Biogas has emerged as an alternative renewable fuel to natural gas. However, the presence of trac... more Biogas has emerged as an alternative renewable fuel to natural gas. However, the presence of trace contaminants and large quantities of CO 2 in biogas necessitates its purification and upgrading to increase its calorific value. Different technologies have been developed to upgrade biogas to biomethane. Among these, chemical absorption is commonly employed due to its high process efficiency and less solvent requirement due to high selectivity compared to physical absorption. However, the chemical decomposition of amine-based solvents, toxicological impact, high plant maintenance costs, high enthalpy of reaction, and corrosivity associated with chemical absorption limit its large-scale application. Recently, ionic liquids (ILs) have garnered attention as alternative absorption media to conventional solvents. ILs have a high CO 2 uptake, thermal stability, and negligible vapor pressure. Recent process simulation studies featuring ILs as solvents for biogas upgrading reveal the suitability of these approaches as alternatives to laborious experimental work to assess the practical, technical, and economic viability of ILs. As per the authors' knowledge, this is the first review comparing biogas upgrading technologies from a technical, environmental, and economic perspective. Primarily, studies relating to IL-based biogas upgrading are considered, and challenges associated with the large-scale adoption of ILs as absorption media are discussed. Process simulations and techno-economic assessments of IL-based biogas upgrading techniques are presented. A conceptual design approach is proposed for the successful scale-up of IL-based biogas upgrading. Based on results, deep eutectic solvents are recommended as next-generation solvents for absorption as technical and economic aspects are found superior to conventional amines and ionic liquids.
The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating elect... more The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating electricity from low-to-high-temperature waste industrial streams. Several ORC-based waste heat utilization plants are already operational; however, improving plant cost-effectiveness and competitiveness is challenging. The use of thermally efficient and cost-competitive working fluids (WFs) improves the overall efficiency and economics of ORC systems. This study evaluates ORC systems, facilitated by biogas combustion flue gases, using n-butanol, i-butanol, and methylcyclohexane, as WFs technically and economically, from a process system engineering perspective. Furthermore, the performance of the aforementioned WFs is compared with that of toluene, a well-known WF, and it is concluded that i-butanol and n-butanol are the most competitive alternatives in terms of work output, exergy efficiency, thermal efficiency, total annual cost, and annual profit. Moreover, the i-butanol and n-butanol-bas...
Biomethane is regarded as a promising renewable energy source, with great potential to satisfy th... more Biomethane is regarded as a promising renewable energy source, with great potential to satisfy the growth of energy demands and to reduce greenhouse gas emissions. Liquefaction is a suitable approach for long distances and overseas transportation of biomethane; however, it is energy-intensive due to its cryogenic working condition. The major challenge is to design a high-energy efficiency liquefaction process with simple operation and configuration. A single mixed refrigerant biomethane liquefaction process adopting the cryogenic liquid turbine for small-scale production has been proposed in this study to address this issue. The optimal design corresponding to minimal energy consumption was obtained through the black-hole-based optimization algorithm. The effect of the minimum internal temperature approach (MITA) in the main cryogenic heat exchanger on the biomethane liquefaction process performance was investigated. The study results indicated that the specific energy consumption o...
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
This paper describes an ejector model for the prediction of on-design performance under available... more This paper describes an ejector model for the prediction of on-design performance under available conditions. This is a direct method of calculating the optimal ejector performance (entrainment ratio or ER) without the need for iterative methods, which have been conventionally used. The values of three ejector efficiencies used to account for losses in the ejector are calculated by using a systematic approach (by employing CFD analysis) rather than the hit and trial method. Both experimental and analytical data from literature are used to validate the presented analytical model with good agreement for on-design performance. R245fa working fluid has been used for low-grade heat applications, and Engineering Equation Solver (EES) has been employed for simulating the proposed model. The presented model is suitable for integration with any thermal system model and its optimization because of its direct, non-iterative methodology. This model is a non-dimensional model and therefore requi...
Deep eutectic solvents (DESs) comprise ChCl/urea, in combination with water, have been considered... more Deep eutectic solvents (DESs) comprise ChCl/urea, in combination with water, have been considered in removing acid gases (CO2 and H2S) from biogas. The evaluation of DES for biogas upgrading at relatively high pressure (i.e., >8.0 bar) has not been reported before. The aqueous DES performance has also not been analyzed compared to conventional amines-based solvent (MEA) and ionic liquid (IL). To the best of our knowledge, this is the first study that presents the integration of DES-based biogas upgrading with a mixed refrigerant liquefaction process to facilitate the safe and economical transportation of biomethane over long distances. The biogas considered in this study consisted of 60% CH4, 39% CO2, and 1% H2S. The aqueous ChCl/urea (70 wt%) results in biomethane with ≥99.0 wt% purity and ≥97.0 wt% recovery. Then, this biomethane was liquefied with ≥90% liquefaction rate. Based on the results obtained herein, overall capital, operating, and total annualized cost savings of 2.8%...
