Automated spray control pays dividends

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By William J. Kohley, Ph. D.

PlantServices.com

Keywords: spray controlled

Just because nozzles are spraying doesn’t mean that they are spraying precisely, and precision spray performance can bring rewards in terms of throughput, quality and bottom-line profits.

While spray applications are regarded as simple on-off valves and regulation systems, the reality is that spray nozzles are precision components designed to yield specific performance under specific process conditions. Just because nozzles are spraying doesn’t mean that they are spraying precisely, and precision spray performance can bring rewards in terms of throughput, quality and bottom-line profits.

Many plants have processes that require spraying, and maintenance professionals can attest to the complexity of maintaining them. In addition, poor spray performance often can’t be detected by the naked eye, so operators might not notice if nozzles need maintenance.

Spray optimization
Every nozzle in your plant has its own performance characteristics, including flow rate, spray pattern (full cone, hollow cone, flat or solid stream), atomization droplet size, spray impact and coverage. A nozzle is optimized when it’s performing as designed and is contributing to high-quality production and maximum throughput.

If a spraying system isn’t calibrated, monitored and maintained properly, it can be a drain on profits. The cost of wasted water alone in a system with worn nozzles can amount to tens of thousands of dollars annually, even with relatively minor performance problems. If wastewater needs to be captured, treated and recirculated, the cost of waste can easily double and more likely triple. Moreover, keep in mind the many related expenses involved if your spray system is not performing at maximum efficiency:

• Excess chemicals.
• Mixing, reclaiming and treating the overspray.
• Wasted energy to deliver the fluids.
• Scrap resulting from overspray or poor coverage.
• Unscheduled production downtime.
• Unnecessary maintenance.

The idea behind optimizing a spray system is to minimize these expenses. Keeping nozzles at optimal performance often falls into the maintenance technician’s job description.

Monitoring and maintaining performance
Numerous conditions affect spray performance, including erosion and wear, corrosion, caking and bearding, clogging, improper assembly and accidental damage. Nozzles must be monitored and maintained on a regular basis to ensure that these conditions are not degrading optimal performance. However, manually monitoring dozens, or even hundreds, of nozzles in use presents a difficult task that can require a significant investment in labor to achieve.

Even with this effort, there is no guarantee that maintenance professionals will be able to improve nozzle performance significantly. It’s important to remember that visual inspection alone doesn’t always tell the full story. Spray patterns from worn nozzles often look identical to those of new nozzles even when spraying 20 percent or more over tolerance. The difficulty of detecting problems with the naked eye may cause maintenance professionals to neglect routine maintenance processes, ultimately leading to increased production costs and quality control issues.

Automation and nozzle performance
The most basic function of an automated spray controller is to maintain optimal nozzle performance by delivering fluids precisely to the desired location at the proper time. This boosts throughput, maintains product quality and reduces system wear, maintenance time and waste stream volume.

Traditionally, the spray functions have been controlled either manually or with PLCs. While it’s possible to program PLCs to manage spray functions, dedicated spray controllers shorten programming time with pre-defined, pre-tested spray control modules and built-in nozzle performance data. Spray controllers optimize nozzle performance because they also provide fast response times. Manufacturers that sacrifice this response time compromise system performance and consume more fluid to produce a quality product.

Dedicated spray controllers adjust other system components to compensate for spray system variation. For example, a worn orifice often causes line pressure to decrease. A spray controller detects this immediately and adjusts the pump to maintain adequate flow and coverage. Variations that the spray controller can’t correct immediately can trigger alarms or shut down the system. Furthermore, controllers also can monitor nozzle use throughout the line and notify operators when maintenance or a replacement is needed.

Most importantly, dedicated spray controllers can link spray performance to production variables. If it’s possible to make a precise measurement of color, temperature, water content, size, texture, weight or other key variable related to fluid delivery, the spray controller can monitor the variable and adjust the spray appropriately. This eliminates the need to monitor and adjust the spray manually.

Spray controllers enable maintenance engineers to manage spraying operations more accurately, making adjustments automatically to maintain efficiency. Data logging also enables tracking system performance and more accurately predicting when spray systems will need maintenance.

Examples
Spray controllers have improved worker safety and increased throughput in baked goods production. Excess spray of butter and oil solutions on baked goods can cause hazardous work conditions. The plant floor can become dangerously slick near these processes. Floor cleanup was an ongoing maintenance challenge and the cost of wasted materials was high.

Programmed specifically for food coating applications, a spray controller was used to monitor and adjust the closed-loop system by regulating liquid and air flow to low-mist air atomizing headers equipped with special nozzles. Air pressure and liquid pressure were both maintained within a precise range, and the distance between the spray header and the conveyor belt was adjustable for maximum efficiency. The controller also regulated liquid and air heating systems to maintain the optimum temperature for the butter and oil solution. A liquid recirculation feature saved on the amount of solution being sprayed.