OPTA-PERIPH 1 SAMPLE TAKE-OFF PROBE & VAPORIZER for LNG SUBJECT: For LNG custody transfer it is now a common practice to determine the composition, density and gross calorific value of LNG delivered by direct on line GC plus indirect lab analysis methods. A precise sampling is prerequisite for both analysis. I- Sample take-off probe: The ISOSAMPLE 8100 SAMPLE TAKE-OFF PROBE has been designed to provide a Thermal insulation of the sample take-off probe by hight vacuum maintained below 1.10-4 torr. The conjonction of this ultra-low residual pressure minimizing heat leak by conduction and convection with layer of radiation shield cryogenic material constitutes a superinsulation system providing apparent thermal conductivity (k) values below 0.4 milliwatt per meter-kelvin (mW/m-k), therefore the enthalpy rise can be controlled to be inferior of the subcooling degree and fractionation will not have occured in the sampling line even for low LNG pressure in line II- Sample vaporizer: The LNG sample is vacuum isolated up to the sample vaporizer coil exchanger sealed in calorific block temperature controlled. At this point, sample is flashing to eliminate any fractionated distillation effect. Inlet / outlet temperatures and pressures are monitored with interlock shut-off system This principle focuses on improving reproducibility between lab and line GC to a value better than 0.15% (ASTM D1945) and WI repeatabily beter than 0.01MJ/m3 (ISO 6976) . 1 III- System descriptive: The sampling probe item1 must be located on the top of horizontal part of pipe to withdraw the LNG from the center and the sampling tube is usually sized 3/8" OD. The flange item 2 is supplied as per customer specifications and the vacuum jacket item 15 is welded on flange and assembled with high vacuum flanged connections. A first sample isolation core valve item 3 is supplied and encapsulated in the vacuum jacket, this valve is only accessible by opening the flange cap to isolate the system from pipe-line if any maintenance work is required, thus, the downstream part of system can be removed and the vacuum re-established in this pre-insulation section without process service disturbance such as outage of the loading line. A capillary assembly item 4 is provided for breaking equilibrium between the sample and pipe-line pressures and the main isolating valve item 5 is supplied with extended bonnet and pneumatic actuator item 9. This actuator is operated via the pneumatic logic unit item 8 to be installed locally: the valve is normally closed and manually turned to open/close by pneumatic switch. A pneumatic port inlet controlled by the interlock shut-off system (when acquired) is provided for switching-off the valve if the temperature at outlet of vaporizer is dropping below the application set point (vaporizer failure or sample flow abnormal increase) then new switching to open is manual. The check valve item 7 is a operating as pressure barrier between sample pressure expansion in the vaporizer and the process line and two thermocouples type K item 11 are supplied at inlet and outlet of vaporizer with 2 meters coils in the vacuum jacket to avoid heat leak by conduction. The high purity bellows valve item 6 with vacuum pressure gauge is provided on the bonnet vacuum jacket for re-establishing the vacuum when required. The LNG sample is vacuum isolated up to the sample vaporizer coil exchanger sealed in calorific block temperature controlled. The vaporizer is supplied with PID temperature controller and inlet / outlet temperature interlock system for auto-shut-off the main valve item 5 if outlet temperature drops to the application set point or if pressure at vaporizer outlet exceeds 10 bar-g. Temperature control set point is automatically changed if temperature at coil inlet warms up. The sample vaporizer is so constructed that the LNG is flashing at the coil inlet and the heavier components of the LNG do not remain in the vaporizer. The capacity of the LNG vaporizer is sufficient to gasify the whole volume of LNG which is being withdrawn for sampling and keeping the enthalpy rise below of subcooling degree compliance The vaporizer is provided in a stainless steel box, protecting code is ATEX II 2G EEx de IICT4 . IV- Main specifications: Pipe-line pressure: 1.5 to 5 bar-g Pipe-line temperature: - 160 °C Volume of gas sample vaporized: approx 1200 Sl/h Lag time through sampling probe and vaporizer: 30 sec approx. Thermal conductivity of probe: 0.4 milliwatt per meter-kelvin (mW/m-k) Heating capacity of vaporizer: 0.5 Kw Sample outlet connection: 1/4" NPTF Protecting electrical code: ATEX II 2G EEx de IICT3 Enclosure rating: IP65 or NEMA 4x VAPORIZER and CONTROL UNIT VAPORIZER: The vaporizer is integrated at the extremity of sample probe spool. It consists in a coil exchanger sealed in calorific block temperature controlled electric type. The coil exchanger item 16 is a 2m x 3 mm ID tubing and the assembly is so constructed for providing sample flushing to avoid fractionated distilation effect and the heavier components of the LNG will not remain in the coil. Four temperature points are monitored: TS 1: thermocouple K: measuring the inlet temperature of LNG, a 2 m extension capillary is provided in the vacuum jacket for thermal insulation and connection is made in the thermocouple junction box model AD 531 certified EExe ia II C T6. A compensation cable has to be connected by customer to the EExi temperaure converter ref 5114B1A integrated in the EExd control unit enclosure ref: AD 442. The range of temperature is set to - 160 to +40 °C . PS1 _ TS3 TS2:PT100 (inserted in well item 16) measuring the vaporizer heat exchanger temperature controlled . A 3 wires cable has to be connected by customer to the PID controller ref 2286B /4114 in the control unit. TS1 TS 3: Pneumatic temperature switch ref FCNFC on the natural gas at outlet of vaporizer, set point is -20°C. . An high temperature trip switch item 7 ,calibrated at 135°C for class T4 is integrated in the vaporizer for safety redundancy. PS1:A pneumatic pressure switch ref FPNFQX is supplied as well on natural gas at outlet of vaporizer; set point is 12 bar-g. The temperature control of TS2 is set at 65°C and the outlet of TS 3 and PS1 are connected to the Pneumatic Logic Controller interlock system for processing the autoshut-off sample take-off valve if outlet temperature T3 drops to -20°C ( normal is +65 °C) or if pressure at vaporizer outlet exceeds 12 bar-g. VAPORIZER CONTROL SYSTEM Temperature controller TS 1 transmitter/indicator control unit with 24 VDC power supply plate assembly 24 VDC power supply TS 2 and heater TS 3 PS1 vaporizer enclosure TS 1 EExi junction box
© Copyright 2024