The world demand for electrical power increasescontinuously, requiring efficient and low-cost methods forpower generation. This thesis investigates two advanced powercycles with mixtures as the working fluid: the Kalina cycle,alternatively called the ammonia-water cycle, and theevaporative gas turbine cycle. These cycles have the potentialof improved performance regarding electrical efficiency,specific power output, specific investment cost and cost ofelectricity compared with the conventional technology, sincethe mixture working fluids enable efficient energyrecovery. This thesis shows that the ammonia-water cycle has a betterthermodynamic performance than the steam Rankine cycle as abottoming process for natural gas-fired gas and gas-dieselengines, since the majority of the ammonia-water cycleconfigurations investigated generated more power than steamcycles. The best ammonia-water cycle produced approximately40-50 % more power than a single-pressure steam cycle and 20-24% more power than a dual-pressure steam cycle. The investmentcost for an ammonia-water bottoming cycle is probably higherthan for a steam cycle; however, the specific investment costmay be lower due to the higher power output. A comparison between combined cycles with ammonia-waterbottoming processes and evaporative gas turbine cycles showedthat the ammonia-water cycle could recover the exhaust gasenergy of a high pressure ratio gas turbine more efficientlythan a part-flow evaporative gas turbine cycle. For a mediumpressure ratio gas turbine, the situation was the opposite,except when a complex ammonia-water cycle configuration withreheat was used. An exergy analysis showed that evaporativecycles with part-flow humidification could recover energy asefficiently as, or more efficiently than, full-flow cycles. Aneconomic analysis confirmed that the specific investment costfor part-flow cycles was lower than for full-flow cycles, sincepart-flow humidification reduces the heat exchanger area andhumidification tower volume. In addition, the part-flow cycleshad lower or similar costs of electricity compared with thefull-flow cycles. Compared with combined cycles, the part-flowevaporative cycles had significantly lower total and specificinvestment costs and lower or almost equal costs ofelectricity; thus, part-flow evaporative cycles could competewith the combined cycle for mid-size power generation. <b>Keywords:</b>power cycle, mixture working fluid, Kalinacycle, ammonia-water mixture, reciprocating internal combustionengine, bottoming cycle, gas turbine, evaporative gas turbine,air-water mixture, exergy

An investigation of binary fluid heat and mass transfer in ammonia-water absorption was conducted. Experiments were conducted on a horizontal-tube falling-film absorber consisting of four columns of six 9.5 mm (3/8 in) nominal OD, 0.292 m (11.5 in) long tubes, installed in an absorption heat pump. Measurements were recorded at both system and local levels within the absorber for a wide range of operating conditions (nominally, desorber solution outlet concentrations of 5 - 40% for three nominal absorber pressures of 150, 345 and 500 kPa, for solution flow rates of 0.019 - 0.034 kg/s.). Local measurements were supplemented by high-speed, high-resolution visualization of the flow over the tube banks. Using the measurements and observations from videos, heat and mass transfer rates, heat and vapor mass transfer coefficients for each test condition were determined at the component and local levels. For the range of experiments conducted, the overall film heat transfer coefficient varied from 923 to 2857 W/m²-K while the vapor and liquid mass transfer coefficients varied from 0.0026 to 0.25 m/s and from 5.51×10^-6 to 3.31×10^-5 m/s, respectively. Local measurements and insights from the video frames were used to obtain the contributions of falling-film and droplet modes to the total absorption rates. The local heat transfer coefficients varied from 78 to 6116 W/m²-K, while the local vapor and liquid mass transfer coefficients varied from -0.04 to 2.8 m/s and from -3.59×10^-5 (indicating local desorption in some cases) to 8.96×10^-5 m/s, respectively. The heat transfer coefficient was found to increase with solution Reynolds number, while the mass transfer coefficient was found to be primarily determined by the vapor and solution properties. Based on the observed trends, correlations were developed to predict heat and mass transfer coefficients valid for the range of experimental conditions tested. These correlations can be used to design horizontal tube falling-film absorbers for ammonia-water absorption systems.

