Recovery Of Low-temperature Waste Heat By Optimization Of Organic Rankine Cycle System With Binary Non-azeotropic Mixtures

It has great significance to recycle the low-temperature waste heat below350℃,which is commonly found in building materials, metallurgy, chemical industry, lightindustry and other industrial production. It’s an effective way to improve the energyutilization rate and reduce environmental pollution by transforming the low-temperaturewaste heat into electrical power. Due to the restrictions of the level of temperature, theperforming of the power generation system which making use of the low-temperaturewaste heat is inefficiency. And in order to improve the economy of the thermodynamicsystem as much as possible, the circulation pattern, working fluids and operatedparameters are optimized chooses.Based on the considerations stated above, binary non-azeotropic refrigerantmixtures are applied to organic Rankine cycle (ORC) with purpose of the deeplyutilization of low-temperature waste heat. The theory of ORC’s thermodynamicperformance is investigated under the conditions of variable and constant heat sourcetemperature. And then, for a given heat source temperature, the influence ofthermodynamic parameters under the design and non-design conditions is also exploredin this paper. Finally, aiming at the given heat source temperature, the author set outresearches for its thermo-economy of the system and make a comparation among theinfluence factors of the system’s thermal economy, the optimized variables, as well asthermo-economy under the design and non-design conditions.The result shows: for the variable heat source temperature of the ORC, binarynon-azeotropic mixtures refrigerant isobutane/hexane (0.65/0.35) and isobutane/hexane(0.6/0.4) has a prominent advantage on thermodynamic properties such as exergyefficiency, the net output power and the exhaust temperature. Comparing to the purerefrigerants, they are more appropriate for the deeply utilization of the low-temperaturewaste heat and have the capacity to replace the pure refrigerants working fluid in theOrganic Rankine Cycle system. Meanwhile, this paper indicate that evaporator andcondenser are the major losses of the available energy and the heat exchanger should beemphasized when considering improve the system performance.As to the given heat source temperature of the system, the thermodynamicproperties of the entire system reach to its maximum efficiency. So the thermodynamicproperties can be taken as the design condition of the system. A new pure refrigerants is added into the original ORC system to constitute the binary non-azeotropic refrigerantmixture and R245fa/R601a (0.6/0.4) makes the thermodynamic performance promotebetter while R245fa/R601a (0.9/0.1) gets the best thermo-economy in the analysis. Butthe value of R245fa/R601a (0.9/0.1) has little difference between R245fa/R601a(0.6/0.4) in the analysis of thermal economy. Therefore, taking its excellentthermodynamic properties into account, R245fa/R601a (0.6/0.4) should be consideredas the working fluid when designing the system. Meanwhile, raising the mass ratio ofR245fa in the binary non-azeotropic mixtures, which leads to a declination in APR andLEC, can improve rate of return on investment and net income.