gas dehydration

TABLE OF CONTENTS

1.0 WATER CONTENT OF NATURAL GAS

2.0 GAS HYDRATES

3.0 GAS DEHYDRATION PROCESS

4.0 GAS DEHYDRATION BY GLYCOL CONTACTING

5.0 GLYCOL REGENERATION SYSTEM

6.0 GAS DEHYDRATION BY GLYCOL INJECTION


OBJECTIVES/ INTRODUCTION

Objectives

At the end of this lesson the participant must be able to:

• State four major reasons for removing water from gas distribution systems.

•State the specification of water content in gas for the transport of gas in pipelines.

•Using the correct graph and given the gas conditions of pressure and temperature, calculate the water content of the gas.

• List the 3 requirements for hydrate formation and describe how hydrates are produced and the dangers of hydrate formation.

•State hydrate removal / prevention methods.

•Identify 3 types of glycol used in industry.

• Explain the absorption process.

•Describe the process of absorption by glycol contacting.

•State the 3 impurities removed in the glycol regeneration system and explain their method of removal within the system.

• Describe the function, principle of operation and component parts of the glycol contactor and regeneration process.

• Identify and describe the operation of all instrument control loops within the glycol contactor and regeneration process.

• Identify and describe alarm and shutdown instrumentation within the glycol contactor and regeneration process.

• Describe the normal operating parameters of level, pressure, temperature and flow within glycol contactor and regeneration process.

•Describe and list routine checks and tasks on the equipment.

•Explain actions required to remedy specific equipment problems.

•Describe the function, principle of operation and component parts of the glycol injection and inhibition system and regeneration process.

•Describe the process of hydrate inhibition by glycol injection.

• Identify and describe the operation of all instrument control loops within the injection and inhibition system and regeneration process.

•Identify and describe alarm and shutdown instrumentation within the injection and inhibition system and regeneration process.

• Describe the normal operating parameters of level, pressure, temperature and flow within injection and inhibition system and regeneration process.

•Describe and list routine checks and tasks on the equipment.

• Explain actions required to remedy specific equipment problems.

OBJECTIVES/ INTRODUCTION - Cont'd

Introduction

The glycol dehydration system removes water from gas flowing into pipelines for distribution and consumption. Most natural gas produced from wells is saturated with water in the form of vapour. If the gas stream is cooled, the water vapour condenses and creates problems in downstream equipment and facilities. Water must be removed from the produced gas before it enters a pipeline for four major reasons:

To prevent corrosion in the downstream equipment and pipelines.

To prevent partial blockages in pipelines caused by condensation of water and the subsequent knock-out and build up of liquids in low points reducing the cross sectional area for the gas flow.

To prevent the formation of hydrates that will restrict or block the flow of gas in the line.

To meet sales gas specification of water content in sales gas.

The amount of water that must be removed from the gas product depends primarily on the lowest temperature to which the gas is exposed in the pipeline or downstream facilities. The standard specification for water content in pipeline gas is 6-7 lbs/MMCFD.

1.0 WATER CONTENT OF NATURAL GAS

1.1 Reservoir Conditions

Nearly all hydrocarbon reservoirs have significant quantities of water in them. Hydrocarbon gas reservoirs are at high pressures, 4000 psig (276 barg) being a typical reservoir pressure, with temperatures of 230OF (110oC) to 240oF (116oC). At these conditions of temperature and pressure the water present in the gas is in the vapour phase and the reservoir gas is, therefore, likely to be saturated with water vapour. As the

gas flows to the surface and experiences reduction in temperature and pressure, some of the water vapour in the gas undergoes a phase change and condenses.

At reservoir conditions of 180oF (82oC) and 2000 psig (138 barg), gas saturated with water vapour contains about 260 lbs of water per MMCF of gas. With a wellhead pressure of 1000 psig (69 barg) and a temperature of 1000F (38o C), the gas contains only 6Olbs/MMCFof water. In this example, 200 lbs/MMCF of water vapour condenses to liquid at the wellhead. The quantity of water vapour present in a gas at saturation under different conditions of temperature and pressure is illustrated in Figure 1-1.

Water in liquid phase entrained in gas is called “free water”. Under certain conditions, free water entrained in gas will produce gas hydrates in the field equipment in the form of (ice-like compounds), making meters, valves and equipment inoperative.

Figure 1-1 Water Content of Gas

1.0 WATER CONTENT OF NATURAL GAS - Cont'd

1.2 Measuring the Water Content of Gas

The water content of gas is usually expressed in units of pounds of water per million standard cubic feed of gas (lbs/MMCF). At a given pressure and temperature the water content indicated is at equilibrium with the gas; the gas is fully saturated with water and the gas is water wet. Stated another way, the temperature is the dew point temperature of the gas at the given pressure.

1.3 Dew Point

Dew point is the temperature, at a given pressure, when the first droplet of water vapour or hydrocarbon begins to condense. In this unit only the dehydration of water from gas is considered.

The performance of the plant operation is measured by determining the quantity of water in the outlet gas (lbs/MMCF), or the dew point temperature of the outlet gas.

2.0 GAS HYDRATES

2.1 General

Hydrates are ice-like solids formed by the physical combination of water molecules and lighter hydrocarbon molecules contained in natural gas. It is an ice -like solid, but possesses different characteristics from ice. Ice is a simple crystalline solid whereas a hydrate has a very complex lattice structure.

Methane and ethane, being the smallest hydrocarbon molecules, are the most common hydrocarbons that combine with free water to form hydrates. In some cases, propane also combines with free water to form hydrates, but butane and the heavier hydrocarbon molecules, because of their larger physical size, seldom form hydrates. Hydrogen sulphide (H2S) and carbon dioxide (CO2) accelerate hydrate formation because they are more soluble in water than hydrocarbons.

Hydrates develop from a jelly-like sludge to a solid ice block which can completely block piping or valves so that no flow occurs. Lines, equipment and devices become inoperative and systems become dangerously over pressured. Once begun, the rate of hydrate development can fill piping and equipment very quickly indeed. Refer to Figure 2-1.

2.2 Hydrate Formation

Three basic conditions are required to exist for gas hydrate formation.

Free water must be present in the gas,

Hydrocarbon molecules must be present (especially methane and ethane),

Conditions of temperature and pressure which are in the “hydrate formation zone” must exist.

Removal of any one of the above components from the gas means that hydrates cannot form. The most effective component to remove is free water and this is achieved by dehydrating the gas to a point where free water cannot condense from the gas when it is cooled.

