moisture monitoring of natural gas - aselco · moisture monitoring of natural gas. ... this process...
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Mission-Critical Sample System for Natural Gas Moisture MeasurementTaking advantage of the uniquely strong and quasi-linear response characteristics of its HTF™ aluminum oxide moisture sensors, Teledyne offers a cost effective sample system for demanding and mission critical moisture monitoring applications. The system is based on a fully automatic self-calibration procedure, in which the sensor is periodically exposed to a certified calibration gas and re-calibrated. The system has proven to produce consistently accurate monitoring results in natural gas applications, where conventional sample systems based on sample conditioning alone have failed.
Natural Gas DryingNatural gas, when leaving the ground, is saturated with water vapor. The water needs to be removed in order to prevent corrosion, condensation and freeze-ups in pipelines, as well as to reduce transportation cost and to assure consistent quality of the gas through custody transfers. Typically, the water is removed by passing the gas through a counter-current of tri-ethylene-glycol, which is hygroscopic and also absorbs other contaminants. The wet glycol is regenerated in distillers and recirculated. This process is expensive and it is desirable to optimize it towards a moisture level of the gas not dryer than necessary for transportation and use. Optimizing the drying process requires continuous moni-toring of the moisture content of the gas. In the US, the moisture level that is considered acceptable for natural gas transport and use, is 7 pounds of water per million standard cubic feet (7 lbs H2O/mm scft.), which corresponds to a dewpoint of -39°C(dp).
Challenges of Natural Gas Moisture MeasurementWhile the glycol contact removes contaminants to a large degree, hydrocarbons as well as traces of hydrogen sulfide and other corrosive contaminants may still be present in the gas after the drying process and additionally, small amounts of glycol are added in the process. These gas components can interfere with moisture sensors in various and unpredict-able degrees. The hydrocarbons, if not treated properly in the sample system, tend to condense and coat the sensors, slowing down response times. If glycol, which is hygroscopic, deposits on the sensors, changes in response characteris-
tics may result, which will depend on the amount of glycol deposited. Corrosive substances may permanently alter the sensor’s response to moisture, if not completely damage the sensor.
Mission-Critical, Self-Calibrating Sample SystemTeledyne offers configurations of its modular sample systems for natural gas applications, which condition the gas sample and remove contaminants sufficiently to protect the sensor from permanent damage and to warrant continuous long term operation.
Additionally, in order to assure highest measurement accu-racy and reliability in mission critical process control or alarm applications, Teledyne sample systems are available with a fully automatic self-calibration feature, in which the sensor is periodically exposed to a certified calibration gas. By periodi-cally adjusting the sensor’s calibration to read accurately when exposed to a certified calibration gas, accurate mea-surements in the vicinity of the calibration gas’s moisture content are also assured when measuring in the sample gas, even if a sensor has drifted as a result of exposure to gas contaminants.
Teledyne’s Self-Calibrating Sample System is available in Intrinsically Safe versions.
Self-Calibration ProcedureTo perform the calibration procedure, an electrically or pneu-matically actuated 2-way valve is activated to feed calibration gas supplied from a certified bottle to the sensor. The sensor output is monitored and after equilibrium with the calibration
Sam
ple
Cel
l
CoalescingFilter
Carbon Adsorber
Regulator
PressureGauge
0-20psig.
OutletInlet
Electrically actuated2-way
switch-over valve
Flo
w m
eter
1-5
LP
MShut-offValve
Sensor Cable
Optional Weatherproof enclosure (IP65) w/ window
Shunt-diodeSafety Barrierin groundedmetal partition
12
34
Xentaur Dewpoint Transmitter XDTwith Hermetically
Sealed Alarm Relays and
Real Time Clock
56 75 Ω Coaxial Cable
typically 12 to 20pF/ft.
Gro
undi
ngB
us b
ar
Associated Apparatus
Protective Component
enclosure (IP65)
IntrinsicSafetyWiring
AC Power
AC Ground
Intrinsically Safe (Simple) Apparatus
Div 1
AC Power distribution
BNC connector
Natural Gas On-Line Moisture Analyzer with integral bottled gas calibration system
max 3000 psig
Calibration Reference
Gas
4/20mA output
Regulator
Valve
AC Power distribution
Cer
tifie
d G
as B
lend
Bot
tle W
arm
er
Glysorb
valve control cable
gas is detected, the calibration curve is linear-ly adjusted over the full range to provide mea-surement computations which correspond to the known dewpoint. The 2-way valve switch deactivates, exposing the sensor again to the sample stream.
The interval at which the sensor needs to be re-calibrated is user programmable and application dependant. A bi-weekly calibration schedule has proven successful in natural gas applications after glycol drying.
