How to solve the freezing problem of refrigerated dryers? 3 effective coping methods

In modern industrial production, compressed air is an important power source, and its quality has a significant impact on production efficiency and product quality. As a key link in the post-processing equipment of compressed air, the main function of the refrigerated dryer is to remove water vapor from the compressed air to ensure the provision of dry and clean compressed air. However, in actual operation, refrigerated dryers often encounter a headache-freezing problem. Freezing not only affects the normal operation of the equipment and reduces the drying efficiency, but may even cause equipment damage and bring unnecessary economic losses to the enterprise.

This article will deeply explore the root cause of freezing of refrigerated dryers, and put forward three effective coping methods to help enterprises better maintain and manage refrigerated dryers, so as to ensure the stable and efficient operation of compressed air systems. In addition, we will also explore how to choose a suitable refrigerated dryer according to actual needs to avoid or reduce the occurrence of icing problems from the source.

Analysis of the causes of freezing of refrigerated dryers

The working principle of refrigerated dryers is to condense water vapor into liquid water and discharge it by lowering the temperature of compressed air. When the temperature inside the equipment is too low or the system is not operating properly, freezing is likely to occur. The following are several main reasons for freezing of refrigerated dryers:

Excessive fluctuations in inlet temperature or pressure

Refrigerated dryers are designed and operated with specific inlet temperature and pressure ranges. If the inlet temperature is much higher than the design value, or the inlet pressure fluctuates violently, the wet air load entering the dryer will be too large, exceeding the normal processing capacity of the equipment. In this case, the refrigeration system may not be able to cool all the water vapor below the dew point in time, causing some of the water vapor to condense into ice in the low-temperature area.

High-temperature inlet air: When the compressor outlet temperature is too high or the cooler efficiency is insufficient, the air temperature entering the refrigerated dryer will be very high. High temperature means that there is more water vapor in the air (high absolute humidity), which increases the burden on the dryer. If the refrigeration system cannot take away this heat in time, it may cause the local temperature of the heat exchanger to be too low, forming an ice point.

Pressure fluctuations: Pressure is an important factor affecting the dew point of the gas. When the system pressure drops suddenly, the partial pressure of water vapor in the air will also decrease, the dew point will increase, and it is easier to reach saturation and condense. On the other hand, the increase in pressure may cause the condensed water to form vortices or impacts in the pipes, and freeze quickly when the temperature drops suddenly.

Improper refrigerant charge or leakage

Refrigerant is the key medium in the refrigeration cycle of the refrigerated dryer. Insufficient or excessive refrigerant charge will directly affect the refrigeration efficiency, thereby causing freezing.

Insufficient refrigerant charge: When the refrigerant is insufficient, the pressure in the evaporator will be too low, resulting in a low evaporation temperature of the refrigerant. Too low an evaporation temperature will cause the surface temperature of the heat exchanger to be lower than the freezing point of water, causing the water vapor to condense and freeze quickly. In addition, insufficient cooling capacity will also lead to inefficient refrigeration cycle, unable to effectively remove heat, and thus affecting the drying effect.

Refrigerant leakage: Refrigerant leakage is a common cause of insufficient charge. Leakage usually occurs at pipe joints, valves or compressor seals. Leakage not only leads to reduced refrigeration efficiency, but also pollutes the environment.

Excessive refrigerant charge: Although relatively rare, excessive refrigerant can also affect system operation. Too much refrigerant will increase the pressure in the condenser, causing the condensation temperature to rise, thereby reducing the efficiency of the refrigeration cycle. At the same time, excessive refrigerant may cause liquid refrigerant to enter the compressor, causing liquid hammer or even damaging the compressor.

Drainage system failure or blockage

The refrigerated dryer will produce a large amount of condensed water during operation, which must be discharged in time. If the drainage system fails or is blocked, the condensed water cannot be discharged in time, it will accumulate inside the equipment and freeze in a low temperature environment.

Automatic drainer failure: Most refrigerated dryers are equipped with automatic drainers (such as electronic drain valves, float drain valves, etc.). If the drainer is damaged, blocked or improperly set, the condensed water cannot be discharged. Common faults include the drain valve being blocked by impurities, the solenoid valve coil being burned, and the float being stuck.

Drainage line blockage: The drainage line may be blocked by impurities such as oil, rust, and scale. Especially in systems without effective pretreatment, these impurities are more likely to enter the drainage line.

Improper slope or backflow of drainage pipe: If the drainage pipe does not have enough slope, or there are structures such as U-bends that are easy to accumulate water, condensate may be retained. In addition, if the drain port is directly inserted into a container full of water or a confined space, water backflow may occur, causing condensate to flow back and accumulate.

