Calculation and determination of gas consumption

The traditional method of determining the compressed air requirements of a new plant is to add up the air consumption (m3/min) of all air-consuming equipment, and then consider adding a safety, leakage and development factor

  In an existing factory, you only need to do some simple tests to know whether the compressed air supply is sufficient. If not, you can estimate how much more needs to be added.

   The output pressure of the general industrial air compressor is 0.69MPa (G), and the pressure sent to the point of use of the equipment is at least 0.62 MPa. This shows that the typical air compressor we use has an unloading pressure of 0.69 MPa (G) and a cylinder loading pressure of 0.62 MPa (G), or system pressure. With these numbers (or the unloading and loading values ​​of a certain system) we can determine.

   If the cylinder pressure is below the nominal loading point (0.62 MPa(G)) or does not gradually rise to the unloading pressure (0.69 MPa(G)), more air may be required. Of course, always check to make sure that there are no major leaks and that the compressor unloading and control systems are operating normally.

If the compressor must work at a pressure higher than 0.69 MPa (G) to provide a system pressure of 0.62 MPa (G), check that the pipe size of the distribution system may be too small, or how much more air volume needs to be added to the air consumption at the blocking point, What effect does the system leak and how to determine the size of the gas storage tank to meet the intermittent peak gas consumption requirements.

1. Test method-check the capacity of the existing air compressor

Timed pumping test is a relatively easy and accurate method to check the air volume or output of existing air compressors. This will help determine that the shortage of compressed air is not caused by machine wear or failure.

The following is the procedure for timing pumping test:

A. Volume of gas storage tank, cubic meter

B. The volume of the pipeline between the compressor tanks in cubic meters

C. (A and B) Total volume, cubic meters

D. Compressor running at full load

E. Close the air valve between the air tank and the factory air system

F. The gas storage tank is abandoned and the pressure is reduced to 0.48 MPa (G)

G. Close the bleed valve soon

H. The time required for the gas storage tank to pump gas to 0.69 MPa (G), seconds Now you have the data needed to determine the actual capacity of the existing compressor. The formula is:


C= Compressor air volume, m3/min

V=volume of gas storage tank and pipeline, m3 (item C)

P2=final loading pressure, MPa (A) (H item + PA)

P1=Initial pressure, MPa (A) (Item F + PA)

PA=Atmospheric pressure, MPa (A) (0.1 MPa at sea level)

T=time, s

   If the calculated result of the test data is close to the rated air volume of your factory’s air compressor, you can be more certain that the load of your air system is too high and you need to increase the air supply.

Two, estimation method

V=V Air consumption of existing equipment + V Air consumption of post-processing equipment + V Leakage + V reserve

Three, determine the required increase in compressed air

Based on the amount of air that increases the system pressure to the required pressure, the amount of compressed air supply that needs to be increased can be determined

.                P2 Required m3/min= existing m3/min

P1 In the formula, required m3/min= required compressed air supply

Existing m3/min = Existing compressed air supply

P2=Required system pressure, MPa (A)

P1=existing system pressure, MPa (A)

Need to increase m3/min=required m3/min-existing m3/min

The result will tell you how much gas you need to increase to meet your existing gas demand. It is recommended to increase enough gas to not only meet the current gas requirements, but also take into account the needs of rewards and leakage factors.

Fourth, the impact of system leakage

Insufficient air supply is often or definitely due to system leakage. Air system leakage is a continuous source of power loss, so it is best to make it as small as possible. Several small leakage points equivalent to 1/4 inch small holes may leak up to 2.8 M3 of compressed air at a pressure of 0.69 MPa, which is equivalent to the loss of air volume of an 18.75Kw air compressor, with electricity per degree 0.4 yuan, 8000 hours of operation per year (three shifts) calculation, these leaked air cost you 60,000 yuan in vain.

Most factories will provide maintenance personnel and parts to repair leaks. Damaged tool. Valves, packing, joints, droppers and hoses should be inspected and repaired in time.

Leakage of the entire plant system can be diagnosed by measuring the time it takes for the system pressure (on the upper side of the air storage cylinder) to drop from 0.69 MPa (G) to 0.62 MPa (G) without air supply. Using the pumping test, we can calculate the leakage of the entire system:


Leakage m3/min=          90 (PA)

If the air leakage green exceeds 5% of the air volume of the entire system, a leak must be built.

Five, choose the compressor specifications

Once you determine the air volume (m3/min) and pressure (MPa(G)) requirements of the factory, you can select the specifications of the air compressor.

Factors you may consider when choosing include:

What is the current gas consumption? What is the gas consumption after the factory expansion? Generally speaking, the annual growth rate of gas consumption is 10%. Do you consider using special manufacturing processes and tools in the future?

Ideally, the specifications of rotary screw compressors and centrifugal compressors should be guaranteed to work normally within the range of modulation and adjustment control.

The specifications of the single-acting air-cooled reciprocating air compressor are guaranteed to have 30-40% unloading time based on the constant speed control system.

The water-cooled reciprocating air compressor can work continuously, but it is best to consider a 20-25% buffer or unloading time when selecting specifications.

Study the performance characteristics of various types of air compressors to estimate power costs, so as to determine which one is the best choice to meet your plant's current and future requirements.

Is the factory leaking serious? Do you need to build a leak plan so that the load on the compressed air system can ultimately be reduced?

Are you satisfied with the operation, maintenance, installation and performance characteristics of the selected air compressor?

Have you considered the quality requirements of compressed air when selecting air compressors and their additional equipment (such as dryers and filters)?

How does additional equipment affect your choice of air compressor?

Have you considered the spare air volume in case the main air compressor fails?

Does each shift need to use the same amount of compressed air?

How does the selected air compressor operate when the air consumption is low?

You may want to consider using a smaller air compressor to save energy and avoid excessive circulation and wear of the main air compressor.

Does the factory have unusual intermittent peak demand loads that need to be considered?