is a type of pressure vessel that receives air from the air compressor or compressed air system and holds it under pressure to provide temporary storage of compressed air. These metal tanks are fabricated in a range of sizes and in both, vertical and horizontal configurations.
This is utilized as a ‘storage’ in combination with active elements like solenoid valves, flow controllers, etc. There are many ways to use storage in a compressed air system to improve the performance and repeatability of production equipment. No one method is a total solution.
When installed in Compressor Room (Supply Side):
- It provides a steady air signal to air compressor controls. In case of Reciprocating compressors, it dampens pulsations in air pressure.
- The sizing needs to be such as to hold enough volume for the pressure to be retained above a minimum acceptable value for the duration as long as the biggest compressor in the system does not start to deliver the air to the system after it restart.
- When used as a “wet tank,” it acts as a secondary heat exchanger that accumulates condensate water to be removed which helps in improving performance of the air dryer.
- When used as a “dry tank”, it reduces the burden on air dryer during high-demand events. Without a dry air tank, air from the wet tank will have to go through the air dryer before it is used. During periods of high demand, the dryer is at risk of becoming over-capacitated as the system tries to pull air through at higher volumes than the dryer is rated for. If the dryer cannot keep up with the demand, drying efficiency is reduced, potentially leading to unwanted water in the air lines.
It stores compressed air that can be used for short time, high-demand events.
When installed on downstream side (Demand Side):
- It provides point of use storage that is used for short time, sudden demand events.
- It avoids increasing the system pressure by holding the pressure during short demand events.
Out of various possibilities, following are the six basic areas where properly engineered storage on the demand side could be applied:
1. Dedicated storage to improve the speed, thrust, or torque of an application.
2. Dedicated storage to protect a critical application from pressure fluctuations.
3. Dedicated storage to meter a high rate of flow application into the system.
4. General or overhead storage to support applications during the transmission time to the supply side and to create transparency between applications.
5. Control storage to support events in the system within an allowable pressure drop.
6. Offline, higher-pressure air stored to support large system events and reduce peak electrical demand.
Calculating the size of an air receiver tank for a known demand or pressure drop event such as in case of applications being in operation
- V = Receiver volume in m3 or ft3
- C = air demand in m3/min or ft3/min
- T = Duration of event in minutes
- P = Atmospheric pressure (1.013 bara or 14.7 psia)
- (P1-P2) = Acceptable drop in pressure in bara or psia
Calculating the size of an air receiver tank for estimated (unknown) demand or pressure drop event such as in case of a new installation
3 of such ‘rule of thumb’ or empirical formulae based on working experience:
- VReceiver = (2 x Vof compressor)/p2*(p1-p2)
e.g. – for a compressor of 1000 m3/hr = 16.67 m3/min, pressure 7.5 – 7.0 bar range then the receiver size would be 9.52 m3 (i.e. 10 m3)
e.g. if compressors deliver 1000 m3/hr (16.7 m3/min) then it should have a 10 m3 receiver.
- VReceiver = 0.5 x (compressor flow in m3/min)
e.g.: if compressors deliver 16.67 m3/min then it should have 8.335 m3 (at least 8 m3) receiver.
It is recommended to size the Receiver tank as large as possible.
It is also important to properly size the inlet pipe and outlet pipe diameters to maintain low velocity (10 m/s).
The air receiver tanks are fabricated as per applicable standards in various countries. Also, they need to be periodically tested for wall / shell thickness with ultrasonic gauge and / or also hydraulically tested.
Following standards for fabrication of air receivers / pressure vessels are used:
