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• Wael Badri

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• Mole (Unidad)
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Presentation on Gas Metering By SNGPL-Metering Department

OVERVIEW Metering Department is responsible for accurate measurement of gas, operation and maintenance of all metering and regulating stations having following major scope of work. 

    

Operation and maintenance of instruments like Valves, Regulators, Relief Valves, Electronic Volume Corrector, Meters etc. Calibration of Instruments such as Pressure / Temperature Recorders, Calorimeters, Gauges etc. Design of metering and Regulating Stations Schedule meter replacement Operation and Augmentation of Distribution network Repair of all types of meters at Central and Regional meter shops and generation of impartial and accurate Meter Inspection Report

What is natural Gas? “Natural gas is a gaseous mixture of hydrocarbons, comprising primarily of methane (CH4) with other hydrocarbons, inert and impurities as minor constituents. ” Composition of natural gas depends on the Production field from which it is extracted

Processes of Natural Gas Extraction & Utilization • Exploration • Extraction • Production – Well Completion – Processing

• Transportation • Distribution

• Exploration In the early days of the industry, the only way of locating underground petroleum and natural gas deposits was to search for surface evidence of these underground formations. Those searching for natural gas deposits were forced to scour the earth, looking for seepages of oil or gas By surveying and mapping the surface and sub-surface characteristics of a certain area, the geologist can extrapolate which areas are most likely to contain a petroleum or natural gas reservoir. Once the geologist has determined an area where it is geologically possible for a natural gas or petroleum formation to exist, further tests can be performed to gain more detailed data about the potential reservoir area. Arguably the biggest breakthrough in petroleum and natural gas exploration came through the use of basic seismology. The basic concept of seismology is quite simple. As the Earth's crust is composed of different layers, each with its own properties, energy (in the form of seismic waves) traveling underground interacts differently with each of these layers. These seismic waves, emitted from a source, will travel through the earth, but also be reflected back towards the source by the different underground layers. It is this reflection that allows for the use of seismology in discovering the properties of underground geology.

Seismology in Practice

Offshore Seismic Exploration

• Extraction

Once a potential natural gas deposit has been located by a team of exploration geologists and geophysicists, it is up to a team of drilling experts to actually dig down to where the natural gas is thought to exist. The exact placement of the drill site depends on a variety of factors, including the nature of the potential formation to be drilled, the characteristics of the subsurface geology, and the depth and size of the target deposit. If the new well, once drilled, does in fact come in contact with natural gas deposits, it is developed to allow for the extraction of this natural gas, and is termed a 'development' or 'productive' well. At this point, with the well drilled and hydrocarbons present, the well may be completed to facilitate its production of natural gas. However, if the exploration team was incorrect in its estimation of the existence of

A Small Drill

Gas Well Schematic

Installing Well Casing

• Production – Well Completion Once a natural gas or oil well is drilled, and it has been verified that commercially viable quantities of natural gas are present for extraction, the well must be 'completed' to allow for the flow of petroleum or natural gas out of the formation and up to the surface. This process includes strengthening the well hole with casing, evaluating the pressure and temperature of the formation, and then installing the proper equipment to ensure an efficient flow of natural gas out of the well.

Well Heads

•

Production Continue ………..

- Processing Natural Gas Natural gas, as it is used by consumers, is much different from the natural gas that is brought from underground up to the wellhead. Natural gas processing consists of separating all of the various hydrocarbons and fluids from the pure natural gas, to produce what is known as 'pipeline quality' dry natural gas. Major transportation pipelines usually impose restrictions on the make-up of the natural gas that is allowed into the pipeline. That means that before the natural gas can be transported it must be purified. While the ethane, propane, butane, and pentanes must be removed from natural gas, this does not mean that they are all 'waste products'.

• ……………. Production

• Transportation The efficient and effective movement of natural gas from producing regions to consumption regions requires an extensive and elaborate transportation system. In many instances, natural gas produced from a particular well will have to travel a great distance to reach its point of use. The transportation system for natural gas consists of a complex network of pipelines, designed to quickly and efficiently transport natural gas from its origin, to areas of high natural gas demand. There are essentially three major types of pipelines along the transportation route: the gathering system, the transmission/interstate pipeline, and the distribution system. The gathering system consists of low pressure, low diameter pipelines that transport raw natural gas from the wellhead to the processing plant. Should natural gas from a particular well have high sulfur and carbon dioxide contents (sour gas), a specialized sour gas gathering pipe must be installed. Sour gas is extremely corrosive and dangerous, thus its transportation from the wellhead to the sweetening plant must be done carefully. To ensure that the natural gas flowing through any one pipeline remains pressurized, compression of this natural gas is required periodically along the pipe. This is accomplished by compressor stations, usually placed at 40 to 100 mile intervals along the pipeline. The natural gas enters the compressor station, where it is compressed by either a turbine, motor, or engine.

Gas Transmission Line

• Distribution Local distribution companies typically transport natural gas from delivery points along transmission pipelines through thousands of miles of small-diameter distribution pipe. Delivery points to (Local Distribution Company) LDCs (i.e. Distribution Regions), especially for large municipal areas, are often termed 'city-gates', and are important market centers for the pricing of natural gas. Typically, LDCs (i.e. Distribution Regions) take ownership of the natural gas at the citygate, and deliver it to each individual customer's location of use. This requires an extensive network of small-diameter distribution pipe.

Why should the gas be measured? 



 

To know the volume of gas being consumed by each consumer for the purpose of billing (revenue collection) Standardize the measurement for each customer, everybody should be treated equally For the reconciliation of the system To minimize the measurement losses

Volume Measurement  



Measurement can be done by filling a known container and passing it to the consumer The above method is not continuous, it can only provide volume of a known quantity in batches For the continuous measurement, rate of flow is determined by time period in which the volume has passed

Volume / Flow Units 

The volume is measured in the following units Gas – cubic feet (ft3), cubic meters (m3), MCF, MMCF



The flow is measured in the following units Gas – cubic feet/hr (ft3/hr), cubic meters/hr (m3/hr), MMCFD

REVIEW OF SOME BASIC CONCEPTS

Pressure of Gas 

Pressure is the force exerted by the gas molecules on the container in which the gas is present

Container

Gas Molecules

Temperature of Gas When the temperature of the gas present in the container rises the gas molecules absorb the heat energy which results in increase in the motion of the molecules (kinetic energy), hence more molecules will strike the walls of the contained meaning that the pressure on the walls will increase

Flow of Gas 



Gas flows when a there is a difference of pressure between two points, the gas flows from a point of higher pressure to the point of low pressure The rate of flow will depend upon the difference of pressures between the points

……REVIEW OF SOME BASIC CONCEPTS



PRESSURE: Force per unit Area, P = F / A (Units: lbforce/inch2 )



ATMOSPHERIC PRESSURE: (PSIA) Ponds per square inch absolute. It is measured by a barometer and considered to be 14.73 psia at sea level. As we go higher the value of atmospheric pressure decreases. For instance atmospheric pressure at Karachi ≈ 14.73 psia , Lahore ≈14.4



GAUGE PRESSURE: Gauges are used to measure pressure in the gas system. They measure pressure above atmospheric pressure. So that absolute pressure = Atmospheric pressure + Gauge pressure.



QUESTION: Will absolute pressure be independent of



It may be remembered that absolute pressure is independent of height effect. The pressure gauge in Karachi measuring zero psig which is equal to 14.73 psia will measure gauge pressure of -0.33 psig at Lahore. This error will be adjusted by adding 0.33 psi to bring gauge reading to zero. So that Absolute pressure = 14.4 + 0.33 = 14.73 100 psig

114.7 psia

75 psig

89.7 psia

50 psig

64.7 psia

25 psig

39.7 psia Zero Absolute Pressure

Vacuum

{

14.7 psia

MEASUREMENT OF GAS 

Gas is a compressible fluid



Volume of gas keeps changing with changing Pressure & Temperature



Define Standard cu-ft of gas.



SNGPL defines one cu-ft as a volume of gas which occupies 1 cuft 3 space at a pressure of 14.65 psia and 60ºF “called base condition”.

1 cuft

L

½ cuft

L/2

After application of Pressure on the plunger

GAS LAWS

Ideal Gas Laws •

Boyle’s Law:



At constant temperature, the volume of a given mass of gas is inversely proportional to the applied pressure. Mathematically,



This means that at constant temperature, the product of Pressure and Temperature of a given mass of gas is always constant. Thus

Volume

(at constant temperature)

1/Pressure

Pressure

P1 V 1 = P 2 V 2

Volume

…..Ideal Gas Laws 

Charles Law:

At constant pressure, the volume of a given mass of gas is directly proportional to its absolute temperature:-

P= 1 atm. P= 2 atm.

Volume

P= 3 atm.

Temperature

Volume of a definite mass of gas (say 1 mole) is plotted against absolute temperature

…..Ideal Gas Laws 

Pressure – Temperature Law:

At Constant volume, the pressure of the given mass of the gas is directly proportional to the absolute temperature. Mathematically

• Avogadro’s Law & Standard Molar Volumes: Equal Volumes of all gasses under the same conditions of pressure and temperature contain the same number of molecules i.e. Standard Molar Volume 1 Mole of and ideal gas at STP = 22.414 dm 3 (1 dm3 = 1 litrs) One mole of a gas i.e. 22.414 dm3 at STP contain 6.022 × 1023 , this number is called Avogadro’s number, NA

The General Gas Equation Boyle’s Law:  Charle’s Law:  Avogadro’s Law: Combining these laws we get: 

In General we can say:

Ideal or Universal Gas Constant  

The Gas Constant R: The value of R is independent of nature of gas but dependent on the number of moles of the gas and units of P, V & T used:

Kinetic Molecular Theory The pressure of a gas is the result of the collisions of the molecules with the walls of the container. The theory is based on following assumptions:

Gases consist of discrete molecules that are similar as regard to the mass and size



Molecules are far apart and they exert no attraction on each other except liquefaction



The volume occupied by the gas molecules is negligible as compared to the total volume



Gas molecules are in continuous random motion, straight line motion with different V



Collision of the gas molecules and wall of the contained are perfectly elastic



Pressure exerted by the gas is due to the elastic collision of the gas with container walls



The average Kinetic energy is equal to the absolute temperature



The motion imparted to the molecules by the gravity is negligible



Laws of mechanics are applicable to the motion of the molecules

Concept of Compressibility: Real gas in general, closely follow the General Gas Law, however, they do deviate, and for accurate measurement this deviation must be considered. This definition is termed as “Compressibility” so another multiplying factor called compressibility (z) is used as another correction factor. In case of orifice meter calculation Fpv (Super Compressibility Factor) = √(1 / Z) However for other meters the super compressibility factor is equal to S = 1 / Z = (Fpv)2

Experiments by Charles and Gay Lussac: At constant pressure, the volume of a given mass of gas increases or decreases by 1/273 of its volume at 0°C for every 1°C rise or fall in temperature

Temperature

This temperature, -273°C (or -273.15 to be exact) is the temperature at which the volume of the gas becomes zero is known as absolute zero and is taken as zero of Kelvin scale.