The reduction of greenhouse gas emission via the transformation of carbon dioxide into methanol r... more The reduction of greenhouse gas emission via the transformation of carbon dioxide into methanol results in several secondary benefits including the production of a valuable by-product that can be used for energy storage and as a fuel source. As such, this is a promising approach for mitigating climate change. Methanol production via the co-electrolysis process using solid oxide electrolyzer cells is an efficacious solution to the issue of excess electricity storage in the context of renewable energy and carbon dioxide utilization. However, this process is an energy-intensive and temperature-sensitive method, mainly due to the requirement of high-temperature electrolysis. In this context, this study investigates and evaluates the potential for overall performance improvement by minimizing energy consumption and increasing methanol production using self-heat recuperation technology. The newly developed vortex search strategy was employed to achieve the maximum potential benefit from retrofitted recuperators. Detailed exergy analysis was performed for the process and the evaluation of its performance. The findings revealed that the electrochemical system for co-electrolysis has the highest exergy destruction rate. By employing the vortex search approach, the exergy loss of the energy process system can be reduced by 61.7% with a total reduction of the exergy loss of 15.9%, while improving methanol production and decreasing distillation reboiler duty. The simple solution of self-recuperation with optimization that was utilized in this study is a flexible approach that can be directly applied to the improvement of coelectrolysis and methanol synthesis.
Industrial & Engineering Chemistry Research, 2019
This study examines control strategies developed for wastewater treatment via partial nitration a... more This study examines control strategies developed for wastewater treatment via partial nitration and the anaerobic ammonium oxidation process with the objective of enhancing nitrogen removal efficiency. The implementation of different control strategies were analyzed and explained with the help of pictorial representations. The benefits of the different control strategies were also briefly discussed. The biological process of nitrogen removal requires appropriate pairing between control and manipulated variables. Furthermore, the approach to follow when selecting suitable candidates and determining the pairing criterion was discussed. Although the conventional feedback−feedforward control logic is easy to implement, incorporation of the nonlinearity and complexity associated with the processes requires the design of advanced control systems.
International Journal of Greenhouse Gas Control, 2019
Natural gas is a cleaner energy source compared to other fossil-based energy sources owing to its... more Natural gas is a cleaner energy source compared to other fossil-based energy sources owing to its low emissions. However, natural gas contains acidic gases (including CO 2 and H 2 S), which may cause equipment corrosion and environmental damage. To date, amine-based absorption techniques have been used to remove acidic gases from natural gas to reach regulated concentration limits. However, a tremendous amount of heating is required to regenerate amine-based solvents, which remains a major issue with traditional absorption-based acid gas removal units. In this context, 1-butyl-3-methyimidazolium methyl sulfate (bmim)(CH 3 SO 4) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmim)(PF 6) were adopted as potential solvents for reducing the heating requirements in the solvent-regeneration step of absorption-based removal techniques. This study shows that by using the imidazolium-based cationic IL, up to 99 wt% of acid gases can be removed while dramatically reducing the heating load and the total annualized cost compared to conventional amine-based absorption units. Flashbased solvent regeneration was used to recover the solvent with a heating loading value of 3978 kW, which is 78.6% lower than that of conventional amine regeneration strippers. Use of only flash column instead of stripper also makes the proposed ionic liquid-based absorption technique most economical with respect to capital investment. To date, several approaches including absorption, adsorption, and membrane separation have been developed to capture acid gases from NG. Absorption-based techniques are the most common and practical approaches for large-scale NG treatment to remove acid gases (Afkhamipour and Mofarahi, 2014). Aqueous alkanolamine solvent-based absorption/ stripper schemes have been developed for acid gas removal, mainly because of their high reliability. Among alkanolamine solvents, ethanolamine (MEA)-based solvents (e.g., MEA and MDEA) are commonly used because of their strong reactivity, high capacity, active kinetics, and widespread availability with low cost (Lepaumier et al., 2009; Venkatraman and Alsberg, 2017). However, a tremendous amount of thermal energy is required for the regeneration of MEA and MDEA, which accounts for around 80% of the total operating cost (Aaron and Tsouris, 2005; Mesbah et al., 2018). Therefore, the heating load for amine solvent regeneration is a major
Bioethanol has garnered a great interest as a potential energy source, mainly due to its sustaina... more Bioethanol has garnered a great interest as a potential energy source, mainly due to its sustainable and green nature. Generally, bioethanol is produced through the microbial conversion of biomass and biomass derived syngas. However, the dehydration and purification steps for achieving fuel-grade ethanol from the microbial production process consume tremendous amounts of energy. This high energy consumption limits the feasibility of microbial ethanol production on the commercial scale. In this context, selection of an optimal technology for product separation is essential for successful commercialization of microbially produced bioethanol. This article presents the recent developments in dehydration and purification technologies for bioethanol production using distillation and membrane based separation. Distillation and pervaporation are analyzed on the basis of the overall energy requirement, consumption, and economics. Pervaporation-assisted distillation approaches are also examined from the perspective of process systems engineering, including factors affecting the system performance. Furthermore, the role of simulation in technological development along with available mathematical models is discussed, and commercial status of pervaporation based separation is presented. Finally, the current status of the existing technology, challenges, and future research directions are identified from the perspective of achieving process sustainability on the industrial scale. Economic comparison between distillation and different hybrid schemes revealed that integrating distillation with membrane based separation techniques reduce the bioethanol production cost. Moreover, hybrid schemes that combine distillation with pervaporation, and steam stripping with vapor permeation are proved to be the best combinations for the cheapest bioethanol production.
