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Abstract:The Terai region in Nepal has water resources with very low head and medium to high discharge conditions. Hence, the people of the Terai region are not being able to utilize the water resources available near them due to the limitation of technology. This study is intended to serve the purpose of further research of ultra-low head gravitational water vortex turbines useful for power generation in the Terai region.Gravitational water vortex turbine is an ultra-low head turbine which can operate in as low head as 0.7m with similar yield as conventional hydroelectric turbines characterized with positive environmental yield. This study has been carried out in two phases. In the first phase, two different turbines are to designed and fabricated and the performance characteristics of the new turbine are to be compared with that of the installed turbine. The second phase includes the design and fabrication of the conical basin. Experimental tests will be carried out and the performance of the system with the use of a conical basin will compared with that of the system using the cylindrical basin. A site testing also has been carried out to ensure the performance of system.

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The analysis of water resources in Nepal identifies two critical impacts of climate change -GLOFs and variability of river runoff -both of which pose significant impacts not only to hydropower, but also to rural livelihoods and agriculture. Temperature differences are most pronounced during the dry winter season, and least during the height of the monsoon. Impacts on water resources and hydropower rank significantly higher than any other sector for several reasons. First, a number of impacts on water resources and hydropower are directly related to rising temperatures that have already been observed, and are projected to increase further over the coming decades. This includes glacier retreat that in turn causes both greater variability in stream flow and glacial lake outburst floods that pose significant risk to hydropower facilities, other infrastructure, and human settlements. GLOFs are not hypothetical; such events have already had significant impacts in Nepal. In this study over the Gandaki river basin, discharge of the rivers, temperature trends, and rainfall patterns are analyzed using data from meteorological stations of the Department of Hydrology and Meteorology (DHM), Government of Nepal. Similarly the hydrological stations over the major glacier rivers of the basin are examined. In the study area, some hydropower stations and their energy production fluctuations over the seasons reflect the climate change impact to the hydro energy production in Nepal.

Gravitational Water Vortex Power Plant (GWVPP) is an appropriate means to convert kinetic energy of water to rotational mechanical energy at the very low head site. This study aims to establish a basic reference for the design of the runner for the Gravitational Water Vortex Turbine (GWVT) with a conical basin. Seven different geometrical parameters have been identified for runner design, and the effect of these parameters on the system efficiency has been studied numerically and experimentally. The effect of these parameters has been studied over the range of speed with torque. The results from performance tests of these runners suggest that runner height is the most significant parameter to be considered in the design of a turbine runner for GWVPP with a conical basin. The results show that the efficiency of GWVT has improved up to 47.85% as obtained from experiments.

The performance of dry anaerobic digestions of cow dung, pig manure, and their mixtures into different ratios were evaluated at 35 ± 1 °C in single-stage batch reactors for 63 days. The specific methane yields were 0.33, 0.37, 0.40, 0.38, 0.36, and 0.35 LCH4/gVSr for cow dung to pig manure ratios of 1:0, 4:1, 3:2, 2:3, 1:4, and 0:1, respectively, while volatile solid (VS) and chemical oxygen demand (COD) removal efficiencies were 48.59, 50.79, 53.20, 47.73, 46.10, and 44.88 % and 55.44, 57.96, 60.32, 56.96, 53.32, and 50.86 %, respectively. The experimental results demonstrated that the co-digestions resulted in 5.10-18.01 % higher methane yields, 2.03-12.95 % greater VS removals, 2.98-12.52 % greater COD degradation and so had positive synergism. The various mixtures of pig manure with cow dung might persuade a better nutrient balance and dilution of high ammonia concentration in pig manure and therefore enhanced digester performance efficiency and higher biogas yields. The dry co-digestion of 60 % cow dung and 40 % pig manure achieved the highest methane yield and the greatest organic materials removal efficiency than other mixtures and controls.

Abstract:Biogas is widely used in villages of Nepal for cooking and lighting. But its commercial use has never been realized due to difficulties in its storage and transportation. Solution identified to the problem is to increase the energy density of the gas through removal of incombustible and corrosive gas and consequent compression which was experimented on a lab-scale model. This paper presents all the results of removal of CO 2 gas from biogas using different chemicals and relative purity with raw gas. Further, compression of biogas and was carried out by methane refrigerant compressor and bottled into normal LPG cylinder. Compression of biogas was carried out under near Isothermal and Adiabatic conditions up to 11bar absolute pressure. The energy efficiency of compression was determined to be 98.71% and if the gas used for generation of electricity using a generator with an efficiency of 30%, the net energy efficiency turned out to be 95.72%. Later, a boiling test was conducted whereby the combustibility of the compressed biogas from the cylinder in normal biogas-stove was tested to validate its use in cooking, the results of which are included.