Thursday, 16 July 2009

What's in a Process Cell

There is currently much discussion about what a Process Cell is as you can see on the Part 5 blog.
As I view it, a Process Cell:
1- is the domain within which batches can be made according to a recipe.
2- contains the collection of equipment (units, and equipment modules) that meet the equipment requirements of the recipes that can be produced in the cell
That is I believe what S88.01 says, but in different words:
S88 (original and latest draft) says
A logical grouping of equipment that includes the equipment required for production of one or more batches. It defines the span of logical control of one set of process equipment within an area.
NOTE - This term applies to both the physical equipment and the equipment entity.

But this really does not define the boundaries of a Cell in the way that we like to put boundaries around Units for example. Why not make an entire plant a process cell? Of course, a cell lives 'in an area' .
So might be that the boundaries of a Process Cell are arbitrary provided they meet the definition.
I have seen several large plants where there are dozens of Units in the Process Cells, and have worked on projects where there were only a few. Why? Because of repetition - if you have many similar units it makes sense to put them into the same process cell because they can run the same recipes. And Recipes execute in Process Cells.
But as Part 1 also says Logical Control
Is that Logical as in mathematics? Or as in intuition?
From the Intuition point of view, it just makes sense to have say solvents handing in a different process cell to reaction doesn't it? Is that enough?
But how about Logical Control? Are we talking about basic control logic - or Procedural Logic?
I think we can forget basic control here so can we somehow make a logical choice based on the Recipes? And one that generally agrees with the intuitive one? I think so.

It depends on finding the Batches, Equipment Requirements and the Routes.
Start by asking where are the batches? If a batch comes out of one unit, and then joins with other batches so that the downstream units are working with bigger batches, or conversely where batches are split up so the downstream units are working on smaller batches then I would have two process cells. In the case of say a plant with feed storage vessels then bioreactor units then intermediate storage then filtration units then product storage I would have something like Feed storage process cell bioreactor process cell intermediate storage process cell filtration process cell product storage process cell And by the way I would call the storage vessels Units.
As for the connectivity, what I mean is that all the euipment in a single Process Cell should permit the transfer connections needed to assemble the instances of required equipment for the Cell's Recipes.