Actual Calculations to Get Plant Require Compressed Air Capacity

There are no set calculations for a plants air requirements. It is the demands of the equipment that the air is supplied to. Most manufactures of the equipment will list requirements on the machines add those up. If not supplied the requirements of the individual devices on the machines can be added up. The volume of a cylinder times the number of strokes in a minute. An air motor if not listed on the motor the manufacture will have the specs. Same with air tools look up for an replacement the specs will be there. In the purchase of the new compressor I would also place in to the calculation the companies future growth. Now if the size of the compressor is over or around 25 hp I recommend a screw compressor with variable speed drive. This type of compressor will produce air on demand. It will save you money on electrical cost.

There is no determined formula for that. When it comes to Compressed air requirements, ther are three essential factors to be cosidered, volume, pressure, and quality of compressed air to be used. As for the volume, it is only a matter of adding up all the consuming points represnted by machines,equipments,devices,instruments air requirements, which is normally specified by the manufacturers, and you can always add a buffer margin of 25% in excess for unforeseen leakage. As for the pressure, you have to calculate the expected pressure drop over the whole air ring main, i.e your compressed air net from the air compressors' out-let to the different consuming points, and to do this, there are few formulaee to be followed. For that, I advise you to refer to this link http://www.pipeflowcalculations.com/airflow/theory.htm By getting the pressure drop, you can then decide up on your air compressors pressure rating.

As for the quality of air, you have to refer to the equipments' manufacturers technical specifications, so as to decide whether it should be dry air and oil free, or oil injected....

My friend,

Alternatively, the pressure drop in compressed air lines can be calculated by using the formula

dp = 7.57 q^1.85 L 10⁴ / d⁵ p (1)

where

dp = pressure drop (kg/cm²)

q = air volume flow (m³/min)

L = length of pipe (m)

d = inside diameter of pipe (mm)

p = initial pressure (kg/cm²)

is 'q' measured in free air volume, or actual volume at pressure? and do you have a formula where the pressure is in bars or psi?

some other thoughts -

a) review your plant needs holistically - don't look just at peak demand, but also what is likely to happen most of the time - let's say your peak demand calculated required a 40 hp unit at 80% of it's capacity during the day and the rest of the time (two more shifts in a 24/5 or 24/7 environment you needed 80% of a 30 hp unit - you might be better with two "lag-loaded" units - a couple consisting of an efficient 30 (agree with screw compressors, and be sure to rig your room to recapture excess heat back into your production area in the winter rather than just blowing it out the window and running the space heater . . .) and a 15 or 20 hp unit so that you are running less electrial through your plant.

b) in any case make sure that your piping allows you to piggy back in another unit for when your demand (even short term) requires more 'blow' than you have available, and to allow for the time(s) that PM must be done or reactive maintenance is required when, not if, you develop problems

good luck

Jim

The way that I would do it is the sure fire way (without caluclations for pressure drops in the air lines): Just find out how many pieces of equipment you want to supply then check the mfg's lit for each piece's cfm - add 'em all up, add 10-15% for line losses, and you will shine. BTW, since you were already supplying air in the first place, the pressure requirements will be the same as your original compresser.

To determine air demand consider the following

1 number of consumers

2 Air consumption per unit

3 Duty time: period during which the operator is active in a work period

4 Simultaneity factor

5 allowance for leakages if a large factory 15 - 20%

allowance for growth over 5 - 10 years 25 - 50%

a formula would be individual consumption of tools x number tools x duty factor x Simultaneity

Ensure you have a ring main around your part of the factory or you will get low flow spots.

depending on how large the plant is i would look at 2 compressors for redundancy and a decent receiver. do a google search and get on to the kaiser website they have some handy tools for sizing pipes, compressors and receivers

I will provide a formula.

You must have:

1. A receiver.
2. 3 ea. shut off valves. Full flow ball valves would work.
3. A couple of assistants would be helpful.
4. Install a shut off valve between the current compressor and the receiver.
5. Install a shut off valve in the supply line for each plant A and B.

During a period of typical production for plant A

Ask plant B to shut down for a few minutes and simultaneously:

1. Record the pressure in the reservoir
2. Close the valve that blocks the supply to the reservoir.
3. Close the valve that blocks the supply to plant B
4. Start a timer.
5. Observe the pressure in the reservoir.

When the reservoir pressure has decayed 10% record the time and quickly open all valves. If you cannot decay precisely 10% let me know.

1. Divide the time to decay 10% by .4088
2. This is the amount of time it would take to empty the reservoir at the initial flow rate. That is the time constant that would empty the reservoir. Tkseconds
3. Determine the volume of the reservoir in cubic feet (eg. gallons/7.48) Vcu ft
4. Determine the compression ratio of the air at original pressure P1 psig/14.7= Cr
5. (V x Cr x 60)/Tk = Standard Cubic Feet per Minute, SCFM

For example a 10% decay was recorded at 14 seconds. Then 14/.4088=34.25sec=Tk and 250 gallon reservoir/7.48 = 33.42 cu ft. [33.42 x 100/14.7 x 60/34.25] = 398 SCFM

With both plant A and B in typical production repeat the steps above but close only the valve that supplies the reservoir.

1. Record the pressure in the reservoir
2. Close the valve that blocks the supply to the reservoir.
3. Start a timer.
4. Observe the pressure in the reservoir

Use the same calculations to get the SCFM for both Plant A and Plant B. Subtract the flow SCFM initially calculated for Plant A from the total to determine the SCFM for Plant B.

When purchasing a compressor for either Plant A or B double the calculated flow for a compressor with a 50% duty cycle.

If you have access to PIP (Process Industry Practices), there are three guidelines available concerning the design (including capacity estimates) and installation of instrument air systems

PCCIA001 - Design of Instrument Air Systems (this has the sizing information)

PCEIA001 - Guidelines for Instrument Air Systems

PCIIA000 - Instrument Air Installations Details

http://www.pip.org/practices/pc/index.asp#IA

If your company is a member, you can login and download them for free, otherwise there is a fee for each one.