Proceedings of the Institution of Mechanical Engineers,Part A: Journal of Power and Energy

Fossil fuels, coal, and natural gas, contribute a major share of electricity generated in India as well as the world and will continue to do so well into the future. With the justified concern of their rapid depletion and the environmental impacts associated with their large-scale use, there is a quest for advanced coal-fired power generation technologies which are energy efficient and environmental friendly. This study analyses the thermodynamic performance of an existing 62.5 MWe conventional Rankine cycle power plant using pulverized coal firing (PF) (reference plant with atmospheric pulverized coal combustion) repowered with a new and potentially advantageous technology, namely, pressurized pulverized coal firing in a combined cycle (PPCC) power plant. The performance of power plants is determined based on energy and exergy analysis. The energy and exergy efficiencies of the PF plant are estimated to be 28.3 and 25.9 per cent, respectively, whereas the PPCC power plant results in a significant increase of 6.3 and 5.7 per cent points, respectively, over the PF plant. Moreover, PPCC power plant results in an increase of about 2.6 times in the gross plant output (162 MWe) compared with the PF power plant. The gas turbine alone contributes to an additional 100 MWe when the steam turbine output is maintained constant at 62.5 MWe as in reference PF power plant.

This article considers the problem of sizing prime movers for combined heating and power (CHP) systems operating at full load to satisfy a fraction of a facility's electric load, i.e. a base load. Prime mover sizing is examined using three criteria: operational cost, carbon dioxide emissions (CDE), and primary energy consumption (PEC). The sizing process leads to consider ratios of conversion factors applied to imported electricity to conversion factors applied to fuel consumed. These ratios are labelled R_Cost, R_CDE, R_PEC depending on whether the conversion factors are associated with operational cost, CDE, or PEC, respectively. Analytical results show that in order to achieve savings in operational cost, CDE, or PEC, the ratios must be larger than a unique constant R_Min that only depends on the CHP components efficiencies. Savings in operational cost, CDE, or PEC due to CHP operation are explicitly formulated using simple equations. This facilitates the process of comparing the tradeoffs of optimizing the savings of one criterion over the other two – a task that has traditionally been accomplished through computer simulations. A hospital building, located in Atlanta, Georgia, was used as an example to apply the methodology presented in this article.

While there are several best practice standards available for minimizing the energy requirement for compressed air use in an industrial context, moving to best practice often requires investment and operational change. In production facilities, there is often a reluctance to commit to this type of change without a clear view of the benefit. Furthermore, there is very little detailed information available in the open literature that allows even a qualitative assessment of priorities. In order to address this shortcoming, a practical approach is proposed to provide detailed compressed air consumption information throughout an industrial site. The energy of the compressed air is evaluated at each key element of the system and the typical end-use application profile assessed. Simple models of the consumption rates are used to relate duty cycle and device count with actual total consumption. This approach is complemented with a novel method of assessing the leak rate from the entire system, based on the pressure decay time. The method, referred to as the ‘end use catalogue’ has been demonstrated at a manufacturing site with a wide range of compressed air applications. The model has been used to identify the most significant energy-intensive compressed air applications and possible strategies to reduce the energy requirement. In the particular site used as a demonstration, it was found that open blowing operations (e.g. fluidizing) are the largest consumers of compressed air which are amenable to intervention. System leakage accounts for almost 21 per cent of the compressed air generated, representing an energy input of 432 kWh per day. It is concluded that this approach can help to identify priorities for optimizing compressed air use at an industrial site without compromising the production yield.

Combustion of solid fuel supplies heat in an iron ore sintering bed and the quality and productivity of the processes are highly dependent on the variation of operational parameters. To set the optimized operation modes through the application of various ideas, a numerical model can be employed prior to the conceptual designing of the actual plant. In this study, the effects of oxygen enrichment, increment of bed height, waste gas recirculation, as well as supplementary gaseous fuel combustion are investigated by employing a previously developed unsteady one-dimensional model of an iron ore sintering bed. Through the simulation, temperature distribution can be observed and used as the key data for the evaluation of the combustion efficiency. Flame front speed and sintering time, which represent propagation speed of the combustion zone, are also employed for quantification of the simulation. Through the parametric studies with numerical analysis, preliminary information about the detailed situation in the bed can be obtained.

