Compressed air is always oily Maybe you misunderstood the oil
In industrial applications, there is a volumetric separator. When the mixed gas passes through the separator, the increase in the flow area and the decrease in the flow rate and pressure make the air lose its carrying effect on the entrainment and achieve the purpose of separation. The basic principle is to use a certain volume of space to slow down the velocity of circulation, and achieve the purpose of separating the mixture from the air under the action of gravity, which can also be called slow separation. This principle is applied in the air pressure system, which can play a great auxiliary role in gas-liquid separation.
What is the equipment that removes the most oil and water from compressed air? Many people may think it is a cold dryer or a filter. But the author believes that it is not these equipments, but the gas tanks that everyone thinks is the least technical. If you think about it carefully, I believe most people will agree with this statement. In addition to gas storage and buffering functions, the gas storage tank is also a simple separation tank, using the principle of volumetric slow speed separation to achieve the purpose of separating part of the oil and water in the compressed air. Therefore, in addition to gas storage tanks and buffer tanks, gas storage tanks can also be called separation tanks.
Everyone knows that the main function of the gas storage tank is to store gas and buffer. It does not belong to the equipment for removing oil and water. Why is the gas storage tank the equipment that removes the most oil and water? ! In fact, the gas storage tank is a typical device that uses the principle of volumetric separation to separate part of the oil and water. If it takes 1 minute and a half for the air compressor to fill the air storage tank, then the time spent in the air storage tank when compressed air enters and exits the air storage tank is about 1 and a half minutes in theory. The compressed air stays in the air tank for 1 and a half minutes. In addition to reducing the temperature, the flow rate is very slow. Under the action of gravity, part of the oil and water in the compressed air is separated.
We give the example of a gas storage tank, mainly to facilitate everyone to understand the principle of volumetric separation, it is not the main content of the article. The volumetric separation is more concealed in the air compressor system, but the two critical aspects are the oil separation system and the post-processing system.
Application of volumetric separation in oil separation system
Careful friends may find that when the air compressor with the same displacement has a larger oil barrel configuration, the oil content stability will be much higher, and the oil content will be relatively lower. Why would such phenomenon happen? First of all, the oil and gas barrels are larger, and the speed of the oil and gas mixture will be much slower when the oil and gas mixtures go up. Because of gravity, the oil content will be much less when the oil and gas reaches the oil, which can naturally improve the stability of the oil and reduce the oil content; If the size of the oil is larger, the size of the oil will be relatively larger. With a larger filtering area of the oil, the flow rate of the compressed air will naturally be slower when passing through the oil, and the effect of the oil and gas core separation will naturally be much better; there is another place that everyone easily overlooks: After the compressed air passes through the oil filter material, there is still a small volume inside the oil separator core. When the oil separator is configured larger, the small volume built into the oil separator will be larger, and the speed of the compressed air reaching the minimum pressure valve will be slower. More oil mist sinks to the bottom of the oil. In addition to helping the stability of the oil, this can also reduce the oil content of some compressed air.
To give an example, it may be easier for everyone to understand: some air compressor manufacturers 75HP and 100HP screw air compressors have the same air filter, oil barrel, oil separator and other configurations. There is no doubt that the oil stability of the 75HP air compressor will be higher than that of the 100HP air compressor, the oil content of the compressed air will be lower, and the operating energy efficiency will be higher.
With the increasing number of permanent magnet frequency conversion and two-stage compression air compressors in recent years, everyone knows that if it is an air compressor of the same brand and same power, the permanent magnet frequency conversion and two-stage compression air compressor will be compared with the power frequency air compressor. For the compressor, the displacement is usually larger. Why do many manufacturers choose to increase the filter area by folding the oil separator to solve the problem of small oil filter area caused by the increase in air displacement, but increase the oil separator barrel and the oil separator at the same time? This is because the increase in displacement without changing the oil barrel means that the amount of oil mist will also increase. The foldable oil separator only solves the problem of small filter area, and cannot solve the problem of oil mist increase from the source. Although the folded oil increases the filtering area, it also has the defect that deep separation cannot be performed.
In addition, even if the oil component is changed to a foldable type, the volume inside the oil component does not change. As the displacement increases, the flow rate of the gas discharged will increase, which means that the effect of the oil mist sinking to the bottom of the oil component is greatly reduced. If only changing to foldable oil separator to increase the filtration area, it cannot be solved well. This is the reason why many manufacturers choose to increase the oil separator barrel and oil separator at the same time, and improve the stability of the oil separation system through volumetric slow separation. , Reduce oil content and improve energy efficiency.
