Power cycles with ammonia-water mixtures as working fluid

Abstract: It is of great interest to improve the efficiency of powergenerating processes, i.e. to convert more of the energy in theheat source to power. This is favorable from an environmentalpoint of view and can also be an economic advantage. To use anammonia-water mixture instead of water as working fluid is apossible way to improve the efficiency of steam turbineprocesses.This thesis includes studies of power cycles withammonia-water mixtures as working fluid utilizing differentkinds of heat sources for power and heat generation. Thethermophysical properties of the mixture are also studied. Theyplay an important role in the calculations of the processperformance and for the design of its components, such as heatexchangers. The studies concern thermodynamic simula-tions ofprocesses in applications suitable for Swedish conditions.Available correla-tions for the thermophysical properties arecompared and their influence on simula-tions and heat exchangerarea predictions is investigated. Measurements of ammonia-watermixture viscosities using a vibrating wire viscometer are alsodescribed.The studies performed show that power cycles withammonia-water mixtures as the working fluid are well suited forutilization of waste heat from industry and from gas engines.The ammonia-water power cycles can give up to 32 % more powerin the industrial waste heat application and up to 54 % morepower in the gas engine bottoming cycle application compared toa conventional Rankine steam cycle. However, ammonia-waterpower cycles in small direct-fired biomass-fueled cogene-rationplants do not show better performance than a conventionalRankine steam cycle.When different correlations for the thermodynamic propertiesare used in simulations of a simple ammonia-water power cyclethe difference in efficiency is not larger than 4 %,corresponding to about 1.3 percentage points. The differencesin saturation properties between the correlations are, however,considerable at high pressures, high temperatures and high massfractions of ammonia. The use of different correlations for thethermodynamic and transport properties causes a noticeabledifference in the predicted heat exchanger areas required fordifferent processes.Keywords:ammonia-water mixture, cogeneration,correlation, direct-fired power cycle, gas engine, Kalinacycle, power cycle, thermophysical properties, waste heat