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Anand R. Sanadi - One of the best experts on this subject based on the ideXlab platform.
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reprint of Pelletizing properties of torrefied wheat straw
Biomass & Bioenergy, 2013Co-Authors: Wolfgang Stelte, Niels Peter K Nielsen, Hans Ove Hansen, Jonas Dahl, Lei Shang, Anand R. SanadiAbstract:Abstract Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and Pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the Pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the Pelletizing analyses have shown that these changes correlate to changes in the Pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.
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Pelletizing properties of torrefied wheat straw
Biomass & Bioenergy, 2013Co-Authors: Wolfgang Stelte, Niels Peter K Nielsen, Hans Ove Hansen, Jonas Dahl, Lei Shang, Anand R. SanadiAbstract:Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and Pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the Pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the Pelletizing analyses have shown that these changes correlate to changes in the Pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.
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fuel pellets from wheat straw the effect of lignin glass transition and surface waxes on Pelletizing properties
Bioenergy Research, 2012Co-Authors: Wolfgang Stelte, Jens Kai Holm, Ulrik Birk Henriksen, Jesper Ahrenfeldt, Craig M Clemons, Anand R. SanadiAbstract:The utilization of wheat straw as a renewable energy resource is limited due to its low bulk density. Pelletizing wheat straw into fuel pellets of high density increases its handling properties but is more challenging compared to Pelletizing woody biomass. Straw has a lower lignin content and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the Pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the Pelletizing process and pellet strength are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively. Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two Pelletizing temperatures were chosen—one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed at 30°C have a lower density and compression strength and a tendency to expand in length after the Pelletizing process compared to pellets pressed at 100°C. At low temperatures, surface extractives have a lubricating effect and reduce the friction in the press channel of a pellet mill while no such effect is observed at elevated temperatures. Fuel pellets made from extracted wheat straw have a slightly higher compression strength which might be explained by a better interparticle adhesion in the absence of hydrophobic surface waxes.
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Fuel pellets from biomass: The importance of the Pelletizing pressure and its dependency on the processing conditions
Fuel, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Søren Barsberg, Jesper Ahrenfeldt, Ulrik Birk HenriksenAbstract:Abstract The aim of the present study was to identify the key factors affecting the Pelletizing pressure in biomass pelletization processes. The impact of raw material type, pellet length, temperature, moisture content and particle size on the pressure build up in the press channel of a pellet mill was studied using a single pellet press unit. It was shown that the Pelletizing pressure increased exponentially with the pellet length. The rate of increase was dependent on biomass species, temperature, moisture content and particle size. A mathematical model, predicting the Pelletizing pressure, was in good accordance with experimental data. It was shown that increasing the temperature resulted in a decrease of the Pelletizing pressure. Infrared spectra taken from the pellets surface, indicated hydrophobic extractives on the pellet surface, for pellets produced at higher temperatures. The extractives act as lubricants, lowering the friction between the biomass and the press channel walls. The effect of moisture content on the Pelletizing pressure was dependent on the raw material species. Different particle size fractions, from below 0.5 mm up to 2.8 mm diameter, were tested, and it was shown that the Pelletizing pressure increased with decreasing particle size. The impact of Pelletizing pressure on pellet density was determined, and it was shown that a Pelletizing pressure above 200 MPa resulted only in minor increase in pellet density.