This work presents an advanced and systematic approach to analytically design the optimal parame... more This work presents an advanced and systematic approach to analytically design the optimal parameters of a two parameter second-order internal model control (IMC) filter that satisfies operational constraints on the output process, the manipulated variable as well as rate of change of the manipulated variable, for a first-order plus dead time (FOPDT) process. The IMC parameters are designed to minimize a control objective function composed of the weighted sum of the error between the process variable and the set point, and the rate of change of the manipulated variable, and to satisfy the desired constraints. The feasible region of the constrained IMC control parameters was graphically analyzed, as the process parameters and the constraints varied. The resulting constrained IMC control parameters were also used to find the corresponding industrial proportional-integral controller parameters of a Smith predictor structure.
Industrial & Engineering Chemistry Research, 2018
For offshore natural gas liquefaction operation, the single mixed refrigerant process is consider... more For offshore natural gas liquefaction operation, the single mixed refrigerant process is considered as one of the best and most suitable processes. However, multivariable nonlinear thermodynamic interactions among operating conditions and flow rates of mixed refrigerant ingredients lead to energy losses, which ultimately contributes to high energy consumption for liquefied natural gas production. The present work investigates the energy saving opportunities in the single mixed refrigerant liquefaction process through "krill-herd" strategy which is based on the biological flocking (herding) behavior of individual krill. To find the energy saving opportunities, the krill-herd approach effectively reduced the exergy losses of the compression units and cryogenic heat exchanger up to 18.6 and 41.1%, respectively, as compared to the published liquefaction process. The figure of merit was found as 27.0% in the krill-herd-optimized single mixed refrigerant process, whereas it was 22.2% in the base case.
Uncertainties are ubiquitous in process system engineering. Hence, to develop a safe and profitab... more Uncertainties are ubiquitous in process system engineering. Hence, to develop a safe and profitable process, uncertainty quantification (UQ) is necessary in a reliability, availability, and maintainability (RAM) analysis. Generalized polynomial chaos expansions can be used as an efficient approach to UQ and work efficiently under the assumption of perfect knowledge with regard to the probability density distribution function of uncertainties. However, this assumption can hardly be satisfied in a real process scenario, mainly because of the limited knowledge regarding the probability density distribution function of uncertainties. To solve these issues, this study investigates the performance of orthogonal polynomial chaos in the UQ of chemical processes, including synthesis gas production and natural gas dehydration. Simultaneously, the limitations of orthogonal polynomial chaos were also investigated by an overwhelming sparse Bayesian learning approach considering a complicated nonlinear crude oil distillation unit with moderate uncertainty numbers. We found that the application of orthogonal polynomial chaos was limited to a small number of uncertainties, mainly because of using the polynomial's tensor product. Finally, the orthogonal polynomial chaos and sparse Bayesian learning approach were rendered computationally effective in comparison with the conventional Monte Carlo method (approximately 96.5% improvement).
This paper proposes the closed-form analytical design of proportional-integral (PI) controller pa... more This paper proposes the closed-form analytical design of proportional-integral (PI) controller parameters for the optimal control of an open-loop unstable first order process subject to operational constraints. The main idea of the design process is not only to minimize the control performance index, but also to cope with the constraints in the process variable, controller output, and its rate of change. To derive an analytical design formula, the constrained optimal control problem in the time domain was transformed to an unconstrained optimization in a parameter space associated with closed-loop dynamics. By taking advantage of the proposed analytical approach, a convenient shortcut algorithm was also provided for finding the optimal PI parameters quickly, based on the graphical analysis for the optimal solution of the corresponding optimization problem in the parameter space. The resulting optimal PI controller guarantees the globally optimal closed-loop response and handles the operational constraints precisely.
h i g h l i g h t s Effects of relative humidity on the performance of SMR was investigated succe... more h i g h l i g h t s Effects of relative humidity on the performance of SMR was investigated successfully. Compression energy for SMR process was reduced significantly. Compression power has a linear relation with the relative humidity. The UA value of LNG cryogenic exchanger increases as 4th-order polynomial function.
