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01 April 2004

General to master

Capturing best engineering practices in recipe generation.

By Dennis Brandl

General and site recipes are the least known elements the ISA-88 ISA Batch Systems Standards describe. However, they can provide significant economic benefits to companies that manufacture the same products at multiple sites or use contract manufacturing. They may also speed up new product deployment and aid in business-to-manufacturing integration.

One of the most controversial aspects of general and site recipes is the process of transforming a general or site recipe to a master recipe. Companies using general or site recipes have traditionally viewed generating master recipes as a manual engineering task. The transformation has generally required significant experience in master recipe construction and detailed knowledge of the target process cells. Historically you needed an understanding of the economic or operational optimizations important to the plant and an understanding of the notations and terminology of the development or pilot plant.

The ANSI/ISA-88.00.03-2003 Batch Control Part 3: General and Site Recipe Models and Representation standard contains a description of transformation that gives a basis for automated transformation of general recipes to master recipes. This section had significant discussion and disagreements, because the algorithms for transformation are not well known and can be hard to implement. However, you can automate the transformation if the general recipe definition strictly conforms to the ISA-88 Part 3 model. Even if transformation is not automated, following the ISA-88 Part 3 standard simplifies a difficult engineering task, resulting in more consistent master recipes, reduced test batches, and faster master recipe generation.

The above methods have seen use in multiple companies. These methods allowed the companies to gain economic advantages from general recipes, reducing the engineering time and cost for new product deployment. General recipe transformation can use each site's best engineering practices in the transformation process. The result is more consistent master recipes, fewer trial batches, and improved multisite product consistency. You can manually perform methods for general recipe transformation, or you can use semiautomated or completely automated methods. Automation requires strict conformance to the ISA-88 Part 3 procedure definitions models.

General and site recipes

The information manufacturers need to make a product is known as general and site recipes. This information defines the basic chemistry and physics a manufacturer would need to make the product without defining specific equipment, unit layout, unit transfers, unit initialization, and unit cleanup. You could view general and site recipes as material-centric, rather than equipment-centric (master) recipes. They may contain constraints on the target equipment, usually when the equipment characteristics can affect the chemistry or the physics of the desired reactions. Typical constraints are the interior lining or material of vessels and pipe construction, mixing types (normal or low shear), and heating ranges or rates.

Where to begin

The first step in effective transformation is for each site to define the best way to implement each process action on each unit that can perform the action. The ANSI/ISA-88.01-1995 Batch Control Part 1: Models and Terminology recipe standard is a good way to do that. There may be a simple one-to-one relationship between process actions and master recipe phases, or there can be a very complex relationship. In ISA-88 Part 1, a new structure is a segment of a master recipe. It is called the master recipe transformation component. The standard defines it as "the part of a master recipe that is used in the transformation of an equipment independent recipe into a complete master recipe." Some users of general recipes use the terms recipe segment, recipe component, or (as in this article) transform component in place of the long name. A transform component may be as simple as a single phase or as complicated as a set of complete unit procedures.

Each site should define the appropriate transform component for each unit or process cell that can perform the action. Transformation of a general recipe to a master recipe uses the mappings, in part to determine which units are possible targets to the master recipe. Actual use of transform components in transformation must also take into account the range of values for parameters in a process action and the corresponding range of parameters within the phases of each transformation component. For example, a process action "HEAT" may define a temperature of 220°C in a general recipe. When determining possible target units, you will need to check the 220°C value against the actual range of the heating phases to ensure the required temperature is within the range of values available for the unit. Not only must a unit be able to implement a process action, but it must be able to meet the requirements contained within the process action parameters.

Unit management

Other elements of information you need to define are how to prepare each unit before using it and how to clean up or finish up each unit after using it. Initialization activities may define such operations as getting the unit up to temperature or pressure and making sure the unit is clean or empty. Finalization activities may define such operations as cleaning, sterilizing, flushing, and cooling the unit. Again, define the initialization and finalization operations as master recipe transformation components. You do not need an initialization or finalization transform component for each unit. Storage units may have no initialization of finalization operations.

The transformation

Once all basic information is in place, transformation can start. First, transform components for each process action available on each unit or unit class. Transform components for material entry to a unit or unit class, for material exit from a unit or unit class, and for material transfer between units. Then you will need to transform components for unit or unit class initialization and finalization.

The first transformation step is to expand the general recipe using the underlying process. If the places where materials are joined is used as a boundary condition, then we can call each collection of process actions a material path because it defines a path of actions for a single material dependency. The next step is to eliminate transform components on units that do not meet the equipment requirements associated with the process stage or process operation. A process stage may require equipment with external heating coils, because the material would foul internal coils. If the equipment (unit) associated with a transform component has internal coils, you would remove that specific mapping from the list of possible mappings.

