An area targeting algorithm for the synthesis of heat exchanger networks

doi:10.1016/j.ces.2004.03.016

Chemical Engineering Science

Volume 59, Issue 12, June 2004, Pages 2517-2520

https://doi.org/10.1016/j.ces.2004.03.016 Get rights and content

Abstract

A new algorithm for the prediction of area requirements in heat exchanger networks (HEN) is presented. The method uses a diverse pinch diagram as a basis, similar to the one suggested by Rev and Fonyo (Chemical Engineering Science, 46 (7), 1623). A numerical application for a problem involving streams with significant differences in their heat transfer coefficient values is included to show how the proposed algorithm provides better estimates for minimum area requirements in HEN than the widely-used Bath formula and the algorithm by Rev and Fonyo.

Introduction

The pinch point method provided a new approach for the design of heat exchanger networks, where the synthesis stage is preceded by a targeting procedure that predicts some of the important characteristics of the network prior to design. Energy consumption is accurately predicted by a heat cascade procedure once a value of ΔT_min has been selected (Linnhoff and Flower, 1978). The prediction of area requirements, on the other hand, is not as reliable. The algorithm based on the Bath formula (Townsend and Linnhoff, 1984) is the method most widely used for that purpose. The method assumes vertical heat transfer between the composite curves, and the prediction of a minimum value for area requirements is valid only if all film heat transfer coefficients for the streams are equal (Linnhoff and Ahmad, 1990); otherwise, nonvertical heat transfer may be required to achieve a minimum area for the network.

The concept of contribution ΔT was proposed to incorporate nonvertical heat transfer for minimum area predictions (Nishimura, 1980; Ahmad et al., 1990). Rev and Fonyo (1991) proposed the diverse pinch concept, which uses an individual contribution ΔT for each stream, according to the following relationship: $Δ T_{j} =κh_{j}^{−z},$ where κ and z are empirical parameters. For a specified energy target, Rev and Fonyo estimate a target for the minimum area required for the network from a modified composite curves graph, in which temperatures are adjusted by adding or subtracting their individual ΔT given by Eq. (1). However, Rev and Fonyo 1991, Rev and Fonyo 1993 did not take into account that temperature shiftments require a distribution of heat duties between exchanges of a spaghetti design. Instead, they used a constant log mean temperature difference (based on modified, or diversed, temperatures) for each enthalpy interval. This approximation is valid only for cases of two streams with different film coefficients, or for multiple streams with the same film coefficient (Serna, 1999). Although the diverse pinch takes into account film heat transfer coefficients from an initial stage, the reported algorithm fails to reasonably improve the Bath formula. In this paper, we take the diverse pinch concept as a basis and propose a new algorithm for area targeting.

Section snippets

Proposed algorithm

Fig. 1 illustrates a diverse composite curve and a spaghetti design for an interval with two hot streams and one cold stream. The minimum area required for interval k is given by $A_{min,k} =(q_{13k} / Δ T_{LM_{13k}})(1/h_{1} +1/h_{3})+ (q_{23k} / Δ T_{LM_{23k}})(1/h_{2} +1/h_{3}),$ where q_ijk, is the heat duty between streams i and j. In general, if the interval k contains I hot streams and J cold streams, I×J is the number of heat exchangers in the spaghetti design. The total area is the addition of individual area requirements for k

An illustrative example

One example is used to show the application of the proposed algorithm. Consider the stream data given in Table 1, taken from Ahmad et al. (1990). Values of film heat transfer coefficients differ by a factor of up to 50. For a value of ΔT_min=30°C, the minimum heating and cooling requirements are 1456.72 and $1248.04 kW$ , respectively, and the estimation for the area target using the Bath formula is $3006.42 m^{2}$ .

Ahmad et al. (1990), using a method with ΔT-shifting on each of the enthalpy intervals of

Concluding remarks

An algorithm for minimum area targeting in heat exchanger networks has been presented. The method is particularly suitable for cases with significant differences in film heat transfer coefficients for process streams. The new algorithm takes into account heat duty distributions and uses real temperature differences for each interval of the diverse composite curves. A significant improvement in the prediction of area requirements for heat exchanger networks has been consistently observed in

Acknowledgements

The authors acknowledge the Consejo Nacional de Ciencia y Tecnologı́a (CONACYT), Mexico, for the economic support of this project through Grant 25970-A.

References (8)

S. Ahmad et al.
Cost optimum heat exchanger networks-2 targets and design for detailed capital cost models
Computers & Chemical Engineering
(1990)
B. Linnhoff et al.
Cost optimum heat exchanger networks-1 minimum energy and capital using simple models for capital cost
Computers & Chemical Engineering
(1990)
E. Rev et al.
Diverse pinch concept for heat exchange network synthesisthe case of different heat transfer conditions
Chemical Engineering Science
(1991)
E. Rev et al.
Comments on diverse pinch concept for heat exchange network synthesis
Chemical Engineering Science
(1993)

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An area targeting algorithm for the synthesis of heat exchanger networks

Abstract

Introduction

Section snippets

Proposed algorithm

An illustrative example

Concluding remarks

Acknowledgements

Computers & Chemical Engineering

Computers & Chemical Engineering

Chemical Engineering Science

Chemical Engineering Science