According to the findings of the study the suppliers of biomass for energy are many and varied from small timers to large scale established suppliers. Most of the small timers are adhoc suppliers of biomass, and are dependent on what is available within short distances, and therefore their supplies are irregular and industries cannot depend on them for obtaining their biomass requirement. These small timers deal with few factories on personal basis. These groups usually engaged in supplying biomass from home gardens (trees removed for various reasons), construction wooden waste, timber off cuts, etc., which are not available on regular basis. Fig. B-1.1 shows a typical biomass source for small scale suppliers.
The large suppliers on the other hand have arrangements to supply large quantities of biomass on regular basis. They usually have entered into agreements with the factories they are supplying. Large scale supply of wood logs, wood chips and sawdust are included in this group. These groups usually engaged in supplying wood logs from rubber trees removed for replanting, saw dust and off cuts from timber mills.
There are a few organisations engaged in the growing and supplying of Gliricidia as a business. Many of them supply Gliricidia for a single industry on mutual agreement and power generation plant through the organisation of an out grower community. One of the big drawback of this system is that suppliers depend more or less on a single client for selling their produced biomass, and in case the client close the operation of the factory/plant the supplier would be in trouble unable to sell their produce.
There is another group engaged in supplying wood chips and briquettes. They are sort of well established entities due to considerable investment needed in setting up their operations. This group have their operations and activities put in the public domain. They add value to the raw biomass – produce wood chips, briquettes, etc. – and sell the products at a premium price.
Technologies and technological equipment used by them can vary depending on the level of operation and the technological processes they employ.
Small timers do their business with minimum facilities. Many of them do it as a part-time activity – coming into action only when some disposable biomass source is available within their reach. Equipment used includes hand tools for preparation of wood before transportation – axes, ropes, chain saw, machete, digging bar, etc. (see Fig. B-2.1), and for transportation – two wheeled tractors with trailer (mostly hired for the purpose), half lorry without cover, four wheeled tractor with tipping trailer, etc. (Fig. B-2.2)
a) Small scale suppliers
b) Large scale suppliers of woody biomass
c) Suppliers of Gliricidia
d) Suppliers of wood chips & briquettes
e) Suppliers of saw dust
Coppicing is cutting back trees or shrubs at ground level to extract fuel wood or timber and to stimulate ratoon growth. Once coppiced, new growth from old stump is called coppice, which is repeatedly harvest to obtain fuel wood. Coppicing ability determines by length of coppicing circle, harvestable volume/weight per circle and number of circles for one stump. Increased rotations compared with other species and increased volume or weight per shorter rotation is merits for selection criteria. Sometimes this is a traditional method used for woodland management still in practice.
Large scale suppliers use hand tools as well as heavy equipment for harvesting and pre-preparation of fuel wood. Hand tools used by this group includes – axes, digging bar, machete, chain saw, etc. (Fig. B-2.1). They use backhoe on track or tirfor (monkey jack) for uprooting trees Fig. B-2.3). Fig. B-2.4 shows how lorries are modified to transport large quantities of wood logs. Several attempts made to witness uprooting of rubber trees did not materialised as the suppliers were not willing to give an opportunity. However, discussions with a few suppliers revealed that most of the heavy equipment such as backhoe, transport lorries, etc., are taken on hired basis. Typical lorry load of wood logs averages 10 tonnes to 12 tonnes. A backhoe can uproot up to 200 rubber trees a day. Once uprooted, logging to desired size is done on the site itself using a hand held chain saw (driven by a petrol engine- Fig. B-2.1). As informed by the suppliers there is no need for storage facilities as the logs are delivered almost immediately when a sufficient load is produced.
Supply of Gliricidia has been developed on ‘Dendro’ concept and was handled by a few organised individuals and organisations. They have developed supply chains for Gliricidia mainly targeting very specific applications on individual basis. For example when a power project based on Dendro concept is implemented the supply chain is established to supply Gliricidia for that project. But, some organisations, who are also suppliers of equipment for BECS, have organised themselves for supplying Gliricidia for their clients – both thermal and power applications. In all cases Gliricidia supply has been based on out grower concept through community participation. Hence, Gliricidia supply chain is more or less a part of the development project and they survive each other just as two sides of a coin.
Today, however, Gliricidia has begun to lose its credibility as a source of biomass for energy. Many BECS, both direct combustion and gasifire systems, which used to depend on Gliricidia a few years ago (say around 2006 onwards) has fully converted to other types of biomass now. Gliricidia wood is cut into small pieces (~ 4″ to 6″) before used in the BECS. Fig. B-2.5 show a few technological equipment used for this purpose. Hand tools (Fig. B-2.1) are used for harvesting Gliricidia.
Source: Tirappane 500kWe Gasifire-Gen power plant (Provided by Eng. P R Wijewardena) Figure B-2.6 shows equipment used to transport harvested Gliricidia wood to the plant and feedstock handling equipment at the plant yard. Fig. B-2.7 shows storage of Gliricidia feedstock at Tirappane 500 kWe power plan
There are very few wood chip suppliers. Some of the industries produce their own wood chips for their BECS. Producing and supplying wood chips require range of equipment and facilities, such as biomass handing equipment inside the chipping plant – loaders, tractors with trailer, etc., conveyors, chippers and storage facilities. Fig. B-2.8 shows some equipment used and typical storage facility of a wood chipping plant.
