Air separation equipment generally uses rivers, lakes or groundwater as cooling water. This kind of water usually contains suspended solids (sand and other dirt) and bicarbonates such as calcium and magnesium [Ca (HCO3)2 and Mg (HCO3)2]. It is called hard water. When there are more suspended solids, it is easy to block the cooling. Channels, filters, valves, etc. When the water temperature rises, bicarbonates such as calcium and magnesium tend to form calcium carbonate CaCO3 and magnesium carbonate MgCO3 precipitates, which form what is commonly known as scale. Generally, scale will begin to form when the water temperature is above 45°C. The higher the water temperature, the easier it is to scale. Scale adheres to the tube wall of the cooler, the filler of the nitrogen water precooler, the nozzle or the screen hole, etc. It not only affects heat exchange and reduces the cooling effect, but also hinders the circulation of cooling water or air. In severe cases, it may cause equipment failure.

  For example, the nitrogen-water precooler carries water, causing the cold storage (or switching heat exchanger) to freeze. Scale is relatively hard and adheres to the walls of the appliance and is difficult to remove. Therefore, it is best to soften the cooling water. It is relatively simple to use a magnetic water heater for softening treatment, and the effect is acceptable. A sedimentation tank should be set up to remove suspended solids. If the cooling water is recycled, it will be beneficial to softening the water quality, but it will occupy a larger area and require larger investment in infrastructure.

   For compressor cooling water, the temperature is generally required to be no higher than 28°C, and the drainage temperature is less than 40°C. The water quality requirements are:

         pH value: 6.5 to 8

         Suspended solid content: not more than 50mg/L

         Temporary hardness: no more than 17°dH.

         Oil content: less than 5mg/L

         Chloride ion (Cl-) [mass fraction]: less than 50 X 10^-6

         Sulfate (SO4-2) [mass fraction]: less than 50X 10-6

  The water supply and drainage of the nitrogen-water precooling system is an independent circulation system. Because the temperature of the cooling water rises greatly in the tower, the drainage temperature is high, and scaling is serious, it is required that the supplementary water of the system be as low-hardness water or soft water as possible, and its temporary hardness is average. It should be less than 8.5°dH, and other requirements are the same as the compressor cooling water. The lubricating water for the cylinder of the high-pressure oxygen compressor used for filling bottles should be distilled water or soft water.