HTF™ TechnologyTeledyne’s Mission-Critical Self-Calibrating Natural Gas Sample System takes advantage of the uniquely large and quasi linear response to moisture of HTF™ aluminum
oxide sensors. The large response to moisture of HTF™ sensors is an absolute requirement for adjusted moisture computations based on a single point calibration.
Certified Calibration GasThe calibration gas is supplied in specially manufactured aluminium bottles, which are certified to discharge gas with a constant moisture content. The moisture standards can be custom ordered in different bottle sizes with moisture contents ranging from 1-140ppm. For general natural gas applications, a moisture content of 140ppm (-39°C(dp) at ambient pressure) which corresponds to 6.9 lbs H2O/mm scft. will assure accurate monitoring at the moisture level critical for natural gas transport and use. The life of a calibra-tion bottle is typically in excess of one year, based on a bi-weekly calibration interval.
Field Proven in Challenging ApplicationsTeledyne’s Mission-Critical Sample system is field proven to work in challenging applications. The graph on the right shows 90 days of dewpoint monitoring data with calibration adjustment in an application where glycol carry-overs have prevent-ed conventional systems from producing reliable results. After a settling period of two weeks, the system has reliably provided accurate results.
∞C DEWPOINT
HI/LO
SET SET
SET SET SET
SET
PSI
NUMBERS CALCULATINGCALIBRATION
Legend: A slash '/' in the display area, is used to depict two alternately shown (flashing back and forth) messages. denotes beeping. Buttons without designator or arrow leading out, perform no function
LOC
-65.0
CAL
XSN/123 END SEN/2LO AC/_AC
CNF/AC?
CAN
30 seconds anywhere (other than "Calibration") without key press
appears when changingsettings of locked unit
Viewing Dewpoint
Sta
rtC
alib
rati
on
ViewingSerial-
number
Power ON initializationand sign on message
Flashing PSI indicatespressure correcteddewpoint
Fla
shin
g H
I an
d/or
LO
in
dica
tes
corr
espo
ndin
g r
elay
s no
t ene
rgiz
ed
SET
SET
SET
SET
∞CDEWPOINT
∞CDEWPOINT
SLF/CAL
-42.0
720/HRS/INTR 150/HRS/LEFT
SET
DISBEG/S.C.
CNF/SC?
SLF/CAL/-41.5 ∞CDEWPOINT
S.C,/STB/-41.5 ∞CDEWPOINT
S.C./FIN/-42.0
values +/-0.1∞C
values +/-1hr.
timeout
timeout
cancel
cancel
abort performing Self Cal Now
disable Self Cal corrections
Scheduled Time Elapsed, Entry Point
dew is stableperform Self Cal
During Self Cal the Analog output and Alarm Relays are frozen to their previous states
Sel
f Cal
C
ompl
eted
go
to
disp
lay
Dew
poin
t
Confirm Entry into Self Cal Menus
Set Scheduled CalibrationInterval in hours 0 (blank)=Scheduled SelfCal disabled, but SelfCal corrections not affected
View Hours left untilnext Scheduled Calibration
The Self Cal Correctionswill not be used in dewcomputations from now on,until another Self Cal isperformed, manually orscheduled. Schedulesare not affected.
Set Reference Gas dewpoint
Begin Self Cal Now
Electric Valve Activation, and15 min. time out for system stabilization, performed only if electric valve is installed.Displays dewpoint being measured now.
Dewpoint stable testing,
0.5∞C for 3 min. Displays dewpoint being measured now.
Electric Valve Deactivation, and final Dewpoint stable testing, 0.5∞C for 3 min.performed only if electric valve is installed.Displays dewpoint being measured now.
Confirm performingSelf Cal NOW
App
ears
onl
y if
unit
is e
quip
ped
with
ele
ctric
val
ve
units
Toggle Pressure Correction
SHORT PRESS
1/2 sec
SensorReading
New calibration values are saved
Can
cel C
alib
ratio
n (it
is n
ot p
erfo
rmed
)
Confirm SpanCheck
ConfirmSpanCheckagain
1 minute
few sec
1 sec
OK
TOO LOW
Press togetherto RESET theinstrument
go toSet-UpState
ignore error
Whe
n A
LAR
M O
PT
ION
S a
re in
stal
led
men
us a
ppea
r he
re
Flow diagram items not related to Self Calibration are shaded in gray.
