Performance analysis of the Takoradi thermal power plant

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Increasing electricity demand of about 10 % per year coupled with falling levels of the Volta Reservoir made it difficult for VRA to reliably meet the domestic loads and also fulfil its contractual obligations to the export market during the 1980s and 1990s. As a result, a series of studies were carried out to find a suitable supplement to VRA’s hydro system [6]. The studies identified and chose combustion turbines as the most attractive generation expansion option to the all- hydro system. Consequently, a 330 MW combined cycle plant made up of two 110 MW Gas Turbines and one 110 MW Steam Turbine with associated Heat Recovery Steam Generators was installed at Aboadze near Takoradi. This was later followed by another 220 MW gas turbine plant which is expected to be upgraded to 330 MW giving the overall plant capacity at Aboadze as 660 MW. This thesis has analysed the performance of the Combined Cycle Plant since its installation in 1997 by determining its actual performance indicators and comparing them with the benchmark values. The analysis was done up to 2003. The main indicators considered are availability factor, plant capacity factor, load factor, thermal efficiency, heat rate and specific fuel consumption. The analysis has shown that the plant has not been doing well due to numerous problems. The plant’s availability factor is generally low. The lowest annual average availability of 47.1 % was recorded in 2002 with the highest of 83.3 % at the start of operation in December 1997. The annual average availabilities for 1998, 1999, 2000, 2001 and 2003 were 64.6 %, 61.0 %, 52.9 %, 70.5 % and 62.2 % respectively. These values do not compare well with the manufacturers rated 85 % availability. The plant has also been operating at less than 50 % capacity: the annual capacity factors for 1997, 1998, 1999, 2000, 2001, 2002 and 2003 were found to be 77.5 %, 59.6 %, 38.2 %, 16.9 %, 25.6 % 30.2 % and 45.8 % respectively. These low values were due to frequent breakdowns and as a result the plant has not been meeting its demand most times. The plant’s combined-cycle and simple-cycle thermal efficiencies and heat rates, on the other hand, compare favourably well with the rated values. The plant’s combined-cycle efficiency varied slightly between 46.3 % in 2001 and 46.6 % in 2003 while heat rate varied between 7782 kJ/kWh in 2001 and 7730 kJ/kWh in 2003. The efficiency and heat rate for 2002 are 46.4 % and 7755.5 kJ/kWh respectively. In the simple cycle mode (from 1997 to 2000), the efficiencies and heat rates were found to be 30.0 %, 11984.0 kJ/kWh; 28.5 %, 12622.9 kJ/kWh; 29.4 %, 12240.2 kJ/kWh and 28.0 %, 12840.6 kJ/kWh for 1997, 1998, 1999 and 2000 respectively. The key issue is the plant’s low availability factors over the years due to long equipment downtimes. Lack of adequately trained staff, delay in acquisition of spare parts and lack of specialised tools have been identified as some of the major factors responsible for the long equipment downtimes and hence the poor performance of the TTPP. For the plant’s performance to be improved upon, it has been suggested that VRA increase personnel level and develop multi-skilled work force among the operation and maintenance staff. It has also been suggested that better agreement with the suppliers of spare parts be secured and the specialised tools be made readily available.
A Thesis presented to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for a Master of Science Degree in Mechanical Engineering, 2004