ARTICLE 16: IS YOUR PUMP BURNING MONEY AWAY?
Obviously, everyone wants their equipment to last long
time and not break down or wear out. Unfortunately, sooner or later, everything
does. The issue is how to extend the life of a pump, and to evaluate if the
existing machinery operates at the conditions conducive to long life.
Our April Editorial addressed
this issue. As you know, when a pump operates at flow away from BEP (best
efficiency point), its efficiency is low: the lower the flow – the lower the
efficiency. A centrifugal pump, operating at 80% efficiency at BEP, will
operate at perhaps 30% efficiency at half flow. The larger the pump – the more
this translates to lost dollars – and, surprisingly – this can be a very big
lost dollars indeed.
Consider, as an example, a 1,000 hp motor, which runs
continuously, 24 hours a day, 360 days a year. At an estimated energy cost of
say $0.07, these 1000 hp (746 kW), will consume 746 x 24 x 360 x 0.07 =
$451,181 per year. If this happens at 30% pump efficiency, then, if the pump
efficiency is improved or restored to the original peak of 80%, then the energy
cost would be only 451,181 x (30/80) = $169,193
The difference is $281,988 per year!
You can substitute your actual numbers, but the point
is – it is not a small matter, but a big dollar value, and an unhappy pump.
Why do pumps operate off-peak? Several
reasons. We find that often the flow usage decreased through the years
due to plant downsizing – less energy demand, workforce reduction, surrounding
areas industry moved out, etc. Or, sometimes the pumps were oversized
originally “just in case”, but, with running experience, a proper flow is lower
then at best efficiency flow point. The extra capacity is thus not needed – so
the pump is throttled, - and that is at big efficiency loss.
Of course, the simplest thing to stop wasting these
dollars is to get a smaller, better sized-for-proper-flow pump. Pump
manufacturers can do it, why not? But it is an expensive “solution”. And not
only because of the pump purchase cost, but the associated changes in piping
can be, as you know, a nightmare. Or prohibitive.
Would it not be much better to keep the same casing, same piping, and just
change over the impeller? Of course it is. A new impeller design can be
fitted - into same casing, no piping
changes, no hustle - the pump BEP point is essentially “shifted” to the left –
smack on where the operating point is - and the efficiency is again restored to
80% (or close to), instead of the 30%, as assumed in our example.
The cost of the impeller change? Not much
comparing to the whole new pump. Price? Often a 3-4 months payback.
Why does not everyone do this if so obvious? First of
all – it is not so obvious, because the inertia and a habit of running the
pumps “to the ground” is the fact of life. The pump does not cry out loud that
it is being abused and runs inefficiently – no one measure the dollars being
burned away by the “wasted-money-meter” at the pump – the lost dollars are
hidden in the overall electric bill. Accountants see them and want to make the
bills smaller – but accountants are not hydraulic designers, and the pumps are
left “until next year… and the next…”. Some of these
wasted dollars are passed on to the consumers, via energy surcharge or product
price – but, when the surcharges reach certain point, it is not so easy to keep
rising the rates indefinitely to recover the wasted energy. Besides, at a given
surcharge to the public – why not save on energy anyway? – changing out the
impeller is not a very difficult thing to do, especially if there is no piping changes required.
Another reason for inefficiently running pumps is that
big pump companies are not in business retrofitted impeller designs and sizing
them to right conditions. To do that means spending time and having their
engineers involved. Designing impellers is easy, but you have to have people
that not only know how, but have time to do that. Goulds,
Flowserve, Sulzer, etc. - are not in business of keeping a huge staff
of hydraulics engineers looking out for customers to fix problems with a, say,
$10K impeller, when they can sell a complete pump for $50K or more. And, -
piping changes are not pump manufacturers problem! – these
expenses come out from the users pockets.
This is why some companies has
been successful doing such retrofits. Impellers can be machined from solid blocks of structural engineered composites:
strong as steel, good to 300 deg. F (special grades to 550 deg. F), and
superior from cavitation standpoint – better then
bronze or stainless steel. Handling to 15% of solids particulate is not an
issue, and resistance to most chemicals is excellent. Sea water, brine and
brackish water do not attack the simsite composites –
cooling water pumps, river raw water intake, etc. are examples of excellent success
of applications. For chemical plants – excellent
opportunities for most acids, caustics and other nasty chemicals. And, -
with 80% lighter then metal – these composites improve pump rotordynamics,
and reduce shaft deflections – solving seal leak problems, improving bearings
life, and saving couplings from failing.
We can help you identify and evaluate such potential
“money-burning” pumps, and recommend a solution. What we need is a performance
curve of your pump, if you have it, and its desired operating point. We will
estimate the radial thrust load, onset of the suction recirculation, and
determine the best impeller design – right to the bull’s eye of the best
efficiency point!
You have nothing to loose, but save a lot of money.
If, after having our evaluation, you still decide not to implement the upgrade
– not a problem and the decision is yours – and we do not charge for the
technical evaluation.
Give us a call. We will provide you references where
other users, like your company, were faced with inefficient operation of pumps
and decided to do something about that. They can provide testimony from their
own experience. Your operators will get a better pump and easier to operate.
Your mechanics will thank you for 80% parts weight reduction. And you
management will love the money saved.