title: Multi-Level process integration of heat pumps in a non-continuous processing site

authors: Klinac, Elsa

subjects: Industrial

abstract: Industrial process heat demands contribute significantly to New Zealand’s greenhouse gas emissions. With a global push towards decarbonization, including New Zealand’s Climate Change Response Amendment Act 2019, there is a need for methods and technologies that can be applied to replace industrial fossil fuel boiler use. With an increasing range of renewable energy sources, electrification provides a promising alternative to fossil fuel use; however, it is also critical to reduce process heat demands where possible. This can be done through the reuse of industrial waste heat via direct heat exchange, thermal storage, or heat pump installations. Existing Heat Integration methods provide a means of identifying waste heat recovery opportunities; however, these methods are typically aimed at steady state industries. In New Zealand, many industries operate in a non-continuous manner, creating challenges in the accurate application of these existing Heat Integration methods. 
This thesis presents a multi-level process integration method for heat pump and thermal storage retrofit on non-continuous industrial processing sites. This method aims to address several gaps in current Heat Integration methodology through the novel amalgamation of several tools discussed in four main chapters: (1) A multi-level heat pump integration tool is developed that sequentially identifies heat pump opportunities to both upgrade waste heat for reuse, and  shift remaining waste process heat towards more favorable temperature ranges, (2) A multi steady state time slice investigation develops a tool for selecting appropriate time slice sizes to accurately represent variable, non-continuous industrial sites, (3) a multi steady state thermal storage identification tool is developed by applying the previously identified time slices to existing heat integration methods with an aim to further buffer fluctuations in heat demand, and optimize the thermal loads on the previously identified heat pump opportunities.
The tools are combined into a final method and applied to a meat processing case study site that is representative of the variable, non-continuous industries that dominate the food sector in New Zealand. In this case study, hourly time slices were used to identify multiple successive heat pump opportunities including a 1.9 MW MVR that recompresses waste steam from the rendering dryers with a COP of 10, and a central 1.5 MW heat pump that supplies heat at 70°C to the site ring main with a COP of 3.4. In addition, it was found that the 90°C heat pump, already installed on the case study site, would have the potential to increase utilization on the case study site if the two other heat pump opportunities identified were implemented. Thermal storage opportunities were also identified that can be used to buffer heat demands on the 70°C heat pump opportunity, thereby allowing the heat pump to be resized to 1.04 MW in comparison to the initially hypothesized 1.5 MW, reducing both capital and operational costs of the heat pump.
This amalgamated method provides novel Total Site Heat Integration additions, which when compared to conventional heat integration methods, provide more accurate and more useful heat pump decarbonization strategies for non-continuous industrial sites, ultimately aiding in industrial decarbonization.

