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Liquid sloshing in vessels subjected to forced acceleration could lead to dangerous operating and safety issues for aerospace vehicles, large dams, oil tankers, marine vessels, storage tanks, and s...

The monoethylene glycol (MEG)-based natural gas (NG) dehydration process often faces significant glycol losses at the stripper column because of vaporization and poor NG liquid recovery because of ...

A typical front-end crude supply process of refineries encompasses many units, such as vessels, port-side storage tanks, long-distance pipeline, refinery-side charging tanks, and crude distillation...

1,3-Butadiene is used in the production of commercially important elastomers. However, the sustained production of 1,3-butadiene is facing challenges due to the reduction in availability of heavier...

Low-temperature separation with a monoethylene glycol (MEG) injection process is a common dehydration technique for natural gas processing. However, the MEG-based dehydration system frequently suffers significant glycol loss during plant upset conditions, causing double penalties of economic loss and air emissions. Thus, it is very important to minimize MEG loss in the dehydration process. In this paper, an efficient and effective methodology to reduce MEG loss under upset conditions of a natural gas dehydration plant has been developed. First, a plant-wide steady-state simulation model is developed and validated at normal operating conditions. Next, the root cause analysis for MEG loss is performed by introducing various process upsets to the simulation model, which indicates that most MEG loss is due to the fluctuating temperature of the stripper column overhead. After that, a plant-wide dynamic simulation model is developed to help generate a new control strategy to regulate the stripper column operati...

Glycerol is the byproduct of biodiesel production plants. The rapid increase of biodiesel production and demand has resulted in excessive glycerol supply in the market. Converting the cheap glycerol into high-value glycerol carbonate (GC) is a potentially valuable solution to the current worldwide excessive glycerol supply. In this paper, a novel process for simultaneous production of biodiesel and GC (SBDG meanwhile, the byproduct of GC production, methanol, is recycled as the feedstock of the biodiesel production. Second, the optimization of the columns duties has been performed via thermal analysis analyzing the Column Grand Composite Curves (CGCC). In addition, a mathematic model for the heat integration of the SBD&...

Chemical hazardous material (Hazmat) transportation has become a very important safety issue to human society and the environment. Great attention has been drawn to reduce potential risks and incidents. In this paper, a new methodology is proposed for the dynamic routing optimization of the chemical Hazmat transportation, which includes four major stages: (i) information collection and preparation; (ii) modeling and solving individual and system routing models; (iii) reactive routing optimization under uncertainties; and (iv) trade-off study for potential shipping delays. A novel MILP model has been developed to determine the optimal shipping path with the minimal transportation risk. This model consists of two parts: the individual and system routing models, which are designed to explore the optimal shipping path for each shipping pair and all transportation tasks, respectively. When uncertainties occur, reactive routing optimization will be performed for handling the leftover transportation tasks. In pa...

Emission reduction becomes increasingly important for petroleum refineries nowadays. Cost-effective solution strategies require emission reductions to be addressed from the entire plant point of vi...

The concept of ethylene epoxidation over methyltrioxorhenium (MTO) catalyst could save the world from global warming since the epoxidation reaction never produces carbon dioxide as byproduct. Unlike the conventional gas epoxidation reaction with oxygen, this reaction takes place in the (ethylene) gas-expanded liquid solvent phase (methanol) while the reaction oxidant is hydrogen peroxide. The reaction takes place at temperatures and pressures close to the ethylene critical point (Pc = 50.42 bar; Tc = 48.56 °F) (Gas Encyclopedia by Air Liquide, https://encyclopedia.airliquide.com/ethylene). In this paper, an optimized design and operation for MTO based ethylene oxide (EO) production processes has been developed, which has less manufacturing costs compared with the one from the current literature ( Ind. Eng. Chem. Res. 2013, 52, 18−29). The developed EO system could produce 200,000 tons of ethylene oxide per year at a purity of 99.9%. It has two reactors for ethylene epoxidation and hydrogen peroxide decomp...