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Pelletizing properties of torrefied spruce
Biomass & Bioenergy, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Jesper Ahrenfeldt, Lei Shang, Craig M Clemons, Ulrik Birk HenriksenAbstract:Abstract Torrefaction is a thermo-chemical conversion process improving the handling, storage and combustion properties of wood. To save storage space and transportation costs, it can be compressed into fuel pellets of high physical and energetic density. The resulting pellets are relatively resistant to moisture uptake, microbiological decay and easy to comminute into small particles. The present study focused on the Pelletizing properties of spruce torrefied at 250, 275 and 300 °C. The changes in composition were characterized by infrared spectroscopy and chemical analysis. The Pelletizing properties were determined using a single pellet press and pellet stability was determined by compression testing. The bonding mechanism in the pellets was studied by fracture surface analysis using scanning electron microscopy. The composition of the wood changed drastically under torrefaction, with hemicelluloses being most sensitive to thermal degradation. The chemical changes had a negative impact, both on the Pelletizing process and the pellet properties. Torrefaction resulted in higher friction in the press channel of the pellet press and low compression strength of the pellets. Fracture surface analysis revealed a cohesive failure mechanism due to strong inter-particle bonding in spruce pellets as a resulting from a plastic flow of the amorphous wood polymers, forming solid polymer bridges between adjacent particles. Fracture surfaces of pellets made from torrefied spruce possessed gaps and voids between adjacent particles due to a spring back effect after pelletization. They showed no signs of inter-particle polymer bridges indicating that bonding is likely limited to Van der Waals forces and mechanical fiber interlocking.
Wolfgang Stelte - One of the best experts on this subject based on the ideXlab platform.
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process optimization of combined biomass torrefaction and pelletization for fuel pellet production a parametric study
Applied Energy, 2015Co-Authors: Magnus Rudolfsson, Wolfgang Stelte, Torbjorn A LestanderAbstract:Torrefaction of plant biomass has the capacity to produce a fuel with increased energy density and homogeneity, but there are reports that it changes the Pelletizing properties of the biomass, making it more difficult to obtain high quality pellets. A parametric study was therefore conducted in which three key qualitative parameters, degree of torrefaction (250–300°C), moisture content (0–10%) and Pelletizing temperature (125–180°C), were varied according to a five level fractional factorial design, also including particle size as a qualitative parameter. Pelletizing at 300MPa (pellet densities: 1.0–1.2mg/mm3) was undertaken using a single pellet press and the responses recorded were compression work (Wcomp), maximal force to overcome static friction (Fmax), kinetic friction work (Wfric), single pellet dimensions and strength. Small particles reduced Wcomp and Fmax, but increased strength. As expected, all other parameters also had significant effects. In general, less energy was required for Wcomp, Wfric and Fmax at lower degrees of torrefaction and higher moisture contents and when Pelletizing was conducted at higher temperatures. The process window to optimize pellet strength was narrow and, surprisingly, somewhat higher moisture content at higher degrees of torrefaction increased strength. This narrow production window in combination with feedstock variations may, in practical Pelletizing situations, result in varying quality. Furthermore, the study illustrates that factorial experiments using single-pellet devices provide new insights that are of importance for the next generation of Pelletizing of torrefied biomass.
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reprint of Pelletizing properties of torrefied wheat straw
Biomass & Bioenergy, 2013Co-Authors: Wolfgang Stelte, Niels Peter K Nielsen, Hans Ove Hansen, Jonas Dahl, Lei Shang, Anand R. SanadiAbstract:Abstract Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and Pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the Pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the Pelletizing analyses have shown that these changes correlate to changes in the Pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.
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Pelletizing properties of torrefied wheat straw
Biomass & Bioenergy, 2013Co-Authors: Wolfgang Stelte, Niels Peter K Nielsen, Hans Ove Hansen, Jonas Dahl, Lei Shang, Anand R. SanadiAbstract:Combined torrefaction and pelletization are used to increase the fuel value of biomass by increasing its energy density and improving its handling and combustion properties. However, pelletization of torrefied biomass can be challenging and in this study the torrefaction and Pelletizing properties of wheat straw have been analyzed. Laboratory equipment has been used to investigate the Pelletizing properties of wheat straw torrefied at temperatures between 150 and 300 °C. IR spectroscopy and chemical analyses have shown that high torrefaction temperatures change the chemical properties of the wheat straw significantly, and the Pelletizing analyses have shown that these changes correlate to changes in the Pelletizing properties. Torrefaction increase the friction in the press channel and pellet strength and density decrease with an increase in torrefaction temperature.
