Publications
Publications about harvesting, drying, preparation and processing of wood fuels and best practice and advice on woodfuel production
Forestry Commission Project Report 43
This report summarises work carried out by Technical Development during 2009-2011 into Short Rotation Forestry (SRF) establishment operations in England. Operational trials into SRF establishment were carried out at the Energy Forestry trial site at Carlshead Farm, North Yorkshire.
Time studies to determine operational outputs, costs and fuel usage have been completed on the following operations:
Subsoiling studies were carried out on previously ploughed ground and unploughed ground.
Subsoiling outputs of 0.340 ha/shr (78.67 £/ha) were achieved on unploughed ground and 0.668 ha/shr (40.06 £/ha) on ploughed ground. Manual herbicide application achieved an output of 0.215 ha/shr (56.58 £/ha). Planting output was 0.0648 ha/shr (154.33 £/ha).
Forestry Commission Project Report 6
Technical Development developed a paper and an electronic version of the ‘Estimating Woodfuel potential: Measurement protocol’ in liaison with Biometrics, Surveys and Statistics Division.
Measurement protocol
Forestry Commission Project Report 28
This report summarises the proceedings of a joint IEA43 and LTSP workshop held 1-4 June 2010 in Kamloops, British Columbia, Canada. This workshop focused on the interface between the growing and harvesting of sustainable biomass and long-term sustainability aspects, specifically in relation to soils.
Potential of Sitka Spruce natural regeneration for biomass markets – Scoping project
Forestry Commission Project Report 13
This report looks into the potential of harvesting natural regeneration of Sitka spruce for woodfuel production. This fuel could prove suitable for large scale biomass plants, but the current economics of the supply chain mean that this type of harvesting would probably not be viable for the forest owner unless it also helped achieve other management objectives.
A range of equipment potentially suitable for harvesting natural regeneration at different growth stages is identified, but performance, impact on stand quality and future operational aspects need to be assessed in field trials to deliver a full evaluation of their potential.
Short rotation forestry
Forestry Commission Project Report 9
Short Rotation Forestry (SRF) and Short Rotation Coppice (SRC) are methods of growing high yielding energy forestry crops. This series of studies aims to establish output and cost information for operational scale establishment of SRC and SRF, gather experience of mechanised planting methods used, and collect information on fuel usage. The efficacy of SRC planting machines has long been established (Deboys 1994). This research show however, that mechanised planting machines are also capable of establishing SRF on ex-agricultural sites with a range of broadleaf and conifer species.
Five establishment studies were carried out over a range of former land uses and with different tree species. Outputs for these planting studies in SRF ranged from 0.13ha/shr for Scots pine/birch mixture on ex-pasture ground (target density 2700 trees/ha) to 0.34 ha/shr for pure Scots pine on ex-arable ground (target stocking 2700 trees/ha; the range of outputs achieved includes crops established at different densities). Planting two mixed species had greater impact on reducing output than any other variable in the study owing to the increased handling when the operator alternated between different species.
Fuel usage figures of 16.7 l/ha for SRF and 5.4 l/ha for SRC will allow comparison with future studies and increase understanding of the energy balance of energy forestry crops.
Small scale briquetting
Forestry Commission Project Report 23
An investigation based on a literature and internet search to establish the scale and nature of woodfuel briquette manufacture and supply in Britain was carried out, and followed up by case studies and further enquiries. The study aimed to identify the potential for production of this fuel as an alternative to wood pellets at the smaller scale.
A wide range of manufacturers and suppliers of briquettes was identified, including several operating at a very small scale, with the product aimed primarily at the domestic space heating market at all scales of production. Smaller markets also exist during the summer for barbecue fuel and outdoor heating.
Two distinct processes were identified; at the small scale the use of dry woodworking co-products in relatively simple, low-cost systems was standard practice, whereas at the larger scale more complex systems included comminution and drying of coarser and wetter material. Both scales of production appeared to be potentially profitable.
Small-scale systems for harvesting woodfuel products (PDF-398K)
Technical Note 9
Stump harvesting literature review
Forestry Commission Project Report 46
This report is a literature review covering the operational aspects of stump harvesting, identifying relevant stump recovery equipment and methods used throughout Europe and North America. Stump harvesting of conifer clearfell was found to be principally used in Scandinavia, destumping in North America confined to reducing fungal root rot. The management, market and ecosystem advantages and disadvantages are described with reference made to current environmental best practice and knowledge.
