11 Utilities

Upstream Process Engineering Course 11. Utilities

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Utilities

1

Offshore Utilities • • • • • •

Seawater Fresh Water Cooling Water Instrument / Plant Air Diesel Oil / Fuel Oil Inert Gas

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• • • • • • •

Fuel Gas Aviation Fuel HVAC Chemical Injection Drilling Requirements Drains Accommodation

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Utilities

2

Seawater 20-30ºC

SEAWATER

CHLORINATION

SEAWATER

PACKAGE

COOLERS COARSE FILTRATION

1ppm 7 - 10 Bara 4-18ºC

Removal 95% over 120 mircons

TO INJECTION WATER SYSTEM

COOLING

30-35ºC

MEDIUM

LIFT PUMP(S)

30-35ºC

COOLERS

BYPASS

TO OTHER USERS POTABLE WATER MAKERS FIREWATER RINGMAIN SERVICE WATER ETC

LAT 12 m

40 - 60 m

Typical Seawater System Seawater is supplied to the facility main deck level at pressure of typically 7 - 10 Bara. Seawater supply temperature ranges from 4 - 18ºC. The seawater is dosed with hypochlorite to minimise marine growth then filtered prior to distribution to the users.

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OVERBOARD

Material Selection Cunifer (CuNi) Stainless Steel Titanium

Seawater is used for : Process Cooling (Oil / Gas) Fire Main Pressurisation Drilling Desalination Chlorination Utility Stations Motor Coolers

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Utilities

3

Seawater Seawater Usage Cooling Services The seawater may be used for direct process cooling and/or cooling a closed loop cooling medium system. Process Cooling Equipment Cooling

-

flowrate set by process requirements Motor specific

The seawater return temperature should not exceed approximately 30°C in order to prevent scale formation. When calculating the seawater cooling requirements, the maximum design seawater temperature and specific heat capacity valve of 4.0 kJ/kg°C should be used. Drilling During normal drilling operations, water at varying rates from 110 to 275 m3/hr may be required. During emergency situations, water at a rate up to 500 m3/hr may be necessary. Service Water Service water is utilised for line flushing, washdown purposes, etc. Typical intermittent flowrate specified is 50m3/hr Other Users Typical consumption rates Fire Main Pressurisation - 10 m3/hr Chlorination -10m3/hr / 600m3/hr seawater Upstream Process Engineering Course

HVAC - 30 m3/hr Desalination (Fresh Water) - 35 m3/hr

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Utilities

4

Seawater Lift For seawater application, the vertical submersible type (as shown on the right) or line shaft type pumps are generally used. The difference between these types is that the position of the electrical motor. For the submersible type the motor is located below the pump whereas for the line shaft type, it is positioned above and connected via a solid shaft.Submerged motor types are usually preferred since they can be operated at higher speeds than equivalent line shaft units which results in smaller units. Design features of the submersible lift pump are:•The lift pumps have centrifugal characteristics and provide flowrates up to 3000 m3/hr and 7 -10 Bara at deck level. • A coarse strainer is fitted at the suction to prevent pump damage from marine life / debris • The pump suction is located normally 40 to 60 metres below sea level to minimise the impact of marine life on operation. • Sodium Hypochlorite is injected at the pump inlet to provide impeller and motor protection against marine growth. For seawater lift applications on FPSOs, the sea-chest pumps used are horizontal centrifugal types. Upstream Process Engineering Course

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Seawater Coarse Filtration Seawater pumped to a facility requires filtration prior to use. The seawater passes through a coarse filter which will typically remove 95% of particle over 120 microns.

Operation In the design shown, the seawater enters the base of the strainer basket, passing radially outwards through the strainer basket and leaves the vessel via the outlet nozzle at the top. On-line Cleaning

The filter will remain in operation during the backflushing operation. On automatic or manual initiation, the back-flushing valve is opened and the hollow shaft rotated, sweeping collector heads around the inner face of the strainer basket. The pressure differential between the vessel and back-flushing system forces filtered water back through the strainer element, washing the collected solids down the hollow shaft to the disposal system.