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fuel pellets from wheat straw the effect of lignin glass transition and surface waxes on Pelletizing properties
Bioenergy Research, 2012Co-Authors: Wolfgang Stelte, Jens Kai Holm, Ulrik Birk Henriksen, Jesper Ahrenfeldt, Craig M Clemons, Anand R. SanadiAbstract:The utilization of wheat straw as a renewable energy resource is limited due to its low bulk density. Pelletizing wheat straw into fuel pellets of high density increases its handling properties but is more challenging compared to Pelletizing woody biomass. Straw has a lower lignin content and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the Pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the Pelletizing process and pellet strength are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively. Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two Pelletizing temperatures were chosen—one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed at 30°C have a lower density and compression strength and a tendency to expand in length after the Pelletizing process compared to pellets pressed at 100°C. At low temperatures, surface extractives have a lubricating effect and reduce the friction in the press channel of a pellet mill while no such effect is observed at elevated temperatures. Fuel pellets made from extracted wheat straw have a slightly higher compression strength which might be explained by a better interparticle adhesion in the absence of hydrophobic surface waxes.
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Fuel pellets from biomass: The importance of the Pelletizing pressure and its dependency on the processing conditions
Fuel, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Søren Barsberg, Jesper Ahrenfeldt, Ulrik Birk HenriksenAbstract:Abstract The aim of the present study was to identify the key factors affecting the Pelletizing pressure in biomass pelletization processes. The impact of raw material type, pellet length, temperature, moisture content and particle size on the pressure build up in the press channel of a pellet mill was studied using a single pellet press unit. It was shown that the Pelletizing pressure increased exponentially with the pellet length. The rate of increase was dependent on biomass species, temperature, moisture content and particle size. A mathematical model, predicting the Pelletizing pressure, was in good accordance with experimental data. It was shown that increasing the temperature resulted in a decrease of the Pelletizing pressure. Infrared spectra taken from the pellets surface, indicated hydrophobic extractives on the pellet surface, for pellets produced at higher temperatures. The extractives act as lubricants, lowering the friction between the biomass and the press channel walls. The effect of moisture content on the Pelletizing pressure was dependent on the raw material species. Different particle size fractions, from below 0.5 mm up to 2.8 mm diameter, were tested, and it was shown that the Pelletizing pressure increased with decreasing particle size. The impact of Pelletizing pressure on pellet density was determined, and it was shown that a Pelletizing pressure above 200 MPa resulted only in minor increase in pellet density.
Jens Kai Holm - One of the best experts on this subject based on the ideXlab platform.
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Fundamentals of Biomass pellet production
2015Co-Authors: Jens Kai Holm, Ulrik Birk Henriksen, Johan E. Hustad, Lasse Holst SørensenAbstract:Pelletizing experiments and theoretical modeling of the Pelletizing process have been carried out with the aim of understanding the fundamental physical-chemical mechanisms that control the quality and durability of biomass pellets. A small-scale California pellet mill (25 kg/h) is used to test the Pelletizing performance of two wood species, the hardwood beech and the softwood pine. In accordance with experiences from large-scale pellets production, the test results show that the production of pellets from beech is significantly more troublesome than production of pellets from pine. Addition of 1 wt% calcium soap to the beech dust lowers the power consumption of the pellet mill. However, the calcium soap furthermore reduces the friction of the channels in the matrix, leading to lower durability of the produced pellets. It is proposed that the difference in Pelletizing performance is a direct consequence of the difference in wood cell structure between hardwoods and softwoods, which in turn affects the mechanical properties of the biomass during pelletization. A novel model gives a theoretical basis for this finding.
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fuel pellets from wheat straw the effect of lignin glass transition and surface waxes on Pelletizing properties
Bioenergy Research, 2012Co-Authors: Wolfgang Stelte, Jens Kai Holm, Ulrik Birk Henriksen, Jesper Ahrenfeldt, Craig M Clemons, Anand R. SanadiAbstract:The utilization of wheat straw as a renewable energy resource is limited due to its low bulk density. Pelletizing wheat straw into fuel pellets of high density increases its handling properties but is more challenging compared to Pelletizing woody biomass. Straw has a lower lignin content and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the Pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the Pelletizing process and pellet strength are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively. Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two Pelletizing temperatures were chosen—one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed at 30°C have a lower density and compression strength and a tendency to expand in length after the Pelletizing process compared to pellets pressed at 100°C. At low temperatures, surface extractives have a lubricating effect and reduce the friction in the press channel of a pellet mill while no such effect is observed at elevated temperatures. Fuel pellets made from extracted wheat straw have a slightly higher compression strength which might be explained by a better interparticle adhesion in the absence of hydrophobic surface waxes.
