Calculation of factory compressed air demand

The calculation of the factory’s compressed air demand must follow the principle of systematic analysis and conduct scientific evaluation based on equipment characteristics and operating conditions. The following is the technical implementation framework:

1. Basic data collection and equipment list preparation

1. Survey of gas equipment: Establish a ledger for the equipment using compressed air in the whole plant, and record the rated air consumption (m³/min), working pressure (MPa) and working system of each equipment. For example, pneumatic polishers need to mark the proportion of continuous working time, and sandblasting equipment needs to clarify the single operation cycle.
2. Process parameter verification: Conduct actual measurement and verification of key equipment, use a gas flow meter to measure the actual air consumption under typical working conditions, and correct the deviation of equipment nameplate data. For variable frequency drive equipment, the air consumption characteristics at different speeds need to be tested.

2. Load characteristic analysis and coefficient correction

1. Simultaneous use factor (Ki): Determine the probability of simultaneous use based on the characteristics of the device group. For independently operated equipment (such as a single CNC machine tool), Ki is 0.8-0.9; for linked production lines (such as automobile assembly lines), Ki is 0.6-0.7.
2. load fluctuation coefficient: Considering the impact of production shifts, the three-shift factory needs to increase the peak-valley adjustment capacity by 15%-20%. For intermittent gas-using equipment (such as pulse dust collectors), time domain analysis methods need to be used to calculate the instantaneous maximum gas demand.
3. loss compensation factor：
   • Pipeline leakage: 5% is reserved for new systems, and 10%-15% for in-service systems. The pressure attenuation method can be used to test, record the time required for the pressure of the gas tank to drop from 0.69MPa to 0.62MPa, and substitute it into the formula to calculate the leakage amount.
   • Filter pressure drop: Each stage of filtration device produces a pressure loss of 0.02-0.05MPa, and the required air pressure of back-end equipment needs to be corrected.

3. Correction for special working conditions

1. Environmental parameter compensation：
   • Altitude correction: For every 300 meters increase in altitude, the air density decreases by about 3%. The volume flow needs to be corrected according to the formula Y=1/(1-0.0000367H)(H is altitude, meters).
   • Temperature correction: When the intake air temperature exceeds 25 ° C, correct the standard flow rate according to Q real =Q standard *(273+T real)/(273+20).
2. Special process requirements：
   • Pulse purging: press Q=0.0036d²P calculation (d is nozzle diameter, mm;P is gauge pressure, MPa).
   • Instrument gas: An independent buffer tank needs to be equipped, and the volume is calculated as V=0.1*Q/ΔP (ΔP is the allowable pressure fluctuation, and it is recommended to take 0.05MPa).

4. System configuration optimization

1. Gas storage tank selection: The volume is selected based on 10%-20% of the compressor displacement. For fluctuating load conditions, it is recommended to adopt a multi-stage gas storage plan. For example, the combined configuration of main air storage tank + peak and valley regulating tank.
2. Pipe diameter calculation: Determine the inner diameter of the pipeline according to the economic flow rate method. It is recommended that the flow rate of the main compressed air pipe be 15-20m/s, and that of the branch pipe be 8-12m/s. The calculation of pipe diameter needs to consider a capacity expansion margin of 20%-30%.
3. energy efficiency assessment: Using the specific power (kW/m³/min) as the selection indicator, the specific power of screw compressors should be better than 0.12kW/m³/min, and that of centrifugal compressors should be better than 0.15kW/m³/min.

5. Dynamic demand management

1. intelligent monitoring system: Deploy IoT flow meters, collect pressure and flow data at all levels of pipe networks in real time, and establish a digital twin model to predict demand curves.
2. Flexible configuration plan: For production expansion reservations, it is recommended to use modular compressor units, and the regulation range of a single unit covers 30%-120% of the basic load.

Through the above methods, a complete demand assessment system covering static calculation and dynamic adjustment can be built. In actual projects, energy efficiency audits need to be carried out every 2-3 years, and the gas supply system configuration should be adjusted and optimized in conjunction with the production plan.