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6

Fresh Water Reverse Osmosis Unit 1

Reverse Osmosis Unit 2 RO Unit 1

Seawater In

Permeate (Product Water)

Permeate

~ ~ Concentrated salt water for overboard disposal

Potable Water Reverse Osmosis Unit •

Fresh water is required for: – Potable water (150 - 250 litres/day/person) – Process users (15 - 25 m3/day) – Drilling operations (50 m3/day): • cement mixing • mud mixing

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•

Fresh water is supplied by supply boat or generated offshore by: – Vacuum distillation – Vapour compression; Note that these units are getting out of date and are being replaced by membrane systems – Reverse osmosis (RO)

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Utilities

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Fresh Water Cont’d •

•

Potable water is used for: – Drinking and domestic water (after further treatment by neutralising and ultra-violet sterilisation) – Safety shower supplies – Service water, i.e. desalting water, cooling medium make-up and drilling water – Accommodation sprinkler system

•

Typical fresh water discharge pressures: – Potable water transfer pumps: 6 barg – Service water transfer pumps: 4 barg – Service water injection pumps: 24 barg – Service water transfer pumps: 3.4 barg

•

The storage capacity is usually based on seven or fourteen days supply

For drinking and domestic purposes the water is fed to neutralising columns, containing a granular lime based mineral to improve taste and impart a degree of alkalinity thereby reducing the corrosivity of the water

•

Typical storage capacities:

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– – –

Potable water tanks: 80 m3 each (one on-line, one filling, one stand-by) Service water break tanks: 5 - 10 m3 Potable water header tanks: 4 - 5 m3

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Utilities

8

Cooling Systems General Cooling for process and utility systems are required. The three types of cooling systems usually considered for use are : •

Direct Seawater (Open Loop)

•

Closed Loop Cooling Water

•

Air Cooling

Direct Seawater (Open Loop) System The open loop system uses raw seawater taken directly from the topsides distribution system and routed to each cooler. The returned seawater is either dumped overboard or routed to the water injection system. The seawater is normally treated with chemicals to minimise corrosion and the exchanger material selection will have to be corrosion resistant. Closed Loop system Closed loop cooling uses a circulated cooling medium. Seawater is used to cool to returned cooling medium. The medium normally consists of a glycol / water mixture (glycol concentration 30-40wt%). Air Cooling System Air cooling is normally used for cooling emergency generators and other essential equipment which must continue to be cooled in the event of open /closed loop cooling system. Their application for process cooling is normally found on onshore facilities due to the large footprint requirements.

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Cooling Systems Cont’d To Atmospheric Vent

Typical Closed Loop System N2 Blanket

Expansion Tank

-

Design Rules of Thumb Expansion Tank -2 mins. Residence time Pump Capacity - 125% of design rate Pump Configuration - 3 x 50%

Medium Filter

Process Coolers Circulation Pumps

Seawater Coolers

Design Supply / Return Temperatures

Temperature Approaches

Open Loop Supply - Max. Ambient Return - 30-35°C (Scale dependent)

Cooling water return temperatures should be limited for practical operation purposes to within :

Closed Loop Supply - 5°C above Seawater Temperature Return - 50°C

• 8°C of a hot process liquid temperature

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• 5°C of a hot condensing hydrocarbon outlet

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Cooling Systems Cont’d Open / Closed System Comparison

System

Advantages

Disadvantages

Open Loop

- simple once through system - less labour intensive - lighter system

- expensive exchanger materials - major constraint on applicable temperature range - potential for scaling - limited choice of exchangers

Closed Loop

- cooling water properties and conditions can be controlled - less expensive exchangers

- additional equipment(CM system) - more labour intensive - heavier system (overall) - system availability

The selection of the cooling system is normally determined on a case by case basis since each system has its benefits. The choice of system is decided by considering Capex and Opex costs over field life.

