Refrigerated dryers: the heart of industrial compressed air drying

In the huge system of industrial production, high-quality compressed air is like blood, continuously providing power support for various equipment and processes. As a key equipment to ensure the drying of compressed air, the importance of refrigerated dryer (referred to as cold dryer) is self-evident. It converts moist compressed air into dry and clean air source through exquisite refrigeration technology, and is widely used in various industrial fields. Next, let us explore the mystery of refrigerated dryer together, from its working principle, typical process, key components, to operation control, application scenarios and future development trends, to fully unveil its mystery and provide readers with detailed and practical reference.

1. Overview of refrigerated dryer

The refrigerated dryer, like an air purification master, cleverly uses the principle of refrigeration cycle to convert water vapor in compressed air into liquid water, thereby achieving the goal of drying air. In the field of industrial drying, it and adsorption dryer can be regarded as the two pillars, but each has its own characteristics.

The advantages of refrigerated dryer are significant, and low operating cost is one of them. Judging from the energy consumption data, its energy consumption is usually only 1/3 to 1/2 of that of an adsorption dryer. Behind this data is real energy saving. Take a medium-sized manufacturing company as an example. If an adsorption dryer is used, the annual electricity bill may be as high as hundreds of thousands of yuan. After replacing it with a refrigerated dryer, the annual electricity bill can be greatly reduced. At the same time, the refrigerated dryer does not need to consume regeneration gas, which further reduces energy consumption and operating costs. Moreover, its equipment is highly reliable, the maintenance cost is relatively low, and the service life of parts is long, which reduces the manpower, material and financial consumption caused by frequent maintenance and replacement of parts.

However, the refrigerated dryer is not perfect. Its dew point is usually between 2℃ and 10℃, which is a certain gap compared with the dew point of -40℃ or even lower that the adsorption dryer can achieve. This determines that it is more suitable for occasions where the dew point of compressed air is not required. For example, in some ordinary manufacturing industries, for compressed air for pneumatic tools and pneumatic control, as long as the basic drying requirements are met, the refrigerated dryer can do the job perfectly.

But in terms of performance stability, the refrigerated dryer performs well. It is less affected by the ambient temperature and can operate stably under different environmental conditions. Its refrigeration system is like a precise temperature controller, which can effectively control the temperature fluctuation of compressed air and ensure the stability of the drying effect.

2. Working principle of refrigerated dryer

The working process of the refrigerated dryer is like a precise physical magic. Based on the refrigeration cycle, it mainly covers four key processes: compression, condensation, throttling and evaporation. Let’s analyze this magical working principle in detail.

(I) Refrigeration cycle

1. Compression process: The compressor is like the heart of the refrigeration cycle, and the refrigerant gas is sucked in and compressed under its strong action. In this process, the pressure and temperature of the refrigerant gas rise sharply, just like injecting powerful energy into the gas, so that it changes from a low temperature and low pressure state to a high temperature and high pressure gas, laying the foundation for the subsequent refrigeration link.
2. Condensation process: The high temperature and high pressure refrigerant gas enters the condenser with full energy, where it exchanges heat with the cooling medium (such as air or water). This process is like putting hot metal into cold water. The refrigerant gas quickly releases heat, gradually cools and condenses into high-pressure liquid, completing the gorgeous transformation from gas to liquid.
3. Throttling process: When high-pressure liquid passes through an expansion valve or capillary tube, it is like water flowing through a narrow pipe, and is subject to throttling and pressure reduction. At this time, the volume of the refrigerant expands rapidly, and the temperature also decreases, becoming a low-temperature and low-pressure liquid and gas mixture, preparing for the subsequent evaporative cooling.
4. Evaporation process: The low-pressure and low-temperature refrigerant enters the evaporator and comes into close contact with the dried compressed air. This is like a cold winter, when humid air encounters an icy object, and water vapor condenses quickly. Here, the refrigerant absorbs the heat in the compressed air and quickly evaporates into gas, while the compressed air is taken away by heat, the temperature is lowered, and the water vapor in it condenses into liquid water, achieving the purpose of drying.

