MODELLING OF AN ORGANIC RANKINE CYCLE SOLAR-THERMAL POWER PLANT

Published ThesisThe purpose of this research is to present a comprehensive numerical model for the conversion of solar energy from sunlight to target mechanical energy of the Organic Rankine Cycle. The terminal processes include intermediate conversion of solar energy to thermal energy in the collector, and from thermal to mechanical work at the turbine. The model also incorporates thermal energy storage. Organic Rankine cycles have unique properties that are well suited for solar power generation. The thermodynamic potential of a varying Organic Rankine Cycle’s working fluids and configurations is analysed. Also, a specific thermodynamic model for STORC power plants is developed in Matlab Simulink ® software and presented. The methodology was implemented based on an existing plant design, which demonstrates opportunities for further optimisation and usability of current design practice. The model has the following elements: the first element is the solar resources model which sources the insolation energy and meteorological input at an instance of time for a specific location to the system. The second element is the solar collector model that accepts output from the solar resources model and presents the output of exit temperature of the collector fluid, the collector efficiency and the useful heat energy gained. The third element is the fluid transfer and storage model that shows the retention and regulation of system heat and temperature from the inlet to the outlet. The last item is the Organic Rankine Cycle model that presents the performance for the expected output power required with a varying fluid and configuration property diagram. Based on the study outcome, the integrated model was created to analyse the variations in geographic, geometrical properties with thermo-physical properties for a specific period of the possible power output from the plant. Case studies on the sensitivity and performance analysis show that the plant will provide more power and higher efficiencies with a larger aperture width of the collector than to the length of the collector. Furthermore, power outputs are higher for elevated and high Direct Normal Irradiance (DNI) locations than those locations with lower elevation and DNI. The report also discusses other results from the analysis of the effect on the model performance

Performance and operational effectiveness of evacuated flat plate solar collectors compared with conventional thermal, PVT and PV panels

The concept of an evacuated flat plate (EFP) collector was proposed over 40 years ago but, despite its professed advantages, very few manufacturers have developed commercial versions. This situation suggests both technical difficulties in manufacturing a competitively-priced sealed for life panel and a lack of awareness of the bene fits of such panels. This paper demonstrates an evacuated flat plate simulation that closely models experimental efficiency measurements. Having established the validity of the model, it compares published data for a commercial EFP collector with predictions for an optimal design to investigate whether any further efficiency improvement might be possible. The optimised design is then evaluated against alternative solar energy devices by modelling a number of possible applications. These comparisons should inform choices about solar options for delivering heat: EFP collectors are well-suited to some of these applications. Evacuated flat plate collectors are a possible alternative to concentrating collectors for Organic Rankine Cycle power generation. The annual output for all the modelled collectors was found to be a quadratic function of delivery temperature: this enabled a novel optimisation of ORC source temperature. Predictions for concentrating and non-concentrating ORC plant are compared with a PV/thermal alternative. The ORC output is significantly less than a PV panel would achieve; applications needing both heat and power are better served by PVT panels. This is an original and novel result

Simulation and performance evaluation of single and double pressure ORC systems on board a LNG carrier including off-design and transient operation

La tesi tratta un caso di applicazione WHR di un impianto di produzione ORC in una nave metaniera, a propulsione elettrica. Modelli di ORC sono stati sviluppati in ambiente MATLAB Simulink, con il doppio obiettivo di valutazione del comportamento durante i transitori del sistema energetico e della produzione elettrica del sistema ORC nell'arco di un anno tipo. Layout considerati: singolo livello di pressione, due livelli subcritici e due livelli con alta pressione supercritic

Numerical Design of a 3-Stage Cascaded Thermal Energy Storage System for Solar Application

The analysis of a three-stage cascaded thermal energy storage is presented in this dissertation. Cascaded thermal energy storage systems has many advantages over conventional thermal energy storages, majorly it allows for maintaining of a nigh-constant temperature between the HTF and PCM during the charging and discharging cycles leading to improved performance of the system. This dissertation investigates the performance and transient response of a packed bed operating under high-temperature conditions with phase change materials in varying encapsulations (cascaded in a three-stage format) during charging and discharging cycle by employing computational numerical techniques via commercially available ANSYS Fluent software. The analysis was performed for nine different encapsulation geometries with increased surface area and constant volume in comparison to the base geometry (sphere) to determine the effects of each new encapsulation on the performance of the thermal energy storage (TES). The computational model used in the development of this work compares well with the experimental results by Raul [1]. Additionally, the effect of packing scheme/PCM layout is also investigated in this work. Comparative data analysis was performed on the TES with the various PCM encapsulation designs and the standard spherical PCM encapsulation to determine which geometry provides better performance during charging and discharging cycles. The results of this study show that the thermal performance of the cascaded thermal energy storage improves with each new encapsulation as evidenced by the decreases in charging and discharging times in comparison to the base encapsulation. This study also highlights which capsule design is most practical when considering the bed dimension increases/ decreases with in increasing thermal performance. This study's findings can serve as a benchmark for future optimization of cascaded thermal energy storage systems

