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Wet or Dry Storage? Distributing Compressed Air Storage

Compressed Air Storage Tank Being manufactured

Simply put, compressed air storage is a necessity for a healthy compressed air system.  Having a compressed air receiver as part of your system reduces the strain on your air compressor. Air receivers provide multiple benefits to your system.

  • Remove liquid moisture formed at the discharge of the compressor;
  • Provide a cooling zone to allow moisture vapor (and oil aerosols) to condense into liquid;
  • Create a volume buffer that reduces compressor cycling on and off;
  • Provide volume for users that are not getting stable air supply or for large, periodic demands that exceed the capacity of the compressor;
  • Reduce compressor run time and save energy.

Compressed Air Receivers give you more control and more wiggle room with your compressed air. Having air that goes into a receiver gives you more air in your system. With air flowing into the air receiver, excess sump blowdowns are reduced, that air is kept in the tank rather than dispelled. This extra compressed air lowers the pressure requirements for your compressor as well.

Compressed air storage is an often-forgotten aspect of building compressed air systems. It can be considered an additional option for your system. In reality, compressed air storage is a necessity, especially if you don’t want to buy a new compressor every few years. Tanks increase the lifespan of your compressed air system

 

Compressed Air Storage: Wet Or Dry

Compressed air can be stored in one of two ways: wet or dry. Wet storage occurs directly after the compression process, while dry storage is after your air dryer. The role your air receiver plays depends on its placement in your system. Wet storage increases the efficiency of your compressed air dryer by removing excess condensation in the tank. Dry Storage reduces the overall load on your compressor by having dry air available for use, even when the compressor is unloading.

Although theoretically possible, you should not run an air compressor without a receiver tank. It is possible, it just won’t have the same lifespan or air quality of a system that has one in place. Our recommendation is to always have at least one compressed air storage tank in place, but the best set up will be with wet and dry storage tanks.

 

Wet Compressed Air Storage

Having compressed air storage in your system should be an expectation, not an additional option. The only options you should consider are where you place the storage in line. The first tank in your compressed air system should be wet storage. The compressed air will exit the compression chamber at a high temperature, and as it cools, the moisture drops out of the air. 

This moisture will drop and collect at the bottom of the compressed air tank, reducing the total amount of moisture that the compressed air dryer has to remove. Removing the moisture before it gets to the dryer reduces the load placed on the equipment. It is then collected and disposed of with a condensate drain. If this moisture sits in the tank, it can destroy it from the inside out.

Extra air in the system gives your compressor opportunities to rest without losing valuable compressed air. This means you get more air for less work than compressors without a receiver tank. The saturated air flows into the tank directly after the compression chamber, where it sits to cool off before continuing downstream. This rest period removes moisture, making it easier for the dryer to remove the remaining condensate.

By having additional compressed air storage, you can avoid Rapid Cycling. Rather than being directly intuned with demand, the compressor runs to fill up the tank completely. The tank is then responsible for fulfilling the system’s demand. The compressor reacts to the fluctuations in the tank, and once it gets low enough, the compressor will kick back on and begin filling the tank again.

 

Potential Problems

These air receivers pose the risk of overloading your air dryer if demand increases. If demand exceeds the dryer’s capacity, it can be easily overloaded. This is the major downside to only having wet storage. When demand calls and air has not had a chance to cool and remove excess condensation in the tank, this moisture is pulled into the dryer. Most likely, the dryer will be sized and rated for the condensate levels after the air has cooled down in the tank. If this occurs, the dryer and your downstream equipment can be overwhelmed, leaving you with no dry compressed air.

Wet Compressed Air Storage is an ideal solution for handling the initial influx of oil carryover and water from freshly compressed air. Eliminating the excess oil and water from the airstream will greatly extend the lifespan of your compressed air dryer. It eases the load on your dryer and prevents oil and water from making it downstream, benefiting your system’s health. 

 

Dry Compressed Air Storage

Unlike wet storage, dry compressed air storage comes after the air dryers and filtration. This way, the air is pre-dried and pre-filtered to reduce peak loads’ effect on the dryer. Opposite of the wet tank, the dry tanks should have little to no water dropping out into the tank. The air is ready for large events or regular demand without this excess moisture. 

