Computational Flow Analysis of Cryogenic Turboexpander

Abstract

In many kind of cryogenic process plant (e.g. - nitrogen and helium liquefier, air separation units) expansion turbine is the most critical part. A cryogenic process plant consists of many components such as compressor, expansion turbine, heat exchanger, chilling and purification units. In the expansion turbine the temperature of the gas decreases due to the reduction in the pressure and helps in producing the lowest temperature in the refrigeration plant. A cryogenic turboexpander is a highly precise device as it is used at very high speed with a bearing clearance of 10 to 40 µm and the rotor is balanced properly. Special attention is given towards the selection of material, tolerance, fabrication and assembly of the cryogenic turboexpander. This project basically deals with the design and fluid flow analysis of the expansion turbine. The determination of the turbine profile is done by taking data from the design charts which are based on the similarity principles. The method given by the Hasselgruber is used for determining the turbine blade profile. The software packages used for fluid flow simulations are ANSYS bladegen, turbogrid and CFX. The blade is modelled in bladegen by taking the hub and shroud data of the blade profile. For meshing of the turbine model turbogrid is used. For fluid flow simulation purpose CFX-pre is used to specify the parameters at inlet and outlet of the turbine and CFX-post is used for determining and analysing the results. Variation in temperature, entropy, velocity and mach number is determined along the streamline through different graph plots.