Environment and control issues in design

Abstract

The basic principles guiding the operation of the processing units of a chemical process are based on the following objectives. Safe operation of the processing units. Specified production rates must be maintained. Product quality specifications must be maintained. Perform satisfactorily under conditions different from the nominal design conditions. While process design aids in performing the principla function of the industry, that is to convert raw materials into products, it is process control and operability that is responsible for satisfying the above objectives. Currently, the most striking flaw in any industrial operation is the lack of associative interaction between the design and control system. An improper interaction between the two not only leads to a design which might be uncontrollable, and hence infeasible, but also incurs a lot of expenses while attempting to operate in the uncontrollable regions. This research mainly focuses on analyzing the importance of the interaction between design, controllability and operability issues. A qualitative and a quantitative analysis of the criterion for operability that could be used during the design phase of a process have also been performed. Then these criteria have been tested on several test processes. Controllability has been assessed by the method of singular value analysis (SVA), which helps in the design of different control strategies, and compare them with a controllability index called condition number. Operability is assessed by the economic feasibility, environmental impact, safety, resiliency (ability to tolerate and to recover from undesirable changes and upsets) and flexibility (ability to operate at a range of feed conditions and parameter variations) of the procss design. Quantitative measures were developed for economic feasibility (by annual equivalent profit) and environmental impact (environmental impact index). The operability and controllability analysis has been incorporated into the design of the process. While the qualitative analysis gave a feel of all the issues that need to be considered to make a process operable, the quantitative of the criterion gave a simple method by which the best operable and controllable alternative can be chosen. Thus, with the above analysis, a procedure to assess the operability and controllability of a process was developed and the importance of their integration with design was proved. This analysis will be described within a framework that evaluates and optimizes processing alternatives where economics, environmental impact, and controllability are considered.