Authors: Ramin Taheri Seresht & Hassan Khodaei JalalabadiPresented by: Ramin Taheri Seresht

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

The objectives of presentation:

Introduce the conventional natural gas pressure reducing station. Introduce the turboexpander & its applications. Express thermodynamically difference between throttle valve and

turboexpander. Select case study. Exergy analysis on the selected case study. Simulate the using of turboexpander in the selected case study. Economical analysis. Conclusion.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the conventional natural gas pressure reducing station

The different types of the conventional station:

1. City gate station (C.G.S.).

2. Town broad station (T.B.S.).

3. Combinatory station (C.G.S./T.B.S.).

4. Station for industrial consumptions.

5. Station for domestic consumptions.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the conventional natural gas pressure reducing station

Comparing the different types of conventional station on the base of pressure:

Type of StationInlet Pressure Outlet Pressure

psi MPa psi MPa

C.G.S. 1000 6.8 250 1.7

T.B.S. 250 1.7 60 0.4

C.G.S. / T.B.S. 1000 6.8 60 0.4

Industrial 1000 6.8 Desired Pressure

Domestic 60 0.4 60 0.4

Home Regulator 60 0.4 0.25 0.0017

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the conventional natural gas pressure reducing station

The main components of a conventional station:

1. Ball / Globe valves.

2. Filter.

3. Regulator (Throttle valve).

4. Relief valve.

5. Safety shut off valve.

6. Meter.

7. Heater.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the conventional natural gas pressure reducing station

Please pay attention:

All of types of gas stations just differ in size, inlet & outlet pressure, capacity and exitence of some components.

But all of them reduce the gas pressure by using throttle valves (regulators).

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the conventional natural gas pressure reducing station

Most important roles of the regulator in a conventional station are:

1. Reducing pressure.

2. Adjusting pressure.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the conventional natural gas pressure reducing station

How does a regulator (throttle valve) reduce the pressure?

In the throttle-valve gas pressure is reduced in result of the isenthalpic expansion.

In this process not only no energy is produced but also the energy of high-pressure gas is lost.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Could the energy of high-pressure gas be recovered?

Yes, of course.

Why not?

$

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

How could the energy of high-pressure gas be recovered?

It is so easy just by using the turboexpander.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the turboexpander & its applications

What are turboexpanders?

1. Turboexpanders are expansion turbines, rotating machines similar to steam turbines.

2. Commonly, the terms “expansion turbines” and “turboexpanders” specially exclude steam turbines and combustion gas turbines.

3. Turboexpanders can also be characterized as modern rotating devices that convert the pressure energy of a gas or vapor steam into mechanical work as the gas or vapor expands through the turbine.

4. If chilling the gas or vapor stream is the main objective, the mechanical work so produced is often considered a byproduct.

5. If pressure reduction is the main objective, then heat recovery from the expanded gas is considered a beneficial byproduct.

6. In each case, the primary objective of turboexpanders is to conserve energy.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the turboexpander & its applications

The different designing types of turboexpanders:

1. Axial Type.

2. Radial Type.

That the each of types has three typpes itself:

Impulse.

Reaction.

Complex.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the turboexpander & its applications

The different power absorption methods in turboexpanders:

1. Direct-connected compressor.

2. Gear and generator.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Introduce the turboexpander & its applications

Turboexpander applications:

1. Recovering high pressure gas energy & power generation.

2. Cryogenic process.

3. Chemical & Petrochemical industries (included: FCC process and producing Nitric acid, Acetic acid, PTA & Terephtalic acid.).

4. Oil & gas industries (included: LPG & LNG processes.).

5. Separating air components.

6. Liquefaction gases (like Helium).

7. Separating condensable components of natural gas.

8. Power generation from geothermal energy.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Express thermodynamically difference between throttle valve & turboexpander

As thermodynamically point of view:

In the throttle-valve gas pressure is reduced in result of the isenthalpic expansion.

In the throttle valve not only no energy is produced but also the energy of high-pressure gas is lost.

In the turboexpander the gas pressure is reduced in the isentropic expansion.

But in the turboexpander the energy of high-pressure gas is recoverd.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Express thermodynamically difference between throttle valve & turboexpander

On the other hand:

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case study

The C.G.S. No. 2 of Tehran was selected as case study for following reasons:

1. Existing enough space for turboexpander installation.2. Existing three heaters that they could be heated the entering gas to

turboexpander if it was needed.3. In this station, the changes of inlet pressure gas is less than the other

stations in the country.4. In this station, the changes of passed flow rate gas is less than the

other stations in the country.5. In this station, just for a few days in the year the passed flow of gas is

cut off when the annual maintenance operations are done.6. This station is next to some residential areas and a few industrial

manufacture so that, it might be used of power generation directly if it was needed.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case study

The chemical compounds of gas that is passed through the C.G.S. No. 2 of Tehran are as table:

No.