Journal of the Taiwan Institute of Chemical Engineers, 2017
In this paper, an optimization-based approach for the closed-form design of an industrial proport... more In this paper, an optimization-based approach for the closed-form design of an industrial proportionalintegral (PI) controller was proposed for the optimal regulatory control of first order process under three typical operational constraints. An ingenious parameterization with Lagrangian multiplier method was used to convert the constrained optimal control problem in the time domain to an unconstrained optimization problem to derive an analytical solution for the optimal regulatory control. Three typical operational constraints could be taken into account in the controller design stage, explicitly. The proposed analytical design method required no complicated optimization steps and guaranteed global optimal closedloop performance and stability. The proposed analytical approach also provides useful insights into the optimal controller design and analysis. A practical and facile procedure for designing optimal PI parameters and a feasible constraint set was also proposed.
An efficient simplified method is proposed for the time domain design of industrial proportional-... more An efficient simplified method is proposed for the time domain design of industrial proportional-integralderivative (PID) controllers and lead-lag compensators for high order single input single output (SISO) systems. The proposed analytical method requires no trial error steps for a lead-lag compensator design in the time domain by using the root-locus method. A practical PID controller design method was obtained based on the corresponding lead-lag compensator to give a required time-domain specification. Simulation studies were carried out to illustrate the control performance of the controllers by the proposed method. The proposed PID controller and lead-lag compensator directly satisfied time domain control specifications such as damping ratio, maximum overshoot, settling time and steady sate error without trial and error steps. The suggested algorithm can easily be integrated with a toolbox in commercial software such as Matlab.
h i g h l i g h t s Simple, compact and energy-efficient SMR processes were proposed. Proposed pr... more h i g h l i g h t s Simple, compact and energy-efficient SMR processes were proposed. Proposed process showed a synergetic advantage of enhancing energy efficiency. Energy saving of 30.6% can be accomplished by a knowledge-inspired optimization. Energy requirement is reduced significantly lowering the intercooler temperature.
This study examined the energy optimal operation of representative natural gas liquefaction cycle... more This study examined the energy optimal operation of representative natural gas liquefaction cycle processes such as propane precooled mixed refrigerant (C 3 MR) process, dual mixed refrigerant (DMR) process, and modified single mixed refrigerant (MSMR) process. Steady-state optimality analysis in dynamic simulation environment was conducted to explore the operational behavior of each cycle. From this analysis, a steady-state optimality map that describes the relation between cost function and decision variable is obtained. By exploring this map a promising optimizing variable is discovered which further can be used to develop an energy optimizing control structure for the liquefaction process. Despite the same basic working principles, the operational behavior of the three cycles is dissimilar. The DMR has the narrowest optimal operation range while in the MSMR cycle the optimum value of cost function spans in relatively wide range of decision variable. The feasible operation of C 3 MR and DMR is bounded by the suction temperature of mixed refrigerant compressor while in the MSMR cycle this constraint is inactive. Based on the steady-state optimality analysis the temperature difference between the warm-end inlet and outlet MR streams (TD) were proposed to be a promising optimizing variable for the C 3 MR and DMR process while for the MSMR process the optimizing variable is the flow rate ratio of heavy and light mixed refrigerant (HK/LK ratio).
Among Floating liquefied natural gas (FLNG) operations, natural gas liquefaction is the most ener... more Among Floating liquefied natural gas (FLNG) operations, natural gas liquefaction is the most energy intensive. Hence, to achieve energy-efficient and eco-friendly FLNG operations that can meet offshore environment requirements, a hydrofluoroolefin-based single mixed refrigerant (SMR) natural gas (NG) liquefaction process is proposed. The proposed process is optimized using a sine cosine paradigm to reduce the overall energy consumption. Then, the economic performance of the proposed process is performed and analyzed against that of the conventional LNG process. Finally, uncertainty quantification is performed to analyze the process outputs under the effects of uncertain key decision variables to guarantee operational reliability. The optimization yields an energy consumption of 0.2317 kW, resulting in a 41.73% energy saving compared to the conventional SMR process. Moreover, the total annualized cost is reduced to 26.02% owing to the appropriate mixed refrigerant selection and process design. The results of the uncertainty quantification analysis indicate that the flow rates of methane and butane, the evaporation pressure, and the condensation pressure are the most influential factors when processing energy consumption and utilizing the minimum internal temperature approach. This study highlights the importance of introducing eco-friendly refrigerants to replace conventional refrigerants used in NG liquefaction processes.
