| 1. |
- Bergström, Dan, et al.
(författare)
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Effects of raw material particle size distribution on the characteristics of Scots pine sawdust fuel pellets
- 2008
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Ingår i: Fuel processing technology. - Amsterdam : Elsevier. - 0378-3820 .- 1873-7188. ; 89:12, s. 1324-1329
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the influence of raw material particle size distribution on the pelletizing process and the physical and thermomechanical characteristics of typical fuel pellets, saw dust of Scots pine was used as raw material for producing pellets in a semi industrial scaled mill (similar to 300 kg h(-1)). The raw materials were screened to a narrow particle size distribution and mixed into four different batches and then pelletized under controlled conditions. Physical pellet characteristics like compression strength, densities, moisture content, moisture absorption and abrasion resistance were determined. In addition, the thermochemical characteristics, i.e. drying and initial pyrolysis, flaming pyrolysis, char combustion and char yield were determined at different experimental conditions by using a laboratory-scaled furnace. The results indicate that the particle size distribution had some effect on current consumption and compression strength but no evident effect on single pellet and bulk density, moisture content, moisture absorption during storage and abrasion resistance. Differences in average total conversion time determined for pellet batches tested under the same combustion conditions was less than 5% and not significant. The results are of practical importance suggesting that grinding of saw dust particle sizes below 8 mm is probably needless when producing softwood pellets. Thus it seem that less energy could be used if only over sized particles are grinded before pelletizing.
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| 2. |
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| 3. |
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| 4. |
- Lindroos, Ola, et al.
(författare)
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Theoretical Potentials of Forwarder Trailers with and without Axle Load Restrictions
- 2014
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Ingår i: Croatian Journal Of Forest Engineering. - 1845-5719. ; 35, s. 211-219
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Tidskriftsartikel (refereegranskat)abstract
- In mechanized ground-based forestry, machines operate on rough soils that, ideally, should remain unaffected by the operation. This implies small (that is, light) loads and careful driving are required. However, economical rationality implies large loads and high speeds. Recently, the concept of adding a trailer to a conventional forwarder has been revived, with the objective of addressing both concerns, and fitting into the current, mechanized, cut-to-length system. Here we present the theoretical benefits of the forwarder-trailer concept compared to conventional forwarding for final-felling operations. The analysis addresses the trailer potential in terms of break-even extraction distances under different scenarios, and estimates the abundance of favorable conditions (as a percentage of final-felling volume) in Swedish final fellings. The results show that the forwarder-trailer concept has potential to reduce costs, and especially if there are restrictions on axle loads. However, the viability of the trailer concept is highly sensitive to changes in the increased purchase costs and the increased work-element time-consumption. That is, small changes in these variables result in large changes in viability. In the scenarios presented here, the increase in time consumption was more influential than the purchase cost. It can be concluded that there are potential economic and possibly also environmental benefits that warrant further investigation of the forwarder-trailer concept, which is currently being evaluated in practice in Sweden.
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| 5. |
- Lindroos, Ola, et al.
(författare)
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Utvärdering av skotning med påhängsvagn
