What is in this article?:
- Air receivers
- Controlling energy costs
Every compressed air system needs a receiver, but the receiver alone is not always the answer to energy efficiency in the system.
With its dumpy fat cylindrical shape, dull-painted exterior, lack of visible dynamic activity, and frequently hidden location, it’s easy to understand why the air receiver usually is the orphan of the plant-air system family. There is confusion and controversy over its function, where it should be located, what size it should be, how it should be piped — and whether it is needed at all. Air receivers are one of the least understood, yet potentially most useful components available to increase operating efficiency. But an air receiver should be an integral part of any plant air system — mainly to enhance its efficiency. Here are the classic purposes:
Contaminant removal — A bare receiver (without a pressure regulator or flow controller) adds a large volume to the piping system. This volume reduces air-flow velocity and encourages finely divided particles of liquid lubricant or condensate to drop out of the air stream. These separated liquids can then be drained from the receiver, rather than traveling with the compressed air or gas to create adverse downstream effects.
Pulsation dampening— A receiver installed near the compressor discharge dampens pressure pulses from positive-displacement compressors (rotary or reciprocating) to a small fraction of their original amplitude. This reduces the probability of excess compressor power or shortened service life resulting from resonant response to the frequency of compressor delivery.
Pressure stabilization— A receiver combined with a pressure regulator or flow controller can create an effective pressure band or differential between the supply side and the demand side. A typical example: 95 psig in the receiver, 90 psig steady to the system. This allows the demand side to operate at its lowest effective pressure, and therefore lowest volume demand. Stored air with a pressure differential creates volume held in reserve to cover short-term peak demands that exceed current air supply — without turning on or loading another compressor.
A one-atmosphere pressure change (less than 15 psi) accommodates a free air volume equal to that of the receiver. This can be used in the primary receiver, in a secondary receiver on the demand side (to serve an operation with surge demand), or even as off-line peak-shaving storage.
Augment compressor controls— Receivers with appropriate volume can reduce and decelerate pressure changes caused by intermittent use of compressed air. Compressor controls, which normally respond to pressure, can smoothly regulate compressor output without frequent ranging through their full control span. If an operation has capacity controls, but only a short run of pipe, a receiver will provide the total storage volume needed for the control to perform effectively.
Other effective ways to manage a stable pressure exist, depending on system dynamics. A networking control system can manage the compressed-air supply to hold a set target pressure at the system entry. Also, a variable-speed drive trim compressor can hold a pressure differential as low as 1 psig throughout its full operating range, eliminating the control band rise.