Multi-Stage Centrifugal Compressors and Defining the Optimum Pressure Ratio According to Temperature Limitations

Abstract

Multistaging is one of the conventional methods in centrifugal compressors to increase their efficiency and meet the process and material-related temperature limitations. Simple single-stage compressor pressure ratio is normally limited by constraints of both aerodynamic and structural types. Minimizing the total required gas head equation, resulting from summation of head for each stage, leads to the definition of pressure ratios of each stage which play an important role for required head determination. For minimum power with perfect inter-cooling between stages, there is a theoretical relation for the intake pressures of succeeding stages. As an assumption, both compression ratio and suction temperature is assumed constant in each stage. This assumption results in the mentioned identical magnitude for each stage pressure ratio. When the suction temperatures of gas leaving the intercoolers are different, assuming an identical pressure ratio for all stages, it increases the power required for compressing the gas up to the specified discharge pressure. A numerical method has been presented in this paper with the consideration of changes in suction temperature, compressibility factor, and poly-tropic efficiency. In conclusion it is shown that in order to optimize the power consumption for compressing the gas with specific properties, a numerical method can be used, so that the pressure ratio of the first stage compressor be higher than the successive stages as experimental results suggest.

Step by Step Derivation of the Optimum Multistage Compression Ratio and an Application Case

“…The optimum compression ratio that should be set in the case of different stage isentropic efficiencies is usually not calculated in practice. A numerical calculation has been developed in [ 16 ]. However, this work will solve the problem analytically in Section 4.1 .…”

Modified one-dimensional analysis and two-zone modelling for predicting the performance of radial compressors

“…The aerodynamic design of a compressor is usually carried out in such a manner that minimum losses occur at the design point operation [2]. The selection of the design point is normally based on the condition at which the compressor spends most of its operating time [3]. The knowledge of compressor characteristics under varying operating conditions is necessary for many purposes to predict how the compressor performs over its entire operating range.…”