Control Techniques advises on electric-motor laws

European energy-efficiency legislation for electric motors and their use with electronic variable-speed drives is now in force to enhance EU climate-protection efforts by 2011: a report from July 2009 by Control Techniques.

Electric motors consumed around 70 per cent of the energy used in industry in 2005, corresponding to 427Mt of CO2 emissions in Europe, according to the EU Commission.

Another interesting figure is that 90 per cent of the lifetime cost of a pump, fan or compressor is the energy it consumes, and these three are the major energy-consuming equipment in industry.

The greatest savings are made when speed control is used to continuously adapt operation to the demand.

The EU Directive 2005/32/EC means that by 2011 all new motors must meet the new ‘IE2’ efficiency rating, which is similar to the current ‘Eff1’.

By 2015, motors from 7.5 to 375kW will have to meet an even higher efficiency rating, ‘IE3’, or alternately meet IE2 and be driven by an electronic variable-speed drive (VSD).

This motor power limit will be lowered to 0.75kW by 2017.

John Murphy, vice-president of strategic planning for Control Techniques, said: ‘In most cases, the additional initial capital outlay of buying higher efficiency motors and variable-speed drives should be recouped relatively quickly through reduced energy bills.

‘We at CT can advise customers on the most cost-efficient route to Directive 2005/32/EC compliance.

However, even the apparent EU endorsement of the benefits of the technology does not mean that all installations will derive a significant benefit from applying VSD drives: Emotron of Sweden has pointed out that an EU survey showed 50 per cent of installations are not suited to variable-speed control and a further 15 per cent are already controlled efficiently.

It estimated the remaining 35 per cent of installations could benefit on average by a 40 per cent saving in energy consumption: for pump applications the typical estimated payback for a VSD is between 12 and 24 months.

At the Civil and Marine Middlesbrough plant, situated on the coast adjacent to the Corus steelworks, blast furnace slag, otherwise a waste product from iron production, is ground into a fine powder called ground granulated blastfurnace slag (GGBS).

This is used to enhance the properties of concrete, replacing between 20 and 80 per cent of the normal Portland cement.

Excessive wear and tear on dampers in particular prompted an examination of alternative means of control of the air flow that extracts the highly abrasive fine powder from the ball mill and Sepol separator.

Rob Thwaites, electrical engineer and assistant works manager, said: ‘As neither fan operated at full speed, we also saw an opportunity for energy-savings.

‘We brought in Control Techniques, which calculated likely savings and predicted that the drive for the Sepol separator would have a payback of just seven months, while the ball mill would pay for itself in nine.

‘The calculations have proved to be very accurate and we have made precisely the savings that Control Techniques predicted.

The Sepol separator is driven by a 200kW motor running at 71 to 75 per cent of full speed.

With the original damper, its energy consumption was 146kWh.

Now, under inverter control using a CT Unidrive SPM drive, this has been reduced to 61kWh, giving a saving of 85kWh.

Total savings on the two installations resulted in a GBP700 per week reduction in the power bill.

Thwaite added: ‘A further benefit we hadn’t anticipated is the reduction in noise, which makes the plant much more comfortable for operators.

‘We also anticipate that fan motors and bearings will last longer and require less maintenance.

Unidrive SP AC drives have been installed on the pre-grinders, resulting in an overall increase in throughput from 50 to 70 tonnes of GGBS per hour, enhancing the energy efficiency of the plant by reducing the energy consumed per ton of output produced.

Control Techniques recommend that any higher-power installation operating a pump or fan, where the output is throttled using a valve or damper, should be reviewed closely to see how the energy consumption could be reduced using VSD control.

Glaston Compressor Services of Skelmersdale provides comprehensive maintenance and total site management services, specialising in intelligent control and energy management for compressed air systems.

A recent installation on a 90kW rotary compressor used a Vacon NXS variable-speed drive controller to replace the existing single-speed unit, in conjunction with a compressor-management system developed by Glaston.

This arrangement ensures that the output of the compressor always matches the instantaneous demand for compressed air.

The project was undertaken for Albion Automotive, a UK automotive supplier, following the results of a free detailed energy survey and audit by Glaston, which forecasted GBP7000 a year in electricity savings.

Michael Douglas, managing director at Glaston, said: ‘We’ve been using Vacon VS drives for some time to upgrade fixed-speed compressor systems and we’ve found them to be robust, reliable and easy to work with.

In addition to the anticipated energy savings resulting from continuously matching the operating speed of the compressor to the instantaneous load, it also proved possible to make further savings by reducing the nominal operating pressure of the installation.

With the much more precise and responsive control achieved by the Vacon drive system, the nominal delivery pressure could be reduced from 7.5 to just 6.05 bar, with total confidence that the actual pressure in the installation will never fall below the required 6 bar minimum.

As a result of this pressure reduction, and a number of other minor energy-saving adaptations, the total cost savings achieved in practice after the installation increased to GBP14,000 a year.

International Specialty Products and Chemicals (ISP) in the US serves the pharmaceutical, beverage and personal care industries.

Reliability engineer Ken Myers needed to prevent regular pump failures and production interruptions where three pumps were costing more than USD90,000 a year in maintenance and downtime.

He said: ‘Our goal was to protect our magnetic drive pumps from dry-run conditions.

Having tried a number of monitoring technologies, which were inefficient at low load conditions, ISP installed Emotron M20 shaft power-monitoring systems.

