Browsing by Person "Ntwali, Janvier"

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Technical evaluation of a modular dryer for medicinal and aromatic plants in practical German conditions
(2025) Ntwali, Janvier; Barati, Ziba; Bonzi, Joévin Wiomou; Esper, Albert; Müller, Joachim
A modular batch dryer with partial recirculation of outlet air to save thermal energy was developed for small-scale medicinal plants producers in Germany. Different operational modes were tested for energy consumption and the quality of the dried product using lemon balm leaves. Fresh air mode, partial recirculation-controlled flap mode and full recirculation-controlled flap mode alternated depending on the progress of drying and the set relative humidity at the inlet. Experiments consisted of comparing two modes of controlled flap modes with relative humidity varying from 80 to 30 % for one mode and fixed at 40 % for the other mode. A total mass of 500 kg of lemon balm leaves were dried in an average of 23 hours to reduce moisture content from 72 % to 7 %. The throughput ranged from 19.7 to 23.7 kg∙h-1 for lemon balm drying. Air recirculation significantly reduced the thermal energy consumption where a specific thermal energy consumption of 3540 kJ·kg-1 H₂O was achieved by controlling the inlet air humidity to 40 % when drying lemon balm compared to the 4075 kJ·kg-1 H₂O achieved under the 80-30 % mode. No significant difference in essential oils content was observed between the two humidity control modes. This research confirmed the energy-efficient attributes of the dryer and recommends the implementation of air recirculation as one of the methods to reduce energy consumption in medicinal plants drying.
Technical evaluation of a solar-biomass flatbed dryer for maize cobs drying in Rwanda
(2023) Ntwali, Janvier; Romuli, Sebastian; Bonzi, Joévin Wiomou; Müller, Joachim
The persistent problem of postharvest losses in the maize value chain poses an arduous challenge for smallholder farmers in Rwanda, ultimately reducing their market bargaining power. As a consequence, there is an exacerbated disparity in revenues that makes farmers, predominantly female farmers, more vulnerable. The existing drying facilities are based on ambient air drying with a long drying time and the alternative mechanical dryers use mostly fossil fuels which is not a sustainable solution. A solar-biomass hybrid flatbed dryer for maize cobs drying was designed and constructed in the high-altitude volcanic zone of Rwanda. The objective was to provide farmers with an affordable and sustainable drying system with a high drying rate compared to the existing method. In this study, we present the results of the technical evaluation of the dryer to rate its capacity to dry maize cobs to the recommended moisture content. Energy balance was assessed by temperature sensors, airflow distribution was measured with a vane anemometer and the solar radiation from weather station were compared to the solar system data recorded through a datalogging charge controller. Maize was dried in three batches and the moisture content was measure with oven method. Results showed a uniform distribution of airflow on the dryer perforated flow. The burner consumed on average 6 kg of empty cobs per hour and the burner efficiency was 59.4 %. The solar system provided a maximum daily yield of 2.6 kWh, and the battery was able to maintain the system during days of low solar energy availability. Maize cobs were dried from an average moisture content of 23.0 % to 13.7 % in an average period of 90.6 hours. This drying time was significantly lower compared to the already existing system which uses more than 6 weeks. The results prove that the solar-Biomass hybrid flatbed dryer was appropriate for drying maize cobs to the recommended moisture content and thus reduce the risk of postharvest losses in maize value chain in Rwanda. The dryer might be further improved by combining the burner with a solar heating system to further reduce the biomass mass consumption.