Mill Screen Size Research Articles

Optimization of Slugging and Compression Process for Bicalutamide Tablets

The critical nature of pharmaceutical dosage forms necessitates the optimization of manufacturing process variables to achieve the desired product quality. In this study, slugging (Dry granulation) was selected as an appropriate granulation method to mitigate poor flow properties in the final bicalutamide blend. The chosen process variables include slug hardness, mill screen size, and mill speed. A 23-factorial design was employed to investigate these variables. Process parameters were reproducible, with minimal impact on tablet properties, even when roller speeds varied. Response surface models effectively examine the relationship between response variables and quantitative parameters. The input and process variables for the compression process were predetermined based on the desired quality attributes of bicalutamide tablets. Notably, the p-value for the slugging process was not more than 0.05, indicating their insignificance in tablet content uniformity. Product quality attributes affected by the compression process step include content uniformity, disintegration time, and dissolution. The optimal hardness range was found to be 2.0 to 7.0 kp.

Quantitative Estimation and Comparative Assessment of Particle Morphological Features and Energy Requirement During Hammer Milling of Softwood Chips and Wheat Straw

Highlights Quantified particle size and shapes generated during hammer milling of softwood and wheat straw. Size reductions in length and width correlated with milling energy requirement. Assessed the validity of existing comminution laws for predicting milling energy requirement. Improved milling energy requirement prediction for softwood based on size reductions. Abstract. The valorization of agricultural and woody residues into higher quality fuels is an attractive pathway and can contribute to decarbonizing the energy system. One essential step for the conversion of these residues to fuels is comminution through commercial mills. This study aimed to investigate the effects of feedstock, input feed size, and milling screen size on particle size and shape, as well as to validate the reliability of existing comminution laws for predicting energy requirements during hammer milling of agricultural and wood biomass. Additionally, the study proposed a new empirical correlation for comminution energy prediction, taking two-dimensional size reduction descriptors into consideration. A machine vision-based image processing method was used to estimate particle size, particle size distribution (PSD), and particle shape factors. The aspect ratio of wheat straw particles was 1.3 to 1.5 times larger than softwood particles, suggesting they are more fibrous. The shapes generated during hammer milling were estimated, with rectangular shapes being predominant. The specific energy requirement (SER) estimated for the hammer milling of softwood chips and wheat straw at different mill screen sizes (4, 8, and 12 mm) was found to be in the range of 153.2–25.5 kJ kg-1 and 38.5–16.1 kJ kg-1, respectively. The validity of existing comminution laws to predict the SER during hammer milling of softwood and wheat straw was tested at a fixed feed rate of 45 kg hr-1, and an improvement in SER prediction for softwood was achieved by formulating a new empirical correlation factoring size reductions in length and width. Further, the correlation developed for the SER for wheat straw was found to lack statistical significance. The findings of this study can be applied to improve the effectiveness of the comminution process, a critical precursor to numerous thermochemical conversion methods used for transforming biomass residues into valuable fuels. Keywords: Bioenergy, Biomass comminution, Machine-vision image analysis, Particle shape, Particle size distribution, Specific energy consumption.

High‐moisture pelleting of corn stover using pilot‐ and commercial‐scale systems: Impact of moisture content, L/D ratio and hammer mill screen size on pellet quality and energy consumption

AbstractHigh‐moisture pelleting of corn stover was tested in pilot‐ and commercial‐scale systems. For the pilot‐scale study, a 6.35 mm screen size hammer mill ground corn stover was reconditioned to moisture between 14 and 29.6% (w.b.), and 5, 7 and 9 L/D ratio pellet die were used. At 29% corn stover moisture content and L/D ratios of 5 and 9, the bulk density and durability of the pellets were ≤450 kg/m3 and <90% and >540 kg/m3 and >90%, respectively. Increasing the feedstock moisture and L/D ratio increased the pelleting energy. Increasing the hammer mill screen size to 11.11 mm reduced the bulk density but not the durability. The response surface models adequately described the pelleting process (R2 ≥ 0.88), and analysis of variance showed a strong interaction between the process variables and pellet properties. Commercial‐scale testing of high‐moisture pelleting using 6.35 mm ground corn stover bales in the moisture range 24–26% (w.b.) produced pellets with a density of >675 kg/m3 and durability of >98%, whereas increasing the hammer mill screen size to 11.11 mm reduced the bulk density by about 100 kg/m3 but not the durability. The energy consumption of the commercial‐scale unit operations for the high‐moisture pelleting process was in the range 98–124 kW h/ton, which is 64–72% less energy than conventional pelleting that requires energy about 350 kW h/ton for biomass drying from 30% (w.b.) to 10% (w.b.) moisture content before pelleting. Pellets produced using high‐moisture pelleting met International Organization for Standardization and Pellets Fuel Institute international standards. Published 2023. This article is a U.S. Government work and is in the public domain in the USA.