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11

Instrument / Plant Air PSHL

Air Compressor Packages

Inert Gas Generation Drilling Instrument Air

Air Filter Packages

Instrument Air Receiver PC

Instrument Air Header HVAC

Cooler Plant Air Receiver Black Start Air Compressor Package

Black Start Air Filter Package

Drilling Conveying Air

Plant Air Header Black Start Air Receiver

Drilling Plant Air

Cooler

Typical Combined Instrument And Plant Air •

Instrument air should be oil free, dust free and dry, is typically provided at 7 - 9 barg and may be used for: – Instrument actuators (largest user) – Motor purging/pressurisation – Flare ignition – Inert gas generation

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•

Plant air does not have any particular specifications, is typically provided at 7 barg (minimum) and may be used for: – Platform hoists – Air driven tools – Paint spraying – Diving (air winches etc.)

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Instrument / Plant Air Cont’d •

•

Instrument Air: Consumption rates for instrument air should be based on all instruments operating simultaneously and then applying a design margin typically 30%. – –

Each instrument component: 8.5 Sm3/h Motors, positioners and purge air: 5 - 18 Sm3/h

Typical instrument air requirements for a ‘large’ offshore type facility may be as follows (drilling excluded): – – – –

Air for instruments: Motor purging/pressurisation: Flare ignition (intermittent): Inert gas generation:

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950 Sm3/h 180 Sm3/h 40 Sm3/h 170 Sm3/h

Plant air: If no specific information is available, the plant air requirements may be taken to be equal to the instrument air requirements. Typical consumption figures: – – – –

Grinder (6”/8”): Sump pump: Paint sprayer: Rotary drill (3/8”)

90 Sm3/h 130 Sm3/h 150 - 250 Sm3/h 40 - 75 Sm3/h

Typically, the plant air requirements for a ‘large’ offshore facility may be as follows: – – – –

Platform hoists: Air driven tools: Paint spraying: Diving:

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400 Sm3/h 120 - 150 Sm3/h 150 - 250 Sm3/h 300 - 1200 Sm3/h

Utilities

13

Instrument / Plant Air Cont’d •

–

•

•

Oil free centrifugal air compressors (2000 - 30000 Sm3/h) Dry running oil free rotary compressor, generally with two stages and intercooling (1000 - 5000 Sm3/h) Oil injected rotary screw compressor (150 - 2500 Sm3/h)

–

Air Dryers: –

Instrument air should be dried to a suitable dewpoint at operating pressure (typically minus 40oC) •

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Air Receivers –

The compressor types preferred are: •

•

•

Air Compression:

Air receivers are necessary to damp pressure surges in the system and provide storage which will maintain an air supply on compressor failure The volume of storage required is given by:

V

t Q 57  P1  P2 

V P1 P2 t Q

Storage volume (m3) Normal operating pressure (bara) Minimum acceptable pressure (bara) Required duration of flow from storage (min) Air flow required (Sm3/h)

The time allowed for start-up of a standby compressor is typically five minutes

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Diesel Systems Crane Drivers Drill Package Diesel Drivers Black Start Air Compressor Driver

To Drill Packages To Drilling Burners Mud Mixing

Chemical Injection

PC

From Supply Boat

PC

Heating Medium Heaters

PC

Inlet Diesel Strainer

Emergency Generators

Bulk Diesel Storage

Diesel Fuel Transfer Pump

Filter

PC Untreated Diesel Fuel Strainer

Auxiliary Fire Pumps Power Plant Main Turbines

Coalescer

PC Raw Diesel Centrifuge

Water Removal

Centrifuged Diesel Storage Tank

Coalesced Diesel Storage Tank

Water Removal

Typical Flow Scheme for Diesel Distribution •

Diesel may be used by: – Gas Turbine Generators – Heating medium Heaters – Diesel (emergency) Generators – Diesel Firewater Pumps – Miscellaneous Diesel Drives – Lifeboats – Cranes – Mobile/Temporary Users – Drilling Package Engines – Drilling Operations Upstream Process Engineering Course

Quality • 10 ppm free water, 1mm solids 200 ppm free water, 5 mm solids 10 ppm free water, 1mm solids 200 ppm free water, 5 mm solids 200 ppm free water, 5 mm solids 200 ppm free water, 5 mm solids 200 ppm free water, 5 mm solids • 200 ppm free water, 5 mm solids 200 ppm free water, 5 mm solids No treatment (raw diesel)

