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GAS DEHYDRATION

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GAS DEHYDRATION

MODEC INTERNATIONAL LLC

MODEC Project #:

Document #:

1072

1072-MI20-OPM1-0022

CNR Project #:

C537-CNC-14461

Baobab Field Development

Document Title:

VOLUME 10 - GAS DEHYDRATION

0

FINAL ISSUE

30-09-04

SHV

SKG

RJW/PL

Rev.

Status

Date

Origin.

Checker

Approved

THIS DOCUMENT INCLUDING, DRAWINGS, PROCEDURES, SPECIFICATIONS, AND ITS CONTENTS IS THE EXCLUSIVE PROPERTY OF MODEC INTERNATIONAL LLC AND IS FURNISHED ON A CONFIDENTIAL BASIS, AND WITH THE EXPRESS AGREEMENT THAT IT WILL NEITHER BE USED, SOLD, TRANSFERRED, COPIED, TRACED, PHOTOGRAPHED, NOR REPRODUCED IN ANY MANNER WHATSOEVER IN WHOLE OR IN PART, NOR ANY ITEM HERIN BE SOLD, MANUFACTURED OR ASSEMBLED WITHOUT THE WRITTEN AGREEMENT OF MODEC INTERNATIONAL LLC THE RECIPIENT OF THIS DOCUMENT AGREES NOT TO DISCLOSE TO ANY OTHER PARTY INFORMATION CONTAINED HEREIN, OR NOT TO USE SUCH INFORMATION, EXCEPT FOR THE SPECIFIC PURPOSE INTENDED AT THE TIME OF RELEASE OF THIS DOCUMENT.

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CHANGE CONTROL SHEET

REVISION INFORMATION

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GAS DEHYDRATION

TABLE OF CONTENTS

Section-Page

1.1 Purpose.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ........ 2-5

1.2 Scope.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .............. 2-5

1.3 References.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w 2-5

1.4 Definitions.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .... 2-5

1.5 Responsibility.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ................. 2-5

2.0 Safety and Environmental CONSIDERATIONS.................... 22222j923w .................... 22222j923w ................ 2-6

3.0 Process Overview.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ......... 3-7

3.1 Major Equipment Summary.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ......... 3-7

3.2 System Summary.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ........... 3-7

4.0 Gas Dehydration.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .............. 4-9

4.1 Gas Filter Separator (MAK-2210).................... 22222j923w .................... 22222j923w .................... 22222j923w ................. 4-9

4.2 Glycol Contactor (MAF-2215).................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .. 4-12

4.3 Gas/Glycol Heat Exchanger (HBG-2220).................... 22222j923w .................... 22222j923w .................... 22222j923w 4-14

5.0 START UP, OPERATING & SHUTDOWN PROCEDURES - Gas Dehydration system 5-17

5.1 Cold Start-up Procedure Following a Planned Shutdown............... 5-17

5.2 Hot Start-up Procedure Following a Process Trip.................... 22222j923w ............ 5-23

5.3 Normal Operational Checks:.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w . 5-28

5.4 Planned Shutdown procedure.................... 22222j923w .................... 22222j923w .................... 22222j923w ................ 5-30

5.5 Emergency Controlled Shutdown Procedure.................... 22222j923w .................... 22222j923w .. 5-31

6.0 Alarm, Trip and PSV Settings.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ...... 6-31

7.0 Valve List.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ....... 7-34

8.0 Acknowledgements.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .... 8-35

Tables

Table 1 Operating and Design Conditions for MAK-2210.................... 22222j923w .................... 22222j923w .................... 22222j923w ................ 4-9

Table 2 Pressure Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ................. 4-10

Table 3 Level Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w . 4-11

Table 4 Temperature Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ........... 4-12

Table 5 Operating and Design Conditions for MAF-2215.................... 22222j923w .................... 22222j923w .................... 22222j923w ............... 4-13

Table 6 MAF-2215 Pressure Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................. 4-13

Table 7 MAF-2215 Level Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .. 4-14

Table 8 Operating and Design Conditions for HBG-2220.................... 22222j923w .................... 22222j923w .................... 22222j923w ............... 4-15

Table 9 HBG-2220 Temperature Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ............. 4-15

Table 10 HBG-2220 Dew Point Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .............. 4-16

Table 11 Flow Monitoring.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w 4-16

Table 12 Cold Start-up Valve Checklist.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w . 5-18

Table 13 Cold Start-up Overrides.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ......... 5-21

Table 14 Cold Start-up Procedure Following a Planned Shutdown.................... 22222j923w .................... 22222j923w .................... 22222j923w .. 5-21

Table 15 Hot Start-up Valve Checklist.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .. 5-24

Table 16 Hot Start-up Procedure Following a System Trip.................... 22222j923w .................... 22222j923w .................... 22222j923w .............. 5-27

Table 17 Planned Shutdown Procedure.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w 5-30

Table 18 Emergency Controlled Shutdown Procedure.................... 22222j923w .................... 22222j923w .................... 22222j923w ................... 5-31

Table 19 Alarm, Trip & PSV Settings.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .. 6-31

Table 20 Valve List.................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w .................... 22222j923w ........ 7-34

figure

Figure 1 Process Flow Diagram of the Gas Dehydration System..................... 22222j923w .................... 22222j923w .................... 22222j923w ..... 3-8


1.0 INTRODUCTION

This document is part of the Operating Manual, which covers the Gas Dehydration System. The Gas Dehydration System operations manual together with other manuals and related documents comprise the Facility Management System or FMS. The Gas Dehydration System is a controlled document maintained by MODEC INTERNATIONAL LLC, the Contract Operator of the Baobab Field. Any question concerning this document or its contents should be addressed to the Contract Operator.

1.1             Purpose

This document gives a general description of and the task lists for the operation of the Gas Dehydration System. Its purpose is to educate those who are unfamiliar with the system in how it works and the way in which the system is to be started, stopped and operated safely. This document can be used as a reference document in formulating maintenance isolation procedures.

1.2             Scope

Information contained in this document applies only to the Gas Dehydration System on the Baobab Field Development project. The information contained gives general design information, alarm settings and trip points for the various components as well as the start up, shut down and normal operating procedures for the Gas Dehydration System.

1.3             References

Refer P&IDs 1072-MI20-9020-0114-01, 1072-MI20-9020-0114-02, Gas Filter Separator Data Sheet (Doc.No.1072-2200-G21-0022),TEG Contactor Data Sheet ( Doc. No. 1072-2200-G21-0028) , Gas - Glycol Exchanger Data Sheet (Doc. No. 1072-MI20-90DS-2200/03) and Vendor P&IDs 935-P-DW-201-1/2

1.4             Definitions

See the Definitions Document of the FMS.

1.5             Responsibility

Every plant system covered by the Gas Dehydration System has been assigned to a single position title in the permanent offshore crew. The person filling the named position is jointly responsible with his off-duty relief for the integrity and the safe operation of the assigned system. In like manner it is that person's responsibility to verify the accuracy of the information contained in this document. Any confirmed inaccuracy shall be tracked by the Offshore Installation Manager (OIM) until formally corrected.

The job title of the position responsible for this system can be found in the System Responsibility Matrix in the Safety Management System (SMS) Manual (1072-MI20-15ST-0170).