Chemical Compounds

Mole PercentName

Chemical Formula

1 Nitrogen N2 3.70

2 Methane CH4 89.80

3Dioxide Carbon CO2 1.10

4 Ethane C2H6 3.70

5 Propane C3H8 0.98

6 Iso Butane C4H10 0.22

7Normal Butane C4H10 0.29

8 Iso Pentane C5H12 0.10

9Normal Pentane C5H12 0.07

10 Hexane C6H14 0.04

Tatol 100.00

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case study

The physical properties of gas that is passed through the C.G.S. No. 2 of Tehran are as following table:

No. Physical Property Unit Quantity

1 Calculated Average Molecular Weight gr/mol 17.93

2 Calculated Gas Specific Gravity, Air = 1.000 (MW of Air = 28.964 gr/mol) --- 0.619

3 Calculated Gas Density (P = 1013.25 mbar , T = 15 °C) Kg/m3 0.758

4 Calculated Net Calorific Value (P = 1013.25 mbar , T = 15 °C)MJ/m3 34.4

Btu/ft3 920.4

5 Calculated Gross Calorific Value (P = 1013.25 mbar , T = 15 °C)MJ/m3 38.2

Btu/ft3 1020.1

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case study

The monthly average quantities of inlet pressure, outlet

pressure, outlet temperature & flow rate

of gas that is passed through the C.G.S. No. 2 of Tehran (in 1385) are

as table:

Months in 1385

Monthly Average Quantities

Inlet Pressure

Outlet Pressure

Outlet Temperature

Flow Rate

MPa psi MPa psi °C °F Nm3/hr Kg/sec

Farvardin 4.4 644 1.7 250 7.7 45.9 176,880 37.24

Ordibehesht 4.6 670 1.7 250 10.7 51.3 104,105 28.31

Khordad 4.9 726 1.7 250 8.0 46.4 170,514 35.90

Tir 5.3 775 1.7 250 8.7 47.7 154,239 32.48

Mordad 5.3 775 1.7 250 8.8 47.9 132,929 27.99

Shahrivar 4.9 726 1.7 250 10.2 50.4 184,663 38.88

Mehr 4.2 619 1.7 250 10.4 50.6 178,689 37.62

Aban 3.9 566 1.8 259 10.4 50.6 262,381 55.25

Azar 2.4 350 1.8 270 10.8 51.4 346,470 72.95

Day 2.3 337 1.7 257 10.9 51.7 427,071 89.92

Bahman 3.2 470 1.8 271 10.3 50.5 398,845 83.98

Esfand 3.0 445 1.8 267 10.4 50.8 355,395 74.83

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case studyThe curves of monthly average inlet & outlet pressure profiles in 1385 for

C.G.S No. 2 of Tehran are as follow:

The Curves of Average Inlet & Outlet Pressure Profiles in the Year of 1385

1 2 3 4 5 6 7 8 9 10 11 12

12

3

4 5

6

78

9 10

1112

0

100

200

300

400

500

600

700

800

900

1000

1 2 3 4 5 6 7 8 9 10 11 12

Months of Year

Pre

ssu

re (

psi

)

0.00.40.81.21.62.02.42.83.23.64.04.44.85.25.66.06.46.8

Pre

ssu

re (

MP

a)

Outlet Pressure Inlet Pressure

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case studyThe curves of monthly average outlet temperature profiles in 1385 for C.G.S

No. 2 of Tehran are as follow:

The Curves of Average Outlet Temperature Profiles in the Year of 1385

1

2

34 5

6 7 8 9 1011 12

1

2

34 5

6 7 8 9 1011 12

0

4

8

12

16

20

1 2 3 4 5 6 7 8 9 10 11 12

Months of Year

Tem

per

atu

re (

C)

32.0

38.0

44.0

50.0

56.0

62.0

68.0

Tem

per

atu

re (

F)

Outlet Temperature

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Select case studyThe curves of monthly average flow rate profiles in 1385 for C.G.S No. 2 of

Tehran are as follow:

The Curve of Average Flow Rate Profiles in the Year of 1385

1

2

34

5

6 7

8

9

1011

12

1

2

34

5

6 7

8

9

1011

12

03800076000

114000152000190000228000266000304000342000380000418000456000494000532000570000

1 2 3 4 5 6 7 8 9 10 11 12

Months of Year

Flo

w R

ate

(Nm

3 /hr)

0.00

12.00

24.00

36.00

48.00

60.00

72.00

84.00

96.00

108.00

120.00

Flo

w R

ate

(Kg/

sec)

Flow Rate

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Exergy analysis on the selected case study

At definition:

Exergy is maximum work (shaft work) can be obtained from a specified quantity of energy.

