Once compressed air has cooled after being produced, water will condense from it. Lubricated air compressors have oil in the discharged air. This oil has been elevated to very high temperatures causing it to to break down into acidic by-products. The combination of water and acidic hydrocarbons from the oil can be corrosive, damaging components of the equipment using the compressed air. to dry and filter or ust filter compressed air is an important decision.
Other than for the most insensitive compressed air uses, compressed air filtration is money extremely well invested. However to be effective in guarding equipment from condensate (water) damage, point of use filters located at every component using compressed air is needed. Undried compressed air distribution systems are filled with air at it saturation temperature. As further cooling of the air occurs as it gets further from the hot air compressor, moisture keeps condensing. When there are a number of users scatter through the distribution system, the cost of the many coalescing filter rise rapidly. The installation of a central dryer is more economical and does a much more effective means of removing moisture.
Water cooled aftercoolers can and do maintain relative dry systems. Water is generally much cooler than the surrounding air. A water cooled aftercooler placed near the compressor will cool the air to within 10 or 15 Deg F. of the cooling water. On a warm summer day, 50 deg F. water will result in a pressure dew point between 60 and 65 Deg F. In most non-air conditioned plants little are no water will be produced. However in the winter in colder climates, piping located near poor sealing or non-insulated windows, outside walls, and roofs will result in the piping cooling below 60 Deg F. and result in large amounts of water in the compressed air. The cost to buy water cooled aftercoolers is relatively low however the operating costs are very high. The large amounts of well or city water is expensive. In most municipalities, you also pay sewage cost for the slightly warmed water going down the drain.
A compressed air dryer is a better and less costly. there are three types available, refrigerated, deliquescent, regenerative.
Refrigerated
The most widely used dryer is the refrigerated compressed dryer. These units provide for pressure dew points between 35 to 50 Deg F. since most environments are warmer than this the air remain dry in the pipe. These units s a refrigeration system to cool the compressed air to just above freezing, separating the water condensed and draining it. this eliminates the corrosion and fouling problems in most applications. these are the most popular compressed air dryer offering good performance at a reasonable price.
Regenerative
The regenerative dryer produce dryer air with pressure dew points typically from -40 to -100 deg F. They are used when the compressed air piping will be below freezing and in certain processes which require low water vapor pressure. The chemical, oil, food, and metal processing industries use these dryers. The are also used in plants that absolutely cannot have any water in the compressed air such as circuit board manufacturing and powder coating. Small point of use regenerative dryers are used for bag houses. These dryers are are more expensive to purchase and use more energy. They use part of the compressed air flow to dry the regenerating bed and can result in the need for larger compressors.
Deliquescent
The deliquescent dryer is little used since the late 1960’s and has been supplanted in most application by the refrigerated dryer. The deliquescent dryer passes the compressed air though a salt bed which absorbs the moisture. As the moisture is absorbed some the salt is dissolved in the water and during periodic draining is lost to the drain. The consumption of this salt is operating expense. In addition, the mixture of salt and water forms a brine that is very corrosive. Even with stainless steel drain vavles and piping, maintenance is high. The dryer’s exit dew point is dependt on the incoming air dew poin (generally 20 to 30 Deg F. below the inlet air dew point). The other types pf dryers maintain a much more constant dew point. When used with a refrigerated dryer dew points below freezing are possible.
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