flow primer

What is an RTU?*
Some Basic Terms and Concepts
Fluid - The state of a substance in which its particles easily move and change their relative position without a separation of the mass and that easily yield to pressure. A fluid can be a liquid (generally considered incompressible) or a gas.
Mass - Quantity of matter that causes it to have weight in a gravitational field. Mass flow is expressed in weight/time, ie kilograms/hr.
Volume - Space occupied or enclosed by cubic units. Volumetric flow is expressed in cubic measure/time i.e. cubic feet/minute or gallons/hour.
Density - Mass of a substance per unit volume.
Specific Gravity - The ratio of the density of a substance to the density of some some substance taken as a standard. For flow of liquids, specific gravity of fluid is compared against that of water, for gases against that of air.
Mole - grams/molecular weight
AUT S.B.S. - Presentation name - Date - Language - Electronic File Name
*
Some Basic Terms and Concepts
Liquids are generally considered incompressible
Ideal Gas Law - The pressure, temperature and volume of a gas are all interrelated.
PV = nRT
V = the volume that the gas occupies(ie ft3)
n = number of moles
T = temperature of the gas in absolute units
For the gas industry flow is most commonly measured as volumetric flow and expressed at base conditions
volume is dependant on temperature and pressure and composition
volumetric measurement must be corrected back to base conditions
usually 60 - 700F and 1 atmosphere (14.73 psia) pressure
*
How much went from one place to another?
Volumetric
Mass
Mass is mass. It doesn’t change with changes in temperature or pressure.
*
Orifice plate meter
Relatively low rangeability
High installation cost
No calibration little maintenance
*
*
Turbine Meter
Much more accurate than orifice plate
Wide flow rangeability
Low relative cost to purchase but comparatively high cost to maintain
Has moving parts that can fail but is easily field repaired
Requires calibration
Intrusive device
*
Use a vaned rotor engaged by the flowing fluid
the fluid spins the rotor at an angular velocity proportional to the flow rate
As the turbine rotates, an AC voltage is induced in a magnetic pickup
mounted externally to the fluid process
As each turbine blade passes the pickup the total magnetic flux density is changed
induces a single voltage pulse
Each pulse represents a finite volume of fluid that has been displaced through 2 adjacent rotor blades.
*
Positive displacement meter
Other less common types
*
Origins of the fluid flow “Laws”
More than 300 years ago, Charles and Boyle discovered that
Uf1 = (P *h)1/2
Qb =(218.573Cd(FT)EvY1d2Tb/Pb)(Pf1Zb Zb air*hw/GiZf1Tf) ½
And it would be,
*
Uf1 = (P *h)1/2
And it would be, except each component of the equation,
*
Uf1 = (P *h)1/2
And it would be, except each component of the equation, for example the Coefficient of discharge term, relies on solving an equation like this:
*
Uf1 = (P *h)1/2
And it would be, except each component of the equation, for example the Coefficient of discharge term, relies on solving an equation like this:
Cd(FT) =Ci(FT)+.000511(106 β/Red)0.7+((0.0210+.0049(19,000β/ Red)0.8) β4(106/ Red)0.35
*
The Names and Numbers to Know
For measuring flow there are 3 equations that are the most common
For orifice plate meters, AGA 3
1992 version
1985 version
ISO 5167 is equivalent and is very similar
ISO is currently upgrading and will probably come into lock step with AGA
For turbine meters AGA 7
AGA 7 is a relatively simple equation compared to AGA 3
Uf1 = (f/K)*M
*
For high accuracy gas measurement a compressibility and sometimes supercompressibility equation is needed
AGA 8 Most common
Multiple methods
Gross methods
2 for 1992 (recommended method for use between 32 to 130 oF and less than 1,200 psia, provided the gas composition is within the normal range)
4 for 1985
*
Other compressibility equations(in order of popularity)
NX-19 (developed in 1962)
