Chris Franklin, MD at Ranheat Engineering Ltd – a leading UK manufacturer of wood combustion equipment – continues his series of articles exclusively for Furniture and Joinery Production. This month, he looks at alternative uses for the energy produced when burning your wood-waste.
The obvious use for wood-waste energy is to space heat a factory, but in the UK, where we don’t get harsh, cold winters many people utilise their wood-waste energy in other ways. Below are some examples of other ways to utilise your energy from wood-waste.
Kiln drying of timber
When trees are harvested, they have a high moisture content, The traditional drying method was to slice the tree into planks and then stack them with thin sticks between the planks and let the timber “air dry”. This is a slow process and depending on the thickness of the timber could take months or even years.
The alternative is a kiln to artificially dry the timber. The next consideration is the quality of the timber you are aiming to produce. Joinery quality timber is different and requires the use of specialist kiln manufacturers such as Kiln Services Ltd. To produce top-quality joinery, standard timber requires a heat and vent kiln. As the name suggests, the kiln heats and then vents to release the moisture from the kiln. The timber is then “misted” with water to re-wet the timber. If you try and heat the wood too quickly you will get splits and shakes.
Traditionally a powerful heat exchanger with an oil-fired boiler would be used but with the move away from conventional fuels enter the wood-waste burning boiler. From a round trunk of a tree when sawed you get waney edge boards. Planks that still have the bark and profile of the tree. This can be chipped and used as the fuel for the boiler.
Heat treatment of pallets
When the United Kingdom left the European single market, changes to the pallet industry came in overnight. Goods moving between EU members on pallets had no requirement for pallets to be heat treated. Goods coming from a non-member into an EU member country must be on a heat-treated pallet.
So, what is heat treatment? Basically, the pallet has to be heated to a given core temperature and then held at that temperature for a given period of time. This is not the same as a kiln-dried pallet.
Some pharmaceuticals need to be transported on a dry pallet to protect the goods. Heat treatment is to kill any boring insects that may be present in the timber that the pallet is made from. This is to prevent the spread of the insects from infecting trees in other countries.
The scheme in the UK is administered by the Forestry Commission and each site that heat treats pallets has a unique identifying number so the source of the pallets is identifiable. Heat treatment is carried out in a kiln but with a different control system and a record kept of each batch. The control of a heat treatment system is not as complex as a heat and vent kiln.
In many cases, broken pallets are used as the source of the fuel for a wood-waste boiler system. A pallet manufacturer will often deliver hundreds of pallets to a customer and as a “service” take away old broken pallets, which are an excellent source of free fuel when put through a woodchipper. Many are also fitted with a magnetic nail collector and the nails are sold as scrap to give further income.
Replacement air for spray facilities
Solvent-based finishes were traditionally used in the UK woodworking industry. The trend, to reduce solvent emissions was to change to water-based paints and finishes. Water-based paints need drying and extraction from spray booths.
The replacement air to the spray facility needs to be at a given temperature, normally in the low 20s C so even on a summer’s day in the mornings and evenings heat is needed to raise the temperature of the replacement air. The air also needs to be dry. This process load is large in the winter but still needed in the summer.
Ranheat use specialist Air Handling Units also known as AHUs. As well as heating the air they also have filters fitted so the replacement air is clean as well as warm. Without specialist replacement air, the spray facility will draw air from the factory which may not be clean, even if it is heated. Most modern robotic spray systems come with AHUs installed on the equipment, most of which require an oil or gas-fired boiler. These can be replaced by a wood-waste boiler.
Drying of wood for the domestic wood-stove market
There has been a huge increase in the need for drying firewood for the domestic market for use in wood burning stoves. The government introduced schemes, that any wood sold as fuel for the domestic market must be below 20% moisture content.
Once again this is carried out in a kiln-type arrangement where logs, normally split and cut to size are stacked in metal cages or stillages, then heated to dry the logs. This is basically an insulated box that heat is blown into, some are direct fired with all of the products of combustion going into the box but also gives the possibility for a warm air variant of a wood burner to be used.
A lot of the drying of domestic logs is carried out using oil-fired burners as they tend to be located in remote locations “off grid”. This almost seems to defeat the object of using domestic logs as a source of heat when the fuel needs oil to dry it down.
Contact Ranheat for further information on all types and sizes of Industrial Woodburning equipment from 75 kW upwards. Ranheat also make spares and services and repairs other makes of wood-burning boilers and heaters.
01604 750005