The boil-off gas (BOG) generation at LNG (liquefied natural gas) exporting terminals is significant and should be minimized and/or recycled efficiently and effectively. In this work, the study of BOG generation, minimization, and recovery has been performed for a typical LNG plant with C3MR (propane precooled mixed refrigerant) process, storage facility, loading facility, and LNG ship with four moss-type spherical tanks. Plant-wide dynamic simulations are employed to quantify dynamic BOG generations during loading and holding mode, under various LNG temperatures at LNG exporting terminals. On the basis of multiple case studies, optimum LNG temperatures under different LNG subcooling and BOG recovery strategies have been identified for the sake of total energy consumptions. This study provides valuable information about the effect of LNG subcooling temperature on BOG generation, which would help in operating LNG plants at optimum conditions and economically minimize BOG generation and recovering BOG at LNG...

The refrigeration system is one of the most important and critical utility systems in the chemical and petrochemical industries. The traditional cascade refrigeration system (CRS) has been used for decades in ethylene plants. However, the mixed refrigerant system (MRS) with higher energy efficiency and less capital expenses than CRS has not widely been applied in ethylene plants. In this paper, a general methodology has been proposed for the synthesis of a tertiary refrigerant of MRS containing a mixture of methane, ethylene and propylene that can satisfy all the cooling/heating refrigeration that the traditional ethylene–propylene CRS serves in an ethylene plant. The exergy-temperature chart combined with the exergy analysis is presented to analyze comprehensively the thermodynamic nature of both CRS and MRS. Furthermore, the comparison of economic performances of these two different systems is also conducted. The efficacy of the developed MRS methodology has been demonstrated by a case study, where the ...

Crude oil planning and scheduling is crucial to petroleum refineries because of the potential for significant economic benefits. In reality, however, crude oil scheduling activities are highly vulnerable to disruptions caused by various uncertainties. In this paper, a new proactive scheduling methodology simultaneously covering crude unloading, transferring, and processing (CUTP) has been developed. The CUTP scheduling methodology is to maximize the total profit subject to various inventory, operation, transportation, and production constraints, while maintaining the refinery normal operating conditions under the uncertainty of crude shipping delays. To quantify shipping delay uncertainties, a combined feasibility index has been developed and embedded into the developed continuous-time mixed-integer nonlinear programming scheduling model, which is solved by the global solver of ANTIGONE. In addition, the relationship between the total profit and the minimum flexibility threshold is also given. The efficac...

The scheduling of an ethylene cracking furnace system should not only focus on the plant profitability but also address the concern of environmental sustainability. On the basis of the previous study (Zhao et al.1), this Article has developed a new scheduling model for the optimal operation of the cracking furnace system in ethylene plants by considering more practical operating features, such as nonhomogeneous last-batch ending times and furnace load makeups, as well as the background air-quality conscious decoking. With the newly developed model, the simultaneous furnace shutdown can be successfully avoided at the end of the scheduling time horizon; meanwhile, certain manufacturing capacity losses and upsets can be alleviated during furnace decoking operations. Furthermore, the obtained scheduling solution will be responsible for background air-quality concerns by wisely allocating furnace decoking emission peaks into time windows that would cause less adverse environmental impacts. The efficacy of the ...

Ground-level ozone is a pervasive air pollutant, which could be formed from substantial flare emissions during chemical plant startup operations. Especially in regions where chemical plants are concentrated, the regional air quality (i.e., the ozone concentration) might be aggravated by simultaneous startup emissions from multiple chemical plants. Thus, it is environmentally important and cost-effective for optimal scheduling of multiplant startups under their manufacturing allowances to minimize possible adverse air-quality impacts. In this paper, a systematic methodology has been developed for air-quality conscious multiplant startups. Through case studies, they demonstrate that multiplant startups without any coordination could result in significant air-quality impacts (15.4 ppb increment). However, an optimal scheduling plan with several-hour tuning on the starting time of their startup operations would significantly reduce such adverse air-quality impacts (only 3.2 ppb increment). Another important f...

A new reactive scheduling model in the form of FRS (full rescheduling strategy) for front-end crude oil operations has been developed. The reactive rescheduling model is triggered off across all the units at the time that tank malfunction is detected. As compared to the previous work (Ind. Eng. Chem. Res.. 2014, 53, 12502–12518) more practical features have been addressed on tank failure handling solutions: (i) failure tank leftover inventory will be first evacuated to a backup tank, and later on directed to downstream units, and (ii) failure tank leftover inventory will be immediately directed to its downstream units. Furthermore, comprehensive strategy analyses have been conducted on partial rescheduling strategy (PRS) and FRS to validate their respective pros and cons. It is found out from case studies that although FRS results in more operational costs than PRS due to an increased number of time events, FRS is more flexible and less susceptible to current scheduling results, which ensures more robust ...

