PLANT OPERATION SYSTEM

Dr. AA

04/21/231

PROCESS SYSTEM

Type of process equipments etc is dependent on the process itself.

Lets take Oil Platform and an example

04/21/232

The heart of Process System is the Distributed Control System (DCS)

Oil and Gas Production Overview

The figure gives a simplified overview of the typical oil and gas production process

Products from wellhead feed into production and test manifolds.

The remainder of the figure is the actual process, called the Gas Oil Separation Plant (GOSP).

While there are oil or gas only installations, the wellstream will consist of a full range of hydrocarbons from gas (methane, butane, propane etc.), condensates (medium density hydro-carbons) to crude oil.

04/21/233

Oil & Gas Block Diagram

4

Wellhead

First StageSeparator

Second StageSeparator

Gas Treatment

Oil

Gas

Water

Gas Treatment

Third StageSeparator

Coalescer

Oil

Water

Gas

Water Treatment

System

Oil ExportTerminal

Gas Export

Fuel GasSystem

Flare

Note: In Some cases, all gases go to flare

Oil and Gas Process

OFFSHORE STRUCTURES 04/21/235

Typical Objectives of Plant Operation

1. Protect people

2. Protect Environment

3. Protect Equipment

4. Maintain Smooth operation

5. Achieve Product rates and quality

6. Profit = optimising first five

7. Monitoring & diagnosis

These are Achieved Through Process Control…

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DCS ArchitectureDCS Architecture

Process Transmitters and Actuators

Data Highway(Shared Communication Facilities)

......

DataStorage Unit

HostComputer

System Consoles

PLC

4-20 mA

LocalConsole

LocalControl

Unit

4-20 mA

LocalControl

Unit

LocalConsole

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Fieldbus TechnologyFieldbus Technology Introduced 1988 but underwent

many development

Standard IEC61158 introduced in 1999

Based upon smart valves, smart sensors and controllers installed in the field.

Uses data highway to replace wires from sensor to DCS and to the control valves.

Less expensive installations and better reliability.

Can mix different sources (vendors) of sensors, transmitters, and control valves.

Now commercially available and should begin to replace DCSs.

CEAG I/O

P5001 0 ... 150 bar

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•Foundation Fieldbus (FF)•Profibus (Process Field Bus)•Others: ControlNet, P-Net, SwiftNet , WorldFIP, Interbus, EtherCAT, SERCODS etc

Fieldbus ArchitectureFieldbus Architecture

Plant Optimization

.................

Smart Sensors

Smart ControlValves and Controllers

LocalArea

Network

Smart Sensors

Smart ControlValves and Controllers

LocalArea

Network

H1 Fieldbus Network H1 Fieldbus Network

H1 Fieldbus H1 Fieldbus

Data Storage

PLCs

High Speed Ethernet

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PLC ArchitecturePLC Architecture

ProcessorPower Supply

Data Highway

PLC Cabinet

Programming Interface

I/O Modules

Input Devices

Output Devices

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We desire independent protection layers, without common-cause failures - Separate systems

sensors

SIS system

i/o i/o………….

sensors

Digital control system

i/o i/o………….

DCS handles controls and alarms functions.

PLC handles SIS and Alarms associated with SIS

Redundancy

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UTILITIES SYSTEM

04/21/2312

Water Treatment

When the water cut is high, there will be a huge amount of produced water. A water cut of 40% gives a water production of about 4000m3 per day (4 million liters) that must be cleaned before discharge to sea.

Often this water contains sand particles bound to the oil/water emulsion.

The environmental regulations limits oil in water discharged to sea to 40 mg/liter (ppm).

It also places limits other forms of contaminants.

04/21/2313

Water Systems

Potable Water

For larger facilities, potable water is provided on site by desalination of seawater though distillation/reverse osmosis.

Seawater

Seawater is used for cooling purposes to Air Compressor Coolers, Gas Coolers, Main Generators and HVAC.

Also used for production of hypochlorite and for Fire Water.

Seawater is treated with hypochlorite to prevent microbiological growth in process equipment and piping.

Ballast Water

Ballast systems are found on drilling rigs, floating production ships and rigs as well as TLP (tension leg platforms). The object is to keep the platform level and at a certain depth under varying conditions.

04/21/2314

Power Generation and Distribution

Power can be provided from mains power or from local diesel generator sets. Large facilities have great power demands, from 30 MW and upwards.

There is a tendency to generate electric power centrally and use electric drives for large equipment rather than multiple gas turbines, as this decreases maintenance and increases uptime.

The power generation system on a large facility is usually several gas turbines diving electric generators, 20-40 MW each.

A power management system is used for control of electrical switchgear and equipment. Its function is to optimize electricity generation and usage and to prevent major disturbances & plant outages (blackouts).

There are also platform without power supplies…

04/21/2315

Flare and Atmospheric Ventilation

The purpose of the Flare and Vent Systems is to provide safe discharge and disposal of gases and liquids

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Flare System

17

Accumulation of gas/liquid from:• Spill-off flaring from the product

stabilisation system. (Oil, Condensate etc.).

• Production testing

• Relief of excess pressure caused by process upset conditions and thermal expansion.

• Depressurisation either in response to an emergency situation or as part of a normal procedure.

• Planned depressurisation of subsea production flowlines and export pipelines

HVAC

The Heat, Ventilation and Air-Conditioning system (HVAC) feeds conditioned air to the equipment rooms, accommodations etc.

Cooling and heating is achieved by way of water cooled or water/steam heated heat exchangers.

Heat may also be taken off gas turbine exhaust. In tropic and sub-tropic areas, the cooling is achieved by compressor refrigeration units. Also, in tropical areas gas turbine inlet air must be cooled to achieve sufficient efficiency and performance.

The HVAC system is usually delivered as one package, and may also include air emissions cleaning.

Some HVAC subsystems include:

• Cool: Cooling Medium, Refrigeration System, Freezing System

• Heat: Heat medium system, Hot Oil System.

04/21/2318

Chemicals and Additives

A wide range of chemical additives are used in the main process.

OFFSHORE STRUCTURES 04/21/2319

Chemicals Functions

Scale inhibitor The scale inhibitor will prevent the contaminants from separating out. Scale or sediment inhibitor is added on wellheads and production equipment.

Emulsion breaker An emulsion breaker is added to prevent formation of, and break down of the emulsionlayer by causing the droplets to merge and grow.

Antifoam Polyelectrolyte is added before the hydrocyclones and causes oil droplets to merge.

Methanol (MEG) Methanol or Mono Ethylene Glycol (MEG) is injected inflowlines to prevent Hydrate formation and prevent corrosion.

TEG Tri Ethylene Glycol (TEG) is used to dry gas.

Corrosion Inhibitor injected in the export pipelines and storage tanks to prevent corrosion

Telecommunication Systems

Public Address & Alarm System/F&G Integration

Drillers talk back System

UHF Radio Network System

Closed Circuit TV System

Mandatory Radio System

Security Access Control

Meteorological System/Sea Wave Radar

Telecom Antenna Tower and Antennas

PABX Telephone System

Marine Radar & Vessel Movement System

Office Data Network and Computer System

Personnel Paging System

Platform Personnel Registration and Tracking System

Telecom Maintenance and Monitoring System

Ship Communication System/PABX Extension

Radio Link Backup System

Mux and Fiber optical Terminal Equipment

04/21/2320