text: Multi-Level process integration of heat pumps in a non-continuous processing site Industrial process heat demands contribute significantly to New Zealand’s greenhouse gas emissions. With a global push towards decarbonization, including New Zealand’s Climate Change Response Amendment Act 2019, there is a need for methods and technologies that can be applied to replace industrial fossil fuel boiler use. With an increasing range of renewable energy sources, electrification provides a promising alternative to fossil fuel use; however, it is also critical to reduce process heat demands where possible. This can be done through the reuse of industrial waste heat via direct heat exchange, thermal storage, or heat pump installations. Existing Heat Integration methods provide a means of identifying waste heat recovery opportunities; however, these methods are typically aimed at steady state industries. In New Zealand, many industries operate in a non-continuous manner, creating challenges in the accurate application of these existing Heat Integration methods. 
This thesis presents a multi-level process integration method for heat pump and thermal storage retrofit on non-continuous industrial processing sites. This method aims to address several gaps in current Heat Integration methodology through the novel amalgamation of several tools discussed in four main chapters: (1) A multi-level heat pump integration tool is developed that sequentially identifies heat pump opportunities to both upgrade waste heat for reuse, and  shift remaining waste process heat towards more favorable temperature ranges, (2) A multi steady state time slice investigation develops a tool for selecting appropriate time slice sizes to accurately represent variable, non-continuous industrial sites, (3) a multi steady state thermal storage identification tool is developed by applying the previously identified time slices to existing heat integration methods with an aim to further buffer fluctuations in heat demand, and optimize the thermal loads on the previously identified heat pump opportunities.
The tools are combined into a final method and applied to a meat processing case study site that is representative of the variable, non-continuous industries that dominate the food sector in New Zealand. In this case study, hourly time slices were used to identify multiple successive heat pump opportunities including a 1.9 MW MVR that recompresses waste steam from the rendering dryers with a COP of 10, and a central 1.5 MW heat pump that supplies heat at 70°C to the site ring main with a COP of 3.4. In addition, it was found that the 90°C heat pump, already installed on the case study site, would have the potential to increase utilization on the case study site if the two other heat pump opportunities identified were implemented. Thermal storage opportunities were also identified that can be used to buffer heat demands on the 70°C heat pump opportunity, thereby allowing the heat pump to be resized to 1.04 MW in comparison to the initially hypothesized 1.5 MW, reducing both capital and operational costs of the heat pump.
This amalgamated method provides novel Total Site Heat Integration additions, which when compared to conventional heat integration methods, provide more accurate and more useful heat pump decarbonization strategies for non-continuous industrial sites, ultimately aiding in industrial decarbonization.

year: 2024

title: Robust mathematical programming for natural resource modelling under parametric uncertainty

authors: Doole, Graeme J.

subjects: parameter uncertainty

abstract: Inaccurate specification of model coefficients can lead to false or distorted findings in modeling investigations of natural resource management. Hence, this paper outlines a decision framework for optimization problems in which only the bounded set of outcomes for uncertain parameters is known. These models can be solved with standard mathematical programming software and are no larger than their deterministic equivalent. The robust approach is contrasted against deterministic analysis and is demonstrated for two applications regarding the management of natural resources. Deterministic plans are infeasible in at least 40% of cases when parameters vary from their point estimates. Inclusion of robust constraints immunizes against this infeasibility, thereby removing errors arising from false certainty. Additionally, incorporation of bounded parameters in the objective function yields interval-valued sets containing potential outcomes. However, this increase in the general relevance of model output introduces some degree of suboptimality as deterministic plans are buffered to proactively account for potential variability. The cost of robustness increases with the simulated spread of uncertain coefficients but may be reduced through accounting for the uncertainty aversion of decision makers.

text: Robust mathematical programming for natural resource modelling under parametric uncertainty Inaccurate specification of model coefficients can lead to false or distorted findings in modeling investigations of natural resource management. Hence, this paper outlines a decision framework for optimization problems in which only the bounded set of outcomes for uncertain parameters is known. These models can be solved with standard mathematical programming software and are no larger than their deterministic equivalent. The robust approach is contrasted against deterministic analysis and is demonstrated for two applications regarding the management of natural resources. Deterministic plans are infeasible in at least 40% of cases when parameters vary from their point estimates. Inclusion of robust constraints immunizes against this infeasibility, thereby removing errors arising from false certainty. Additionally, incorporation of bounded parameters in the objective function yields interval-valued sets containing potential outcomes. However, this increase in the general relevance of model output introduces some degree of suboptimality as deterministic plans are buffered to proactively account for potential variability. The cost of robustness increases with the simulated spread of uncertain coefficients but may be reduced through accounting for the uncertainty aversion of decision makers.

year: 2010

title: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2014

authors: Hicks, Brendan J.