The drainage diameter is too small: When the amount of condensate is large, if the drainage diameter is too small, it may not be possible to drain all the condensate in time, causing the accumulated water to freeze.

The manual drain valve is not opened or forgotten to be closed in time: For dryers equipped with manual drain valves, if the operator forgets to open the drain valve or forgets to close it after draining the water, it will affect normal drainage.

Low ambient temperature

Although refrigerated dryers mainly work at low temperatures, if the ambient temperature of the equipment is too low, especially below freezing, it will increase the possibility of freezing inside the equipment.

The equipment is placed in a cold area without heating: In winter or cold areas, if the refrigerated dryer is placed outdoors or in a factory building without heating, the temperature of the equipment body and pipelines will be greatly reduced. In this case, even if the system is operating normally, the risk of freezing will increase.

Inlet temperature is too low: If the compressed air is already very low, even close to freezing point, after passing through the precooler or long-distance pipeline transmission, it is easy to freeze quickly in the evaporator when entering the refrigerated dryer.

Failure or missing of pretreatment devices

Before entering the refrigerated dryer, the compressed air usually needs to pass through a prefilter to remove solid particles and liquid water. If these pretreatment devices fail or are missing, a large amount of solid particles, oil and liquid water will directly enter the refrigerated dryer, exacerbating the freezing problem.

Prefilter is blocked or failed: The main function of the prefilter (such as precision filter, oil-water separator) is to remove large particles of impurities and liquid water. If these filters are blocked or failed, a large amount of liquid water and solid particles will enter the dryer with the airflow, adhere to the surface of the heat exchanger, become the “core” of ice, and accelerate the freezing process.

Lack of precooler: For systems with high-temperature air intake, if there is no precooler, directly sending high-temperature compressed air into the refrigerated dryer will bring huge heat load to the dryer and increase the risk of freezing.

Unreasonable system design

Sometimes, freezing of refrigerated dryers is caused by unreasonable system design, such as too small selection, improper pipeline configuration, etc.

Dryer selection is too small: If the processing capacity of the refrigerated dryer is much smaller than the actual compressed air flow, it will cause the equipment to be overloaded for a long time and unable to effectively handle wet air, which will cause freezing.

Unreasonable pipeline design: For example, if the pipeline is too long, there are too many elbows, and the diameter is too small, it will increase the pressure loss and reduce the air flow velocity, which may cause condensation water to accumulate and freeze in local areas.

No bypass pipeline: If there is no bypass pipeline, the dryer cannot be bypassed during equipment maintenance or failure, resulting in system shutdown. In some occasions where continuous air supply is required, the drying quality may be sacrificed for emergency response, which indirectly increases the risk of freezing.

3 Effective Ways to Deal with the Icing Problem of Refrigerated Dryers

For the above-mentioned causes of icing, we can take a series of effective measures to prevent and solve the icing problem of refrigerated dryers. The following are the three most important ways to deal with it:

Optimize operating parameters and strengthen daily maintenance

Optimizing operating parameters and strengthening daily maintenance are the cornerstones of preventing and solving the icing problem of refrigerated dryers.

Strictly control intake parameters

Stabilize intake temperature: Ensure that the compressor outlet temperature is stable and reduce the air temperature entering the refrigerated dryer as much as possible. If the compressor outlet temperature is high, consider installing an efficient aftercooler in front of the refrigerated dryer to further reduce the intake temperature and reduce the heat load of the dryer. The cooler should be checked and cleaned regularly to ensure good heat dissipation.

Stabilize intake pressure: Avoid drastic pressure fluctuations in the compressed air system. The system pressure can be maintained stable by setting a pressure regulator, optimizing the pipeline design, and reasonably dispatching the air compressor. At the same time, regularly check whether the pressure gauge is accurate to ensure that the pressure is controlled within the rated range of the equipment.

Ensure the normal operation of the refrigeration system

Regularly check the refrigerant charge: By observing the suction pressure, exhaust pressure, sight glass, etc. during the operation of the dryer, determine whether the refrigerant charge is normal. If the refrigerant is insufficient, the leak should be found and repaired in time, and then the refrigerant should be replenished. The refrigerant charge should be strictly in accordance with the guidance of the equipment manufacturer.

Clean the condenser: The condenser is a key component for heat dissipation in the refrigeration system. If there is too much dust and oil on the surface of the condenser, it will affect the heat dissipation efficiency, resulting in increased condensation pressure and decreased refrigeration effect. Therefore, the condenser fins should be cleaned regularly with compressed air or special cleaning agents to ensure that they are clean.