XTR-100
Conventional
200
0
50
100
150
nF
Hyper-Thin-Film vs. Conventional Al2O3 SensorChange of Capacitance with Dewpoint
-90 3010-10
-30
-70
-50
Dewpoint (∞C)
200
0
50
100
150
DAY
De
wp
oin
t °C
lbs H
2O
/ M
M s
cft.
-50
-48
-46
-44
-42
-40
-38
-36
1.9
2.5
3.1
3.9
5.0
6.2
7.8
9.7
0 7 14 21 28 35 42 49 56 63 70 77 84 91 98
no correction
with correction
Dewpoint measurements of reference gas,
immediately before a calibration, when
calibration adjustments are made.
Dewpoint measurements of reference gas,
immediately before a calibration, when no
calibration adjustments are made. These are
indicative of the drift that occured over time.
Self Calibrating System Test in Natural Gas, at DOW Sep- 27- 99 to Jan- 6- 00
7 lbs H2O / MM scft.
Specifications of Transmitter:Sensor type . . . . . . . . . . High capacitance HTF™ Al2O3Input Resolution . . . . . . 0.1°C(dp)Indicators . . . . . . . . . . . . LCD with backlight, 3.5 digits and custom legends for units and mode, audio alertEngineering units . . . . . °C(dp), °F(dp), ppmv, g H2O/m3, lbs H2O/mm scfControls . . . . . . . . . . . . . 4 push buttons, all settings stored in EPROMOutput options . . . . . . . . 4-20 mA or 0-24mA outputs, linear to selected engineering units, programmable span and range, 0.1°C(dp)
resolution . . . . . . . . . . . . . . . . . . . . RS-232, baud rate 9600, resolution 0.1°C(dp)Isolation . . . . . . . . . . . . . Sensor is isolated from the power supply, analog output and RS-232Alarm relays option: . . . Two programmable alarm relays with programmable variable hysteresis, rated at 10A@240V Failure indication
programmable to trigger alarm relays.Power requirements: . . . 100-250 VAC, 50 or 60 Hz, autorangingConnections . . . . . . . . . pluggable screw terminalEnclosure . . . . . . . . . . . Polycarbonate, Nema 4/4x 4.7”x6.3”x3.5”Temperature range of electronics: . . . . . . . . 14° to 122°F (-10° to 50°C)
Specifications of Sensor Element:Type: . . . . . . . . . . . . . . . High capacitance HTF™ Al2O3Dew point range:XTR-100 . . . . . . . . . . . . -148°F(dp) to +68°F(dp) (-100°C(dp) to +20°C(dp))XTR-65 . . . . . . . . . . . . . -85°F(dp) to +68°F(dp) (-65°C(dp) to +20°C(dp))Capacitance . . . . . . . . . 15nf to 200 nfAccuracy: . . . . . . . . . . . . ±5.5°F(dp) (±3°C(dp))Response time: . . . . . . . For a step change from -40°C(dp) to
-60°C(dp):63% in 90 seconds, 90% in 450 seconds
Temperature range . . . . -22°F to +104°F (-30°C to +50°C)Storage temperature: . . -40°F to +120°F (-40°C to 50°C)Calibration method: . . . . Sensor saturates at dew point above
+68°F (+20°C)
Specifications of Sample System:Mounting plate and hardware............ 300 series stainless steelWetted parts................... 316 or 316L stainless steelBulkheads, Fittings......... 1/4” Swagelok™ Valves ............................. Integral bonnet needle valve with regu-
lating stemCoalescing filter:............. borosilicate glass microfiber and flu-
orocarbon binder, efficiency rating of 99.99% against 0.1 micron particles and aerosols.
Particulate filter .............. stainless steel mesh with 1 micron effi-ciency
Regulator........................Maximum inlet pressure 3000psi, outlet 1-30psi adjustable (higher optional)
Pressure Gauge: ............ 2.5” dial, 1% accuracy, max pressure 20,000 PSI
Flow meter...................... 1-10.5LPM, 3” scale. Borosilicate glass tube, SS wetted metal parts, black glass float, max pressure 250 PSI
Calibration Gas ..............Certified Nitrogen
Dimensions:
Teledyne Analytical InstrumentsWarranty:Instrument is warranted for 1 year agaist defects in material or workmanshipNote: Specifications and features will vary with application. The above are established and validated during design, but are not to be construed as test criteria for every product. All specifications and features are suject to change without notice.
A Teledyne Technologies Company
16830 Chestnut StreetCity of Industry, California 91748 USA
TEL: 626-934-1500 FAX: 626-934-1651 TOLL FREE: 888-789-8168
Visit Our Web Site at:www.teledyne-ai.com
© 2001 Teledyne Analytical Instruments, A Teledyne Technlogies CompanyAll rights reserved in the USA