Normally one completed compressor unit including the following:
Many factories use refrigerant dryers directly behind the air compressor. First of all, this is not correct. The pressure of the compressed air just coming out is unstable. Besides it contains a lot of moisture and magazines. So you have to install a storage tank in front of dryer. Not only it helps to stabilize the pressure, but it also cools temperature and removes water. Moreover, it will protect our refrigerated compressed air dryer.
Then, behind the storage tank, it should install a pre-filter. It can remove solid particles and impurities from the compressed air. Let the clean air enter the refrigeration dryer.
In addition, we need install a water and oil removal filters in front of desiccant air dryer. Because the adsorbent needs to avoid oil. Otherwise, it will affect the effect and service life of the desiccant beads. Then behind the adsorption dryer you also need to install a dust-removal filter. Because the adsorbent may be powdered over time, it is necessary to remove dust.
Therefore, the correct installation order is as follows: air compressor — storage tank — pre-filter — refrigerated air dryer — moisture / oil-removal filter — adsorption air dryer — dust-removal compressed air filter. Next, introduce the installation of refrigerated and desiccant air dryer separately.
(1) Installation site requirements
① Firstly, avoid exposing the air compressor dryer to direct sunlight. At the same time, not install in a humid and corrosive gas environment.
Otherwise it will lead to corrosion of the dryer heat exchange system pipes. This can cause damage to the equipment.
② Secondly, the ambient temperature should be below 45°C. And the room should have good air circulation.
If the ambient temperature is too high, it will cause the refrigeration compressor exhaust pressure to be too high. Then make the refrigerated air dryer overload. Eventually the machine will stop working.
③ Keep the compressed air dryer at least 800 mm away from around. Otherwise it will cause inconvenient maintenance or poor heat dissipation.
④ Regarding installation: The dryer does not need to be installed using a foundation. It is only necessary to fix on a solid horizontal surface.
(2) Dryer installation piping requirements
① First of all, use flange connections for the compressed air inlet and outlet. So it can facilitate disassembly.
② Next, install a main line pipe filter. Then it can avoid solid impurities and oil mist contamination. Otherwise it will affect the heat exchange performance of the air compressor dryer.
③ Thirdly, the piping diameter can't be smaller than the dryer inlet size. Besides the pipeline length should be short as much as possible. Then it can avoid too much bending to reduce the pressure drop.
④ In order not to affect normal production during maintenance. Consider installing a bypass line.
⑤ Sometimes there will be debris blocking the pipeline. And they will affect the normal operation of the refrigerated air dryer. Therefore, when piping, we must blow the main air line and the bypass.
⑥ There should be on-off valves for cooling water pipeline. Also install pressure gauge and temperature gauge for maintenance.
After installation of compressed air dryer, must check for leakage with soapy water. Otherwise it will waste air supply. Or the pressure may not reach the customer's usage requirements.
(3) Power supply connection of refrigerant air dryer
① Firstly, please connect to the power supply as indicated on the dryer nameplate.
② Secondly, the power supply must be with an earth leakage switch.
③ Thirdly, the voltage should comply with ±5% of the standard voltage.
④ Also, the refrigerated air compressor dryer must be with a grounding wire. Ensure reliable earthing.
⑤ The power supply line must not be barged in the middle. Otherwise, it will cause a voltage drop in the line. Finally, it will affect normal operation of compressed air dryer.
⑥ When setting the earth leakage circuit breaker, please refer to the maximum operating current of dryer.
⑦ Finally, please do not share the same protector with other machines.
If the voltage falls below 5% for a long time, it will damage the refrigerant compressor.
The refrigerant air dryer may cause personal injury if there is no earth wire.
If the power supply does not have an earth leakage switch, an electric shock may occur.
(1) Installation place
Similar to refrigerated compressed air dryer, desiccant dryer also has requirements for temperature. Don't install the adsorption air dryer in areas where the ambient temperature exceeds 45°C. And it also avoid extremely cold environment. If possible, advise to insulate the dryer's A/B twin towers. Also do not install outdoors.
Please reserve adequate space around the desiccant air compressor dryer. So it's good for later maintenance. And fix the dryer to the foundation with bolts.
(2) Pipe installation
Connect the compressed air lines to the dryer inlet/outlet fittings. And there needs two filters before the adsorption air dryer. Also, to minimize pressure drop, use as few elbow connections as possible.
Frequent air discharge of A/B towers will cause noise. To reduce noise, consider connecting the dryer exhaust pipe to the outside. Besides, it is good for the discharge of condensate.
Likewise, after installing all piping, test for leaks. This ensures that the air compressor air dryer can work without problems.
(3) Compressed air filter installation
In addition to installing 2 filters in front of the desiccant dryer, you also need to install a filter in the back. The front coalescing filters are for water and oil removal. This ensures a long service life for the adsorbent. Also helps to reduce costs.
And the post-filter can help to eliminate the possibility of desiccant dust into the air system.
