Hardwood Pellets Research Articles

Energetic Features of Hardwood Pellet Evaluated by Effect Size Summarisation

Energetic Features of Hardwood Pellet Evaluated by Effect Size Summarisation

Role of Primary Freeboard on Staged Combustion of Hardwood Pellets in a Fixed Bed Combustor

In staged fixed bed biomass combustion, primary air is supplied beneath the fuel bed with secondary air then provided above in the freeboard region. For fixed bed configurations, the freeboard is further divided into a primary freeboard length (LI), which is upstream of the secondary air and a secondary freeboard length (LII), measured from the secondary air all the way to the exhaust port. Despite extensive research into fixed bed configurations, no work has been successfully completed that resolves the effects of changing LI on fuel conversion, both in the fuel bed and within the freeboard of batch-type biomass combustors. In this study, experiments on a 202 mm diameter and 1500 mm long batch-type combustor have been conducted to determine the effects of changing primary freeboard length over three secondary to total air ratios (Qs/Qt) and two total air flow rates (Qt). The impact of these conditions has been studied on (i) intra-bed fuel conversion, measured through burning rate (kg/m−2 s−1), fuel bed temperature (°C) and ignition front velocity (mm-s−1), as well as (ii) post-bed fuel conversion in the freeboard, expressed through freeboard temperatures and emissions (NOx ppm, CO2%, CO ppm, O2%). The fuel used throughout the above experiments was Australian hardwood pelletised biomass. Results show that changes to primary freeboard length over LI = 200 mm, 300 mm and 550 mm, or LI/D = 1.00, 1.48 and 2.72, respectively, affect both intra-bed and freeboard (post-bed) performance indicators. The highest values of burning rate, ignition front velocity and fuel bed temperature were observed for interim values of LI/D = 1.48 at Qs/Qt = 0.25 and Qt = 0.358 kg/m−2 s−1. Primary freeboard lengths of LI/D = 1.00 and 1.48 were found to have higher freeboard temperatures, NOx and CO2 as well as lower CO and O2 values as compared to LI/D = 2.72 at Qs/Qt = 0.50 and 0.75. Increasing Qs/Qt from 0.25 to 0.50 for LI/D = 1.00 and 1.48 initially increased freeboard temperatures, with an accompanying increase in NOx and CO2 as well as decrease in CO values. However, further increase in Qs/Qt to 0.75 lead to lower freeboard temperatures for all primary freeboard lengths.

Impacts of wood species and moisture content on emissions from residential wood heaters

ABSTRACT Homeowners burn wood of a wide range of species and moisture content (MC) in residential cordwood and pellet stoves. An effective emission certification test protocol must account for and accurately measure the impact of those variables in order to ensure a reasonable correlation between laboratory results and in-use emissions and to promote the design and manufacture of cleaner burning appliances. This study explored the effect of wood species and MC on emissions and efficiency in four cordwood and four pellet stoves. PM emissions were consistently lower with pellets manufactured from softwood than for hardwood species and were highly correlated with ash content. Higher MC oak fuel substantially increased PM emissions in a non-catalytic cordwood stove; however, a hybrid cordwood stove was able to meet federal emissions limits even with the higher MC fuel. The results of this study, in combination with previous research, suggest that certification tests that use softwood fuel likely report lower emissions than tests that use hardwood. Requiring hardwood and higher MC cordwood fuel in certification tests would enable the assessment of an appliance’s ability to operate well even when fuel conditions are not optimized. Implications: The emission testing results reported in this paper call into question the adequacy of the fuel moisture content and fuel species specifications in testing protocols approved for certifying compliance with EPA’s New Source Performance Standards for cordwood and pellet stoves. We recommend changes in those specifications, including the prohibition of testing with Douglas fir and other low ash softwood species, requiring the use of cordwood test fuel with a higher moisture content, and requiring pellet stoves to be tested using hardwood pellets. Adoption of these measures would increase the replicability of tests. allow for the identification of stoves that are unlikely to perform well in the field when fuel conditions are not ideal, and, ultimately, result in the design of cleaner burning stoves.

