The aim of my BRISK2 visit to CENER in Pamplona, Spain was to test the torrefaction of spent coffee grounds in a pilot plant, in order to compare the results that I previously obtained in a thermogravimetric analyzer. The proposed visit was approved for the duration of one week although the whole operational work has been carried out during 2 weeks.. Before my arrival, CENER organized the supply of 21 tons of spent coffee grounds from a Spanish supplier and, then, biomass was dried at a moisture content of about 10%. During my visit, firstly we decided the following operating conditions for the torrefaction runs: 

  1. Thermal oil temperature: 240°C; Residence Time: 93 min ; Heating rate 6 °C/min
  2. Thermal oil temperature: 270°C; Residence Time: 72 min ; Heating rate 6 °C/min
  3. Thermal oil temperature: 265°C; Residence Time: 93 min ; Heating rate 6 °C/min
  4. Thermal oil temperature: 290°C; Residence Time: 93 min ; Heating rate 6 °C/min

Tests were carried out in a torrefaction pilot plant, consisting of a horizontal reactor with rotating shaft and indirect heating by thermal oil and with a production capacity of about 500 kg/h. During each test, about 5 kg of torrefied biomass were sampled every 15 minutes. Furthermore samples of the gases and liquids formed as a result of the biomass torrefaction were collected and examined using various analytical techniques. The gaseous stream was sampled at the exit of the reactor and analysed online using a micro gas chromatograph equipped with a thermal conductivity detector (GC-TCD). The condensable products formed during the torrefaction were measured offline using gas chromatograph-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), and a gas chromatography flame ionisation detector (GC-FID). Torrefied material was also characterized by analyzing the higher heating value and the elemental composition. Samples of 5 kg of raw material, 20 kg of torrefied biomass for each conditions, and torrefaction condensate produced at different operating conditions were prepared for shipping in Italy, in order to carry out the pelletizing and BMP tests, as foreseen in the submitted proposal. 

The results of the experiments helped to better understand how the temperatures affect the solid, liquid and gaseous yields of the spent coffee grounds during the torrefaction process, conducted in a semi-industrial plant (Fig. 1). 

The experimental campaign was supervised by Ibai Funcia Muguerza. Before starting work he showed me the laboratory facilities and during testing we worked with other technicians as a team to coordinate activities and help each other. l would like to thank the BRISK team for making my visit so fruitful and pleasant and also because I was able to finish all of the expected experiments in a short period of time.