as temperatures reach around 270 °C [14]
It can be seen that torrefaction improves the fuel properties of pine: the fixed carbon and higher heating values (HHV) increases while the moisture and volatiles contents decrease

Summary

Introduction

Several EU countries are endeavouring to increase the use of renewable energy and reduce greenhouse gas emissions by 2020 with further targets set for 2030 [1,2]. In addition to the targets set out in the European Renewable Energy Directive, the UK is bound by legal framework to reduce its GHG emissions by at least 80% relative to 1990 levels by 2050 in accordance with the Climate Change Act 2008 [3]. In fulfilling these emissions reduction targets, it is widely accepted that bioenergy will play a significant role as outlined in the UK bioenergy strategy [4] and as a result is being increasingly mobilised to help achieve these policy goals domestically as well as across several EU states.

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Conclusion