Hiren Shethna - Academia.edu (original) (raw)
Papers by Hiren Shethna
Industrial & Engineering Chemistry Research, 2006
Industrial & Engineering Chemistry Research, 1997
The variation of the phase-equilibrium behavior of chemisorbed gases with solvent concentration i... more The variation of the phase-equilibrium behavior of chemisorbed gases with solvent concentration in mixed-solvent systems and resulting effects on the design of split-loop chemisorption processes are studied. Split-loop absorption as currently practiced is thermodynamically inefficient due to variations in solvent concentration during stripping. Adding equipment to enable better control of solvent composition results in improved process economics relative to single-loop absorption. Examination of concentration-enthalpy plots identifies the supply of stripping vapor as the main thermodynamic bottleneck of absorption-stripping processes. This suggests an alternative split-loop flow sheet in which the solvent for gas polishing is regenerated using a small fraction of the clean processed gas. This novel recycle arrangement has lower energy and capital costs and can be further integrated with other gas-processing technology. The new processes are illustrated with the example of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2) removal from hydrocarbons using aqueous methyldiethanolamine. Ultrahigh separation of H 2 S at much-reduced energy use is possible, either selectively or nonselectively with respect to CO 2 .
Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial proce... more Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial process. Examples of this process include recovery of hydrogen sulfide and carbon dioxide from acid gases such as natural gas, refinery gas and coke-oven gas using aqueous alkanolamine solutions, and absorption of sulfur dioxide using alkali metal sulfite-bisulfite solutions. 1,2 The solvents for such processes are chosen such that the absorption step can be reversed by changing the conditions of temperature and pressure. Absorption takes place at high pressure and low temperature, giving high loadings of absorbed component in the solvent. The solvent is then sent to a regenerator, which operates under conditions of high temperature and low pressure, causing desorption of the absorbed components and regenerating the solvent. Heat is added in the regenerator to provide for the heat of reaction, the sensible heat change of the solvent, and to generate a vapor flow for stripping by partially reboiling the solvent.
Industrial & Engineering Chemistry Research, 2003
A method is presented for calculating an area target for a heat exchanger network (HEN). The app... more A method is presented for calculating an area target for a heat exchanger network (HEN). The
approach is based on the solution of a linear programming problem modeled as an optimal
transportation task. The transportation model uses temperature intervals and does not require
knowledge of enthalpy intervals for the fixed heat recovery level. Restricted matches can be
directly accounted for. A heuristic rule has been developed on a number of temperature intervals
that keeps the number of variables and constraints in reasonable limits while ensuring accurate
results. The targeting method can also be applied to HENs consisting of multipass (1-2) heat
exchangers. The results from case studies have shown that solutions from the developed approach
are very close to those calculated by complex nonlinear programming based methods.
Computer Aided Chemical Engineering, 2002
... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijnde... more ... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijndel ... In the case of partially defined systems, the approach determines and solves the ... cleaning schedules and their influence in the total annual cost applying techniques existing in ...
… ANNUAL CONVENTION-GAS …, 1997
Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial proce... more Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial process. Examples of this process include recovery of hydrogen sulfide and carbon dioxide from acid gases such as natural gas, refinery gas and coke-oven gas using aqueous alkanolamine solutions, and absorption of sulfur dioxide using alkali metal sulfite-bisulfite solutions. 1,2 The solvents for such processes are chosen such that the absorption step can be reversed by changing the conditions of temperature and pressure. Absorption takes place at high pressure and low temperature, giving high loadings of absorbed component in the solvent. The solvent is then sent to a regenerator, which operates under conditions of high temperature and low pressure, causing desorption of the absorbed components and regenerating the solvent. Heat is added in the regenerator to provide for the heat of reaction, the sensible heat change of the solvent, and to generate a vapor flow for stripping by partially reboiling the solvent.
Applied Thermal Engineering, 2000
A new approach has been developed for establishing cost-optimal targets for a heat exchanger netw... more A new approach has been developed for establishing cost-optimal targets for a heat exchanger network (HEN). We formulate a mixed-integer-linear-programming (MILP) transportation problem that simultaneously optimizes for heat exchanger units, heat exchange area and loads on each utility. Heat exchange matches are placed between each hot stream in each temperature interval and all cold streams in all the subsequent lower temperature intervals. The objective function is linear and minimizes the total annual cost of the HEN subject to heat balance constraints. The temperature intervals are generated with a temperature shift just greater than zero. Each temperature interval is small enough that we can linearize the log-mean temperature dierence on each match while maintaining the accuracy. Flowrate continuity constraints are written on utility streams so that we could account for non-point utilities. Furthermore, constraints on heat exchange area that occur in retro®t scenarios are incorporated into the model. The solution of the optimization model provides the heat loads on each utility, in case of multiple hot and cold utilities, the heat load on every match pair, the heat exchange area target and the number of units target such that the total annual cost is minimum. Using these targets, it is straightforward to construct heat exchanger networks.
