In this section you will learn
- Recipe types
- Information in a recipe
- The procedural control model
Batch processing requires equipment actions to occur in a defined sequence. More or less, defining a particular sequence is the primary function of a recipe.
According to S88.01, a recipe is defined as:
the necessary set of information that uniquely identifies the production requirements for a specific product
In other words, a recipe tells us how to combine ingredients (raw materials) using equipment to make a product.
We’ve all used recipes before to make scrumptious things like marinades and desserts. Of course, not all products made from recipes are edible. The last time we checked, shampoo didn’t taste very good. Eating it isn’t very nutritious either. From a different perspective, if you’ve had projects in your career like some of ours, you’ve also had recipes for disaster.
Different parts of a company may require different types of information about a product or the process to manufacture it. Consider this scenario:
- An R&D group is probably concerned with the properties of a product and general processing procedures necessary to make it, but may not care exactly what specific equipment is used.
- A corporate engineering group tasked with creating a process to manufacture a product may be very focused on the type of equipment used, but not the specific piece of equipment used per batch.
- A site production team is very interested in what specific pieces of equipment are available at a certain time to make a batch.
Different types and amounts of information are necessary for each of the three groups above. Using only one recipe to hold the necessary information for all three groups will be complex and cumbersome for everyone, so S88 defines four types of recipes that focus on varying levels of specific information. Figure 4 shows those four recipe types.
Figure 4: The Recipe Model
The general recipe is used at the company level and is the basis for lower-level recipes. It defines raw materials and their quantities, and the required processing to make the product. However, the general recipe is usually created without specific knowledge of a particular site or the equipment that will manufacture a product; it is supposed to communicate processing requirements to multiple manufacturing locations. People with knowledge of both the product characteristics and processing requirements —such as a development group— create this recipe.
As its name suggests, a site recipe is specific to a manufacturing site. It is usually derived from the general recipe to meet specific conditions or constraints of the site manufacturing the product. The site recipe provides the level of detail necessary for long-term production scheduling for a site. Site recipes might differ as to the language in which they are written or specifications for local raw materials. While it may still not be specific to a particular set of equipment, a site recipe may be specific to on-site processing or storage capacity and constraints.
A master recipe is targeted to a processing area and is derived from either a general or site recipe. Master recipes depend on equipment types or classes, such as a glass-lined reactor or mixing vessel. These recipes can contain product-specific information required for detailed scheduling, such as equipment requirements. But unlike the general and site recipes, S88 batch control requires a master recipe. A master recipe is the template for recipes used to create individual batches. Without this template, no specific batch recipes can be created, and therefore, no batches can be produced.
A control recipe is used to create a single, specific batch. It starts as a copy of a master recipe and is modified as necessary to create a batch. The modifications may account for batch size, characteristics of raw materials on-site (e.g., potency), or actual equipment to be used. While several (dozens, hundreds, or thousands of) batches may use the same master recipe, every batch has a single control recipe unique to that batch and that batch alone. Two control recipes may be identical in ingredients, quantities, or equipment used, but they are identified individually nonetheless. Control recipes unique to individual batches allow product tracking or genealogy to occur.
For example, ice cream companies may have master recipes that assume the potency of fat and non-fat solids in their cream and milk. However, since some dairy companies do not order dairy products standardized to specific potencies, each raw dairy storage tank most likely will have different potency values. This means that control recipe quantities will vary from the master recipe if the raw dairy tank potencies are different from those the master recipe specifies (as often happens). Also, the master recipe does not care from what raw dairy tank cream or milk is transferred. However, for reasons of product tracking and process variability, the raw dairy tank used needs to be recorded. This is captured in the control recipe. Companies also capture other important information, such as which batch tank is holding the mix, and the desired speed of the tank agitator.
Figure 5 shows an exploded view of a recipe managed in a two-site company. Note that plant 2 only has one process cell. In this case, the formal need for a site recipe may not be needed, but might be maintained for consistency with the other site.
