Conversion of Coleson Cove oil-fired unit to natural gas-fired combined cycle

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Date
2015
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University of New Brunswick
Abstract
Coleson Cove Generating Station (CCGS) is a key player in managing New Brunswick's electricity demand. Coleson Cove, NB Power􀇯s largest generating station, consists of three 350 MW oil-fired units for a total plant capacity of 1,050 MW. Due to the current price of expensive heavy fuel oil, Coleson Cove tends to operate only during peak energy demand periods. Operating CCGS's oil-fired units at minimum load while providing back-up stability for the electrical grid is expensive due to high operating costs while running with expensive heavy fuel oil. It is therefore crucial to be able to operate these units at the lowest load possible to minimize fuel consumption during these periods. NB Power is exploring the feasibility of converting Unit #1 at Coleson Cove from an oil-fired unit to a more modern, highly efficient, natural gas-fired combined cycle. The flexibility of a combined cycle would give CCGS the ability to better load follow wind power as well as to help cut down on greenhouse gas emissions in the province. The target plant start-up date is 2020 and the proposed design seeks to make use of the existing steam turbine for the new combined cycle and boiler house to support the new heat recovery steam generator (HRSG). The proposed design for CCGS􀇯s new combined cycle consists of a new gas turbine, a new (RSG and the re-use of the existing steam turbine. The General Electric GT-7HA.01 gas turbine was selected for the proposed design. This turbine operates at a maximum load of 275 MW with a minimum turndown of 30%. The new HRSG will be a vertical-style unit due to the space limitation constraint at CCGS and will be comprised of three pressure levels in order to extract as much heat from the exhaust gases as possible for generating mechanical work. The existing Hitachi steam turbine will not undergo any significant modification. The proposed design generates 390 MW (gross) of electricity to the electrical grid with a full load efficiency of 49% (HHV), which represents a 13% increase from the current efficiency of 36% (HHV). The total capital investment for the proposed design was determined to be $277 million. The new gas turbine and HRSG make up the bulk of the total capital investment, at $111 million and $121 million, respectively. The total annual operating costs were estimated to be $134 million/yr., based on current natural gas markets. CCGS is expected to generate an average revenue of $144 million/yr. from electricity sales, which represents an average annual profit of $10 million/yr. Assuming an estimated plant life of 30 years starting in 2020, the internal rate of return was calculated to be 0.6%. The results from the economic analysis showed that the profitability of the project is highly sensitive to the purchase price of natural gas and the selling price of electricity. The completion of current natural gas pipeline construction in the Northeastern United States is expected to reduce the price of natural gas in New Brunswick, which would significantly improve the profitability of the project. In summary, converting Unit #1 at CCGS to burn natural would reduce fuel costs, increase efficiency, decrease greenhouse gas emissions and give NB Power the ability to better load follow for wind power.
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