Briquetting of Poplar Wood from Short Rotation Coppice—The Effects of Moisture Content and Hammer Mill Screen Size

Studies on the use of biomass from short rotation coppices for briquette production as a sustainable biofuel have been scarce in the literature. This study investigated the effects of two process variables, hammer mill screen size at three levels (5.3, 10.3, and 25.4 mm) and moisture content at three levels (13.6, 19, and 25% (w.b.)), on the properties of briquettes from poplar Max-4 trees. The whole tree was divided into two fractions, the crown and the stem, and briquettes were produced from them. The effects of the variables on compressed density, relaxed density, relaxation ratio, and the shatter index of the briquettes were analyzed. The results showed that the combined interaction of the variables had no significant effects (p > 0.05) on the compressed density, relaxed density, and relaxation ratio of the briquettes. However, hammer mill screen size and moisture content both significantly influenced the shatter index irrespective of the tree fraction (p < 0.05). Hammer mill screen sizes of 5.3 and 10.3 mm at moisture contents of 13.6 and 19% (w.b.) resulted in good quality briquettes across the properties investigated for both the crown and stem poplar tree fractions. This study shows that high-quality briquettes can be produced from poplar Max-4 woody biomass.

Physicochemical and ultrastructural changes in fungal treated switchgrass and their impact on enzymatic digestibility

Solid-state fermentation of switchgrass using white-rot basidiomycete fungi including wild-type Trametes versicolor strain 52J (Tv 52J), a cellobiose dehydrogenase-deficient strain (mutant) T. versicolor strain m4D (Tv m4D), and wild-type Phanerochaete chrysosporium (PC) was conducted at a temperature of 34 °C, time of 28 d, hammer mill screen size of 6.4 mm and inoculum volume of 10 mL. Pretreatment with PC resulted in a significant cellulose loss (13.5 %) and slightly higher delignification compared to the other fungal strains. XRD analysis showed that fungal pretreatment increased the crystallinity index of switchgrass with PC-treated sample having 5.6 % more than untreated sample. Pretreatment resulted in approximately 5-fold and 7.7-fold increase in surface area and volume of pores, respectively, in Tvm4D-treated samples as compared to the control. SEM and TEM images revealed a significant change in cell wall morphology upon pretreatment with all three fungal strains. Fungal pretreatment of switchgrass enhanced the output of enzymatic hydrolysis.

The Effect of Moisture on the Particle Size Characteristics of Knife-milled Beech Chips

The paper presents the effect of moisture on the particle size distribution of knife-milled beech chips. The beech chips of 0.5, 7.5, 15.9 and 30.9 wt % in moisture were milled by a knife mill equipped with a single-bladed rotor under the constant peripheral speed of revolution of 10.2 m·s-1 (1,500 min-1). It was found that the RRSB model precisely fits cumulative mass particle size distribution. The Rosin–Rammler size parameter 0.412 - 4.240 mm varies concerning biomass moisture and size of drum screen sieve. Assuming empiric modelling approaches, it was found that the Rosin–Rammler particle size exponentially decreases with a decrease in knife mill screen sizes and linearly increases with biomass moisture. The polydispersity index was independent of wood chips moisture and knife mill screen size, evincing the value of 2.224 ± 0.328.

Ultrasonic Delignification and Microstructural Characterization of Switchgrass

This present study was undertaken to investigate the ultrasonic delignification of switchgrass (Panicum virgatum L.) and the effects of ultrasonic irradiation on the molecular and microstructure of switchgrass. We investigated this question using response surface methodology (RSM) featuring a four-factor, three-level Box–Behnken experimental design with acoustic power (120, 180, and 240 W), solid–solvent ratio (1/25, 1/20, and 1/15 g/mL), hammer mill screen size (1.6, 3.2, and 6.4 mm), and sonication time (10, 30, and 50 min) as factors, while delignification (%) was the response variable. The native and treated switchgrass samples were further characterized through crystallinity measurements and electron microscopy. The results of lignin analysis show that the percent delignification ranged between 1.86% and 20.11%. The multivariate quadratic regression model developed was statistically significant at p < 0.05. SEM and TEM micrographs of the treated switchgrass grinds resulted in cell wall disruption at the micro- and nano-scales. XRD analysis revealed a reduction in the mean crystallite size and crystallinity index from 15.39 to 13.13 Å and 48.86% to 47.49%, respectively, while no significant change occurred in the d-spacings. The results of this investigation show that ultrasonic irradiation induces chemical and structural changes in switchgrass, which could enhance its use for biofuel and bioproducts applications.

