| 11. |
- Rezk, Kamal, 1983-
(författare)
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Methods for Reducing the Complexity of Geometrical Structures Based on CFD Programming : Time Efficient Simulations Based on Volume Forces Coupled with Single and Two-phase Flow
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Throughout recent years, computer based programs have been applied to solve and analyse industrial problems encountered global fields such as automobile design for reduction of CO2-gas, designing wind parks aimed at increasing power output etc. One of these developed programs is Computational Fluid Dynamics (CFD) which numerically solves complex flow behaviour based on computer power.As there is an ongoing expansion of CFD usage in industry, certain issues need to be addressed as they are becoming more frequently encountered. The general demand for the simulation of larger control volumes and more advanced flow processes result in an extensive requirement of computer resources. Moreover, the implementation of commercial CFD codes in small-scaled industrial companies seems to generally be utilised as a black box based on the knowledge of fluid mechanic theory. Increased partnerships between industry and the academic world involving various CFD based design processes generally yield to a verbal communication interface, which is a crucial step in the process given the level of dependency between both sides.Based on these notions, a method for establishing time efficient CFD-models with implementation of volume forces as sink terms in the momentum equation is presented. The internal structure, or parts of the structure, in the simulation domain is removed which reduces the geometrical complexity and along with it, computational demand. These models are the basis of assessing the benefits of utilizing a numerical based design process in industry in which the CFD code is used as a communication tool for knowledge sharing with counterparts in different fields.
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| 12. |
- Shabani, Masoume
(författare)
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Techno-economic viability of battery storage for residential applications
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Battery storage has emerged as a promising solution in various energy systems. However, challenges exist regarding the viability of batteries in practical stationary applications. Factors such as the capital and operational costs, relatively short lifetime, and battery degradation are among crucial factors which have significant impact on battery profitability. To make batteries more viable technology, effective battery management is a necessity. However, there are multiple critical factors which need to be addressed for effective battery utilization and management in real-life applications under dynamic operational conditions.In this thesis, different battery modelling approaches within battery operational management are proposed. Each proposed scenario consists of a set of specific methods for the estimation of battery performance, capacity degradation, remaining useful life, state-of-charge, state-of-health, and state-of- power.Moreover, the study explores strategies for efficient battery utilization to maximize sustained profitability. Accordingly, the study deals with 32 different state-of-charge operating control strategies as well as different charge/discharge rates (low, moderate, high) to evaluate their impact on techno-economic profitability of a battery system in a grid-connected residential application. Moreover, two day-ahead and optimization-based operation scheduling strategies to maximize battery profitability are proposed. Each scenario employs unique approaches to make optimal decisions for optimal battery utilization. The first scenario aims to optimize short-term profitability by prioritizing revenue gains. Conversely, the second scenario proposes a smart strategy capable of making intelligent decisions on a wide range of decision-variables to simultaneously maximize daily revenue and minimize daily degradation costs.The key findings reveal that overlooking or simplifying assumptions about multiple critical aspects of battery behavior led to an improper battery management system in practical applications under dynamic operational conditions. Selecting a proper state-of-charge control strategy positively affects the profitability in which alteration of the allowable SOC window from (40%–90%) to (10%–60%) increase the battery lifetime from 10.2 years to 14 years leading to 31.6% improvement in net present value. The key findings showcase how a smart battery scheduling strategy that strike optimal balance between revenue and degradation achieves impressive profit (18-20 €/kWh/year), short payback (7.5 years), and extended lifespan (12.5 years), contrasting revenue-focused scenarios, ensuring sustained profitability for battery owners in residential applications. The findings offer valuable insights for decision-makers, enabling informed strategic choices and profitable solutions.
