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Raw Material Source Of Wood Sawdust Pellet Machine

Date: 08/21/2020 08:33:04 From: Clicks:

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We know that the raw materials of wood pellet machine are mainly wood and sawdust. Where do they come from? The raw materials of wood sawdust mainly come from forest residues, mill-site generated wood waste, and integrated production. The following is a detailed introduction from the manufacturer of richi machinery wood pellet machine.

The residues generated from the forest products industry may be divided into two parts; that which results from harvesting and extracting logs from the forest, and generally considered of no economic use for further processing, and that which is generated by the forest industries themselves during the process of manufacturing timber, plywood, particleboard and the like (refer to Figures 1, 2 and 3), namely:

Source Type of residue
Forest operations Branches, needles, leaves, stumps, roots, low grade and decayed wood, slashings and sawdust;
Sawmilling Bark, sawdust, trimmings, split wood, planer shavings, sanderdust;
Plywood production Bark, core, sawdust, lillypads, veneer clippings and waste, panel trim, sanderdust;
Particleboard production Bark, screening fines, panel trim, sawdust, sanderdust.

In general it may be said that of a typical tree, less than two-thirds is taken from the forest for further processing, the remainder being either left, burnt or collected as fuelwood by the local inhabitants. After processing, only 28 percent of the original tree becomes lumber, the remainder being residues, as indicated in Table 1.

Table 1. Division of a typical tree harvested for sawntimber

Tree part or product Portion
Left in the forest:  
Top, branches and foliage 23.0
Stump (excluding roots) 10.0
Sawdust 5.0
Slabs, edgings and off-cuts 17.0
Sawdust and fines 7.5
Various losses 4.0
Bark 5.5
Sawn timber 28.0
Total 100.0

It is only in the last few years that, due to the economics of rapidly rising fuel and wood costs, industry in the developed countries have invested in ways and means to extract the maximum quantity of recoverable wood during logging operations. Although this document draws attention mainly to the energy value of residues produced during the manufacturing operations, consideration should be given to the potential industrial use of residues left in the forest.

I. Forest Residues

It is not uncommon for some 60 percent of the total harvested tree to be left in the forest and for non-commercial species to be subjected to slash and burn, or merely felled and left to rot so as to make access easier for logging. Such practices as sawing and squaring logs in the forest, rather than at the sawmill, wastes a further eight to ten percent and 30 to 50 percent respectively .

Raw Material Source Of Wood Sawdust Pellet Machine
Raw Material Source Of Wood Sawdust Pellet Machine

Proper training and provision of appropriate tools and logging equipment can do much to improve the methods of harvesting so as to substantially reduce the excessive wastes, which could otherwise represent a higher yield of solid wood or a source of fuel.

However, although forest residues may appear to be an attractive fuel source, collection and handling costs must be taken into consideration, as well as its loss as a valuable soil nutrient. The viability of its use may be improved if collection be undertaken at the same time as log extraction, with shared equipment and management, whereby logging slash and marginal timber may be collected and chipped using portable or semi-portable chippers placed in the immediate logging areas. By ensuring that leaves, bark and thinnings are left behind, the soil's nutrients would not be depleted.

Transport costs are also a critical factor in the use of forest residues, due to the low heat values of such bulky material, for which reason distances are to be kept low so as not to incur unnecessary expense if the waste is to remain economically attractive as a fuel source. Chipping of the residues does afford some degree of compaction, also several processes are in operation which further compress the waste into more manageable forms, such as pellets, thus improving their bulk handling characteristics. However, due to the high capital and operating costs involved, densification tends to be only financially viable when the waste needs to be transported over long distances.

Whilst regarding wood as a renewable energy resource, consideration should also be given at regional or national level to encourage the collection and use of logging residues, be they branches, tops or whole-tree utilisation, to the establishment of energy plantations using quick growing species especially selected for their value as a fuel.

II. Mill-site Generated Wood Waste

If one considers that approximately 45 to 55 percent of the log input to a sawmill or plywood plant is to become waste, it would be illogical not to maximize its use as a fuel source, if no other profitable market outlet can be found.

II. Mill-site Generated Wood Waste
Mill-site Generated Wood Waste

The actual production of residues, or waste, generated from the manufacture of wood products, differs from plant to plant and depends on several factors, from the properties of the wood to the type, operation and maintenance of the processing plant. However, mean averages apply to each type of industry, which, for developing countries have been detailed in Tables 1, 2 and 3 of Appendix VI, and summarized in Table 2.