Briquetting characteristics of woody and herbaceous biomass blends: Impact on physical properties, chemical composition, and calorific value

AbstractIntercropping (or polyculture) is gaining a lot of interest as it increases yields, allows better utilization of resources (water and nutrients), and provides better land management. The objective of this study is to understand the briquetting characteristics of woody and herbaceous biomass blends, which might result from intercropping. Tests were conducted on blends of lodgepole pine, switchgrass, and corn stover biomass using three hammer mill screen sizes (i.e., 4.8, 12.7, and 19.05 mm), three blend moistures (12%, 15%, and 18%, w.b.), and two‐ and three‐blend ratios (i.e., 1:1 and 1:1:1) using a pilot‐scale hydraulic briquette press. The briquette properties, such as unit and bulk density, durability rating after 5 days of storage (as they tend to attain stable density), and the energy consumption of the process were measured. The results indicate that moisture content of 12% and 15% (w.b.) and smaller hammer mill screen size of 4.8 mm increased the unit and bulk densities to >750 and >430 kg/m3 and moisture content (15% and 18% (w.b.)) and hammer mill screen size of 12.7 and 19.05 mm produced briquettes with durability rating values of >95%. The higher moisture content of 18% (w.b.) and the hammer mill screen size of 12.7 and 19.05 mm had the highest energy consumption. The proximate and ultimate analysis showed that energy content improved by blending lodgepole pine with both corn stover and switchgrass and also showed increased calorific value and reduced ash content. Scanning electron microscopy micrographs showed interlocking of particles and cracks in the briquettes. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd

Comparative Effect of Hammer Mill Screen Size and Cell Wall-Degrading Enzymes During Olive Oil Extraction.

The influence of hammer mill screen size (4.5 and 8.5 mm) and enzyme addition (control and 500 ppm) on olive fruit cell wall breakdown and its consequences in terms of oil recovery and the phenolic content of olive oil was studied at the laboratory scale for “Arbequina” and “Koroneiki” at two different maturities. Water recovery and water-soluble carbohydrates in olive paste after malaxation were measured as an indicator of cell wall breakdown. Smaller screen size and enzymes increase oil recovery for Arbequina with a maturity index of 1.6 (6.3–6.6%); and for Koroneiki at a maturity index of 0.2 (15.0–38%) and 2.6 (1.3–4.3%). For both cultivars, the increase in oil recovery is larger in green fruits compared to more ripe fruit. Water recovery and water-soluble carbohydrates increase with small screen size and the enzyme treatments, even when no increment in oil recovery is observed. The water recovery range was 143–239% for Arbequina and 150–262% for Koroneiki; water-soluble carbohydrate range was 1.8–12.7 g/kg for Arbequina and 0.5–5.4 g/kg for Koroneiki. In general, smaller hammer mill screen size and enzymes increase total phenols in the oil, with a larger difference between control and treatment for green fruit than for the ripe fruit. For Arbequina, increases in total phenol content were in the range of 45–60 and 5–20% at maturity index 1.6 and 3.3, respectively. For Koroneiki, the increases were in the range of 31–121 and 7–9% at maturity index 0.2 and 2.6, respectively. Application of cell wall-degrading enzymes improves the cell wall breakdown caused by hammer mill, leading to higher oil recovery and total phenol content. The magnitude of the effect depends on the cultivar and olive fruit maturity.

Influence of the particle size and form of feed on growth performance, digestive tract traits and nutrient digestibility of white egg-laying pullets from 1 to 112 D of age.

