Why pump energy matters, and where to start
Pumps are among the biggest electricity users in a plant. A few checks on the system and the duty point usually find savings before any money is spent on new equipment.
The size of the prize
Pumping systems are widely quoted as using close to a fifth of the world's electricity, and between a quarter and a half of the energy used in some process plants. In a thermal power station, the boiler feed pumps alone can be around a quarter of the plant's own (auxiliary) power. A centrifugal pump is a simple machine, so most of the savings come from how it is matched to the system, not from the pump itself.
Where pumps sit in a plant
| Plant type | Typical large pumps | Why they matter for energy |
|---|---|---|
| Thermal power station | Boiler feed, condensate extraction, cooling water, make-up and ash slurry pumps | Boiler feed pumps are the largest single auxiliary load; cooling and slurry pumps run all year |
| Cement and minerals | Process water, cooling circuits, slurry and dewatering pumps | Long running hours, duty often changes with kiln or mill load |
| Process industry | Circulation, transfer and booster pumps | Many pumps are throttled to hold a flow or pressure |
| Buildings and utilities | Chilled water, cooling tower, potable and booster pumps | Flow demand changes with the day and the season |
Five questions to ask first
- Is the pump running near its best efficiency point, or far to the left or right of it?
- Is a valve throttled to hold the flow or pressure? Throttling is a sign of wasted head.
- Is the flow demand constant, or does it vary during the day?
- Is the impeller larger than the duty needs, because the pump was sized with a safety margin?
- Is more than one pump running when one could do the job?
How this section is organised
The topics follow the order of the work. Start with the head, the curves and the operating point. Then look at where the power goes, the affinity laws that connect speed to power, the options for saving energy, and cavitation, which limits how low you can go on suction conditions. The worked examples use round numbers so you can follow the arithmetic.