Drying systems for the wood-based panel industry – efficient, low-emission, future-proof

The final moisture content of the dried material directly determines the quality of the finished board: If the material is too moist, the glue reacts uncontrollably during pressing, "blow-ups" form in the board, and there are fluctuations in strength – scrap that cannot be tolerated in ongoing production. STELA low-temperature belt dryers regulate the final moisture content fully automatically to the exact target value – with a uniformity of +/-0.5% while simultaneously maintaining a natural, light product surface; drum dryers cannot technically achieve this, or only rarely.

The target moisture content depends on the end product and the type of glue used. The following are considered guidelines:

• Particle board (chips): approx. 2–4% oven-dry before gluing
• OSB strands: 1.5–3% oven-dry – varies depending on the pressing process
• Sawdust for block production (EURO pallets): <5% oven-dry before gluing
• Sawdust for pelletizing: target water content 8–12% 

Drum dryers are widely used in the wood-based materials industry, but have structural disadvantages that are primarily based on rising energy costs and environmental regulations:

• Higher process temperatures (>200 °C) lead to increased release of volatile organic compounds (VOCs) and wood components – exhaust air treatment becomes more complex and expensive
• Energy consumption is higher, as integrated heat recovery is often not installed
• Mechanical and thermal stress can damage sensitive chips and strands
• Uneven residence times lead to wider moisture variation in the final product

STELA low-temperature belt dryers operate below 120 °C and therefore generate significantly fewer VOC emissions than drum dryers – the exact difference depends on the respective wood species. Energy savings of 35–55% are achieved through the optional RecuDry® heat recovery system. The uniform flow through the belt provides a more precise final moisture content – directly measurable in less scrap and better board quality.

STELA belt dryers process all types of wood – hardwood, softwood, and tropical woods – in almost all degrees of comminution: from sawdust to wood chips and wood shavings to OSB strands. The belt configuration, feeding technology, and ventilation intensity are individually designed for the respective product.

During the drying process, naturally occurring volatile organic compounds (VOCs) are released from wood chips – terpenes, aldehyde compounds, as well as pinenes and limonenes. High-temperature drying significantly increases this release, thereby increasing the effort required for exhaust air purification and approval procedures. 

STELA low-temperature belt dryers significantly reduce VOC release due to the gentle process temperatures (material heating). Exhaust air treatment systems are not required.

Yes – low-temperature drying is particularly advantageous for OSB strands. High-temperature processes can damage the strands and lead to uneven drying. The STELA belt dryer operates with gentle temperatures and a feeding system tailored to OSB strands, which avoids segregation and breakage. The result is a homogeneous final moisture content, which directly improves board quality. Typical initial values: input moisture approx. 100% oven-dry (wood moisture based on dry mass), target moisture 1.5–3% – variable depending on the requirements of further processing.

The BTL (belt width 2,000–3,000 mm) is the cost-efficient system for small to medium capacities – ideal for sawmills and smaller producers. The BT (belt width 6,200–8,400 mm) is the high-performance dryer for large industrial producers with drying capacities of over 80 t/h. Both series share the same basic technology (top-down ventilation, modular design, fully automatic operation)

RecuDry® divides the drying process into two modules: In the Recu module, a portion of the exhaust air is circulated and optimally saturated. In the condensation module, this energy-rich air is condensed, and the released latent heat is used via an air-to-air heat exchanger to preheat the fresh air. Depending on the drying area, drying temperature, and outside temperature, this results in energy savings of 35 to 55% compared to a standard belt dryer. 

Existing systems can be retrofitted with RecuDry®.

The question of payback time is somewhat different in wood-based materials drying than in other industries: Drying is not an optional add-on, but an absolutely essential process step in every particleboard or OSB production line. The key economic question is therefore not “whether,” but which system represents the better investment—and here, the comparison provides clear answers.
Essentially, three types of systems compete in the wood-based materials industry: drum dryers, low-temperature belt dryers, and belt dryers with RecuDry® heat recovery.
Compared to drum dryers, stela belt dryers offer significantly lower operating costs due to lower process temperatures, reduced VOC emissions (which eliminates the need for costly exhaust air treatment), less mechanical stress and thus lower maintenance costs, as well as a more uniform final moisture content, which directly reduces scrap in panel production.
Within the belt dryer systems, RecuDry® technology offers the greatest potential for savings: With energy savings of 35 to 55% compared to a standard belt dryer, ongoing operating costs are significantly reduced—and since energy costs represent by far the largest cost component in fully automated operation, this has a direct impact on profitability. Under favorable conditions—high throughput, expensive energy, and available waste heat—the additional costs for RecuDry® can be recouped in less than 24 months.
As part of its project consulting services, stela prepares a robust cost-benefit analysis for the specific site, based on throughput, initial moisture content, available heat sources, and regional energy prices.

Wood dust is flammable and, under certain conditions, can form explosive dust mixtures. stela takes this into account when designing every system by implementing appropriate design measures, dust extraction, and monitoring systems.

As early as the sales phase, stela works with the customer to assess explosion risks as part of a CE risk assessment and defines the necessary protective measures. In the subsequent project planning phase, the system is then designed in detail, and all necessary protective measures are implemented.

Yes. STELA belt dryers can be operated with hot water, steam, as well as heat from flue gases. 
Important note: Flue gases, usually with high water content from biomass combustion, are highly corrosive and are therefore not used directly as a drying medium. Usually, the customer transfers the heat from flue gases first to an intermediate medium – typically water or air – which is then fed to the belt dryer. 
In the wood-based panel industry, the use of biomass waste heat from the combustion of bark, sawdust, and residual wood is a very economical solution, as the resulting residues are used directly as an energy source. In combination with RecuDry®, a nearly closed energy cycle can thus be realized.
 

Yes. The RecuDry® system is available as a retrofit solution for existing STELA belt dryers. A retrofit is technically possible and economically attractive, especially with rising energy costs. 
As part of an individual consultation, STELA checks which savings potentials are achievable for the specific existing system.

Every system is individually designed for the drying product, the throughput requirement, and the heat source. Before project planning, STELA conducts individual drying tests in its in-house technical center to determine exact drying curves. From order placement to commissioning, the typical project duration is 10 to 15 months – depending on system size, configuration, and on-site structural conditions. For a non-binding initial assessment, please contact the STELA sales team directly.