2.0           Safety and Environmental CONSIDERATIONS

In the execution of the subsequent procedures all permit to work, PPE and isolation procedures required by the Baobab SMS (1072-MI20-15ST-0170) shall be followed. If any doubt exists as to the correctness of valve positions or sequence of operations then they should be discussed with the supervisor and approval sought from the Facility Manager to change the procedure. These changes shall then be captured on a permanent basis by submitting them through the required document control procedures. Specific requirements for HSE are given in each section of the procedures.

Shut down overrides for this system can be invoked only when the system is continuously monitored. Proper procedures and systems should be followed while testing the trips. Where overrides are put in place for testing, these shall be removed at the end of testing so as not to inhibit shutdown functions.


3.0           Process Overview

3.1             Major Equipment Summary

The main items of equipment within the Gas Dehydration facilities are as follows:

                  Gas Filter Separator MAK-2210

                  Glycol Contactor MAF-2215

                  Gas/Glycol Heat Exchanger HBG-2220

3.2             System Summary

The gas dehydration unit is required to condition the gas to meet the following specifications.

Maximum Water Content : 5 lbs./MMSCF at 15.5C, 1.0 barg

The moisture must be removed to meet the export gas/water dew point specification. The compressed gas from the 2nd Stage discharge of the Booster Gas Compressors enters the bottom of the Gas Filter Separator (MAK-2210) to remove the bulk of the water contained in the gas. The gas then proceeds to the Glycol Contactor (MAF-2215) which contains structured packing. This packing is designed to promote contact between the gas and the TEG. In the Contactor, gas enters the vessel at the bottom section of the vessel, it is contacted with the lean glycol (contains very little water) which enters at the top, the gas is then in counter-current flow to the TEG. Most of the water is removed from the gas into the glycol. This is because the water has a greater affinity for the glycol than the gas.

The dry gas exits the top of the Contactor passing through the Gas/Glycol Heat Exchanger (HBG-2220) to increase the temperature of the gas and then on to the 3rd stage BGC. The rich TEG (contains more water) exits at the base of the Contactor and is sent to the TEG (Triethylene glycol) Regeneration Unit for removal of the water and for reuse. See Figure 1 for a diagram of the dehydration system.


Figure 1 Process Flow Diagram of the Gas Dehydration System.

4.0           Gas Dehydration

The gas dehydration system function is to remove water in the gas from the 2nd stage of the booster gas compressors. The water content must be lowered to less than 5 lbs./MMSCF, producing gas suitable for sales / export or for the gas lift system.

4.1             Gas Filter Separator (MAK-2210)

The inlet separator removes liquid water and heavy hydrocarbons from the compressed gas. Several factors need to be considered when operating a gas filter separator. The liquid level should be regulated or checked regularly so that plugs or upsets do not result in carryover. This is achieved with a high-high-liquid-level shutdown system and level control valves 10M-LV-2210-1 and 10M-LV-2210-2.

Gas from the 2nd stage of the booster compressors enters the bottom section of the separator where the fluids are removed due to the different densities of the gas/liquids being handled. The liquids collected flow back to the 2nd stage suction scrubber of the booster compressors under level control. The gas in the separator moves up the vessel through the baffles to the fibre filter cartridges where particulate and additional liquids are coalesced / removed under a second level control system for the top of the vessel. The gas flow is from the top of the vessel to the Glycol Contactor (MAF-2215).

If the Gas Filter Separator is poorly operated, contaminants may be carried over into the contactor, resulting in the following problems in downstream equipments:

                  Free liquid water may enter the absorber and overload the glycol in the absorber, which may prevent the gas from being dried to pipeline specifications.

                  Hydrocarbon contamination of the glycol may cause foaming.

                  Heavy hydrocarbons may foul the heat exchange surfaces in the reboiler, resulting in poor heat transfer, localized thermal degradation of the glycol, inadequate glycol regeneration etc.

                  Sodium chloride and calcium chloride may enter the system. Sodium chloride often precipitates in the reboiler; calcium chloride precipitates in the coldest portions of the system such as the absorber. Salt contamination may ultimately necessitate replacement of the glycol.

4.1.1             Equipment Description and Control

The Gas Filter Separator (MAK-2210) is a vertical vessel made of carbon steel with an outer diameter of 610 mm and T/T height of 3050 mm.

Table 1 Operating and Design Conditions for MAK-2210

Parameter

Value

Design Pressure

64 barg

Design Temperature

177oC

Operating Pressure

56.2 barg

Operating Temperature

40.5C

Capacity

2.12 MMSM3/d

 

Pressure Monitoring, Control and ESD Instruments:

The vessel is provided with the following pressure/differential pressure transmitter to alert the operator to blockages over the filters within the separator. The differential pressure high alarm will alert the operator when filter element cleaning or replacement is required.

Table 2 Pressure Monitoring

Instrumentation Tag

Description

10M-PDT-2210-14

Differential Pressure Transmitter - Across filter and separator

10M-PDI-2210-14

Differential Pressure Indicator - Across filter and separator

10M-PDI-2210-14/ PDAH

Differential Pressure Alarm High - Across filter and separator

10M-PIT-2210-15

Pressure Indicator Transmitter - Gas Filter Separator

10M-PI-2210-15

Pressure Indicator - Gas Filter Separator

10M-PI-2210-15/PAH

Pressure Alarm High - Gas Filter Separator

10M-PI-2210-15/PAL

Pressure Alarm Low - Gas Filter Separator

10M-PI-2210-15/PALL

Pressure Alarm Low Low - Gas Filter Separator

10M-PDT-2210-18

Differential pressure transmitter- Across the valves XV-2210-16/17

10M-PDI-2210-18

Differential pressure indicator - Across the valves XV-2210-16/17

10M-PDI-2210-18/PDAH

Differential pressure alarm high - Across the valves XV-2210-16/17

Process variable from 10M-PIT-2210-15 is used for activation of high, low and low low-pressure alarms. Low low pressure alarm on 10M-PIT-2210-15 will cause bypass of gas dehydration unit (refer to cause and effect matrix). PDAH-2210-14 will alert the operator that there is some blockage in the filter i.e. some cleaning operation is required for the filter in the gas filter separator. PDAH-2210-18 will be used at the start up time when XV-2210-17 will be used for initial pressurization of the system. After equalization of pressure PDAH-2210-18 will disappear and the system to be lined up by opening XV-2210-16.