<p>The world demand for electrical power increasescontinuously, requiring efficient and low-cost methods forpower generation. This thesis investigates two advanced powercycles with mixtures as the working fluid: the Kalina cycle,alternatively called the ammonia-water cycle, and theevaporative gas turbine cycle. These cycles have the potentialof improved performance regarding electrical efficiency,specific power output, specific investment cost and cost ofelectricity compared with the conventional technology, sincethe mixture working fluids enable efficient energyrecovery.</p><p>This thesis shows that the ammonia-water cycle has a betterthermodynamic performance than the steam Rankine cycle as abottoming process for natural gas-fired gas and gas-dieselengines, since the majority of the ammonia-water cycleconfigurations investigated generated more power than steamcycles. The best ammonia-water cycle produced approximately40-50 % more power than a single-pressure steam cycle and 20-24% more power than a dual-pressure steam cycle. The investmentcost for an ammonia-water bottoming cycle is probably higherthan for a steam cycle; however, the specific investment costmay be lower due to the higher power output.</p><p>A comparison between combined cycles with ammonia-waterbottoming processes and evaporative gas turbine cycles showedthat the ammonia-water cycle could recover the exhaust gasenergy of a high pressure ratio gas turbine more efficientlythan a part-flow evaporative gas turbine cycle. For a mediumpressure ratio gas turbine, the situation was the opposite,except when a complex ammonia-water cycle configuration withreheat was used. An exergy analysis showed that evaporativecycles with part-flow humidification could recover energy asefficiently as, or more efficiently than, full-flow cycles. Aneconomic analysis confirmed that the specific investment costfor part-flow cycles was lower than for full-flow cycles, sincepart-flow humidification reduces the heat exchanger area andhumidification tower volume. In addition, the part-flow cycleshad lower or similar costs of electricity compared with thefull-flow cycles. Compared with combined cycles, the part-flowevaporative cycles had significantly lower total and specificinvestment costs and lower or almost equal costs ofelectricity; thus, part-flow evaporative cycles could competewith the combined cycle for mid-size power generation.</p><p><b>Keywords:</b>power cycle, mixture working fluid, Kalinacycle, ammonia-water mixture, reciprocating internal combustionengine, bottoming cycle, gas turbine, evaporative gas turbine,air-water mixture, exergy</p>

Les machines frigorifiques à absorption ammoniac-eau sont prometteuses dans les domaines de la climatisation solaire et de la valorisation des rejets thermiques pour l’industrie. Pour permettre à ces machines de devenir compétitives par rapport aux systèmes à compression mécanique de vapeur, l’amélioration de leur efficacité et la baisse de leur coût sont nécessaires. C’est dans ce contexte que s’inscrit ce travail de thèse.L’étude se concentre sur l’absorbeur qui est un des composants les plus critiques de la machine à absorption en matière de taille, de coût et d’efficacité. L’objectif est d’étudier numériquement et expérimentalement les transferts couplés de masse et de chaleur dans l’absorbeur dans le but de prédire et d’améliorer ses performances.Deux absorbeurs à film tombant sont étudiés, dans lesquels la solution pauvre et la vapeur entrent en haut et le fluide caloporteur entre en bas. Le premier est un échangeur à plaques soudées et le deuxième est un échangeur à plaques et joints avec des dimensions et des profils de plaques différents.L’analyse expérimentale de ces deux absorbeurs est réalisée dans des conditions réelles de fonctionnement sur un prototype instrumenté de machine à absorption ammoniac-eau de 5 kW. Ce dispositif permet une analyse globale des débits de vapeur absorbés, des flux thermiques évacués et des efficacités d’absorption. Une analyse plus locale est aussi réalisée à l’aide de mesures de températures à l’intérieur des canaux de refroidissement dans l’absorbeur plaques et joints. Les résultats montrent une importante corrélation entre la puissance frigorifique produite par la machine à absorption et les performances de l’absorbeur. Mais ce prototype étant une machine réelle, les variables d’entrée de l’absorbeur ne peuvent pas être contrôlées. Un modèle numérique est donc nécessaire pour dissocier l’impact des différentes variables sur les performances de l’absorbeur.Un modèle 1D d’un absorbeur à film tombant est donc développé. Il est basé sur des bilans de masses, d’espèces et