This report aims to investigate how fluid-based heat-recovery systems for ventilation can be optimized. A high proportion of existing systems operate at lower efficiency than possible, and thus do not reach their full potential in terms of energy savings. The aim of this report has been to find out why, to identify which parameters affect the efficiency of such systems, and to develop a general methodology for optimization. As a method for execution, a literature study and field experiments were chosen. The results from the literature study showed that dimensioned efficiency, fluid flow in the circuit and degree of contamination of the system were important parameters that greatly affected performance. The field experiments largely confirmed this, but also showed that an implementation of the theoretically optimal fluid flow is not always beneficial to the performance, but higher flow should always be considered. The results also indicated a correlation between the fluid flow and the convective heat-transfer coefficient (U-value) in the heat exchangers. A methodology for optimization is presented in the discussion section. As a suggestion for further research, two possible directions are proposed - the potential of cleaning and the effect of the fluid flow. / Den här rapporten har syftat till att utreda hur vätskekopplade värmeåtervinningssystem för ventilation kan optimeras. En hög andel befintliga system fungerar med lägre verkningsgrad än vad som är möjligt, och uppnår därmed inte sin fulla potential vad gäller energibesparing. Målet med den här rapporten har varit att ta reda på varför, att identifiera vilka parametrar som påverkar dylika systems verkningsgrad, och att ta fram en generell metodik för optimering. Som metod för utförande gjordes först en litteraturstudie och senare fältexperiment som utgick ifrån vad litteraturstudien indikerade. Resultatet från litteraturstudien visade att dimensionerad verkningsgrad, vätskeflödet i kretsen och försmutsningsgrad av systemet var viktiga parametrar som påverkade prestandan i hög grad. Fältexperimenten bekräftade detta till stor del, men visade också att en implementering av det teoretiskt optimala vätskeflödet inte alltid är till gagn för prestandan, utan högre flöde borde alltid övervägas. Resultaten indikerade också en korrelation mellan vätskeflödet och det konvektiva övergångstalet (U-värdet) i värmeväxlarna. En metodik för optimering presenteras i diskussionsavsnittet. Som förslag på vidare forskning föreslås två möjliga inriktningar – rengöringens potential samt vätskeflödets inverkan.

Rapid growth of digitalization has urged Data Centres (DC) to be more energy efficient by recovering waste heat from server racks that would otherwise be wasted. This techno-economic study is focused on upgrading low temperature waste heat from typical Air-Cooled DC for District Heating Network (DHN) market in Stockholm region. The methodology is carried out by four system configurations that are experimented with different historical electricity data, impacts of climate change with simulated weather data, and variations in DHN temperature as the heat supply scenario development. The results show that DC configuration with combination of both free-cooling and waste heat recovery can foster techno-economic benefits by reducing cooling consumption by 55.6%, compared to DC configuration with free-cooling only; and further lowering Power Usage Effectiveness (PUE) from 1.95 to 1.52. Lifecycle Operational Expenditure (LCO) has also been used as the economic indicator to represent the maximum initial investment that data centre should accept when deciding to recover the waste heat to the DHN. Moreover, the new technical Key Performance Indicators (KPIs) were introduced to support the decision-making in the supply of recovered waste heat to DHN. The electricity price was further identified to have greater impact than the effect of climate change for the overall techno-economic performance. On one specific hand, heat supply with Price-Limit scenario concluded that 40.18% of available waste heat from DC is not profitable should it be injected to DHN in the case of low electricity price. In the case when the electricity price is high, the amount of waste heat not injected to DHN increases to 58.57%. / <p>The thesis defense presentation was held digitally on Zoom on June 19th 2023 at 09.00 CEST</p>

