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To achieve net-zero carbon emissions by 2050, the UK government emphasizes the pivotal role of sustainable bioenergy in electricity, transportation, and heating. However, challenges persist in handling biomass particulate solids in production facilities, leading to economic impacts. This study investigates the flow characteristics of stemwood chips from four tree species using a novel drum chipper. Experimental analyses include bulk density measurements, silo discharge studies, biomass flow property assessments, and wall friction measurements. Comparative analyses are performed using Jenike's procedure for building wedge-shaped silos, with a focus on predicting the critical opening size to prevent arching. Additionally, the paper delves into the creation of statistical models aimed at identifying key factors influencing the flow behaviour during silo discharge. Emphasis is placed on understanding potential discrepancies between theoretical predictions and experimental results concerning critical silo openings for arch-free discharge. The results contribute to understanding the factors influencing the flow behaviour of wood chips, informing silo design considerations. Our findings suggest limitations in applying traditional silo design methods, urging further research for more accurate predictions.

Resource-efficient wood chipping for forest-industrial processes demands large fractions of accept chips and small fractions of small-sized material, such as pin chips and fines. In Kraft pulping, a narrow distribution of wood chip thickness is important for even impregnation and for making high-quality pulp. Using newly developed forest-industrial drum-chipping technology, the investigation covered wood of varying moisture content, frozen versus unfrozen wood, and the use of different wood species. Using conventional techniques for analyzing wood chip dimensions, fast-grown spruce wood with high moisture content gave 4.2 % pin chips and fines, which was less than half of the fractions obtained with spruce wood with lower moisture content. A comparison between frozen and unfrozen pine resulted in slightly thinner and shorter chips for the frozen wood, but in both cases accept yields of up to ∼85 % were achieved. A comparison of different tree species (aspen, birch, pine, and spruce) resulted in larger accept fractions (∼90 %) for the hardwood species, even though the average length of these wood chips was as low as 17 mm. The results provide a first indication of how basic wood log properties affect the yields of accept chips and small-sized material when using modern industrial drum-chipping technology.

Heartwood and sapwood of Scots pine were procured and chipped using a newly developed pilot drum chipper, which for the heartwood resulted in a combined fraction of pin chips and fines of ~ 3%. Heartwood wood chips were processed using a set of 15 different reaction conditions that differed with respect to impregnation and cooking procedures. The result was evaluated with regard to absorption of impregnation liquid, pulp yield, fraction of reject, viscosity, kappa number, brightness, fiber properties, and chemical composition measured using two different techniques (compositional analysis using two-step hydrolysis with sulfuric acid and Py-GC/MS). The chemical analyses provided detailed information about how all main organic constituents of the wood, cellulose, hemicelluloses, and lignin, were affected by operational parameters. Inclusion of a pressurized (9 bar) impregnation step resulted in a more efficient cook, but the duration of the impregnation step (five minutes and four hours were compared) was not decisive for the outcome. Omission of the impregnation step or using low-pressure impregnation resulted in high fractions of reject, poor delignification, and, with a cooking time of two hours, no advantages with regard to fiber length and fraction of fines. The results indicate that the conditions used during impregnation, such as pressure, temperature, and acidity of impregnation liquid, warrant further attention in future studies.

Wood chips from a novel type of drum chipper were compared to wood chips from a conventional disc chipper in an evaluation based on demonstration-scale and industrial-scale machinery. The evaluation was performed as the wood chippers were used as production machines in a kraft pulp mill using softwood. The average bulk density of the wood chips from the disc chipper and the drum chipper was similar and within the range of 138-140 kg/m(3). The size distribution of the wood chips was investigated using a conventional screening method, and by using an automatized image-analysis system based on laser scanning. The average length was set to be the same, but the wood chips from the drum chipper had a more uniform length. The average thickness was similar, but the drum chipper generated slightly more thinner wood chips. Compared to the disc chipper and using the screening method, the drum chipper generated a similar fraction of oversized and over-thick wood chips, 51% more large accept chips, 11% more total accept chips, and 74% less pin chips and fines. Image analysis resulted in similar data. The results indicate that drum chippers warrant further attention as an alternative to conventional industrial-scale disc chippers.

Wood chipping and the supply of high-quality wood chips are of critical importance for most forest-industrial processes. The quality of wood chips affects product yield, product quality, and processability. Wood chips from a novel type of forest-industrial drum chipper, with a large drum and specially designed wood-chip channels, were evaluated with regard to wood chips for the Kraft and sulfite processes. Wood chips from a full-scale demonstration version of the drum chipper and from a conventional disc chipper at a Kraft mill were compared. The average bulk density and the fractions of oversized and overthick wood chips were similar, but the demonstration drum chipper produced 51% more large accept chips, 11% more total accept chips, and 74% less pin chips and fines. A pilot-scale drum chipper based on the new technology was used to produce short wood chips designed for acidic processes. When the drum velocity was 30-34 m/s and the average wood-chip length 21-22 mm, the fraction of pin chips and fines was 4.2% and the fraction of total accept was 89-90%. When the average wood-chip length was decreased to 17 mm, the fraction of pin chips and fines increased to 8.5% and the fraction of total accept decreased to 80-82%. The pilot drum chipper was used to investigate the influence of using different tree species (aspen, birch, pine, and spruce), processing of wood with different moisture content, and frozen wood. For hardwood (aspen and birch), the fraction of total accept reached ~90% when the average wood chip length was 17 mm. The pilot drum chipper was also used to generate wood chips of heartwood of pine for a comparison of 15 sulfite-process reaction conditions that differed with regard to impregnation and cooking procedures. The analyses included absorption of liquid in a specially designed impregnation reactor, pulp yield, reject, viscosity, kappa number, brightness, fiber properties, and chemical composition as determined using compositional analysis based on two-step hydrolysis with sulfuric acid and pyrolysis-gas chromatography/mass spectrometry. The results reveal in detail how the individual wood constituents were affected by the different treatments, and demonstrate the benefits of using a pressurized impregnation step prior to sulfite cooking.

