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- Anheden, Marie
(författare)
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Analysis of gas turbine systems for sustainable energy conversion
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased energy demands and fear of global warming due tothe emission of greenhouse gases call for development of newefficient power generation systems with low or no carbondioxide(CO2) emissions. In this thesis, two different gasturbine power generation systems, which are designed with theseissues in mind, are theoretically investigated and analyzed.Inthe first gas turbine system, the fuel is combusted using ametal oxide as an oxidant instead of oxygen in the air. Thisprocess is known as Chemical Looping Combustion (CLC). CLC isclaimed to decrease combustion exergy destruction and increasethe power generation efficiency. Another advantage is thepossibility to separate CO2without a costly and energy demanding gasseparation process. The system analysis presented includescomputer-based simulations of CLC gas turbine systems withdifferent metal oxides as oxygen carriers and different fuels.An exergy analysis comparing the exergy destruction of the gasturbine system with CLC and conventional combustion is alsopresented. The results show that it is theoretically possibleto increase the power generation efficiency of a simple gasturbine system by introducing CLC. A combined gas/steam turbinecycle system with CLC is, however, estimated to reach a similarefficiency as the conventional combined cycle system. If thebenefit of easy and energy-efficient CO2separation is accounted for, a CLC combined cyclesystem has a potential to be favorable compared to a combinedcycle system with CO2separation.In the second investigation, a solid, CO2-neutral biomass fuel is used in a small-scaleexternally fired gas turbine system for cogeneration of powerand district heating. Both open and closed gas turbines withdifferent working fluids are simulated and analyzed regardingthermodynamic performance, equipment size, and economics. Theresults show that it is possible to reach high power generationefficiency and total (power-and-heat) efficiency with thesuggested system. The economic analysis reveals that the costof electricity from theEFGT plant is competitive with the moreconventional alternatives for biomass based cogeneration in thesame size range (<10 MWe).Keywords:power generation, Chemical Looping Combustion,CO2separation, oxygen carrier, biomass fuel, closedcycle gas turbine, externally fired gas turbine
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- Marques, Marcia
(författare)
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Solid waste and the water enviroment in the new European Union perspective
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Processes that occur during storageand final disposal ofsolid waste were studied, with emphasis on physical andchemical aspects and their effects on the water environment,within the New European Union perspective for landfilling(Council Directive 1999/31/EC, 1999).In the new scenario, landfilling is largely restricted;waste treatments such as incineration, composting, recycling,storage and transportation of materials are intensified.Landfill sites are seen as industrial facilities rather thanmerely final disposal sites. Four main issues were investigatedwithin this new scenario, infield- and full-scale, mostly atSpillepeng waste management park, southern Sweden.Adequacy of storage piles. Regarding the increasing demandfor waste storage as fuel, the adequacy of storage in piles wasinvestigated by monitoring industrial waste (IND) fuel pile andrefuse derived fuel (RDF) storage. Intense biodegradationactivity, which raised the temperature into the optimum rangefor chemical oxidation reactions, was noticed during the firstweeks. After about six months of storage, self-ignitionoccurred in one IND fuel pile and in the RDF storage. Heat, O2and CO2distribution at different depths of the monitoredINDpile suggested that natural convection plays an importantrole in the degradation process by supplying oxygen andreleasing heat. The results suggested that storage techniquesthat achieve a higher degree of compaction, such as baling, arepreferable to storage in piles.Discharge from landfill for special/hazardous waste.Regarding changes in the composition of the waste sent tolandfills and the consequences for its hydrological performancein active and capped landfills, discharge from a full-scalelandfill for special/hazardous waste (predominantly fly ashfrom municipal solid waste (MSW) incineration) was modelledusing the U.S. EPAHELP model. Hydraulic properties of thespecial waste were compared with those from MSW. Lowerpractical field capacity and higher hydraulic conductivity atspecial waste cells led to faster production of greater amountsof discharge (already during operation) in response toinfiltration, than that observed in MSW landfill cells. Thisfeature must be considered when designing on-site leachatetreatment systems for special waste landfills.Stormwater runoff and pollutant transport. Theintensification of waste handling practices exposed to rainfallat waste management parks in the new scenario led to aninvestigation of about 22 constituents of stormwater runoff andpollutant transport from different areas/activities and roadswithin the Spillepeng site. The concentration values for someparameters in some areas and roads exceeded the concentrationsfound in leachate from covered landfill. Concerning chemicaloxygen demand and nutrients, the stormwater from Spillepengshowed a higher range of median concentration values in thestormwater than is typical of ranges for roadways, andresidential and industrial areas in Sweden. The reverseoccurred for heavy metals, excluding copper.Groundwater monitoring programmes. In particular, theadequacy of groundwater monitoring programmes at landfillsites, was investigated. Significant differences between up-and down-gradient wells as well as trends not visualized bydirect inspection of time series data were detected withstatistical analyses. The non-parametric rank-sum test was morepowerful and robust than the t-test in detecting differencesbetween up- and down-gradient paired monitoring wells. Theseasonal Kendall test was more powerful than the Mann-Kendalltest to detect trends for individual constituents.Non-parametric slope estimators and the Winter's Method wereused to estimate the time needed to reach the EU mandatorylimits of nitrate and ammonia in potable water. However,indications of aquifer heterogeneity suggest that these trendsmay reflect local effects, rather than a real improvement in,or degradation of, the groundwater quality. Nevertheless, theinclusion of statistical procedures in landfill monitoringprogrammes is suggested, as an additional useful tool.Keywords: convective flow, groundwater pollution, leachatemodelling, non-parametric statistics, self-ignition, solidwaste, storage of fuel material, stormwater runoff, timeseries.
