Bomsock Lee

Scheduling of non-sequential multipurpose batch processes under finite intermediate storage policy

Abstract In this study, we present a mathematical model for optimal scheduling of non-sequential multipurpose batch processes under finite intermediate storage (FIS) policy. In non-sequential multipurpose batch processes, the production routes of products may be different from one another and may be in opposite direction. Consequently, in order to reduce idle time of units and to raise the efficiency of process, we have to make operation sequences of products in each unit different by considering the production route of each product. For the formulation of this problem, we represented the starting and finishing time of a task in each unit with two coordinates. One is based on products, and the other is based on operation sequences. Then, we matched the variables used in the two coordinates into one with binary variables and logical constraints. We formulated this problem as an MILP model. Compared with Jung, J. H., Lee, H., Yang, D. R. and Lee, I. (1994) [Completion times and optimal scheduling for serial multi-product processes with transfer and setup times in zero wait (ZW) policy. Computers & Chemical Engineering , 18(6), 537] and Kim, M. S., Jung, J. H. and Lee I. (1996) [Optimal scheduling of multiproduct batch processes for various intermediate storage policies. Industrial Engineering & Chemical Research , 27, 1840] who used an MINLP model for multiproduct scheduling problems, we su9ggest an MILP model, even though we handle sequence dependent setup times in multipurpose processes. Therefore, the proposed model can guarantee the optimality of the solutions. We applied this model to two examples to show the effectiveness of the model. The MILP solver we used to solve these problems is GAMS/ OSL and H/W is IBM RS/6000 (model 350).

Optimal operation of quality controlled product storage

Abstract The mixed integer linear programming model has been developed for the production scheduling of polybutene (PB) process of Daelim Industrial Co. (DIC) in Korea. The PB process is composed of one reactor, 13 storage tanks and two package types. It produces seven reactor products. Most of the tanks are practically dedicated to a specific product but in general, any tanks can be shared by multiple products. Also, two major products use multiple tanks. The reactor is operated on block mode. The products are liquid and they should be stored in tanks before packaging. The unique characteristics of this scheduling problem exists on the fact that the product in tank should be locked for 3–15 days in order to check the quality specifications after run-down from the reactor. The primary objective of scheduling is reducing the number of quality checking process because it causes great loss in production time and tank utilization. The model is composed of about 1500–2000 integer variables. The branching priorities are adjusted according to the importance of variables based on current manual scheduling practice and it greatly enhanced the convergence of mixed integer model. The scheduling system was successfully implemented in real plant and replaced the manual work of scheduler.

Simulation of 1,3-butadiene extractive distillation process using N-methyl-2-pyrrolidone solvent

A computer simulation was performed using a commercial process simulator, Aspen Plus, for NMP (Nmethyl-2-pyrrolidone) extractive distillation process to separate 1,3-butadiene from the C4 hydrocarbon mixtures. The Redlich-Kwong equation of state and NRTL activity coefficient model were used to calculate thermodynamic properties in the simulation of the extractive distillation process. Binary parameters of the NRTL model not provided in the simulator were estimated using the UNIFAC method. The simulation results of the 1,3-butadiene recovery from the C4 mixtures were in good agreement with the plant operation data. The process simulation showed that the material balances in the extractive distillation were successfully predicted for various NMP solvent flow rates. The results obtained in this work provided the optimum solvent rate and the reflux ratio for the NMP extractive distillation process to separate 1,3-butadiene from the C4 mixtures.

Effect of Geometric and Chemical Anisotropy of Janus Ellipsoids on Janus Boundary Mismatch at the Fluid–Fluid Interface

We investigated the geometric and chemical factors of nonspherical Janus particles (i.e., Janus ellipsoids) with regard to the pinning and unpinning behaviors of the Janus boundary at the oil–water interface using attachment energy numerical calculations. The geometric factors were characterized by aspect ratio (AR) and location of the Janus boundary (α) separating the polar and apolar regions of the particle. The chemical factor indicated the supplementary wettability (β) of the two sides of the particle with identical deviations of apolarity and polarity from neutral wetting. These two factors competed with each other to determine particle configurations at the interface. In general, the critical value of β (βc) required to preserve the pinned configuration was inversely proportional to the values of α and AR. From the numerical calculations, the empirical relationship of the parameter values of Janus ellipsoids was found; that is, λ=Δβc/Δα≈0.61AR−1.61. Particularly for the Janus ellipsoids with AR > 1, the βc value is consistent with the boundary between the tilted only and the tilted equilibrium/upright metastable region in their configuration phase diagram. We believe that this work performed at the single particle level offers a fundamental understanding of the manipulation of interparticle interactions and control of the rheological properties of particle-laden interfaces when particles are used as solid surfactants.

