Durable Pellets Research Articles

Structural and molecular modifications of woody biomass under minimal torrefaction conditions toward making durable pellets

Extensive research has been published on pelletizing severely torrefied biomass with the aid of binders, but limited studies have investigated the structural modifications of biomass during mild torrefaction. This study investigates the effects of several combinations of minimal torrefaction temperatures (230°C and 250°C) and relatively short durations (10, 15, and 30 minutes) on the thermophysical and molecular structure of the model woody biomass loblolly pine (Pinus Taeda) residues. The low severity treated biomass is compared with the untreated biomass and the biomass torrefied at 270°C for 30 minutes. Structural characterization methods include laser diffraction for particle size distribution and Brunauer-Emmett-Teller (BET) analysis to evaluate specific surface area. Additionally, FTIR, XRD, and TGA are used to assess changes in crystallinity and thermochemical composition. The woody residue torrefied at 250°C for 10 minutes exhibited a higher BET surface area (4.7 m²/g) than torrefied at 250°C for 15 minutes (3.5 m²/g). At a constant temperature of 250°C, the crystallinity index increases with the treatment duration, emphasizing the effect of time on retaining more hydroxyl groups that may act as binders for pelletization. This study demonstrates that minimizing the combination of torrefaction time and temperature can help control the degree of biomass molecular structure degradation thus minimizing overall mass loss, offering potential applications in the emerging biocarbon pellet industry.

Utilizing hydrolysis residue from bioethanol production as an additive for solid fuel pellets

Cellulosic bioethanol is produced from the structural carbohydrates (cellulose and hemicellulose) in non-food biomass feedstocks via biochemical conversion. A great amount of non-hydrolyzed material, mainly lignin, is left out as a residual byproduct in this process. For the overall process economy, a possible value added use of this hydrolysis residue is to produce solid fuel pellets to power the bioethanol production itself or residential combustion because lignin has a high net energy value and a low fuel-ash content. Moreover, lignin with its self-bonding behavior can serve as a natural binder if used as an additive to make stronger and more durable pellets for energy and other biorefinery applications. In this study, solid fuel pellets fully or partially made from corn stover hydrolysis residue were evaluated from physical, thermochemical, and hygroscopic perspectives. With 10% hydrolysis residue additive, pellet durability increased from 80.7% to 90.1% and reached 92.8% with further hydrolysis residue addition. Enhancements on pellet mechanical properties were also observed by adding 50% or more hydrolysis residue. Energy density increased from 13.7 GJ/m3 to as high as 17.6 GJ/m3 with the amount of additive increasing from none to 100%. Thermal gravimetric and differential scanning calorimetry results revealed that hydrolysis residue strengthened pellet thermal properties (heating value, thermal stability, and exothermal performance). FTIR and NMR spectra were studied to identify inner-unit linkages in aromatic and side-chain regions of lignin to understand its self-bonding behavior. Pellets also showed increased hydrophobicity and better water resistance when a higher percentage of hydrolysis residue additive was used.

Characterization and Energy Densification of Mayhaw Jelly Production Wastes Using Hydrothermal Carbonization.

Mayhaw jelly, made from mayhaw berries from the southern United States, is a popular food product that on processing produces a berry pomace waste. Little information is available in the literature about this waste or how to valorize it. This study investigated this food production waste and its possibilities for conversion to a biofuel. Dried mayhaw berry wastes were characterized with fiber analysis using the US National Renewable Energy Laboratory methods. After drying and grinding, hydrothermal carbonization was applied to the mayhaw berry wastes, the mayhaw waste without seeds, and mayhaw waste seeds. Fourier transform infrared spectroscopy (FTIR) was performed on mayhaw berry wastes, mayhaw waste without seeds, and mayhaw waste seeds. Calorimetry revealed the fuel value of each component of the waste and of the dried mayhaw berry wastes without any component separated. Friability testing on pellets of the biomass investigated their durability. Fiber analysis indicated a high proportion of lignin compared to cellulose in the dried mayhaw waste. Hydrothermal carbonization did not enhance the fuel value of the seeds due to their tough outer coat that inhibited hydrothermal carbonization's high ionic-product water penetration. Other mayhaw berry waste samples had enhanced fuel value after treatment at 180 or 250 °C for 5 min, with a higher fuel value attained for 250 °C treatment. After hydrothermal carbonization, the wastes were easily pelletized into durable pellets. Fourier transform infrared spectroscopy characterization indicated raw seeds had high lignin content, as did the hydrothermal carbonization-treated mayhaw berry wastes. Hydrothermal carbonization is a process not previously applied to mayhaw berry wastes. This study fills in the gaps of this waste biomass' potential to become a biofuel.