Stump harvesting is generally carried out using an excavator and forwarder combination. Excavators are equipped with either a static rake attachment or a splitter-puller attachment. Stumps are uprooted, split, shaken to remove soil and piled for later extraction by forwarder. Vehicle outputs were found to be broadly comparable between Scandinavia and the UK, although yields were greater in UK trials. Cost of stump harvesting in the UK is in the region of £21.00–£29.00 (£6.00– 8.50/t (green) to uproot, £3.00–8.50/t (green) to extract and £12.00/t (green) to transport to point of use). As stumps can include contamination from soil and rock, comminution is best suited to large crushers, either at terminals or large end users.
The chip quality also limits stump-chip use to larger facilities. Stump fuel quality does however improve with storage making it an ideal blending fuel for moderation of seasonal demand. The high cost of stump harvesting and transport, and the limited number of large biomass facilities close to large forest areas, appear to be the principal reasons for its limited UK uptake (as of 2011). Energy input is also high for stump harvesting. Whilst the energy balance is very much positive, stump harvesting has higher energy inputs and CO2 outputs than residue bundling or other forest woodfuel chip production systems.
TDB_ODW1203.pdf (PDF-107K)
OutDoor Workshop 12.03
Technical Development short rotation forestry project update 2011
Forestry Commission Project Report 44
This report summarises work carried out by Technical Development during 2010–2011 into Short Rotation Forestry (SRF) establishment operations in Scotland. During 2008–2009 Technical Development undertook time study of establishment operations in SRF and SRC at the Forestry Commission trial site at East Grange with follow-up studies on the management operations on these sites carried out in 2009-2010.
During 2010–2011, time studies have been carried out into establishment operations for SRF in the north (Sibster Farm, Caithness) and west (Aros, Isle of Mull) of Scotland, allowing output comparisons with the site at East Grange. Time studies have been completed on the following operations:
Technical Development woodfuel research catalogue 1998-2008
Forestry Commission Project Report 3
This report provides a catalogue of summaries from 28 woodfuel-related reports produced by Technical Development (TD) within the last 10 years. Report summaries are organised into the themes: harvesting, chipping, drying, woodfuel & burner specifications, wood pellets, residues, small scale harvesting, short rotation coppice, supply chain, transport and other subjects.
Tractor based mechanised harvesting in sweet chestnut coppice
Forestry Commission Project Report 40
Increasing the use of wood as fuel and the proportion of woodlands under management are both Forestry Commission objectives for Great Britain. Coppice woodlands are a common stand type in southeast England and a large proportion are undermanaged.
Coppicing has historically been carried out using manual and motor manual methods. The use of a harvester presents an alternative to declining manual working.
A Valtra T160 tractor fitted with a roof-mounted crane and Keto 51 felling head was studied in neglected coppice stands. The sweet chestnut (Castanea sativa) stands had been coppiced 17 and 27 years previously. Mean diameter and stems per hectare >7 cm were 8.2 cm and 4333 for the younger stand, and 12.0 cm and 3800 for the older stand. Three products were cut from the stands; 4 m woodchip poles, 7 foot firewood logs and 1.5 m signposts. Volume yield was 202 m3/ha for the younger stand and 305 m3/ha for the older. Machine costs and outputs for the older and younger stands were 2.00 m3/shr and £21.22/m3, and 1.67 m3/shr and £26.08/m3 respectively. The machine coped well with coppice working although a greater than normal number of chainsaw malfunctions were experienced due to the tendency for the densely packed stems to pinch the saw. The delays associated with this lead to a suggestion of a greater allowance to be made for this. The conversion factor of 1.416 that is normally used for grapple harvesters would be increased for this harvester and operation to 1.664 to allow for 41% of other work.
Trial of portable moisture meters
Forestry Commission Project Report 10
This project aimed to identify the types of portable moisture meter which are most likely to be suitable for use by woodfuel suppliers at the small to medium scale and to test their accuracy against the oven dry method of determining moisture content (MC).
The materials used during the trial were roundwood billets of broadleaved and coniferous species, both green and seasoned, and woodfuel chip samples of varying MC. Two types of meter were tested, measuring MC in relation to either resistance or capacitance. The first type used electrode pins or probes to measure electrical conductivity between two points, while the second used a metal container to measure the dielectric constant within a known weight of material.
