About the Approximate Calculation and Process Description for CIP Tank Cleaning
A few days ago, a friend told me about an issue with incomplete cleaning of an aseptic tank. The details of this case are as follows:
1) After production, a defective package was discovered. An ATP test revealed that the aseptic tank was not being cleaned properly.
2) The aseptic tank is 40 cubic meters in size, has side agitation, and has two rotating cleaning balls.
3) The CIP cleaning flow rate is 12.000 L/H.
Let's analyze this case:
Because the ATP test was performed, it was confirmed that the issue was with CIP, not SIP.
The aseptic tank has side agitation and cleaning balls, so the possibility of incomplete cleaning of the side agitation is unlikely.
Side-Agitation Cleaning: Auxiliary cleaning ball 1" 360°, recommended cleaning pressure 2 bar, maximum cleaning radius 1.4m. These parameters indicate that this cleaning ball is used for side cleaning, cleaning agitator blades. At an inlet pressure of 2 bar, the flow rate is 5500 L/H, and the cleaning radius is 1m.
Tank Cleaning: Main cleaning ball 1/2" 360°, recommended cleaning pressure 2 bar, maximum cleaning radius 2m. These parameters indicate that this cleaning ball is used for main cleaning, cleaning tanks. At an inlet pressure of 2 bar, the flow rate is 15.500 L/H, and the cleaning radius is 2 meters.
Let's look at the dimensions of the sterile tank. The inner diameter of the sterile tank is 3.300 mm, and the spray ball is centrally mounted, so the cleaning radius is 1.650 mm, less than 2 meters. The inner surface area of the sterile tank is approximately 54 square meters.
In terms of cleaning flow, the two cleaning balls have cleaning flow rates of 5.500 L/H and 15.500 L/H, respectively (at a cleaning pressure of 2 bar), while the actual flow rate provided is 12.000 L/H.
We checked The curve shows that at a cleaning pressure of 1 bar, the cleaning flow rates are 11.000 L/H and 4.000 L/H, respectively. Therefore, the two cleaning balls must be switched for cleaning, otherwise insufficient cleaning flow and pressure will result. As we know, the rotational power of the rotating spray ball is derived from the cleaning pressure. Insufficient pressure will result in insufficient rotational power, resulting in incomplete cleaning.
However, if the cleaning is switched, the cleaning flow rate of the side-agitating cleaning ball will reach 12.000 L/H, and the cleaning pressure will exceed 3 bar, causing the cleaning fluid to atomize and thus failing to achieve a good cleaning effect. Therefore, the cleaning flow rate must be increased to above 15.000 L/H, ideally reaching the recommended flow rate of 15.500 L/H.
If the flow rate reaches 15.000 L/H, both cleaning balls should be activated simultaneously to prevent switching between the side-stirring cleaning balls and atomizing the cleaning solution. The cleaning pressure is now 1 bar, at the minimum operating limit.
If the flow rate reaches 15.500 L/H, the side-stirring system can be flipped to perform cleaning. This allows the tank wall to be cleaned without side-stirring, and the cleaning pressure is 2 bar. During side-stirring cleaning, both the side-stirring cleaning ball and the main cleaning ball operate simultaneously, with a cleaning pressure of 1 bar, which also allows normal operation.
In terms of cleaning radius, the main cleaning ball has a cleaning radius of 2 meters, while the tank diameter is 3.3 meters. The cleaning balls can meet the operating requirements.
Considering the tank cleaning flow rate, the internal surface area of the tank is 54 m2. The tank cleaning flow rate follows the following principle: 0.08 L/m2 (tank internal surface area)/s.
Based on practical experience, this friend increased the cleaning flow rate to 16.000 L/h and conducted another cleaning verification, completely resolving the issue.
Steps for determining tank cleaning:
Based on this case study, we can summarize the steps for determining tank cleaning:
Calculate the tank surface area to determine the tank cleaning flow rate;
Determine the diameter of the pipes connecting to the tank, and based on a cleaning flow rate of 1.5 m/s, determine the pipe cleaning flow rate;
Based on the two flow rates, the larger of these two flow rates is the tank cleaning flow rate;
Based on the flow rate and the configuration of the tank equipment, determine the type and quantity of cleaning balls; this primarily involves determining the cleaning diameter;
Determine the diameter of the CIP supply pipe and the capacity of the cleaning line pressure pump;
Determine the capacity of the CIP return pump;
Regarding the cleaning radius, we need to understand two concepts: the wetting radius and the cleaning radius. Radius;
Both the wetting radius and the cleaning radius refer to horizontal distances, not maximum distances; that is, the horizontal distance from the spray ball's installation location to the tank wall.
The wetting radius is the maximum distance the spray ball can reach when spraying CIP liquid; this maximum distance is without impact force.
The cleaning radius is the radius at which the liquid sprayed by the spray ball exerts a certain amount of impact force.
For fixed spray balls, the cleaning liquid primarily relies on forming a complete liquid film on the tank wall. The downward flow of this film under the influence of gravity creates shear forces, and the liquid also has a certain degree of solubility. These two forces clean the tank wall.
Rotating spray balls, on the other hand, rely partially on impact force and partially on shear force to clean the tank wall. When the cleaning radius of the cleaning ball is greater than the maximum distance, cleaning can rely entirely on impact force. When the cleaning radius is less than the maximum distance, cleaning relies partially on impact force, shear force, and solubility.
Shear and impact forces are key cleaning parameters; another crucial parameter is coverage.
When cleaning liquid from a fixed spray ball hits the tank wall, impact forces create a circular pattern. These circular patterns connect to each other, ensuring coverage of the entire tank. The remaining areas rely on film flow for cleaning. Insufficient impact force can result in partial coverage loss, leading to cleaning failure. Fixed spray balls only have a 10% coverage rate, meaning impact forces only clean 10% of the area, while solubility and shear forces are responsible for the remaining area.
Rotating spray balls, due to their rotational nature, achieve a 70% coverage rate, resulting in shorter cleaning times. Fixed spray balls rely on both impact and shear forces, placing them somewhere between jet cleaners and fixed spray balls.