An unusual characteristic of hydrate formation is that hydrates form at temperatures well above the freezing point of water. It is difficult to imagine ice forming at a temperature of 68oF (20oC), but under certain conditions of flow which are not unusual in the gas field, hydrates form in lines at 68oF. The temperature at which hydrates form in a gas stream depends upon the pressure of the stream. As the pressure increases the hydrate formation temperature also increases. The graph shown in Figure 2-2 indicates the average conditions of pressure and temperature at which hydrates start to form when free water is present.

Hydrates only form when free water is present in a stream of hydrocarbons containing methane, ethane or propane and

temperature and pressure conditions are in the hydrate formation zone.

2.0 GAS HYDRATES

2.2 Hydrate Formation - Cont'd

Figure 2-1 Hydrate Formation in Pipelines

2.0 GAS HYDRATES

2.2 Hydrate Formation - Cont'd

Figure 2-2 Hydrate Formation

2.0 GAS HYDRATES - Cont'd

2.3 Methods of Removing Hydrates

If piping and equipment becomes completely blocked with hydrates, the only and most effective solution is to depressurise the system completely and allow temperatures to increase to ambient temperature. Hydrates cannot exist at atmospheric pressure and ambient temperature and the hydrates will eventually melt. Another method of hydrate removal is localised heating of the section of piping in which the hydrate blockage is located. This method is not as thorough as the previous method and is usually not practical because the exact location of the hydrate blockage is not known.

If the hydrate formation has not completely blocked the gas flow through the line, methanol (methyl alcohol) can be injected into the gas stream to dissolve the hydrate crystals. However, this method is costly and unless the methanol can be recovered downstream. In certain cases methanol content in the gas stream is not acceptable e.g. feed gas to an LNG plant.

2.4 Hydrate Prevention

The most effective method of preventing hydrate formationis to reduce the water content of the gas by dehydration. If no free water exists in piping and equipment, hydrates cannot form. One of the most common methods of dehydrating or drying gas is that of contacting the gas with a liquid desiccant such as ethylene glycol.

3.0 GAS DEHYDRATION PROCESS

3.1 Introduction

The most common field process for gas dehydration to normal pipeline requirements of 6-7lb/MMCF water content is by a dehydration absorption process using a liquid desiccant (desiccants are substances, available in either liquid or solid state, having a great affinity for water). Liquid desiccants

commonly used in the gas dehydration absorption process are Monoethylene Glycol (MEG), Diethylene Glycol (DEG) and Tri-ethylene Glycol (TEG).

Table 1 Physical Properties of The Common Glycols

Glycol Monoethylene Glycol (MEG)

Diethylene Glycol (DEG)

Triethylene Glycol (TEG)

Chemical Formula

C2H6O2 C4H10O3 C6H14O4

Relative Molecular Mass

62.1 106.1 150.2

Boiling Point at 760 mmHg

197.3°C 244.8°C 278°C

Density at 25°C

1110 kg/m3

1113 kg/m3 1119 kg/m3

Density at 60°C

1085 kg/m3

1088 kg/m3 1092 kg/m3

Freezing Point

- 13oC -10oC - 7oC

Flash Point (COC)

- 111oC - 138oC - 165oC

MEG – Monoethylene Glycol is used for injection into gas pipelines to inhibit hydrate formation. MEG does not achieve low dewpoints compared with DEG and TEG.

DEG – Diethylene Glycol is used for both injection and dehydration but is a compromise in performance between the speciality glycols.TEG – Triethylene Glycol is the most common glycol used for closed loop dehydration and achieves a very low dewpoint with minimum vapour losses.

3.1.1 The Process of Absorption

The process of absorption occurs in a vessel known as an Absorber when a liquid desiccant (absorbent) and an impurity (absorbate) are brought together. The absorbate is absorbed, or taken into the body of the absorbent.

3.1.2 Absorption Systems

Basically there are two glycol based dehydration absorption systems in use in the oil and gas industry.

Absorption by Glycol Contacting, normally TEG is the glycol of choice,

Absorption by Glycol Injection, hydrate inhibition is normally achieved by injection of MEG.

3.0 GAS DEHYDRATION PROCESS - Cont'd

3.1 Dewpoint Depression

Dewpoint depression, or reduction, is the amount of reduction of the gas dewpoint temperature achieved by the absorption process i.e. the dewpoint temperature difference between the water wet inlet and dry outlet gas.

4.0 GAS DEHYDRATION BY GLYCOL CONTACTING

4.1 Simple Description

Refer to Figure 4-1.Absorption of water moisture from the wet process gas takes place in the absorber section of the Glycol Contactor at high pressure (81 barg) and relatively low temperature (45 oC).Generally, for a given pressure, as the absorber operating temperature increases, water absorbed by the Triethylene

Glycol (TEG) also increases and this can overload the glycol regeneration system. (The TEG regeneration system is designed to handle a maximum of 4% wt water content in the glycol solution at the reboiler, which equates to a maximum operating temperature of 45 oC in the absorber).The contact media in the Glycol Contactors is structured packing, which provides the large surface area required for intimate contact to occur between the lean glycol (absorbent) and the water vapour (absorbate) contained in the wet process gas. A large contact surface area provides more efficient mixing of the absorbent and absorbate and consequently a more efficient process of absorption. The contact media is installed inside the column in such a way that a turbulent, serpentine flow pattern is created for the

absorbent flowing down the column and the wet gas flowing counter currently upwards to the top of the column.As the downward flowing lean glycol comes into intimate contact with the upward flowing wet gas it becomes enriched with water vapour. The upward flowing wet gas progressively becomes less wet until exiting the top of the column as a dry, dew point specified, process gas.

The impurities, listed below, are gained by the rich glycol during the process of absorption and are removed in the glycol regeneration system thereby producing a regenerated lean glycol for reuse.

GLYCOLREGENERATION

PACKAGE

GAS / GLYCOLHEAT EXCHANGER

GLYCOLCONTACTOR

WET GASINLET

LIQUIDSOUTLET

WATER VAPOUR(STEAM)

HYDROCARBONLIQUIDS

HYDROCARBONGAS

SUSPENDEDSOLIDS

DRY GASOUTLET

RICHGLYCOL

LEANGLYCOL

HEAT

Figure 4 -1 Glycol Dehydration Block Flow DiagramAndy Marr

2004

Hydrocarbons

Suspended solids

Water

4.0 GAS DEHYDRATION BY GLYCOL CONTACTING –Cont’d

The process of flash separation in a 3-phase separator flash vessel removes the hydrocarbons from the rich glycol stream. The rich glycol stream is then filtered to remove particulate matter before being routed to the reboiler.

The regeneration of the rich glycol takes place in the TEG Reboiler, at high temperature (204 oC) and relatively low pressure (0.1 barg) where heated vapours are produced to drive off the water contained in the glycol. The glycol, minus the water content, can now be reused as lean glycol. The flows of lean and rich glycol circulated to and from the absorber are continuous.