Volume



Gas Measurement Through Gas Equations: Pb = Base Pressure = 14.65 psia Vb = Needs to be calculated Tb = Base Temperature = 60 °F = 459.67+ 60 = 519.67°R Pf = Flowing gas Pressure on the meter, fixed pressure or measured by a recorder/ volume corrector (measured value) Vf = Flowing gas volume at the flowing pressure and temperature (volume recorded by the meter) Tf = Flowing gas temperature (measured value) Pressur e Factor

Temp . Facto r

Uncorrect ed Vol.

For correction due to compressibility multiply the equation by appropriate Compressibility Factor.

…..Gas Measurement Through Gas Equations: 

The equation of gas measurement becomes

Compressibility natural gas at base conditions is assumed to be 1

Where S is Compressibility factor



For meters other than the orifice meters, we need to measure following flowing gas parameters.



 

Flowing volume at line pressure and temperature conditions. This is accomplished by installing a meter (P.D. meters/ Turbine meters) Flowing gas Pressure Flowing gas Temperature



Bernoulli’s Equation : V2 / 2g + P / ℓ + Z = constant V = velocity g = Acc. Due to gravity P = Static Pressure

ℓ = Sp. Wt. of fluid = 62.416 for H2O

Z = Feet of Height above

Terms: V2 / 2g = velocity Head in feet (Kinetic Energy) P / ℓ =Pressure Head in feet (energy stored as pressure) Z = Head in feet (Height, Potential Energy) Given Q = 1000 Gallons/min Dia. = 6”

(nominal 6” = 6.065” inside dia.),

conversion 1 cu-ft = 7.48 Gallons

ℓ = 62.4 lb/ft3

P= 100 psi = 100×144 psft

Pressure P2 = ?

Q = 1000 Gal/min × 1/60 = 16.67 Gallons/sec Q = 16.67 / 7.48 Gall/sec × cu-ft / gallons = 2.23 cu-ft / sec, A=

=3.14(6.065)2/4=28.89in2

=28.89/144 = 0.2005 ft2

V = Q / A = 2.23 / 0.2005 = 11.15 ft/sec V12 / 2g + P1 / ℓ + Z1 = V22 / 2g + P2 / ℓ + Z2 (11.15)2 /2×32.2 + 100×144/62.4 +100 = (11.15)2/2×32.2 + P2 / 62.4 +150

Solving Equations we get P2=11300 lbs/ft2 P2= 11300 / 144 = 78.5 psi NOTE: (i) each 2.31ft of head of water is equal to one pound per square inch pressure (ii) The Bernoulli’s equation is considered the foundation for study of fluid motion (liquids as well as gas) and it may be used to solve majority of problems in fluid flow. (iii) The equation we have discussed is for idealfrictionless system. If friction is to be considered this equation will look like V12 / 2g + P1 / ℓ + Z1 – f1 = V22 / 2g + P2 / ℓ + Z2

For gas flow Bernoulli’s equation reduces to V12 / 2g + P1 / ℓ = V22 / 2g + P2 / ℓ Or

P2 – P1 / ℓ = V12 – V22 / 2g

the above equation can only be used if the pressure difference is less than 3% otherwise the expression for relationship between pressure and density would be incorporated.

Volume Measurement by Gas Meters Gas meters are used for the accurate and continuous measurement of gas Gas Volume Meters

Positive Displacement Meters The meters which measure gas by filling in the chambers of known volume and then displacing the gas, hence direct measurement

Inferential Meters The meters which uses some property of fluid flow usually velocity to inference volume, hence in-direct measurement

Diaphragm Meters

Turbine Meters

Rotary Meters

Orifice Meters Sonic Meters

Meters 

Meter Capacity:



Maximum Allowable Operating Pressure (MAOP): The maximum pressure at which meter can be

The maximum flow of gas that a meter can provide is known as meter capacity. As the flow of gas through the meter increases, the differential pressure (between meter inlet and outlet) also increases

operated is called MAOP



Rangebility:



Cyclic Volume:



Pressure absorption or Differential Pressure:

The band of lowest and highest flow which a meter can accurately measure The Volume of gas that has passed in one complete cycle of the gas meter i.e. movement of all the moving components has completed The difference of pressure measured at inlet and outlet of connections of the meter during meter operation

Types of Gas Meters and their Principles of Operation 1.

Positive Displacement Meters: These meters measures the known volume of gas in the fixed chamber and displaces this volume. The no of fixed volumes displaced are calibrated to provide volume of gas passed through the meter on its index. These meters have deformable chamber walls in which volume of gas fills and displaces out. These meters are further subdivide into :(i) (ii)

Diaphragm Meters Rotary Meters

A is emptying B is filling C is empty D is full

A is empty B is full C is emptying D is filling

A is filling B is emptying C is full D is empty

A is full B is empty C is emptying D is filling

Operation Schematic of Diaphragm Meters

Range ability 100 : 1

DIAPHGRAM METERS REMUS G4 MKM250 RW275 AC250 SP250 RW310 MKM400 RW415 AL425 RW750 AL800 SP1000 AL1400 RW1600 RW3000 AL2300 RW5000 RW10000

DIAPHGRAM METERS

RW-750

SP-1000 1400

RW-1600

RW-5000

RW-5000

Al-2300

RW-3000

Al-

Rotary Meters

Fundamentals of Rotary Measurement Clearance b/w impeller tips cylindrical walls & head plates: 0.001” – 0.015”

0.05” w.c. Differential pressure causes the impellers to move and flow of gas starts



Rotary Meter Operation Range ability 25 : 1

Rotary Measurement Advantages 





Disadvantages

Compact, smaller sizes



Heavy, larger sizes



Low-flow limitations

Various sizes available



Maximum pressure limitation



Potential service interruption



Susceptible to contamination



Requires lubrication

Wide variety of readouts

ROTARY METERS RC3M175 RC5M175 RC7M175 RC11M175 RC16M175 RC23M175 RC38M175 RC56M175 RC102M175 D5 D6 D7 D8.8 D14 D23 DELTA G400 UGI 56M RVG100 RVG160 RVG250 ROMET3000 ROMET11000 ROMET23000

ROTARY METERS CVM-5.3 38M175

D-9 Delta D-23

RVG-250

Rc 7M175

Delta G-100

Rm-38000

Rc6M175

Delta D-23

UGI-56000

G-1000

Rc



Inferential Meters : These meters do not directly measure the volume of gas but uses some property of fluid flow to inference the gas volume. Usually velocity of fluid stream is measured through the fixed Area and volume is computed by using formula Q = V×A These meters are further sub divided into: (i) Turbine Meters (ii) Orifice Meters (iii) Sonic Meters (iv) Vortex Meters

Turbine Meters Gas turbine meters are velocity sensing devices as are orifice meters. The direction of flow through the meter is parallel to a turbine rotor axis and the speed of rotation of the turbine rotor is nominally proportional to the rate of flow. Gas volumes are derived or “inferred” from the rotations of the turbine rotor.

A turbine meter introduces a restriction (called a nose cone) of known cross-sectional area into the gas stream as does an orifice meter. However, the turbine meter determines flow velocity through this restriction by counting rotations of a turbine rotor mounted in the open or “throat” area of the restriction. The turbine blade rotations are transferred through a gear train to a wide variety of readout devices where totalized volume at line conditions is displayed.

FLOW PROFILES “LAMINAR”

56

TURBULENT FLOW PROFILE

57

SWIRL FLOW PROFILE

58

Assuming a “Perfect” Turbo-Meter 

A single gas molecule impinging on the rotor blade would cause the blade to move with:  No retarding forces to resist movement (mechanical friction)  No loss of energy from the flowing gas (fluid friction)  Constant velocity and the  Direction & angle of flow would remain constant

Actual Turbo-Meter 

Under actual operating conditions, the speed of the rotor is affected by: 

Mechanical Friction  



Fluid Friction   



Bearing and gearing wear Readout devices Windage drag of rotor Surface roughness Interaction of flow layer

Installation Effects    

Negative swirl Positive swirl Jetting Pulsation

The Worst-case Single Rotor Turbo-Meter Condition

 Gas flow deflects off the

locked rotor at the angle of the rotor blades

Turbo-Meter Fundamentals Inferential

Measurement Device

“Infers” volume of gas by measuring the velocity of gas through a known area.

Basic Components of a Turbo-Meter Readout

Gear Train

Q= V× A Flow Rate

Velocity

Area Nose Cone Rotor

Installation Consideration ?

Body

Auto Adjust Turbo Meters Operating Conditions Adjusted Volume Pulse Output

Main Rotor

Mechanical Volume

Sensing Rotor

(MR Volume – SR Volume)

Main Rotor

Sensing Rotor

Auto-Adjust Turbo-Meter Technology  Self-Adjusting Feature 

 

Detects and adjusts for changes in upstream flow conditions, meter component wear, and contamination Avoids over and under-billing Self-adjusted output  

Provides constant accuracy Provides continuous measurement certainty

Auto-Adjust Turbo-Meter Technology  Self-Checking Feature 

Up-to-the-minute remote monitoring  

 

Advises accuracy changes Advises required meter adjustments

Verifies the accuracy of the entire installation Reduces spin-testing and site visits

Auto-Adjust Turbo-Meter Technology 

Performance     

Superior flow rangeability (10:1 min to over 200:1) as pressure increases Wide operating pressures (vacuum to 1440 psig) Good repeatability (0.05%) and reproducibility (0.1%) Linearity 0.5% or better available at high pressure calibration Module interchangeability of +/- 0.1%

Self-Checking vs. Self-Adjusting 

Self-Checking Feature  

 

Detects changes in retarding torque Detects changes in upstream flow conditions Detects installation effects Indicates deviation from factory calibration



Self-Adjusting Feature 





Adjusts to original calibration for changes in retarding torque Adjusts to original calibration for changes in upstream flow conditions Records deviation from factory calibration for long-term analysis

Note: Compatible electronics required

AAT Operating Principles 

 



Adjusted Volume at Initial Calibration Basic Adjustment Principle Operating Changes in Retarding Torque Self-Checking Feature

110% of Flow Rate

10% of Flow Rate

Self-Adjusting Principle Assume

main rotor slows by 2% due to increase in Field condition w/ Factory Calibration drag mechanical drag Results in an increase in exit angle, slowing sensing rotor 2% in proportion to main rotor MR

Vol. - SR Vol. = Adj.

