Showing papers by "Shahab Sokhansanj published in 2019"

Effect of Moisture on Gas Emissions from Stored Woody Biomass

Abstract: Biomass materials have been increasingly used due to their renewable nature. The problems occurring during the storage of fresh woody materials include gas emissions and dry matter losses as a result of degradation. The objective of this study was to investigate and quantify the effect of moisture content on gas emissions from stored wood chips. Experiments were conducted under non-aerobic and aerobic conditions using fresh Western Red Cedar (WRC) chips with different initial moisture contents over a range of temperatures. The peak CO2 emission factor of 2.9 g/kg dry matter (DM) was observed from high moisture chips at 20 °C under non-aerobic conditions after two-month storage, which was an order of magnitude greater than that from low moisture chips. In the case of volatile organic compounds, a range of compounds were detected from all tests. The concentration of VOCs was found to be positively correlated with moisture content. Gas emissions from the aerobic reactors exhibited similar trends as non-aerobic reactors with respect to the effect of moisture content, although higher values were observed under aerobic conditions. Slight reduction of dry mass from all tests at the end of storage indicated the decay-resistance characteristics of WRC.

Constitutive modelling of compression and stress relaxation in pine pellets

Abstract: The increasing pellet production and a demand for making high quality biofuel pellets call for tools that can facilitate producers to meet these requirements and help understanding the effect feedstock and process parameters. In this study, mechanical and rheological properties of pine pellets made of different particle sizes and compression speeds were studied via pelleting tests and numerical simulations. Single pelleting tests were performed with six different particle size samples, ranging between 0.25 and 2.8 mm, and pelleted at compression speeds of 1, 5, and 10 mm min−1. The experimental results of specific compression and extrusion energy showed a positively linear correlation between particle size and energy consumption. The highest pellet durability was observed for pellets produced from small and mixed particle sizes. Eight different constitutive models were evaluated on their ability to simulate compression and stress relaxation, and their level of complexity. A non-linear Maxwell representation of the Standard Linear Solid (SLS) model was setup and fitted to the experimental compression data. The model coefficient of spring 1 composes the asymptotic stress level of the relaxed pellet, and the coefficient of spring 2 was found to be positively correlated with particle size. The viscosity of the dashpot is also found to be positively correlated with particle size, likewise it depends on the compression speed, where higher compression speed resulted in lower viscosities. The results of the study elucidate new insight into mechanical behavior of biomass particle compression, and the resultant simulations have utility for predicting the pressure requirements to produce pellets.

Comparative Analysis of Sorption Isotherms for Wood Pellets and Solid Wood

Abstract: The published data on equilibrium moisture content vs. equilibrium relative humidity (EMC-ERH) for wood pellet do not cover the range of temperature and relative humidity to which a pellet is exposed to during its storage and handling. A few published EMC-ERH relations covering a wider range of temperatures and relative humidity are available for solid wood (lumber) and wood chips. The question is whether the data for solid wood is applicable to wood pellets. For this research, we examined the sorption isotherms of wood pellets and solid wood. The analysis shows that EMC for solid wood is higher than the EMC for wood pellet for a relative humidity larger than 30%. The slope of EMC-ERH isotherm for solid wood in the range of 30%-70% is slightly steeper than the slope of isotherm for wood pellet, indicating the pellet‘s EMC is less sensitive to ERH when compared to EMC-ERH for solid wood.

A simplified logistics model for integrating BIMAT and IBSAL to estimate harvest costs, energy input and emissions

Abstract: The Agriculture and Agri-Food’s Biomass Inventory Mapping and Analysis Tool (BIMAT) provides internet-based GIS functionality to query and visualize biomass inventory data in Canada. The Integrated Biomass Supply Analysis and Logistics (IBSAL) model is a modularized simulation of biomass supply chain. In this study, IBSAL modules are assembled to simulate harvesting of straw, stover, and switchgrass yields. The operations in this study started from combining for grain crop residues and ended in stacking bales on the field side. The equation C=aR^b Y^c was fitted to the simulated data to estimate constants a, b, and c for cost in $/dry tonne, energy input in MJ/dry tonne, and carbon emissions in kg CO2/dry tonne. Variable R is the fraction of above ground biomass removed during harvest and Y is the yield defined as biomass above ground (dry tonne/ha). These functions are supplied to the BIMAT portal and developed specific values for costs, energy input, and emissions on the map. The farm gate cost cost for the stacked bales ranged from $20 per dry tonne for high yielding regions of southwest Edmonton and Ontario to $27 per dry tonne for the eastern Ottawa region, and $31 per dry tonne for low yielding regions of central Saskatchewan. The costs are validated with published custom rates. It is recommended that the next step is to integrate IBSAL and BIMAT codes so the logistics values are generated and shown automatically on the map.