Air compressors are extremely proficient at compressing anything in the air they are intaking. With that air that is taken in, moisture is going to be present. The amount of moisture will all depend on where you are located geographically and the ambient conditions in the area. Here in Ohio, we experience all 4 seasons so the moisture content is higher in the air during the summer months, rather than the winter months. When this air is saturated with water vapor and the conditions are right, the air reaches a point it cannot hold any additional water vapor. This point is known as the dew point of the air and water vapor will begin to condense to form droplets.
When ambient air is compressed, heat is generated and the air increases in temperature. In most industrial compressed air systems, the air is then processed to an aftercooler, and that is where condensation begins to form. To remove the condensation, the air then goes into a separator which traps the liquid water. The air leaving the aftercooler is typically saturated at the temperature of the discharge, and any additional cooling that occurs as the air is transferred will cause more liquid to condense out of the air. To address this moisture, compressed air dryers are used.
It is critical to the quality of the system and components downstream that actions are taken to prevent this condensation in the air. Condensation is generally detrimental to any point of use application and or the piping that conveys the air. Rust and/or corrosion can occur anywhere in the piping, leading to scale and contamination of the compressed air and processes. When trying to dry products off using compressed air or using the air to atomize a liquid such as paint, adding in these contaminants and moisture will cost production losses.
There are several options when it comes to the type of dryer that one may consider installing on their compressed air supply side.
• Refrigerant Dryer – the most commonly used type, the air is cooled in an air-to-refrigerant heat exchanger. • Regenerative-Desiccant Type – use a porous desiccant that adsorbs (adsorb means the moisture adheres to the desiccant, the desiccant does not change, and the moisture can then be driven off during a regeneration process). • Deliquescent Type – use a hygroscopic desiccant medium that absorbs (as opposed to adsorbs) moisture. The desiccant is dissolved into the liquid that is drawn out. Desiccant is used up and needs to be replaced periodically. • Heat of Compression Type – are regenerative desiccant dryers that use the heat generated during compression to accomplish the desiccant regeneration. • Membrane Type– use special membranes that allow the water vapor to pass through faster than the dry air, reducing the amount of water vapor in the air stream. The air should not be dried any more than is needed for the most stringent application, to reduce the costs associated with the drying process. A pressure dew point of 35°F to 38°F (1.7°C to 3.3°C) often is adequate for many industrial applications. Lower dew points result in higher operating costs. If you have questions about compressed air systems and dryers or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR, and I or any of our Application Engineers can help you determine the best solution.
If you operate an air compressor, you’re drawing water vapor into your compressed air system. Factors like climate control (or lack thereof,) and humidity will dictate how much. If (or more to the point, when) it condenses, it becomes an issue that must be addressed. There are several types of dryer systems to choose from, usually when you buy your compressor…we’ve covered those in a number of blogs. Some of these can leave a little more water vapor than others, but remain popular and effective, when considering the cost, and cost of operation, of the different types.
So, how do you handle the condensate that the dryer doesn’t remove?
Receivers, or storage tanks (like EXAIR Model 9500-60, shown to the right,) are commonly used for several reasons:
By providing an intermediate storage of compressed air close to the point of use, fluctuations across the system won’t adversely affect an application that needs a constant flow and pressure.
This also can keep the air compressor from cycling rapidly, which leads to wear & tear, and additional maintenance headaches.
When fitted with a condensate drain (more on those in a minute,) they can serve as a wet receiver. Condensate collects in the bottom and is manually, or automatically emptied.
Condensate drains, while popularly installed on receivers, are oftentimes found throughout larger systems where the vapor is prone to condense (intercoolers, aftercoolers, filters and dryers) and where the condensation can be particularly problematic (drip legs or adjacent to points of use.) There are a couple of options to choose from, each with their own pros & cons:
Manual drains are self explanatory: they’re ball valves; cycled periodically by operators. Pros: cheap & simple. Cons: easy to blow down too often or for too long, which wastes compressed air. It’s also just as easy to blow down not often enough, or not long enough, which doesn’t solve the condensate problem.
Timer drains are self explanatory too: they cycle when the timer tells them to. Pros: still fairly cheap, and no attention is required. Cons: they’re going to open periodically (per the timer setting) whether there’s condensate or not.
Demand, or “zero loss” drains collect condensate until their reservoir is full, then they discharge the water. Pros: “zero loss” means just that…they only actuate when condensate is present, and they stop before any compressed air gets out. Cons: higher purchase price, more moving parts equals potential maintenance concerns.
