Page 197 - Design of Simple and Robust Process Plants

182 Chapter 5 Process Simplification and Intensification Techniques
Table 5.6. Some directly coupled separation functions.

Functions Applications

Divided wall column Figure 5.7 Replacement two distillations
Two direct coupled distillations Figure 5.12±5.13 Feed and outlet of reactor
Extractive distillation with overhead stripper Figure 5.10 Benzene from non-aromatics
Extractive distillation with solvent stripper Figure 5.11 Benzene from non-aromatics
Absorber with stripper Figure 5.30 HNO 3 absorption and stripping
Several extractions in one column (2 or 3) Figure 5.16 Neutralization, washing
Stripper with evaporator Figure 5.17 Evaporative concentrator
Filtration and washing Filter cake wash L/S
Centrifuging and washing Filter cake wash L/S
Reaction in furnace with drying and cooling Figure 5.18 Calcination furnace

5.6.1.6 Energy integration
The overall energy integration needs to include pinch and exergy analysis ± both of
which are powerful tools (see Chapter 4). It is not the intention to repeat here all
what was said about energy integration, though it is worth recalling the objectives of
pinch analysis:

. Minimize the energy target by modifying the process flowsheet .
. Raise the temperature of energy producers (exothermal reactors, conden-
sers), and lower the temperature of energy consumers (endothermal reactors,
reboilers), to enable improved integration.
. Develop the heat exchanger network by clever integration and follow the
basic implementation rules referred to in Chapter 4:
± Apply process integration in the following order of priority: unit; section; pro-
cess; site (complex).
± Apply heat exchange between flows of similar heat capacity (mass flow ” spe-
cific heat).
. Design the process energy system with enough flexibility to avoid excess in
steam grids that result in the dumping of steam.
In the previous Section 5.6.1.5, which outlined the coupling of separation units, the
focus was on the thermal coupling of units. The main challenge for energy integra-
tion is to develop project alternatives that will achieve lower energy targets, based on
the flowsheet after any coupling has been studied. The lower targets are to be real-
ized by the adaptation of process conditions to enable surface heat exchange. The
options available for modification of distillation column energy conditions (Fig-
ure 4.33 in Chapter 4) as being a major energy consumer are to:

. adapt the operational pressure/minimize pressure drop;
. change the composition(s) of separation;
. consider using a side re-boiler/condenser;