Page 145 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

142 Chapter 5 Heat exchanger network analysis

5.8.4 True utility streams
A true utility stream i.e., steam, cooling water, refrigerant, etc., is one that can in principle be replaced
by any other stream (process or utility) for heat exchange purposes. Some streams like the live stream
used for stripping in strippers that provide energy as well as reduce the partial pressure in the column
are to be treated as process streams. Live stripping stream is not considered as ‘true’ utility as it cannot
be replaced with any other thermal fluid supplying the heat.

5.9 Applications
In a nutshell, the applications of pinch technology are

(a) Improvement of energy efficiency of a system/process
(b) Process debottlenecking where utility system is the main bottleneck by reducing utility
consumption and providing additional scope for increasing production.
(c) Significant reduction in process water demand and waste
water generation via improved re-use of water within the
Importance of Pinch Analysis process
(d) For low temperature processes, pinch technology in
combination with energy analysis allows the designer to
assess the impact of various design changes on refrigerator power consumption

5.10 Design illustration

Problem 5.1. A chemical process involves 4 streams, the details of which are provided in Table P5.1A
(the last column in the Table refers to heat Transfer Coefficient).
Design the optimum heat exchanger network when (a) hot utility, high pressure steam and cold
utility, refrigerated brine are available at 220 and 12 C, respectively. (b) Utilisation of utilities at

multiple levels is suggested to reduce operating cost. Consider that the cheaper utilities e MP steam
o
o
and cooling water are additionally available at 170 C and at 35 C.
Table P5.1A Stream details.
Stream no. Type TS ( C) TT ( C) CP ¼ mC p (kW/ C) h (kW/m C)

2

1 Hot 180 40 2.0 h1
2 Hot 150 40 4.0 h2
3 Cold 60 180 3.0 h3
4 Cold 30 105 2.6 h4
HU Hot utility 220 e e hh
CU Cold utility 12 20 e hc