När vi producerar massa till papper och kartong vill vi använda så mycket av vedråvaran som möjligt, dvs. ha ett högt utbyte när råvaran konverteras till produkt. Det är viktigt för att minimera transporter, råvaruåtgång och kemikalieåtgång, vilket bidrar till en ekonomiskt bärkraftig process. Ett av processens första steg är att sönderdela stockarna till flis. Hur jämn flisen är i storlek, dess fukthalt och dess packdensitet påverkar hur bra massa det blir.

Idag huggs nästan all flis som blir massa med skivhuggsteknik. Skivhuggen uppvisar en hastighetsgradient, vilket leder till att en större andel av råvaran blir till pinnflis och spån. Pinnflis och spån har för små dimensioner för att fungera bra som råvara vid impregnering med kokkemikalier och vid massakok.

En ny typ av trumhugg har utvecklats. Trumman har inte den hastighetsgradient som skivhuggen har och borde teoretiskt sett kunna producera en mindre andel pinnflis och spån. För att utvärdera den nya tekniken så jämfördes en fullstor demonstrationshugg baserad på den nya trumhuggstekniken med en konventionell skivhugg på ett sulfatmassabruk. För att utvärdera effekten av trummans hastighet och stockens inmatningsvinkel användes istället en pilothugg baserad på den nya tekniken. Med hjälp av pilothuggen undersöktes också hur fliskvalitén påverkades av stockarnas fukthalt, vilket trädslag det var och om veden var fryst eller tinad.

Den nya trumhuggstekniken skapade flis som visuellt liknade den från skivhuggen. För att få bra massa behöver en andel på ungefär 85% av flisen vara acceptflis, dvs. dess dimensioner ligger inom de storleksintervall som industrin har valt att definiera som acceptabel. Den nya trumhuggen gav en andel på 85% acceptflis direkt efter huggning i demonstrationsskala, ett värde som brukar uppnås först efter sållning av flis. Framför allt minskade andelarna av de fraktioner som kan ses som förlust, pinnflis och spån. Dessa småfraktioner stör massaprocessen och även om de kan användas som bränsle innebär det en värdeförlust. Bra huggresultat gick också att få med andra inställningar och varierande råvara. När flis som var betydligt kortare än normalt producerades gick som väntat andelen acceptflis ner, dock fortfarande inom gränser som är industriellt acceptabla. Detta pekar på att den nya trumhuggstekniken kan vara speciellt fördelaktig för sura processer där kortare flis är att föredra.

Den nya flisningstekniken användes också för att producera flis från kärnved av tall. En stor andel av vedråvaran i Sverige består av tall, men det är utmanande att använda en stor andel tallkärnved i sulfitprocessen. Flisen användes till försök där 15 olika reaktionsförhållanden jämfördes. Skillnaden mellan de 15 olika reaktionsförhållandena bestod i hur impregnering och sulfitkok utfördes. Resultatet utvärderades genom analys av upptaget av impregneringsvätska i en specialkonstruerad impregneringsreaktor, bestämning av utbytet av massa, rejekt, viskositet, kappatal, ljushet och fiberegenskaper, samt detaljerad analys av råvarans och de 15 produkternas kemiska sammansättning. Försöket gav detaljerad information om hur veden påverkas under olika reaktionsbetingelser och visar tydligt de positiva effekterna av att inkludera ett trycksatt impregneringssteg innan sulfitkoket.

Impregnation of wood chips with acidic pulping liquors is improved when using short chip lengths. If the average wood chip length is too short, conventional chipping technology will generate excess small material, such as pin chips and fines. The possibility of using newly developed drum chipping technology to produce short-length wood chips was evaluated with a pilot drum chipper operating at different drum velocities and in-feed angles. With a drum velocity of 30 m/s, the average wood chip lengths and the combined fractions of pin chips and fines were 24 mm and 3.3%, 22 mm and 4.2%, and 17 mm and 8.5%. The highest fractions of total accept chips (large and small accepts), 89% to 90% without screening, were observed for drum velocities of 30-34 m/s and average wood chips lengths of 21-22 mm. The results indicate the potential of drum chipping technology for producing short wood chips with relatively high fractions of accept chips and tolerable fractions of pin chips and fines.