Mechanical Technology June 2016

⎪ Pump systems, pipes, valves and seals ⎪

for process cooling. The level of the water in the sump is below the intakes of the pumps, which can cause ongoing problems for the pumps due to loss of priming and suc- tion lift. Vent pipes had been installed on the discharge of the pumps to facilitate the removal of air from the system when priming the pumps. Plant operators found that if they left these pipes open during normal pumping operation, the stream of water back into the hot well was a visible means of identifying any loss of priming and thus avoiding cavi- tation and the pumps running dry (See Figure 2). The opportunity: Adopting the systems approach above, these vent lines are functioning similar to a permanently open bypass line, meaning the energy consumed to pump this portion of the flow is wasted. The flow was measured to be in the region of 3.0% of pump flow, which superficially does not seem a lot. However this translates to between 3.0 and 5.0 kW per pump – and in a single pump house operating with three hot- well pumps of 160 kW each and three cold-well pumps of 100 kW each, the total power loss comes to 25 kW, or 197 000 kWh of wasted energy per year. The Philippines currently has the second highest cost of power in Asia (Japan has the highest) and at 10 Pesos per kWh, this ‘waste’ amounts to 1.97-million Pesos (R630 000). In addition, there were at least anoth- er 14 pumps in the plant operating with open-vent pipes, causing total energy wastage of around 410 000 kWh costing P4.1-million (R1.3-milion). During a pump performance test, we found that the flow rate through Pump #3 was dramatically down, and the pump ef- ficiency was as low as 30%. Even though the vent line was full, the pump had not been primed correctly and had been operating in that condition for more than 24 hrs, wasting excess energy as well as systematically destroying the insides of the pump. This proved that observing a stream of water through the vent line was ineffective in determining whether the pump was primed correctly or not. The proposal Proposed options for rectifying the prob- lem include: • Install cheap pressure gauges on the suction of each pump to identify any loss of priming as well as the onset of

Figure 2: Plant operators found that if they left the vent pipes open during normal pumping operation, the stream of water back into the hot well was a visible means of identifying any loss of priming.

valves should be closed. • Use the energy savings from the above project to invest back into more capital-intensive projects, and save even more energy. In my next column, I will look at the is- sue of throttling losses through control valves. q

cavitation. By alerting operators to any suction issues and remedying them, energy consumed is reduced and the reliability and life of the pumps is extended. • Only open the vent (bleed) lines when priming the pump, to get rid of any air in the system. The rest of the time the

Harry Rosen: a UNIDO International Pump Expert H arry Rosen, with 25 years of experi- ence in the pumping industry, is the managing director of TAS Online, an iron and steel manufacturing; petrochemical and process plants; mining (underground, open cast and dune mining) and minerals processing plants; power stations; pulp and paper plants; and sugar mills.

international market leader in engineering software and consulting services for both users and manufacturers of pumps. The company’s global service offering includes pump selection software, pump monitoring products, on site system assessments and performance tests, in addition to Testbed automation systems. Rosen studied at Wits University and qualified with a BSc Mech Eng in 1987, receiving his Pr Eng in 1992. He is a past chairman of the SA Institution of Mechanical Engineering, Central Branch and was instru- mental in setting up the International Pump User Conference (IPUC), which brought to- gether the world’s experts in energy efficient pumping systems. He has carried out more than 50 pump- ing system assessments, both in South Africa and around the world, for applications including: bulk and municipal water supply;

Harry Rosen was recently appointed as one of only two International Pump Experts for the United Nations Industrial Development Organisation (UNIDO) deliv- ering expert pump training programmes in South Africa, Malaysia, Indonesia, Thailand and Philippines. He has also been involved in the UNIDO ‘Train the Trainer’ programme, whereby a group of pump experts is selected to be developed as pump systems efficiency trainers. He also presents a three-day workshop for 2KG Training on improving the efficiency and reliability of pumping systems. This workshop is CPD approved and has been supported by Eskom and the National Energy Efficiency Agency as a valuable tool for helping industry achieve its targeted 15% savings in electricity. q

Mechanical Technology — June 2016

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