MODELLING OF GAS COOLER FOR S-CO2 BRAYTON POWER CYCLE

Supercritical Carbon dioxide (S-CO2) based Brayton power plants are being extensively researched as an alternative to steams-based power cycles due to high degree of recuperation favoured by higher heat capacities in supercritical state. Several studies revealed that PCHEs are suitable candidate for S-CO2 applications. Although, PCHEs have been well researched for various applications, there is very little information pertaining to the design or performance of PCHEs in S-CO2 applications. This paper presents a novel methodology for design of a PCHE as gas cooler for a S-CO2 power block. In the first part, a thermal resistance network (TRN) model developed using MATLAB is used for full scale modelling of gas cooler. The geometrical information obtained from TRN model is used to optimize the overall footprint. In the second part, the MATLAB code coupled with a 1-D design tool (Flownex SE) and an optimization software; Isight, is used to optimize the inlet-exit manifold based on flow admittance approach. The 1-D design tool discretizes the inlet-exit manifolds to achieve optimum combination of flow admittances which facilitates identical channel mass flow rate and inlet pressure across each channel/stack ensuring minimum overall pressure drop. In the current paper a case study for a 10 MW PCHE based gas cooler used in a simple recuperated S-CO2 cycle rejecting heat to ambient at 45 degrees C and 90 bar, is presented. The gas cooler uses water as the primary heat transfer maintained at 4 bar pressure to facilitate single phase heat transfer. Pinch temperature of 5 K is assumed to exist in all heat transfer surfaces. The MATLAB program is coupled with REFPROP property data base to retrieve the thermodynamic properties across all the nodes.