Vol. 108% - 8% = 100%

Ideal

Self-Checking Principle Amount Field Factory of Change = Adjustment Adjustmen t

A = 

 

100  - A Vm -1  Vs

A = Change in mechanical output accuracy from original calibration (Delta A) A = Average amount of adjustment at factory calibration (A-Bar)  Vs = Ps/Ks  Vm = Pm/Km

Pm = Pulses from main rotor Km = MR factor (pulse/ft3)

Ps = Pulse from sensing rotor Ks = SR factor (pulse/ft3)

Self-Checking Example 2% Main Rotor Slowdown Amount of Change = Field AdjustmentFactory Adjustment

A = 

 

A =    A = 

 

100  - A Vm -1  Vs

100 Vm -1  Vs 100 108 -1  8

     

100 Vm  Vs -1  100 110  10 -1 

A = 8%-10% = -2%

Self-Checking Feature   Compatible Electronics







Measures inaccuracies in the entire piping set Documents changes in accuracy vs. suspected wear and provides early detection of line or meter problems Tests your meter in-line without interruption of service, or easily monitor accuracy & performance remotely Reduces spin testing and maintenance costs with fewer site visits Provides ability for in-line spin testing

The Sonic Meters • The Sonic meters are based on ultrasonic and electronic platform

The Added Value of Electronics 

Logs operating and consumption data 



Programmable measurement factors 



60 days of hourly data

Fixed factor

Recordable evidence of tampering and fraud  

Reverse flow Air in meter

Ultimate in Flexibility 

Sonix 12,16, & 25  

Standardized and compact installations In an inferential meter, the capacity expands in direct proportion to the pressure multiplier factor

Measurement Principle 

Transducer A

Piezoelectric transducers generate and detect waves 







Waves travel at the speed of sound relative to the moving fluid Sound will travel faster with the flow of gas than against the flow of gas Enabling the meter to determine gas velocity

Volume = velocity x cross sectional area of flow tube

Transducer B

Fundamentals of Ultrasonic Measurement Single Path – Low Flow

Ultrasonic pulses are produced with - and against - the gas stream. Pulses flowing with the gas velocity speed up; pulses flowing against the gas velocity slow down. The difference is used to calculate the gas speed or velocity within the known area.

Front and Bottom View of Measuring Element Cross section of flow tube. Inlet section is sealed from outlet section ensuring that all the gas passes through the flow tube Inlet of Meter

Inlet of Flow tube

Outlet of Flow tube

Outlet of Meter

Positive O-ring seal prevents leakage from inlet to outlet and to atmosphere

 Disadvantages Ultrasonic Measurement  No

 Advantages  Low

pressure loss across meter  No mechanical components  Bi-directional flow

mechanical backup  Reliability on electronics  Velocity profile effects  Complex calibration requirements  On site power requirements  System complexity

Vortex Meters The vortex meter like turbine meters measure the angular velocity with the Rotar. Rotron USA used to manufacture these meters but due to financial loss its manufacture has been stopped now. Only a few of these types of meters were used on our system.

METER READING

Meter Type: SP - 1000

0195100

6590383

7618700

0776919

Classification of Diaphragm Meters ANSI B109.1 & B109.2 

Class Capacity Range Approx: Designation Min. Max OIMLMODEL Ft3 /h Ft3 /h Equivalents



1.Class-50



2.Class-175 175 249 G4 RW-175, RW- 200, Gallus 6/20-C, UGI-200, UGI-DO7, Sprauge-175, AL-175



3.Class-250 250 399 G6 Sprauge-400, AL-250.



4.Class-400 400 499 G10 RW-415 ¾“, RW-415, 1-1/2“, AL-425 ¾“, AL-425 1-1/2“



5.Class-500

500 899 G16 RW-750, RW-1600, AL-800



6.Class-900

900 1399



7.Class-1400

1400

2299

G40 RW-3000, AL-1400.



8.Class-2300

2300

3499

G65 RW-5000, AL-2300.



9.Class-3500

3500

2259

G100



RW- Rockwell Sp- Sprague AL- Singer American Meter



 

50

METER

174 G2.5 Yazaki, Remus, Ricoh, RW-150, Wilson.

RW-310, RW-315, RW-275, Sprauge-250,

G25 RW-1000, Sprauge-1000, AL-1000.

RW-10000, AL-3500.

Determination of Flow Rate at Site 

Determine, in how much time the meter counter completes circle of 10 Cuft or passes 10 Cuft gas FLOWRATE 10 FT3 / 6 SEC 10/6 X3600 6000 FT3 / Hr



Alternatively we can determine flow rate by noting that how much volume of gas has passed in one minute. Suppose that it comes = 100 Cuft in 1 minute then flowrate will be 100 X 60 = 6000 Cuft/Hr Determination of flow rate of the meter in video?

Calculation of Bill Domestic Consumer: Meter Reading (Previous Month) = 0.450 M3 Meter Reading (Current Month) = 68.000 M3 Difference (Gas Consumed) = 67.550 M3 Apply P and T factors to arrive at Standard Volume. In case of Domestic Consumers such factors are not applied Conversion to Hm3 = 67.550/100 = 0.67 Hm3

If the Readings are in Cuft then conversion to Hm3 as follows: (Cuft × 0.02817385) / 100 Conversion of Hm3 to MMBTU = (0.67 × 100)/0.02817385 × CV

(Btus/SCF)

Complete Bill also includes GST and Meter Rent Slab = (no of days/30) × (Hm3 × GCV ) × 100 × 35.31467 / 1000,000

× 1/1000,000

Domestic Slab Rates Slab

Usage of gas in Hm3

Rs. Per MMBtu

1

Upto 1 Hm3

95.0

2

1 to 3

190.0

3

3 to 5

800.0

4

Over 5 and Above

1006.4

1.57× 95.01 = 149.16 0.62× 99.48 = 61.68

Conversion Factors 1 m3 (Cum) = 35.31467 ft3 (Cuft) 1 MCF = 1000 CF

(MCF means thousand Cubic feet)

1 MMCF = 1000 MCF Btu = Cuft × GCV

(MMCF means Million Cubic feet)

(Gross Calorific Value in Btus per SCF)

MMBtu = MMCF × GCV °F = 1.8 × °C + 32 1 bar = 14.50377 psi

Metering Stations in Distribution CMS (Consumer Meter Station) supplies consumers at the desired pressure. Regulators

ON/OFF VALVE

Meters ON/OFF VALVE

Pressure Gauge

Regulators

gas to



Different Methods used for Gas Measurement:  Fixed Factor Measurement: A very precise regulator is installed upstream of the meter which ensures fixed pressure to the meter all times. The temperature of gas is normally measured by the P/T recorder in the close vicinity of the CMS  Important Guidelines:  Regulator should have minimum droop (pilot operated)  Regulator should be properly sealed  Regulator should be adjusted at low flows i.e. within the capacity of the regulator at operating conditions.  Restricting orifice should be used at the downstream of the meter to avoid overloading of the meter/sudden jerk to the meter.

Measurement Techniques in Gas Industry • Fixed Factor Billing: Precise Regulator

Gas Flow



High Pressure Measurement: By the use of volume correctors / P/T recorders

The inlet pressure (metering pressure) is usually not fixed  Fluctuating line pressure enters into the meter (metering pess.)  The volume corrector or P/T recorder on the meter senses /records instantaneous line pressure and flowing temperature (EVCs only) and applies corresponding conversion factor automatically / manually in case of P/T recorders to compute standard volume at the base conditions.  The capacity of the meter enhances with increase in metering pressure.  If the line pressure is more than the MAOP of the meter / volume corrector, a suitable regulator should be installed upstream of the meter to set the pressure within the MAOP. Important Guidelines:  Monthly volume correction ratio report must be prepared to check the performance of volume corrector. 



Monthly downloads of EVCs should be taken to check / analyze the data and any alarm conditions. During site inspections, it is a good practice to note corrected and uncorrected readings at an interval of ½ to 1 hour and compute the metering pressure applied by the volume correctors which should be cross checked with physical metering pressure.  The pressure gauges to note inlet/delivering pressure should be installed downstream of the meter  In case of P/T recorders the monthly calibration of P/T recorders must be performed and consumer/his representative’s endorsement must be taken. This will help in resolving any billing disputes at the later stages. 

Measurement Techniques in Gas Industry • Billing with Pressure/Temperature Recorder: 

The Meter is supplied at higher pressure than the usual delivery pressure. The pressure at the meter is continuously recorded by the Pressure/Temperature Recorder & corresponding Pressure/Temperature factors are applied manually on the gas volume registered on the meter to arrive at the corrected billed volume of gas at Base Conditions. Pressure / Temperature Recorder Regulator

Regulators

Valv e Meter Gas Flow

Gas Flow

RECORDER CHARTS 

LINEAR CHARTS (DAILY / WEEKLY)



SQUARE ROOT CHARTS (DAILY / WEEKLY)



COMBINATION OF LINEAR & SQUARE-ROOT CHARTS (DAILY / WEEKLY)

READING THE CHARTS FOR READING THE CHART ONE MUST 

KNOW THE FOLLOWINGS



BOURDEN TUBE RANGE (BTR)



TEMP. ELEMENT RANGE



DIFF. PRESSURE ELEMENT RANGE



TOTAL NO OF DIVISIONS ON CHARTS

READING OF LINEAR CHARTS   

BTR = 1500 PSIG TEMP RANGE = 150 OF TOTAL NO. OF DIVISIONS = 30

ONE DIVISION OF CHART = BTR / T.D PSIG = 1500/30 = 50 PSIG PRESSURE = 9.4 X 50 = 940 PSIG O ONE DIVISION OF CHART = T.R / 30 F = 150/30 = 5 OF TEMPERATURE = 13 X 5 = 65 OF

Measurement Techniques in Gas Industry

• Upstream Measurement with Volume Correctors: 

A Volume Corrector is mounted on the meter, which automatically applies Pressure/Temperature factors on the volume of gas registered by the meter to calculate corrected volume at Base Conditions. Volume corrector Regulators Regulator

Meter



General Checking of CMS by an Officer:  

 

  







The relevant forms for general checking should be used The complete information such as cons. no., name & address, meter/volume corrector sr. no., meter type, regulator type, types of measurement, metering pressure, valve sizes, piping sizes, filter stainer size etc. should be noted. Any discrepancy needs to be reported Sealing: Meter/Regulator seals or seals at any other vulnerable points must be inspected and any discrepancy should be noted. Check general condition of meters Check oil levels in case of rotary meters Check volume corrector ratio by taking two corrected/uncorrected readings after some time. Check record of last P/T recorder calibration and compare the existing pressure with the instantaneous pressure recorded by recorder. Take flow rate and metering pressure and perform analyses against the metering pressure and under sizing of meters. The load limiting devices should be checked.

