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Simple and inexpensive method of wood pellets macro-porosity measurement.

A novel simplified stereometric measurement method for determining the macro-porosity of wood pellets through geometrical approach was successfully developed and tested. The irregular ends of pellets of circular cross-section were sanded flat so that their geometry becomes cylinder and their volumes evaluated using mensuration formula. Such formed cylindrical pellets were loose or tap filled to selected volumes to evaluate the macro-porosity and the constant specific weight. The method was extended to evaluate actual wood pellets properties. Overall macro-porosity of actual wood pellets was determined as 41.0+/-2.5% and 35.5+/-2.7%, mean bulk density as 670+/-29 kg m(-3) and 731+/-31 kg m(-3), and classified as Class-3:Medium and Class-3&4:Medium to Low for loose and tapped fills, respectively. Hausner ratio and Carrs compressibility index classify wood pellets as freely flowing. The developed stereometric method can be used as a handy inexpensive laboratory procedure to estimate the macro-porosity of different types and makes of wood pellets and other similar packaged materials.

Colorimetry applied to steam-treated biomass and pellets made from western douglas fir (Pseudotsuga menziesii L.).

Wood pellets made from sawdust and shavings are white in color and low in ash content. Pellets made from a mix of bark and white wood are darker in color, and bark increases the ash content of pellets. Steam treatment of biomass prior to pelletization improves the durability of pellets. Both wet (steam) and dry thermal (torrefaction) treatments of biomass darken the pellets. The off-color pellets have a lower commercial value than white wood pellets in residential applications. In this research, ground white wood (western Douglas fir, Pseudotsuga menziesii L.) was treated with saturated steam at 200°C and 220°C for 5 and 10 min. The colors of the treated and untreated powders and pellets were evaluated. The Hunter color coordinates L*, a*, and b* were recorded using a Minolta CM-5 spectrophotometer. Compared to untreated samples, the steam-treated samples became darker; the hues shifted from red to green and from blue to yellow. Multi-linear regression models of three color coordinates with elemental composition of carbon and hydrogen were developed. The values of L*, a*, and b* showed good correlation with percentage of carbon, hydrogen, and oxygen of the samples, with R2 values of 0.97, 0.99, and 0.97, respectively. The developed equations can be useful tools for the bioenergy industry for a quick estimation of fuel properties by a simple color measurement.

Effect of Steam Treatment on Pellet Strength and the Energy Input in Pelleting of Softwood Particles

Three whitewood species (spruce, Douglas fir, and pine) and one sample of bark (Douglas fir) were treated with high-pressure steam at 220°C for 5 min. The steam treatment resulted in a reduction in average particle size by as much as 25%. Pine particles showed the largest reduction in size, while bark showed the least. Despite a slightly lower density, pellets made from treated particles had a higher mechanical strength (hardness) than untreated pellets. The mechanical energy required to compact steam-treated material was higher than the energy required to make pellets from untreated wood. Douglas fir required the least energy input among debarked samples. Spruce was the stickiest pellet to be pushed out of the cylindrical die. Bark pellets required the lowest energy to be compacted and pushed out of the cylindrical die. The overall conclusion is that steam treatment reduces particle size, reduces pellet density slightly, but increases the mechanical strength of the produced pellets. Steam treatment increases the energy input required to make pellets, and more energy is required to push pellets out of the die compared to pellets made from untreated biomass.

Development of Size Reduction Equations for Calculating Energy Input for Grinding Lignocellulosic Particles

Size reduction is an essential and often first operation in preparing biomass for subsequent operations. Size reduction is energy intensive especially for cases where the target particle is small and precise in dimension. Mineral and food industries have developed empirical and semi-empirical equations to calculate energy input for grinding. It is uncertain if these equations can be applied to fibrous biomass. This research presents laboratory grinding data to evaluate the applicability of a set of generalized industrial-size reduction equations to the grinding of lignocellulose biomass. Batches of Douglas-fir (a soft wood) and hybrid willow (a hard wood) particles conditioned to 11.5% moisture content were ground in a rotary knife mill. Input and output particle sizes and the level of energy used to grind the material were acquired electronically and recorded. Specific grinding energy (J/g) was correlated with size parameters of three popular industrial equations: Kick, Rittinger, and Bond. All three equations fitted to the experimental data linearly but the best fitted lines did not go through the origin, i.e. the fitted lines had a slope and intercept. Rittinger equation had the best fit, followed by Bond equation and Kick equation.

Permeability of wood pellets in the presence of fines.

Broken pellets and fines are produced when pellets are handled. The resistance to air flow was measured for clean pellets and for pellets mixed with 1-20% broken pellets (fines). A pellet diameter was 6mm. The lengths ranged from 6 to 12 mm. Clean pellets were defined as particles that remained on a 4mm screen. A typical sieve analysis showed 30% of the mass of particles that passed through the 4mm screen was smaller than 1mm. The airflow rates used in the experiment ranged from 0.004 to 0.357 ms(-1). The corresponding pressure drop ranged from 1.9 to 271 Pam(-1) for clean pellets, from 4.8 to 1100 Pam(-1) for 10% fines content, and from 7.9 to 1800 Pam(-1) for 20% fines content. Coefficients of Hukill and Ives equation were estimated for clean pellets and a multiplier was defined to calculate pressure drop for pellets mixed with fines.