Lateral capillary interactions between colloids beneath an oil–water interface that are driven by out-of-plane electrostatic double-layer interactions

We study the lateral capillary interactions between colloids beneath an oil-water interface that lead to closely packed two-dimensional self-assembled colloidal crystals. These capillary forces are caused by the overlap of deformed interfaces above colloids on a solid substrate. The interface deformation is due to the electrostatic disjoining pressure between the charged particles and the charged oil-water interface. It is notable that the short-range (i.e., on the nanometer scale) and out-of-plane electrostatic double-layer interactions, which occur through an aqueous phase, can generate the long-range lateral capillary attraction (i.e., on the micrometer scale).

Process simulation for the recovery of lactic acid using thermally coupled distillation columns to mitigate the remixing effect

The objective of this study was to find process simulations of the plant-wide scale lactic acid recovery process using thermally coupled distillation columns to mitigate the remixing effect. The remixing effect has been widely discussed because in a conventional column arrangement it induces a need for a significant amount of energy for repurification in lactic acid recovery processes. One way to overcome high energy consumption is by using thermally coupled distillation columns. This paper suggests and compares two types of thermally coupled distillation columns applied to the plant-wide scale lactic acid recovery process for removing the remixing effect considering a heavy organic impurity and lactic acid oligomerization in the process. The equilibrium stage model based on the RADFRAC module of Aspen Plus was employed for simulating the thermally coupled distillation columns. Simulation results showed that thermally coupled distillation columns can eliminate the remixing effect and reduce energy consumption compared to conventional lactic acid recovery processes.

Optimal design of batch-storage network under sporadic operating time loss

Abstract The purpose of this study is to find the analytic solution of determining the optimal capacity(lot-size) of batch-storage network to meet the finished product demand under periodic or sporadic operating time losses. Batch processes are bound to random but infrequent operating time losses. Two common remedies for these failures are duplicating another process or increasing process and storage capacity, which are very costly. An optimization model minimizing total cost composed of setup and inventory holding costs as well as the capital costs of constructing processes and storage units is pursued with the framework of batch-storage network of which flows are susceptible to periodic or sporadic operating time losses. The superstructure of the plant consists of a network of serially and/or parallel interlinked batch processes and storage units. The processes transform a set of feedstock materials into another set of products with constant conversion factors. A novel production and inventory analysis method, PSW(Periodic Square Wave) model, is applied. The advantage of PSW model comes from the fact that the model provides a set of simple analytic solution in spite of realistic description of the material flow between processes and storage units. The resulting simple analytic solution can greatly enhance the proper and quick investment decision at the early plant design stage confronted with diverse economic situations.

Optimal Production Sequence and Processing Schedules of Multiproduct Batch Processes for Heat Integration and Minimum Equipment Costs

The production sequence and the processing schedules of multiproduct batch processes can be changed for maximum heat recovery and minimum equipment costs between batch streams. However, the modified production sequence and processing schedule may increase the production cycle time, which causes the bigger equipment sizes required in batch processes. In this study, the required equipment sizes, the production sequence and the processing times of the multiproduct batch processes are mathematically formulated for maximum heat integration and low equipment costs in a mixed integer nonlinear programming. The optimal solution of this formulation was obtained by GAMS/DICOPT programming solver. Examples are presented to show the capabilities of the model.

The optimal manipulation of cooling water flow rates in a heat exchanger network

Abstract In a large, complex heat exchanger network, cooling water flow rates are manipulated by adjusting the valves located at the rear of each heat exchanger. Since the heat exchangers are connected in a network, the change of the cooling water flow rate in a heat exchanger by adjusting the valve bring about the changes of the cooling water flow rates in the other heat exchangers. The manipulation techniques are required to operate cooling water flows efficiently. This paper presents the analysis and the manipulation method of the cooling water flow rates at all heat exchangers in a network simultaneously. A nonlinear programming (NLP) formulation is proposed to determine the optimal adjustment of the valves for the required flow rates of the cooling water in the heat exchangers. Solution of this formulation is obtained with a commercial NLP solver (GAMS/MINOS).