| 16531. |
- Markström, Pontus, 1980
(författare)
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Design, modelling and operation of a 100 kW chemical-looping combustor for solid fuels
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the increasing threat of global warming, technologies for efficient capture and storage of the greenhouse gas CO2 are sought after. Chemical-looping combustion is a novel CO2 capture technology that can be applied when burning gaseous, liquid or solid fuels. By using two interconnected fluidised beds with a bed material capable of transferring oxygen from air to the fuel, a nitrogen-undiluted stream of CO2 can be obtained with no direct efficiency loss. This thesis is focused on design, modelling and operation of a 100 kW chemical-looping combustor for solid fuels. The goal of the test rig is validation of chemical-looping combustion at a scale giving both high operational flexibility and semi industrial conditions.Two analytical models that can be applied to any chemical-looping combustor for solid fuels are presented. The first model finds the residence-time from batch-experiments. The second model estimates the gas conversion of a general fuel as a function of the oxygen carrier bed inventory. Furthermore, a cold-flow model of the 100 kW unit has been constructed. Details about the cold-flow model design and experimental results regarding fluidisation, slugging, residence-time and circulation are presented.The 100 kW unit has been operated for over 23 hours with an ilmenite oxygen carrier, using three different fuels. During this time, no instabilities in the bed inventories have been detected. Experiments aiming for optimal performance showed that gas conversion above 84% and CO2 capture over 99% are possible. A detailed analysis of the relation between the global solids circulation, the fuel reactor bed inventory and the gas conversion was conducted. The results revealed that the bed inventory in the fuel reactor had a strong impact on gas conversion, whereas little effect of overall circulation could be seen under the present conditions.
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| 16532. |
- Markström, Pontus, 1980
(författare)
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Modeling Aspects of Chemical-Looping Combustion for Solid Fuels
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chemical-looping combustion is a novel technology for combustion of fossil fuel. By using a circulating bed material to transfer oxygen to the fuel, a pure stream of carbon dioxide can be obtained from the flue gas, undiluted by nitrogen. The main advantage of this capture technology is that there is no direct efficiency loss in obtaining the CO2 in a separate stream.The work presented in this thesis is divided into two parts. The first part deals with the behaviour of a 10 kW chemical-looping combustor for solid fuels. This combustor is normally operated in continuous mode but has here been studied with addition of fuel batches. From analysis of gas leaving the air reactor, it was possible to determine the residence-time and residence-time distribution of particles in the fuel reactor. Knowing the solids inventory in the fuel reactor, the circulation mass flow could be directly correlated to measured operational data, i.e. pressure drop, temperature and gas flow in air reactor riser. Using results for carbon-capture efficiency and residence-time distribution, a model was developed which could determine a mass-based reaction-rate constant for char conversion. This reaction-rate constant could also be determined independently from the conversion rates of char during the batch tests. The results showed a good agreement between the two approaches, indicating that the model well describes the behaviour of the unit.The second part of this work presents the design and experimental evaluation of a cold-flow model system, built to simulate a 100 kW chemical-looping combustor for solid fuels. A theoretical background with details on design and calculations on the dynamic similarity is provided. The system has been operated for about 10 hours and shows no indication of imbalances in the bed inventories. Both the internal circulation in the fuel reactor and the circulation between air and fuel reactor could be varied in a large range with only minor impact on the solids inventories. Studies were made on the mass flows, mass fluxes and residence-times in the air and fuel reactors using air as fluidization medium.
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| 16533. |
- Markusson, Caroline S, 1976
(författare)
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Effektivisering av pump- och fläktdrifter i byggnader. Elanvändning och systemlösningar.
