A Mathematical Programming Approach for Synthesis andDesign of Mass/Heat Exchanger Networks in Batch Plants

• Main Authors: Ying-Jyuan Ciou, 邱瑩鵑
• Other Authors: 陳誠亮
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/06955023760928846445

博士 === 國立臺灣大學 === 化學工程學研究所 === 96 === This dissertation aims to confer the mass and heat integrated problems in batch processes by mathematical programming. Under the situation that does not consider the problem of production scheduling, although the production cycle and starting and ending times of each process stream in batch processes are both known, the existing time of streams is still the main difficulty for designing the networks in the batch processes. Hence, comparing with the mass and heat integrated problems in continuous processes, besides considering the composition/temperature limitation for synthesis the material or energy of process streams in batch plants, storage tanks are often used to overcome the constraint, the drop of the existing times for process streams. The first part in this dissertation is to analyze the mass exchange network synthesis problem in batch processes. To exhibit amply the mathematical programming feature that is to ponder all possible conditions first and then to merge the feasible optimized design, the entire production cycle of batch process is divided into several operating periods according the given of production cycle and starting and ending times of each process. Therefore, the mass exchange network synthesis problem within each operating period resembles the mass integration problem of continuous process. This research presents a superstructure including storage tanks and mass exchange network (MEN) for all possible operations, where the mass exchange network is operating in intermittent and the continuous modes. The synthesis problems of two operating modes are formulated as mixed-integer nonlinear programs (MINLPs) based on the objectives of minimizing the external mass separating agents (MSAs) or the total annual cost (TAC). Finally, a coke oven gases (COGs) purification problem from the literature is used to demonstrate the applicability of the proposed MEN synthesis method for semi-continuous processes. The second part in this dissertation aims at proposing a generic superstructure of a heat exchange network (HEN) focusing on indirect heat integration and its associated thermal storage policy. The thermal storage uses a heat transfer medium (HTM) that initiated in a cold tank. It is then sent to absorb surplus heat from hot process streams and results at an elevated temperature, before it is to be temporarily stored in a hot tank. The accumulated hot HTM is then utilized to heat subsequent cold process streams, and the cooled HTM is circulated back into its source cold tank. By applying the re-circulated HTM storing in indirect thermal storages, the limitation of heat interchange between time-dependent hot/cold process streams in batch plants can be relaxed. The heat storage system consist of two types, the fixed temperature/variable-mass (FTVM) heat storage and the variable-temperature/variable-mass (VTVM) heat storage. Based on the proposed heat exchange network superstructure, the synthesis problems of indirect HENs for different types of thermal storages are formulated as two MINLPs, where the objective is to minimize the utility consumption and the total annual cost. One numerical example are analyzed to compare results from the pinch analysis technique and the newly proposed methods, and two complex processes are used to demonstrate the applicability of proposed indirect heat integration synthesis method.