Q&A: Spray Tech Trends & Best Practices

The speed and accuracy of automated spray devices and the ability to precisely control them have also changed in recent years. The development of faster automatic spray guns and more advanced control software are good examples of how spray technology has become more efficient over the years. One specific example is the emergence of Pulse Width Modulated (PWM) flow control. PWM flow control allows a single nozzle to provide an extremely wide range of flowrates without changing spray pressure. By simply adjusting the duty cycle and frequency of the nozzle at the spray controller, flowrate can be increased or decreased to account for changes in line speed. And because spray pressure isn’t changed, spray angle and drop size aren’t affected. That’s a big deal when you need to coat products on a moving conveyor uniformly. Another technological advance that’s improved the efficiency of spray applications is Computational Fluid Dynamics (CFD). CFD software enables nozzle manufacturers to model the performance of spray systems before they are installed in order to optimize them. Ten years ago, cutting-edge technology involved intensive laboratory testing on particle sizing, coating uniformity, and how droplets and spray patterns behave in turbulent environments. Now this type of application information can be replicated and modeled through CFD to predict the outcome much more accurately.
Q: What are some of the common nozzle types employed in spray applications? How do these nozzle types differ from each other in terms of their application capability?
There are literally tens of thousands of variations, so this is a big question to answer. General-purpose hydraulic nozzles are used for a wide variety of applications. Full-cone nozzles are often used for washing and rinsing applications. Flat-fan nozzles can be positioned in a manifold for uniform coating across a conveyor. Hollow cones are often used in dust-control applications. Air-atomizing nozzles use compressed air to produce a fine mist that’s used for applications like humidification or evaporative cooling.More advanced products like high-speed automatic spray nozzles are used for precise coating applications requiring intermittent sprays. Special air atomizing lances are used to produce precise drop sizes for evaporative gas cooling or conditioning applications. Stationary and rotary nozzles are commonly used for cleaning the inside of processing and storage vessels. Air nozzles are also available using both compressed air and blower air for drying and blowoff applications.With so many varieties of nozzles available, it’s important for users to work with an expert to optimize their spray performance. Sales engineers and application engineers knowledgeable about spray technology can save users a lot of time and money by designing a system that works right the first time.
Q: What are some best practices you can offer end-users in the areas of specification, installation and maintenance of spray technology to ensure long-term performance?
The very best "best practice" advice I can give is for nozzle users to establish a good nozzle maintenance program at the time of installation and then stick to it. This may sound self-serving, but it really makes financial sense for the users. In the United States, industry uses 45 percent of freshwater annually. The heaviest users of water include the food, chemical, petrochemical, primary metal and paper industries. In the last 10 years, water costs have more than doubled in some areas, causing all manufacturers and processors to take a hard look at this expense. When you factor in wastewater disposal costs, this becomes an even bigger issue. The average cost per 1,000 gallons of water, including sewer charges, is about $7.00 U.S. Spray nozzles are at the heart of many operations that consume water and chemicals in manufacturing and processing plants. So these seemingly simple components have a significant impact on performance and operating costs in cleaning, coating, cooling, moisturizing and dozens of other applications. As spray nozzles wear, their orifices become larger and the flowrate will increase. Even slight nozzle wear that can’t be detected visually can be extremely wasteful, costing tens – sometimes hundreds – of thousands of dollars annually in increased operating expenses. And worn nozzles that spray over capacity are wasting more than water. Electricity costs due to excess pump operation, chemical consumption and wastewater disposal costs will all increase as well. It all adds up.
Q: What are some pitfalls you see end-users commonly encountering in spray applications? How can end-users best avoid and/or respond to such application pitfalls?

In most industrial plants there are routine objective measures for important processes, but that’s often not the case with spray equipment. The mentality that "if it sprays, it must be OK" is pretty common in a lot of plants we visit. There seems to be a perception that liquid is soft and metal is hard, therefore spray nozzles don’t wear. Sprays are usually visible in a plant, and that’s the means by which they are often inspected – i.e., just by looking at them. The problem with this approach is that a spray nozzle that is worn 30 percent more than its original capacity with distribution much heavier in the center than when it was first installed looks much like it did when it was new. Without objectively measuring flow and distribution, end-users don’t find out there is a problem until there is defective product or there has been tremendous waste of water, chemicals and the energy to pump them. So again, the need for routine inspection and maintenance is high. Even more effective than periodic inspection and maintenance are automated spray systems, which monitor flow and can adjust as needed or provide warnings when spray performance falls outside an accepted range.
Q: From a monetary perspective, why is it important to examine the efficiency of the spraying process? Can you provide some specific application examples that demonstrate the monetary gains and/or losses that can be incurred from spraying efficiently and/or inefficiently?A very simple example of nozzle maintenance providing a quick payback occurred at a food processing plant where our customer discovered that the nozzles on their conveyor rinsing headers were worn to 15 percent over the flow capacity they desired. Changing out those 60 nozzles was a minor investment, but because the system was in use 20 hours per day, five days per week, 51 weeks per year, the financial impact was significant. The company avoided more than 3,300,000 gallons of wasted water over the course of a year. Based on average costs for water and disposal, that change saved them over $23,000 U.S. annually. Another expensive plant resource is compressed air. We worked with a bottling plant not too long ago that was using compressed-air nozzles to dry soft drink bottles after washing. The plant was operating 250 days per year, 16 hours each day, and the cost of operating this system was estimated at over $35,000 per year. High-impact, blower-fed air knives were a much more efficient answer to the plant’s drying problem and provided savings of almost $30,000 annually. Those are just two simple examples of how proper nozzle selection and maintenance can provide significant financial payback. Spraying Systems offers an online calculator to help users understand how much money they can save by optimizing their spray system. This calculator can be found at www.spray.com/save. 
Q: Why is drop size an important consideration in many spray applications? How does the process of atomization affect spray quality? Two good examples of applications where drop size is critical are dust control and gas conditioning/cooling. Dust control is most effective when dust particles collide with water drops of an equivalent size. Drops that are too large won’t collide with the smaller dust particles, and drops that are too small evaporate too quickly and simply release the captured dust particles back into the atmosphere. So understanding the particle size of the dust and the droplet size are both critical to the effectiveness of the system design.In gas conditioning applications, problems can result from premature or incomplete evaporation. If drops are too small, they evaporate quickly and the desired level of absorption may not occur, thus resulting in less efficient or damaged downstream equipment. If drops are too large and don’t evaporate quickly enough, wetting will occur, entrained liquid may result, and dust can accumulate in the duct or tower and obstruct gas flow.Q: What is on the horizon in terms of spray technology? How will the spray technology of tomorrow be more effective/efficient than the spray technology of today?The future will bring more advances in precision spray nozzles, spray control technology, and spray modeling. We’ll see more intelligence built directly into the nozzle – things like thermal sensors, acoustic sensors, and vibration sensors that will provide real-time monitoring. New spray controllers will take advantage of improved sensors like these and others to tightly monitor and control the quality and moisture content of things, such as tissue paper and roofing shingles and the amount of chocolate sprayed on an éclair. Modeling software and the spray input data will continue to improve as universities and leading industry spray experts cooperate to model new flow characteristics of droplet behaviors for new products, such as injection systems, drug inhalers, and high-efficacy process towers.www.spray.com