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this licentiate work the energy savings potential by more efficient pump and fan operation in buildings has been examined. The national savings potential in Sweden has been estimated based on available statistics and on information gained in a limited inventory. The estimated energy use for pump operation in residential and commercial (i.e. non-industrial) buildings in Sweden today is 2.2 TWh. If all pumps are replaced with the most efficient units available on the market today the savings potential is 1.5 TWh. The corresponding estimate of energy use for fan operation is 4.4 TWh. Replacement of all fans with the most energy efficient alternatives on the market would save 1.7 TWh. The development of electric motors and their control has led to small units being considerably better and cheaper. These small units can complement or replace traditional central units, which opens up for new system designs. Replacing the conventional large centralised unit with small decentralised units has been analysed theoretically and experimentally. For this purpose, two alternatives to the conventional temperature control of hydronic systems have been investigated. The alternatives are indirect flow control using valves and direct flow control using a pump. For ventilation applications, traditional VAV-systems are compared to a design that replaces the VAV-boxes with small decentralised fans. The focus in the analysis of the new system design is on the pressure drops that are introduced only for system control purposes. For decentralized designs, the largest energy savings appear at reduced capacity, i.e. at flows lower than the design flow. The savings potential is also dependent on the efficiency of the pump or fan. Efficiency measurements have been conducted on four pumps. Two of the pumps have maximum wire-to-water efficiencies exceeding 40 % and these high efficiencies are maintained over a wide operating range. The main factor to raise the efficiency is the use of permanent magnet motors.Measurements of the electricity use of a pump in a radiator system throughout a year were used as input for simulations of a radiator system. Two alternative flow control system designs were modelled; one system with flow control using a valve and one system with direct flow control using a pump. The results show that switching to direct flow control decreases the needed pump power to 5 % and the electric energy consumption to 0.5 % of the original values.
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| 16534. |
- Markusson, Caroline S, 1976
(författare)
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Efficiency of building related pump and fan operation - Application and system solutions
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electric energy use in Swedish non-industrial buildings is 71 TWh per year out of which 30 TWh per year is used for the operation of technical systems. A significant part of those 30 TWh/year is used for pump and fan operation. The Swedish parliament decided in 2009 on a national energy and climate plan. By the year 2050 the energy use per unit conditioned floor area in the Swedish building stock must be halved compared to the year of 1995. The objective of this thesis is to find means to reduce pump and fan energy in the non-industrial buildings. The aim is to find systems and components that can provide energy reduction in pump and fan systems by 50 %. In the thesis the current situation in non-industrial buildings regarding pump and fan systems has been described and the energy saving potentials, both at component and at system level, have been identified and discussed. Furthermore, the possibility of decentralized pump and fan systems has been examined. The calculated saving potential is 50 % and 40 % respectively for pump and fan operation in non-industrial buildings. This may be achieved by improving pump efficiency and specific fan power to state-of-the-art efficiency and recommended SFP values. System changes can also provide major additional energy savings in pump and fan operation. A decentralized pump heating system has been implemented in real life and results show a reduction of pump energy by 70 %. The theoretical parts of the thesis are supported by four case studies in real buildings and by three laboratory studies.
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| 16535. |
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| 16536. |
- Markusson, Henrik, 1976
(författare)
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New Electrolyte Materials for Lithium Batteries and Fuel Cells - an ab initio and vibrational spectroscopy study
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to reduce our fossil based energy consumption there is an urge for new energy storage and conversion devices such as lithium batteries and fuel cells for more efficient energy use. The heart of these devices is an ion conducting electrolyte which needs to provide high performance at low cost. This thesis focuses on new electrolyte materials; the first part concerns lithium salts with prospects to increase the performance and safety of lithium batteries, and the second part deals with protic ionic liquids (pILs), a new electrolyte material for low temperature fuel cells. By combining high accuracy quantum mechanical calculations with vibrational spectroscopy, an increased understanding of the properties of these new materials was obtained. This knowledge is important in the development of improved materials. Two promising types of binary lithium salts were investigated; lithium salts incorporating one (azole type) and two (orthoborate type) ring structures with pending electron drawing groups for charge delocalisation. The calculated lithium binding energies of both these types of salts are 10-15% lower than for the lithium salt used in batteries today. From the calculated and characterised salt structures new improved salts have been proposed for synthesis at collaborating laboratories, completing our feedback cycle. An oligomeric lithium salt with single ion conducting properties was investigated to pinpoint structural features limiting the lithium ion transport in these special systems. pILs are non-volatile low temperature melting salts with high proton conductivity, formed by proton transfer from an acid to a base, that can swell polymers even at elevated temperatures. pILs thus has the potential to replace both the role of water and the ionomer part in polymer electrolyte membranes and improve the fuel cell efficiency considerably. By calculating molecular level properties an increased understanding of important macroscopic properties for fuel cell performance such as melting temperature, fluidity and conductivity was obtained.