(II) Compressed air drying process

1. Precooling: The humid compressed air is like a sweaty athlete, and first enters the precooler (usually a heat exchanger). Here, it exchanges heat with the dried low-temperature compressed air, just like two objects with different temperatures come into contact with each other, and heat will be transferred from the high-temperature object to the low-temperature object. The temperature of the compressed air gradually decreases, and some water vapor condenses into liquid water first, taking the first step of drying.
2. Evaporative cooling: The pre-cooled compressed air enters the evaporator, which is the core component of the refrigerated dryer. Its internal structure design is like a precise maze, which directly affects the drying effect. In the evaporator, the compressed air exchanges heat with the low-temperature refrigerant, the temperature is further reduced, and a large amount of water vapor condenses into liquid water. At this time, the evaporator is like a powerful moisture capturer, capturing almost all the moisture in the compressed air.
3. Gas-liquid separation: The compressed air containing liquid water flows out of the evaporator and enters the gas-liquid separator. The gas-liquid separator is like a magical magician, using centrifugal force, gravity or filtration to accurately separate liquid water from the compressed air. The separated liquid water is smoothly discharged from the equipment through the automatic drain valve, and the separated compressed air continues its drying journey and enters the aftercooler.
4. Post-cooling: The compressed air exchanges heat with the cooling medium again in the post-cooler, and the temperature is further reduced. This step is like cooling down an already cooled object. Further reducing the temperature of the compressed air can effectively reduce the risk of re-condensation in the subsequent pipeline and ensure the dryness of the compressed air.
5. Reheating (optional): In order to prevent the compressed air from condensing again during pipeline transportation, some dryers are equipped with reheaters. The dried compressed air is heated to a certain temperature through the reheater to increase its ability to carry water vapor. This is like putting a layer of protective clothing on the dry air to ensure that it remains dry during transportation.
6. Detailed explanation of the typical process of refrigerated dryer

Below, we take the common air-cooled refrigerated dryer as an example to deeply interpret its typical process and see how it can achieve compressed air drying in an orderly manner.

(I) Refrigerant cycle process

1. Compressor: The refrigerant gas is sucked in under the strong suction of the compressor, and then undergoes strong compression, and the pressure and temperature rise sharply. The compressed high-temperature and high-pressure refrigerant gas is like a cannonball full of energy, which is quickly discharged from the compressor, and it is a key step to start the refrigeration cycle.
2. Air-cooled condenser: The refrigerant gas enters the air-cooled condenser without stopping. Here, the air blown by the fan is like a warm partner, exchanging heat with the refrigerant gas. The refrigerant gas releases a lot of heat, gradually cools and condenses into high-pressure liquid, completing an important state transition.
3. Liquid reservoir: The condensed refrigerant liquid enters the liquid reservoir, which is like a stable warehouse, storing and buffering the refrigerant liquid to ensure a stable refrigerant supply for subsequent processes.
4. Dry filter: When the refrigerant liquid passes through the dry filter, it is like passing through a fine filter. The moisture and impurities are completely removed, effectively preventing the expansion valve from clogging and ensuring the smooth operation of the refrigeration system.
5. Expansion valve: Under the action of the expansion valve, the refrigerant liquid undergoes throttling and pressure reduction, the volume expands rapidly, and the temperature drops significantly. At this time, the refrigerant becomes a low-pressure and low-temperature liquid and gas mixture, which is fully prepared for the subsequent evaporative refrigeration in the evaporator.
6. Evaporator: The low-pressure and low-temperature refrigerant enters the evaporator and exchanges heat with the compressed air. In this process, the refrigerant absorbs the heat in the compressed air and evaporates rapidly. The evaporated refrigerant gas returns to the compressor with full vitality, completing a complete refrigerant cycle.