Figure 5: A Recipe Explosion
Now, the reality is that many S88-aware batch control solutions in the marketplace today start managing recipes at the master recipe level. Engineers or scientists may define master recipes. When a batch is scheduled for production, the S88 batch engine creates a control recipe in memory and downloads batch-specific information to a DCS or one or more PLCs. The batch engine then creates a batch record for each control recipe, storing time-stamped default and user-specified information about the batch as it is made. As an option, it can also archive the control recipe batch record to a database. When the batch is finished, the control recipe no longer exists, but the data collected from the recipe and batch remains.
Information in a Recipe
Per the founding fathers (and mothers) of S88.01, a recipe contains five categories of information:
- Header – Administrative information (recipe ID, author name, version number, revision history, approvals, etc.) and a process summary.
- Equipment Requirements – Information about specific equipment necessary to make a batch or a specific part of the batch. (Since general and site recipes don’t usually call out specific equipment, the requirements in these recipes are typically described in general terms.)
- Procedure – Defines the strategy for carrying out a process. That is, the procedure is really the recipe steps or “instructions” provided to a control system or operator.
- Formula – Describes recipe process inputs (e.g., ingredients, quantities), process parameters (e.g., processing temperature, ingredient transfer rate, mixing speed ), and process outputs (the product and its quantity resulting from a single batch). Formulas can be used to distinguish between different products or different product “grades” defined by the same procedure.
- Other Information – Anything that doesn’t fit in the other categories (this can be miscellaneous operator instructions, safety comments, etc.).
The rest of this section will be explaining the recipe procedure, as it is most complex of the five categories above.
The procedure explains how ingredients (raw materials) are to be combined, reacted, or otherwise processed to make a batch. S88.01 defines two models for representing recipe procedures:
- The Process Model for general and site recipes. This model focuses on describing process functionality, rather than equipment.
- The Procedural Control Model for master and control recipes. This model focuses on describing the process as it relates to physical equipment.
Curious about the Process Model?
The tutorial, Applying S88, Batch Control from a User’s Perspective, provides good detail with examples.
As we said above, current S88 batch engines start managing recipes at the master recipe level. And so, to keep this tutorial short (but sweet), we’re going to skip the Process Model, and jump right to the Procedural Control Model.
Figure 6 shows the Procedural Control Model.
Figure 6: The Procedural Control Model
A procedure is the highest-level in the procedural control hierarchy. It defines the overall strategy for making a batch. It consists of an ordered set of unit procedures.
A unit procedure is an ordered set of operations that is carried to completion on a single unit. That is, a unit procedure is a contiguous production sequence acting on one and only one unit. Only one unit procedure is allowed to be active on a unit at any time. Multiple unit procedures can run concurrently as part of the same procedure, as long as they are active on different units.
An operation is an ordered set of phases carried to completion within a single unit. Operations usually involve taking the material being processed through some type of physical, chemical, or biological change. Like unit procedures, the standard presumes only one operation is active on a particular unit at a time.
A phase is the smallest element of procedural control that can accomplish process-oriented tasks. Phases perform unique and generally independent, basic process-oriented functions, such as charging an ingredient or agitating a tank. Simply put, phases are the workhorses of recipes. All other elements (procedures, unit procedures, and operations) simply group, organize, and direct phases.
Figure 7 is a recipe procedure for making ice cream. There are four unit procedures associated with this procedure: Make Mix, Flavor Mix, Fill Pints, and Package.
Figure 7: An Ice Cream Recipe Procedure
Figure 8 looks into the Make Mix unit procedure and shows the two operations associated with making mix: Blend Ingredients and Pasteurize.
Figure 8: The Make Mix Unit Procedure
Notice that the two operations are sequential. That follows the rule allowing no more than one operation to run on a unit at a time.
Figure 9 double-clicks into the Blend Ingredients operations and shows the eight phases associated with blending ingredients:
Figure 9: The Blend Ingredients Operation
As you can see, there is no rule on running only one phase at a time. In fact, it is very common for multiple phases to be running simultaneously.
Okay, enough about recipes (for now, at least). Remember the three important elements to define a batch control system:
- How to make the product (recipes)
- What physical tools are needed to make the product (equipment)
- How to run that equipment (control activities)
Now, it’s time learn about the second element: equipment.