Ice rinks are highly energy-intensive commercial buildings with an average annual energy consumption of 1,000 MWh, most of it being used to cover the simultaneous heating and cooling demands. The aim of this thesis is to find the most energy efficient energy system for ice rinks by evaluating different system modifications and refrigerants. A comparative analysis of ammonia, CO2 and propane energy systems based on a representative ice rink for northern climates has been conducted. A traditional integrated ammonia ice rink consumes about 340 MWh per year to cover the thermal demands. The most promising energy efficiency measures for ammonia are using aqua ammonia as the secondary fluid and using an auxiliary heat pump to aid with covering heating demands. Thanks to these measures, energy savings of 12.9% can be achieved. A state-of-the-art trans-critical CO2 system using parallel compression consumes approximately 42.6% less energy than a conventional ammonia system, making it the most energy efficient solution for ice rinks with an SPF of 7.5. The good performance is largely linked to the possibility of operating CO2systems as direct systems, eliminating the need for indirect heat transfer and minimizing auxiliary equipment energy consumption. Propane, which has not been investigated as a refrigerant in ice rinks yet, was evaluated and compared against ammonia and CO2. A modern integrated propane system using parallel compression and an auxiliary heat pump is more energy efficient than a traditional ammonia system but requires more energy than modern ammonia or CO2 systems. Propane proved to be feasible and represents a potential alternative solution in ice rinks. Waste heat recovery is beneficial in every system and should be a key feature in ice rink energy systems. All systems use environmentally friendly refrigerants and their environmental impact is almost exclusively indirect and caused by electricity consumption. / Las pistas de hielo son edificios comerciales que consumen mucha energía, con un consumo medio anual de 1,000 MWh, la mayor parte de la cual se utiliza para cubrir las demandas simultáneas de calefacción y refrigeración. El objetivo de esta tesis es encontrar el sistema energético más eficiente para las pistas de hielo evaluando diferentes modificaciones del sistema y refrigerantes. Se ha realizado un análisis comparativo de los sistemas energéticos de amoníaco, CO2 y propano basado en una pista de hielo representativa de los climas nórdicos. Una pista de hielo de amoníaco integrada tradicional consume unos 340 MWh al año para cubrir las demandas térmicas. Las medidas de eficiencia energética más prometedoras para el amoníaco son el uso de aqua amoníaco como fluido secundario y la utilización de una bomba de calor auxiliar para ayudar a cubrir las demandas de calefacción. Gracias a estas medidas, se puede conseguir un ahorro energético del 12.9%. Un sistema de CO2 transcrítico de última generación que utiliza compresión paralela consume aproximadamente un 42.6% menos de energía que un sistema de amoníaco convencional, lo que lo convierte en la solución más eficiente desde el punto de vista energético para pistas de hielo con un SPF de 7.5. El buen rendimiento está ligado en gran medida a la posibilidad de operar los sistemas de CO2 como sistemas directos, eliminando la necesidad de transferencia indirecta de calor y minimizando el consumo de energía de los equipos auxiliares. El propano, que aún no se ha investigado como refrigerante en pistas de hielo, se evaluó y comparó con el amoníaco y el CO2. Un sistema moderno integrado de propano que utiliza compresión paralela y una bomba de calor auxiliar es más eficiente energéticamente que un sistema tradicional de amoníaco, pero requiere más energía que los sistemas modernos de amoníaco o CO2. El propano demostró ser viable y representa una posible solución alternativa en las pistas de hielo. La recuperación del calor residual es beneficiosa en todos los sistemas y debería ser una característica clave en los sistemas energéticos de las pistas de hielo. Todos los sistemas utilizan refrigerantes respetuosos con el medio ambiente y su impacto ambiental es casi exclusivamente indirecto y causado por el consumo de electricidad.

The data centre industry is becoming more and more important due to the rapid increase of digitalisation in our society. However, data centres are large electricity consumers since electricity is needed for both the Information Technology (IT) equipment and the cooling systems, as a certain temperature must be maintained in the server rooms in order to guarantee service operations. Thus, it is important to make data centres less energy intensive and implement a circular economy approach in the sector. One possible way to implement circularity is to reuse the waste heat generated in data centres in district heating networks. However, the potential of using waste heat from low-temperature sources, such as data centres, is mainly unexploited; therefore, more studies are needed in order to inform such use. In particular, it is essential to understand how this potential could be assessed.  