1、Wet Gas Flowmetering GuidelineASME MFC-19G2008(Technical Report)Wet Gas Flowmetering Guideline ASME MFC-19G2008 THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS Three Park Avenue New York, New York 10016-5990 Date of Issuance: July 11, 2008 This Technical Report will be revised when the Society approves
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7、ERS All rights reservedPrinted in U.S.A. iii CONTENTS Foreword. v Standards Committee Roster. vi 1 Introduction.1 2 Symbology and Definitions .1 3 Types of Wet Gas Flows.12 4 Flow Pattern12 5 Flow Pattern Maps16 6 Meters Used With Wet Gas Flows 18 7 Wet Gas Sampling57 8 Pressure, Volume, and Tempera
8、ture (PVT) Phase Property Calculations58 9 Wet Gas Flowmetering Practical Problems and Recommended Practices.59 10 Uncertainty of a Wet Gas Metering System72 Figures 4-1 Horizontal Wet Gas Flow Patterns14 4-2 Vertical Wet Gas Flow Patterns 15 5-1 A Horizontal Flow Pattern Map .17 5-2 General Flow Pa
9、ttern Map17 6.1.1-1 Reproduction of Murdocks Two-Phase Flow Orifice Plate Meter Plot21 6.1.1-2 Wet Gas Flow Venturi Meter Data 22 6.1.1-3 Wet Gas Flow Venturi Meter Data With Separated Pressure .22 6.1.1-4 Gas Flow Venturi Meter Data With Separated Frg .22 6.1.1-5 NEL Wet Gas 4-in. Venturi Data for
10、31 Bar(a), Frg= 1.5 24 6.1.1-6 NEL 4-in., Schedule 80, 0.75 Beta Ratio Venturi Meter, Gas-to-Liquid Density Ratio of 0.046, Gas Densiometric Froude Number of 1.5 .25 6.1.1-7 NEL 4-in., Schedule 80, 0.75 Beta Ratio Venturi Meter, Gas-to-Liquid Density Ratio of 0.046, Gas Densiometric Froude Number of
11、 2.5 .25 6.1.1-8 NEL 4-in., Schedule 80, 0.75 Beta Ratio Venturi Meter, Gas-to-Liquid Density Ratio of 0.046, Gas Densiometric Froude Number of 4.5 .26 6.1.1-9 4-in. and 2-in. Venturi Meters With Similar Wet Gas Flows Showing a DP Meter Diameter Effect .26 6.1.2.1-1 NEL/Stewarts Turbine Meter Wet Ga
12、s Response for Liquid Mass Fraction of 2%.28 6.1.2.1-2 Tings Turbine Meter Wet and Dry Gas Flow Rate Results at CEESI.29 6.1.2.1-3 Turbine Meter Wet Gas K-Factor Deviation Results .30 6.1.2.2-1 Washington 25, 26 Field Data for Wet Natural Gas Flow31 6.1.2.2-2 NEL Nitrogen/Kerosene 30 bar Vortex Shed
13、ding Meter Data.32 6.1.2.2-3 NEL Nitrogen/Kerosene Vortex Shedding Meter Data Capped at Maximum LockhartMartinelli Parameters Before Data Becomes Erratic.33 6.1.2.2-4 Results of the Linear Fit Wet Gas Correlations Presented in Fig. 6.1.2.1-2 for Known Liquid Flow Rates .33 6.1.2.3-1 NEL 4-in. Coriol
14、is Meter 30 bar Wet Gas Data .35 6.1.2.3-2 NEL 4-in. Coriolis Meter 30 bar Total Mass Flow Rate Wet Gas Data35 6.1.2.3-3 2-in. Micro Motion Coriolis Flow Meter Wet Gas Test Data 36 6.1.2.3-4 Endress + Hauser Coriolis Flow Meter, XLM, due to the blocking effect of the liquid phase causing a gas veloc
15、ity increase. For low liquid loading, dry gas meters are often used to predict the gas flow rate. These meters are often sized using an expected Reynolds number range based on eq. (2). It should be noted that as the liquid loading increases for a given gas flow rate, the assumption that single-phase
16、 flowmetering methods and eq. (2) can be utilized becomes increasingly invalid. LockhartMartinelli parameter: a dimensionless number used to express the liquid fraction of a wet gas stream, and is the square root of the ratio of the liquid inertia if the liquid flowed alone in the conduit to the gas
17、 inertia if the gas flowed alone in the conduit. It is denoted here by the symbol XLMand it is calculated by eq. (4). glg.l.lgg.l.LMQQmmAloneFlowingGasofInertiaAloneFlowingLiquidofInertiaX= (4) There can be considerable confusion over the origins and the physical meaning of this parameter. This is d
18、iscussed in detail in Nonmandatory Appendix A. The natural gas production industry tends to use the LockhartMartinelli parameter to describe the relative amount of liquid in a gas flow. The LockhartMartinelli parameter is often denoted in wet gas metering papers by the upper case letter “X.” It is a
19、lso occasionally denoted as “LM.” Due to the similarity that the upper case “X” has to steam “quality” (or “dryness fraction”), which is symbolized by the lower case “x,” in this Report, the LockhartMartinelli parameter is denoted by “XLM.” Note that in eq. (4) the volume flow rates are at actual fl
