1.4.1 Compressor-Pump Curves

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Compressor & Pump Curves


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2 Compressor & Pump Curves

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Workshop

In this module, compressor and pump curves will be used to model the

behaviour of simulated compressors and pumps. Using curves to model

these unit operations allows HYSYS to accurately simulate actual plant

equipment.

Learning Objectives

Once you have completed this module, you will be able to:

Specify and attach head and efficiency curves to compressors

Use single and multiple curves to model compressors

Attach head curves to pumps

Accurately model existing plant equipment with HYSYS

Prerequisites

Before beginning this module, you need to know how to:

Define and import a fluid package Add streams and unit operations to the PFD


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Compressor Curves

Using compressor curves in your HYSYS simulation allows you to

accurately model existing plant equipment. You can determine if an

existing compressor is able to meet the specifications of your process.

Using compressor curves allows HYSYS to calculate heads and

efficiencies that are dependant on the flow rate. If the flow rate through

the compressor is known to be constant, a single flow rate and efficiency

can be supplied. If, however, the flow rate is expected to change, using a

compressor curve will allow HYSYS to calculate new heads and

efficiencies based on the current flow rate.

This results in greater accuracy in the simulation, and allows HYSYS to

more closely model actual plant equipment.

Defining the Fluid Package

Before we begin any simulation in HYSYS, we must first define the

appropriate fluid package.

1. Start a New Case and add a Fluid Package.

2. Select the Fluid Package tab.

3. Select theAdd button.

4. Select the Sour PREOS package.

5. Select the Componentstab.

6. Add a components list.

7. Add the following components: H2O, H2S, CO2, C1, C2, C3, i-C4, andn-C4.


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Installing a Stream

1. Add a Material Steam to the PFD with the following data:

Adding the Compressor

1. Add a Compressorto the PFD.

2. Enter the following information on the Connectionspage:

In This Cell... Enter...

Name Feed

Temperature 70C (160F)

Pressure 130 kPa (19 psia)

Molar Flow 500 kgmole/h (1100 lbmole/hr)

Mole Fraction [H2O] 0.24

Mole Fraction [H2S] 0.07

Mole Fraction [CO2] 0.06

Mole Fraction [C1] 0.04Mole Fraction [C2] 0.11

Mole Fraction [C3] 0.25

Mole Fraction [i-C4] 0.08

Mole Fraction [n-C4] 0.15


Inlet Stream Feed

Outlet Stream Outlet

Energy Stream Comp Duty

Compressor icon


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3. On the Parameterspage, ensure that the Polytropic and Adiabaticefficiency boxes both read .

These values must read because the efficiencies will be

calculated from the compressor curves, and defining the same value in

two places will alwaysresult in a consistency error.

4. On the Curvespage (on the Ratingtab), select theAdiabaticradiobutton in the Efficiencygroup. Click theAdd Curvebutton, and

enter the data as shown here:

Figure 1

Figure 2Be sure to use the correctunits for the curve.


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5. Close the above view and activate Curve-1 on the Curvespage.Ensure that the Enable Curves box on the Curves page is checked.

6. The pressure of the outlet stream can be seen on theWorksheetpage, or you can choose Show Tablewhen object-inspecting theoutlet stream on the PFD. The compressors efficiencies can befound on the Resultspage.

Optional Exercise

It is desired to have an outlet pressure of300 kPa (44 psia).

Use an Adjust operation with the following information:

Figure 3

What is the Outlet Pressure of the compressor? __________________________

What is the Adiabatic Efficiency? ______________________________________

The Polytropic Efficiency?_____________________________________________

In This Cell... Enter...Adjusted Variable Feed - Molar Flow

Target Variable Outlet - Pressure

Specified Target Value 300 kPa (44 psia)

Step Size 5 kgmole/h (10 lbmole/hr)

Iterations 50

We do not need to enter acompressor speed becausewe are only entering onecurve. However, multiplecurves with different speedscan be used.


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Multiple CurvesTypically, industrial compressors are able to run at multiple speeds

depending on the current demand. HYSYS allows users to enter multiple

compressor curves that each represent a specified speed. Once the

curves are entered, any compressor speed can be specified and the head

and efficiency are calculated automatically.

In this exercise, a Natural Gas compressor will be examined to

determine the outlet pressure of a multi-speed compressor.

