Sustainability is key at Norbord’s factory

What: Norbord SterlingOSB factory
Where: Inverness, Scotland

A cloud of steam emanates from the giant chimney of the Wet Electrostatic Precipitator, at Norbord’s Inverness manufacturing plant. Known as ‘the WESP’ by those that work at the plant, nicknamed ‘the cloud machine’ by locals and loved by nearby Inverness Airport as a ready-made wind direction indicator, the Wet Electrostatic Precipitator is actually a highly efficient, low-energy filtration device. It has been installed at the Oriented Strand Board (OSB) factory to remove fine particles of dust and smoke and soluble organics from the factory exhaust systems and the flue of the biomass burner that provides heat to the plant.

‘The WESP is a massive scrubber to clean the air extracted from points along the production line before it is released in to the atmosphere,’ says Allison Day, process engineer for Norbord Europe. It is one of many environmental initiatives that Norbord has introduced at the plant.

When it opened in 1985, Norbord’s Inverness mill was the first in Europe to manufacture OSB. Now, following a £110 million investment to increase production the plant is once again blazing a trail, this time as the first plant in the UK to use formaldehyde-free resins in the manufacture of OSB board. It currently produces a family of zero-added formaldehyde precision-engineered SterlingOSB boards in thickness from 9mm to 22mm, including: SterlingOSB Zero OSB3, SterlingOSB Zero Tongue and Groove, SterlingOSB Zero Site Coat, Sterling OSB Zero Fire Solutions and Sterling OSB Zero StrongFix

The binder that is used to coat and bind the flakes together cures at a lower temperature which reduces the amount of energy required in board manufacture. The production process also uses water as a catalyst in the curing process to harden the resin. ‘The precise moisture level is critical for heat transfer to cure the resin in the board-forming press,’ explains Day.

The timber too is sourced sustainably: all the SterlingOSB Zero range is manufactured using forest thinnings as the primary raw material. These are taken from sustainably managed UK forests. In fact, this mill was the first OSB plant in Europe to receive Forestry Stewardship Council (FSC) accreditation. The mill also uses timber chips – a waste product from the nearby sawmills – which are flaked for use in the dense core of the OSB boards. 

Timber residue from the plant is used to fuel a biomass burner. This includes bark stripped from the logs at the start of the manufacturing process, wood dust extracted from various production processes around the plant, along with any timber residue and non-specification timber flakes. The burner generates heat for use in the drying and curing stages in board production – see panel, right. ‘Moisture content of fuel is critical,’ says Day. ‘Too wet and it can kill the fire; too dry and it will combust too quickly.’

Even rainwater run-off from the facility’s new building and the hardstanding is treated to minimise its environmental impact. It is treated in a new three-stage drainage system of reed beds to remove large particles, oily residues, fine grit and sediment from the run-off before it is allowed to enter the local watercourses. 

As with all Norbord manufacturing sites, the Inverness plant is certified to ISO14001, the international standard for environmental management. 

1 Raw material

Timber from responsibly managed forests in the UK is delivered to Norbord’s Inverness production facility by truck. The plant uses a mix of pine, spruce and birch to manufacture its OSB 3 boards. The timber is loaded onto the log deck for processing in the wood room. Logs are stripped of their bark before a pusher drives them into the strander where spinning blades tear them into the flakes that are the basis of OSB.

The dryer 
A conveyor delivers the wood flakes to the wet bin, and they drop into the dryer below – a giant spinning drum by heated to 40MW supplied by the biomass burner. Dry flakes then pass through a cyclone (the same technology Dyson uses in its vacuum cleaners), where dust and fine particulates are removed.

Screening

Dust-free, the wood flakes pass to a primary screening machine which separates the flakes into two sizes: over 10mm for the board’s outer layers and 4mm-10mm for its core. A conveyor delivers the flakes to their respective storage bins: two for the surface flakes, two for the core. In a separate plant, the fine particulates removed by the cyclone pass through a secondary screening process whereby the larger particulates are reclaimed and added to the core bin. The remaining dust and tiny particulates are sent to the biomass burner for use as fuel.

Forming the mat 

The smaller flakes progress to a blender where wax and formaldehyde-free resin are added. The wax acts as a coating and lubricant to ensure flakes are evenly coated in resin. The process is identical for larger flakes, but water is also added to increase their moisture content to help with heat transfer later. Coated flakes are then conveyed to the board forming line. First a layer of larger flakes is laid parallel to the conveyor. Next the first of two layers of core flakes is added, perpendicular to the surface layer to give the board its strength. Flakes in these two layers get progressively smaller the closer they are to the eventual core of the board. Finally the top layer is added, perpendicular to the core flakes to form the ‘mat’, or uncured board. An X-ray machine scans the mat to ensure it conforms to specification. 

Curing and cooling the mat 

The mat is sprayed with water to help with heat transfer before it enters the press. Steel belts enclose it top and bottom and are squeezed between platens to compress the mat. Oil heated in the biomass plant keeps the platens warm. Along the press 42 platen frames control heat and pressure to cure the resin and form a continuous length of board.  As it leaves the press, the OSB is cut into lengths by a saw which moves diagonally at the same speed as the conveyor to give the board a straight cut. Boards are weighed and subjected to ultrasound to ensure consistency of product before being stamped with Norbord’s branding, a CE mark and a code to ensure traceability. Finally, the still warm ‘master boards’ are cooled in rotating racks.

Cutting the boards 

When the master boards have cooled they are sawn into six standard-sized boards. The finished boards are then stacked and taken to the warehouse for distribution. The whole process from raw material to finished board takes about three hours.