Dynamic Model of an Organic Rankine Cycle System Exploiting Low Grade Waste Heat on board a LNG Carrier

Il lavoro presenta il modello di design e il modello dinamico di off-design di un ciclo ORC che sfrutta il calore a bassa temperatura a bordo di una nave metaniera. I componenti sono stati modellati singolarmente seguendo l'approccio sequenziale. Sono state modellizzate e analizzate due configurazioni di ciclo: a vapore saturo con R245fa e a vapore surriscaldato con R134a. I test di applicazione del modello simulano due scenari di variazione di carico della nave metanier

Exhaust system energy management of internal combustion engines

Today, the investigation of fuel economy improvements in internal combustion engines (ICEs) has become the most significant research interest among the automobile manufacturers and researchers. The scarcity of natural resources, progressively increasing oil prices, carbon dioxide taxation and stringent emission regulations all make fuel economy research relevant and compelling. The enhancement of engine performance solely using incylinder techniques is proving increasingly difficult and as a consequence the concept of exhaust energy recovery has emerged as an area of considerable interest. Three main energy recovery systems have been identified that are at various stages of investigation. Vapour power bottoming cycles and turbo-compounding devices have already been applied in commercially available marine engines and automobiles. Although the fuel economy benefits are substantial, system design implications have limited their adaptation due to the additional components and the complexity of the resulting system. In this context, thermo-electric (TE) generation systems, though still in their infancy for vehicle applications have been identified as attractive, promising and solid state candidates of low complexity. The performance of these devices is limited to the relative infancy of materials investigations and module architectures. There is great potential to be explored. The initial modelling work reported in this study shows that with current materials and construction technology, thermo-electric devices could be produced to displace the alternator of the light duty vehicles, providing the fuel economy benefits of 3.9%-4.7% for passenger cars and 7.4% for passenger buses. More efficient thermo-electric materials could increase the fuel economy significantly resulting in a substantially improved business case. The dynamic behaviour of the thermo-electric generator (TEG) applied in both, main exhaust gas stream and exhaust gas recirculation (EGR) path of light duty and heavy duty engines were studied through a series of experimental and modelling programs. The analyses of the thermo-electric generation systems have highlighted the need for advanced heat exchanger design as well as the improved materials to enhance the performance of these systems. These research requirements led to the need for a systems evaluation technique typified by hardware-in-the-loop (HIL) testing method to evaluate heat exchange and materials options. HIL methods have been used during this study to estimate both the output power and the exhaust back pressure created by the device. The work has established the feasibility of a new approach to heat exchange devices for thermo-electric systems. Based on design projections and the predicted performance of new materials, the potential to match the performance of established heat recovery methods has been demonstrated

Electricity and Water Cogeneration Utilizing Aluminium Furnaces Waste Heat Integrating Thermal Storage Organic Rankine Cycle

High energy-intensive industries, including steel, chemicals, cement, and aluminium, contribute to about 75% of the industrial emissions of carbon dioxide globally and expelling large amounts of unrecovered waste heat into the atmosphere. Yet, there has been a challenge of studies that are conducted on recovering waste heat in the aluminium industry, especially in cast-house facilities, due to technical difficulties such as energy fluctuations in mass flow rate and temperature. In this study, the waste heat to power system is designed to generate power and freshwater in a cast-house facility with 18 furnaces by evaluating three methods in which the temporal waste heat from holding furnaces can be damped and exploited. These methods are: (1) implementing a temporal air injection, (2) optimising furnaces operation time shift, and (3) integrating sensible thermal heat storage. Organic Rankine Cycle is used for the waste heat to power conversion. The appropriate thermal energy storage design and a thermodynamic model of an Organic Rankine Cycle are investigated using temporal flue gas data that are collected on site from three furnaces. Reverse Osmosis technology is applied to produce water using the generated electricity. Results show that sensible heat thermal energy storage is the most suitable technology for damping the fluctuations of waste heat. By utilising waste heat from 18 remelting furnaces, a net power output of 323 kW can be produced to operate a Reverse Osmosis plant supplying 2419 m3 of fresh water daily, saving up to 2000 metric tons of carbon dioxide emissions annually. This study gives a comprehensive approach to deal with temporal waste heat in aluminium furnaces for smooth cogeneration

Thermofluid optimisation of turboexpanders for mobile organic Rankine cycle systems

