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‘Locally made wood-drying kilns to mitigate deforestation’

By Femi Ibirogba
26 October 2021   |   4:01 am
Wood is a versatile raw material and the only renewable construction material. The global timber sector currently faces the dual challenges of meeting the growing demand of quality timber products...

Prof. Hussaini Ibrahim Doko

• Short shelf life of woods encourages frequent tree felling

The Director-General, Raw Material Research and Development Council (RMRDC), Prof. Hussaini Ibrahim Doko, lists advantages of processing wood with adequate technologies. He told FEMI IBIROGBA in this interview that such merits include long shelf life of wood and lower consumption of forest resources. reports.

What is the status of the wood products sector in Nigeria?
Wood is a versatile raw material and the only renewable construction material. The global timber sector currently faces the dual challenges of meeting the growing demand of quality timber products and minimising possible adverse impacts on the environment and on forest degradation and deforestation. 

In Nigeria, more than 92 per cent of the wood processors, most especially those in the sawmill and furniture industries, are cottage and small-scale enterprises. They utilise sub-optimal processing methods.

The World Bank has also forecast that global timber demand is set to quadruple by 2050. As a result, there is growing global concern of fulfilling increasing demand for timber products without deteriorating the forest resources.

How does this impact the forest and how can this be addressed?
Wood processing affects the environment and promotes forest degradation and deforestation. As awareness of climate and environment issues increases and consumption habits change, new opportunities are opening up for the forest industry to develop functional green solutions to meet consumers’ needs.

Major sources of environmental impacts occur throughout the wood supply chain, from sawmills to final products. As a result, the rate of deforestation and consumption of industrial timber products are increasing. 

The rate of deforestation is expected to increase by 35 per cent in the next five years in view of the high rate of urbanisation, housing construction and poor wood processing practices. This can be addressed by promoting best practices in the industry to promote efficiency of timber production process.  It will also mitigate forest degradation and deforestation with the accompany environmental challenges.

Timber products are products produced from renewable and sustainable environmental resources. However, as with other processing industries, timber production may create various kinds of environmental impacts at different stages of the timber product supply chain, from harvesting to their disposal. Production of timber products also involves emission of carbon. As a result, the forestry sector in general and removal of trees through deforestation contributes up to 17 per cent of Greenhouse Gas (GHG) emission into the atmosphere.

In Nigeria, the present methods of wood processing by cottage, small and medium enterprises subject the final products to short shelf life. The products therefore require frequent replacement. For instance, most SME operators use air drying method.  In most cases, because of the issue of time and need for immediate profit, wood products are not fully dried before usage, leading to frequent replacements. 

Frequent replacements mean recourse to virgin lumber and this frequently leads to forest degradation and deforestation. Drying is one key steps in processing timber into high-value finished products. This is why research is being conducted globally into optimal drying technology in different climes. 

One of the objectives is to reduce deforestation as the world continues to lose some 15 million hectares of forests every year. Deforestation and forest degradation directly threaten as many as 400 million people, including 50 million forest indigenous people who depend on forest for subsistence in sub-Saharan Africa. Deforestation estimates for Nigeria is about six per cent yearly.

The regional breakdown of deforestation from 1979 to 1995 shows that total forest declined by 48 per cent in the North-Central, seven per cent in the North East, 60 per cent in the North-West, 53 per cent in the South East, 13 per cent in the South-South and 12 per cent in the South West.

In 2000, the forest cover was estimated at 13.5 million hectares compared to 17.5 million hectares in 1990, indicating a forest cover loss of close to 400,000 hectares yearly, or a decline of about 2.6 per cent. Forest/woodlands now stand at only 13 per cent of the total land area. With global outcry on the consequences of continuous unsustainable forest destruction topping major intellectual discourses, the need to optimise wood processing patterns, particularly among the SME’s, has become critical.
 
What is wood seasoning?
Wood seasoning or wood drying is one of the major operations wood must undergo during processing to increase its life in service. Seasoning reduces the moisture content of wood before its use.

