The obvious use for wood waste energy is to space-heat a factory. However, since we don’t get harsh cold winters here in the UK, many people explore alternative wood waste solutions. Here are some examples of transforming wood waste into valuable resources for energy and heating.
When trees are harvested, the wood contains a high moisture content. Traditionally, the drying process involved cutting the tree into planks, stacking them with small gaps in between, and letting them “air dry.” This method can take months or even years, depending on the thickness of the timber.
A faster alternative is to use a kiln to dry the wood artificially. The quality of the timber you want to produce is crucial, especially if you’re aiming for joinery-grade wood, which requires specialised kilns such as those from Kiln Services Ltd.
To achieve high-quality timber, a heat and vent kiln is essential. It heats the wood and vents the moisture, followed by misting the timber with water to prevent it from drying too quickly, which can cause splits and cracks.
In the past, oil-fired boilers were used to power these kilns. However, as we move away from traditional fuels, wood-waste burning boilers have become a more sustainable option. Offcuts from timber processing, such as waney edge boards (planks with bark and the tree’s natural profile), can be chipped and used as fuel for these boilers.
Heat and Vent kiln, large hogger in building and storage silo and wood-waste boiler room.
When the United Kingdom left the European single market, changes to the pallet industry came in overnight. Pallets used to move goods between EU countries didn’t need to be heat treated. However, goods entering the EU from non-member countries now require pallets that have been heat-treated.
So, what exactly is heat treatment? It’s a process where the pallet is heated to a specific core temperature and held there for a set amount of time. This differs from kiln drying, which is sometimes required for pharmaceuticals to protect the goods by keeping the pallets dry. Heat treatment, on the other hand, is used to kill any boring insects that may be present in the wood, preventing the spread of pests to other countries.
In the UK, the Forestry Commission oversees the heat treatment scheme. Each site that performs heat treatment is given a unique identifier so the source of the pallets can be identified. While heat treatment takes place in a kiln, it uses a simpler control system compared to a heat and vent kiln, and each batch is carefully recorded.
Often, broken pallets serve as fuel for wood-waste boilers. Many pallet manufacturers provide a service where they deliver new pallets and collect broken ones, which are chipped and used as free fuel. Some systems even include a magnetic nail collector, allowing the nails to be sold as scrap for additional income.
Traditionally, solvent-based finishes were widely used in the UK woodworking industry. However, to reduce solvent emissions, the shift towards water-based paints and finishes has become the norm. These water-based products require drying and air extraction from spray booths.
The air that replaces what is extracted must be at a specific temperature, usually in the low 20s°C. Even during summer, heating is often necessary in the mornings and evenings to maintain this temperature. The air must also be dry. This creates a significant demand for heating, especially in winter, but is still required year-round.
Ranheat addresses this need by using specialist Air Handling Units (AHUs). These units not only heat the replacement air but also filter it, ensuring the air is both warm and clean. Without such systems, spray facilities would pull in air from the factory, which may be heated but not necessarily clean.
Most modern robotic spray systems are equipped with AHUs, which typically rely on oil or gas-fired boilers. However, these can be replaced by more sustainable wood waste solutions such as biomass boilers.
There has been a huge increase in the demand for drying firewood for the domestic market, especially for wood-burning stoves. In line with this, government regulations now require that any wood sold as fuel must have a moisture content below 20%.
This drying process typically takes place in a kiln-like setup. Logs, usually split and cut to size, are stacked in metal cages or stillages and heated to reduce moisture. The kiln is essentially an insulated box where heat is blown in. Some kilns are direct-fired, meaning the combustion products enter the box, while others use a warm air system that allows for a wood burner to be used.
Many domestic firewood drying operations still rely on oil-fired burners, as they are often in remote, off-grid locations. Ironically, this approach somewhat defeats the purpose of using logs as a sustainable heat source if oil is required to dry the wood.
For further information on all types and sizes of industrial wood-burning equipment from 75 kW upwards, contact Ranheat on 01604 750005 or [email protected]. You may also visit www.ranheat.com. Ranheat makes spares and services and repairs other makes of wood-burning boilers and heaters.
