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Applications of compressed air in formulations: In pharmaceutical factories, compressed air is primarily used in filling machines for liquid formulations, as well as in granulators, slurry mixers, fillers, packaging machines, printing machines, and extraction tanks in the extraction process. Additionally, compressed air can be used as a testing gas in laboratory tests, for material transportation, drying, purging, pneumatic instruments, and automatic control systems. There are two common types of compressed air. One is a conventional oil-lubricated compressed air system, which is used for the pneumatic components of instruments and does not come into direct contact with drugs. The other is an oil-free compressed air system, which does come into direct contact with drugs. Since the quality of compressed air that comes into direct contact with drug production directly affects the quality of the drugs, oil-free compressed air systems are still the most commonly used in drug manufacturing facilities today. To ensure the quality of compressed air, it is particularly important to implement strict purification measures for it. At the same time, the compressed air system must be verified to prove that it meets the production requirements and passes the GMP certification inspection. What is compressed air? Compressed air is air that has been compressed by an external force. Air is compressible; air to which mechanical work is applied by an air compressor, resulting in a reduction of its volume and an increase in pressure, is known as compressed air. Air occupies space, but it has no fixed shape or volume. When pressure is applied to the air in a closed container, its volume is compressed, resulting in an increase in the internal pressure. When the external force is removed, the air, under the influence of the internal pressure, returns to its original volume. If there is a movable object inside the container, when the air returns to its original volume, that object will be pushed outward by the pressure of the air inside the container. Compressed air is an important power source. Compared to other forms of energy, it has the following distinct advantages: it is clear and transparent, easy to transport, lacks any special harmful properties, poses no fire risk, is not susceptible to overload, and can operate in many adverse environments. Air is available everywhere on the surface of the earth and is inexhaustible. Compressed air is widely used in production and daily life. For example: Compressed air is injected into a ball, and the more air there is, the harder the ball becomes; compressed air is used in tires to enable them to bear a certain weight; in large vehicles, compressed air is used to operate doors and brakes; hydraulic presses use compressed air to apply pressure to water; in factories, compressed air is used to power pneumatic hammers for forging; in coal mines, it is used to operate pneumatic drills for drilling holes; it is also used for transporting liquids and granular materials through pipelines. The normal air pressure in the atmosphere is 0.1 MPa, and it can be raised to the desired pressure by using an air compressor. Compressed air is the second most important source of power after electricity, and it also serves as a process gas with various applications. Its use spans industries and sectors such as petroleum, chemicals, metallurgy, power generation, machinery, light industry, textiles, automobile manufacturing, electronics, food processing, pharmaceuticals, biochemistry, national defense, and scientific research. Compressed air for pharmaceutical use 1 Requirements for the gas source in drug production. Generally, the quality standard of the gas source used in drug production should meet the requirements specified in \"Compressed Air – Part 1: Contaminants and cleanliness grades\" (ISO8573.1—2001)1 and \"Quality standards for compressed air for general use\" (GB/T13277—1991)2. In other words, the dew point should be -40 °C, the particle size of solid particles should be ≤0.1 um, and the oil content should be ≤0.1 mg/m³. The quality standards and grade specifications for compressed air are shown in Table 1. https://pic.ouryao.com/data/attachment/forum/202012/26/092434m7qwlhlh3zhbqii1.jpg.thumb.jpg The effects of foreign substances mixed in compressed air: When foreign substances such as lubricating oil, water vapor, and dust are present in compressed air, it can lead to the following negative effects: (1) Oil vapor mixed in the compressed air can accumulate to such an extent that it becomes a source of fire and explosion risk. Moreover, when lubricating oil vaporizes, it forms organic acids that can corrode the inner surfaces of compressed air pipes and cause blockages in the systems’ pipelines. (2) The tiny particles that get mixed in (such as dust, rust, etc.) can easily damage pneumatic components and clog the throttle holes; more seriously, they can cause severe contamination of the material. (3) The moisture mixed in compressed air will reach saturation and form water droplets under certain temperature and pressure conditions; when compressed air comes into contact with materials, it can easily have a serious impact on the quality of those materials. (4) Excessively high compressed air temperature can also cause aging of the seals, hose materials, diaphragms, and other components in the air compression system. Therefore, compressed air must undergo purification processes such as cooling, oil removal, water removal, and removal of solid dust particles before being delivered to the point of use, in order to meet GMP requirements. Compressed air purification system for pharmaceutical use. The compressed air purification system, also known as a post-compression air treatment system, has a process flow as shown in Figure 1. Compressed air exits the compressor, undergoes simple treatment, and then enters the air storage tank. After buffering, it proceeds to the post-treatment stage of the air compressor. The configuration can be as follows: compressor → water-steam separator → air storage tank → refrigerated dryer → water-steam separator → oil removal and purification equipment → adsorption dryer → three-stage filter → sterilization filter. The compressor system consists of an intake system, the main unit, a gas supply system, and an oil-gas separation system. Air passes through the filter and, via a butterfly valve, reaches the suction inlet of the compressor unit. The screw compressor uses axial intake at its end face; suction begins once the mesh line between the teeth reaches the mating point on the end face. As the rotor rotates, the meshing line extends toward the exhaust side, and more air is drawn in. The suction phase ends when the tooth profile at the end face moves away from the intake opening. The inhaled air is within a closed chamber formed by the male and female rotors and the housing. Oil-water separator: An oil-water separator is used to remove impurities such as water and oil that have condensed in compressed air, thereby providing preliminary purification of the compressed air. Working principle of the oil-water separator: When compressed air enters the oil-water separator, there is a sudden change in direction and velocity; thanks to inertia, oil droplets and water droplets with a higher density than compressed air are separated out. After compressed air enters the separator housing through the inlet, the airflow is first blocked by the partition, causing it to turn downward; it then rises upward again, resulting in circular motion. In this way, under the action of centrifugal force and inertial force, the water droplets and oil droplets separate from the air and settle at the bottom of the container; by opening the valve at the bottom periodically, the oil droplets and water droplets can be removed. The initially purified air is sent from the outlet to the gas storage tank. The Class C centrifugal oil-water separator has a filtration precision of 3 μm, a water removal rate of >99%, and an oil mist removal rate of ≥40%; it is primarily used as a separator for rear coolers and as a pre-filter for freeze-dryers. Freeze dryer. Working principle of a freeze dryer: Moist and hot compressed air flows into the pre-cooler to lose heat, and then enters the heat exchanger where it exchanges heat with the cold air coming out of the evaporator, thereby reducing the temperature of the compressed air entering the evaporator. The compressed air after heat exchange flows into the evaporator, where it exchanges heat with the refrigerant through the evaporator’s heat exchange function. The heat in the compressed air is absorbed by the refrigerant, causing the compressed air to cool down rapidly. The moisture in the humid air reaches its saturation temperature and condenses quickly. The condensed moisture forms water droplets; these droplets pass through a special gas-water separator that rotates at high speed, and due to centrifugal force, the moisture is separated from the air. The separated water is then discharged through an automatic drain valve. The dew point of the air pressure after cooling can reach as low as 2 ℃. After cooling, the cold air flows through the air heat exchanger, where it exchanges heat with the hot and humid air entering from the inlet. The cold air, having absorbed heat from the incoming air, rises in temperature. Meanwhile, the compressed air also passes through the secondary condenser of the refrigeration system, where it exchanges heat once more with the hot refrigerant, thereby ensuring that the temperature at the outlet is sufficiently high and preventing dew formation in the air ducts at the outlet. At the same time, it makes full use of the cold source from the exhaust air, ensuring the condensation efficiency of the refrigeration system and thus guaranteeing the quality of the exhaust air. Oil pollution treatment devices: There are three types of such devices, including cartridge-type oil removal filters, activated carbon oil removal filters, and catalytic oxidation oil removal filters. All of them can effectively remove oil contamination. It should be noted, however, that activated carbon and cartridge-type filters require regular replacement of their adsorbents, while catalytic oxidation filters are much more stable and do not need extensive maintenance. An oil removal unit is generally installed after the cold dryer to ensure that the air is free of oil. Adsorption dryers work by utilizing \"pressure changes\" (the principle of pressure swing adsorption) to achieve drying. Since the capacity of air to hold water vapor is inversely proportional to pressure, a portion of the air after drying (referred to as regenerated air) expands under reduced pressure to atmospheric pressure. This change in pressure makes the expanded air drier, and it is then allowed to flow through the desiccant layer that requires regeneration and through which no air flow is present (i.e., the desiccator that has already absorbed sufficient water vapor). The dried regenerated air removes the moisture from the desiccant, carrying it out of the desiccator thereby achieving dehumidification. The two towers operate in rotation, without the need for a heat source, to continuously supply dry compressed air to the user’s air consumption systems. Its compressed air dew point can generally reach -40°C. Air terminal sterilizing precision filter: As a high-precision terminal filter, the air precision filter serves to ensure that the air after filtration meets sterile standards. The filter elements of air terminal sterilization precision filters are made of polytetrafluoroethylene membranes, and they feature strong hydrophobicity, high filtration accuracy (filtration precision of 0.01 μm, oil mist removal rate of ≥99.9999%), low pressure drop, high temperature resistance, and a long service life. They represent an ideal and reliable filtering solution for removing contaminants and phages from the air. Storage and delivery of compressed air: For the storage and delivery of filtered and purified compressed air, compressed air storage tanks serve to reduce flow fluctuations and store compressed air, thereby compensating for sudden consumption of this gas to avoid frequent fluctuations and startups. They also have functions such as water removal and waste discharge. Storage tanks should be installed between compressors and drying equipment, as well as between purification equipment and end-use devices. In actual use, delivery pipelines shall meet the requirements for pipelines specified in the **Standard ‘Design Code for Compressed Air Stations’ (GB50029—2003). For isolation valves on pipelines with low water vapor content, stainless steel valves are recommended ； For the pipes between compressors, gas storage tanks, freeze-dryers, and gas distributors, stainless steel pipes must be used ； For drying and purification pipelines that require dust particles to be less than 0.1 μm, stainless steel pipes can be used to ensure the quality of the dried and purified compressed air. In the pharmaceutical industry, pipelines for compressed air systems are generally made of stainless steel of sanitary grade 316L. Disinfection of compressed air pipes: Connect the pipes of the pure steam generator to the compressed air pipes. Close the valves at all compressed air usage points (except at the farthest point of use), open the valve at the farthest point of compressed air use, start the pure steam generator, open the pure steam valve, and allow the steam to reach the compressed air system; the compressed air system is then disinfected with this flowing pure steam for 30 minutes. After 30 minutes of disinfection, open the valves at each usage point and blow air through them for 30 minutes. As a special type of product, pharmaceuticals are closely related to people’s health and well-being; therefore, the **Food and Drug Administration has established strict quality standards for the pharmaceutical industry. As a key medium in the pharmaceutical industry, compressed air requires regular inspection of its piping systems; integrity tests must be conducted on compressed air filters and breathing filters, and tests should be carried out to detect oil vapors, moisture, and microorganisms present in the compressed air, so as to ensure that its quality meets GMP requirements.