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Electro-pneumatic Positioners

Economical Handling of Compressed Air Using Intelligent Electro-pneumatic Positioners Increases Energy Efficiency

| Editor: Dr. Jörg Kempf

With the right positioner, cost savings, return on investment, environmental protection, and high-quality control can all be achieved simultaneously in the process industries. (Pictures: BASF, Fotolia)
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With the right positioner, cost savings, return on investment, environmental protection, and high-quality control can all be achieved simultaneously in the process industries. (Pictures: BASF, Fotolia)

Particularly in these times of increasing global competition, companies in the process industries are searching intently for ways to optimize their operations and cut their costs. Consumption of compressed air — long neglected in cost considerations — has regained significance in recent years, and with it, the use of modern electro-pneumatic positioners.

Control valves that influence the flow of process media — gases and liquids — for the purpose of regulating process variables such as pressure, temperature or flow, can be found in every process industry. Together with their positioners, which represent the interface to the control system, control valves are elementary components of all automated process plants. They are moved using many different types of actuators: pneumatic, hydraulic, and electric.

Pneumatic actuators are widely used because they are low in cost, fast-acting, and inherently suitable for potentially explosive atmospheres. They require a permanent supply of compressed air at a suitable pressure, quality, and quantity. Air from the surrounding atmosphere must be compressed for this purpose, and then purified of oil and particles to ensure the maximum service life of the components to be supplied. The cost of compressed air is important: the European Union’s Save II study states that around 18 percent of the total energy consumed by industrial electric motors is used to generate compressed air. Energy used by compressors makes up the largest component (65 percent) of the cost of compressed air, with the remainder attributed primarily to maintenance costs.

Compressed Air Is Often Outsourced

In chemical industry parks where several companies share a central infrastructure, the supply of compressed air is often outsourced. The companies can then concentrate on their core business, but pay for this to a greater or lesser extent with higher prices for compressed air. More attention is therefore being paid to this cost factor than in previous times when there seemed to be a surfeit of in-house compressed air available without a separate bill.

To reduce the costs of generating compressed air in their plants, companies have in recent years made a greater effort to optimize their compressors, and selectively renovated their compressed air distribution networks to reduce leakage.

Until now, however, most air users have neglected an equally large source of savings at the point of use: the positioners that monitor and maintain the position of pneumatic actuators. The main guzzler of compressed air is not generally the actuator itself, which typically moves infrequently. Positioners, on the other hand, consume compressed air all the time.

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