Diesel Usage Rates: – Gas Turbines: – –

25 to 30% efficiency on installed power Engines: 0.25 kg/kWh Fired Heaters: 75 to 80% efficiency on thermal rating

Storage Capacity: – Drilling: – Life support: – Production:

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5 to 7 days 10 to 14 days 0 days Utilities

15

Inert Gas To N2 Distribution PCV N2 Receiver

Instrument Air Membrane

Standby N2 Bottles

Typical N2 Generation Scheme (Membrane) •

•

Inert gas is utilised for purging and blanketing purposes: – Purging of: • gas compression trains • gas pig launchers/receivers – Blanketing of: • produced water flotation units • heating medium expansion tanks • lube and seal oil tanks – Gas freeing of vessels for maintenance – Snuffing of local vents HP inert gas may be used to kick off wells, in which case further HP compression is required

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•

•

• •

The inert gas system should be sized to fully purge the largest section of isolated equipment within one shift, whilst meeting blanketing requirements For pressure purge (typically 5 barg) the system is purged 2 or 3 times. For sweep purging at atmospheric pressure, the inert gas requirement is 3 times the system volume Blanketing of flotation units typically requires 0.015 to 0.03 m3/h per m3 of cell volume Source of inert gas: – Inert gas generator (diesel or gas fired; purity 0.5% O2) – Pressure swing absorption (PSA; 0.5 - 3.0% O2) – Membrane generated N2 (0.1 - 5.0% O2) – Air liquefaction (99.999+% N2)

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Inert Gas •

Advantages of liquid nitrogen over the other sources: – – – –

– –

Very pure nitrogen (99.999+%) High inert gas rates achievable No gas compression required - pressure vessel can operate at 10 barg Low heating requirement - ambient air vaporiser can raise temperature to within 10oC of ambient No cooling water Low maintenance

•

Disadvantages: – –

Not suitable when a continuous demand exists Liquid nitrogen pods delivered by supply boats, which must be well protected in a cradle

•

Nitrogen is stored in high pressure cylinders. Batteries consist of of 12 to 15 cylinders and are manifolded together to provide 80 to 100 Nm3 of high purity nitrogen

•

Cylinders are usually chosen when no continuous inert gas flow is required and purging/blanketing flows are relatively small Inert gas need not necessarily be Nitrogen. Tankers and FPSO’s use combustion products from burning diesel as inert gas for tank blanketing

•

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17

Fuel Gas Systems To Vent / Flare PC

Fuel Gas Knockout Drum

Fuel Gas from Supply Source

LC

To Fuel Gas Manifold Fuel Gas Heater

To LP users To Closed Drains

Power Supply

Typical Fuel Gas Conditioning Scheme •

Fuel gas is used for/as: – Gas Turbines for Power Generation – Gas Turbines for Compressor Drivers – Fired Heaters – Stripping Gas • Glycol Regeneration – Blanket and Purge Gas

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•

Usually two pressure levels: – HP Gas Turbines (10 - 20 bar) – LP Fired Heaters, Blanket Gas, Purge Gas, Stripping Gas (0.1 - 2.0 bar)

•

Some gas engines need very high inlet pressures (Foinaven, approx. 300 bar)

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Fuel Gas Systems •

•

The fuel gas quality is set by the user that demands the highest specification, which normally is the power generation or machinery drivers – Solids content: < 30 ppm (wt) – Water content: < 0.25% water above saturation at the point of use – Supply temperature: A fall in temperature of 11oC should not result in condensation or hydrate formation – Calorific value: Ideally the net calorific value should be between 33.5 and 41 MJ/Sm3 – Sulphur components: Moderate levels of sulphur bearing components are not a problem provided that the temperature of the combustion products is maintained above the acid gas dewpoint. Fuel Gas Conditioning: – Fuel gas should be heated to approx. 20oC above its water and hydrocarbon dewpoints – Fuel gas should be filtered to remove 99.5% of particles > 5 mm

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–

A fuel gas knock out drum should be provided upstream of the heater to remove any entrained particles