When green wood dries, free water from the cell lumina, held by the capillary forces only, is the first to go. The fibre saturation point (FSP) is the point at which free water is completely gone, while the cell walls are saturated with bound water. In most types of woods, the fibre saturation point is at 25 to 30 per cent moisture content, while, wood expected to be used for most products, should be dried to between 10 and 12 per cent moisture content before deployment.

Many properties of wood show considerable change as the wood is dried below the fibre saturation point. Among these are the volume of wood, its strength (strengths generally increase consistently as the wood is dried below the FSP (except for impact-bending strength and, in some cases, toughness), electrical resistivity, all of which increases very rapidly with the loss of bound water when the wood dries below the FSP. 

However, as wood is a hygroscopic substance, it has the ability to take in or give off moisture in the form of vapour.  As a result, wood must be dried to the stage where the vapour pressure within the wood will be equal to vapour pressure in the ambient space. 

The amount of moisture that remains in the wood at this stage is in equilibrium with water vapour pressure in the ambient space, and is termed the equilibrium moisture content or EMC. At this stage, the wood is stable and it stops absorbing moisture from or releasing moisture into the surrounding air.  Wood products produced at this level have optimal shelf life.  This stage is, however, reached through optimal seasoning.    

What are the major ways of seasoning wood?
There are two major methods. These are natural (air) or traditional method and the artificial (kiln) drying methods. The traditional method of seasoning timber is to stack it in air and let the heat of the atmosphere and the natural air movement around the stacked timber remove the moisture. This allows air to circulate around each piece. Nevertheless, it is a slow process, particularly for hardwoods. It takes about six to nine months for the wood to be dried by this method to reach about 20-25 per cent moisture content.

This method is mostly adopted by the cottage, small and medium scale wood processors in Nigeria.  In view of the long drying period it entails, and the fact that most processors cannot wait for nine months, most wood used by these processors are not properly dried.  This leads to various problems when wood is deployed in service.

Which one is the most effective?
Kiln drying of lumber is the most effective and economical method available. Although there are different variants of the kiln drying process, the principles are generally the same. Drying rates in a kiln can be carefully controlled and defect losses reduced to a minimum.

Length of drying time is also greatly reduced and is predictable.  Where staining is a problem, kiln drying is often the only reasonable method that can be used unless chemical dips are employed.  It can dry wood quickly close to the average EMC conditions to which it will be exposed. This, according to global best practices, is between 10 and 12 per cent.  Also, at this level, shrinkage and further dimensional changes will be kept to a minimum.

How will these profit wood processors?
Kiln drying significantly adds value to sawn products. According to the Australian Forest and Wood Products Research and Development Corporation (FWPRDC), if green sawn hardwood is sold at about $350 per cubic metre, the value will increase significantly to $2,000 per cubic metre or more with kiln drying. 

Also, kiln drying, if carried out promptly after felling of trees, also protects timber against primary decay, fungal stain and attack by certain kinds of insects, as most organisms which cause decay and stain cannot thrive in timber with moisture content below 20 per cent.

In addition, kiln dried timber is lighter, and the transportation and handling costs are reduced.  It is also stronger than green timber in most strength properties. Paints and finishes last longer on dry timber, while the electrical and thermal insulation properties are generally improved.

What has RMRDC done to address the challenges of the SMEs in the sector with regards to optimal wood drying?
 To address the challenge and ensure that global best practices is enthroned locally, the council, in collaboration with Nova Palcon Nig. Ltd. Enugu, designed and developed two variants of wood-seasoning kilns with a capacity of 25m3 each.

The primary objective was to domesticate the kiln seasoning technology to reduce deforestation caused by short lifespan of wood in service and to increase the income generated by the SMEs. 

This will also promote the export of wood products from Nigeria. Two types (A&B) of seasoning kilns have been designed and fabricated.  They have been test-run and calibrated. The Variant A kiln adopts the condensation method and has a capacity of 20m3. It uses electricity for its operations while variant B uses wood waste to fire boiler with fan induced hot air and both are insulated with 100m polystyrene insert.

 

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