Increasing the efficiency of the Rankine cycle using a thermoelectric heat pump

TA Engineering (General). Civil engineering (General);TJ Mechanical engineering and machinery;TK Electrical engineering. Electronics Nuclear engineering

Siviter, Jonathan Peter ; Knox, Andrew R.

University:University of Glasgow

Department:School of Engineering

关键词: thermoelectric, Rankine cycle, heat engine, energy, efficiency increase, heat pump, green energy;   

Others  :  http://theses.gla.ac.uk/5802/1/2014siviterphd.pdf

来源: University of Glasgow

【 摘 要 】

Thermal plants operating on the Rankine cycle are by far the most common method of global electrical power generation. The Rankine cycle, first developed in the late19th century, continues to this day to be one of the most important practical implementations of a heat engine. Innovation and enhancement of the cycle continues and today's emphasis is directed towards reduced carbon emissions from the combustion of fossil fuel as well as improvement of the absolute efficiency. This thesis presents an increase in the Rankine cycle efficiency through reducing the waste heat rejected from the process by the use of a thermoelectric heat pump.A thermoelectric heat pump converts a flow of electrical charge carriers to a flow of thermal energy via phonon transport through a semiconductor lattice, described by the Peltier effect. The heat flux through the device can be modulated by varying the electrical voltage and current applied to the semiconductor. Unlike a conventional heat pump, however, the direction of heat transport is determined by the direction of migration of the charge carriers. The efficiency with which the device operates isdetermined by complex relationship amongst the differential temperature across the device, the geometry of the semiconductor pellets forming the device and the electricalcurrent flow. Peltier effect devices are typically used in small-scale refrigerators, on high-power lasers to aid cooling and to maintain the wavelength stability of opticalcommunications networks.In this thesis the application of a heat pump to recover a portion of the waste thermal energy normally rejected from the Rankine cycle process after the re-condensation of feedwater in the condenser of a steam turbine is considered. Firstly, a theoretical statement of the required Coefficient of Performance for economic operation of such a system is derived. This is followed by an experimental investigation to determine if the calculated performance is available using today's thermoelectric technology point. The thesis then presents a rigourous analysis of novel experimental apparatus used to characterise the impact of redirecting enthalpy normally rejected from the process to instead reducing the fuel load to the plant and concludes with an assessment of the economic benefits such a heat pump system would bring.