Compressed Air Efficiency

Moisture Measurement Can Help Meet The BCAS 10% Energy Efficiency Target

The British Compressed Air Society (BCAS) has recently launched a new initiative: the 10% Taskforce. This is a call for British manufacturers to cut their compressed air energy usage by at least 10%, in a bid to reduce operating costs and make a positive impact to the environment.

According to BCAS, the generation of compressed air can account for up to 30% of the total energy costs on a typical industrial site. The organisation estimates that in many instances around a third of this energy is wasted through a combination of aging equipment and inefficient practices, costing industry an extra £485 million every year, while contributing significantly to CO2 emissions.

The 10% Taskforce aims to help manufacturers reduce their energy consumption by taking simple steps to develop best practice. These include minimising leaks, recovering heat and improving maintenance routines, as well as upgrading drives and control systems.

A number of the measures recommended by BCAS have the potential to create short-term energy savings; for example, simply inspecting a compressed air system for leaks and taking remedial action will immediately begin to reduce energy consumption.

Other measures, such as adopting variable speed drives, will have longer payback periods. This does not, of course, make them any less valuable. Included in this category is the importance of improving the operation and control of compressed air dryers, as these can consume considerable quantities of energy.

Compressed air dryer efficiency

Eliminating or reducing moisture content is generally a key requirement for most compressed air systems, either to protect equipment from corrosion and other water-induced damage, or to ensure the purity of an air flow that comes into contact with moisture-sensitive ingredients or components during the manufacturing process.

Although there are various devices used for reducing the moisture content of compressed air, the most common are refrigerant and adsorption dryers.

Refrigerant dryers typically use an air-to-air or air-to-water heat exchanger combined with a Freon circuit to cool down the warm, moist incoming air flow from the compressor to around 3oC. This allows moisture vapour to condense into a liquid, which runs to drain; at this stage, the relative humidity (RH) of the air remains at 100%. The warmed refrigerant is regenerated and cooled in a condenser, while the air flow is reheated to ambient temperature, which reduces the relative humidity to 50% or less – a level that is sufficient to prevent problems of corrosion. As a result, refrigerant compressed air dryers tend to be used in general manufacturing applications.

For more critical applications, such as the production of pharmaceuticals or food items where ISO 8573.1 Class 1, 2 or 3 air quality is often required, then desiccant or adsorption air dryers are normally used. These are capable of reducing the pressure dew-point (PDP) of the compressed air to levels as low as -70oC.

Adsorption air dryers use hygroscopic beads to remove moisture from the compressed air flow. Most systems have a twin-tower or column configuration, with one column being in use while the saturated desiccant beads in the other are automatically regenerated.

Moisture measurement

In each of the examples above, the crucial factor is the ability to measure the moisture content of the air flow accurately as it exits the dryer. This enables the operating efficiency of the dryer to be controlled, which in turn allows energy consumption to be minimised; it is worth noting that it is common practice for dryers to operate for longer than is necessary to achieve a set level of moisture reduction, simply ‘to be on the safe side’. Although this may offer peace of mind it also wastes energy and can add considerably to operating costs.

Precise moisture measurement can easily be achieved by fitting a dew-point sensor or transmitter on the outlet line of each dryer. These sensors use proven ceramic-metal oxide or polymer thick film technologies, with standard mechanical and electrical connections, to offer a simple but highly effective method of determining the exact level of moisture in the compressed air flow. With an appropriate control loop, the output from each sensor can be used to optimise the operation of the dryer and, in critical applications, provide essential traceability.

Plan for moisture measurement

One of the key points addressed in the BCAS 10% plan is the fact that for many applications different purities of compressed air are used at varying stages in many manufacturing processes, and that it may be that only a percentage of air used needs to be produced to the highest purity. Energy and cost savings may therefore be possible by reviewing the compressed air requirements across each production facility and, where appropriate, generating air to the lowest acceptable quality.

This approach does, however, require careful monitoring so that that air quality remains within precisely controlled parameters at each stage of the process. In turn, this depends on the support of a suitable partner, with the knowledge and experience to ensure that sensors – especially moisture sensors – are correctly installed, calibrated and maintained at all times, to provide true peace of mind.

PST recommends

With over 45 years of experience in trace moisture measurement, Michell Instruments is the application expert when it comes to controlling moisture in compressed air. Contact us to discuss your application.

Learn more about our latest Easidew sensors.

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