US 6,546,809 B1Granted

Method for measuring the flow rates of the single phases in a multiphase fluid stream and relevant apparatus

OwnerPaolo Andreussiinventor

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Abstract

A method for measuring the liquid and gas flow rates (QL and QG) of a multiphase fluid stream which comprises: withdrawing a portion of the overall flow rate (Q) under isokinetic conditions, measuring the liquid and gas flow rates (qL, qG) of the withdrawn portion, measuring the pressure drop in correspondence of a t least one of the constricted sections located upstream and downstream of the sampling section and calculating said liquid and gas flow rates (QL, QG) from the sampling section and calculating said liquid and gas flow rates (QL, QG) from the relation QL=(A1/A2) qG, where A1 and A2 are the areas of the constricted section and of the sampling section respectively. There is described an apparatus operating according to this method, comprising a measurement unit coaxial to the conduit with at least a constricted section, sampling probes for withdrawing a portion of flow, a separator of the phases connected to the probes, flow meters located downstream of said separator and pressure meters at the constricted sections.

Claims15

Dependent claims

Method for the measurement of the liquid and gas flow rates QL and QG in a multiphase fluid stream flowing in a conduit (2) and having an overall flow rate Q, comprising:

withdrawing a portion of the overall flow rate Q of said stream from a section of area A1 in which substantially isokinetic conditions are established, at a sampling section of area A2, A2 being a fraction of A1;
separating out said withdrawn portion of fluid stream into single liquid and gas components;
measuring the liquid and gas flow rates qL and qG forming said withdrawn portion of fluid stream and calculating their sum q;
obtaining pressure signals to measure the pressure drop Δp occurring in said fluid stream in at least one of a first constricted section (3) and a second constricted section (4) located upstream and, respectively, downstream of said sampling section;
from said pressure drop Δp calculating the overall flow rate Q, or at least the flow rate QG of the gas fraction thereof, flowing in the corresponding constricted section, on the basis of the relation Δp=αQ2, α being the calibration coefficient of the constricted sections;
calculating the ratio between the flow rate value obtained from said relation and the flow rate q of said withdrawn portion, to verify that it is at least approximately equal to ratio A1/A2;
varying the sampled portion flowrate if the ratio between the overall flowrate to the withdrawn portion flowrate is not approximately equal to A1/A2 and repeating the measure;
and,
calculating the overall liquid and gas flow rates QL and QG from the liquid gas phase flow rates qL and qG in said withdrawn portion from the relations QL=(A1/A2).qL and QG=(A1/A2).qG.

6 more elements

Apparatus for measuring the flow rates of each phase of a multiphase fluid stream comprising a measurement unit (1) coaxially intercepting a conduit (2), including at least one constricted section (3,4) having a smaller cross section than the conduit, means (24) located upstream of said at least one constricted section for sampling a portion of said fluid stream defining a sampling section in which uniform flow conditions are established, the area of said sampling section being A2 that is a fraction of the area A1 of the conduit where the sample is taken, separator means (8) for separating out the phases of said portion associated to said sampling means (24), metering means (12,13,15) for producing flow rate measure signals representing the values of the flow rates of each phase of said sampled portion associated to said separator means (8), means for controlling the flow rates of at least one of said sampled portion and the separated phases, means for providing pressure signals (5,6) associated to said at least one of said sampled portion and the separated phases, means for providing pressure signals (5,6) associated to said at least one constricted section (3,4), and computer means for processing the pressure signals and the flow rate measure signals and controlling the flow through said sampling means, in such a way that the ratio between the sampled flow rate and the total flow rate is approximately equal to A2/A1.

Dependencies are inferred from the claim text.