Applied Thermal Engineering, 2003
ABSTRACT
Hydrocarbon engineering, 2004
Process simulation has been widely used in refineries for more than 30 years. Steady state and dy... more Process simulation has been widely used in refineries for more than 30 years. Steady state and dynamic simulations are established tools for the design of new process units and optimisation (off and online) of existing facilities. While mathematical models of separation systems and other unit operations are available in most commercial process simulators, refinery reactors are very specialised models and, in most cases, are simulated as standalone units. As a consequence, the interactions between different processing units are not fully explored and the true operating window is never captured. Many refiners have recognised the potential benefits of extending rigorous modelling to refinery wide simulations that model all of the process units as an integrated system. This approach would provide a powerful tool to help optimise refinery operations, and would be an important element in sustaining a competitive advantage in light of new regulations, growing competition and decreasing mar...
A design approach for multicomponent distillation columns is presented. Based on a geometric anal... more A design approach for multicomponent distillation columns is presented. Based on a geometric analysis of pinch point solutions of composition profiles, the approach provides a suite of accurate and efficient methods for determining minimum reflux, the number of stages and the optimum feed-tray location. Tangent pinches are taken into account in the design. The approach applies to ideal, nonideal and azeotropic mixtures with no restrictions on the number of components. It is demonstrated with applications to column design and column sequencing for multicomponent azeotropic distillation.
Computational Biology and Chemistry / Computers & Chemistry, 2000
This paper deals with heat recovery calculations in integrated chemical process systems. A level ... more This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cost of heat energy consumed in a total system and influences environmental pollution. Even though well established approaches to the problem of calculating minimum cost of utilities in a HEN are available at present, they do not fully account for complex industrial scenarios. The aim of methods developed in this work is to extend applications for the following cases: 1. multiple utilities of great temperature spans (so called non-point utilities), and 2. disturbances of flow-rates of heat exchanging streams. To solve the problems, methods have been developed based on optimisation models. The models are linear though one of them involves mixed-integer variables. Linearity ensures the possibility of solving the models to global optimum, even for large-scale industrial problems. The description of solution methods and exampl...
Computer Aided Chemical Engineering, 2002
... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijnde... more ... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijndel ... In the case of partially defined systems, the approach determines and solves the ... cleaning schedules and their influence in the total annual cost applying techniques existing in ...
… ANNUAL CONVENTION-GAS …, 1997
The removal of trace components from a gas by absorption using a chemical solvent is of importanc... more The removal of trace components from a gas by absorption using a chemical solvent is of importance to the gas processing industry. There is a growing interest in reaching lower outlet concentrations for reasons of health and safety; however, this ...
Applied Thermal Engineering - APPL THERM ENG, 2000
A new approach has been developed for establishing cost-optimal targets for a heat exchanger netw... more A new approach has been developed for establishing cost-optimal targets for a heat exchanger network (HEN). We formulate a mixed-integer-linear-programming (MILP) transportation problem that simultaneously optimizes for heat exchanger units, heat exchange area and loads on each utility. Heat exchange matches are placed between each hot stream in each temperature interval and all cold streams in all the subsequent lower temperature intervals. The objective function is linear and minimizes the total annual cost of the HEN subject to heat balance constraints. The temperature intervals are generated with a temperature shift just greater than zero. Each temperature interval is small enough that we can linearize the log-mean temperature difference on each match while maintaining the accuracy. Flowrate continuity constraints are written on utility streams so that we could account for non-point utilities. Furthermore, constraints on heat exchange area that occur in retrofit scenarios are in...
Computers & chemistry, 2000
This paper deals with heat recovery calculations in integrated chemical process systems. A level ... more This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cost of heat energy consumed in a total system and influences environmental pollution. Even though well established approaches to the problem of calculating minimum cost of utilities in a HEN are available at present, they do not fully account for complex industrial scenarios. The aim of methods developed in this work is to extend applications for the following cases: 1. multiple utilities of great temperature spans (so called non-point utilities), and 2. disturbances of flow-rates of heat exchanging streams. To solve the problems, methods have been developed based on optimisation models. The models are linear though one of them involves mixed-integer variables. Linearity ensures the possibility of solving the models to global optimum, even for large-scale industrial problems. The description of solution methods and exampl...
