4.3. Choice of feed pump and drive system
A full description of feed pump design and development is given in Chapter 3. In this section, feed pump size, number, duty, margins and the need for variable-speed are discussed; comparisons on economic grounds are also made between steam turbine and electric-motor drives, and between variable-speed motor (VSM) and induction motor/fluid coupling drives.
The section is concluded with a typical example of an overall comparison of through-life costs of four feed-pump system options, that was performed for a future 900 MW turbine-generator unit.
Boiler feed pumps now being designed for future large units are tandem arrangements, i.e., the slow-speed booster pump (suction stage pump) is driven in tandem with the main pressure stage pump, using either a step-up gearbox (to the high speed pressure stage) or a reduction gearbox (to the suction stage), depending on the speed of the driving motor or steam turbine.
The position of the feed pumps in the steam cycle of a modern turbine-generator unit was shown in Fig 1.65 (in this case for a PWR unit) physically they are situated beneath the de-aerator, upstream of the HP heaters.