The main purpose of this study is to identify the barriers to more heat recovery utilisation and the opportunities that heat recovery contracts can bring from the perspective of key stakeholders linked to DCs’ systems operation and service use, such as DC operators, DH operators, and municipalities. The study also aims at understanding how municipalities can enhance a greater integration of waste heat from data centres in district heating systems. To reach the objectives, this study is constructed as an explorative case study on the use of excess heat from data centres in the Stockholm district heating system. Eight stakeholders belonging to those categories were interviewed and the data collected were analysed with a Strengths – Weaknesses – Opportunities and Threats (SWOT) analysis.   The study concludes that the main barriers preventing the implementation of heat recovery investments, in the explorative analysis for the Stockholm county, seem to be more business related than technical. For example, not having a clear business model in place. In terms of main opportunities, these are related to an improvement in sustainability, such as saving resources by replacing them with excess heat and exploiting an inevitable product instead of wasting it. Moreover, this study also concludes that municipalities can help find suitable places for data centres near the district heating grids both through initiatives like Stockholm Data Parks and city planning. / Datacenterbranschen blir allt viktigare på grund av den snabba ökningen av digitaliseringen i vårt samhälle. Datacenter är dock stora elkonsumenter eftersom el behövs både för IT-utrustningen och för kylsystemen, eftersom en viss temperatur måste hållas i serverrummen för att garantera serviceverksamheten. Det är därför viktigt att göra datacenter mindre energikrävande och införa en cirkulär ekonomi inom sektorn. Ett möjligt sätt att genomföra cirkulär ekonomi är att återanvända den spillvärme som genereras i datacentren i fjärrvärmenäten. Potentialen för att använda spillvärme från källor med låg temperatur, t.ex. datacenter, är dock i huvudsak outnyttjad, och därför behövs fler studier för att informera om sådan användning. I synnerhet är det viktigt att förstå hur denna potential kan bedömas.  Huvudsyftet med den här studien är att identifiera hindren för ett ökat utnyttjande av värmeåtervinning och de möjligheter som avtal om värmeåtervinning kan ge ur de viktigaste intressenternas perspektiv när det gäller drift av DC-system och användning av tjänster, t.ex. DC-operatörer, DH-operatörer och kommuner. Studien syftar också till att förstå hur kommunerna kan främja en ökad integrering av spillvärme från datacenter i fjärrvärmesystemen. För att nå målen är denna studie uppbyggd som en explorativ fallstudie om användningen av överskottsvärme från datacenter i Stockholms fjärrvärmesystem. Åtta intressenter som tillhörde dessa kategorier intervjuades och de insamlade uppgifterna analyserades med en SWOT-analys (Strengths - Weaknesses - Opportunities and Threats).  I studien dras slutsatsen att de främsta hindren för investeringar i värmeåtervinning, i den explorativa analysen för Stockholms län, verkar vara mer affärsrelaterade än tekniska. Till exempel att man inte har en tydlig affärsmodell på plats. När det gäller de viktigaste möjligheterna är dessa relaterade till en förbättring av hållbarheten, t.ex. att spara resurser genom att ersätta dem med överskottsvärme och utnyttja en oundviklig produkt i stället för att slösa bort den. I studien dras dessutom slutsatsen att kommunerna kan hjälpa till att hitta lämpliga platser för datacenter nära fjärrvärmenäten, både genom initiativ som Stockholm Data Parks och stadsplanering.

HEMAB’s biogasanläggning har bytt rötningsprocess till våtrötning. En utmaning med våtrötning är stora mängder rötrest, som kan begränsas genom minskad vattentillsatts i processen. En minskad vattentillsats kan göra processen instabil och ge lågt gasutbyte. Tillsatser kan behövas för att göra processen stabil. Ett ökat rötrestflöde gör även att mer värme kan återvinnas från rötrest. I detta examensarbete undersöks hur rötrestflödet kan begränsas och samtidigt ge en stabil biogasprocess med en metanhalt om minst 55 % samt ett biogasutbyte om minst 190 Nm3 per ton matavfall exklusive vattentillsats, för HEMAB’s biogasanläggning. Tillsatsämnen som ökar gasutbytet i en våtrötningsanläggning som rötar matavfall har också undersökts. Värmeåtervinning från rötrest genom ett värmeväxlarsystem har undersökts för studerad anläggning för att se ifall biogasanläggningen kan bli mer ekonomisk och ekologisk hållbar. Ett flödesschema över den studerade anläggningen gjordes för att se hur rötrestflödet beror av mängd vatten som tillsätts i processen. Hur mängden tillsatt vatten påverkar metanhalten och biogasutbytet undersöktes genom att ta fram relationer mellan rötsubstrats torrsubstans (TS) och metanhalt samt biogasutbyte, både för studerad anläggning och genom litteraturstudie. Möjliga tillsatsämnen undersöktes genom litteraturstudie. Ett värmeväxlarsystem dimensionerades för värmeåtervinning från rötrest, till