Industrial Engineering Chemistry Research, Mar 17, 2003
ABSTRACT
Hydrocarbon Engineering, 2004
Industrial & Engineering Chemistry Research, 2006
Industrial & Engineering Chemistry Research, 1997
The variation of the phase-equilibrium behavior of chemisorbed gases with solvent concentration i... more The variation of the phase-equilibrium behavior of chemisorbed gases with solvent concentration in mixed-solvent systems and resulting effects on the design of split-loop chemisorption processes are studied. Split-loop absorption as currently practiced is thermodynamically inefficient due to variations in solvent concentration during stripping. Adding equipment to enable better control of solvent composition results in improved process economics relative to single-loop absorption. Examination of concentration-enthalpy plots identifies the supply of stripping vapor as the main thermodynamic bottleneck of absorption-stripping processes. This suggests an alternative split-loop flow sheet in which the solvent for gas polishing is regenerated using a small fraction of the clean processed gas. This novel recycle arrangement has lower energy and capital costs and can be further integrated with other gas-processing technology. The new processes are illustrated with the example of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2) removal from hydrocarbons using aqueous methyldiethanolamine. Ultrahigh separation of H 2 S at much-reduced energy use is possible, either selectively or nonselectively with respect to CO 2 .
Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial proce... more Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial process. Examples of this process include recovery of hydrogen sulfide and carbon dioxide from acid gases such as natural gas, refinery gas and coke-oven gas using aqueous alkanolamine solutions, and absorption of sulfur dioxide using alkali metal sulfite-bisulfite solutions. 1,2 The solvents for such processes are chosen such that the absorption step can be reversed by changing the conditions of temperature and pressure. Absorption takes place at high pressure and low temperature, giving high loadings of absorbed component in the solvent. The solvent is then sent to a regenerator, which operates under conditions of high temperature and low pressure, causing desorption of the absorbed components and regenerating the solvent. Heat is added in the regenerator to provide for the heat of reaction, the sensible heat change of the solvent, and to generate a vapor flow for stripping by partially reboiling the solvent.
Industrial & Engineering Chemistry Research, 2003
A method is presented for calculating an area target for a heat exchanger network (HEN). The app... more A method is presented for calculating an area target for a heat exchanger network (HEN). The
approach is based on the solution of a linear programming problem modeled as an optimal
transportation task. The transportation model uses temperature intervals and does not require
knowledge of enthalpy intervals for the fixed heat recovery level. Restricted matches can be
directly accounted for. A heuristic rule has been developed on a number of temperature intervals
that keeps the number of variables and constraints in reasonable limits while ensuring accurate
results. The targeting method can also be applied to HENs consisting of multipass (1-2) heat
exchangers. The results from case studies have shown that solutions from the developed approach
are very close to those calculated by complex nonlinear programming based methods.
Computer Aided Chemical Engineering, 2002
... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijnde... more ... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijndel ... In the case of partially defined systems, the approach determines and solves the ... cleaning schedules and their influence in the total annual cost applying techniques existing in ...
… ANNUAL CONVENTION-GAS …, 1997
Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial proce... more Chemical absorption of gas-phase compounds into a liquid sorbent is an important industrial process. Examples of this process include recovery of hydrogen sulfide and carbon dioxide from acid gases such as natural gas, refinery gas and coke-oven gas using aqueous alkanolamine solutions, and absorption of sulfur dioxide using alkali metal sulfite-bisulfite solutions. 1,2 The solvents for such processes are chosen such that the absorption step can be reversed by changing the conditions of temperature and pressure. Absorption takes place at high pressure and low temperature, giving high loadings of absorbed component in the solvent. The solvent is then sent to a regenerator, which operates under conditions of high temperature and low pressure, causing desorption of the absorbed components and regenerating the solvent. Heat is added in the regenerator to provide for the heat of reaction, the sensible heat change of the solvent, and to generate a vapor flow for stripping by partially reboiling the solvent.
Applied Thermal Engineering, 2000
A new approach has been developed for establishing cost-optimal targets for a heat exchanger netw... more A new approach has been developed for establishing cost-optimal targets for a heat exchanger network (HEN). We formulate a mixed-integer-linear-programming (MILP) transportation problem that simultaneously optimizes for heat exchanger units, heat exchange area and loads on each utility. Heat exchange matches are placed between each hot stream in each temperature interval and all cold streams in all the subsequent lower temperature intervals. The objective function is linear and minimizes the total annual cost of the HEN subject to heat balance constraints. The temperature intervals are generated with a temperature shift just greater than zero. Each temperature interval is small enough that we can linearize the log-mean temperature dierence on each match while maintaining the accuracy. Flowrate continuity constraints are written on utility streams so that we could account for non-point utilities. Furthermore, constraints on heat exchange area that occur in retro®t scenarios are incorporated into the model. The solution of the optimization model provides the heat loads on each utility, in case of multiple hot and cold utilities, the heat load on every match pair, the heat exchange area target and the number of units target such that the total annual cost is minimum. Using these targets, it is straightforward to construct heat exchanger networks.
