The Thermodynamic Analysis Of Modified KCS34with Two-phase Expander

In the context of ever-increasing consumption of fossil energy, improving theenergy efficiency meets the demand of the national policy of “Energy conservation andemission reduction”. Efficient recovering and utilizing the low is one of varietiesmethods of improving the energy efficiency. Low-grade waste heat emerges in a lot ofindustry departments. In China, power plant boiler and industrial boiler are the first andsecond main energy-consuming equipments respectively, which results in the greatimportance of recovering such parts of low-grade waste heat. A research on thethermodynamic performance of Kalina Cycle System34(KCS34) which uses theammonia-water mixing working medium is carried out in this paper, and furtherimproved technique is also proposed. The main research details and conclusions areillustrated as follows:The KCS34is analyzed in the EES simulation platform while the industrial boilerflue gas of400K is taken as the heat source. The conditions of working fluid at turbineinlet exerts great influence on system’s net work as well as thermal efficiency, exergyefficiency and distribution of component’ exergy loss. Results shows that for a constantturbine inlet pressure, the heat absorption will increase as the basic ammonia massfraction increases; for a constant ammonia mass fraction, however, the heat absorptionwill decrease as the basic turbine inlet pressure increases. As both the turbine inletpressure and ammonia mass fraction increase, system’s net work will increase. Thermalefficiency will increase as the turbine inlet pressure increases and decrease as theammonia mass fraction increases. The evaporator, condenser and expander account themain exergy loss of the system. The sum of exergy loss of the three equipmentsmentioned above accounts for70.24%and96.04%at0.90and0.65ammonia massfraction for2.5MPa. As the ammonia mass fraction increases, the sum of exergy loss ofevaporator, condenser and expander also increases. and as the turbine inlet pressureincrease, the sum of exergy loss of evaporator, condenser and expander will decrease.After analyzing the thermodynamic performance of KCS34, further study onimproving the general performance. The technically available two-phase screwexpander is used to replace the throttle valve to recover the expansion work. Twodifferent layouts of the two-phase expander is analyzed, and a comparison between themodified cycles and KCS34is also performed. Results show that different characters appear in the two modified cycles.C-modified cycle shows more thermodynamically beneficial than KCS34, especially atlow ammonia mass fraction for all investigated pressures. Even though no thermalsynergy exits in B-modified cycle, the range of ammonia mass fraction is enlarged.When the turbine inlet pressure is equal to2MPa, B-modified cycle still can operate asthe ammonia mass fraction at0.5, while the C-modified cycle and KCS34only canoperate at0.7of ammonia mass fraction. Normally, a larger ammonia mass fractionrange leads to a safer off-design working condition.The optimization of ammonia mass fraction shows that both C-modified cycle andKCS34almost yield the optimum working conditions at the same ammonia massfraction, while B-modified cycle yields at a lower ammonia mass fraction. The coolestcooling water leads to the optimum working condition for all the three systems.