Heat exchanger retrofit

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. 

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. 

Pressure drop. Rather than specify a fluid velocity, it is often preferred to specify the pressure drop across the heat exchanger. In retrofit situations, where a new heat exchanger is to be installed in an existing plant, the allowable pressure drop is often highly constrained. This is because in a retrofit situation, it is often desirable to avoid... 

In retrofit situations, existing heat exchangers might be subjected to changes in flowrate, heat transfer duty, temperature differences or fouling characteristics. Heat transfer coefficients and pressure drops can be approximated from... 

Zhu XX, Zanfir M and Klemes I (2000) Heat Transfer Enhancement for Heat Exchanger Network Retrofit, Heat Transfer Eng, 21 7. 

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 ... 

It should be noted that a resequence or repipe does not involve zero capital cost, even though no new heat exchanger equipment might be purchased. The pipework modifications for a resequence or repipe might be very expensive. Also, equipment might need to be relocated. Methods for capital cost estimation for retrofit were discussed in Chapter 2. 

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... 

Asante NDK and Zhu XX (1997) An Automated and Interactive Approach for Heat Exchanger Network Retrofit, Trans... 

Zhu XX and Asante NDK (1999) Diagnosis and Optimization Approach for Heat Exchanger Network Retrofit, AIChE J, 45 1488. 

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... 

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

Economic analysis of designs at lower natural hypochlorite strengths equally show potential investment benefits. They are, however, much less significant than the batch and high concentration cases described above. While an economic case can be made for retrofitting an in-loop reactor to a system that already has an end-of-pipe treatment system based on payback, it is not always clear that this is a better option than an end-of-pipe hybrid system as described earlier in the chapter. For a particular system the optimum solution is often as much a function of the required expenditure on the heat exchangers as it is the relative cost of the reactor options. 

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