Pump up the efficiency

A world without pumps would be a world with no water from taps. It would also be a world flooded with water in all the wrong places. And of course, it would be a world where sewage treatment is nearly impossible.

Given the indispensability of pumping to the water sector, one would think that maximising the performance of pumps would be a priority at every water utility and pumping station. This is especially so when the ‘energy-water nexus’ has been a hot topic at forums over the past decade. But, no. Despite the fact that pumping often accounts for 80% of energy used in drinking water production, and a good part of sewage treatment, there is a strange disregard for optimising the energy consumption of pumping stations in the Asian water sector.

Almost every pump expert I meet informs that the biggest mistake made by buyers of pumps is that they base their choice on the purchase price. But the purchase price accounts for only 3% to 5% of the costs of the pump over its lifetime. Not only does an inefficient pump consume more energy than it should, but it also has higher maintenance costs and downtime.

A number of utilities economise on the purchase price and make it worse by going for the cheapest installation via unskilled contractors. Wrongly commissioned pumps are the ideal recipe for downtime.

Another common practice is to over-size pumps. Engineers often incorporate a margin of safety in specifying the size of pumps in order to compensate for uncertainties or for anticipated expansions. Unfortunately, over-sizing adds hugely to system operating costs because not only do such pumps consume more energy but they also wear out faster. According to a study by the US Department of Energy, matching pumps to the system requirements so that no more flow and pressure are pumped than needed, would help in reducing energy consumption by 10 to 30%. Apart from switching to a smaller pump, other possibilities are to trim the impeller, go for a smaller impeller, reduce pump speed, and for a multi-stage pumps, perhaps to reduce one or more stages.

Wherever appropriate, using variable speed drives (VSD) can greatly help to achieve energy cost savings. This reduces the power needed to drive the pump during periods of low demand. A pump running at half-speed may consume as less as one-eighth of the energy consumed at full-speed. VSDs are becoming increasingly popular at water and wastewater facilities, however their full potential has still not been realised.

Optimising pumping systems can easily lead to 20% energy savings, with some inefficient systems gaining as much as 40%. An audit can help to identify opportunities for improvements. Free software is available for the purpose, and it is possible to pinpoint equipment that runs when it does not need to or valves that are unnecessary.

Apart from an initial set of efficiency measures, it is vital to make improved practices a part of the routine operations and maintenance protocol. Managers should develop a facility layout showing the location of all the critical pumps and use that as a guide for the maintenance technicians to use during troubleshooting, preventive inspection, cleaning and minor adjustments. While all this might sound like standard procedure, its prevalence is abysmally low in the Asian water sector. Even in developed countries, pumping efficiencies are usually well below optimum.

Pumps are amazing wonders of human innovation and serve as our lifelines. There is no excuse for wasting millions of dollars globally on over-sized, inefficient, unsmart, poorly-commissioned pumps. Surely the users can approach pumps with more intelligence and discipline?

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