A constant temperature of 204 oC maintained in the reboiler ensures glycol purity of 98.4% wt. The use of stripping gas must be used if greater glycol purity is required. Glycol purity of 99.95% wt may be achieved through the increased flow of stripping gas into the base of TEG Stripping Column.

4.2 Detailed Description

Refer to Figure 4-2 & Figure 4-3

Wet process gas from an upstream 2-phase separator at a pressure of approximately 81 barg enters the scrubber section of the Glycol Contactor via a vaned inlet gas disengaging device where gas and free liquids are separated.

The lighter gas flows upward through a demister coalescer before entering the chimneys located on the chimney tray. The gas flowing into the chimneys comes into contact with the structured packing inside the chimneys which forces the gas into a turbulent, serpentine flow pattern. The structured packing

acts as a coalescer allowing entrained liquid droplets to coalesce on its large surface area and drop back into the separator section of the column. To exit the chimneys and enter the absorber section of the column, the gas flow must execute an 1800 turn before flowing upwards once again.

The upward flowing gas in the absorber section is met by a counter current flow of lean glycol flowing down through the column. As the wet gas flows through the large surface area of structured packing located in the absorber column, it comes into intimate contact with lean glycol flowing over the packing allowing the process of absorption to take place. The lean glycol progressively strips water moisture from the wet gas as it flows upward until on exiting the structured packing the gas has been dehydrated and the water dew point temperature meets specification at -30oC.


4.2 Detailed Description - Cont'd

RP

Contactor Gas / GlycolHeat Exchanger

TEG FlashDrum

Surge Drum

Wet GasInlet

Dry GasOutlet

Reboiler

StillColumn

StrippingColumn

Hot Lean / Rich TEG H.E.

Cold Lean / Rich TEG H.E.

Lean TEGCirculation Pump

Still ColumnOverheads

Reflux

TEG Cartridge Filter

Carbon FilterLiquids toDisposal

HydrocarbonLiquid toDisposal

Make-upGas

Gas toFlare

Figure 3-2 Glycol Dehydration Contactor Unit & Glycol Regeneration Package

Dry Gas Outlet

Andy Marr 2004

Figure 4-2 Glycol Dehydration Conatctor Unit & Glycol Regeneration Package



Figure 4-3 Glycol Dehydration Contactor Unit & Glycol Regeneration Package

Glycol Contactor

Wet Gas Inlet

Liquids to Disposal

Scrubber Section

Absorber Section

Dry Gas Outlet

Lean Glycol Distributor

Lean GlycolDistributor Tray

Structured Packing

Chimney

SkimmingCompartment

Structured Packing

Vaned type Gas / LiquidDisengaging Device

Vortex Breaker

Lean Glycol

Rich Glycol

Demister

Chimney Tray

Andy Marr 2004



Entrained glycol droplets in the dry gas are removed by a demister protecting the dry gas outlet nozzle on top of the column.

Liquids separated from the wet gas in the separator section of the column are routed, under level control to the condensate header.

Hydrocarbon liquid build-up forming an interface with the rich glycol on the chimney trays overflows a weir into a skimming compartment.

Dry gas flows from the gas outlet nozzle on the absorber to the tube side of the Glycol / Gas Exchanger, a shell and tube type heat exchanger. The dry gas absorbs heat from hot lean glycol flowing on the shell side of the exchanger and exits the heat exchanger in a temperature range of 45oC to 55oC. Gas flow and dew point temperature measurement is performed prior to the gas flowing into a downstream product gas scrubber.

The product gas scrubber functions to remove glycol entrained in the dry gas prior to gas export. Glycol separated from the dry gas is routed, under level control to the TEG Regeneration Package.

The dry product gas flows to the gas outlet nozzle on top of the product gas scrubber via a demister pad, which minimizes liquid carryover of glycol in the export gas.

Dehydrated product gas, under back pressure control, then flows to gas metering and export.



Rich TEG Flow

As lean glycol flowing down through the absorber section contacts wet gas flowing upwards, the glycol absorbs water moisture and progressively becomes enriched as it flows down the column. The rich glycol forms a level on the chimney tray where it is routed, under level control, and flows through the Cold Lean / Rich TEG Exchanger to the TEG Flash Drum.

The skimming compartment located at chimney tray level permits the manual skimming of condensed hydrocarbons from the rich glycol level, which is routed into the scrubber section of the contactor.

Cold Lean / Rich TEG Exchanger

Cool rich glycol is pre-heated in the Cold Lean / Rich TEG Exchanger against a hot medium flow of lean glycol from 51 oC to 85 o0C. The hot lean glycol flow is cooled from 118 oC to 77 oC before flowing to TEG Surge Drum.

TEG Flash Drum

Refer to Figure 5-1

The TEG Flash Drum is a 3-phase separator and functions by the process of ‘flash separation’ to separate rich glycol, hydrocarbon liquid and entrained hydrocarbon gases.

Rich glycol from the Glycol Contactor at 81 barg is flashed across a level control valve controlling the chimney tray level, into the TEG Flash Drum operating at 4 barg and 85 oC via the Cold Lean / Rich TEG Exchanger.

The decrease from high pressure to relatively low pressure conditions boiling point temperatures of the hydrocarbon components in the stream effecting the separation of hydrocarbon gas and hydrocarbon liquid entrained in the rich glycol.

The rich glycol stream enters the TEG Flash Drum and impinges on an internal splash baffle enhancing the separation of gas and liquids in the stream.

Separated gases flow to the top of the vessel whilst liquids drop into the rich glycol section in the base of the drum. Flash gas produced in separation maintains the drum pressure at 4 barg. If insufficient flash gas is produced to maintain 4 barg pressure in the vessel then fuel gas as make-up gas is imported, under pressure control, into the drum to maintain the pressure.

If excessive flash gas is produced by flash separation the excess gas is routed, under pressure control, to flare.

The liquids in the bottom section of the drum settle and separate due to the disparity in density between rich glycol and hydrocarbon liquid.

The denser rich glycol liquid settles in as the bottom liquid phase whilst the lighter, less dense hydrocarbon liquids float on top.

Sufficient gas and liquid residence times are built in to the design of the vessel to ensure efficient 3-phase separation.

The rich glycol liquid stream exits the TEG Flash Drum under level control, via a bottom liquid outlet nozzle located at the opposite end of the vessel to the rich glycol stream entry point.

5.0 GLYCOL REGENERATION SYSTEM – Cont’d

5.1 Detailed Description – Cont’d

Hydrocarbon liquid as a second liquid phase forms an interface with the rich glycol and overflows into an internal collection bucket. The collected hydrocarbon liquid is then routed under level control to the process closed drain.

TEG Cartridge Filters

The rich glycol stream exiting the TEG Flash Drum flows through one of two cartridge filters, TEG Cartridge Filters. The

filters contain natural synthetic fibre cartridges and guarantee the removal of 99% of particles > 5 microns from the rich glycol stream.

Figure 5-1 TEG Flash Drum & Filtration



TEG Carbon Filter

TEG Flash Drum

Rich Glycol

LiquidHydrocarbons

GasRich

Glycol

Make-up Gasfrom Fuel Gas

Skid

Excessgas toFlare

Liquid Hydrocarbonsto Disposal

Glycol Cartridge Filters

Carbon Filter

To Still Columnvia Plate HeatExchangers

Figure 3-4 TEG Flash Drum & Filtration

FI

Level Control Signal toLCV on inlet to TEG Still

Column

PCVPCV

LCV

LTLTLC LC

Andy Marr 2004

Filtered rich glycol from the TEG Cartridge Filter is routed to the Hot Lean / Rich TEG Exchanger however a slipstream of filtered rich glycol, approximately 20% of the total stream flow, is routed through the TEG Carbon Filter to remove any residual trace elements of hydrocarbon liquid. The slipstream flow recombines with the main filter bypass flow of rich glycol downstream of the filter.

The carbon filter guarantees removal of 99% of inorganic impurities from the rich glycol stream.

Hot Lean / Rich TEG Exchanger

Cool rich glycol is further pre-heated in the Hot Lean / Rich TEG Exchanger against a hot medium flow of lean glycol from 85 oC to 150 oC. The hot lean glycol flow is cooled from 194 oC to 118 oC before flowing to the TEG Surge Drum via the Cold Lean / Rich TEG Exchanger.

Pre-heating the rich glycol in the Cold Lean / Rich TEG Exchanger and Hot Lean / Rich TEG Exchanger serves to decrease the electrical load requirements for the TEG Reboiler. The exchange of heat also conditions lean glycol temperature by cooling to design temperature prior to final cooling in the Glycol / Gas Exchanger.

TEG Still Column

Refer to Figure 5.2

The pre-heated rich glycol stream at 150 oC exits the Hot Lean / Rich TEG Exchanger and, after passing through the level control valve for the TEG Flash Drum enters the mid point of the TEG Still Column between two beds of random packing located in the column. The column operates at 0.1 barg and a temperature range of 900 to 110 oC.

A liquid distributor distributes the rich glycol flow downwards on to the lower of the two random packing beds. The random packing consists of stainless steel Pall Rings that provide a large surface area for contact between rich glycol flowing downwards and hot stripping gas vapours at 204 oC flowing

upwards from the TEG Reboiler in a counter current flow. As the hot stripping gas vapours contact the rich glycol, the water moisture is stripped from the glycol and is driven towards the upper random packing bed.

The downward flowing glycol stream minus water moisture content flows into the TEG Reboiler where it is heated to 204 oC.

The water vapour driven off from the rich glycol stream flows into the upper random packing bed and is met with a downward flow of cooler reflux water, under flow control, from the TEG Still Vent Condensate Pumps. The controlled reflux flow to the column minimizes liquid carryover of glycol from the column thus minimizing glycol losses.

TEG Still Vent Cooler

Refer to Figure 5-3

Hot vapours exiting the TEG Still Column are cooled from 86 oC to 55 oC in the TEG Still Vent Cooler against a cooling medium flow of cooling water.



TEG Still Vent KO Drum

The condensed vapour stream from the TEG Still Vent Cooler enters the TEG Still Vent KO Drum where liquid and vapour are separated. Vapour is routed from the vessel to the flare header.

TEG Still Vent Condensate Pumps

The liquid from the TEG Still Vent KO Drum is pumped, under level control, to the Water treatment Unit by one of the TEG Still Vent Condensate Pumps. The reflux flow to the TEG Still Column is taken off the common pump discharge header upstream of the level control valve.

Lean TEG Flow

TEG Reboiler

Glycol temperature in the reboiler is maintained at 204 oC by a submersed; thyristor controlled Electrical Heater. A constant temperature of 204 oC in the reboilers ensures glycol purity of 98.4% wt.

TEG Stripping Column

Regenerated glycol overflows from the TEG Reboiler into the top section of the TEG Stripping Column which contains a random packing bed. The down flowing glycol is met by a counter current flow of hot stripping gas which is pre-heated in a submersed coil in the reboiler. Intimate contact between the hot stripping gas and the regenerated glycol increases the glycol purity by driving off a portion of residual water vapour. Glycol purity of 99.95% wt may be achieved through the increased flow of stripping gas into the base of the TEG Stripping Column.

A 4” pressure equalising line connecting the vapour spaces in both vessels maintains pressure equilibrium between the TEG Stripping Column and the TEG Reboiler.

TEG Surge Drum

Lean glycol is routed from the base of the TEG Stripping Column to the TEG Surge Drum via the Hot Lean / Rich TEG Exchanger where the lean glycol temperature is decreased from 204 oC to 118 oC and through the Cold Lean / Rich TEG Exchanger where the temperature of the lean glycol is further reduced to 77 oC.



Figure 5-2 TEG Reboiler

Reboiler

Still Column

StrippingColumn

Still Column Overheads toOverheads Vent KO Drum

Reflux from Overhead VentKO Drum Reflux Pump

Pre-heated Rich Glycolfrom TEG Flash Drum

RandomPacking

Thyristor ControlledElectric Heater

Heating Bundle Electrodes

RandomPacking

FI Stripping Gas fromFuel Gas SkidLean Glycol flow to Surge Drum

via plate heat exchangers

Pressure Balanceline to Surge Drum

Figure 3-5 TEG Reboiler

Control Signal from TEGFlash Drum Rich Glycol

Level Controller

LCV

Andy Marr 2004



A 2” pressure equalising line connecting the vapour spaces in both vessels maintains pressure equilibrium between the TEG Stripping Column and the TEG Surge Drum.

The addition of fresh glycol make-up to the system is via a 2” top fill line on the top of the TEG Surge Drum.



Lean TEG Circulation Pumps

Overheads fromTEG Still Column

OverheadsVent

Condenser

Cooling Water Flow

Overheads VentKO Drum

Non-condensiblesto Flare

FT

FC

FCV

LCV

LTLC

To WaterTreatment Plant

Reflux Flow to TEG StillColumn

Figure 3-6 Overheads Vent System Andy Marr 2004

The lean glycol circulating pumps are motor driven positive displacement, piston type reciprocating pumps. One pump is in-line whilst the other is standby. The Lean TEG Circulation Pumps take suction from the TEG Surge Drum at 0.1 barg and a suction temperature of 77 oC. The pump increases the lean glycol pressure to 81 barg and routes the lean glycol flow to the Glycol / Gas Exchanger.

Glycol / Gas Exchanger

Lean glycol flows from the Lean TEG Circulation Pumps to the shell side of the Glycol / Gas Exchanger. The lean glycol gives up heat to the dry gas on the tube side and exits the exchanger at a temperature between 3o and 6 oC above the inlet temperature of the wet gas to the Glycol Contactor. The temperature differential between the wet inlet gas and lean glycol return to the contactor is maintained to prevent condensation of hydrocarbon components in the gas and subsequent foaming in the top section of the column.

Glycol Contactor

Lean glycol from the shell side outlet of the Glycol / Gas Exchanger enters the top of the Glycol Contactor below the dry gas outlet demister and is distributed over the full cross section of the column via a liquid distributor system. The lean glycol flows down over the structured packing coming into intimate contact with wet gas flowing upwards, absorbing the water moisture and becoming progressively enriched until reaching the chimney tray where the rich glycol is routed to the glycol regeneration unit and the continuous process of glycol regeneration begins again.

TEG Still Vent KO Drum

The condensed vapour stream from the TEG Still Vent Cooler enters the TEG Still Vent KO Drum where liquid and vapour are separated. Vapour is routed from the vessel to the flare header.

TEG Still Vent Condensate Pumps

The liquid from the TEG Still Vent KO Drum is pumped, under level control, to the Water treatment Unit by one of the TEG Still Vent Condensate Pumps. The reflux flow to the TEG Still Column is taken off the common pump discharge header upstream of the level control valve.

5.2 Variations in Older Glycol Contactor Units

The operator may be required to operate older Glycol Contactor Units (pre-1980) and therefore must be aware that there are 3 major variations in these units from the unit described above.

The 3 major variations in older Glycol Contactor Units are:

1.Absorption in the Glycol Contactor is achieved by the use of distillation trays.

2. Pre-heating of the rich glycol to the TEG Flash Drum and control of the TEG Still Column top temperature is achieved via a tube type reflux condenser coil installed in the top section of the TEG Still Column and its bypass.

3. The lean glycol circulation rate is required to be adjusted to changes in gas flowrate through the contactor.


5.2 Variations in Older Glycol Contactor Units – Cont’d

1. Distillation Trays

Distillation trays, normally of the bubble cap type, are installed in the Glycol Contactor instead of structured packing in present day units. Structured packing are approximately 50% more efficient than distillation trays and provide more effective absorption in the contactor.A brief description of the bubble cap distillation trays is given below.

The bubble cap trays (refer to Figure 5-4) cause the rising gas to disperse through the glycol and allows the required intimate contact, and mixing for absorption to take place. The gas flows through a riser such that the gas re-diverts from the top of the cap down through the annulus formed between the riser and

the cap. The gas then disperses through slots in the bottom of the cap rim and bubbles up through the glycol liquid. The level of glycol is maintained near the top of the caps by weirs on the tray decks. The deeper the glycol level around each cap, the more intimate the glycol/gas contact and the greater the absorption efficiency. Glycol flows in an alternating flow path from one tray down onto the tray below via a series of weirs and downcomers; this tray arrangement is called single pass.

The intimate contact on the trays allows the glycol, with its high hygroscopic ability, to absorb the water vapour from the gas stream. The largest amount of water is removed on the bottom tray, where the gas contains the most water. Progressively the gas contains less water as it moves through each successive tray; therefore, the glycol absorbs less water and is more hygroscopic higher up the contactor. On the last few trays, the glycol is at its leanest and only trace amounts of water vapour remain in the gas. These top trays remove the last trace amounts of water in the gas to meet the specified outlet gas dew point or water content.

Rate of gas and glycol flow is crucial in the contactor. If the gas velocity is too high it may result not only in the gas having too little contact time (exposure) with the glycol, but also cause the bubble caps to lift off. The caps on some contactors are, therefore, tack welded into place on the tray.



Figure 5-4 Distillation Trays – Bubble Cap Type



2. Reflux Condenser Coil & Bypass

Refer to Figure 5-5.

A reflux condenser coil located in the top section of the TEG Still Column pre-heats cool rich glycol from the Glycol Contactor flowing through the coil prior to entering the TEG Flash Drum. The cool rich glycol flowing inside the coil functions to cool and condense the hot glycol vapours flowing up the TEG Still Column in contact with the outside of the coil. The reflux condenser coil reduces the amount of glycol lost from the system.

In older TEG Still Columns the water vapour as steam is generally routed to atmosphere at a safe location.

A reflux condenser coil bypass allows the operator to control the TEG Still Column top temperature.

Rich Glycolfrom GlycolFlash Drum

Rich Glycol toPlate Type Heat

Exchanger

RefluxCondenser CoilBypass Valve

Water Vapour (Steam)Outlet to Atmosphere

Rich Glycolfrom Plate Heat

Exchanger

Lean Glycol

Reboiler

SprayDistributor

Reflux CondenserCoil

Random PackingCeramic Saddles

460 C

520 C

189 0 C

196 0 C

Glycol StillColumn

820 C

Andy Marr 2004

Figure 5-5



3. Lean Glycol Circulation Rate Adjustment

In older units it is necessary to adjust the lean glycol circulation rate to match changes in gas flow through the contactor.

Determining Glycol Flowrate

As conditions on the Glycol Contactor change, the operator must be aware of the steps required to determine the new lean glycol, circulation flowrate. The graph for Water Content of Gas shown in Figure 1-1 is again used for this operation.

Glycol dehydration units are usually designed for a glycol/water absorption rate of 25 gallons of glycol per pound of water to be removed from gas.

Glycol =AbsorptionxWeight of water flowrate rateremoved from gasExample:

A glycol dehydration plant is designed to remove 5904 lbs / day of water from a stream of well gas. The glycol absorption rate is 3 gal / lb of water removed. Determine the glycol flowrate from the glycol pumps.

Water removed from gas 5904 lbs/day

Glycol absorption rate 3 galls/lb

Daily glycol flowrate 5904 x 3

= 17712 galls/day

Glycol flowrate per minute 60 × 24

17712 =

= 12.3 gpm

The specified glycol absorption rate should be maintained with the lean glycol flowrate changed for each change in gas flowrate or water content

6.0 GAS DEHYDRATION BY GLYCOL INJECTION

6.1 Simple Description

Monoethylene Glycol (MEG) solution in 90% wt. and 80% wt. glycol/water solutions is injected as a spray into pipelines and process streams to inhibit hydrate formation. In this case, unlike absorption by glycol contacting, the water content in the streams is not reduced. Meg solution is injected at various points in the process where the potential for hydrate formation is high. The lean Meg solution absorbs the water and as a rich glycol is recovered downstream by 3-phase gravity separation similar to that described for the TEG Flash Drum in the last section.

An example of this type of hydrate inhibition process is glycol injection into an export subsea pipeline from an offshore production platform. The Meg solution is finely mixed and distributed through the process stream by injection effectively inhibiting the formation of hydrates in the pipeline when the pipeline stream is cooled by the cool seawater.

On arrival at the receiving facility onshore the pipeline stream undergoes 3-phase gravity separation and the rich glycol settles out to form the bottom liquid layer in the vessel with hydrocarbon condensate forming a liquid interface on top of the rich glycol. Sufficient gas and liquid residence time is avaialble to ensure effective 3-phase separation takes place.

The rich glycol from the inlet separator flows to a Rich MEG Flash Drum where any dissolved gases in the rich glycol are flashed off to a low pressure flare. The stabilised rich glycol is then routed to a Rich TEG Storage Tank from where the glycol

regeneration process begins. After regeneration the regenerated MEG solution is pumped back offshore to the platform for continuous re-use.



On the offshore production platform, a 90% wt MEG solution is injected into the pipeline export stream consisting of a gas and hydrocarbon condensate mixture and flows via the sub sea pipeline to the onshore facility. On entering the Gas Liquid Receiver, gravity separation occurs, and the rich glycol and hydrocarbon condensate form a liquid interface in the bottom of the separator.

The separated gas exits the gas outlet nozzle on top of the Gas Liquid Receiver and is routed downstream for further gas processing.

The hydrocarbon condensate is routed to condensate stabilisation, under level control, via a Condensate Filter which removes solid particles such as sand, salt or pipe scale. The cartridge type filters are designed to remove 99% of all particles of 1 micron or above in size. Two filters are provided, with one filter in-line whilst the other filter is standby.

6.0 GAS DEHYDRATION BY GLYCOL INJECTION – Cont’d


Offshore ProductionPlatform

Gas Liquid Receiver

LCV

LT

LC

LCV

LTLC

Condensate Filters

Rich Glycol Filters

To Gas Processing

To CondensateStabilisation

To MEG RegenerationPackage

Hydrocarbon Condensate

MEG

Figure 3-9 Inlet Facilities

Injection 90 wt. MEG/Water Solution

Methanol Injection

Andy Marr 2004

Figure 6-1 Inlet Receiving Facilities

The rich glycol settles out in the boot of the Gas Liquid Receiver and forms an interface level with the hydrocarbon condensate before being filtered and routed to the MEG Regeneration Package. The Rich Glycol Filters are cartridge type filters and are designed to remove 95% of all particles of 50 micron or above in size. Two filters are provided, with one filter in-line whilst the other filter is standby.



Refer to Figure 7-1

Rich MEG Flash Drum

After initial filtration the rich glycol solution at approximately 70% wt. flows, under interface level control from the Gas Liquid Receiver to the Rich MEG Flash Drum where dissolved gases are allowed to disengage from the rich glycol and are then safely disposed of to a Low Pressure (LP) Flare. The Rich MEG Flash Drum operates at flare header pressure and a temperature of approximately 25o C.

Demulsifier chemical is injected into the inlet stream of rich MEG solution flowing into the flash drum to prevent the formation of an emulsion in the vessel. pH control chemical is also injected into the same line to maintain the pH of the rich MEG solution. The elevation of the Rich MEG Flash Drum is such that the rich glycol solution flows by gravity to the Rich MEG Storage Tank.

FC

Rich MEGStorage Tank

Rich MEGFlash Drum

Rich 70%wt. MEG

Fuel Gas Blanket

LP Flare

Rich MEG Pumps

MEG Coarse Filters

MEG CharcoalFilter

MEG GuardFilter

From MEGSump

From MEG ClosedDrain Drum

Demulsifier + pH ControlChemical Injection

Corrrosion Inhibitor + pHControl Chemical Injection

From 90 MEG Tank

80 wt. Meg Solutionto Onshore Process

Facilities

Gravity Flow

To MEGReflux

Condenser

Heating Coil

Andy Marr 2004

FT

Figure 7-1 Rich MEG Flash Drum & Storage



Rich MEG Storage TankThe Rich MEG Storage Tank is a coned, fixed roof tank which is maintained under a positive pressure of 0.05 barg by blanketing with fuel gas in order to prevent the ingress of oxygen into the rich MEG solution.A heating coil which is connected to the MEG/Water heating system is installed in the Rich MEG Storage Tank. In the event of a breakthrough of hydrocarbons into the tank with the rich MEG solution, the tank contents can be heated to vaporise the hydrocarbons which are routed to the LP Flare.The tank is fitted with a fill connection for MEG make-up.Rich MEG PumpsRich MEG solution at 25o C is pumped from the Rich MEG Storage Tank to the MEG Regeneration Unit by three parallel operating Rich MEG Pumps which raise the pressure of the rich MEG solution from 0.05 barg to 8 barg. Pump minimum flow protection is achieved through a minimum flow line routed back into the Rich MEG Storage Tank inlet line.Corrosion inhibitor and pH control chemicals may be injected at the suction header of the Rich MEG Pumps as required.Rich MEG Coarse FiltersRich MEG solution discharged from the Rich MEG Pumps flows through cartridge type MEG Coarse Filters which removes solid particles such as sand, salts or pipe scale. The filters are designed to remove 95% of all particles 5 micron or above in

size. Two filters are provided, with one filter in-line whilst the other filter is standby.The filtered MEG stream is then divided such that the majority of the flow is routed to the Glycol Regeneration Unit whilst the smaller remaining flow is routed, under flow control, to the suction of the MEG Process Pumps where it is blended with 90% wt. MEG solution to make an 80% wt. Meg solution for use in the onshore process streams.7.0 GLYCOL REGENERATION SYSTEM – Cont’d


MEG Charcoal FilterOn exiting the MEG Coarse Filter, a sidestream of approximately 19% of the total Rich MEG solution flow is routed through the MEG Charcoal Filter, containing a bed of activated carbon, to remove residual trace amounts of hydrocarbons from the stream. Removal of trace hydrocarbons prevents foaming in the MEG Still Column and MEG Reboiler. Only one MEG Charcoal Filter is provided.Meg Guard FilterThe MEG Guard Filter is located immediately downstream of the MEG Charcoal Filter and functions to remove any carbon fines that enter the rich MEG solution sidestream from the MEG Charcoal Filter. The filter is designed to remove 98% of all particles 5 micron or above in size. Only one MEG Guard Filter is provided.The filtered rich Meg solution sidestream exiting the MEG Guard Filter is recombined with the main stream from the MEG Coarse Filters before being routed to the MEG Still Column via the MEG Reflux Condenser and Lean/Rich Meg Heat Exchanger.



