06_gasgathering

Gas Gathering 1

Gas Gathering

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© 2003 AspenTech. All Rights Reserved.EA1031.31.0506 Gas Gathering.pdf

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WorkshopIn this example, a gas gathering system located on varied terrain is simulated using the steady state capabilities of HYSYS. The following figure shows the physical configuration of this system superimposed on a topographic map. The system consists of four wells distributed over an area of approximately 2.0 square km, connected to a gas plant via a network of pipelines.

The gas in this case is varied, both sour and sweet gas are being combined in the pipeline, as well as a gas condensate mixture. A Mixer combines all of the incoming gas streams from the outlying wells into one common header. Flowlines extending from this central site to each of the individual wells are modelled in HYSYS using the Pipe Segment operation. Since the plant is located in an area with mixed terrain, the elevation changes, must be accounted for in the Pipe Segments.

Additional Mixer operations are used to model mixing points where flows from remote wells are combined in common lines.

Figure 1

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Learning ObjectivesOnce you have completed this module, you will be able to use the Pipe Segment in HYSYS to model pipelines.

PrerequisitesBefore beginning this module you need to know how to add streams and unit operations.

Process OverviewPipe Diameters for each of the branches are:

Schedule 40 steel pipe is used throughout and all branches are buried at a depth of 1 m (3 ft). All pipes are uninsulated.

Pipe Branch Diameter

Branch 1 76.2 mm (3")

Branch 2 101.6 mm (4")

Branch 3 76.2 mm (3")

Branch 4 101.6 mm (4")

Branch 5 76.2 mm (3")

Branch 6 152 mm (6")

Branch 7 152 mm (6")

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Elevation data for each of the branches are provided in the following table. Branches that traverse undulating terrain have been subdivided into a number of segments with elevation points assigned at locations where there is a significant slope change. Such locations in the network are labeled on the schematic diagram with the elevation value in italics.

Branch Segment Length

meters (feet)

Elevation

meters (feet)

Elevation Change

meters (feet)

Branch 1 GasWell 1 639 (2095)

1 150 (500) 645 (2110) 6 (15)

2 125 (410) 636.5 (2089) -6.5 (-21)

3 100 (325) 637 (2090) 0.5 (1)

Branch 2 GasWell 2 614 (2015)

1 200 (665) 637 (2090) 23 (75)

Branch 3 GasWell 3 635.5 (2085)

1 160 (525) 648 (2125) 12.5 (40)

2 100 (325) 634 (2080) -14 (-45)

3 205 (670) 633 (2077) -1 (-3)

Branch 4 Branch 1 & 2 637 (2090)

1 355 (1165) 633 (2077) -4 (-13)

Branch 5 GasWell 4 632.5 (2075)

1 180 (590) 625 (2050) -7.5 (-25)

2 165 (540) 617 (2025) -8 (-25)

Branch 6 Branch 3 & 4 633 (2077)

1 300 (985) 617 (2025) -16 (-52)

Branch 7 Branch 5 & 6 617 (2025)

1 340 (1115) 604 (1980) -13 (-45)

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Building the SimulationThe gas field will be modelled using the Peng Robinson property package. The fluid package needs to contain the components from the Getting Started module as well as the oil components from the Gas Chromatograph module.

Rather than adding the components and the oil again, open the case from the Oil Characterization module (containing the four Gas Well streams).

The following components should appear in the fluid package, N2, H2S, CO2, C1, C2, C3, i-C4, n-C4, i-C5, n-C5, C6, C7+*, H20, NBP[0]92*, NBP[0]171*, NBP[0]243*, NBP[0]322*, NBP[0]432*.

The four streams should have the following values:

Adding the Pipe SegmentsThe pipe segment is used to simulate a wide variety of piping situations ranging from single/multiphase plant piping with rigorous heat transfer estimation, to large capacity looped pipeline problems. It offers the common pressure drop correlations developed by Gregory, Aziz, and Mandhane, and Beggs and Brill. A third option, OLGAS, is also available as a gradient method. In addition there are a large number of specialty pressure drop correlations available. Consult the on-line help and the manual for more information on these methods. Four levels of complexity in heat transfer estimation allow you to find a solution as rigorously as required while allowing for quick generalized solutions to well-known problems.

