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On synthesis and optimization of cooling water systems with multiple cooling towers / Khunedi Vincent Gololo in Industrial & engineering chemistry research, Vol. 50 N° 7 (Avril 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 7 (Avril 2011) . - pp. 3775–3787 Titre : On synthesis and optimization of cooling water systems with multiple cooling towers Type de document : texte imprimé Auteurs : Khunedi Vincent Gololo, Auteur ; Thokozani Majozi, Auteur Année de publication : 2011 Article en page(s) : pp. 3775–3787 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimization Résumé : Cooling water systems are generally designed with a set of heat exchangers arranged in parallel. This arrangement results in higher cooling water flow rate and low cooling water return temperature, thus reducing cooling tower efficiency. Previous research on cooling water systems has focused mainly on heat exchanger network thus excluding the interaction between heat exchanger network and the cooling towers. This paper presents a technique for grassroot design of cooling water system for wastewater minimization, which incorporates the performances of the cooling towers involved. The study focuses mainly on cooling systems consisting of multiple cooling towers that supply a common set of heat exchangers. The heat exchanger network is synthesized using the mathematical optimization technique. This technique is based on superstructure in which all opportunities for cooling water reuse are explored. The cooling tower model is used to predict the thermal performance of the cooling towers. Two case studies are presented to illustrate the proposed technique. The first case resulted in nonlinear programming (NLP) formulation and the second case yield mixed integer nonlinear programming (MINLP). The nonlinearity in both cases is because of the bilinear terms present in the energy balance constraints. In both cases, the cooling towers operating capacity were debottlenecked without compromising the heat duties. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie101395v [article] On synthesis and optimization of cooling water systems with multiple cooling towers [texte imprimé] / Khunedi Vincent Gololo, Auteur ; Thokozani Majozi, Auteur . - 2011 . - pp. 3775–3787. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 7 (Avril 2011) . - pp. 3775–3787 Mots-clés : Optimization Résumé : Cooling water systems are generally designed with a set of heat exchangers arranged in parallel. This arrangement results in higher cooling water flow rate and low cooling water return temperature, thus reducing cooling tower efficiency. Previous research on cooling water systems has focused mainly on heat exchanger network thus excluding the interaction between heat exchanger network and the cooling towers. This paper presents a technique for grassroot design of cooling water system for wastewater minimization, which incorporates the performances of the cooling towers involved. The study focuses mainly on cooling systems consisting of multiple cooling towers that supply a common set of heat exchangers. The heat exchanger network is synthesized using the mathematical optimization technique. This technique is based on superstructure in which all opportunities for cooling water reuse are explored. The cooling tower model is used to predict the thermal performance of the cooling towers. Two case studies are presented to illustrate the proposed technique. The first case resulted in nonlinear programming (NLP) formulation and the second case yield mixed integer nonlinear programming (MINLP). The nonlinearity in both cases is because of the bilinear terms present in the energy balance constraints. In both cases, the cooling towers operating capacity were debottlenecked without compromising the heat duties. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie101395v

On synthesis and optimization of steam system networks. 1. / Thokozani Majozi in Industrial & engineering chemistry research, Vol. 49 N° 19 (Octobre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 9143–9153 Titre : On synthesis and optimization of steam system networks. 1. : Sustained boiler eficiency Type de document : texte imprimé Auteurs : Thokozani Majozi, Auteur ; Tim Price, Auteur Année de publication : 2010 Article en page(s) : pp. 9143–9153 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimization  Steam  system Résumé : The traditional steam system comprises a steam boiler and the associated heat exchanger network (HEN). Most research published in literature tends to address both the elements of the steam system as separate entities instead of analyzing, synthesizing, and optimizing the overall system in a holistic manner. True optimality of the steam system can only be achieved if the analysis is conducted within an integrated framework. Process integration has proven to be a powerful tool in similar situations. This paper presents a process integration technique for network synthesis using conceptual and mathematical analysis without compromising boiler efficiency. It was found that the steam flow rate to the HEN could be reduced while maintaining boiler efficiency by utilizing sensible heat from the high pressure steam leaving the boiler. In the event of too little sensible energy being available, a compromise in either minimum steam flow rate or boiler efficiency must be made. A dedicated preheater can also be added to the HEN so as to guarantee the boiler efficiency is maintained; however, this will compromise the minimum steam flow rate. It was found that the flow rate could be reduced by 29.6% while still maintaining the boiler efficiency for an example problem. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1007008 [article] On synthesis and optimization of steam system networks. 1. : Sustained boiler eficiency [texte imprimé] / Thokozani Majozi, Auteur ; Tim Price, Auteur . - 2010 . - pp. 9143–9153. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 9143–9153 Mots-clés : Optimization  Steam  system Résumé : The traditional steam system comprises a steam boiler and the associated heat exchanger network (HEN). Most research published in literature tends to address both the elements of the steam system as separate entities instead of analyzing, synthesizing, and optimizing the overall system in a holistic manner. True optimality of the steam system can only be achieved if the analysis is conducted within an integrated framework. Process integration has proven to be a powerful tool in similar situations. This paper presents a process integration technique for network synthesis using conceptual and mathematical analysis without compromising boiler efficiency. It was found that the steam flow rate to the HEN could be reduced while maintaining boiler efficiency by utilizing sensible heat from the high pressure steam leaving the boiler. In the event of too little sensible energy being available, a compromise in either minimum steam flow rate or boiler efficiency must be made. A dedicated preheater can also be added to the HEN so as to guarantee the boiler efficiency is maintained; however, this will compromise the minimum steam flow rate. It was found that the flow rate could be reduced by 29.6% while still maintaining the boiler efficiency for an example problem. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1007008