A novel ignition system was studied experimentally, in which small volumes of hydrogen peroxide – of the order of µL/s – were injected at the site of ignition, during the firing of a focus discharge igniter. Experiments were made at an atmospheric testing facility using an industrial Rolls-Royce olympus combustion chamber with kerosene Jet A₁ as the fuel and atmospheric air as the oxidizer. The study concentrated on the determination of the lean ignition limits of the Jet A₁–air mixture at various air mass flowrates with and without the addition of H₂O₂. Notable improvements, from 6.5 per cent to 44 per cent, in the ignition limits of the kerosene–air mixture were attainable using only a small amount of H₂O₂ during the ignition process. The study suggests that these improvements are directly related to the increase in the ignition efficiency of the igniter.

A new practical way of modelling direct-driven permanent magnet synchronous generator (PMSG) wind turbines is proposed. The model emphasizes on the wind-rotor-to-PMSG-to-converter-to-grid system, which is the main energy flow system of the direct-driven wind turbine. In this article, a new wind-rotor back propagation neural network is proposed, which consists of a four-layer network and is used to describe the wind-rotor aerodynamic characteristics. According to the orthogonal experimental method, 1200 sets of wind-rotor aerodynamic data, which are calculated based on combining blade element momentum-modified theory with a dynamic stall model, are adopted as the sample data; and the wind-rotor neural network is trained using the Levenberg–Marquardt algorithm. Then, the coupling dynamic models of the wind-rotor and PMSG, and AC–DC–AC converter model are established, respectively; the control strategies for the generator-side and grid-side converters are constructed, too. The mechanical model, electric model, and control model are integrated into the whole simulation model, and the numerical simulation are carried out. The research results show that all the wind-rotor aerodynamic characteristics, electrical characteristics, and control characteristics can be obtained quickly and efficiently from the constructed model, and are helpful for optimization design and control for large-scale direct-direct PMSG wind turbines.

A novel solar and wind energy extraction system is proposed and described in this article. The system is a combination of the solar chimney and tornado-type wind tower, with the wind tower installed at the exit of the solar chimney. The proposed system can considerably increase the driving force in the chimney using high-elevation wind energy. The higher the wind speed, the greater the driving force. This will lead to an obvious rise in maximum power output of the novel system. Theoretical models of this novel system are also developed, and the calculated results agree well with the numerical simulations. It is found that the pressure deficit produced by the tornado-type wind tower plays a key role in the increase of the power output. By using the high-elevation wind energy, this novel system can considerably alleviate the difficulty of constructing a gigantic concrete chimney in the solar chimney system.

Almost all small wind turbines have a tail vane to point the wind rotor into the wind direction. Various types of control mechanisms are used to protect the wind turbines from high-wind speeds. In this study, a generic model of a wind turbine is developed to investigate the yaw operation of small-scale horizontal axis wind turbines (HAWT) with a single tail vane. A tilt-up wind turbine is considered here as most of the other HAWT types can be simplified to a state of this model. In the tilted up wind turbines, the wind rotor is free to move around the horizontal axis as well as the vertical one. When the wind speed exceeds the rated value, the wind rotor tilts upwards, taking up a stable position with an inclination towards the direction of the wind, thus controlling the wind component responsible for power generation. This article describes the development of a mathematical model of small-scale HAWT using the D'Alembert's principle to investigate the complex behaviour of the wind turbine under transient and steady-state operating conditions. In this model, the blade element theory was adapted to predict the aerodynamic forces on the wind rotor at each rotor position. Combining the modified blade element with the momentum theories makes it possible to evaluate flow fields of induced velocities around the wind rotor. Yaw movements are modelled by considering dynamic responses of the tail vane. Finally, simulation results are presented to illustrate the yaw behaviour of a small wind turbine.

Wave energy has the potential to be a major provider of renewable energy, especially in the UK. However, there is the major problem of producing efficient devices for a wide variety of sites with different operating conditions. This article addresses the time domain modelling of a heaving point absorber connected to a hydraulic power take-off (PTO) unit in regular waves. Two cases for the hydraulic PTO unit are considered: an ideal model and a model containing losses. Component losses are included to give a more accurate prediction of the maximum power production and to discover if the parameters to optimize the device change when losses are included. The findings show that both cases are optimized by varying the size of the hydraulic motor and the optimal size is only dependent on wave period and the trend is the same for both cases. Results also showed that to maximize the power produced for both cases, there is an optimal force that the unit produces, which can be derived from theory. Finally, power reduction as a result of the hydraulic losses is also observed with efficiencies reducing at larger wave heights.

This article studies the effects of viscous loss, flow separation, and base pressure for ducted turbine designs using computational fluid dynamics (CFD) simulations. Analytical model coefficients for inlet and diffuser efficiency and base pressure coefficient parameterize these effects and have been identified from CFD results. General trends are that the inlet efficiency is nearly unity for the simulated designs; the diffuser efficiency has a significant impact on performance and is degraded by flow separation; and that the base pressure effect can provide a significant performance enhancement. Geometric features influencing each of the aforementioned parameters are identified and a regression-based model has been developed to predict ducted turbine performance.

This paper presents the results of an experimental study carried out on a prototype of a hermetic scroll expander, integrated into a gas cycle test rig, whose working fluid is HFC-245fa. This system is designed to test only the performance of the expander. It is made up mainly of a scroll compressor, a scroll expander, a heat exchanger, and a by-pass valve. The latter is used to adjust the pressure ratio imposed to the expander. The expander was originally a compressor designed for heat pump applications and is characterized by a nominal power input of 2.5 kWe. Performance of the expander is evaluated in terms of isentropic effectiveness and filling factor as functions of the main operating conditions. The study also investigates the impact of oil mass fraction on the expander performance. Maximum overall isentropic effectiveness of 71.03 per cent is measured, which is partly explained by the good volumetric performance of the machine. Using the experimental data, parameters of a semi-empirical simulation model of the expander are identified. This model is used to analyse the measured performance of the expander. Finally, a polynomial empirical model of the expander is proposed for fast and robust simulations of organic Rankine cycle systems.

Three-dimensional unsteady turbulent flow through the entire flow passage of a model Francis hydraulic turbine is simulated using the transition shear-stress transport turbulence model and verified with experimental data. Pressure oscillations with the original runner cone, an extended runner cone, an extended runner cone with grooves, and a round-top runner cone are analysed under five operating conditions. The computational results show that (1) runner cone design can change the distribution pattern of the vortex rope in the draft tube and narrow the zone of special pressure oscillation; (2) the dominant frequency of pressure oscillation in the draft tube at guide vane opening angle, α = 17°, is significantly decreased by runner cone design while the peak-to-peak amplitude increased; (3) varying guide vane opening alters the influence of runner cone design on pressure oscillation; (4) the modified runner cones are effective for low frequency pressure oscillations induced by the vortex rope in the draft tube but have little effect on blade frequency pressure oscillation induced by rotor–stator interaction; (5) the cavitation performance at α = 17° is decreased while that at α = 18°, 19°, and 20° is increased by runner cone design; and (6) the round-top runner cone is most effective in decreasing pressure oscillations and increasing turbine cavitation performance.

The aim of this study is to develop a seawater hydraulic piston pump for the power pack of an underwater tool system. A pump with check valves and oil–water-separated structure was selected for the purpose of improving its tolerance to particles when applied in open-circuit system. A novel ‘anti-loosening’ structure was introduced for the piston/shoe assembly. To improve the anti-wear and anti-corrosion performances of the piston and sleeve pairs under seawater lubrication, carbon fibre-reinforced polyetheretherketone was injected as an inner of the sleeve, and synthesized WC was formed on the piston with improved surface hardness. The unbalance problem of the shaft assembly was solved based on Solidworks software by adjusting the centre of mass of the shaft to its rotation axis and making all the products of inertia close to zero for an arbitrary-given coordinate system in which one of its axes is at the rotation axis. Basic performances and reliability experiments for the pump were carried out on a test rig. The shaft assembly was verified by experiment to reach very desirable balance effect. The pump has relative high efficiency at 10 MPa rated pressure and 14 MPa maximum pressure. After 300 h durability test, neither excessive wear could be found for the piston/sleeve pairs as well as other parts in the pump, nor obvious performance degradation happened to the pump. The dynamic balancing method presented in this article provides an easy and effective way to solve the unbalance problem for a shaft with special structure and can be widely used in other rotating machines. New design on the seawater hydraulic pump was initially confirmed to be feasible, although further research needs to be conducted. The pump has been successfully applied in an underwater seawater hydraulic tool system.