And exergy is equal to summation of all its components:

ChDiPhPK exexexexexex Where:

exK = kinetic exergy.

exP = potential exergy.

exPh = physical (termomechanical) exergy.

exDi = diffusion exergy.

exCh = chemical exergy.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Exergy analysis on the selected case study

In the selected case stydy:

exK = exP = exDi = exCh = 0.

And:

For calculating CP:

00

000 lnln

P

PRT

T

TTTTCex PPh

32 dTcTbTaCP

iPiPmix CxC

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Exergy analysis on the selected case study

With substituting the monthly average quantities in the recent relations is obtained:

Months in 1385Calculated Monthly Average Exergy

KJ/Kgmole KW KWhr

Farvardin 2,158.452 4,483.031 3,335,375

Ordibehesht 2,277.888 3,596.599 1,812,686

Khordad 2,406.358 4,818.085 3,584,655

Tir 2,591.160 4,693.858 3,492,230

Mordad 2,591.866 4,046.087 3,010,288

Shahrivar 2,420.588 5,248.882 3,905,168

Mehr 2,066.357 4,335.548 3,121,594

Aban 1,768.406 5,449.216 3,923,436

Azar 660.584 2,687.652 1,935,110

Day 691.912 3,469.981 2,498,386

Bahman 1,314.629 6,157.422 4,433,344

Esfand 1,167.514 4,872.566 3,391,306

Annual Summation 38,443,578

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Exergy analysis on the selected case study

The curves of monthly average exergy profiles in 1385 for C.G.S No. 2 of Tehran are as follow:

The Curves of Average Exergy Profiles in the Year of 1385

12

3

4 5

6

7

8

9 10

1112

1

2

34

5

6

7

8

9

10

11

12

500

1000

1500

2000

2500

3000

1 2 3 4 5 6 7 8 9 10 11 12

Months of Year

Exe

rgy

(KJ/

Kgm

ole)

2500

3300

4100

4900

5700

6500

Exe

rgy

(KW

)

Exergy (KJ/Kgmole) Exergy (KW)

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Simmulate the using of turboexpander in the selected case study

Simulation has been done by using the Thermoflow software at two following states:

1. One turboexpander is installed so as parallel with the station.2. Three turboexpanders are installed so as parallel with each unit

of the station.

So that each of these states has two other states:

1. Without gas preheating.2. With gas preheating.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Simmulate the using of turboexpander in the selected case studyThe state of one turboexpander and without gas preheating:

Q+

Q+

Q+

12

3

4

5

6

7

89

10

11

12

13 14

15

16

17

18

19

20

21

168.025.0126

217.0-60.8126

368.025.00

468.025.00

568.025.00

617.025.00.013

717.0-60.8126

868.025.0126

968.025.042.010

68.025.0

0

1168.025.042.012

68.025.0

0

1368.025.042.014

68.025.0

0

15

68.025.042.0

1668.025.042.0

1768.025.042.0

18

68.025.0126

1968.025.00.013

20

68.025.0

0

2168.025.00

2268.025.0

0

2317.025.0

0

2417.025.0

0

2517.025.0

0

THERMOFLEX Version 13.0 Ramin Taheri Home1130 File = H:\Final Project\Work\Modified Typed Files\Simulation Files by Thermoflow\Case 7-1-1-1.tfx 01-12-2009 15:55:03

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Simmulate the using of turboexpander in the selected case studyThe state of one turboexpander and with gas preheating:

Q+

Q+

Q+

12

34

5

6

7

89

10

11

12

13 14

15

16

17

18

19

20

21

168.025.0126

217.0-44.1126

368.045.042.0

468.045.042.0

568.045.042.0

617.045.00.013

717.0-44.0126

868.045.0126

968.025.042.010

68.025.0

0

1168.025.042.012

68.025.0

0

1368.025.042.014

68.025.0

0

15

68.025.042.0

1668.025.042.0

1768.025.042.0

18

68.045.0126

1968.045.00.013

20

68.045.0

0

2168.045.00

2268.045.0

0

2317.045.0

0

2417.045.0

0

2517.045.0

0

THERMOFLEX Version 13.0 Ramin Taheri Home1130 File = H:\Final Project\Work\Modified Typed Files\Simulation Files by Thermoflow\Case 7-1-1-2.tfx 01-12-2009 00:53:44

