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Nitrogen displaces oxygen that may result in asphyxiation. This procedure must be performed in a well ventilated area. |
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Nitrogen used in this process exceeds |
| NOTICE |
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Do not allow dirt to enter the fuel system. Thoroughly clean the area around a fuel system component that will be disconnected. Fit a suitable cover over any disconnected fuel system components. |
Nitrogen from a liquid cylinder or compressed gas cylinder is the recommended purge gas. Use a compressed gas pressure regulator to reduce the pressure from the nitrogen gas source to approximately
| Parameter | Value |
|---|---|
| Dew Point | |
| Level sensor | 498+/-20 pF |
This procedure is used for drying moisture/water out of an empty Liquid Natural Gas (LNG) tank. If any of the plumbing components needs to be removed or changed, the plumbing must be opened and this allows the moist atmosphere to enter the LNG tank. Moisture in the LNG tank can cause several issues. One concern is that the moisture can cause error in the LNG level sensing. Due to the nature of the level sensor moisture causes the reading to be high and give the appearance of LNG in the tank when there is none. Another concern for moisture in the LNG tank is that if the moisture freezes the moisture can cause a blockage and restrict LNG flow out of the tank.
This procedure utilizes heated nitrogen to dry out the LNG tank. The nitrogen runs through a heater at low pressure and gets heated. The heated nitrogen then goes right into the inner tank to begin thoroughly heating the inner tank and inner tank components. Once the inner tank and internal components gets to water boiling temperature, the water/moisture is displaced by the hot nitrogen and forced out of the tank. The dryness of the tank is verified using a dew point meter to assure confidence.
- Leather work gloves
- Safety glasses (with side shields)
- Steel toe boots
| Required Tools | Qty |
|---|---|
| BAK Type S36 Heater | 1 |
| Keysight Technologies U1733C LCR Meter | 1 |
| Traceable Hygrometer Thermometer Dew Point Meter Model 4085CC | 1 |
| Compressed Nitrogen | 1 |
| JC Carter Vent Nozzle 662600-1 | 1 |
| Heater nozzle to JIC adapter (7/8” ID pip to 1” JIC) | 1 |
- Before starting procedure check valve positions to ensure proper drying:
- Valve 1: Closed
- Valve 2: Closed
- Valve 5: Closed
- Valve 6: Closed
- Valve 9: Closed
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Illustration 1 g06312072 - Depressurize/Empty LNG tank completely by opening tank isolation valve "Valve Tag 2". Close valve once the tank has no pressure left.
Note: Stand clear of outlet port, tank will depressurize through this valve.
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Illustration 2 g06312074 - Check capacitance of LNG tank with the LCR meter, before drying process for a baseline reference.
- Plug in leads to LCR meter and zero leads by depressing the "Null/Cal" button.
- Then long hold the "Range/Auto" button until auto function is activated
- Note the capacitance reading and units.
- Disconnect the LCR meter.
- Remove the inlet line that contains the SV2 for the heated air enter the tank with minimal back pressure. Set aside the section with SV2 and cap the ends to prevent debris and moisture from getting into section that was removed.
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Illustration 3 g06312078 (1) Heater nozzle (outlet) Show/hide table
Illustration 4 g06312085 - Add the valve to inlet port for isolation. Plumb the heater into the tank inlet port upstream from the valve.
- Make sure that the heater is set to 0 until ready to heat the nitrogen.
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Illustration 5 g06312087 - Plumb the nitrogen into the back of the heater.
- Make sure the valves "1, 2, 5, 6, and 9" are closed.
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| Illustration 6 | g06312089 |
- Open the added valve in front of the heater.
- Turn up the supply nitrogen discharge pressure to
138 to 207 kPa (20to 30 psi) .Note: The drying process may take several days depending on the amount of water in the tank, make sure to have sufficient nitrogen 10.
- Slowly open the tank isolation valve "valve 2" until a steady stream of nitrogen is discharging from outlet port
- Turn on the heater to MAX, 8. Be careful not to touch any tank shroud components from this point forward as plumbing will become extremely hot and could result in a burn.
- Periodically measure the capacitance and see tread head downward towards 498 pF.
Note: Be sure to zero LCR meter before every measurement, refer to
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Illustration 7 g06312091 - Once the capacitance reading is 498 +/- 20 pF, use dew point meter to measure moisture in tank. Place the dew point meter probe into the outlet port, hold steady for the dew point reading. Make sure that the gas is flowing for dew point reading. If dew point meter reads -40 C and level sensor is 498+/-20 pF, then the drying process is complete. If not, continue the drying process until BOTH requirements are met.
- Turn off heater and shut off nitrogen supply.
- With gloves close valve in front of heater.
Note: The valve will be hot. Wear correct protective equipment to prevent burns
- Close the tank isolation valve "valve 2".
- Once tank has cooled, disconnect heater and valve and replace plumbing.
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Illustration 8 g06312095 - Attached the vent nozzle with nitrogen supply behind the nozzle, to use this as a nitrogen fill port.
- Open the vent valve "valve 1" all the way.
- Turn up the supply nitrogen discharge pressure to
276 to 345 kPa (40 to 50 psi) . - Slowly open the tank isolation valve "valve 2", until a steady stream of nitrogen is discharging, allow 30 to 40 minutes for the nitrogen to purge.
- While the nitrogen is purging through the tank, double check the capacitance level and dew point to make sure still within specs above.
- If still within specs complete the purge, if not resume drying process
- After 30 to 40 minutes, close off the tank isolation valve completely.
- Allow the nitrogen to continue filling the tank.
- Charge the tank to
138 to 207 kPa (20 to 30 psi) of nitrogen. - Shutoff the nitrogen supply.
- Completely close the vent valve "valve 1".
- Remove the vent nozzle.
If the tank drying process needs to be paused for safety reasons (example, running unattended), follow the steps to pause the drying process and then resume as soon as possible.
- Turn off the nitrogen supply pressure/flow.
- Shut off the heater from 8 to 0.
- Close the valve in front of the heater.
- Shut the tank isolation valve "valve 2".
- To resume begin at Step 1.