It was noted that there are three basic designs of chippers. Box B-1 give a description of commonly used wood chippers for producing wood chips for BECS.
Disk chippers consist of a large diameter steel disk, generally set either at right angles to the direction of feed, or at an angle, that incorporates one or more hardened chopping blades, each with an associated slot in the disk. The disk rotates at high speed and the blade cuts regular chips from the end of the biomass as it is fed in, usually by a ridged roller system. A fixed steel anvil or knife in the throat of the chipper forms the opposing cutting edge. The knives may be set radially on the disk, or at a slight offset. They are usually straight, but may be curved. On the back face of the disk there may be paddles to generate airflow to eject the chips and they may incorporate serrations to act as sliver breakers to attempt to prevent the ejection of long slivers.
The size of chip produced by most disk chippers is principally determined by the number of knives and their settings, by the rotational speed of the disk and the material feed speed, which is usually determined by the feed roller speed. Varying these parameters or removing one or more blades in a multi-blade unit and blanking off the associated slot allows chip dimensions to be adjusted. Some disk chipper can have difficulties with thin, whippy material especially when it is fed in at a slight angle, as this can lead to the material being torn rather than cut cleanly, producing long slivers which can cause bridging in fuel feed systems.
Blades are replaceable and can generally be re-sharpened. Blades can be blunted or damaged by dirt, grit, inclusions, ice or frozen timber, and in high throughput situations can require sharpening or replacing more than once a day. Blunt blades can lead to irregular chip sizes, more slivers and greater power requirements. It is highly advisable to ensure a supply of spare blades so that they can quickly be replaced as required and sharpened at convenience. One design uses circular blades that can be rotated when one section becomes blunt to allow a new, sharp face to be presented.
These use a rotating drum with one or more hardened blades, cutting onto an anvil(s) mounted in the throat of the feed. The drum may be parallel sided or waisted in the middle. The feed mechanisms are similar to those of disk chippers or may use a conveyor or gravity. A separate fan may be incorporated, or the blades themselves may generate the airflow to blow the chips out.
Chip size is determined by drum speed, feed speed and the number of blades. The axis of the drum is at right angles to the direction of feed, and the whole width can be used. If material can twist in the throat during infeed it can result in long slivers. One design uses a drum that is tapered to the centre, partly to try to minimise this. High quality chips can be achieved with some designs, particularly in combination with a screen. Drum chippers are flexible in being able to handle a range of different material, including twiggy material and round wood.
As with disk chippers, blades are replaceable and can generally be re-sharpened. Blades can be blunted or damaged by dirt, stones inclusions or ice, and in high throughput situations can require sharpening or replacing up to several times a day. Blunt blades can lead to irregular chip sizes, more slivers and greater power requirements. It is highly advisable to ensure a supply of spare blades so that they can quickly be replaced as required and sharpened at convenience.
These operate on a different principle to disk and drum chippers. The cutting blade is a rotating, tapered, helical screw thread with a hardened cutting edge, which cuts against the inside of the housing. The axis of rotation is in line with the direction of feed and the helix draws material into the chipper and is the only feed mechanism required. Chip size is determined by the pitch of the screw, and can be varied by replacing the blade with one of a different pitch. The base of the blade generally includes a disk to generate the airflow to propel the chips out, and may also incorporate a sliver breaker. As material is drawn into the chipper by the action of the screw a separate mechanical feed system is not usually employed.
Screw chippers can produce high quality, even sized chips, with good throughput. However they typically require high drive powers. Owing to the feed mechanism it is very difficult to withdraw material once it has started to be drawn in. Screw chippers tend to be quieter in operation than other types.
As with all chippers it is important to ensure that the blade remains sharp, especially if high quality chips are required. The entire helical blade can be replaced, or can be sharpened in situ using a jig provided by the manufacturer. The hardened face can be reconditioned by welding and grinding
Source: Biomass Energy Centre; www.biomassenergycentre.org.uk
For delivery of wood chips to the end users, the chippers use large lorries and tippers with specially build closed bodies to enable unloading of wood chips easily. Fig. B-2.5 shows such transporters unloading wood chips inside a factory storage yard.
Sawdust in retrievable form is produced only by timber mills mainly due to processing (mainly sawing) of timber in large scale. Saw dust is first packed into bags (mainly polypropylene woven bags) and load into Lorries and transported to industrial users. There is no special equipment used for this purpose other than normal lorries meant for goods transport.
One of main barriers for improving efficiency in technology used in supply chain is the non-availability of standards for biomass used in BECS. This has prevented introduction of new technology, especially for improving quality of biomass produced and transporting biomass. For example, size of wood logs vary widely and, therefore, introduction of standardised handling equipment and transportation vehicles are difficult. Similarly, no standards are available for the wood chips, and, therefore, there is no requirement for introducing modern wood processing equipment which can produce wood chips of pre-determined quality. Refer item 6.2.2 in Part A for more details. Lack of standards/regulations against overloading of biomass, especially wood logs, prevents proper adaptation/modification of existing lorries/tippers/tractors, etc. for safe transportation of biomass to end users. Fig. B-2.6 shows a truck overloaded with biomass undermining road safety