Level Monitoring, Control and ESD Instruments:

The vessel is provided with the following produced liquid level sight glass, control, alarm and trip instrumentation to aid in monitoring the interface:

Table 3 Level Monitoring

Instrumentation Tag

Description

10M-LG-2210-5

Level Gauge - Gas Filter Separator

10M-LV-2210-1

Level Control Valve - Gas Filter Separator Liquid outlet

10M-LY-2210-1

Level Transducer - Gas Filter Separator Liquid outlet

10M-LIC-2210-1

Level Indicator Controller - Gas Filter Separator Liquid outlet

10M-LIC-2210-1/LAL

Level Alarm Low - Gas Filter Separator Liquid outlet

10M-LIC-2210-1/LAH

Level Alarm High - Gas Filter Separator Liquid outlet

10M-LT-2210-1

Level Transmitter - Gas Filter Separator Liquid outlet

10M-LG-2210-6

Level Gauge - Gas Filter Separator

10M-LV-2210-2

Level Control Valve - Gas Filter Separator Liquid outlet

10M-LY-2210-2

Level Transducer - Gas Filter Separator Liquid outlet

10M-LIC-2210-2

Level Indicator Controller - Gas Filter Separator Liquid outlet

10M-LIC-2210-2/LAL

Level Alarm Low - Gas Filter Separator Liquid outlet

10M-LIC-2210-2/LAH

Level Alarm High - Gas Filter Separator Liquid outlet

10M-LT-2210-2

Level Transmitter - Gas Filter Separator Liquid outlet

10M-LI-2210-3

Level Indicator - Gas Filter Separator

10M-LI-2210-3/LAHH

Level Alarm High High - Gas Filter Separator

10M-LI-2210-3/LALL

Level Alarm Low Low - Gas Filter Separator

10M-LT-2210-3

Level Transmitter - Gas Filter Separator

10M-LI-2210-4

Level Indicator - Gas Filter Separator

10M-LI-2210-4/LAH

Level Alarm High - Gas Filter Separator

10M-LI-2210-4/LALL

Level Alarm Low Low - Gas Filter Separator

10M-LT-2210-4

Level Transmitter - Gas Filter Separator

Both 10M-LT-2210-1 and 10M-LT-2210-2 are level transmitters located on the top and bottom sections of the vessel respectively. They modulate control valves 10M-LV-2210-1 and 10M-LV-2210-2, via the respective controllers, to direct the liquid flow out of the vessel to the second stage suction scrubber of the booster gas compressors. Both of these control loops have high and low level alarms used to alert the operator of an upset condition.

The process variables from 10M-LT-2210-3 and 10M-LT-2210-4 are used in the gas separator the process shutdown logic system for activation of both high high and low low-level alarms respectively. High high on 10M-LT-2210-3 will result in by pass of gas dehydration unit, as per the Cause & Effects matrix. Activation of the low low on both the transmitters will result in the closing of the shut down valve 10M-SDV-2210-11, stopping the liquid flow to the second stage booster gas compressors suction scrubber. Refer to section 6.0 for the alarm trip settings.

Temperature Monitoring, Control and ESD Instruments:

The vessel is provided with the following local temperature indicator used to determine the temperature of the gas out into the contactor:

Table 4 Temperature Monitoring

Instrumentation Tag

Description

10M-TT-2210-8

Temperature Transmitter - Gas Filter Separator gas outlet

10M-TI-2210-8

Temperature Indicator- Gas Filter Separator gas outlet

10M-TI-2210-8/TAH

Temperature Alarm High - Gas Filter Separator gas outlet

10M-TI-2210-8/TAL

Temperature Alarm Low - Gas Filter Separator gas outlet

Process variable from temperature transmitter 10M-TT-2210-8 will activate for temperature alarm low and high in the gas outlet line of gas filter separator and it is also used for differential temperature indication and alarm between glycol and gas inlet to contactor on TDI-2210-8.

Over-Pressure Protection:

Over-pressure protection of the vessel is provided by pressure safety valve 10M-PSV-2210-9 set at 63.8 barg, relieving to the HP flare header. Only one PSV is required to meet the relief capacity of the separator. A PSV set at 29.3 barg, 10M-PSV-2210-12, has been provided for over pressure protection of liquid outlet line of the separator.

4.2             Glycol Contactor (MAF-2215)

The Glycol contactor is a packed column where lean glycol is pumped to the top. Gas (from the Gas Filter Separator MAK-2210) rises from the bottom in countercurrent flow with lean glycol. The moisture content in the gas is absorbed by the hygroscopic glycol flowing down from the top. Moisture free gas from the top is directed to Gas/Glycol Heat Exchanger (HBG-2220) for heating, and is sufficiently analyzed for moisture content using the online water Dew Point analyzer AT-2220-5 and sent to the 3rd stage suction scrubber of booster gas compressor system for further compression and thereafter to the sales gas meters or gas lift system.

The contactor is vertical to allow proper glycol flow with sufficient gas/liquid contact and operates at the pressure of the incoming gas (approximately 57 barg). A vane mist eliminator at the top of the contactor will reduce glycol losses by preventing glycol from being carried out with the dry gas.

4.2.1             Equipment Description and Control

Glycol Contactor (MAF-2215) is a vertical Carbon Steel vessel with an inner diameter of 1067 mm and height (T/T) 8000-mm. The contactor has the following internal features:

Structured Packing

Wire Mesh Mist Eliminator

Glycol Distributor.

Table 5 Operating and Design Conditions for MAF-2215

Parameter

Value

Design Pressure

64 barg

Design Temperature

177oC

Operating Pressure

57 barg

Operating Temperature

40.5C (Gas) /45.5C (Glycol)

Capacity

88490 STD m3/h

Packing Type

Structured

Pressure Monitoring, Control and ESD Instruments:

The vessel is provided with the following differential pressure transmitter to alert the operator to blockages over the structured packing within the contactor. The high alarm will alert the operator when cleaning of the structured packing is required, or the gas velocity across the packing is too high.

Table 6 MAF-2215 Pressure Monitoring

Instrumentation Tag

Description

10M-PDT-2215-5

Differential Pressure Transmitter - Glycol Contactor

10M-PDI-2215-5

Differential Pressure Indicator - Glycol Contactor

10M-PDI-2215-5/PDAH

Differential Pressure Alarm High - Glycol Contactor

10M-PI-2215-9

Pressure Indicator - Glycol Contactor Inlet line

10M-PI-2215-9/PAL

Pressure Alarm Low - Glycol Contactor Inlet line

10M-PI-2215-9/PAH

Pressure Alarm High - Glycol Contactor Inlet line

10M-PT-2215-9

Pressure Transmitter - Glycol Contactor Inlet line

Level Monitoring, Control and ESD Instruments:

The vessel is provided with the following glycol level sight glass, control, alarm and trip instrumentation:

Table 7 MAF-2215 Level Monitoring

Instrumentation Tag

Description

10M-LG-2215-3

Level Gauge - Glycol Contactor

10M-LV-2215-4

Level Control Valve - Glycol Contactor TEG level control.

10M-LY-2215-4

Level Transducer - Glycol Contactor TEG level.

10M-LIC-2215-4

Level Indicator Controller - Glycol Contactor TEG level,

10M-LIC-2215-4/LAL

Level Alarm Low - Glycol Contactor TEG level.

10M-LIC-2215-4/LAH

Level Alarm High - Glycol Contactor TEG level.

10M-LT-2215-4

Level Transmitter - Glycol Contactor TEG level.

10M-LI-2215-2

Level Indicator - Glycol Contactor TEG level.

10M-LI-2215-2/LALL

Level Alarm Low Low- Glycol Contactor TEG level.

10M-LI-2215-2/LAHH

Level Alarm High High- Glycol Contactor TEG level.

10M-LT-2215-2

Level Transmitter- Glycol Contactor TEG Level.

10M-LT-2215-4 is a level transmitter located at the base of the vessel. It modulates control valve 10M-LV-2215-4, via controller 10M-LIC-2215-4, to direct the rich glycol flow out of the vessel to TEG regeneration unit. Both high and low level alarms are installed to alert the operator to of the upset conditions within the vessel.