The Organic Rankine Cycle (ORC) is a closed-loop thermodynamic cycle used for low-temperature heat recovery, from sources as diverse as solar, geothermal and industrial processes. Within the ORC, power is produced with the use of a dense-gas vapour expansion in a suitable device and the efficiency of this process is a key influence on cycle efficiency. This thesis therefore investigates the design, optimisation and validation of nozzled radial-inflow turboexpanders, applied to the recovery of vehicle exhaust waste heat. A 1-dimensional meanline performance prediction methodology is developed, capable of modelling the real-gas effects prevalent in dense, organic working fluids. In addition, choking effects within flow passages are explicitly accounted for in both nozzle and rotor, allowing accurate prediction at the high Pressure Ratios typically observed in ORC expanders. A validation case is subsequently presented, tuning loss correlation coefficients to match 6 high Pressure Ratio experimental test cases, reducing average mass flow rate and efficiency errors to 1.33% and 2.04%, respectively. This 1D model is used to create a methodology in which expander optimisation is performed across an entire vehicle duty cycle. A discretised heat exchanger model is developed, capable of modelling multiple fluid phases and real gas effects. A number of simplifications including surrogate models generated by neural network fits, lead to an O(10^3) reduction in computing effort. A case study is performed to quantify benefits to a 11.7 L diesel engine running a 1200-point Non-Road Transient Cycle, resulting in a 21.9% improvement in total cycle energy recovery against a single-point baseline case. The methodologies contained within this thesis are used to design a turboexpander for an industrial research project, focusing on a 15 L diesel Tier 4 engine. Across two generations of design, a combination of computational and experimental methods are applied to produce an expander containing non-radial rotor inlet blading, producing a simulated power output of 12.4 kW at the design point. Finally, in order to facilitate validation of real-gas Computational Fluid Dynamics (CFD) simulations and better understand the underlying flow physics, a blowdown facility is constructed for working fluid r1233zd(E), centred around a converging-diverging test section producing a Mach 2 expansion at the exit plane. Comparison of CFD and centreline pressure measurements for both nitrogen and refrigerant produced maximum errors in Pressure Ratio of 5.7% and 12.1% respectively, suggesting an overestimation by computational methods in predicting expander output power. The methodologies, designs and experimental results contained within this thesis provide improvements to the modelling, optimisation and validation of dense-gas turboexpanders, with the aim of improving design processes and aiding the implementation of ORC for vehicle waste heat recovery.Open Acces

Modelling and control of waste heat recovery systems for heavy-duty applications

Internal combustion engines (ICEs) are likely to be used in heavy-duty applications for many years and it is important to continue improving their efficiency. Undesirable emissions in internal combustion engines are of major concern due to their negative effect on the human health and global warming. One approach is to recover waste heat from the exhaust of heavy-duty diesel engines (HDDEs) using waste heat recovery (WHR) technologies. WHR based on organic Rankine cycle (ORC) is a promising technology, which offers potential to reduce the fuel consumption of HDDEs by converting the wasted thermal energy to alternative useful electrical or mechanical energy. In the ORC, the evaporator is considered the most critical component of the system. Careful modelling of the evaporator unit is both crucial to assess the dynamic performance of the ORC system and challenging due to the high nonlinearity of its governing equations. This study uses an Adaptive Network-based Fuzzy Inference System (ANFIS) modelling technique to provide efficient control-oriented evaporator models for prediction of heat source and refrigerant temperatures at the evaporator outlet. The ANFIS model benefits from feed-forward output calculation and backpropagation capability of neural network, while keeping the interpretability of fuzzy systems. The effect of training the models using hybrid gradient-descent least-square estimate (GD-LSE) and particle swarm optimisation (PSO) techniques is investigated and the performance of both techniques are compared in terms of RMSE and correlation coefficients. The simulation results indicate strong learning ability and high generalisation performance for both techniques beyond capability of numerical models. However, a better accuracy is achieved for the models trained using the PSO algorithm. Experimentally-measured data is collected from a 1-kWe ORC prototype developed in Clean Energy Processes (CEP) laboratory at Imperial College London and the proposed ANFIS techniques is applied in order to investigate the application of the neuro-fuzzy technique for modelling the evaporator unit. Comparison of the experimental data and the neuro-fuzzy models predictions reveals an acceptable accuracy in predicting the evaporator outlet temperature and pressure. A novel control approach is also proposed to ensure the safe operation of ORC waste heat recovery system and stabilize its work output when subjected to transient heat sources in a range of waste heat from heavy-duty diesel engines. The control strategy comprises a neuro-fuzzy controller based on the inverse dynamics of the ORC system to control the superheating at the evaporator outlet by adjusting the pump speed and a PI controller to maintain the expander work output by regulating the mass flow rate at the expander inlet. The performance of the control strategy is investigated with respect to set-point tracking and its robustness is tested in the presence of noise. The simulation results indicate an enhancement in the controller performance by combination of feedforward and feedback controllers based on neuro-fuzzy techniques. The proposed control scheme not only can obtain satisfactory transient response under various loading conditions, but also can achieve desirable disturbance rejection performance