    











Filter strainers must be installed at the CMS, arrange its cleaning Check lubrication of plug valves, arrange lubrication if required Check leakages and arrange rectification if required Check regulator shutdown if required Check meter replacement record and include in the list of schedule meter replacement if required Consumer /his representative’s signature should be taken to endorse the checking records Checking of paint condition, enclosure condition, locking arrangement and do whatever required Few P/T recorders should be calibrated in the presence of an engineer on monthly basis Any other remarks should be noted and remedial action if required should be taken In case CMS needs to be modified. Complete proposal with necessary drawings and list of material should be prepared for approval from the competent authority





1.

2.

3.

Estimation of Human Resource Requirements Based on the Work Load Work Load Estimation: it is the work load per year in each identifiable activity Identify all activities in the region, such as schedule maintenance, CMSs/TBSs etc, General Checking of CMSs / TBSs, P/T Calibration, High Gas Bill complaints, Emergencies, Condensate Drainage, Schedule and Defective meter replacement Identify schedule maintenance requirements (as mentioned in the metering manual) and estimate frequency of such occurrences which are not prescribed but needs to be estimated from the statistical field data. Have data about the no of consumers in each category, no of TBSs / DRSs, no of pressure/temperature recorders, large capacity CMSs (cement, fertilizers, power etc)



Example of Work Load Calculations:  Maintenance of General Industrial CMSs: Total no of General Industry CMSs = 100 Schedule maintenance period / frequency of schedule maintenance per year = 1 (once a year) Work Load per Year = 100  General Checking of General Industry CMSs: Total no of consumers = 100 Frequency of checking per year =02 (twice a year) work load per year = 200  Emergencies and Complaints: Estimated no complaints per year needs to estimated from the statistical data, which will be the work load in this activity



Estimation of Teams to accomplish Metering Activities  Need to define work norm in each activity Example1: work norm for schedule maintenance of general industry = 3 CMS/day No of working days in a year is taken as = 250 days work norm per year = 750 Example2: work norm for attending emergencies (based on experience and averaging time for various emergencies) =2 per day no of working days = 250 Work norm per year = 500  now we know the yearly work load and work norms in each category, it is simply to work out the no of teams required = work load / work norm

Consolidated worksheet in excel for these activities



Activity

No of cons.

Frequency of Operation

Work load

Work norm

No of teams required

Gen. Ind.

100

1

100

750

0.13

General Checking Ind

100

2

200

1500

0.13

Emergenci es

-

1000

500

2.00

. . . Total

2.26



Word about Record Keeping: 







Maintain separate file for each high pressure commercial and industrial consumer Region should be suitably segregated into geographical areas (best way to do it is by using meter reading books) about 12 groups of commercial and domestic consumers may be formed. A group of commercial consumer should be =500-1000 A group of domestic consumers should be = 30000 – 50000 list of all commercial consumers in each group should be properly filed having master data. This data should also be available on the computer. Data base of all industrial and commercial consumers should be maintained, allowing entry of activities performed in the fields such as schedule maintenance, meter replacement (schedule and defective), consumer category w.r.t. pilferage (vulnerable or otherwise)





A list of meters against schedule replacement should be able to be generated from this software The data base should be capable of segregating meters / regulators wise lists e.g. lists of CMSs with EVC meters, meters with mechanical volume correctors, meters with IDs but without volume correctors etc.

REGULATORS Fundamentals of Pressure Control

GAS REGULATOR A DEVICE USED TO CONTROL OR DECREASE THE PRESSURE IN GAS FLOW DEFINITION: -

A regulator is defined as a mechanism for controlling or governing the moment of machines, the flow of liquids and gases. It is often referred to as control valve, governor, pressure reducer.

WORKING PRINCIPLE IT CONTROLS THE PRESSURE BY DECREASING OR INCREASING THE GAS FLOW RATE

APPLICATIONS GAS REGULATORS ARE USED TO CONTROL / DECREASE THE GAS PRESSURE AT: • • • •

SALES METER STATIONS (SMS’s) TOWN BORDER STATIONS (TBS’s) DISTRICT REGULATING STATIONS (DRS’s) CONSUMER METER STATIONS (CMS’s)

BASIC ELEMENTS OF REGULATORS •

REGULATING ELEMENT (VALVE OR EXPANSIBLE SLEEVE)

•

SENSING ELEMENT (DIAPHRAGM OR BOURDEN TUBE)

•

LOADING ELEMENT (SPRING OR DIAPHGRAM)

BASIC REGULATOR: There are three essential elements for a regulator. 1. 2.

3.

To measure / sense the desired level of control pressure If the desired pressure deviates due to changing conditions, there must be a device to change the flow of material in the system to suit the system conditions, usually this element is a variable restriction or a valve. There must be some means of positioning the valve in response to the deviation detected by the sensing element.

Three basic regulator control actions normally encountered are: on-off, proportional action, proportional reset. In this figure at 50% level, the valve is half open and the pressure in the gauge is 50, pressure is 100 psig at open and ‘0’ at close. This system operates between 0 and 100 for full open and close position. This is unacceptable regulation having 100% proportional band. If the operator is told to open / close the valve by one no. for each 1/10 line change on the gauge. In this case gauge would vary between 45 & 55 for full open to close. The final action to considered is proportional plus reset. The operator is instructed to open the valve one mark for a decrease of one mark on the gauge and then open slightly more until the gauge reads its original OK, regardless of the valve position. The initial valve changes are proportional, therefore, the valve is repositioned to bring the sensing element back to the desired level. Thus valve is reset to maintain the desired pressure level.

The previous is for manual operated regulator. The Automatic Self Operated Regulator. Three elements in this case are: 1. Sensing Measuring element: diaphragm bourden tube etc. 2. Restricting Element: Variable restriction in valve, it could be single port, double port etc. 3. Loading Element: Weight spring etc.

Basic Principle of Operation: Downward Force = 100 lbs Diaphragm Area = Area of Diaphragm = 10 in2 Downstream Pressure = Set Pressure = 10 psig Upward Force = P2 × A = 10 × 10 = 100 System is in Equilibrium Weight

Valve

Diaphragm

Out Let Pressure

Regulator Performance Characteristics Regulation Curve

Rate of Flow

The above curve shows the ideal performance of a regulator. Actual performance of the regulator differs from this curve. The curve deviates from its ideal behavior due to following reasons (i) Diaphragm Effects (ii) Spring Effects (iii) Body Effects (iv)Inlet Pressure Effect

B- Actual Performance : Diaphragm Effects : The diaphragm effects arises due to change in the effective diaphragm area as the valve travels

The Upward Force = Fu = Diaphragm Area × D/S Pressure The Downward Force = Weight Dr = Effective Diaphragm Area Let Initial Diaphragm Area = 10 in2 in initial position when the valve is almost in a closed position Fu = Fd => 10 = Ad × P(D/S) 10 = 10 × P so P(D/S) = 1.0 psi

Later when regulator valve is in open position the effective diaphragm area increases. Let it be now Ad = 12 Fu = Ad × P 10 = 12 × P So P = 10 / 12 = 0.833 psi The Curve will look like

Out let Pressure

Ideal Diaphragm Effect

Rate of Flow

 How to Reduce Diaphragm Effects: 1. 2.

Use Larger Diaphragms Use Roll-Out Diaphragm to keep the effective Diaphragm Area Constant.

Spring Effects : In a self operated regulator spring is used as a loading force. Let us see the behavior of a spring having spring constant (K) = 5 lbs

Initial Diaphragm Area = 10 in2 The Spring is Compressed to = 2 in2 Force Produced = 10 lbs if the diaphragm did not move downwards Let us assume the diaphragm moves 0.2 in (Valve travel) for full open condition In this condition the spring has not compressed to 2 inches, but in fact it has compressed 0.2 inches lesser

The less force exerted by the spring = 0.2 × 5 lbs/inch = 1 lbs Fu = Fd Fd = K × Compression = 5 × (2 – 0.2) = 9 lbs Fu = Ad × P 9 = 12 × P or P = 0.75 which is less than the pressure due to diaphragm effect alone Body Effect: Effect of turbulence between diaphragm and point of measurement on D/S pressure. Out let Pressure

} Diaphragm Effects } Spring Effects } Body Effects

Rate of Flow

Inlet Pressure Effects: The inlet pressure acts on the front side of the regulator seat, whereas outlet pressure acts on its back. The force due to differential pressure acts in the direction of the force exerted by the diaphragm i.e. this force should be added to the upward force., which means that as the inlet pressure will increase from the initial conditions.

Example: Area of Seat = As = 1 in2 Inlet Pressure = 10 psig Outlet Pressure = 1 psig Fu = Fd (Upward Force) = (Downward Force) Force on Seat + Force on Diaphragm = Force of Weight / Spring As (Pi – Po) + Ad × Po = Force of Weight / Spring 1 (10 – 1) + 10 × 1 = 19 = Force of Spring or Weight Now if the inlet pressure is increased to 11 psig what happens to the outlet pressure Fu = Fd 1 (11 – Po) + 10 (Po) = 19 Po = 8 / 9 = 0.89

This means that outlet pressure decreases with an increase of inlet pressure by 1 psig. This is the reason that :  Appliances regulator have narrow inlet pressure limits and have relatively larger diaphragm areas in comparison to the seat area.  High pressure regulators such as our domestic regulators have smaller orifice sizes  High pressure large capacity regulators imposes limits on inlet pressure with respect to the orifice size to be used.

Body Effects: It is normally the impinging effect of flow of gas on the diaphragm giving an additional upward force.

The downstream pressure immediately after the valve is imposed on the diaphragm. The impact pressure due to flow impinges on the diaphragm is produced which tend to close the regulator valve.

Zero Flow: The hard seat does not provide complete lockup at zero / low flows. The soft seats provide complete lockup at zero flow. Boosting Outlet Pressure: All effects such as diaphragm effect, spring effect and body effect tend to reduce the outlet pressure from the set point. Out let Pressure

} Diaphragm Effects } Spring Effects } Body Effects

Rate of Flow

In order to overcome this short coming a technique called Boosting outlet pressure is used. The pressure at the bottom of the diaphragm is reduced by causing an aspiration effect.

In this design a restriction has been constructed in the flow of gas stream after the valve. The increased velocity tend to cause low pressure resulting in loss of pressure under the diaphragm, which helps to enhance outlet pressure.

Valve Body:  Main fluid boundary and pressure containing component  Secures internal parts (Trim Components) and end connections

Bonnet:  It is also a major pressure containing component and fluid boundary  Bolted or threaded onto the main valve body  Guides valve stem  Provide means to mount an actuator

Trim:  All internal process wetted components e.g. valve plug, valve plug stem, cage, seat ring, plug sealing rings

Gaskets:  Bonnet Gasket (Provide sealing between body and bonnet)  Cage Gasket (Provide sealing between bonnet and cage )  Seat Ring Gasket (Provide Sealing between seat ring and body ) )

Packing:  Prevents leakage between valve plug stem and bonnet

ANSI Class Body and Bonnet PRESSURE &TEMPERATURE Ratings

Valve Plug Guiding Methods  Cage Guiding  Post Guiding  Stem Guiding

 Plug Balancing  Unbalanced Valve Plug Tight Shot off because only one leak path when closed Suitable for high temperature application when metal to metal seating is specified Because of unbalanced design very large stem force is required so these are available in smaller sizes

Balanced Valve Plug Stem force required is greatly reduced hence a much smaller actuator is required Disadvantage of balanced plug is that is gives a second leak path between the plug and cage wall when valve is closed, seal rings or piston rings used to prevent this type of leakage.

Flow Direction Flow-up

Flow-Down

Pressure-tends-to-open PTTO Pressure-tends-to-close PTTC

PTTO is recommended as it prevents valve plug from slamming into the seat In an unbalanced plug PTTO is achieved when valve is installed in flow-up configuration In an balanced plug PTTO is achieved when the valve is installed in a flow-down configuration

Unbalanced Plug Flow Direction is Flow up Pressure Tends To Open

 Balanced Plug

Flow Coefficient (CV) The flow coefficient refers to the number of U.S. gallons water at 60 degrees F that will pass through the valve with a 1 psi pressure drop across the valve.

 The following factors influence the flow coefficient of a control valve: Port size Percentage of valve travel opening. To prevent excessive fluid velocity at low flow, control valves are sized to pass to pass the minimum flow at 10-20% travel and max. flow at 80-90% travel. The flow geometry. The flow geometry has little impact on gas flow capacity, for gases flow is a function of the port area alone. Q = CVP1√x

X = dP/P1

Flow Characteristics Relationship between the flow coefficient and valve travel as the valve travels from 0 – 100% open. The three most common flow characteristics are illustrated below.

ANSI Class Shutoff Ratings The ability of a Control valve to stop Flow is SHUTOFF. Depends on plug and seat construction and material

Design Variations – Fisher E Series  ES:unbalanced plug (Metal Seated), cage guided Typically used for wide variety of liquid and gas application that require better shutoff (normally Class-IV) and/or High temperature application. Typically flow up design. (Limitations: Large Actuator force)

 ED:

Balanced plug (metal seated), cage guided, Used for clean fluids over a range of temperature (1100F). Reduces stem force. Piston ring material affects shut off class normally-II but class-III,IV,V are optional. (Limitations: Shut off class-very moderate)

 ET: Balanced, Cage Guide, Soft seated Reduced Actuator force. Shutoff class achieved is IV,V and TSO over a temperature range of up to 600F

 EZ:Unbalanced, Post guided, Metal or soft seat Used for Hydrocarbon and Dirty or viscous fluids. Limitations: Actuator force

Various Types of Regulator Loading and Principles of Operations 1.Self Operated Regulator 2.Pilot Operated Regulator

1.

Self Operated Regulator: Spring / Weight Loading

2

Pilot Operated Regulators: Constant Pressure Loading:

This loading system enables to reduce spring and diaphragm effects because: (i) Use of spring has been eliminated by a gas pressure (ii) Gas pressure on both sides of the diaphragm allow use of larger sized diaphragm to reduce diaphragm effect.

Relay Gas Loading:

• Inlet pilot regulator is set at higher pressure than the required downstream pressure • Outlet pilot regulator is set at the desired downstream pressure • Diaphragm is loaded with a pressure between these two pilots • Increase in the downstream pressure will tend to close final pilot resulting in increase of pressure under the diaphragm to close / restrict gas flow by closing main regulator valve. • In this regulator a small change in the outlet pressure will cause relatively a larger change in the diaphragm chamber.

Pilot Control Variable Pressure Loading:

• It is combination of gas loading and pilot control • It senses the outlet pressure and correspondingly varies the loading pressure • If the pipeline pressure decreases, the pilot opens, increasing the pressure on top of the main diaphragm • Downstream pressure simultaneously acts beneath the diaphragms of the main regulator and the pilot to give quick speed of response.

 Main diaphragm is thin because of gas pressure on its both sides. This system has a drawback for high pressure operation. As the pipeline pressure increases, the pilot tends to close. If the pilot closes completely, the gas over the diaphragm bleeds off and pipeline pressure under the diaphragm can cause rupture in the diaphragm. Variable Pressure Loading – Bleed to Line:  It has bleed in line  Pilot uses two diaphragms  A valve closing spring has been provided  This loading system allows high pressure operation  Loading pressure is inside both diaphragm so the effect of changing loading pressure is cancelled out due to two diaphragms

 As downstream pressure decreases, the pilot opens and provides additional loading pressure to overcome the spring. Bleed gas is discharged to the pipeline, thus no gas is lost to atmosphere. As the downstream pressure increases, loading pressure is decreased and spring forces the valve to closing position. When pilot shuts off, the spring force closes the valves, since no pressure differential exists across the main diaphragm due to the bleed. • This system provides excellent regulation at any operating pressure • It requires minimum differential pressure to operate the regulator

Pilot Unloading Type Regulator: Inlet of the pilot has a restriction Inlet pressure acts on the elastomeric element/diaphragm Pilot regulator controls it outlet pressure to the pipeline

If

the outlet pressure decreases, the pilot regulator opens and permits flow into the pipeline, since the restriction exists in its inlet or supply line, the pressure on the elastomeric element is decreased permitting the differential pressure to open the main regulator to restore the pressure Proportional band setting should be made carefully A very small restriction will make the regulator sensitive, while a large opening of the restriction valve will make the unit sluggish. Care must be taken in case of dealing with the dirty gas as clogging of restriction can cause the main valve to go wide open.

Instrument Loading: These are another class of regulators with wide application Normally used for larger pressure cuts such as SMSs Have inherent advantage of pressure sensing from downstream of the regulator, eliminating chances of freezing within small orifice of the pilot. Principle of Operation: • Main valve is operated with pressure applied to one side by the instrument controller with the other side exposed to atmosphere and a spring • Spring pulls the valve open • Valve is air to close type

Main valve is operated with pressure applied to one side by the instrument controller with the other side exposed to atmosphere and a spring Spring pulls the valve open Valve is air to close type Supply pressure of 20 psig is supplied through a supply regulator Spring on the diaphragm operator are designed to provide full stroke over 3 – 15 psig output pressure from the controller Bellow moves the flapper according to the outlet pressure, as outlet pressure increases the distance between flapper/nozzle increases, creating low pressure in the bellows of the Relay Valve, which moves the Relay pilot spindle upwards (open) to allow increased flow to diaphragm to increase pressure causing the valve to move in the closure position.

 When flapper closes the relay valve closes, resultant loading pressure is zero, when flapper/nozzle is wide open loading pressure is 20 psig thus closing the control valve  By proper selection of the spring and proper setting of the preload, the closure of the control valve at 15 psig and full opening at 3 psig could be accomplished  In this example if the bellow required 100 psig to open the flapper to a position that 15 psig would result from the relay valve and at zero, 3 psig would result, the valve would be wide open at 0 psig D/S pressure and fully closed at 100 psig. That means it has 100% proportional band i.e. it require 0 – 100 psig range to move the valve from one extreme to the other.

In the above figure another device, small set point spring is added  If set point spring is compressed to produce 50 psig pressure. It will restrict the movement of the bellows up to 50 psig. The movement of the flapper will occur after the downstream pressure exceeds 50 psig. This means that control valve remains full open up to 50 psig downstream pressure.  This set point spring permits the lower limit of control point  In this case the valve will half open at 100 psig This picture shows further refinement in arrangement/pressure regulation. • The nozzle has been shifted close to open point of the flapper.

 The full opening of the flapper that have occurred at the downstream pressure of 100 psig in the old arrangement will take place at a pressure of say 60 psig in the new arrangement.  Now the control valve move from full close to full open position within the downstream pressure change of 10 psig i.e. at 50 psig - full open and at 60 psig – full closed hence the proportional band is reduced to 10%

441-57S Roll-Out Diaphragm Regulator As the downstream pressure decreases below the set point. The force on the lower side of the diaphragm decreases than the force of the spring As a result the spring force pushes the plug downwards (double seated, balanced plug), which allows flow of gas from inlet to outlet The flow of gas from inlet increases pressure in the downstream piping which eventually increases pressure on the bottom of the diaphragm As this pressure has increases to the level of set point the pressure on the diaphragm becomes greater than spring

Fisher 299H Series Regulator, Operation Schematic When outlet pressure is less than the set point . The top side of the pilot diaphragm assembly ‘F’ will have a lower pressure than the setting of the control spring ‘A’. The control spring ‘A’ forces the diaphragm assembly upward, opening the pilot orifice ‘C’. Additional loading pressure is supplied from the pilot orifice to the top side of the main diaphragm ‘E’ This creates a higher pressure on the top side of the main diaphragm ‘E’ than on the bottom side, forcing the diaphragm downward. This motion is transmitted through a lever, which pulls the valve disk open, allowing inlet pressure to flow through the valve. When demand in the downstream has been satisfied, outlet pressure increases. This increased pressure is transmitted through the downstream control line and acts on pilot diaphragm ‘F’. Closing it.