Biogas has emerged as an alternative renewable fuel to natural gas. However, the presence of trac... more Biogas has emerged as an alternative renewable fuel to natural gas. However, the presence of trace contaminants and large quantities of CO 2 in biogas necessitates its purification and upgrading to increase its calorific value. Different technologies have been developed to upgrade biogas to biomethane. Among these, chemical absorption is commonly employed due to its high process efficiency and less solvent requirement due to high selectivity compared to physical absorption. However, the chemical decomposition of amine-based solvents, toxicological impact, high plant maintenance costs, high enthalpy of reaction, and corrosivity associated with chemical absorption limit its large-scale application. Recently, ionic liquids (ILs) have garnered attention as alternative absorption media to conventional solvents. ILs have a high CO 2 uptake, thermal stability, and negligible vapor pressure. Recent process simulation studies featuring ILs as solvents for biogas upgrading reveal the suitability of these approaches as alternatives to laborious experimental work to assess the practical, technical, and economic viability of ILs. As per the authors' knowledge, this is the first review comparing biogas upgrading technologies from a technical, environmental, and economic perspective. Primarily, studies relating to IL-based biogas upgrading are considered, and challenges associated with the large-scale adoption of ILs as absorption media are discussed. Process simulations and techno-economic assessments of IL-based biogas upgrading techniques are presented. A conceptual design approach is proposed for the successful scale-up of IL-based biogas upgrading. Based on results, deep eutectic solvents are recommended as next-generation solvents for absorption as technical and economic aspects are found superior to conventional amines and ionic liquids.
The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating elect... more The organic Rankine cycle (ORC) has recently emerged as a practical approach for generating electricity from low-to-high-temperature waste industrial streams. Several ORC-based waste heat utilization plants are already operational; however, improving plant cost-effectiveness and competitiveness is challenging. The use of thermally efficient and cost-competitive working fluids (WFs) improves the overall efficiency and economics of ORC systems. This study evaluates ORC systems, facilitated by biogas combustion flue gases, using n-butanol, i-butanol, and methylcyclohexane, as WFs technically and economically, from a process system engineering perspective. Furthermore, the performance of the aforementioned WFs is compared with that of toluene, a well-known WF, and it is concluded that i-butanol and n-butanol are the most competitive alternatives in terms of work output, exergy efficiency, thermal efficiency, total annual cost, and annual profit. Moreover, the i-butanol and n-butanol-bas...
Biomethane is regarded as a promising renewable energy source, with great potential to satisfy th... more Biomethane is regarded as a promising renewable energy source, with great potential to satisfy the growth of energy demands and to reduce greenhouse gas emissions. Liquefaction is a suitable approach for long distances and overseas transportation of biomethane; however, it is energy-intensive due to its cryogenic working condition. The major challenge is to design a high-energy efficiency liquefaction process with simple operation and configuration. A single mixed refrigerant biomethane liquefaction process adopting the cryogenic liquid turbine for small-scale production has been proposed in this study to address this issue. The optimal design corresponding to minimal energy consumption was obtained through the black-hole-based optimization algorithm. The effect of the minimum internal temperature approach (MITA) in the main cryogenic heat exchanger on the biomethane liquefaction process performance was investigated. The study results indicated that the specific energy consumption o...
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
This paper describes an ejector model for the prediction of on-design performance under available... more This paper describes an ejector model for the prediction of on-design performance under available conditions. This is a direct method of calculating the optimal ejector performance (entrainment ratio or ER) without the need for iterative methods, which have been conventionally used. The values of three ejector efficiencies used to account for losses in the ejector are calculated by using a systematic approach (by employing CFD analysis) rather than the hit and trial method. Both experimental and analytical data from literature are used to validate the presented analytical model with good agreement for on-design performance. R245fa working fluid has been used for low-grade heat applications, and Engineering Equation Solver (EES) has been employed for simulating the proposed model. The presented model is suitable for integration with any thermal system model and its optimization because of its direct, non-iterative methodology. This model is a non-dimensional model and therefore requi...
Deep eutectic solvents (DESs) comprise ChCl/urea, in combination with water, have been considered... more Deep eutectic solvents (DESs) comprise ChCl/urea, in combination with water, have been considered in removing acid gases (CO2 and H2S) from biogas. The evaluation of DES for biogas upgrading at relatively high pressure (i.e., >8.0 bar) has not been reported before. The aqueous DES performance has also not been analyzed compared to conventional amines-based solvent (MEA) and ionic liquid (IL). To the best of our knowledge, this is the first study that presents the integration of DES-based biogas upgrading with a mixed refrigerant liquefaction process to facilitate the safe and economical transportation of biomethane over long distances. The biogas considered in this study consisted of 60% CH4, 39% CO2, and 1% H2S. The aqueous ChCl/urea (70 wt%) results in biomethane with ≥99.0 wt% purity and ≥97.0 wt% recovery. Then, this biomethane was liquefied with ≥90% liquefaction rate. Based on the results obtained herein, overall capital, operating, and total annualized cost savings of 2.8%...
