When cold weather hits, it can cause havoc with outdoor compressed air lines if the dew point of the air not adequate. Moisture will form if pipes are exposed to cold temperatures, and if conditions are below freezing ice will form and cause line blockages, restricting the compressed air flow and causing low pressure.
Often a plant with outdoor lines will use desiccant dryers to reduce the compressed air dew point to -40° F or lower. This removes all but the smallest amount of water vapor, and if the dryer is working correctly, eliminate any troublesome freeze-ups.
But many plants make the mistake of using main desiccant dryers for all their air, rather than just for a small amount of air going outdoors. This can significantly increase compressed air costs. Consider a fixed cycle central desiccant dryer sized at 500 cfm, the size you might use for a 100-hp compressor. This will consume about 75 cfm of continuous compressed air, costing about $13,000 per year if in full time 24 x 7 operation.
An alternative might be to use a refrigerated dryer for all the air that is used in indoor heated areas, something that might cost only about $3,000 per year, about 20% of the cost of a large desiccant dryer. A small desiccant dryer, perhaps 25 cfm in size (this depends on the outdoor usage), could feed the outside piping for a cost of perhaps $650 per year.
Some other energy saving tips for dry air in cold weather:
• Use of cycling refrigerated dryers will save even more power for indoor systems that are not fully loaded or have low moisture loading
• Using dew point controls on desiccant dryers can reduce the purge air requirement and lower operating costs significantly, especially if most of the water vapor has already been removed by the refrigerated dryer
• Desiccant drying may not be needed in summer, many plants have a summer and winter mode for drying outdoor lines
• Sometimes membrane dryers, or single tower desiccant styles, can be used to save operating costs for small outdoor compressed air uses.
• Be sure to use the heat of compression from the compressors to help heat your building. If you have oil free compressors there are heat of compression dryers that can dry air at a fraction of the cost of desiccant style.