vattentanken som tillsätter vatten till rötsubstratet. Flödesschemat visar hur rötresten minskar genom minskad vattentillsats till rötsubstratet. Litteraturstudien visade att metanhalt möjligtvis ökar med ökad TS-halt, för låga TS-halter. För studerad anläggning fanns indikationer om att metanhalt möjligtvis minskar med ökad TS-halt, för höga TS-halter. Litteratur visar att det finns en linjär avtagande trend mellan biogasutbyte och TS-halt, för låga TS-halter. Studerad anläggning gav indikationer om att biogasutbytet eventuellt ökar med ökad TS-halt, för höga TS-halter. För att studerad anläggning ska erhålla ett lågt rötrestflöde och ett tillräckligt högt gasutbyte rekomenderas en TS-halt på 20 %, vilket motsvarar vattentillsatsen 0,65 ton vatten per ton matavfall och rötrestflödet 55,8 ton per dygn. Tillsatser av Ni, Mo, Co, Se och Fe ökar biogasproduktionen, Co och Se högre organisk belastning, och alkalinitetshöjare ökar metanproduktion. Det föreslagna värmeväxlarsystemet är inte ekonomiskt lönsamt om dess intäkter utgörs av det pris deponigas säljs för till fjärrvärmenätet. Det är ekonomiskt lönsamt ifall priset på deponigas är detsamma som dess pris från fjärrvärmenätet till kund. Intäkterna av deponigas som säljs till fjärrvärmenätet tros öka i framtiden, p.g.a. ökat intresse och efterfrågan av alternativ till fossila bränslen. I framtiden kan ett värmeväxlarsystem vara mer ekonomiskt lönsamt i och med eventuella bidrag och högre intäkter från såld deponigas. Det är möjligt att utvinna mer värme från rötresten till andra värmekrävande processer än till att endast värma vattentanken. / HEMAB's biogas plant has changed their digestion process to wet digestion. A challenge with wet digestion is large amounts of digestate, which can be limited by reducing the amount of water added to the process. A reduced water addition can make the process unstable and give a low gas yield. Additives may be necessary to make the process stable. An increased flow of digestate enables for more heat to be recovered from the digestate. This work examines how the digestate flow can be limited and at the same time provide a stable biogas process with a methane content of at least 55% and a biogas yield of at least 190 Nm3 per ton of food waste excluding water addition, for HEMAB's biogas plant. Additives that increase the gas yield in a wet digestion plant, digesting food waste, has also been investigated. Heat recovery from digestate through a heat exchanger system has been investigated for the studied plant to see if the plant can become more economically and ecologically sustainable. A flowchart for the studied facility was made to see how the digestate flow depends on the amount of water added to the process. How the amount of water added affects the methane content and biogas yield was investigated by finding relationships between substrates dry matter (TS) and the methane content and biogas yield, both for the studied plant and by studying literature. Possible additives were investigated through a literature study. A heat exchanger system was dimensioned for heat recovery from the digestate, to the water tank that adds water to the substrate. The flowchart shows how digestate is reduced by reducing the addition of water to the substrate. The literature study indicated that methane content possibly increases with increased TS content, for low TS levels. For the studied plant, there were indications that methane content possibly decreases with increased TS content, for high TS levels. Literature shows there is a linear decreasing trend between biogas yield and TS content, for low TS content. The plant studied gave indications that the biogas yield possibly increases with increased TS content, for high TS levels. To obtain a low digestate flow and a sufficiently high gas yield in the studied plant, a TS content of 20% is recommended, which corresponds to a water addition of 0.65 ton water per ton food waste and a digestate flow of 55.8 tons per day. Additions of Ni, Mo, Co, Se and Fe increases the biogas production, Co and Se enable a higher organic load, and alkalinity increaser enhances the methane production. The suggested heat exchanger system is not economically profitable if its income depends on the price of landfill gas sold to the district heating network. It is economically profitable if the price of landfill gas is equal to its price from the district heating network to customer. The price of landfill gas sold to the district heating network is expected to increase in the future, due to increased interest and demand of alternatives to fossil fuels. In the future, it is possible for a more economically profitable heat exchanger system due to possible subsidies and higher price of landfill gas. It is possible to extract more heat from the digestate than is required to heat the water in the tank, for other heat-demanding processes.

Ice rinks are energy intense industrial applications. A typical single sheet ice rink in Sweden uses about 1000 MWh/season. A state-of-the art ice rink systems can use less than 500 MWh/season, indicating the potential for improvements. According to several investigations CO2 refrigeration system with heat recovery has proven to be energy-efficient and cost-effective solution in ice rinks.To further improve the efficiency, geothermal function may be added feature. The objective of this study is to evaluate the geothermal function from techno-economic perspective for a typical ice rink in Sweden. Modelling of several scenarios has been performed. Obtained results suggest that CO2 refrigeration system with 2-stage heat recovery, if upgraded with geothermal function, can save between 1.7 to 6.8% of energy annually. In the best case, this study suggests the geothermal function would pay back in 16.4 years. / Ishallar är energikrävande industriella applikationer. En typisk ishall i Sverige använder cirka 1000 MWh / säsong. Ett toppmodernt ishallsystem kan använda mindre än 500 MWh / säsong, vilket indikerar stora förbättringsmöjligheter. Enligt flera undersökningar har CO2-kylsystem med värmeåtervinning visat sig vara energieffektivt och kostnadseffektivt i ishallar.För att ytterligare förbättra effektiviteten kan geotermisk funktion läggas till. Syftet med denna studie är att utvärdera den geotermiska funktionen ur ett tekno-ekonomiskt perspektiv för en typisk ishall i Sverige. En modellering av flera scenarier har utförts. Resultaten antyder att CO2-kylsystem med 2-steg värmeåtervinning, om det uppgraderas med geotermisk funktion, kan spara mellan 1,7 och 6,8% energi årligen. I bästa fall antyder denna studie att den geotermiska funktionen skulle betala tillbaka om 16,4 år.

Copper processing plants involved in smelting, electro-refining and electro-winning are heat-intensive undertakings that provide extensive challenges for attainment of high energy efficiency. Literature has shown that most of these plants, especially smelters, operate at low overall energy efficiency due to the seemingly complex energy scenario where heat and electricity as forms of energy are treated distinctively from each other. Many copper processing plants have not yet explored both available and emerging waste heat recovery technologies hence remain operating at lower energy efficiencies. In the copper processing plants under study in particular the Nchanga tailings leach plant (TLP), plant operators hinted that some of the processes that ought to operate in heated environments operate at ambient temperatures because of lack of a heating mechanism. The project discusses possible heating mechanisms from available local resources and applicable technologies. As the competing options for providing the required heat at the Nchanga TLP present different carbon emission scenarios, the carbon emissions associated to the recommended installations shall be quantified against a suitable baseline. Flue gas waste heat from the nearby Nchanga smelter has been taken as the available local energy source on which the applicable heating scenarios at TLP are analyzed. The project analyzed waste heat scenarios for three furnaces at Nchanga smelter where it has been established that flue gases from the furnaces contain 37.31 MW of waste heat. Analysis for channeling the waste heat into heat recovery steam generators gave the steam turbine power generation potential of 7.06 MW. The project also demonstrated how energy efficiency undertakings can be used as a driver for carbon emission reduction measures and for participation to the available carbon trading mechanisms such as CDM. Selection of suitable baseline scenarios revealed a lot of potential for carbon finance undertakings in the three case study plants. At the Nchanga smelter, the 7.06 MW power generation capacity has an associated potential of 61,820 tCO2/year emission reductions that can be monetized through the available carbon trading markets. The research established that Nchanga TLP has a heating demand of 10.87MW. If this heating demand was to be met by using the smelter waste heat, the undertaking can be taken as CDM activity or other carbon trading platform with an associated potential of 95,183 tCO2/year.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Concerns surrounding the world’s current dependence on quickly depleting fossil fuels and their negative environmental impacts have brought about much research into renewable and sustainable energy sources. With population and economic growth not only is this dependence increasing but there is an increasing production of waste by society in general. With space becoming a premium commodity and environmental protection a necessity, landfilling of the majority of the world’s waste is no longer feasible. Thus, research is being carried out into waste-to-energy (WTE) processes and refuse derived fuels (RDF). This study focuses on thermochemical conversion, specifically pyrolysis of solid wastes as a means of energy product recovery. Before a specific waste stream can be used in WTE or RDF contexts its composition and degradation behaviour needs to be investigated. For this reason, a full physical characterisation of the municipal solid waste (MSW) from the Stellenbosch municipality was carried out. It was