Check the compressor and fan: Regularly check whether the refrigeration compressor is operating normally, whether there are abnormal sounds, overheating, etc. At the same time, check whether the condenser fan is rotating normally, whether the wind direction is correct, and whether the air volume is sufficient.

Monitor the pressure and temperature of the refrigeration system: Regularly record and analyze key parameters such as the suction pressure, exhaust pressure, evaporation temperature, and condensation temperature of the refrigeration system. These data can help detect problems in the refrigeration system early and avoid the expansion of faults.

Improve the management of drainage system

Regularly check and clean the automatic drain: The automatic drain is an important guarantee for the discharge of condensate. Check its working status regularly and listen for regular drainage sounds. For electronic drains, manual tests can be performed; for float drains, ensure that the float can float up and down freely without jamming. At the same time, regularly dismantle and clean the filter and valve body inside the drain valve to remove impurities and oil to prevent blockage.

Check the drainage pipeline: Ensure that the drainage pipeline is unobstructed, without bends, collapses or blockages. Check whether the drainage pipeline has enough slope to avoid water accumulation. The drain outlet should be set at a position lower than the dryer drain outlet, and ensure smooth drainage to avoid backflow.

Regular manual drainage: Even if there is an automatic drain, it is recommended to perform manual drainage regularly to flush out stubborn impurities that may accumulate and ensure thorough drainage.

Keep the environment suitable

Provide a suitable operating environment: Ensure that the refrigerated dryer is placed in a well-ventilated, dust-free area with moderate ambient temperature. Avoid placing it in a humid, hot or extremely cold environment.

Winter antifreeze measures: In cold areas or in winter, if the ambient temperature may be below freezing, antifreeze measures should be taken. For example, add a heat preservation cover to the dryer, or set up auxiliary heating equipment near the equipment to ensure that the temperature of the equipment body is not lower than 0℃. When the equipment is shut down for a long time, the condensed water inside the equipment should be completely drained.

Strengthen the maintenance of pretreatment equipment

Regularly replace the filter element: The precision filter and oil-water separator in front of the refrigerated dryer are the “first line of defense” to protect the dryer. The filter element should be checked and replaced regularly in strict accordance with the manufacturer’s recommendations. Clogged filter elements will increase pressure loss, affect airflow, and may cause a large amount of liquid water and oil to enter the dryer.

Check the oil-water separator: Make sure that the oil-water separator works properly and can effectively separate liquid water and oil.

Improve equipment configuration and system design

In addition to daily maintenance, improvements from the level of equipment configuration and system design can also fundamentally solve the problem of refrigerated dryers freezing.

Scientific and reasonable selection

Leave enough margin: When selecting a refrigerated dryer, you should leave enough margin based on the maximum flow rate, maximum inlet temperature, maximum inlet pressure and minimum ambient temperature of the compressed air system. It is better to choose a slightly larger model of dryer than to choose equipment with barely sufficient processing capacity. Too small selection will cause the equipment to be overloaded for a long time and easily freeze.

Consider dew point requirements: Select a suitable dryer according to the actual production requirements for compressed air dew point. For applications with higher dew point requirements, you may need to choose a dryer model with better performance.

Add pretreatment equipment

Install an aftercooler: For systems with high compressor outlet temperature, it is strongly recommended to install an efficient aftercooler (or intercooler) in front of the refrigerated dryer to reduce the compressed air temperature to a lower level, greatly reducing the heat load of the refrigerated dryer, thereby effectively reducing the risk of freezing.

Improve filter configuration: Multi-stage precision filters, including large particle filters, oil-water separators and precision filters, should be configured in front of the refrigerated dryer to remove solid particles, liquid water and oil mist in the compressed air to the maximum extent and protect the internal heat exchanger of the dryer.

Optimize pipeline design

Shorten pipeline length: Try to shorten the pipeline length from the compressor to the refrigerated dryer to reduce pressure loss and heat loss.

Avoid dead corners and low points: In pipeline design, dead corners and low points should be avoided as much as possible to prevent condensate accumulation. For unavoidable low points, a drain valve should be set.

Reasonable selection of pipe diameter: Ensure that the pipe diameter is large enough to meet the flow requirements and minimize pressure loss. Too small a pipe diameter will cause the air flow velocity to be too fast and increase friction resistance, which may cause uneven local temperature increase or decrease.

Install bypass pipeline: Set up a bypass pipeline next to the refrigerated dryer so that it can switch to bypass mode when the equipment is maintained or fails to avoid production stagnation. At the same time, in bypass mode, the condensed water inside the dryer can be completely discharged for deicing and maintenance.