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| 13. |
- Udomsri, Seksan
(författare)
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Combined Electricity Production and Thermally Driven Cooling from Municipal Solid Waste
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasingly intensive efforts are being made to enhance energy systems via augmented introduction of renewable energy along with improved energy efficiency. Resource constraints and sustained high fossil fuel prices have created a new phenomenon in the world market. Enhanced energy security and renewable energy development are currently high on public agenda worldwide for achieving a high standard of welfare for future generations. Biomass and municipal solid waste (MSW) have widely been accepted as important locally-available renewable energy sources offering low carbon dioxide (CO2) emissions. Concerning solid waste management, it has become a critical issue in Southeast Asia since the most popular form for waste disposal still employs open dumping and landfilling. While the need for a complete sustainable energy solution is apparent, solid waste management is also an essential objective, so it makes sense to explore ways in which the two can be joined. Electricity production in combination with energy recovery from flue gases in thermal treatment plants is an integral part of MSW management for many industrialized nations. In Sweden, MSW is considered as an important fuel resource for partially meeting EU environmental targets within cogeneration. However it is normally difficult to justify traditional cogeneration in tropical locations since there is little need for the heat produced. Similarly, MSW-fired cogeneration usually operates with low capacity during non-heating season in Sweden. Therefore, it is very important to find new alternatives for energy applications from waste, such as the implementation of thermally driven cooling processes via absorption cooling in addition to electricity production. The work presented herein concentrates first on an investigation of electricity generation from MSW power plants and various energy applications from waste in tropical urban areas. The potential for various types of absorption chillers driven by MSW power plants for providing both electricity and cooling is of particular interest. Additionally a demonstration and analysis of decentralized thermally driven cooling in district heating network supplied by low temperature heat from a cogeneration of MSW have been conducted. This study aims at developing the best system configuration as well as finding improved system design and control for a combination of district heating and distributed thermally driven cooling. Results show that MSW incineration has the ability to lessen environmental impacts associated with waste disposal, and it can contribute positively towards expanding biomass-based energy production in Southeast Asia. For electricity production, the proposed hybrid dual-fuel (MSW/natural gas) cycles feature attractive electrical efficiency improvements, leading to greenhouse gas emissions reduction. Cogeneration coupled with thermally driven cooling is a solution that holds promise for uniting enhanced sustainability with economic advantages. The system offers great opportunity for primary energy saving, increasing electrical yield and can significantly reduce CO2 emissions per unit of cooling as compared to compression chiller. The demonstration and simulation have also revealed that there is a potential with some modifications and improvements to employ decentralized thermally driven cooling in district heating networks even in temperate regions like Sweden. Thus, expanding cogeneration towards trigeneration can augment the energy supply for summer months in Europe and for year-round cooling in tropical locations.
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| 14. |
- Win, Kaung Myat
(författare)
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Emissions from realistic operation of residential wood pellets heating systems
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emissions from residential combustion appliances vary significantly depending on the firing behaviours and combustion conditions, in addition to combustion technologies and fuel quality. Although wood pellet combustion in residential heating boilers is efficient, the combustion conditions during start-up and stop phases are not optimal and produce significantly high emissions such as carbon monoxide and hydrocarbon from incomplete combustion. The emissions from the start-up and stop phases of the pellet boilers are not fully taken into account in test methods for ecolabels which primarily focus on emissions during operation on full load and part load. The objective of the thesis is to investigate the emission characteristics during realistic operation of residential wood pellet boilers in order to identify when the major part of the annual emissions occur. Emissions from four residential wood pellet boilers were measured and characterized for three operating phases (start-up, steady and stop). Emissions from realistic operation of combined solar and wood pellet heating systems was continuously measured to investigate the influence of start-up and stop phases on total annual emissions. Measured