Experimental Investigation of Biogas As A Supplementary Energy Source for SolarBiogas Hybrid Drying System
Creators: name: Biniyam Mekonnen
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2022
Subjects: greenhouse dryer, biogas, preheated air, solar radiation, reabsorption, dewing

description: A direct, active type, environmentally friendly, and low-cost solar dryer was sized and<br> constructed from locally available materials to dry agricultural products. Because<br> Ethiopia produces banana peels which are about 91,095.44 tons annually, it is chosen<br> for experimentation purposes. Therefore, banana peels should be dried, processed, and<br> can play a crucial role in fighting cancer, for food and vehicle industries…etc. In this<br> era of energy shortage and chaos from fossil fuels, biogas was found to be an ecofriendly, low cost, and renewable energy source. Thus this paper utilized biogas as a<br> supplementary energy source for tackling reabsorption (dewing) at night time inside<br> solar dryers.<br> In this research, no-load, solar alone, solar with biogas 1st, and solar with biogas 2nd<br> drying tests were conducted with 5kg of banana peel. Besides, in the solar with biogas<br> 1st and 2nd drying tests, more than one banana peel samples were considered. In the<br> solar with biogas 1st drying test, biogas was provided from 7pm-8pm for three<br> consecutive nights. In the solar with biogas 2nd test, biogas was provided from 7pm-<br> 8pm, 7pm-11pm and 12am-3am for first, second, and third consecutive nights. In the<br> solar with biogas 1st and 2nd drying tests, a respective total amount of 0.3672m3 (7.6KJ)<br> and 0.9792m3 (20.5KJ) biogas was utilized. For comparison seek two greenhouse<br> dryers, G.D1 and G.D2, were employed with and without supplementary heat from<br> biogas, respectively.<br> On the no-load test, the dryer’s temperature profile was found out to be matching with<br> the sizing requirement. Besides, the temperature profile of both dryers was similar. In<br> the solar alone drying test, 5kg of banana peel was observed to reduce its moisture from<br> 82.53(w.b%) to 45.10(w.b%) and reabsorption had happened on each night of the<br> drying test. But, significant reabsorption of 3.36 (w.b%) occurred on the second night<br> of the drying test.<br> In the solar with biogas 1st drying test, the heat supplemented for G.D1 for three<br> consecutive test nights generated a mean temperature difference of 4.14°C, 4.51°C, and<br> 0.79°C. This temperature difference between the preheated and ambient air at night<br> time didn’t minimize the reabsorption happening inside the dryer. Instead, mean<br> reabsorption of 1.62 (w.b%) had happened. However in the solar with biogas 2nd drying<br> test the heat supplemented for G.D1, for three consecutive test nights, generated a mean<br> <br> temperature difference of 1.36°C, 3.69°C, and 15.86°C. The reabsorption of the banana<br> peel was found out to be 0.7 (w.b%). Also, the 5kg banana peel under the solar with<br> biogas 1st and 2nd drying tests maintained 15(w.b%). This 15(w.b%) moisture content<br> was achieved 2.37hrs and 1.67hrs (1st and 2nd drying tests) earlier than the banana peel<br> under the solar alone drying test conducted simultaneously. Therefore, when lower<br> direct solar radiation existed it was found out that at least 20.5kJ of supplementary<br> energy for 8hrs should be provided to minimize reabsorption.