Thermal conditioning of remoistened wheat straw to produce durable pellets

Agricultural biomass like wheat straw is known to be lacking natural binders to form durable pellets. Our previous research had shown that steam explosion of wood improved the durability of pellets. However, treated wood required drying prior to pelletization. Thermal conditioning is practiced in the animal feed industry to modify the ingredients of animal feed to produce high quality pellets. We hypothesized that thermal treatment of straw would result in biomass pellets with improved durability when compared to pellets made from untreated biomass. To test this hypothesis, the moisture content (mc) of the straw samples was adjusted to 5%, 10%, and 15% (wet basis). The moistened samples were subjected to dry heat in a sealed reactor set at 80, 100, and 120 °C for 5, 10, and 15 min. The treated straw samples were pelletized by using a single piston cylinder system. The highest durability 91.5% belonged to the treatment of 10% mc straw at 100 °C for 5 min. A response surface method confirmed that the initial mc 10%, treatment temperature 100 °C, and treatment time 5 min, produced the most durable pellets with the lowest unit energy input in forming pellets.

Effect of Die Geometry and Moisture Content on Pelletizing of Palm Pruning Residues

Palm pruning residues are potential pellet raw material, which are quite abundant in regions with hot climates. In pelletizing process, raw material properties and pellet machine features are the main factors affecting the final pellet quality. In this study, 5 mm sieve hole diameter milled palm pruning residues was pelleted using two different pellet dies and two different pelletizing moisture. First die (D1) has 25 mm total length, 17° inlet angle and 10 mm inlet depth. The second die (D2) has 35 mm total length, 33° inlet angle and 5 mm inlet depth. The inlet and outlet hole diameter of both die are 11 mm and 8 mm, respectively. Pelleting moisture is fixed at two different levels as 10% (M10) and 14% (M14). The change of production parameters and pellet physical properties were investigated according to the die type and moisture content parameters. Increasing pelletizing moisture had a positive effect on the production capacity and it was obtained as 82.44, 103.1, 134.05, 145.49 kg h-1 for D1-M10, D1-M14, D2-M10 and D2-M14 pellets, respectively. The increase in pelletizing moisture caused degradation of the pellet forms, which is more evident in the pellets produced in the D1 die. Pellets produced in the D2 die are more compressed and denser and lower moisture content. The increase in total die length resulted in heavier and denser pellet production, resulting in higher production capacity and low specific energy consumption. Pellet durability index (%, ar) of D1-M10, D1-M14, D2-M10 and D2-M14 were measured as 95.53; 92.29 and 97.74; 98.32, respectively. It was concluded that the longer active die length can tolerate high moisture content pelletizing, and durable pellets can be produced in a wide moisture content range. In addition, die conical dimensions and die length are the factors that needs to be optimized according to different raw materials.

Improvement of the pellet quality and fuel characteristics of agricultural residues through mild hydrothermal treatment

