Jin-Kuk Ha

Intermediate storage tank operation strategies in the production scheduling of multi-product batch processes

Abstract Multi-product batch processes use intermediate storage tanks to increase plant productivity and operational efficiency. In this paper, relations are developed for production scheduling models of the multi-product batch processes with storage time constraints of the intermediate storage tank. Numerical formulas are obtained to determine the makespan and the completion times of products on each unit. These results are extended to accommodate the general serial process networks with storage time and the product constraints of the intermediate storage tank. Next, the effects of the location and the number of the intermediate storage tank on the production scheduling are considered. From the above analysis, a MIPL model to find the maximum makespan is proposed. Applications of the developed model are presented with an example.

Kinetic mechanism of dimethyl ether production process using syngas from integrated gasification combined cycle power plant

In a 1-step synthesis gas-to-dimethyl ether process, synthesis gas is converted into dimethyl ether (DME) in a single reactor. Three reactions are involved in this process: methanol synthesis, methanol dehydration and water gas shift, which form an interesting reaction network. The interplay among these three reactions results in excellent syngas conversion or reactor productivity. The higher syngas conversion or reactor productivity in the syngas-to-DME reaction system, compared to that in the syngas-to-methanol reaction system, is referred to as chemical synergy. This synergy exhibits a strong dependence on the composition of the reactor feed. To demonstrate the extent of this dependence, simulations with adjusted activity for each reaction were performed to reveal the relative rate of each reaction. The results show that the water gas shift reaction is the most rapid, being practically controlled by the equilibrium. Both methanol synthesis and methanol dehydration reactions are kinetically controlled. The role of the dehydration reaction is to remove the equilibrium barrier for the methanol synthesis reaction. However, the role of the water gas shift reaction is more complex; it helps the kinetics of methanol dehydration by keeping the water concentration low, which in turn enhances methanol synthesis. It also readjusts the H2 : CO in the reactor as the reactions proceed. In the CO-rich regime, the water gas shift reaction supplements the limiting reactant and H2, by reacting water with CO. This enhances both the kinetics and thermodynamic driving force of the methanol synthesis reaction. In the H2-rich regime, water gas shift consumes the limiting reactant, CO, which harms both the kinetics and thermodynamics of methanol synthesis. An understanding of these complex roles of the methanol dehydration and water gas shift reactions and of their dependence on the syngas composition explains why the synergy is high in the CO-rich regime, but decreases with the increasing H2 or CO2 content in the reactor feed. The analysis shows that the optimal H2 : CO for the LPDME reactor is around 1-to-1, in good agreement with the results from the simulation. While the 1-to-1 feed provides a good foundation for some process configurations, it does not match the composition of syngas, which typically has a H2 : CO of 3 : 1 or greater.

Development of an optimal multifloor layout model for the generic liquefied natural gas liquefaction process

Liquefied natural gas (LNG) is attracting significant interest as a clean energy alternative to other fossil fuels, mainly for its ease of transport and low carbon dioxide emission. As worldwide demand for LNG consumption has increased, liquefied natural gas floating, production, storage, and offloading (LNG-FPSO) operations have been studied for offshore applications. In particular, the LNG-FPSO topside process systems are located in limited areas. Therefore, the process plant layout of the LNG-FPSO topside systems will be optimized to reduce the area cost occupied by the topside equipment, and this process plant layout will be designed as a multifloor concept. We describe an optimal layout for a generic offshore LNG liquefaction process operated by the dual mixed refrigerant (DMR) cycle. To optimize the multifloor layout for the DMR liquefaction cycle process, an optimization was performed by dividing it into first and the second cycles. A mathematical model of the multifloor layout problem based on these two cycles was formulated, and an optimal multifloor layout was determined by mixed integer linear programming. The mathematical model of the first cycle consists of 725 continuous variables, 198 equality constraints, and 1,107 inequality constraints. The mathematical model of the second cycle consists of 1,291 continuous variables, 286 equality constraints, and 2,327 inequality constraints. The minimization of the total layout cost was defined as an objective function. The proposed model was applied to DMR liquefaction cycle process to determine the optimal multifloor layout.

Fuel Inventory of the Multi-Bed Storage System of the SDS Considering Daily Operation of the Tokamak

Abstract A Tokamak has startup and shutdown periods during which demand specifications differ from those during steady fueling operation. These periods can affect the required number of getter beds of the Storage and Delivery System. In this study, we developed a mathematical model based on the State Task Network, and an algorithm that considers daily operation which includes the period from startup to shutdown to find the optimal number of getter beds. This algorithm can estimate the optimal initial inventory of tritium or deuterium in a getter bed to compensate for fuel consumption until shutdown. The inductive operation mode of the Tokamak is analyzed to illustrate the applicability of the model and algorithm.

Optimal Operation Strategy and Production Planning of Sequential Multi-purpose Batch Plants with Batch Distillation Process

Manufacturing technology for the production of high value-added fine chemical products is emphasized and getting more attention as the diversified interests of customers and the demand of high quality products are getting bigger and bigger everyday. Thus, the development of advanced batch processes, which is the preferred and most appropriate way of producing these types of products, and the related technologies are becoming more important. Therefore, high-precision batch distillation is one of the important elements in the successful manufacturing of fine chemicals, and the importance of the process operation strategy with quality assurance cannot be overemphasized. Accordingly, proposing a process structure explanation and operation strategy of such processes including batch processes and batch distillation would be of great value. We investigate optimal operation strategy and production planning of multi-purpose plants consisting of batch processes and batch distillation for the manufacturing of fine chemical products. For the short-term scheduling of a sequential multi-purpose batch plant consisting of batch distillation under MPC and UIS policy, we proposed a MILP model based on a priori time slot allocation. Also, we consider that the waste product of being produced on batch distillation is recycled to the batch distillation unit for the saving of raw materials. The developed methodology will be especially useful for the design and optimal operations of multi-purpose and multiproduct plants that is suitable for fine chemical production.

Optimal operation strategy and production planning of multi-purpose batch plants with batch distillation process

Abstract Fine chemical production must assure high-standard product quality as well as characterized as multi-product production in small volumes. Installing high-precision batch distillation is one of the common elements in the successful manufacturing of fine chemicals, and the importance of the process operation strategy with quality assurance cannot be overemphasized. In this study, we investigate the optimal operation strategy and production planning of a sequential multi-purpose plants consisting of batch processes and batch distillation with unlimited intermediate storage for the manufacturing of fine chemical products. Illustrative examples show the effectiveness of the approach.