Page 26 - Design of Simple and Robust Process Plants

1.3 Design Philosophies 9
1.3.3
Optimize Design

This effort can be split into optimization of the process design and of the supply
chain. To pursue process optimization, techniques and process synthesis tools are
available in commercial simulators. For the optimization of the supply chain (in-
cluding feed, intermediate and product supply), information must be gathered on
reliability and availability (with its probabilities) of feed and product deliveries, pro-
cess reliability and availability (planned or unplanned) with its repair and recovery
times. This can be accomplished with reliability modeling (Koolen et al., 1999).

1.3.4
Clever Process Integration

There is a trend in process design to maximize process integration. The trend set by
the energy optimization is now extended with the integration of water, and hydrogen
and in fact counts for all streams that are subject to re-usage. A high level of integra-
tion can result in high savings from a steady-state perspective. The disadvantages of
integration are the availability of the ªserviceº stream and its dynamics that need to
be understood in all its aspects. We must differentiate between: (i) integration with-
in a unit where we must watch for start-up and unit stability; and (ii) integration
between units (processes) that asks for careful design of the system to handle distur-
bances and availability. Dynamic studies in close consultation with control engineer-
ing are a requirement, where provisions for de-coupling in terms of hardware and
software are a requirement for robust control and operational design.

1.3.5
Minimize Human Intervention

Human beings are able to develop and exploit new things. They have ± next to
others ± a characteristic which, depending on the situation, can be either an advan-
tage or a disadvantage. Humans like to learn and improve, often by trial and error,
but this means they are not consistent in performing tasks. For the operation of
chemical plants, this is a handicap which leads to many process upsets and often
must be resolved by human intelligence at a later stage. The best way to overcome
this is by implementing a high level of automation for routine operations and robust
control design, yielding reliable closed loop performance. Currently, most processes
have an operator in a control loop to obtain the required quality of operation.

1.3.6
Operation Optimization Makes Money

Process plants are always operated in a variable business climate that has an impact
on its economic operation. The variations in prices of raw materials, energy and
products and their demand will have a large impact on plant's economic perfor-