The readings obtained in roundwood with the resistance meter were extremely variable, particularly in coniferous species. It is not thought that the system tested is likely to provide a simple, accurate way of assessing MC in roundwood due to the apparent variability of moisture levels within a log, compared with the very localised measurements the system obtains.
The readings obtained in woodchips using both types of meter were more consistent, both with each other and with laboratory figures obtained by oven drying and weighing samples. However, only the capacitance meter readings matched laboratory values with both chip samples. The resistance meters may be less accurate at moisture levels around 30%, which could be problematic given that target MC for woodfuel chip in small to medium scale applications may be greater than this. More work would be required to confirm this initial indication. As with roundwood, the resistance meters obtained very localised measurements in woodchip, which would require relatively intensive sampling to obtain a reliable estimate of average MC, whereas the capacitance meter measures a larger sample.
Woodchip drying
Forestry Commission Project Report 45
Increasing the use of wood as fuel and the proportion of woodlands under management are both Forestry Commission objectives for Great Britain. Production of woodchips for fuel is increasing, and the sector is developing quickly. Interest in woodchip drying has increased as many suppliers have run short of seasoned timber and chips during trading though recent winters, requiring unseasoned wood to be chipped. There is also a desire to reduce the capital and space tied up in timber seasoning. Active drying would allow chip suppliers to be more reactive to markets whilst minimising the need to hold large stores of drying timber.
In a review of the literature covering commercial chip drying, this report has identified a shortfall of operational information and guidance. Whilst the mechanisms of chip drying are well understood, particularly those associated with short rotation coppice (SRC), information on operational drying is scarce.
Large scale drying occurs on an industrial scale of tens or hundreds of cubic metres per hour and has a large demand for infrastructure. Small scale drying often uses converted trailers and buildings, using fans to force air through chip piles. Data suggests that green chip can be dried relatively quickly (2–3 days) to 25–30% with minimal energy input, using fan and ambient air. Further reduction of moisture content to below 20% requires longer drying time if energy input is not to be excessive. Reduction can take place in around 6 days for warmed air or over several weeks for ambient air. Reduction of moisture content from 34 to 7.5% was found to be possible in 24 hours, but the energy used far exceeded the energy gained by a factor of 3–4. Case studies are required to confirm drying rates for these approaches and calculate energy balances.
Woodfuel boilers installation design guidance (calculators and spreadsheets)
Forestry Commission Project Report 51
Three calculators developed to assist with the design of wood-fuelled installations have been created by Technical Development, providing guidance for:
TDB_ODW1201.pdf (PDF-370K)
OutDoor Workshop 12.01
Woodfuel harvesting from coppice restoration
Forestry Commission Project Report 27
This report presents the results of a coppice restoration with motor-manual felling and forwarder extraction in an oak (Quercus robur) and ash (Fraxinus excelsior) stand of c. 75 years of age. The mean diameter at breast height (dbh) and volumes were respectively 20 cm and 0.282 m3 for the ash and 20 cm and 0.299 m3 for the oak. The operation consisted of cutting all trees and understorey and only keeping selected standards at a density of approximately 40 stems/ha. A short wood system was adopted where 2.2 m length firewood products were cut in majority.
The observed outputs were 0.67 m3/shr for motor-manual felling corresponding to a £24.28/m3 felling cost, and 2.22 m3/shr/100 m extraction distance with a tractor based forwarder, corresponding to a cost of £22.28/m3/100 m extraction distance.
The substantial amount of unmarketable material contributed greatly to the felling costs, and the forwarding costs were affected by the relatively small size of the loads.
A low-impact extraction system, the Iron Horse, was also evaluated as part of this study. It showed a good ability to travel creating a minimal impact, but its full potential could not be evaluated as the forwarding configuration, as well as the products’ specification, limited the load size.
Careful consideration of harvesting systems and equipment best suited to a given operation will help to achieve the best quality work and minimise costs.
Woodfuel information pack
Brings together key basic information about many aspects of using wood for fuel. These include background on benefits, renewable energy targets and policy, conversion, end users and systems
Woodfuel processors for the small and medium scale
Forestry Commission Project Report 42
Increasing the use of wood as fuel and the proportion of woodlands under management are both Forestry Commission objectives for Great Britain. The domestic firewood log market is buoyant and represents a potentially valuable end-use for timber from undermanaged woodland. In order to decrease production costs, firewood processors can be used rather than manual cutting and splitting. Most information on firewood processors is derived from the manufacturers, either processing in Scandinavian conditions or using solely coniferous roundwood in GB conditions. This study aims to provide information on working practices and outputs for timber types likely to be produced by undermanaged woodlands.
