1. Correct sizing
When faced with a new or application, it is often difficult to resist overdesign as no one wants to be the supplier that underperforms in a system. The tendency to overdesign—a little extra horsepower or a larger-than-necessary discharge pipe spool—can create waste and inefficiency because a higher performance (in terms of flow and pressure) requires more power from the motor, an oversized pump can result in unnecessary energy consumption.
Whilst a degree of oversizing may be good common sense to compensate for uncertainties, selecting a pump that will be operating as close to its Best Efficiency Point as possible can significantly reduce energy usage.
In addition to the pump size, the pipe diameter is just as important to get correct; keeping costs at a minimum, proper pipe diameter can prevent sedimentation or settling of slurries. An optimally sized discharge line would be one that is large enough to control excess backpressure but small enough to prevent sedimentation in the pipeline.
2. Conduct an energy audit and life-cycle cost estimate
Whilst this seems obvious, it’s surprising how often pumps are in operation unnecessarily.
Control systems can be implemented to shut down pumps not in use and the use of pressure switches can control the number of pumps in service when duty requirements vary. This can ensure that multiple pumps aren’t in use at the same time, when the current system conditions only need one pump in action.
Before replacing a worn-out thickener underflow pump or a troubling absorber recycle pump, perform an energy audit to find the true cost of operation. Though many require higher initial capital investments, the life-cycle cost may prove more beneficial to the cost centre.
Remember: greater energy efficiency, less downtime, less maintenance and lower operating costs all make their way to the balance sheet. And do not be afraid to consider the use of new and alternate technologies.
3. Monitor pump performance
Gauges can be used in both the suction and discharge side of the pump. These serve as the best early warning of wear or poor performance caused by blockage or system anomalies.
A low discharge pressure could signify wear on internal pump components, leading to reduced efficiency. The gauges must be monitored and trigger maintenance or other remedial action when readings trend beyond the established control limits.
4. Limit pipework pressure loss
Optimising the system pipework to limit the frictional pressure drop is another way to save energy, as it reduces the power the pump requires to overcome such losses.
Pipe diameter, length, layout internal surface and components installed within the pipework all affect system pressure drop and therefore consideration should be given to these when looking at energy improvements.
At the design stage, attempts should be made to minimise the number of bends, expansions and contractions in the pipework, keeping the piping as straight as possible and the diameter the same. However, due to space constraints this is not always possible. Any fittings or valves specified for the installation should also have a relatively low pressure drop.
5. Variable frequency drives
As their name suggests, variable frequency drives vary the rotational speed of the motor to achieve the actual head and flow demand of the application, rather than what the pump can produce.
VFDs are typically used to limit unnecessary energy consumption in two scenarios; the first being to slow the motor down on a pump that has been oversized at specification stage.
The second use of a VFD is where there are differing duty demands on the pump at different times. When this is the case, the pump needs to be able to run at maximum capacity when required but may operate at less than this for long periods of time.
Although VSDs do come at a cost, usually the energy cost saving they can make justify the investment.
6. Conduct routine maintenance
Undertaking routine maintenance on your pump can also reduce energy consumption, as like with any equipment, wear can reduce efficiency.
Timely replacement of parts results in greater pump efficiency. Upkeep including the replacement of eroded wear rings is vital, as increased wear ring clearance increases leakage and therefore the pump power requirements to produce the same flow is increased.
A pump’s energy efficiency can degrade as much as 10-25% before it’s replaced!
7. Train the operators.
A well-trained operator is vital for efficient operation.
Train key staff members to ensure that system performance is monitored and that routine maintenance is performed to keep the system operating at its most efficient levels.