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| 16537. |
- Marmon, Oscar, 1980
(författare)
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Counting solutions to Diophantine equations
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents various results concerning the density of rational and integral points on algebraic varieties. These results are proven with methods from analytic number theory as well as algebraic geometry. Using exponential sums in several variables over finite fields, we prove upper bounds for the number of integral points of bounded height on an affine variety. More precisely, our method is a generalization of a technique due to Heath-Brown — a multi-dimensional version of van der Corput’s AB-process. It yields new estimates for complete intersections of r hypersurfaces of degree at least three in A n , as well as for hypersurfaces in A n of degree at least four. We also study the so called determinant method, introduced by Bombieri and Pila to count integral points on curves. We show how their approach may be extended to higher-dimensional varieties to yield an alternative proof of Heath-Brown’s Theorem 14, avoiding p-adic considerations. Moreover, we use the determinant method to study the number of representations of integers by diagonal forms in four variables. Heath-Brown recently developed a new variant of the determinant method, adapted to counting points near algebraic varieties. Extending his ideas, we prove new upper bounds for the number of representations of an integer by a diagonal form in four variables of degree k ≥ 8. Furthermore, we use a refined version of the determinant method for affine surfaces, due to Salberger, to derive new estimates for the number of representations of a positive integer as a sum of four k-th powers of positive integers, improving upon estimates by Wisdom.
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| 16538. |
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| 16539. |
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| 16540. |
- Marmon, Sofia, 1982
(författare)
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Protein isolation from herring (Clupea harengus) using the pH-shift process - Protein yield, protein isolate quality and removal of food contaminants
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Herring (Clupea harengus) contain valuable proteins but is difficult to process into high-quality foods due to its small size and high content of bones, heme-proteins and lipids. Herring is among the most abundant fish species in the world, but is currently utilized largely for fish meal and oil production.The work presented in this thesis has aimed at evaluating pH-shift processing as a method to isolate proteins from herring and thereby increase its potential as a food raw material. The pH-shift process solubilizes muscle proteins at low or high pH (pH ≤3 or ≥10.8) whereafter impurities can be removed and the solubilized purified proteins are precipitated near the isoelectric point (~pH 5.5). The focus has been the yield and quality of the proteins. Specific aims have been to investigate: i) possible differences between the acid and alkaline version of the pH-shift process, ii) the possibility to remove dioxins and PCBs, and iii) the effect of alkaline pH-shift processing on the microstructure, salt solubility and in vitro digestibility of the proteins.The acid and alkaline versions of the pH-shift process performed similarly when applied to gutted herring, with protein yields of 57-59%. The protein isolates had significantly higher protein concentration and less ash and lipids than the gutted herring, and also a significantly improved color and a well-balanced amino acid profile. The two process versions isolated proteins with similar ability to form a gel, but the acid process version induced proteolysis. Furthermore, the pH-shift process was highly efficient at removing dioxins and PCBs from contaminated Baltic herring, which was correlated to the removal of lipids. The microstructure analyses of the alkali-processed herring proteins revealed a loose protein network, with no remaining myofibrillar structure. The salt solubility of the proteins was significantly decreased after processing, and this was mainly due to exposure to low pH (5.5) during precipitation of the proteins. Precipitation at pH 6.5 was therefore evaluated and resulted in higher protein salt solubility, less lipid oxidation and higher gelation ability of the proteins compared to precipitation at pH 5.5. Despite the changes in protein salt solubility and microstructure, the in vitro digestibility of the alkali-processed proteins precipitated at pH 5.5 remained the same as that of the herring raw material.To conclude, pH-shift processing is a promising tool to isolate proteins from herring and other small pelagic fish species, resulting in high protein yield and an isolate with good gelation capacity, nutritional characteristics, and low content of lipophilic contaminants. Protein isolation using the pH-shift process therefore has the potential to enhance the value of small pelagic fish species and increase their use for human consumption.
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