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Att utöka lastkapaciteten med hjälp av vagn(ar) efter ett dragfordon är givetvis ingen nyskapande innovation. Inom de flesta transportarbeten maximeras lastkapaciteten under de givna fysiska och ekonomiska begränsningarna. Påhängsvagn för skotare har testats tidigare och slutsatserna var att även om själva transporteffektiviteten ökade, så var lastningen av vagnen betydligt svårare än lastningen av själva skotaren. Kostnadseffektivitet uppnåddes därför bara vid relativt långa terrängtransportavstånd. Tack vare teknisk utveckling och ökat fokus på att begränsa markpåverkan finns det dock ett pånyttfött intresse för skotarvagnar. Dagens kranar är betydligt mer kraftfulla och det finns i dagsläget ett stort fokus på att minska skogsbrukets markpåverkan. Att fördela last på fler hjulaxlar skulle kunna vara ett sätt att minska skotningens markpåverkan. Syftet med denna studie var därför att med hjälp av fältstudiedata jämföra skillnaderna i tidsåtgång, bränslekonsumtion samt markskador vid skotning med och utan påhängsvagn, samt med reducerad last (för att minimera markskador). Skillnaderna i tids- och bränsleåtgång nyttjades till ekonomiska jämförelser under olika skotnings¬förutsättningar. Den studerade skotarens lastade vanligtvis 15 ton, och vagnen ökade kapaciteten med 10 ton (dvs med 66%). Att använda vagnen ökade tidsåtgången och bränsleförbrukningen under transportarbetet, men räknat per skotat ton behövdes 25-33% kortare tid samt 22-27% mindre bränsle jämfört med om transporten gjordes utan vagn. Att lasta och lasta av vagnen tog 44% respektive 94% mer tid och bränsle än att göra motsvarande arbete till och från skotarens lastutrymme. Om användningen av skotarvagnen är lönsam beror därför på transportavståndet. Resultaten visar att användningen av vagnen minskar bränsleförbrukningen vid transport¬avstånd över 400 m enkel väg. Givet kostnaden för den testade vagnen (220 000 kr), blir det kostnadseffektivt att använda vagnen vid transportavstånd över 600 m enkel väg. Dessa brytpunkter gäller dock under mer eller mindre optimala förhållanden (tex plan mark). Kostandsberäkningarna för studiens traktbanksdata över slutavverkningar, visar att i grundscenariot var skotarvagns¬användning bara lönsam för 12-19% av volymen. Om skotarvagnen skulle användas till all skotning skulle den totala kostnaden öka med 4-7% jämfört med skotning utan vagn. Känslighetanalyser visade att det fanns förhållandevis lite att vinna på att använda vagnen som en standardutrustning vid all skotning, medan det skulle kunna bli stora extra kostnaderna. Slutsatsen av de ekonomiska analyserna blir därför att det troligtvis vore lämpligt om flera skotare delar på en skotarvagn, som används på trakter där vagnens fördelar kommer till sin rätt. Testområdet hade god bärighet tack vare dess ovanligt stenrika morän, så det var svårt att utvärdera generella skillnader i markpåverkan mellan skotning med och utan vagn. Studien gav dock stöd för resonemanget om mindre markpåvekan om lasten fördelas på skotare och vagn, även om totala lastvikten är högre än om skotning görs utan vagn. Ytterligare studier behövs dock för att belysa frågan bättre, och då på känsligare mark. Studierna visade på tekniskt förbättringsbehov rörande vagnsdraget, avståndet mellan skotar- och vagnsvirke samt lastsäkring. Dessutom bör de mer långsiktiga effekterna på framförallt skotares kran och drivlina utredas ytterligare. Sammantaget indikerar studien att det finns en ekologisk, och till viss del också ekonomisk potential, som gör att skotarvagnsanvändning förtjänar fortsatt uppmärksamhet.
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| 6. |
- Nordfjell, Tomas, et al.
(författare)
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Changes in technical performance, mechanical availability and prices of machines used in forest operations in Sweden from 1985 to 2010
- 2010
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 25, s. 382-389
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Forskningsöversikt (refereegranskat)abstract
- This study describes developments in large-scale logging technology in Sweden from 1985 to 2010. Data were collected from manufacturers' sales material and from large forest enterprises. On average, forwarders manufactured in 2010 had 27-33% higher boom lifting torque than those manufactured in 1985-1989. The inflation-adjusted prices of medium-sized single-grip harvesters remained the same, but prices of forwarders increased by 30-50% in this period. The mechanical availability of various classes of machinery used increased from 70-80% to 85-88% between 1985 and 2008. The harvesting costs of thinning decreased between 1990 and 1998, while those of final fellings decreased from 1985 to 2006. However, in 2008 costs of both thinning and final felling tended to increase. The productivity of logging by the Swedish forest enterprise SCA increased almost three-fold in the period 1985-2010. However, since 2003 there have been signs of declining productivity. Currently, there is considerable interest in harvesting forest biomass for energy production. The new work tasks involved will affect the configuration of forest machines. A possible trend is that a new generation of forest machines and methods will be developed to facilitate integrated handling of roundwood and forest biomass for energy generation.
