Economic comparison of the constant and variable speed motor-driven boiler feed pumps in today's steam electric power station

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Virginia Polytechnic Institute

Owing to the continued increase in kilowatt capacity of new power stations being built today, proper sizing and selection of mechanical equipment has a vital effect on dollar savings, both for operation and maintenance costs as well as the initial cost of unit installation.

In today's steam-electric plants, the power consumption of the motor-driven boiler feed pumps has been rising along with the increase of operating pressures and capacities. Power savings thus becomes a more significant factor than ever in selection of boiler feed pumping arrangement. Therefore, use of a more economical and justifiable boiler feed pumping arrangement with constant speed drive or variable speed drive through hydraulic couplings would vastly improve power plant economy and operation.

This study compares the costs and operating characteristics of two constant-speed boiler feed pumps operating in parallel, against those of one constant-speed pump operating in parallel with one variable speed pump which is driven through hydraulic coupling (all pumps are of half-size capacity, motor-driven).

This cost comparison shows that the former pumping arrangement is more economical than the latter at the unit base load.