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Fuel pellets from biomass: The importance of the Pelletizing pressure and its dependency on the processing conditions
Fuel, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Søren Barsberg, Jesper Ahrenfeldt, Ulrik Birk HenriksenAbstract:Abstract The aim of the present study was to identify the key factors affecting the Pelletizing pressure in biomass pelletization processes. The impact of raw material type, pellet length, temperature, moisture content and particle size on the pressure build up in the press channel of a pellet mill was studied using a single pellet press unit. It was shown that the Pelletizing pressure increased exponentially with the pellet length. The rate of increase was dependent on biomass species, temperature, moisture content and particle size. A mathematical model, predicting the Pelletizing pressure, was in good accordance with experimental data. It was shown that increasing the temperature resulted in a decrease of the Pelletizing pressure. Infrared spectra taken from the pellets surface, indicated hydrophobic extractives on the pellet surface, for pellets produced at higher temperatures. The extractives act as lubricants, lowering the friction between the biomass and the press channel walls. The effect of moisture content on the Pelletizing pressure was dependent on the raw material species. Different particle size fractions, from below 0.5 mm up to 2.8 mm diameter, were tested, and it was shown that the Pelletizing pressure increased with decreasing particle size. The impact of Pelletizing pressure on pellet density was determined, and it was shown that a Pelletizing pressure above 200 MPa resulted only in minor increase in pellet density.
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Pelletizing properties of torrefied spruce
Biomass & Bioenergy, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Jesper Ahrenfeldt, Lei Shang, Craig M Clemons, Ulrik Birk HenriksenAbstract:Abstract Torrefaction is a thermo-chemical conversion process improving the handling, storage and combustion properties of wood. To save storage space and transportation costs, it can be compressed into fuel pellets of high physical and energetic density. The resulting pellets are relatively resistant to moisture uptake, microbiological decay and easy to comminute into small particles. The present study focused on the Pelletizing properties of spruce torrefied at 250, 275 and 300 °C. The changes in composition were characterized by infrared spectroscopy and chemical analysis. The Pelletizing properties were determined using a single pellet press and pellet stability was determined by compression testing. The bonding mechanism in the pellets was studied by fracture surface analysis using scanning electron microscopy. The composition of the wood changed drastically under torrefaction, with hemicelluloses being most sensitive to thermal degradation. The chemical changes had a negative impact, both on the Pelletizing process and the pellet properties. Torrefaction resulted in higher friction in the press channel of the pellet press and low compression strength of the pellets. Fracture surface analysis revealed a cohesive failure mechanism due to strong inter-particle bonding in spruce pellets as a resulting from a plastic flow of the amorphous wood polymers, forming solid polymer bridges between adjacent particles. Fracture surfaces of pellets made from torrefied spruce possessed gaps and voids between adjacent particles due to a spring back effect after pelletization. They showed no signs of inter-particle polymer bridges indicating that bonding is likely limited to Van der Waals forces and mechanical fiber interlocking.
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effect of fiber orientation on compression and frictional properties of sawdust particles in fuel pellet production
Energy & Fuels, 2009Co-Authors: Niels Nielsen, Jens Kai Holm, Claus FelbyAbstract:The increasing production of wood pellets has increased the importance of optimizing the raw materials. The Pelletizing process is affected by differences in the raw materials, but knowledge of which of the wood’s properties that cause these differences is limited. The present study investigates the effect of fiber orientation in the raw material particles of sawdusts from European beech (Fagus sylvatica L.) Quaking aspen (Populus tremula L.) and Scots pine (Pinus sylvestris L.) on their Pelletizing properties. Sawdusts with the fibers oriented along the plane of the particles (longitudinal fiber orientation) and across the plane of the particles (transverse fiber orientation), respectively, were prepared, and the effect was quantified by measuring the compression and frictional properties of the sawdust in single-pellet productions, along with measuring the pellet strength. The results showed that sawdust with transverse fiber orientation required less energy to compress, and to press through the die, wh...
