Save up to 80% on compressed air drying costs!

Nigel Morris of Zander (UK) suggests that chemical manufacturing plants could save up to 80% on compressed air drying costs by changing to the latest vacuum technology

Nigel Morris, managing director of compressed air treatment specialists Zander (UK), suggests that chemical manufacturing plants could save up to 80% on compressed air drying costs by changing to the latest vacuum technology.

Over the years the chemical manufacturing industry has pioneered many processes and has always been in the forefront of new technology.

But this may now be working against the industry as compressed air treatment equipment installed a few decades ago, starts to show its age.

Compressed air is a vital ingredient in the chemical plant, as it is used for control and instrumentation, conveying of powders and granules and in biochemistry for fermentation.

In the 1950's, 60 and 70s most chemical plants were equipped with 'Heatless' desiccant dryers to bring compressed air to the dryness required for chemical processing, which is usually a pressure dew point of -40C.

This type of dryer was state of the art equipment at the time.

'Heatless' units are based on an American design that had the advantage of being simple and reliable.

However in today's manufacturing environment they are as out-dated as they are wasteful of energy.

The problem with the 'Heatless' dryer is that it uses at least 14.5% of the compressed air flow generated to re-generate the desiccant beds.

And as compressed can cost up to eight times as much as electricity it is a very wasteful process to use in a large plant.

For instance...

a plant using 3000 m3/h (1765cfm) at 7 bar e, with a temperature of 35C and a dew point of -40C on a 24 hour, 365 day regime, the 'Heatless' dryer costs approximately £35,000 a year to run.

(This may be an optimistic calculation as some old fashioned dryers can use up to 20% purge flow).

So chemical plants that were pioneers a couple of decades ago, and are still using out-dated equipment, are wasting unnecessary and expensive amounts of energy.

The modern solution to the problem is the more efficient vacuum heat regenerated dryer, patented by Zander, who are specialists in the treatment of compressed air and gas.

Instead of using 14.5% of the compressed air stream, they use heat to regenerate the beds.

Ambient air is heated and sucked over the saturated desiccant bed by a specially designed vacuum pump.

This evaporates the moisture and leaves the bed dry for the changeover.

The main advantage of this system, apart from using no expensive compressed air, is that the heat source can either be electricity, super-heated water, steam or gas.

Using waste steam for example would, in practical terms, reduce the running costs to zero! Another advantage of the vacuum system is that the regeneration temperature of approximately 100øC is half that of some types of heat regenerated dryer, which means that the desiccant is less stressed and therefore lasts longer.

We would expect desiccant life under normal conditions to be between five and seven years.

And the running costs for a 3000 m3h Zander WVN vacuum regenerated dryer will amount to approximately ?7,000 per annum based on the example quoted above - an annual saving of at least £28,000! This means an extremely fast payback on the initial investment and significant savings over the 15-20 year life of the dryer.

The running costs can be further reduced by fitting a dew point meter control that measures the outlet dew point of the dryer and prevents the vessels changing over until the one adsorbing moisture reaches its optimum saturation.

The cycle time can also be doubled if the dryer loading, due to lower inlet temperature or flow, is less than the specification.

An additional advantage of vacuum heat regenerated dryers is their ability to dry the compressed air to dew points below -70C, a feature that is becoming more and more necessary in chemical manufacturing processes.

Zander dryers, with their patented vacuum design, have established a reputation in a wide variety of manufacturing industries including chemical installations for Bayer AG, BASF and Wacker Chemie.

Zander (UK) Ltd, based in Tamworth, sells and services the equipment in the UK.

Customers include GM (Vauxhall Motors), Monsanto and British Aerospace.

The company also manufactures special pleated filters for the chemical industry that are so efficient that tests using a gas chromatograph were unable to measure the oil content in a compressed air system after the element.

Remarkably, the oil content of less than 0.00037mg/m3 was achieved without an increase in the clean pressure drop! This means that a compressed air system fitted with this type of filter will achieve higher efficiency than a system using a number of conventional graduated filters.

The filter elements are also available as direct replacements to upgrade the performance of compressed air filters from other manufacturers.

The pleated elements provide at least four times greater surface area than conventional wrapped elements and are machine made to ensure consistent performance.

Independent tests show that the lower pressure differential of 0.2 bar between these pleated elements and conventional wrapped elements achieves significant energy and cost savings.

In practice this means that fitting the element on a 320kW compressed air installation could achieve annual savings of around £3000, in addition to the savings made by using a Zander WVN dryer!.

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