Four kinds of deep eutectic solvents (DESs) based on choline chloride (ChCl) with ethylene glycol (EG), malonic acid (MA), urea, and thiourea as hydrogen bond donors were prepared and characterized. All these DESs show good thermal stability and can be stable at 363 K, which is beneficial for the application in flue gas desulfurization. Then, SO2 absorption capacities of these DESs were determined at different temperatures and SO2 partial pressures. The absorption results demonstrate that ChCl–EG (1:2) and ChCl–thiourea (1:1) DESs exhibit excellent absorption performances, and the absorption capacities are 2.88 and 2.96 mol SO2 per mol DES at 293 K and 1 atm, respectively. In addition, the SO2 absorption and regeneration experiments were conducted. All solvents can be regenerated at 343 K with N2 bubbling, and the absorption capacities of DESs remain without a significant loss after six absorption and desorption cycles. What’s more, the absorption mechanism of SO2 in these DESs were investigated by IR and...

For an industrial zone heavily populated by petrochemical and chemical plants, the design of an effective air-quality monitoring network (AQMN) is very important for local environmental and industrial sustainability. In this paper, a general methodology with multiobjective and deterministic optimization for AQMN design and redesign is developed. Generally, a Gaussian dispersion model is employed to create spatial pollution distributions according to historical meteorological conditions and updated emission source profiles. Then, a multiobjective mixed-integer linear programming model is developed to optimally design an AQMN, which allows the relocation of existing monitoring stations and/or the addition of new monitoring stations. The optimization will maximize the detectable air-quality threshold violation frequency (AQTVF) for potential pollution events in the studied industrial zone as well as minimize the total budget cost for the AQMN implementation with considerations of existing monitoring station ...

Flare minimization under normal and abnormal operating conditions in large-scale industrial processes, especially for refineries and petrochemical plants, is a double-win practice, which simultaneously benefits industrial and environmental sustainability. Unfortunately, proactive and cost-effective flare minimization (PCFM) approaches under abnormal situations are still lacking. In this study, a PCFM approach for an ethylene plant is presented for its start-up operations. This approach employs rigorous steady-state and dynamic models of a front-end deethanizer ethylene plant to serve as a foundation to explore flare root causes during plant start-ups and subsequently a test bed to support both design and operational strategies for start-up flare minimizations. It has been demonstrated that the charge gas compressor (CGC) start-up is the most critical operation, which results in the largest amount of flaring sources. Several start-up strategies at different CGC feed rates and compositions, including scenar...

In this paper, an effective reactive scheduling methodology for short-term crude oil operations has been developed to manage crude movements from ship unloading to distillation processing under various uncertainties. It contains a two-stage solving procedure for handling uncertainties such as shipping delay, crude mixture demand change, and tank unavailability. On the first stage, a deterministic schedule is initially obtained based on a continuous-time global event model using nominal data provided/projected at the beginning of each scheduling time horizon. On the second stage, indicator binary variables are implemented respectively under any occurrence of different uncertainties to collect information from the current deterministic schedule through defining “executed” tasks. On the basis of the information, rescheduling models are configured correspondingly under diverse uncertainty scenarios by combining the first-stage scheduling model and amendment constraints associated with those “executed” tasks. ...

The integrated cryogenic separation system (ICSS), which includes a chilling train and a demethanization section, is a crucial production system in an ethylene plant. It accounts for up to 50% of the total start-up time and flare emissions of the whole ethylene plant. Traditional start-up scenarios are developed on experience and improved by trial and error, which is inefficient and dangerous. This paper employs rigorous dynamic simulations to examine the potential infeasibilities and operational risks of different start-up scenarios. The best start-up scenario with minimal start-up time and flare emissions is determined. To obtain the initial start-up state with ambient nitrogen filling in the whole system, an initialization algorithm based on parameter modification for the dynamic ICSS model is presented. This novel initialization algorithm greatly saves time and effort of the initialization of the start-up model compared with previous studies. In addition, if time-related variables are important for sc...