abstract: The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (eels, goldfish, and koura). In the current study, we present the findings from the eighth year of sampling (2014) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 642 fish (11.3 kg) 11 sites on 9 December 2014, which comprised 2,914 lineal m and 11,656 m² in area. Koura and 4 fish species were present, with common bully most abundant (up to 27 fish 100 m⁻² at the site 5, edge habitat). Goldfish (up to 5.92 g m⁻²) was the next most abundant species, and was most abundant in sites 8-11 the lower channel, especially at site 11, the excavated side channel. Rainbow trout were next the most abundant species (up to 0.25 fish 100 m⁻² ). Mean bully biomass (5.25 g m⁻²) was much higher than for smelt (0.07 g m⁻²). Koura had a patchy distribution; 5 individuals were caught.
Comparing catches over the 8 years of sampling, the abundance of common bullies in 2014 (4.81 fish 100 m⁻²) was consistent with catch rates in most post-wall years (after 2007; range 0.81-5.72 fish 100 m⁻²), but lower than in 2013. The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, suggesting that bully density estimates might decrease with decreasing BDD. However, common bully densities in 2012 and 2011 were inversely related BDD. In 2014, catches of smelt, a similar sized fish to bullies, were extremely low.
Goldfish biomass increased initially 2009 and 2010 because of targeted fishing in the excavated side channel (site 11), which has dense macrophyte beds that provide good habitat for goldfish. The continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers has occurred. Eels were scarce in the Ohau Channel and catches were very variable. Longfin eels were caught in most years, and in 2012 and 2013 shortfin eels were also caught, but in 2014 no eels were caught.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 7 years of post-wall data, and comparison of means and standard deviations suggest that the number of bullies has decreased.
An intriguing trend of decreasing rainbow trout densities with increasing BDD, which is a measure of both water clarity and phytoplankton abundance, has occurred following wall construction (Figure 3). The trend is opposite to the usual decline of catch rate by boat electrofishing with reduced water clarity. The explanation for this is not immediately clear, and could be increased avoidance of the electrofishing boat by trout in clearer water. It is also possible that reduced BDD indicates high algal productivity in Lake Rotorua, which in turn could increase trout abundance in the Ohau Channel. This remains to be tested

text: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2014 The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (eels, goldfish, and koura). In the current study, we present the findings from the eighth year of sampling (2014) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 642 fish (11.3 kg) 11 sites on 9 December 2014, which comprised 2,914 lineal m and 11,656 m² in area. Koura and 4 fish species were present, with common bully most abundant (up to 27 fish 100 m⁻² at the site 5, edge habitat). Goldfish (up to 5.92 g m⁻²) was the next most abundant species, and was most abundant in sites 8-11 the lower channel, especially at site 11, the excavated side channel. Rainbow trout were next the most abundant species (up to 0.25 fish 100 m⁻² ). Mean bully biomass (5.25 g m⁻²) was much higher than for smelt (0.07 g m⁻²). Koura had a patchy distribution; 5 individuals were caught.
Comparing catches over the 8 years of sampling, the abundance of common bullies in 2014 (4.81 fish 100 m⁻²) was consistent with catch rates in most post-wall years (after 2007; range 0.81-5.72 fish 100 m⁻²), but lower than in 2013. The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, suggesting that bully density estimates might decrease with decreasing BDD. However, common bully densities in 2012 and 2011 were inversely related BDD. In 2014, catches of smelt, a similar sized fish to bullies, were extremely low.
Goldfish biomass increased initially 2009 and 2010 because of targeted fishing in the excavated side channel (site 11), which has dense macrophyte beds that provide good habitat for goldfish. The continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers has occurred. Eels were scarce in the Ohau Channel and catches were very variable. Longfin eels were caught in most years, and in 2012 and 2013 shortfin eels were also caught, but in 2014 no eels were caught.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 7 years of post-wall data, and comparison of means and standard deviations suggest that the number of bullies has decreased.
An intriguing trend of decreasing rainbow trout densities with increasing BDD, which is a measure of both water clarity and phytoplankton abundance, has occurred following wall construction (Figure 3). The trend is opposite to the usual decline of catch rate by boat electrofishing with reduced water clarity. The explanation for this is not immediately clear, and could be increased avoidance of the electrofishing boat by trout in clearer water. It is also possible that reduced BDD indicates high algal productivity in Lake Rotorua, which in turn could increase trout abundance in the Ohau Channel. This remains to be tested

year: 2015