emission data from the pellet devices were used to build an emission model to predict the annual emission factors from the dynamic operation of the heating system using the simulation software TRNSYS. Start-up emissions are found to vary with ignition type, supply of air and fuel, and time to complete the phase. Stop emissions are influenced by fan operation characteristics and the cleaning routine. Start-up and stop phases under realistic operation conditions contribute 80 – 95% of annual carbon monoxide (CO) emission, 60 – 90% total hydrocarbon (TOC), 10 – 20% of nitrogen oxides (NO), and 30 – 40% particles emissions. Annual emission factors from realistic operation of tested residential heating system with a top fed wood pelt boiler can be between 190 and 400 mg/MJ for the CO emissions, between 60 and 95 mg/MJ for the NO, between 6 and 25 mg/MJ for the TOC, between 30 and 116 mg/MJ for the particulate matter and between 2x1013 and 4x1013 /MJ for the number of particles. If the boiler has the cleaning sequence with compressed air such as in boiler B2, annual CO emission factor can be up to 550 mg/MJ. Average CO, TOC and particles emissions under realistic annual condition were greater than the limits values of two eco labels. These results highlight the importance of start-up and stop phases in annual emission factors (especially CO and TOC). Since a large or dominating part of the annual emissions in real operation arise from the start-up and stop sequences, test methods required by the ecolabels should take these emissions into account. In this way it will encourage the boiler manufacturers to minimize annual emissions. The annual emissions of residential pellet heating system can be reduced by optimizing the number of start-ups of the pellet boiler. It is possible to reduce up to 85% of the number of start-ups by optimizing the system design and its controller such as switching of the boiler pump after it stops, using two temperature sensors for boiler ON/OFF control, optimizing of the positions of the connections to the storage tank, increasing the mixing valve temperature in the boiler circuit and decreasing the pump flow rate. For 85 % reduction of start-ups, 75 % of CO and TOC emission factors were reduced while 13% increase in NO and 15 % increase in particle emissions was observed.
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| 15. |
- Zimmerman, Nathan, 1983-
(författare)
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Modelling Towards Control of Dynamic Systems : Applications on RDF Fired CFB Performance and DHN Distribution
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The combination of global warming along with increasing energy demand necessitates the importance of improving processes pertaining to the production and consumption of energy in combined heat and power plants. This thesis brings to light transient factors currently burdening process performance for circulating fluidized bed boilers (CFBs) combusting refuse derived fuels (RDFs) and district heating networks (DHN). These two domains are not completely disconnected from one another, which is the case for Northern European countries. Heat can be generated from a central location to be distributed through a network of customers to meet a heating demand. Results show that first-principle modelling techniques have the capacity to capture transients factors associated within the aforementioned entwined energy systems.On the production side, obtaining real-time information pertaining to the lower heating value of refuse derived fuel affords the ability to implement feed-forward model predictive control. Therefore, feed-forward model predictive control has the potential to minimize combustion temperature swings by making the necessary controls moves before changes in the fuel’s composition are actualized by the process. On the consumption side, attaining a deeper understanding of district heating network dynamics, e.g. heat propagation, network losses, distribution delays, and end-user requirements, introduces the possibility to analyse network performance and reduce peak load production. The perspective of quick network performance can be achieved by an automated approach to building and simulating district heating networks. Nonconventional end-user heating configurations, e.g. homes utilizing district heating and a heat pump, has the potential of illustrating how heating consumption patterns may change over time. Peak load reduction is achievable in district heating networks when it is possible to reduce network supply temperature. This can be achieved by predicting end-user heating requirements and using this information for feed-forward model predictive control.The overall observations made in this thesis demonstrates that process improvements are obtainable for transient energy systems. Despite the presented work focusing on only one type of energy production and one type of consumption, the approach described unlocks a flexibility that eliminates the need for unambiguous modelling and simulations by allowing for the reusability of model components. The exportability of these models further distinguishes them, as they can be used to test new control approaches within an energy system as real-time predictions within each energy sub-system become more accessible.
