In Situ Pressure Amplifier Sample Take-off Probe "ISOPROBE 8200"

LNG LOW PRESSURE SAMPLING
IMMERSED PRESSURE AMPLIFIER SAMPLE PROBE VAPORIZER «Model: IPAP 8400 »
for PRESSURE HEADERS NEAR TO BUBBLE POINT

Further to the world success of LNG vacuum /supercritical Sample Probe /Vaporizer, the necessity occurred to develop an Immersed Pressure Amplifier integration creating the only available solution when the two phases envelope calculated diagram demonstrates a liquid sample at saturated conditions (i.e. already at or near from bubble point) in process line or in a vessel.

This development is mainly addressed to the recent interest for the Floating LNG technology which may become in the future a significant part of liquefaction plants.

The same device covers as well applications on export or bunkering facilities, side by side LNGC to FSRU transfer or Small scale LNG production plants as well as for NGL plants.

In usual marine applications such FLNG, the LNG is stored in tank loading deck beneath represented on figure 1: a cargo pump tower is installed reaching from the bottom to the top of the tank and the pressure in the header where the sample take-off probe is installed is corresponding to the level of LNG with a minimum of 0.6 barg to 1 barg, means very near from bubble point as represented in the figure 2 with a degree of subcooling of 6 702 J/kg versus the enthalpy rise of 6 690 J/kg.

Figure 1                                                                                  Figure 2

The only way to avoid fractionation is to amplify the pressure at sample take-off, on purpose; the immersed Pressure Amplification Probe represented fig 3 is installed at sample take-off.

Target of his principle is to avoid the light ends evolving in probe as soon as the system pressure is decreased and/or the system temperature is increased from the point where the sample is taken.

1- The LNG Immersed Probe Pressure Amplifier :

Figure 3: Immersed pressure amplifier principle and on line mounting 

 The vacuum thermal insulated pressure amplifier is constructed in S.S.316 L dynamic metal seal less for operation at -196°C design temperature and features bellows offering absolute leak integrity.

The plunger/cylinder assembly is realized with high endurance treatment Rockwell hardness (HRC 70).

The pressure amplifier is based on a first circulation chamber accepting the volatile liquid at line pressure and a predetermined volumetric flow will be pumped-up by the pressure boosting section to the probe capillary.
This volumetric flow, usually calibrated at 30 cc /min of LNG is corresponding to the plunger square area, the stroke length and the adjustable low velocity stroking speed for accurate and constant flow pattern.
Referring to the figure 3, the immersed pressure amplifier functionality is broken down in the following steps:

1. LNG sample invasion: the top actuator drives to open the injection poppet; a fresh sample penetrates the compression bellows in the annular chamber.
Figure 3: Immersed pressure amplifier principle and on line mounting

2. Bellows compression step 1: low actuator extension for pressure amplification and liquid sample flushing for precooling of the circuitry.

3. Bellows compression step 2: the top actuator shut-off the injection poppet and the sample pressure is amplified for ejection of pressurized sample through the probe capillary.

4. Reset lock actuation.

The mounting on line of the Pressure Amplifier with pipe tying cradle supplied as option is show on figure 3

With regard to the data acquisition of the system, the predominant focus is the sub- cooling compliance to avoid sample fractionation and the ISO 8943 standard gives the calculation method to determine that the sample enthalpy rise is below the subcooling degree.

The Immersed Pressure Amplifier Probe and Vaporizer complete assembly features storied
temperature and pressure sensors and during sampling operation, the advanced control
software of system modelises in real time the curve of saturated liquid at consecutives stages from the acquisition of the gas chromatograph molecular fractions measurement and the successive stages of system pressure and temperature by Peng Robinson state equations in order to check in continuous the sub-cooling compliance with ISO 8943 standard up to the liquid / gas conversion chamber. The figure 4 gives the date acquisition.

Figure 4: Control Unit data acquisition 

The main parameters collected for qualification in real time of the Pressure Amplifier are the Saturated liquid curve modelisation, the pressure at sample take-off and vaporizer outlet points; the temperature at sample take-off, nozzle of vaporizer and outlet of vaporizer points and the sample flow-rate.

The figure 6 curves are representing the Pressure and temperature recorded during Factory acceptance test.

Figure 5: Saturated liquid curve modelisation   Figure 6: Pressure and temperature curves

At the outlet of the Pressure Amplifier

At outlet of the Probe Pressure Amplifier, the well-known LNG vacuum /supercritical Vaporizer referring to the Probe /Vaporizer brochure is integrated and the Immersed Pressure Amplifier makes possible to vaporize liquid sample at saturated conditions (i.e. already at or near from bubble point).