State of the art compressed air system at Seagate

A patented vacuum regeneration dryer supplied by Zander has solved a production issue for Seagate Technology at its media substrates manufacturing plant in Northern Ireland

A patented vacuum regeneration dryer supplied by Zander, specialists in the treatment of compressed air and gas, has solved a production issue for Seagate Technology at its media substrates manufacturing plant in Limavady, Northern Ireland.

Seagate Technology Media Ireland is part of Seagate, which manufactures the majority of the hard disc drives installed in the world's computers.

Its state-of-the-art Limavady factory overlooking Lough Foyle is an important link in the production chain, plating and polishing 125,000 discs a day to the strictest and most precise standards.

Compressed air plays a vital role in the processing of the discs, as James McAlorum, facilities maintenance manager at the plant, explains.

"In such a critical process it is essential that the compressed air is clean and dry to a dew point of -70degC, so when we began to experience problems with our compressed air system I asked Team Air of Belfast to come up with a solution." Faced with a combination of compressors running consistently hot, a drying process that was unreliable and erratic and a system that used up to 25% of the expensive compressed air for regeneration, Team Air asked their dryer supplier, Zander (UK) Ltd, to suggest an alternative.

The specification drawn up by James McAlorum was exacting and included a maximum flow of 2860 cfm (4862 m3/h); a minimum pressure of 7 bar e; and a pressure dew point of -70C or better.

Meeting the specification meant overcoming two significant problems.

First, a -70C dew point is the equivalent of relative humidity in the Antarctic! Air at this dew point contains only 0.003 gm/m3 compared to 39.286 gm/m3 at 35C.

Energy is required to remove this amount of moisture in vapour form from the compressed air.

Second, when sizing and specifying a dryer for the application, Zander needed to consider the erratic compressed air temperature, which could reach 45C in summer, representing a water loading of 64.848 gm/m3.

As there must be no more than 100C difference between the inlet temperature and the pressure dew point when sizing desiccant dryers, the solution needed to provide a regular inlet temperature of 30C or less! Fortunately, during discussions it was discovered that chilled water at 6øC was available close to the compressor house.

This allowed Zander to install a water-chilled aftercooler to create an efficient heat exchange between incoming hot air from the compressor and the required maximum inlet temperature of 30øC to the dryer.

As there is a continual discharge of condensed water, a centrifugal separator with automatic electric drain is installed after the aftercooler.

Seagate's compressors are oil lubricated and, as the company had previously experienced oil contamination, Zander recommended fitting two pre-filters to the dryer system.

The first, a Zander Z grade filter, removes dust down to one micron and oil to 1mg/mü.

It also acts as a 'Police' filter by sensing oil surges and relaying data to a Building management System (BMS) to warn of impending problems.

The second, a Zander X grade, provides effective pre-filtration, removing condensed oil down to 0.01mg/m3.

After pre-filtration the compressed air passes into a wet air receiver fitted with a Zander Ecodrain.

Stainless steel pipework is used throughout to improve the appearance of the installation and prevents corrosion by the saturated air before it enters the dryer.

From the wet air receiver the air enters a Zander WVN-G 2000 dryer, which operates on the vacuum regeneration principle for maximum efficiency and minimum energy consumption.

At this point the air is filtered but saturated and the inlet temperature is now down to 12-15C.

The air then passes through a wedge wire desiccant support into a bed of molecular sieve in one of the WVN's two vessels.

The dwell time on the desiccant is sufficient to adsorb moisture to a dew point equivalent to at least -70C.

Operating on a fixed cycle, the WVN processes air for six hours before changing vessels, after which the first vessel is regenerated by passing heated air (at 170-200C) through the desiccant bed and cooling it under vacuum.

A dew point control is fitted to prevent the dryer switching over if the dew point has not reached -70C.

This allows the drying time to be extended from six hours to 16 hours or longer depending on the loading, and provides considerable savings in energy consumption.

After drying and before entering a dry air receiver, the air passes through two further filters - a dust filter to remove any dust caused by the flow of air through the desiccant bed and an activated carbon filter to remove oil vapour.

And did the WVN dryer installation meet Seagate's exacting specification? When it was first commissioned the compressed air reached a low dew point of -100C.

However, in order to limit energy consumption, this was adjusted to run at approximately -80C.

Commenting, James McAlorum says: "With the installation of the new WVN dryer, we have a 'state of the art' compressed air system to match the rest of the Seagate Technology plant." He adds that it is a credit to the co-operation between Seagate, Team Air and Zander.

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