The influence of the grinding and physical form of diets on growth performance, gastrointestinal tract (GIT) development and nutrient digestibility was studied in layer pullets from hatch to 112 d of age. Diet formed a 2 × 2 factorial with 2 hammer mill screen sizes to grind cereals (4 and 8 mm) and 2 forms (mash and crumble). A total of 864 1-day-old layer chickens were randomly assigned to 1 of the 4 treatment groups with 8 replicates (27 birds per replicate). Cumulatively, pullets fed crumbles consumed less feed (P < 0.05) and had better feed conversion ratio (FCR; P < 0.01) than those fed mash. Coarse grinding cereals (CG) improved FCR (P < 0.05) without significant change in cumulative feed consumption compared to that of fine grinding (FG). With regard to body weight gain (BWG), pullets benefited from crumbles from 1 to 56 d of age (P < 0.01). There were interactions (P < 0.05) between screen size and feed form in relation to FCR (1 to 28 d) and overall BWG. At 112 d of age, the relative weight (RW, g/100g body weight) of the crop, gizzard, pancreas, and liver of crumble-fed birds were lower (P < 0.05) than those for birds fed mash. Pullets fed coarsely ground feed had higher RW of the crop, proventriculus, gizzard, liver, and caecum compared to those fed finely ground feed. Compared to mash feeding, pullets fed crumbles increased (P < 0.05) total tract digestibility of ether extract and crude protein and the activities of pancreatic amylase and lipase. Digestibility of ether extract (P < 0.05) and pancreatic amylase activity (P < 0.01) were higher in birds fed a CG diet than in birds fed the FG regimen. Regarding the nutrition of egg-laying pullets, crumbles might be preferred to mash feed when the main objective is to improve FCR. Data also suggested that cereals used for pullet feed can be ground more coarsely than is in current practice.

Effect of Moisture Content and Hammer Mill Screen Size on the Briquetting Characteristics of Woody and Herbaceous Biomass

Effect of Moisture Content and Hammer Mill Screen Size on the Briquetting Characteristics of Woody and Herbaceous Biomass

Development of a Densification Equipment for Organic Biomass Solid Fuel Pellets

In South Western Nigeria, after the harvesting of maize cobs from the field, large amount of maize stock remains as agricultural residues and wastes. The maize stock constitutes a menace to the environment if not property handled. In this study, densification equipment was designed, fabricated and tested using maize stock grind as raw material. The equipment consists of mixer/ moisture conditioner and a pelleting machine. The power rating for the mixer/moisture conditioner is 0.069 kW with an input capacity of 81 kg/h while the power consumption of the pellet machine is 0.8 kW with throughout capacity of 40 kg/h. The result of the test showed that the highest product temperature, which gives an indication of the quality and durability of the pellets produced was 930C at 0.8 mm hammer mill screen size, 10% moisture content and 150 rpm die speed, at this temperature the machine is operating at optimum efficiency of 74%. High product temperature is an important parameter during pelleting/briquetting operations because it gives the degree of compaction and binding of the pellets/briquettes. The densification equipment for organic biomass was developed using locally sourced materials as a means of converting agricultural wastes into pellets for domestic cooking and cottage industry uses.

Optimization of biological pretreatment to enhance the quality of wheat straw pellets

Pelleting increases the efficiency of handling and transportation of biomass for conversion into biofuels either through biochemical or thermochemical process. Pretreatment of biomass makes lignin fragments accessible by disrupting the lignocellulosic structure, and ensures the production of high-quality pellets. In this study, biological pretreatment using solid-state fermentation (SSF) was investigated as a means to improve the quality of pellets produced from wheat straw. SSF of wheat straw using Trametes versicolor 52J (TV52J), T. versicolor m4D (TVm4D) and Phanerochaete chrysosporium (PC) were conducted. Response surface methodology was employed by using a four-factor, three-level Box-Behnken design with moisture content (% mass fraction of water), hammer mill screen size used for chopping wheat straw (mm), fermentation time (days) and fermentation temperature (°C) as process parameters. Pellet density, dimensional stability and tensile strength were the response variables. The fermentation temperature significantly affected all the responses. The optimization options of moisture content (70% mass fraction of water), hammer mill screen size (50–52.8 mm) and fermentation temperature (22–22.1 °C) of wheat straw with pretreatment using the three fungal strains were very similar. The optimized fermentation time of wheat straw pretreated with PC was the longest at 35 days; the shortest at 21 days was for wheat straw pretreated with TV52J. The microscopic structural changes induced by microbial pretreatment were examined by scanning electron microscopy (SEM). Results showed that the combination between single fibers became relatively loose, and the connection was never tight which was advantageous to improve the physical quality of the compressed pellets.