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| 16. |
- Ahlgren, Fredrik, 1980-
(författare)
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Reducing ships' fuel consumption and emissions by learning from data
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the context of reducing both greenhouse gases and hazardous emissions, the shipping sector faces a major challenge as it is currently responsible for 11% of the transport sector’s anthropogenic greenhouse gas emissions. Even as emissions reductions are needed, the demand for the transport sector rises exponentially every year. This thesis aims to investigate the potential to use ships’ existing internal energy systems more efficiently. The thesis focusses on making existing ships in real operating conditions more efficient based logged machinery data. This dissertation presents results that can make ship more energy efficient by utilising waste heat recovery and machine learning tools. A significant part of this thesis is based on data from a cruise ship in the Baltic Sea, and an extensive analysis of the ship’s internal energy system was made from over a year’s worth of data. The analysis included an exergy analysis, which also considers the usability of each energy flow. In three studies, the feasibility of using the waste heat from the engines was investigated, and the results indicate that significant measures can be undertaken with organic Rankine cycle devices. The organic Rankine cycle was simulated with data from the ship operations and optimised for off-design conditions, both regarding system design and organic fluid selection. The analysis demonstrates that there are considerable differences between the real operation of a ship and what it was initially designed for. In addition, a large two-stroke marine diesel was integrated into a simulation with an organic Rankine cycle, resulting in an energy efficiency improvement of 5%. This thesis also presents new methods of employing machine learning to predict energy consumption. Machine learning algorithms are readily available and free to use, and by using only a small subset of data points from the engines and existing fuel flow meters, the fuel consumption could be predicted with good accuracy. These results demonstrate a potential to improve operational efficiency without installing additional fuel meters. The thesis presents results concerning how data from ships can be used to further analyse and improve their efficiency, by using both add-on technologies for waste heat recovery and machine learning applications.
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| 17. |
- Campillo, Javier, 1982-
(författare)
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From Passive to Active Electric Distribution Networks
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large penetration of distributed generation from variable renewable energy sources, increased consumption flexibility on the demand side and the electrification of transportation pose great challenges to existing and future electric distribution networks. This thesis studies the roles of several actors involved in electric distribution systems through electricity consumption data analysis and simulation models. Results show that real-time electricity pricing adoption in the residential sector offers economic benefits for end consumers. This occurs even without the adoption of demand-side management strategies, while real-time pricing also brings new opportunities for increasing consumption flexibility. This flexibility will play a critical role in the electrification of transportation, where scheduled charging will be required to allow large penetration of EVs without compromising the network's reliability and to minimize upgrades on the existing grid. All these issues add significant complexity to the existing infrastructure and conventional passive components are no longer sufficient to guarantee safe and reliable network operation. Active distribution networks are therefore required, and consequently robust and flexible modelling and simulation computational tools are needed for their optimal design and control. The modelling approach presented in this thesis offers a viable solution by using an equation-based object-oriented language that allows developing open source network component models that can be shared and used unambiguously across different simulation environments.
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| 18. |
- Foskolos, Georgios, 1976-
(författare)
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Current harmonic modeling of aggregated electric vehicle loads in the low voltage grid
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The proliferation of Electric Vehicles (EVs) poses new challenges for the Distribution System Operator (DSO). For example, the rectifiers that are used for charging EV batteries could significantly influence Power Quality (PQ), in terms of harmonic distortion. The emissions from individual EV, are well regulated by current harmonic emission standards. But what the aggregation of multiple EV loads will look like is still uncertain and the research being made in this area is still in its early stage. The DSO responsibilities include ensuring grid code compliance confirmed by PQ metering. In general, 10 minute RMS values are sufficient. However, the large scale integration of non-linear loads, like EVs, could lead to new dynamic phenomena, possibly lost in the process of time aggregation.In this thesis PQ and, in more detail, the concept of harmonics, and how this is related to EVs, is presented. A current-harmonic load model using power exponential functions and built from actual measurement data during the individual charging of four different fully electric vehicles was constructed. The model was based on individual emitted current harmonics as a function of state of charge (SOC), and was used to deterministically simulate the simultaneous charging of six vehicles fed from the same bus. The aggregation of current harmonics up to the 11th was simulated while randomizing battery SOC, the start of charging, and the kind of vehicle. Additionally, an investigation of the impact on aggregation in time was conducted.The analysis clearly shows the importance of phase angle information, its correlation to SOC, and how the aggregation of EV loads is influenced by these factors. The analysis also shows that 10 minute RMS aggregation could lead to significant deviations from the “actual” (200ms) data. This indicates that 10 minute value monitoring could lead to information losses.
