Page 298 - Design of Simple and Robust Process Plants

284 Chapter 8 Instrumentation, Automation of Operation and Control
better have few good reliable instruments than lots of unreliable ones.

Simple and robust plants minimize on instrumentation versus conventional design;
in other words, fewer components results in fewer failures.
The automation of processes to operate consistently by minimizing human opera-
tion is applicable based on reliable, robust instruments and instrumentation sys-
tems and provided with robust operational programs.
Robust control must meet the criteria of hands-off operation; this means that the
operator is not in the control loop, although in most processes this is not yet a rea-
lity. The control technology is on the brink of major change. Currently, the basic
process control is based on heuristic rules for the selection of the control strategies.
The design of predictive or model-based controllers (multi-variable controllers) to
enable operation at its constraints has been developed during the past decades. The
design of these controllers is based on linearized input and output models around
working points. These models have been developed with process identification tech-
niques on existing processes.
The technology of dynamic simulations of operations is sufficiently mature to
enable the design of control strategy and controllers. The control design parameters
have been developed in parallel. The control strategies and controllers designs can
be verified in a closed loop simulation before being implemented in the field. Now,
the change can be made from an heuristic design and empirical techniques to fun-
damental, model-based designs.
In the previous chapters the attention was drawn to process and equipment
design. In this chapter, the emphasis is on hands-off operation of the process. It is
not the intention here to elaborate on instrument or control design, but to make the
reader aware of the opportunities to achieve the objective of hands-off operation.
The realization of the design philosophies, ªDesign for total quality control and first
pass prime operationsº, forms the starting point for automation and control. The
basic control system and instrumentation are the base for operation optimization
(see Chapter 9), and site-wide and remote operations as reflected in the operational
hierarchy (Figure 8.1). It is the combination of process design and control design
which makes the concept of simple and robust process plants a reality.

Business
optimization
Process
optimization
Model based
control
Basic control

Plant Instruments

Fig. 8.1. Hierarchy in operation.