On synthesis and optimization of steam system networks. 3. / Tim Price in Industrial & engineering chemistry research, Vol. 49 N° 19 (Octobre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 9165–9174 Titre : On synthesis and optimization of steam system networks. 3. : Pressure drop consideration Type de document : texte imprimé Auteurs : Tim Price, Auteur ; Thokozani Majozi, Auteur Année de publication : 2010 Article en page(s) : pp. 9165–9174 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimization  steam  system Résumé : Heat exchanger networks in steam systems are traditionally designed to operate in parallel. Coetzee and Majozi (Ind. Eng. Chem. Res. 2008, 47, 4405−4413) found that by reusing steam condensate within the network the steam flow rate could be reduced. This was achieved by restructuring the networks into a series design, with the consequence of greatly increasing the pressure drop of the system. The boiler return condensate temperature was also reduced, which was found to decrease the boiler efficiency. Maintaining the boiler efficiency has been considered in the first two papers in this series, and pressure drop is introduced in this paper. The formulations from the previous two papers are used to find the minimum steam flow rate for a HEN while maintaining the boiler efficiency. The network exhibiting the minimum pressure drop for this flow rate is then designed using the critical path algorithm. The boiler efficiency is maintained using the constraints explored in papers I (Ind. Eng. Chem. Res. DOI: 10.1021/ie1007008) and II (Ind. Eng. Chem. Res. DOI: 10.1021/ie1008579) of this series. The minimum pressure drop for the network exhibiting the minimum flow rate found in paper I was 344.4 kPa; however, the flow rate was reduced by 29.6% as shown in paper I. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1008585 [article] On synthesis and optimization of steam system networks. 3. : Pressure drop consideration [texte imprimé] / Tim Price, Auteur ; Thokozani Majozi, Auteur . - 2010 . - pp. 9165–9174. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 9165–9174 Mots-clés : Optimization  steam  system Résumé : Heat exchanger networks in steam systems are traditionally designed to operate in parallel. Coetzee and Majozi (Ind. Eng. Chem. Res. 2008, 47, 4405−4413) found that by reusing steam condensate within the network the steam flow rate could be reduced. This was achieved by restructuring the networks into a series design, with the consequence of greatly increasing the pressure drop of the system. The boiler return condensate temperature was also reduced, which was found to decrease the boiler efficiency. Maintaining the boiler efficiency has been considered in the first two papers in this series, and pressure drop is introduced in this paper. The formulations from the previous two papers are used to find the minimum steam flow rate for a HEN while maintaining the boiler efficiency. The network exhibiting the minimum pressure drop for this flow rate is then designed using the critical path algorithm. The boiler efficiency is maintained using the constraints explored in papers I (Ind. Eng. Chem. Res. DOI: 10.1021/ie1007008) and II (Ind. Eng. Chem. Res. DOI: 10.1021/ie1008579) of this series. The minimum pressure drop for the network exhibiting the minimum flow rate found in paper I was 344.4 kPa; however, the flow rate was reduced by 29.6% as shown in paper I. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1008585