GasWell 1 GasWell 2 GasWell 3 GasWell 4

Temperature °C (°F) 40 (105) 45 (115) 45 (115) 35 (95)

Pressure kPa (psia) 4135 (600) 3450 (500) <empty> <empty>

Flow kgmole/h (lbmole/hr) 425 (935) 375 (825) 575 (1270) 545 (1200)

If you are using Field units, the oil components will have different names, corresponding to the different NBP.

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The pipe segment offers three calculation modes: Pressure Drop, Flow, and Length; the appropriate mode will automatically be selected depending on the information supplied. In order to solve the pipe, you must supply enough information to completely define both the material balance and energy balance.

In this simulation, we will be using seven individual pipe segment operations in the gathering system. In addition, each Pipe Operation may contain multiple segments to represent the various elevation rises and drops.

Adding the first Pipe Segment

1. Double-click on the Pipe Segment icon.

Connections page

On the Connections page, the Feed, Product and Energy stream connections are made.

2. Complete the Connections page as shown below:

Figure 2

Pipe Segment icon

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Parameters page

On this page, you can select the gradient method which will be used for two-phase (VL) flow calculations. The options are:

• Aziz, Govier & Fogarasi• Baxendell & Thomas• Beggs & Brill• Duns & Ros• Gregory, Aziz, Mandhane• Hagedorn & Brown• HTFS, Liquid Slip• HTFS, Homogeneous Flow• OLGAS2000_2P• OLGAS2000_3P• Orkiszewski• Poettman & Carpenter• Tacite Hydrodynamic Module• Tulsa99

For all of the pipes in this example, use the Beggs and Brill correlation for two-phase flow.

The pressure drop for the pipe can be supplied on the Parameters page. In this example, it will be left empty and calculated.

Rating tab

Sizing page

On the Sizing page, you construct the length-elevation profile for the Pipe Segment. Each pipe section and fitting is labeled as a segment. To fully define the pipe sections segments, you must also specify pipe schedule, diameters, pipe material and a number of increments.

The first pipe, Branch 1 is broken into three segments.

For single phase streams, the Darcy equation is used for pressure drop predictions.

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3. Add the first segment to the pipe unit operation by clicking the Append Segment button. Specify the following information for the segment.

4. To specify the diameter, click the View Segment button.

5. Select Schedule 40 as the Pipe Schedule.

6. From the Available Nominal Diameters group, select 76.20 mm (3 inch) diameter pipe and click the Specify button. The Outer and Inner Diameter will be calculated by HYSYS.

7. Use the default Pipe Material, Mild Steel and the default Roughness, 4.572e-5 m (0.0018 inch).

8. Two more segments are needed to complete the branch.

In this cell... Enter...

Fitting/Pipe Pipe

Length 150 m (500 ft)

Elevation Change 6 m (15 ft)

In this cell... Enter... Enter...

Segment 2 3

Fitting/Pipe Pipe Pipe

Length 125 m (410 ft) 100 m (325 ft)

Elevation -6.5 m (-21 ft) 0.5 m (1 ft)

Schedule 40 40

Nominal Diameter 76.2 mm (3 inch) 76.2 mm (3 inch)

Horizontal pipe sections have an Elevation of 0. Positive elevation indicates that the outlet is higher than the inlet.

HYSYS contains a database for three pipe schedules, 40, 80 and 160.

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When all three segments have been added and defined, the view should look like this:

The Pipe Segment is not yet able to solve because we have not specified any information about the heat transfer properties of the pipe.

Heat Transfer page

On this page, you select the method that HYSYS will use for the heat transfer calculations.

You have the option of specifying the heat transfer information By Segment or Overall.

• By Segment. You specify the Ambient Temperature and HTC (Heat Transfer Coefficient) for each segment that was created on the Dimensions page.

• Overall. One of four heat transfer methods will be applied to the whole pipe segment.

• Duty Method. If the Overall heat duty of the segment is known, the energy balance can be calculated immediately. Each increment is assumed to have the same heat loss.

• Stream Temperatures. If both inlet and outlet and ambient temperatures are specified, a linear profile is assumed and the overall heat duty can be calculated.

• Overall Heat Transfer Coefficient Specified. If the overall HTC and Ambient Temperature are known, then rigorous heat transfer calculations are performed on each increment of the pipe.

Figure 3

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• Heat Transfer Coefficient Estimation. The overall HTC can be found from its component parts.• Inside Film Convection• Outside Conduction/Convection• Conduction through Insulation

For all pipes in this simulation, use the Estimate HTC method.

