Simultaneous synthesis of heat exchanger networks with operability considerations: Flexibility and controllability

Abstract

In this work a computational framework is proposed for the synthesis of flexible and controllable Heat Exchanger Networks. The synthesis is projected to operate over a specified range of expected variations in the inlet temperatures and flowrates of the process streams using a decentralized control system, such that the Total Annual Cost involving the utility consumption and the investment are optimized simultaneously. The framework is based on a two-stage strategy. A design stage is performed prior to the operability analysis where the design variables are chosen. In the second stage, the control variables are adjusted during operation on the realizations of the uncertain parameters. The framework yields a HEN design, which is guaranteed to operate with the designed control system under varying conditions ensuring stream temperature targets and optimal energy integration. The application of the proposed framework and its computational efficiency are illustrated with some numerical examples.

A Multi-Period Synthesis Approach to Designing Flexible Heat- Exchanger Networks

“…The methods that have been used for the synthesis of flexible heat-exchanger networks have been both sequential [1][2][3] and simultaneous in nature [4][5][6][7][8][9][10][11][12][13][14][15][16]. Some of the sequential methods are an automated multi-period version of the mixed integer linear programme (MILP) transshipment model [17] and the non-linear programme (NLP) minimum investment network cost model [18].…”

“…A further criterion that needs to be considered while designing the representative candidate multi-period network, which has erstwhile been ignored by existing flexible HENS methods, is the length of periods for each of the critical operating points used to generate the representative candidate multi-period network in the first step. The existing methods [5,[9][10][11][12][13][14] used the average costs of utility usage by each period of operation present in the first-step candidate multi-period network to determine its minimum TAC and associated network structure as shown in Eqs. (1) and (2) …”

“…Furthermore, additional costs and complex controllability issues will be incurred due to excessive piping and associated instrumentations. Hence, some other synthesis methods that result in networks that have a greater degree of flexibility have been presented in the literature [10][11][12][13][14][15]. One of the methods entails [10] a three-step approach where a network is designed based on a finite set of operating points in the first step.…”

“…The flexibility test of this method is carried out on a large number of randomly generated parameters within the range of uncertainty. Another method [13] in the area of flexible HEN designs used a two-stage strategy which is based on the SWS model for the synthesis of flexible and controllable networks. Li et al [14] developed a two-step approach for flexible HENS.…”

Efficient Method for Flexibility Analysis of Large-Scale Nonconvex Heat Exchanger Networks

“…1 Obviously, it is a key component of chemical process operability. The flexibility analysis of the heat exchanger network (HEN) has been widely discussed over the last three decades, such as Zheng et al 2 designed flexible HEN under severe operational uncertainty, Bakar et al 3 studied flexibility and operability in HENs, Jiang and Chang 4 analyzed flexible HEN with timesharing mechanisms, Adi and Chang 5 discussed the temporal flexibility, Chandra and Grabis 6 worked on the flexibility in supply chain, and Tan et al 7 developed a floating pinch method.…”