| CPC G01F 1/88 (2013.01) [F17D 3/18 (2013.01); G01F 1/74 (2013.01)] | 5 Claims |
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1. A flow metering method based on converted slip ratio fitting for wet natural gas, being implemented according to the following steps:
step 1, acquiring a fitting array, wherein
the fitting array comprises some one-to-one corresponding data comprising a gas Froude number Frg, Venturi pressure loss PL, Venturi differential pressure DP1, a converted slip ratio SS, a dryness fraction X and an overrated factor OR;
step 2, fitting relationships between the gas Froude number Frg and the Venturi pressure loss PL and Venturi differential pressure DP1 according to Formula (1) as follows:
Frg=F(DP3) Formula (1),
wherein
DP3=DP1−PL,
and
a gas Froude number calculation formula is obtained by means of fitting;
step 3, setting a division range according to a data size of the gas Froude number Frg, and dividing the fitting array into three sections, namely a high Frg section, a medium Frg section and a low Frg section;
fitting, according to the section to which the fitting array belongs, relationships between the converted slip ratio SS and the Venturi pressure loss PL and the Venturi differential pressure DP1 in sections, as shown in Formula group (2) as follows:
 wherein
x1,x2 are both natural numbers, x1<x2,
k=DP1/DP3,
and
a piecewise converted slip ratio calculation formula is obtained by means of fitting;
step 4, fitting a relationship between the overrated factor OR and the converted slip ratio SS according to Formula (3) as follows:
OR=f4(SS) Formula (3),
thereby obtaining an overrated factor calculation formula;
fitting a relationship between the dryness fraction X and the converted slip ratio SS according to Formula (4) as follows:
 thereby obtaining a dryness fraction calculation formula;
step 5, acquiring a calculation array of wet gas to be measured, wherein
the calculation array comprises some one-to-one corresponding data comprising real-time Venturi pressure loss PLs, real-time Venturi differential pressure DP1s, and a real-time gas phase density ρg, wherein the method comprises measuring at least the real-time Venturi pressure loss PLs and the real-time Venturi differential pressure DP1s with a Venturi flow meter,
a real-time ks value is calculated according to Formula (5) as follows:
 and
a real-time DP3s value is calculated according to Formula (6) as follows:
 step 6, calculating a real-time overrated factor ORs and a real-time dryness fraction Xs;
plugging the real-time DP3s value into the gas Froude number calculation formula obtained in step 2 to obtain a real-time gas Froude number Frgs, comparing the three values of Frgs,x1 and x2, and determining the section to which the calculation array belongs by taking the division range set in step 3 as a standard;
plugging the real-time ks value into the corresponding section in the piecewise converted slip ratio calculation formula obtained in step 3 to calculate and obtain a real-time converted slip ratio SSs;
plugging the real-time converted slip ratio SSs into the overrated factor calculation formula obtained in step 4 to calculate and obtain a real-time overrated factor ORs;
plugging the real-time converted slip ratio SSs into the dryness fraction calculation formula obtained in step 4 to calculate and obtain a real-time Xs;
step 7, calculating an overrated gas mass flow rate Mtp according to Formula (7) as follows:
 wherein C and E are both constants, and d represents a diameter of the throat of a Venturi;
step 8, calculating a real-time gas phase mass flow rate Mg of wet gas to be measured according to Formula (8) as follows:
 and
step 9, calculating a real-time liquid phase mass flow rate Ml of the wet gas to be measured according to Formula (9) without requiring application of gamma ray technology as follows:
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