BPF: Characterize system operation

Process Classification

One of the first things that ChE's need to know about processes is the many different ways in which we may operate a process.

There are three major classification of processes:


In a batch process, material is placed in the vessel at the start and (only) removed at the end --no material is exchanged with the surroundings during the process.

Batch Examples: baking cookies, fermentations, small-scale chemicals (pharmaceuticals)


In a continuous process, material flows into and out of the process during the entire duration.

Continuous Examples: pool filter, distillation processes


A semi-batch process is one that does not neatly fit into either of the other categories (i.e., it is a catch-all classification).

Semi-Batch Examples: washing machine, fermentation with purge.

Process Operation

Each of the above classes of process may be further distinguished by their mode of operation with respect to time.

Continuous processes may be run:


At steady-state, none of the process variables change with time (if we ignore small, random fluctuations).

or it may be run


At unsteady-state, the process variables change with time. (One class of unsteady-state processes are oscillatory, where they process variables change with time in a regular way. All other unsteady processes may be called Transient meaning that the process variables continuously evolve over time).


Give original examples of (and identify) batch, semi-batch, continuous, steady, and transient processes


Under what modes of operation may batch or semi-batch process be run?