The reduction of greenhouse gas emission via the transformation of carbon dioxide into methanol r... more The reduction of greenhouse gas emission via the transformation of carbon dioxide into methanol results in several secondary benefits including the production of a valuable by-product that can be used for energy storage and as a fuel source. As such, this is a promising approach for mitigating climate change. Methanol production via the co-electrolysis process using solid oxide electrolyzer cells is an efficacious solution to the issue of excess electricity storage in the context of renewable energy and carbon dioxide utilization. However, this process is an energy-intensive and temperature-sensitive method, mainly due to the requirement of high-temperature electrolysis. In this context, this study investigates and evaluates the potential for overall performance improvement by minimizing energy consumption and increasing methanol production using self-heat recuperation technology. The newly developed vortex search strategy was employed to achieve the maximum potential benefit from retrofitted recuperators. Detailed exergy analysis was performed for the process and the evaluation of its performance. The findings revealed that the electrochemical system for co-electrolysis has the highest exergy destruction rate. By employing the vortex search approach, the exergy loss of the energy process system can be reduced by 61.7% with a total reduction of the exergy loss of 15.9%, while improving methanol production and decreasing distillation reboiler duty. The simple solution of self-recuperation with optimization that was utilized in this study is a flexible approach that can be directly applied to the improvement of coelectrolysis and methanol synthesis.
Industrial & Engineering Chemistry Research, 2019
This study examines control strategies developed for wastewater treatment via partial nitration a... more This study examines control strategies developed for wastewater treatment via partial nitration and the anaerobic ammonium oxidation process with the objective of enhancing nitrogen removal efficiency. The implementation of different control strategies were analyzed and explained with the help of pictorial representations. The benefits of the different control strategies were also briefly discussed. The biological process of nitrogen removal requires appropriate pairing between control and manipulated variables. Furthermore, the approach to follow when selecting suitable candidates and determining the pairing criterion was discussed. Although the conventional feedback−feedforward control logic is easy to implement, incorporation of the nonlinearity and complexity associated with the processes requires the design of advanced control systems.
International Journal of Greenhouse Gas Control, 2019
Natural gas is a cleaner energy source compared to other fossil-based energy sources owing to its... more Natural gas is a cleaner energy source compared to other fossil-based energy sources owing to its low emissions. However, natural gas contains acidic gases (including CO 2 and H 2 S), which may cause equipment corrosion and environmental damage. To date, amine-based absorption techniques have been used to remove acidic gases from natural gas to reach regulated concentration limits. However, a tremendous amount of heating is required to regenerate amine-based solvents, which remains a major issue with traditional absorption-based acid gas removal units. In this context, 1-butyl-3-methyimidazolium methyl sulfate (bmim)(CH 3 SO 4) and 1-butyl-3-methylimidazolium hexafluorophosphate (bmim)(PF 6) were adopted as potential solvents for reducing the heating requirements in the solvent-regeneration step of absorption-based removal techniques. This study shows that by using the imidazolium-based cationic IL, up to 99 wt% of acid gases can be removed while dramatically reducing the heating load and the total annualized cost compared to conventional amine-based absorption units. Flashbased solvent regeneration was used to recover the solvent with a heating loading value of 3978 kW, which is 78.6% lower than that of conventional amine regeneration strippers. Use of only flash column instead of stripper also makes the proposed ionic liquid-based absorption technique most economical with respect to capital investment. To date, several approaches including absorption, adsorption, and membrane separation have been developed to capture acid gases from NG. Absorption-based techniques are the most common and practical approaches for large-scale NG treatment to remove acid gases (Afkhamipour and Mofarahi, 2014). Aqueous alkanolamine solvent-based absorption/ stripper schemes have been developed for acid gas removal, mainly because of their high reliability. Among alkanolamine solvents, ethanolamine (MEA)-based solvents (e.g., MEA and MDEA) are commonly used because of their strong reactivity, high capacity, active kinetics, and widespread availability with low cost (Lepaumier et al., 2009; Venkatraman and Alsberg, 2017). However, a tremendous amount of thermal energy is required for the regeneration of MEA and MDEA, which accounts for around 80% of the total operating cost (Aaron and Tsouris, 2005; Mesbah et al., 2018). Therefore, the heating load for amine solvent regeneration is a major
Bioethanol has garnered a great interest as a potential energy source, mainly due to its sustaina... more Bioethanol has garnered a great interest as a potential energy source, mainly due to its sustainable and green nature. Generally, bioethanol is produced through the microbial conversion of biomass and biomass derived syngas. However, the dehydration and purification steps for achieving fuel-grade ethanol from the microbial production process consume tremendous amounts of energy. This high energy consumption limits the feasibility of microbial ethanol production on the commercial scale. In this context, selection of an optimal technology for product separation is essential for successful commercialization of microbially produced bioethanol. This article presents the recent developments in dehydration and purification technologies for bioethanol production using distillation and membrane based separation. Distillation and pervaporation are analyzed on the basis of the overall energy requirement, consumption, and economics. Pervaporation-assisted distillation approaches are also examined from the perspective of process systems engineering, including factors affecting the system performance. Furthermore, the role of simulation in technological development along with available mathematical models is discussed, and commercial status of pervaporation based separation is presented. Finally, the current status of the existing technology, challenges, and future research directions are identified from the perspective of achieving process sustainability on the industrial scale. Economic comparison between distillation and different hybrid schemes revealed that integrating distillation with membrane based separation techniques reduce the bioethanol production cost. Moreover, hybrid schemes that combine distillation with pervaporation, and steam stripping with vapor permeation are proved to be the best combinations for the cheapest bioethanol production.
