European Technology and Innovation Platform
SearchPrintSitemapImprint

Pilot plant for the torrefaction of wood residues

by Jean-Bernard Michel, University of Applied Sciences and Arts Western Switzerland

Torrefaction is a thermal pre-treatment process that reduces the oxygen content, increases the calorific value and reduces the variability in the heating value of the incoming biomass, making possible its use as a solid fuel of high added value. Woody biomass, once torrefied, offers the following main advantages:

  • High efficiency fuel and with a constant calorific value
  • Hydrophobic fuel, enabling external storage
  • Favourable transport costs
  • Favourable grinding costs
  • Seasonal storage and trading

The high energy density of the torrefied pellets (33% more than normal pellets), greatly improves the economics of the fuel logistics and of combustion or gasification. The cost of the final energy is favourable compared to fossil fuels and normal wood pellets, owing to the utilisation of low cost woody biomass locally available and poorly exploited so far (forest residues, green wastes, roadside greenery, agriculture or horticulture…).

The torrefaction plant in Orbe has been constructed in the framework of the TORPLANT project, co-financed by the State of Vaud in the framework of the program “100 million for renewable energies and energy efficiency”. The system is based on a concept developed and tested at laboratory scale by the School of Engineering and Management Vaud (HEIG-VD) which is part of the University of Applied Sciences Western Switzerland (HES-SO). The realization of this pilot plant of nominal capacity of 100 kg/h is the first step towards the validation of the operational parameters and so, towards its industrialisation.

HEIG-VD, has been leading the project and is in charge of pilot plant testing with the support of the other partners: 

 

  • Granit Technologies and Engineering (GRT) SA, (Orbe, Switzerland) in charge of the development, engineering, construction, and implementation of the pilot-plant.
  • Ökozentrum (Langenbruck, Switzerland), who supplied the heating system using a FLOX burner coupled to a gas-turbine/compressor to recover the energy from the torrefaction gases.

The innovation lies in the design of the plant, compact and automated with remote supervision, and in the use of poor quality hog fuel, locally sourced, to produce a high value fuel that respect ISO-17725-8 new specifications for thermally treated biomass. The torrefaction gas represents about 20% of the mass and 8% of the energy of the raw biomass and is recovered in a Flox® burner, in order to provide heat to the process

Results: The detailed physico-chemical analysis of the raw and torrefied material was made following seven test runs of a total duration of 211 hours and production of about 8 tons of torrefied material (shredded branches and wood chips).

Combustion tests were carried out on two commercial 30 kW wood-chip boilers. Particulate emissions were reduced by approximately 10% compared to the raw biomass chips. Unburnt hydrocarbons and carbon monoxide were also reduced (resp. 40-94% and 39-85%). The emissions levels and thermal efficiency were found identical to that obtained with good quality wood chips.

Economic calculations show that a commercial plant of small capacity (500 kg/h output) can achieve good profitability and a reasonable PBT (around 5 years) when integrating low-cost residues at the current cost. 

Further information is available here.

Please click here to download the project presentation.

end