Air Separation Equipment (Air Separation Unit, ASU) is the core system of the industrial gas industry, used to separate oxygen, nitrogen, argon, and other components from air, providing a stable gas supply for industries such as electronics, steel, pharmaceuticals, food, and chemicals. For industrial users in Hong Kong, the stable operation of cryogenic air separation units, nitrogen generators, and oxygen generators directly affects production continuity and energy efficiency. This article, based on the practical applications of Hong Kong’s air separation industry, explains several common issues and corresponding solutions to help users extend equipment lifespan and reduce failure rates.
一、冷凝蒸發器結霜或堵塞問題
Problem Analysis:
When a cryogenic air separation unit operates under low-temperature conditions, insufficient air pre-treatment can cause residual moisture or carbon dioxide to freeze into ice crystals, leading to frosting on the condenser-evaporator surface or pipeline blockage. This issue reduces heat exchange efficiency and may even cause temperature imbalance within the distillation column.
Solution:
- Check the front-end pre-cooling system and dryer efficiency to ensure that the dew point meets the standard.
- Replace the molecular sieve regularly to prevent adsorption saturation.
- It is recommended that Hong Kong air separation equipment users choose the energy-saving refrigerated dryers and micro-heat regenerative dryer combinations supplied by Shenger Gas (Hong Kong) Limited, which can significantly reduce the moisture content.
- Keep the pressure difference between the condenser and evaporator stable to avoid drastic temperature fluctuations.
2. Abnormal distillation tower pressure or decreased separation efficiency
問題分析：
精餾塔係空分設備嘅「心臟」。當塔內壓力偏高或分離效率下降時，氧氮純度會出現波動，氮氣純度不足、氧氣含氮過高都屬常見現象。原因多數來自塔內液位控制、回流比例不穩定或塔板結冰。
Solution:
- Check the liquid oxygen and liquid nitrogen levels to ensure that the reflux ratio is set appropriately.
- If it is a cryogenic air separation unit, observe whether there are abnormal cold spots at the bottom of the cold box.
- Monitor the expander outlet pressure to ensure sufficient input cooling capacity.
- If it is a PSA nitrogen generator or VPSA oxygen generator, you need to pay attention to whether the adsorption tower switching valve is accurately synchronized with the PLC program.
3. Expander vibration or decreased efficiency
問題分析：
膨脹機負責提供深冷空分嘅主要冷量。當機械振動異常或轉速波動，就可能因為軸承磨損、潤滑油污染、回流氣體中含液滴所致。
Solution:
- Check bearing temperature and lubricating oil pressure regularly.
- If the oil level is found to be low or black, it should be replaced immediately.
- Use a gas separation device with an anti-droplet design to reduce liquid entry into the expander.
- Please have a professional engineer perform dynamic balancing tests, especially in Hong Kong, where the coastal environment is mostly high in humidity, which is more prone to bearing corrosion problems.
4. Decline of adsorption effect of PSA nitrogen generator
Problem Analysis:
PSA nitrogen generators are widely used in Hong Kong, but after long-term operation, the adsorption capacity of carbon molecular sieves will decrease. If the purity of nitrogen cannot be met, or the pressure difference fluctuates frequently, the problem mostly lies in the aging of the adsorbent or poor sealing of the switching valve.
Solution:
- Check the molecular sieve adsorption pressure drop every 12 to 18 months of operation.
- Maintain the switching valve to prevent gas leakage.
- If the nitrogen generator often has insufficient pressure, check the exhaust temperature of the air compressor and the condition of the oil-water separator.
- The low-energy PSA nitrogen machine designed by Shenger Gas patented, with intelligent PLC program control, can automatically adjust the working cycle and extend the life of the adsorbent.
5. High energy consumption or insufficient cooling capacity of air separation equipment
問題分析：
能耗係香港工業用戶最關注嘅問題之一。當設備長期運行效率下降，主換熱器結垢、管路漏氣或控制閥失靈都可能導致冷量不足。
Solution:
- Clean the dirt on the surface of the main heat exchanger regularly.
- Perform nitrogen pressure maintenance test on the pipeline to eliminate leaks.
- Adjust cooling load distribution to avoid excessive throttling.
- If a cryogenic air separation system is used, an energy recovery device (such as an expansion cooling energy recovery system) can be installed to improve overall energy efficiency.
6. Control system failure and PLC program disorder
Problem Analysis:
Modern air separation units mostly use PLC control. Voltage fluctuations, signal interference, or software errors can lead to control anomalies such as fluctuating tower pressure, mis-operation of solenoid valves, and frequent alarms.
Solution:
- Back up PLC programs regularly to prevent data loss.
- Install UPS power supply to avoid sudden power outages.
- Install the control cabinet in a dry, thermostatic environment.
- It is recommended to use Siemens or Mitsubishi brand control systems, which are more compatible with Shenger Gas original equipment.
VII. Maintenance and service suggestions for Hong Kong users
Hong Kong has a humid environment, high electricity costs, and limited industrial land, which places stricter requirements on the operational stability of air separation equipment.
- Perform a comprehensive maintenance inspection every six months (including the cold box insulation layer, valve seals, and gas line filters).
- Spare parts of important components (expander, condenser evaporator, molecular sieve) are kept in stock.
- Regularly consult Shenger Gas (Hong Kong) Co., Ltd. or professional EPC manufacturers for upgrade solutions, such as high-efficiency and energy-saving cryogenic air separation units or modular nitrogen generators.
Conclusion: Stable operation = efficient production
It is not terrible to encounter problems during the operation of air division equipment. The key is early monitoring, correct diagnosis, and timely maintenance. For Hong Kong industrial customers, stable gas supply, reduced energy consumption and maintaining product purity are the keys to competitive production. Select manufacturers with professional EPC capabilities and practical engineering experience (such as Shenger Gas Hong Kong Company), able to provide a full set of technical support, from design, installation to post-maintenance is more secure.