Consider frequency conversion technology

Frequency conversion refrigerated dryer: Traditional refrigerated dryers usually use fixed-frequency compressors, which have low energy efficiency when the load fluctuates. The frequency conversion refrigerated dryer can automatically adjust the refrigeration capacity according to the actual processing capacity, keep the outlet dew point stable, avoid over-refrigeration, and thus reduce the risk of icing. Frequency conversion technology can not only save energy, but also effectively cope with load fluctuations and improve the adaptability of the equipment.

Use advanced anti-icing technology

With the development of science and technology, some advanced anti-icing technologies have been applied to refrigerated dryers, which can more effectively prevent and solve the icing problem.

Hot gas bypass valve control technology

Principle: Hot gas bypass valve is a common anti-icing technology. It directly introduces the high-temperature and high-pressure gas (hot gas) of part of the refrigeration system into the evaporator inlet and mixes it with the low-temperature and low-pressure refrigerant. This can increase the refrigerant temperature in the evaporator, thereby avoiding icing caused by the evaporator surface temperature being too low.

Advantages: The hot gas bypass valve control technology responds quickly and can adjust the evaporator temperature in time when the load fluctuates, effectively preventing ice. At the same time, it can also stabilize the outlet dew point to a certain extent and improve the adaptability of the dryer.

Application: Most mid-to-high-end refrigerated dryers are equipped with hot gas bypass valves. When choosing equipment, you can focus on whether this function is available.

Microcomputer intelligent controller

Principle: Modern refrigerated dryers are generally equipped with microcomputer intelligent controllers. These controllers can monitor multiple operating parameters in real time, such as inlet temperature, outlet dew point, refrigeration system pressure, ambient temperature, etc. Through the built-in algorithm, the controller can accurately adjust the start and stop of the refrigeration compressor, the opening of the hot gas bypass valve, and the operating frequency of the automatic drain valve, so as to optimize the operating status and prevent ice.

Advantages: The intelligent controller has a high level of automation and intelligence, can realize self-diagnosis and fault alarm, greatly reduces the need for manual intervention, and improves the reliability of the equipment. Through precise control, over-refrigeration can be avoided and ice can be effectively prevented.

Function: Some advanced intelligent controllers also have functions such as data recording, remote monitoring, fault diagnosis and energy-saving optimization, which facilitates the management and maintenance of equipment.

Frequency conversion control technology (mentioned above, here we emphasize its anti-icing effect)

Principle and anti-icing effect: The frequency conversion refrigeration dryer changes the cooling capacity by adjusting the speed of the refrigeration compressor. When the compressed air flow is small or the inlet temperature is low, the compressor speed decreases and the cooling capacity decreases accordingly, thereby avoiding the evaporator temperature from being too low and freezing. Conversely, when the load increases, the compressor speed increases to provide sufficient cooling capacity.

Advantages: Frequency conversion technology can not only save energy, but its most significant anti-icing advantage is that it can dynamically adjust the cooling capacity according to the actual load, avoiding the over-cooling and icing problems that may occur in traditional fixed-frequency machines at low loads. It enables the equipment to maintain optimal operating conditions under various working conditions.

Composite Drying Technology (Adsorption + Freezing)

Principle: For application scenarios with extremely high dew point requirements (such as pressure dew point below 0℃, even reaching -40℃ or lower), a single refrigerated dryer may not meet the requirements, and the refrigerated dryer is more likely to freeze when achieving extremely low dew points. At this time, you can consider using a composite dryer, that is, using a refrigerated dryer and an adsorption dryer in series. The refrigerated dryer is responsible for removing most of the water vapor and reducing the dew point to a lower level (such as 2-10℃), and then the adsorption dryer further dehumidifies deeply.

Anti-freezing effect: This combination can effectively avoid the icing problem of the refrigerated dryer when pursuing an extremely low dew point. The refrigerated dryer only needs to reduce the dew point to a relatively easy-to-achieve level, avoiding freezing due to its internal temperature being too low. At the same time, the adsorption dryer is not affected by low-temperature freezing.

Applicable scenarios: Suitable for industries with extremely high requirements for compressed air quality, such as precision electronics, medical, food, spraying, etc.

How to choose a suitable refrigerated dryer?

Choosing a suitable refrigerated dryer is the first and most critical step to prevent icing problems. The following are the key factors to consider when choosing:

Clarify the compressed air parameters

Processing flow: This is the most core parameter for selecting a dryer. The processing capacity of the dryer must be determined based on the maximum flow of the compressed air system. It is usually expressed in Nm³/min (standard cubic meters/minute) or m³/h (cubic meters/hour). When calculating the flow, future expansion needs should be considered and a 10%-20% margin should be left.