1. Begin a new case and import the fluid package Nat-Gas.fpkfrom thediskette provide with this course.

2. Add a new stream to the PFD with the following data:

What is the Molar Flow rate if the Outlet Pressure is set at 300 kPa (44 psia)?____________________________________________________________________

Can you think of an easier way of doing this? __________________________

How? _______________________________________________________________


Name LP Gas



Molar Flow Rate 1500 kgmole/h (3300 lbmole/hr)

Comp. Mole Fraction - C1 0.99



Comp. Mole Fraction - N2 0.005

Comp. Mole Fraction - CO2 0.0025

Save your case!


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3. Add a Compressorto the PFD with this data:

4. Delete the default Adiabatic Efficiency value on the Parameterspage. Again, the efficiency will be calculated from the compressorcurves.

5. Add the four curves shown below to the compressor. Note that thecurves have been supplied in Field units. (If you are using SI units,

you must change the Flow and Head units to those shown herebeforeyou enter the curve data).


Inlet LP Gas

Outlet HP Gas

Energy Comp Duty

Figure 4

Figure 5

Note that compressor speedsmust be entered here asmultiple curves are beingused.


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6. Ensure that all of the curves are activated, and the Enable Curvesbox is checked. These curves are polytropic curves, therefore the

Polytropicradio button must be checked in the Efficiencygroup onthe Curves page.

Figure 6

Figure 7

The plots for efficiency andhead versus flow can be seenby pressing the Plot Curvesbutton on the Curves page.

Instead of entering all of thecurve data, open the HYSYS

case Comp_Shortcut.hsc onthe disk supplied with thismodule, and begin on step 6.


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7. On the Curvespage, enter a speed of 11 000 per min.

Optional Exercise

1. Delete the specified compressor speed of 11 000 per minute.

2. Enter a pressure of 5000 kPa (725 psia)for the HP Gasstream.

3. HYSYS will automatically calculate the compressor speed needed tomeet this outlet pressure.

Figure 8

What is the pressure of the HP Gas stream? _____________________________

What is the compressor speed needed to achieve the specified outletpressure? ___________________________________________________________

What are the Adiabatic and Polytropic efficiencies of the compressor underthese conditions? ____________________________________________________

What is the temperature of the HP Gas? ________________________________

Save your case!


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Pump Curves

As with compressor curves, pump curves are used to allow HYSYS to

accurately model existing pumps. Pump curves allow the pressure rise

across the pump to be dependent on the flow rate of liquid.

The pump curves are entered into HYSYS using a form different than the

form used for compressor curves. With pump curves the coefficients of

an expression, up to the fifth order, are entered into HYSYS rather than

the actual data points.

Defining the Fluid Package1. Begin a new case and select the Peng RobinsonEOS package.

2. Add the components n-Hexane, n-Heptane, andn-Octane.

Installing a Stream

Add a new stream to the PFD and enter the following information:

In This Cell... Enter...Name LP Mixture



Liquid Volume Flow 500 m3/hr (76,000 BPD)

Comp. Mass Fraction (Hexane) 0.60

Comp. Mass Fraction (Heptane) 0.30

Comp. Mass Fraction (Octane) 0.10

The coefficients can beobtained from a spreadsheetprogram capable of nonlinearregression, such as EXCEL,or may be supplied by the

pumps manufacturer.


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Adding the Pump

1. Add aPumpto the PFD and enter the following information:

2. On the Curvespage, enter the following data:

3. Ensure that theActivate Curvesbox is checked.


Inlet LP Mixture

Outlet HP Mixture

Energy Pump Duty

Efficiency (Parameters Page) 75%


Coefficient A 3000

Coefficient B -2.0

Coefficient C -0.005

All Other Coefficients 0

Units for Head m

Flow Basis Act. Vol. Flow

Units for Flow m3/h

Figure 9

Pump icon


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4. The pressure of the product stream can be seen on theWorksheettab.

What is the outlet pressure of the pump?________________________________

The pump sales representative, who supplied the curve data, guaranteed an

outlet pressure of 5000 kPa (725 psia) at the specified flow rate. Should you

fill out the purchase order? ____________________________________________

Save your case!


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1.4.1 Compressor-Pump Curves

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