Experimental method for determining Forchheimer equation coefficients related to flow of air through the bales of soy straw

Abstract

The paper presents results of experimental investigation conducted to determine permeability coefficient of a porous bed formed by biomass bales, whereby the said coefficient represents one of the most important parameters of the bed material specified when considering its combustion in the pusher-type furnaces (i.e. combustion of biomass bales in cigar burners). Correlations obtained are deemed very important for optimization of biomass bale combustion, as well as for modeling transport phenomena occurring in the porous bed formed by biomass bales during their combustion in cigar burners. In order to determine permeability coefficient of air flow through soy straw bales, appropriate experimental method was developed and suitable experimental apparatus designed and constructed. The relevant coefficients were determined in such manner as to be representative of the viscous and inertial terms of the Forchheimer equation. Experimental investigation conducted examined the effects of relevant biomass bale parameters i.e. porosity and the moisture content on the abovementioned Forchheimer coefficients. Measurements conducted, as well as analysis of the results obtained, defined functional dependencies of the permeability coefficients on the porosity (which was varied in the range 0.62-0.78, for moisture content of 0.0948) and the sample's moisture content (which was varied in the range 0.0948-0.6394, for the selected value of porosity of 0.68) to be established. The correlations obtained are deemed suitable to be used in a broad spectrum of operating conditions that usually occur during real operation. Results obtained indicate that reduction in biomass bed porosity results in reduced permeability, with Forchheimer coefficients exhibiting a hyperbolic dependence on the bed porosity. Since it has been observed that increased moisture content of the sample (porosity value of 0.68) caused a decrease in permeability, a functional dependence of the sample moisture content on the porosity has been established. The dependence established is valid for the range of the sample moisture content between 0.0948 and 0.6394. Permeability coefficients, as well as their dependencies on the relevant factors (porosity and moisture content), represent basic data used in mathematical modeling of biomass bale combustion in cigar burners. In addition, the ones may also be very important when considering modifications of furnaces utilizing the combustion principle mentioned.