Availability and use of mill residues

According to comparisons of ten countries (Dykstra, 1992, cited in Pulkki, 1997), only about 53 percent of felled timber is actually available for further processing. After logs are extracted from the forest, loading and transport losses and damages reduce volumes further. Such losses are often not considered, but can be nonetheless substantial. In Papua New Guinea, 10 to 35 percent of the anticipated export volume was left at the harbor after failing to meet export grade rules (Kilkki, 1992, cited by Pulkki, 1997).

Statistics for the wood-processing sub-sectors in Asia-Pacific are extremely weak with few exceptions. Wood processing is very diverse and has in recent years experienced a slow but steady shift towards the production of wood-based panels and pulp (Table 8). The following discussion on the availability and potential uses of mill residues will take account of the existing situation. It focuses on residue generation in sawmills and plywood mills, which together account for the biggest share of the wood-processing sector. Second, although the share of wood-based panel producers is slowly increasing, from a residue-generation point of view, with the exception of plywood, this can only be welcomed. Plywood processing recovery rates are below 50 percent. In the other panel sub-sectors, however, rates are substantially higher. Chen (Appendix 1) estimated the recovery rate for particleboard to be 70 percent and for MDF 93 percent. Considering that some of the latest production lines installed recover all of their waste for energy production, virtually no waste remains.

Table 8. Wood processing in Asia from 1994 to 1988 (1,000 cum, pulp in 1,000 MT)

Source: FAO, 2000

Recovery rates of sawmills and plywood mills

Numerous factors influence the volume of mill residues. The recovery rate is especially dependent on log dimensions. For logs in the range of 30 to 70 cm in diameter, recovery rates drop to about half when the log diameter is halved (Ravn and Jensen, 1999). Recovery rates are also determined by log quality, tree species, defects, sawmilling equipment, mill maintenance, production methods, grading, storage and drying. Ravn (1999a) estimated that improvements in these factors could reduce residue volumes by 5 to 10 percent. However, log dimensions have been decreasing in Asia and the Pacific, and will decrease even further in the future. Hence, even investing in more efficient equipment will not increase overall recovery from present levels, but rather will only avoid further declines. In the short term, however, and for individual mills where equipment upgrades are made, improvements are tangible.

Small-spindle rotaries reducing residue generation

The growing adoption of small-spindle rotaries by Indonesian plywood producers may be having just the same effect [i.e. accelerate the pace of forest destruction]. Introduced in the mid-1990s, the new rotaries allow panel producers to peel logs as small as 15 cm in diameter, leaving a core of 6–8 cm. The old, large-spindle rotaries, by contrast, would generally leave a 15–25 cm core that could not be peeled. According to several producers interviewed, the use of the new technology has had the practical effect of raising their log recovery rates - particularly when their preexisting machinery had become highly depreciated - from the 45–50 percent range to that of 55–60 percent.

Source: Barr, 2000

According to detailed studies in numerous countries, sawmill recovery rates range from 42 to 60 percent with an average of 50.8 percent. Plywood recovery rates range from 43 to 50 percent with an average of 46.9 percent (Table 9). In 1998, researchers interviewed 24 mill managers in the State of Terengganu, Malaysia representing about 70 percent of the production in the State. According to the responses of the managers, sawmills recovered about 52 percent and plywood mills about 49 percent of total input (Ravn, 1999b). Recovery rates can also be substantially lower, however. In Lao PDR, average recovery rates in the sawmilling sub-sector are estimated at 30 to 40 percent (Thongleua Southavilay and Castrén, 1999). This is because of the use of inappropriate machinery that was originally installed to process large-diameter timber but now has to accept smaller dimensions. The teak export mills of the Myanmar Timber Enterprise turn about 65 percent of the log input into waste (Castrén, 1999b). Tze (1999, cited in Zerbe et al., 2000) reported an even lower recovery rate of 30 percent for teak logs with sawmill quality.

There are no clear discernable trends over time. It appears that any increases in recovery rates are balanced by declines in log dimensions and quality.

Table 9. Recovery rates in the sawnwood and plywood sub-sectors

Note:

^a cited by Ravn (1999b),

^b cited in Pulkki (1997),

^c from Appendices 1 and 2 of this publication

Composition, types and attributes of mill residues

The large-scale use of mill residues demands considerable investments in transport and processing capacities. Investments will only be made if a constant supply of raw material can be assured, which, as noted earlier, is already causing problems for some users of mill residues. In addition, the composition and quality of mill residues must be well known.