The process variable from 10M-LT-2215-2 is used in the process shutdown logic system for activation of both high high and low low-level alarms. Activation of the high high will result in a package shutdown, where the lean glycol pumps will be stopped and bypass of the gas dehydration system will be done. The low low alarm will result in the closure of shutdown valve 10M-SDV-2215-1, as per cause and effect matrix.

Refer to section 6.0 for the alarm trip settings.

Over-Pressure Protection:

Over-pressure protection of the vessel is provided by pressure safety valve on gas inlet line10M-PSV-2215-6 set at 63.78 barg, relieving to the HP flare header. Only one PSV is required to meet the relief capacity of the contactor.

4.3             Gas/Glycol Heat Exchanger (HBG-2220)

This is a shell and tube type heat exchanger using the exiting compressed and dehydrated gas to further cool the lean glycol, being pumped from the regeneration package, before entering the contactor. The temperature of the lean glycol leaving the gas/glycol heat exchanger should be about 5 to 10C higher than the dry product gas temperature to prevent hydrocarbons from condensing in the contactor. A minimum lean glycol temperature of 27C should be maintained to avoid excessive absorption of natural gas components.

4.3.1             Equipment Description and Control

Gas/Glycol Heat Exchanger (HBG-2220) is a shell and tube heat exchanger constructed from carbon steel.

Table 8 Operating and Design Conditions for HBG-2220

Parameter

Value

Design Shell Pressure

63.78 barg

Design Tube Pressure

63.78 barg

Design Shell Temperature

176.7oC

Design Tube Temperature

176.7oC

Operating Shell Pressure

59.67 barg

Operating Tube Pressure

55.19 barg

Operating Shell Temperature

92.5C/48.2C (IN/OUT)

Operating Tube Temperature

48.2C/50C (IN/OUT)

Duty

78.46kW

Temperature Monitoring, Control and ESD Instruments:

The heat exchanger is provided with the following temperature, control, alarm and trip instrumentation:

Table 9 HBG-2220 Temperature Monitoring

Instrumentation Tag

Description

10M-TT-2220-6

Temperature Transmitter - Gas Outlet

10M-TI-2220-6

Temperature Indicator - Gas Outlet

10M-TI-2220-6/TAL

Temperature Alarm Low - Gas Outlet

10M-TI-2220-6/TAH

Temperature Alarm High - Gas Outlet

10M-TT-2220-2

Temperature Transmitter - TEG Outlet

10M-TI-2220-2

Temperature Indicator - TEG Outlet

10M-TDI-2210-8

Differential Temperature Indicator-TEG Outlet

10M-TDI-2210-8/TDAH

Differential Temperature Alarm High-TEG Outlet

10M-TDI-2210-8/TDAL

Differential Temperature Alarm Low -TEG Outlet

10M-TI-2220-3

Temperature Indicator - Gas Outlet

The outlet line stream temperature for both the shell and tube are monitored in the control room through the use of the transmitters and indicators. It is important to monitor the temperatures for all inlets and outlets of the heat exchanger to determine when the heat transfer has decreased and cleaning is required. As previously mentioned it is also important to monitor the lean glycol temperature entering the contactor to ensure there is minimal absorption of contaminants. Differential temperature indicator provided between the lean glycol inlet to the contactor and the gas inlet to the contactor to ensure that there are sufficient temperature differences between these two streams to prevent hydrocarbons from condensing in the contactor.

Dew Point Monitoring

The moisture content of the gas must be less than 5 lbs/MMSCF to be suitable for export. A moisture dew point analyzer and indicator have been installed on the tube outlet of the heat exchanger to determine the dew point. A high alarm is installed on the indicator to alert the operator to a high water content. The following instrumentation is available.

Table 10 HBG-2220 Dew Point Monitoring

Instrumentation Tag

Description

10M-AT-2220-5

Dew point Analyzer Transmitter- Gas Outlet to meters

10M-AI-2220-5

Dew point Analyzer Indicator - Gas Outlet to meters

10M-AI-2220-5/AAH

Analyzer Alarm High - Gas Outlet to meters

Flow Monitoring

In the gas/glycol heat exchanger (HBG-2220) the lean TEG inlet line to HBG-2220 provided with a flow element FE-2215-10 to monitor the TEG inlet flow to the glycol contactor through gas/glycol heat exchanger.

Table 11 Flow Monitoring

Instrumentation Tag

Description

10M-FE-2215-10

Flow Element - TEG inlet line to HBG-2220

10M-FT-2215-10

Flow Transmitter - TEG inlet line to HBG-2220

10M-FI-2215-10

Flow Indicator - TEG inlet line to HBG-2220

10M-FI-2215-10/FAL

Flow Alarm Low - TEG inlet line to HBG-2220


5.0           START UP, OPERATING & SHUTDOWN PROCEDURES - Gas Dehydration system

5.1             Cold Start-up Procedure Following a Planned Shutdown.

The following procedure details the steps to be undertaken to start-up the Gas Dehydration system following maintenance activities that may have involved piping intrusion works on part / all of the systems / subsystems.

This start-up procedure assumes that the system has been purged of all oxygen with an inert gas and that no explosive mixture exists within the system. Failure to do so may expose the Facility / personnel to unnecessary risks.

The following conditions are assumed to exist in executing this procedure: -

                  No Permits to Work are in force on any part of the system that may prohibit, or hinder, the safe start-up of the equipment.

                  The Fire and Gas Detection System, ESD Systems and control facilities within the CCR are operational including all alarms, trips and controllers.

                  All vents, purge points and manual sample points are closed and blanked, or capped off, where necessary.

5.1.1             Ancillary system requirements

The following ancillary systems must be available for operation prior to commencement of this procedure: -

Power is available to the skid

The instrument air system must be in operation.

The flash and booster gas compressors must be ready for operation.

The fuel gas supply system must be operational.

Flare and separation facilities are operational.

Glycol regeneration system must be ready for operation

5.1.2             Cold Start-up Valve Checklist

Refer to the P&ID 's identified as pertaining to the relevant system whilst carrying out this procedure.

The system operator should check the system valves are in the positions detailed below.

Where valves are found to be out of position, the operator must satisfy himself it is safe to move the valve before doing so. This may involve referencing to an Isolation Permit or relevant Permit to Work.


Table 12 Cold Start-up Valve Checklist


Cold start-up Valve Checklist (Gas Dehydration)

line # / vALVE spec

VALVE DESCRIPTION

POSITION

Gas Dehydration System

(Refer to P&ID DWG No 1072-MI20-9020-0114-01 & 1072-MI20-9020-0114-02 )

10"-PG-d1-1237

Gas inlet spectacle blind to Gas Filter Separator

open

10"-PG-d1-1237 / xv-2210-16

Gas inlet ball valve to Gas Filter Separator

CLOSED

10"-PG-d1-1237 / xv-2210-17

Gas inlet ball valve to Gas Filter Separator across the XV-2210-16

open

6"-PG-D1-1239/ 6" D2RRK

Gas Filter Separator bypass line isolation valve

locked close

2" d2rfk

PSV-2210-9 inlet block valve

locked open

2"-fh-a1l-4023 / 2"A2rfLK

PSV-2210-9 outlet block valve

locked open

2"-PL-D1-1153

Liquids outlet line spectacle blind

open

2"-PL-D1-1153 / 2" D2RRK

Liquids outlet line; block valves up and downstream of LV-2210-1.

open

1" D4ZK

LV-2210-1 bypass line valve

KKKKK

closed

1" D2ZRK

LV-2210-1 bypass line valve

LOCKED close

2"-PL-D1-1116

Separator liquids outlet line spectacle blind

open

2"-PL-D1-1116 / 2" D2RRK

Separator outlet line, block valves up and downstream LV-2210-2

open

1" D4ZK

LV-2210-2 bypass line valve

closed

1" D2ZRK

LV-2210-2 bypass line valve

LOCKED close

2"-PL-B1-1149/ sdv-2210-11

Shutdown valve on liquid outlet

open

2"-PL-B1-1149

Spectacle blind on liquid outlet line to second stage BGC's suction scrubber

open

2"-PL-B1-1149/ 2" B2RRK

Isolation valve on liquid outlet line to second stage BGC's suction scrubber

open

2"-PL-B1-1171/ 2" B2rfK

PSV-2210-12 Inlet Isolation Valve

locked open

3"-FH-A1L-4040/ 3" A2RFK

PSV-2210-12 Outlet Isolation Valve

locked open

2"-pl-b1-1171/ 2" b2rfk

Future PSV Inlet Isolation Valve

locked close

3"-fh-a1l-4040/ 3" a2rfk

Future PSV Outlet Isolation Valve

locked close

10"-pG-D1-1240

Gas outlet spectacle blind

open

10"-pG-D1-1240 / 10" D2RRK

Gas outlet isolation valve - Filter separator

closed

10"-pG-D1-1240

Spectacle blind on the gas inlet to the contactor

open

2"-fh-a1l-4041 / 2" D2RfK

Ball valve from gas filter separator to H.P. flare header

locked close

2"-fh-a1l-4041 / 2" D4RK

Globe valve from gas filter separator to H.P. flare header

closed

2"-dc-D1-5021 / sp-122

Spectacle blind on gas filter separator drain line

open

2"-dc-D1-5021 /5041/ 2" D2RRK

Drain line ball valves (Two Nos.)

LOCKED close

2"-pg-D1-1257 / 2" D2RFK

PSV-2215-6 inlet block valve

locked open

2"-fh-a1L-4024 / 2"A2rfLK

PSV-2215-6 outlet block valve

locked open

2"-dc-D1-5042

Spectacle blind on the drain line from the contactor.

open

2"-dc-D1-5042 / 2" D2RRK

Ball valve on the drain line from the contactor.

LOCKED close

2"-dc-D1-5042 / 2" D4RK

Globe valve on the drain line from the contactor

closed

2"-dc-D1-5040

Spectacle blind on the drain line from the contactor.

open

2"-dc-D1-5040 / 2" D2RRK

Ball valves (Two Nos.) on the drain line from the contactor.

LOCKED close

2"-gl-D1-2402 / 2"D2RRK

LV-2215-4 upstream and downstream block valve to the glycol regeneration unit

open

1" D2ZRK

LV-2215-4 bypass line isolation valve

LOCKED close

1" D4ZK

LV-2215-4 bypass line isolation valve

closeD

2'-GL-D1-2402/ sdv-2215-1

Glycol outlet line from Glycol Contactor to Glycol regeneration unit shutdown valve

open

2" GL-D1-2402

Glycol outlet line from Glycol Contactor spectacle blind

open

10"-Pg-D1-1242

Spectacle blind on glycol contactor gas outlet to gas/glycol exchanger.

open

2"-gl-d1-2401

Spectacle blind on lean glycol inlet to glycol contactor from gas /glycol exchanger.

open

2"-pg-D1-1245 / 2"D2RFLK

Up and downstream block valves for BDV-2220-1

locked open

bdv-2220-1

Blow down valve to the HP flare header

closed

2" D4RLK

BDV-2220-1 bypass valve

closed

2" D2RfLK

BDV-2220-1 bypass valve

locked close

10"-pg-d1-1326

Spectacle blind on gas outlet line from gas / glycol heat exchanger to 3rd stage booster gas compressor suction scrubber

open

10"-pg-d1-1326 / 10" d2rrkd

Isolation valve on gas outlet line from gas / glycol heat exchanger to 3rd stage booster gas compressor suction scrubber

CLOSED

2"-GL-D1-2400

Spectacle blind on lean TEG inlet line to gas/glycol heat exchanger from TEG circulation pumps PBE-2325A/B

open

Gauge, transmitter and indicator isolation valves

open

Sample points

closed

5.1.3             Cold Start-up Overrides

During the cold Start-up of the Gas Dehydration system the following inputs to the shutdown system may require to be overridden at the Shutdown Panel in the Central Control Room until steady operating conditions are established:

Table 13 Cold Start-up Overrides

Switch

Function

Parent Equipment

LALL-2210-4

Gas Filter Separator Level Alarm Low Low

MAK-2210

LALL-2210-3

Gas filter separator liquid level Low Low

MAK-2210

PALL-2210-15

Gas filter separator pressure alarm Low Low

MAK-2210

5.1.4             Cold Start-up Procedure

Note: This procedure assumes that the system has had all oxygen removed and is under nitrogen blanket, which has been confirmed with manual measurements. Do not proceed with this procedure if this is not the case due to explosion hazards and degradation of the TEG in the presence of oxygen.

Table 14 Cold Start-up Procedure Following a Planned Shutdown

Cold Start-up Procedure following a Planned Shutdown

STEP

DESCRIPTION

LOCAL

CCR

1.     

Confirm that all valves are aligned as per the Cold Start-up Valve Checklist and all overrides are on.

*

*

2.     

Confirm that all controllers are in automatic mode and are set to control the process at the process set point.

*

3.     

Ensure that all control valves are at their process control set points and functional e.g., Instrument air regulators.

*

4.     

Confirm that flare systems are operational

*

5.     

Line walks the system to ensure the system is ready for operation and confirm that it is oxygen free.

6.     

Confirm that the booster gas compressors are ready to receive hydrocarbon gas

*

*

7.     

Confirm that glycol regeneration system ready to regenerate lean glycol and TEG surge drum adequately filled with glycol.

8.     

To pressurize the gas dehydration system by L.P. fuel gas set the PIC-2530-4B at 6.75 barg at the outlet of L.P. Gas Scrubber (MBF-2530). Connect a suitably pressure rated " hose from the drain valve (3/4"D2YFEK) downstream of PV-2530-4A to the test valve on PT-2215-9. Slowly open the drain valve downstream of PV-2530-4A, to pressurize the dehydration system to approximately 6.75 barg. while pressurizing check for any leaks in the system.

9.     

Once pressurized close the drain valve (3/4"D2YFEK) and test valve on PT-2215-9. Leave the hose connected at the moment. Confirm that there is pressure within the Glycol Contactor to drive the TEG through the system.

10. 

Start the duty TEG circulation pump (PBE-2325A/B). Confirm that the pump is running by checking FI-2215-10, which should show the required flow to the gas/glycol heat exchanger.

Note : The glycol contactor pressure will have to be monitored, if the pressure drops during circulation reopen the drain valve downstream of PV-2530-4A, to top up the contactor pressure. If contactor pressure remains stable, isolate, depressure and disconnect the jumper hose.

*

*

11. 

