Page 130 - Design of Simple and Robust Process Plants

4.2 The Methodology of Process Synthesis 115
. integration within a process (section);
. integration between specific processes; and
. integration at site level.
Another differentiation can be made by splitting the streams into the functions
which they perform; thus, we may differentiate between:
. Raw material streams; raw materials are in general totally consumed and
often depend on a single source supplier.
. Utility streams, such as energy -power and heat-, process water, cooling
water, refrigeration, fuel, nitrogen etc.; these might be obtained from suppli-
ers, and can be rated in quality terms (voltage, purity, temperature/pressure
level). These streams might be consumed like fuel and power or pass the pro-
cess and are exported at another purity or energy level.
The constraints ± which are clearly an important part of integration ± will be dis-
cussed initially, after which specific aspects of integration with raw material and uti-
lity streams will be detailed. An overview of trends and developments in process
integration has been presented by Gundersen (1999).

4.2.3.1 Constraints
There is a strong drive to integrate all kind of streams in order to improve the
designs. Limited attention is given to the constraints, which are inherently coupled
to integration. From a design perspective, while all stream are considered constant,
in actuality they are subject to availability, variability, and disturbances.
Violation of the constraints will not be dramatic, but will result in penalties that
manifest as production loss or quality of operation.
It is essential that different aspects of constraints are recognized:

. Dependent or independent operation of a process (section)
. Operability
. Controllability
. Safety and environmental
. Economical
Dependent or independent operation of a process This is a choice that must be
made. The initial operational remarks should be made about the level of integration,
as integration within a process requires careful consideration of the operational stra-
tegy. Is the process operated as one train, or is it divided in sections? A process is
often designed to have logically identifiable sections, and a division in operational
sections always includes some intermediate provisions between sections. In the
example of 1-octene the different operational split can be made between the telome-
rization, hydrogenation, and ether cleavage (see Figure 4.2). We may create three,
two, or one independent operable section(s) in this situation. With two independent
sections the choice might be to couple the telomerization and hydrogenation as one
operational section, or to couple the hydrogenation with the ether cleavage as one
operational section. Similar situations occur when there is a one-by-one situation