We know that compressed air dryers contain both refrigerated and adsorption dryers. The former can only reach a dew point of around 3°C. If requires a lower dew point, it only use adsorption air dryer. Depending on the regeneration method, the following types of machines are available. That is, heatless, micro-heat, HRB and HOC desiccant air compressor dryer.
Firstly, here we discuss the working principle of the HOC type regenerative air dryer. Then compare the energy consumption of various dryers with an engineering example. In addition, the discussion will focus on the problems of HOC desiccant dryers. And give solutions in two aspects.
Adsorption air dryer usually uses twin-tower structure. One is for air drying. The other takes action during the regeneration of adsorbent. Currently the common adsorbent materials are activated alumina and molecular sieve.
The former is sensitive to the temperature of the working medium. When the temperature reaches 130°C or more, the water content of the adsorbent is only about 1%. It is almost completely desorbed.
On the other hand, molecular sieves have a higher adsorption capacity. The regeneration process includes following 4 stages. That is, heating - pressure reduction - cold blowing - equal pressure. The A/B towers switch according to the dryer PLC signal.
High temperature compressed air (above 110°C) enters the air compressor dryer. Then flows directly into the regeneration tower. And it will vaporise the moisture in the desiccant beads. Next, they will enter the cooler of the desiccant dryer. Cooling to around 40°C. At this time, the compressed air is in a supersaturated state. Therefore, many liquid water will precipitate.
Then the cooled air enters the drying tower. After reaching the dew point, most air is output to the compressed air pipe. This supplies the workshop and the air-using stations.
Another small part air flows into the regeneration tower via the control valve. They will blow adsorbent. At this stage, air consumption is about 2%. Finally discharge this part of compressed air via a silencer.
Firstly, briefly introduce the regeneration process of different adsorption air dryers. Then make a comparison of their energy consumption.
(1) Heatless air compressor dryer
The regeneration process does not require heating. It uses the regeneration air to purge the adsorbent. The air consumption is 13% of the total air volume.
(2) Micro-heat regenerative dryer
The difference lies in the heating stage. There requires an external heat source. The air consumption of the regeneration process is about 7%.
(3) HRB adsorption air dryer
The compressed air for heating comes from the outside. The air consumption is around 2~3%.
Take a example: make an adsorption dryer (60m³/min) as a basis for comparison. Choose an oil-free screw air compressor. The power of the compressor is 315kW. And air pressure is 0.75MPa. Finally air flow is 51.3m³/min.
The table below shows the energy consumption data for various desiccant dryers.
In summary, the HOC dryer has the lowest total regeneration power consumption. Besides, the unit power consumption is also lowest. The energy efficiency ratio is the highest.
On the contrary, heatless air compressor dryer has lowest energy efficiency ratio. The micro-heat and HRB dryers have the middle of the range.
Optimum regeneration temp. for adsorbents is above 130°C. And the regeneration effect will drop sharply when lower than 100℃。
Therefore the air temperature entering the dryer should not be below 110°C. This makes it impossible to set a pre-filter before air compressor dryer. The air oil content into dryer must be low. So only centrifugal and oil-free screw air compressors can meet this requirement.
How to ensure the dew point?
Firstly, it depends on the type and filling capacity of desiccant beads. Secondly, it depends on whether the regeneration of the adsorbent is complete.
Activated alumina has fast desorption speed So the regeneration process is short. But the adsorption capacity is not as good as molecular sieve. So when require a dew point of -40°C, only fill the activated alumina. However, when the dew point needs to reach -70°C, it must fill a certain amount of molecular sieve.
To ensure the dew point, should follow the below principles:
(1) Air compressors should match compressed air dryers one to one.
Each dryer should match to the corresponding air compressor.So it can avoid hydraulic disconnection due to the many units. Besides, the shorter the connection pipe, the smaller the heat loss.
(2) HOC dryer is not suitable for matching with variable speed air compressor.
Because the air flow of VSD air compressor ranges from 60% to 100%. If air flow is too small, the desiccant heating time becomes longer. So the effect of desiccant regeneration is not satisfactory.
(3) It should insulate the air inlet pipeline of the air compressor dryer.
The higher the air inlet temperature, the more ideal the regeneration effect of desiccant beads. If no insulation treatment, the air temperature will be down in the process of conveying. Besides it may cause scalding accident.
(4) For the compressed air system with big air-load change:
It should choose dew point and time control. When in the peak of air consumption, and the operating conditions are relatively smooth, use the time control mode. Conversely, switch to the dew point control mode. So it can ensure dew point of desiccant compressed air dryer.
(5) When the dryer inlet temp. is likely to be low, advise adding an electrical auxiliary heating system. It allows for the secondary heating for the inlet air.
In summary, the HOC desiccant dryer is suitable for such applications. That is, the air load is large and the load fluctuation is small. The regular time control mode can achieve the good operating effect. Besides the energy saving effect is remarkable.
When the air load fluctuates much, it needs to improve air compressor dryer. Change to a dew point control mode. And add electric auxiliary heater. So it can allow dryer convert automatically to micro-heat dryer when the dew point mode fails.