بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ

Unit-016, On-shore Gas and Condensate Receiving Unit
Direct pressure control at ORF outlet header shall be used for well head chock valves control to decrease a peak pressure caused by one LNG train emergency shut down.

Accordingly, well choke valves are controlled by low selector signal between the following three (3) signals: feed gas flow rate at feed gas pipeline manifold, feed gas pipeline manifold pressure, and pressure at ORF outlet header.

When ORF outlet header pressure is increased quicker than other above two control parameters, well choke valves should be regulated immediately. Auto verification function and deviation alarm is provided for 016-PT-1203A/B to avoid miss-measurement of each pressure transmitter. When auto deviation alarms are annoying, the auto verification selects the correct signal by referring to 016-PI-1202 on 016-D-1006 or 016-PI-1212 on 016-D-1007.

Vorwata-A wellhead is dedicated for ORF Gas Treating Facility Train#1 and Vorwata-B is for ORF Gas Treating Facility Train#2. During Two (2) LNG Train operation, the wellhead supply the same feed gas flow rate, i.e., all the well choke valves on Vorwata A and B control the outlet pressure of well choke valves to supply the same feed gas flow rate and same ORF arrival pressure considering the differential pipeline length.

Two feed gas flow elements (016-FE-1001 and 016-FE-1011) are installed on the vapor outlet lines from Scrubbers (016-D-1006/1007) respectively. The summation of these two-flow elements is means the total feed gas flow rate to two LNG Trains.

Unit-021, Acid Gas Removal Unit
Pressure
The pressure of the feed gas from Unit 016 is controlled by two identical Pressure Control Valves 021-PV-1202A and 021-PV-1202B which installed in series. The purpose of these control valves is to reduce the feed gas pressure to 58.3 kg/cm2G at the inlet of Feed Gas Knock Out Drum 021-D-1004. A high selector signal 021-PY-1202A will select the highest deviation pressure between upstream and downstream pressure of 021-PV-1202A and take quick control action to the control valve. 021-PIC-1202B shall control 021-PV-1202B based on the deviation pressure of outlet control valve. Two pressure transmitters 021-PT-2800A/B will provide 1 out of 2 voting system to protect Acid Gas Removal Unit from overpressure by closing shut-off valve 021-USVE-2010.

Temperature
No temperature control for the feed gas at normal condition. Temperature controller 021-TIC-1471 shall be activated in case the feed gas from ORF is lower than 40 ^oC, the feed gas shall be heated up to by using LP steam in the Feed Gas Pre-heater 021-E-1005. Temperature controller shall adjust the LP Steam flow rate in the heater to maintain the feed gas temperature at the inlet of Feed Gas KO Drum 021-D1004 at 40 ^oC.

Flow
There is no flow control for the feed gas.

Level
Under normal operating conditions the feed gas entering 021-D-1004 will be saturated and free of hydrocarbon liquid; therefore, there should not be any significant ingress of liquids to form a level in the bottom of vessel. Thus, the level controller 021-LIC-2890 which is an on/off controller should normally be closed. A rising level would indicate carry over from unit 016. Condensate collected will be returned to Hydro-cyclone Rejected Oil Separator 016-D-1011 with maximum flow rate 1950 kg/h (based on rated capacity of Condensate Transfer Pump 016-P-1001).

Unit-031, Dehydration/Hg Removal Unit
Pressure & Flow
There are no feed gas controls for flow and pressure in the feed and adsorption part of the Dehydration and Mercury Removal unit. Flow rate and pressure are resultant. The pressure of the feed gas into the system is maintained as the result of upstream pressure controlled at 59.35 kg/cm²A by pressure controller (021/022-PIC-1202B).

Temperature
The feed gas temperature into the Dehydration Pre-cooler Separator (031/032-D-1001) is controlled at 22 °C by the temperature controller (051/052-TIC-1301) which is cascaded by the pressure controller at the propane vapor of the Dehydration Pre-cooler (031/032-E-1001). High and low temperature alarms on 051/052-TIC-1301 are provided to warm the operator of any abnormalities in the system.

Level
The hydrocarbon level of the Dehydration Pre-cooler Separator (031/032-D-1001) is automatically controlled by 031/032-LIC-2740P which discharges hydrocarbon liquid to the Condensate Stabilizer (011-T-1001A/B). The water level is controlled automatically by 031/032-LIC-1102 which discharges water to the Hydro-cyclone Rejected Oil Separator (016-D-1011).

Unit-041, Liquefaction and Fractionation Unit
Control of Feed Gas

Natural Gas Flow Rate

The natural gas flow rate to Unit 041 and the outlet temperature from Main Cryogenic Heat Exchanger 041-E-1001 is flow controlled 041-FV-1303A at the outlet of LNG Expander 041-GC-1001 or 041 FV-1305 LNG JT valve. The outlet temperature from Main Cryogenic Heat Exchanger 041-E-1001 is held almost constant.

When the refrigeration capacity of the MR circuit is insufficient to achieve the required outlet temperature of Main Cryogenic Heat Exchanger, the flow controller 041-FIC 1305 is reset by temperature to reduce the natural gas flow rate. This condition occurs when the ambient temperature is high and the gas turbine for the MR circuit is operating at the maximum available power.

When the ambient temperature is low and the available power from the MR gas turbine is greater than the required power for refrigeration, the natural gas flow rate is increased by the flow controller 041-FIC-1305 which set point is reset by a temperature controller 041-TIC-1305.

Feed Gas Pressure

The pressure of the feed circuit is controlled by 021-PIC-1202B at the inlet of Feed Gas KO Drum 021-D-1004 in Unit 021. Thus the operating pressure of Scrub Column depends on the friction loss between the Feed Gas KO Drum in Unit 021 and the inlet of Scrub Column and therefore varies slightly with throughput.

Feed Gas Temperature

The natural gas feed temperature at outlet of Dehydration Pre-cooler 031-E-1001, which is located in Dehydration Unit 031, is maintained 22 ^oC by controlling the propane side vaporizing pressure 051-PV-1301 to avoid hydrate formation and hydrocarbon condensation in the feed, while maximizing the water condensation up-stream of driers. Any water that is condensed reduces the load on the driers thereby reducing the duty of the Dehydration unit 031.

The temperature of the feed gas to Liquefaction unit is indicated on 031-TI-1309 of Mercury Removal Drum 031-D-1004. The inlet gas temperature to Liquefaction unit is 22.3 ^oC.