MST-Department of Energy Engineering

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Browsing MST-Department of Energy Engineering by Subject "Performance Evaluation"

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    Design and Performance Evaluation of a Biomass Gasifier: Case Study of Coffee and Rice Husks
    (Kenyatta University, 2021) Mutuku, Kilaka; Thomas F. N. Thoruwa; Jeremiah Kiplagat
    About 36.1% of Kenya’s population lives below the poverty line. Low income has forced most of the Kenyans to opt for the cheapest available sources of energy. Biomass fuels are the most important source of energy in Kenya with wood-fuel (firewood and charcoal) accounting for over 68% of the total primary energy consumption. In spite of past efforts to promote substitutes for wood-fuel, the number of people relying on them is not decreasing. Consequently, it is projected that biomass will continue to be the main source of energy for the majority of the rural population and urban poor. Each year, over 2.8 million people in the world die prematurely from diseases caused by inhaling smoke from indoor fires due to incomplete combustion of biomass fuels in open fires and inefficient stoves. As a result of deforestation, biomass resources (fire wood and charcoal) are getting scarce. Waste products from agro-processing industries such as coffee husks, rice husks have been a major challenge in disposal. Biomass gasification is one of the few technologies that can potentially turn these wastes into energy for both industrial and domestic use. Although gasification has been around for more than 200 years, the technology is still new in Kenya. This study involved designing and developing a household-size biomass gasifier for the production of syngas using locally available biomass fuels namely; rice husks and coffee husks. Characterization of test fuels was based on their calorific value, percentage moisture content, volatile matter, ash content, fixed carbon, bulk density and porosity. Calorific value of rice husks and coffee husks was 15.9±0.8kJ/g and 18.1±0.8 kJ/g respectively. Bulk density of sampled rice husks and coffee husks was 127.4±1.2 kg/m3 and 218.0±1.6 kg/m3 respectively. Porosity of sampled rice husks and coffee husks was 87.4±0.9% and 71.9±0.6% respectively. Moisture content of sampled rice husks and coffee husks was 8.0±0.0% and 8.8±0.3% respectively. The percentage volatile matter of sampled rice husks and coffee husks was 62.8±0.3% and 78.4±0.0% respectively. The percentage ash content of sampled rice husks and coffee husks was 20.2±0.4% and 3.9±0.1 respectively. The percentage fixed carbon of sampled rice husks and coffee husks was 17.0±0.7% and 17.7±0.1% respectively. The maximum temperature obtained inside the gasifier reactor was mainly in the range 800°C to 1100°C. 1.5 liters of water at an average temperature of 24°C boiled in the stove within 4.7 to 8.5 minutes. Economic analysis of the gasifier found out that if a family shifts from LPG to using the constructed gasifier the payback period is 1.09 years, net benefit is Ksh45,000 (450USD) and rate of return on investment is 214.29%.
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    Development and Performance Evaluation of Solar green house Dryer with Desiccant Energy Storage system for Tomatoes
    (Kenyatta University, 2021) Mbacho, Susan Andrew; Thomas F.N. Thoruwa; Nickson K. Lang’at
    Tomato is one of the most important horticultural crops widely grown in the tropical East Africa countries. It is mostly used as vegetable recipe for food preparation at most homes or consumed raw as a salad. However, during the rainy season, tomato farmers experience widespread post-harvest losses due to insect and molds infestation. Also, during harvesting seasons, most markets in East Africa are flooded with the produce leading to over- supply against low demand resulting to heavy postharvest losses. Therefore, it is necessary to use appropriate drying technologies especially solar drying technology to reduce these losses. The use of solar drying technology is a good alternative solution to the problem of crop drying and especially the perishable tomato crop. Literature review show that most solar crop drying technologies developed for the past 50 years have very small loading capacity and cannot operate during the night. Therefore, in this study, we developed an integrated greenhouse solar dryer with Clay-CaCl2 solid desiccant energy storage system. Solar greenhouse drying systems have an advantage over other solar drying systems because its structural simplicity combined with high loading capacity. In addition, they have relatively good thermal crop drying performance compared to most solar dryers. The system was tested under no-load and load conditions. The experimental study with no-load condition exhibited the mean collector temperature of 41.9 °C giving an average temperature rise of 14.7 °C (35%) above the ambient (27.2 °C) with an average R.H. value of 32.6% at the flow rate of 0.28 m3/s on the test date. When the desiccant energy storage was used during night an average greenhouse temperature recorded within the drying chamber was 26.5 °C higher than the ambient temperature of 15.9 °C (40 % temperature rise). The results obtained under desiccant energy storage showed that at a 0.07 m3/s air flow rate with an average rise in temperature of about 13.6 (32.3%) against the average ambient temperature of 28.5°C. The average relative humidity within the system was found to be 36.5% lower than the ambient R.H. (84.1%). The collector efficiencies obtained from no load test was 46.2% and 40.8% for the dryer and desiccant chamber respectively. The performance of the dryer was evaluated with fresh tomato load during the month of September - December 2019 at Kenyatta University field site. The dryer demonstrated capacity to dry fresh tomatoes from 93.9% (wb) to 8.3% (wb) within 27 hours with solar greenhouse drying efficiency of 23% while at night the dryer demonstrated desiccant drying efficient of 19.9%. The drying rate for the two-day solar drying was 0.985 kg/h and 0.875 kg/h respectively and that in night drying using desiccants was 0.34 kg/h. The economic analysis of the drying system shows a payback period of less than a year (0.54 year) with benefit-cost ratio of 8.4 implying that the system is economically viable. On the basis of these results, it was concluded that prototype solar greenhouse dryer with Clay-CaCl2 energy storage system has great potential for tomato drying and other high moisture agricultural products in East African countries.