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.

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.

Thesis (M.S.)--Mississippi State University. Department of Mechanical Engineering. / Title from title screen. Includes bibliographical references.

The Organic Rankine Cycle (ORC) may be the superior cycle for power generation using low temperature and low power heat sources due to the utilization of high molecular mass fluids with low boiling points. They are flexible, simple, easy to operate and maintain, and offer many possible areas of applications including waste heat recovery and power generation from biomass, geothermal and even solar energy. Therefore, they may prove to be of significant importance in reducing global greenhouse gas emission and in the mitigation of climate change. In this thesis the technical feasibility and economic profitability of implementing an ORC in a district heating boiler station is investigated. A model of ORC connected to the hot water circuit of one of the biomass boilers of the boiler station is simulated. The achieved evaporation temperature is estimated to 135 degrees C and the condensation temperature is found to vary in the range of about 70-100 degrees C. The results show that it is both possible and profitable to implement an ORC in the studied boiler station. A maximum net present value of 2.3 MSEK is achieved for a 400 kW system and a maximum internal rate of return of 8.5%, equivalent to a payback period of 9.5 years, is achieved for a 300 kW system. Furthermore, the investment is found to be most sensitive to changes in the electricity price, net electric efficiency and capital expenditure cost.

No description available.

In this dissertation, different configurations of solar powered organic Rankine cycles (ORC) are investigated. The configurations include: a basic ORC, a regenerative ORC (R-ORC), and a basic ORC with electric energy storage (EES) (ORC-EES). The basic ORC and the R-ORC are evaluated using different dry organic fluids based on the first and second laws of thermodynamics and electricity production. The performance of both ORC systems is based on the potential for primary energy consumption (PEC) and carbon dioxide emission (CDE) savings, the electricity production, and the available capital cost (ACC) for the system. The R-ORC and basic ORC are both evaluated in Jackson, MS and Tucson, AZ to determine the effect of hourly solar irradiation and ambient temperature on both systems. For the basic ORC a parametric analysis is performed to determine the effects of cycle pressure, temperature, solar collector area, and turbine efficiency on the system performance. Similarly, for the R-ORC, a parametric analysis investigating the effect of open feed organic fluid heater intermediate pressure and turbine efficiency on the R-ORC is performed. Finally an ORC connected to an EES device located in Tucson, AZ is studied. The ORC-EES supplies electricity to three different commercial buildings. The ORC-EES is modeled to be charging when irradiation is available and discharging when there is not enough irradiation to generate electricity from the ORC. The performance of the system is based on the amount of electricity supplied, the potential for PEC, CDE, and cost savings, and the ACC. The effect of solar collector area on the percentage of supplied electricity, EES device size, and cost savings is also studied. It was determined that all the evaluated ORC configurations have the potential to produce PEC, CDE, and cost savings, but their performance is affected by the organic working fluid, solar collector area, and the location where the system is installed.

No description available.