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- Thorin, Eva
(författare)
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Power cycles with ammonia-water mixtures as working fluid
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is of great interest to improve the efficiency of powergenerating processes, i.e. to convert more of the energy in theheat source to power. This is favorable from an environmentalpoint of view and can also be an economic advantage. To use anammonia-water mixture instead of water as working fluid is apossible way to improve the efficiency of steam turbineprocesses.This thesis includes studies of power cycles withammonia-water mixtures as working fluid utilizing differentkinds of heat sources for power and heat generation. Thethermophysical properties of the mixture are also studied. Theyplay an important role in the calculations of the processperformance and for the design of its components, such as heatexchangers. The studies concern thermodynamic simula-tions ofprocesses in applications suitable for Swedish conditions.Available correla-tions for the thermophysical properties arecompared and their influence on simula-tions and heat exchangerarea predictions is investigated. Measurements of ammonia-watermixture viscosities using a vibrating wire viscometer are alsodescribed.The studies performed show that power cycles withammonia-water mixtures as the working fluid are well suited forutilization of waste heat from industry and from gas engines.The ammonia-water power cycles can give up to 32 % more powerin the industrial waste heat application and up to 54 % morepower in the gas engine bottoming cycle application compared toa conventional Rankine steam cycle. However, ammonia-waterpower cycles in small direct-fired biomass-fueled cogene-rationplants do not show better performance than a conventionalRankine steam cycle.When different correlations for the thermodynamic propertiesare used in simulations of a simple ammonia-water power cyclethe difference in efficiency is not larger than 4 %,corresponding to about 1.3 percentage points. The differencesin saturation properties between the correlations are, however,considerable at high pressures, high temperatures and high massfractions of ammonia. The use of different correlations for thethermodynamic and transport properties causes a noticeabledifference in the predicted heat exchanger areas required fordifferent processes.Keywords:ammonia-water mixture, cogeneration,correlation, direct-fired power cycle, gas engine, Kalinacycle, power cycle, thermophysical properties, waste heat
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- Ågren, Niklas, 1967-
(författare)
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Advanced Gas Turbine Cycles with Water-Air Mixtures as Working Fluid
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the early 80's, the worldwide utilization of gas turbines for thermal power generation has increased rapidly. They have less pollution than any other major combustion energy converters. One important development trend in gas turbine technology is new processes for better flue gas heat recovery (gaining better efficiency, power density and environmental impact), so called advanced cycles. The purpose of this work has been to evaluate the performance and process system and subsystems of advanced gas turbine cycles with air/water mixture as working medium. The focus of the thesis is on the evaporative gas turbine cycle. This cycle has extraordinary heat recovery possibilities. An increased understanding of the interaction of the different process components is sought, with an emphasis on modeling the high pressure humidification column. Efforts have been made to synthesize innovative strategies for EvGT humidification. Theoretical and experimental work concerning the water recovery and purification issues are also presented.Some important results are that the flow of air through the humidifier should be optimized. For the different cases presented in this thesis, the optimal fraction (with regard to efficiency) varies from about 12% to 40% of the compressor inlet air. Savings in heat exchanger area and reduced pressure work for booster fan are advantages of using only a part of the compressor air in the humidifier. For obtaining best efficiency of the evaporative cycle, the heat flows above the boiling point should preferably be taken care of by conventional boilers for steam injection or by a separate humidifier section working only slightly below boiling temperature. This is particularly important in gas turbines without intercooling or without recuperation due to high temperatures in exit streams. The unique nature of the humidifier is its ability to evaporate water below the boiling point, by the use of air dilution. However, the best temperature performance (lowest temperature of outlet water from humidifier) is reached if the thermal loading on the humidifier is not excessive.The need for large quantities of demineralized water has previously been identified as a possible drawback for the EvGT cycle. In favor of the EvGT-technology, the first water testing experiments on a pilot EvGT-plant, presented in this work, contradict this notion. It is theoretically and experimentally shown that an EvGT-plant can be run with no external water feed at all, by means off lue gas condensation and condensate recovery. After internal condensate treatment, the recycled condensate was of equal quality or better than the deionized fresh feed used for initial system fill-up.
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