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Chemical Engineering Design
The subject of this book is chemical engineering design, but the methodology
of design described in this section applies equally to other branches of engineering
design.
Design is a creative activity, and as such can be one of the most rewarding and satisfying
activities undertaken by an engineer. It is the synthesis, the putting together, of ideas to
achieve a desired purpose. The design does not exist at the commencement of the project.
The designer starts with a specific objective in mind, a need, and by developing and
evaluating possible designs, arrives at what he considers the best way of achieving that
objective; be it a better chair, a new bridge, or for the chemical engineer, a new chemical
product or a stage in the design of a production process.
When considering possible ways of achieving the objective the designer will be
constrained by many factors, which will narrow down the number of possible designs;
but, there will rarely be just one possible solution to the problem, just one design. Several
alternative ways of meeting the objective will normally be possible, even several best
designs, depending on the nature of the constraints.
These constraints on the possible solutions to a problem in design arise in many ways.
Some constraints will be fixed, invariable, such as those that arise from physical laws,
government regulations, and standards. Others will be less rigid, and will be capable of
relaxation by the designer as part of his general strategy in seeking the best design. The
constraints that are outside the designer’s influence can be termed the external constraints.
These set the outer boundary of possible designs; as shown in Figure 1.1. Within this
boundary there will be a number of plausible designs bounded by the other constraints,
the internal constraints, over which the designer has some control; such as, choice of
process, choice of process conditions, materials, equipment.
Economic considerations are obviously a major constraint on any engineering design:
plants must make a profit.
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