Tank cleaning methods continue to develop and improve for the food and beverage industry with automated processes that use less water and solvents. The traditional static spray ball was the first basic design utilized for tank cleaning, but newer rotational spray devices have proven to be vastly more effective. Rotational spray devices are designed to produce larger droplets that provide greater impact. These factors reduce cleaning cycle times and consume less water, ultimately providing cost savings.
We’ll examine two different operating principles that define rotational nozzles; free spinning and controlled rotation. Each delivers a unique cleaning power that is more efficient than the traditional static spray ball. Free spinning devices are driven by fluid and made from food grade materials, making them perfect for hygienic applications. Controlled rotation nozzles use an internal turbine to keep rotation consistent, even at higher pressures, so that larger droplets are consistently produced. These nozzles create an even higher impact making them an excellent choice for medium to heavy soiled tanks.
Aside from nozzle operating principles there is additional criteria that you should take into consideration for your tank cleaning process. For this answer, we interviewed Bob Garstki, Senior Application Engineer at Lechler Inc., a global leader and manufacturer of spray devices.
1. What key factors should you consider when choosing a tank cleaning nozzle?
Well, there are several key factors to consider simultaneously. Namely, the classification of the soil in the tank; the sheer size of the tank; any possible internal features such as agitators, mixers, baffles, or anything that can present an obstacle to the spray or even a physical collision with the nozzle. Finally, consider if it is to be a clean-in-place device or a clean-out-of-place situation.
2. Impact and droplet size play an important role in tank cleaning. Can you explain how these are related and why they matter?
Tank cleaning nozzles produce the best cleaning in the shortest time frame when the spray emitted by the tank cleaning nozzle produces impact force against the soil (i.e. the substance that is to be removed from the inner surfaces in the tank). Typically, the larger the droplet size that emanates from the tank cleaning nozzle, the greater impact force that is generated. This relates to the formula: Impact=Force/Area. The droplet size is Mass in that equation, impact being Force. Thus, larger mass should yield a greater impact force. Another factor is the spray impact force’s dwell time. How long is the force residing on a particular area? That is an important feature of the controlled rotational speed device.
Another force that acts upon the tank’s surfaces is “shear stress.” For areas that do not receive direct impingement (impact force) but are below the area of direct impact force, the cascading of the liquid down the side walls of the tank and its internal components produce a cleaning effect too. However, the shear stress is not as beneficial as direct impact force in reducing the time it takes to thoroughly clean soil from the vessel.
3. What do you recommend for cleaning difficult areas inside the tank such as agitators and baffles?
Tank cleaning nozzles rely upon the “line of sight” principle, which means the spray is targeted towards a specific direction. If there is an object inside the tank, this becomes an obstacle for the spray and now the targeted areas are missed, which means the tank cannot be properly cleaned. Most tanks are equipped with agitator blades and baffles that cause these spray shadows or hard to reach areas inside the tank. In order to overcome these obstacles, we must augment tank cleaning nozzles with special devices that can be mounted is special ways.
One option is our PopUp Whirly, this device has a pop-up feature that is powered by pressurized liquid and emits a narrow angle hollow cone spray. When properly positioned inside the vessel, the impact of the spray cleans the undersides of the agitator and mixer blades. Some of the spray could also be directed to some baffle surfaces as well.
Other helpful practices are to have the agitators/mixers rotate during the cleaning process to allow more surfaces to be targeted. It can also be beneficial to partially fill the bottom of the vessel while the agitator blades are in motion during the cleaning process. This produces some additional access to other surfaces near the bottom of the vessel. This should be followed up by draining the tank then running the main tank cleaning nozzles for another cycle.
4. What are common causes of pressure loss, and does this have any effect on tank cleaning?
We select the optimum nozzles for each cleaning task, observing the available pressure and flow rate from the customer’s pump based upon information provided to us by the customer. Occasionally, we receive reports from customers that they do not understand why the nozzle is not properly cleaning their tank. We ask if the customer can provide a pressure reading, which is located near the inlet to the nozzle. This is where the rating for the nozzle is determined. Most customers do not take into account that the pump rating is for the pump and doesn’t account for the size of the pipe, the number of fittings and valves in the line which all account for pressure loss.
In fact, sometimes a customer maybe using that same pump infrastructure simultaneously feeding other processes or using a diaphragm type pump with oscillating pressure. When these factors come into play, the nozzle cannot properly develop the required pressure and flow. So, the nozzle spray may not reach to its full coverage radius or impact force. This will result in less than effective cleaning.
5. In your experience, are rotational nozzles more cost effective and why?
It has been proven that rotating nozzles produce their cleaning effect using less than half the flow volume of a comparable static spray ball type nozzle. So, the rotating nozzle not only consumes less fluid to clean (water and possible chemicals along with their costs), and the resultant reduction of effluent waste disposal. In addition, the cleaning of the vessel can be more uniform, repeatable, and accomplished in a much shorter time span, resulting in less production down time. That equals a greater volume of the customer’s product and more potential profit for them.
There is no simple solution when it comes to properly cleaning a tank and even the experts are challenged because of all the factors that must be taken into consideration. For this reason, engineers at Lechler developed TankClean, a proprietary software used for selecting the right nozzle for perfectly cleaning your tank. The software replicates the tank geometry and then simulates the spraying operation and can be used for existing tanks or for new tanks in the planning phase.
Lechler is constantly researching and developing tools for improving spray processes. Ending Statement
If you have any further questions for our team, please contact us today – we look forward to providing the best methods for your specific applications!