Design of flexible heat exchanger networks.
Design for process flexibility is an industrially important topic so
it is not surprising that it is attracting much research work. Given
the size of the problem it is also not surprising that workers have
concentrated on heat exchanger networks, which can be considered to
be a self-contained sub-problem.
Unfortunately, recent research has suffered from a number of major
drawbacks. Problem formulation has often been unrealistic. Proposed
procedures tend to be 'clinical' rather than practical. Academic
research has often been conducted without proper consideration of
the industrial environment. Very few research results have been
tested on full scale industrial problems.
In this thesis a new problem formulation and new solution techniques
are presented. They have been designed to fulfil the needs of
In problem formulation it is recognised that the specification of
flexibility is primarily an economic problem. The amount of
flexibility industry will demand is a function of how much it costs.
The methodology developed here allows both, the flexibility cost and
the existing trade-off between flexibility needs, capital costs and
energy costs to be fully evaluated.
Flexibility problem formulation is mainly based on Multiple Base
Cases. Different plant operating scenarios are set and a design
found that is able to satisfy each case. This is a formulation that
has found a wide acceptance in industry.
To be industrially practical, process design techniques must be
intelligible to the non-specialist. The techniques developed here
are simple and straightforward and give insight.
Two new design techniques have been developed. The first of these is
'Downstream Paths'. These are used to identify and evolve the
network structures that permit cost effective flexibility.
The second technique is 'Sensitivity Tables'. These can be used to
analyse the performance of a given structure. In addition they
determine the cost effective modification to elements of the
structure which provide the specified flexibility needs. The
technique is rapid, simple to apply and easy to repeat.
Consequently, many scenarios can be screened without much effort and
a cost profile developed in order to evaluate the cost trade-off
The approach proposed in this thesis, involving the new problem
formulation and solution techniques, has been applied to a number of
case studies of industrial scale. These case studies have covered
problems as diverse as catalyst deactivation, fouling, and plant
One major spin-off from the work is a new approach to the design of
heat exchanger networks subjected to fouling. Large potential
savings have been identified.