In Ukraine plant biomass from crop fields and forests is the dominant renewable energy source and it is suitable to replace fuels by producing bio-gas, bio-ethanol as well as solid bio-fuel. Tubes of Jerusalem artichoke are used as functional food ingredients such as inulin, fructose and oligofructose as well as bioactive ingredient sources for pharmaceutical and cosmetic applications. Jerusalem artichoke stems, that are about 1–3 m tall, as lignocellulosic by-products are of interest because they are not currently exploited but they can be successfully used as a raw material for solid bio-fuel production. The use of biomass pellets creates new market opportunities in the agricultural sector, reduces dependence on fossil fuels and cuts greenhouse gas emissions associated with their use.
The process of solid bio-fuel manufacturing consists of different energy intensive unit operations and among them drying process consumes a large share. From the drying process moisture content of grinded artichoke stems should be reduced from about 65-70% to 4-12% before pressing. Therefore, improving the drying process and adaption of more efficient systems with innovative equipment in drying will help conserve energy.
There are several types of dryers that are commonly used in industry for drying plant biomass, but the most common are rotary and fluidized bed dryers. By incorporating the advantages and the disadvantages of rotary and fluidized bed dryers, filtration dryer has been introduced for grinded artichoke stems drying due to its expected lower energy consumption. During the filtration drying the heat agent flows down through the channels of the fixed layer formed by particles of grinded biomass that is supported on a perforated belt. The large contact area for heat and mass transfer between the heat agent and the wet material results in high drying rates.
The influence of the heat agent temperature (from 313 to 373 K) on kinetics during filtration drying of grinded artishoke stems has been investigated. The kinetic curves of grinded artichoke stems has been characterized by long period of partial saturation of the heat agent by moisture according to the filtration drying mechanism. Due to the complexity of the filtration drying mechanism, the necessity of the effective moisture diffusivity determinаtion has been proved.Effective moisture diffusivity has been determined using the Fick`s law at five heat agent temperatures (293, 313, 333, 353 and 373 K). Effective moisture diffusivity values at different temperatures have been determined to be from 0.396 × 10–10 to 11,103 × 10–10 m2/s for grinded artichoke stems:
According to Arrhenius equation, the activation energy Ea and the pre-exponential factor Do have been calculated to be 24 kJ/mol and 1,24.10-6 m2/s, respectively. Deduced equation allows to calculate theoretically the effective moisture diffusivity for the grinded artichoke stems within temperature range of 293‒373 K.
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