Transcript LNG SAMPLE TAKE-OFF PROBE

LNG SAMPLE
TAKE-OFF PROBE
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
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 < 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
CALCULATION OF SUBCOOLING DEGREE
Fractionation
4460J/Kg
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.
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/mk for conventional probe insulation system.
Sample Sample probe is
supplied with certification of
enthalpy rise to be < to
subcooling degree.
THUS FRACTIONATED DISTILATION effect
will not occur upstream of vaporizer even for
low pressure in line
SYSTEM DESCRIPTIVE
.Flange item 2 tied with vacuum jacket and assembled with high vacuum technolog
.Sample isolation core valve item 3 encapsulated in vacuum jacket to isolate system
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
auto-switch off is provided from pneumatic logic item 8 if the temperature at outlet
vaporizer is dropping below the application set point.
. Check valve item 7 is operating as pressure barrier between process line and samp
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 prov
facility for re-establishing vacuum if required.
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.
Constant and varying OD probes
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
PROBE & VAPORIZER
STANDARDS COMPLIANCE
- Sample probe resonant frequency calculation: -BS IEC 61831:1999 for on line velocity <7 m/s
-API RP 551 for on line velocity > 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 18*10 -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 3.0*10 -4 kg/m3
Density maximal random error.
VAPORIZER &
CONTROL UNIT
+ 50°C process
THERMODYNAMIC
pressure
+ 65°C
LNG transformation in supercritical state to eliminate fractionated
vaporization which generates fluctuations in gas composition
-80°C
P> 80 bar
Critical
point
-150 °C
Process pressure
liquid
Liquid +vapor
Vaporizer
inlet
2 phases max pressure
highest dew point temp
Liquid state ceases
vapor
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) .
Probe / Vaporizer processing
. The TS1 temperature at vaporizer coil inlet is monitored in the range of
–160 to + 40°C ; the expected value is –80°C .
. The vaporizer calorific block TS2 temperature is controlled at 65 °.
. If TS1 rises over -50°C the TS2 controller set point is decreased from 65
to 15°C.
. The TS3 temperature at vaporizer outlet is 65°C , if this temperature
drops below –20°C the sample probe actuated valve is shut-off.
. Processing is controlled by PLC in autosampling system or by
instruments for manual sampling.
LNG
AUTOMATIC
SAMPLING SYSTEM
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
SPOT and CHARGE
AUTOSAMPLING PID
SPOT
AUTOSAMPLING PID
Charge Holder
Piston Cylinder
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.
Charge bombs train
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.
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.
Spot bombs train
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
Processing System
System PLC
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 3.0*10 -4 kg/m3 Density maximal random error.