Phani Adapa - One of the best experts on this subject based on the ideXlab platform.
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Life cycle assessment of densified wheat straw pellets in the Canadian Prairies
The International Journal of Life Cycle Assessment, 2012Co-Authors: Edmund Mupondwa, Satyanarayan Panigrahi, Lope G. Tabil, Phani AdapaAbstract:Purpose Densification, a process used to manufacture pellets in order to increase biomass bulk density, plays a crucial role in the economics of biomass utilization. The Canadian Prairies produce large quantities of agricultural residues each year, in particular wheat straw. This study performs life cycle assessment of wheat straw pellets by evaluating environmental effects of the entire pellet production system comprising feedstock production (on-farm wheat straw production), harvesting, baling, transportation, and the industrial processing involving drying, grinding, Pelletizing, and packing in the densification plant. The effects of each process on the environmental performance of wheat straw pellets were investigated. Methods This study was conducted using LCA software and incorporating the Ecoinvent database supplemented with literature data for the Canadian Prairies. Wheat straw pellets manufactured from the densification plant are evaluated with respect to their use of resources and energy consumption. Environmental emissions associated with the agricultural processing and manufacturing systems are quantified. Sensitivity analysis is conducted to compare allocation methods and investigate the environmental impact of Pelletizing and drying processes. The functional unit is defined as 1 kg wheat straw pellet. Results and discussion The study quantified the environmental impact of producing wheat straw pellets in terms of global warming potential, acidification, eutrophication, ozone layer depletion, abiotic depletion, human toxicity, photochemical oxidation, fresh water aquatic ecotoxicity, and terrestrial ecotoxicity. Drying, Pelletizing, and fertilizer are the main contributors to global warming, acidification, abiotic depletion, human toxicity, terrestrial ecotoxicity, photochemical oxidation, and most of the other environmental impacts. Wheat seed has more impact on eutrophication. Transportation has an impact on ozone layer depletion, while grinding has an effect on freshwater aquatic ecotoxicity. Conclusions The environmental impact of materials and energy fluxes on producing wheat straw pellet in the Canadian Prairies is assessed. The effect of each processing step on the entire manufacturing process is described. Overall, drying and Pelletizing processes contribute the most environmental burdens except eutrophication and terrestrial ecotoxicity which are dominated by agricultural fertilizer/seed utilization and harvesting. In order to mitigate the environmental impact of wheat straw pellet production, minimizing energy consumption and machinery burdens from the drying and Pelletizing processes are the main intervention points for wheat straw densification. Fertilizer production and utilization are key variables in strategies to lower eutrophication and terrestrial ecotoxicity.
