4. chapter 3_gas gathering transportation_v2 (part 1)

8/12/2019 4. Chapter 3_Gas Gathering Transportation_V2 (Part 1)

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CONTENTS

3.1 Introduction3.2 Pipeline Design3.3 Reynolds Number

3.4 Relative Roughness3.5 Friction Factors3.6 Pipeline Equations (Weymouth, Panhandle, Modified

Panhandle, Clinedist )

3.7 Series, Parallel, and Lopped Lines

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LESSON LEARNING OUTCOME

At the end of the session, students should be able to:

Apply pipeline flow equations

Design gas transportation, gathering, and distributionsystems.

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3.1 INTRODUCTION

Transmission of natural gas to consumer be divided into threedistinct pipeline units: gathering system , main trunk line transportation system , and distribution system .

Focuses on design and operation of natural gas pipelines inonshore and offshore gas fields.

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3.2 Pipeline Design

Factors to be considered in the design of long-distance gaspipe-lines.

the volume and composition of the gas to be transmitted,

the length of the linethe type of terrain to be crossed

maximum elevation of the route

Note: Pipe line must be larger to accommodate the greatervolume of gas.

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3.2 Pipeline Design

Several designs are usually made so that the economical onecan be selected.

Maximum capacity of a pipeline is limited by highertransmission pressures and strong materials .

For economic operation, better to preserve full pipelineutilization.

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3.2.1 Sizing Pipelines

Capacity of gas transmission is controlled mainly by its size .

Complex equations have been developed for sizing naturalgas pipelines in various flow conditions.

o The Weymouth equationo The Panhandle equationo The Modified-Panhandle equation

By using these equations, various combinations of pipediameter and wall thickness for a desired rate of gasthroughout can be calculated.

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3.3 Friction Factor

Friction losses:

o Internal losses due to viscosity effectso losses due to the roughness of the inner wall of the

pipeline

Friction factor is a function of the Reynolds number and of

the relative roughness of pipe.NRe = Reynolds Numbere = absolute roughness of pipeD = diameter of pipe

f = f (N Re , e D )

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Equation that relates lost work per unit length of pipe andthe flow variables is

3.3 Friction Factor

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Reynolds Number

Reynolds number ( N Re ) is defined as the ratio of fluid

momentum force to viscous shear force . The Reynolds number can be expressed as a dimensionless

group defined as

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Reynolds Number

Reynolds number is used as a parameter to distinguish

between flow regimes .

Flow Type NRe , smooth pipes

LaminarCriticalTransitionTurbulent

< 20002000 30003000 -4000

> 4000

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Reynolds Number

For all practical purposes , the Reynolds number for

natural gas flow problems may be expressed as

12

(11.8)


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Relative Roughness

From a microscopic sense, wall roughness is not uniform ,and thus the distance from the peaks to valleys on the wallsurface will vary greatly.

This is measured in terms of absolute roughness ,

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Relative Roughnesse D , is defined as the ratio of the absolute roughness to the

pipe internal diameter :

and D have the same unit.

If roughness not known, take =0.0006

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(11.9)


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3.4 Equation for Friction Factor Figure is a Moody friction factor chart log-log graph of

(log f ) versus ( log N Re ).

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Turbulent Single-Phase Flow

Out of a number of empirical correlations for friction factorsare available, only the most accurate ones are presented.

For smooth wall pipes in the turbulent flow region.

Valid over a wide range of Reynolds numbers

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(11.13)


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For rough pipes fully developed turbulent flow :

Nikuradses Correlation

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(11.14)

Note: Velocity profile and pressure gradient are very sensitive to piperoughness.


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Colebrook equation

Jain equation

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Jain presented an explicit correlation for friction factor.

(11.15)

(11.16)

Applicable to smooth pipes and transition and fully turbulent flow.Eqn is not explicit in friction factor f . Use Newton -Raphso n Iterat ion .


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Weymouth Equation for Horizontal Flow

Basic pipeline flow equation for steady state horizontal flowwhere unit of gas flow rate is in scfh(standard cubic feet/hour)is:

where q h = scf/hr

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(11.22)

(11.24)


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Variables in horizontal pipeline flow equation are;

L = length of pipe (mile)D = Diameter of pipe(in.)P 1 = upstream pressure(psia)P 2 = downstream pressure(psia)z = compressibility factorTb = base temperature(R)P b = base pressure (psia)


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When applying the above Eqn (11.22), trial and errorcalculation procedure is needed.

To eliminate trial and error calculation, Weymouth proposed

that f varies as a function of diameter in inches as follows:

(11.25)

With this simplification, Eqn (11.22) reduces to


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where q h = scf/hr

which is the form of the Weymouth equation commonly usedin the natural gas industry.

D = pipe internal diameter, inL = Length of pipe, mile

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(11.26)

With this simplification, Eqn(11.22 reduces to

h f l l


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Assumption s for use of the Weymouth equation including

no mechanical work, steady flow,

isothermal flow, Constant compressibility factor, horizontal flow, and no kinetic energy

change.

These assumptions can affect accuracy of calculation results.

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E l (1 )


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Example (1 )For the following data given for a horizontal pipeline, predict gasflow rate in cubic ft/hr through the pipeline.

The problem can be solved using (a) Equation (11.22) with the

trial-and-error method for friction factor, and (b) Weymouthequation without the Reynolds number-dependent frictionfactor(Eqn 11.26) .

Solution

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E l (1 )


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Example (1 )

The average pressure is:

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Secon d Trial :

31

(11.22)

(11.24)

(11.16)


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Third Trial :

32

(11.22)

(11.24)

(11.16)


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Q & A

4. chapter 3_gas gathering transportation_v2 (part 1)

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