The calculation of the air volume of the ship air compressor needs to be combined with the specific purpose, equipment parameters and industry standards. The following are the key steps and key points:
basic formula for calculation of 1. air volume
the basic formula of air volume (Q) of air compressor is:
Q = V / T
- Q air flow (unit: m & sup3;/min or L/s)
- V: Volume (unit: m & sup3; or L)
- T: Time (in min or s)
note: The volume and time range shall be selected according to the actual working conditions, usually the time from intake to exhaust of the compressor.
Sources of air demand for air compressor in 2. ships
- pneumatic Equipment Requirements
- according to the total air consumption of pneumatic equipment on the ship (such as pneumatic valves, pneumatic pumps, pneumatic tools, etc.).
- Formula: Q = & Sigma;(single air consumption of equipment x quantity x usage factor)
for example, if the single air consumption of a pneumatic tool is 0.5m & sup3;/min, 2 sets are used at the same time, and the usage coefficient is 0.8, then qf1 = 0.5 × 2 × 0.8=0.8m & sup3;/min.
- Purging and Cleaning Requirements
- estimate air consumption in areas of ship cabins, ducts, etc.
- Formula: Q₂ = chamber volume x number of air changes
for example, if the cabin volume is 50m & sup3; If air needs to be exchanged twice per hour, Q₂ = 50 × 2=100m & sup3;/h & asymp; 1.67m & sup3;/min.
- Start-up diesel engine demand
- large ships may require an air compressor to provide high-pressure air to start the diesel engine.
- Formula: Qgreater = single start-up air consumption × start-up frequency
for example, if a single start requires 5m & sup3; Air, start 4 times a day, then Q = 5 × 4=20m & sup3;/day & asynmp; 0.014m & sup3;/min (need to be converted to real-time air volume).
3. safety margin and total air volume calculation
- safety margin
- it is suggested to add 10%-20% margin on the basis of theoretical calculation value to deal with equipment aging, leakage and other emergencies.
- Formula: Q_total = (Q + Q + Q + Q) × (1 + margin ratio)
for example, if the theoretical total air volume is 10m & sup3;/min, the balance is 15%, then Q_total = 10 × 1.15=11.5m & sup3;/min.
4. industry standards and codes for reference
- international Maritime Organization (IMO) requirements
- ship air compressors are required to meet relevant safety and performance standards, such as the IMO International Convention for the Safe Construction of Ships.
- Classification Society Specification
- each classification society (such as CCS, DNV, LR, etc.) has specific regulations on air volume, pressure and other parameters of air compressor, and relevant specifications shall be consulted according to the type and purpose of the ship.
- Cabin Classification Requirements
- engine room: To meet the requirements of pneumatic equipment, starting diesel engine and purging, with large air volume.
- CARGO COMPARTMENT: Mainly used for purging and cleaning, with moderate air volume requirements.
- Living area: The air volume demand is small, but the noise and air quality requirements are high.
5. case analysis
case Background: The engine room of a cargo ship needs to meet the requirements of pneumatic equipment, purging and starting the diesel engine at the same time.
- Pneumatic equipment: 3 pneumatic pumps, single air consumption 0.6m & sup3;/min, usage coefficient 0.9.
- Q₁ = 0.6 × 3 × 0.9 = 1.62m³/min
- purge demand: cabin volume 200m & sup3;, air exchange once per hour.
- Q₂ = 200 × 1 = 200m³/h ≈ 3.33m³/min
- start the diesel engine: 8m & sup3 for a single start; Air, start 3 times a day.
- QVi = 8 × 3=24m & sup3;/day & asymp; 0.017m & sup3;/min (negligible)
- total air volume calculation:Q_total = (1.62 + 3.33) × 1.15 ≈ 5.69m³/min
conclusion: Air compressor with air volume ≥ 5.69m & sup3;/min shall be selected to meet relevant classification society specifications and IMO requirements.
6. considerations
- unification of units: Make sure that all parameters are in the same unit during calculation (e. g. m & sup3;/min or L/s).
- Dynamic adjustment in actual operation, it may be necessary to adjust the air volume according to the load change. It is recommended to choose an air compressor with frequency conversion adjustment function.
- Maintenance and inspection regularly clean the air compressor and pipeline dust, and check whether the air volume and pressure meet the requirements.
