Qingwei Meng

Synthesis of Large-scale Multi-stream Heat Exchanger Network Based on Pseudo-temperature Enthalpy Diagram Method Combined with Superstructure Method

Abstract This paper introduces a new approach for optimizing heat exchanger networks (HEN), which combines pseudo-temperature enthalpy diagram method and superstructure method. The approach focusing on the minimization of total annual cost, uses a simplified superstructure to solve the sub-networks which obtained by a pseudotemperature enthalpy diagram, and also involves multi-stream heat exchangers as exchange units. An example taken from literature is studied here. The result of the study indicates the effectiveness and advantages of this methodology.

Simultaneous Synthesis of WHEN Based on Superstructure Modelling Considering Thermodynamic and Economic Factors

Abstract To explicitly reveal the interaction mechanism between work and heat integration considering both thermodynamic and economic analysis, an improved superstructure, coupling of work exchange networks (WEN) and heat exchange networks (HEN), is proposed for simultaneous synthesis of work and heat exchange networks (WHEN) in this paper. The formulations based on exergy analysis are developed to determine the cold or hot identity of process streams. Afterwards, economic analysis is performed by formulating a cost-based mixed-integer nonlinear programming (MINLP) model to optimize the sequence of work and heat integration, aiming to minimize the total annual cost (TAC). Finally, an example study selected from the open literature is conducted to demonstrate the efficacy of the proposed methodology, where the solutions show a diminution of 40.4% in TAC of HEN prior to WEN, compared with that of WEN prior to HEN.

GC-COSMO based Reaction Solvent Design with New Kinetic Model using CAMD

Abstract Reaction solvents have been playing an important role in liquid-phase organic synthesis. To identify the optimal solvents for accelerating reaction rates, a GC-COSMO based computer-aided molecular design model is formulated, in which a new reaction kinetic model is proposed with the help of parameter reformulation strategy based on the conventional transition state theory. The high-performance solvent with the maximum reaction rate constant is generated using the proposed design model. This solvent design method can be applied to various reaction types. The validity of our method is demonstrated for the selected Menschutkin reaction.

Water networks synthesis for industrial parks respecting to unpredictable scenarios

Abstract Cooperative reuse of water resource across the plants placing in same industrial park would bring significant benefit to each participant plant, the park, and also the realization of resource-saving society. Different from designing water reusing networks merely subjecting to one or several pre-known operation scenarios, this study concentrates on solving the retrofit problem towards the unpredictable scenario which is upcoming yet unrealizable with current water allocation system. A hierarchical procedure is proposed, wherein by introducing series of specific constraints, the mixed integer non-linear programming model formulated for design purpose (Liu et al., 2017) is developed for achieving the optimal retrofit measures respecting to different retrofit specifications of decision-maker requires. At last, an industrial park example containing three retrofit cases at several typical scenarios is illustrated to show the application of the method.

Active bypass design for optimal operation of heat exchanger networks

Optimal operation space of heat exchanger networks (HENs) is largely influenced by either their hard constraints or limitation of operation margin when a bypass or utility unit is selected as a manipulated variable (MV), but previous methods generally focused on solving the identification of inactive bypasses and active pairings in sequence, wherein the inactive bypasses features hard constraints or even saturation during adjustment, and these can result in overly conservative solutions. To improve the operation space of HENs, this paper proposes a feasible solution of bypass design to simultaneously find the inactive bypasses and their active pairings with auxiliary bypasses. In a given network containing disturbance information, they are expressed by mixed integer non-linear programming (MINLP) with the objective function providing minimum control action and utility consumption. A case is subsequently studied to analyse the feasibility of the above framework. The principal orientations and contents of the proposed method lay the groundwork for the integration of HENs synthesis and control.

Synthesis of indirect work exchanger network based on transshipment model

Abstract The synthesis of indirect work exchanger network (WEN) based on transshipment model is first studied considering the compression ratio and expansion ratio as the variables in this paper. Compared with superstructure method, the transshipment model is simpler to obtain the minimum utility consumption taken as the objective function, which is also easier to get the optimal WEN configuration in which the number of units is minimized. The proposed approach for WEN synthesis is a linear program model applied to isothermal process. All the streams are divided into several pressure intervals, also called sub-networks. Then the energy balance is calculated in each sub-network according to the analysis of work cascade in isothermal process. In addition, the adjacent intervals are merged according to the proposed merging rules in order to decrease utility consumption and optimize the network structure. Finally, this method is proved to be feasible and effective by an example.

Optimization of split fractions and cleaning schedule management in heat exchanger networks

Abstract Fouling is a non-negligible problem to heat exchange operation, because it will cause sustained reduction to the overall heat transfer coefficient due to the growth of deposit over heat transfer surface of heat exchange equipments. Implementing regular (routine) cleaning is a recommendable means to remove fouling. As heat load distribution of parallel branches is related to split fractions, this paper presents an approach to arrange the cleaning schedule with having split fractions optimized concurrently. To avoid the numerous integer decision variables produced in time discretization method, the maximum allowable fouling resistance of a heat exchanger is taken as the optimization variable in this study. Then the proposed method is formulated into a Mixed Integer Nonlinear Programming (MINLP) model, to aim for the minimum operating cost of an existing HEN. At last of the study, an example from literature is studied, and the effectiveness of the method has been demonstrated by the proper results.