A Life Cycle Assessment of integrated dairy farm-greenhouse systems in British Columbia.

The purpose of this study was to evaluate the anticipated environmental benefits from integrating a dairy farm and a greenhouse; the integration is based on anaerobic digestion of manures to produce biogas energy, biogenic CO2, and digested slurry. A full Life Cycle Assessment (LCA) has been conducted on six modeled cases applicable in British Columbia, to evaluate non-renewable energy consumption, climate change, acidification, eutrophication, respiratory effects and human toxicity. Compared to conventional practice, an integrated system has the potential to nearly halve eutrophication and respiratory effects caused by inorganic emissions and to reduce non-renewable energy consumption, climate change, and acidification by 65-90%, while respiratory effects caused by organic emissions become negative as co-products substitute for other materials. Co-digestion of other livestock manures, greenhouse plant waste, or food and food processing waste with dairy manure can further improve the performance of the integrated system.

DEVELOPMENT OF A POPULATION BALANCE MODEL TO SIMULATE FRACTIONATION OF GROUND SWITCHGRASS

The population balance model represents a time-dependent formulation of mass conservation for a ground biomass that flows through a set of sieves. The model is suitable for predicting the change in size and distribution of ground biomass while taking into account the flow rate processes of particles through a grinder. This article describes the development and application of this model to a switchgrass grinding operation. The mass conservation formulation of the model contains two parameters: breakage rate and breakage ratio. A laboratory knife mill was modified to act as a batch or flow-through grinder. The ground switchgrass was analyzed over a set of six Tyler sieves with apertures ranging from 5.66 mm (top sieve) to 1 mm (bottom sieve). The breakage rate was estimated from the sieving tests. For estimating the breakage ratio, each of the six fractions was further ground and sieved to 11 fractions on a set of sieves with apertures ranging from 5.66 to 0.25 mm (and pan). These data formed a matrix of values for determining the breakage ratio. Using the two estimated parameters, the transient population balance model was solved numerically. Results indicated that the population balance model generally underpredicted the fractions remaining on sieves with 5.66, 4.00, and 2.83 mm apertures and overpredicted fractions remaining on sieves with 2.00, 1.41, and 1.00 mm apertures. These trends were similar for both the batch and flow-through grinder configurations. The root mean square of residuals (RSE), representing the difference between experimental and simulated mass of fractions, was 0.32 g for batch grinding and 0.1 g for flow-through grinding. The breakage rate exhibited a linear function of the logarithm of particle size, with a regression coefficient of 0.99.

Quantification of gas emissions from stored softwood chips as solid biofuels

Western Red Cedar (WRC) is one of the abundant softwood species, which is considered as a good source of biofuel. This paper aims at quantifying gas emissions from stored WRC woodchips and studying the potential health impact during storage and transportation. Experiments were conducted using lab-scale reactors for a range of temperatures under both non-aerobic and aerobic conditions depending on oxygen level. Results from tests using non-aerobic reactors showed that the highest carbon dioxide emission factor of 2.8xa0g/kg dry matter (DM) was observed at 20xa0°C for a storage period of 2xa0months. Although the carbon monoxide emission factor was much lower at 0.03xa0g/kg DM, it increased with increasing temperatures due to chemical oxidation. Carbon dioxide and carbon monoxide emissions from the aerobic reactors exhibited similar trends as the non-aerobic reactors with respect to the effect of temperature. Total gas emissions were higher from the aerobic reactors compared with those from non-aerobic reactors. Results from the qualitative gas chromatography–mass spectrometry analysis indicated a range of volatile organic compounds was emitted from the stored WRC woodchips. Some of these volatile organic compounds might be associated with the characteristic pungent smell of WRC which could cause odor nuisance to the neighboring community. The total volatile organic compounds concentration was found to be positively correlated with temperature. At the end of the storage period, percent DM loss was below 1xa0% for both the non-aerobic and aerobic reactors, reaffirming the decay-resistance characteristics of WRC.

The effects of storage on the net calorific value of wood pellets

The wood pellet export from Canada to Europe has been increasing steadily in recent years (roughly 1.8 million ton in 2013). Due to distances involved, wood pellets remain in transit and storage for months before their final consumption. The net calorific value determines the price of wood pellet purchase in Europe. There have been concerns about the changes of net calorific values over time. In this study, the effects of storage time, storage configuration, storage temperature, and wood pellet quality on the net calorific value of wood pellets for a period of 6 months were investigated. Storage configurations were open or closed and storage temperatures were 25 °C, 35 °C and 45 °C. Two types of wood pellets used were whitewood and mixed. The results in closed storage indicated that storage time had a positive effect on the net calorific value where the net calorific value increased by 1% to 2% over the storage period. In open storage, the moisture content had the most significant impact on the net calorific value. The net calorific values of the two types of wood pellets were found to be significantly different at p < 0.001. A multivariable linear regression and analyses of variancemorexa0» performed verified the graphical results. Lastly, the authors postulated that the higher energy potential compounds, such as aldehyde and ketone, produced during pellet storage, caused the increase in net calorific values.«xa0less