3 ׀ RESULTS AND DISCUSSION
Prior to solving the CDU network synthesis problem, the reliability of
the HINT software was first investigated by solving the Example problem
of Colberg and Morari whose stream and cost data was presented in
presented in Table 2. The goal was to predict the area target of the HEN
in that study. A comparison was then made between their results and the
results obtained in the present study which showed similar area targets
thus confirming the reliability of HINT software. The grid diagram of
the heat exchanger network, and the composite curve as generated in the
HINT for the problem adapted from Coldberg and Morari is presented in
Figures 3 and 4 respectively. A total number of 6 exchangers and area
target of 298.227 m2 were obtained in this study. The
area target obtained in this study is within 1% of the one obtained in
simple area targeting of Colberg and Morrari . This suggests that the
HINT software employed in this study is an effective package for pinch
analysis. It gives operating and capital cost of 31,000 $/yr and
34,215.5$/yr respectively. This amounts to total cost of
65,215.5$/year. The NLP of Colberg and Morari could not target for the
operating cost and the total cost.
[CHART]
Figure 3 Composite curve of Example problem showing total
heating and cooling targets of 620 and 230 kW respectively.
[CHART]
Figure 4 Optimum ΔTmin of 8.84 K at area target
of 301.88 m2 obtained from HINT
Results were compared with that of Colberg and Morari as shown in Table
3. Colberg and Morari obtained with their NLP, a total area target of
259.7 m2 as the starting point solution using MINOS
5.0 software with a spaghetti structure. With no restriction in stream
matching, the NLP yielded an area target of 258.8 m2;
but the authors’ simple area targeting method based on composite curves
predicted a target of 295.6 m2. They also observed
that the optimal ΔTmin of 4.2 K was less than the
ΔTmin (10 K) specified for utility targeting in that
case study. A comparison of results revealed that the simple area
targeting method of Colberg and Morari overestimated the area target by
14.22% while the matching used in the present study overestimated the
target by 15.23%, which is just about 1% different from the NLP
solution of Colberg and Morari. However given the closeness of the areas
between this study and that of Colberg and Morari, the HINT software is
therefore considered a reliable tool that can be used in the study of
pinch technology.
Table 3 Results comparison