Drying of biomass for energy purposes
Over the last decades, at much of our planet population has seen a significant increase in living standards. This also results in greater energy consumption.
Today, fossil fuels are the most important source of energy, but they are non-renewable, and experts are increasingly loud about their eventual exhaustion. In the future, great emphasis will be placed on using of renewable energy sources - use of biomass, landfill gases, wind energy, hydropower, geothermal and solar energy.
The greatest importance for the Czech Republic is the use of biomass, either intentionally grown or waste biomass. When processing biomass, there is a problem with moisture content, which reduces the calorific value of the crop. Decreasing of moisture can be achieved either by delivering energy while reducing of drying time = active drying, or spontaneous process and by proper storage, but at the cost of a longer drying time = passive drying.
Drying of biomass is an operation, which is neccesary for its long-term storage. It must be get rid of practically all moisture either before storage or before combustion itself - high humidity reduces overeall energy efficiency.
As far as passive drying is concerned, it is the cheapest method of reducing moisture and requires the least amount of equipment and inserted energy, but it is also the slowest and also not suitable for some combustion and gasification systems or for the production of pellets.
Active drying requires energy input from and external source to speed up the drying process and the total humidity value will be lower. Utilization of this energy means an additional costs and increased energy input. To achieve a maximum drying efficiency, the ratio of the surface area is exposed to the airflow, the better result is. Additional airflow is provided by ventilators, usually with air heating. The movement, rotation and spreading of the material will help to increase the surface area and will help to better drying. Unused heat from different process can be used to heat the air, or a direct heating unit will be used. For this method of active drying, the ratio of supplied energy to the energy obtained from the dried, is very important.
Knezeves, 4th of May 2017 Studnickova Renata