PELLETS


INDUSTRY NEWS


Mass and energy balance of torrefied biomass in question


By Cristina Calderón, General Manager, European Biomass Association. E-mail: calderon@aebiom.org


A moisture content feedstock


1,089 GJ 101,4 kg 36,2 wt%


Production Process


torrefied wood pellets 1,000 GJ


50,2 kg 4,5 wt%


Elec. (GJ/GJ prod) 0,034


Heat (GJ/GJ prod) 0,015


90,6%


188 kWh/ton 9,4 kWh/GJ


total electricity consumption


B moisture content


feedstock


0.952 GJ 87,1 kg 36,2 wt%


Production Process


white wood pellets 1,000 GJ


58,0 kg 6,0 wt%


Elec. (GJ/GJ prod) 0,032


I


n most scenarios, bioenergy is expected to continue playing a key role in the global energy transition. However, questions persist regarding what the future of the biomass fuel mix will look like. The types of potential biomass that can be used for bioenergy go beyond wood, but the alternatives are usually resilient and fibrous, bulky, non-homogeneous or high in moisture content. In order to overcome these issues, torrefaction can be used as a biomass pre-treatment process, having already demonstrated a considerable number of advantages, but how efficient is the process in terms of the mass yield and energy efficiency in comparison to other biomass upgrading technologies, such as regular ‘white’ wood pellets? In order to bring clarity to the debate, the International Biomass Torrefaction Council (IBTC)* commissioned a study to compare the mass and


6 Summer 2018 6


Heat (GJ/GJ prod) 0,145


energy balances of torrefied and traditional pellets. ECN, CENER and UMEA University conducted an anonymous online survey in 2017 among all producers of torrefied biomass, using different technologies and feedstocks. Aggregated values were computed from the torrefaction data received and compared to literature values for large-scale, white wood pellet production facilities. The mass and energy balances were calculated in a ‘black box’ approach, as shown in the figure above, and the results were normalised on energy output basis.


Results clearly showed that the average energy efficiency for both torrefied and white wood pellet plants is comparable (with a difference of 0.5%) when a conventional drying technology is assumed. The latter outcome suggested that using the heat resulting from the combustion of the torrefaction off-gases system for feedstock pre-drying at a


higher temperature, improves the conditions for torrefaction. Therefore, a lower supplementary heat input is required during torrefaction, in comparison with white wood pellets. However, the lack of a lower additional heat is compensated by a lower mass input for the feedstock in the case of white wood pellet production.


As the results estimated, the average electricity consumption of torrefaction plants is of about 0.6kWh/GJ higher than in white wood pellet plants (excluding debarking). This difference is in line with the current experience of the pellet press suppliers. Expressed on energy output basis, the gap at an energy consumption level is smaller as a result of the higher energy content of torrefied wood pellets.


With these results, the study scientifically proves that white pellets and torrefied pellets are relatively close in efficiency,


Comparison of (A)


torrefaction versus (B) white wood pellet production.


from both a mass and energy balance perspective. As no major disadvantage was estimated on either side, the expected advantage of torrefied products in transport and consumption can be translated as a significant gain for those products. More information from www.aebiom.org


*The IBTC is a Brussels-based international platform founded in 2012, which brings together 23 companies from all over the world. It was founded by the European Biomass Association and major torrefied biomass stakeholders, who decided to join forces and create a discussion platform of companies with similar interests. IBTC was also initiated in collaboration with the Dutch Torrefaction Association.


91,1%


152 kWh/ton 8,8 kWh/GJ


total electricity consumption


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