CONTINGENCIAS Y COMPROMISOS

The solvent used for the removal of water is Tri-Ethylene Glycol (TEG). After absorption of water, the rich TEG is regenerated in TEG Regeneration system and recycled back to the Dehydration Column as Lean TEG. The mass transfer is achieved by a packing column where the lean TEG is counter-currently contacted with wet gas. The wet gas from the Feed Gas Compressor at a pressure of 87 barg and temperature of 50C enters the Gas Dehydration Column (305-C-001). During the HP case, when the Well head pressure is high enough, the Feed Gas Compressor system is totally bypassed and joins the inlet of the Gas Dehydration Column. The wet gas enters the bottom section of the Column. It flows into the Inlet Scrubber section of the Column where any entrained liquid is removed before the gas is introduced into the dehydration section of the contactor. All the liquids (condensate hydrocarbons or liquid water) recovered in the bottom of the inlet scrubber are drawn down under level control and drained to Flare Drum through a Check Valve, ESD Valve 305-XV-3001 and a Level Control Valve 305-LV-3013 during HP mode of operation. During LP operation, the condensate is returned to the Production Separator. There are two Level Transmitters,

one for bottom level control of condensate in the inlet scrubber 305-LT-3013 and the other for ESD control 305-LT-3015. For the effects of 305-LAHH-3015 and

305-LALL-3015, refer Cause & Effect Diagram 250-EPR-CNE-05001.

The inlet gas separation device allows a large gas flow turndown while assuring even gas distribution. The gas separation device (vane type) uses curved plates to disperse all inlet gas evenly beneath a wire mesh Mist Eliminator and to separate gas and liquid efficiently. The purpose of the mist eliminator is to coalesce the condensate droplets from the gas stream. The gas then flows through the gas risers of the glycol chimney tray, which allows a uniform distribution of the gas before it enters in the gas/glycol contacting section. The structured packing in the Gas Dehydration Column is to ensure uniform distribution and contact between the liquid and the vapour. There are two level transmitters 305-LT-3017 which control the rich TEG level and 305-LT-3016 for trip purpose. There are High-High and Low-Low level alarms 305-LAHH-3016 and

LALL-3016, the effects of which are detailed in Cause & Effect Diagram 250-EPR-CNE-05001.

The lean glycol from the discharge of Glycol Circulation Pumps (305-P-003A/B) enters at 55C in order to have a contact temperature of 10C above the wet gas inlet

temperature. The lean glycol enters at the top of the column and is equally distributed over the whole section of the column by the Glycol Distributor installed above the packed bed. The dehydration by absorption takes place as the gas flows upwards through the packing, contacting the wetted surface of the packing. A high efficiency Demister removes entrained glycol droplets from the dehydrated gas stream before it leaves the top of the contactor. The dehydrated gas from the top of 305-C-001 enters Dry Gas/Lean TEG Heat Exchanger (305-E-004) where the lean TEG is cooled to maintain the difference of 5 to 10C between the lean TEG and wet gas (entering the dehydration column).

The rich TEG comes down the structured packing after absorption of moisture and is sent to TEG Regeneration system. There are two Safety Relief Valves 305-PSV-119A and 305-PSV-119B which are set at a pressure of 95.2 barg provided on the top of 305-C-001 which will release to Flare header during over-pressurization of Dehydration Column. The differential pressure across the packed column is monitored by Differential Pressure Transmitter 305-PDI-3007 and sounds a high differential pressure alarm when the pressure reaches the alarm set point. The higher differential pressure across the contactor indicates foaming in the Contactor. There are high-pressure and low-pressure alarm set points indicated by 305-PAL-3009 and 305-PAH-3009. The flow of dehydrated gas from the outlet of 305-E-004 is measured by 305-FI-3006. At the downstream of ESD Valve 305-XV-3004, the dry condensate from Coalescer and the dehydrated gas are mixed and transferred to GTP through the trunk line. There are methanol injection points ME-711 and ME-713 on the top vapour lines. There is a Moisture Analyzer 304-AI- 3022 which measures the moisture content of the dehydrated gas. The analyser is provided with High alarm and High-High alarm set at 1.3 lb/MMSCF and 1.5 lb/MMSCF respectively.

GAS DEHYDRATION COLUMN

Equipment Tag No. 305-C-001

Type Packed Column

Process Medium Hydrocarbon Gas & TEG

Description Maximum Minimum Unit

Design Temperature 82 –15 ºC

Design Pressure 95.2 — barg

Operating Temperature 12.5 55 ºC

Operating Pressure 67.2 85.2 barg

Liquid- Flow 6201 kg/h Density at WPT 1100 kg/m3 Vapour Quantity 97980 kg/h Molecular Weight 19.28 Density at WPT 20.66 kg/m3 Structured Packing 4600 mm Material of Construction

Top Shell: A516 Gr7 ON

Bottom Shell: A516 Gr7ON + 3mm SS-316L Cladding: Internals: A516 Gr 70 Cladding: 3 mm SS-316L Dimensions: OD Length (T/T) Bottom: 1714;Top: 1494 12600 Mm mm

4.4.2 Gas Dehydration Controls 4.4.2.1 305-C-001 Pressure Control

Under normal operation, the Dehydration Column (305-C-001) pressure is governed by the pressure losses in the downstream trunk line up to the GTP facility. However, to prevent a low pressure occurring in the contactor during low flow or upset conditions, 305-PIC-3009 will control the column pressure by throttling 305-PV-3009A and

305-PV-3009B in split control. Under normal conditions, the Full-Bore Valve

305-PV-3009A on the dry gas line and 305-PV-3009B located in parallel to 305-PV-3009A remain fully open. In case of very low pressure, i.e. when the dry gas pressure falls below the set point, 305-PV-3009A fully closes and the gas is routed via 305-PV-3009B, to elevate the pressure in the gas dehydration column. The minimum pressure to be maintained in dehydration column is 68.2 bara during the turn-around operation. The Split range control valve is illustrated as given below in Fig. 5:

Fig. 5 – Split Range Control

During the start-up phase, the pressure is controlled by Pressure Controller

305-PIC-3024 which opens to flare by operating 305-PV-3024 which acts as a spill-off control valve as well to dump gas to the flare system upon detection of high pressure.

4.4.2.2 305-C-001 Rich TEG Level Control

The rich TEG after the absorption of water is routed to TEG Regenerator system by level control. The Rich TEG level is controlled by a Level Controller 305-LIC-3017 which controls 305-LV-3017 to TEG Regenerator system.

4.4.2.3 305-C-001 Bottom Level Control

All the liquids (condensate hydrocarbons or liquid water) recovered in the bottom of the Inlet Scrubber are drawn down under level control and returned to the Production Separator/Flare during LP/HP Mode. 305-LIC-3013 controls the bottom level of the Inlet Scrubber. It is a Gap Controller which has On/Off action on Control Valve

305-LV-3013 through which the knocked out condensate liquid is returned back to the inlet of Production Separator during LP mode operation. During HP mode operation, all liquid recovered in the bottom of dehydration column is routed to flare.