Synthesis of heat exchanger networks featuring batch streams Yufei Wang a , Ying Wei b , Xiao Feng a,⇑ , Khim Hoong Chu b a State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China b Department of Chemical Engineering, Xi’an Jiaotong University, Xi’an 710049, China highlights  Heat integration of heat exchanger networks featuring batch streams is firstly considered.  A new method based on the heat duty–time (Q–t) diagram is proposed.  Energy targeting and network design can be obtained easily.  Both direct and indirect heat integration of batch streams are considered. article info Article history: Received 30 May 2013 Received in revised form 27 August 2013 Accepted 17 September 2013 Keywords: Heat exchanger network Graphical method Batch stream Intermediate media Energy target abstract A new method based on the heat duty–time (Q–t) diagram is proposed for heat integration of heat exchanger networks featuring batch streams. Using the Q–t diagram method, the energy targets and the structure of the initial heat exchanger network can be easily obtained. The method can be used both for direct and indirect heat integration of batch streams. For indirect heat integration, the heat degrada- tion of intermediate media is considered. A case study on optimizing the heat exchanger network of a hydrazine hydrate plant is used to illustrate the application of the method. The results show that integra- tion of this heat exchanger network without considering its batch streams can limit the total energy savings. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Chemical processes can be broadly divided into continuous and batch operations. Although not common, there exist some contin- uous processes featuring batch streams. Notable examples include the hydrazine hydrate production process and the delayed coking process. Because chemical processes consume large amounts of fi- nite energy resources, many heat integration techniques have been developed over the years to improve their energy efficiency. For example, heat exchanger networks in numerous continuous and batch processes in the chemical industry have become highly en- ergy efficient as a result of heat integration. Nevertheless, despite this remarkable success, heat integration analysis has not yet been applied to continuous processes featuring batch streams. Although usually only a limited number of key batch streams are present in such processes, the heat content of these batch streams could be quite substantial. As such, heat integration analysis that treats this type of hybrid processes as strictly continuous by ignoring the small number of batch streams can limit the total energy savings. Synthesis of heat exchanger networks of continuous processes has been studied extensively, either by pinch technology [1,2] or by mathematical programming techniques [3,4]. Because pinch technology offers the advantages of intuitiveness, simplicity and clarity when compared to the mathematical programming ap- proach, it is widely used in industry. In recent development of heat exchanger networks synthesis of continuous processes, Wang et al. [5] proposed a methodology to consider heat transfer enhance- ment in the optimization of heat exchanger network. Zhang et al. [6] developed a method for optimizing the operation condition of heat exchanger network and distillation columns simultaneously. This methodology allows the industry to improve its economic and environment performance at the same time. Vaskan et al. [7] developed a multi-objective design method for heat exchanger network by using a MILP based model. Life cycle assessment and environment were involved in this method. Markowski et al. [8] proposed a heat exchanger network synthesis methodology con- sidering fouling. This methodology can monitor long-term changes in the heat exchanger network efficiency. With suitable adaptations, most of the heat integration meth- ods developed for continuous processes can be used to search for heat integration opportunities in batch processes which are 0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2013.09.040 ⇑ Corresponding author. Tel.: +86 15811168976. E-mail addresses: xfeng@mail.xjtu.edu.cn, xfeng@cup.edu.cn (X. Feng). Applied Energy 114 (2014) 30–44 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy