What is Compressor Air Receiver: Compressor Air receiver is an essential item for the air compressor system to act as storage and medium. The compressor air receiver is placed between the compressor and the consumption system. Compressor air receivers are generally of two types as below mentioned.
- Primary Air Receiver: Primary Air receiver is principally located near to the compressor, placed after the aftercooler (before the filtration and dryer system).
- Secondary Air Receiver: Secondary Air Receiver is to be located at the consumption tapping (Where intermittent air consumption is larger).
In general, the Maximum compressor capacity for Well designed system always exceeds or is greater than the maximum mean air consumption for the entire system. The compressor may be the modulating type which means having the capability of variation in capacity during normal operation or load. Modulation strategies can be primitive or advanced.
Primitive strategies Very often used for the compressor is on/off, whereas advanced modulation techniques such as VFD (Variable frequency drive) and inverter based. The pressure band (Pressure Variation) is higher in the case of primitive modulation techniques than the advanced modulation techniques.
Air consumption is principally dependent upon the processing system, sometimes air consumption requirements for the process may be greater than the maximum capacity of the compressor for short time. In a well-designed system, compressors are not designed for maximum air consumption or peak load for the process requirement.
Purposes of Compressor Air receiver:
- To fulfill the pressure band or Variation from the modulating sequence of the compressor and stop-start.
- Storage of air volume to equalize the difference between the consumption and demand systems.
- It can also be used for condensate collection and water from the air downstream (after) the compressor.
Sizing Basics for Compressor Air Receiver: Compressor Air receiver must be sized as follows:
- Based on the variations in demand of consumption.
- Based on the compressor size and modulation techniques.
Calculation of the maximum consumption can be calculated from the demand of each consumer point. This calculation value can be multiplied with a factor of 0.1 – 1. This factor is called as usage factor.
In general, Manufacturer decides the size of the air receiver based on the models used for the compressor capacity including the technology (Know-how).
Sizing of the Compressor Air receiver, the Pressure band needs to be known and plays an important role in the sizing procedure.
Illustration:
- Process consumption requires 150 PSIG and Compressor is also set at 150 PSIG, hence no storage will take place at all and neither it can be used as a buffer system. If demand increases then there will be the pressure that reaches below 150 PSIG until the compressor is set to increase the compressed air volume.
- In the case of the Compressor operating at 160 PSIG whereas the consumption process needed 150 PSIG, this difference of 10 PSIG is known as the pressure band and this accounts for the volume of air stored in the air receiver.
- If in any situation where demand increases, a pressure band of 10 PSIG drops before the minimum requirement can be met.
- Installation of Pressure and flow transmitter downstream of the air receiver to maintain pressure up to 100 PSIG and controlling of peak demands respectively.
- Compressed air system, the piping is also serves the purpose of buffer volume.
- Method of Air receiver sizing: Typically no method is accepted as sizing for air receivers, but commonly equation used for air receiver sizing on basis of mass balance as mentioned below:
C.Pa.t = V. (P1-P2). – Equation 1
Where V is the volume of the receiver tank (ft3)
t is the time taken for pressure variation adjustment (i.e. high to lower pressure or pressure band), minutes
C is free air needed (SCFM – Standard cubic feet per minute)
Pa is atmospheric pressure (14.7 PSIA)
P1 and P2 are the maximum and minimum pressure of the air receiver tank respectively.
Example sizing calculation: A compressor system in which the mean consumption of air is 50 SCFM, tank pressure maximum, and the minimum is 150 and 140 PSIG respectively, and time taken for higher pressure to lower pressure variation adjustment is 50 seconds minutes. Calculate the Compressor air receiver tank volume.
Solution:
V = C.Pa.t / (P1-P2)
C = 50 SCFM
P1 = 150 PSIG
P2 = 140 PSIG
t = 50 Seconds
V = to be calculated
V = 50 x 14.7 x (50 / 60) / (150 – 140)
V= 61.25 Ft3
The calculator Used for the sizing of the instrument air receiver will be uploaded soon!