How to Calculate Parallel Flow of Air Compressor

Technical Guide for Flow Calculation of Parallel Systems of Air Compressors

parallel operation of air compressors is a common technical scheme to improve gas supply capacity, and its flow calculation needs to comprehensively consider equipment characteristics, pipe network resistance and gas load. The flow calculation method of parallel system and the key points of engineering practice are as follows:

basic Principle of 1. Parallel Operation

1. ideal flow superposition
   when two identical air compressors are running in parallel, if the system resistance is zero, the total flow rate is theoretically equal to twice the single flow rate. In practical engineering, when the gas supply pressure is maintained at the rated value, the parallel unit can achieve 85%-95% flow superposition efficiency.

2. resistance effect mechanism
   the resistance of the pipe network is proportional to the square of the flow, following the Darcy-Weisbach formula:
   ΔP = λ * (L/D) * (ρv²/2)
   where: & Delta;P is pressure loss, & lambda; is friction coefficient, L is pipe length, D is pipe diameter, & rho; is air density, and v is flow velocity
   when two units are connected in parallel, the pressure loss increases exponentially due to the increase of the main pipeline flow, and the actual gas supply volume needs to be determined by hydraulic calculation.

2. flow calculation method

1. performance curve superposition method
   step 1: Obtain the performance curve (flow-pressure curve) of a single unit.
   Step 2: Overlay the curves of the two units horizontally on the same pressure axis.
   Step 3: Consider the resistance curve of the pipe network and determine the actual working point.
   Example: the flow rate of a single unit is 20m & sup3 at 0.7MPa;/min, the theoretical flow rate after two units are connected in parallel is 40m & sup3;/min, the actual flow rate is about 34-38m & sup3 after considering the resistance of the pipe network;/min.

2. law of proportion calculation
   when the speed changes, the flow is proportional to the speed, and the pressure is proportional to the square of the speed:
   Q2 = Q1 * (n2/n1)
   P2 = P1 * (n2/n1)²
   parallel units can achieve proportional flow distribution through frequency conversion adjustment, but pay attention to the minimum speed limit (usually not less than 50% of the rated speed).

Key Points of 3. Engineering Practice

1. selection and matching principle

• capacity matching: capacity difference of parallel unit shall be controlled within ± 5%
• pressure ratio coordination: the rated pressure difference of the unit should not exceed 0.05MPa
• adjustment characteristics: give priority to the unit with the same adjustment mode (such as frequency conversion/power frequency)

2. pipe network design requirements

• calculation of main pipe diameter: the pipe diameter is determined according to the economic flow rate of 15-20 m/s.
• Gas gathering pipe configuration: annular pipe network design is adopted, and the pressure fluctuation is controlled within ± 0.02MPa
• setting of buffer tank: the total volume shall not be less than 30% of the exhaust volume of a single unit

3. control System Configuration

• joint control device: configure master-slave controller to realize automatic rotation operation
• pressure balance: set up a pressure balance valve to ensure uniform load distribution of the unit
• protection logic: when a single unit fails, the system will automatically reduce the frequency to the safe operation area.

4. debugging calibration process

1. no-load commissioning

• verify the reliability of joint control signal transmission
• check pressure sensor synchronization (error ≤ 0.01MPa)
• test the safety valve linkage protection function

2. load Commissioning

• load to rated pressure step by step and record flow superposition curve
• optimizing Inverter Parameters to Eliminate Flow Oscillation Between Units
• draw the actual operating conditions and determine the economic operation interval.

3. Acceptance Criteria

• flow deviation: flow difference of parallel unit ≤ 5%
• pressure stability: within the rated pressure ± 0.02MPa
• energy efficiency index: system specific power ≤ 5.5kW/(m & sup3;/min)

enterprises should establish a parallel air compressor system debugging specification, combined with GB 50029 "compressed air station design specification" requirements, the development of exclusive debugging program. It is recommended to conduct system performance evaluation once a year, focusing on checking key indicators such as flow superposition efficiency (≥ 85%), pressure stability (≤ ± 0.02MPa), equipment operation synchronization rate (≥ 95%), and continuously optimize system operation quality.