(II) Compressed air process

1. Intake: The humid compressed air enters the dryer from the air inlet, just like a traveler with moisture entering the starting point of a dry journey.
2. Precooler: The compressed air first comes to the precooler and exchanges heat with the dried low-temperature compressed air to achieve preliminary cooling. Part of the water vapor condenses into liquid water, laying the foundation for subsequent deep drying.
3. Evaporator: The precooled compressed air enters the evaporator and exchanges heat with the low-temperature refrigerant. The temperature is further reduced and a large amount of water vapor condenses into water. The evaporator is like an efficient moisture factory, separating the moisture in the compressed air to the maximum extent.
4. Gas-liquid separator: The compressed air containing liquid water enters the gas-liquid separator, where the liquid water is accurately separated and discharged, and the compressed air becomes purer.
5. Aftercooler: The compressed air enters the aftercooler and exchanges heat with the cooling medium again. The temperature is reduced again, further ensuring the dryness of the compressed air.
6. Reheater (optional): The dried compressed air is heated by the reheater to improve its ability to carry water vapor and prevent it from condensing again during pipeline transportation.
7. Exhaust: The compressed air that has undergone a series of drying treatments is discharged from the air outlet and is available to users in a dry and clean state, providing reliable air source support for various industrial equipment and processes.
8. Introduction to key components
9. Compressor: As the core power source of the refrigeration cycle, the role of the compressor is crucial. Common types of compressors are scroll, piston or screw. Scroll compressors are favored in places with high noise and energy consumption requirements due to their high efficiency and energy saving, smooth operation and low noise; piston compressors are widely used in some small industrial applications due to their simple structure and convenient maintenance; screw compressors have the advantages of large exhaust volume and good stability, and are suitable for large-scale industrial production.
10. Condenser: The task of the condenser is to condense the refrigerant gas into liquid. Common cooling methods are air cooling and water cooling. The air-cooled condenser uses air as the cooling medium, has a simple structure and is easy to install. It is suitable for occasions where there is insufficient water or low requirements for installation space; the water-cooled condenser uses water as the cooling medium, has high cooling efficiency, and is suitable for large-scale industrial equipment with high requirements for cooling effects.
11. Evaporator: The evaporator is the core component of the cold dryer, where the refrigerant evaporates and absorbs heat to reduce the temperature of the compressed air. Its internal structure is exquisitely designed and is directly related to the drying effect. An efficient evaporator can ensure sufficient heat exchange between the refrigerant and the compressed air, and remove moisture from the compressed air to the maximum extent.
12. Expansion valve: The expansion valve is like a regulating valve in the refrigeration system, which controls the flow and evaporation pressure of the refrigerant. It accurately adjusts the supply of refrigerant according to the load changes of the refrigeration system to ensure the stable operation of the refrigeration system.
13. Gas-liquid separator: The function of the gas-liquid separator is to separate the liquid water in the compressed air to ensure that the discharged compressed air is dry and pure. It uses centrifugal force, gravity or filtration principles to efficiently separate liquid water from the compressed air.
14. Precooler: The precooler uses the principle of heat exchange to precool the compressed air and improve the efficiency of the system. It recovers the coldness of the dried low-temperature compressed air and preliminarily cools the moist compressed air, reducing the load of the subsequent evaporator and realizing the effective use of energy.
15. Reheater (optional): The function of the reheater is to reheat the dried compressed air to prevent condensation in the pipeline. It heats the dried compressed air to a suitable temperature according to actual needs to ensure the stability of the compressed air during transportation.
16. Automatic drainer: The automatic drainer is responsible for automatically draining the separated liquid water to ensure that there is no water accumulation inside the equipment. It can automatically open and close the drain valve according to the change of liquid level to achieve efficient and convenient drainage function.
17. Application scenarios

The refrigerated dryer has found a broad application space in many fields due to its unique performance characteristics.