Observed that level is build up in the glycol contactor through LG-2215-3 to ensure that the glycol contactor is flooded with lean glycol. Confirm that glycol is flowing through the level control valve LV-2215-4 to reflux condenser (HBG-2340)

*

12. 

Observe that glycol inlet temp to the contactor is higher than the gas temperature which will come from 2nd stage booster gas compressors discharge cooler outlet through TI-2220-2

13. 

Refer to the export/gas lift part (Doc. No. 1072-MI20-OPM1-05) of the operations manual to prepare the gas lift and/or the export meter systems taking gas into the system.

*

*

14. 

Start the booster gas compressors, Refer doc. No. 1072-MI20-OPM1-20 of BGC of the operations manual for the procedure.

*

*

15. 

With the 2nd stage boost gas compressor/s on line - confirm that TEG is still circulating from the Reboiler into the Contactor. .

*

16. 

Gas will pass through the 2" XV-2210-17 from 2nd stage booster gas compressor discharge cooler and start pressurization of gas filter separator.This will observed through the PI-2210-15 on gas filter separator.The PDAH-2210-18 across the XV-2210-17 will appear at this time till there is pressure equalization of the line.

*

17. 

Observe the pressure build up in the gas filter separator through PI-2210-15 and slowly open the gas outlet line isolation valve 10" D2RRK on the line no 10"-PG-D1-1240 to allow the gas to the glycol contactor.

*

18. 

The dry gas from the top of the contactor will pass through the gas/glycol heat exchanger to the 3rd stage suction scrubber of the booster gas compressors. Confirm the reading from the water Dew Point analyser AT-2220-5 and that it is functional.

*

19. 

When the PDAH-2218-18 across the XV-2210-17 will disappear I,e, the gas dehydration system is completely pressurized then open the XV-2210-16 to take it on line and then close the XV-2210-17.

*

*

20. 

Confirm that there is a D/P across the glycol contactor structural packing through PDI-2215-5 - this will indicate that the contactor is liquid filled and that TEG is flowing through the contactor.

*

21. 

Confirm that the TEG level in the Contactor is operating at normal level . If required - refill the system via the fill line through the glycol transfer pump on the Glycol surge drum.

*

22. 

Open the gas outlet isolation valve downstream of gas/glycol heat exchanger(HBG-2220)

23. 

Remove the overrides listed in cold start-up overrides.

*

24. 

When a stable operation is established, check the level controls on the glycol contactor. Controls on the glycol system should be adjusted to give a relatively steady flow rather than an on/off operation.

*

25. 

Monitor all temperatures, pressures/differential pressures and levels in the system.

*

*

26. 

Confirm the reading from AT-2220-5 to ensure that water Dew Point depression is occurring on the process gas.

*

5.2             Hot Start-up Procedure Following a Process Trip

The following hot start-up procedure details the steps to be taken to re-start the Gas Dehydration system facilities following a system trip.

The procedure assumes all the facilities listed below have been operating normally but have shutdown as a result of a system trip or by manual initiation.

The reason for the shutdown has been investigated and rectified and it is considered safe to re-start the system.

The procedure assumes that the system is still O2 free and that an explosive mixture has not accumulated within the system / piping.

The levels, pressures and temperatures within the Gas Dehydration system are at or near normal conditions.

The following conditions are assumed to exist in executing this procedure: -

                  No Permits to Work are in force on any part of the system that may prohibit, or hinder, the safe start-up of the equipment.

                  The Fire and Gas Detection System, ESD Systems and control facilities within the CCR are operational including all alarms, trips and controllers.

                  It is assumed that in a short duration shutdown it is unlikely that spades or blinds would be moved, or drain and vent valves opened unless required to take corrective action on the cause of the shutdown. It is therefore unnecessary to recheck these items other than if they have been disturbed.

                  All vents, purge points and manual sample points are closed and blanked, or capped off, where necessary.

                  Communications have been established between all the personnel involved with the start-up procedure.

                  Safety/Briefing Meetings have been held with all directly concerned parties outlining the workscope and procedures.

The following Utility and Ancillary Systems are available:

                  Electrical Power Distribution

                  Instrument Air

                  Flash and boost gas compressors

                  Fuel gas system

Table 15 Hot Start-up Valve Checklist


Hot start-up Valve Checklist (Gas Dehydration)

line # / vALVE spec

VALVE DESCRIPTION

POSITION

Gas Dehydration System

(Refer to P&ID DWG No 1072-MI20-9020-0114-01 & 1072-MI20-9020-0114-02 )

10"-PG-d1-1237

Gas inlet spectacle blind to Gas Filter Separator

open

10"-PG-d1-1237 / xv-2210-16

Gas inlet ball valve to Gas Filter Separator

open

10"-PG-d1-1237 / xv-2210-17

Gas inlet ball valve to Gas Filter Separator across the XV-2210-16

closed

6"-PG-D1-1239/ 6" D2RRK

Gas Filter Separator bypass line isolation valve

locked close

2" d2rfk

PSV-2210-9 inlet block valve

locked open

2"-fh-a1l-4023 / 2"A2rfLK

PSV-2210-9 outlet block valve

locked open

2"-PL-D1-1153

Liquids outlet line spectacle blind

open

2"-PL-D1-1153 / 2" D2RRK

Liquids outlet line; block valves up and downstream of LV-2210-1.

open

1" D4ZK

LV-2210-1 bypass line valve

closed

1" D2ZRK

LV-2210-1 bypass line valve

LOCKED close

2"-PL-D1-1116

Separator liquids outlet line spectacle blind

open

2"-PL-D1-1116 / 2" D2RRK

Separator outlet line, block valves up and downstream LV-2210-2

open

1" D4ZK

LV-2210-2 bypass line valve

closed

1" D2ZRK

LV-2210-2 bypass line valve

LOCKED close

2"-PL-B1-1149/ sdv-2210-11

Shutdown valve on liquid outlet

open

2"-PL-B1-1149

Spectacle blind on liquid outlet line to second stage BGC's suction scrubber

open

2"-PL-B1-1149/ 2" B2RRK

Isolation valve on liquid outlet line to second stage BGC's suction scrubber

open

2"-PL-B1-1171/ 2" B2rfK

PSV-2210-12 Inlet Isolation Valve

locked open

3"-FH-A1L-4040/ 3" A2RFK

PSV-2210-12 Outlet Isolation Valve

locked open

2"-pl-b1-1171/ 2" b2rfk

Future PSV Inlet Isolation Valve

locked close

3"-fh-a1l-4040/ 3" a2rfk

Future PSV Outlet Isolation Valve

locked close

10"-pG-D1-1240

Gas outlet spectacle blind

open

10"-pG-D1-1240 / 10" D2RRK

Gas outlet isolation valve - Filter separator

open

10"-pG-D1-1240

Spectacle blind on the gas inlet to the contactor

open

2"-fh-a1l-4041 / 2" D2RfK

Ball valve from gas filter separator to H.P. flare header

locked close

2"-fh-a1l-4041 / 2" D4RK

Globe valve from gas filter separator to H.P. flare header

closed

2"-dc-D1-5021 / sp-122

Spectacle blind on gas filter separator drain line

open

2"-dc-D1-5021 /5041/ 2" D2RRK

Drain line ball valves (Two Nos.)