Heavy-metal uptake by plants growing in contaminated soil poses a potential harm to human health because of its transition into the food chain, and the removal of heavy metals from beverages has attracted considerable attention. In the present article, a facile ionic-liquid-assisted synthesis of nanopowder ammonium cadmium phosphate (NPACP) using an ionic liquid with a large anion, namely, 1-butyl-3-methyl imidazolium tetraphenylborate, [BMIM][BPh4], as a template is reported. This simple one-step method can suitably be scaled up for large-scale synthesis. The adsorption properties of the nanopowder were evaluated, NPACP was used as an adsorbent for lead ions from glucose solution, and it was found that NPACP has excellent adsorption properties for Pb(II). The feasibility of using NPACP for lead removal was confirmed, and the film diffusion mechanism was found to dominate the adsorption process of Pb(II) ions on NPACP. Its adsorption kinetics were modeled by a pseudo-second-order rate equation. Therefore,...

Chemical facilities, where large amounts of chemicals and fuels are processed, manufactured, and housed, are at high risk to originate air emission events, including intensive flaring and toxic gas release caused by various uncertainties such as equipment failure, false operation, natural disaster, or terrorist attack. Based on an available air-quality-monitoring network, to detect the possible emission sources (chemical plants) for an observed emission event, so as to support diagnostic and prognostic decisions in a timely and effective manner, a systematic method for abnormal emission identifications should be employed. In this article, a systematic methodology for such applications has been developed. It includes two stages of modeling and optimization work: (1) the determination of background normal emission rates from multiple emission sources and (2) multiobjective optimization for emission-source identification and quantification. This method not only can determine emission source location, startin...

The unique chemical and physical properties of gold are increasingly being sought for use in a growing number of industrial and medical applications. The agricultural residue spent buckwheat hulls (60 mesh) modified with organodiphosphonic acid (denoted as ODPA-BH) was successfully developed and characterized, and cellulose with an organodiphosphonic acid group was calculated at the B3LYP/6-31G(d) level. ODPA-BH was employed to adsorb Au(III) ions in both spiked samples and industrial wastewater samples, and the relevant adsorption kinetics and isotherms were investigated. A better interpretation for the experimental data was obtained with the Langmuir isotherm equation, and the maximum adsorption capacity for Au(III) was found to be 465.16 mg/g at 35 °C. The adsorption kinetics were modeled by a pseudo-second-order rate equation, and the thermodynamic parameters ΔG, ΔH, and ΔS were determined to be −8.89 kJ·mol–1, 70.93 kJ·mol–1, and 257.25 J·K–1·mol–1, respectively.

Crude-oil blending is a common practice to obtain qualified mixing oils for refinery processing at low costs. The blending component crudes are subject to inventory constraints, which in turn are dynamically affected by the refinery purchase plan including the crude-oil types, amounts, and delivery over a planned period of time. As the crude-oil price and availability constantly changes in a volatile market, the crude-oil blending and purchase planning should be coordinated and simultaneously optimized to maximize the potential profitability of a refinery plant. This becomes even more important when the uncertainty of crude-oil delivery time is also taken into account. In this paper, a general MINLP (mixed-integer nonlinear programming) model is developed to address the profit optimization of crude-oil blending and purchase planning in refinery plants. Inventory-related flexibility indexes are developed to characterize the ability of a refinery for handling the uncertainty of crude-oil delivery delays. In...

The natural gas liquefaction process is an important sector of the overall liquefied natural gas (LNG) value chain. In this article, a thermodynamic-analysis-based study of the minimization of the energy consumption of a typical natural gas liquefaction process is performed. First, a rigorous simulation of the natural gas liquefaction process is conducted. According to the simulation results, the operating states of the refrigerant and natural gas streams are revealed, along with the operating conditions of the entire liquefaction process. Then, the energy consumption roadmap is determined through in-depth thermodynamic analysis, where the opportunities for energy consumption minimization are identified. Based on the thermodynamic analysis, a rigorous optimization model is developed and solved for energy consumption reduction of the same natural gas liquefaction process. Finally, the optimization results are examined again through rigorous simulation to check the feasibility of the obtained optimal solution.

The cracking furnace system is crucial for an olefin plant. Its operation needs to follow a predefined schedule to process various feeds continuously, meanwhile conducting a periodically decoking operation for each furnace when its performance apparently decreases. In practice, because the feed supply changes dynamically, the routine furnace scheduling is better performed in a dynamic and reactive way, through which the furnace operations can be smartly rescheduled with respect to any delivery of new coming feeds. Thus, the feeds from the new delivery and the leftover inventories can be timely, feasibly, and optimally allocated to different furnaces for processing to obtain the maximum average net profit per time. Facing this challenge, this paper develops a new MINLP-based reactive scheduling strategy, which can dynamically generate reschedules based on the new feed deliveries, the leftover feeds, and current furnace operating conditions. It simultaneously addresses all the major scheduling issues of a c...

