S88 Redefines Clean in Place Operations
Class-based programming simplifies design, testing and validation of reusable modules, such as those found in CIP processes.
By Christie Deitz and Dan Lorenzo, Senior Principal Engineers, Emerson Process Management, and Sean Stephan, Senior Automation Engineer, Biogen Idec
When ISA’s SP88 committee began development of the now familiar ANSI/ISA-S88 (Parts 1-3) Batch Control standard (S88), few people outside the software engineering environment knew much about object-oriented and class-based programming techniques.
SP88 committee members understood that there was a great need for improving how batch processes were defined. They also knew that batch processes, regardless of company, industry or locale, contained similar unit operations with similar equipment, such as fermenters, batch reactors, holding tanks, filtration systems, and Clean-in-Place (CIP) skids and valves.
Today, S88 is an internationally recognized standard that emphasizes good automation practices, is suitable for a broad variety of batch processes, is effective for any degree of automation being applied, and fits nicely into the class-based programming environment.An iterative design process
One of the things that makes S88 universally appealing for batch processes is that it promotes a structure of identifying and reusing identical and/or similar physical entities. S88 models define a hierarchy of physical entities and associated procedural elements (Figure 1, below). In S88 terms, these become the physical model and the procedural model.
|Figure 1. ANSI / ISA S88 as a modular design tool — Work top-down when defining physical entities. Work bottom-up when defining procedural actions.
When defining batch processes, it is best to apply a top-down/bottom-up design approach. Begin at the top of the physical model and work downward, defining boundaries (process cells, units, etc.) and the specific equipment within each boundary (vessels, pumps, headers, valves, etc.). Once physical entities are identified, work upward from the bottom of the procedural model to define the actions that each piece of equipment and unit will perform.
This model supports an iterative design process that helps identify reusable objects. The benefit becomes apparent when a process is undergoing initial designs, perhaps for budgeting purposes. Usually at this point, Piping and Instrumentation Diagrams (P&IDs) are not available and preliminary designs are based on Process Flow Diagrams (PFDs). Because equipment specifics are still undefined, automation designs are developed at a high level.
Later, when P&IDs become available, the S88 model and its support for top-down/bottom-up designing makes expanding the details of the preliminary design easier. Additionally, the iterative design approach is well suited for achieving the true objective of object-oriented programming techniques—identifying reusable software objects.The CIP process — from concept to practice
For many of us, a top-down/bottom-up iterative design approach, identifying class-based entities, and developing reusable objects, makes a lot of sense. But it is harder to understand what this approach looks like, and it is helpful to have a practical example.
Clean-In-Place, or CIP, is a process frequently used in pharmaceutical and biotech manufacturing facilities to ensure that process lines, vessels and reactors are free of inorganic and organic contaminants. At the laboratory scale, equipment can be cleaned manually, but in large-scale production processes it is impractical to disassemble equipment and transfer lines to clean individual components. Instead, this must be done by sending cleaning solution through the process path, or CIP circuit, without disassembly. This introduces unique design challenges.
Within flexible manufacturing facilities, other factors complicate CIP. Because process connections frequently change, it is necessary to identify, track and clean the multitude of possible product transfer paths from upstream to downstream vessels, and to supply CIP solution from a few shared CIP sources to a number of process units distributed throughout the facility.
Even with preconfigured modules and efficiency tools, automating CIP activities and finding a solution that is easy to use, validate and maintain remains a challenge. Defining the boundaries and responsibilities of the various elements is a key step. There are several suggestions to keep in mind when defining boundaries:
- Seek identical or very similar entities
- Identify unique and one-of-a-kind entities
- Select several smaller objects, which provide more flexibility than a few large objects, and are easier to develop, validate and maintain.
To ensure a robust CIP design, examine the pros and cons of various boundary assignments and seek partners experienced in designing such applications. Where and how boundaries are defined not only influences an object’s reusability, but can also impact schedule and cost.
CIP sources are typically self-contained process skids that deliver cleaning solutions based on requests from process units, such as tanks, fermenters, filter skids and chromatography skids. A few CIP skids often provide cleaning for an entire production facility.
CIP skids respond to requests from process units to drain, rinse, clean, wash and perform final rinsing on “dirty” equipment and transfer lines. Cleaning solutions are commonly delivered through mix-proof, multiport (MP) valves. MP valves have a unique design. When a valve is closed, upper and lower valve cavities are separated and fluid passes straight through. When the valve is opened, the cavities are joined and fluid is routed to a different line based on pressure. Grouped together, MP valves make up a valve manifold (VM) that delivers cleaning solutions to different destinations.Design once, use often