title: New high temperature transcritical CO2 heat pump concept for spray drying

authors: Kong, Lana

subjects: high temperature heat pump

abstract: The need to decarbonise the industrial sector requires new innovations in high temperature heating. The development of an industrial high temperature heat pump presents not only great emissions reduction potential but also cost saving potential for industrial process heat users. Compared to boilers with efficiencies ranging from 70 to 99%, heat pumps have the ability to leverage renewable electricity to supply heating as a standalone technology (air-source heat pumps), with one unit if electricity being able to supply multiple units of heat (Coefficient of Performance > 1) or integrate with existing boilers to reduce steam demand (air-source or waste heat recovery).
This thesis investigates a novel high temperature transcritical CO2 heat pump concept using a case study in milk powder spray drying. A series of cycle architectures were modelled that incorporated internal heat exchangers and cascade arrangements to assess their effect on thermodynamic performance for not only large temperature lifts (>150 °C) but also large temperature glides (>150 °C). A transcritical-transcritical cascade configuration was found to achieve a sink temperature of 200 °C with a COP of 2.22 at moderate discharge pressures (150 bar) compared to what is currently available in the literature (>200 bar). Expansion work recovery, using ejectors and expanders, was further explored to reduce exergy losses, achieving incremental COP gains up to 2.35. However, it was determined that, at this stage, the marginal increases in COP did not overcome the challenges in complexity of integrating an expander or ejector within the system.

A comparison of integration options was undertaken that compared the high temperature heat pump integration with fuel switching to electrode or biomass boilers. Hybrid configurations of heat pump and boilers were also assessed at varying utility prices to determine whether an optimum sink temperature existed to minimise the operational cost. With this, a multi-temperature heat pump configuration was found to improve the COP of the heat pump to 2.55 for air heating to 200 °C, which emphasises the importance of temperature profile matching in heat pump design. Operating costs depended on the electricity-to-biomass price ratio and grid emissions intensity. In all cases, electrode boiler conversions had the highest operational cost. Price ratios below 2.75 were favourable for full electrification using a heat pump, while price ratios above 3.67 favoured a full biomass conversion. Between these two price ratios, the optimal hybrid configuration was to supply the air heating up to the temperature level for the fluidised bed (102 °C) using a heat pump and supply the remainder of the heating using a biomass boiler. In comparison to coal, the proposed solutions achieved emissions savings between 55 and 94 %.

The wider potential for the high temperature heat pump concept was then estimated, revealing a broader potential for CO2 high temperature heat pumps to supply hundreds of petajoules per year of low-carbon heat across a diverse range of industrial sectors. Due to being able to produce both large temperature glides and large temperature lifts, the CO2 high temperature heat pump was particularly suited for a range of drying processes (further than milk powder spray drying). Potential source and sink streams for the heat pump were identified for each application to estimate possible COPs, which ranged between 2.0 and 3.05 for sink outlet temperatures ranging from 110 to 280 °C. Emissions reduction was shown to be viable for nearly all regions when displacing coal, but requires cleaner electricity grids or higher COPs when displacing natural gas.

This thesis contributes an in depth thermodynamic analysis of both a novel high temperature heat pump cycle architecture and a novel application of high temperature heat pumps into the milk powder spray drying process. Additionally, this thesis contributes a cross-sectoral analysis for implementation, collating potential source and sink streams across a variety of applications.

text: New high temperature transcritical CO2 heat pump concept for spray drying The need to decarbonise the industrial sector requires new innovations in high temperature heating. The development of an industrial high temperature heat pump presents not only great emissions reduction potential but also cost saving potential for industrial process heat users. Compared to boilers with efficiencies ranging from 70 to 99%, heat pumps have the ability to leverage renewable electricity to supply heating as a standalone technology (air-source heat pumps), with one unit if electricity being able to supply multiple units of heat (Coefficient of Performance > 1) or integrate with existing boilers to reduce steam demand (air-source or waste heat recovery).
This thesis investigates a novel high temperature transcritical CO2 heat pump concept using a case study in milk powder spray drying. A series of cycle architectures were modelled that incorporated internal heat exchangers and cascade arrangements to assess their effect on thermodynamic performance for not only large temperature lifts (>150 °C) but also large temperature glides (>150 °C). A transcritical-transcritical cascade configuration was found to achieve a sink temperature of 200 °C with a COP of 2.22 at moderate discharge pressures (150 bar) compared to what is currently available in the literature (>200 bar). Expansion work recovery, using ejectors and expanders, was further explored to reduce exergy losses, achieving incremental COP gains up to 2.35. However, it was determined that, at this stage, the marginal increases in COP did not overcome the challenges in complexity of integrating an expander or ejector within the system.

A comparison of integration options was undertaken that compared the high temperature heat pump integration with fuel switching to electrode or biomass boilers. Hybrid configurations of heat pump and boilers were also assessed at varying utility prices to determine whether an optimum sink temperature existed to minimise the operational cost. With this, a multi-temperature heat pump configuration was found to improve the COP of the heat pump to 2.55 for air heating to 200 °C, which emphasises the importance of temperature profile matching in heat pump design. Operating costs depended on the electricity-to-biomass price ratio and grid emissions intensity. In all cases, electrode boiler conversions had the highest operational cost. Price ratios below 2.75 were favourable for full electrification using a heat pump, while price ratios above 3.67 favoured a full biomass conversion. Between these two price ratios, the optimal hybrid configuration was to supply the air heating up to the temperature level for the fluidised bed (102 °C) using a heat pump and supply the remainder of the heating using a biomass boiler. In comparison to coal, the proposed solutions achieved emissions savings between 55 and 94 %.

