Why there is still water after using a refrigerated air dryer for compressor?

Writer： admin Time：2022-09-22 00:00:00 Browse：676℃

Refrigerated dryer is a compressed air treatment equipment. The function is to remove moisture and impurities for air compressor. So keep the compressed air dry and clean. Refrigerant air dryer can remove more than 90% of the moisture and impurity particles. However, sometimes even if we install a refrigerated dryer, there is still water in the compressed air. Why does this happen?

How about the water removal effect of refrigerated air dryer?

The refrigeration dryer uses refrigerant to exchange heat with compressed air. During air compressor dryer working, the refrigerant will absorb heat. So it let moisture in the air condense. Thereby generating liquid water. The key performance indicator of refrigerant dryer is the dew point temperature. The dew point of most refrigerated dryer manufacturers is 2~10℃.

(1) Atmospheric dew point, pressure dew point and condensing temperature

The water vapor in the air reaches saturation. It begins to condense to form liquid water. At this time, the temperature is called the dew point temperature. In general, if water content is high, the dew point is high. Conversely, the dew point is low.

There is a corresponding relationship between pressure dew point and atmospheric pressure dew point. It has to do with the “compression ratio”. We use the above diagram to represent. Under the same “pressure dew point”: the larger the “compression” ratio, the lower the corresponding atmospheric dew point.

Assume a compressed air pressure dew point of 2℃ at 0.7MPa. At this time, the normal pressure dew point is -23°C. In addition, assume that the pressure is increased to 1.0MPa. Likewise, the pressure dew point is still 2°C. But corresponding atmospheric dew point drops to -28°C.

Relationship between atmospheric dew point and water content:

DewPoint (℃)	Water Content (g/m³)	DewPoint (℃)	Water Content (g/m³)	DewPoint (℃)	Water Content (g/m³)	DewPoint (℃)	Water Content (g/m³)
14	12.07	-5	3.407	-24	0.7678	-43	0.1298
13	11.35	-6	3.169	-25	0.7074	-44	0.1172
12	10.66	-7	2.946	-26	0.6463	-45	0.1055
11	10.01	-8	2.737	-27	0.5922	-46	0.095
10	9.309	-9	2.541	-28	0.5422	-47	0.0854
9	8.819	-10	2.358	-29	0.496	-48	0.0768
8	8.27	-11	2.186	-30	0.4534	-49	0.0689
7	7.5	-12	2.006	-31	0.4141	-50	0.0617
6	7.26	-13	1.876	-32	0.3779	-51.1	0.054
5	6.797	-14	1.736	-33	0.3445	-53.9	0.04
4	6.36	-15	1.605	-34	0.3138	-56.7	0.029
3	5.947	-16	1.483	-35	0.2856	-59.4	0.021
2	5.559	-17	1.369	-36	0.2597	-62.2	0.014
1	5.192	-18	1.261	-37	0.2359	-65	0.011
0	4.847	-19	1.165	-38	0.2141	-67.8	0.008
-1	4.523	-20	1.074	-39	0.194	-70.6	0.005
-2	4.217	-21	0.9884	-40	0.1757	-73.3	0.003
-3	3.93	-22	0.9093	-41	0.159
-4	3.66	-23	0.8359	-42	0.1438

From the table above, we can see the water removal effect of the refrigerant air dryer. If dew point is 10℃ at 0.7Mpa, the atmospheric dew point is -16℃. So the water content in compressed air is 1.483g/m³. In addition, if 3℃ dew point at same pressure, the atmospheric dew point is about -22℃. So the corresponding water content is 0.9093g/m³.

In short, refrierant air dryer can remove most of the moisture. If your industry has no high requirement for water content, it is completely sufficient. However, if the dew point requirements are high, it also needs to install a desiccant dryer.

(2) Compressed air quality class and applications

First of all, we see the purity classes of compressed air from ISO 8573-1:2010 standard. It grades particulate matter, oil content and water content.

① Solid particle level of compressed air

Class	Maximumnumberofparticlespercubicmeter
	Particlesized/μm
	≤0.10	0.10＜d≤0.5	0.5＜d≤1.0	1.0＜d≤5.0
0	Higherrequirementsthanlevel1establishedbytheequipmentuserormanufacturer
1	notspecified	100	1	0
2	notspecified	100000	1000	10
3	notspecified	notspecified	10000	500
4	notspecified	notspecified	notspecified	1000
5	notspecified	notspecified	notspecified	20000

② Humidity class of compressed air

Class	PressureDewPoint(℃)
0	Higherrequirementsthanlevel1establishedbytherefrigerantdryeruserormanufacturer
1	≤-70
2	≤-40
3	≤-20
4	≤+3
5	≤+7
6	≤+10

③ Oil content class of compressed air

Class	TotalOilContent(liquidoil,suspendedoil,oilvapor)/(mg/m³)
0	Higherrequirementsthanlevel1establishedbytherefrigerateddryeruserormanufacturer
1	≤0.01
2	≤0.1
3	≤1
4	≤5