Steam system network synthesis using process integration / Sternberg W. A. Coetzee in Industrial & engineering chemistry research, Vol. 47 N° 13 (Juillet 2008) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 47 N° 13 (Juillet 2008) . - p. 4405–4413 Titre : Steam system network synthesis using process integration Type de document : texte imprimé Auteurs : Sternberg W. A. Coetzee, Auteur ; Thokozani Majozi, Auteur Année de publication : 2008 Article en page(s) : p. 4405–4413 Note générale : Bibliogr. p. 4413 Langues : Anglais (eng) Mots-clés : Steam  system;  Network  synthesis Résumé : Steam boilers are used to generate steam in order to meet the duty requirements of cold process streams. The most common heat exchanger network layout associated with the boiler is a completely parallel design, where the duty of each cold process stream is met by an external hot utility stream. This observation suggests that the flow rate of steam needed for the system can be reduced, while maintaining the required duty, simply by introducing series connections to the layout of the network (Kim, J. K.; Smith, R. Cooling water system design. Chem. Eng. Sci. 2001, 56, 3641−3658). Phase change of saturated steam to saturated liquid plays a vital role in the targeting method as well as the design of the network layout, since the saturated liquid (and resulting reuse liquid) is also used to meet the cold process duty requirements. A hybrid graphical and mathematical technique for targeting and network synthesis is presented. The main objective of the technique is to reduce steam flow rate without compromising the duty requirements of the process heat exchangers. In order to assess the advantage of a hybrid technique, a case study is used where a steam savings of 29.6% is obtained, compaired with using just saturated steam. We further present a complete mathematical technique to demonstrate the advantage of the graphical targeting concept in solution time improvement. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie071195n [article] Steam system network synthesis using process integration [texte imprimé] / Sternberg W. A. Coetzee, Auteur ; Thokozani Majozi, Auteur . - 2008 . - p. 4405–4413. Bibliogr. p. 4413 Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 47 N° 13 (Juillet 2008) . - p. 4405–4413 Mots-clés : Steam  system;  Network  synthesis Résumé : Steam boilers are used to generate steam in order to meet the duty requirements of cold process streams. The most common heat exchanger network layout associated with the boiler is a completely parallel design, where the duty of each cold process stream is met by an external hot utility stream. This observation suggests that the flow rate of steam needed for the system can be reduced, while maintaining the required duty, simply by introducing series connections to the layout of the network (Kim, J. K.; Smith, R. Cooling water system design. Chem. Eng. Sci. 2001, 56, 3641−3658). Phase change of saturated steam to saturated liquid plays a vital role in the targeting method as well as the design of the network layout, since the saturated liquid (and resulting reuse liquid) is also used to meet the cold process duty requirements. A hybrid graphical and mathematical technique for targeting and network synthesis is presented. The main objective of the technique is to reduce steam flow rate without compromising the duty requirements of the process heat exchangers. In order to assess the advantage of a hybrid technique, a case study is used where a steam savings of 29.6% is obtained, compaired with using just saturated steam. We further present a complete mathematical technique to demonstrate the advantage of the graphical targeting concept in solution time improvement. En ligne : http://pubs.acs.org/doi/abs/10.1021/ie071195n

Synthesis and optimization of steam system networks. 2. / Tim Price in Industrial & engineering chemistry research, Vol. 49 N° 19 (Octobre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 9154–9164 Titre : Synthesis and optimization of steam system networks. 2. : Multiple steam levels Type de document : texte imprimé Auteurs : Tim Price, Auteur ; Thokozani Majozi, Auteur Année de publication : 2010 Article en page(s) : pp. 9154–9164 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Optimisation  steam  system  multiple Résumé : The use of steam in heat exchanger networks (HENs) can be reduced by the application of heat integration with the intention of debottlenecking the steam boiler and indirectly reducing the water requirement [Coetzee and Majozi. Ind. Eng. Chem. Res. 2008, 47, 4405−4413]. By reducing the steam flow rate, the return condensate temperature to the boiler is compromised which adversely affects the boiler operation. A means of maintaining efficient boiler operation is to reheat the return flow to the boiler. Steam systems typically employ turbines of which the exhaust is frequently used as a heating utility in the background process. Since turbines operate at various steam levels, a means for incorporating these steam levels into the HEN optimization framework is necessary. Consequently this paper concerns the restructuring of all steam system heat exchangers using conceptual and mathematical analysis to create a series HEN with the aim of reducing the overall steam flow rate, while maintaining the boiler efficiency. In an example problem, it was found that the steam flow rate could be reduced by up to 26.3% while still maintaining the boiler efficiency. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1008579 [article] Synthesis and optimization of steam system networks. 2. : Multiple steam levels [texte imprimé] / Tim Price, Auteur ; Thokozani Majozi, Auteur . - 2010 . - pp. 9154–9164. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 19 (Octobre 2010) . - pp. 9154–9164 Mots-clés : Optimisation  steam  system  multiple Résumé : The use of steam in heat exchanger networks (HENs) can be reduced by the application of heat integration with the intention of debottlenecking the steam boiler and indirectly reducing the water requirement [Coetzee and Majozi. Ind. Eng. Chem. Res. 2008, 47, 4405−4413]. By reducing the steam flow rate, the return condensate temperature to the boiler is compromised which adversely affects the boiler operation. A means of maintaining efficient boiler operation is to reheat the return flow to the boiler. Steam systems typically employ turbines of which the exhaust is frequently used as a heating utility in the background process. Since turbines operate at various steam levels, a means for incorporating these steam levels into the HEN optimization framework is necessary. Consequently this paper concerns the restructuring of all steam system heat exchangers using conceptual and mathematical analysis to create a series HEN with the aim of reducing the overall steam flow rate, while maintaining the boiler efficiency. In an example problem, it was found that the steam flow rate could be reduced by up to 26.3% while still maintaining the boiler efficiency. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie1008579

Water minimization techniques for batch processes / Jacques F. Gouws in Industrial & engineering chemistry research, Vol. 49 N° 19 (Octobre 2010) 

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