Thermo-catalytic reforming of alberta-based biomass feedstock to produce biofuels

The depletion of fossil fuels as well as the greenhouse gas emissions from fossil fuel use have led to growing interest in biofuel production from biomass. A new technology, thermo-catalytic reforming (TCR), is one of the contributing interests. TCR technology integrates intermediate pyrolysis with a post-reforming stage to convert biomass into a high-quality bio-oil, biochar, and syngas. In this study, experiments were carried out using three Alberta-based biomass feedstocks – hardwood pellets, softwood pellets, and chips – in a 2 kg h−1 laboratory-scale TCR plant. The results show that the composition of the biomass has little effect on product yield and quality. The TCR gases had a higher heating value of 12.5–12.8 MJ kg−1 and a hydrogen content of 13–15 vol %. The produced TCR bio-oil had low water content (~5 wt %) and a heating value of 32–34 MJ kg−1. The high quality of the bio-oil is reflected in the low O/C ratio of 0.15 and TAN of 6–15 mg KOH g−1. The TCR biochar from all three feedstocks had a high heating value and a high carbon content, as well as low O/C and H/C ratios. A parametric study was conducted for the softwood pellets to observe the effect of reformer temperature (500–700 °C) and reactor temperature (400–550 °C). It was observed that at a reformer temperature of 700 °C, the gas yield increases at the expense of a reduction in bio-oil and biochar. The optimum reactor temperature for the TCR of softwood pellets was found to be 500 °C, in terms of both bio-oil quality and yield.

Comparative Analysis of Pelletized and Unpelletized Sunflower Husks Combustion Process in a Batch-Type Reactor.

This paper describes characteristics of the combustion of sunflower husk (SH), sunflower husk pellets (SHP), and, for comparison, hardwood pellets (HP). The experiments were carried out using a laboratory-scale combustion reactor. A proximate analysis showed that the material may constitute an alternative fuel, with a relatively high heating value (HHV) of 18 MJ/kg. For SHP, both the maximum combustion temperatures (TMAX = 1110 °C) and the kinetic parameters (temperature front velocity vt = 7.9 mm/min, combustion front velocity vc = 8 mm/min, mass loss rate vm = 14.7 g/min) of the process were very similar to those obtained for good-quality hardwood pellets (TMAX = 1090 °C, vt = 5.4 mm/min, vc = 5.2 mm/min, vm = 13.2 g/min) and generally very different form SH (TMAX = 840 °C, vt = 20.7 mm/min, vc = 19 mm/min, vm = 13.1 g/min). The analysis of ash from SH and SHP combustion showed that it has good physicochemical properties (ash melting point temperatures >1500 °C) and is safe for the environment. Furthermore, the research showed that the pelletization of SH transformed a difficult fuel into a high-quality substitute for hardwood pellets, giving a similar fuel consumption density (Fout = 0.083 kg/s·m2 for SHP and 0.077 kg/s·m2 for HP) and power output density (Pρ = MW/m2 for SHP and 1.5 MW/m2 for HP).

Mutagenicity- and pollutant-emission factors of pellet-fueled gasifier cookstoves: Comparison with other combustion sources

Emissions from solid-fuel burning cookstoves are associated with 3 to 4 million premature deaths annually and contribute significantly to impacts on climate. Pellet-fueled gasifier stoves have some emission factors (EFs) approaching those of gas-fuel (liquid petroleum gas) stoves; however, their emissions have not been evaluated for biological effects. Here we used a new International Organization for Standardization (ISO) testing protocol to determine pollutant- and mutagenicity-EFs for a stove designed for pellet fuel, the Mimi Moto, and for two other forced-draft stoves, Xunda and Philips HD4012, burning pellets of hardwood or peanut hulls. The Salmonella assay-based mutagenicity-EFs (revertants/megajouledelivered) spanned three orders of magnitude and correlated highly (r = 0.99; n = 5) with EFs of the sum of 32 particle-phase polycyclic aromatic hydrocarbons (PAHs). The Mimi Moto/hardwood pellet combination had total-PAH- and mutagenicity-EFs 99.2 and 96.6% lower, respectively, compared to data published previously for the Philips stove burning non-pelletized hardwood, and 100 and 99.8% lower, respectively, compared to those of a wood-fueled three-stone fire. The Xunda burning peanut hull pellets had the highest fuel energy-based mutagenicity-EF (revertants/megajoulethermal) of the pellet stove/fuel combinations tested, which was between that of diesel exhaust, a known human carcinogen, and a natural-draft wood stove. Although the Mimi Moto burning hardwood pellets had the lowest fuel energy-based mutagenicity-EF, this value was between that of utility coal and utility wood boilers. This advanced stove/fuel combination has the potential to greatly reduce emissions in contrast to a traditional stove, but adequate ventilation is required to approach acceptable levels of indoor air quality.