Influence of moisture content and hammer mill screen size on the physical quality of barley, oat, canola and wheat straw briquettes

In order to determine the briquetting characteristics of biomass in a commercial setting, a hydraulic briquetter was used to study the compaction behavior of biomass grinds from barley, oat, canola and wheat straw. The selected straw samples were ground with a hammer mill using screen sizes of 19.05, 25.40 and 31.75 mm and conditioned to three moisture content levels of 0.09, 0.12 and 0.15 (w.b.). The residence time was about 6–10 min before being extruded from the briquetter. The specific energy, throughput, as well as the density, and durability of manufactured briquettes were measured during or after briquetting. The applied compression pressure at different parameter combinations ranged from 7 to 14 MPa. Higher pressure resulted at higher biomass moisture content. Hammer mill grinding of biomass with a large screen size (31.75 mm) resulted in high energy consumption and low throughput during briquetting. The increase in moisture content decreased the total energy consumption and increased the throughput of the briquetter. Briquette densities were of consistently higher value when biomass samples were compressed at a lower moisture level. The moisture content and hammer mill screen size indirectly influenced the briquette densities by affecting the pressure and residence time in commercial briquette production. Briquettes were successfully formed without adding a binder.

The effect of storage time and moisture content on grindability of loblolly pine (Pinus taeda L.)

Specific grinding energy and particle size distribution of grinds are usually used to assess the efficiency of grinding equipment and material grindability. The objective of this study was to quantify the effects of moisture content and storage time on the specific grinding energy of loblolly pine woodchips and the physical properties of the resulting grinds. Samples were ground in a hammer mill fitted with 3.18 and 6.35 mm screen sizes. The specific grinding energy, moisture loss during grinding, particle size distribution, and bulk density of the grinds were measured. Moisture loss during grinding increased with increase in moisture content of woodchips and decreased with increase in hammer mill screen size. Bulk density of grinds reduced from 273.64 to 106.03 kg/m3 and from 251.14 to 131.40 kg/m3 (for 3.18 mm and 6.35 mm hammer mill screen size, respectively), when the moisture content of woodchips was increased from 13.6 to 100.0 % (dry basis). Results also showed that storage time did not significantly affect (p < 0.05) the specific grinding energy. However, specific grinding energy was significantly affected (p < 0.05) by the moisture content of woodchips and hammer mill screen size. The specific grinding energy of woodchips ground through 3.18 mm hammer mill screen size increased with increase in moisture content of woodchips. However when loblolly pine woodchips were ground through 6.35 mm hammer mill screen size, the specific grinding energy initially increased as moisture of woodchips increased from 13.6 to 42.9 % (dry basis), then decreased with further increase in moisture content of woodchips from 42.9 to 100.0 % (dry basis).

Compression and relaxation properties of selected biomass for briquetting

Compression and relaxation properties of selected biomass for briquetting (barley, oat, canola and wheat straw) were investigated to determine the correlation with variables (pressure, particle size (hammer mill screen size) and moisture contents). The applied pressure ranged from 7.03 to 14.06 MPa. Three hammer mill screen sizes (19.05, 25.40 and 31.75 mm) were used to grind the biomass samples. The ground biomass materials were conditioned to moisture contents of 9%, 12% and 15% (w.b.). The results indicated that the compact density of biomass increased with increasing pressure and moisture content. The relaxation properties of selected materials were affected by the set variables. Biomass materials had a higher stress relaxation speed with higher applied pressure and lower moisture content.

Impact of AFEX™ Pretreatment and Extrusion Pelleting on Pellet Physical Properties and Sugar Recovery from Corn Stover, Prairie Cord Grass, and Switchgrass.

The effects of AFEX™ pretreatment, feedstock moisture content (5,10, and 15% wb), particle size (screen sizes of 2, 4, and 8mm), and extrusion temperature (75, 100, and 125°C) on pellet bulk density, pellet hardness, and sugar recovery from corn stover, prairie cord grass, and switchgrass were investigated. Pellets were produced from untreated and AFEX™ pretreated feedstocks using a laboratory-scale extruder. AFEX™ pretreatment increased subsequent pellet bulk density from 453.0 to 650.6kgm(-3) for corn stover from 463.2 to 680.1kgm(-3) for prairie cord grass, and from 433.9 to 627.7kgm(-3) for switchgrass. Maximum pellet hardness of 2342.8, 2424.3, and 1298.6N was recorded for AFEX™ pretreated corn stover, prairie cord grass, and switchgrass, respectively. Glucose yields of AFEX™ corn stover pellets, prairie cord grass, and switchgrass pellets varied from 88.9 to 94.9%, 90.1 to 94.9%, and 87.0 to 92.9%, respectively. Glucose and xylose yields of AFEX™ pellets were not affected by the extruder barrel temperature and the hammer mill screen size. The results obtained showed that low temperature and large particle size during the extrusion pelleting process can be employed for AFEX™-treated biomass without compromising sugar yields.