The LNG (liquefied natural gas) receiving terminal is an important component of the entire LNG value chain. The handling of unloading BOG (boil-off gas) during LNG regasification at LNG receiving terminals significantly influences the BOG flare emission and energy consumption. In this work, thermodynamic-analysis-based design and operations are simultaneously considered to recover BOG with the minimum total energy consumption, a goal of which is to provide a cost-effective flare minimization strategy at LNG receiving terminals. A rigorous simulation-based optimization model and its solution algorithm are developed based on an LNG regasification superstructure. Case studies are used to demonstrate the efficacy of the developed methodology. The presented general optimization model and thermodynamic analysis also provide fundamental understandings of the LNG regasification process that are valuable for industrial applications.

The chilling train is a very important section for ethylene plants, as its design and operation significantly influence energy consumption and product loss rates. In this paper, a systematic methodology for the optimal design and operation of a chilling train system has been presented. A multiobjective mixed-integer nonlinear programming (MINLP) model has been developed, which aims at minimizing the ethylene loss rate and the exergy-accounted energy consumption, meanwhile maximizing the hydrogen recovery rate. Also presented are the technologies for obtaining reliable thermodynamic properties based on rigorous simulation and the methods for removing redundant variables for MINLP model simplification. On the basis of the methodology, the optimal design and operating conditions of a chilling train system can be simultaneously achieved. A real case study has demonstrated the efficacy of the developed methodology. The results show that the optimized chilling train system has better economic performance than t...

Cracking furnaces of ethylene plants are capable of processing multiple feeds to produce smaller hydrocarbon molecules, such as ethylene, propylene, and ethane. The best practice for handling the produced ethane is to recycle it as an internal feed and conduct the secondary cracking in a specific furnace. As cracking furnaces have to be periodically shut down for decoking, when multiple furnaces processing different feeds under various product values and manufacturing costs are considered, the operational scheduling for the entire furnace system should be optimized to achieve the best economic performance. In this paper, a new MINLP (mixed-integer nonlinear programming) model has been developed to optimize the operation of cracking furnace systems with the consideration of secondary ethane cracking. This model is more practical than the previous study and can simultaneously identify the allocation of feeds with their quantity, time, and sequence information for each cracking furnace. A case study has demo...

Ethylene plant start-ups generate huge amounts of off-spec products for flaring, which cause negative environmental and societal impacts, as well as tremendous raw material and energy losses that could be unitized to generate much more needed products. Thus, cost-effective start-up flare minimization strategies through proactive process design and operation are becoming more important and attractive to the industry. However, fundamental and quantitative studies on start-up flaring emissions are still lacking, such as (i) what kinds of emission species are contained in the flaring sources; (ii) how much of each emission source will be generated during one start-up; and (iii) what is the dynamic emission profile of each emission source with respect to the start-up time? In this paper, rigorous plant-wide dynamic simulations are employed to characterize flaring emission sources under different flare minimization strategies for an ethylene plant start-up. Deep insights of the emission source distribution and ...

Ethylene oxide (EO) is an important chemical intermediate for the production of various chemical products. The manufacturing of EO involves critical exothermic reactions at high temperature and high pressure, whose failure may cause catastrophic personal injury, severe air pollution, and tremendous economic loss. Thus, an EO plant must be well controlled under various situations, especially during its start-up operations. In this paper, a general methodology for improving chemical plant start-up operations through plant-wide dynamic simulation has been developed. It undergoes modeling and validations for steady-state, dynamic, and historian start-up operations. On the basis of the validated dynamic simulation model, the original plant start-up strategy is further examined and optimized to speed-up the plant start-up operation with enhanced safety considerations. A case study on an EO plant start-up has demonstrated the significant operational and economic benefits of the proposed methodology.

Multistage compression systems (MSCS) are the most important and valuable facilities in chemical plants, whose failure may cause severe accidents and/or tremendous economic loss. Thus, operation for MSCS needs sufficient care under various situations, especially during plant startup. This paper employs rigorous pressure-driven dynamic simulations to examine and improve operation safety of the cracked gas compression system during an ethylene plant startup. For safety consideration, antisurge process design and control strategies are dynamically evaluated along with startup procedures. Operating point trajectory for each compressor and their potential safety problems are identified. Assisted by the rigorous dynamic simulation, the plant startup procedure is improved with better safety performance.