9. Switch to the Overall HTC radio button, and enter an Ambient Temperature of 5°C (40°F)

10. Switch to the Estimate HTC page, and complete it as follows:

Figure 4

What is the outlet pressure of Branch 1? _______________________________

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Completing the SimulationNow add the remaining unit operations to your case.

1. Add two Pipe Segments with the following values:


Connections

Name Branch 2

Inlet GasWell 2

Outlet B2 Out

Energy B2-Q

Dimensions

Segment 1


Elevation 23 m (75 ft)

Nominal Diameter 101.6 mm (4 in)

Schedule 40

Heat Transfer

Estimate the Inner, Outer and Pipe Wall HTC

5° Ambient temperature


Connections

Name Branch 3

Inlet GasWell 3

Outlet B3 Out

Energy B3-Q

Dimensions

Segment 1


Elevation 12.5 m (40 ft)


Segment 2


Elevation -14 m (-45 ft)


Segment 3

Remember for all pipes in this example, use Schedule 40, an Ambient Temperature of 5°C and do not estimate the HTC for Insulation.

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2. Add a Mixer with the following information:

3. Add two Pipe Segments to your case with the values provided in the following tables.




Heat Transfer



Connections

Name Junction 1

Inlets B1 Out, B2 Out

Outlet J1 Out

Parameters

Pressure Assignment Set Outlet to Lowest Inlet


Connections

Name Branch 4

Inlet J1 Out

Outlet B4 Out

Energy B4-Q

Dimensions

Segment 1




Heat Transfer



Connections

Name Branch 5

Inlet GasWell 4


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4. Add a second Mixer to your case.

5. Add a Pipe Segment to your case.

Outlet B5 Out

Energy B5-Q

Dimensions

Segment 1


Elevation -7.5 m (-25 ft)


Segment 2




Heat Transfer



Connections

Name Junction 2


Outlet J2 Out

Parameters

Pressure Assignment Equalize All

What is the pressure of GasWell 3? _____________________________________

How was this calculated? _____________________________________________


Connections

Name Branch 6

Inlet J2 Out

Outlet B6 Out

Energy B6-Q

Dimensions

Segment 1



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6. Add a Mixer to the simulation.

7. Add another Pipe Segment to the simulation with the following values:



Heat Transfer



Connections

Name Junction 3


Outlet J3 Out

Parameters

Pressure Assignment Equalize All

What is the pressure of GasWell 4? _____________________________________

How was this calculated? _____________________________________________


Connections

Name Branch 7

Inlet J3 Out

Outlet B7 Out

Energy B7-Q

Dimensions

Segment 1




Heat Transfer



Save your case!

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Optional

Analyzing the ResultsIf you saved your case as a template, close the template and open the saved case.

The Profiles page on the Performance tab provides a summary table for the segments which make up the Pipe Segment. The distance, elevation and number of increments are displayed for each segment.

By clicking the View Profile button, you access the Pipe Profile view, which consists of a Table tab and a Plot tab. The Table tab shows the following information for each increment along the Pipe Segment.

• Length• Elevation• Pressure• Temperature• Heat Transferred• Flow Regime• Liquid Holdup• Friction Gradient• Static Gradient• Accel Gradient• Bulk Liquid and Vapour Reynolds Number• Bulk Liquid and Vapour Velocity

The Plot tab graphically displays the profile data that is listed on the Table tab.

Convert your case to a template and save!

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Open the property view for Branch 1 and examine the Table and Plots on the Profiles page of the Performance tab.

Figure 5

Figure 6

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Exploring the Simulation

Exercise 1: Pipe FlowThe flow of gas being produced by GasWell 2 increases to about 1000 kgmole/h (2200 lbmole/hr). Can the existing pipeline handle this increased flow? If not, what pipe is limiting the flow in the system? What size will be required for this branch? Do any other parts of the pipeline need to be changed?

ChallengeYou instruct your summer student, Peter Reynolds to go out to the field and measure the temperature and pressure of the gas that is being delivered to the Gas Plant. He reports that the temperature is 38°C (100°F) and the pressure is 7457 kPa (1080 psia). Using your HYSYS simulator, what do you find the pressure of each of the Gas Wells to be?

Hint: you will have to make some changes to the simulation in order for it to solve completely.

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