Managing chipper knife wear to increase chip quality and reduce chipping cost

Wood biomass is turned into industrial fuel through chipping. The efficiency of chipping depends on many factors, including chipper knife wear. Chipper knife wear was determined through a long-term follow-up study, conducted at a waste wood recycling yard. Knife wear determined a sharp drop of productivity (>20%) and a severe decay in product quality. Dry sharpening with a grinder mitigated this effect, but it could not replace proper wet sharpening. Increasing the frequency of wet sharpening sessions determined a moderate increase of knife depreciation cost, but it could drastically enhance machine performance and reduce biomass processing cost. Since benefits largely exceed costs, increasing the frequency of wet sharpening sessions may be an effective measure for reducing overall chipping cost. If the main goal of a chipper operator is to increase productivity and/or decrease fuel consumption, then managing knife wear should be a primary target.     

Determining long-term chipper usage,productivity and fuel consumption

The Authors surveyed 6 industrial chipping operations for a whole work year, collecting data about machine usage, product output, fuel consumption and chipper knife wear. Despite the challenging work conditions offered by mountain operations, industrial chipping contractors manage to achieve a high machine use, ranging from 500 to over 2,500 h year⁻¹. Product output varies between 18,000 and over 120,000 m³ loose chips per year. In order to acquire enough jobs, operators may travel between 1,500 to over 20,000 km in a year. Industrial chipping contractors adopt different operational strategies to achieve their production targets, and they equip accordingly. Some operators prefer to tap smaller local areas and opt for smaller tractor-powered chippers, which are less powerful and productive than larger independent-engine units, but cheaper and capable of negotiating low-standard forest roads. Others prefer to explore larger areas and achieve higher product outputs, and they opt for larger independent-engine chippers, often mounted on trucks. Long term productivity varies with machine type: tractor-powered units produce between 40 and 50 m³ loose chips per hour, whereas larger independent-engine chippers produce between 60 and 90 m³ loose chips per hour. Specific fuel consumption is about 0.5 L diesel per m³ loose chips, regardless of chipper type. A sharp knife set can process between 200 and 1,500 m³ loose chips before getting dull. Disposable knives last longer and are cheaper to manage than standard re-usable knives.     

The improvement of hog fuel by removing fines,using a trommel screen

The study tested the use of a trommel screen originally designed for compost materials to reject oversize particles from hog fuel, processed from several sources and by two different comminution devices. The experiment consisted in screening material previously comminuted by a convertible crusher, designed to use both hammers and knives. Three different feedstock types were used, and namely: discarded pallets, logs and branches from park maintenance. Each feedstock type came in two different qualities, depending on the tool used for comminution, i.e. hammers or knives. Trommel screen productivity varied between 4.2 t h⁻¹, and 5.2 t h⁻¹ of oven dry material. Screening hog fuel derived from pallets was 30% and 40% less productive than screening fuel derived from logs and branches, respectively. Screening cost varied from 16.2 € t⁻¹ dry material in the case of branches, to 19.9 € t⁻¹ oven dry material for pallets. Screening allowed an increase of fuel quality only when applied to pallet-derived hog fuel.     

An agile chipper truck for space-constrained operations

A new chipper-truck was developed for extending the benefits of industrial chipping to space-constrained landings, normally inaccessible to industrial operations. The new machine was taken for a European test tour, so that it could be tested under conditions considered typical of Mediterranean, Alpine, Central and Nordic Europe. The same machine and operator were used for all tests, which lasted 65 h and produced over 100 chip containers. Productivity varied between 13 and 19 tonnes of green chips per scheduled hour, inclusive of all delays. Fuel consumption ranged from 1.8 to 2.8 dm³ of diesel per tonne of green chips. Machine utilization ranged from 68 to 89%, and it was highest in the Nordic trials, due to the use of pre-parked containers, which dramatically reduced the occurrence of interaction delays. Regional differences were only related to operational layout and organization, which set the Nordic trial apart from all others. Knife wear and screen size had a major impact on chipper performance. The same accounted for cut length. Production of small chips is only justified when the market offers premium prices for this assortment.     