20、owing conditions and not at any reference condition. In eq. (4) the gas mass or volume flow rate terms indicates the total gaseous phase (i.e., it includes liquid vapor) mass or volume flow rate. The gas density is the density of the overall gas and liquid vapor phase mix. That is, it includes the e
21、ffect of any liquid component mass saturated in the gas. ASME MFC-19G2008 7 Froude number and the densiometric Froude number: the gas densiometric Froude number (Frg) is a wet gas flow modification of the standard Froude number (Fr). The standard Froude number is defined as the square root of the in
22、ertial force to the gravitational force ratio and is calculated by eq. (5). ForceGravityForceInertiaFr = (5) The gas densiometric Froude number is defined as the square root of the gas inertial force if the gas phase flowed alone to the liquid gravity force ratio. The gas densiometric Froude number
23、is calculated by eq. (6). glgsgggDUForceGravityLiquidForceInertiaGaslSuperficiaFr=(6) Where the term sgU_is the superficial gas velocity as found by eq. (3). Equation (6) is derived from first principles in Nonmandatory Appendix A. The liquid densiometric Froude number is defined as the square root
24、of the ratio of the liquid inertial force if the liquid flowed alone to the liquid gravity force. It is calculated by eq. (7). gllsllgDUForceGravityLiquidForceInertiaLiquidlSuperficiaFr=_(7) whereslU is the superficial liquid flow average velocity, which is calculated by eq. (8). AmUllsl._= (8) Occa
25、sionally, the LockhartMartinelli parameter (XLM) may be described as the ratio of the liquid densiometric Froude number and the gas densiometric Froude number as it will be noted that the liquid gravity forces cancel out in this case. That is: glgllgglglsgslglLMQQmmUUFrFrX.=(9) Weber number: there a
26、re only a few technical papers that discuss the effect liquid properties have on flowmeters being used to meter wet gas flow. These generally discuss gross differences in response when changing liquid types. No technical paper is known to “us” that give details of the effect on meters of changing in
27、dividual liquid properties (i.e., viscosity and surface/interfacial tension). Many researchers suspect that the interfacial tension may have an effect. Fluid mechanics literature defines the Weber number as the ratio of the liquid inertial force to the liquids surface tension force eq. (10). With we
28、t gas flow, this Report defines the Weber number to be the gas inertial force if the gas flowed alone in the conduit to the liquid surface tension force eq. (11). That is: ASME MFC-19G2008 8 ForcesTensionSurfaceForcesInertiaWe = (10) 32.DmWeglgtp= (11) density ratios: many wet gas meters have output
29、s dependent on pressure. When correction factors are required to correct liquid-induced gas metering errors, these factors sometimes include pressure effects. To keep correction factors dimensionless (as well as for other theoretical reasons) phase density ratios are often used instead of the pressu
30、re. That is, gas-to-liquid density ratio lgor liquid-to-gas density ratio gl. In this Report the term “DR” denotes the gas-to-liquid density ratio. gas volume fraction: the fraction of gas volume flow rate compared to the total volume flow rate (i.e., the sum of the gas and liquid volume flow rates)
31、. It is calculated by eq. (12). l.g.g.QQQGVF+= (12) Equation (12) is at actual flowing conditions. The GVF is often expressed as a percentage see eq. (13). () %100*QQQ%GVFl.g.g.+= (13) Note that in eqs. (12) and (13) the gas volume flowing is the volume of the humid gas at flow conditions. That is,
32、the gas volume flow rate is the gas phase and the liquid vapor component. The liquid volume flow rate is the volume of the “free liquid” flow rate. There is often confusion caused by the fact that the parameter called the “gas volume fraction” (or “GVF”) is actually the gas Volume flow rate fraction
33、. It is therefore possible (and common) for engineers to mistake the GVF to be defined as the gas to total unit pipe volume ratio for a steady wet gas flow. It is not. It is the gas volume flow rate to the total volume flow rate ratio of a steady wet gas flow. These two different parameters are only
34、 the same value when there is no “slip” (i.e., no average velocity difference; see para. 2.3.2) between the gas and liquid phases. This condition rarely exists in practice and usually the slip value is unknown. These statements are discussed in further detail in Nonmandatory Appendix B. The liquid f