Inlet temperature: Determine the maximum air temperature from the compressor outlet to the dryer inlet. If the temperature is high (such as over 45°C), additional cooling measures or a high-temperature resistant dryer should be considered.

Inlet pressure: Understand the working pressure of the system. The processing capacity of the refrigerated dryer is usually calculated based on the standard pressure (such as 7 bar). If the actual working pressure is significantly different from the standard pressure, it needs to be corrected.

Outlet dew point requirement: Determine the required pressure dew point based on the actual production process requirements for the dryness of the compressed air. The dew point of common industrial applications is usually between 2℃ and 10℃. For precision industries, a lower dew point may be required.

Consider environmental conditions

Ambient temperature: Understand the highest and lowest ambient temperatures at the equipment installation site. The ambient temperature will affect the heat dissipation efficiency of the condenser and the overall performance of the equipment, especially in high or low temperature environments, and a more adaptable model needs to be selected.

Installation space: Consider the size and weight of the equipment to ensure sufficient installation space and good ventilation conditions.

Power supply conditions: Confirm that the power supply voltage, frequency and power of the equipment are consistent with the on-site power supply conditions.

Inspect equipment performance and characteristics

Refrigeration system:

Refrigeration compressor: Pay attention to the brand, type (such as fully enclosed, semi-enclosed) and energy efficiency rating of the refrigeration compressor.

Condenser: Understand the heat dissipation area and material of the condenser. A good condenser can provide more efficient heat dissipation.

Evaporator: Investigate the design of the evaporator, such as plate-fin type, shell and tube type, etc. A good evaporator design can improve heat exchange efficiency and reduce the risk of icing.

Refrigerant: Understand the type of refrigerant used and whether it meets environmental protection requirements (such as R134a, R404a, etc.).

Control system:

Intelligent control: Whether it is equipped with a microcomputer intelligent controller with functions such as fault diagnosis, dew point display, and parameter adjustment.

Anti-icing function: Whether it has anti-icing functions such as hot gas bypass valve and frequency conversion control.

Drainage system:

Automatic drainer: Understand the type and reliability of the automatic drainer and whether it is easy to maintain.

Drainage capacity: Ensure that the drainage system can drain condensed water in a timely and effective manner.

Energy efficiency ratio (EER): Choosing equipment with a high energy efficiency ratio can reduce operating costs.

Noise level: Consider whether the noise level of the equipment meets the requirements of the site.

Pay attention to brand and service

Brand reputation: Choose well-known brands and manufacturers with good market reputation. These brands usually have mature technology, strict quality control and perfect after-sales service.

After-sales service: Understand the after-sales service content provided by the supplier, including warranty period, repair response time, spare parts supply, technical support, etc. Perfect after-sales service can ensure that the equipment is solved promptly and effectively when problems occur.

Installation and commissioning: Confirm whether the supplier provides professional installation and commissioning services to ensure that the equipment can be installed correctly and operate efficiently.

Training: Whether the supplier provides operation and maintenance training to help users better master the use and maintenance of the equipment.

Economic evaluation

Initial investment cost: the cost of purchasing equipment.

Operating cost: including electricity, maintenance, spare parts, etc. Choosing equipment with high energy efficiency and low failure rate can reduce long-term operating costs.

Maintenance cost: Equipment that is easy to maintain can save manpower and time costs.

By comprehensively considering the above factors, enterprises can choose the most suitable refrigerated dryer according to their actual needs, so as to minimize the occurrence of icing problems and ensure the stability and reliability of the compressed air system.

Conclusion

Icing of refrigerated dryers is a common challenge in the operation of compressed air systems, but it is not unsolvable. By deeply understanding its causes and adopting the three major response strategies of “optimizing operating parameters and strengthening daily maintenance”, “improving equipment configuration and system design” and “adopting advanced anti-icing technology”, enterprises can effectively prevent and solve the icing problem, ensure the quality of compressed air, and thus ensure the smooth progress of production.

At the same time, fully considering various factors in the equipment selection stage and choosing a refrigerated dryer with excellent performance, reasonable configuration and perfect service is the key to avoiding the risk of icing and achieving long-term stable operation. Investing time and resources in equipment maintenance and management can not only extend the service life of the equipment, but also provide a solid guarantee for the production efficiency and product quality of the enterprise. Let dry and clean compressed air become a powerful driving force for industrial development.