Changes in mechanical properties of wood pellets during artificial degradation in a laboratory environment

Shalini Graham,Ibrahim Ogunfayo,Matthew R Hall,Colin Snape,Will Quick,Susan Weatherstone,Carol Eastwick

doi:10.1016/j.fuproc.2016.03.020

Shalini Graham, Ibrahim Ogunfayo + Show 5 more

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In stockpiles exposed to high relative humidity (RH) and rainfall, woody biomass pellets lose structural integrity, often assumed to be due to the uptake of moisture from the environment. In this study three different types of biomass pellet were artificially degraded in a laboratory environment under controlled exposure to RH (10% and 90% RH) and temperature (range of 10 to 30°C). White, torrefied and steam-exploded wood pellets were investigated. Daily shear tests were conducted with durability and moisture content measured. The exposure of all three pellet types to high RH coupled with elevated temperatures caused a substantial decrease of shear modulus with values of 50% to 92% decrease compared to fresh pellets after 4days of exposure.The steam exploded pellets saw the lowest drop in mechanical durability (5%) but saw the largest decrease in shear modulus, whilst the white wood pellets disintegrated in situ after 4days. In contrast storage at 10% RH did not cause any observable degradation, with mechanical behaviour of steam exploded and torrefied pellets showing an improvement. This paper presents both testing methodology as well as clear indication of the behaviour of three woody biomass pellets on exposure to high relative humidity.

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As power generators continue their search for alternative energy sources to coal, biomass remains a promising carbon-based renewable fuel [1]
Effects of relative humidity (RH) and surrounding temperature on the structural changes in wood pellets was carried out using laboratory investigations where the impact of continuous exposure to high RH at ambient and elevated temperatures on the mechanical properties of three different wood pellets was undertaken
Wood pellets were enclosed in sealed containers and subjected to uncontrolled high relative humidity for several days; and in the second pellets were tested in an environmental chamber at controlled temperatures and relative humidity for varying time periods The first method was trialled to establish whether simple testing would provide sufficient indicative trends to allow a low cost and quick method to be utilised in the biomass transport and storage industry in assessing the resistance of pellets to moisture uptake and mechanical degradation in outdoor/not enclosed storage scenarios

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As power generators continue their search for alternative energy sources to coal, biomass remains a promising carbon-based renewable fuel [1]. Biomass fuel dedicated combustion and co-firing with coal are being utilised and optimised to improve fuel flexibility in powerplants and reduce greenhouse gas (GHG) emissions. Densified biomass fuels such as pellets are preferred as they provide better economic viability for transport, storage and handling [2]. The systematic investigation of short term storage humidity and temperature on mechanical properties on biomass wood pellets has not been studied. A study on the effects of relative humidity (RH) and surrounding temperature on the structural changes in wood pellets was carried out using laboratory investigations where the impact of continuous exposure to high RH at ambient and elevated temperatures on the mechanical properties of three different wood pellets (white wood, torrefied and steam exploded) was undertaken

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