title: Automated retrofit of heat exchanger networks

authors: Lal, Nathan S.

subjects: Heat recovery

abstract: In a large industrial processing plant, a significant amount of process heat is generated using fossil fuels, contributing to New Zealand’s overall greenhouse gas emissions. While New Zealand’s renewable energy sources present potential alternatives to fossil fuels, reducing the process heat demand of industrial processing plants is another critical step for emissions reduction, with multiple long-term economic and environmental benefits. Reducing process heat demand often centres on retrofitting the heat exchanger network to improve heat recovery and lower the hot utility consumption. 
This thesis presents a comprehensive automated retrofit design method for heat exchanger networks, fulfilling several gaps in current knowledge. The novel contributions are presented and discussed in four main chapters: (1) two retrofit tools are developed that enable visualisation of the problem – the Modified Energy Transfer Diagram and the Heat Surplus-Deficit Table, (2) an algorithm called Automated Retrofit Targeting that searches for all possible retrofit modifications of the heat exchanger network that unlocks energy savings, (3) a comprehensive energy retrofit planning tool that uses a multi-stage retrofit analysis to provide strategic long-term and cost-effective retrofit plans, and (4) an heat exchanger network simulation method, incorporating using Monte Carlo Simulation, to quantify the effect of variable process flows and temperatures on flexibility and steady state performance. 
The developed methods are illustrated using a simple four-stream network and then applied to two industrial case studies that are representative of some of the large industrial energy-users in New Zealand: a paper mill at a Kraft pulp and paper mill cluster and a petrochemical complex. In both case studies, numerous potential retrofit designs have been identified. These options are reduced to those that ranked as the most cost-effective, using thermodynamic and economic constraints with Pareto front analysis. By successive application of the retrofit method, long-term retrofit plans have been proposed, enabling strategic sequencing of modifications and minimising process heat demand. For the petrochemical complex, the hot utility consumption could decrease by 9.58 MW (63% of the total possible savings) using four separate stages of retrofits. The total retrofit profit would reach 1.5 million Euros per year with a simple payback of 1.7 years. The paper mill could achieve its process heat demand reduction target using four retrofit stages, achieving a total retrofit profit of 0.78 million NZD per year. These modifications resulted in an inflexibility of 51.3% (probability of the heat exchanger network failing to meet all target temperatures), but this could be reduced to 4.1% using bypass control. 
This thesis provides a novel retrofit method, which uses graphical and numerical tools, in combination with automated analysis, generating and evaluating cost-effective retrofit designs. The retrofit design method has been implemented in Microsoft ExcelTM as a critical and functional output that can be rapidly applied to complex industrial heat exchanger networks.

text: Automated retrofit of heat exchanger networks In a large industrial processing plant, a significant amount of process heat is generated using fossil fuels, contributing to New Zealand’s overall greenhouse gas emissions. While New Zealand’s renewable energy sources present potential alternatives to fossil fuels, reducing the process heat demand of industrial processing plants is another critical step for emissions reduction, with multiple long-term economic and environmental benefits. Reducing process heat demand often centres on retrofitting the heat exchanger network to improve heat recovery and lower the hot utility consumption. 
This thesis presents a comprehensive automated retrofit design method for heat exchanger networks, fulfilling several gaps in current knowledge. The novel contributions are presented and discussed in four main chapters: (1) two retrofit tools are developed that enable visualisation of the problem – the Modified Energy Transfer Diagram and the Heat Surplus-Deficit Table, (2) an algorithm called Automated Retrofit Targeting that searches for all possible retrofit modifications of the heat exchanger network that unlocks energy savings, (3) a comprehensive energy retrofit planning tool that uses a multi-stage retrofit analysis to provide strategic long-term and cost-effective retrofit plans, and (4) an heat exchanger network simulation method, incorporating using Monte Carlo Simulation, to quantify the effect of variable process flows and temperatures on flexibility and steady state performance. 
The developed methods are illustrated using a simple four-stream network and then applied to two industrial case studies that are representative of some of the large industrial energy-users in New Zealand: a paper mill at a Kraft pulp and paper mill cluster and a petrochemical complex. In both case studies, numerous potential retrofit designs have been identified. These options are reduced to those that ranked as the most cost-effective, using thermodynamic and economic constraints with Pareto front analysis. By successive application of the retrofit method, long-term retrofit plans have been proposed, enabling strategic sequencing of modifications and minimising process heat demand. For the petrochemical complex, the hot utility consumption could decrease by 9.58 MW (63% of the total possible savings) using four separate stages of retrofits. The total retrofit profit would reach 1.5 million Euros per year with a simple payback of 1.7 years. The paper mill could achieve its process heat demand reduction target using four retrofit stages, achieving a total retrofit profit of 0.78 million NZD per year. These modifications resulted in an inflexibility of 51.3% (probability of the heat exchanger network failing to meet all target temperatures), but this could be reduced to 4.1% using bypass control. 
This thesis provides a novel retrofit method, which uses graphical and numerical tools, in combination with automated analysis, generating and evaluating cost-effective retrofit designs. The retrofit design method has been implemented in Microsoft ExcelTM as a critical and functional output that can be rapidly applied to complex industrial heat exchanger networks.

