Thorough cleaning is a price of doing business in food processing. Food manufacturers should analyze clean-in-place (CIP) processes for efficiency improvements just as might be done with the primary process. Improving efficiency while maintaining food safety requires both careful analysis and a flexible control system. One manufacturer “found” eight hours of availability per week by optimizing their CIP recipes, reducing cleaning time while improving food quality and safety.
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Cleaning process equipment in place generally requires four basic tasks or routes. These are combined into a loop from the CIP system or skid, through the process and back to the CIP system. These are:
• Route within the process equipment to be cleaned,
• Route for returning used solution from the process,
• Cleaning solution source, and
• Cleaning solution return destination.
When cleaning solution does not pass through a tank, the control engineer might treat the two theoretical routes through the process equipment as one. The routes form a loop from the cleaning source, through the process equipment, to the return destination.
The cleaning solution source route may contain instrumentation to monitor the quality of the delivered fluid such as monitoring temperature, flow rate, and conductivity. The cleaning solution return destination may include instrumentation to allow recycling of CIP fluids. Equipment is generally exercised to enhance cleaning. For example, valves may be cycled or pulsed. Maintaining proper flow rates often requires that the route within the process equipment be adjusted to clean one portion of the total route and then another.
Determining the cleaning methods of a CIP system includes defining:
• What is to be cleaned by a cleaning procedure?
• What must be interlocked to safely allow cleaning in parallel with processing activities?
• What items can be cleaned in parallel or must be cleaned serially?
• How individual items are to be exercised (or not) while they are being cleaned?
The myriad of requirements makes CIP a very complex process, often more complex than the process used to make the products. While CIP control may be mostly manual—f raught with opportunity for human error, a programmed system is complex and rigid. A better, but less often used, alternative is recipe managed CIP control.
In programmed CIP, a programmer builds a program that includes all of the routes, interlocks, cleaning orders, and equipment exercises required to complete the cleaning methods. Lists of timers or pinning charts allow the end user to modify the duration of cleaning methods, providing some flexibility. Changing the cleaning methods themselves usually requires modification of programming by the original or another competent programmer.
The complexity of CIP requires complex software. Complex software is generally more rigid and difficult to optimize without creating software bugs. In a validated system, any modification to the CIP requires expensive and time consuming re-validation of the process.
The traditional approach of custom programming and pinning charts has been the gold standard of CIP control for a long time, up until now.
Recipe Managed CIP
The ISA-88 standard (S88) can help resolve many of these issues. In a paper entitled “Clean-in-Place Made Simple” delivered to the World Batch Forum in May of 2010, John Parraga of Rockwell Automation showed how to apply S88 to CIP. Applying S88 allows the control engineer to separate control of the equipment from how the equipment is to be used, i.e. “What the equipment can do,” from “What to do with the equipment.”
In an S88 compliant control system, coordination control occurs at runtime. Instead of constructing complex scenarios for arbitration, allocation, and interlocking or imposing the limitation of cleaning the entire process cell at once, CIP can start on portions of a process cell while other portions are finishing a batch of product. Improvement in equipment utilization increases available production capacity.