Many industrial processes have low-temperature waste heat sources that cannot be efficiently recovered. Low grade waste heat has generally been discarded by industry and has become an environmental concern because of thermal pollution. This has led to the lookout for technologies which not only reduce the burden on the non-renewable sources of energy but also take steps toward a cleaner environment. One approach which is found to be highly effective in addressing the above mentioned issues is the Organic Rankine Cycle (ORC), which can make use of low- temperature waste heat to generate electric power. Similar in principle to the conventional cycle, ORC is found to be superior performance-wise because of the organic working fluids used in the cycle. The focus of this study is to examine the ORC using different types of organic fluids and cycle configurations. These organic working fluids were selected to evaluate the effect of the fluid boiling point temperature and the fluid classification on the performance of ORCs. The results are compared with those of water under similar conditions. In order to improve the cycle performance, modified ORCs are also investigated. Regenerative ORCs are analyzed and compared with the basic ORC in order to determine the configuration that presents the best thermal efficiency with minimum irreversibility. The evaluation for both configurations is performed using a combined first and second law analysis by varying certain system operating parameters at various reference temperatures and pressures. A unique approach known as topological method is also used to analyze the system from the exergy point of view. Effects of various components are studied using the exergy-wheel diagram. The results show that ORCs using R113 as working fluid have the best thermal efficiency, while those using Propane demonstrate the worse efficiency. In addition, results from these analyses demonstrate that regenerative ORCs produce higher efficiencies compared to the basic ORC. Furthermore, the regenerative ORC requires less waste heat to produce the same electric power with a lower irreversibility.

La récupération et la valorisation des rejets thermiques industriels à basse température et leur conversion en électricité constituent un moyen efficace pour la diminution de la consommation énergétique et l'augmentation de l'efficacité énergétique industrielle. Parmi les technologies actuelles et potentiellement utilisées pour la valorisation de l'énergie thermique rejetée par les différents secteurs industriels, on cite les cycles de Rankine utilisant des fluides de travail organiques. La plupart des études qui ont été faites sur ces derniers ne considèrent que l'aspect de l'analyse énergétique interne. Ce projet propose une étude détaillée d'une configuration de cycle de Rankine sans régénérateur et présente une méthodologie permettant la comparaison de cinq fluides de travail (R134a, R123, R141b, NH[indice inférieur 3] et H[indice inférieur 2]O). Ainsi, plusieurs études sont présentées dans ce projet. La première utilise la première loi de la thermodynamique et l'analyse énergétique interne permettant la détermination du rendement thermique et le travail spécifique du cycle. La deuxième considère l'analyse exergétique qui détermine le rendement de la deuxième loi ainsi que les irréversibilités présentes dans chaque composant du cycle. La troisième analyse se penche sur l'optimisation du cycle et la détermination de la plage de la pression d'évaporation. Cela consiste à minimiser la conductance thermique totale des échangeurs thermiques et maximiser la puissance nette du cycle. Il s'en suit une analyse permettant le dimensionnement de la turbine. Dans ce contexte, le paramètre de la taille de la turbine ainsi que le rapport des débits volumiques à l'entrée et à la sortie de la turbine pour chaque fluide de travail sont déterminés. Des valeurs optimales de ces paramètres sont ensuite obtenues dans les conditions qui minimisent la conductance thermique totale des échangeurs de chaleur. De plus, une autre analyse permet la critique des résultats apparus dans une récente publication et prouve l'efficacité du modèle implémenté dans ce projet de recherche. Finalement, une analyse a été réalisée pour obtenir des corrélations généralisées aux conditions de la puissance nette maximale. Les résultats obtenus ont montré la nécessité d'une étude économique qui se base sur le calcul des surfaces d'échange et les coûts d'installation du cycle.

Recently, attention has been drawn to the viability of using S-CO(2) as a working fluid in modern reactor designs. Near the critical point, CO2 has a rapid rise in density allowing a significant reduction in the compressor work of a closed Brayton Cycle. Therefore, 45% efficiency can be achieved at much more moderate temperatures than is optimal for the helium Brayton cycles. An additional benefit of the S-CO2 system is its universal applicability as an indirect secondary Power Conversion System (PCS) coupled to most GEN-IV concept reactors, as well as fusion reactors. The United States DOE's GNEP is now focusing on the liquid Na cooled primary as an alternative to conventional Rankine steam cycles. This primary would also benefit from being coupled to an S-CO2 PCS. Despite current progress on designing the S-CO2 PCS, little work has focused on the principal supporting systems required. Many of the required auxiliary systems are similar to those used in other nuclear or fossil-fired units; others have specialized requirements when CO2 is used as the working fluid, and are therefore given attention in this thesis. Auxiliary systems analyzed within this thesis are restricted to those specific to using CO2 as the working fluid. Particular systems discussed include Coolant Make-up and Storage, Coolant Purification, and Coolant Leak Detection. / Contract number: N62271-97-G-0026. / US Navy (USN) author

[pt] Esta simulação considera um ciclo Rankine que utiliza um fluido de trabalho orgânico, com a particularidade que a fonte de energia de entrada ao sistema será solar. Esta energia renovável que provem do potencial do Sol é aproveitada com a utilização de coletores concentradores lineares parabólicos. Estes dois circuitos: do ciclo Rankine orgânico e do conjunto de coletores interatuam termicamente mediante um trocador de calor chamado de gerador de vapor. Adicionalmente, existe um sistema de armazenamento térmico que permite acumular parte da energia solar coletada para ser utilizada em períodos sem radiação solar ou com níveis baixos da mesma. A primeira parte deste trabalho mostra os aspectos teóricos introdutórios e as considerações para trabalhar com um ciclo Rankine de tipo orgânico, o tipo de coletores escolhido e a utilização de armazenamento térmico. O segundo capítulo mostra o modelo matemático apropriado para simular um sistema de geração de potência de baixa capacidade (50 kW) e os componentes de cada circuito: ciclo (bomba, expansor, condensador, recuperador, gerador de vapor), coletores (cobertura, refletor, absorvedor, etc.) e armazenamento (tanques, etc.). A simulação foi desenvolvida no software EES. O terceiro analisa os parâmetros do modelo, seus possíveis valores físicos, a sensibilidade da sua variação e sua seleção adequada com o objetivo de efetuar uma simulação bastante similar à realidade e as incertezas presentes. No capítulo final se apresentam os resultados em base as condições de desenho consideradas. / [en] This simulation considers a Rankine cycle that works with an organic fluid, but has the particularity of using solar power as the font of input energy. This renewable energy that comes from the sun’s potential is taken with the use of parabolic trough collectors. These two circuits: that of the organic Rankine cycle (ORC) and the other of collector’s ensemble interact termically in a heat exchanger called as vapor generator. Adicionally there’s a thermal storage system that allows accumulating part of the collected solar energy to be used for periods of time when there’s no solar radiation or with very low levels of it. The first part of this work shows the introductory theoretical aspects and the considerations to work with an organic Rankine cycle (ORC), the type of chosen collector and the use of heat storage. The second chapter shows the appropriate mathematic model to simulate a system of power generation of low capacity (50 kW) and the components of each circuit: ORC (pump, expander, condenser, recuperator, vapor generator), collectors (glass cover, reflector mirror, absorber tube, etc.) and thermal storage (storage tanks, etc.). The simulation was developed using EES software. The third chapter analyzes the parameters of the model, specially its values and possible variations to approach the simulation to the reality. In the final chapter, some results are presented based on some considered design conditions.

Low grade heat (LGH) sources, here defined as below 80ºC, are one group of abundant energy sources that are under-utilised in the production of electricity. Industrial waste heat provides a convenient source of concentrated LGH, while solar ponds and geothermal resources are examples of sustainable sources of this energy. For a number of years RMIT has had two ongoing, parallel heat engine research projects aimed at the conversion of LGH into electricity. The Thermosyphon Rankine Engine (TSR) is a heat engine that uses water under considerable vacuum. The other research stream uses a hydrocarbon based working fluid in a heat engine employing the Trilateral Flash Cycle (TFC). The TSR Mk V was designed and built as a low cost heat engine for the conversion of LGH into electricity. Its main design advantages are its cost and the employment of only one moving part. Using the data gained from the experimental rig, deviations from the expected results (those derived theoretically) were explored to gain insight for further development. The results from the TSR rig were well below those expected from the design specifications. Although the experimental apparatus was able to process the required heat energy, the efficiency of conversion fell well below the expected 3% and was approximately 0.2%. The inefficiency was explained by a number of contributing factors, the major being form drag upon the rotor that contributed around 2/3 of the losses. Although this was the major cause of the power loss, other factors such as the interference with the rotor by the condensate on its return path contributed to the overall poor performance of the TSR Mk V. The RMIT TFC project came about from exploration of the available academic literature on the subject of LGH conversion. Early work by researchers into applying Carnot's theory to finite heat sources led them to explore the merits of sensible heat transfer combined with a cycle that passes a liquid (instead of a gas) though an expander. The results showed that it was theoretically possible to extract and convert more energy from a heat source of this type using this method than using any other alternative. This previous research was targeted at heat sources above 80ºC and so exploration of the theoretical and empirical results for sources below this temperature was needed. Computer models and an experimental rig using isopentane (with a 28ºC boiling point at atmospheric pressure) were produced to assess the outcomes of employing low temperature heat sources using a TFC. The experimental results from the TFC research proved promising with the efficiency of conversion ranging from 0.8% to 2.4%. Although s uch figures seem poor in isolation, it should be noted that the 2.4% efficiency represents an achievement of 47% of the theoretical ideal conversion efficiency in a rig that uses mainly off-the-shelf components. It also confirms that the TFC shows promise when applied to heat sources less than 80ºC.

In this thesis, an experimental research is conducted on scroll-based Organic Rankine Cycle (ORC) focusing on the expansion process. An important feature of the ORC is the ability to utilize low or moderate temperature heat sources derived from renewable energy such as concentrated solar radiation, biomass/biofuels combustion streams, geothermal heat and waste heat recovery. The ORC is more appropriate than steam Rankine cycle to generate power from low capacity heat sources (5-500 kW thermal). For example, expansion of superheated steam from 280oC/1000 kPa to a pressure corresponding to 35oC saturation requires a volume ratio as high as 86, whereas for the same operating conditions toluene shows an expansion ratio of 6 which can be achieved in a single stage turbine or expander. The objective of this work is to experimentally study the performance of a selected refrigeration scroll compressor operating in reverse as expander in an ORC. To this purpose, three experimental systems are designed, built and used for conducting a comprehensive experimental programme aimed at determining the features of the expansion process. In preliminary tests the working fluid utilized is dry air while the main experiments are done with the organic fluid R134a. Experimental data of the scroll expander are collected under different operating conditions. Power generation in various conditions is analyzed in order to determine the optimum performance parameters for the scroll expander. In addition, thermodynamic analysis of the system is conducted through energy and exergy efficiencies to study the system performance. Based on the experimental measurements, the optimum parameters for an ORC cycle operating with the Bitzer-based expander-generator unit are determined. The cycle energy and exergy efficiencies are found 5% and 30% respectively from a heat source of 120oC. / UOIT

This thesis presents numerical modelling and analysis of a solar Organic Rankine Cycle (ORC) for electricity generation. A regression based approach is used for the working fluid property calculations. Models of the unit&rsquo / s sub-components (pump, evaporator, expander and condenser) are also established. Steady and transient models are developed and analyzed because the unit is considered to work with stable (i.e. solar + boiler) or variable (i.e. solar only) heat input. The unit&rsquo / s heat exchangers (evaporator and condenser) have been identified as critical for the applicable method of analysis (steady or transient). The considered heat resource into the ORC is in the form of solar heated water, which varies between 80-95 0C at a range of mass flow rates between 2-12 kg/s. Simulation results of steady state operation using the developed model shows a maximum power output of around 40 kW. In the defined operation range / refrigerant mass flow rate, hot water mass flow rate and hot water temperature in the system are identified as critical parameters to optimize the power production and the cycle efficiency. The potential benefit of controlling these critical parameters is demonstrated for reliable ORC operation and optimum power production. It is also seen that simulation of the unit&rsquo / s dynamics using the transient model is imperative when variable heat input is involved, due to the fact that maximum energy recovery is the aim with any given level of heat input.

This research project was about the combined organic Rankine cycle which extracted energy from the exhaust gas of a diesel engine. There was a study about significant properties of suitable working fluids. The chosen working fluid, R134a, was used to operate at the dry condition when it exited the steam piston engine. Furthermore, R134a is environmentally friendly with low environmental impact. It was also compatible with sealing materials. There were calibrations for the components of the combined Rankine cycle. The efficiency of the heat exchanger converting exhaust heat from the diesel engine to vaporize R134a was 89%. The average efficiency of the generator was 50%. The hydraulic pump used for the combined Rankine cycle showed a transporting problem, as vapor-lock occurred when the pump ran for about 1 minute. The output of the combined Rankine cycle was normalized to compensate for the parasitic losses of a virtual vane pump used in hydraulic systems for the 6 liter diesel engines. There were three different vane pump widths from different pumps to compare frictional loss. The pump with the smallest vane width presented the least frictional mean effective pressure (fmep) (0.26 kPa) when scaled with the displacement of the GMC Sierra 6 liter diesel engine. The power output of the Rankine cycle was scaled to brake mean effective pressure (bmep) to compare with the frictional mean effective pressure. The maximum bmep was at 0.071 kPa when diesel engine had rotational speed at 2190 RPM. The power outputs of the organic Rankine compensated partially the frictional loss of the vane pumps in the 6 liter diesel engine. By using R134a, the condensing pressure was 0.8 MPa; hence, the power outputs from steam engine were limited. Therefore, refrigerants with lower condensing pressure were needed. There were proposal for improvement of the organic Rankine by substituting R134a by R123 (0.1 MPa), R21 (0.2 MPa), and R114 (0.25 MPa) . / text

The growth in renewable electricity generation is forecast to continue as fossil fuel levels decrease and carbon dioxide emissions are penalized. The growth in geothermal is becoming constrained as conventional high-temperature sources are fully exploited. Geothermal can be a cost competitive base load power source. Governments and utilities are looking at the potential of electricity generation from low temperature geothermal resources for future development. This technology, unlike the high and medium temperature, is not mature and there are a number of companies looking at entering the Organic Rankine Cycle (ORC) market. This thesis aims to provide a necessary step for reliable commercial develop this technology by developing the first draft of a low temperature geothermal ORC standard. The standard outlines the critical stages of a geothermal ORC project as the Prospecting stage; Pre-Feasibility stage, Feasibility stage, and the Detailed Design stage. The standard is unlike other standards that are used to design one component; this standard guides the engineers though the various critical steps of the ORC design to correctly assess the geothermal resource and to inform design and investment decisions. The standard provides particular guidance on critical factors in ORC design, primarily the working fluid selection and component selection limitations. Experienced industry engineers have provided advice and insight regarding the critical design points and processes. The draft standard was reviewed by a number of geothermal industry engineers who have worked with large scale, conventional ORCs. They each commented on the standard from their prospective in the industry and gave general feedback was that it is a technically relevant standard that can be used as a potential start point to develop a new standard for the low temperature binary ORC industry. The final draft standard has been submitted to the ISO for consideration. This thesis first sets out the general background on the state of the art and the industry for lowtemperature binary ORC power plants, and provides the review assessment of the standard draft. However, the bulk of the thesis is the standard itself. The standard represents a substantial contribution to the mechanical and thermal systems engineering field.

The global growth in electricity consumption and the shortcomings of renewable electricity generation technologies are some of the reasons why it is still relevant to evaluate the performance of power conversion technologies that are used in fossil fuel power stations. The power conversion technology that is widely used in fossil fuel power stations is the Rankine cycle. The goal of this study was to determine if the efficiency of a typical Rankine cycle can be improved by adding a heat pump as a bottoming cycle. Three simulation models were developed to perform this evaluation. The first is a simulation model of a Rankine cycle. A quite detailed Rankine cycle configuration was evaluated. The simulation model was used to determine the heating requirements of the heat pump cycle as well as its operating temperature ranges. The efficiency of this Rankine cycle was calculated as 43.05 %. A basic vapour compression cycle configuration was selected as the heat pump of the combined cycle. A simulation model of the vapour compression cycle and the interfaces with the Rankine cycle was developed as the second simulation model. Working fluids that are typically used in vapour compression cycles cannot be used for this application, due to temperature limitations. The vapour compression cycle’s simulation model was therefore also used to calculate the coefficient of performance (COP) for various working fluids in order to select a suitable working fluid. The best cycle COP (3.015 heating) was obtained with ethanol as working fluid. These simulation models were combined to form the simulation model of the Rankine-heat pump combined cycle. This model was used to evaluate the performance of the combined cycle for two different compressor power sources. This study showed that the concept of using steam turbine or electrical power to drive a compressor driven vapour compression cycle in the configuration proposed here does not improve the overall efficiency of the cycle. The reasons for this were discovered and warrant future investigation. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013.