Movement Technique During Jump-Landing Differs Between Sex Among Athletic Playing Surfaces.

Pryor, JL, Burbulys, ER, Root, HJ, and Pryor, RR. Movement technique during jump-landing differs between sex among athletic playing surfaces. J Strength Cond Res 36(3): 661-666, 2022-Whether athletic surface type affects movement technique, a causal factor for lower extremity injury, is unclear. This study evaluated the influence of 4 common athletic surfaces on movement technique using the Landing Error Scoring System (LESS). Secondarily, we aimed to evaluate differences in movement technique between men and women among surfaces. Recreationally active men and women (n = 38) completed jump-landing tests on 4 common athletic surfaces in a quasi-randomized crossover fashion. Vertical jump height, perceptual fatigue, and muscle soreness were evaluated before jump-landing movement analyses and were similar across testing sessions (p > 0.05). Men achieved higher LESS scores on hardwood and artificial pellet turf compared with women (p ≤ 0.037). Women exhibited lower LESS scores on grass and artificial turf vs. concrete (p ≤ 0.048). Data indicate differential lower extremity movement technique and therefore injury risk across athletic surface types and sex, challenging the generalizability of the LESS construct. Athletic playing surface should be considered during movement technique assessment and implementation of injury prevention programs.

Investigation 0f Beef Brisket Palatability from Three USDA Quality Grades

ObjectivesBarbecuing and smoked meat continues to grow in popularity for food service and consumers at home. However, little research has examined the eating quality differences of point (pectoralis superficialis) and flat (pectoralis profundi) muscles across USDA quality grade. The objective of this study was to investigate differences in smoked beef brisket palatability from three USDA quality grades.Materials and MethodsBeef briskets from the USDA Prime, Average Choice, and Select quality grades (n = 54; 18 per treatment) were collected at a commercial abattoir in Omaha, NE. Briskets were trimmed to 6 mm of external fat, seasoned with a blend of 1:1 coarse kosher salt/coarse black pepper by hand (0.05% of the brisket raw weight), and were held at 2–4° for 12 h prior to cooking. Briskets were cooked in an electric pellet smoker utilizing Gold Blend Hardwood Pellets (red oak, hickory, and maple wood) for ∼4 h to an internal temperature of 63°C; wrapped in aluminum foil, placed back in the smoker for ∼4 h, and cooked to 93°C, then held in an insulated cooler until slicing. Approximately 90 min prior to serving, briskets were separated in point and flat portions, and then sliced (6 mm × 50 mm x cooked depth) perpendicular to the muscle fiber for consumer evaluation and held in warmers at (∼50°C) until serving. Each consumer (n = 360) received six test samples representing all quality grade × muscle combinations to evaluate tenderness, juiciness, flavor liking, overall liking, as well as the acceptability of these traits. Additionally, willingness to pay (WTP) was collected on an individual sample basis.ResultsAn interaction between quality grade and muscle was observed (P ≤ 0.03) for all palatability traits, proportion of acceptable samples, and WTP. Consumers could not distinguish between quality grades of the point portions for tenderness, juiciness, flavor and overall liking (P > 0.05). Point samples, regardless of quality grade were scored greater than Prime flat samples, which were intermediate (P < 0.05). Consumers similarly (P > 0.05) scored Choice and Select flat samples lower for all palatability traits compared to all other treatment combinations. In alignment with palatability traits, consumers were willing to pay the most for point portions, regardless of quality grade (P < 0.05). Consumers WTP of the Prime flat portion was intermediate, and consumers were willing to pay the least for Choice and Select flat portions (P < 0.05).Consumer acceptability followed similar trends as palatability scores. However, a greater proportion of consumers classified Choice and Select point samples as acceptable than that of Prime point samples in all categories of acceptability (P < 0.05). Consumers struggled to distinguish differences in acceptability for Choice and Select flat portions (P > 0.05) in all factors except juiciness acceptability.ConclusionQuality grade had no effect on the eating quality of the point portions of smoked briskets, and point portions received superior palatability scores to flat portions. Briskets from the Prime flat portions had greater eating quality than Choice and Select briskets from the flat portion, and consumers were willing to pay more for what they perceived as superior eating quality. This data suggests that unless consumers prefer the flat portion of the brisket there is no benefit to paying the premium for a prime brisket from a palatability standpoint.

