STUDIES ON HEAT EXCHANGER TRAIN

Abstract

With the acute shortage of energy and vast demand for it for the fulfilment of present growing industrialisation, it has become necessary to find out new strategies and also improvements and new techniques in the already available, well known techniques. Base pinch design method is one of the most matured field in heat exchanger design. The present work, which has been undertaken, is based on the above mentioned method. Research along three different Lines which are the use of thermodynamic concepts, mathematical methods and the use of knowledge based system for process design have been taken into account. The pinch design method is based on the fact that design starts at that portion which is most constrained, i.e., at the pinch point. It divides the whole portion into two different regions, above and below the pinch point, respectively. Both these regions are designed separately using thermodynamic constraint of operatibility and then combined together to form one complete design. Using loop breaking, energy trade off optimisation is carried out for a particular value of (AT)min. The design of the heat exchanger network has been carried out for various values of (a T)min. An optimal ( A T)min can be generated for which annualized total cost is minimum. The present analysis has been done for two sets of streams, one of four-streams and other of seven-streams. The four -stream problem contains two hot and two cold streams. For a given supply and target temperatures, (t T)min opt. has been found to be 16-C and the corresponding annualized total cost is Bs. 626442 per year. Similarly, same exercise has been done for the 7- stream problem, comprising four hot streams and three cold streams. ( A T)min opt. has been found to be 20°C. Annualized total cost has been found to be Rs. 8871162 per year. Multiple utilities (steam of different pressures and cold water at different temperatures instead of only one st-eau of the highest pressure and the other at the lowest temperature) have been employed to reduce the total cost. Using this, annualized total cost in case of the 4-stream problem has been found out to be Rs. .611708 pex year and that of the 7-stream problem comes out Rs. 8351699 per year for an optimal value of (E T)min. It is interesting to note that savings of Rs. 15000 and Rs. 520000 per year have been realised for 4-stream and 7-stream problems, respectively with the use of multiple utilities in the heat exchanger network,