Page 27 - Design of Simple and Robust Process Plants

10 Chapter 1 Introduction
mance. These variations may occur on a daily, weekly or monthly basis, although
there may also be variations on an hourly basis. Other quite common variations are:

. the day and night temperature cycle that might challenge ongoing maximiza-
tion of the operational capacity;
. production schedules, product transients;
. raw material composition; and
. fouling or catalyst aging.
As all these variations have an impact on the economic optimum for operation, an
optimization effort is more than attractive, that often justifies a closed loop optimi-
zation. The objective of the optimization is to maximize the profit of the operation.
The introduction of a profit meter (as described by Krist et al. 1993) is an essential
element of operation optimization. The profit meter is based on plant mass balance
streams (preferably calculated by reconciliation of the plant mass balances) in con-
volution with the individual stream economic prices to make a continuous real-time
financial balance, to support real-time optimization.

World-class Manufacturing Perspective

1.3.7
Just-in-time Production (JIP)

This concept has been developed since the early 1980s, and was focused on the
production of components or a set of integrated components The principle of mini-
mizing the feed, intermediate and product storage can also be applied in the process
industry, and is fully in line with the basics of simple and robust design. The mini-
mization of storage is accomplished through the integration of production lines and
storage in transport. The minimization or even elimination of storage was in the
past applied in case of low-boiling liquids or extremely hazardous materials, for
example hydrogen, methane, ethylene, chlorine, and ammonia. This demonstrated
that, from a logistic and a technical point of view, the techniques to deal with these
situations are available. The key is the mind set to evaluate this also for other situa-
tions.

1.3.8
Design for Total Quality Control (TQC)

The concept of TQC can be divided in two different philosophies:
1. Prevent upsets versus cure. Nowadays, it is common practice to design process
plants with many provisions for recycling, such as recycle tanks and check
tanks. All these provisions are ªrequiredº to deal with any off-spec situation
during start-up and ªnormalº operation. Next to the investment cost of these
provisions, recycling of material always costs capacity and additional opera-
tional cost. On occasion, we even design the capacity of the plant to include a