1 Intricacies of Design of a Gas Pipeline & Main Equipment, System in Gas Pipeline by Rahul Gautam Chief Manager (Pipeline) Project Development GAIL(INDIA)

Intricacies of

Design of a Gas Pipeline&

Main Equipment , System in Gas Pipeline

Rahul GautamChief Manager (Pipeline)

Project Development

GAIL(INDIA) LTD

PETROFED (6th Programme on Oil & Gas transportation through Pipeline)

IIPM GURGAON 8th- -10th July , 2009

Contents

Rahul Gautam Chief Manger (Pipeline) Project Development GAIL(INDIA) LTD

Typical Pipeline System

Typical Input Parameter for designing

Design Basis

Modeling & Simulation

Optimization

3Rahul Gautam Chief Manger (Pipeline) Project Development GAIL(INDIA) LTD

Gas Source

Pipeline Types

Gas Gathering System

Gas Treatment

Gas Transmission

Gas Distribution

DT SV IP RT

RT DT: Dispatch TerminalSV: Sectionalizing ValveIP : Intermediate Pigging StationRT : Receiving Terminal

Typical Gas Transmission & Distribution

Contd.…

Typical Schematic for Pipeline System

GAS FIELD

GAS RECEIVING STATION

RECEIVING TERMINAL / DELIVERY TERMINAL

x- ingsRAIL/ROAD/RIVER

SV: Sectionalizing ValveIP : Intermediate Pigging StationCS: Compressor StationRT : Receiving TerminalGGS : Gas Gathering SystemGT: Gas Treatment

GGS &GT CTP

A typical gas pipeline system comprise of the following • Gas Receiving Station - Place where pipeline receives the gas.

• Sectionalizing Valve Station - To carry out routine maintenance or emergency maintenance of pipeline venting of gas is to be restricted.

• Intermediate Pigging Station - To ensure continuous gas flow through pipeline, regular and periodical cleaning of pipeline is required.

- The pigging is carried out various kind of Pig e.g. Scrapper Pig, Gauzing Pig, Foam Pig etc.

TYPICAL SV STATION

Utility Connection – 2”

By pass Line

MAINLINE

MANIFOLD FOR PG /TG

From -OriginatingStn

To Terminal Stn

To Utilities PRS

Blow Down

FLOW TEE

BALL VALVE

GLOBE VALVE

GATE VALVE TEG-THERMO

ELECTRIC GENERATOR(Utilities)

R-LNG FLOW DIRECTION

TYPICAL INTERMEDIATE PIGGING STATION -

• Compression System - To economize the flow through pipeline - Located enroute of the pipeline to boost the gas pressure - Reciprocating compressor verse Centrifugal compressor - Reciprocating compressor : up to gas volume of 200000 SCM/Hr higher compression ration ( up to 10) - Centrifugal compressor : higher volume flow Compression ratio 1.5 to 2.0 Compressor installation like a process plant requiring all kind of utilities (Power, Water, Air, Fuel , Fire Fighting and Control Room System)•Receiving Terminal

- For supplying gas to various customers : designed to handle the required flow for single and multiple users. - The terminal contain filters, pressure regulator, heater, metering device, online gas chromatograph, flow computer and odorizing unit (if required)

Contd.…

Gas Supply Pressure

Off take of Gas

Delivery of gas

TRANSPORTATION OF GAS WITH COMPRESSOR STATIONS (TYPICAL)

Meter-2Flow computer-2

Schematic (Typical ) for Receiving Terminal at Customer site

P R Unit Metering Unit

SDV-1PCV-1

PCV-2SDV-2

Meter-1 Flow computer-1

Scrubber Custody T/PFilters

40 Meter

15 Mts

Not to Scale

By-Pass

Gas Chromatograph

Typical Input Parameters

Type of Natural Gas - Associated Gas - Non Associated Gas / Free Gas - Dry Natural Gas - Wet Natural Gas - Sour Natural Gas Gas Composition Gas Supply Pressure and Temperature

Gas Volume ( To be Transported) and off-Take of gas enroute pipeline ( if any)

