2.2.2 ׀ PINCH ANALYSIS USING THE HINT SOFTWARE
HINT software procedure for carrying out pinch analysis has been summarized in Figure 1. The HINT was used to create a grid diagram of the existing heat exchanger network from which composite curves were generated. The composite curves were used to identify cooling and heating requirements, and to evaluate possible heat integration opportunities. A retrofit grid diagram was obtained by improving the grid diagram using utilities and optimization of the minimum Delta T. The cost data comprises of the operating cost for utilities and the capital cost for heat exchangers. The annualized cost data was based on 86,000 hours per year, pay-back period of 10 years with no interest rate. Utility cost data was taken from Azeez et al. . The capital cost used is that given by Eq. (2) which is found in Azeez et al.; Al-Mutairi and Elkawad :
\(Capital\ cost(\$)=a+b{(Area)}^{c}\) (2)
Where Area represents area of heat exchangers, a is the fixed cost of installation, b and c represents the cost of area per unit which both depend on the material of constructions of heat exchanger. In Equation 2, a = 0, b = 1200, c = 0.6, and Area is area of exchangers (m2). In this study, it was assumed that the same equation holds for all types of heat exchangers in the network, process to process and utilities exchangers.
The cost data used for utilities was that provided by Yee and Grossmann , where the heat transfer coefficient, h = 1 kW/ (m2K), hot utility (S1) cost = 140 $/ (kW yr), and cold utility (W1) cost = 10 $/ (kW yr). In their work, steam was used as the heating utility and cooling water as the cold utility in the popular magnets problem. Water was used as a coolant because it is cheap, non-hazardous and a good heat transfer medium. The thermodynamics data used in this work, and as provided by Yee and Grossmann (1990) were as follows:
Steam (S1); cost = 140 $/kWa, h = 1, Ts = 700 K, Tt = 700 K
Cooling water (W1); 10 $/kWa, h = 1, Ts = 300 K, Tt = 320 K.
The shifted composite curve was obtained by using the following Eq. (3) and (4) to calculate the shifted temperatures (Ajao and Akande, 2009):
\(\text{Shifted}\ \text{Hot}\ \text{Stream}\ \text{Temp.}=\text{Unshifted}\ \text{Hot}\ \text{Stream}\ \text{Temp.\ }-\frac{{T}_{\min}}{2}\)(3)
\(\text{Shifted}\ \text{Cold}\ \text{Stream}\ \text{Temp.}=\text{Unshifted}\ \text{Cold}\ \text{Stream}\ \text{Temp.\ }+\frac{{T}_{\min}}{2}\)(4)
In order to be sure that HINT software will produce a reliable result, the software was first applied to a problem that has been investigated by Colberg and Morari where the authors targeted for minimum area using pinch technology. The example is presented below: