Moisture Monitoring of Natural Gas - ASELCO · Moisture Monitoring of Natural Gas. ... This process is expensive and ... corresponds to 6.9 lbs H2O/mm scft. will assure

Mission-Critical Sample SystemModel 8800B-NG

Moisture Monitoring ofNatural Gas

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.

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