title: Heat Integrated Milk Powder Production

authors: Walmsley, Timothy Gordon

subjects: Process integration

abstract: Dairy processing is critical to New Zealand’s (NZ) economy producing NZ$13 billion in exports for 2012 while consuming 32 PJ of fossil fuels for process heat. Three quarters of NZ dairy exports are milk powders. This thesis presents methods to reduce process heat use in Milk Powder Plants (MPP) through improved heat integration and addresses key technical challenges preventing industrial implementation. My original contributions to literature include: (1) a novel design method called the Cost Derivate Method (CDM) that cost optimally allocates area in direct heat exchange networks, (2) a new design methodology for integration of semi-continuous process clusters using a Heat Recovery Loop (HRL) with a Variable Temperature Storage (VTS) system for improved heat recovery, (3) an experimentally validated deposition model for predicting critical air conditions that cause milk powder fouling, and (4) a thermo-economic assessment tool for the optimisation of industrial spray dryer exhaust heat recovery projects via a Liquid Coupled Loop Heat Exchanger (LCHE) system.
By applying Pinch Analysis to an industrial MMP, this work confirms that heat must be recovered from the milk spray dryer exhaust air (~75 °C) to achieve maximum heat integration in MPPs. For stand-alone MPPs exhaust heat is best used to indirectly preheat the inlet dryer air reducing steam use by 12.7 % for a 55 °C exhaust outlet. Additional economic heat recovery from condensate and vapour flows decreased steam use by a further 6.9 %. Application of the CDM to the liquid and vapour sections of new MMP maximum energy recovery networks reduced total cost by 5.8 %. For multi-plant dairy factories, a second industrial case study showed the exhaust heat may be integrated with neighbouring plants via a HRL with VTS to increase site heat recovery by 10.8 MW including 5.1 MW of exhaust heat recovery, compared to 7.9 MW using a conventional HRL design method with constant temperature storage. 
A key barrier preventing exhaust heat recovery implementation in NZ MPPs is the possibility of milk powder fouling. Dryer exhaust air contains a low concentration of powder that when exposed to low temperatures at high humidity becomes sticky. For a heat exchanger face air velocity of 4 m/s, experimental data from milk powder fouling tests of flat plates, tubes and fins indicates particulate fouling becomes severe when the exhaust air temperature reaches 55 °C. Higher face velocities are shown to lower this critical exhaust temperature for avoiding severe fouling, which gives potential for increased heat recovery but for increased pressure drop. Lower face velocities show the opposite effect. Designing exhaust heat recovery systems entail an acute trade-off between heat transfer, pressure drop and fouling. Two important design parameters are the number of tube rows in the exhaust heat exchanger and the face velocity. The outputs of a thermo-economic spreadsheet tool suggest LCHE systems for a dryer producing 23.5 t/h is economic. With a face velocity of 4 m/s and 14 rows of finned round tube, the project had an estimated payback of 1.6 years, a net present value of NZ$3 million and internal rate of return of 71 %. This tool will empower industry with greater confidence to uptake exhaust heat recovery technology as a vital method for improving the heat integration of MPPs in NZ.

text: Heat Integrated Milk Powder Production Dairy processing is critical to New Zealand’s (NZ) economy producing NZ$13 billion in exports for 2012 while consuming 32 PJ of fossil fuels for process heat. Three quarters of NZ dairy exports are milk powders. This thesis presents methods to reduce process heat use in Milk Powder Plants (MPP) through improved heat integration and addresses key technical challenges preventing industrial implementation. My original contributions to literature include: (1) a novel design method called the Cost Derivate Method (CDM) that cost optimally allocates area in direct heat exchange networks, (2) a new design methodology for integration of semi-continuous process clusters using a Heat Recovery Loop (HRL) with a Variable Temperature Storage (VTS) system for improved heat recovery, (3) an experimentally validated deposition model for predicting critical air conditions that cause milk powder fouling, and (4) a thermo-economic assessment tool for the optimisation of industrial spray dryer exhaust heat recovery projects via a Liquid Coupled Loop Heat Exchanger (LCHE) system.
By applying Pinch Analysis to an industrial MMP, this work confirms that heat must be recovered from the milk spray dryer exhaust air (~75 °C) to achieve maximum heat integration in MPPs. For stand-alone MPPs exhaust heat is best used to indirectly preheat the inlet dryer air reducing steam use by 12.7 % for a 55 °C exhaust outlet. Additional economic heat recovery from condensate and vapour flows decreased steam use by a further 6.9 %. Application of the CDM to the liquid and vapour sections of new MMP maximum energy recovery networks reduced total cost by 5.8 %. For multi-plant dairy factories, a second industrial case study showed the exhaust heat may be integrated with neighbouring plants via a HRL with VTS to increase site heat recovery by 10.8 MW including 5.1 MW of exhaust heat recovery, compared to 7.9 MW using a conventional HRL design method with constant temperature storage. 
A key barrier preventing exhaust heat recovery implementation in NZ MPPs is the possibility of milk powder fouling. Dryer exhaust air contains a low concentration of powder that when exposed to low temperatures at high humidity becomes sticky. For a heat exchanger face air velocity of 4 m/s, experimental data from milk powder fouling tests of flat plates, tubes and fins indicates particulate fouling becomes severe when the exhaust air temperature reaches 55 °C. Higher face velocities are shown to lower this critical exhaust temperature for avoiding severe fouling, which gives potential for increased heat recovery but for increased pressure drop. Lower face velocities show the opposite effect. Designing exhaust heat recovery systems entail an acute trade-off between heat transfer, pressure drop and fouling. Two important design parameters are the number of tube rows in the exhaust heat exchanger and the face velocity. The outputs of a thermo-economic spreadsheet tool suggest LCHE systems for a dryer producing 23.5 t/h is economic. With a face velocity of 4 m/s and 14 rows of finned round tube, the project had an estimated payback of 1.6 years, a net present value of NZ$3 million and internal rate of return of 71 %. This tool will empower industry with greater confidence to uptake exhaust heat recovery technology as a vital method for improving the heat integration of MPPs in NZ.

