Abstract: In order to solve the problem concerning the lack of design methods for the external supply of secondary high-pressure steam to supercritical thermal power units, this paper studies the design methods for low-capacity supercritical high back-pressure steam turbines. Thermodynamic calculation and structural design methods for small-capacity supercritical high-multiplier-pressure turbines have been developed on the basis of supercritical steam parameters, back-pressures and flow ranges. The turbine designed with this method has a back pressure of 4.0 MPa, a power rating of 25 MW, and a steam capacity of 241 t/h. The nozzle meridian shrinkage profile was used in the flow structure, which effectively solved the problem of big loss caused by short blades. Meanwhile, the turbine adopted a barrel-type cylinder structure, which effectively enhances the response speed of turbine starting and stopping. In addition, the design method solved the problem of assembling the barrel-type cylinder turbine, which can check the feasibility of the turbine design quickly.

Key words: supercritical, high back-pressure, low-capacity, barrel-type cylinder