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Life cycle assessment of densified wheat straw pellets in the Canadian Prairies
International Journal of Life Cycle Assessment, 2012Co-Authors: Xue Li, Edmund Mupondwa, Satyanarayan Panigrahi, Lope G. Tabil, Phani AdapaAbstract:Densification, a process used to manufacture pellets in order to increase biomass bulk density, plays a crucial role in the economics of biomass utilization. The Canadian Prairies produce large quantities of agricultural residues each year, in particular wheat straw. This study performs life cycle assessment of wheat straw pellets by evaluating environmental effects of the entire pellet production system comprising feedstock production (on-farm wheat straw production), harvesting, baling, transportation, and the industrial processing involving drying, grinding, Pelletizing, and packing in the densification plant. The effects of each process on the environmental performance of wheat straw pellets were investigated. This study was conducted using LCA software and incorporating the Ecoinvent database supplemented with literature data for the Canadian Prairies. Wheat straw pellets manufactured from the densification plant are evaluated with respect to their use of resources and energy consumption. Environmental emissions associated with the agricultural processing and manufacturing systems are quantified. Sensitivity analysis is conducted to compare allocation methods and investigate the environmental impact of Pelletizing and drying processes. The functional unit is defined as 1 kg wheat straw pellet. The study quantified the environmental impact of producing wheat straw pellets in terms of global warming potential, acidification, eutrophication, ozone layer depletion, abiotic depletion, human toxicity, photochemical oxidation, fresh water aquatic ecotoxicity, and terrestrial ecotoxicity. Drying, Pelletizing, and fertilizer are the main contributors to global warming, acidification, abiotic depletion, human toxicity, terrestrial ecotoxicity, photochemical oxidation, and most of the other environmental impacts. Wheat seed has more impact on eutrophication. Transportation has an impact on ozone layer depletion, while grinding has an effect on freshwater aquatic ecotoxicity. The environmental impact of materials and energy fluxes on producing wheat straw pellet in the Canadian Prairies is assessed. The effect of each processing step on the entire manufacturing process is described. Overall, drying and Pelletizing processes contribute the most environmental burdens except eutrophication and terrestrial ecotoxicity which are dominated by agricultural fertilizer/seed utilization and harvesting. In order to mitigate the environmental impact of wheat straw pellet production, minimizing energy consumption and machinery burdens from the drying and Pelletizing processes are the main intervention points for wheat straw densification. Fertilizer production and utilization are key variables in strategies to lower eutrophication and terrestrial ecotoxicity.
Ulrik Birk Henriksen - One of the best experts on this subject based on the ideXlab platform.
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Fundamentals of Biomass pellet production
2015Co-Authors: Jens Kai Holm, Ulrik Birk Henriksen, Johan E. Hustad, Lasse Holst SørensenAbstract:Pelletizing experiments and theoretical modeling of the Pelletizing process have been carried out with the aim of understanding the fundamental physical-chemical mechanisms that control the quality and durability of biomass pellets. A small-scale California pellet mill (25 kg/h) is used to test the Pelletizing performance of two wood species, the hardwood beech and the softwood pine. In accordance with experiences from large-scale pellets production, the test results show that the production of pellets from beech is significantly more troublesome than production of pellets from pine. Addition of 1 wt% calcium soap to the beech dust lowers the power consumption of the pellet mill. However, the calcium soap furthermore reduces the friction of the channels in the matrix, leading to lower durability of the produced pellets. It is proposed that the difference in Pelletizing performance is a direct consequence of the difference in wood cell structure between hardwoods and softwoods, which in turn affects the mechanical properties of the biomass during pelletization. A novel model gives a theoretical basis for this finding.
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fuel pellets from wheat straw the effect of lignin glass transition and surface waxes on Pelletizing properties
Bioenergy Research, 2012Co-Authors: Wolfgang Stelte, Jens Kai Holm, Ulrik Birk Henriksen, Jesper Ahrenfeldt, Craig M Clemons, Anand R. SanadiAbstract:The utilization of wheat straw as a renewable energy resource is limited due to its low bulk density. Pelletizing wheat straw into fuel pellets of high density increases its handling properties but is more challenging compared to Pelletizing woody biomass. Straw has a lower lignin content and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the Pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the Pelletizing process and pellet strength are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively. Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two Pelletizing temperatures were chosen—one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed at 30°C have a lower density and compression strength and a tendency to expand in length after the Pelletizing process compared to pellets pressed at 100°C. At low temperatures, surface extractives have a lubricating effect and reduce the friction in the press channel of a pellet mill while no such effect is observed at elevated temperatures. Fuel pellets made from extracted wheat straw have a slightly higher compression strength which might be explained by a better interparticle adhesion in the absence of hydrophobic surface waxes.
