• Energy Research

Abstract Combined heat and power (CHP) systems offer high energy efficiencies as they utilise both the electricity generated and any excess heat by co-suppling to local consumers. This work presents the potential of a combined heat and hydrogen (CHH) system, a solution where Proton exchange membrane (PEM) electrolysis systems producing hydrogen at 60–70% efficiency also co-supply the excess heat to local heat networks. This work investigates the method of capture and utilisation of the excess heat from electrolysis. The analysed system was able to capture 312 kW of thermal energy per MW of electricity and can deliver it as heated water at either 75 °C or 45 °C this appropriate for existing district heat networks and lower temperature heat networks respectively. This yields an overall CHH system efficiency of 94.6%. An economic analysis was conducted based on income generated through revenue sales of both hydrogen and heat, which resulted in a significant reduction in the Levelized Cost of Hydrogen.

This paper presents a thermodynamic analysis and a numerical simulation of a heat pipe heat exchanger which recovers both sensible and latent heat from the exhaust gases of boiler with a temperature range from 450K to 600K. Compared with the conventional methods of preventing corrosion by avoiding acid dew point or using the anticorrosive material, a water spray is proposed in this work as an innovation to integrate with the heat pipe heat exchanger, which absorbs the corrosive gas such as SO2, SO3 and NOx from the outlet of boiler. The comprehensive theoretical study has shown the convective heat transfer coefficient under wet condition is 1.5-3 times higher than that of dry condition and the optimal location of the water spray in the system has been identified. Meanwhile a the heat and mass transfer in a thirty-row heat pipe heat exchanger with different locations of a water spray has been established by the FLUENT to analyze the flow field and temperature gradient of the heat pipe heat exchanger. The overall analysis has proven that system efficiency of the boiler and the lifetime of heat exchanger can be effectively enhanced with the application of the water spray.

Abstract Nitrogen oxides (NO x ) is one of the harmful emissions from power plants. Efforts are made to reduce NO x emissions by researchers and engineers all the times. NO x emissions are from three resources during the combustion: prompt NO, fuel NO and thermal NO. The last one – thermal NO, which is described by ‘Zeldovich-mechanism’, is the main source for NO x emissions. The thermal NO emission mainly results from the high combustion temperature in the combustion process. In order to control the NO formation, the control of peak combustion temperature is the key factor, as well as the oxygen concentration in the combustion areas. Flameless oxidation (FLOX) and continuous staged air combustion (COSTAIR) are two relatively new technologies to control the combustion temperature and the reaction rate and consequently to control the NO x emissions. In this study both FLOX and COSTAIR technologies are assessed based on a 12 MW e , coal-fired, circulating fluidised bed combustion (CFBC) power plant by using ECLIPSE simulation software, together with a circulating fluidised bed gasification (CFBG) plus normal burner plant. Two different fuels – coal and biomass (straw) are used for the simulation. The technical results from the study show that the application of FLOX technology to the plant may reduce NO x emissions by 90% and the application of COSTAIR technology can reduce NO x emissions by 80–85% from the power plant. The emissions from the straw-fuelled plants are all lower than that of coal-fuelled ones although with less plant efficiencies.

The formation and evolution of the initial spray structure of diesel fuel in the near-nozzle region under different injection and ambient pressures were studied. A visualisation experiment study on diesel fuel using long-distance microscopy and nanosecond-pulse flashlight was performed. Four types of spray tip structure were identified and named as ‘needle’, ‘bubble’, ‘mushroom’ and ‘umbrella’. The obtained high-resolution images revealed that both injection pressure and ambient pressure had a significant influence on the evolution of the spray tip structure. The measurement of the spray penetration and spray angle showed that the increase of injection pressure enhanced spray dispersion while the increase of ambient pressure exhibited an opposite effect. In order to provide a better understanding on the formation mechanism, a numerical study based on large eddy simulation (LES) and volume of fluid (VOF) interface capturing technique was conducted.

Pumped Thermal Energy Storage (PTES) is an increasingly attractive area of research due to its multidimensional advantages over other grid scale electricity storage technologies. This paper built a model and numerically studied the performance of an Argon based Brayton type PTES system. The model was used to optimise total work output and round-trip efficiency of the system. The aspect ratio of the thermal storage tanks and operation of packed bed segmentation have been varied to assess their impacts on round-trip efficiency. Longer and thinner tanks were found to increase efficiency, with the hot tank length affecting system performance to a greater extent than the cold tank. Larger ‘temperature ratio’ in segmentation operation were found to develop higher round-trip efficiency, with higher exit working fluid temperature from hot storage over a shorter duration demonstrating better performance. Key features describing the power output were identified as the duration of the region of maximum power and the steepness of the ‘power front’. To maximise the duration of the high power region and decrease the width of the power front, additional latent heat storage was used, the effect of which on round-trip efficiency was then assessed with predicted efficiencies of up to 80% using isentropic reciprocating compressor/expander architecture, which is close to the theoretically predicted limit.

AbstractAs an alternative to conventional engines, free-piston engine generator (FPEG) is a promising power generation system due to its simplicity and high thermal efficiency. One crucial technical challenge in the FPEG operation is the initial process of overcoming the compression force to achieve a certain speed which allows a stable and continuous operation, i.e. starting process. This paper proposes a novel method to start the engine by mechanical resonance. A closed-loop control model was developed and implemented in a prototype FPEG which was driven by a linear machine with a constant driving force. Both numerical and experimental investigation was carried out. The results show that once the linear motor force have overcome the initial friction force, both the in-cylinder peak pressure and the amplitude of the piston motion would increase gradually by resonance and quickly achieve the target for ignition. With a fixed motor force of 110N, within 0.8 second, the maximum in-cylinder pressure can achieve 12 bars, the compression ratio can reach 9:1, and the engine is ready for ignition. The results demonstrated that it is feasible to start the FPEG by mechanical resonance in a constant motor force in the direction of the natural bouncing motion.