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6:00 am
August 1, 2008
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Utilities Manager: Spray Optimization Strategies

Using less compressed air, electricity and water in your drying and spraying operations can lead to significant savings. The right approach and the right device for the application are critical.

Systems that dry, clean, cool, coat and lubricate are easy to overlook as long as they seem to be providing the expected performance. That’s because the components in these systems are perceived to be quite simple. After all, if air is coming out holes in pipes and nozzles are spraying, everything is working properly, right? Wrong! Optimizing these operations can save tens or even hundreds of thousands of dollars annually by dramatically reducing compressed air, electricity and water consumption.

Let’s take a look at two strategies that are relatively easy to implement, eliminate unnecessary profit leaks and improve product and process quality.

Strategy 1: Slash or eliminate compressed air consumption
Most plants use compressed air to dry, cool or move parts. Typically, open pipes or pipes with drilled holes or slits are used. While this approach accomplishes the desired task, compressed air consumption is excessive when compared with alternate approaches. In fact, using air nozzles, air amplifiers or air knives instead of open pipes can reduce air consumption by as much as 92%. In some operations, the use of compressed air can be eliminated completely by using an air knife package powered by a regenerative blower. (An overview of the options and estimated reductions in air consumption is shown in Table I. Refer to Table II for specific cost savings.)

Air nozzles and air knife packages offer benefits in addition to reducing or eliminating the use of compressed air, including:

  • Perceived noise reductions from 28 to 60% with air nozzles; additional reductions achieved with air knife packages;
  • Improved worker safety;
  • More precise, repeatable drying and blow-off.

0808_um_spray_img11Air nozzles: versatile, efficient and suitable for many operations…
Air nozzles convert a low-pressure volume of compressed air into a targeted, high-velocity, concentrated air stream, flat fan or curtain of high-impact air. They come in a variety of types, capacities, sizes and materials. In addition, air nozzles can be used with CO2, nitrogen, steam or other compatible gases for special heating and cooling applications.

Air amplifiers: increased intensity and efficiency…
A variable air amplifier is another option when using compressed air. Air amplifiers produce a constant, highvelocity air stream for spot drying, blow-off, exhaust and robotic applications. Efficiency is maximized because additional free air is pulled through the unit along with the compressed air. Air amplifiers deliver higher volumes of air and operate at higher pressures than air nozzles for fast drying and blow-off.

Low-flow air knives: maximum efficiency in small areas…
Low-flow air knives deliver a high velocity, uniform air flow across the entire length of the knife. Drying and blow-off are fast and efficient and minimal air is used.

Designed for small areas, low-flow air knives are typically mounted close to the target. Maximum knife length (or combined length of all knives) is limited to less than 2′ (61 cm). Applications that only require one or two air knives can experience significant operating cost reductions by using low-flow models.

Some drying and blow-off operations are well suited to using regenerative blowers and air knives. Using blower air to power an air knife eliminates the need for compressed air and can result in substantial savings—including a reduction in operating costs by 95% or more. Air knife/ regenerative blower packages are rugged/reliable and require infrequent, minimal maintenance. They are ideal for applications that require:

  • High air velocity;
  • Oil-free operation;
  • Large application areas—more than 2′ (61 cm);
  • Heated air.

How much can you save?
Any plant with a drying, cooling or blow-off operation can likely experience savings. Table II provides estimated savings for a single operation.

If you currently are using open pipes, reductions in compressed air consumption are possible—and will quickly offset the cost of any new equipment. If you’re already using air nozzles, evaluating alternatives such as variable air amplifiers, low-flow air knives or air knife/blower packages is a good idea to see if further savings can be realized.

Strategy 2: Eliminate water waste by optimizing spray operations
Spray nozzles are precision-engineered components designed to deliver very specific performance. And, like all technology, newer, more efficient versions are introduced on a regular basis. Routinely monitoring the nozzles you use and exploring changes in the way you spray can lead to significant reductions in water consumption.

Nozzle wear = wasted water…
Using worn spray nozzles can be extremely wasteful—often going undetected, especially in the early stages, where the signs of wear aren’t readily visible. Monitoring nozzles closely and taking the appropriate action can save thousands of gallons (liters) of water per day.

As nozzles wear, their orifices become larger and, at any given pressure, the flow rate will increase. Nozzles that spray over capacity are not only wasting water. Electricity costs will rise due to excess pump operation, chemical consumption will increase and wastewater disposal costs will escalate as well. As shown in Table III, even slight nozzle wear can be extremely wasteful.