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Fuel pellets from biomass: The importance of the Pelletizing pressure and its dependency on the processing conditions
Fuel, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Søren Barsberg, Jesper Ahrenfeldt, Ulrik Birk HenriksenAbstract:Abstract The aim of the present study was to identify the key factors affecting the Pelletizing pressure in biomass pelletization processes. The impact of raw material type, pellet length, temperature, moisture content and particle size on the pressure build up in the press channel of a pellet mill was studied using a single pellet press unit. It was shown that the Pelletizing pressure increased exponentially with the pellet length. The rate of increase was dependent on biomass species, temperature, moisture content and particle size. A mathematical model, predicting the Pelletizing pressure, was in good accordance with experimental data. It was shown that increasing the temperature resulted in a decrease of the Pelletizing pressure. Infrared spectra taken from the pellets surface, indicated hydrophobic extractives on the pellet surface, for pellets produced at higher temperatures. The extractives act as lubricants, lowering the friction between the biomass and the press channel walls. The effect of moisture content on the Pelletizing pressure was dependent on the raw material species. Different particle size fractions, from below 0.5 mm up to 2.8 mm diameter, were tested, and it was shown that the Pelletizing pressure increased with decreasing particle size. The impact of Pelletizing pressure on pellet density was determined, and it was shown that a Pelletizing pressure above 200 MPa resulted only in minor increase in pellet density.
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Pelletizing properties of torrefied spruce
Biomass & Bioenergy, 2011Co-Authors: Wolfgang Stelte, Jens Kai Holm, Anand R. Sanadi, Jesper Ahrenfeldt, Lei Shang, Craig M Clemons, Ulrik Birk HenriksenAbstract:Abstract Torrefaction is a thermo-chemical conversion process improving the handling, storage and combustion properties of wood. To save storage space and transportation costs, it can be compressed into fuel pellets of high physical and energetic density. The resulting pellets are relatively resistant to moisture uptake, microbiological decay and easy to comminute into small particles. The present study focused on the Pelletizing properties of spruce torrefied at 250, 275 and 300 °C. The changes in composition were characterized by infrared spectroscopy and chemical analysis. The Pelletizing properties were determined using a single pellet press and pellet stability was determined by compression testing. The bonding mechanism in the pellets was studied by fracture surface analysis using scanning electron microscopy. The composition of the wood changed drastically under torrefaction, with hemicelluloses being most sensitive to thermal degradation. The chemical changes had a negative impact, both on the Pelletizing process and the pellet properties. Torrefaction resulted in higher friction in the press channel of the pellet press and low compression strength of the pellets. Fracture surface analysis revealed a cohesive failure mechanism due to strong inter-particle bonding in spruce pellets as a resulting from a plastic flow of the amorphous wood polymers, forming solid polymer bridges between adjacent particles. Fracture surfaces of pellets made from torrefied spruce possessed gaps and voids between adjacent particles due to a spring back effect after pelletization. They showed no signs of inter-particle polymer bridges indicating that bonding is likely limited to Van der Waals forces and mechanical fiber interlocking.
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Experimental Verification of Novel Pellet Model Using a Single Pelleter Unit
Energy & Fuels, 2007Co-Authors: Jens Kai Holm, Ulrik Birk Henriksen, Johan E. Hustad, Kim Wand, Dorthe PosseltAbstract:Pelletization of biomass for bioenergy purposes has established itself as an important step toward a reduction in the emissions of greenhouse gases. A novel pellet model describing the pressure forces in a press channel of a pellet mill has previously been published. The model gives a theoretical explanation of how the biomass-specific parameters, such as the friction coefficient and Poisson's ratio, influence the Pelletizing pressure. The model showed that the Pelletizing pressure increases exponentially as a function of the channel length. In the present paper, the pellet model is verified experimentally. When the back pressure needed to press pellets of different lengths out of the press channel is measured, it is shown that the Pelletizing pressure does increase exponentially as a function of the pellet length. Second, the back pressures of the hardwood beech are higher than the corresponding pressures of the softwood pine for all tested pellet lengths. Least-squares fit of the model to the data shows that the fitted parameters are in agreement with values from the literature. The procedure for using a single pelleter unit as a means for simulating an industrial Pelletizing process in a controllable way is described.