JB-T 5967-2007 Air medium quality grade for pneumatic components and systems

Compressed Air Quality	Specific Requirements			Content Standard			ApplicationRange
	Particles	Moisture	Oil	Particles (μm)	Moisture (℃,Pressure DewPoint)	Oil (ppm)
Generalair	2	–	2	≤1	microscale	≤0.1	Generalfactoryair-use, suchaspurging, miningmachinery
Oilfreeair	1	–	1	≤0.01	microscale	≤0.01	Airagitation,granular productconveying
Oil-freeand odorlessair	1	–	1	≤0.003	microscale	≤0.003	Brewingandcanning
Generaldryair	2	4	2	≤1	3～10	≤0.1	Pneumaticmechanical instruments , control valves
Dryoil-freeair	1	4	1	≤0.01	3～10	≤0.01	Printingandpackaging, powderproductconveying
Dry,oil-freeand odorlessair	1	4	1	≤0.01	3～10	≤0.003	Food, beverage processing, dairyproduction...
Extremelydry, oil-freeair	1	2	1	≤0.01	–20～-40	≤0.01	Precisionpneumaticequipment, electronic components processing
Extremelydry, oil-free, odorlessair	1	2	1	≤0.01	–20～-40	≤0.003	Cleanrooms,food&beverage processing, dairyproduction…
Deepdry oil-freeair	1	1	1	≤0.01	–40～-70	≤0.01	High-precisioncontrolinstruments, fine-sealed gas instruments
Deepdry,oil-free andodorlessair	1	1	1	≤0.01	–40～-70	≤0.003	Precisionelectronic components processing, food and drug processing

From the above table, we can notice that the general industry does not have high requirements for dew point. They just ask for general dry compressed air. That is, the dew point of 3~10℃ can meet the production demand. There are many such industries, such as general printing and packaging industry, general pneumatic instruments, etc. So only needs refrigerated air dryer to meet the water removal requirements. There are even some industries that do not need a refrigerant dryer to remove water.

Of course, lots of industries require very dry compressed air. The water content must be much low. For example, the food industry requires at least -20 ° C dew point. Besides, some food industry requires -40 ° C dew point. For example, the pharmaceutical industry also requires at least -40 ° C. In addition, some industries even require -70 ° C dew point, such as the aerospace industry. So it must also install the adsorption air dryer.

Why there is still water after installing a refrigerant dryer for my air compressor? (1) Incorrect selection of air compressor dryer

We know that the correct selection should include several factors. That is, air capacity, intake air temperature, inlet pressure, ambient temperature and dew point. Especially the two temperatures have a great influence. For example, the temperature in many places is very high in summer. The air moisture content is also high. At this time, the working load of refrigerated dryer will be relatively large. If the selection is wrong, it will greatly affect the water removal effect. At this time, we need to choose a high temperature refrigerant dryer. Moreover, it usually choose the bigger model air compressor dryer.

Likewise, we sometimes choose the wrong dryer dew point. Refrigeration dryer can remove most of the moisture. But the air compressor system will still contain moisture. If your industry has strict requirement, then refrigerated air dryer is not enough. We may have made a mistake in our assessment when purchasing.

In addition, sometimes we do not take into account the actual air consumption. We only purchase refrigerant dryer according to the average air consumption. But sometimes the air consumption will be large in an instant. This may cause the dryer to fail to handle it. Eventually it will result in water in the compressed air.

(2) Bad refrigerant air dryer quality

① Some manufacturers regard the “evaporation temperature” as the dew point temperature of the dryer

Actually this is incorrect. Firstly, there is a temperature difference during heat exchange in the evaporator. And the efficiency of the air-water separator is less than 100%. So the actual outlet dew point will be higher than the evaporation temperature. In addition, the dew point of many manufacturers’ dryers is not necessarily true. Their refrigerated dryer often does not reach the dew point of 2 ~ 10 ° C. It is actually much larger than this. Therefore, this will seriously affect water removal efficiency.

② Use low quality spare parts and not strict quality control

Our refrigerant dryers have a reliable water removal effect. This is because we use high quality accessories. For example, we use the famous Panasonic, Copeland and Danfoss compressors. Besides, we do multiple leakage tests. So it can ensure the dryer quality and water removal effect. But many manufacturers use cheap parts. The cooling efficiency does not meet the requirements. Moreover, there are often leaks during the operation of the refrigerated dryer.

In addition, our refrigerant dryer has heat exchanger. Some people call it “heat regenerator”. It can heat up the compressed air after cooling. So it can prevents the outlet temperature from being too low. Also can avoid water in the exit tube wall of the dryer. But some manufacturers’ dryers do not have this part.

(3) Poor maintenance for compressed air system

① The refrigerated air dryer is faulty.

At this time, there is definitely no way to remove the water. For example, the common faults are as follows: refrigerant leakage, high temperature shutdown, etc.

② The drainer doesn’t exhaust water in time

If the drainer has blockage or damage, it will not drain properly. Then the water removal function of refrigerant dryer will fail. The moisture in the compressed air will flow to back pipeline.

③ The air receiver tank also doesn’t drain in time

The air receiver itself has the function of accumulating water. If you forget to drain it, it will also cause water in the air.

How to remove the water effectively in the compressed air

① Firstly, carefully check whether choose air compressor dryer correctly. For example, check if the air capacity can meet the actual requirements. And check if the intake air temperature and ambient temperature are higher than the rated value. If notice that the selection is incorrect, needs to replace refrigerant air dryer. And if the dew point is to be lower than 0°C, it must also install an adsorption air dryer. Of course, we need to select a good refrigerated air dryer manufacturer.

② Secondly, we must do daily maintenance on the air compressor system. Check drainer operation frequently. Once there is a blockage, clean it in time. If the blockage is serious, replace the drainer immediately. Likewise, regularly open the drain valve under the air tank to exhaust water. Or install an automatic drain.

③ Thirdly, install a cyclone air-water separator before refrigerated dryer. Its removal efficiency of liquid water can reach 99%. In addition, use the compressed air filters with auto drainer.