Dehydration of air compressors: Understanding the advantages and disadvantages of various types of desiccators

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1 Compressed air: As the main device for providing power air in industry, air compressors are used in virtually all sectors as industry continues to develop. And the dryer, as a post-treatment device for compressed air, is equally essential. Currently, dryers are mainly divided into two types based on their working principle: cold dryers and suction dryers. Depending on the regeneration method, desiccators are further divided into pressure-reduction regeneration, mild-heat regeneration, blower regeneration, and compression-heat regeneration types. 2. Cryogenic dryer: A cryogenic dryer is also known as a freeze-dryer. Its working principle is based on the refrigeration cycle; it involves the refrigerant absorbing heat in the evaporator (while compressed air releases heat). It cools the compressed air. After cooling, at the same pressure, the saturated humidity varies with temperature; as a result, liquid condensate is formed, which is automatically removed through a drain valve. The cooled compressed air exchanges heat with the warmer compressed air at the inlet, is heated again, and then discharged, thereby achieving the goal of reducing the dew point temperature of the compressed air. Since its working principle relies on a refrigeration cycle to reduce temperature, the dew point temperature of the compressed air ranges from 2 to 10°C. Given its low cost, ease of installation, and the fact that its energy source is mainly electrical power with no associated environmental pollution, it can be given priority as an option when the dew point temperature of the compressed air is not too low. 3 Comparison between heat-free regeneration and heated regeneration: The full name of a desiccant dryer is adsorption-type dryer; it works by using adsorbents to absorb the moisture from compressed air, thereby reducing the dew point of that compressed air. The adsorbents, after having absorbed moisture, need to be regenerated in order to maintain their adsorption capacity for the next cycle. Therefore, based on the regeneration method, adsorption dryers can be further divided into pressure-reduction regeneration, mild heat regeneration, and forced-air heating regeneration. 3.1 Heat-free regeneration: The regeneration process in heat-free regeneration dryers involves removing moisture from the adsorbent by reducing pressure, thereby regenerating the adsorbent. This type of dryer does not require a heat source; instead, it uses dried compressed air as the gas for regeneration, and the dew point temperature can reach -20°C to -40°C. The drawback is the significant waste associated with the need for a regenerative gas source. 3.2 Microheat regeneration: Microheat regeneration involves the use of an additional heat source, taking advantage of the heating regeneration principle inherent in the regeneration properties of the adsorbent, in order to heat the regenerated gas and gradually cause the moisture contained in the adsorbent to desorb. It enables the adsorbent to regain its ability to absorb moisture. The feature of micro-heating equipment is that, with a heating source, it can reduce the waste of regenerated compressed air, and the dew point temperature can reach -20°C to -40°C. But the drawback is that a heating source is required, which increases the volume accordingly. If the equipment can make use of waste heat locally, it can also be appropriately selected. 3.3 Forced-air thermal regeneration: Dryers using forced-air thermal regeneration are characterized by the use of an external blower; heated air is blown through to remove the water that has been desorbed from the adsorbent, thereby achieving regeneration. Its feature is that the waste of regenerated compressed air is further reduced, and the dew point temperature can reach -20°C to -40°C. However, a heating source is still required, and at the same time the electrical power consumption of the blower increases, further increasing the volume. A comparison table of the various performance characteristics and energy consumption for heat-free regeneration, mild heat regeneration, and air-heated regeneration is shown in Table 1. https://pic.ouryao.com/data/attachment/forum/202107/22/151940mlllwt4nwgugxlwl.png.thumb.jpg 4 Compression heat regeneration: The compression heat regeneration adsorption dryer is a type of desiccant dryer that makes efficient use of energy in the market. It makes full use of the large amount of heat generated during the compression process by the compressor; by utilizing part of the high-pressure, high-temperature heat from the compressor’s exhaust gas to heat the adsorbent, the adsorbent can be regenerated. The cooled compressed air is further cooled before being mixed with another portion of compressed air and fed into the adsorption tower for water removal, thereby reducing the dew point. The dew point of the treated compressed air can reach -20°C to -30°C. It is fully capable of achieving the dew point temperature of compressed air required by ordinary enterprises. Adsorption dryers that utilize waste heat avoid energy waste, and thus achieve significant cost savings over long-term operation. It is currently the preferred choice for businesses in the market. However, due to their complex structure and the fact that they must be used in conjunction with air compressors, all heat-recovery adsorption dryers available on the market today are equipped with oil-free compressors, specifically centrifugal compressors or oil-free screw compressors. Therefore, its price is also significantly higher than that of other adsorption dryers that do not use heat regeneration or external heat sources for regeneration when making investments.