Research On Characteristics Of Wet Gas Flow Measurement Using X-shaped Gas Ultrasonic Flow Meter

Energy is the most important power for society development nowadays. As thevery common and widely used energy, wellhead produced nature gas and coal bedmethane are both belong to the category of wet gas. In order to realize the onlinenon-separation measurement of wet gas flow in the industrial field and improve theaccuracy of wet gas flow online measurement, X-shaped gas ultrasonic flow meterwas selected to be tested to discover its characteristics of measuring wet gas flow.The structure and principle of measuring single gas-phase flow of X-shaped gasultrasonic flow meter is introduced. On these bases, the measuring principle when itwas used to test wet gas is analyzed. Under the assumption of uniform annular flow, aone-to-one relationship between void fraction and over-reading of X-shaped gasultrasonic flow meter is deduced. Thus, over-reading could be calculated by thiscorrelation directly under annular flow condition if the value of void fraction wasmeasured or calculated. Then results measured by X-shaped gas ultrasonic flow metercould be corrected.The laboratory tests were conducted in TJU adjustable medium-pressure wet gastest loop. Results show that pressure and gas phase superficial velocity are not themajor factors which affect the relationship between over-reading and L-M parameter.A regular relationship between over-reading and L-M parameter is observed thatover-reading will grow with L-M parameter increasing. The reason for largeover-reading and bad repeatability in some work conditions is analyzed with the helpof Mandhane flow pattern map.Five typical void fraction correlations of gas/liquid two-phase flow in horizontalcircular pipe were selected to calculate the predicted value of over-reading.Consequences indicate that the most appropriate void fraction correlation forpredicting over-reading of X-shaped gas ultrasonic flow meter is Armand-Massinacorrelation. The over-reading prediction model based on this void fraction correlationhas a prediction average relative error of3.98%, with a modle uncertainty of4.27%. Acorrelation between over-reading and gas volume fraction was worked out so that thereal situation of flow floating in the pipe will be expressed better.X-shaped gas ultrasonic flow meter and standard venturi tube were installed inseries to measure wet gas flow. Using the method of determining L-M parameter bypressure loss and differential pressure of standard venturi tube introduced in technical report ISO/TR11583, a solution for combination of X-shaped gas ultrasonic flowmeter and standard venturi tube to calculating gas mass flowrate and liquid massflowrate was made. This solution is based on over-reading prediction model and fitsfor work conditions in laboratory.The characteristics of wet gas flow measurement and corrected results of V, Zand X-shaped gas ultrasonic flow meter were summarized. Comparisons between gasultrasonic flow meters with single channel and double channels were made tosummarize the similarities and the differences on several aspects, such as measuringprinciple, characteristics of wet gas flow measurement, over-reading predictionmodels and the combining schemes with long throat venturi tube.