Characteristics of ash formation in the process of combustion of pelletised leather tannery waste and hardwood pellets

This paper presents a characterisation of the combustion of mixtures of pelletised leather tannery waste (LTW) and hardwood pellets (HP) on a grate. The experimental investigation was carried out in a laboratory-scale combustion reactor with the use of thermogravimetric analysis (TGA). Proximate and ultimate analysis showed that leather tannery waste may constitute a promising fuel, with a relatively high heating value at the level of 16 MJ/kg. The highest value of thermal degradation of leather was reached at 326 °C; the combustion characteristics of leather waste are include by two peaks corresponding to 406 and 432 °C. The results of the combustion process showed that doping hardwood pellets with leather waste does not significantly affect combustion temperatures in the fuel bed on the perforated flat gate of the test reactor. Furthermore, high ash content in leather waste significantly affects the formation of the ash layer, which increases along with increased contents of pelletised tannery waste.

Bioenergy production to improve value-creation potential of strategic forest management plans in mixed-wood forests of Eastern Canada

The relationship between forest management and biomass sourcing is fundamental to the achievement of sustainable bioenergy production. Few biomass-sourcing studies have directly addressed the complex interactions between sustainable forest management and additional demand created by bioenergy production. The first objective of this research was to provide a method for estimating profits for a value chain that harvests volumes scheduled in a sustainable forest management plan. The second objective was to measure the financial and sustainable benefits generated by integrating bioenergy production into this value chain. Using data from a large management unit, a forest management plan was developed to generate an annual flow of timber that can be produced sustainably. We then proposed a network flow optimization model that links the optimal solution of a long-term wood supply optimization model with the processing capacity of an industrial network. Results revealed that the weak demand for lower-quality trees could be a serious impediment to achieving full value-creation potential. Simulations of the implementation of a hardwood pellet mill improved the value-creation potential for hardwood pulp (direct effect) and also for other wood products by providing access to otherwise unprofitable mixed-wood forest strata (synergistic effect). Our experiment showed that integrating a lower-quality timber user, such as a bioenergy production unit, could lead to higher financial profits (up to three-fold), and improve alignment between the sustainable forest management objectives and the industrial network capacity (harvested scheduled area increased from 79% to 98%). Implementing a bioenergy mill also grants a higher return on capital employed compared to historical values for the manufacturing sector. Strengthening the link between strategic planning and industrial processing capacity provides new insights into the impact on value-creation of bioenergy production from forest biomass.

Experimental tests of co-combustion of pelletized leather tannery wastes and hardwood pellets

This study examines the possibility of using pelletized leather tannery wastes (LTW) in the co-combustion process with hardwood pellets (HP). The experiments were carried out in a small-scale combustion reactor and were followed by thermogravimetric analysis (TGA) of fuels in the nitrogen and air atmosphere. The experimental investigation has indicated that the leather tannery wastes can be an interesting fuel with a relatively high heating value (HHV), at the level of 16 MJ/kg, and the volatile content of about 68%. Thermal decomposition of the leather tannery sample occurs at temperatures ranging between 220 and 420 °C, with the maximum of intensity at 320 °C. The experimental results indicated that the averaged maximum temperatures obtained during the combustion reached similar values for all samples, which indicates that doping wood pellets with leather waste pellets does not have a significant impact on the temperature characteristics of the combustion process. However, decreasing the amount of hardwood pellets in the mixture reduces the bulk density of the fuel bed and the combustion front velocity. The emission of nitrogen oxides for combusting blends is twice as high as for combustion of pure HP, which is related to higher nitrogen content in leather waste as well as higher ash content.

Influence of Bed Movement and Amount of Supplied Air on Updraft Gasification of Hardwood Pellet

Influence of Bed Movement and Amount of Supplied Air on Updraft Gasification of Hardwood Pellet

Torrefied biomass as feed for fast pyrolysis: An experimental study and chain analysis

A torrefaction pre-treatment could enhance the fast pyrolysis process to produce bio-oil by decreasing the required energy for grinding biomass particles and by improving bio-oil characteristics so they resemble more those of fossil fuels. To evaluate this hypothesis, this work compares fast pyrolysis experiments of raw and torrefied woody biomass feedstocks, using a 500 g h−1 entrained down flow reactor. The feedstocks used were hardwood (ash wood), softwood (spruce) and mixed waste wood. These feedstocks were torrefied at various temperatures between 250 °C and 300 °C by means of two torrefaction processes: a directly heated moving bed, and the Torbed® process. The effect of pelletizing was also analyzed for the hardwood feedstock, comparing torrefied chips and torrefied pellets. The obtained bio-oils from experiments with torrefied feedstock had overall improved oxygen and heating value properties compared to bio-oils from raw feedstock. Hardwood pellets torrefied at 265 °C with a residence time of 45 min produced the oils with the highest quality with respect to oxygen mass fraction (decreased from 45.7% to 37.2%) and higher heating value (increased from 19.1 MJ kg−1 to 23.1 MJ kg−1), compared to bio-oil produced from raw hardwood feedstock. However, these properties came at a severe loss of oil yield, decreasing from 44% for raw feedstock to an average of 31% for torrefied feedstock. Nonetheless, a chain analysis shows that a torrefaction pre-treatment could be more attractive on energy basis compared to a conventional fast pyrolysis process with a deoxygenation upgrading step.