LOCKED close

2"-pg-D1-1257 / 2" D2RFK

PSV-2215-6 inlet block valve

locked open

2"-fh-a1L-4024 / 2"A2rfLK

PSV-2215-6 outlet block valve

locked open

2"-dc-D1-5042

Spectacle blind on the drain line from the contactor.

open

2"-dc-D1-5042 / 2" D2RRK

Ball valve on the drain line from the contactor.

LOCKED close

2"-dc-D1-5042 / 2" D4RK

Globe valve on the drain line from the contactor

closed

2"-dc-D1-5040

Spectacle blind on the drain line from the contactor.

open

2"-dc-D1-5040 / 2" D2RRK

Ball valves (Two Nos.) on the drain line from the contactor.

LOCKED close

2"-gl-D1-2402 / 2"D2RRK

LV-2215-4 upstream and downstream block valve to the glycol regeneration unit

open

1" D2ZRK

LV-2215-4 bypass line isolation valve

LOCKED close

1" D4ZK

LV-2215-4 bypass line isolation valve

closeD

2'-GL-D1-2402/ sdv-2215-1

Glycol outlet line from Glycol Contactor to Glycol regeneration unit shutdown valve

open

2" GL-D1-2402

Glycol outlet line from Glycol Contactor spectacle blind

open

10"-Pg-D1-1242

Spectacle blind on glycol contactor gas outlet to gas/glycol exchanger.

open

2"-gl-d1-2401

Spectacle blind on lean glycol inlet to glycol contactor from gas /glycol exchanger.

open

2"-pg-D1-1245 / 2"D2RFLK

Up and downstream block valves for BDV-2220-1

locked open

bdv-2220-1

Blow down valve to the HP flare header

closed

2" D4RLK

BDV-2220-1 bypass valve

closed

2" D2RfLK

BDV-2220-1 bypass valve

locked close

10"-pg-d1-1326

Spectacle blind on gas outlet line from gas / glycol heat exchanger to 3rd stage booster gas compressor suction scrubber

open

10"-pg-d1-1326 / 10" d2rrkd

Isolation valve on gas outlet line from gas / glycol heat exchanger to 3rd stage booster gas compressor suction scrubber

open

2"-GL-D1-2400

Spectacle blind on lean TEG inlet line to gas/glycol heat exchanger from TEG circulation pumps PBE-2325A/B

open

Gauge, transmitter and indicator isolation valves

open

Sample points

closed

5.2.1             Hot Start-up Procedure

During the Hot Start-up of the Gas Dehydration System there should be no requirement to have any input over-ride to the to the shutdown system. Note 1 - Dependant upon the pressure remaining within the system, there may be the requirement to over-ride the TEG circulation pumps PALL 2325A/B-2 to enable a pump re-start. This will depend on the length of time that the pumps are shutdown, and at what trip point this switch is set at.

Note-2: This procedure assumes that the temperature of the system has not dropped significantly. It also assumes that the pressure in the system has not been lost through the opening of the blow down valve. This valve will open on an ESD and PSD in the event that this occurs the system will have to be repressurized following the cold start-up procedure.

Table 16 Hot Start-up Procedure Following a System Trip

Hot Start-Up Procedure Following A System Trip

STEP

DESCRIPTION

LOCAL

cCR

1.     

Confirm that the valves are aligned as per Hot Start-up Valve checklist.

*

*

2.     

Confirm that all controllers are in automatic mode and are set to control at the process set point.

*

3.     

Check pumps oil levels.

*

4.     

Start the duty glycol circulation pump. Confirm that the pump is running by checking PI-2325A/B-2, it should slightly higher than the pressure in the glycol contactor.

*

5.     

Start the booster gas compressors (if not already operating); see Doc No. 1072-MI20-OPM1-20 of the operations manual for the procedure.

*

*

6.     

When a stable operation is established, check the level controls on the glycol contactor. Controls on the glycol system should be adjusted to give a relatively steady flow rather than an on/off operation.

*

7.     

Confirm the reading from the water Dew Point analyser AT-2220-5 and that it is functional.

*

8.     

Monitor all temperatures, pressures/differential pressures and levels in

the system

9.     

Confirm the reading from the water Dew Point analyser AT-2220-5and that Dew point depression is occurring with the gas being processed.

*

5.3             Normal Operational Checks:

The normal operational conditions, together with alarm and trip set points for each item in the Gas Dehydration are provided in section 6.0.

On a regular basis the field operator should conduct the following routine checks:

                  Regularly line walk the system to visually inspect for leaks and noise from rotating equipment and other defects in the equipment such as leaking control valves and filter housings etc.- particular attention should be paid to any abnormal noise coming from the pumps.

                  Check all levels, pressures and temperatures in the process system.

                  Periodically conduct cross checks between the field instruments and the respective CCR controller indications to determine the accuracy of the instruments. Remedial action should be taken when significant discrepancies are noted.

                  Monitor the differential pressure on the Gas Filter Separator (MAK-2210) on a regular basis, high differential pressure indicates that the filter elements are plugged and will require changeup. Open the by-pass line around the vessel if filter changeup is required whist the dehydration system is still online, if this is permissible under the Isolation policy. If not, then the dehydration system will require shutdown / depressurization / isolation to change the filter elements.

                  TEG CONDITION - Take a sample of rich and lean glycol once a week and conduct the following testing:

o        Examine for finely divided precipitate. This normally contains iron products of corrosion (FeS and Fe3O4). This can lead to substantial operating problems within pumps and reboilers if allowed to accumulate to any degree. Good filtration practices should adequately cope with this problem.

o        Two-phase separation for condensate contamination. Possible causes are incorrect operation of production separator, glycol flash drum or carbon filter.

o        Check for thermal degradation. Usually can be determined by visual inspection of the TEG. If the sample appears darker and smells of burnt sugar it is an indication of degradation occurring. This can be the result of excessive reboiler temperatures.

o        Check the TEG for purity - i.e. Lean TEG purity should be ~99% with Reboiler temps of ~204 deg C.

o        Check the TEG pH. The pH should be in the range of 6.0 to 6.2 for rich glycol and between 7.6 to 8.0 for lean glycol. Add M.E.A / T.E.A as required for pH control. High pH can tend the glycol to foam and be carried out the overhead line with the gas phase, resulting in excessive TEG losses. IF pH control chemical is added, it should be added slowly by means of a small dosing pump if possible whilst the TEG is circulating as opposed to a slug dose of the pH buffer.

                  Duty pump selection is to be reviewed weekly or as required by the Operations Supervisor.

                  Routine checks should be performed to collect level, pressure, pump deliverability and TEG composition data in order to ensure optimum operation of the glycol circulation pumps and pumping capacity is maintained. Regularly check the in-line suction strainers on the TEG circulation pumps for plugging. Low delivery pressure / rates can be caused by the suction strainer being fouled.

                  Check the glycol circulation pumps, pumping elements for leakage. Maintain the pump / splined drive coupling frame space for the correct lubrication level on a routine basis.

                  CONTACTOR - The primary operating problems associated with the contactor are as follows:
Insufficient Dehydration - Resulting in out of spec gas, in this case the lean TEG flow must be reviewed.
Foaming - Resulting in loss of TEG with the vapor stream. High gas velocities and chemical contamination can result in this scenario.
Calcium Chloride - Dissolves in the liquid at higher temperatures and precipitates in the cooler areas leading to plugging of the packing, resulting in foaming and glycol losses.

                  Monitor the Differential pressure across the Contactor as indicated on PDT 2215-5, high differential indicates plugging / fouling of the structured packing section on the vessel. This will require further investigation and possible removal cleaning / replacement of the contactor packing.

                  Regularly check the temperature difference between the gas inlet to the contactor and the lean glycol inlet to the contactor through TDI-2210-8 to ensure that glycol inlet temperature 5C-10C higher than that of gas inlet temperature. This will prevent any hydrocarbon condensation from the gas in the glycol contactor.

5.4             Planned Shutdown procedure

The following procedure details the steps to be taken to conduct a planned shutdown of the Gas Dehydration System as part of an overall shutdown of the FPSO process facilities in preparation for inspection / maintenance activities.

The following conditions are assumed to exist in executing this procedure: -

                  Safety / Briefing Meetings have been held with all directly concerned parties outlining the workscope and procedures.

                  Communications have been established between all persons involved in this procedure.

o        No operations or Permits to Work are in force that may prohibit the shutdown of the system.

Note: When shutting down the gas dehydration system the flash gas and boost compressors should be shut down at the same time, and gas will be sent to the HP Flare. This will leave the dehydration system pressurized and the glycol circulating through the regeneration system.

Table 17 Planned Shutdown Procedure

Planned Shutdown Procedure

STEP

DESCRIPTION

LOCAL

CCR

1.     

Ensure that the dehydration system is no longer required for processing of gas.

*

*

2.     

Shutdown the Booster Compressors. Confirm that the suction and discharge SDV of the booster compressors have closed.

*

*

3.     

Stop the duty glycol circulation pumps.

*

4.     

Open BDV bypasses to depressurise the TEG system to flare (if required).

*

*

5.     

Confirm that all systems have shutdown and are depressurised (if required).

*

*

6.     

Drain liquids from the relevant systems as required to the closed drain sump tank.

*

7.     

Operate the pumps to drain any liquids as required.

*

8.     

If intervention work is planned, ensure that the system has cooled enough, prior to draining vessels and commencing work.

*

9.     

If required rig a fresh water flush to the vessel and flush all process residues from the vessels using fresh water.

*

5.5             Emergency Controlled Shutdown Procedure

The following procedure details the steps to be taken to conduct an emergency controlled shutdown of the Gas Dehydration system.

Plant Status -The assumption is that an upset condition has occurred on the process or downstream facilities detected by the automatic shutdown systems, that requires the immediate controlled shutdown of the Gas Dehydration system by the ESD system. There should be no cause for intervention by operators.

Table 18 Emergency Controlled Shutdown Procedure

Emergency Controlled Shutdown Procedure

STEP

DESCRIPTION

LOCAL

CCR

1

The Gas Dehydration System is shutdown as part of the process shutdown systems onboard. As per the Cause & Effect listings for ASD, ESD & PSD.

*

*

2

After a Process trip occurs and the Facility has been confirmed as being in a safe condition, the operator in conjunction with the Control Room should confirm that outputs as listed in the C&E charts have effected as per the shutdown philosophy, prior to production restart.

*

*

6.0           Alarm, Trip and PSV Settings

Table 19 Alarm, Trip & PSV Settings

EQUIPMENT

gas dehydration

TAG NO

Alarm Type

DESCRIPTION

alarm/ TRIP set points

PSV set points

Gas Filter Separator, Filter Section Liquid Level.

10M-LI-2210-3

LAHH

Liquid Level High High

1446 mm

10M-LI-2210-3

LALL

Liquid Level Low Low

1190 mm

10M-LIC-2210-1

LAH

Liquid Level High

1396 mm

10M-LIC-2210-1

LAL

Liquid Level Low

1240 mm

Gas Filter Separator, Bottom Section Liquid Level.

10M-LI-2210-4

LAH

Liquid Level High

400 mm

10M-LI-2210-4

LALL

Liquid Level Low Low

195 mm

10M-LIC-2210-2

LAH

Liquid Level High

400 mm

10M-LIC-2210-2

LAL

Liquid Level Low

245 mm

Contactor Liquid Level

10M-LI-2215-2

LAHH

Liquid Level High High

650 mm

10M-LI-2215-2

LALL

Liquid Level Low Low

250 mm

10M-LIC-2215-4

LAH

Liquid Level High

550 mm

10M-LIC-2215-4

LAL

Liquid Level Low

350 mm

Differential Pressure

10M-PDI-2210-18

PDAH

Across the XV-2210-16/17-Differential pressure alarm high

0.689 barg

10M-PDI-2210-14

PDAH

Gas Filter Separator - Differential Pressure Alarm High

0.689 barg

10M-PDI-2215-5

PDAH

Contactor - Differential Pressure Alarm High

1.172 barg

Pressure

10M-PI-2210-15

PAH

Gas Filter Separator- Pressure Alarm High

58.6 barg

10M-PI-2210-15

PAL

Gas Filter Separator- Pressure Alarm Low

53.43 barg

10M-PI-2210-15

PAll

Gas Filter Separator- Pressure Alarm Low Low

27.57 barg

10M-PI-2215-9

PAH

Glycol Contactor Inlet - Pressure Alarm High

60.32 barg

10M-PI-2215-9

PAL

Glycol Contactor Inlet - Pressure Alarm Low

55.2 barg

Differential Temperature

10M-TDI-2210-8

TDAH

Gas filter separator outlet - Differential Temperature Alarm High

(HOLD)

10M-TDI-2210-8

TDAL

Gas filter separator outlet - Differential Temperature Alarm Low

(HOLD)

Temperature

10M-TI-2210-8

TAH

Gas Filter Separator Gas Outlet - Temperature Alarm High

65.6 C

10M-TI-2210-8

TAL

Gas Filter Separator Gas Outlet - Temperature Alarm Low

15.6 C

10M-TI-2220-6

TAH

Gas/Glycol Heat Exchanger Gas Outlet - Temperature Alarm High

(HOLD)

10M-TI-2220-6

TAL

Gas/Glycol Heat Exchanger Gas Outlet - Temperature Alarm Low

(HOLD)

Flow

10M-FI-2215-10

FAL

Lean Glycol Inlet To Gas/Glycol Heat Exchanger - Flow Alarm Low

(HOLD)

Water Dew Point

10M-AI-2220-5

AAH

Dew Point Analyser Alarm High

(HOLD)

Pressure Relief Valves

10M-PSV-2210-9

Gas Filter Separator

63.8 Barg

10M-PSV-2210-12

Gas Filter Liquid Separator drains piping.

29.3 Barg

10M-PSV-2215-6

Contactor Vessel

63.8 Barg


7.0           Valve List

Table 20 Valve List

gas dehydration

Valve

DESCRIPTION

Tag Number

Pressure Relief Valves

10M-PSV-2210-9

10M-PSV-2210-12

10M-PSV-2215-6

Level Control Valves

10M-LV-2210-1

10M-LV-2210-2

10M-LV-2215-4

Diverter Valves

10M-XV-2210-16

10M-XV-2210-17

Shutdown Valves

10M-SDV-2210-11

10M-SDV-2215-1

Blow Down Valve

10M-BDV-2220-1


8.0           Acknowledgements

With my signature I do hereby acknowledge that I have read and understood the preceding document.

Signature

Date

Signature

Date


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