Patent ID: 9416790
Filing Date: 2016-08-16
CPC Classification: F04D

Claim Text:
1. A method for surge protection of a compressor with an inlet and outlet side, wherein an inlet gas flow or stream of the compressor comprises time-varying amounts of water and/or non-aqueous liquid, by continuously or discontinuously measuring and/or determining various parameters of the fluids passing through said compressor, the method comprising the steps of: a) measuring temperature at the compressor inlet and/or outlet side, b) measuring pressure at the compressor inlet and outlet sides in order to determine a compressor pressure ratio, c) measuring fluid mixture density at the compressor inlet and/or outlet side, d) measuring individual volume fractions of gas, water and non-aqueous liquid at the compressor inlet and/or outlet side, e) measuring fluid velocity at the compressor inlet and/or outlet side, f) determining individual flow rates of gas, water and non-aqueous liquid on the basis of the measured individual volume fractions of gas, water and non-aqueous liquid and the fluid velocity at the compressor inlet and/or outlet side, g) based on the determined individual flow rates of gas, water and non-aqueous liquid, determining an actual fluid mixture total volumetric flow rate of gas and liquid at the compressor inlet and/or outlet side, and h) on the basis of the determined compressor pressure ratio and the determined actual fluid mixture total volumetric flow according to steps a-g, controlling a recirculation valve position of at least one recirculation valve arranged between the inlet and outlet side of said compressor in order to ensure that the compressor does not enter into a surge regime; wherein a compressor performance is determined on the basis of the measured fluid mixture total density and determined parameters such as gas composition, gas and liquid properties and by means of a polytropic head equation: where Y TP reflects that the equation is valid also for two-phase flow, and where ρ H1 is the inlet bulk density of the gas and liquid mixture, ρ H2 is the outlet bulk density of the gas and liquid mixture, p 1 is the inlet pressure, p 2 is the outlet pressure, and n TP is determined by: and where a compressor efficiency is then calculated according to: where h TP2 (n=2) and h TP1 (n=1) are defined as: where β is the mass fraction of each of the gas (G), condensate (C), non-aqueous liquid (nonA) and water (W) phases present in the flow at the inlet (n=1) and outlet (n=2).