found that the composition of waste differs between areas within the municipality but the composition of the waste in general compares well with international data. It was found that six main components present in the recyclables stream; namely high and low density polyethylene (HD/LDPE), poly(ethylene terephthalate) (PET), glossy paper, office paper and newspaper would be suitable for thermochemical conversion. The thermal properties and pyrolytic degradation of these six components were investigated by multi heating rate thermogravimetric analysis (TGA) from which kinetic parameters (activation energy, pre-exponential factor and kinetic rate constants) were calculated by a differential isoconversional method. The volatiles released during degradation were identified by way of online mass spectrometry (TGA-MS) yielding six individual kinetic schemes. In order to gauge to what extent milligram pyrolytic experimentation (TGA-MS) can be used to predict larger scale pyrolytic behaviour, runs were performed on one plastic (HDPE) and one paper (glossy paper) sample on a gram scale pyrolytic plant under both slow and vacuum conditions. It was found that, especially for high thermal conductivity samples, yields on gram scale experimentation can be accurately predicted on a milligram scale. Further, the compositions of slow pyrolysis oils from glossy paper, obtained by gas chromatography–mass spectrometry (GC-MS), were compared to TGA-MS results as well as off gases captured from TGA runs by thermal desorption (TGA/TD-GC-MS). It was found that TGA-MS and TGA/TD-GC-MS can be used to predict the main functional groups in pyrolysis oil produced on a gram scale. Thus small scale experimentation can be used to determine the suitability of different waste components for pyrolytic conversion. / AFRIKAANSE OPSOMMING: Kommer oor die wêreld se huidige afhanklikheid van fossielbrandstowwe en die negatiewe uitwerking op die omgewing het baie navorsing oor hernubare en volhoubare energie bronne meegebring. Bevolking en ekonomiese groei veroorsaak 'n toename in hierdie afhanklikheid en in die produksie van afval deur die samelewing. Daar is baie min onbenutte grond oop en die beskerming van die omgewing het noodsaaklik geword. Dus is storting van die meeste van die wêreld se afval nie meer ‘n aanvaarbare opsie nie. As gevolg daarvan word daar tans navorsing in afval-tot-energie (ATE) prosesse en afval afgeleide brandstowwe (AAB) gedoen. Hierdie studie fokus op die termochemiese omskakeling van afval, spesifiek pirolise, as 'n methode vir energie-produk hernuwing. Voordat 'n spesifieke afvalstroom gebruik kan word as 'n AAB moet die samestelling en afbrekings gedrag eers ondersoek word. Daarom is 'n volledige fisiese karakterisering van die munisipale afval (MA) van Stellenbosch munisipaliteit uitgevoer. Resultate het getoon dat daar ‘n verskil in die samestelling van afval tussen die gebiede binne die munisipaliteit is. Afgesien daarvan vergelyk die samestelling van die afval in die algemeen goed met internasionale data. Daar is gevind dat daar ses belangrike komponente teenwoordig is in die herwinbare stroom wat geskik sou wees vir termochemiese omskakeling, naamlik; hoë en lae digtheid poliëtileen (HD/LDPE), poli(etileen tereftelaat) (PET), glans, kantoor en koerant papier. Die termiese eienskappe en termiese afbreking van hierdie ses komponente is ondersoek deur middel van multi-verhittimgs tempo termogravimetriese analise (TGA) waaruit kinetiese parameters (aktiveringsenergie, pre-eksponensiële faktor en kinetiese snelheidskonstantes) deur 'n differensiële omskakelings metode bereken is. Die vlugtige komponente wat tydens die afbreking vrygestel is, is geïdentifiseer deur aanlyn-massaspektrometrie (TGA-MS) wat ses individuele kinetiese skemas verskaf. Om vas te stel tot watter mate milligram pirolitiese eksperimente (TGA-MS) gebruik kan word om op ‘n groter skaal die pirolitiese gedrag te kan voorspel, is eksperimentele lopies op een plastiek- (HDPE) en een papier (glans papier) monster op 'n laboratorium skaal pirolise opstelling onder stadige- en vakuum omstandighede uitgevoer. Daar is gevind dat, veral met hoë hitte geleiding komponente, die opbrengs op gram skaal eksperimente akkuraat voorspel kan word op ‘n milligram skaal. Verder was die samestelling van die stadige pirolise olies uit glans papier, wat verkry word deur gaschromatografie-massaspektrometrie (GC-MS), vergelyk met TGA-MS resultate sowel as af-gasse gevang van TGA lopies deur termiese desorpsie (TGA/TD-GC –MS). Daar is gevind dat TGA-MS en TGA/TD-GC-MS gebruik kan word om die belangrikste funksionele groepe in pirolise olie, wat op 'n gram skaal geproduseer word, te voorspel. Dus kan milligram eksperimente gebruik word om die geskiktheid van afval komponente vir pirolitiese omskakeling te bepaal.