The “last line of defense” (literally) is point-of-use condensate removal. This is done with products like EXAIR Automatic Drain Filter Separators. They’re installed close to compressed air operated devices & products, oftentimes just upstream of the pressure regulator and/or flow controls…the particulate filter protects against debris in these devices, and the centrifugal element “spins” any last remaining moisture from the compressed air flow before it gets used.
Efficient and safe use of your compressed air includes maintaining the quality of your compressed air. If you’d like to find out more about how EXAIR Corporation can help you get the most out of your compressed air system, give me a call.
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Air… We all breathe it, we live in it, we even compress it to use it as a utility. What is it though? Well, read through the next to learn some valuable points that aren’t easy to see with your eyes, just like air molecules.
Air is mostly a gas.
Comprised of roughly 78% Nitrogen and 21% Oxygen. Air also contains a lot of other gases in minute amounts. Those gases include carbon dioxide, neon, and hydrogen.
Air is more than just gas.
While the vast majority is gas, air also holds lots of microscopic particulate.
These range from pollen, soot, dust, salt, and debris.
All of these items that are not Nitrogen or Oxygen contribute to pollution.
Not all the Carbon Dioxide in the air is bad.
Carbon Dioxide as mentioned above is what humans and most animals exhale when they breathe. This gas is taken in by plants and vegetation to convert their off gas which is oxygen.
Think back to elementary school now. Remember photosynthesis?
If you don’t remember that, maybe you remember Billy Madison, “Chlorophyll, more like Bore-a-fil.”
Carbon dioxide is however one of the leading causes of global warming.
Air holds water.
That’s right, high quality H2O gets suspended within the air molecules causing humidity. This humidity ultimately reaches a point where the air can simply not hold anymore and it starts to rain. The lack of humidity in the air leads to static, while lots of moisture in the air when it gets compressed causes moisture in compressed air systems.
Air changes relative to altitude.
Air all pushes down on the Earth’s surface. This is known as atmospheric pressure.
The closer you are to sea level the higher the level of pressure because the air molecules are more densely placed.
The higher you are from sea level the lower the density of air molecules. This causes the pressure to be less. This is also why people say the air is getting a little thin.
Hopefully this helps to better explain what air is and give some insight into the gas that is being compressed by an air compressor and then turned into a working utility within a production environment. If you would like to discuss how any of these items effects the compressed air quality within a facility please reach out to any Application Engineer at EXAIR.
We’ve seen in recent blogs that Compressed Air Dryers are an important part of a compressed air system, to remove water and moisture to prevent condensation further downstream in the system. Moisture laden compressed air can cause issues such as increased wear of moving parts due to lubrication removal, formation of rust in piping and equipment, quality defects in painting processes, and frozen pipes in colder climates. The three main types of dryers are – Refrigerant, Desiccant, and Membrane. For this blog, we will review the basics of the Refrigerant type of dryer.
All atmospheric air that a compressed air system takes in contains water vapor, which is naturally present in the air. At 75°F and 75% relative humidity, 20 gallons of water will enter a typical 25 hp compressor in a 24 hour period of operation. When the the air is compressed, the water becomes concentrated and because the air is heated due to the compression, the water remains in vapor form. Warmer air is able to hold more water vapor, and generally an increase in temperature of 20°F results in a doubling of amount of moisture the air can hold. The problem is that further downstream in the system, the air cools, and the vapor begins to condense into water droplets. To avoid this issue, a dryer is used.
Refrigerant Type dryers cool the air to remove the condensed moisture and then the air is reheated and discharged. When the air leaves the compressor aftercooler and moisture separator (which removes the initial condensed moisture) the air is typically saturated, meaning it cannot hold anymore water vapor. Any further cooling of the air will cause the moisture to condense and drop out. The Refrigerant drying process is to cool the air to 35-40°F and then remove the condensed moisture. The air is then reheated via an air to air heat exchanger (which utilizes the heat of the incoming compressed air) and then discharged. The dewpoint of the air is 35-40°F which is sufficient for most general industrial plant air applications. As long as the compressed air stays above the 35-40°F temperature, no further condensation will occur.
The typical advantages of Refrigerated Dryers are-
– Low initial capital cost
– Relatively low operating cost
– Low maintenance costs
If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.