Beyond Leaks—Factory Continues Reducing Compressed Air Demand

A significant manufacturing operation, in the U.S. Midwest, had successfully deployed a compressed air leak management program. This on-going leak management program, along with tuning the air compressor control system, had delivered energy savings and a more reliable compressed air system.

Plant maintenance and facilities management then asked our firm to identify more ways to reduce compressed air demand, while they continued on with the leak management program.

Our compressed air audit found the following further compressed air demand reduction opportunities. The objective of this article is to provide examples of how plants can further reduce compressed air demand – after having implemented a successful, on-going compressed air leak management program.

All projected savings in this audit reflect an air compressor control system able to translate demand reduction into energy savings. The system operates 8,760 hours per year and the local electric rate was $0.07 per kWh. Average system pressure is 90 psig. Please note, due to article space limitations, this is an excerpt from a larger audit, and should be used only as an idea generator.

Summary of Demand Reduction Projects

 
Project #1: Compressed Air Leak Survey

Prior to our site visit, plant personnel have aggressively found and repaired a significant number of compressed air leaks. As a result, we found a very small number. Plant personnel have acquired an ultrasonic leak detector able to help them detect, photograph, quantify and record leaks. 
    
Most plants can benefit from an ongoing air leak management program, like the one this plant has deployed. Generally speaking, the most effective programs are those that involve the production supervisors and operators working in concert with the maintenance personnel. 
    
A partial survey of compressed air leaks was conducted at the plant and 11 leaks were identified, quantified, tagged, and logged. Potential savings totaled 41 cfm for the 11 leaks that were identified. 

Project #2: Install Automatic No-Air-Loss Condensate Drains

These condensate drains come in a number of varieties, including ones that receive the signal to open from a condensate high level and the signal to close from a condensate low level. These drains waste no compressed air and are the best selection from a power cost standpoint. Their reliability is usually many times greater than the level operated mechanical drains. 

Ensure that automatic condensate drains are set up to work effectively. Some guidelines include making sure all drains:

• Are not tied together to a common header
• Can be checked easily for operation
• Are properly “vented” to atmosphere, if necessary
• Are sized, piped “to” and “from” with the full capability to handle anticipated highest humidity weather loads
• Include a bypass bleed on the feed pipe
• Can be easily checked to see if they are passing condensate

Connect each drainage point (after-cooler, pre-filter, dryer, after-filter, receivers, and all risers) separately to individual drains to collect and direct the condensate to a proper handling point. Be sure maintenance personnel can effectively and visually monitor the drain’s action. 

Project #3: Open Blows / Blow-off Air

Many plants have “open blows” where turbulent compressed air blasts straight out of the pipe or tube in order to dry a product or “blow off” unwanted materials from a product. This not only wastes huge amounts of compressed air, but also violates OSHA noise and dead ended pressure requirements.

One savings approach is to use an air amplifier, which requires less compressed air. Air amplifiers use “venturi” action to pull in significant amounts of ambient air and mixing it directly into the air stream, which amplifies the amount of air available at the point of use. Air amplifiers have amplification ratios up to 25:1. Using 10 cfm of compressed air can supply up to 250 cfm of blow-off air to the process and generate a savings of a 15 cfm compressed air per 1/4-inch blow off. Savings may be available using 1/8-inch lines, but the cost effectiveness will not be as great.

In many cases, an appropriately selected and applied venturi amplifier will deliver lower net energy cost blow-off air than blower-generated blow-off air. The capital cost for the amplifiers is relatively low.
    
Tips for Using Air Control Nozzles

• Always select the lowest flow nozzles that will achieve the desired result to maximize air consumption savings and noise reduction.

• Install a pressure regulator and gauge in the air line before the air control nozzles and regulate pressure down to the absolute minimum necessary to achieve the desired result. Lower pressures improve safety, reduce noise, and could save hundreds of dollars a year in electricity operating costs.

• To minimize noise, increase the distance between the target surface and the nozzle, if possible. Remember that noise is caused by air impacting on the target work piece, particularly edges or holes.

• Install adjustable ball joints in the supply line, if required, with air control nozzles to provide simple, accurate adjustment of nozzle orientation.

• Do not aim the nozzle straight at the target for cleaning applications. Angle the nozzle 15º to 45º to ensure that the contaminants are removed from the product surface.

• Most nozzles, in an appropriate material, can be used with CO₂, Nitrogen, steam, or other compatible gases for special heating or cooling applications.

• To create an air curtain, nozzles do not always need to be positioned as closely as on an air knife. Nozzles can be up to 12” (30 cm) apart depending on the application.

• You can aim the nozzle to “wipe” sideways across a moving target at a comparatively shallow angle for many blow-off applications. This can reduce the number of nozzles needed.

• Angle the nozzle manifold like a snowplow above a moving conveyor so that the contaminants are forced off the belt, rather than back.

• Proper filtration of compressed air is important for efficient nozzle performance. Be sure to use a filter/separator to remove excess oils and water just prior to your nozzle application.

Venturi Inducer Nozzles in Place of Open Blow

Misapplied Compressed Air

High-pressure compressed air (90-120 psig) being used for low-pressure applications (7-60 psig), is not an efficient use of energy. A close review of the plant’s system should be made and measurements taken to identify whether there are any potential energy savings from using an alternate source of low-pressure air for specific applications in the production area. Typical misapplications include aeration and spraying.

In this plant, there are three dip tanks being aerated. Two of them are rinse tanks, being aerated using 90 psig compressed air, and the acid tank is being aerated by a 25 horsepower roots blower at 7 psig. This blower is oversized and is being throttled back.

We estimate approximately 85 cfm is being used in each tank. All tank liquids were “boiling” very well, with a lot of turbulence in the tanks.

Our recommendation is to replace the 90 psig compressed air aeration with the 7 psig low pressure blower system already being used in the acid tank and adding a 10 horsepower low pressure blower able to produce 96 cfm at 10 psig with a maximum working pressure of 17 psig.

    
Conclusion

Plant maintenance and facilities personnel should implement on-going compressed air leak management programs. Once up and running, there are many other ways to reduce compressed air demand – beyond leaks.

For more information on APenergy visit apenergy.com or call 740.862.4112.

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