Productivity and woodchip quality of different chippers during poplar plantation harvesting

In this work, the productivity and work quality of different types of chipping machines used for biomass comminution produced by dedicated plantations were evaluated. Drum and disc chippers with different powers were compared with feller-chippers and grinders. Machines were tested using only one tree species (poplar) and two different feedstocks: branchwood (seven-year-old treetops and biomass produced by a vSRC) and whole-trees (materials produced by an SRC). This study showed a similar performance for all types of machines tested in terms of working rate using different feeding systems, i.e., automatic and forestry crane. However, different results were obtained for woodchip quality. The whole tree comminution was able to guarantee the best woodchips, and chippers produced better wood chips in comparison to grinders. The results obtained indicate that productivity is linked to engine power and that feedstock size can influence wood chip quality. Furthermore, feller-chippers are able to guarantee the same productivity and wood chip quality as “conventional” chippers.     

Industrial supply chains and production machinery of forest chips in Finland

Metsäteho Oy surveyed the industrial supply chains used in the production of forest chips in 2006 in Finland. The Metsäteho study also conducted a survey of the production machinery of forest chips used by energy plants in 2007, and provided an estimate of industrial supply chains and future machinery requirements for forest chip production in Finland.The majority of the logging residue chips and chips from small-sized thinning wood were produced using the roadside chipping supply chain in 2006. The chipping at plant supply chain was also significant in the production of logging residue chips. The majority of all stump wood chips consumed were comminuted at the plant, and with only around one fifth comminuted at terminals. The role of the terminal chipping supply chain was also significant in the production of chips from logging residues and small-sized wood chips. It was predicted that the roles of both terminal chipping of logging residues and chipping at the plant will increase by the year 2010. Regarding the production of chips from small-diameter wood, it was estimated that the role of chipping at the plant will also increase in coming years. The proportion of roadside chipping in the production of small-sized wood chips and logging residue chips is expected to decrease.The study estimated that a total of 1100 machine and truck units were employed in the production of forest chips for energy plants in 2007. Increasing forest chip consumption will create considerable demand for additional forest chip production resources in the future.     

Energy and greenhouse gas balance of the use of forest residues for bioenergy production in the UK

Life cycle analysis is used to assess the energy requirements and greenhouse gas (GHG) emissions associated with extracting UK forest harvesting residues for use as a biomass resource. Three forest harvesting residues were examined (whole tree thinnings, roundwood and brash bales), and each have their own energy and emission profile. The whole forest rotation was examined, including original site establishment, forest road construction, biomass harvesting during thinning and final clear-fell events, chipping and transportation. Generally, higher yielding sites give lower GHG emissions per ‘oven dried tonne’ (ODT) forest residues, but GHG emissions ‘per hectare’ are higher as more biomass is extracted. Greater quantities of biomass, however, ultimately mean greater displacement of conventional fuels and therefore greater potential for GHG emission mitigation. Although forest road construction and site establishment are “one off” events they are highly energy-intensive operations associated with high diesel fuel consumption, when placed in context with the full forest rotation, however, their relative contributions to the overall energy requirements and GHG emissions are small. The lower bulk density of wood chips means that transportation energy requirements and GHG emissions are higher compared with roundwood logs and brash bales, suggesting that chipping should occur near the end-user of application.     

The economics of chipping logging residues at roadside: A study of three systems

Three biomass chipping operations of roadside logging residues were studied in New Brunswick and Maine. Two of the operations used a skidder-loader to form the roadside debris into larger piles closer to the road edge prior to chipping. Average chipping productivity ranged from 8.l oven dry Mg per Productive Machine Hour (OdMg PMH⁻¹) to 28.2 OdMg PMH⁻¹ depending on the site and chipping system used. The average cost of chips on board the chip vans ranged from $15.29 CAN OdMg⁻¹ to $25.86 CAN OdMg⁻¹. The chips were transported to three energy plants in Maine. One-way hauling distances varied from 29 km to 105 km.     

Poplar wood chip storage: Effect of particle size and breathable covering on drying dynamics and biofuel quality

Used as alternative energy sources, solid biofuels have the advantage of simultaneously reduce fossil fuel dependence and mitigate climate changes by reducing greenhouse gas emissions. Biomass storage and handling play a key role for wood fuel quality assessment: in particular, the presence of covering systems influences biomass drying process and factors leading to bulk compaction (e.g. reduced particle size) negatively affect woody biomass preservation till final use. To study the effect that particle size and covering have on biofuel quality, Short Rotation Forestry (SRF) poplar trees were harvested and chipped by means of a Claas Jaguar 890 operating machine equipped with a “GBE-1” header for SRF. The chipping procedure was carried out in March 2009 using on the same header both the standard chipping drum and a special on purpose drum designed by CRA-ING to obtain coarser particles. The chipped biomass was subsequently stored in stacks on a paved surface for a 120 days period to evaluate: i) effect of particle size on uncovered stacks drying dynamic and fuel quality, ii) effect of the presence of non-woven tarp on drying and fuel quality of biomasses standardly chipped with the conventional drum. Coarser stack was found to have a less prompt dehydration and, at the end of the storage period, have less energy and dry matter loss. In case of biomass chipped with the conventional drum, at the end of the storage period the effect of covering ended up in wood fuel with significantly higher heating value.     

