A Code for the Preliminary Design of Cooled Supercritical CO2 Turbines and Application to the Allam Cycle

Abstract

This paper documents a thermo-fluid-dynamic mean-line model for the preliminary design of multi-stage axial turbines with blade cooling applicable to supercritical CO2 turbines. Given the working fluid and coolant inlet thermodynamic conditions, blade geometry, number of stages and load criterion, the model computes the stage-by-stage design along with the cooling requirement and ultimately provides an estimate of turbine efficiency via a semi-empirical loss model. Different cooling modes are available and can be selected by the user (stand-alone or combination): convective cooling, film cooling, thermal barrier coating. The model is applied to attain the preliminary aero-thermal design of the 600 MW cooled axial supercritical CO2 turbine of the Allam cycle. Results show that a load coefficient varying from 3 to 1 throughout the machine, and a reaction degree ranging from 0.1 to 0.5 lead to the maximum total-to-static turbine efficiency of about 85 %. Consequently, as opposed to uncooled CO2 turbines, a repeated stage configuration is an unsuited design choice for cooled sCO2 machines. Moreover, the study highlights that film cooling is considerably less effective compared to conventional gas turbines, while increasing the number of stages from 5 to 6 and adopting higher rotational speeds leads to an increased efficiency.

Evaluation of the cooling flow rate of the cooled steam turbine for a novel H₂/O₂ cycle

“…It is sure that the turbine efficiency and cooling flow requirements have a considerable effect on the cycle efficiency (Scaccabarozzi et al, 2019). Therefore, in order to assess the performance of novel cycles, it is necessary to perform a preliminary evaluation of the turbine efficiency and cooling flow requirements based on a few (or even without) experimental data.…”

“…Fiaschi et al (2009) used the semi-empirical cooling model to evaluate the performance of an oxy-fuel combustion CO 2 power cycle. Scaccabarozzi et al (2019) applied the analytical model to assess the performance of the cooled supercritical CO 2 turbine for the conceptual design.…”