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.

      4.3.1   Feed pump size and number

      4.3.2   Feed pump duty, margins, and the need for variable speed

      4.3.3   Economic comparison of steam turbine drives with electric motor drives

      4.3.4   Economic comparison of variable-speed motor (VSM) drive with induction motor plus fluid-coupling drive

      4.3.5   Example of the results of an overall comparison of the through-life costs of four feed pump system options


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