Effect of grinder configuration on forest biomass bulk density,particle size distribution and fuel consumption

The effect of the grinder configuration, bit type and screen size, on bulk density and fuel consumption when processing forest harvest residues for energy purposes is analyzed. Residues were divided in three size classes based on the piece diameter and length and were processed in a six treatment structured randomized test using a horizontal grinder. For each treatment the basic density, moisture content, bulk density, particle size distribution, fuel consumption and bark and other non-wood substances content was estimated. No effect of bit type or screen size on bulk density was found when processing branches-and-tops size class residue. For the pulpwood and butt-log-chunks size classes, the knife-edge bits tend to produce a denser material explained in part by their cutting capabilities across the grain compared to the normal hammering process using carbide hammer bits. Fuel consumption was only affected by screen size when processing the branches-and-tops size class. For pulpwood and butt-log-chunks size classes, the use of carbide hammer bits for processing increased fuel consumption between 42 and 48% compared to knife-edge bits. Bark and other non-wood substances content accounted for 11% of the total grinding mixture in the branches-and-tops size class compared to 2.5% in grindings from pulpwood and butt-log-chunks size classes. The branches-and-tops size class residue produced denser bulk material compared to the other classes and consumed less fuel due in part to the higher basic density and increasing amount of fine particles compared to the other analyzed size classes.     

Influence of particle size and moisture content on tendency to bridge in biofuels made from willow shoots

Different systems for harvesting and storage of wood fuel from willow shoots give fuels with different particle size distribution, particle shape and moisture content. These factors influence the tendency for wood fuel particles to form a stable bridge over openings, which prevents the feeding of the fuel. The influence of cutting and storage method on the tendency to bridge was studied for chips and chunks made from 3 to 5 year old willow shoots harvested in January and December. Shoots were cut with four different machines to produce five fuel assortments with nominal particle length from 28 to 200 mm, and stored outdoors, in central Jutland, Denmark, in 160 m³ loose volume piles. Some piles were uncovered, some covered with plastic and two were sealed in an airtight silage plastic film enclosure. The bridging tendency was measured at the end of May and September by determination of how wide a “bridge” of fuel over a slot opening could be before it collapsed. With a 500 mm thick layer of fuel above the slot opening, the bridge width varied between 58 mm for the small chips and 977 mm for the large chunks. Most of the variation was due to two fuel properties, the proportion of particles longer than 100 mm and the moisture content of the fuel.     

Recovering of forest biomass from Spanish hybrid poplar plantations

Residues recovering from traditional poplar plantations for timber production are a potential relevant biomass source in Spain and other temperate countries. Three different residual biomass harvesting systems have been work-studied in order to characterize the work methods and analyze their productivity and cost. Two were oriented to branches, top and/or energy wood collection, chipping and transport using different work methods, while the other one consisted of after-logging stumps removal and shredding. Different sized and powered chippers worked in the two first cases, besides different farm tractors with trailers for off-road chips transport. Also the trucks and the loading machines were different. In the third site, a backhoe excavator removed the stumps, and a bucket loader collected them to be grinded by a shredding machine. Productivity and cost have been analyzed using IUFRO standards, providing average figures and, when possible, predictive productivity equations. Most capital-intensive equipment option has shown to be most productive, but less investment requiring system is cheaper and may be most interesting for some enterprise and plantation sizes. In addition, logistics of biomass and timber supply has been analyzed, and some indications about equipment sizing, machine annual production and relocation costs related to supply area and average plantation size are provided.     

