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The equilibrium moisture content (EMC) of biomass affects transportation, storage, downstream feedstock processing, and the overall economy of biorenewables production. Torrefaction is a thermochemical process conducted in the temperature regime between 200 and 300 °C under an inert atmosphere that, among other benefits, aims to reduce the innate hydrophilicity and susceptibility to microbial degradation of biomass. The objective of this study was to examine water sorption properties of torrefied corn stover. The EMC of raw corn stover, along with corn stover thermally pretreated at three temperatures, was measured using the static gravimetric method at equilibrium relative humidity (ERH) and temperatures ranging from 10 to 98% and from 10 to 40 °C, respectively. Five isotherms were fitted to the experimental data to obtain the prediction equation that best describes the relationship between the ERH and the EMC of lignocellulosic biomass. Microbial degradation of the samples was tested at 97% ERH and 30 °C. Fiber analyses were conducted on all samples. In general, torrefied biomass showed an EMC lower than that of raw biomass, which implied an increase in hydrophobicity. The modified Oswin model performed best in describing the correlation between ERH and EMC. Corn stover torrefied at 250 and 300 °C had negligible dry matter mass loss due to microbial degradation. Fiber analysis showed a significant decrease in hemicellulose content with the increase in pretreatment temperature, which might be the reason for the hydrophobic nature of the torrefied biomass. The outcomes of this work can be used for torrefaction process optimization, and decision-making regarding raw and torrefied biomass storage and downstream processing. ABSTRACT:The equilibrium moisture content (EMC) of biomass affects transportation, storage, downstream feedstock processing, and the overall economy of biorenewables production. Torrefaction is a thermochemical process conducted in the temperature regime between 200 and 300°C under an inert atmosphere that, among other benefits, aims to reduce the innate hydrophilicity and susceptibility to microbial degradation of biomass. The objective of this study was to examine water sorption properties of torrefied corn stover. The EMC of raw corn stover, along with corn stover thermally pretreated at three temperatures, was measured using the static gravimetric method at equilibrium relative humidity (ERH) and temperatures ranging from 10 to 98% and from 10 to 40°C, respectively. Five isotherms were fitted to the experimental data to obtain the prediction equation that best describes the relationship between the ERH and the EMC of lignocellulosic biomass. Microbial degradation of the samples was tested at 97% ERH and 30°C. Fiber analyses were conducted on all samples. In general, torrefied biomass showed an EMC lower than that of raw biomass, which implied an increase in hydrophobicity. The modified Oswin model performed best in describing the correlation between ERH and EMC. Corn stover torrefi...

Large scale biofuel production will be possible only if significant quantities of biomass feedstock can be stored, transported, and processed in an economic and sustainable manner. Torrefaction has the potential to significantly reduce the cost of transportation, storage, and downstream processing through the improvement of physical and chemical characteristics of biomass. The main objective of this study was to investigate the effects of particle size, plant components, and gas residence time on the production of torrefied corn (Zea mays) stover. Different particle sizes included 0.85 mm and 20 mm. Different stover components included ground corn stover, whole corn stalk, stalk shell and pith, and corn cob shell. Three different purge gas residence times were employed to assess the effects of interaction of volatiles and torrefied biomass. Elemental analyses were performed on all of the samples, and the data obtained was used to estimate the energy contents and energy yields of different torrefied biomass samples. Particle density, elemental composition, and fiber composition of raw biomass fractions were also determined. Stalk pith torrefied at 280 °C and stalk shell torrefied at 250 °C had highest and lowest dry matter loss, of about 44% and 13%, respectively. Stalk pith torrefied at 250 °C had lowest energy density of about 18-18.5 MJ/kg, while cob shell torrefied at 280 °C had the highest energy density of about 21.5 MJ/kg. The lowest energy yield, at 59%, was recorded for stalk pith torrefied at 280 °C, whereas cob and stalk shell torrefied at 250 °C had highest energy yield at 85%. These differences were a consequence of the differences in particle densities, hemicellulose quantities, and chemical properties of the OPEN ACCESSEnergies 2012, 5 1200 original biomass samples. Gas residence time did not have a significant effect on the aforementioned parameters.

Torrefaction of biomass early in the supply chain is one method of enhancing or preservin biomass quality during storage; reducing storage and transportation costs; attaining uniformity among different feedstock types; and meeting biorefi neries' quality and quantity demands for feedstock in a cost effective and sustainable manner.The main objectives of this study were to analyze the mass and energy balance, to assess the techno-economic feasibility of a production-scale torrefaction system, and to quantify the sensitivity of energy and cost results to changes in initial feedstock moisture content, torrefaction process temperature, plant operating window, and initial capital investment. The output from this analysis provides clear guidance on the opportunities and costs associated with production-scale torrefaction of biomass as a feedstock intermediate. Analysis of energy results indicated that the net external energy required for the torrefaction process increased and energy effi ciency of the torrefaction system decreased with increasing moisture contents. However, both of these energy metrics exhibited a decreasing trend with increasing process temperatures. In addition to the energy results, unit torrefaction process cost exhibited a decreasing trend with decreasing initial moisture contents of feedstock and decreasing torrefaction process temperatures. For the typical moisture content of 30% wb , process temperature of 240°C, plant operating window of 6 mo.yr −1 and initial capital investment of $7.5 million for the system with rated capacity of 25 Tton.hr -1 , unit torrefaction process cost was estimated to be 17.5 $-Tton −1 . Additional system improvements through capital cost reduction and wider operating windows can yield a torrefaction product cost of ~12 $-Tton -1 . Overview of the mass and energy balance modelA model was developed to simulate the mass and energy balance and the techno-economic aspects of a production-scale continuous-fl ow torrefaction system under diff erent initial conditions. Model input parameters included initial moisture content of biomass, torrefaction process temperature,

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