Agricultural residues such as straw and grasses lack lignin and other natural binders, which make them difficult to produce durable pellets. Hydrothermal treatment modifies the complex hemicellulose, cellulose and lignin structure, which holds promise for making durable pellets from crop residues. However, most hydrothermal treatment applies mild temperature (180−260 °C), which is an energy-intensive process. In this research, mild hydrothermal treatment was applied to pine woodchip, wheat straw, timothy hay, and canola straw prior to pelletization. The mild hydrothermal treatment consisted of exposing the ground biomass to 135℃ for 90 min in an autoclave unit. The results show that mild hydrothermal treatment is a promising way to improve agricultural pellet quality and fuel properties. After treatment, the durability and hardness of all pellets increased, especially for canola straw (from 2.21 N/mm2 to 4.67 N/mm2 and 83.42%–95.41% respectively). The mass density of woodchip, wheat straw, timothy hay and canola pellets increased by 2.89 %, 5.85 %, 3.69 %, and 9.21 %. and the volumetric energy density increased by 8.04 %, 7.46 %, 8.34 % and 12.59 %, respectively. The elevated devolatilization index and decreased activation energy show volatile matters of all pellets are easier to release during pyrolysis. Thus, mild hydrothermal treatment is a clean and economical method for improving agricultural pellets quality and the heat applications. It has the potential to be applied in industrial pellet manufacture.

Effect of binding materials on physical and fuel characteristics of bagasse based pellets

Growing energy demand and environmental issues are demanding the use of biomass based energy generation processes. However, inherent low bulk density of biomass poses problems of handling, storage and transportation which hinders its large scale application and demands its pretreatment. Pelletization process can address this inherent issue of biomass by converting it into a dense pellet having a regular shape and size. The strength of raw biomass pellet is very low and requires the use of binders. Therefore, in this study, cow dung and molasses were used as binders for the formation of bagasse based pellets. The effects of operating parameters, biomass composition, molasses concentration and drying time, on the physical and fuel characteristics of the pellets were studied and the response was recorded in terms of bulk density, pellet density, durability index, calorific value and proximate analysis. Based on experimental results, a significant trade off between durability index and calorific values of the pellets was observed and thus, the optimization of operating parameters was carried out. At optimal conditions, the pellet has the calorific value of 16.43 MJ kg−1 with 84.2% durability index. Subsequently, torrefaction of biomass was performed to upgrade the energy quality of the pellets. Thermal treatment resulted in 10% improvement in energy content of the biomass and also raised the durability of the pellet slightly. Moreover, the application of cow dung as a binder can be considered as a sustainable approach to improve the physical and fuel properties especially durability index of the pellets. Thus, these durable pellets can be used as a fuel in energy generation processes and for heating purposes in rural regions.

Investigation on hydrochar and macromolecules recovery opportunities from food waste after hydrothermal carbonization

In this paper, the performance of hydrothermal carbonization (HTC) was investigated on real food waste (FW) to improve resource recovery opportunities. The HTC was performed in a high pressure batch reactor (without addition of water) at desired temperatures for different durations to study the properties of solid hydrochar (HC) and process water (PW) produced during the process. The reaction temperature and run time of 200 °C and 1 h, respectively were found suitable to produce the HC (high heating value = ~30 MJ/kg) having properties similar to that of the peat/lignite coal. Moreover, durable pellets could also be prepared from HC without addition of binder. The kinetic constants for HC combustion were also predicted using non-isothermal model-free approach for the data obtained from thermo-gravimetric analysis. In the PW samples recovered after HTC, several value-added compounds like 2,5-hydroxymethyl furfural, humic-like substances (HLS), proteins, carbohydrates and volatile fatty acids could be detected in appreciable quantities. However, longer reaction resulted in further degradation of above macromolecules into VFAs. Based on the observations, a pathway for FW degradation during HTC process is proposed. Moreover, the HLS and proteins mixture recovered from the PW sample exhibited no adverse impact on seed growth. The present study demonstrates that the HTC can be a potential treatment method for FW to recover a variety of useful materials. Further studies should focus on developing cost-effective methods for the recovery of various macromolecules from PW.

Pelletization of Refuse-Derived Fuel with Varying Compositions of Plastic, Paper, Organic and Wood

The combustible fraction of municipal solid waste (MSW) is called refuse-derived fuel (RDF). RDF is a blend of heterogeneous materials and thus its handling is challenging. Pelletization is an efficient treatment to minimize the heterogeneity. In this research, typical RDF compositions were prepared by mixing several mass fractions of paper, plastic, household organic and wood. The collected compositions were ground, wetted to 20% moisture content (wet basis) and pelletized. Increasing the plastic content from 20% to 40% reduced the pelletization energy but increased the pellet’s calorific value. Pellets with higher plastic content generated more dust when exposed to shaking. Making durable pellets with 40% plastic content needed an increase in die temperature from 80 °C to 100 °C. Increasing the paper content from 30% to 50% increased the durability but consumed higher energy to form pellets. Paper particles increased the friction between pellet’s surface and die wall as was evident from expulsion energy. Force versus displacement curve for material compression revealed that the RDF compositions have rigid material characteristics.

