Page 436 - Design of Simple and Robust Process Plants

10.3 The Design of High-quality Plants 423
. In conceptual design, the emphasis is on mass and energy balances, control
diagrams showing all instruments hooked up to the control system (in a sim-
plified notation) including basic control loops, and preliminary equipment
sizing for cost estimation only, preliminary plot plan and equipment layout.
. Basic engineering includes P&IDs for process as well as utilities, equipment
specifications for engineering, piping specifications, process data for piping
and instruments, final plot plan and equipment layout.
Conceptual design has a lower level of definition, and therefore has a less accurate
estimate. The advantage is that the business does not spend all the cost for the prep-
aration of a full definition package while they have other business options under
evaluation. Another advantage is that basic engineering can easily be carried out
externally on a conceptual design package The disadvantage is that the company
loses time in the preparation for this additional phase and its decision steps.
As discussed previously, the efficiency in engineering (speed and cost) is realized
by the application of a work process that incorporates the functions at the right time
to prevent rework.
10.3.1.4 Bench-marking
A work process can be judged by the evaluation of project executions with external
evaluators. External bench-marking has the benefit that it not only shows your
own performance, but also your relative position to other companies. A generic
report on bench-marking was made by Ahmad and Benson (1999). Companies
active in this field are the well-known Solomon studies for technology compari-
sons. A commercial company that has long experience in project evaluation of
chemical plants is Independent Project Analysis Inc. (I.P.A. Inc.), who initially
gained experience in project evaluation by performing specific studies to explore
the reasons behind project failures. Later, they started evaluating different projects
in the process industry for a wide range of processes. During these evaluations
they collected project information over the total project lifetime from the start of
the project until full capacity was realized. This information was ordered and col-
lected in a knowledge database, with which I.P.A. Inc. have developed correlati-
on's between elements of design and project results.
The project results were measured in terms of capital and timing realized versus
budget and time plan. They also record the time needed to reach full capacity after
construction. Other results measured were design and engineering time. Different
elements of design information were collected through answers on questionnaires
which were evolving over time.
The ultimate conclusion, found through a parametric statistical technique, was
that there exists a strong correlation between the completeness of the design before
engineering starts and the project result (Merrow and Yarossi, 1994). Based on this
information, the term front end loading (FEL) was introduced, which expresses the
level of completeness of the design in a number before engineering starts. The effect
of FEL versus relative capital cost is shown in Figure 10.6.
In conclusion is can be said the an effective work process includes front end load-
ing, a well defined design basis for engineering and is based on a feed forward
approach with feed back (reviews) adjustment to support concurrent engineering