SEMINAR AGA REPORT NO 7

AGA REPORT NO.7

MEASUREMENT OF NATURAL GAS BYTURBINE METERS.

NJOKU, WILLIAM. CHIBUZOR,ITEC/SCAAP TRAINEE1ST AUGUST – 31ST OCTOBER,2014

TABLE OF CONTENTS CHAPTERS PAGE1.INTRODUCTION……………….…………………… 3-62.OPERATION CONDITION…..…………………… 7-133.PERFORMANCE REQUIREMENTS.…………. 14-174.TURBINE METER CALIBRATION..……………. 18-195.TURBINE METER INSTALLATION

SPECIFICATIONS………………………………….. 20-296.ENVIRONMENTAL CONSIDERATIONS…….. 30-387.VOLUMETRIC FLOW AND MASS FLOW

MEASUREMENT…………………………………... 38-43

1. INTRODUCTIONSCOPE

Turbine meter is an axial flow meter which can be used for measurement of natural gas. About 2inch/50.8mm and larger bore diameter in which the entire gas stream flows through the meter rotor relative to its rotational speed.

It could be used to measure a broad range of fluid other than natural gas .e.g. Well effluents/crude oil on the well head.

PRINCIPLE OF MEASUREMENT OF TURBINE METERS

Turbine meters are inferential meters that measures flow by counting the revolutions of a rotor, with blades, which turns in proportion to the gas flow velocity.

From the geometry and dimensions of the rotor blades and flow channel, for a particular turbine meter size and model, the gas volume at line conditions can be inferred from counting the number of rotor revolutions.

The revolutions are transferred into digital readout or electronic signals by some combination of mechanical gearing, generated electronic or optical pulses, or frequency. The accumulated line volume can be converted to base volume at standard or contract conditions by accessory devices.


Turbine can operate over a wide range of gas and ambient conditions.

The upper flow capacities are established and limited by maximum local internal gas velocities, noise generation, erosion, rotor speed, shaft bearing wear and pressure losses.

The maximum flow capacity at line conditions is fixed for a particular turbine meter regardless of the operating pressure and temperature.

The maximum base flow capacity increases in accordance with Boyle’s laws and charles’ law ie Pα1/V(mass and temperature constant) and VαT(Pressure constant) respectively. Minimum flow capacities are limited by fluid and non fluid drag (i.e., wind age and mechanical friction losses, respectively) that cause a particular turbine meter design to exceed the desired or prescribed performance limits.

Turbine meter is calibrated base on the k-factor :Pulse/unit volume or liter.

2. OPERATING CONDITIONSGAS QUALITY

The meter should operate with any of the normal range natural gas composition mixture, reference to table 1 of AGA Report No.8, Compressibility factors of natural gas and other related hydrocarbon gases. See table below:

RANGES OF GAS MIXTURE CHARACTERISTICS CONSISTENT WITH THIS REPORT

QUALITY NORMAL RANGE

EXPANDED RANGE

Relative density*

.554 to .87 0.07 to 1.52

Gross heating value**

447 to 1150 Btu/Scf

0 to 1800 Btu/Scf

Gross heating value***

18.7 to 45.1mj/m3

0 to 66mj/m3

Mole percent Methane

45.0 to 100.0 0 to 100.0

Mole percent Nitrogen

0 to 50.0 0 to 100.00

Mole percent carbon dioxide

0 to 30.00 0 to 100.00

Mole percent ethane

0 to 10.0 0 to 100.00

Mole percent propane

0 to 4.0 0 to 12.0

Mole percent total butanes

0 to 1.0 0 to 6.0

Mole percent total pentanes

0 to 0.3 0 to 4.0

Mole percent hexanes plus

0 to 0.2 0 to dew point

Mole percent helium

0 to 0.2 0 to 3.0

Mole percent hydrogen

0 to 10.0 0 to 100.0

Mole percent carbon monoxide

0 to 3.0 0 to 3.0

Mole percent argon

# 0 to 1.0

Mole percent oxygen

# 0 to 21.0

Mole percent water

0 to 0.05 O to dew point

Mole percent hydrogen sulfide

0 to 0.02 O to 100.0

RANGES OF GAS MIXTURE CHARACTERISTICS CONSISTENT WITH THIS REPORT

*Reference Condition: Relative density at 60OF/15.556OC, 14.73 Pisa.

