Heat Transfer Model and Its Experimental Validation in a Small Scale Biodigestor
A small scale anaerobic digester was installed in a region of Argentina with important thermal amplitude. The digester operated in semi-batch mode and was fed with a mixture of rabbit manure, sorghum crops and water and operated with a hydraulic retention time of 45 days. The performance of the anaerobic digester was studied with special focus on thermal effects. A simple non- stationary model was developed in order to predict the slurry temperature and determine the challenges associated with biogas production in our region. Radiative, convective and conductive heat transfer phenomena were taken into account and the model has been validated with experimental data. Biogas stream was quantitatively evaluated in terms of volumetric total flowrate (bubble soap meter) and pH were measured over a long period of time. Biogas composition was determined by means of gas chromatography. Previously, the presence of sulfur in the biogas stream was analyzed using the silver nitrate tritation method through its reaction to yield silver sulfide (black precipitate). The produced digestate was also characterized by determining, in samples with different period of storage, the organic content and dry weight by gravimetric analysis, pH and conductivity, size distribution of suspended solids by laser diffraction, hydrogen, nitrogen and total carbon content by elemental analysis, potassium content by flame spectrophotometry and phosphorus content by the colorimetric method of Scheel.
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