This work presents an advanced and systematic approach to analytically design the optimal parame... more This work presents an advanced and systematic approach to analytically design the optimal parameters of a two parameter second-order internal model control (IMC) filter that satisfies operational constraints on the output process, the manipulated variable as well as rate of change of the manipulated variable, for a first-order plus dead time (FOPDT) process. The IMC parameters are designed to minimize a control objective function composed of the weighted sum of the error between the process variable and the set point, and the rate of change of the manipulated variable, and to satisfy the desired constraints. The feasible region of the constrained IMC control parameters was graphically analyzed, as the process parameters and the constraints varied. The resulting constrained IMC control parameters were also used to find the corresponding industrial proportional-integral controller parameters of a Smith predictor structure.
Industrial & Engineering Chemistry Research, 2018
For offshore natural gas liquefaction operation, the single mixed refrigerant process is consider... more For offshore natural gas liquefaction operation, the single mixed refrigerant process is considered as one of the best and most suitable processes. However, multivariable nonlinear thermodynamic interactions among operating conditions and flow rates of mixed refrigerant ingredients lead to energy losses, which ultimately contributes to high energy consumption for liquefied natural gas production. The present work investigates the energy saving opportunities in the single mixed refrigerant liquefaction process through "krill-herd" strategy which is based on the biological flocking (herding) behavior of individual krill. To find the energy saving opportunities, the krill-herd approach effectively reduced the exergy losses of the compression units and cryogenic heat exchanger up to 18.6 and 41.1%, respectively, as compared to the published liquefaction process. The figure of merit was found as 27.0% in the krill-herd-optimized single mixed refrigerant process, whereas it was 22.2% in the base case.
Uncertainties are ubiquitous in process system engineering. Hence, to develop a safe and profitab... more Uncertainties are ubiquitous in process system engineering. Hence, to develop a safe and profitable process, uncertainty quantification (UQ) is necessary in a reliability, availability, and maintainability (RAM) analysis. Generalized polynomial chaos expansions can be used as an efficient approach to UQ and work efficiently under the assumption of perfect knowledge with regard to the probability density distribution function of uncertainties. However, this assumption can hardly be satisfied in a real process scenario, mainly because of the limited knowledge regarding the probability density distribution function of uncertainties. To solve these issues, this study investigates the performance of orthogonal polynomial chaos in the UQ of chemical processes, including synthesis gas production and natural gas dehydration. Simultaneously, the limitations of orthogonal polynomial chaos were also investigated by an overwhelming sparse Bayesian learning approach considering a complicated nonlinear crude oil distillation unit with moderate uncertainty numbers. We found that the application of orthogonal polynomial chaos was limited to a small number of uncertainties, mainly because of using the polynomial's tensor product. Finally, the orthogonal polynomial chaos and sparse Bayesian learning approach were rendered computationally effective in comparison with the conventional Monte Carlo method (approximately 96.5% improvement).
This paper proposes the closed-form analytical design of proportional-integral (PI) controller pa... more This paper proposes the closed-form analytical design of proportional-integral (PI) controller parameters for the optimal control of an open-loop unstable first order process subject to operational constraints. The main idea of the design process is not only to minimize the control performance index, but also to cope with the constraints in the process variable, controller output, and its rate of change. To derive an analytical design formula, the constrained optimal control problem in the time domain was transformed to an unconstrained optimization in a parameter space associated with closed-loop dynamics. By taking advantage of the proposed analytical approach, a convenient shortcut algorithm was also provided for finding the optimal PI parameters quickly, based on the graphical analysis for the optimal solution of the corresponding optimization problem in the parameter space. The resulting optimal PI controller guarantees the globally optimal closed-loop response and handles the operational constraints precisely.
h i g h l i g h t s Effects of relative humidity on the performance of SMR was investigated succe... more h i g h l i g h t s Effects of relative humidity on the performance of SMR was investigated successfully. Compression energy for SMR process was reduced significantly. Compression power has a linear relation with the relative humidity. The UA value of LNG cryogenic exchanger increases as 4th-order polynomial function.
