Drying woody biomass in a solar enhanced convective dryer

Sustainable biomass resources are limited, especially regionally. The energy content of sustainable woody biomass resources can be maximized through drying. On the other hand, there is an urgent need for low-cost energy storage applications, related to solar energy in particular. Biomass dried with solar energy could serve as a seasonal energy storage. It also improves the quality of biomass and helps preserve its quality.
In order to study the technology and economy of solar enhanced drying, several drying experiments were conducted on wood chips and hog fuel of used wood in VTT’s convective dryer in Jyväskylä. The drying system at VTT comprises six flat plate solar heat collecting modules with the total collector surface area of 12 m2 and corresponding to roughly 10 kWpeak, with air ducting for supply of heated air to the biomass drying equipment. In calculations, the drying system was calculated to comprise 90 and 5,000 m2 of solar collectors.
VTT’s experiments prove solar heat energy can be well applied to biomass drying. Particularly, because moderate drying temperatures are favoured in order to ensure homogenous drying of wood particles in one hand, and to prevent changing the physical structure of biomass or loosing volatiles with applying high temperatures on the other.
In general, because of the low efficiency and high investment cost of the system the calculated payback times did not become highly attractive from the entrepreneur’s point of view. With technical improvements and a better design, however, the efficiency of the dryer could be improved significantly. The calculations show that if most of the heat could be utilized for evaporation, the selling price of dried biomass is higher than that of wet, and with moderate investment subsidies, the payback time with drying seasoned wood would be reduced below 10 years.