Page 170 - Sustainability in the Process Industry Integration and Optimization

Fu r t h e r A p p l i c a t i o n s o f P r o c e s s I n t e g r a t i o n 147

Nie and Zhu (1999) developed a strategy for considering pressure
drop in HEN retrofits. They assumed that any additional area would
involve only a few heat exchange units in order to minimize the
piping and civil engineering work. The optimization procedure
consists of two stages. The first stage involves selecting a small
number of units that require additional area; the second stage
considers series or parallel shell arrangements for those units. The
topology change options are initially established by applying the
Network Pinch method (Asante and Zhu, 1997). Then a two-stage
optimization procedure is used to determine area distribution and
shell arrangement under pressure-drop constraints. Area distribution
and shell arrangement are the design properties that have the greatest
effect on pressure drop.
Václavek, Novotná, and Dedková (2003) analyzed in more detail
the circumstances under which pressure plays a significant role in
Heat Integration. The authors formulated some heuristic heat recovery
rules for combinations of process streams (tracks), not merely
individual streams.
Aspelund, Berstad, and Gundersen (2007) described a new
methodology, called extended Pinch Analysis and Design (ExPAnD),
to account for pressure drops in process synthesis that extends the
traditional Pinch Analysis to incorporate exergy calculations. The
authors focus on the thermo-mechanical exergy, which is the sum of
pressure- and temperature-based exergy. Compared with traditional
Pinch Analysis, the problem that Aspelund, Berstad, and Gundersen
(2007) consider (a subambient process) is much more complex; there
are many alternatives for the manipulation and integration of
streams. The authors also provide a number of (general and specific)
heuristics that complement the ExPAnD methodology. In a further
development, Aspelund and Gundersen (2007) used the concept of
an attainable region in proposing a graphical representation of all
possible CCs for a pressurized, subambient cold stream along with
the cooling effect of the stream expanding to its target pressure. The
attainable region is a new tool for process synthesis, extending Pinch
Analysis by explicitly accounting for pressure and including exergy
calculations. The methodology shows great promise for minimizing
total shaft work in subambient processes.
For designing a de-bottlenecking retrofit (as distinguished from
an energy-saving retrofit), Panjeshahi and Tahouni (2008) suggested
a method for optimizing pressure drop. The technique proceeds in
two main stages as follows. (1) Simulation of the existing process
operating at the desired increased throughput: additional utility is
used to maintain required temperatures in the process. (2) Area
efficiency specification for the existing network after the area–energy
plot is used to increase throughput: a new virtual area, a pseudonetwork,
is introduced.
Zhu, Zanfir, and Klemeš (2000) suggested a heat transfer enhance-
ment procedure for HEN retrofits. The methodology features a