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| 7. |
- Pirnazarov, Abdurasul, 1981-
(författare)
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On forestry machine and soil interaction for sustainable forestry
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- More than 50 percent of the land area of the Nordic countries Finland, Norway, and Sweden are covered by dense forests and they are among the most important producers of forest products in the world. Forestry in these countries is based on sustainable management principles – reforestation follows harvesting. Furthermore, increasing demands for more gentle techniques and technologies with less negative impact on the environment ask for development and implementation of new processes and new machine solutions. The increasing interest in developing forest management approaches that are based on gentleness to the environment requires better understanding of the interaction between the forestry machines and the terrain in the harvesting process.Paper A describes the purpose for model-based and simulation design of the next generation of forestry machines and proposes an enabling modeling and model configuration framework.Paper B presents the measured soil properties, ground pressure, and multi-pass rutting results from a field test with medium-sized forwarders operating on soft soil. The test data was then correlated with results from empirically-based WES-models.Paper C presents multi-pass rutting results for a tracked forwarder, with and without loading, operating on soft soil. Various models for predicting rutting was compared with the measured single- and multi-pass results for straight and S-curve driving.Paper D presents the reasons for, and the realization of, a test rig for characterizing the shear properties of rooted soil.
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| 8. |
- Rhén, Christofer, et al.
(författare)
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Effect of raw material composition in woody biomass pellets on combustion characteristics
- 2007
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Ingår i: Biomass and Bioenergy. - Oxford : Pergamon Press. - 0961-9534 .- 1873-2909. ; 31:1, s. 66-72
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Tidskriftsartikel (refereegranskat)abstract
- Char yield, char combustion time and char combustion rate of pellets made from different tree parts of Norway spruce and industrially made stem wood pellets of Norway spruce and Scots pine were studied. The pellets were incinerated in a laboratory scale oven at various temperatures, gas flows and oxygen concentrations. It was found that the combustion time for a single pellet mostly depended on the raw material composition and to a minor extent on the density. Pellets made of bark had up to a 50% longer char combustion time compared to that of stem wood pellets, due to differences in char yield. Industrially made stem wood pellets of pine and spruce sawdust were found to have small differences in combustion characteristics. The variations in combustion characteristics of pellets are discussed in relation to composition of raw material.
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| 9. |
- Rhen, Christofer, et al.
(författare)
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Effects of raw material moisture content, densification pressure and temperature on some properties of Norway spruce pellets
- 2005
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Ingår i: FUEL PROCESSING TECHNOLOGY. - : Elsevier BV. - 0378-3820. ; 87:1, s. 11-16
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Tidskriftsartikel (refereegranskat)abstract
- In order to study the pelletising process, Norway spruce sawdust pellets were produced under strictly controlled conditions on a laboratory scale. The aim of the work was to investigate how the moisture content of raw material and the densification parameters, pressure and temperature, affect compression strength, dry density and moisture uptake of the formed pellets. In the experiments performed, temperature (26–144 °C), moisture content (6.3–14.7 wt.% of d.b.) and pressure (46–114 MPa) were the factors which varied according to a prescribed central composite design. The relationships between the factor settings and the responses (dry density, moisture uptake and compression strength) were evaluated by multiple linear regressions.In the present study, it was found that high compression strength was strongly correlated with the density of the pellets. High temperature (at least up to 144 °C) and low moisture content at the start of compression (down to 6.3 wt.% of d.b.) increased the dry density of the pellets. Remarkably, compression force had very little effect in the tested range of 46–114 MPa, indicating that pressure in the die does not need to be higher than 50 MPa.Similarly, compression force had very little effect on moisture uptake in the pellets. The least moisture uptake occurred when the pellets were produced at 90 °C.
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| 10. |
- Ringdahl, Ola, 1971-, et al.
(författare)
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Estimating wheel slip for a forest machine using RTK-DGPS
- 2012
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Ingår i: Journal of terramechanics. - : Elsevier BV. - 0022-4898 .- 1879-1204. ; 49:5, s. 271-279
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Tidskriftsartikel (refereegranskat)abstract
- Wheel slip may increase the risk for wheel rutting and tear up ground vegetation and superficial roots and thereby decreasing the bearing capacity of the ground, but also reducing the growth of nearby standing forest trees. With increased slip, more energy is consumed for making wheel ruts in the ground, with increased fuel consumption as a result. This paper proposes a novel method for measuring slip in an uneven forest terrain with an 8WD forestry machine. This is done by comparing the wheel velocity reported by the machine and velocity measured with an accurate DGPS system. Field tests with a forestry machine showed that slip could be calculated accurately with the suggested method. The tests showed that there was almost no slip on asphalt or gravel surfaces. In a forest environment, 10–15% slip was common. A future extension of the method enabling estimation of the slip of each wheel pair in the bogies is also suggested.
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