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| 19. |
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| 20. |
- Hu, Yukun
(författare)
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CO2 capture from oxy-fuel combustion power plants
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To mitigate the global greenhouse gases (GHGs) emissions, carbon dioxide (CO2) capture and storage (CCS) has the potential to play a significant role for reaching mitigation target. Oxy-fuel combustion is a promising technology for CO2 capture in power plants. Advantages compared to CCS with the conventional combustion technology are: high combustion efficiency, flue gas volume reduction, low fuel consumption, near zero CO2 emission, and less nitrogen oxides (NOx) formation can be reached simultaneously by using the oxy-fuel combustion technology. However, knowledge gaps relating to large scale coal based and natural gas based power plants with CO2 capture still exist, such as combustors and boilers operating at higher temperatures and design of CO2 turbines and compressors. To apply the oxy-fuel combustion technology on power plants, much work is focused on the fundamental and feasibility study regarding combustion characterization, process and system analysis, and economic evaluation etc. Further studies from system perspective point of view are highlighted, such as the impact of operating conditions on system performance and on advanced cycle integrated with oxy-fuel combustion for CO2 capture. In this thesis, the characterization for flue gas recycle (FGR) was theoretically derived based on mass balance of combustion reactions, and system modeling was conducted by using a process simulator, Aspen Plus. Important parameters such as FGR rate and ratio, flue gas composition, and electrical efficiency etc. were analyzed and discussed based on different operational conditions. An advanced evaporative gas turbine (EvGT) cycle with oxy-fuel combustion for CO2 capture was also studied. Based on economic indicators such as specific investment cost (SIC), cost of electricity (COE), and cost of CO2avoidance (COA), economic performance was evaluated and compared among various system configurations. The system configurations include an EvGT cycle power plant without CO2 capture, an EvGT cycle power plant with chemical absorption for CO2 capture, and a combined cycle power plant. The study shows that FGR ratio is of importance, which has impact not only on heat transfer but also on mass transfer in the oxy-coal combustion process. Significant reduction in the amount of flue gas can be achieved due to the flue gas recycling, particularly for the system with more prior upstream recycle options. Although the recycle options have almost no effect on FGR ratio, flue gas flow rate, and system electrical efficiency, FGR options have significant effects on flue gas compositions, especially the concentrations of CO2 and H2O, and heat exchanger duties. In addition, oxygen purity and water/gas ratio, respectively, have an optimum value for an EvGT cycle power plant with oxy-fuel combustion. Oxygen purity of 97 mol% and water/gas ratio of 0.133 can be considered as the optimum values for the studied system. For optional operating conditions of flue gas recycling, the exhaust gas recycled after condensing (dry recycle) results in about 5 percentage points higher electrical efficiency and about 45 % more cooling water consumption comparing with the exhaust gas recycled before condensing (wet recycle). The direct costs of EvGT cycle with oxy-fuel combustion are a little higher than the direct costs of EvGT cycle with chemical absorption. However, as plant size is larger than 60 MW, even though the EvGT cycle with oxy-fuel combustion has a higher COE than the EvGT cycle with chemical absorption, the EvGT cycle with oxy-fuel combustion has a lower COA. Further, compared with others studies of natural gas combined cycle (NGCC), the EvGT system has a lower COE and COA than the NGCC system no matter which CO2 capture technology is integrated.
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