Compressed Air Systems - Technology gives a clearer picture01 October 2004

Standard air compressors are often linked in banks to accommodate varying base loads throughout the working week, with a speed-regulated compressor making up the module to cope with peak and variable loads. And modular makes sense. It is easy to add more compressors or to utilise speed regulation to top up demand for changing practices or production. Moreover, this approach is also relevant for backup compressed air: if one unit goes down, the others can shoulder the workload.

Intelligent controls can also rotate the use of compressors, ensuring one unit does not run longer than others and keeping maintenance costs as low as possible. At the same time, as manufacturing becomes more complex and certain processes (such as food processing and pharmaceuticals) demand clean air, there is an emergence of total oilfree air products that are also highly efficient, negating the need for items such as oil filters.

The use of datalogging - running an audit of existing equipment and producing a computer model of the comparative energy savings that a different configuration or a new system could achieve, coupled with advanced computer modelling - can make sure that the best compressor package is designed and produced. Datalogging helps to understand a company's needs, while the latest computer software can model a package to meet these requirements, maximising energy efficiency.

Again, with energy costs soaring, the move is towards a 'whole life' cost model, looking to minimise the amount of equipment maintenance and to maximise, from the customer's point of view, the service or warranty available. This is where new energy-efficient products are being brought to market with an hours-based, as opposed to yearsbased warranty (in other words, a 'work when you are' approach).

So, what's new in the world of compressed air systems? Here is a round-up of some of the latest offerings available, all of which have greater efficiency, improved uptime or lower running costs as their raison d''tre.

Two of the leading compressor manufacturers have recently produced new ranges of waterinjected screw compressors to produce oil-free air. These have been designed for applications where there is a need for high-quality 'active' air - air that comes into direct contact with the process it serves.

As well as oil-free air, the AQ compressor concept from Atlas Copco offers a high-pressure capability and improved energy efficiency. The compression element features optimised-profile polymer ceramic rotors, supported by waterlubricated hydrodynamic and hydrostatic bearings. Producing near-isothermal compression, it contributes to a compression energy efficiency increase of some 20% over traditional methods. It is available in 30, 37, 45, 55 fixed-speed and 55kw variable-speed drive variants, with three pressure ratings of 7.5, 10 and 13 bar.

Lubricated by water

CompAir's new DH-Series offers a cost-effective oilfree solution in the smaller size ranges. At the heart of the series is a single-stage, single-screw, waterinjected compression element. It has a bronze single six-flute main rotor, with two carbon-fibre composite eleven-tooth gate rotors. The compression element delivers 12 pulses of air per revolution, compared to six pulses for a conventional screw. This, together with the elimination of metal-to-metal mating parts, offers low vibration and noise levels.

During the compression cycle, atmospheric air enters the compression element and fills the flutes of the main rotor. The gate rotors engage with the flutes and form two compression chambers, above and below the main rotor. The gate rotors automatically follow the rotation of the main rotor, reducing the volume in the flutes and compressing the air along the compression chambers. Purified water injected into the compression element seals, cools and lubricates the process. When the flutes align with the discharge port, the compressed air and water mixture is discharged from the compression element and the water is separated from the compressed air into a vessel.

Matching the generation of compressed air to the demands of the application as closely as possible has long been a potential source of energy, and therefore cost, savings. Boge Compressors has launched the MCS Professional Plus range, a predictive compressed air energy management system. By sending signals to and from the compressor's controllers, the management system can predict, and switch, the compressor combinations being used, so that the specific pressure required at each point, at any given time, is met in the most efficient way. Users can programme the system to their specific compressed air requirements, regardless of which manufacturer's compressors are used.

The MCS Professional Plus works with, but independently of, the compressor's own control system. By constantly monitoring the compressed air system, the management programme also identifies process misuse and wastage, pinpointing if, where and why this is occurring. Action can then be taken once again to optimise the system. A visualisation/communication software package enables the live system to be viewed from a remote computer and an on-going efficiency report in kW/m3min can be produced.

According to Boge, the following benefits can be typically gained:
- Air generation costs reduced by up to 27%
- Load kW costs reduced by up to 20%
- Idle running kW costs reduced by up to 30%
- Compressor wear reduced by up to 50%.

Poorly managed condensate drains are a notorious source of compressed air loss. The latest technological development in the Donaldson Ultrafilter range of condensate drains is the UFMT05 model. The technology allows operational parameters to be programmed, so that the drain's level sensors are calibrated to the most effective settings for a given application. Not only does this mean more effective control of condensate, but it also ensures that no energy, in the form of compressed air, is lost while condensate is drained.

The drain also benefits from an advanced control system, as well as an LED display showing the unit's operational status. Data on the unit's operational status can be sent via the internet to an external control room or directly to a service technician. Similarly, if defined parameters are exceeded or drop below the pre-defined value, an emergency signal is sent out to facilitate immediate handling and rectification of the problem.

Condensate removed by filtration

Another development in condensate treatment is Atlas Copco's OSC oil/water separator range. Here, the condensate is separated through filtration, not gravitation as is more usually the case. Two or three conjoined towers - depending on the required capacity - house the principal stages of the filtration process. Condensate from the compressor enters through mufflers into a central expansion chamber where it is depressurised. It then passes into the first stage filter tower and through an oleophilic filter, which removes the bulk of the oil, but not the water, from the incoming condensate. Significantly cleaner condensate then flows from the first tower to the second via a channel at the bottom of the separator unit. The second tower, in a three-stage unit, contains another oleophilic pre-filter to protect the final stage carbon filters contained in the third tower which 'polish' the condensate, ensuring a final oil content of less than 15 ppm. In two-stage configurations, condensate then passes through the second tower main filter containing activated carbon pellets - to absorb any residual oil from the condensates - and then exits to drain.

Turning to air filtration, a new development comes from Parker Hannifin. The company claims that its new filter element - the XE - saves users significant costs in terms of energy and maintenance. According to the company, the XE filter elements start life with a lower pressure differential (though Parker Hannifin is keeping the how and why of this to itself as it tries to steal a march on its rivals). As with most filters, when the pressure drop across the element gets too high, the filter has to be replaced. However, with its lower initial pressure differential, the working life of the XE is significantly longer.

This longer working life means there is also less of a maintenance requirement. Maintenance is also reduced because the compressor will be required to do less work as a result of the lower pressure drop.

Typical savings can be as much as £252 per year per installed filter cartridge, depending on the number of work shifts. This is based on £10/ 100kWh as a European average electrical cost.

Finally, for companies that would like flowmeters permanently installed in multiple locations, but find the cost prohibitively high, PVL has come up with an alternative: a flowmeter that can be moved between any number of pipes quickly and easily, with press-in, pull-out insertion and removal.

Making this possible is a new design of manifold, with a built-in ball valve. When the flowmeter needs to be moved to a new location, the ball valve is closed to stop the gas flow, the probe is removed, the pipe is capped off and then the ball valve is reopened to restart the gas flow - an operation that takes seconds, says PVL. The manifold has been designed so that the flowmeter probe auto-inserts to the correct depth and in the correct orientation. The probe itself is a mass flow meter design, optimised for accuracy, and suitable for pipe diameters from 1 in right up to 6 in.

In addition to compressed air, the flowmeter can be used with a range of gases including oxygen, nitrogen, helium, argon, carbon dioxide, hydrogen, nitrogen dioxide, carbon monoxide, and many different hydrocarbons.


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