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Why overclean compressed air?

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article image PNEUDRI MX heatless dryer.

As many companies undertake their annual shutdowns for maintenance early in the New Year it is a good time for the engineers and safety officers involved to take a close look at their preparations for new air quality standards being adopted internationally.

More industries in Australia and New Zealand are becoming aware of the range of changes implicit in the new International Standards Organisation compressed air classes ISO 8573.1: 2001 air quality standard.

While not a law in itself, the ISO standard is the foundation on which international best practice is founded. It is progressively becoming the basis of regulations upon which each country founds its own best practices, so that we can remain an internationally acceptable part of the international trading world.

Broadly, ISO 8573.1-4: 2001 is the set of compressed air quality standards that specifies contamination levels allowed for each quality class, including oil aerosol, water vapour, solid particles, micro-organisms and oil vapours.

As industry in Australasia feel the impact of these ISO engendered changes (initially through their dealing with international companies adopting them) it is easy to become alarmed by the headline figures of the improvements they require. For example, the new Quality Classes 1 standard governing allowable dirt requires the air to be 1.9 billion times cleaner than the 1991 requirement it replaced. Quality Classes two and three have to be 19,000 times cleaner and 7,000 times cleaner than the 1991 class they replace respectively. Water (dewpoint levels), oil and microorganism tolerances are also substantially tightened up.

But as I have stressed in articles and lectures on the subject, these are extreme examples for situations where ultra high cleanliness is required (such as scientific, medical and some razors-edge industrial technology). However, down on the factory or workshop floor, the changes are realistic and achievable.

How to achieve the new standards

To achieve the levels of cleanliness specified by ISO 8573.1 2001, a careful approach to system design, commissioning and operation must be employed.

As a worldwide leader in the field of gas and liquid purification - and inventor more than 40 years ago of the coalescing compressed air filter - we at domnick hunter recommend that compressed air is treated:

* prior to entry into the distribution system;

* and also at critical usage points and applications. This ensures that contamination already in the distribution system is removed.

Purification equipment should be installed where the air is at the lowest temperature possible (ie, downstream of aftercoolers and air receivers). Point-of-use purification equipment should be installed as close as possible to the application.

If running an aseptic process (ie, free from microbiological contamination, as in high technology, food and beverage applications, for example) it is essential that a sterile gas filter is installed at the point of use. Sterility can only be guaranteed and maintained if the filter and associated downstream process equipment is sterilized regularly. It is recommended that sterile gas filters are tested for efficiency on a regular basis.

Cost of ownership V purchase price

When selecting the best products to maintain your system's purity, product selection is important. The purchase equation requires a proper analysis of the total cost of ownership (not only cost of purchase).

Just as there is no point in buying an old-fashioned, unreliable and gas-guzzling car that may only go half the distance you want it to, there is no point in buying compressed air products that save a little up front but cost you double later. This is false economy (see "Cost of Ownership Analysis" graph).

Compressed air drying equipment provides a good example of the factors to be considered in a prudent selection decision. There are three types of regenerative drying equipment: Heatless, Heat Regenerative and Zero Purge.

HEATLESS. Advantages included reliable dewpoint (which governs much of the efficiency of such equipment), lower capital investment, reduced maintenance costs, ease of installation and safety. Disadvantages include purge air consumption, which is typically 15-20 per cent of air consumption.

HEAT REGENERATIVE. Advantages include reliable dewpoint, medium capital investment, plus relatively easy installation and service. Disadvantages include higher capital investment, electrical consumption of heaters, and safety issues (high temperatures). Purge consumption is typically calculated at 5 per cent, but it can be 10 per cent or more.

ZERO PURGE Nominally these lower capital investment in compressors (because they need no air capacity for purging) with reduced running costs as a result. The downside is higher capital investment in the products, increased electrical consumption, greater noise and potentially high installation and maintenance costs. They may also require greater expertise to install and maintain and have the potential for contamination from ambient air. Despite their description, they are not necessarily zero purge. Purging costs could in fact be as high as 15 per cent.

Technologies that meet the challenge

Obviously many manufacturers have different solutions.

Our advanced technologies at domnick hunter include the PNEUDRI MX range of heatless dryers, which provide one of the most simple and cost effective solutions for the provision of clean dry compressed air.

The PNEUDRI family includes the latest compact and electronically controlled PNEUDRI MX and MPX systems, which feature patented modular construction that allows for rapid expansion of systems as industrial plants expand, as well as providing 100 per cent standby drying capacity at a fraction of the cost of larger conventional systems.

With aluminium formed towers typically half the size and weight of traditional twin tower designs- taking up less floor space and making installation easy - the heatless dryers will deliver air at - 40 deg C pressure dewpoint as standard, in accordance with ISO 8573.1 :2001 class 3.2.1.

When combined with domnick hunter's extensive range of filters, the dryers can achieve Air Quality Class 1.2.1 and 1.1.1. Flow rates of individual units extend from 408 Nm3/h to 2815 Nm3/h.

Release of the new PNEUDRI systems in Australia is part of a worldwide product introduction following the global release of domnick hunter's complementary OIL-X EVOLUTION compressed air filters, which use aerospace technology to optimise air flow paths and reduce system operating costs. The advanced design means the performance of OIL-X EVOLUTION filters exceeds the latest International ISO 8573.1 air quality standard. The filters' efficiency has been verified not only by domnick hunter, but also independently confirmed by testing at Northumbria University.

Maintaining System Efficiency

Whichever technology you choose, regular service is essential to maintaining system performance. To maintain your guaranteed compressed air quality, purification equipment must be maintained annually. Failure to do so invalidates performance guarantees and could result in:

* Reduced production performance

* Degraded air quality

* Increased running costs

Proper maintenance obviates these issues while continuing to protect downstream equipment and processes - which is why the protective equipment is there in the first place.

Air Quality Management Programme

In many plants worldwide, air compressors are the single largest energy consumers. They are also often the single largest energy wasters, with up to 40 per cent of energy being used unnecessarily.

In response to the needs of industry domnick hunter has introduced an Air Quality Management Programme to provide an independent analytical study of your existing compressed air quality. The programme, available upon request, suggests ways to maximize the efficiency of your system through:

* Measurement of system pressure

* Measurement of system temperature

* Measurement of system dewpoint

* Measurement of air flow

* Air Quality Test (CO2, water content, oil content, O2)

* Ultrasonic air leakage detection and identification

* Measurement of systems' particle count

* Measurement of energy consumption

* Cost calculation of existing compressed air system

* Identification of compressed air system deficiencies

* Report presentation and recommendations

A keynote of such tests is practical cost efficiency. There is no point whatsoever in overcleaning air, to the point where costs far outweigh benefits And the ISO standards, after all, are not there to put people out of business.

The key focus of any review (either internal or involving outside authorities such as our own organisation) is to achieve the right balance between air quality and energy savings. The aim is to present a realistic approach to ISO 8573 that will deliver attainable targets cost-efficiently.

*John Davis is Business Development Manager of domnick hunter Australia .

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