Abstract
This paper describes a study of the relative influences of different system design decisions upon the performance of an organic Rankine cycle (ORC) used to generate electricity from foundry waste heat. The design choices included concern the working fluid, whether to use a regenerator and the type of condenser. The novelty of the research lies in its inclusion of the influence of both the ORC location and the auxiliary electricity used by the pumps and fans in the ORC power system. Working fluids suitable for high temperature applications are compared, including three cyclic siloxanes, four linear siloxanes and three aromatic fluids. The ORC is modelled from first principles and simulation runs carried out using weather data for 106 European locations and a heat input profile that was derived from empirical data. The impact of design decisions upon ORC nominal efficiency is reported followed by the impact upon annual system efficiency in which variations in heat input and the condition of outdoor air over a year are considered. The main conclusion is that the location can have a significant impact upon the efficiency of ORC systems due to the influence of climate upon the condenser and auxiliary electricity requirements.
Highlights
In many industrial facilities, waste heat represents a significant source of energy, some of which might be recovered to reduce primary energy use
In order to model the performance of an organic Rankine cycle (ORC) in a system for the recovery of industrial waste heat, one must model the operation of heat exchangers as they respond to variations in both input energy and heat rejection
Since the main aim of this paper is to investigate the annual performance of the ORC system, including auxiliary energy requirements, a yearly waste heat profile was developed from the available
Summary
Waste heat represents a significant source of energy, some of which might be recovered to reduce primary energy use. One of the reasons for a wide variation in hot source temperature is the cyclic nature of many industrial processes in which material is loaded into a vessel before heating, cooling and unloading ready for the cycle Under such conditions, the temperature of waste process heat will inevitably vary significantly, and the actual performance might be expected to differ significantly from predicted performance based on a simulation study. Fluid at state 1 enters the pump where its pressure is increased to the maximum pressure of the cycle before it is heated in an isobaric process, firstly by the regenerator (if present) and by the evaporator until it reaches the maximum temperature of the cycle at which point it may be superheated It is expanded in an expander where the work extracted is used to generate electricity, after which it is cooled firstly in the regenerator (if present) the condenser, where it is cooled isobarically until it reaches state 1 again. The performance of the condenser itself depends upon the climatic conditions in which it operates, including outdoor air wet-bulb temperature (for a cooling tower) and outdoor air dry-bulb temperature for a dry condenser
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