The wider potential for the high temperature heat pump concept was then estimated, revealing a broader potential for CO2 high temperature heat pumps to supply hundreds of petajoules per year of low-carbon heat across a diverse range of industrial sectors. Due to being able to produce both large temperature glides and large temperature lifts, the CO2 high temperature heat pump was particularly suited for a range of drying processes (further than milk powder spray drying). Potential source and sink streams for the heat pump were identified for each application to estimate possible COPs, which ranged between 2.0 and 3.05 for sink outlet temperatures ranging from 110 to 280 °C. Emissions reduction was shown to be viable for nearly all regions when displacing coal, but requires cleaner electricity grids or higher COPs when displacing natural gas.

This thesis contributes an in depth thermodynamic analysis of both a novel high temperature heat pump cycle architecture and a novel application of high temperature heat pumps into the milk powder spray drying process. Additionally, this thesis contributes a cross-sectoral analysis for implementation, collating potential source and sink streams across a variety of applications.

year: 2026

title: Building bridges: Treating a new transport link as a real option

authors: Grimes, Arthur

subjects: transport investment

abstract: A transportation investment that materially improves links between centres opens up previously unavailable options for new activities. Traditional cost-benefit analysis does not adequately take account of the value of this option; real options theory must be added to the analysis to evaluate the full benefits. This paper uses a specific example, Auckland’s Harbour Bridge, to motivate the importance of real options analysis. Using illustrative, multi-period models of the real options problem, it highlights how inclusion of real options factors may either increase or decrease the attractiveness of a proposed investment. The models identify situations in which it is optimal to invest even where a standard benefit-cost ratio is less than one.

text: Building bridges: Treating a new transport link as a real option A transportation investment that materially improves links between centres opens up previously unavailable options for new activities. Traditional cost-benefit analysis does not adequately take account of the value of this option; real options theory must be added to the analysis to evaluate the full benefits. This paper uses a specific example, Auckland’s Harbour Bridge, to motivate the importance of real options analysis. Using illustrative, multi-period models of the real options problem, it highlights how inclusion of real options factors may either increase or decrease the attractiveness of a proposed investment. The models identify situations in which it is optimal to invest even where a standard benefit-cost ratio is less than one.

year: 2011

title: The Impact of Colonisation on the Maori community: An exploration of the attitudes and perspectives held by Maori in relation to the active reclamation of Maori sovereignty/tino rangatiratanga.

authors: Baty, Tina Amy

subjects: Maori

abstract: Whāia te iti kahurangi ki te tūohu koe me he maunga teitei
Seek the treasure you value most dearly: If you bow your head, let it be to a lofty mountain
The purpose of my research was twofold. I first sort to explore the attitudes and perspectives held by Māori in relation to the active reclamation of Māori sovereignty, tino rangatiratanga. I further wanted to know how Māori sovereignty, tino rangatiratanga could lead to the improvement of Māori health.
My research collected information pertinent to these two inquiries from current literature and from interviews I conducted with five Māori individuals from different iwi, hapu groups. All whom were actively engaged with the Māori community in some form. My research data found that colonisalism has and continues to negatively impact the Māori community. This negative impact manifests in a variety of behaviours that effect Māori health and leads to poor outcomes for Māori. Māori sovereignty, tino rangatiratanga was thought of as the solution to overcome and neutralise the negative effects of colonialism experienced by Māori. Māori sovereignty, tino rangatiratanga was found to be related with Māori idenity and instrumental in all things pertinent to the Māori communities.
My research found that Māori sovereignty, tino rangatiratanga can be identified as existing on a philosophical level, governance-structural level, and on a day-to-day basis. This research found that the reclamation of Māori sovereignty, tino rangatiratanga is a process that is currently in motion. Finally, the exercising of Māori sovereignty, tino rangatiratanga in relation to Māori health provides a well-established argument that it can produce positive health benefits to the Māori community, because it is responsive to Māori and better meets the needs of our Māori community simply because it is a Māori way of being, doing and knowing.

text: The Impact of Colonisation on the Maori community: An exploration of the attitudes and perspectives held by Maori in relation to the active reclamation of Maori sovereignty/tino rangatiratanga. Whāia te iti kahurangi ki te tūohu koe me he maunga teitei
Seek the treasure you value most dearly: If you bow your head, let it be to a lofty mountain
The purpose of my research was twofold. I first sort to explore the attitudes and perspectives held by Māori in relation to the active reclamation of Māori sovereignty, tino rangatiratanga. I further wanted to know how Māori sovereignty, tino rangatiratanga could lead to the improvement of Māori health.
My research collected information pertinent to these two inquiries from current literature and from interviews I conducted with five Māori individuals from different iwi, hapu groups. All whom were actively engaged with the Māori community in some form. My research data found that colonisalism has and continues to negatively impact the Māori community. This negative impact manifests in a variety of behaviours that effect Māori health and leads to poor outcomes for Māori. Māori sovereignty, tino rangatiratanga was thought of as the solution to overcome and neutralise the negative effects of colonialism experienced by Māori. Māori sovereignty, tino rangatiratanga was found to be related with Māori idenity and instrumental in all things pertinent to the Māori communities.
My research found that Māori sovereignty, tino rangatiratanga can be identified as existing on a philosophical level, governance-structural level, and on a day-to-day basis. This research found that the reclamation of Māori sovereignty, tino rangatiratanga is a process that is currently in motion. Finally, the exercising of Māori sovereignty, tino rangatiratanga in relation to Māori health provides a well-established argument that it can produce positive health benefits to the Māori community, because it is responsive to Māori and better meets the needs of our Māori community simply because it is a Māori way of being, doing and knowing.

year: 2018