Installation of 441-57S Regulator as Monitor Both the sketches show the monitor in the downstream position when installed in this way, the 441-57S is usually set for an outlet pressure 2 – 4 psi higher than the operating regulator and thus is wide open during normal operation. The monitor can be located upstream, with this arrangement, the regulator is usually set for an outlet somewhat higher than the above. These regulators have a fast response and therefore will take control quickly in case of emergency.

Fisher 399 Pilot Operated Regulators

As long as the outlet pressure is above the set point, the pilot valve plug or disk remains closed. Inlet pressure bleeding through the type112 restrictor provides loading pressure to keep the main diaphragm TSO. When outlet pressure decreases below set point, the pilot plug opens. Loading pressure bleeds downstream through the pilot faster than it is replaced through 112 restrictor. This reduces pressure on the main diaphragm and 399diaphragm is opened slightly to allow flow, increases downstream pressure.

Fisher 399 Pilot Operated Regulators

Downstream Wide-Open (Standby) Monitoring System The upstream regulator is in working condition and the downstream monitoring regulator opens only far enough to pass the required flow and changes position with each flow rate change. The upstream working regulator automatically supplies the correct intermediate pressure required to keep the downstream monitoring regulator open to the correct position

Operation of Two Sets of Regulators at TBSs

Regulator orifices must be carefully selected. Larger orifice in a regulator can handle lower pressures but can provide larger flows, whereas smaller orifices can handle larger inlet pressures but lower flows. Normally maximum inlet pressures are marked with thick lines on the capacity tables.

If

larger orifices are used at high pressure, regulator will not give a tight lock-up. Calculation of Regulator Capacity of Rockwell Regulators: Q = K √ (Pi (Pi – Po)) when Pi/Po >1 Q = K Pi / Z

when Pi/Po 1.894

K factor for various orifices Orifi ce

Single Port

Double Port

1/8”

¼”

3/8”

½”

3/4”

1”

1”

1 ½”

1 ¾”

2 1/8”

3”

K

33

132

292

520

850

1300

2000

4270

5450

8880

17740

…Regulator Sizing  Example: P1 = Minimum inlet pressure = 100psia P0 = outlet pressure = 60 psia Capacity = 200,000 SCF/Hr P1/P0 = 100/6- = 1.66 0.5 where P1 = Inlet Pressure P0 = Outlet Pressure C1 = C g / C v

, Cg = Gas Sizing Co-efficient, See tables

from Fisher catalog for 399 regulators

Important Considerations A regulator is usually capable of having more than one orifice size. MAOP of the regulator defines the maximum operating pressure of the regulator body, but pressure rating for different orifices may be less than MAOP. So great care should be taken for the selection of orifice for a particular orifice size, otherwise regulator would not provide tight lock-up.

Shutoff Valve Selection Two types are generally used  Plug Valves  Ball Valves PLUG VALVES  Reduced port  Lubricated  Recommended to be used downstream of regulator or meter BALL VALVES  Full opening (lesser pressure drop)  Non-lubricated  Recommended to be used upstream of the meter / regulator

…Shutoff Valve Selection The capacities of the valve can be calculated from the AGA formulas for regulators if Cv is given. However as a thumb rule one step lower than pipe size can be used for valve size (i.e. for 4” pipe 2” valve is normally OK. Some designers prefer to use same size valves for symmetry and to avoid fittings like reducers / expanders.  Block valves are installed on the inlet / outlet of the metering and regulating stations, other locations could be.  Isolations of different sections such as filters, regulators, meter stations, by-pass legs, blow downs, relief valves, scrubbers etc.

Valve Joint Selection  Weld neck flanges are used for above ground applications for ease of disassembly  Welded valves eliminate potential for leaks, these are more suitable for underground applications  Thread valve joints have high potential for leakage, these should be avoided as far as possible. Can be used for small instrument valves

Pipe Sizing / Configuration  AGA recommend velocities in piping system from 50 ft/sec to 200 ft/sec. Different companies use their own limits on pipelines velocities. Lower velocities are used to have a quieter system and to have low wear and tear of instruments  SNGPL may use the value of pipeline velocity of 80ft/sec for designing purposes formula for calculation of velocity: V = 0.75 Qh/D2Pf V=velocity (ft/sec), Qh=volumetric flow rate (SCF/Hr) D= inside diameter (inch), Pf=flowing pressure (psia)  From this formula we can calculate the diameter of piping in various sections of the metering regulating stations D= √(0.75Qh/VPf)

Measurement  First of all determine the type of meter that will be best suited for the load applications  In SNGPL following types of meters are generally used Domestic / Low Capacity Commercial Metering Station  These consumers have very large variations in load which require very high rangibility as such diaphragm meters having rangibility of 1:100 are used General Industry /High Pressure Large Capacity Commercial Metering Stations  Comparatively lower fluctuations in load. Normally large capacity diaphragm or positive displacement rotary meters are used which have rangibility of 1:20  In case of process industry where it is not desirable to have gas supply shutoff, turbine meters are more suitable

…Measurement Large Capacity Meter Stations such as fertilizers Cement and Power  Normally inferential meters, orifice or turbine meters are used for such applications  Orifice meters have a rangibility of 1:3.5 and turbine meters have rangibility of 1:18 (at 40) and 1:44 at a pressure of 75psig  For diaphragm and rotary meters there is no specific requirement of straight upstream and downstream piping

…Measurement Selection of Diaphragm and Rotary Meters  Load in SCF /Hr (maximum and minimum)  Metering Pressure (Minimum)  In diaphragm meters the capacity does not increase corresponding to the pressure factor, as such consult table against the maximum load and minimum metering pressure to find select the adequately sized meters  Company is presently switching over to rotary meters due to their sustained accuracy, smaller size and nonadjusting accuracy features

…Measurement Rotary Meter Selection  Calculate the pressure factor against the metering pressure, suppose metering pressure = 40psig (min.) P.F. = (40+14.65) / 14.65 = 3.73  Maximum load = 12,000 Cuft/Hr  Calculate uncorrected volume i.e. compressed volume of the gas to be passed through the meter at metering pressure = 12,000 / 3.73 = 3217 ft3/Hr  Divide this volume by 0.85 as a facor of safety = 3785  Capacities of rotary meters in company used are: RC3M175 = 3000 ft3/Hr , RC5M175 = 5000 ft3/Hr RC7M175 = 7000 ft3/Hr , RC11M175 = 11000 ft3/Hr

…Measurement  

 

In this example the uncorrected flow rate is more than 3000 ft3/Hr and less than 5000 ft3/Hr, so we will select meter RC5M175, the suffix 175 depicts its MAOP Company has decided to go for the automatic Electronic Volume Correction by use of Electronic Volume Correctors. So meter RC5M175 with EVC will be selected Similar principle shall be applied for the selection of Turbine meters. However, great care should be taken to have straight run piping upstream and downstream of the meter as recommended in AGA-7 Normally 10 pipe dia upstream of the turbine meters and 5 pipe dia. Downstream are to be used A ¼” dia by-pass line across the inlet valve of the turbine meter leg is very essential which is needed for commissioning of the meter

…Measurement

¼” Line & Valve

Orifice Meter Sizing for sizing orifice meters formula Q = C √(hwPf) is used Beta Ratio = ß =d/D =Orifice Dia / pipe dia = 0.5 may be used for design purposes As a thumb rule C = Fb (AGA-3) ×1.291 minimum value of hw may be taken as = 28 in H2O pf = Absolute Static Pressure = 500 psia Q = Fb ×1.291 √(28 × 500)

…Measurement Q = 167,000 Fb= 167,000 / (1.291 ×118) = 10970 (given value of about 7” orifice dia.)  Now find the value of orifice dia from the tables of AGA-3 report  Meter run dia can be found by using ß ratio=d/D=0.5, hence D= d/0.5, D=7/0.5 =14” pipe dia for meter tube  The meter run can also be sized by using a computer software programme developed by manufacturers  Normally 100” differential pressure recorder is used for recording hw in the company  Provide maximum possible straight pipe upstream and downstream of the orifice fittings as recommended in AGA-3 other pertinent instructions of AGA-3 should be followed

Normal Piping Arrangement of Distribution Metering Stations Regulators Filter

ON/OFF VALVE

Gas Flow

Diaphragm /Rotary Meters

ON/OFF VALVE

Pressure Gauge

Regulators

…Normal Piping Arrangement of Distribution Metering Stations

Regulators

Regulators

Filter ON/OFF VALVE

Meter

Gas Flow

ON/OFF VALVE

Regulat ors

Gas Flow

Regulat ors

Mete r

Filter

…Normal Piping Arrangement of Distribution Metering Stations

Large Capacity Metering Station These stations normally have four blocks 1. Filtration 2. Regulation for the Meter 3. Meters 4. Regulation for the delivery pressure if required. Typical sketches of piping of large capacity meters in the company

…Large Capacity Metering Station Gas Flow

…Large Capacity Metering Station

Gas Flow

Example 

Load and Pressure Requirements Load = 20 MCF/Hr maximum = 2 MCF/Hr Minimum Inlet Pressure = 90 psig maximum = 40 psig minimum Outlet Pressure = 8 psig



Other Information Type of Industry = General Industry in Private Sector Monitoring Required = Yes, by way of Data Logging Delivery Pressure Required = Constant Gas Quality = Probability of Presence of Dust

…Example  Proposal Type of Measurement = Meter with EVC will be suitable Filters = Filters will be required for the removal of dust Regulation = Pilot Operated with minimum droop  Filter Pressure (minimum) = 40 + 15 = 55 psia Q(max) = 20 MCF/Hr