Comparison of Drying Rates of Ground Western Red Cedar with Hemlock, Birch, Aspen, and Spruce/Pine/Douglas Fir

HighlightsWRC and SPF generate the largest fraction of small particles (<0.5 mm) during grinding.WRC is slightly low in total sugars, high in lignin content (should make durable pellets), and high in extractives.Aspen followed by WRC has the highest drying rate and the shortest drying time amongst all samples.Smoke point is similar for all wood species and is ~180°C.Abstract.Western red cedar () and yellow cedar () are among the most valuable tree species in British Columbia. These species make up about 20% of the coastal timber volumes and mostly are used as lumber for construction applications where resistance against decay is important. The use of red cedar for pellet production has been uncertain because it appears cedar has a tendency to cause fires in rotary drum dryers when compared to other wood species like pine and Douglas Fir. The scientific reasons for the reported fire incident are not known. The goal of the current study is to investigate the drying rates and the range of combustion temperature for western red cedar and five other wood species that either are used or have potential to be used for palletization purposes in British Columbia. Red cedar and Spruce/Pine/Fir (SPF) generate the largest fraction of small particles (<0.5 mm) during grinding. Almost 93% of cedar particles are less than 1 mm. Cedar has a high carbon content and low oxygen content that causes cedar has higher calorific value than other species. During a drying process, aspen following by cedar has the highest drying rate and the shortest drying time amongst all samples. The smoke point is similar for all wood species and is ~180°C. So, in the case of high temperature drying (beyond the smoke point) of mixed feedstocks with similar size, red cedar dries faster and starts smoking at dryer output. Keywords: Chemical composition, Drying rate, Physical characterization, Smoke point, Western red cedar.

Physico-mechanical properties and thermal decomposition characteristics of pellets from Jatropha curcas L. residues as affected by water addition

Fruit hulls and seed shells from Jatropha curcas L. are considered valuable biomass residues to be used as fuel. In this study, J. curcas hulls and shells were blended and pressed into pellets. Different amounts of water were added to the raw materials before pelleting (0, 5, 10 and 15 g/100 g fresh matter) to improve the pellet durability. The outlet temperature of the pellets was inversely proportional to the amount of water added to the raw material. The thermal decomposition of all pellets showed typical decomposition kinetics between 180 and 500 °C. Moisture content, ash content, calorific values, dimension and solid density of the pellets fulfilled German standard requirements for commercial pellets, but not for highly durable pellets. The static and dynamic angle of repose and coefficient of static friction of the pellets were also studied. Bulk density and porosity were considerably influenced by water addition. To some extent, pellet durability was improved significantly (p ≤ 0.05) by water addition, whereas the highest abrasive resistance of pellets was achieved by the highest water addition. Jatropha curcas pellets have a good potential as a solid biofuel and a raw material for biochar production.

Effect of Torrefaction Temperature on Lignin Distribution of Larix kaempferiC. and Liriodendron tulipiferaL. Cubes and the Impact of Binder on Durability of Pellets Fabricated with the Torrefied Cubes