Table 2. Proportion of residues generated in selected forest products industries

  Sawmilling Plywood Manu. Particleboard Manu. Integrated Operations
% % % %
Finished product (range) 45-55 40-50 85-90 65-70
Finished product (average) 50 47 90 68
Residues/Fuel 43 45 5 24
Losses 7 8 5 8
Total 100 100 100 100

All wood waste and bark, which is also commonly referred to as hog fuel due to the process of reducing the residues in size in a "hogger", has a value as a fuel, although it is produced in a wide range of sizes with varying moisture contents, as shown in Table 10, and comprises mainly of the following:

- Bark, which makes up some 10 to 22 percent of the total log volume depending on size and species, can in itself represent a serious waste disposal problem unless it can be used as a fuel or removed prior to log preparation;

- Coarse residues, such as slabs, edgings, off-cuts, veneer clippings, sawmill and particleboard trim, when reduced in size, make ideal fuel, especially when dry. They also have a resale value as pulp and particleboard furnish;

- Cores, from plywood peeler logs, are generally sold to sawmills or lumber or as pulp chips;

- Sawdust, being a product of all mechanical wood processing operations, particularly sawmilling, is generally not regarded as a prime pulping material due to its small size, although it proves to be acceptable for the manufacture of particleboard;

- Planer shavings result from dimensioning and smoothing lumber, plywood and particleboard with planers during the finishing stage. They are considered ideal for particleboard production and are particularly good for heating kilns and dryers;

- Sanderdust is produced during the abrasive sanding of lumber, plywood and particleboard during the finishing stage. Due to its size and very low moisture content it is well suited for direct firing;

- Particleboard waste, being in the order of five percent, is negligible compared to that generated in other mechanical wood-based industries, as it is largely recycled within the production process. In fact the waste from sawmilling and plywood manufacture make up a large part of particleboard furnish.

III. Integrated Production

As previously indicated, the sawmilling and plywood industries each produce between 40 to 55 percent of waste from their incoming wood supply, with heat values in the range of 17 to 23 MJ/kg (dry weight), more than sufficient to meet their own energy requirements. Nonetheless, it is considered uneconomical to generate their own electricity from residues unless they have an additional sales outlet for the surplus power.

However, particleboard production produces little waste, being in the order of five to ten percent, and insufficient to cover the needs for heat, yet, would be resolved in the case of an integrated operation of all three industries - market forces permitting (25).

Sawmilling, veneer, plywood and particleboard production lend themselves quite readily to integration, with the advantages of shared waste handling processing facilities and services, and the maximum benefit derived from the use of the residues as a raw material and fuel, whereupon the surplus energy could be fully and economically used to the best advantage. But, the scale of such a complex may be beyond the means- of some developing countries.

IV. Alternative Uses Of Residues

Residues derived from the forest industries normally do have alternative outlets, as chips for pulp manufacture, raw materials for particleboard and fibreboard manufacture and as fuelwood and building materials to local inhabitants - all dependent on market location and demand. Listed below are several outlet areas.

Sawmilling - edgings and slabs - low cost building materials, fuelwood and pulp manufacture
- barked edging chips - pulp manufacture and fuelwood
Plywood Manufacture - peeler log cores - lumber manufacture
- core chips - pulp manufacture
- veneer chipping and chips - fuelwood
Particleboard - uses all the above mentioned residues as raw material for board manufacture, and the majority of its own residues are recycled within the process.  

Alternative markets and the sale value of wood residues must, of course, be taken into consideration when undertaking a feasibility study of a specific manufacturing plant, so as to assess its availability for fuel and to account for its opportunity value in manufacturing cost analysis.

Apart from the use of residues as a potential fuel source to meet a plant's own energy requirements, its direct sale, or as pellets or briquettes, as fuel to other industrial users or electricity generating companies is becoming an attractive venture for some mills in developed countries. However, one must take into account its historic use in certain regions, as being a basic fuel for domestic heating and cooking in the smaller cities, villages and rural areas.

In some countries the use of wood residues as a raw material for the production of say pulp and paper and particleboard, is deemed to be more beneficial to both the local and national economic and social well-being, than its use as a fuel. (100) This being due to the value added element in the form of labour and trade derived during the various stages of processing the residues into a saleable product, whereas its impact as an alternative fuel is solely to reduce oil imports - a debatable issue.

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