35、low rate term is the “free liquid” flow rate. The term “free liquid” indicates a flowing component that is in liquid form and is distinct from any liquid vapor phase commingling with the gas phase. A gas flow with a finite relative humidity below saturation is not considered to be wet gas. Saturated
36、 gas flow (i.e., a relative humidity of 100%) is also not considered to be a wet gas flow as long as there is no free liquid. In cases of single component flows (e.g., steam, refrigerants, etc.) there is no difference between “free liquid” quantity and the total liquid component quantity. From here
37、on, unless ASME MFC-19G2008 9 otherwise stated, this document drops the term “free liquid” and uses “liquid” to describe the liquid components flowing in excess to that saturated in the gas phase. For the ASME wet gas flow definition GVF values need to be converted to LockhartMartinelli parameter va
38、lues when evaluating whether a flow is wet gas flow or general two-phase/multiphase flow. This is discussed in para. 2.3.3. liquid volume fraction: the term liquid volume flow (or “LVF”) is sometimes used. This is the liquid flowing volume to the total flowing volume ratio. It is calculated by eq. (
39、14). GVFQQQQQLVFgllgl*.=+= (14) Equation (14) is at actual flowing conditions. The LVF is often expressed as a percentage see eq. (15). %100*QQQ(%)LVFlg.l+= (15) For the ASME wet gas definition, LVF values need to be converted to LockhartMartinelli parameter values when evaluating whether a flow is
40、wet gas flow or general two-phase/multiphase flow. This is discussed in para. 2.3.3. flow quality/dryness fraction: industries dealing with steam flows tend to use “steam quality” (often called the “dryness fraction” or the “gas mass fraction”) to describe the liquid content of the flow. Steam quali
41、ty is denoted as lowercase “x.” The definition of quality is the vapor mass flow rate to the total mass flow rate ratio see eq. (16). g.l.g.mmmx+= (16) This is often expressed in terms of percentage as shown by eq. (17): %100*.+=glgmmmx (17) In steam-based industries, steam is sometimes called wet s
42、team if it is not superheated regardless of the steam quality. That is any quality value greater than zero is sometimes called wet steam flow. In other instances steam is considered wet if the quality is greater than 50%. These wet gas definitions do not agree with the ASME wet gas flow definition.
43、To compare with the ASME definition steam quality values should be converted to LockhartMartinelli parameter values when evaluating whether a flow is wet or general two-phase/multiphase flow. This is discussed in para. 2.3.3. gas-to-liquid flow rate ratio: the liquid content in a gas flow can be des
44、cribed directly as the liquid mass flow rate to gas mass flow rate ratio (or vice versa). A liquid-to-gas ratio can be described by mass or volume ratio. If a volume ratio is used, then it must be stated if the gas volume is at flow conditions or at standard conditions. Metering engineers rarely use
45、 this method of describing liquid content in a two-phase flow but oil industry reservoir engineers often describe flows as a number of barrels of liquid per million standard cubic feet of gas. That is, a liquid volume to a gas volume if the gas flowed at standard conditions. As the actual flow condi
46、tions are usually at nonstandard conditions, a conversion is required to get the gas-to-liquid ratio in actual conditions. Liquid-gas mass or volume ratios should be converted to LockhartMartinelli parameter values when evaluating whether a flow is wet or general two-phase/multiphase flow. This is d
47、iscussed in para. 2.3.3. ASME MFC-19G2008 10 liquid loading: it should be noted that the term “liquid loading” is commonly used in industry and is utilized often in this Report. This term is a nonquantitative expression that relates relative amounts of liquid flowing with a gas flow. That is, a ligh
48、t liquid loading indicates that there is a relatively small amount of liquid flowing with the gas, and a heavy liquid loading indicates that there is a relatively large amount of liquid flowing with the gas. multiphase flow: there is some ambiguity in industry over the meaning of the phrase “multiphase flow.” Technically there are three phases. These are the solid, liquid, and gaseous states of matter. Therefore, technically a multiphase flow is a flow with all three phases, and a two-phase flow is a flow with a com