**Reference Conditions: Combustion at 60OF

, 14.73psia; density 60OF/15.556OC, 14.73psia

***Reference Conditions: Combustion at 25OC, 0.101325mpa; density at 0OC, 0.101325mpa.

# The normal range is considered to be zero for these compounds.

OPERATING PRESSURE The operating condition is always with the range

specified by the meter manufacturer.TEMPERATURES, GAS AND AMBIENT

The turbine meter should operate within the given manufacturers flowing gas and ambient temperature specification.

Depending on the material of construction, turbine flow meters can operate over a flowing gas and ambient range of -40OF to 165OF (-40OC to 74OC).

It is important the flowing gas temperature remain above the hydrocarbon dew point of the gas to avoid positive meter damage and error in measurement.

EFFECT OF GAS DENSITY The density could have three principle effects on the

meter performance of the gas turbine meter; RANGEABILITY : The rangeability of a turbine meter

increases as gas density increases ie Turndown ratio(Ratio of the maximum to minimum flow rates base on specified performance requirement)

PRESSURE DROP: The pressure loss across a turbine meter increases as the gas density increases.

ERROR: The operating characteristics may change as gas density changes.

GAS FLOW RATE CONSIDERATIONS The manufacturer shall provide the range of flow rate at

various pressures.CHOICE OF TURBINE BLADE TYPE

For precision applications, the use of Helical blade turbines rather than Flat blade turbines is recommended as the helical blade have;

Better flow stability Lower sensitivity to viscosity variations Very good linearity(±0.15% or better) Greater operating flexibility owing to the possibility of less

frequent calibration and of using performance table or curves(k-factor versus flow rate); ISO4124 or APIMPMS5.3

FLAT AND HELICAL BLADE TURBINE METER

3. PERFORMANCE REQUIREMENTS GENERAL PERFORMANCE TOLERANCE Flow limits for Qmin, Qt and Qmax for each meter

design and size are specified by the manufacturer.Under atmospheric pressure the meter performance shall be within the following tolerances after calibration;

Repeatability........................ ±0.2% from Qt to Qmax Maximum peak-to-peak error….. 1.0% above Qt Maximum error…………. ±1.0% from Qt to Qmax, and

±1.5% from Qmin to Qt Transition flow rate…… Qt not greater than 0.2 Qmax.

IMPORTANT POINTS The tolerances apply after adjustment of the change

gears(if any) and/or k-factor setting and final application of the final meter factor.

The tolerances apply after any corrections carried out within meter but prior to the application of any linearization algorithms by equipment auxiliary to meter.

These tolerances are applicable at atmospheric pressure. Turbine meter performance are expected to improve dramatically relative to the operating gas pressure increase. The increase in meter performance is with smaller values for repeatability and maximum peak-to-peak error, provided the meter is calibrated for the intended condition.

PRESSSURE INFLUENCE According to the research on effect of

pressure on turbine meter performance conducted in 2002 and 2003,to minimize error, the turbine meter should be calibrated for the applicable operating conditions.

INDIVIDUAL METER TESTS The manufacturer shall test the

integrity of all pressure-containing components for every turbine meter. This test shall be conducted in compliance with the appropriate industrial standard, (ANSI/ASME B16.1, B16.34 etc)

4. TURBINE METER CALIBRATION For establishment of satisfactory performance

characteristics, every turbine meter should be calibrated under a condition acceptable and agreed upon between the parties of the transaction.

For best performance, the calibration conditions should correspond to the expected in-service conditions such as;Fluid characteristics, operating pressure, expected flow rates, the use of a dedicated meter body, inlet and outlet piping characteristics, including other factors that can affect meter performance.

CALIBRATION CONDITION Research has shown that the performance of

turbine flow meters varies with changes in flow rate and operating pressures.

This significant variations are related to changes in Reynolds number; Re= U.D.ρ/μ.

The changes in some cases also relates to density and are significant at low and intermediate operating pressure and flow rates.

Therefore for optimal measurement, attention to these variations and changes are very important.