Applied Thermal Engineering, 2003
ABSTRACT
Hydrocarbon engineering, 2004
Process simulation has been widely used in refineries for more than 30 years. Steady state and dy... more Process simulation has been widely used in refineries for more than 30 years. Steady state and dynamic simulations are established tools for the design of new process units and optimisation (off and online) of existing facilities. While mathematical models of separation systems and other unit operations are available in most commercial process simulators, refinery reactors are very specialised models and, in most cases, are simulated as standalone units. As a consequence, the interactions between different processing units are not fully explored and the true operating window is never captured. Many refiners have recognised the potential benefits of extending rigorous modelling to refinery wide simulations that model all of the process units as an integrated system. This approach would provide a powerful tool to help optimise refinery operations, and would be an important element in sustaining a competitive advantage in light of new regulations, growing competition and decreasing mar...
A design approach for multicomponent distillation columns is presented. Based on a geometric anal... more A design approach for multicomponent distillation columns is presented. Based on a geometric analysis of pinch point solutions of composition profiles, the approach provides a suite of accurate and efficient methods for determining minimum reflux, the number of stages and the optimum feed-tray location. Tangent pinches are taken into account in the design. The approach applies to ideal, nonideal and azeotropic mixtures with no restrictions on the number of components. It is demonstrated with applications to column design and column sequencing for multicomponent azeotropic distillation.
Computational Biology and Chemistry / Computers & Chemistry, 2000
This paper deals with heat recovery calculations in integrated chemical process systems. A level ... more This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cost of heat energy consumed in a total system and influences environmental pollution. Even though well established approaches to the problem of calculating minimum cost of utilities in a HEN are available at present, they do not fully account for complex industrial scenarios. The aim of methods developed in this work is to extend applications for the following cases: 1. multiple utilities of great temperature spans (so called non-point utilities), and 2. disturbances of flow-rates of heat exchanging streams. To solve the problems, methods have been developed based on optimisation models. The models are linear though one of them involves mixed-integer variables. Linearity ensures the possibility of solving the models to global optimum, even for large-scale industrial problems. The description of solution methods and exampl...
Computer Aided Chemical Engineering, 2002
... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijnde... more ... European Symposium on Computer Aided Process Engineering - 12 J. Grievink and J. van Schijndel ... In the case of partially defined systems, the approach determines and solves the ... cleaning schedules and their influence in the total annual cost applying techniques existing in ...
… ANNUAL CONVENTION-GAS …, 1997
The removal of trace components from a gas by absorption using a chemical solvent is of importanc... more The removal of trace components from a gas by absorption using a chemical solvent is of importance to the gas processing industry. There is a growing interest in reaching lower outlet concentrations for reasons of health and safety; however, this ...
Applied Thermal Engineering - APPL THERM ENG, 2000
A new approach has been developed for establishing cost-optimal targets for a heat exchanger netw... more A new approach has been developed for establishing cost-optimal targets for a heat exchanger network (HEN). We formulate a mixed-integer-linear-programming (MILP) transportation problem that simultaneously optimizes for heat exchanger units, heat exchange area and loads on each utility. Heat exchange matches are placed between each hot stream in each temperature interval and all cold streams in all the subsequent lower temperature intervals. The objective function is linear and minimizes the total annual cost of the HEN subject to heat balance constraints. The temperature intervals are generated with a temperature shift just greater than zero. Each temperature interval is small enough that we can linearize the log-mean temperature difference on each match while maintaining the accuracy. Flowrate continuity constraints are written on utility streams so that we could account for non-point utilities. Furthermore, constraints on heat exchange area that occur in retrofit scenarios are in...
Computers & chemistry, 2000
This paper deals with heat recovery calculations in integrated chemical process systems. A level ... more This paper deals with heat recovery calculations in integrated chemical process systems. A level of heat recovery in a heat exchanger network (HEN) determines the cost of heat energy consumed in a total system and influences environmental pollution. Even though well established approaches to the problem of calculating minimum cost of utilities in a HEN are available at present, they do not fully account for complex industrial scenarios. The aim of methods developed in this work is to extend applications for the following cases: 1. multiple utilities of great temperature spans (so called non-point utilities), and 2. disturbances of flow-rates of heat exchanging streams. To solve the problems, methods have been developed based on optimisation models. The models are linear though one of them involves mixed-integer variables. Linearity ensures the possibility of solving the models to global optimum, even for large-scale industrial problems. The description of solution methods and exampl...
Industrial Engineering Chemistry Research, Mar 17, 2003
ABSTRACT
Hydrocarbon Engineering, 2004