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.