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Att välja trä
- 2020. - 10
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Samlingsverk (redaktörskap) (populärvet., debatt m.m.)
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| 2. |
- Bengtsson, Peter, 1974-
(författare)
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Development towards an efficient and sustainable biofuel drying
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of biofuel as well as wood fuel has increased in Sweden and all of Europe during recent decades, and there are several reasons to believe that this increase will continue. An important reason for this increase is that the environmental and climate problems caused by fossil fuels are becoming even more evident. By replacing fossil fuel with biofuel, the problem of emissions from, among others carbon dioxide and sulphur compounds can be alleviated. However, substitution requires in many cases high quality processed biofuel. An early stage in the processing of biofuel is drying. Previous work treats the possibility of drying wood fuel in an efficient and environmentally sustainable manner.This thesis studies the bed drying technique, conducted both experimentally and through modeling of the drying process. The experimental work is based on continuous temperature measurements in the fuel bed and provides characteristics of the drying zone that develops in the bed during drying. The character of the drying zone is affected by both the qualities of the fuel and the operating parameters, and is decisive regarding the possibility of making the drying more efficient, i.e. optimize the usage of energy and produce a fuel with low and homogeneous moisture content.A mathematical simulation model has been developed to increase the understanding of bed drying. The model is based on fundamental physical principles and is made up of five differential equations that describe vapor flow, air flow, the fuel’s moisture content, and the bed’s pressure and temperature. The modeling work complements the experimental work and a simulation of the temperature distribution, pressure and the drying zone’s dispersion is in agreement with the experimental result.The drying of wood can signify an environmental and human health risk, since volatile organic compounds (VOC) are emitted during drying. The thesis studies these emissions with regards to type and quantity. The measurements show that the majority of the emitted compounds from Norway spruce and Scots pine are volatile monoterpenes, but also that other compounds are emitted, especially higher terpenes. Further, major differences between how the compounds are emitted and the quantities of the emitted compounds from heartwood and sapwood are shown. There are also large differences between types of wood, i.e. spruce and pine. It can be stated that both emission rate and total amount of emitted compounds increase with an increase in temperature.To reduce VOC emissions, the drying temperature should be maintained low. To develop an efficient bed drying process for wood biofuels, additional parameters must be analyzed further and weighed against each other. Based on the experimental method and the simulation model presented here, the drying can be optimized towards a more efficient use of thermal energy and a low and even moisture content in the dried biofuel.
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| 7. |
- Blom, Åsa, et al.
(författare)
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Above Ground Durability of Swedish Softwood
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes aspects of durability of Swedish softwood in above ground applications. The thesis consists of a summary of nine papers, which all aim to explain the existing variation in above ground microbial durability and moisture sensitivity of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). The methods used were two field tests, one accelerated durability test, and three water permeability tests. The main conclusions made in the study were that Norway spruce sapwood is more susceptible to discolouring fungi than heartwood. With respect to Scots pine, the only important factor for its natural durability above ground was whether the samples consisted of heartwood or of sapwood. There was also no systematic variation between pine heartwood from different stand origins in above ground conditions. Origin had no influence on durability in practice for neither spruce nor pine. Furthermore, in contradiction with traditional thinking, annual ring width and density had no influence on durability in any of the tests. The material came from two different samplings. The ‘old’ material was sampled in the beginning of the 1980s and consisted of Scots pine and Norway spruce from three different origins: the north, the central area, and the south of Sweden. The material was subjected to different handling conditions and surface and end-grain treatments. The ‘old’ material was used in a large above ground field test, carried out between 1985 and 1994. Unfortunately, the spruce sapwood and heartwood was not separated in this field test. In the field trial with the ‘old’ material, the most important factor for the durability of Norway spruce was the samples’ surface- and end-grain treatment. It was also observed that untreated spruce showed better durability than samples that were painted but without proper end-grain treatment. Samples originating from one of the stands were more sensitive towards air-drying than samples from the other two, which was reflected in a higher average moisture content and mass loss for the untreated samples. With respect to Scots pine, the most important factor was whether the sample consisted of heartwood or of sapwood. The heartwood samples were durable irrespective of their previous treatment. The Scots pine sapwood samples, on the other hand, had a very fluctuating moisture content if they were not surface- and end-painted. This was also reflected in higher mass losses in these samples. Even when properly surface- and end grain treated, the sapwood samples did not perform as well as the heartwood samples. The ‘new’ material consisted of Scots pine taken from six different stands, and Norway spruce from five different stands, all from areas in southern Sweden. The sampling was performed in order to achieve a large variation in wood properties. Thus, logs from areas with different climate and growth conditions were collected. This material was used for laboratory tests, and also for the second field test, which was evaluated after a test period of two years. In the second field test untreated Scots pine and Norway spruce samples from the ‘new’ material were investigated. Effects of origin and different tree diameters were examined. Furthermore, Scots pine was separated to heartwood and sapwood, and Norway spruce to mature and juvenile wood. The Norway spruce samples were sawn with vertical or horizontal annual rings. For the Norway spruce in the second field test, vertical annual rings were shown to be very beneficial for avoiding crack formation, while samples with horizontal annual rings displayed a large number of cracks. Despite this, the larger number of cracks did not result in a higher moisture content or more fungal discoloration. Juvenile wood had a slightly higher average discolouring fungal growth grading than the other spruce samples. For Scots pine, the only factor of importance was whether the samples consisted of heartwood or of sapwood. Annual ring width, density and origin had no significant effect on either fungal growth or moisture uptake. This observation held for both Norway spruce samples and Scots pine samples. An accelerated test was run in order to investigate Norway spruce sapwood and heartwood with respect to their differences in durability towards discolouring fungi and moisture uptake. The Mycologg method was used to accelerate fungal growth during a number of forced moisture cycles. The results showed that sapwood was much more sensitive to discolouring fungi than heartwood. Sapwood also recorded a higher average moisture content than heartwood. The differences that were observed between the types of samples were not due to annual ring width, density or origin. It was observed that Norway spruce sapwood samples and heartwood samples showed differences in liquid water permeability. This observation was made especially evident in a droplet absorption test. Water droplets were absorbed much faster on the sapwood samples in comparison with the heartwood samples. This higher affinity to water suggested that a sapwood surface would reach a higher moisture content than a heartwood surface. This observation provides a major explanation of why the sapwood samples showed poorer durability towards discolouring fungi in the Mycologg trials.