year: 2020

title: Brown seaweed Sargassum siliquosum as an intervention for diet-induced obesity in male Wistar rats

authors: du Preez, Ryan

abstract: The therapeutic potential of Sargassum siliquosum grown in Australian tropical waters was tested in a rat model of metabolic syndrome. Forty-eight male Wistar rats were divided into four groups of 12 rats and each group was fed a different diet for 16 weeks: corn starch diet (C); high-carbohydrate, high-fat diet (H) containing fructose, sucrose, saturated and trans fats; and C or H diets with 5% S. siliquosum mixed into the food from weeks 9 to 16 (CS and HS). Obesity, hypertension, dyslipidaemia, impaired glucose tolerance, fatty liver and left ventricular fibrosis developed in H rats. In HS rats, S. siliquosum decreased body weight (H, 547 ± 14; HS, 490 ± 16 g), fat mass (H, 248 ± 27; HS, 193 ± 19 g), abdominal fat deposition and liver fat vacuole size but did not reverse cardiovascular and liver effects. H rats showed marked changes in gut microbiota compared to C rats, while S. siliquosum supplementation increased gut microbiota belonging to the family Muribaculaceae. This selective increase in gut microbiota likely complements the prebiotic actions of the alginates. Thus, S. siliquosum may be a useful dietary additive to decrease abdominal and liver fat deposition.

text: Brown seaweed Sargassum siliquosum as an intervention for diet-induced obesity in male Wistar rats The therapeutic potential of Sargassum siliquosum grown in Australian tropical waters was tested in a rat model of metabolic syndrome. Forty-eight male Wistar rats were divided into four groups of 12 rats and each group was fed a different diet for 16 weeks: corn starch diet (C); high-carbohydrate, high-fat diet (H) containing fructose, sucrose, saturated and trans fats; and C or H diets with 5% S. siliquosum mixed into the food from weeks 9 to 16 (CS and HS). Obesity, hypertension, dyslipidaemia, impaired glucose tolerance, fatty liver and left ventricular fibrosis developed in H rats. In HS rats, S. siliquosum decreased body weight (H, 547 ± 14; HS, 490 ± 16 g), fat mass (H, 248 ± 27; HS, 193 ± 19 g), abdominal fat deposition and liver fat vacuole size but did not reverse cardiovascular and liver effects. H rats showed marked changes in gut microbiota compared to C rats, while S. siliquosum supplementation increased gut microbiota belonging to the family Muribaculaceae. This selective increase in gut microbiota likely complements the prebiotic actions of the alginates. Thus, S. siliquosum may be a useful dietary additive to decrease abdominal and liver fat deposition.

year: 2021

title: Nobody knows me even though I’m always there: Why Māori men do exist - in all the wrong places

authors: Stanley, Paul

subjects: Maori

abstract: In the study of psychology, Māori men are often only seen as the perpetrators of the problems. There is very little focus on finding solutions for Māori men, with Māori men. In the top eight causes of death for Māori males aged 15 to 24 are car crashes, homicide, and suicide. With respect to car crashes, there is a close link between alcohol-related car crashes and suicide. As a nation, we should be concerned with all of the above issues, as each of them is preventable. Invariably, we fail see the deaths of these young men as warning signs of much wider issues about why they wanted to die, or why they felt the need to kill someone close to themselves. The argument tendered in this paper is that the same way in which Māori as a group have been researched, as being “the problem”, equally applies to the way in which Māori men have continued to be have been researched: Māori men are only ever portrayed as “the problem” and are never portrayed as part of a solution subjected to this process as well. The lyrics of a well known song by UB40, One in Ten, exemplify this notion of being unknown, even though Māori men do exist in Aotearoa.

text: Nobody knows me even though I’m always there: Why Māori men do exist - in all the wrong places In the study of psychology, Māori men are often only seen as the perpetrators of the problems. There is very little focus on finding solutions for Māori men, with Māori men. In the top eight causes of death for Māori males aged 15 to 24 are car crashes, homicide, and suicide. With respect to car crashes, there is a close link between alcohol-related car crashes and suicide. As a nation, we should be concerned with all of the above issues, as each of them is preventable. Invariably, we fail see the deaths of these young men as warning signs of much wider issues about why they wanted to die, or why they felt the need to kill someone close to themselves. The argument tendered in this paper is that the same way in which Māori as a group have been researched, as being “the problem”, equally applies to the way in which Māori men have continued to be have been researched: Māori men are only ever portrayed as “the problem” and are never portrayed as part of a solution subjected to this process as well. The lyrics of a well known song by UB40, One in Ten, exemplify this notion of being unknown, even though Māori men do exist in Aotearoa.

year: 2003