d’énergies, des équations de transferts de masse et de chaleur et des conditions d’équilibre à l’interface liquide-vapeur. Les résistances aux transferts de masse sont considérées dans les phases liquide et vapeur et des corrélations empiriques sont utilisées pour calculer les coefficients de transfert de masse et de chaleur.Ce modèle est validé expérimentalement avec les données globales aux bornes des deux absorbeurs et avec les mesures de températures le long des canaux du fluide de refroidissement puisqu’une différence maximale de 15% est observée. Il permet donc l’analyse détaillée des phénomènes de transferts de masse et de chaleur le long de l’absorbeur et facilite l’étude du procédé d’absorption.Enfin, une étude de sensibilité paramétrique est réalisée avec ce modèle pour discuter des résultats expérimentaux et pour identifier les pistes d’amélioration des performances de l’absorbeur et donc de la machine à absorption. / Ammonia-water absorption chillers are promising both for solar air conditioning and for industry processes. To become competitive compared to electric compression chillers, their efficiency needs to be improved and their cost has to be decreased. This thesis study takes place in this context.The focus is put on the absorber, which is one of the most critical component of absorption chillers in terms of compactness, cost and efficiency. The purpose is to study numerically and experimentally coupled heat and mass transfers which occur in the absorber in order to predict and improve its overall performances.Two falling film absorbers are analysed. In both of them, the poor solution and the vapour enter at the top and the coolant fluid enters at the bottom of the absorber. The first absorber is a brazed plate heat exchanger and the second is a gasketed plate-and-frame heat exchanger with different geometric dimensions and plates corrugations.The experimental study of these two absorbers is performed in real working conditions on an instrumented ammonia-water absorption chiller prototype of 5 KW. Thanks to this device, a global analysis of vapour absorbed mass flow rates, absorbed heat fluxes and mass effectiveness is achieved. A local analysis is also performed thanks to temperature measures inside channels of coolant fluid in the gasketed plate-and-frame heat exchanger. Results show a strong correlation between the absorption chiller cooling capacity and the absorber performances. However, since this prototype is a real chiller, absorber inlet variables cannot be controlled. Thus, a numerical model is necessary to dissociate the impact of these variables on the absorber performances.A 1D numerical model of the absorber is developed. It is based on mass, species and enthalpy balances, mass and heat transfer equations and equilibrium conditions at the vapour/solution interface. Mass transfer resistances in both liquid and vapour phases are considered while heat and mass transfer coefficients are calculated using empirical correlations.This model is validated experimentally with global data at the inlet and the outlet of the absorber and temperature measures along the absorber coolant fluid channels. A maximal relative error of 15 % is observed. Therefore, a detailed analysis of combined heat and mass transfers along the absorber and the absorption process study is performed thanks to this model.A parametric study is also performed with this model to discuss experimental results and find ways to improve the absorber performances and thus the absorption chiller performances.

<p>Detta är ett examensarbete som genomförts hos Göteborg Energi AB och syftar till att utreda omkryogen uppgradering av biogas med fördel kan ske genom att producera nödvändig kyla medvärmedriven absorptionskylmaskin. Göteborg Energi är en av tre parter som tillsammans ska bygga enbiogasanläggning i Lidköping som ska vara i drift 2010. Anläggningen ska producera 30 GWhflytande biogas per år.</p><p>Arbetet utreder om det är fördelaktigt ur ekonomiskt, energimässigt och miljömässigt perspektiv attuppgradera biogas med kryogen teknik med värmeproducerad kyla. En jämförelse görs först medkryogen teknik där kylan är producerad med el och sen med andra uppgraderingstekniker. Som stödhar två olika processimuleringsprogram används, Hysys och DESIGN II.</p><p>Resultatet visar att energianvändningen ökar då värmedriven kyla används i jämförelse med kylaproducerad med el. 0,47 kW/Nm3 rågas för kryo med absorptionskyla och 0,29 kW/Nm3 rågas medel. Om det finns avsättning för spillvärmen kan energianvändningen i uppgraderingen minska till 0,29kW/Nm3 rågas och 0,15 kW/Nm3 rågas för systemet med värmedriven respektive eldriven kyla. Ijämförelse med andra uppgraderingstekniker ligger 0,47 kW/Nm3 bland de teknikerna med högstenergianvändning medans 0,29 kW/Nm3 placerar sig bland de teknikerna med lägstenergianvändning.