 Air quality – the vital ingredient
July 01st 2005
Adrian Lee, managing director of compressor manufacturer JUN-AIR discusses air quality standards for industrial plant, and offers advice on equipment to meet quality standards In a modern manufacturing environment the machines and equipment will usually draw compressed air from the plant’s fixed compressor.
However, equipment such as weighing and packaging machines, sampling equipment and analytical and other instrumentation, may need to rely on stand-alone compressors to provide the air for pneumatics or some other aspects of their operation. In these circumstances it is easy to take compressed air for granted, and, provided the compressor and ancillary equipment is in good condition and well maintained, this is understandable. However, compressors that are old, poorly maintained or both, can present the very real danger that poor quality air will contaminate sensitive products and affect production, and in extreme cases, even damage reputations.
Compressed air contaminants, which may take the form of particulates, liquids or vapours, can enter a compressed air system at the compressor intake or be introduced into the air stream by the system itself. This means that in a modern manufacturing plant where 100% reliability is essential, the equipment supplied for stand-alone applications needs to meet the same exacting requirements as the factory compressor.
Many industries use compressed air to operate and control process valves, instrumentation regulators, modulating control valves, etc., and will use either a large plant compressor or a local compressor to supply the air required.
Typically, the valves and regulators used in these industries are not operating or using air continuously, and only open when extra pressure is required.
This means that for potentially long periods of time the compressed air is not being used.
If a compressor that is required to provide high-purity air for instrumentation or other applications is sited outside, its supply can be compromised by a number of factors. Water can collect in the supply pipework with the potential to freeze and damage the equipment it is supplying, and the pipework itself can be damaged due to ice forming.
Oil-free compressors can prevent this type of damage by producing dry air with a pressure dew point of – 30 to – 40ºC.
Fitted with desiccant dryers and filters, the air supplied is of the highest purity and will eliminate the possibility of water contamination and freezing. The oil-free operating principle also means that the compressor will continue to work at a much lower ambient temperature.
From the operation of pneumatic actuators to the provision of air for blow guns, to maintaining pressure in sprinkler systems, oil-fee compressors provide high quality air in a reliable, compact package for local usage in large factories, and offer a complete factory supply solution for small manufacturing companies.
The Industrial Laboratory Traditionally, laboratory gases have been supplied in cylinders and distributed through a network of pipes. However, as consumption has increased so has the use of gas generators to replace the traditional and often uneconomic cylinders.
Gas generators produce gases at the precise levels of flow and purity required for a wide range of laboratory applications, eliminating contaminants and providing the supply of high quality compressed air and other gases that are an integral part of the operation of many laboratory instruments and analytical processes.
Machinery On the subject of cylinder gases, current Health and Safety legislation concerning confined spaces and the use of cylinder gases in for example, dispensing systems, has led to a huge increase in the demand for compressed air for packaging machinery, especially for food, healthcare and pharmaceutical processing applications.
Besides reducing the number of gas cylinders that need to be stored, onsite compressed air generators are also used extensively by machinery manufacturers to operate the pneumatic systems in their machinery.Air compressors provide an excellent alternative to the use of cylinder gas and, besides improving the environment and removing potentially hazardous gas cylinders from the site, can also provide substantial cost savings.
The increasing sophistication of modern machinery and the growth of robotics and automation create other applications where stand-alone compressed air is in demand. An independent supply can provide the ideal solution for continuous applications such as pneumatically operated handling installations.
Compressor specification The range of equipment available is vast, but the choice is simple and focused on the latest oil-less compressor technology. Rated for continuous duty and virtually maintenance-free they are ideally suited for single and multiple applications.
To ensure the highest air quality throughout the lifetime of oil-less compressors, receivers are internally powder-coated to avoid corrosion. Features such as special cooling systems, wear-resisting piston rings, etc., are designed to ensure 100% continuous operation up to 10 bar maximum pressure and beyond.
The need for pure, dry air in more sensitive manufacturing operations will also require compressors to be equipped with air-intake filters, post-compression filters and dryers to minimise the risk of contamination. Where stringent levels of filtration are required systems can provide dust filtration down to 1µm and bacterial filtration to 0.01 µm.
Be aware however, that these filters will not remove water vapour.
The water vapour in atmospheric air condenses to water droplets when the compressed air cools. At the same time, moisture and heat from the compressor create favourable conditions for the growth of bacteria.
Adsorption dryers are recommended to remove water vapour before compressed air accumulates in the receiver and can ensure a constant and absolute pressure dew point down to –40ºC. Bacteria become inactive at a pressure dew point below –23ºC and may subsequently be removed, and the risk of corrosion is eliminated at –30ºC.
By removing particles, water and vapour from the air line this additional equipment ensures that the air supply is of the highest quality.
The slide in Figure 1* shows a typical sample from a compressor without a dryer, where contamination in the air has provided ideal conditions for bacterial growth. The sample in Figure 2* was taken from an oil-less compressor fitted with a dryer that has eliminated the risk of bacterial growth. (Source: “Focus on hygiene in dental compressors” by Finn Djurhuus, chief adviser and head of section for DTI Industry. A copy of this article is available from JUN-AIR).
Besides meeting the growing demand for clean, dry air for industrial and OEM applications manufacturing companies also need to comply with health and safety regulations requiring lower noise. Fortunately, today’s compressor technology is capable of achieving decibel ratings as low as 47dB(A) when housed in a soundproof cabinet. This makes oil-less compressors ideal for installations that require an independent air supply, but where noise in the workplace could cause health and safety problems. Even stand-alone compressors for OEM installations can achieve noise levels of 57dB(A).
Oil-less compressors can be supplied as separate units or complete solutions, with multiple outlet ports and adjustable feet, allowing flexibility for mounting positions. This makes them ideal for custom-designed applications to meet the requirements of OEM manufacturers.
With so many points to consider, manufacturing and process engineers should check before buying new equipment that their compressor supplier can provide a complete system, including filtration and drying equipment that is optimised for the specific needs of their equipment or process.
The starting point for a professional service should be a free Air Quality Audit to establish precise requirements. If it isn’t offered, ask. Or find another supplier! For further information contact: Adrian Lee, JUN-AIR (U.K.) Ltd. U1, Buntsford Hill Business Park Bromsgrove, B60 3DX United Kingdom.
Tel: +44 1527 57 6666, Fax: +44 1527 57 6676 E-mail: info@jun-air.co.uk Internet: www.jun-air.co.uk More articles from Gast Group Limited: | 