Development of bio-physical properties during storage of poplar chips from 15 ha test fields

A novel tractor-mounted mower-chipper for harvesting of short rotation coppice has been developed and tested in the field. The cutting length of the chipping module is adjustable in the range of 20–100 mm. Measurements during storage of the poplar chips in either a bunker silo or a covered pile (500 m³ each), over a period of about eight months, include the pile or bunker temperature, the loss of dry matter, the change in moisture content, and the mould formation. The effect of particle size has been examined as well. It appeared that fine chips, having an average chip length of 25 mm, show slightly better results than the coarse chips (75 mm). During storage of the fine chips in a pile, the moisture content decreased from around 60 to 33 weight percent, while the loss of dry matter was approximately 24 weight percent. The differences with the results obtained for coarse chips were however marginal. As a matter of fact, the favorable storage conditions expected for the coarser chips could not be confirmed at practice scale, despite significant differences in the development of the pile temperature and mould contamination.     

Transport and handling of forest energy bundles—advantages and problems

Bundling is a technology used to create a compressed and uniform handling unit from logging residues and other small size energy wood. The bundles may be handled and transported with the same equipment that is used for conventional roundwood. Bundles also offer other advantages such as “cool systems”, good storing characteristics etc. This study deals with some advantages and problems of transport and handling bundled small size energy wood as an alternative to chips.Transport cost, from stump to consumer, is calculated. Two types of material were included in the analysis: bundles and fuel chips.Transport alternatives included transports directly to consumer as well as transports of bundles via a terminal for drying and chipping, and then, in the form of fuel chips directly to consumer with a bulk cargo truck.The study shows that bundles (especially if dry) are cheaper to transport than fuel chips in road transport bins. The useful cargo space is the limiting factor for trucks when transporting dry material. Transport cost decreased until the moisture content reached the critical levels, below 40.9% for chips in road transport bins and below 44.7% for bundles on timber truck. However, there are also other advantages with a dryer material.Chipping cost is lowest in the terminal alternative and highest in the system with chipping loose logging residues in the stand. However, transport via terminal sharply increases the total costs, due to handling and increased transportation work, especially on shorter distances.Transport of uncovered bundles on conventional log trucks can be dangerous because of the risk for pieces of wood falling off. Bundles may also disintegrate during handling. The risk increases if the bundles are not reinforced with e.g. long tops and small trees, or if the strings are damaged during storing. Sisal strings deteriorate and lose their strength after a relatively short period. Thus, they are less suitable than strings of, e.g. polypropylene.Cost savings in transport and chipping indicate an allowed cost for bundling of approximately 4–5 Euro/MWh for short to medium transport distances, to be competitive to the chip alternative. Cost estimates of bundling and covering of stacks with paper indicate that the handling cost is about the same as for chips for short to medium transport distances. However, for longer transport distances and through other advantages such as possibilities for return transports, a dryer and more storable material, cooler systems etc. may increase acceptable bundling-cost substantially.     

Storage dynamics and fuel quality of poplar chips

Poplar cultivation for wood/timber production has a growth production cycle of about 10–15 years. Usually the stem is separated from the crown and used to produce material of different kind such as veneer, pallets, panels, etc. For wood industries, crowns generally represent waste material to be disposed of, causing economic and time losses. It is generally believed that the costs of managing crown biomass are higher than the potential incomes obtainable. Nonetheless, it is worthwhile investigating the possibility of using these byproducts as energy source and evaluating their value as a fuel. However, storing such residues presents several problems connected with spontaneous microbial degradation.The aim of this work was to evaluate the storage effects on chipped biomass deriving from the crown and stem wood of poplar and how they affect fuel quality and dry matter losses.A storage trial was carried out with three piles of stem wood chips and three of crown chips coming from a 15 year old poplar plantation. The piles were stored outdoors for six months under the same climatic conditions.The effect of storage on fuel quality was evaluated with respect to moisture content, gross and net calorific values, chemical composition, ash content, and bulk density.The variation of temperatures inside each pile due to heat development was continuously monitored and showed different trends between piles depending on source material. Results showed that chips from crown material had better storage properties and exhibited lower decay than chips from stem wood.     