Journal of the Taiwan Institute of Chemical Engineers, 2017
In this paper, an optimization-based approach for the closed-form design of an industrial proport... more In this paper, an optimization-based approach for the closed-form design of an industrial proportionalintegral (PI) controller was proposed for the optimal regulatory control of first order process under three typical operational constraints. An ingenious parameterization with Lagrangian multiplier method was used to convert the constrained optimal control problem in the time domain to an unconstrained optimization problem to derive an analytical solution for the optimal regulatory control. Three typical operational constraints could be taken into account in the controller design stage, explicitly. The proposed analytical design method required no complicated optimization steps and guaranteed global optimal closedloop performance and stability. The proposed analytical approach also provides useful insights into the optimal controller design and analysis. A practical and facile procedure for designing optimal PI parameters and a feasible constraint set was also proposed.
An efficient simplified method is proposed for the time domain design of industrial proportional-... more An efficient simplified method is proposed for the time domain design of industrial proportional-integralderivative (PID) controllers and lead-lag compensators for high order single input single output (SISO) systems. The proposed analytical method requires no trial error steps for a lead-lag compensator design in the time domain by using the root-locus method. A practical PID controller design method was obtained based on the corresponding lead-lag compensator to give a required time-domain specification. Simulation studies were carried out to illustrate the control performance of the controllers by the proposed method. The proposed PID controller and lead-lag compensator directly satisfied time domain control specifications such as damping ratio, maximum overshoot, settling time and steady sate error without trial and error steps. The suggested algorithm can easily be integrated with a toolbox in commercial software such as Matlab.
h i g h l i g h t s Simple, compact and energy-efficient SMR processes were proposed. Proposed pr... more h i g h l i g h t s Simple, compact and energy-efficient SMR processes were proposed. Proposed process showed a synergetic advantage of enhancing energy efficiency. Energy saving of 30.6% can be accomplished by a knowledge-inspired optimization. Energy requirement is reduced significantly lowering the intercooler temperature.
This study examined the energy optimal operation of representative natural gas liquefaction cycle... more This study examined the energy optimal operation of representative natural gas liquefaction cycle processes such as propane precooled mixed refrigerant (C 3 MR) process, dual mixed refrigerant (DMR) process, and modified single mixed refrigerant (MSMR) process. Steady-state optimality analysis in dynamic simulation environment was conducted to explore the operational behavior of each cycle. From this analysis, a steady-state optimality map that describes the relation between cost function and decision variable is obtained. By exploring this map a promising optimizing variable is discovered which further can be used to develop an energy optimizing control structure for the liquefaction process. Despite the same basic working principles, the operational behavior of the three cycles is dissimilar. The DMR has the narrowest optimal operation range while in the MSMR cycle the optimum value of cost function spans in relatively wide range of decision variable. The feasible operation of C 3 MR and DMR is bounded by the suction temperature of mixed refrigerant compressor while in the MSMR cycle this constraint is inactive. Based on the steady-state optimality analysis the temperature difference between the warm-end inlet and outlet MR streams (TD) were proposed to be a promising optimizing variable for the C 3 MR and DMR process while for the MSMR process the optimizing variable is the flow rate ratio of heavy and light mixed refrigerant (HK/LK ratio).
Among Floating liquefied natural gas (FLNG) operations, natural gas liquefaction is the most ener... more Among Floating liquefied natural gas (FLNG) operations, natural gas liquefaction is the most energy intensive. Hence, to achieve energy-efficient and eco-friendly FLNG operations that can meet offshore environment requirements, a hydrofluoroolefin-based single mixed refrigerant (SMR) natural gas (NG) liquefaction process is proposed. The proposed process is optimized using a sine cosine paradigm to reduce the overall energy consumption. Then, the economic performance of the proposed process is performed and analyzed against that of the conventional LNG process. Finally, uncertainty quantification is performed to analyze the process outputs under the effects of uncertain key decision variables to guarantee operational reliability. The optimization yields an energy consumption of 0.2317 kW, resulting in a 41.73% energy saving compared to the conventional SMR process. Moreover, the total annualized cost is reduced to 26.02% owing to the appropriate mixed refrigerant selection and process design. The results of the uncertainty quantification analysis indicate that the flow rates of methane and butane, the evaporation pressure, and the condensation pressure are the most influential factors when processing energy consumption and utilizing the minimum internal temperature approach. This study highlights the importance of introducing eco-friendly refrigerants to replace conventional refrigerants used in NG liquefaction processes.
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Papers by Moonyong Lee