Retrofit of Heat Exchanger Networks

In practice, if the network pinch is being identified in a design study, then a practical minimum temperature 

Consider now how the network pinch might be overcome. There are four ways in which the network pinch can be overcome and the performance of the existing heat exchanger network improved beyond that for the pinched condition14. 

it should be emphasized that in practice a finite practical A Tmin should be used rather than 0°C. However, any assumption of A Tmin to identify, and then overcome, the network pinch does not guarantee 

If the capital cost of new heat transfer area is expressed in the form of Equation 18.6, then this will lead to poor retrofit projects. The problem with Equation 18.6 is that the optimization is likely to spread the new heat transfer area in the network in many locations, without incurring a cost penalty associated with the many modifications that would result. To ensure that new heat transfer area is not spread around throughout the existing heat exchanger network, a capital cost correlation should be used that is of the form  

In Equation 18.7, the coefficient a is a threshold cost that is incurred even if a small amount of heat transfer area 

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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. 

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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. 

This approach to heat exchanger network retrofit allows modifications to be introduced one at a time. In this way, the designer has control over the complexity of the network retrofit. At each stage, a suggested modification can be... 

Enforced matches. There are often some features of the heat exchanger network that the designer might wish to accept as fixed. This is often the case in retrofit. For example, a match between a hot and a cold stream might exist that is considered to be already appropriate or too expensive to change. If this is the case, then the part of the hot and cold stream involved in the enforced match should be left out of the analysis and added back in at the... 

Automatic design techniques of the heat exchanger network can increase dramatically the designer s productivity, making free more time to conceptual tasks. New techniques are available for retrofitting existing networks, as well as for guiding the implementation of heat intensification devices. 

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