•

Fuel Gas Storage: – The fuel gas knock out drum should be sized for a holding capacity of 20 seconds to enable automatic changeover to liquid fuel in the event of loss of fuel gas

•

Materials: – Normally carbon steel is adequate for fuel gas systems. If wet gas with carbon dioxide is expected, stainless steel may be required for equipment and pipework. – If hydrogen sulphide presence is expected, equipment and piping should be designed in accordance with NACE std. MR-01-75

•

Emissions –

Fuel gas should preferably be treated in order to minimise harmful combustion emissions eg. Remove any H2S to prevent SOx emissions

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Heating Ventilation & Air Conditioning •

•

HVAC systems are designed to achieve the following: – Ensure a safe environment under all working conditions – Ensure adequate standard of personnel comfort and equipment operating environment

Air Inlet Fire & Gas Damper

HVAC facilities contain: – Air conditioning systems • •

–

–

MCC

Extractor Fan

–

Fan Telecoms

Fan

Heating / AC Unit

Quarters

Recirculation Fan

Supply air temperature range: 19.5oC max design ambient ventilation only; 13.0oC ventilation with cooling

System to enable pressurisation of the modules •

Fixed Blade Louvres

Fan

Mechanical ventilation systems •

Process Modules

Supply air temperature range: 13.5 - 15.0oC Relative humidity: 35 - 65%

Controlled pressurisation levels of between 70 N/m2 and 120 N/m2 above atmospheric pressure are maintained by pressure control dampers, mounted in the enclosure extract/relief systems

Natural ventilation system; A key variable in the design of HVAC systems is the amount of air changes per hour. • For respiration purposes a minimum of 12 liters per second per person should be supplied. • For analyser houses/control rooms the number should be 12 volume changes per hour

Typical HVAC System Upstream Process Engineering Course

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Chemical Injection •

Chemicals are often required to ensure the satisfactory operation of the process and utility systems installed on offshore platforms

•

Most chemicals are supplied in either 55 US gallon drums or 2 tonne bulk units

•

Chemical Injection Pumps: – positive displacement variable flow – spared for continuous or frequent duty – multiple heads for multiple injection points – IRCDS-system (Injection Rate Control + Distribution System)

•

Storage: – Two storage or mix tanks should be provided for each chemical – Total volume should be sufficient for 10 - 14 days injection at rated capacity – The tank size of a mix tank should be suitable for making up a batch from a standard sized container

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Chemical Injection Skid Schiehallion

Chemical Injection Skid Curlew Utilities

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Chemical Injection Chemicals for Crude Oil Streams Chemical (1)

Emulsion Breaker

Anti-Foam Pour Point Depressant Scale Inhibitor Corrosion Inhibitor

Typical Injection Points 1st Stage and Test Separator Inlets Desalter Inlet Atmospheric Separator Inlet Coalescer Inlets 1st Stage and Test Separator Inlets Desalter Inlet Downhole Export Pump Inlet Heater Inlets Downhole Export Pump Inlet

Typical Dosing Rates ppm 10 to 60 5 to 10 5 to 10 5 to 10 1 to 100 1 to 10 50 to 100 5 to 100 1 to 5 5 to 10

Preliminary Rate Estimates ppm 25 5 (2) 5 (2) 5 (2) 5 2 (2) 100 10 (2) 2.5 5

Typical Dosing Rates ppm 0.5 to 5.0 0.1 to 5.0 5.0 to 10.0 5 to 15 50 to 200

Preliminary Rate Estimates ppm 2.0 1.0 5.0 5.0 50 (2)

5.0 5.0 30

5.0 (3) 5.0 30 (4)

Notes: 1 2

Required chemicals depend on particular application Replenishment to bring chemical additive to effective dosage

Chemicals for Water Injection Streams Chemical (1)

Coagulent Anti-Foam Oxygen Scavenger Scale Inhibitor Biocide

Surfactant Corrosion Inhibitor Sodium Hypochlorite

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Typical Injection Points

Filter Inlet Deaerater Inlet Deaerater Outlet Deaerater Outlet Deaerater Outlet/ Injection Water Filters/ Injection Pump outlet Water Injection wells Injection Pump Inlet Injection Pump Outlet

