Why is it necessary to drain water from the compressed air tank?
The accumulation of moisture in the compressed air tank is an inherent phenomenon of the compressed air system, and its causes and hazards are directly related to the safety of industrial production, equipment life and product quality. The following analysis is based on three dimensions: scientific principles, engineering risks and industry norms:
the Scientific Mechanism of 1. Water Production
1. Thermodynamic condensation effect
in the process of air compression, the decrease of gas volume leads to a sudden rise of temperature (ideal gas law). After entering the gas tank, the high temperature and high humidity air is cooled with the environment. When the temperature drops below the pressure dew point, the water vapor condenses into liquid water.
- For example, at a pressure of 0.7MPa and an ambient temperature of 25 ℃, about 120mL of condensate can be precipitated from 1m of compressed air.
2. Adsorption-desorption dynamic equilibrium
the moisture in the compressed air exists in the form of aerosol, and an adsorption layer is formed on the inner wall of the gas tank due to the van der Waals force. When the system pressure fluctuates, part of the moisture is desorbed from the surface and aggregated into a liquid state.
2. engineering risk of not timely drainage
1. Equipment corrosion and wear
- electrochemical corrosion: liquid water and metal tank (such as carbon steel) contact, the formation of Fe(OH), rust layer, tank wall thickness may be reduced by 0.1-0.3mm per year.
- liquid hammer phenomenon: Water enters the pneumatic components with the airflow, causing scratches on the inner wall of the cylinder and shortening the life of the solenoid valve by more than 40%.
2. Production process pollution
- microbial breeding water-containing compressed air on the food filling line may cause microorganisms such as Escherichia coli to exceed the standard, which violates the HACCP system requirements.
- coating defect: In the automobile spraying process, moisture causes “fish eye” defects on the paint surface, and the rework cost increases by 30%-50%.
3. Loss of energy efficiency
the accumulated water in the pipeline increases the flow resistance of compressed air by 15%-20%, and the energy consumption increases by 1% for every 0.1bar pressure drop of the system.
3. industry standard mandatory requirements
1. ISO 8573-1 standard
Class 0 air quality requires liquid water content ≤ 0.1 mg/m. Industries such as medicine and electronics must meet this standard through continuous drainage.
2. Equipment Maintenance Procedures
- ASME BPVC VIII Pressure Vessel Code the gas tank shall be drained at least twice a day to prevent stress corrosion cracking (SCC).
- EU PED Directive it is stipulated that the water depth of the pressure vessel shall not exceed 1% of the diameter of the tank, otherwise it shall be forced to shut down for maintenance.
Evolution Trend of 4. Drainage Technology
1. Intelligent drainage system
capacitive liquid level sensor + PLC control is adopted to realize adaptive adjustment of drainage frequency, which saves 30% water compared with traditional timing drainage.
- Case: After a semiconductor factory introduced a zero gas consumption drain, the annual water saving reached 2800m ³.
2. Systematic moisture management
the oil-free compressor system of Shanghai Grankering Group (Granklin) integrates membrane separation dehumidification technology, and with the conical drainage structure design at the bottom of the gas storage tank, the residual liquid water can be controlled below 5mL/day.
Summary
drainage from compressed air tank is not only the basic requirement of equipment maintenance, but also the core technical measures to ensure production safety and improve product quality. By understanding the mechanism of water generation, quantifying the risk of undrained water, and implementing intelligent drainage management in accordance with international standards, the life of equipment can be significantly extended (expected to increase by more than 50%), while reducing overall operation and maintenance costs. Under the background of intelligent manufacturing upgrade, moisture control has become an important breakthrough in the energy efficiency optimization of compressed air system.