2” FA AND FS FILTER CAPACITY TABLE

…Example  Regulators P1/P0 = 55/23 = 2.39 >1.890 so, we will use Q = K × P1/2 or K = 381 for K=381, orifice size of ½” is suitable for monitoring K=381/0.7 = 544 implied orifice size of ¾” Consult Regulator catalog of various regulator manufacturers and select regulator size with orifice ¾” or equilent P0/P1 = 23/55 =0.41 use formula Q= Pabs × Cg × 1.29 Cg = 20,000 / 1.29 × 55 = 281 Fisher 1” 399 at 60% has Cg =359 Fisher ½” 299 has Cg=200 and ¾” has Cg=430 So Fisher 299 will be selected for monitoring

…Example

…Example  Meter Rangibility = 2:20 i.e 1:10 Diaphragm or Rotary Meters can be selected. since Rotary meters are more rugged and EVC is required, we will go for Rotary Meter with EVC Minimum Metering Pressure = 40 psig Pressure Factor = 40+14.65 / 14.65 =3.73 Uncorrected Volume = 20 /3.73 = 5.36 MCF/Hr maximum flow through the meter should be 0.85 of the maximum rated capacity of the meter. so uncorrected volume for design purpose = 5.36/0.85=6.3MCF RC 5M = 5 MCF and RC 7M = 7 MCF So meter RC 7M175 with EVC or equivalent will be selected which has connection size of 3”

…Example  Piping Inlet Piping: Inlet Pressure (Minimum) = 55 Qmax = 20 MCF/Hr D = √(0.75×20,000)/(65×55) = 2.00” Outlet Piping: Outlet Pressure = 23 Qmax = 20 MCF/Hr D = √(0.75×20,000)/(23×50) = 3.16”≈ 4” To check if relative 2” dia section of pipe can be used against calculated 4” dia pipe, assume pipe section = 1ft Darcy Equation: dp=(w/144)xfx(L/D)x(V2/2g) dp=0.0471/144×0.85×1/2×(50×50)/(2×32.17) dp=0.0054 psig≈ 0.148

…Example Filter ON/OFF P/VALVE

2” Pipe 3”×2”

Gas Flow Diaphragm /Rotary Meters

ON/OFF VALVE 2”

3”×2” Pressure Gauge

Regulators

…Example Regulators 2” dia. Filter 2”×2” ON/OFF VALVE 1”

6”

Meter

12”

12”

6” 3”

Gas/Air Flow

Pipe Dia. 2” 1/2” Needle Valve (0 – 100psig) Tee to be connected with Air Compressor

1/2” Needle Valve (0 – 100psig)

ON/OFF VALVE 1”

Height from Floor 42”

3”

6”

Selection of shutoff valve 1.

For pressure drop in psig (subject to ∆P=3% of Pinlet) dp = 0.116×F/Ppsia×Z(Q/A)2 Q in MSCF

2.

For pressure drop in inches of water column dp(inches of H2O) = 3.22×F/Ppsia×Z×(Q/A)2 where dp = pressure drop Ppsia = Absolute Static Pressure in upstream pipe Q(SCFH)=Gas Flow in SCF/Hr A = Pipe Flow Area in inches Z = compressibility Factor

…Selection of shutoff valve  Calculations Inlet valve since pipe sizing =2” so we will first analyze 2” dia valve F=0.43 (from table) Assume = dp=1psi , Q=20MSCF/Hr, Pressure=55psia Z=0.98 Use dp=0.116×F/Pabs ×Z×(Qscfh/A)2 1=0.116×0.43/55×0.98(20/A) A2=0.355 or A=0.6 From table for A=0.6, 1” dia valve is sufficient. However for symmetry 2” dia valve can also be recommended, which will provide lower differential pressure.

…Selection of shutoff valve Downstream / Outlet Valve dp=10 inches of H2O (as downstream pressure is very low we have to keep pressure loss to be minimum) Z=0.99 from graph Since pipe size is 4” we will initially calculate A for 4” use formula F=0.7 dp (inches of H2O)=3.22×F/Pabs ×Z(Q/A)2 10=3.22 ×0.7/23 ×0.99(20/A)2 A=1.6 from table again A=1.6, valve size b/w 1 ¼” to 1 1/2” is good, so we will select 2” valve.

Electronic Volume Correctors

WHY WE USE VOLUME CORRECTORS ? The gas meters measure volumes at the metering pressures. The correction factors such as pressure factor, temperature factor, and super compressibility factor need to be applied on the volume recorded by the meter in order to get the corrected volume at base conditions. Volume Correctors convert the actual volume of gas measured by gas meters to reference conditions. Conversion is based on measurement of values of volume, pressure and temperature by using the formula: Vb = V x P/Pb x Tb/T x Zb/Z where Vb = Converted volume V = Primary volume ( from LF or HF meter output ) T = Absolute gas temperature at measurement conditions Tb= Absolute temperature at base conditions p = Absolute pressure at measurement conditions pb= Absolute pressure at base conditions Z = Gas compressibility factor at measurement conditions Zb= Gas compressibility factor at base conditions

237

Emcorrectors: A mechanical Volume Corrector

Prior to the use of EVCs Emcorrectors were used

Emcorrectors are actually mechanical Correctors which senses and apply the metering pressure on the uncorrected volume and gives corrected volume. Emcorrectors were not capable of applying Temperature factor

238

Electronic Volume Correctors

EMCORRECTORS

1. Electronic Volume Correctors are capable of applying pressure and Temp. factor

1. Emcorrectors were not capable of applying Temperature factor

2. Electronic Volume Correctors have logging capabilities

2. Emcorrectos had no logging capabilities

3. Electronic Volume Correctors have quick response

3. Emcorrectors had much more response time

4. It can detect meter tampering

4. Meter Tampering evidences were not detectable

5. Logged Parameters prove beneficial in determining overloading and other instances 6. Much more accurate

5. It does not have such capabilities

6. Less accurate 7. Mechanical Recorders were becoming obsolete

239

PRINCIPLE OF OPERATION OF EVC 

EVC is a dedicated microcomputer that takes metered volume in the form of pulses and uses transducers to measure gas pressure and temperature and hence corrects the metered volume.



Analog signals of gas pressure, gas temperature etc. are multiplexed through the A/D converter and sent to the microprocessor for processing. The microprocessor converts the digitized analog signals to an equivalent numeric value and stores this information in memory.



If any of the measured parameters are out of range, the microprocessor jumps to an alarm subroutine.



After the alarm subroutine is complete, or if no alarm conditions are present, the microprocessor computes new correction factors based on the new measurements and parameters already in memory. Parameters in memory are items such as; Base Pressure, Base Temperature, Specific Gravity, etc. The new correction factors are then 240 applied to the uncorrected volume input to obtain the corrected volume. The amount of corrected volume just calculated is added to the totalized corrected volume.

When the microprocessor has completed the updating of its memory registers, it will update the LCD with the new corrected volume information.



The device obtains data on the gas flowing through via impulses (N) from an LF or HF sensor located in the gas meter.



The volume at the measuring conditions (V) is calculated from the number of impulses (N) and gas meter constant (kp).

The

device obtains other data on the gas flowing through from the temperature and pressure converters – gas temperature (t) and absolute pressure at measuring conditions (p). This data is used to calculate the conversion coefficient (C) which is influenced also by these other factors: Absolute temperature at base conditions (Tb), 

absolute pressure at base conditions (pb) and compressible factor of the gas at base conditions (Zb). Volume

at measuring conditions (operational volume):



Gas compressibility degree:



Conversion coefficient:

Volume

at base conditions (standardized volume):

Gas

compressibility factor expresses the deviation of properties of natural gas from the properties of an ideal gas. By setting the parameters, it is possible to choose a specific method for calculation of the compressibility factor pursuant to the standard (AGA NX-19 mod, AGA8-G1, AGA8-G2, SGERG-88 or AGA8-92DC). A constant compressibility

242

value can be used for other gases besides natural gas. If the pressure or temperature value gets out of the limits of validity of the chosen standard for calculation of compressibility, the device calculates using a default compressibility value.

Operation of EVCs V unc, Vflt,err Volume

Alar m

If P or T violated the P T limits/range

A/D Conve r.

Micro Proce ssor

If P or T within limits

Low Batt Alarm

Firm war e

C

V unc, Vb, Volume updated in the memory and then on LCD

EL-GAS EVCS Normal Condition Pulse

ERROR CONDITION

V

Pulse

Ve

P T

C

V Ve

Pd Vb

Veb

Td

C

Vb

Veb 244

DRESSER EVCS Normal Condition Pulse

ERROR CONDITION

V

Pulse

Vf

P T

C

V Vf

P Vb

T

C

Vb

245

Defined mode with life cycle of the supply battery 4 years:      

• • • • • •

Archiving period of the data archive 1 hr Communication with device 2 min/day Showing on the display 2 min/day Period of input impulses ≤10 Hz Measuring period 15 s Surrounding temperature 25 °C

246

EVC COMPONENTS An EVC typically consists of  enclosure  index or pulse-input device (normally a reed switch which senses a magnet passing by it and generates a pulse against each magnet rotation )  pressure transducer (a device used to convert the pressure into electrical signals)  temperature transducer (a device used to convert temperature into electrical signals, usually an RTD, Resistance Temperature Detector)  display  keypad  electronic circuit boards  communication port  power supply

247

EVC COMPONENTS

248

Accuracy . Computation: ±0.3% of corrected volume reading . Pressure transducer: ±0.4% of full scale . Temperature Sensor: ±1.0°F. . Combined computation: ±0.5% of full scale (pressure & temperature)

249

METER READING THROUGH LCD DRESSER EVCs

         

The LCD display is permanently active. Depending on the configuration of the unit, following parameters can be displayed on the LCD. Corrected Volume Uncorrected Volume Correction Factor Drive Rate Line Pressure Temperature Uncorrected Volume Under Fault Base Pressure Pressure Factor Atmospheric Pressure 250

       

Flow Rate Supercomressibility Battery Voltage Current Date Current Time Corrected Residual Uncorrected Residual Firmware Version Corrected and uncorrected volume may be scaled by a factor of 10 or 100 to enable synchronization with mechanical counters. It is possible to specify which parameters are displayed on the LCD and which one is displayed by default. We select the corrected volume as the default parameter during initial configuration of the units. However in the event of an error condition the display defaults to give an error message. In alarm and/or fault conditions a message is displayed on the LCD indicating the nature of the alarm/fault.

