Effect of Operating Parameters on the AWL during torrefaction in a rotary kiln 

Doing my PhD at the European Bioenergy Research Institute (EBRI), I heard about the BRISK2 project from my colleague, who gave me the information about it. From the very beginning, the pilot-scale rotary kiln (500 kg/h) for torrefaction in CENER drew my attention, because my PhD consists of the design of an industrial rotary kiln for pyrolysis. 

I contacted Inés del Campo and Ibai Funcia from CENER’s Biomass Department and they helped me with the proposal concerning timing, experimental design and potential improvements. After the approval from my supervisor Dr. Katie Chong at Aston University and CENER´s Biomass Department team, I submitted the proposal in late September and had the approval mid-November to go to CENER at the end of November till the beginning of December 2018, it was an easy and smooth process. 

The Transnational Access (TA) 

My visit consisted of one week of experimental work and another one to analyse the results and see the tools they employ in CENER whose basics can be used within my research. 

The biomass selected for the experiments was beech wood. Due to the intermittent operational mode in CENER, the plant required two days to chip and dry enough feedstock for the experimental process. During those two days, most of the work was done by the operators, but I could see the controllable parameters in the plant and how they were measured and modified. Simultaneously, people from CENER and I discussed the experiments we were going to conduct. Besides the throughput of the process and the temperature range, there were two other restrictions in the process, the maximum amount of gas produced during torrefaction and the minimum rotation speed of the reactor. 

The primary objective of torrefaction is to achieve a high Anhydrous Weight Loss (AWL), which was easily correlated with the Net Calorific Value (NCV). The increase in the energy density is achieved through the loss of the volatiles and this loss is measured through the AWL. Prior to the experiments, the conditions had to be simulated to estimate the AWL. This simulation is done through a tool where the two main variables that are adjusted are the temperature and the throughput. 

Due to a leak of air at the fan of the oxidation chamber the first day of experimentsbcould not be conducted due to safety reasons and the TA had to be divided into two parts. It was decided that the second part would take place in early January 2019. Both CENER and the BRISK2 coordinator helped with this issue and no one objected to it.  

After fixing the leak and other minor problems, the experiments were conducted. The conditions and the results are shown in Table 1 and the torrefied product from the first experiment can be seen in the Figure 1. The parameters studied were temperature and throughput: 

  • Temperature: a higher temperature increased the AWL, because more material volatilised and goes to the gas phase. 
  • Throughput: a decrease in the feeding rate increases the AWL because the same heat is distributed within less mass.  


I want acknowledge everyone in CENER who made the process so easy and smooth, regarding experimental design, who help with problems that appeared and their flexibility and expert advice. I also want to express my gratitude to my supervisors Dr. Katie Chong and Prof. Tony Bridgwater for helping with the application and Philippa Try for the support and advice during the process.