Effects of temperature and material on sensing moisture content of pelleted biomass through dielectric properties

The production of pelleted biomass represents a significant emerging industry in the United States. Solid biomass can be formed from the waste products of different natural and manufactured products. In this study, the effects of temperature and pellet material type on the dielectric properties were investigated. The resulting information was used to develop temperature- and material-independent moisture prediction equations. Dielectric properties of peanut-hull, pine, and hardwood pellets were measured at microwave frequencies for temperatures between 10 °C and 50 °C and at moisture contents between 4.9% and 16.0%. Further work was performed in investigating the dielectric properties of pine, peanut-hull, and hardwood pellets to determine whether a “unified” calibration for moisture content might be developed. Results showed that a temperature-compensated calibration for moisture content could be developed for different pellet types with standard errors of calibration between 0.50% and 1.04%. In addition, a unified calibration for pine, peanut-hull and hardwood pellets at 20 °C was developed that provides moisture content for the materials with a standard error of calibration between 0.48% and 0.56%.

Inactivation ofE. coliO157:H7 in Cultivable Soil by Fast and Slow Pyrolysis-Generated Biochar

An exploratory study was performed to determine the influence of fast pyrolysis (FP) and slow pyrolysis (SP) biochars on enterohemorrhagic Escherichia coli O157:H7 (EHEC) in soil. Soil + EHEC (inoculated at 7 log colony-forming units [CFU]/g of soil) + 1 of 12 types of biochar (10% total weight:weight in soil) was stored at 22°C and sampled for 8 weeks. FP switchgrass and FP horse litter biochars inactivated 2.8 and 2.1 log CFU/g more EHEC than no-biochar soils by day 14. EHEC was undetectable by surface plating at weeks 4 and 5 in standard FP switchgrass, FP oak, and FP switchgrass pellet biochars. Conversely, EHEC populations in no-biochar control samples remained as high as 5.8 and 4.0 log CFU/g at weeks 4 and 5, respectively. Additionally, three more SP hardwood pellet biochars (generated at 500°C for 1 h, or 2 h, or generated at 700°C for 30 min) inactivated greater numbers of EHEC than did the no-biochar control samples during weeks 4 and 5. These results suggest that biochar can inactivate E. coli O157:H7 in cultivable soil, which might mitigate risks associated with EHEC contamination on fresh produce.

Comparison of biochars derived from wood pellets and pelletized wheat straw as replacements for peat in potting substrates

Biochar is the solid, carbon-rich product resulting from the pyrolysis of biomass in the absence of oxygen. We are examining biochars for several horticultural applications, including as a replacement for peat moss in soilless substrates used in the production of containerized greenhouse and nursery crops. Biochars were prepared from hardwood pellets and from pelletized wheat straw. Straw biochar had a higher potassium content and pH than the wood biochar. Fourier transform infrared spectroscopy analyses of the biochars showed much greater volatile content in the straw biochar. Both biochars had significantly higher bulk densities than either peat moss or vermiculite. Substituting biochar pellets (at rates of 5%, 10%, and 15%, v/v) for peat moss increased substrate pHs, bulk densities, and electrical conductivities, while having variable effects on physical properties (air porosities, container capacities, and total porosities). Greenhouse experiments were conducted using tomato (Solanum lycopersicum L.) and marigold (Tagetes erecta L.) plants grown in 3.0-L pots. Addition of either biochar had no effect on dry weights of tomato plants after 4 weeks of growth, but significantly increased plant heights in all treatments. Marigold plant heights were greater than the control in all but the 5% wood biochar, but had only a minor effect on plant dry weights. These results indicate that both pelletized biochars would be suitable as replacements for peat in soilless substrates when used at these replacement rates.

