Laboratory air quality

Adrian Lee, of compressor manufacturer Jun-Air, highlights compressor features that can influence air quality standards in chemical production plants.

In a chemical manufacturing environment, when surrounded by the latest analytical instrumentation, it is easy to take compressed air for granted. Provided the compressor and ancillary equipment are in good condition and well maintained, this is understandable.However, equipment that is old, poorly maintained or both presents the very real danger that poor quality air will contaminate samples and affect data.

Compressed air contaminants - 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 chemical manufacturing plants where 100% reliability is essential and continuous data sampling is required, the equipment needs to meet exacting requirements.

contaminant-free

Eliminating contaminants is vital when providing a supply of high quality compressed air and other gases for analytical processes, or as an integral part of the operation of some instruments.

Products created in fermentors, for example, are susceptible to contamination from sources such as airborne particles and wet or oil-contaminated compressed air. In such cases, a filtered compressed air system, free of moisture and oil, is an essential part of the working environment.

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 often less economic cylinders. These generators, several types of which are available, produce gases at the precise levels of flow and purity required for a wide range of chemical manufacturing applications.

The range of equipment available is vast, but the choice is simple and is focused on the latest 'oil-less compressor' technology. Rated for continuous duty and virtually maintenance-free, these systems are ideally suited for single and multiple workstations, and when housed in a soundproof cabinet to reduce noise levels to between 47 and 55 dB(A), they can be installed directly in the manufacturing or laboratory environment.

In the oil-less compressor range, the receivers are internally powder-coated to avoid corrosion, ensuring the highest air quality throughout the system's lifetime. Units also feature a unique cooling system and wear-resisting piston rings. They are designed for continuous operation at up to 10 bar maximum pressure. Higher pressure units are also available.

To ensure a supply of clean, dry air and minimise the risk of bacterial contamination, compressors need to be equipped with air-intake filters, post-compression filters and dryers. Especially stringent levels of filtration and drying have led to the development of systems that can provide dust filtration down to 1µm and bacterial filtration to 0.01µm. Dryers are capable of producing air with a dewpoint not less than -20°C. By removing particles, water and vapour from the air line this additional equipment ensures that air supplied to the chemical manufacturing plant is of the highest quality.

Be aware, however, that 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 bacterial growth. Figure 1 shows a typical sample from a compressor without dryer, where contamination in the air has provided ideal conditions for bacteria to grow.¹ The sample in figure 2 was taken from an oil-less compressor fitted with a dryer which has eliminated the risk of bacterial growth.¹

adsorption dryer

Removing water vapour will require an adsorption dryer to be fitted. This will remove water vapour immediately after compression of the air, ensuring that the conditions for the survival of bacteria are completely eliminated before compressed air accumulates in the compressor tank. The compressed air is, therefore, 100% dry, clean and bacteria-free.

With so many points to consider, chemical manufacturing plants 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 chemical manufacturing plants.

The starting point for a professional service should be a free air quality audit to establish a plant's precise requirements. If this isn't offered, ask for it - or find another supplier.