How Operations with Heated Regenerative Dryer Systems Can Save 4 Times (or More) on Energy Costs

When it comes to improving compressed air efficiency, compressed air drying systems are an often overlooked and underutilized area of cost-saving opportunity.

Does your plant need dry compressed air or a relative -40°F pressure dew point for reliable operation? If so, you most likely operate or have considered using heated regenerative dryers.

Compared to heatless regenerative dryers, heated regenerative dryers (such as a blower purge or internally heated dryers) can offer significant energy savings. Heatless dryers have one drawback in that they typically purge more than 15% of the compressed air consumed in the regeneration process. Heated dryers, however, can eliminate or greatly reduce the amount of compressed air that’s purged, improving overall system efficiency.

Add Chilled Water Pre-Coolers For More Cost Savings

Adding a chilled water pre-cooler to the system can help plant operators achieve even greater efficiencies and cost savings by lowering the pressure dew point of the compressed air before it reaches the heated regenerative dryer.

Here’s how it works: For every 20°F reduction in compressed air temperature, the amount of water in the air reduces by approximately 50%. For example, if compressed air temperature can be reduced from 100°F to 60°F, the water vapor in compressed air will be reduced by 75%. This means that a heated regenerative air dryer can be at least 4 times more efficient when used in conjunction with a chilled water pre-cooler.

This concept has been proven at numerous industrial facilities around the country. All it takes is introducing a small amount of chilled water to achieve these savings while improving system reliability at the same time.

Schematic of a Compressed Air System with a Heated Regenerated Dryer and Chilled Water Pre-Cooler:

 

In the above example of a heated regenerated dryer with a chilled water pre-cooler system, the average compressed air demand is 1500 SCFM, and the average chilled water consumption for this system is about 13 GPM with an average energy cost of 13 tons (156,000 BTU/Hour).

Using a rate of $.07/KWH and assuming 24/7 operation, the total energy cost of adding a chilled water pre-cooler is roughly $5,580 per year. This is actually a conservative estimate because much of the year, inlet air temperature from the compressors will be under 100°F.

However, this expense can lead to significant savings by reducing the overall cost of compressed air drying by up to four times – or nearly $20,000 per year. It is important to note, however, that in order to achieve this level of cost savings, the heated air dryers must have a reliable energy management system.

In larger systems, energy-saving opportunities are far greater.

Other Benefits of Chilled Water Pre-Coolers

 Using this concept of a chilled water pre-cooler and operating both heated regenerative dryers in parallel provides two additional benefits:

  • Instead of the air dryers shifting tanks and running the blower and heaters 3.5 hours out of each 4-hour regeneration period, the cycle is increased to run 3.5 hours out of a 20 hour regeneration period, for improved efficiency.
  • By operating both dryers at 100% redundancy, dryer cycles were increased to more than 40 hours per tower, resulting in even greater system reliability and a significant reduction in pressure drop.

Fluid Flow has recommended systems of all sizes and complexity for a wide range of industrial facilities.

Industrial operations that want to learn how the application of a heated regenerated dryer and chilled water pre-cooler can help them save on energy costs should work with a knowledgeable compressed air consultant. The experts at Fluid Flow have extensive experience working with plant managers, maintenance, production, project and planning engineers and can take a data-driven approach to provide you with a complete evaluation with long-term tailored solutions to address your unique needs.

 

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