Compressed air goes to the tank after it has already passed through the dryer. Thus, you don’t get the benefits of reduced load on your dryers as you would with wet compressed air storage; however, they also cannot overload your dryer during peak demand periods. The moisture has already made it through the dryer and filters by the time it is stored in your dry air tank.

With storage of dry air on hand, your system is prepared for any increase in demand. You won’t need to worry about your dryer being overworked, the air being pulled will be ready for use. Unlike wet storage, dry storage does not reduce the load/unload cycle as effectively. The compressor has to “look” through the pressure differentials of each step between the compressor and the receiver. 

They may not be as good at reducing the load on your air compressor as wet storage, but that is because wet and dry storage provides you with different benefits. Rather than choose one or the other, most experts recommend a combination of wet and dry storage. By using both types of compressed air storage, you don’t have to choose between the benefits to your system.

 

Both Wet And Dry Storage

Each type of compressed air storage has its advantages and disadvantages. The recommended distribution is ⅓ wet and ⅔ dry storage. This allows you to capitalize on the load reduction benefits of wet storage and the demand benefits of dry storage. Wet storage is directly after the air compressor, allowing the air to have a period to rest before being sent to the dryers and filtration. Lower velocities in the tank cool the air down and let excess moisture drop out of the air. 

Removal of this moisture makes your air dryer’s job easier. Not only does it reduce the dryer’s work, but it also lets the compressor “see” into the receiver. This allows the compressor to adjust production to keep the receiver full and not overwhelm the dryer. By looking into the compressed air tank, the compressor reduces cycling frequency. It gives the compressor more time to rest in between cycles. Without a wet tank, the compressor load changes from 0 to 100% every time the compressor loads/unloads. The installed wet tank smooths this process so the flow is not entirely stopped when the compressor is unloaded. 

So, Wet Storage improves the process near the compressor, and Dry Storage improves the process near the demand point. Dry air storage cannot be “seen” into by the compressor, so they are not as beneficial to reducing the load of your compressor, but they cover you for any sudden spikes in demand. That means the best setup for your compressed air system is having both wet and dry storage in place.

 

The Ideal System Layout

Reduce the load on your compressor and dryer with wet storage and be prepared for any increase in demand with dry storage. To correctly distributing your compressed air storage, ⅓ of your total volume should be dedicated to wet storage, and ⅔ should be devoted to dry storage. 

 

Figure 1: Ideal System Layout

Reference Figure 1 for an idea on how an ideal compressed air system is laid out. Whether you have one compressor or two in your system, this diagram will give you an understanding of how you want to lay out your system.

 

Additional Considerations

When you are selecting compressed air tanks for your operation, you want between 5-10 gallons of storage per CFM. So if your system out puts 20 CFM, you would want 100-200 gallons of storage. Applying this to wet and dry storage, you would want around 60 gallons of storage in your wet tank and 120 gallons in your dry tank. This allows you to have enough storage to capitalize on the benefits of wet and dry storage.

If you plan to include wet storage in your compressed air operation, make sure you have a condensate drain for the tank. Condensate being dropped out is beneficial to your dryers, but moisture staying in your tank is not beneficial to anything. By forgetting to include a drain valve, you will minimize the effectiveness of your air receiver. Moisture will deteriorate the tank from the inside out.

Having storage in place is a great benefit to your compressed air system, just make sure you have enough space to implement it into your system. The larger the quantity of air being stored by your tank, the bigger it is. Large tanks need a considerable amount of space to be implemented, but it is necessary for high-quality compressed air.

Another thing to consider before purchasing a compressed air tank is the shipping costs required to get the tank from our warehouses to you. Shipping tanks is costly: they are large and hollow. Taking up a large amount of space while not weighing the same as other shipments of that size makes them more expensive per pound. Not only do they take up the physical space of the tank, but also the space above it. Tanks are non-stackable shipping items to maintain their quality.

 

Getting Your Own Compressed Air Tank

Getting a compressed air tank can be costly. Upfront costs might be more than you initially thought, but the savings from a smoother operation will pay for itself in time. By reducing the work your other equipment has to do, you will spend less on daily operations. Compressed air tanks are an investment in the health and lifespan of your compressed air system.

Warthog carries the best tanks from the best brands, get on for your operation here.

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