The water removal issue prior to the PSA nitrogen generation unit
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Our company uses the PSA nitrogen production process. During operation of the equipment, the gas coming out of the centrifugal air compressor passes through a rear cooler before reaching the nitrogen production unit. A large amount of moisture is generated before the gas enters this unit. I have two questions for the experts here: 1. Are there any effective methods for removing this moisture? Or what devices need to be added? 2. How is the water content in compressed air calculated? Thank you so much!
The following suggestions are offered: 1. Add pre-cooling units to lower the temperature of the gas, which helps to precipitate moisture from the gas. It also helps the adsorbent function. 2. Separation can be achieved using a single vapor-liquid separator, but the effect is not as good as that of option 1.
1. There are many ways to remove water, depending on your requirements regarding the dew point. If the nitrogen dew point requirement is around -40, a cold dryer can be used ； For higher requirements, a desiccator can be used. Other methods include deliquescence tanks or packed beds, but they are rarely used in PSA ； 2. Different dew points correspond to specific moisture contents; you can look them up online ；
Mechanical separation can be carried out first, followed by the use of a cold dryer to reduce its water content (to the saturation level at that temperature). The moisture content in the gas can be expressed in terms of dew point (in degrees Celsius) or as a volume fraction~~
A water-cooled freeze dryer can reduce the dew point at atmospheric pressure to -20°, which is sufficient for use in a PSA system; by adding water-removing molecular sieves to the PSA system, the nitrogen output can have a dew point of -40° at atmospheric pressure.
What devices are included in a pre-cooling unit? Freeze dryer? Is it necessary to install any water removal or buffering device in front of the pre-cooling unit?
What kind of devices are generally used for mechanical separation?
1. The pre-cooling unit, also known as a chiller, is used to cool the gas entering the molecular sieve, allowing some of the water to precipitate out before the gas reaches the molecular sieve and thereby reducing the load on the molecular sieve adsorbent. 2. A cooler should be installed at the final stage of the compressor, before the chiller, in order to reduce the temperature at the compressor outlet and maintain it at a level consistent with the temperature of the circulating water. 3. A water delivery device is required for the cold-start unit. There is no need for a buffer device.
Depending on your process selection, it can be a baffle-type or cyclone separator, or a mesh packing separator can also be used~~
Agree with the second floor’s opinion. Our screw air compressors output air at 40°C; it is then cooled to 2–8°C using a pre-cooling unit before entering the purifier. The separator at the end of the pre-cooler can remove a considerable amount of moisture. It extends the lifespan of the molecular sieve.