A chemical plant spends an estimated \$587,000 annually on electrical energy to operate their compressed air system. In addition, the plant has an expenditure on rental air compressors of equal or greater size - but this will not be covered in this article. The plant was built in the 1940s and modernized in the 1970s. The plant generates its own power and serves many processes. The average cost per kWh is \$0.0359.
There are basically seven different operating compressed air systems running from a combination of central compressed air supply and decentralized systems.
- • Powerhouse Air
- • East Chlorine
- • West Chlorine
- • Pels
- • Caustic
- • Cal Hypo
- • Paint
There are three types of main compressed air systems in this sprawling facility. Most systems operate between 90-100 psi in the headers.
- Plant Air – normally not dried
- Instrument Air – normally dried to a -40°F pressure dew point
- Dry Air – normally dried to a -80°F pressure dew point (this is the air that goes to the chlorine processes)
The system assessment data logged and did a comprehensive analysis of every single lubricated and non-lubricated air compressor (18 units). We recommended a completely new supply side strategy involving the creation of one main compressed air system. This system would be powered by either one large oil-free centrifugal air compressor or by four oil-free rotary screw air compressors - both sending air to a Heat of Compression compressed air dryer.
Due to article space limitations, this article will focus on a few of the demand reduction projects recommended.
Demand Reduction Project #1: Condensate Drain Survey
The system assessment identified a total number of twenty-six (26) condensate drains, which were either cracked or simply not functioning and leaking compressed air. Most of the drains were “no air loss” drains” but simply needed maintenance attention – to be cleaned and repaired. Many of these drains are in the Plant Air System and are bypassed, but still running due to the high condensate load in the system. Once the Plant Air System is dried, the system will not generate condensate and these drains can be eliminated.
Repairing these drains will save 349 cfm of compressed air. This equates to an annual energy cost savings of \$17,502. The cost to repair the drains was estimated to be \$8,000.
Demand Reduction Project #2: Compressed Air Leak Survey
A partial survey of compressed air leaks was conducted at the plant and 115 leaks were identified, quantified, tagged, and logged. Potential savings totaled 609 cfm for the 115 leaks that were identified.
We recommend an ultrasonic leak locator be used to identify and quantify the compressed air leaks. We use either a VXP AccuTrak manufactured by Superior Signal or a UE Systems Ultraprobe.
Shutting off or valving off the air supply to these leaks when the area is idle would save significant energy use from leaks. Reducing the overall system pressure would also reduce the impact of the leaks, when air to the machine cannot be shut off.
Repairing the leaks can save additional energy. The savings estimates associated with a leak management program are based on the unloading controls of the compressors being able to effectively translate less air flow demand into lower cost.
Repairing these leaks will save 609 cfm of compressed air. This equates to an annual energy cost savings of \$30, 541. The cost to repair the leaks was estimated to be \$11,600.
Demand Reduction Project #3: Misapplied High-Pressure Air
High-pressure air being used for very low-pressure applications is not an efficient use of energy. A close review of the plant’s system discovered aeration and open-blow applications using 100 psig compressed air. This project replaces compressed air with blower-produced air at 8 psi.
Using low-pressure blowers instead of 100 psig compressed air will save 619 cfm of compressed air. This equates to an annual energy cost savings of \$31,043. The cost to purchase and install the blowers is estimated at \$55,000.
Better maintenance practices focusing on condensate drains and compressed air leaks can make a difference at this plant. The systems are currently a patchwork of seven compressed air systems. We have attempted to show how one can begin a huge project like this by simply trying to understand what is happening in the different areas of a huge campus. The second step can be to get some “easy wins” by working on compressed air leaks and misapplications.
To read more about Chemical Industry Applications, please visit www.airbestpractices.com/industries/oil-gas.