Page 147 - Design of Simple and Robust Process Plants

132 Chapter 4 Process Synthesis and Design Optimization
An alternative for this structure is a furnace provided with a gas turbine (Fig-
ure 4.40). In this alternative, the process streams are cross-exchanged but the option
for air pre-heating is not available. Therefore, the flue-gases must be cooled at
decreasing temperature; this is shown as high, medium, and low heat recovery.
For separation systems, we have a similar type of integration effort. The activities
to minimize energy targets through flowsheet modification (as shown in the distilla-
tion train example; Figures 4.16±4.20), has to be extended by clever energy integra-
tion, which is a challenge. The application of an order of priority: unit, section, pro-
cess, site (complex) is also applicable for separations. One might consider heat inte-
gration between an extractive distillation column and the successive solvent from
the stripper column. In the case of a large difference in pressure between an absor-
ber and desorber, a reverse-running pump to drive the solvent circulation might also
offer a clever integration option.
With the above designs the basic rules for heat integration are reflected.

4.2.3.6 Is there conflict between process integration and process simplification?
The target for simplification was to explore options from a simplicity perspective to
achieve a high-quality, economical, optimal process. The objective for process integra-
tion was to determine minimum consumption levels ± to challenge the targets and,
based on a minimum target, to design integrated networks that optimize the design.
By following the approach of pinch networking without restrictions, the result
might be complicated configurations. Both approaches must respect the constraints
as applicable, including operability and controllability requirements. In particular,
these requirements will put a damper on unrestricted integration. An integrated
process which does not have sufficient disturbance rejection capability will not be
exploited to its design intent. The answer to the above question is that, as long as
the decisions are based on the most economical solution while respecting the con-
straints, there should not be a conflict.

Summary
Process integration is an activity that is applied extensively, its initial objective being
to reduce energy consumption. Nowadays, the objective is extended to minimize the
use of natural resources from the perspective of creating a sustainable world. Pro-
cess integration may result in complex operations, and therefore requires careful
design, with recognition of its limitations.
. Process integration can be differentiated in:
± Level of process integration; per unit, section, overall process, between differ-
ent processes and at site level.
± Streams, as raw material and utility streams.
. Constraints are a major issue during integration, and these need to be ana-
lyzed carefully to avoid large disappointments during operation, the factors
that play a major role are; availability, variability and disturbances.
. Constraints may be notified if we address the following questions:
± How dependent or independent is the operation of the integrated streams?