Larch (LAR) and yellow poplar (YP) cubes were torrefied at 180, 220 and 260°C for 50 min to investigate the effect of torrefaction temperature on chemical composition, fuel properties and pelletability. When increasing the torrefaction temperature from 180 to 220°C, lignin content of torrefied LAR and YP increased from 28 to 34% and from 21 to 23%, respectively. Xylose contents of LAR and YP decreased to 11% at the torefaction temperature of 260°C. The thermal degradation of xylose by the torrefaction treatment has a significant impact on increasing the ash content, higher heating value and weight loss of the torrefied LAR and YP. When the lignin distribution of untreated and 180°C‐torrefied cubes were measured quantitatively by the microscopic analysis of SEM–EDX, the amount of lignin existing on the radial‐sectional areas of LAR and YP increased from 7.89 to 18.84% and from 6.37 to 17.71%, respectively. Durability of pellets fabricated with torrefied LAR and YP cubes decreased with the increase of torrefaction temperature. By the adjustment of a moisture content for the torrefied particles, durability of torrefied LAR pellets improved by 8–11% but that of YP decreased by 2–21%. Addition of 2 wt% starch, lignin and protein as a binder to 180°C‐ and 220°C‐torrefied LAR and YP affected the increase of pellets durability. Accordingly, it can be concluded that the addition of binder or moisture is needed to produce durable pellets made with torrefied LAR and YP while accounting for costs associated with the binders. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019

Waste to Carbon: Densification of Torrefied Refuse-Derived Fuel

In this work, for the first time, the feasibility of obtaining carbonized refuse-derived fuel (CRDF) pelletization from municipal solid waste (MSW) was shown. Production of CRDF by torrefaction of MSW could be the future of recycling technology. The objective was to determine the applied pressure needed to produce CRDF pellets with compressive strength (CS) comparable to conventional biomass pellets. Also, the hypothesis that a binder (water glass (WG)) applied to CRDF as a coating can improve CS was tested. The pelletizing was based on the lab-scale production of CRDF pellets with pressure ranging from 8.5 MPa to 76.2 MPa. The resulting CS pellets increased from 0.06 MPa to 3.44 MPa with applied pelletizing pressure up to the threshold of 50.8 MPa, above which it did not significantly improve (p < 0.05). It was found that the addition of 10% WG to 50.8 MPa CRDF pellets or coating them with WG did not significantly improve the CS (p < 0.05). It was possible to produce durable pellets from CRDF. The CS was comparable to pine pellets. This research advances the concept of energy recovery from MSW, particularly by providing practical information on densification of CRDF originating from the torrefaction of the flammable fraction of MSW–refuse-derived fuel. Modification of CRDF through pelletization is proposed as preparation of lower volume fuel with projected lower costs of its storage and transportation and for a wider adoption of this technology.

Codensification of Eucommia ulmoides Oliver stem with pyrolysis oil and char for solid biofuel: An optimization and characterization study

This paper presents the results regarding the parametric optimization and characterizations on codensification of Eucommia ulmoides Oliver stem using biochar and bio-oil as additives. The results reveal that the relative importance of different parameters contributing to the pellet physical stability follows the order of: particle size > bio-oil content > biochar content > pressure > bio-oil type, and smaller particles size (0.1–0.3 mm) is critical for the formation of durable pellets. The biochar functioned as the fuel promoter and improved the higher heating value and energy density, however, caused poor physical stability by secondary size reduction during densification. The apple tree branch pyrolysis oil acted as an effective binder, improved the surface morphology and enabled strong interlocking of the particles, therefore, enhanced the physical stability. Above all, codensification of Eucommia ulmoides Oliver stem with biochar and bio oil generated pellets with excellent physical stability and moisture resistance. The pellets also showed better fuel characteristics than the Eucommia ulmoides Oliver stem pellets, and the cost is significantly lower than the char pellets. With comprehensiveness, these results can guide the future industrial implementation of codensification technology for the production of clean, sustainable, and efficient fuel with low cost.