5. TURBINE FLOW METER INSTALLATION SPECIFI CATIONS

GENERAL CONSIDERATIONS FLOW DIRECTION Turbine flow meters designed only for one directional

flow, shall be installed as stipulated. Reverse flow could damage meter internals and may result to registration of error.

The manufacturer may be consulted if reverse flow has ever occurred. In the case for a reverse flow expected, additional valving is necessary to allow gas to flow through the meter in the forward direction only, unless the meter is recommended for bi-directional flow.

METER ORIENTATION AND SUPPORT

Turbine meter designed for horizontal installation, shall be installed as stipulated.

For vertical installation, the manufacturers recommendations for piping configuration and maintenance should be followed. The meter piping should be adequately supported and installed so as to minimize strain on the meter body.

METER RUN CONNECTION

Meter and adjacent pipe section should have same nominal diameter. Meter inlet and outlet connections and flanges shall be aligned correctly concentrically and gasket shall not protrude into the flowing gas to avoid affecting the flow performance.

TEMPERATURE WELL LOCATION Temperature well shall be located downstream

of the meter to keep distances to a minimum. Temperature well are installed between one

and five nominal pipe diameters from the meter outlet but upstream from any valve or flow restrictor. It is important that the temperature well be installed to ensure that heat transfer from the adjacent piping and radiation affect from the sun do not influence the temperature reading of the flowing gas.

PRESSURE TAP LOCATION

The pressure tap designed by the manufacturers on the meter shall be used as the point of pressure sensing for recording or integrating instruments and during calibration.

FLOW CONDITIONING The conditioner is installed at the upstream

of the turbine meter to eliminate the effect of swirl and or asymmetric flow. Headers, Pipefitting's, valves and regulators preceding the inlet may cause disturbed flow conditions which will be absorbed by the flow conditioner. There shall be no protrusion into the pipe between the meter and flow conditioner to avoid gas flow disturbances.

RECOMMENDED INSTALLATION CONFIGURATIONS

Turbine meters may be operated according to the recommended installation configuration with acceptable results, while more severe piping arrangements may result in considerable error. The magnitude of error, if any, will be a function of the extent of the flow disturbances, the meter’s design, the quality of external and internal flow conditioning, and/or the meter’s ability to adjust to such conditions. More so other configurations may be used provided they are shown to be acceptable based on published experimental data.


The recommended installation, diagram below, includes at least 10 nominal pipe diameter of straight pipe upstream of the meter inlet, with a flow conditioner outlet located 5 nominal pipe diameters upstream of the meter inlet.

A minimum length of 5 nominal pipe diameter of straight pipe is included downstream of the meter. There shall be no pipe connections within the upstream or downstream piping other than pressure taps, temperature wells or flow conditioning elements.


NOTES:[1] Recommended spacing, unless

otherwise supported by published test data for the flow conditioning element.

[2] No pipe connections or protrusions allowed within this upstream section.

[3] For recommended size of blow down valve see table 2, Located downstream of the meter.

6. ENVIRONMENTAL CONSIDERATIONS

TEMPERATURE Turbine meter should be installed and used within

the ambient flowing gas temperature limits based on manufacturers specifications.VIBRATION

Though turbine meters are not susceptible to vibration. Vibration frequency need to be avoided as it might excite the natural frequencies of the piping set, potentially leading to excessive noise, structural damage to the pipe and as well reduce bearing service life of the meter.

PULSATION Pulsation may occur depending on the design of

the system and the operating condition. Equipments like compressors and fast-cycling

regulators connected near the turbine will cause the meter to over register due to the generated flow pulsations from those equipments.

So pulsation dampers installed between the source of pulsation and the meter helps to eliminate pulsation induced measurement error.

FILTRATION AND STRAINERS Filtration is recommended for most meter applications.

The accumulation of deposits due to a mixture of dirt, mill scale, condensates and or lubricating oils will detoriate meter performance. Under such conditions, it is recommended that a strainer with a basket of 3/32inch maximum hole size and 40 mesh wire liners be installed upstream of the meter to trap the major part of this foreign material. Preferably 10-micron filters could be installed for fine dust/particle removal to save the bearing life.

A pressure differential gauge should be installed across the filter or strainer to indicate pressure drop increase resulting from build up of foreign materials.

