BAT (best available technologies) for drying of plant materials

An extensive literature study is conducted to highlight the current situation and includes technology that has not yet been extensively applied in industry for drying of plant materials. A ranking based on energy efficiency, technical suitability and economy will be performed. The quality of the material after drying is a very important parameter in these comparisons.

Existing and successful energy efficient drying facilities will be visited to learn about best practices. Project team will participate in relevant exhibitions and conferences and visit enterprises in order to benchmark BAT.

According to the report A brief introduction to drying of plant-based materials the energy efficiency of a dryer could be improved by recirculation and a heat pump. However, an economic evaluation is always needed for each case to determine what type of a dryer is the best option. Duration of the drying season, product quality requirements and the scale of the operation will all affect the economics.

Download the report here


Survey of potential waste energy sources

Different potential waste energy sources with focus on rural areas such as wood chip power plants, energy cooperatives and farms and other enterprises will be surveyed for drying. Enterprises will be evaluated for sufficient available drying energy and suitable location for drying purposes especially during summer time. Rural heating power plants will be evaluated in order to utilize power plants for drying purposes in the summer time as well which would be a new business opportunity for power plants since typically those are closed during the summer months. Bakeries will also be considered as target enterprises. Evaluation of the possible energy sources for drying can be carried out partly as purchased services.

Download the map of potential waste energy sources for drying


Recommendations for drying

In order to be able to produce northern high quality dried natural products, we have to study the effects of different temperatures and different drying techniques on non-wood forest products (NWFP). Lots of information about drying temperatures of cultivated herbs and spices is available, but information about the northern natural products is missing. Birch leaves and stinging nettle shoots are used as model plants. There exists at the moment very little scientific evidence on suitable drying environments for these raw materials. Similarly the optimal vacuum drying process for these plants will be studied.


The energy efficiency of the Orakas dryer was enhanced.

Proposals in Finnish to update Orakas vegetable dryer: Orakas hyötykasvikuivurin päivitys.

Proposals in Swedish to update Orakas dryer: Växttorkaren, som blev noggrann och energisnål.


A modular dryer utilizing waste energy

A modular dryer utilizing waste energy from a CHP plant at Ilpo Wennström`s farm in Central Ostrobothnia has been designed. ”WIth the help of the modular dryer design I am able to construct a more economically feasible dryer in order to promote green circular economy and to prevent climate change.”, says Ilpo Wennström.


Figure 1:  A modular dryer utilizing waste energy


Building and testing a demo dryer and a mobile dryer for non-wood forest products (NWFP)

A demo dryer will be constructed at Öjeby Agro Park in Piteå. Planning of the demo dryer will done by LTU and Oamk.

A mobile energy efficient flatbed or a tipping bed dryer will be constructed. The trailer dryer can be filled already in the forest or on the field and during the transport it works as a pre-drying unit with unheated air.

A mobile dryer will be tested by the local NWFP producers.


Figure 2: Teemu Huotari from OUAS checking the installations in the mobile dryer. 


CFD modelling

It’s important to have as uniform air flow distribution as possible otherwise the product will dry unevenly and manual mixing, moving trays and stirring the product, will be needed during operation. Overly dried product means decreased mass and lower incomes, the product quality may also be affected. Uniform air flow distribution in this case means that each tray in the dryer and different zones in the tray receives the same mass flow of air. To help design the dryer with a uniform air flow distribution in mind Computational fluid dynamics, CFD, is used. Using CFD means that models of critical parts of the dryer is built digitally in a software. The environment and operation of the dryer can then be simulated to test the effect of various parameters such as inlet/outlet area, and volume flow has on the air flow distribution. This probably results in a more optimized dryer and saves money, time and headaches that would come from a trial and error approach of just building a dryer and try the optimize the build afterwards.  For example, a set of 20 simulations can be run that changes the inlet area with small increments between a minimum and maximum value based on the dryer geometry. From the results, a optimization algorithm can decide what the optimal inlet area are in regard to the airflow distribution.

Download the brochure on development of dryers 



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