Mechanical properties and characteristics of wheat straw and pellets

Wheat straw pellets can be easily handled, transported and stored with reduced costs as compared with the raw material. The effect of pelletization process and densification parameters on the properties of the mixture of wheat straw powder and 40% epoxy 1092 as a binder was investigated. The samples were compressed into pellets using the lab-scale hydraulic press under various compacting pressures of 10, 12 and 15 bars and different die shapes and sizes (two cylindrical dies with diameters 10 and 18 mm (S1, S2), respectively, and a new hexagonal die of side length (s) = 6 mm (S3)). It was found that the pelleting process increased the fixed carbon content from 7.14% to 17.36%, the heating value from 15,600 kJ kg−1 to 27,800 kJ kg−1 and the bulk density 10 times when compared to a raw wheat straw powder. It was also found that type S2 at pressure 15 bar is the densest pellet and it had the maximum compression stress that reached 2798.54 kg m−3 and 70.02 MPa, respectively. The cylindrical pellet (type S1) of D = 18 mm at a pressure of 15 bar had the lowest water permeability of 2.35%. Pelletizing process had improved combustion characteristic parameters compared to raw biomass where combustion temperature ranges became higher, maximum weight loss rates and residues became lower that led to a higher combustion efficiency. Thermogravimetric analysis of wheat straw before and after pelleting process was analyzed to evaluate the combustion properties. Scanning electron microscopy images showed that the particle bonding was formed mainly from solid bridges, areas of cohesive failure due to lignin flow, and inter-diffusion between neighboring biomass particles. Images were investigated to explore the importance of compaction process. The images also showed that as the pressure decreases, the gap between the particles increases and produces the less durable pellet. It was found that the slagging index equals 0.38, which indicates that the pellet has a medium slagging inclination and for the fouling inclination (1.79), the wheat straw pellet has a relatively high fouling inclination.

Pelletization of Refuse-Derived Fuel Fluff to Produce High Quality Feedstock

Municipal solid waste (MSW) may be a suitable feedstock for thermochemical conversion. Current technologies process the MSW into refuse-derived fuel (RDF) fluff before conversion. Bench- and pilot-scale densification trials were conducted to determine the parameters required to produce a high quality feedstock from the MSW-RDF material in pellet form. The RDF was densified, as well as the biodegradable (paper and wood) fraction of the RDF stream to compare quality of pellets for the two material compositions. A single pelleting trial was conducted to examine the compaction parameters that would produce high quality pellets: sample material, grind size, moisture content, temperature, and pelleting pressure. It was determined that quality pellets, for both materials, were formed at a grind size of 6.35 mm at 16% moisture under pelleting conditions of 90 °C and 4000 N applied load. Pilot-scale pelleting was then completed to emulate industrial pelleting process utilizing the parameters from the single pelleting trials that were deemed to produce quality pellets. All of the samples produced durable pellets (88–94%), with the ash content around 20%. A techno-economic feasibility study determined that 6.35 mm diameter pellets could be produced for an average cost of $38/Mg, although the aggressive process of the size reduction required indicates that it may not be a technically feasible option.

The Role of Biomass Composition and Steam Treatment on Durability of Pellets

Steam treatment has been reported to improve the durability of wood pellet likely by changing the physical and chemical structures of wood particles, but published literature is inconclusive about which structure change is the major reason for enhanced durability. In this work, steam treatment was combined either with alkaline or with SO2 to study. The solids obtained after steam treatments along with a control sample were dried and each was compacted into pellets. The pellets were then tested for durability. Steam treatment alone dominated improvements in durability. The pellet durability increased with the amount of xylose, but xylose performed better in the pellet from raw poplar than did in the pellet from treated poplar. Water-soluble components contributed a maximum 4% of the durability of poplar pellets. The addition of lignin and sugars to substrates after steam treatment did not improve durability significantly. The surface modification that took place as a result of size reduction during steam treatment was the major reason, contributing about 50% of the durability of the pellet from steam-treated poplar. The acidity of steam treatment slightly affected the relative contributions of these structure changes on the durability. The new knowledge helps tailor the chemical and/or mechanical pretreatment involved in pelleting biomass to durable pellets.

Effects of extruder die head temperature and pre-gelatinized taro and broken rice flour level on physical properties of floating fish pellets

