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An air pre-cooling system generally consists of an air cooling tower, a water cooling tower, a chiller, and water pumps. It is installed between the air compressor and the molecular sieve adsorber to reduce the temperature and moisture content of the air entering the molecular sieve adsorber. Before the 1990s, cross-flow tray plates and large-pore drop tube trays were commonly used in air-cooled and water-cooled towers. In actual operation, numerous problems arose, such as water accumulation in air-cooled towers, issues with water-cooled towers, high tray resistance, high cooling capacity required by refrigeration units, and poor pre-cooling efficiency. Since the 1990s, air separation plant manufacturers both domestically and internationally have widely adopted polypropylene Bauler ring packed towers; some also use a small amount of stainless steel Bauler ring packing at the bottom of the air-cooled towers, approximately 2 meters worth. The standard diameters for these Bauler rings are generally DN50, DN70, and DN90. Air-cooled and water-cooled towers use Baffle rings as packing, which are arranged in a free-heap manner. During mass and heat transfer, the liquid flows uniformly downward from the top of the tower, moving in a film-like manner along the packing; meanwhile, the gas rises from the bottom of the tower and comes into contact with the liquid film as it passes through the packing (whose specific surface area ranges from 80 to 110 m2/m3), thereby facilitating heat and mass exchange. For air separation units manufactured around the 1970s, ceramic Lassie ring packing was also used in the air-cooling towers and water-cooling towers. Due to significant improvements made by the German company BASF to the Lassie rings, although the outer diameter of these rings remained equal to their height, two rows of openings with internal tabs were created on the ring walls. Each layer has 5 window openings; this design improves the distribution of gas and liquid and makes full use of the inner surface of the ring. Compared to Raschig rings, Pall rings can handle more material by over 50%, while reducing pressure by half. Practice has shown that when a Bower ring packed tower is used in an air pre-cooling system, it has the following notable advantages over a sieve plate tower: (1) Strong mass and heat transfer capacity. The temperature difference between the air exiting the air-cooled tower and the cold water entering it in the upper section can be less than 1°C, while in a water-cooled tower, a negative temperature difference of 4–5°C can exist between the temperature of the water exiting the tower and the temperature of the wastewater entering it ； (2) Since the packing void ratio reaches 94–95%, it is not prone to clogging, and it is less likely to cause foam entrainment; this facilitates operation under varying conditions. When the air volume increases, water is not easily carried along ； (3) The pressure drop is low; the resistance per meter of packing is approximately 10 mm of water column ； (4) The water consumption of air-cooled towers can be reduced by 30% ； (5) It can reduce the cooling capacity of the chiller. It can be turned off in winter, and the cooling capacity can be reduced by 80% in summer, making it possible to implement an air pre-cooling system without a chiller ； (6) Easy to install, low manufacturing cost ； (7) A fairly low density (0.9 kg/m3), resulting in a light weight of the final product. Polypropylene is a flammable material; its operating temperature ranges from 10 to 120°C, and it becomes brittle below 0°C. Its structure provides greater chemical stability, allowing it to resist most acids, salts, and many organic solvents, but it cannot withstand high-concentration strong acids. Polypropylene is divided into two types: ordinary (with a maximum operating temperature of +80°C) and reinforced (with a maximum operating temperature of +120°C). Ordinary polypropylene Bower ring packing can be used for water cooling towers ； When starting an air-cooled tower, if no end cooler is installed on the air compressor, the air temperature during startup is around 90°C; therefore, enhanced Borex ring packing is chosen, or in most cases, ordinary polypropylene Borex ring packing is used. At a height of about 2 meters below the packing layer, stainless steel Borex ring packing should be used to prevent a decrease in the compressive strength and heat resistance of the polypropylene Borex ring packing.