How to determine and calculate gas consumption

How to determine and calculate 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

　　 Timing pumping test is a relatively easy and accurate method to check the air volume or output of existing air compressors, which 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=V(P2-P1)60/(T)PA

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

　　 According to 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, the required m3/min=the 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 the 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.

　　The leakage of the entire plant system can be diagnosed by measuring the time required 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:

V(P2-P1)60

Leakage m3/min=

90 (PA)

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

　　 5. Select 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?

　　The ideal production is that the specifications of the rotary screw compressor and centrifugal compressor should ensure normal operation within the modulation and adjustment control range.

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

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

　　 Research the performance characteristics of various types of air compressors to estimate the power cost, 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 the air compressor and its additional equipment (such as dryers and filters)?

　　How does the 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 work 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.

　　　 Is there any unusual intermittent peak demand load that needs to be considered?　

　　 Selection of working pressure (exhaust pressure):

When the user is preparing to purchase an air compressor, first determine the working pressure required by the air end, add a margin of 1-2 bar, and then select the pressure of the air compressor (the margin is considered from the air compressor The pressure loss from the installation site to the actual gas end pipeline distance, according to the length of the distance between 1-2 bar, appropriately consider the pressure margin). Of course, the size of the pipeline diameter and the number of turning points are also factors that affect the pressure loss. The larger the pipeline diameter and the fewer turning points, the smaller the pressure loss; on the contrary, the greater the pressure loss.

　　 Therefore, when the distance between the air compressor and each gas end pipeline is too far, the diameter of the main pipeline should be appropriately enlarged. If the environmental conditions meet the installation requirements of the air compressor and the working conditions permit, it can be installed near the gas end.

　　 Volume flow selection:

　　① When selecting the volumetric flow rate of an air compressor, you should first understand the volumetric flow rate of all air-consuming equipment, and multiply the total flow rate by 1.2 (that is, enlarge the margin by 20%);

　　② The new project can be selected according to the flow value provided by the design institute;

　　③ Learn about the volumetric flow parameters of the gas-consuming equipment from the gas-consuming equipment supplier for selection;

　　④ The air compressor station can be selected with reference to the original parameter value and the actual gas usage in the transformation of the air compressor station;

　　 Appropriate selection is beneficial to both the user and the air compressor equipment. Excessive selection is wasteful, and too small selection may cause the air compressor to be in a long-term loading state or insufficient air or pressure can not reach the disadvantages.

　　The relationship between power, working pressure and volume flow

In the case of constant power, when the speed changes, the volumetric flow and working pressure also change accordingly; for example: a 22KW air compressor, the working pressure is determined to be 7bar at the time of manufacture, calculated according to the main compressor technical curve Speed, the displacement is 3.8 m3/min; when the working pressure is determined to be 8bar, the speed must be reduced (otherwise the drive motor will be overloaded), at this time, the displacement is 3.6 m3/min; because the speed is reduced, the displacement Qi is also reduced accordingly, and so on.

　　The selection of power is to meet the working pressure and volume flow conditions, and the power supply capacity can meet the power of the matched drive motor.

　　 Therefore, the steps for selecting an air compressor are: first determine the working pressure, then determine the corresponding volume flow, and finally the power supply capacity.