Retrofit of Heat Exchangers

Although an increase in flowrate can result in increased film transfer coefficients, an increase in flowrate is also usually accompanied by an increase in heat transfer duty. In turn, this might lead to a need for increased heat transfer area. 

For example, an increase in the process throughput might result in an increase in the heat duty, and hence an increase in the heat transfer area, if the temperatures are unchanged. More generally, additional heat transfer area might be required as a result of increased heat duty, operation under reduced temperature differences, operation under reduced heat transfer coefficients or increased fouling. 

If the new increased heat duty and new log mean temperature difference are fixed, then the additional surface area above the existing area using a plain tube surface is given by9  

U = overall heat transfer coefficient Aexisting = existing heat transfer area A A = additional area requirement ATim = logarithmic mean temperature difference Fj = logarithmic mean temperature difference correction factor 

If the same duty is to be serviced by enhanced heat transfer without additional area  

---

Polley, G. T., Panjeh Shahi, M. H., and Jegede, F. O., Pressure Drop Considerations in the Retrofit of Heat Exchanger Networks, Trans. IChemE, part A, 68 211, 1990. 

Briones, V. and A. Kokossis. A New Approach for the Optimal Retrofit of Heat Exchanger Networks. Comput Chem Eng 20 (Suppl) S43-S48 (1996). 

Sreepathi, B.K. and Rangaiah, G.P. (2015) Retrofitting of heat exchanger networks involving streams with variable heat capacity Application of single and multi-objective optimization. Applied Thermal Engineering, 75, 677-684. 

Nguyen, D.Q., Barbaro, A., Vipanurat, N., and Bagajewicz, M.J. (2010) AU-at-once and step-wise detailed retrofit of heat exchanger networks using an MILP Model. Industrial Engineering Chemistry Research, 49 (13), 6080-6103. 

Smith, R., Jobson, M., and Chen, L. (2010) Recent development in the retrofit of heat exchanger networks. Applied Thermal Engineering, 30 (16), 2281-2289. 

Ahmad S, PoUey GT, PetelaEA (1989) Retrofit of heat exchanger networks subject to pressure drop considerations. Paper No. 34a, AlCHE Meeting, Houston, April. 

Polley GT, Panjeh Shahi MH, Jegede FO (1990) Pressure drop considerations in the retrofit of heat exchanger networks. Transactions of IChemE, Part A, 68, 211. 

Shokoya CG, Kotjabasakis E (1991) A new targeting procedure for the retrofit of heat exchanger networks. International Conference, Athens, Greece, June 265-279. 

A. R. Ciric and C. A. Floudas. A retrofit approach of heat exchanger networks. Comp. Chem. Eng., 13(6) 703,1989. 

K. Papalexandri and E. N. Pistikopoulos. An MINLP retrofit approach for improving the flexibility of heat exchanger networks. Ann. Open Res., 42 119,1993. 

III. Heat/Process Integration Study Pinch analysis is well established for finding optimal utilities, heat transfer area, optimal fresh water consumption, minimum cooling water demand, reduced emissions targets and so on (Smith, 2005 Kemp, 2007). One application of pinch analysis to retrofitting the heat exchanger network of a crude... 

The best way to approach the retrofit synthesis of the heat-exchanger network is to model all five tasks simultaneously. A mixed-integer nonlinear programming model is usually formulated to accomplish this goal. 

---