The composition of mill residues depends on a number of factors. Sawmills produce quite different residues, or by-products, than plywood mills (Tables 10 and 11). Basically, mill waste can be divided into two main groups. The first is made up of larger pieces, the bulk waste, while the second group, consisting of shavings, sawdust and sander dust, is made up of fine wood particles. Waste in the first group are easier to segregate and handle, which explains the increase in their use.

Finally, waste or mill by-products are categorized by six main attributes that determine their appropriateness for further use and processing (Wan Tarmeze Wan Ariffin et al., 1999):

• Species

• Segregation (species mixture)

• Purity (clean or contaminated)

• Moisture content

• Storage (in silos, bins or left on the ground)

• Size

Table 10. Types of residues generated during sawmilling (10-country average)

Source: adapted from Dykstra, 1992, cited in Pulkki 1997

Table 11. Types of residues generated during the production of plywood (10-country average)

Source: adapted from Dykstra 1992, cited in Pulkki, 1997

In assessing the volume of residues that are actually available and can be used, horizontal and vertical integration of processing facilities are crucial. The recovery of solid mill off-cuts, which make up a substantial percentage of total sawmill residues, depends on the degree of integration in market and downstream production (Ravn and Jensen, 1999). Therefore, it is crucial to distinguish between real waste that can only be disposed of by dumping or burning, and by-products that can be used as firewood, livestock bedding or further production processes. Even bark can be used as mulching material, although the cost-effectiveness of such an alternative depends on a number of factors.

Integration turning waste into useful by-products

Sawmills with little integration have few opportunities for recovery of short-length pieces. If supplying a moulding plant, small dimension pieces down to 60 cm can be delivered, raising recovery rate. A moulding plant also using finger jointing can use pieces as short as 20 cm, thereby reducing the amount of remaining mill residues.

Source: Ravn and Jensen, 1999

Potential availability of sawmill and plywood mill residues

Estimating the volume of mill residues available for further processing is difficult. Production figures are often not reliable. Recovery rates vary within and among countries depending on log sizes, dominant species processed, standard of processing equipment and level of horizontal and vertical integration. Hence aggregate figures should be viewed with caution.

The total amount of residues produced per year in the sawmilling and plywood sub-sectors in the selected countries is about 42 million m³ (Table 12) and 19 million m³ (Table 13), respectively. Close to 90 percent of the sawmill residues is generated in only four countries (i.e. China, India, Indonesia and Malaysia). More than 95 percent of the plywood mill residues is generated in only three countries (i.e. China, Indonesia and Malaysia). These percentages were even greater before the financial crisis that began in June 1997. For example, in 1996 Indonesia produced 7.3 million m³ of sawnwood compared to 2.5 million m³ in 1998 (FAO, 2000). In Malaysia, sawnwood production decreased by almost 40 percent and in China by 30 percent between 1996 and 1998. The decline in the plywood sector was not as drastic but also quite pronounced in the main producer countries. Hence, total volumes prior to the crisis were probably 30 to 40 percent higher.

Depending on the assumptions that calculations are based upon, estimated volumes of residues vary (e.g. compare results in Tables 12 and 13 with the case studies in the Appendices 1 and 2). Gintings and Roliadi estimated the total residues generated in the wood-processing sector in Indonesia at 11.6 million m³ per year. Chen estimated a similar volume of 11.3 million m³ for China (Appendix 1).

Unlike the very small volume of logging residues currently being used, it is apparent that much larger percentages of mill residues are already utilized. Thus, the total estimated volume of mill residues (61 million m³ per year) is not the volume that is currently available. Especially in wood-deficit areas, residues are unlikely to simply be dumped. Rather, the residues are likely to be used by local people as fuelwood or claimed for further industrial processing. This indicates that, although primary processing may produce huge volumes of residues, in many countries they are not viewed as “waste” but as by-products that are already used by the urban and rural populations, the informal sector and/or secondary wood-based industries.

Table 12. Sawnwood production and residues in 1998 (1,000 cum)

Table 13. Plywood production and residues in 1998 (1,000 cum)

Large quantities of mill residues are used as fuelwood for brick making, tobacco curing and domestic cooking in Terengganu, Malaysia. Smaller amounts are used for fencing, resawing for fish boxes and local furniture production. The secondary wood processors in Peninsular Malaysia discovered rubberwood as a valuable raw material during the 1990s and now hardly use hardwood residues. Hence, not all mill waste is considered a useful by-product. In the State of Sarawak, on the other hand, mill residues are used to the extent that shortages of raw materials are locally imminent (Ravn, 1999a). The efforts of the Sarawak Timber Industry Development Corporation (STIDC) to promote the use of wood waste appear to be “too successful”.

There is a serious lack of data indicating the extent to which the potentially available mill residues are already being used. The volume that is not used and may be of interest from a financial point of view probably does not surpass 45 million m³ per year.

Successful transformation

The situation is quite different in East Malaysia [Sarawak], where a substantial number of secondary processing facilities have been set up during the last 3–4 years [second half of the 1990s]. The raw material is mill residues of mixed hardwood species. The chipboard and MDF plants, chipping stations, co-generation and boiler plants and briquetting and carbonizing plants in Sarawak are all modern, large-scale operations…. The total investment in the plants visited amounts to around 600 million RM [at that time about US$ 240 million] invested in 1995, 1996 and 1997. This development can be credited to the efforts of industrial development made by the State of Sarawak through the Sarawak Timber Industry Development Corporation (STIDC).

Source: Ravn, 1999a

Potential utilization of mill residues

Many sawmills in Asia are set up and managed in traditional ways (i.e. they are equipped with bandsaws and set up to cut large-diameter logs). It is difficult to envision significant investments in this sector in the near- to medium-term future as log supplies are uncertain in many areas. However, some retooling should be considered to increase recovery rates by raising the performance and productivity of breakdown saws and resaws. Water storage of logs or sprinkler storage can also minimize waste experienced during dry periods (Havelund, 1999).

Even substantial investments in the sawnwood and plywood sub-sectors would likely reduce mill residues by only 5 to 10 percent. Thus, the question of how best to utilize residues remains.

Wan Tarmeze Wan Ariffin et al. (1999, p. 7) disaggregated potential utilization into three broad categories:

1. Energy production, such as:

   • Boiler fuel for kiln-drying, wood conditioning, lacquer-curing, etc.

   • Co-generation plant fuel

   • Industrial fuelwood (e.g. for brick making, noodle production, tobacco curing, and steam generation.

2. Secondary raw materials to be used by the wood-based industries for:

   • MDF

   • Particleboard

   • Block board

   • Laminated board

   • Charcoal briquettes

   • Parquet

   • Pallet manufacturing

   • Small-scale wood products, e.g., in cottage industry

   • Use in paper and pulp industry

3. Secondary raw materials to be used by industries outside the wood industry sector:

   • Fertilizer and mushroom growing

   • Livestock litter/bedding

In addition, sawmill residues are an important raw material for the moulding industries, and in the small-scale artisan sector in the rural areas, wood waste is used in a myriad of ways (see also Appendix 2). Horticultural and agricultural uses are also possible.

Any wood-waste management strategy should follow the “4R” approach (i.e., reduce, reuse, recycle and recover) (Wan Tarmeze Wan Ariffin et al., 1999).

• Reduce: minimize waste during primary processing and storage

• Reuse: use waste in downstream industries without changing its mechanical structure (e.g. off-cuts to the joinery)

• Recycle: use waste for reconstituted panel production such as MDF

• Recover: use residues as fuel

The most attractive options for using large volumes are turning waste into charcoal briquettes, using it for co-generation, and using it as secondary raw material within the wood-based panel sub-sector.

Charcoal briquettes⁷

Wood briquetting includes the conversion of loose wood waste into a dense, compact and consolidated unit through the application of high temperature and pressure (Wan Tarmeze Wan Ariffin et al., 1999). Both sawdust and bark are suitable for briquetting, although sawdust is the preferred raw material (Ravn, 1999a). Briquettes can also be carbonized to create charcoal of very high quality. In 1998, there were 11 briquetting factories in Malaysia. Briquettes have to compete with other fuels, such as wood and agricultural residues, kerosene and diesel, which are often cheaper. Hence, most briquettes are exported from Malaysia. Major markets include South Korea and Japan. Due to the economic downturn, the commissioning of new plants has slowed down, although financial analysis conducted by the Forest Research Institute Malaysia (FRIM) indicates that the industry is attractive to new investors (Hoi, 1999, cited by Ravn, 1999a).