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Notes: 1 2

3 4

Required chemicals depend on particular application Batch injection based on 4 hours twice a week Batch injection based on 6 hours once a fortnight Batch injection based on 24 hours once a fortnight (alternative to Biocide) Utilities

22

Chemical Injection Miscellaneous Chemicals Stream

Produced Water Ballast Water

Seawater Cooling Medium/ Hot Water Circuits Fresh Water

Gas Streams Glycol System Sludge Recovery

Chemical (1)

Emulsion Breaker Anti-Foam Coagulent Sodium Hypochlorite Scale Inhibitor Corrosion Inhibitor Scale Inhibitor (Potable Grade) Chlorine/Hypochlorite Corrosion Inhibitor Methanol PH Control Chemical Anti-Foam Emulsion Breaker

Typical Injection Points

Produced Water Degasser Inlet Ballast Water Separators Ballast Water Degasser Inlet Flotation Unit Inlet Lift Pump Suction Lift Pump Discharge Circulation Pump Suction

Typical Dosing Rates ppm 5 to 10 5 to 10 1 to 5 5 4 (2) 5 1000

U/S & D/S of Potable Water Makers D/S of Potable Water Makers Gas Pipeline As required By Glycol Package Vendor By Glycol Package Vendor Upstream of Sludge Heater

Preliminary Rate Estimates ppm 5 5 1 5

5

5 1000 (top-up only) 5

1 to 2 1 to 10

5

5 to 10

25

Notes: 1 2

Required chemicals depend on particular application Typical regulatory requirement for cooling water discharge: < 1 mg/litre residual chlorine

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23

Drilling Requirements •

Apart from the actual drilling equipment (rotary rig, drill string, drill pipes etc.) a basic drilling system requires: –

–

– – –

A drilling fluid or mud to cool the drill bit and remove the cuttings. Drilling mud can be based on: • Oil (OBM) which is no longer considered environmentally acceptable, or • Water (WBM), which is most frequently used A mud circulation (clean up) system, which requires: • Shale shaker, to remove cuttings • Desander and desilter (hydrocyclone) to remove fine particles • Mud tanks, to store the cleaned mud (very large) • Mud pumps, to circulate the mud A blowout prevention system (BOP) to control formation fluids entering the wellbore A cement system to provide support for the casing and create a hydraulic seal between formation and casing The usual utilities, i.e. diesel, seawater, potable water etc.

•

Generally the difference in dry and operating weight on a drilling rig can be huge (stored mud etc.)

•

Drilling systems are usually designed by specialist engineers

Drilling Rig

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Drilling Requirements Basic Mud Mixing Method

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Drilling Requirements High Pressure Mud Pumps

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Drilling Requirements Mud Processing Schematic

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Drilling Requirements Typical Bulk Cement System

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Drilling Requirements Cement Mixing System

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Drains Closed Drains System Closed Drains

Open Drains System To LP Flare

Closed Drains Vessel

LC

Open Drains Haz. Deck Area

Open Drains Safe deck Area

Open Drains Haz. Modules

Open Drains Safe Modules

Closed Atmosferic Drains

Chemical Injection Purge Vent

O/Flow

O/Flow

M

Vent

Purge Vent M

Return Oil To Production Separators

To Sludge Cell Reclaimed Oil Tank/Pumps

GFU Oily Water Tank/Pumps

Seawater Discharge

Oily Water Separator

Typical Drainage System –

Closed Drains: • To collect hydrocarbon drainage from pressurised and hazardous equipment • Vapours from the closed drains vessel are routed to the LP flare • Liquids from closed drains vessel are either routed to the oily water tank or the production separators

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–

–

Hazardous Open Drains • Drainage from hazardous areas, including fire water deluge drainage • Gravity flow to oily water tank Non-hazardous Open Drains • Drainage from safe areas • Gravity flow to oily water tank, including fire water deluge drainage