THROTHLING Throttling devices like closed valves or

regulators are not to be installed at close proximity as recommended, especially upstream to the meter.

Close installation of such a device may result to an increased uncertainty and/or possibly reduce bearing life.

PRECAUTIONAL MEASURES INSTALLATION RESIDUES For possible damage prevention,

measurement cartridge or meter should be removed if any work such as welding, hydrostatic testing etc., is being carried out very close to the meter. Inside of the turbine meter and piping shall be cleaned thoroughly and inspected for construction debris prior to replacement.

VALVE GREASE Grease can possibly flow from pipeline valve into the gas stream during

lubrication, as such could adhere to turbine blades, thereby affecting meter performance. Such valve type should not be installed upstream of a turbine meter.RUN-PRESSURIZATION

Good practice to provide isolation block valves for meter runs so that the meter(s) can be maintained and calibrated without service interruptions. For single meter run stations, a flow by pass line should also be considered. The isolation valve must be operated in the proper sequence and slowly to avoid reverse spinning and/or over speeding the meter during start up which could damage the stationery rotor.

If operating pressure are over 200psig, a small pressure-loading line and valve around a large or fast acting inlet block valve will allow the meter run to be pressurized slowly to avoid the above damage.

RUN-PRESSURIZATION

Recommended sizes for pressure loading lines and valves are the same as those for blown down valves and the blown down valves are sized to suit the meter capacity to avoid creating extreme gas velocity

TABLE 2- METER TO BLOWN DOWN VALVES SIZING

METER RUN VALVE SIZEMM INCHES MM INCHES50 2 6 0.2580 3 13 0.50100 4 13 0.50150 6 25 1.0200 8 25 1,0300 12 25 1.0

7. VOLUMETRIC AND MASS FLOW MEASUREMENT

Turbine meter is a velocity-measuring device. Rotor revolutions are counted mechanically or electrically and can be converted to a continuously totalized volumetric registration since the flowing volume is at flowing pressure and temperature conditions, it must be corrected to the specified base conditions for account purposes.

EMPLOYING GENERAL GAS EQUATION/LAW b= base condition, f= flowing condition r= rated condition. (Pf )(Vf)= (Zf)(N)(R)(Tf)………. For flow condition. (Pb)(Vb)= (Zb)(N)(R)(Tb)…….. For base condition.

P= Absolute pressureV= volumeZ= compressibility factorN= Number of moles of gasT= Absolute temperatureR= Universal gas constant.

EMPLOYING GENERAL GAS EQUATION/LAW

Since R is an independent gas constant from pressure, temperature and for the same number of moles, Therefore the two equation can be combined to yield:

Vb = Vf (Pf/Pb)(Tb/Tf)(Zb/Zf)FLOW RATE AT FLOWING CONDITION :

Qf = Vf/t……… Qf = Volumetric flow rate at flowing conditionVf = Volume measured at flowing condition during a time interval ‘t’.t = time.

FLOW RATE AT BASE CONDITION Qb = Qf (Pf/Pb)(Tb/Tf)(Zb/Zf).

EQUATIONS FOR CALCULATING MASS FLOW.

Mass flow measurement can be employed to arrive at base volume (Vb) or base volume flow rate (Qb) through the use of a densitometer or calculations from compositional analysis. The mass or mass rate of flow is:

M= (Vf)(ρf)M= Total mass through the meterVf = Total volume through the meterρf= Density of flowing gas.And Qm = (Qf)(ρf)

EQUATIONS FOR CALCULATING MASS FLOW

Where Qm= Mass rate of flow

Qf= Volume rate of flow(actual or registered)

ρf = Density of flowing gas.

since the mass or mass rate of flow at flowing conditions equals the mass at base conditions, it can be stated that: (Vb) (ρb) = (Vf)(ρf) or(Vb)=(Vf) ρf/ρb

EQUATIONS FOR CALCULATING MASS FLOW

(Qb)= (Qf) ρf /ρb. This equations shows that the base

volume (Vb) or base volume flow rate (Qb) can be calculated by knowing the density of the fluid at both flowing and base conditions without the need to measure the flowing pressure (Pf) or the flowing Temperature (Tf) and calculating the compressibility multiplier.

YOUTHANK

SEMINAR AGA REPORT NO 7

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