What is Forestry Brash?
Forestry brash is the woody material (branches, tree tops, twig) leftover after trees have been harvested from commercial woodlands or created from thinnings as part of forestry management schemes, habitat restoration or for building developments.
At point of chipping / shredding, the moisture content of forestry brash varies depending on season, heap size and recent weather. Moisture content is often high and inconsistent across the load, meaning it is often not suitable as a saleable boiler fuel, even after a period of air drying. When flow dried to the correct % moisture for boiler fuel specification, farmers, forestry owners and wood fuel businesses can sell brash chip as a valuable boiler fuel, compliant with local/regional boiler specifications and wood fuel standards (e.g. BS EN ISO 17225), helping to offset billions of tonnes of fossil fuels each year.
Fresh wood brash typically contains 55-65% moisture, making it challenging to utilise. By chipping and flow drying wood brash chip, professional biomass fuel suppliers gain a consistent, controlled wood fuel with moisture content between 20-30% optimised to meet fuel contract specifications, whatever the season. This unlocks significant financial value from each m³ of woodchip fuel sold to the market as boiler fuel.
The image below shows a Stronga HookLoada trailer collecting wet brash ready for chipping and flow drying. More information on Stronga's transport solutions is available on stronga.com.
Flow Drying Reduces Risk of Fuel Load Rejection
FlowDrya wood brash drying equipment transforms wet low-value forestry waste into premium, consistently dry, high value biomass fuel that can be sold to CHP plants, commercial scale boilers, domestic wood fuel boilers, district heating systems and industrial boilers. Low moisture brash chip feedstock:
- Increases the calorific value of brash chip (thermal kWh) – dry brash (20%) contains more than double the usable energy per kg of wet brash (60%). Drying brash from 60% to 20% increases the net calorific value from circa 6MJ/kg to 14MJ/kg – more than doubling it.
- Improves the temperature of the boiler flame – reducing flue losses, increasing peak output of heat and removing ash issues.
- Improves combustion efficiency – shredded brash with suitable moisture content wastes significantly less energy during combustion. Evaporating moisture in the boiler is a huge energy problem, significantly reducing the amount of useful heat the boiler can produce. Dry brash chip increases combustion efficiency and lowers particulate emissions during heat production.
- Extends storage life – wet brash chip degrades rapidly through biological activity, mould and composting; dry material can be stored for extended periods without risk of quality loss.
- Optimises briquette production – for the production of high-quality, durable fuel briquettes, shredded brash needs to be dried down to a moisture content of 12-16% which is easily achievable with FlowDrya.
- Complies with regional 'Ready to Burn' certification requiring solid fuels to be compliant with UK Air Quality Regulations <20% moisture content for sale and immediate domestic use.
- Enables compliance with wood fuel regulations – speak to Stronga to ensure FlowDrya can meet the requirements of your local biomass fuel specifications.
- Reduces emissions & ash problems – lower particulate emissions, carbon monoxide, tar etc.
- Protects the boiler – biomass boilers are designed for a specific moisture range. Forestry brash with high moisture content causes corrosion, blockages in fuel handling systems and unplanned shutdowns. FlowDrya ensures compliance with boiler moisture requirements, extending the life of the boiler.
Forestry Brash Chips
Moisture Content vs. Calorific Value vs. Energy Content
FlowDrya increases the calorific value of every m³, during every season.
| Moisture content (% wet basis) | Calorific value (kWh/kg) | Energy content (kWh/tonne) |
|---|---|---|
| 20% MC | 4.2 kWh/kg | 4,200 kWh/t |
| 25% MC | 3.9 kWh/kg | 3,900 kWh/t |
| 30% MC | 3.6 kWh/kg | 3,600 kWh/t |
| 35% MC | 3.2 kWh/kg | 3,200 kWh/t |
| 40% MC | 2.9 kWh/kg | 2,900 kWh/t |
Why Moisture Matters for Brash to Biofuel Production
On a global-scale, there is increasing demand for in-profile low moisture, biomass to generate heat and power, making shredded forestry brash particularly valuable when harvested sustainably and dried to the correct moisture profile. In the UK, after harvesting, wood brash typically has a high moisture content of around 60-65%. Even after air drying for 12 months, the moisture content of say 35-40% often remains too high to be useful as a boiler fuel, making the FlowDrya a critical piece of equipment for suppliers.
With at least 3X more demand from customers during winter months, there is a strong seasonal demand dilemma for forestry brash boiler wood fuel. FlowDrya delivers value by enabling businesses to meet high demand in winter periods, drying wood fuel directly to the required moisture content for each client's boiler. This often means removing 80-100 litres/m³ of moisture in order to get a consistent biofuel of 20%, 25% or 30% moisture content.
The chart below shows the general effect of seasonality on forestry wood chip boiler fuel market demand in the Northern Hemisphere. Demand for boiler fuel in the Southern Hemisphere is the reverse of the below, with higher demand between April-September during the Southern Hemisphere winter.
Why is FlowDrya Suitable for Drying Wood Brash?
FlowDrya offers a stunning return on investment for businesses with access to forestry brash, adding approximately 30% to the calorific value vs. air drying alone. Discover the benefits.
Brash Chip Drying FAQs
Target dry output moisture varies depending on specific boiler fuel requirements. FlowDrya can be configured to dry brash chips down to specific target boiler fuel specifications. For briquette production, forestry brash chips should be dried to circa 12-16%.
Operating costs of the flow dryer depend primarily on heat source selection. Using residual heat, flue gases or sawmill kiln drying surplus heat, will reduce operating costs significantly. Inherently, the Stronga FlowDrya is a low opex wood brash dryer with extremely low electrical energy demand.
The typical residence time for drying forestry brash varies depending on intended application, input moisture content, particle size, season, tree species, target drying % and other factors. Please speak to Stronga about your specific wood brash drying project requirements.
Yes. The FlowDrya and hopper is designed for hard to handle, clumpy and heavy biomass materials while PulseWave™ agitation systems ensure forestry brash material is tumbled along the drying bed, leading to uniformly dry output, even with non-homogenous, hard to handle materials like wood brash chip.
Ready to discuss your forestry brash drying project?
Our team can help you specify the right FlowDrya system for your wood brash drying requirements.