</p><p>Resultat visar att klimatpåverkan från uppgraderingen, som kommer av metanslip och elanvändningen,minskar marginellt om kylan produceras med värme istället för el. Resultatet varierar mycket beroendepå hur koldioxidutsläppen från marginalelen beräknas. I jämförelse med andra uppgraderingsteknikerligger kryo lägre än de flesta andra. Undantaget är COOAB-tekniken som är överlägset bäst tack varalågt metanslip och liten elanvändning.</p><p>Ekonomisk jämförelse med andra uppgraderingstekniker visar att kostnaden för energianvändningenligger i samma nivå som övriga uppgraderingstekniker i jämförelsen, ca 0,03 kr/kWh uppgraderad gas.Om det finns avsättning för spillvärmen sjunker kostnaden till 0,024 och 0,02 kr/kWh uppgraderad gasför kryoteknik med kyla ifrån värme respektive el.</p><p>Min slutsats är att utnyttjande av spillvärmen är av stor vikt för att få god ekonomi och lågenergianvändning med kryogen uppgradering. En marginellt förbättrad miljöprestanda kan erhållas omnödvändig kyla produceras med värme istället för el då kryogen uppgradering används. Annars är detalltid mer fördelaktigt att använda el för att producera nödvändig kyla.</p> / <p>This is a master thesis that has been carried out at Göteborg Energi AB. It refers to investigate ifcryogenic upgrading of biogas with advantage can be done by producing necessary cold with a heatdriven absorption cooling machine. Göteborg Energi is one of three actors that together will build abiogas plant in Lidköping that will be up and running in 2010. The plant will produce 30 GWhliquefied biogas annually.</p><p>This thesis investigastes whether it is advantageous, to upgrade biogas with heat driven cooling, in aperspective of economy, energy use and environment. It compares cryogenic upgrading with coldproduced by electricity, but also by other techniques. Two different process simulation softwares havebeen used as support to this thesis; Hysys and DESIGN II.</p><p>The result shows that energy usage increases when the necessary cold is produced with heat instead ofelectricity; 0,47 kW/Nm3 rawgas for cryo upgrade with absorptions cooling and 0,29 kW/Nm3 rawgaswith cold produced by electricity. If it’s possible to use the waste heat to warm the digester, the energyconsumption for the upgrading can be reduced to 0,29 kW/Nm3 for the system with heat-driven cold,and 0,15 kW/Nm3 rawgas for cold produced by electricity. In comparison with other techniques forupgrading, 0,47 kW/Nm3 rawgas is a high value while 0,29 kW/Nm3 rawgas is among the lowestvalues for energy use.</p><p>The impact on the climate emerges from the use of electricity and when methane slips out from theupgrading plant. The result shows that the impact on the climate is slightly decreased for cryogenicupgrading when the cold is produced with a heat driven absorption machine instead of electricity. Theresult varies a lot due to how one calculate the emission of carbon dioxide from the electricity on themargin. In comparison with other upgrading techniques, the climate impact from cryogenic upgradingis less, other than the COOAB-technique that is superior because of its low methane slip and lowdemand of electricity.</p><p>An economical comparison shows that the cost for energy usage is about the same for cryogenic as forother techniques; approximately 0,03 SEK/kWh upgraded gas. If one can utilize the waste heat, thecost would be decreased to 0,024 and 0,02 SEK/kWh upgraded gas for the system with cryogenicupgrading with cooling from absorption machine respectively cooling produced with electricity.</p><p>My conclusion is that the utilization of the waste heat is essential if one wishes to get good economyand low energy use for the upgrading of biogas with cryogenic methods. A slightly increasedenvironmental improvement can be received if one change the cold production from electricity to heat,otherwise it is always more advantageous to use electricity for cryogenic methods.</p>

