Scheduling Multiproduct Chemical Batch Processes using Matrix Representation

Batch process plants are usually designed for the production of specialty and fine
chemicals such as paint, food and pharmaceutical to meet specific product requirements
as set by current market demand. Batch process plants can be operated as single product
in which only one product is produced and multiple products which allow production of
more than one product using same batch facility. The economics of the batch process
heavily depends on efficient scheduling of the different tasks involved in manufacturing
the range of products. The main objective of scheduling is generally to minimize
completion time known as the makespan of the batch process. Product sequencing, which
is used to set order of products to be produced, has a direct impact on the makespan
particularly in the multiple products case. Another effect on makespan is observed for
different transfer policies used to transfer the product intermediates between process
stages. The generally adopted intermediate transfer policies are (i) zero wait (ZW), (ii) no
intermediate storage (NIS), (iii) unlimited intermediate storage (UIS) and (iv) finite
intermediate storage (FIS). In the past, the determination of makespan for each transfer
policy has been done using a number of mathematical and heuristics approaches.
Although these approaches are very efficient and are currently being applied in many
chemical process industries but most of them end up with the solution in terms of
complex mathematical models that usually lack user interactions for having insights of
the scheduling procedure. This motivated the current work to develop relatively simple
and interactive alternate approaches to determine makespan. The proposed approach uses
matrix to represent the batch process recipe. The matrix is then solved to determine the
makespan of a selected production sequence. Rearrangement of the matrix rows
according to the varied production sequences possible for the specified batch
process recipes enables the makespan to be determined for each sequence. Designer is
then provided with the production sequence options with its corresponding makespan
from which a selection could be made according to the process requirements.