Optimization of Aluminum Smelter Casthouse Operations

Prasad, P. H.; Maravelias, Christos T.; Kelly, Jeffrey D.

doi:10.1021/ie060652h

Cited by 21 publications

(20 citation statements)

References 40 publications

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“…We employ two modeling concepts to preserve batch identity around states in sequential subsystems: (1) explicitly account for connections between units and vessels, 28 and (2) disaggregate inventory variables. 15 Given is a set of processing units, j [ J P , and a set of storage vessels j [ J V .…”

Section: Batch Integritymentioning

confidence: 99%

A general framework for process scheduling

Sundaramoorthy

Maravelias

2011

AIChE Journal

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in Wiley Online Library (wileyonlinelibrary.com).Existing methods for process scheduling can be broadly classified as network-based or sequential. The former are used to address problems where different batches of the same or different tasks are freely mixed or split, whereas the latter are used to address problems where batch mixing/splitting is not allowed. A framework is proposed that allows us to: (1) express scheduling problems in facilities that consist of network and sequential, as well as continuous subsystems, (2) formulate mixed-integer programming (MIP) scheduling models for such problems, and (3) solve the resulting MIP formulations effectively. The proposed framework bridges the gap between network and sequential approaches, thereby addressing the major formulation challenge in the area of process scheduling, namely, the development of a framework that can be used to address a wide spectrum of problems. Keywords: process scheduling, mixed-integer programming IntroductionThe increasing product customization and diversification in the chemical industry have led to the installation (or retrofit) of facilities where multiple products compete for limited resources (equipment units and utilities) and which can be operated in multiple modes. The flexibility of these so called multiproduct facilities allows for higher resource utilization, lower inventory costs, and better responsiveness to demand fluctuations. Nevertheless, these advantages can only be materialized if the production is planned well, a task which is hard mainly due to the increased flexibility, and, thus, multiplicity of solutions.To address this challenge, researchers in the area of process systems engineering (PSE) have developed a number of systematic scheduling approaches, typically mixed-integer programming (MIP) formulations. These approaches can be generally classified as: (1) network-based, used to address problems where batch mixing (blending) and splitting are allowed; and (2) sequential, or ordered-based, used to address problems where batch splitting and mixing are forbidden. Hence, there is no single approach that can be used to represent and address all scheduling problems. Furthermore, there is no method for the solution of problems in processes with different restrictions on batch splitting/mixing. Consequently, one of the two major outstanding challenges in the area of scheduling is the development of a framework capable of addressing all process scheduling problems. The second major challenge is the reduction of the computational requirements of scheduling methods. In this article, we address the former by developing a general strategy for process scheduling, which is based on the representation of network-based and sequential subsystems using a common formalism, and the formulation of a computationally effective MIP model for the unified problem.The article is structured as follows. In the next section, we review scheduling problems and solution methods and present motivation for our work. In the following two sections, we...

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Section: Batch Integritymentioning

confidence: 99%

A general framework for process scheduling

Sundaramoorthy

Maravelias

2011

AIChE Journal

Self Cite

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“…The second group of research works that simultaneously solve batching and scheduling problems are as follows. The simultaneous batching and scheduling system with MILP formation models were presented by Prasad et al (2006), Prasad and Maravelias (2008), and Maravelias (2008a, 2008b). Castro and Novais (2008) presented a multiple time grid formulation that is based on the resource-task network process representation.…”

Section: Literature Reviewsmentioning

confidence: 99%

“…However, some of those methods mentioned alternative objectives where those are optimized separately. Prasad et al (2006) suggested multiple factors in the objective function of the model but those factors are not conflicting with each other.…”

Section: Literature Reviewsmentioning

confidence: 99%

Multi-Objectives Finite Capacity Scheduling of Make-and-Pack Production with Options to Adjust Processing Time

Horng¹,

Yenradee²

2015

EPPM-Journal

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Make-and-pack production is characterized by two stages of production namely, "make-stage" and "packstage" where each stage consists of parallel processing units. In make-stage, raw materials are converted into final products by batch processing. Then, the final products are packed into containers in pack-stage. This paper develops finite capacity scheduling (FCS) system of make-and-pack production with multi-objectives and options to adjust processing time (OAPT). Multi-objectives including minimizations of total tardiness, total earliness, total flow time, and total processing costs are conflicting and a compromised solution is needed. Moreover, the processing time can be adjusted by adding some special chemicals. This paper proposes mixed-integer linear programming models to determine the compromised solution by using weighted average of satisfaction levels (WASL) of all objectives as performance measure. The proposed compromised solution method consists of three steps, (1) determining the best and worst values of each objective, (2) determining the initial compromised solution of all objectives when OAPT is not included in the model, and (3) determining the compromised solution with OAPT. The effect of chemical costs to the OAPT is evaluated. The results showed that the proposed FCS system offered a compromised solution between conflicting objectives. The compromised solution is relatively good but not the best for all objectives. The OAPT can improve the performance of the system and it is significantly affected by the chemical cost per unit. When the chemical cost per unit is reduced, the special chemical is used more to reduce processing time per batch and then the performance measure is more improved.

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“…Finally, most problems involve charging and withdrawing operations which, if resource‐constrained, should be modeled because they may lead to connectivity restrictions. Furthermore, transfer operations are linked with storage levels; e.g., a withdrawing operation cannot start unless the inventory is above a threshold level 41, 44. Finally, we note that material storage and transfer constraints when coupled with unit capacity constraints may induce a type of processing.…”

Section: Chemical Production Environmentsmentioning

confidence: 99%

From Eight‐Membered 10π Electron Sulfur–Nitrogen Cycles to Bicycles and Cages: A Theoretical Approach

Gleiter

Haberhauer

Woitschetzki

2014

Chemistry A European J

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A simple way of rationalizing the structures of cyclic, bicyclic, and tricyclic sulfur-nitrogen species and their congeners is presented. Starting from a planar tetrasulfur tetranitride with 12π electrons, we formally derived on paper a number of heterocyclic eight-membered 10π electron species by reacting the 3p orbitals of two opposite sulfur centers with one radical each, or by replacing these centers by other atoms with five (P) or four (Si, C) valence electrons. This led to planar aromatic 10π electron systems, nonplanar bicyclic structures with a transannular S-S bond, and tricyclic structures by bridging the planar rings with an acceptor or donor unit. The final structures depend on the number of π electrons in the bridges. Intermediate biradicals are stabilized by Jahn-Teller distortion, giving transannular S-S bonds between the NSN units. This procedure may be summarized by two rules, which provide a rationale for the structures of a large number of sulfur-nitrogen-based molecules. The long bonds between the NSN units show a p character of >95 %. The qualitative results have been compared with known molecular structures and the results of B3LYP/cc-pVTZ calculations as well as CASSCF and CASVB calculations. B3LYP/cc-pVTZ calculations have also provided the UV/Vis spectra and the NICS values of the planar 10π systems.

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Optimization of Aluminum Smelter Casthouse Operations

Cited by 21 publications

References 40 publications

A general framework for process scheduling

A general framework for process scheduling

Multi-Objectives Finite Capacity Scheduling of Make-and-Pack Production with Options to Adjust Processing Time

From Eight‐Membered 10π Electron Sulfur–Nitrogen Cycles to Bicycles and Cages: A Theoretical Approach

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