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The focus of this project was on the potential application of waste heat recovery and utilisation (WHR&U) systems in pebble bed modular reactor (PBMR) technology. The background theory provided in the literature survey showed that WHR&U systems have attracted the attention of many researchers over the past two decades, as using waste heat improves the system overall efficiency, notwithstanding the cost of extra plant. PBMR waste heat streams were identified and investigated based on the amount of heat rejected to the environment. WHR&U systems require specially designed heat recovery equipment, and as such the used and/or spent PBMR fuel tanks were considered by the way of example. An appropriately scaled system was designed, built and tested, to demonstrate the functioning of such a cooling system. Two separate and independent cooling lines, using natural circulation flow in a particular form of heat pipes called thermosyphon loops were used to ensure that the fuel tank is cooled when the power conversion unit has to be switched off for maintenance, or if it fails. A theoretical model that simulates the heat transfer process in the as-designed WHR&U system was developed. It is a one-dimensional flow model assuming quasi-static and incompressible liquid and vapour flow. An experimental investigation of the WHR&U system was performed in order to validate the theoretical model results. The experimental results were then used to modify the theoretical heat transfer coefficients so that they simulate the experiments more accurately. Three energy conversion devices, the dual-function absorption cycle (DFAC), the organic Rankine cycle (ORC) and the Stirling engine (SE), were identified as suitable for transforming the recovered heat into a useful form, depending on the source temperatures from 60 ºC to 800 ºC. This project focuses on a free-piston SE with emphasis on the thermo-dynamic performance of a SE heat exchanger. It was found that a heat exchanger with a copper woven wire mesh configuration has a relatively large gas-to-metal and metal-to-liquid heat transfer area. Tube-in-shell heat exchanger configurations were tested, with the working fluid flowing in ten copper inner pipes, while a coolant flows through the shell tube. A lumped parameter model was used to describe the thermo-fluid dynamic behaviour of the SE heat exchanger. In order to validate the theoretical results, a uni-directional flow experimental investigation was performed. The theoretical model was adjusted so that it simulated the SE heat exchanger. It was found that after this correction the theoretical model accurately predicts the experiment. Finally, a dynamic analysis of the SE heat exchanger experimental set-up was undertaken to show that, although vibrating, the heat exchanger setup assembly was indeed acceptable from a vibrational and fatigue point of view. / AFRIKAANSE OPSOMMING: Die hoofoogmerk met hierdie projek was die moontlike aanwending van afvalhitteherwinningen- benutting-(WHR&U-) stelsels in modulêre-gruisbedreaktor-(PBMR-) tegnologie. Agtergrondteorie in die literatuurondersoek toon dat WHR&U-stelsels al menige navorser se belangstelling geprikkel het, hetsy vanweë die moontlike ekonomiese voordele wat dit inhou óf vir besoedelingsvoorkoming, bo-en-behalwe die koste van bykomende toerusting. Die PBMRafvalhittestrome is ondersoek en bepaal op grond van die hoeveelheid hitte wat dit na die omgewing vrystel. Om in die prosesbehoeftes van WHR&U-stelsels te voorsien, moet goed ontwerpte, doelgemaakte hitteherwinningstoerusting in ʼn verkoelings- en/of verhittingsproses gebruik word, dus is die PBMR as voorbeeld gebruik vir die konsep. ʼn Toepaslik geskaleerde WHR&U-stelsel is dus ontwerp, gebou en getoets om die geldigheid van die stelselontwerp te toon. Twee onafhanklike verkoelingslyne, wat van natuurlike konveksie gebruik maak, in die vorm van hitte-pype of termoheuwel lusse, was gebruik om te verseker dat verkoeling verskaf word wanneer die hoof lus breek of instandhouding nodig hê. ʼn Teoretiese model is ontwikkel wat die hitteoordragproses in die ontwerpte WHR&U-stelsel simuleer. Dié model was ʼn eendimensionele vloeimodel wat kwasistatiese en onsamedrukbare vloeistof- en dampvloei in die WHR&U-stelsel-lusse veronderstel. ʼn Eksperimentele ondersoek is op die WHR&U-stelsel uitgevoer ten einde die teoretiese model se resultate te bevestig. Die eksperimentele resultate was dus geneem om die teoretiese hitteoordragkoëffisiënte aan te pas sodat dit die eksperimente kon simuleer. Drie energieomsettingstoestelle, naamlik die dubbel funksie absorpsie siklus (DFAC), die organiese Rankine siklus (ORC) en die Stirling enjin (SE), is as geskikte toestelle uitgewys om die herwonne hitte op grond van brontemperature tussen 60 ºC en 800 ºC in ʼn bruikbare vorm om te sit. Hierdie tesis het op vryesuier-SE’s gekonsentreer, met klem op die hitteruiler. Meer bepaald is die termodinamiese werkverrigting van ʼn SE-hitteruiler ondersoek. Daar is bevind dat ʼn hitteruiler met ʼn geweefde koperdraadmaas-samestelling oor ʼn betreklik groot gas-totmetaal- en metaal-tot-vloeistof-oordragoppervlakte beskik. Die verhitter en verkoeler is in ʼn buis-in-mantel-vorm ontwerp, met die werksvloeistof wat deur tien koperbinnepype vloei en ʼn koelmiddel deur die mantelbuis. ʼn Saamgevoegde-parameter-model is gebruik om die termodinamiese gedrag van die SEhitteruiler te beskryf. Ten einde die teoretiese resultate te bevestig, is ʼn eenrigtingvloeiproefondersoek uitgevoer. Die teoretiese model is aangepas sodat dit die SE-hitteruiler kon simuleer. Ná die nodige verstellings is daar bevind dat die teoretiese model die proefneming akkuraat voorspel. Laastens was ʼn dinamiese ontleding van die SE-hitteruiler ook onderneem om te toon dat, hoewel dit vibreer, die hitteruiler proef samestel inderdaad veilig is.