Some signs of nozzle wear may be visible. As drop size increases, spray patterns may change or become distorted. If the wear is due to erosion or corrosion, a quick look at the nozzles will reveal the problem.

What to do about nozzle wear…

  • Replace nozzles on a regular schedule. Many processors elect to changeout spray nozzles annually. Depending on the number and type of spray operations, the cost of replacement nozzles can be far less than the cost of wasted water even if the nozzles are only 15 to 20% worn.
  • Evaluate nozzle material. Changing nozzle material may minimize wear and waste. Nozzles made from harder materials generally provide longer wear life. In addition to standard materials such as brass, steel, cast iron, various stainless steels, hardened stainless steels, many plastics and various carbides, spray nozzles can also be supplied in other materials upon special request. Materials that offer better corrosion resistance also are available. The rate of chemical corrosion on specific nozzle materials, however, is dependent on the corrosive properties of the liquid being sprayed, its percent concentration and temperature, as well as the corrosion resistance of the nozzle material to the specific chemical.
  • Explore reducing spray pressure. Although it is not always possible, decreasing pressure, which will slow the liquid velocity through the orifice, may help reduce the orifice wear/corrosion rate.
  • Add line strainers or change to nozzles with built-in strainers. In many applications, orifice deterioration and clogging is caused by solid dirt particles in the sprayed liquid. This is particularly common in systems using continuous spray water recirculation. Strainers, or nozzles with built-in strainers, can trap larger particles and prevent debris from entering the nozzle orifice or vane to significantly reduce wear.

Consult the accompanying “Spray Nozzle Checklist” sidebar at the end of this article for more pointers.

0808_um_spray_img3

Consider changing the way you spray…
You may be able to conserve vast amounts of water by making some simple changes to your spray operations. As a starting point, you may want to consider taking these steps.

  • Use nozzles that precisely spray the target. Overspray is not only wasteful, it can cause excess maintenance and impede production.
  • Add handheld spray guns to open hoses to ensure water is “on” only when needed.
  • As spray nozzles wear out, replace with water-saving models.
  • Equip all hoses with spring-loaded shutoff nozzles and make sure they aren’t removed.
  • Instruct workers to use hoses—equipped with spray guns—sparingly, and only when necessary.
  • Change shower heads to smaller nozzles.
  • Install high-pressure, low-volume nozzles on spray washers.
  • Use fogging nozzles to cool products.

Consult the experts to maximize benefits
An on-site evaluation of your drying, cleaning, cooling, coating and lubrication operations from your spray nozzle manufacturer is the most expedient and thorough way to identify possible improvements and quantify the resulting savings. Leading manufacturers don’t charge for this service and will conduct a comprehensive audit of all your operations in a single visit and provide a written summary report that includes recommended changes. It’s a risk-free way to learn more about how to lower energy and water consumption and a valuable service for every processor with spray operations.

Spray Nozzle Checklist

Flow Rate – Each Nozzle
Centrifugal Pumps: Monitor fl ow meter readings to detect increases. Or collect and measure the spray from the nozzle for a given period of time at a specifi c pressure. Then compare these readings to the fl ow rates listed in the manufacturer’s catalog or compare them to fl ow rate readings from new, unused nozzles.

Positive Displacement Pumps: Monitor the liquid line pressure for decreases; the fl ow rate will remain constant.

Spray Pressure – In Nozzle Manifold
Centrifugal Pumps: Monitor for increases in liquid volume sprayed. (Spraying pressure likely to remain the same.)

Positive Displacement Pumps: Monitor pressure gauge for decreases in pressure and reduction in impact on sprayed surfaces. (Liquid volume sprayed likely to remain the same.) Also, monitor for increases in pressure due to clogged nozzles. Visually inspect for changes in spray coverage.

Drop Size
Examine application results for changes. Drop size increases cannot be visually detected in most applications. An increase in fl ow rate or a decrease in spraying pressure will impact drop size.

Spray Pattern
Visually inspect each nozzle for changes in the uniformity of the pattern. Check spray angle with protractor. Measure width of spray pattern on sprayed surface.

Jon Barber is a director at Spraying Systems Co., based in Wheaton, IL. The company, which is celebrating its 70th anniversary, offers nozzles in thousands of sizes, hundreds of configurations and dozens of materials. Designed to improve efficiency, these products range from quick-change units that require no tools for installation to anti-bearding nozzles that increase throughput. For more information, contact Barber directly. Telephone: (630) 665-5000; e-mail: jon.barber@spray.com


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