Yingzong Liang

Convexification of Head Loss Equation: Application to Water Distribution System Optimizations

AbstractThe optimization of a water distribution system (WDS) is challenging because of its nonconvex head loss constraint. To address this issue, this paper proposes a modeling technique to repres...

Simultaneous subtour elimination model for single-stage multiproduct parallel batch scheduling with sequence dependent changeovers

Abstract In this paper a mixed-integer linear programming (MILP) model is presented to minimize makespan of single-stage multiproduct parallel batch production with sequence dependent changeovers. The computational inefficiency and suboptimal problems are addressed by the tight and rigorous formulation of the proposed model. Subtours (subcycles) are eliminated simultaneously so that the optimal solution is obtained in one step. The proposed model is tested with two examples. The results show that the model obtains the global optimal solutions with significant improvement in solution time.

Convex Model for Global Optimization of Water Distribution System

Abstract In this paper, a convex model is proposed for the optimal design of water distribution system (WDS). The WDS problem is well known for its poor solution efficiency and difficulty in finding global optimal solution due to the nonconvex head loss equations. To address the nonconvex issue, the head loss equations are rigorously reformulated into convex inequalities. Mixed-integer programming (MIP) method is applied to facilitate the convexification. The proposed model is formulated as mixed-integer nonlinear programming (MINLP) model. Since the model is convex and rigorously formulated, global optimality is guaranteed. The effectiveness of the model is illustrated by a benchmark example.

Population Balance Equation Applied to Microalgae Harvesting

Abstract Population Balance Equation is extended to model microalgae harvesting processes, such as centrifugation and sedimentation, to provide an accurate prediction of cell recovery rates. By analyzing changes in cell size distributions, the model can effectively examine how harvesting efficiencies would affect or be influenced by cell characteristics, such as size and density. Cell behaviors at different size ranges in the dewatering methods are studied to evaluate their variations with harvesting time as well as recovery rate for process optimization. Experiments of sedimentation and centrifugation on a microalgae species called Chlorella are carried out to validate the model. With measurements of optical densities and size distributions of the cell cultures, size specific densities of microalgae are derived to further improve the mathematical model.

Simultaneous Optimization of Multistream Heat Exchangers and Processes

Abstract Multistream heat exchangers (MHEXs) find application in a variety of energy intensive cryogenic processes. However, simultaneous optimization of process and MHEXs is often hindered by its nonlinear behavior and combinatory difficulties, which lead to low computational efficiency and poor solution qualities. In this paper, we present a mixed-integer nonlinear programming (MINLP) framework that comprises heat recovery of MHEXs, thermodynamics, vapor-liquid equilibrium, and other unit operations of the process. The MHEXs model combines the concept of Pinch analysis and multi-M formulation that improves solution efficiency by reducing the number of binary variables and nonconveixty of the model. The framework is applied to an industrial air separation unit (ASU) with multiple MHEXs to demonstrate its effectiveness.

Population Balance Applied to Microalgae Growth

Abstract Renewable energies are considered a possible solution to the increasing world energy demand and they gain even more importance thanks to the lower environmental impact when compared to fossil fuels. Microalgae are one of the most promising biomass sources due to their rapidity in growth and their high lipid content. Increasing the productivity of microalgae in the system is therefore relevant. A possible way to study the growth of the cells is using population balances. This method can help to better understand the different phases of the cells life cycle. Other than that, it can give useful information on a biological point of view. Finally, the possibility to better define the population size distribution can favourite the choice of the most suitable harvesting technology. A general overview and possible application of population balances on microalgae is presented in this work.