Flaring is crucial to chemical plant safety. However, excessive flaring, especially the intensive flaring during the chemical plant start-up operation, emits huge amounts of volatile organic compounds (VOCs) and highly reactive VOCs, which meanwhile results in tremendous industrial material and energy loss. Thus, the flare emission should be minimized if at all possible. This paper presents a general methodology on flare minimization for chemical plant start-up operations via plantwide dynamic simulation. The methodology starts with setup and validation of plantwide steady-state and dynamic simulation models. The validated dynamic model is then systematically transformed to the initial state of start-up and thereafter virtually run to check the plant start-up procedures. Any infeasible or risky scenarios will be fed back to plant engineers for operation improvement. The plantwide dynamic simulation provides an insight into process dynamic behaviors, which is crucial for the plant to minimize the flaring w...

The optimality of design and operation of an electroplating system determines largely coating quality, productivity, and waste reduction efficiency. Industrial practice shows that, in a usual operation, the solution loss from an electroplating unit through drag-out can be as high as 30% of overall consumption. This has dramatically increased operating cost as well as waste treatment cost. On the other hand, plating quality in terms of coating thickness on workpieces is always a concern in plants. To improve the economic and environmental performance, a key step is to have a deep understanding of the system. Model-based simulation has proven to be a cost-effective approach along this venue. This paper introduces a fundamental-based general modeling methodology for characterizing an integrated electroplating system that consists of a plating unit and a solution recovery subsystem. The methodology allows detailed system analysis and complete process information integration, which will be crucial for optimal design and operation of a closed-loop electroplating for prevention of plating solution loss and assurance of coating thickness on workpieces. A case study on an alkali zinc electroplating system will demonstrate the efficacy of the model-based design and operation approach.

Hoist scheduling is a class of production scheduling of batch systems in the manufacturing industries. Cyclic hoist scheduling (CHS) is a type of hoist scheduling that deals with the scheduling that involves one hoist and produces some type of product in a multistage production line. The only “resource” in the production is the hoist for which various operations compete with each other in every production cycle. Currently available CHS approaches, regardless of whether they are algorithmic or heuristic based, are almost all designed to maximize the production rate by optimizing hoist movements; environmental issues are not a concern during development of the hoist schedule. This paper introduces a methodology for solving a general CHS problem where the production rate and waste reduction are simultaneously taken into account. Using this methodology, all feasible hoist schedules for a given CHS problem can be rapidly identified using a graph-assisted search algorithm. The schedules are then evaluated in te...

The hydrogenation of carbon dioxide was examined over various composite catalysts composed of Fe−Zn−M catalyst and zeolite. Fe−Zn−Zr/HY composite catalyst was confirmed to be efficient for the highly selective production of isobutane, which is regarded as a synthetic intermediate of MTBE (methyl tert-butyl ether). The composite catalyst of Fe−Zn−Zr catalyst with H-ZMS-5 formed C5+ hydrocarbons in good yield. The ratios of branched hydrocarbons in C5+ ones, which are suitable for high-octane gasoline, were over 90%.

Multistage material-handling (MSMH) processes are broadly possessed by industries for manufacturing massive amounts of workpieces (jobs), where hoists are usually employed by following certain movement schedules based on the job-processing recipes. In this paper, we consider a common situation that an existing MSMH production line has reached its maximum productivity; in order to debottleneck the production and increase its productivity, some units will be retrofitted to increase their job-processing capacity under a fixed budget. Under this situation, which units need to be retrofitted and how many additional capacities will be added to those retrofitted units have to be optimally determined. Correspondingly, since process design has changed, the hoist schedule also needs to be adjusted. Apparently, the best way to deal with such an MSMH debottleneck problem requires the consideration of both the process retrofit and hoist rescheduling at the same time. In this paper, an MILP (mixed integer linear programming) based model is developed to simultaneously identify the best retrofit design and hoist schedule to obtain the maximum productivity under a fixed retrofit budget. On the basis of this development, different retrofit and hoist-scheduling scenarios under different budgets can also be examined, so that the Pareto frontier balancing both retrofit investment and productivity can be identified, which will provide the comprehensive decision support for an MSMH debottleneck problem. The efficacy of the proposed methodology has been demonstrated by case studies.