Two experiments were conducted to investigate the effects of pre-gelatinized (PG) taro and broken rice and extruder die temperatures on the physical properties of extruded pellets. The first experiment was conducted to evaluate the effects of PG taro and extruder die head temperature (125, 140, 155 and 170 °C) and a subsequent experiment was conducted using PG broken rice instead. All the blends were preconditioned to a 40% moisture content and then extruded using a single screw extruder. The three zones of the barrel temperature profile (70, 90 and 100 °C) and screw speed (150 rpm) of the extruder were constant throughout the extrusion cooking process. The physical properties of the pellets included floatability, expansion ratio, bulk density, pellet durability, water absorption and solubility, moisture content and pellet microstructure. The findings showed in both experiments that PG taro and broken rice inclusion levels and die temperature had significant effects on most of the physical properties of the pellets except for pellet durability index. Changing the inclusion rate of PG taro and broken rice from 15 to 25% significantly increased the expansion ratio and floatability of the extruded pellets. Similarly, as the die temperature was elevated in both experiment, the floatability of the extruded pellets in diet containing PG taro and broken rice increased by 114.62% and 21.88%, respectively. It was also noted that use of PG taro and broken rice resulted in highly durable pellets in all treatments. Further, microstructure analysis of the extruded pellets revealed that using PG taro and broken rice, the surface of the extruded pellets became coarser when the die temperature was elevated from 125 to 170 °C and the PG taro and broken rice inclusion level was at 15%. In conclusion, pre-gelatinized taro and broken rice could be used to manufacture higher quality floating pellets.

Method to Produce Durable Pellets at Lower Energy Consumption Using High Moisture Corn Stover and a Corn Starch Binder in a Flat Die Pellet Mill

A major challenge in the production of pellets is the high cost associated with drying biomass from 30 to 10% (w.b.) moisture content. At Idaho National Laboratory, a high-moisture pelleting process was developed to reduce the drying cost. In this process the biomass pellets are produced at higher feedstock moisture contents than conventional methods, and the high moisture pellets produced are further dried in energy efficient dryers. This process helps to reduce the feedstock moisture content by about 5-10% during pelleting, which is mainly due to frictional heat developed in the die. The objective of this research was to explore how binder addition influences the pellet quality and energy consumption of the high-moisture pelleting process in a flat die pellet mill. In the present study, raw corn stover was pelleted at moistures of 33, 36, and 39% (w.b.) by addition of 0, 2, and 4% pure corn starch. The partially dried pellets produced were further dried in a laboratory oven at 70 °C for 3-4 hr to lower the pellet moisture to less than 9% (w.b.). The high moisture and dried pellets were evaluated for their physical properties, such as bulk density and durability. The results indicated that increasing the binder percentage to 4% improved pellet durability and reduced the specific energy consumption by 20-40% compared to pellets with no binder. At higher binder addition (4%), the reduction in feedstock moisture during pelleting was <4%, whereas the reduction was about 7-8% without the binder. With 4% binder and 33% (w.b.) feedstock moisture content, the bulk density and durability values observed of the dried pellets were >510 kg/m3 and >98%, respectively, and the percent fine particles generated was reduced to <3%.

Method to Produce Durable Pellets at Lower Energy Consumption Using High Moisture Corn Stover and a Corn Starch Binder in a Flat Die Pellet Mill.

A major challenge in the production of pellets is the high cost associated with drying biomass from 30 to 10% (w.b.) moisture content. At Idaho National Laboratory, a high-moisture pelleting process was developed to reduce the drying cost. In this process the biomass pellets are produced at higher feedstock moisture contents than conventional methods, and the high moisture pellets produced are further dried in energy efficient dryers. This process helps to reduce the feedstock moisture content by about 5-10% during pelleting, which is mainly due to frictional heat developed in the die. The objective of this research was to explore how binder addition influences the pellet quality and energy consumption of the high-moisture pelleting process in a flat die pellet mill. In the present study, raw corn stover was pelleted at moistures of 33, 36, and 39% (w.b.) by addition of 0, 2, and 4% pure corn starch. The partially dried pellets produced were further dried in a laboratory oven at 70 °C for 3-4 hr to lower the pellet moisture to less than 9% (w.b.). The high moisture and dried pellets were evaluated for their physical properties, such as bulk density and durability. The results indicated that increasing the binder percentage to 4% improved pellet durability and reduced the specific energy consumption by 20-40% compared to pellets with no binder. At higher binder addition (4%), the reduction in feedstock moisture during pelleting was <4%, whereas the reduction was about 7-8% without the binder. With 4% binder and 33% (w.b.) feedstock moisture content, the bulk density and durability values observed of the dried pellets were >510 kg/m3 and >98%, respectively, and the percent fine particles generated was reduced to <3%.