Page 144 - Design of Simple and Robust Process Plants

4.2 The Methodology of Process Synthesis 129
cess heat can be generated at a steam level between the utility levels, for usage
at another plant section a plant intermediate steam level might be appropriate.
5. Develop a plant energy system which is largely independent from external
steam supply, without violating the benefits of site integration. This to reduce
its vulnerability, the transfer of large amounts of steam across the site and its
related dynamic effects.
6. For network integration, the following implementation rules need to be
applied:
± Apply process integration in the following order of priority: unit, section,
process, site (complex).
± Apply heat exchange between flows of similar heat capacity (mass flow ”
specific heat, M ” C p ) are preferred, rule of Gommers.
The inlet and outlet streams of reactor systems are often counter currently
crossed as well as the inlet and outlet of a furnace (air pre-heater with flue
gas). Another example is the exchange between solvent streams of inlet and
outlet of absorber/desorber. The above examples comply with the integration
per unit/section, and will also give close to parallel temperature profiles
which lead to limited number of exchangers.
± Apply process simplification in relation to process integration, avoid pro-
cess stream splitting unless operability and controllability problems are
adequately solved while saving are considerable.
7. Develop a strategy for drivers in the process (electrical versus steam versus
gas turbine, which fit in the site infrastructure). The desire to avoid a com-
mon cause failure is a point for consideration

The above approach is applied during process integration 1, and upgraded at step 2.
During process integration 1, the preliminary energy structure is developed and the
energy values for the different steam levels must be determined as these need to be
used for the level 2 reactor and separation synthesis. In step 2, the challenge is to
adapt the process conditions to minimize the energy targets before energy integra-
tion is applied.

4.2.3.5 Simplification with integration
During the development of an energy structure it is important to avoid many cross-
connections and ultimately to keep a well-ordered process. This is one of the reasons
why operability and controllability were introduced as constraints for integration.
The following basic rules are to be applied:
. The application of an order of priority for process integration from unit, section,
process and complex is one of the starting points for process simplification.
. The application of heat exchange between flows of similar heat capacity
(mass flow ” specific heat).
The design philosophy of clever process integration finds its starting point here. In
this section, some reference is made to simple design solution that is specific for
energy integration.