Abstract
The firing and co-firing of biomass in pulverized coal fired power plants around the world is expected to increase in the coming years. Torrefaction may prove to be a suitable way of upgrading biomass for such an application. For transport and storage purposes, the torrefied biomass will tend to be in pellet form. Whilst standard methods for the assessment of the milling characteristics of coal exist, this is not the case for torrefied materials—whether in pellet form or not. The grindability of the fuel directly impacts the overall efficiency of the combustion process and as such it is an important parameter. In the present study, the grindability of different torrefied biomass pellets was tested in three different laboratory mill types; cutting mill (CM), hammer mill (HM) and impact mill (IM). The specific grinding energy (SGE) required for a defined mass throughput of pellets in each mill was measured and results were compared to other pellet characterization methods (e.g., durability, and hardness) as well as the modified Hardgrove Index. Seven different torrefied biomass pellets including willow, pine, beech, poplar, spruce, forest residue and straw were used as feedstock. On average, the particle-size distribution width (across all feedstock) was narrowest for the IM (0.41 mm), followed by the HM (0.51 mm) and widest for the CM (0.62 mm). Regarding the SGE, the IM consumed on average 8.23 Wh/kg while CM and HM consumed 5.15 and 5.24 Wh/kg, respectively. From the three mills compared in this study, the IM seems better fit for being used in a standardized method that could be developed in the future, e.g., as an ISO standard.
Highlights
Over the past few years there has been a significant effort worldwide to increase the utilization of renewable energy sources for electricity and heat production
In order to compare the relative change of the material caused by torrefaction, the change in volatile content was chosen as TFdgr, which, in this case, ranged between 6 and 9% dry matter (DM)
Regarding the HHV, which is increased during torrefaction, values found by other torrefaction studies were in some cases similar to what was obtained in this study and in other cases not
Summary
Over the past few years there has been a significant effort worldwide to increase the utilization of renewable energy sources for electricity and heat production. The firing of biomass and the co-firing of biomass with coal in power plants originally designed for coal play a significant role This approach to the generation of renewable energy has been demonstrated in more than 200 power plants over the recent years taking advantage of the infrastructure already in place within the electricity supply industry, and the associated low capital investment requirements [3]. Besides the expected reduction in both NOx and SOx levels, there are still some difficulties in using raw biomass for co-firing with coal [4]. The ash content as well as volatiles and oxygen content can be higher in biomass than in coal resulting in lower gross calorific value of the Energies 2016, 9, 794; doi:10.3390/en9100794 www.mdpi.com/journal/energies
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