year: 2014

title: Digitally-supported collaboration: An exploration of teachers' and students' understandings and practice.

authors: Mangino, Leesa

abstract: Education is evolving over time. The use of digital technology in our schools continues to grow and develop at a rapid pace, supported by the introduction of ultra-fast broadband and the availability of mobile technology.  There is change occurring in the teaching and learning environments in our schools, walls are coming down between classrooms and teachers are increasingly being expected to work in co-teaching situations.  An expectation is being set that educators need to equip students with the 21st century skills necessary to be successful in today’s world, one of the key skills being the ability to collaborate with others.

This study draws together the key ideas introduced above - that is, developing knowledge of collaborative, digitally-supported innovative learning environments (ILEs).  A collective case study approach was used to investigate the understandings teachers and students in three primary schools have about collaboration, and how this was reflected in practice.  This interpretive study also explored the nature of digitally mediated interactions occurring in these learning environments including teacher-to-teacher, teacher-to-student, and student-to-student, to gain a better understanding of any role digital technology might play in collaborative teaching and learning within these spaces.

Data was collected through observations, interviews, and the collecting of artifacts.  These data were then analysed thematically.  The findings suggest that building trusting relationships is essential to collaboration but can take time to establish.  Teachers and students need to have a shared understanding of what collaboration is and their role within this. Clarity of purpose is fundamental to effective digitally-supported collaboration, teachers and students need to know why they are collaborating, how digital technology could support their collaborative needs, and how they can best make use of their physical environment.

text: Digitally-supported collaboration: An exploration of teachers' and students' understandings and practice. Education is evolving over time. The use of digital technology in our schools continues to grow and develop at a rapid pace, supported by the introduction of ultra-fast broadband and the availability of mobile technology.  There is change occurring in the teaching and learning environments in our schools, walls are coming down between classrooms and teachers are increasingly being expected to work in co-teaching situations.  An expectation is being set that educators need to equip students with the 21st century skills necessary to be successful in today’s world, one of the key skills being the ability to collaborate with others.

This study draws together the key ideas introduced above - that is, developing knowledge of collaborative, digitally-supported innovative learning environments (ILEs).  A collective case study approach was used to investigate the understandings teachers and students in three primary schools have about collaboration, and how this was reflected in practice.  This interpretive study also explored the nature of digitally mediated interactions occurring in these learning environments including teacher-to-teacher, teacher-to-student, and student-to-student, to gain a better understanding of any role digital technology might play in collaborative teaching and learning within these spaces.

Data was collected through observations, interviews, and the collecting of artifacts.  These data were then analysed thematically.  The findings suggest that building trusting relationships is essential to collaboration but can take time to establish.  Teachers and students need to have a shared understanding of what collaboration is and their role within this. Clarity of purpose is fundamental to effective digitally-supported collaboration, teachers and students need to know why they are collaborating, how digital technology could support their collaborative needs, and how they can best make use of their physical environment.

year: 2018

title: Whangai: remembering, understanding and experiencing

authors: McRae, Karyn Okeroa

subjects: adoption

abstract: The Māori customary practice of whangai is often equated with adoption or foster care.
There are, however, significant differences between the institutions. Adoption or foster care, tends to be mainly focused on the interests of the child. The institution of whangai, while being cognizant of the interests of the child, is weighted more towards establishing, nurturing and cementing relationships between individuals, families and broader relational networks. In this paper we draw on the lived experiences of six people who have been raised as whangai and/or have raised whangai. We were interested in their understanding of the cultural concept of whangai, how the customary practice of whangai has changed over time, and their projected thoughts on future generations’ experience of whangai. Findings suggest that the institution of whangai remains as a strong vehicle for both the care of children and for the nurturing of whangai kinship relationships. While participants recognised that contemporary Māori social environments have contributed toward multiple manifestations of whangai, most felt it to be an institution that will be valued and carried into the future.

text: Whangai: remembering, understanding and experiencing The Māori customary practice of whangai is often equated with adoption or foster care.
There are, however, significant differences between the institutions. Adoption or foster care, tends to be mainly focused on the interests of the child. The institution of whangai, while being cognizant of the interests of the child, is weighted more towards establishing, nurturing and cementing relationships between individuals, families and broader relational networks. In this paper we draw on the lived experiences of six people who have been raised as whangai and/or have raised whangai. We were interested in their understanding of the cultural concept of whangai, how the customary practice of whangai has changed over time, and their projected thoughts on future generations’ experience of whangai. Findings suggest that the institution of whangai remains as a strong vehicle for both the care of children and for the nurturing of whangai kinship relationships. While participants recognised that contemporary Māori social environments have contributed toward multiple manifestations of whangai, most felt it to be an institution that will be valued and carried into the future.

year: 2006