and operations may be further organized into phases. The following text-book recipe illustrates the organization. Charge and Mix materials A and B in a heated reactor, heat to 80C and react 4 hours to form C. Transfer to blending tank, add solvent D, Blend 1hour. Solid C precipitates. Centrifuge for 2 hours to separate C. Dry in a tray dryer for 1 hour. A simplified S88-style procedural organization of the recipe might appear as follows: Unit Procedure 1: Reaction Operation 1: Charge A & B (0.5 hours) Operation 2: Blend / Heat (1 hour) Operation 3: Hold at 80C for 4 hours Operation 4: Pump solution through cooler to blend tank (0.5 hours) Operation 5: Clean (1 hour) Unit Procedure 2: Blending Precipitation Operation 1: Receive solution from reactor Operation 2: Add solvent, D (0.5 hours) Operation 3: Blend for 2 hours Operation 4: Pump to centrifuge for 2 hours Operation 5: Clean up (1 hour) Unit Procedure 3: Centrifugation Operation 1: Centrifuge solution for 2 hours Operation 2: Clean Unit Procedure 4: Tote Operation 1: Receive material from centrifuge Operation 2: Load dryer (15 min) Unit Procedure 5: Dry Operation 1: Load Operation 2: Dry (1 hour) Note that the organization here is intended to capture the entire process for scheduling. A recipe for process-control purposes may have a more narrow scope. Most of the constraints and restrictions described by Pinedo are applicable in batch processing. The various operations in a recipe are subject to timing or precedence constraints that describe when they start and or end with respect to each other. Furthermore, because materials may be perishable or unstable, waiting between successive operations may be limited or impossible. Operation durations may be fixed or they may depend on the durations of other operations. In addition to process equipment, batch process activities may require labor, materials, utilities and extra equipment. Cycle-time analysis In some simple cases, an analysis of the recipe can reveal the maximum production rate and the rate limiting unit. In the process example above if a number of batches or lots of Product C are to be produced, it is useful to calculate the minimum time between consecutive batch starts (cycle-time). If a batch is allowed to start before the end of the prior batch the minimum cycle-time is given by the following relationship: Where CTmin is the shortest possible cycle time for a process with