Effects of Moisture Content and Temperature on the Quality of Water Hyacinth Pellets

Moisture content and temperature are two important process parameters that greatly influence the quality of biomass pellet fuels. The moisture content of raw material was varied at five levels (8%, 10%, 12%, 14%, 16%) to test its effect on water hyacinth pellet density and diametric compression strength. The experimental conditions included a compressing force of 6 kN, hammer mill screen size of 2 mm, and temperature of 100 °C. Five temperature conditions (80, 90, 100, 110, and 120 °C) were studied under the same conditions and 12% moisture content. In these conditions, the optimal moisture contents for water hyacinth pellet density and diametric compression strength were 12.2% and 11.5%, respectively, and the optimal temperatures were 100.4 °C and 104.3 °C, respectively.

Effect of ammonia fiber expansion (AFEX™) pretreatment on compression behavior of corn stover, prairie cord grass and switchgrass

Understanding the fundamental mechanisms involved in densification of bulky lignocellulosic feedstocks is imperative. This study was carried out to understand the effect of ammonia fiber expansion (AFEX™) pretreatment on the compression behavior of corn stover, prairie cord grass, and switchgrass. Samples were ground using three different hammer mill screen sizes (2, 4, and 8mm) and were subjected to AFEX™ pretreatment. Untreated and AFEX™ pretreated samples were moisture adjusted to four levels (8, 12, 16, and 20% wb) and were compressed using a single pelleting unit. Physical properties comprising bulk density, particle density of the samples and unit density of pellets were determined for each combination. AFEX™ pretreated corn stover with moisture content of 20% at screen size of 2mm produced pellets with 21% higher unit density compared to untreated corn stover pellets. AFEX™ pretreated prairie cord grass and switchgrass with 20% moisture content at a screen size of 2mm produced pellets having 25% and 21% higher unit density. The decrease in hammer mill screen size and the increase in moisture content and applied pressure increased the pellet unit density. Data obtained from the compression experiments were fitted with different compaction models viz. Jones, Walker, and Kawakita and Ludde. The Kawakita and Ludde model exhibited high degree of accuracy (R2 – 0.99 and 1.00) in all the samples. The constant value ‘1/b’ in Kawakita and Ludde model represents the yield strength of the compacts, and the lower 1/b values were obtained for AFEX™ pretreated samples compared to untreated samples. This implies the impact of pretreatment, which in turn made the biomass easier to compress. Lower values of yield strength were obtained at high moisture content (16–20% wb) signifying that AFEX™ pretreated biomass at high moisture content leads to onset of deformation at relatively low pressure to produce highly compacted pellets.

Effect of glycerol on densification of agricultural biomass

Experiments were conducted to verify the effect of adding glycerol for pelleting of selected agricultural crop residues, namely, wheat, barley, oat and canola straw. Single pelleting tests were conducted to study the effect of biomass type, hammer mill screen size, and crude glycerol content (co-product of biodiesel industry) on pellet quality (density and durability), ash content and gross heat of combustion. Four types of biomass were ground at three different hammer mill screen sizes of 6.4, 3.2 and 1.6 mm. Each biomass was mixed with three levels of glycerol of 2.5%, 5.0% and 7.5% by weight. Pellets were made at a pre-set load of 4 400 N (138.9 MPa) using single-pelleting unit attached to an Instron testing machine. Quality of pellets was determined by measuring pellet density, relaxed density, durability (measured by pellet drop test) and specific energy required to make a pellet. The gross heat of combustion and ash content of pellets were also determined and compared. The highest pellet density (988-1 133 kg/m3) and relaxed density (992-1 142 kg/m3) were obtained from biomass ground using a hammer mill screen size of 6.4 mm. A decrease in hammer mill screen size resulted in reduced durability. The highest durability of biomass obtained from hammer mill screen size of 6.4 mm ranged from 97%-100%. Addition of glycerol resulted in lower ash content in majority of pellets. The highest gross heat of combustion was observed in pellets made from wheat straw with 7.5% glycerol content (38.3 MJ/kg). Addition of glycerol resulted in lower pellet densities, lower ash content, no change in durability and higher gross heating values. DOI: 10.3965/j.ijabe.20150801.009 Citation: Emami S, Tabil L G, Adapa P. Effect of glycerol on densification of agricultural biomass. Int J Agric & Biol Eng, 2015; 8(1): 64－73.