⁷ For more information on briquettes visit http://www.frim.gov.my.

Co-generation

Co-generation is the process by which a factory uses its waste energy to produce heat or electricity. The steam produced can provide large amounts of lower-temperature energy for such applications as kiln drying. Considerable overall energy savings can be obtained, and investment in co-generation is thus very attractive with short payback periods.

Investments in co-generation have been supported by the EC-ASEAN COGEN Programme, an economic co-operation program between the European Commission (EC) and the Association of Southeast Asian Nations (ASEAN). It aims to accelerate the implementation of proven co-generation technologies within the industrial sectors of the ASEAN region through partnerships between European and ASEAN companies. COGEN provides information services and maintains databases on European technology suppliers and potential ASEAN customers. It supports the development of full-scale demonstration projects by providing 15 percent seed money for approved projects.⁸

The reasons for investing in a new boiler and a complete biomass co-generation plant were the energy potential of wood waste and our growing concern to reduce pollution.

Leong, C.S., Plant Manager of Sim Hoe Wood Industry Sdn. Bhd.

COGEN has been involved in more than 15 full-scale demonstration projects in Southeast Asia. Investments for individual facilities range from less than US$ 500 000 to above US$ 7 million with typical payback periods of 1 to 3.5 years after commissioning (Table 14).

⁸ For more information on COGEN visit http://www.cogen.ait.ac.th.

Table 14. Examples of co-generation plants constructed in Asian countries in the late 1990s

Co-generation as a solution to greenhouse gas mitigation

A wood waste-fired co-generation plant with a capacity of 1.65 Mwe installed at a wood-working complex in Malaysia would result in a reduction of 4 677 tons CO₂ equivalent compared to the old system where fueloil was used for the boiler while a diesel gen-set provided electric power and the wood waste was burnt in the open.

Source: De Castro et al., 1999

Considerable cost reductions can be achieved and negative environmental impacts can be drastically reduced through co-generation and the installation of new technologies that replace conventional diesel engines. Co-generation is particularly attractive since the costs for wood waste will not fluctuate as extremely as the prices for fossil fuels. In addition, bioenergy offers opportunities to meet Kyoto Protocol commitments. Bioenergy is thus increasingly being incorporated into national energy policies. Co-generation would become even more attractive if the factories could feed their surplus energy to national grids, as is the case in the United States of America.

Wood chips, particleboards and MDF

Sawmill and plywood mill residues of mixed hardwood species can form an important raw material for the chip and board industries. This is particularly attractive for large-scale uses where mills have the opportunity to sell their unwanted waste in a cyclic, well-organized manner based on long-term contracts. In fact, under such conditions, wood residues are no longer viewed as a problem. Rather, they are viewed as valuable by-products that can help increase profit margins (Ravn, 1999a). However, the relative location of residues and markets for final products have to be analyzed carefully.

World production of five major wood-based boards was 106 million m³ in 1990 and reached a maximum of over 150 million m³ in 1997 (Table 15). Due to the downturn in many Asian economies, consumption and production fell in 1998. Plywood production was most affected while particleboard and MDF producers registered slight increases. This difference can probably be explained by the very different raw material requirements. Particleboard and MDF manufacturers have a considerable comparative advantage in that they can make use of much cheaper raw material. This price divergence will probably continue, as new technologies make it increasingly possible to use mixed tropical hardwoods. In the future, the role of wood residues as raw material for the expanding particleboard and MDF sub-sectors will increase and, as has already been reported in Sarawak, local raw material shortages and higher prices for mill residues will likely result.

Table 15. Production of major boards during the 1990s (million cum)

Vertical and horizontal integration in wood processing favors the use of wood residues, as transport costs are a significant factor in pricing raw material. The price ultimately determines availability as Walsh et al. (1999) have shown for the biomass feedstock availability in the United States. The estimated annual cumulative forest residue quantities nearly doubled when prices were increased from US$ 30 to US$ 50/dry ton delivered. However, such price levels are much higher than those reported in Ravn's case studies in Sarawak (1999a), which ranged from RM 12 to RM 40 per MT (RM 3.8 = US$ 1). Hence, non-use of residues in Sarawak is much lower.

A thorough analysis of raw material availability and spatial distribution should indicate strategic locations for additional secondary wood processors as well as chipping plants, to avoid concentration of factories and subsequent shortages of raw material.