Variable load modes and operation characteristics of closed Brayton cycle pumped thermal electricity storage system with liquid-phase storage

Abstract

As a new type of large-scale energy storage system, pumped thermal electricity storage (PTES) requires frequent load variation to smooth out grid fluctuations. However, there is a lack of research on the variable load of PTES systems. Therefore, five variable load methods are innovatively proposed in this paper, and the dynamic characteristics of the closed Brayton cycle PTES system with liquid-phase storage are simulated for variable load, separately. The results show that: for the same total air discharge time, during charge process, the rotor speed fluctuation rates of the five modes are “air charge + low-pressure and high-pressure sequential air discharge (CLHS)” (+0.80%), “air charge + low-pressure air discharge (CL)” (+1.07%), “air charge + high-pressure air discharge (CH)” (+1.40%), “air charge + high-pressure and low-pressure sequential air discharge (CHLS)” (+1.51%), “air charge + high-pressure and low-pressure simultaneous air discharge (CHL)” (+2.51%), from small to large. During discharge process, the rotor speed fluctuation rates are “CL” (-3.31%), “CHLS” (-3.96%), “CLHS” (-4.39%), “CH” (-5.61%), “CHL” (-9.83%), from small to large. During both charge and discharge processes, the load regulation ranges are “CHL”, “CLHS”/“CHLS”, “CH”, “CL”, from large to small. It can be seen that the modes with smaller rotor speed fluctuation rates also have smaller load regulation ranges, while the modes with larger load regulation ranges have larger rotor speed fluctuation rates. Therefore, in operation, different variable load modes should be selected according to the actual needs of rotor stability and load regulation range. The results of this study can provide a reference for the actual operation of pumped thermal electricity storage system.