LNG SAMPLE TAKE-OFF PROBE

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LNG SAMPLE TAKE-OFF PROBE
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PURPOSE LNG custody transfer requires WI ,
composition and density measurements with better
repeatability than 0.01 mj/m 3 (ISO 6976) and
reproducibility between lab and in line GC better
than 0.15 (ASTM D 1945). Precise sampling is
periquite for both analysis. SAMPLING
MODES Contiuous sampling continuous collection
of LNG which is subsenquently vaporized and
stored in gas holder . Discontinuous sampling
continuous collection of LNG which is
subsenquently vaporized and analyse or sampled in
bombs at regular intervals
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APPLICABLE STANDARDS
ISO 8943-1991 LNG continuous sampling method ISO
8943-2004 draft of sampling with piston
cylinder EN 12838 test to assess the LNG
sampling suitablility
SAMPLING SUITABILITY KEYS
Enthalpy rise of LNG lt subcooling degree (
boiling boling point at given temperature)
Thermal insulation LNG transformation in
supercritical state to eliminate fractionated
vaporization which generates fluctuations in gas
composition
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CALCULATION OF SUBCOOLING DEGREE
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Fractionation
4460J/Kg
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KEY PARAMETERS
1-Pressure drop to decreases subcooling degree
reducing pressure regulator vaporizer cannot be
applied. 2- With conventional probe insulation
material, process pressure must be above of 2
bar-g the fractionation point is near of 1.5
bar-g, during loading on unloading process the
pumps pressure is frequently dropping below 2
bar-g . 3- Insulation thermal conductivity is
the only factor to be upgraded for low process
pressure compensation 4- Sample flow vaporized
is reverse proportional to enthalpy rise with
conventional probe insulation material this flow
rate has to be above of 10 000 SL/H gas.
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KEY FEATURES OF PROBE
.Super thermal insulation by high vacuum
below.10-4 torr minimizing heat link by
conduction and refraction with radiation shield
material. Apparent thermal conductivity k value
is below 0.4 milliwatt per meter- kelvin versus
18 mw/m-k for conventional probe insulation
system.
Sample Sample probe is supplied with
certification of enthalpy rise to be lt to
subcooling degree.
THUS FRACTIONATED DISTILATION effect will not
occur upstream of vaporizer even for low pressure
in line
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SYSTEM DESCRIPTIVE .Flange item 2 tied with
vacuum jacket and assembled with high vacuum
technology. .Sample isolation core valve item 3
encapsulated in vacuum jacket to isolate system
from pipe-line without process service
disturbance for any maintenance work. . Capillary
item 4 for breaking equilibrium between pipe-
line and sample take-off pressures. . Operated
isolation valve item 5 with extended bonnet and
pneumatic actuator item 9 auto-switch off is
provided from pneumatic logic item 8 if the
temperature at outlet of vaporizer is dropping
below the application set point. . Check valve
item 7 is operating as pressure barrier between
process line and sample volume expansion at
nozzle of vaporizer. . Two thermocouple type K
item 11 at inlet and outlet of vaporizer for
system temperature monitoring . . High purity
bellows valve item 6 with vacuum pressure gauge
and generator provide facility for
re-establishing vacuum if required.
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PROBE OTHER TESTS

• Resonant frequency calculations
• As the probe tip, is recommended to be located at
  the centre of pipe-line , the vortex induced
  vibration is to be considered, mainly above of 7
  m/s LNG velocity in line.
• The standard BS IEC 61831 calculation with
  constant OD probe is applied up structural
  frequency at 7 m/s above this value a dedicated
  test program has been undertook to determine the
  vortex shedding (wake frequency) with varying OD
  probe according to the ASM PTC 19-3 standard.

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Constant and varying OD probes
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TECHNICAL SPECIFICATIONS
. Pipe-line pressure 1 to 15 bar-g . Pipe-line
temperature from 180 C . Volume of gas
vaporized approx. 1200 l/h . Lag time through
probe and vaporizer 30 sec. approx . Thermal
conductivity of probe 0.4 milliwatt per meter-
kelvin . Heating capacity of vaporizer 0.5
Kw. . Protecting electrical code ATEX II 2 G
group 2B- class T4 . Enclosure rating IP 65
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PROBE VAPORIZER STANDARDS COMPLIANCE
  - Sample probe resonant frequency calculation
-BS IEC 618311999 for on line velocity lt7 m/s


-API RP 551 for
on line velocity gt 7 m/s   -Main welding test
APAVE certified under CODAP 2000- Rev
04-04-IA4--ASME V- APIRP 551   - Probe subcooling
degree calculation ISO 8943-1991- Annex
A   -Vaporizer - capacity calculation ISO
8943-1991- Para 6.5.2 6.6 -
Ex-proof ATEX II 2G EExde II C T4
- Probe
vaporizer pressure test PED 97 23 EC -
calcualtions approved Bureau Veritas -
Suitability testing of discontinuous sampling
with lab and process GC by supplier EN 12838-
Class A of accuracy with 54 kJ/kg Gross Calorific
Value and 1810 -4 kg/m3 Density maximal random
error.  - Suitability testing of continuous
sampling with ISOSAMPLE 8100 piston cylinder
holder and process GC by supplier EN 12838-
Class A of accuracy with 9.0 kJ/kg Gross
Calorific Value and 3.010 -4 kg/m3 Density
maximal random error.                      

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VAPORIZER CONTROL UNIT
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THERMODYNAMIC
50C process pressure
LNG transformation in supercritical state to
eliminate fractionated vaporization which
generates fluctuations in gas composition
65C
-80C Pgt 80 bar
Critical point
-150 C Process pressure
vapor
liquid
Liquid vapor
Vaporizer inlet
2 phases max pressure
highest dew point temp
Liquid state ceases
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SYTEM DESCRIPTIVE . Vaporizer integrated at
extremity of sample probe. . Vacuum insulation is
continuous from sample take-off in pipe-line to
vaporizer coil exchanger . Coil exchanger is a 2
m 3 mm OD tubing sealed in calorific block
temperature controlled. . Critical point is
located at check valve and vaporization occurs in
the 0.5 CC tubing volume at vaporizer coil
exchanger inlet FRACTIONATED DISTILATION effect
does not occur . . Coil exchanger designed for
not remaining heavier fractions . Temperature
points monitored TS1 at coil inlet - TS2
controlled at the exchanger calorific block
TS5 at vaporiser outlet TS6 trip alarm
calibrated at 135 (T4) .
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Probe / Vaporizer processing
. The TS1 temperature at vaporizer coil inlet is
monitored in the range of 160 to
40C the expected value is 80C . . The
vaporizer calorific block TS2 temperature is
controlled at 65 . . If TS1 rises over -50C the
TS2 controller set point is decreased from 65 to
15C. . The TS3 temperature at vaporizer outlet
is 65C , if this temperature drops below 20C
the sample probe actuated valve is shut-off. .
Processing is controlled by PLC in autosampling
system or by instruments for manual sampling.
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LNG AUTOMATIC SAMPLING SYSTEM
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SAMPLE LINE COMPONENTS . Back Pressure Regulator
item 10 to stabilise the pressure at outlet of
vaporizer under 1000 SL/H in order to comply
with subcooling degree requirement . The
microflow regulator item 14 is provided for
controlling the flow of charge holder. The charge
holder cylinder is interfacing the vaporizer and
the portable containers (bombs) train
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SPOT and CHARGE AUTOSAMPLING PID
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SPOT AUTOSAMPLING PID
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Charge Holder Piston Cylinder
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Charge Holder filling procedure
The holder piston cylinder features PTFE seals
double piston barrier with a piston scrapper to
auto-clean the cylinder electropolished wall
between two samplings. Original purging is
compliant with the ISO 8943-91 section 6 6 2 and
7 2 a this purging is made through the piston
shaft bore On the "ISOSAMPLE 8100" this
procedure is fully automated the buffer gas
chamber been pre charged by compressed air with
piston in down position, the sample chamber is
reduced to the nominal zero volume before of
sampling. Then the sample purge valve is actuated
to open for purging the tiny  dead volume between
piston/end plate through the piston shaft venting
to atmosphere. For a sampling line from vaporizer
of 5 m with 3 mm ID tubing electropolished a
purging cycle of 1min (programmable) is operated,
then the purge valve is closed. Direct mounted
position indicator and level switch (high and
low) are provided. Stirrer is not supplied for
this application.
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Charge bombs train
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Charge bombs filling procedure
Charge aggregate bombs are provided with
automatically/manual interchange sequential
control system as well as time programmed
automatically purging and filling for complete
unloading sampling (about 14 hr.
programmable). The accumulated average sample gas
of charge unloading is transferred to the bombs
and the gas will be controlled in constant
pressure of 7 bar-g at final charging.. -Procedure
for purging will be as per the fill and empty
method refer to Annex D of ISO 10715 and Appendix
C of ISO 8943-91defined according to the final
pressure in cylinder i.e 5 cycles
(programmable) at 7 bar-g.
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Spot holder filling procedure
-        The spot  holder is made and operated
within the same technologie than charge holder
but the volume is usually 6 time lower. The
system microflow is controlling a time
proportional charging of the holder piston
cylinder during a period of 1 to 3 H
(programmable) . At the end of this period , the
holder piston cylinder supposed to store 13.5 to
40.5 L of gas is automatically isolated and
connected to the spot containers train for
loading a new bumb. -          The six spot bumbs
are loaded during the batch transfer of 10 to 12
H , then the system is stopped waiting for
operator new cycle validation once the six spot
bombs have been collected and replaced in the
rack .   The loading pressure of floating piston
holder is controlled at 4 bar-g for charging and
purging and at 4 bar-g as well for the bombs end
charging.
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Spot bombs train
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System processing
Application processed via a solenoid valve
actuator BUS manifold with profibus data-link.
Sampling sequence and alarm history reported on
screen with data acquisition by keyboard.
Communication with user via RS-232 slave MODBUS
over multi-mode fiber . As addition to sampling
sequence following data's are provided to / from
DCS. - High / low level alarm of gas sample
holder - Sample take-off valve closing - Pressure
alarm at vaporizer outlet - Temperature
measurement at vaporizer inlet outlet -
Temperature at vaporizer core - Sampling
suspended from customer DCS
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Processing System
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System PLC
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AUTOMATIC SAMPLING SYSTEM STANDARD COMPLIANCES
-Constant pressure piston cylinder holder - ISO
8943 - Sept 04- draft- para 6.9 - holder
residual gas purging to ISO 8943-91 sect. 6 6 2
and 7 2 a - pressure test PED 97 23 EC - holder
capacity calculation to ISO 8943 para 6.6.1
  - Holder to portable container transfer fill
and empty method Annex D of ISO 10 715 or ISO
8943 para 7.3-b   - Suitability testing of
continuous sampling with ISOSAMPLE 8100 piston
cylinder holder and process GC by supplier EN
12838- Class A of accuracy with 9.0 kJ/kg Gross
Calorific Value and 3.010 -4 kg/m3 Density
maximal random error.