251

252

LCD AND ALARM CONDITIONS

LCD Alarm Code

Alarm Condition

Additional Symbols

HP AL

HIGH PRESSURE ALARM

N/A

LP AL

LOW PRESSURE ALARM

N/A

Ht AL

HIGH TEMP. ALARM

N/A

Lt AL

LOW TEMP. ALARM

N/A

HF AL

HIGH FLOW ALARM

N/A

LF AL

LOW FLOW ALARM

N/A

LCD Fault Code

Fault Condition

Additional Symbols

Lo bAtt

LOW BATTERY

BATTERY ICON

P FLt

PRESSURE FAULT

ALARM BELL ICON

T FLt

TEMPERATURE FAULT

ALARM BELL ICON

Int FLt

INTERNAL OPERATIONS FAULT

ALARM BELL ICON 253

ERROR AND ALARM CODES The Error code is a decimal representation of a number built from a series of flags where each flag represents a single bit in an 8 bit binary number. The flags are set on the occurrence of any of these events and remain until cleared.

Flag

Value

Condition

HIGH PRESSURE

1

>1.2 * Full Scale

LOW PRESSURE

2

< 0.8 barA or 65 deg C

LOW TEMPERATURE

8

< -45 deg C

WATCHDOG

16

Timeout

CORRECTION FACTOR

32

Any pressure or temp. fault

Z CALCULATION

64

Z1.1

LOW BATTERY

132

Low battery

254

MERCURY EVCs The LCD of Mercury EVCs (Model Mini-Max AT) can display any Mini-Max item but we configure it to display the corrected volume by default. The LCD is also used to indicate alarm conditions and to display the items in the Meter Reader List. Normally we configure the Meter Reader List to display the following parameters       

Corrected Volume Uncorrected Volume Drive Rate Unit Serial Number Live Pressure Live Temperature Battery Voltage

The LCD will display decimal points between each numerical digit when the instrument has recognized an alarm.

255

256

MINI-MAX ALARM CODES

ALARM DESCRIPTION

ITEM CODE

E CODE

MAIN BATTERY LOW

099

.0.9.9.

INDEX SWITCH #1 FAULT

102

.1.0.2.

INDEX SWITCH #2 FAULT

103

.1.0.3.

A/D FAULT

104

.1.0.4.

PRESSURE LOW

143

.1.4.3.

TEMPERATURE LOW

144

.1.4.4.

PRESSURE HIGH

145

.1.4.5.

TEMPERATURE HIGH

146

.1.4.6.

DAILY CORRECTED VOLUME

222

.2.2.2.

REPLACE MAIN BATTERY

.H.E.L.P.

.H.E.L.P. 257

ELSTER EVCs The data display in the EK210 is structured in a tabular form. The individual columns in the table contain the following lists: 1.

User list

2.

Standard volume list

3.

Actual Volume list

4.

Pressure list

5.

Temperature list

6.

Correction list

7.

Status list

8.

System list

9.

Service list

10.

Inputs list

11.

Outputs list

258

259

STATUS LIST

Messages in system status 1

Restart ; The device was started without usable data. Counter readings and archives are empty, the clock has not been set.

3

Data Restored ; The device was temporarily without any power supply. Data has been retrieved from the non volatile memory.

4

Voltage too low : The voltage of the internal batteries is too low to ensure trouble free device operation.

5

Data error ; During a cyclical check of the data an error was found in the memory.

8

On account of the programming that has been carried out, an unusable combination of settings arose, e.g. a value which cannot be processed in a certain mode.

260

MESSAGES IN STATUS REGISTERS 1 TO 7 1 2 4 5 8

Alert for C,T and P No usable input values for T and P Output error at output A1 or A2 Error on pulse comparison on input E2 Warning for input E2 or E3

EK 210 and EK230 differentiates between four access parties:



Calibration lock Manufacturer lock Supplier lock



Customer Lock

 

261

El-Gas EVCs The LCD display is normally in-active/off. On Pressing either of two available buttons the LCD display becomes active/on. It has two list of parameters that can be displayed on the LCD by pressing respective Buttons. The following parameters can be displayed on the LCD. FIRST LIST 

Base Volume Vb



Primary Volume V



Gauge Pressure



Absolute Pressure



Temperature



Compressibility Factor



Correction Factor



Status 262

Second List  Error Base Volume eVb  Error Primary Volume eV  Flow Rate  Gas Meter Constant: Drive Rate  %age Composition  Time and Date  %age Battery Power 

In alarm and/or fault conditions a message is displayed on the LCD indicating the nature of the alarm/fault.



The Error volume is generated in the event when pressure / temperature of the flowing gas goes beyond the set limits



In the event of error volume, there is no mismatch



The Pressure limits are being set 18 – 150 psig so, if a EVC is to be installed at sites where line pressure is likely to go beyond this limit then please advise to change the limits 263

264

 

EL-Gas EVCs Indication of Error State:       

St 000000 (Normal, No Error) St 100000 (Pressure Limits Exceeded) St 010000 (Temperature Limits Exceeded) St 001000 (Max Flow Rate Exceeded) St 000100 (Drop of Battery below 10%) St 000010 St 000001 (Hardware Error)

DATA DOWNLOADING USING COMPUTER DRESSER EVCs The micro correctors models MC & IMC have a non-volatile (EEPROM) memory and on battery failure will retain the totals obtained within the last hour of operation and all settings of the corrector. These will be available and ready for use as soon as power is restored. Data is continually stored in memory with following capacity:   

840 hourly logs 48 daily logs 15 monthly logs The audit log is updated whenever a parameter identity value is changed or user calibration occurs. Up to 128 audit logs can be stored. 267

The data logging facility in Dresser EVCs model MC2 and IMC/C2 provides the operator with 3 independent operator configurable logging periods. The total number of logs depends on the configuration of both the log parameters and logging periods. A data log may contain any of the following information.        

Corrected Volume Uncorrected Volume Correction Factor Uncorrected Volume Under Fault Line Pressure Temperature Average Corrected Flow Rate Peak Corrected Flow Rate 268

DRESSER EVCs INSTALLED OVER THE METERS

269

MERCURY EVCs The Mercury EVC Model Mini-Max AT records operational information of 40 days on an hourly or daily basis. At the beginning of each interval, the instrument records four items into memory. We configure the following four Audit Trail Report Items for Audit Trail Memory. (Any Mini-Max item can be selected for the Audit Trail) 1.

Corrected Volume

2.

Uncorrected Volume Interval Average Pressure Interval Average Temperature

3. 4.

270

MERCURY EVC INSTALLED OVER A METER

271

ELSTER EVCs ARCHIVES The EK 210 & EK230 have three archives: Logbook (event logbook); Here, the last 250 status changes are archived. Changes logbook (audit trail); Here, the last 200 settings changes are archived. Measurement period archive; Here, the counter readings and measurements are archived in the cycle of the measurement period. The archive has 1500 data rows, corresponding to a memory depth of about 2 months for a measurement period of 60 minutes. 272

EVC TYPE

Manufact urer

DRESSER

EVC READING DIGITS CORRECTED READING

UNCORRECTED READING

VOLUM E UNITS

Dresser Inc.

9 DIGITS 12345678 × 10

9 DIGITS 12345678 × 10

ft3 or m3

Dresser Inc.

9 DIGITS 1234567 × 100

9 DIGITS 1234567 × 100

ft3

DRESSER (Older Version of EVC/IMC )

(only if installed on 16M & above meter for other above configuration applies) Dresser Inc.

8 DIGITS 12345678 × 1

8 DIGITS 12345678 × 1

m3

MERCURY

Mercury Instrume nts

9 DIGITS 12345678 Cuft × 10

9 DIGITS 12345678 Cuft × 10

ft3 or m3

ROMET

Romet Intl.

9 DIGITS 12345678 Cuft × 10

9 DIGITS 12345678 Cuft × 10

ft3

El-Gas (up to 11M

El-Gas Corp.

9 DIGITS 123456789.000 Cuft

9 DIGITS 123456789 Cuft

ft3

El-Gas Corp.

10 DIGITS 1234567890.00 Cuft

10 DIGITS 1234567890 Cuft

ft3

8 DIGITS 12345678.0000 Cuft

8 DIGITS 12345678 Cuft

m3

CuM UOM)

El-Gas Corp.

El-Gas on a RVG-

El-Gas

7 DIGITS

7 DIGITS

m3

meters)

El-Gas (16M & above meters)

El-Gas (meter of

Configuration of EVC and Mismatch   





Matching of EVC Readings with mechanical counter reading of meter/EVC at the time of configuration. Hence the Uncorrected Reading of the EVC should always match with mechanical counter reading If at any time the EVC uncorrected reading is found less or greater than mechanical counter reading, the phenomenon is known as MISMATCH Since no two counters can match exactly so a mismatch up to 1MCF is negligible and can be ignored but any mismatch beyond this value (i.e. 1MCF) should be considered as MISMATCH The difference of reading should be corrected by the application of correction factors and +adjustment in the bill should be made

EVC RATIO 

READING 1 CORR= 076658000 UNCORR= 004573600 Mech. CTR = 4573500 EVC PRESSURE = 75 PSIG EVC Temperature = 63 F



READING 2 (AFTER 10-15 MIN) CORR= 076659200 UNCORR= 004573800 Mech. CTR = 4573700 EVC PRESSURE = 72 PSIG EVC Temperature = 61 F



DIFFERENCE OF CORR READINGS 076659200 – 076658000 = 1200



DIFFERENCE OF UNCORR READING 004573800 – 004573600 = 200



DIFFERENCE OF Mechanical Counter READING 004573700 – 004573500 = 200



AVG. OF EVC PRESSURE = (75+72) / 2= 73.5 PSIG Pf = 6.02 AVG. OF EVC Temperature = (75+72) / 2= 62 F Tf = 0.996 Total Factor = 6.0



 •

RATIO of EVC Readings = 1200 / 200 = 6.0 RATIO of EVC Mech. Counter and EVC Corrected Readings = 1200 / 200 = 6.0

Example 

READING 1 CORR= 087657000 UNCORR= 005673800 Mech. CTR = 5673300 EVC PRESSURE = 77 PSIG EVC Temperature = 65 F



READING 2 (AFTER 10-15 MIN) CORR= 087658200 UNCORR= 005674000 Mech. CTR = 5673500 EVC PRESSURE = 70 PSIG EVC Temperature = 59 F

276