The M20 uses the drive motor as a sensor, feeding a unique shaft-power calculation technique that detects pump-load changes due to dry running or other abnormal process conditions, across the whole motor load range.

This offers reliable monitoring with direct correlation to the pump curve.

Myers summarised the results by saying: ‘After the monitors were installed, the failure costs for the next years dropped to zero.

‘The functionality of the Emotron M20 is built into the new Emotron soft-starters and variable-speed drives installed on other ISP applications, such as positive displacement pumps, transfer elevators and product blenders.

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Level measurement accuracy

One of the hassles with top down level measurement systems, for liquids or solids, is that the user measures tank contents from the bottom up, so when the reading is zero, the tank is empty. This would be fine, except this is the extreme range for the top down measurement system, and likely to be where the reading errors are most significant, in absolute terms of cms of error. Not too good if the user is measuring the flow through a V-notch weir, with an ultrasonic system, or boiler water level above the fire tubes, with a GWR (Guided Wave Radar) system: the measurement error becomes a significant zero error.

Having asked the question, “What effect do the vapour layers in the ullage space have on system accuracy?” of most suppliers of GWR systems, or “What is the effect of the top layer in an interface measurement system?” – the normal answer is that vapours, or foam, or light hydrocarbons, have minimal effect. I think this is wrong: the effect is proportional to the relative permittivity (and also permeability) of the vapour through which the GWR or radar pulse travels. So the error depends on the actual site conditions and vapours involved. Have you asked your supplier for any figures relevant to your application, to see that this is indeed a negligible effect on your tank?

Rosemount have launched a GWR probe system that uses the classic built-in reference reflector system to calibrate out the vapour effects of the ullage space, that they realize are particularly significant in steam drums, for example in boiler and de-aerator applications: see the Top Ten story from Mobrey this week (Link). Here Rosemount suggest a final achievable accuracy figure of 2%, compared to the possible errors from standard systems of 20%: while these figures need to be seen in the actual tank and application context, they are far larger then the normal accuracies quoted for general GWR systems.

When a supplier does submit a good technical article discussing higher temperature GWR measurement accuracy, through vapours, I will be delighted to highlight it. Meanwhile, why not ask the manufacturers showing GWR systems at Offshore Europe, what additional error is introduced in a GWR pressurized tank level measurement where for example an aqueous liquid is covered by 2 metres of a saturated vapour at 60, 80 and 100C. (Then tell me the answers!).

Another interesting product launch this week comes from Flir Systems, with their new radiometric versions of some special purpose IR cameras and video recorders. The GF series use Sterling cooled detectors: the GF309 can see through flames in furnaces and boilers, to inspect the internal surfaces, tubes and refractories at up to 1500C: the GF320 wavelength sensitivity is configured to detect the gas leaks that are of relevance to petrochemical installations. Both cameras also offer the best features needed for radiometric condition monitoring duties, including GPS and colour imaging, 25mK sensitivity and 1C accuracy, to make them true dual or multi-purpose equipments for use in preventive maintenance (Link).

Technologies found… on holiday

If you have ever wondered why there are so many stories on Processingtalk, the answer is that it has been publishing them every weekday for over 6 years: and similarly the issue of the regular newsletter is now up to number 286. So it was high time that I took a week off last week and tried to get away from Processing.

Naturally it did not work, you cannot get away from processing, it is a part of everything. As reported in the June 06 newsletter, one of the first processes that was thrust to my attention was the “Bio-bubble” sewage treatment system operated by the National Trust at Kynance Cove, on the Lizard in Cornwall, which is a batch sewage treatment system situated miles from anywhere to treat effluent from a cafe and toilet that serves that remote cove and beach. It uses forced aeration, then batch biological treatment, and UV sterilisation to polish the final effluent before discharge into the stream leading to the cove, all powered by solar tiles on the roof of the cafe there. This time I took a photo of the explanation thoughtfully provided on the wall of the Gent’s toilet (without getting arrested) and hopefully will add that to a better description in a later Processingtalk report.

Then there was another National Trust example of processing, this time in the mining industry: a Beam winding (whim) steam engine, originally built to the design of Francis Michell in 1840, which ran operationally for 90 years till 1930: not a bad asset life! But it still goes on, after a little maintenance and some loving restoration, and can now be seen using steam power to pump water up from the Levant tin, copper and arsenic mine: it also drives cable drums that wound up the skips full of ore to the surface. Once on the surface the ore was stamped, or pulverized, to allow separation of the heavy ore from the rock, in settling and washing ponds. The main things obviously different today related to the worker safety (as well as health of course), particularly looking at the cages used to lower miners down below sea level, introduced to replace the nodding donkey “man engine shaft”, a continuously oscillating shaft with standing platforms, that moved up and down 12 feet at a time, so that the miners could jump on and off, moving from level to level. This was introduced in 1857, and collapsed while in operation in 1919, sending 31 miners to their deaths. Strangely, I actually remember using a similar open access moving lift system in the atomic energy design offices in Warrington not so many years ago: it seems designers in such advanced, forward looking industries possibly do think along similar lines! If anyone has a different view, or a better account of these historic systems, or other similar attractions, I would be delighted to publish them as an article on Processingtalk.

Then, to round off the week, I went back to my old college for an alumni lunch, and in the first conversation met a guy who has invented a new design for a PD flowmeter, and is seeking a manufacturer to commercialize it! Years ago it was my job to go seeking such developments for licensing from Universities! Maybe you will read about that one later, on Processingtalk, when I can match him up with an interested flow metering company.