There has been renewed significance for innovative energy conversion technologies, particularly the heat recovery-to-power technologies for sustainable power generation from renewable energies and waste heat. This is due to the increasing concern over high demand for electricity, energy shortage, global warming and thermal pollution. Among the innovative heat recovery-to- power technologies, the proposed trilateral flash cycle (TFC) is a promising option, which presents a great potential for development. Unlike the Rankine cycles, the TFC starts the working fluid expansion from the saturated liquid condition rather than the saturated, superheated or supercritical vapour phase, bypassing the isothermal boiling phase. The challenges associated with the need to establish system design basis and facilitate system configuration design-supporting analysis from proof-of-concept towards a market-ready TFC technology are significant. Thus, there is a great need for research to improve the understanding of its operation, behaviour and performance. The objective of this study is to develop and establish simulation tools of the TFCs for improving the understanding of their operation, physics of performance metrics and to evaluate novel system configurations for low-grade heat recovery-to-power generation. This study examined modelling and process simulation of the TFC engines in order to evaluate their performance metrics, predictions for guiding system design and parameters estimations. A detailed thermodynamic analysis, performance optimization and parametric analysis of the cycles were conducted, and their optimized performance metrics compared. These were aimed at evaluating the effects of the key parameters on system performances and to improve the understanding of the performance behaviour. Four distinct system configurations of the TFC, comprising the simple TFC, TFC with IHE, reheat TFC and TFC with feed fluid-heating (or regenerative TFC) were examined. Steady-state steady-flow models of the TFC power plants, corresponding to their thermodynamic processes were thermodynamically modelled and implemented using engineering equation solver (ESS). These models were used to determine the optimum synthesis/ design parameters of the cycles and to evaluate their performance metrics, at the subcritical operating conditions and design criteria. Thus, they can be valuable tools in the preliminary prototype system design of the power plants. The results depict that the thermal efficiencies of the simple TFC, TFC with IHE, reheat TFC and regenerative TFC employing n-pentane are 11.85 - 21.97%, 12.32 - 23.91%, 11.86 - 22.07% and 12.01 - 22.9% respectively over the cycle high temperature limit of 393 - 473 K. These suggest that the integration of an IHE, fluid-feed heating and reheating in optimized design of the TFC engine enhanced the heat exchange efficiencies and system performances. The effects of varying the expander inlet pressure at the cycle high temperature and expander isentropic efficiency on performance metrics of the cycles were significant. They have assisted in selecting the optimum-operating limits for the maximum performance metrics. The thermal efficiencies of all the cycles increased as the inlet pressures increased from 2 - 3 MPa and increased as the expander isentropic efficiencies increased from 50 - 100%, while their exergy efficiencies increased. This is due to increased net work outputs that suggest optimal value of pressure ratios between the expander inlets and their outlets. A comprehensive evaluation depicted that the TFC with IHE attained the best performance metrics among the cycles. This is followed by the regenerative TFC whereas the simple TFC and reheat TFC have the lowest at the same subcritical operating conditions. The results presented show that the performance metrics of the cycles depend on the system configuration, and the operating conditions of the cycles, heat source and heat sink. The results also illustrate how system configuration design and sizing might be altered for improved performance and experimental measurements for preliminary prototype development.