Route / Terrain

Delivery Point

Gas volume at delivery point

Required Pressure and Temperature at Delivery Point

Contd.…

Design Basis

Pipeline System

Starting Point - Supply Gas Pressure (Kg/Cm2g) - Supply Gas Temperature (deg. C) - Gas Volume - Gas Quality and Gas Composition Route /Terrain - Class location - x-ings ( NH/SH/RAIL/ROAD/RIVER/MAJOR RIVER)

Delivery Point - Delivery Gas Pressure (Kg/Cm2g) - Delivery Gas Temperature (deg. C) - Gas Volume - Gas Quality and Gas Composition

Contd.…

Design Basis

Linepipe - Design Pressure - Wall Thickness - Roughness with internal coating and without internal coating - Gas Composition - Soil temperature - Elevation - Efficiency - Flow - Configuration -Velocity in pipe

Metering - Supply Pressure and temperature - Flow - Gas Quality and Gas Composition - Type of meter (Orifice / Turbine Meter / USM) - Configuration - Pressure Loss - Accuracy - Rangeability

Contd.…

Design Basis

Compressor Station - Gas arrival pressure and Temperature - Compressor Ratio - Discharge Pressure and Temperature of Gas - Flow - Gas Quality and Gas Composition - Compression efficiency - Compression spacing - Compressibility - Configuration - Compression Power

Contd.…

Pipeline modeling constitutes a Graphical Representation of the pipeline system involving receiving stations Sectionalizing Valve Station, Intermediate Pigging Station, Compressor / Pump Station and Receiving Terminal.

- Pipeline design (optimal Line pipe size, compressor requirement, loop line and other equipments location including SCADA & Telemetry System)

- Pipeline performance (Throughput optimization)

- Tracking gas composition

- Minimize fuel consumption

- Pipeline systems operation

- Create Emergency Plan

- Leak Detection Module

- Alarms Generation

Contd.…

Modeling and Simulation

TYPICAL SCHEMATIC FOR MODELLING PIPELINE SYSTEM

TRUNK LINE

CUSTOMER LOCATION

TAP-OFF POINTS

SPURLINES

770 KM

Trunk Line

Spurline

Dedicated Pipeline

Starting Point

End Point

Compressor

- Compressibility

- Improving delivery by making use of line pack which being function of Pipeline pressure.

Simulator model basically works with various equation of state to compute the desire result by employing advance numerical solutions technique. Most of the simulator models have been developed by various companies who have been involved in pipeline design or information technology solution including monitoring & Control of Physical parameters.

Contd.…

Rahul Gautam Chief Manger (Pipeline) Project Development GAIL(INDIA) LTD Contd.…

Hydraulics /Simulation Flow Equation - General flow equation - Cole-Brook white equation - Modified Cole-Brook White equation - AGA equation - Weymouth equation - Panhandle A Equation - Panhandle B equation The General Flow equation , also called the fundamental flow equation, for the steady state isothermal gas flow in a gas pipeline is the basic equation for relating the pressure drop with flow rate Qb = 1.15 x 10^-3 * (Tb/ Pb) ( P1^2-P2^2 / G Tf L Z f ) ^0.5 * D^2.5 WhereQb- gas flow rate in m3/day, Tb- base temperature , K (273+deg.C), P1- U/S pressure in kpa f- friction factor, P2 –down stream pressure , kpa, G- gas gravity (air=1.00) Pb- base pressure in kpa , Tf –average gas flow temperature, K (273+deg.C)Z-gas compressibility factor at the flowing temperature , D-pipe inside diameter

Modeling and SimulationVelocity in Pipes - Represents the speed at which gas molecules move from one point to another - Due to compressibility , the gas velocity depends upon the pressure - Vary in pipeline, even the pipe diameter is constant - Highest velocity at the down stream of pipeline where the pressure is the least - Least velocity at the up stream where pressure is higher

The gas velocity at any point in a gas pipeline is given by

u=14.74 (Qb/D^2) (Pb/Tb) (ZT/P)Where u – gas velocity( m/s) , Qb - gas flow rate, measured at standard condition ( m^3/day), D- pipe inside diameter ( mm ), Pb- Base pressure (Kpa), Tb- average gas flowing temperature (deg. K), Z- compressibility factor at the flowing temperature, dimensionless

Erosional Velocity -Gas velocity is directly related the flow rate. As the flow rate increases, so the gas velocity increases. -As the velocity increases, vibration and noise are evident -Higher velocities will cause erosion of the pipe interior over a long period of time.

u (max) =100 / (d) ^1/2 u (max) – ft/ s, d = gas density at flowing temperature , lb/ ft ^3

Reynolds Number -Reynolds number is used to characterize the type of flow in a pipe, such as laminar, turbulent or critical flow - It is also used to calculate the friction factor in pipe flow - It depends upon property of gas, pipe diameter etc.