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Simmulate the using of turboexpander in the selected case studyThe state of three turboexpanders and without gas preheating:

Q+

Q+

Q+

12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

168.025.0126

217.0-60.842.0

317.0-60.842.0

417.0-60.842.0

568.025.00

668.025.00

768.025.00

817.0-60.8126

917.0-60.842.0

1017.0-60.842.0

1117.0-60.842.0

1268.025.042.013

68.025.0

0

1468.025.042.015

68.025.0

0

1668.025.042.017

68.025.0

0

18

68.025.042.0

1968.025.042.0

2068.025.042.0

21

68.025.042.0

2268.025.0

0

23

68.025.042.0

2468.025.0

0

25

68.025.042.0

2668.025.0

0

2717.025.0

0

2817.025.0

0

2917.025.0

0

THERMOFLEX Version 13.0 Ramin Taheri Home1130 File = H:\Final Project\Work\Modified Typed Files\Simulation Files by Thermoflow\Case 7-1-2-1.tfx 01-12-2009 01:25:57

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Simmulate the using of turboexpander in the selected case studyThe state of three turboexpanders and with gas preheating:

Q+

Q+

Q+

12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

168.025.0126

217.0-44.142.0

317.0-44.142.0

417.0-44.142.0

568.045.042.0

668.045.042.0

768.045.042.0

817.0-44.042.0

917.0-44.042.0

1017.0-44.042.0

1117.0-44.0126

1268.025.042.013

68.025.0

0

1468.025.042.015

68.025.0

0

1668.025.042.017

68.025.0

0

18

68.045.042.0

1968.045.0

0

20

68.045.042.0

2168.045.0

0

22

68.045.042.0

2368.045.0

0

24

68.025.042.0

2568.025.042.0

2668.025.042.0

2717.045.0

0

2817.045.0

0

2917.045.0

0

THERMOFLEX Version 13.0 Ramin Taheri Home1130 File = H:\Final Project\Work\Modified Typed Files\Simulation Files by Thermoflow\Case 7-1-2-2.tfx 01-12-2009 01:58:37

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Simmulate the using of turboexpander in the selected case study

The results of simulation has been summarized as following:

The States of Simullation Produced Power (KW) Produced Annual Energy (KWhr)

One Turboexpander without Gas Preheating 19,347.6 164,841,552

One Turboexpander with Gas Preheating 20,728.1 176,603,412

Three Turboexpanders without Gas Preheating 19,347.6 164,841,552

Three Turboexpanders with Gas Preheating 20,728.5 176,606,820

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Economical analysisTuboexpander price is obtainable by using following relation or figure:

7294.0(kW)Output 005312.0$)(million icePr

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Economical analysis

The local price of electrical energy is as the following table:

Year

Local Price of Electrical Energy (KWhr / Rls.)

Domestic General

1383 104.20 151.41

1387 773.00 1123.22

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Economical analysis

The global price of electrical energy is obtained by the following curve:

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Economical analysis

The results of economical calculations is summarized into the tables:

Table Legend:A = The Installation & Commissioning Cost (mil. Rls.).B = The Maintenance Cost (mil. Rls.).C = The Investment Cost (mil. Rls.).D = The Annual Income of Produuced Electrical Energy with Considering Local Price (mil. Rls.).E = The Annual Income of Produuced Electrical Energy with Considering Global Price (mil. Rls.).F = The Time of Investment Payback with Considering Local Price (Years.).G = The Time of Investment Payback with Considering Global Price (Years).

Turbine Numbers

The Price of One Turbine (mil. Rls.)

The Price of Total Procurement

(mil. Rls.)A B C D E F G

1 75,000 75,000 1,500 750 76,500 43,181 46,132 1.8 1.7

3 34,000 102,000 2,040 1,020 104,040 43,181 46,132 2.5 2.3

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Conclusion

According to that was mentioned, using turboexpanders at natural gas pressure reducing stations not only is economical but also its produced electrical energy in compare of other sources has following advantages:

1. For producing that doesn’t need to very high investment like power plants & water dams systems.

2. For producing that doesn’t need to consumption of fossil fuel.3. Producing that doesn’t emit any pollutant in environment.4. Maintenance cost of its facilities is so less than a power plant or a

water dam.5. For producing that doesn’t need to a lot personnel.6. For producing that doesn’t need to occupy a lot space.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Last Word

Using the turboexpanders at the natural gas pressure reducing stations could be a

historical opportunity.

And if we don’t apply them now, perhaps tomorrow would be too late.

Retrofit of Tehran City Gate Station C.G.S. No.2 by Using Turboexpander

Yasun Farayand Company & K.N. Toosi University of Technology

Any Question?

Thanks for your attention.