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Drains •

Closed Drains: – All equipment drains should be protected by locked closed block valves – Where there is a risk of blockage by sludge or hydrates, individual drain lines from equipment up to the drain headers should be rated for the same pressure as the equipment being drained – Where there is a possibility of hydrate formation, lines should be heat traced and insulated – The closed drains vessel may be designed as a two or three phase separator: • Three phase separator: water is directed to the oily water (open drains) tank for final clean up • Two phase separator: oil/water returned upstream of the last three phase production separator – The reclaimed oil tank overflow may be directed to the sludge cell in a GBS platform. Otherwise it should be directed to a drains disposal caisson with oil recovery pump

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•

Closed Drains Headers: – Sized to allow drainage of the largest vessel in one hour – If the capacity of the closed drains vessel is not greater than the largest vessel, the outflow line(s) from the closed drains vessel should be sized for a higher capacity than the inflow

•

Closed Drains Vessel: – Capacity of closed drains vessel = volume of largest vessel + 10% This size is generally impractical for large production trains. Therefore, reduce the capacity by the storage volume in the reclaimed oil tank. Further capacity reduction may be gained by dumping the crude or sludge to storage cells

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Accommodation Modules •

An accommodation module usually contains: –

– – – – – – – – – – • • •

Basic requirements e.g. beds; function of manning level and simultaneous operations, galley etc. Fresh water (250 litre/day/man) Power supply (2.5 - 3.0 kW/man) Seawater Cooling/Heating medium Black water / Grey water disposal HVAC Lifeboats Helideck ATK system Sprinkler system

•

A typical manning breakdown for a deepwater North Sea platform is as follows: – – – – – – –

Management Services Catering Production Maintenance Construction Drilling Visitors/Contingency

11% 10% 12% 23% 15% 21% 8%

The utilities used in the accommodation blocks should be physically separated from the process utilities The accommodation often serves as temporary refuge and should therefore be fire proofed The accommodation should be remote from drilling and process areas

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Onshore Utilities Utilities required for onshore processing differ mainly due to the size of onshore facilities and the extra space available. Some of the key systems are discussed briefly below:Cooling Water Most onshore facilities make use of a closed circuit cooling water system, with the water cooled by fin-fan coolers or cooling water towers. If the location is suitable, use may be made of water from sources such as rivers or sea. Steam Steam is normally used onshore as the prime form of heating medium. It as also used for a number of other purposes eg. machinery drives, purging and inerting, cleaning, snuffing. Steam is generated in the works power station, often using waste heat as input. A key utility required for steam generation is boiler quality feed water. This requires a significant amount of water treatment equipment (demineralisation etc).

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Onshore Utilities Plant Air & Instrument Air The plant and instrument air requirements for an onshore plant are very similar to those of an offshore facility - simply more space to locate them. Inert Gas

Most onshore facilities will provide on site Nitrogen generation. The method will depend on the volume required. Liquid nitrogen plants are economic if the demand is very high but for small to medium demands, Pressure Swing Absorption or Membrane generation is more applicable. Fuel Gas/Fuel Oil

Fuel is normally required for power generation onshore. If fuel gas from the hydrocarbon stream being processed is available, this is treated and used in the same way as offshore. Combustion emission constraints may be more strict onshore, and power turbine and fuel gas requirements have to be designed to take account of this. Where fuel gas is unavailable, storage of diesel/fuel oil is provided (SVT approx. 1000 m3 capacity). Upstream Process Engineering Course

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Onshore Utilities Drains The design of an onshore facility drains system should be settled at an early stage as it is not usually practical to increase drain capacity once installed. The intent of an effluent drains system is similar to offshore in that discharges should be limited to clean water. Onshore, however, the water quality constraints are much more stringent. This leads to the use of settling tanks/ponds etc. Drain systems need to be designed to avoid flooding of vulnerable points such as pump pits etc. Flooding by rain water, and the potential for effluent carryover into water courses etc should also be reviewed carefully. Flare

Gaseous effluents onshore should be burnt or discharged from a tall stack so that fumes are not obnoxious to the site or public. Flare stacks are normally sited long way from the process plant and the immediate area around it is “sterilised” due to high noise and radiation. Ground flares can also be used in areas where no visible flame is required (eg Wytchfarm)

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