In general manufacturing industries that do not require high dew point of compressed air, such as the use of pneumatic tools, when workers operate pneumatic wrenches, air drills and other tools, the dry compressed air provided by the refrigerated dryer can ensure the normal operation of the tools and extend their service life; in terms of pneumatic control, it provides a stable and reliable air source for the pneumatic control system of the automated production line to ensure the smooth progress of the production process.

In the spraying industry, for some occasions that do not require strict requirements on air dryness, the refrigerated dryer can also meet the needs. For example, for ordinary metal surface spraying, as long as the moisture content of the compressed air is within a certain range, the spraying quality can be guaranteed. At this time, the refrigerated dryer is an economical and practical choice.

In laboratories and medical institutions, where air quality requirements are high but ultra-low dew point is not required, refrigerated dryers also play an important role. Some experimental equipment in the laboratory requires dry compressed air as a power source or gas source. The dry air provided by the refrigerated dryer can meet the experimental requirements; some pneumatic equipment in medical institutions, such as dental equipment, ventilators, etc., also rely on the dry compressed air provided by the refrigerated dryer to ensure the safe operation of the equipment and the health of the patients.

In situations where cost control is required, the refrigerated dryer has become an economic alternative to the adsorption dryer. Its lower operating and maintenance costs enable enterprises to effectively reduce production costs while ensuring production quality.

1. Future development trends
2. High efficiency and energy saving: As energy issues become increasingly prominent, refrigerated dryers will continue to develop in the direction of high efficiency and energy saving in the future. Using more efficient compressors, such as new permanent magnet synchronous variable frequency compressors, can automatically adjust the speed according to the actual load to further reduce energy consumption; optimize the design of the heat exchanger, use new heat exchange materials and structures, improve heat exchange efficiency, and reduce energy loss; develop new refrigerants to improve refrigeration efficiency and reduce environmental impact.
3. Intelligent control: Intelligence will be an important trend in the future development of refrigerated dryers. The introduction of intelligent control system can realize real-time monitoring and automatic adjustment of the operation status of the cold dryer. Through the real-time collection of temperature, pressure, flow and other parameters of the equipment by sensors, the intelligent control system automatically adjusts the operation parameters of the equipment according to these data to ensure that the equipment is always in the best operating state. At the same time, it has remote monitoring and fault diagnosis functions. Users can monitor the operation of the equipment anytime and anywhere through mobile phones, computers and other terminals. Once the equipment fails, the system can issue an alarm in time and provide fault diagnosis information, which greatly improves the maintenance efficiency of the equipment.
4. Environmentally friendly: With the increasing awareness of environmental protection, refrigerated dryers will also pay more attention to environmental protection performance. Use environmentally friendly refrigerants such as carbon dioxide and R290 to reduce the damage to the ozone layer; improve the sealing of the equipment, prevent refrigerant leakage, and reduce pollution to the environment. At the same time, optimize the structural design of the equipment, reduce the use of materials, and reduce energy consumption and environmental pollution in the equipment manufacturing process.
5. Compact design: With the increasing tension of industrial land, the requirements for equipment volume and floor space are also getting higher and higher. In the future, the refrigerated dryer will optimize the equipment structure design, adopt a new compact layout and integrated technology, reduce the size and floor space of the equipment, and improve the space utilization of the equipment.
6. Modular design: The modular design concept will be widely used in the development of refrigerated dryers. By standardizing the design of each functional module of the equipment, users can flexibly select and combine different modules according to their own needs to achieve functional expansion and upgrading of the equipment. This not only improves the adaptability and flexibility of the equipment, but also reduces the manufacturing and maintenance costs of the equipment.

In short, the refrigerated dryer plays an indispensable role in industrial production with its advantages of low operating cost and stable and reliable performance. With the continuous advancement of technology, it will continue to move towards high efficiency, energy saving, intelligence, and environmental friendliness.