Design Concept and Performance of a Multistage Ifitegrally Geared Centrifugal Compressor Series for Maximum Efficiencies and Operating Ranges

Abstract

By its very design principle, the multistage integrally geared centrifugal compressor offers a number of advantages over other compressor concepts. They lead to distinctly higher machine efficiencies and wider operating ranges. This paper will report on the design concept and performance of a multistage integrally geared centrifugal compressor series. With this design concept a solution optimizing machine efficiency, operating range, and construction expenditure is achieved in each particular case. To meet the concept requirements two impeller families featuring different blade exit angles have been developed. Both impeller families, each including three impeller types, cover the required flow coefficient range of 0.025 ≤ Ø ≤ 0.125 The high specific speed impeller versions are equipped with splitter blades. Adaptation of the flow within the range assigned to each type is achieved by trimming the shroud contour. The impellers were optimized with the aid of quasi-three-dimensional flow field calculations and finite element stress analyses. Systematic stage experiments helped to examine and further optimize the performance. The application range of the VK compressor series covers volume flow rates from 8,000 m 3 /h to 250,000 m3/h. By varying the number of stages it is possible to obtain pressure ratios up to about 50. These compressors operate under approximately atmospheric inlet conditions. A modified series (HVK series) of the same design principle permits inlet pressures up to about 10 bar and outlet pressures up to about 80 bar. The basic design concept is the same for both series. It will be explained in detail how systematic grading of compressor frame sizes and subdividing main components into standard subassemblies helps to arrive at a solution that offers high technical quality and yet involves low cost in each application. The capability of the series (efficiencies and operating ranges) will be demonstrated by examples of characteristic performance maps measured on some of the machines built, such as a four-stage compressor designed for a volume flow rate of 250,000 m3/h in which stage efficiencies have been proved to be above 87 % (cf. Fig. 19).