MEG Reflux CondenserRefer to Figure 7-2.

Figure 7-2 MEG Regeneration – MEG Reboiler & Surge Drum



MEG StillColumn

MEGReboiler

Hot Oil Return

Hot Lean MEG @ 147 0 C

FC

Signal from LC on RichMEG Storage Tank

From OilyWater Pump

Tray 1

Tray 5

MEG Surge Drum

Balance Line

Hot Oil Supply

Standpipe

To LeanMEG

Pumps

Lean/Rich MEGHeat Exchanger

To MEG Still Condenser

FC

TTTC

Rich70%MEG

SolutionMEG RefluxCondenser

Andy Marr 2004

The condenser is a shell and tube type heat exchanger and is mounted at the top of the MEG Still Column. In the condenser heat exchange occurs between the hot medium in the tube side (MEG Still Column overheads at 0.05 barg and the cool medium, (rich MEG solution flow) in the shell side of the condenser at 5 barg.

The heat exchange functions to pre-heat the rich MEG solution from 25oC to 68oC, prior to entry to the MEG Still Column, thus conserving power requirements. The heat exchange also cools and partially condenses the still column overhead vapours from 108oC to 104oC and thus provides continuous reflux flow for the still column thereby minimising glycol losses. The non-condensable vapours in the overhead stream exit the top of the condenser and are routed to the MEG Still Condenser.

A temperature control loop, sensing the non-condensable overhead flow outlet temperature from the MEG Reflux Condenser is cascaded to a flow control loop on the minimum flow line of the Oily Water Pump thus controlling and maintaining the overheads non-condensable flow temperature at 104oC.

The pre-heated MEG solution flows under flow control into the MEG Still Column.

MEG Still Column

The MEG Still Column is a vertical pressure vessel and is directly mounted on the top of the MEG Reboiler. The column internal mechanical mechanisms consist of an inlet distributor and 8 valve type distillation trays constructed of stainless steel. The valve trays serve the same function as the bubble cap trays discussed previously in section 3.2.5.

The preheated rich MEG solution is fed onto tray 5 of the MEG Still Column via an inlet distributor where the process of distillation as described previously in section 3.2.5 takes place. The flowrate into the MEG Still Column is controlled by a flow control valve located on the inlet to the still column and reset by the level in the Rich MEG Storage Tank. When the storage tank

level is low, the flow control valve is set to minimum flow into the MEG Still Column.The reflux stream from the Oily Water Pump previously mentioned is routed onto tray 1 (the top tray) via an inlet distributor.

An antifoam chemical injection point is provided upstream of the flow control valve to prevent foaming in the still column. Antifoam should only be used as a last resort and efforts should be made initially to identify and eliminate the foam promoter.

MEG Reboiler

The MEG Reboiler is a shell and tube kettle type heat exchanger using Hot Oil in the tube side as the heating medium. The MEG Reboiler is directly mounted beneath the MEG Still Column.

Liquid flowing down from the MEG Still Column into the shell side of the reboiler is heated from 122oC to 147oC whilst the Hot Oil in the tube side is cooled from 210oC to 155oC. Produced vapours flow upwards into the still column from the reboiler. The reboiler level is controlled by an internal standpipe installed inside the reboiler; lean 90% wt. MEG solution overflows the standpipe and flows to the MEG Surge Drum.



MEG Surge Drum

The MEG Surge Drum is a horizontal pressure vessel operating at 0.26 barg and 147oC. An equalising line between the vapour space of the surge drum and the vapour space of the reboiler ensures that both vessels are maintained at the same pressure which in turn ensures gravity flow of the lean MEG from the reboiler to the surge drum.

Lean MEG solution flows from the surge drum to the Lean MEG Pump via the Lean/Rich MEG Heat Exchanger previously discussed and which cools the hot lean glycol from 147oC to 107oC.

Lean MEG Pump

Figure 7-3 90 MEG Tank & Lean MEG Pumps



The Lean MEG Pump is a centrifugal pump which increases the pressure of the lean MEG solution from 0.26 barg to 5 barg. A continuous minimum flow spillback is provided returning to the Meg Reboiler. Two pumps in parallel are provided, one in service whilst the other pump is standby.

Lean 90% MEG solution is pumped to the 90 MEG Tank via the 90 MEG Air Cooler however a sidestream flow is routed to the MEG Reclaimer Package from a point upstream of the 90 MEG air Cooler.

MEG Reclaimer Package

RP

TC

MM

TT

RP

PT

PC

PT

PC

MEG Fill

90 MEG Tank

MEG ReclamationPackage

Fuel Gas Blanket

Variable SpeedMotors

Speed Control Signal

Lean MEG Pumps

From MEGSurge Drum

To MEG Reboiler

Enclosure Inlet & OutletLouvres controlled by InletAir temperature

LP Flare

MEG ShippingPumps

MEG ProcessPumps

90% wt. MEG toc o mb i n e wi t hsidestream from MEGCoarse Filters toprovide 80% wt. MEGSolution

Removal ofcontaminantsby VacuumDistillation

MEG Make-up toMEG Still Column

To OffshoreProduction

Platform

RegeneratedMEG

Andy Marr 2004

TT

90 MEG AirCooler

A side stream of approximately 17% of total MEG flow of 90% wt. MEG solution is routed to the MEG Reclaimer Package for the regeneration and reclamation of contaminated glycol. Contaminants such as salts and other compounds from the produced water are removed by the process of vacuum distillation.

Regenerated concentrated Meg is routed to the 90 MEG Tank from the package whilst non-condensable vapours are routed to the LP Flare.

90 MEG Air Cooler

The 90 MEG Air Cooler is a fin fan cooler with two 100% variable speed fans contained in an enclosure with automatic inlet and outlet louvres. The cooler reduces the temperature of the 90% wt. MEG solution from 107oC to 40oC prior to the MEG flowing into the 90 MEG Tank. An outlet temperature controller senses the MEG outlet temperature and adjusts the speed of the fans to maintain an outlet temperature of 40o C.

In the event of very low ambient temperatures the cold air entering the air cooler tube bundle is sensed and the position of the louvres are adjusted automatically to reduce the volume of cold air passing across the air cooler tube bundle. A hot oil coil also provides supplementary heat in the event of very low ambient temperatures.

90 MEG Tank

The 90 MEG Storage Tank is a coned, fixed roof tank which is maintained under a positive pressure of 0.05 barg by blanketing with fuel gas in order to prevent the ingress of oxygen into the 90% wt. MEG solution.

Two electrical heaters with a duty of 20 kW each are provided in the storage tank to maintain the temperature of the MEG above 10oC in order to prevent the crystallisation of the MEG solution.

