Optimizing Operation Conditions Of Organic Rankine Cycle System With Dry Working Fluids And Designing Solar Thermal Generation System

With the new energy scenario, the renewable energy develops fast and expands itsapplication range. Solar electricity is one of the most competitive kinds of energy, withinwhich the solar thermal generation technology develops further. For now, the parabolictrough is the most mature solar concentrating technology, providing medium temperature tothe generation cycle. Compared with the steam Rankine Cycle, the Organic Rankine Cyclegets better efficiency under the medium temperature heat sources, with much simplersystem and less initial investment.Within the temperature range of solar trough system,100~400℃, R245fa, pentane, toluene,MDM (Octamethyltrisiloxane) and D4(Octamethylcyclotetrasiloxane) are selected to bethe candidate working fluids. Using MATLAB and NIST Refprop to program thecalculating process of basic ORC and ORC with IHE (Internal Heat Exchanger), the resultsshow that R245fa fits well with operation temperature below150℃, and the basic ORC ofR245fa has got a good efficiency. According to the results, pentane can be used atapproximate300℃, while its autoignition temperature limits its application in such a hightemperature, so its proper operation temperature is250℃. Cycle efficiency declines in turnas toluene, MDM and D4, but the operation temperature increases in this turn. The ORCswith IHE of MDM and D4get much higher efficiency than their basic ORCs.According to the analysis of5fluids above, toluene and MDM are chosen to be workingfluids in the following calculation of solar ORC system. With fix operation temperature300℃, MDM gets its best performance when evaporating pressure is1MPa, while thetoluene gets its best performance when evaporating pressure is2.3Mpa. Comparing thesetwo working fluids, the common point of them is the high temperature exhausted gas atturbine outlet, which leads to the large exergy destruction in condemser. In the analysis ofKA (heat transfer coefficiency K multiplys the heat transfer area A) of their evaporatingsystem, MDM has a larger KA than toluene, moreover, KA number of its preheatingprocess and superheating process is much larger than toluene. Considering various aspects, toluene has better performance than MDM in solar ORC generation system under the fixoperation temperature. Based on the optimized operation conditions of MDM and toluene,the paper also involves calculation of main heat exchangers in solar ORC generationsystem, which is helpful with the real system facilities.