MechTech June 2016 Final

⎪

Pump systems, pipes, valves and seals

⎪

Mechanical Technology — June 2016

Harry Rosen:

a UNIDO International Pump Expert

arry Rosen, with 25 years of experi-

ence in the pumping industry, is the

managing director of TAS Online, an

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;

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.

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.

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.

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

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

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.