Damodar Valley Corporation (DVC) will switch over to methane as the feedstock for its three 30-mw gas turbines at Maithon in Bihar. Besides, the corporation will also use methane gas in lieu of fuel oil at its thermal power stations.
The methane gas will be supplied by Great Eastern Energy Corporation, an Indo-US venture, which proposes to commence commercial production of methane by April 1998.
The prospects of striking methane gas in the Damodar valley area is opening up many possibilities. All thermal power units need fuel oil to stabilise the flame in the boilers. This oil is expensive in comparison to methane gas.
DVC is in talks with General Electric of the US to finalise the package for conversion of the feedstock from naphtha to methane gas, and convert the gas turbine station into a combined-cycle operation plant. This will increase the capacity of the 90-mw station by 50 per cent. There will be no operational expenditure for the additional 45 mw generation, besides the capital expenditure for the conversion.
The corporation proposes to use the renovated combined-cycle gas turbine station as a base load station, instead of the current practice of using the capacity only to meet infrequent peaking requirements. This will reduce the cost of generation to Rs 2 per unit of energy from the current Rs 5.50 a unit. The cost can also be reduced by spreading the fixed cost of the gas turbines over round-the-clock energy output, in place of an average two-hour operation now. The turbines will be run by the exhaust steam generated at the gas turbines.
The capital expenditure for the proposed changes will be a maximum of Rs 150 crore and General Electric has been asked to organise the funds.
Sources said the capital cost could be halved if DVC was able to utilise the turbogenerator from its old Bokaro-A station. The 75-mw unit, supplied by MAN of Germany, had been installed at Bokaro in 1953. At that time it was considered the largest thermal power unit in Asia.
After four decades, the turrbogenerators capacity has been derated to 45 mw. DVC has decided to close down the first unit at Bokaro-A. Since the turbogenerator still has some life left, it may be shifted to Maithon, where it will operate on the exhaust steam from the gas turbine station.
The derated 45 mw capacity of the turbogenerator fits the requirement of the combined-cycle operation at Maithon. The three gas turbines had been installed in 1991. It will be necessary to change the burner nozzles if the feedstock is chang- ed from naphtha to methane. General Electric is being given the report of the methane gas found in the nearby Chinakuri coal mine area.
If the methane gas is found suitable, General Electric will go ahead with the necessary feedstock conversion.
It is also being assessed if the new 630-mw thermal power station of DVC at Mejia in West Bengal can be run by the dual firing method. Some experts believe that the boiler can burn 80 per cent coal and 20 per cent methane. However, this theory has yet to be tested.
When DVC had set up two 75-mw MAN units at Durgapur in 1959, it had planned to have dual-fired boilers so that the unit could be run alternately by coal or coal gas from the coke oven batteries of the Durgapur steel plant. However, the MAN equipment was found unsuitable for using the coal gas.