A study of a Hakki Pilke 2X processor was made, investigating costs and outputs in comparative studies of good and bad form conifer (pine), chestnut and birch, of a hardwood mix, and of oak of very poor form. The mean volume of the timber being processed had the greatest effect on outputs; around 61% of variation being explained. Poor form led to difficulties in processing and handling, and a consequent drop in outputs of around 25%. Very poor form such as presented by the oak led to a drop in output of around 60% and was virtually unworkable. Processing costs were found to be as low as £33/m3, for good and larger volume material, around £41/m3 for average material, and up to £108/m3 for very small and poor quality material. Processing rates were found to be lower than generally quoted by manufacturers; 0.43 –1.40 m3/bhr, 0.29 to 0.96 m3/shr.
Whilst firewood can be seen to be a good market for timber from undermanaged woodland, issues such as small piece volumes and poor quality mean that work cannot be fully mechanised and processing costs are likely to remain relatively high.
TDB_ODW1202.pdf (PDF-190K)
OutDoor Workshop 12.02
Woodfuel supply chain best practice: Guidance review
Forestry Commission Project Report 47
Woodfuel supply chains include the steps involved in the woodfuel production process from standing tree to the point of use. Supply chain elements include harvesting, processing, drying, conversion, storage and transport of woodfuel through the production process. The woodfuel supply sector in Britain is still developing, and there is a need for information to support supply chain logistics and best practice. This report identifies existing published guidance on woodfuel supply chains, details of which have been gathered through literature search and consultation with woodfuel country representatives in England, Scotland and Wales.
This review indicates that while woodfuel supply chain information is available, it is fragmented. Much guidance is case study based, reporting experience from existing supply chains, sometimes without any optimisation or refinement. Some of the best information is based on European experience, however due to different site, crop, market and resource considerations some of this experience cannot be directly applied to Great Britain. Further comprehensive guidance on some aspects of woodfuel supply chains including harvesting methods, moisture content and quality assessment, and point of use handling and storage would benefit the development of the woodfuel sector in Britain.
Woodfuel supply chain case study: Medium scale woodchips supply
Forestry Commission Project Report 17
As part of the ongoing programme of work aimed at identifying and promoting good practice in the woodfuel supply chain, Technical Development (TD) studied the operations of Midlands Wood Fuel Ltd, a woodchip supply company based in the West Midlands, and Worcestershire County Council, one of their customers.
This work highlighted that effective communication between boiler user/operator, fuel supplier and boiler installer is critical to ensure an appropriate design, and smooth daily functioning of wood-fuelled applications. A clear understanding of mutual requirements and of how they translate into technical and practical terms needs to be established during the planning phase of any boiler installation.
As woodchips are a relatively low value product, all efforts also need to be made to reduce unnecessary production and delivery costs by optimising logistics. To ensure the boiler is run efficiently and with minimal emissions it is also important that fuel supply contracts that support the supply of good quality fuel are developed.
Woodfuel supply chain case study: Small scale log supply
Forestry Commission Project Report 8
As part of the ongoing programme of work aimed at identifying and promoting good practice in the woodfuel supply chain, Technical Development studied the operations of Edistone Ltd., a small scale firewood processing business based in Wales. The study also took into account the views of some local firewood customers.
This work highlighted that at all stages of the supply chain, simple steps can be taken to ensure efficient use of resources and time, and to limit the physical strain on machinery operators. Customers’ requirements need to be clearly identified, and the successive organisation and timing of operations defined to meet these requirements.
Woodfuel supply chain research requirements
Forestry Commission Project Report 32
In order to update the research priorities for the Technical Development Woodfuel Operations programme, a number of stakeholders within the Forestry Commission and the wider industry were interviewed.
The requirements identified were prioritised and built into work proposals for the coming years, and relayed when relevant to other parts of Forest Research or the Forestry Commission.
See also research related woodfuel publications
These publications were produced by Technical Development.
Some (mainly older) publications are not available online. If you do not find what you are looking for, please contact Bill Jones.