Page 204 - Design of Simple and Robust Process Plants

5.7 Simplification and Ranking per Unit Operation 189
. Overall process simplification is based on critical review of the overall process
functions to identify areas for elimination and combination by modification
of the process flowsheet structurally. Areas for consideration are:
± Design for 100% conversion does not require expensive recycle systems.
± Critical review of all additives to prevent expensive recovery and destruction
sections.
± Prevention of waste streams does not require waste treatment facilities.
± Adiabatic reactor operation might result in lower capital and lower energy
consumption.
± Combination and coupling of functions is an essential part of simplification.
± Energy integration of units needs to apply exergy and pinch analysis for heat
exchanger network design, but reduction of the energy targets is the first
priority.
± Implementation of energy networks should follow the basis implementation
rules:
(i) Apply process integration in the following order of priority: unit, section ,
process, site (complex).
(ii) Apply heat exchange between flows of similar heat capacity (mass flow times
specific heat).
± Design of a single train versus multiple trains creates large capital benefits.
± Externally supplied services do not require capital, and also avoid operation
and maintenance activities for the organization.
± Redundant provisions versus reliable robust designs points to single equip-
ment.
These approaches have led to major successes.

5.7
Simplification and Ranking per Unit Operation

The first sections of this chapter have focused on the techniques of achieving simple
and robust process designs, and incorporated the following categories:

. Avoidance or elimination of process functions.
. Combination of process functions.
. Integration of equipment.
. Intensification of process functions.
. Overall process simplification.
In the following sections, an alternative approach is taken, and opportunities for the
simple and robust design of specific units will be discussed. These include:

. Reactors
. Distillation and absorption
. Extraction
. Adsorption