Detta är ett examensarbete som genomförts hos Göteborg Energi AB och syftar till att utreda omkryogen uppgradering av biogas med fördel kan ske genom att producera nödvändig kyla medvärmedriven absorptionskylmaskin. Göteborg Energi är en av tre parter som tillsammans ska bygga enbiogasanläggning i Lidköping som ska vara i drift 2010. Anläggningen ska producera 30 GWhflytande biogas per år. Arbetet utreder om det är fördelaktigt ur ekonomiskt, energimässigt och miljömässigt perspektiv attuppgradera biogas med kryogen teknik med värmeproducerad kyla. En jämförelse görs först medkryogen teknik där kylan är producerad med el och sen med andra uppgraderingstekniker. Som stödhar två olika processimuleringsprogram används, Hysys och DESIGN II. Resultatet visar att energianvändningen ökar då värmedriven kyla används i jämförelse med kylaproducerad med el. 0,47 kW/Nm3 rågas för kryo med absorptionskyla och 0,29 kW/Nm3 rågas medel. Om det finns avsättning för spillvärmen kan energianvändningen i uppgraderingen minska till 0,29kW/Nm3 rågas och 0,15 kW/Nm3 rågas för systemet med värmedriven respektive eldriven kyla. Ijämförelse med andra uppgraderingstekniker ligger 0,47 kW/Nm3 bland de teknikerna med högstenergianvändning medans 0,29 kW/Nm3 placerar sig bland de teknikerna med lägstenergianvändning. Resultat visar att klimatpåverkan från uppgraderingen, som kommer av metanslip och elanvändningen,minskar marginellt om kylan produceras med värme istället för el. Resultatet varierar mycket beroendepå hur koldioxidutsläppen från marginalelen beräknas. I jämförelse med andra uppgraderingsteknikerligger kryo lägre än de flesta andra. Undantaget är COOAB-tekniken som är överlägset bäst tack varalågt metanslip och liten elanvändning. Ekonomisk jämförelse med andra uppgraderingstekniker visar att kostnaden för energianvändningenligger i samma nivå som övriga uppgraderingstekniker i jämförelsen, ca 0,03 kr/kWh uppgraderad gas.Om det finns avsättning för spillvärmen sjunker kostnaden till 0,024 och 0,02 kr/kWh uppgraderad gasför kryoteknik med kyla ifrån värme respektive el. Min slutsats är att utnyttjande av spillvärmen är av stor vikt för att få god ekonomi och lågenergianvändning med kryogen uppgradering. En marginellt förbättrad miljöprestanda kan erhållas omnödvändig kyla produceras med värme istället för el då kryogen uppgradering används. Annars är detalltid mer fördelaktigt att använda el för att producera nödvändig kyla. / This is a master thesis that has been carried out at Göteborg Energi AB. It refers to investigate ifcryogenic upgrading of biogas with advantage can be done by producing necessary cold with a heatdriven absorption cooling machine. Göteborg Energi is one of three actors that together will build abiogas plant in Lidköping that will be up and running in 2010. The plant will produce 30 GWhliquefied biogas annually. This thesis investigastes whether it is advantageous, to upgrade biogas with heat driven cooling, in aperspective of economy, energy use and environment. It compares cryogenic upgrading with coldproduced by electricity, but also by other techniques. Two different process simulation softwares havebeen used as support to this thesis; Hysys and DESIGN II. The result shows that energy usage increases when the necessary cold is produced with heat instead ofelectricity; 0,47 kW/Nm3 rawgas for cryo upgrade with absorptions cooling and 0,29 kW/Nm3 rawgaswith cold produced by electricity. If it’s possible to use the waste heat to warm the digester, the energyconsumption for the upgrading can be reduced to 0,29 kW/Nm3 for the system with heat-driven cold,and 0,15 kW/Nm3 rawgas for cold produced by electricity. In comparison with other techniques forupgrading, 0,47 kW/Nm3 rawgas is a high value while 0,29 kW/Nm3 rawgas is among the lowestvalues for energy use. The impact on the climate emerges from the use of electricity and when methane slips out from theupgrading plant. The result shows that the impact on the climate is slightly decreased for cryogenicupgrading when the cold is produced with a heat driven absorption machine instead of electricity. Theresult varies a lot due to how one calculate the emission of carbon dioxide from the electricity on themargin. In comparison with other upgrading techniques, the climate impact from cryogenic upgradingis less, other than the COOAB-technique that is superior because of its low methane slip and lowdemand of electricity. An economical comparison shows that the cost for energy usage is about the same for cryogenic as forother techniques; approximately 0,03 SEK/kWh upgraded gas. If one can utilize the waste heat, thecost would be decreased to 0,024 and 0,02 SEK/kWh upgraded gas for the system with cryogenicupgrading with cooling from absorption machine respectively cooling produced with electricity. My conclusion is that the utilization of the waste heat is essential if one wishes to get good economyand low energy use for the upgrading of biogas with cryogenic methods. A slightly increasedenvironmental improvement can be received if one change the cold production from electricity to heat,otherwise it is always more advantageous to use electricity for cryogenic methods.