Large-scale transportation and storage of wood pellets:Investigation of the change in physical properties

The change in physical properties of wood pellets,with a focus on particle size distributions due to pellet breakage and attrition,was studied in a large-scale(∼450 ton/h)transportation system.Critical locations with a high probability of breakage through the whole transportation system were chosen and sampled to study the effect of transportation system design and operation on the mechanical properties of pellets.Bulk density,mechanical durability,moisture content,and particle size distribution of pellets were characterized for each sample.Analysis of variance showed that there were significant differences between the percentages of small particles(<5.6 mm)in the samples taken at different locations,especially at one with a vertical free fall of 7.8 m.On average,this relatively long drop increased the proportion of particles<5.6 mm in the samples from 8.73%to 14.09%,and that of particles<3.15 mm from 4.82%to 9.01%.Moreover,the measurements showed a wide deviation in the mechanical durability values,between a minimum of 90.8%and a maximum of 98.7%,which were not correlated to the sampling points but related to pellet properties.It can be concluded that pellet transportation systems require more dedicated design strategies to prevent breakage and attrition.

Environmental and Economic Assessment of Wood Pellet Production from Trees in Greece

Biomass is a renewable, economic and readily available resource of energy that has potential to substitute fossil fuels in many applications such as heat, electricity and biofuels. The increased use of the agricultural biomass can help the agricultural based societies in achieving energy security and creating employment without causing environmental degradation. However, the viability and feasibility of electricity generation from agricultural biomass depends upon the availability of biomass supply at a competitive cost. The present study investigates the availability of agricultural biomass for distributed power generation in Greece (Kozani). The study concludes with a discussion on significance and challenges of decentralized electricity generation for rural energy supply, including brief description about economical, social, environmental and technical aspects of bioelectricity. With the application of the life cycle analysis applied, the environmental and economic impacts that will occur in the region of Kozani in Greece, where a biomass wood pellets production workshop is operating, have been assessed. The total annual emission of CO 657.9 gr, HC 22.36 gr, PM 67.94 and NOx 8.832,2 gr was calculated. The economic evaluation estimated the payback period for the investment in this plant to be approximately 3 years.

Life cycle cost and economic assessment of biochar-based bioenergy production and biochar land application in Northwestern Ontario, Canada

Background:Replacement of fossil fuel based energy with biochar-based bioenergy production can help reduce greenhouse gas emissions while mitigating the adverse impacts of climate change and global warming.However,the production of biochar-based bioenergy depends on a sustainable supply of biomass.Although,Northwestern Ontario has a rich and sustainable supply of woody biomass,a comprehensive life cycle cost and economic assessment of biochar-based bioenergy production technology has not been done so far in the region.Methods:In this paper,we conducted a thorough life cycle cost assessment(LCCA) of biochar-based bioenergy production and its land application under four different scenarios:1) biochar production with low feedstock availability;2) biochar production with high feedstock availability;3) biochar production with low feedstock availability and its land application;and 4) biochar production with high feedstock availability and its land application-using SimaPro~,EIOLCA~ software and spreadsheet modeling.Based on the LCCA results,we further conducted an economic assessment for the break-even and viability of this technology over the project period.Results:It was found that the economic viability of biochar-based bioenergy production system within the life cycle analysis system boundary based on study assumptions is directly dependent on costs of pyrolysis,feedstock processing(drying,grinding and pelletization) and collection on site and the value of total carbon offset provided by the system.Sensitivity analysis of transportation distance and different values of C offset showed that the system is profitable in case of high biomass availability within 200 km and when the cost of carbon sequestration exceeds CAD $60 per tonne of equivalent carbon(CO_2e).Conclusions:Biochar-based bioenergy system is economically viable when life cycle costs and environmental assumptions are accounted for.This study provides a medium scale slow-pyrolysis plant scenario and we recommend similar experiments with large-scale plants in order to implement the technology at industrial scale.

Two-dimensional CFD simulation and pilot-scale experimental verification of a downdraft gasifier: effect of reactor aspect ratios on temperature and syngas composition during gasification

This paper focuses on a two-dimensional CFD simulation of a downdraft gasifier and a pilot-scale experiment for verification using wood pellet fuel.The simulation work was carried out via the ANSYS-Fluent CFD software package with in-house coding via User Defined Function.Three gasification parameters were taken into account in the simulation and validation to achieve highly accurate results;namely,fuel consumption,temperature profile,and syngas composition.After verification of the developed model,the effects of aspect ratios on temperature and syngas composition were investigated.Results from simulation and experimental work indicated that the fuel consumption rate during the steady state gasification experiment was 1.750±0.048 g/s.The average steady state temperature of the experiment was 1240.32±14.20 K.In sum,the fuel consumption and temperature profile during gasification from modeling and experimentation show an error lower than 1.3%.Concentrations of CO,CO2,H2,and CH4 were 20.42 vol%,15.09 vol%,8.02 vol%,and 2.6 vol%,respectively,which are comparable to those of the experiment:20.00 vol%,15.48 vol%,8.00 vol%,and 2.65 vol%.A high concentration of syngas is observed in the outer radial part of the reactor because of the resistive flow of the air inlet and the synthesis gas produced.The average temperatures during the steady state of the gasifier with aspect ratios(H/D)of 1.00,1.38(experiment),and 1.82 were 978.77±11.60,1256.46±9.90,and 1368.94±9.20 K,respectively.The 1.82 aspect ratio reactor has the smallest diameter,therefore the radiative heat transferred from the reactor wall affects the temperature in the reactor.Syngas compositions are comparable.Inverse relationships between the aspect ratios and the syngas LHV,(4.29–4.49 MJ/N m3),cold gas efficiency(29.66%to 31.00%),and carbon conversion(79.59%to 80.87%)are observed.

Evolution of biomass particles during pelletization process

Pulverizing is an essential unit operation in co-firing biomass with coal.Pulverizers are only compatible with pellet forms of fibrous biomass materials and crush them down to their original forming particle sizes.That is why the data on the size distribution of the particles forming a biomass pellet is crucial to achieving optimum combustion conditions.The current study determines the internal particle size distribution of pellets after wet disintegration,following Iso 17830 standard,and aims to suggest improvements to the mentioned standard based on new measured evidence.Experiments were carried out on white wood pellets(no bark)and brown wood pellets containing bark at four water temperatures:20,40,60,and 95℃,with or without stirring.The particle size distribution of the pre-pelletizer wood particles was also measured and compared with particles in the formed pellets.Ambient water temperature of 20℃ was found to be adequate for the complete disintegration of pellets,and no mechanical stirring was required.About 30% of particles in the disintegrated pellets were 0.5-1.0 mm.Pelletization changes the particle size distribution to smaller particles.The disintegrated bark pellets contained more fines than white pellets.