The tank is fitted with a fill connection for MEG make-up. Oxygen may enter the system during tank filling operations

therefore an oxygen scavenger chemical injection facility is provided at the inlet to the tank.

MEG Shipping Pump The MEG Shipping Pump is a reciprocating pump which increases the pressure of the lean MEG solution from 0.05 barg to 113 barg to produce sufficient pressure differential for the transfer of the 90% wt. Meg solution back to the offshore production platform.



Two pumps in parallel are provided, one in service whilst the other pump is standby. Pump discharge pressure control routes excessive pressure back into the 90 MEG Tank.

A takeoff line from pump discharge provides make-up MEG to the MEG Still column if required.

MEG Process Pump

There are three reciprocating MEG Process Pumps in parallel operation, two pumps in operation with one pump standby.

The pumps raise the pressure of the 90% wt. Meg solution from 0.05 barg to 89 barg and the discharge flow is combined with the rich MEG take off under flow control from downstream of the MEG Coarse Filters in order to produce 80% wt. MEG solution for use in the onshore process facilities. Pump discharge pressure control routes excessive pressure back into the 90 MEG Tank.

MEG Still Condenser


Figure 7-4 MEG Still Column Overheads & Oily Water Tank



The MEG Still condenser is a fin fan cooler with two 100% variable speed fans contained in an enclosure fitted with automatic inlet and outlet louvres. The cooler reduces the temperature of the non-condensable flow from the top of the MEG Reflux Condenser from 104oC to 50oC cooling and condensing the vapours prior to flowing into the MEG Still Overhead Drum. An outlet temperature controller senses the MEG outlet temperature and adjusts the speed of the fans to maintain an outlet temperature of 50oC.

MEG Still ColumnOverheads FromM E G R e f l u xCondenser

TC

MM

TT

Variable SpeedMotors

Enclosure Inlet & OutletLouvres controlled by InletAir temperature

TT

MEG StillCondenser

Speed Control Signal

Oily Water Oily Water

Hydrocarbon Liquids

LTLC LT

LC

RP

DisengagedGas

VariableSpeed Motor

To LP Flare KO Drumvia Closed Drain Header

Recovered Oil Pumps

Oily Water Pumps

To DisposalTank

Figure 3-13 MEG Regeneration (4)

LP Flare

Andy Marr 2004

In the event of very low ambient temperatures the cold air entering the air cooler tube bundle is sensed and the position of the louvres are adjusted automatically to reduce the volume of cold air passing across the air cooler tube bundle. A hot oil coil also provides supplementary heat in the event of very low ambient temperatures.

MEG Still Overhead Drum

The MEG Still Overhead Drum is a horizontal pressure vessel which operates at 0.08 barg. An underpass and overpass weir arrangement illustrated in Figure 3 -13 allows separation of the liquid phases.

The condensed liquid entering the still drum is water with traces of MEG, hydrocarbon vapour and hydrocarbon liquid.

The still drum acts as a 3-phase separator with the vapours disengaging from the condensed inlet stream and exiting via the gas outlet nozzle to the LP Flare.

The water being denser than the hydrocarbon liquid settles to the bottom of the vessel and flows under a weir then over a lower elevation weir into the oily water compartment in the vessel. The oily water is pumped from the compartment, under level control, via the Oily Water Pump to the Disposal Tank. As previously discussed the Oily Water Pump minimum flow is routed to the MEG Still Column.

The hydrocarbon liquid forms an interface on top of the denser water and overflows a weir into the hydrocarbon liquid compartment where the liquid is pumped out of the still drum, under level control, by the Recovered Oil Pump to the LP Flare KO Drum via the closed drain header.

Oily Water Pump

The Oily Water Pump is a centrifugal pump which increases the pressure of the oily water 0.08 to 3.5 barg to enable the transfer to the Disposal Tank from where the water is routed to an injection well for disposal.

Two pumps in parallel are provided, one in service whilst the other pump is standby. Pump minimum flow control routes excessive pressure back into the MEG Still Overhead Drum.

Recovered Oil Pump

The Recovered Oil Pumps are reciprocating pumps which increase the pressure of the recovered hydrocarbon liquid from 0.08 to 3.5 barg to enable transfer of the liquid to the LP Flare KO Drum via the closed drain header. The pumps are provided with variable speed motors which are controlled by the level controller on the still drum. The pumps operate on an intermittent basis with normally no flow going to the closed drain system.



Two pumps in parallel are provided, one in service whilst the other pump is standby. Pump minimum flow control routes excessive pressure back into the MEG Still Overhead Drum.

MEG Closed Drain System

The MEG Closed Drain system comprises a MEG Closed Drain Drum, MEG Closed Drain Heater (3kW) and MEG Closed Drain Pump. MEG closed drains are routed via a closed drain header to the MEG Closed Drain Drum. A heater is provided in the drum to maintain the contents above 5oC to prevent freezing. The drum is equipped with a MEG Closed Drain Pump to pump out the contents of the drum.

Normally the drum contents will be MEG solutions at various concentrations and will be returned to the Rich MEG Storage Tank for reprocessing. In the event that the drum contains mainly water, the contents can be routed to the Disposal Tank or if hydrocarbons to the Condensate Storage Tank. The MEG Closed Drain Drum floats on the LP Flare header pressure.

MEG Closed Drain Drum

The MEG Closed Drain Drum is a horizontal pressure vessel located in a concrete pit. The vessel operates at 0.01 barg and 30o C.

MEG Closed Drain Pump

The MEG Closed Drain Pump is a vertical multi-stage centrifugal pump mounted inside the drum, the pump suction being located in the drum sump or boot. The pump increases the pressure on the liquid from 0.01 to 3 barg.

MEG Open Drain System

The MEG Open Drain system comprises a MEG Sump, MEG Sump Heater and MEG Sump Pump. MEG contaminated rainwater run-off from the MEG Regeneration area of the site and open drains from tank bunds are routed via an open drain header to the MEG Sump. A heater is provided in the MEG Sump to maintain the contents above 5oC to prevent freezing. The drum is equipped with a MEG Sump Pump to pump out the contents of the sump.

In the event that the sump contents are MEG, the contents are pumped to the Rich MEG Storage Tank for reprocessing. Normally the sump contains mainly water contaminated with MEG, the sump contents in this case can be routed to the Disposal Tank.

MEG Sump

The MEG Sump is an atmospheric sump tank located in a concrete pit and operates at approximately 37oC.

MEG Sump Pump

The MEG Sump Pump is a vertical multi-stage centrifugal pump mounted inside the sump tank and increases the pressure on the liquid from atmospheric pressure to 5 barg.