Energy content of the fuel;
Bulk density; Moisture content ; Dust content ; Tar content ;
Ash and slagging characteristics.
4.2 VIABILITY OF FOREST RESIDUE RECOVERY FOR BIOENERGY
A biomass recovery industry cannot succeed without being integrated into the forest industry as a whole. The recovery of logging residue can be carried out with a number of different systems, depending on where the residue is made available and on whether the current operation planning can be aptly modified (Visser, Spinelli and Stampfer, 2007).
Efficient recovery of high quality in-forest residues depends on good communication between biofuel contractors, harvesting operators and harvest planners. There are several factors critical to producing a biofuel which include: good access to residue for on- highway truck and trailer units; high volumes of residue collected in one place; and dry and clean residue (BKC, 2009b).
In Sweden, Finland and Norway a significant proportion of their harvest is from ground- based systems, which are highly mechanized. These have in many areas had their work methods adjusted to leave the logging residue in piles (as opposed to spread out) to enhance the efficiency of the residue harvesting operation (Visser et al., 2007). Three principal systems have been developed for harvesting these residues (Visser et al., 2007):
Extract to roadside with a forwarder, pile and cover, store, chip with a trailer mounted mobile chipper, transport to point of use;
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Pile in the cut-over, bale with purpose-built residue baler mounted on a forwarder, extract bales to roadside, store, transport bales to point of use, chip whole bales at point of use;
Pile in the cut-over, store, chip with a chipper forwarder, tip into setout bins, transport bins to point of use.
The chipper forwarders/terrain chippers are reported to be losing favour, in part due to handling issues around getting the chipped residues from the forwarder on to a truck, and in part due to the low utilization and subsequently high cost of the chipper function. A large fixed installation chipper may operate at one-third of the cost of a mobile unit (EECA, 2007).
Much modelling and research has been done in assessing the efficiency of residue recovery systems. Those with the least handling that take the residues from the forest directly to the point of use were found to be the most efficient. In general there are five different production systems or flows that can be used. Intermediate handling and processing add cost. The following flows are the simplest and most efficient, depending on the specifics of the situation, including transport distances (EECA, 2007):
1. Raw residues transported directly from forest to the point of use and then processed;
2. Raw residues transported from forest via a central yard or accumulation point to the point of use and then processed;
3. Raw residues transported to a central yard for storage and/or processing; comminuted material transported to point of use;
4. Raw residues processed at source and transported via a central yard to a point of use;
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To improve the viability of using forest residues as a biofuel, various issues need to be addressed at harvest planning stages. Harvesting operations can affect forest residues in a variety of areas:
Access to residue: Planning is required for on-highway configured trucks and/or low- loaders to access residue piles. This access must be maintained for periods of up to 6 to 12 months following completion of harvesting operations (BKC, 2009b).
Storage of residue: Planning is required for either in-forest storage or residue removal to an alternative site. In-forest storage on dry, open ground can result in reduced moisture content, minimal dry matter losses and reduced cost of delivered energy (BKC, 2009b).
Residue location: There are three possible systems of residue location. They are (BKC, 2009b):
Landing residues: Landing residues are the most cost effective residue for producing biofuels as they are already at roadside. Hauler apparatus tend to produce more residues and often have slash disposal issues which are mitigated by removal (BKC, 2009b).
Ground-based cutover: Residues from a ground-based harvesting operation can be collected from the cutover by forwarders or bundlers. This will only be viable if the demand for biofuel increases, with an accompanying increase in value (BKC, 2009b).
Hauler cutover: Collection of residues from steep hauler country is not currently viable or practical.
Log making systems: The volume and size distribution of residue is influenced by the type of log making being used: motor manual, computer optimized, or mechanized.
Computer optimized log making tends to produce more residues in longer sections than motor manual operations. Mechanized operations tend to produce more residues in more
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pieces than motor manual operations (BKC, 2009b). Segregation of different residue types (pulp or chip logs, stem sections and large branch pieces) is important and can enable separate processing of residue types into higher value products such as pulp chips (BKC, 2009b).
Crop factors: The nature of the crop can also have a marked influence on the volume of residues. Open grown crops with significant stem malformation will produce relatively high volumes of residue. A high quality crop, with well formed stems and limited branching will produce low volumes of residue (BKC, 2009b).
4.3 CONSIDERATIONS FOR FOREST BIOENERGY FACILITY