Page 57 - Design of Simple and Robust Process Plants

3.3 Design Philosophies 41
izing, concentration±dilution±re-concentration, or separation±mixing±separation
(Figure 3.2).
In the above examples it was the intention to illustrate that sequential thinking
and default design approaches lead to conservative designs. The solution is to stimu-
late creative thinking, particularly during the conceptual design phase of a project.
Within a value engineering technique a methodology known as ªfunction anal-
ysisº was first developed during the 1960s (Bytheway, 1965), and later described
more extensively (Snodgrass and Kasi, 1986). This methodology (which will be de-
scribed in more detail in Chapter 10) is based on setting up a brainstorming team to
achieve simpler and more economical designs. After the initial design has been
developed, the team is challenged to reduce/simplify the design. At that stage, the
brainstorming often achieves limited results with marginal proposals. The reason is
that the team members often have difficulties in achieving a sufficiently high level
of abstraction to identify ªout-of-the-boxº ideas. The methodology of function analysis
creates a higher abstraction level, with help from a trained value engineer, by defining the
basic function of the design steps.
For a process plant design the index flowsheet is reviewed step by step on its prin-
cipal functions. The function is described as an ªactive verbº and ªa nounº. The ques-
tion is, does the step add value and if so, can the function be realized/improved by
alternatives? All options to achieve the objective of lower cost with maintaining the
ultimate objective to make long-term maximum profit are evaluated.
The most generic questions are:

. Do we need this process, unit, equipment, utility?
. Can we replace this functionality by an external service?
. Can we avoid this step by combining it with another step?
. Does it add value for the customer?
The brainstorm team lists the potential project alternatives and evaluates these in
concert with the project team on added value for application, see Chapter 10, Appen-
dix 2 for more details.
Minimization of piping and instruments should be addressed during the develop-
ment of the P&IDs ( process and instrument diagram) and the HAZOP (hazard and
operability) studies. Historically, during P&ID development the addition of lines
and instruments is a ªsportº, which is seldom lost by anyone who likes to add an
item. All the items will form part of the final estimate, and from that perspective are
not a burden for the project manager. There are mountains of rationales and argu-
ments to justify the inclusion of an additional item. In general, a situation is pic-
tured which will result in an unacceptable situation if it is not dealt with at this
time. The likelihood of such an occurrence is often beyond discussion at this point,
and the only way to solve the increasing levels of items during P&ID's development
is through the participation of critical engineers, by questioning the inclusion of
items, based on the following points:

. Why do you need this item?
. What would happen if we did not have the item?