Re = u D d / n Where Re- dimensionless, u-average velocity (m/s), D- inside diameter (mm), d- gas density(kg/m^3), n-gas viscosity (kg /m-s) The Reynolds number is

Re =0.5134 (G Qb/n D) (Pb/Tb)

Where G – specific gravity of gas (air=1.0), Qb - gas flow rate, measured at standard condition ( m^3/day), D- pipe inside diameter ( mm ), Pb- Base pressure (Kpa), Tb- average gas flowing temperature (deg. K), n-viscosity of gas , poise

Laminar flow – The Re. No. is less than and equal to 2000Turbulent flow - The Re. No. is greater 4000Critical flow - The Re. No. is undefined and in between 2000 and 4000

Rahul Gautam Chief Manger (Pipeline) Project Development GAIL(INDIA) LTDContd.…

Friction factor - Friction factor is dimensionless parameter and depends upon Reynolds Number of flow. - Darcy and Fanning two friction factor are generally used, But Darcy friction factor is more common.

Friction factor (ff ) = Darcy Friction factor (fd) /4

Moody diagram is graphic plot of the variation of the friction factor with the Reynolds number for various values of relative pipe roughness. It is a dimensionless parameter obtained by dividing the absolute (or internal pipe roughness )by the pipe diameter. Where Re- dimensionless, u-average velocity (m/s), D- inside diameter (mm), d- gas density(kg/m^3), n-gas viscosity (kg /m-s) Relative roughness : e / D

Where e = absolute or internal roughness of the pipe (mm)D= pipe inside diameter (mm)

Moody diagram

Reynolds Number

Laminar Critical Turbulent

Pipe internal RoughnessPipe Material Roughness (mm)•Riveted Steel 0.9 to 9.0•Commercial/ 0.045 Welded Steel •Cast Iron 0.26•Galvanized Iron 0.15•Asphalted Cast Iron 0.12•Wrought Iron 0.045•PVC, drawn tubing, glass 0.0015•Concrete 0.3 -3.0

Other Parameters

- The effect of intermediate delivery volumes and gas injection rates along a gas pipeline

- The effect of contract delivery pressure, and regulating the pressure through control valve

- Thermal effects due to heat transfer between the gas and the surrounding soil in the buried pipe due to

Soil temperature Thermal Conductivities Joule Thompson Effect

Contd.…

Optimization

- Without Intermediate Compressor

- With Intermediate Compressor

- With Intermediate Compressor and Loop Lining

Pipeline Configuration

Contd.…

Pipeline Configuration - The total pressure required for transporting gas in a pipeline under various configuration, such as series and parallel

100MMSCMD 80 MMSCMD 50MMSCMD

Series 20 MMSCMD 30 MMSCMD

50MMSCMD Parallel

100MMSCMD

50 MMSCMD

Optimization

Metering System Orifice Turbine Ultrasonic

Standard AGA Rep 3 AGA Rep. 7 AGA Rep. 9

Accuracy < 1% +/_0.5 % < +/- 0.5%

Rangeability 3:1 10:1 50:1

Pressure Loss 0.5 0.1 Negligible (Kg/Cm2g)

Cycle Flow Generally Appreciable Not Affected Variation over reg.

Liquid in gas Corrosion & Corrosion & Corrosion possible erosion damage to moving parts

Optimization

Contd.…

Thank You

1 Intricacies of Design of a Gas Pipeline & Main Equipment, System in Gas Pipeline by Rahul Gautam Chief Manager (Pipeline) Project Development GAIL(INDIA)

pipeline system gas

temperature of gas

gas enroute pipeline

typical gas pipeline

gas source pipeline

following gas

c gas volume gas quality

temperature gas volume

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