In terms of overall probability, the oil content of the external oil will be higher than that of the built-in oil, and the stability will be lower than that of the built-in oil. Most people may think that this is due to the small filter area of the external oil. It is indeed one of the main reasons, but not all of them. For example, the filter area of the foldable external oil is increased, but it can only alleviate the oil content and stability, but cannot completely solve the problem that the oil content of the external oil is higher than the internal oil. The probability that the stability is lower than the built-in oil content is sufficient to show that it is not entirely a problem of the filter area.
The other part of the reason besides the filtering area is:
1. The external oil component itself is equivalent to a small volume. The external oil component has a small volume, and the gap between the shell and the filter element is naturally small. If the gas flow rate is too fast, it will be difficult for the lubricating oil to flow back down. The oil and gas are separated before the filter element. The oil content will be higher, which is part of the reason why the external oil content is slightly higher than the internal oil content;
2. The external oil filter element is very small, and the space inside the filter element is naturally smaller. After the gas passes through the filter material, there is almost no residence time, and the gas will be discharged soon, and the oil mist will settle into the oil return system. This is a big discount, which is part of the reason why the external oil content is slightly higher than the internal oil content.
When the external oil separator is a larger model, in addition to the larger filter area, the space on the outside and inside of the filter element is also enlarged, which greatly improves the stability of the external oil separator and reduces the oil content. In other words, the oil content and stability of the external oil have a certain relationship with the outside and inside volume of the filter element in addition to the filter area factor.
Application of volumetric separation in post-processing system
In the article "Analysis of Post-processing Problems with Oil and Water in Air Compressors" published by the author in January this year, the main core content of the article is to achieve the purpose of improving the effect of post-processing through volumetric slow separation. Whether it is recommended to add 1 to 2 models when selecting a precision filter or oil mist separator, or install a gas tank or oil-water separator at the back, the purpose is the same-to improve the after-treatment system by slowing down Separation and filtration effect.
Let's take a practical case to help everyone understand: some friends encountered a lot of oil content at the gas end, and thought many ways to help users solve it. Finally, the oil content was solved by installing an oil-water separator in front of the gas end. High question. Many people may only know that the installation of an oil-water separator has solved the problem, but they do not know the principle of separation and filtration very well. It is a problem of accidental collision.
This kind of oil-water separator is equipped with an oil separation core in a larger volume. Some people may mistakenly think that the good separation and filtering effect of this oil-water separator is due to the oil separation core inside. This understanding is rather one-sided. The oil separation core does have some effect on separating and filtering the oil mist in the compressed air, but the main credit does not belong to the oil separation core. Imagine that the principle of the filter element inside the multiple precision filters or oil mist separators installed before is almost the same as the principle of the oil separation element. So many precision filters or oil mist separators can’t solve the oil mist problem. How could it be solved immediately by an oil separation core? !
I have already mentioned that this oil-water separator is equipped with an oil separation core in a larger volume. That is to say, the volume of the oil-water separator will be many times larger than the precision filter or the oil mist separator. After the oil-water separator, it is equivalent to adding a miniature air tank, and the compressed air does not flow directly to the gas end, but first passes through this miniature air tank. In this way, the pressure difference of the previous precision filters or oil mist separators will be reduced, and the flow rate will naturally be reduced, and their separation and filtering effect of oil mist will naturally be improved.
Let's discuss the oil-water separator's own separation and filtering effect of oil mist. The volume of this oil-water separator is many times larger than the precision filter or oil mist separator installed in the front. It is equivalent to a miniature air tank. The time required for the compressed air to pass through this oil-water separator is through the precision filter or Many times the oil mist separator is basically equivalent to the passage speed many times slower, and its effect of separating and filtering oil mist will inevitably be greatly improved.
The author is not to promote the effect of the oil-water separator, but to analyze the cases that many people have actually used, so that after the problem is solved, it is clear what the principle is to solve the problem. The pressure difference and flow rate of the compressed air are lowered, and the effect of separating and filtering oil mist will naturally be greatly improved. Only by mastering the principle of volumetric separation, can it be used flexibly in the air compressor system according to the actual situation. Free to play.
The laser cutting air compressor, which has been popular in the past two years, some people mistakenly think that the air compressor, refrigeration dryer, filter, air storage tank, etc. are combined together. It is called an integrated laser cutting air compressor. Cognition is very one-sided. The most critical core technology of the laser cutting air compressor is to solve the problem of oil mist stability, and even consider the problem that the temperature difference is too large, which may cause the lens to easily produce fog. Only when the principles of oil and gas separation, volumetric separation, and post-processing systems are thoroughly studied, and several factors are combined for research and development, can the integrated laser cutting air compressor take a step forward.
Separation is very extensive, volumetric slow speed separation is only a very small part of the field of separation, and this article is only a brief discussion. Those in the industry who wish to communicate in detail can add the author's WeChat or contribute to this journal, and we will discuss together and make progress together.