Productivity and cost of mechanized energy wood harvesting in Northern Scotland

At present, the utilization of timber in the Northern part of the Scottish Highlands is low due to a lack of a wood utilizing industry. As a consequence, the majority of forest owners do not receive any income from timber and in some cases stumpage prices can even be negative. At the same time, increasing prices of oil, gas and electricity pose a great challenge for local industries and homeowners. The establishment of wood fueled heating systems is therefore expected to improve the situation and at the same time create a market for the local timber resources. Consequently, a local energy source to produce heat and electricity at a competitive price would have positive benefits for both local industries and forest owners. Due to the current lack of competition, roundwood could be chipped for fuel, which has many associated benefits compared to the harvesting and chipping of logging residues. It is the aim of this research to apply existing Finnish know-how in regards to wood fuel harvesting in order to develop and investigate the price level of sustainable and local wood fuel supply chains.To determine the most suitable supply chain for forest fuels, various research methods were applied. An estimation of the forest resources in the Wick area was the first step of the research. The different cost components of the supply chain such as cutting, forwarding and chipping were then calculated based on Finnish experiences and adapted to conditions in Northern Scotland. Detailed transportation distance calculations and cost of transportation were calculated using GIS tools.Of the various supply chain designs considered, chipping at the landing seems to be the most suitable option. Chipping the roundwood at a central terminal would also be feasible; however, a suitable site would have to be identified since chipping of the material at the heating plant is not an option. Calculations indicate that forest chips can be delivered starting from approximately 20 € MWh⁻¹ within a 50 km transportation distance when chipping is at roadside. If the transportation distance is 100 km wood chips could be delivered at approximately 23 € MWh⁻¹. Results from the GIS analysis indicate that a sufficient supply of raw material will be available in the future. According to these calculations forest fuels can be a competitive energy source for heat and electricity production in Northern Scotland.     

Efficiency of a compactor in wood chip volume reduction

The baling of freshly harvested wood chips was tested in an Orkel MP2000, a baling machine extensively used in agriculture and industry to densify residues. Wood chips from two different feedstocks: poplar (Populus x euroamericana) and black locust (Robinia pseudoacacia). Baling effected a volume reduction of 43% with respect to the loose bulk density of the piled chips. Each bale has an average mass of 638 kg, and the time consumption to produce one bale was typically 98 s – 122 s. Productivity then varied from 19.8 t h⁻¹ and 21.7 t h⁻¹ of the fresh (green) wood chips. Diesel fuel consumption ranged from 1.4 L t⁻¹ to 1.5 L t⁻¹ of fresh chip weight and represented about 12% of the production cost. The packaging cost is approximately 23 € t⁻¹ of fresh chips equivalent to a bale cost of 15 €. Comminuted wood pressed into bales could provide a valid solution in the use of conventional agricultural and forestry machines. In fact, the handling and transportation of bales can be performed by means of equipment normally used in other agro-forestry activities (front loaders of tractors). In addition, pressed woodchips in packaged bales with waterproof sheets also guarantees a useful storage technique with significant storage surface reduction relative to loose wood chips.     

燃料物性和喷油策略对船用柴油机性能和排放影响的模拟研究

采用多维数值模拟的方法系统研究了不同燃油性质和喷油策略对船用柴油机性能和排放的影响。研究结果表明:无论使用重油还是轻油,采用顺序喷射、预喷和后喷都能在降低燃油消耗率的同时降低NO_x排放;顺序喷射方案能在两个喷油器的喷射间隔为4°时达到最低的燃油消耗率;大比例预喷匹配合适的主预喷间隔容易获得较低的燃油消耗率,小比例预喷匹配合适的主预喷间隔容易获得较低的NO_x排放;后喷策略对燃油消耗率改善不明显,随着主后喷间隔增大或者后喷油量的增加,燃油消耗率均呈现增加的趋势。     

Experimental study about the effects of disc chipper settings on the distribution of wood chip size

Nowadays wood should be of principal sources of biomass. This wood is transformed into chips in order to increase automatic operations and to decrease the technical effort needed at the energy conversion plant. Typical high quality chips, which are used to feed small woodchip boilers, vary in size from 10 × 10 × 5 mm to 15 × 15 × 8 mm. Chips that are relatively square and flat are easily conveyed, augured, and fed into the system smoothly. We are mainly interested in the raw material of inferior quality. A disc chipper test bench was constructed in our laboratory to study the chipping process in cutting conditions which are similar to those used in the industry. The test bench design allows many factors to be varied include cutting speed, feed per tooth, cutting angles, anvil height and cutting direction. In this paper, we attempt to understand the effect of several factors on chip size distribution. Four feeds per tooth, four cutting angles, two sharpness angles and three cutting speeds were chosen to cut wet logs of oak and fir wood, while the other factors remained constant. The results are similar for both oak and fir. The proportion of small chips decreases when we increase the feed per tooth, the cutting angle and the sharpness angle, whereas it increases when the cutting speed is increased. The feed per tooth and the cutting speed have a linear effect on the variations in the size distribution, while the cutting angle has a non-linear effect on these variations.