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| 8. |
- Blom, Åsa, 1977-, et al.
(författare)
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Live storage and drying of storm-felled Norwayspruce (Picea abies, L. Karst.) and Scots pine (Pinussylvestris L.) trees
- 2014
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 9:4, s. 209-213
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Tidskriftsartikel (refereegranskat)abstract
- Storm-felled trees left in the forest for a shorter or longer period, affect the quality of the logs. The change in quality ismainly because of attack of fungi and insects, which in turn depends on the moisture content (MC) of the sapwood. Thepurpose of this study was to receive more knowledge about drying of storm-felled trees by investigating how fast winterstorm-felled Norway spruce and Scots pine dried when left in the forest. Sixteen storm-felled spruces with part of the rootsstill in ground contact were selected from three stands and in addition to 10 pines from one of the stands. The trees wereexamined for MC in the sapwood until 21 months after the storm. This study indicates that wind-thrown trees with rootsstill connected to the soil can survive one summer without any value loss caused by draught, fungi and insects. The standconditions can be of importance as the storm-felled trees in the stand, with scattered windthrow, were in best condition afterone year, as they were shadowed by the trees still standing. Comparing spruces and pines with the stand with scatteredwindthrow, pines were more sensitive to drought and reached critical MC earlier.
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| 9. |
- Blom, Åsa, 1977-, et al.
(författare)
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Outdoor exposure of untreated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst) wood samples
- 2010
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Ingår i: Wood Material Science & Engineering. - : Taylor & Francis. - 1748-0272 .- 1748-0280. ; 5:3-4, s. 204-210
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Tidskriftsartikel (refereegranskat)abstract
- Untreated Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) samples were exposed above ground in a durability test for six years. The samples consisted of three pieces of wood, 22x95x500 mm, screwed together; two pieces lengthwise with a third piece overlapping. Weight was measured, to calculate moisture content (MC), and samples checked regularly for cracks and fungal growth. Parameters investigated were heartwood/sapwood (pine), annual ring orientation (spruce), stand site, annual ring width and density.Stand site, annual ring width or density had no influence on MC or fungal growth for neither pine nor spruce. Spruce samples with vertical annual rings had lesser amounts of cracks than samples with horizontal annual rings.Regarding pine sapwood samples, they showed high MC and large amount of rot fungi, while heartwood had lower MC and no rot. Most spruce samples were similar to pine heartwood, except from a few samples that had high MC and fungal growth. Those were all sawn from the outer part of the log. Therefore, it can be stated that spruce sawn from the inner part has almost the same properties as pine heartwood while spruce from the outer part of the log has properties similar to pine sapwood.
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| 10. |
- Blom, Åsa, 1977-, et al.
(författare)
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Presence of longitudinal cracks in planks from storm-felled pine (Pinus sylvestris L.) and spruce (Picea abies (L.) Karst.)
- 2012
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Ingår i: Wood Material Science & Engineering. - : Informa UK Limited. - 1748-0272 .- 1748-0280. ; 7:4, s. 237-241
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Tidskriftsartikel (refereegranskat)abstract
- After the severe storm Gudrun in southern Sweden in 2005, a quantitative study was done in order to investigate the presence of lengthwise crack on planks taken from storm-felled trees in southern Sweden, compared to planks from standing trees not subjected to this storm (central Sweden). The main yield from each log was examined. In total, 1087 pine (Pinus sylvestris) planks and 3626 spruce (Picea abies) planks from the storm-struck area were investigated and compared to 1953 spruce and 2000 pine planks from trees outside the storm-struck area. The examination of cracks was done visually on dried planks. For pine, 51.7% of the planks from storm-felled trees had a total length longer than 0.5 m, compared to 7.3% for the reference material. As for spruce, 11.0% of the planks from storm-felled trees had a total crack length of more than 0.5 m, compared to the reference material where 2.2% had cracks longer than 0.5 m. The results show that the storm-felled trees had more longitudinal cracks than the reference material and that pine was more likely to develop storm-related cracks than spruce.
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