If you cannot find any transform components on units that meet the equipment requirements, then no transformation is possible. Also, effective use of equipment requirements can simplify the transformation process—if you eliminate inappropriate equipment early.

All possible combinations

Using the remaining transform component actions, build a list of all possible combinations of transform components and units that can perform the required set of actions. You could call these transform paths because they define possible transformation paths through units.

You can identify each transform path (TP) by its starting unit and ending unit. The right side of the figure below illustrates the combination of the transform paths with the material path. In the example below, there are four possible ways to perform the right top material path segment and two possible ways to perform the final material path segment. At this point it is sometimes possible to eliminate transform paths because of illegal transfers between units. For example, if a material path required a transfer from Unit 1 to Unit 3, then the associated transform path could be eliminated because there is no legal transfer defined between these units. In the examples there are multiple possible transform paths for a single material path; in practice there is usually less complexity because many process actions are limited to specific units. In the figure below, the identification of a transform path indicates the starting and ending unit, for example (U2-U5) indicates the transform path starts in Unit U2 and finishes in Unit U5.

Next you need to construct each possible combination of transform path and material path. Each combination can be called a recipe path. Each recipe path is a possible combination of transform components and material dependencies that can perform the actions the general recipe requires. Obviously this can generate a large number of possible recipes. Eliminating any path with an illegal material transfer can reduce the number of recipe paths. If any recipe path required a material transfer from Unit 3 to Unit 5, you could eliminate it.

Hopefully, you will have at least one recipe path remaining after considering undefined unit-to-unit transfers and equipment requirements. If no recipe path remains, then you will not be able to construct a valid master from the general recipe. If that is the case, you will need additional unit-to-unit transfers or process action-to-unit mappings. If multiple recipe paths exist, you can use various optimization strategies to determine the best master recipe. Or you can generate multiple recipes, and the schedule can define which recipe to use. For example, there may be a cost or efficiency associated with each unit or with each process action on a unit. You can calculate the cost or efficiency for each recipe path and choose for transformation the path with the lowest cost or highest efficiency.

Transform paths (left) and material paths (right)

Construct the elements

The next steps in transformation involve generating the master recipe from the recipe path. There are two main elements of master recipe generation: building the operations and building the unit procedures. The general steps are:

• For each unit used, create a unit procedure.
• When you first use a unit, add the transform component associated with unit initialization. A good practice is to make this the first operation in the unit procedure.
• When you last use a unit, after material is transferred out, add the transform component associated with unit finalization. A good practice is to make this the last operation in the unit procedure.
• Add the transform components associated with each process action.
• Use the process operation boundaries to define operation boundaries.
• When process actions are in parallel, create a parallel structure within the operation.
• For each material transfer between units, add the transform component for each unit into each unit's operation. This step actually defines the overall structure of the master recipe.

Material dependency map and process action to unit mapping

Master recipe structure

Because you organize master recipes by unit procedure, it is vital that you determine the correct unit procedures. The material transfer between units actually defines the overall master recipe structure. Apply the following rules to master recipe structure:

• For each starting unit in the recipe path, add a unit procedure under a common parallel. Eventually, there may be timing phases or allocation elements added before these unit procedures, but theoretically they could all start in parallel. Practically, there are usually timing considerations you should consider. Path P6 may take six hours, while Path P5 may take twenty minutes.
• If a transfer occurs and no parallel process actions are required during the transfer, then you can place the transfers in separate unit procedures from the previous processing.
• If parallel actions are required during a transfer out and the transfer in, then you will need to define the unit procedures in parallel.
• If there are parallel actions on the transfer out but not on the transfer in, then the transfer in can be a separate parallel unit procedure, but the transfer out cannot.
• If there are parallel actions on the transfer in but not the transfer out, then the transfer out can be in a separate parallel unit procedure.
• You might need to add deallocation elements after the unit finalization.
• Some transformation components may involve multiple units, such as preparation of a material mixture. Where possible, implement these as separate unit procedures, using the same rules above for material transfer rules.

Final steps

The final step in master recipe generation involves mapping the parameters in the process actions into phase, operation, and unit procedure parameters in the master recipe. There may be a one-to-one correspondence between the parameters, but it is more likely there is a complex relationship. For example, a process action parameter may have a single value for the amount of a material addition, and you could implement this using several phases. Phase 1 could add 25% of the total amount using a shot add method. Phase 2 could add 50% of the total using a rate controlled add method. And Phase 3 could add the remaining 25% using a temperature controlled add method. You should copy formula values and header information from the general recipe to the master recipe, along with any equipment requirements beyond those you use in transformation.

Behind the byline

Dennis Brandl is president of BR&L Consulting in Cary, N.C. He presented at the World Batch Forum North American Conference in Woodcliff Lake, N.J., in April 2003.