Co-Gasification of Coal and Hardwood Pellets: A Case Study

This paper presents the effect of feedstock mixtures on the composition of syngas produced from a commercially available down-draft gasifier. Commercial hardwood pellets and bituminous coal (Pittsburgh seam) were used as fuel for the experiments. Five types of feedstock mixtures having composition(by weight) of 100% hardwood pellets, 20% coal-80% hardwood pellets, 50% coal-50% hardwood pellets, 80% coal-20% hardwood pellets and 100% coal were prepared. Air and an air plus water mist mixture were used as a gasifying agent. Syngas with 20.95% carbon monoxide and 16.05% hydrogen was produced from the gasification of wood pellets at 1200°C in the combustion zone and 450°C in the reduction zone of the reactor. The hydrogen and carbon monoxide content in the product gas decreased with an increase in the coal proportion in the mixtures. A significant increase in carbon efficiency was observed with an increase of coal proportion in the mixtures. Syngas carbon and syngas energy efficiency increased with injection of the water mist along with air in the system for the hardwood pellet gasification.

Fast pyrolysis of biomass thermally pretreated by torrefaction

Torrefied biomass samples were produced from hardwood and switchgrass pellets using the biochar experimenter's kit (BEK) reactor and analyzed for their utility as pretreated feedstocks for biofuels production via fast pyrolysis. The energy efficiency for the BEK torrefaction process with propane gas as fuel source was about 50% for hardwood pellets and over 67% for switchgrass, but the energy retained in the torrefied product ranged between 72 and 92% of the initial biomass energy content resulting from a high product yield of 70–88wt%. The liquid pyrolysate by-product of the torrefaction process was an aqueous solution of mainly acetic acid and levoglucosan associated with dehydration of the carbohydrate fraction of the raw biomass. Subsequent fast pyrolysis in a fluidized bed led to production of pyrolysis oil with lower acidity and increased energy content compared with pyrolysis of non-torrefied biomass. However, the yield, carbon conversion and energy conversion to these pyrolysis oils were decreased with the torrefection pretreatment which predisposed the biomass for conversion to biochar rather than liquid products.

Emissions characterization of residential wood-fired hydronic heater technologies

Residential wood-fired hydronic heaters (RWHHs) can negatively impact the local ambient air quality and thus are an environmental concern in wood burning areas of the U. S. Only a few studies have been conducted which characterize the emissions from RWHHs. To address the lack of emissions data, a study was conducted on four appliances of differing design using multiple fuel types to determine their thermal, boiler, and combustion efficiency as well as the emissions of carbon dioxide (CO2), carbon monoxide (CO), total hydrocarbons (THC), nitrous oxide (N2O), methane (CH4), total particulate matter (PM) mass, and particle number as well as particle size distribution (PSD). Three of these appliances were fired with split-log cordwood with the fourth unit using hardwood pellets. The measured thermal efficiencies for the appliances tested varied from 22 to 44% and the combustion efficiencies from 81 to 98%. Depending on appliance and fuel type, the emission factors ranged from about 1300 to 1800 g kg−1 dry fuel for CO2, 8–190 g kg−1 dry fuel for CO, <1–54 g kg−1 dry fuel for THC and 6–120 mg kg−1 for N2O. For the particle phase pollutants, the PM mass emission factors ranged from 0.31 to 47 g kg−1 dry fuel and the PM number emission factors from 8.5 × 1010 to 2.4 × 1014 particles kg−1 dry fuel, also depending on the appliance and fuel tested. The PSD for all four appliances indicated a well established accumulation mode with evidence of a nucleation mode present for Appliances A and B. The average median aerodynamic particle diameters observed for the four appliances ranged from 84 to 187 nm while burning red oak or pellets. In general, the pellet-burning appliance had the highest overall operating efficiency and lowest emissions of the four units tested.

Compression and springback properties of hardwood and softwood pellets

A multiple linear regression analysis was carried out to predict the length of pellets under compression in the die based on moisture, temperature, pressure, hold time, and their interaction terms. Excellent correlations were obtained in the dependency of the considered parameters on length of compressed material inside the die. Springback characteristics based on axial changes after the compaction process were analyzed. The expansion for hardwood pellets (16.28%) was found to be lowest at particle size 0.150 to 0.300 mm with 8% moisture (w.b), 60 °C, 139.3 MPa pressure, and a hold time of 15S. The expansion for softwood pellets (20.56%) was lowest with particle size 0.300 to 0.425 mm, at 8% moisture (w.b), 70 °C, 159.2 MPa, and a hold time of 30S.