Performance assessment of the stand-alone diesel power plant at San, Mali

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Long-standing and pressing demands for minimum supply of electricity coupled with the small size of the grid and limited capacity of the existing hydroelectric plants, led the Malian power utility company EDM-SA (Energie Du Mali SA) to install diesel plants in the major district towns for the electricity needs of the population. This option was strengthened in 1991 as recommended by a study carried out by ESMAP. In this context a diesel plant was installed at San. The plant at San is rated 135 MW as at January 2004 and consists of three 450 kWe Caterpillar generator sets (known at the plant as G5, G6, and G7). The plant was commissioned in 1 996 but continuous power production started in 2000. This thesis has carried out a performance assessment of the diesel plant at San. The assessment covered the period 2002-2003 for which data were available. It focused on technical, economic and environmental aspects of the performance. Power plant performance indicators used in this assessment were identified from the literature; the main ones are plant capacity factor, load factor, plant availability factor, thermal efficiency, specific fuel consumption, heat rate, energy generation cost and the emission rates of CO2 and SO2. Sensitivity analysis was also conducted on the energy generation cost to determine its dependence on parameters such as the plant capacity factor, thermal efficiency, the plant life time and the discount rate. The annual plant capacity, load and availability factors were respectively: 37%, 75% and 89% for 2002 and 22%, 75% and 99% for 2003. The annual total outage duration, failure rate and reserve margin are respectively 937 hours, 11%, 103% for 2002 and 59 hours, 0.7% and 235% for 2003. Thermal efficiency, specific fuel consumption and heat rate were respectively 36%, 0.24 kg/kWh and 10,135 kJ/kWh for the year 2002 and 33%, 0.26kg/kWh and ll,O7lkJ/kWh, for 2003. The availability factor, load factor, failure rate, specific fuel consumption and thermal efficiency compare favourably to typical values for diesel plants as reported in the literature. But the reserve margin is higher than typical values reported in the literature. The levelised energy production cost excluding transmission and distribution costs was estimated to be USS 0.2854/kWh for 2003. The quantities of CO2 and SO2 emitted per unit of electrical energy generated were also estimated; they were respectively 749x103 kg/kWh and 95xl0 kg/kWh for2002 and 817x103 kg/kWh and 95xl0 kg/kWh for2003. The capacity factor decreased from an already low value of 37% in 2002 to 22% in 2003; this is due to the addition of new generating capacity in 2003, which was not done in accordance with the load growth. As a result of the low capacity factor, the generation cost of US$ 0.2854/kWh for 2003 was far above the average electricity generation cost in Mali of USS 0.1 9/kWh (average for hydro thermal and diesel plants). Furthermore, it exceeded the average electricity tariff of US$ 0.261/kWh. The sensitivity analysis showed that for plant capacity factors above 35%, the generation cost is comparable with the average for the diesel generating plants, which is US$ 0.2624/kWh. Furthermore, the generation cost varies linearly from 0.285 to 0.3 06 US$/kWh with discount rate in the range of 6-12%. In conclusion the technical performance indicators of the diesel plant at San are in a good range except the plant capacity factor, which is very low and the reserve margin, which is very high. The levelised energy generation cost is higher than the national average. The low plant capacity factor and the high energy generation cost have to do respectively with a high annual reserve margin of 235% in 2003, and with the capital invested in the reserve plant. For these two indicators to improve, it is recommended that more attention should be given to the addition of new generating capacity, which should be done in accordance with the load growth, and to load promotion programmes to increase demand for electricity.
A Thesis presented to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the Requirements for the Degree of Master of Science in Mechanical Engineering, 2004