Abstract
As a new type of energy storage technology utilizing thermal energy, the Carnot battery is one of the most promising large-scale energy storage technologies due to its unlimited geographical conditions, simple structure, and high energy storage density. In this work, a thermodynamic model is established for a Carnot battery energy storage system that makes full use of waste heat resources, and the effects of the heat storage temperature, the components and mass fractions of the zeotropic working fluids on the various performances of the system are investigated. The temperature matching of the working fluids with different temperature glides in the heat exchangers are analyzed by using different mass fractions of R1234ze(E)/ R601a in heat pump and organic Rankin cycle systems, and the exergy flow charts and exergy loss of each component in the system are further investigated. The results show that the selection of the zeotropic working fluid with an appropriate temperature glide can effectively improve the system performance by improving the temperature matching degree and reducing the exergy loss in the heat transfer process. Compared with the evaporator, the temperature match of the condenser plays a more important role in the system performance. The use of R1234ze(E)/R601a in the heat pump improves the cofficient of performance by 4.46%-8.98% compared with that of pure R601a when the heat storage temperature increases from 110.0℃ to 140.0℃, and the use of zeotropic working fluid in the organic Rankin cycle also improves the performance by 8.12%-11.58%. For the power recovery of the whole pumped thermal energy storage system, the power-to-power efficiency improvement of the system using R1234ze(E)/R601a is 12.69%-20.11% and that using R1234yf/R601a is 12.46%-17.73% compared with the use of pure R601a. The power-to-power efficiency of R1234ze(E)/R601a (60/40) and R1234ze(E)/R601a (20/80) in the heat pump and organic Rankin cycle, respectively, are as high as 73.93% at a heat storage temperature of 130.0℃, which is 19.75% higher than the 61.74% for pure R601a.
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