Approximate Calculation and Process Description for CIP Tank Cleaning
Recently, one of my friend encountered an issue with inadequate cleaning of a sterile tank. The details of this case are as follows:
1) Post-production inspection revealed product contamination. An ATP test confirmed that the sterile tank was not properly cleaned.
2) The sterile tank has a volume of 40 cubic meters, features side-mounted agitators, and is equipped with two rotary spray balls.
3) The CIP cleaning flow rate is 12,000 L/H.
Based on these observations, we will analyze the potential causes and propose solutions to ensure effective cleaning.
Analysis:
The ATP test results confirm that the issue lies within the CIP (Cleaning-In-Place) process rather than SIP (Sterilization-In-Place). The tank's design includes side-mounted agitators with integrated cleaning nozzles which may contribute to incomplete cleaning.
Specifications of Cleaning Equipment:
Side Agitator Cleaning Ball:
- Type: 1" 360° rotary spray ball
- Recommended pressure: 2 bar
- Maximum cleaning radius: 1.4 m
- Flow rate at 2 bar: 5,500 L/H
- Main Tank Cleaning Ball:
- Type: 1/2" 360° rotary spray ball
- Recommended pressure: 2 bar
- Maximum cleaning radius: 2 m
- Flow rate at 2 bar: 15,500 L/H
Tank Dimensions and Surface Area:
- Inner diameter: 3,300 mm
- Spray ball installation position: Center
- Cleaning radius: 1,650 mm (< 2 m)
- Internal surface area: Approximately 54 m²
Flow Rate Analysis:
The current CIP flow rate of 12,000 L/H is insufficient to achieve optimal cleaning pressure for both spray balls simultaneously. According to the flow-pressure curve:
- At 1 bar, the flow rates are 11,000 L/H and 4,000 L/H for the main and side cleaning balls, respectively.
- Insufficient flow leads to inadequate pressure, reducing the rotational power of the spray balls and compromising cleaning effectiveness.
Proposed Solutions:
1. Increase Flow Rate: To ensure adequate pressure and rotation, increase the flow rate to at least 15,000 L/H, ideally reaching the recommended 15,500 L/H.
2. Sequential Cleaning: Operate the cleaning balls sequentially to avoid excessive pressure on the side agitator cleaning ball. This ensures proper atomization and cleaning efficiency.
3. Optimal Pressure: Maintain a cleaning pressure of 1 bar during sequential cleaning to stay within operational limits.
4. Simultaneous Operation: When cleaning the tank walls, operate both cleaning balls simultaneously at 2 bar to ensure thorough coverage.
Verification:
Increasing the flow rate to 16,000 L/H and conducting a re-verification resulted in complete resolution of the cleaning issue.
Summary of Tank Cleaning Steps:
1. Calculate the tank's internal surface area to determine the required cleaning flow rate.
2. Determine the pipe diameter connecting to the tank and set the cleaning flow rate based on a velocity of 1.5 m/s.
3. Use the higher of the two calculated flow rates as the tank's cleaning flow rate.
4. Select appropriate cleaning balls based on equipment configuration and cleaning diameter requirements.
5. Ensure the CIP supply line diameter and pump capacity meet the flow rate requirements.
6. Verify the return pump capacity.
Key Concepts:
- Wetting Radius: The maximum horizontal distance the CIP liquid can reach without impact force.
- Cleaning Radius: The effective cleaning range with sufficient impact force.
- Coverage: Ensures all areas are adequately covered by the cleaning solution.
Rotary spray balls provide better coverage (70%) compared to fixed spray balls (10%), leading to more efficient cleaning.
Future discussions will focus on optimizing cleaning time.