Soave Redlich Kwong (SRK)
*
API 2540
Used for liquid measurement with turbine or rotary displacement meters
Provides temperature and pressure compensation
*
Putting it all Together
For measuring gas with an orifice plate meter use one of these
AGA 3 alone
AGA 3 with NX-19
AGA 3 with other
*
For measuring gas with a turbine meter
AGA 7 alone
*
For measuring liquid with an orifice plate meter
AGA 3 alone
AGA 7 alone
For measuring liquid with a rotary displacement meter
API 2540
*
API 21.1 Audit Trail and Event Log
Custody transfer applications are those where the fluid being measured changes ownership at the meter point
If the measurement application is not custody transfer it is
Allocation (often requires API 21.1 for convenience)
Control
For custody transfer applications a detailed audit trail and event log are required
The Industry expects a minimum of
7 days of hourly averages of specified variables
35 days of daily averages of the same variables
A copy of the configuration of the meter parameters
A 100 entry time stamped log of events
All parameter changes
*
If You Don’t Know for Sure, Just Ask
If a customer says he needs an RTU that does AGA that doesn’t mean anything!
Ask the customer some basic questions and consult your notes.
What is being measured?
How accurate does the measurement need to be?
Is the customer doing custody transfer?
If a customer is just doing control based on flow measurement
AGA 3 or 7 alone are often accurate enough.
*
Orifice Plate Meters
mil.
Turbine Meters
Revenues $mil. Increasing by % annually through 2002
Source: Frost & Sullivan Worldsearch May,1996
Under Construction
*
Starling Associates Gas Flow Loadable Function Block Library
To run loadables on a continuous basis you must use the proper enabler, 130 HEK 301 01 or 130 HEK 301 02
Fits in the bus expansion port of a Compact or Micro PLC.
Disallows the use of the AS HDTA 202 2 slot rack.
Must be used with a IA WBXT 204 cable if an AS WBXT 201 is used.
Loadables can be run, without an enabler, in demo mode for 48 hours after program load.
*
consists of 5 blocks that cover the different calculation combinations
G392 - up to 8 meters of AGA 3 1992 alone. API 21.1 audit trail
GD92 - meter of AGA 3 1992 and AGA 8 detailed method.
GFNX - up to 8 meters of AGA3 1985 and NX-19. API 21.1 audit trail
GG92 - up to 8 meters of AGA 3 1992 and AGA 8 both gross methods. API 21.1 audit trail
GM92 - up to 8 meters of AGA 3 1992 and AGA 8 detailed method. API 21.1 audit trail
130 HEK 301 02
130 HEK 301 01
*
What does Schneider offer?
Orifice plate meters (continued)
Flow calculations run only on Compact and Micro 612 04 CPUs
Except for the 612 04 you must have a minimum of 16K 984 LL capable CPU to run GG92, GFNX or GM92
The 612 04 is a special case which can run any of the flow loadables and have a large amount of program space left.
GD92 and G392 may be run in as small as a Compact 141 CPU
Using these loadables in an 8 K controller leaves little space for other programming.
*
AS BVRC 200, AS BCTR 205 and AS BCTR 224
High speed counter input cards, for the Compact and Modicon Micro, that perform the AGA 7 Calculation in the module
“K” and “M” factors are configured in the module and a corrected count or rate is delivered to the CPU.
BVRC 200 takes direct turbine meter sine frequency input signal
BCTR 205 and 224 take square wave DC input signals, 5 VDC and 24VDC respectively.
API 2540 temperature compensation and pressure compensation is currently not supported as a solution but can be programmed by the end user.
*
What does Schneider offer?
Orifice plate meters (continued)
Flow calculations run only on Compact and Micro 612 04 CPUs
Except for the 612 04 you must have a minimum of 16K 984 LL capable CPU to run GG92, GFNX or GM92
The 612 04 is a special case which can run any of the flow loadables and have a large amount of program space left.
GD92 and G392 may be run in as small as a Compact 141 CPU

flow primer

Documents