aspen plus simulation for performance improving of al

Journal of Mechanical Engineering Research and Developments

ISSN: 1024-1752

CODEN: JERDFO

Vol. 44, No. 4, pp. 400-411

Published Year 2021

400

Aspen Plus Simulation for Performance Improving of Al-Khayrat

Power Plant Using Heat Recovery Steam Generation (HRSG)

System

Mohammed Alhwayzee†, Hayder Jawad Kadhim‡, Farhan lafta Rashid†

† Petroleum Engineering Department, College of Engineering, University of Kerbala, Iraq ‡ Mechanical Engineering Department, College of Engineering, University of Kerbala, Iraq

*Corresponding Author Email: [email protected]

ABSTRACT

This research paper investigates the studying of how the performance and efficiency of the Al-Khairat power

plant, which is located in Kerbala city in Iraq, can be enhanced. This plant is currently operated with a simple gas

turbine cycle. A Heat Recovery Steam Generator (HRSG) principle, which depends mainly on the waste heat

energy of exhaust gases produced from a simple gas turbine unit is one method that can be utilized for enhancing.

The present plant was simulated using an Aspen HYSYS version 2016 software. Simulation results were

compared to the actual operating data, net power output, and cycle thermal efficiency at the same conditions for

validation purposes. These results show a high agreement between theoretical and practical data. This agreement

permits, gives a good realization, to use this software to simulate an overall combined cycle. In addition, operating

parameters that affect the power plant performance were investigated. The results show that at the same operating

conditions, the combined cycle improved thermal efficiency and net power output by 50.9% and 54.46%,

respectively. Also, the results revealed that the compressor pressure ratio and inlet air temperature have significant

effects on the thermal efficiency and net produced power for both simple and combined power plant.

KEYWORDS

Simple gas turbine cycle, combined power plant cycles, power plant simulation, Aspen HYSYS software, power

plant net power output, power plant thermal efficiency.

INTRODUCTION

A simple gas turbine is one of a famous class of heat engines which is widely used in power plants for electricity

generation. Mechanical output power can be produced from this engine when a working gaseous fluid with high

pressure and heat passes through a turbine unit. This output power can be utilized to generate electrical power [1,

2]. Also, due to a high temperature of exhaust gases of the turbine unit about 450-650 oC, a significant amount of

heat is lost at this simple gas turbine. Many improving methods have been modified to enhance the efficiency of

the cycle by utilizing this wasted heat [3]. A combined-cycle power plant is one method for enhancing power

plant efficiency. It consists of two co-operation units: a simple gas turbine cycle and a heat recovery steam

generator cycle (HRSG). In the steam cycle, heat is recovered from turbine exhaust gases from a simple cycle, by

transferring it to water for steam producing, and finally, this steam can be used to drive a steam turbine for power

generating [4].

Zuming Liu et al. [5] simulated a model and systematic procedure for the off-design operation of a triple-pressure

reheat Combined Cycle Gas Turbine power plant in which its full details were captured using Aspen HYSYS

software. They evaluated their model performance and simulation results by comparing them to an equivalent

model by Gate Cycle. Their results show the average differences for the thermal efficiencies and power outputs

of the three cycles: simple gas turbine cycle, steam cycle, and combined cycle plant are lower than 2.0 %, 1.5 %,

and 0.6 %, respectively. Saddiq H.A. et al. [6] studied the modeling of a simple gas turbine and gas turbine exhaust

utilizing Aspen HYSYS software for various possible configurations. They studied the effect of the operating

parameters of the power plant on the performance of simple and combined gas turbine cycles. Their results

mailto:[email protected]

Aspen Plus Simulation for Performance Improving of Al-Khayrat Power Plant Using Heat Recovery Steam Generation (HRSG) System

401

obtained gives a good indication for a gas turbine in a combined cycle power plant performance, design, and

operation.

E.N. Achimnole et al. [7] simulated a gas turbine power plant cycle for with and without air intake cooling system

using Aspen Hysys simulator. For performance evaluation, they applied the actual operating conditions. They

studied the effect of the ambient temperature on the power output and thermal efficiency, specific fuel

consumption, and heat-rate. From their analysis, they show that the simulation results give a high reality

comparing with the actual operating data. In their comparative study for Al-Kayrat power plant performance for

various fuel types, Hayder Jawad et al. [8] modeled and simulated this power plant using the Aspen HYSYS

simulator. Their simulation results show high validity comparing to the actual field conditions and data of the

plant. Many researchers [9-29] enhanced the heat transfer from the gas turbine blade using different

configurations. In this research work, an Aspen HYSYS simulator is used as a powerful tool for power plant

modeling to improve the performance of the simple gas turbine for the Al-Khairat gas power plant by making use

high amount of wasted energy which is accompanied with the exhaust outlet gases in turbine gas unit. This energy

is recovered by building a Heat Recovery Steam Generator (HRSG) model represented in a combined gas turbine

power plant. A high validation of modeling results comparing with practical data for simple gas turbine gives high

reliability to use an Aspen HYSYS for Combined Cycle modeling.

THERMODYNAMIC PRINCIPLES OF POWER PLANT CYCLES

Gas turbine cycle (Ideal Brayton cycle)

Gas turbine cycle follows thermodynamically an ideal cycle which is called Brayton. In this cycle the processes

compression and expansion can operate in the same rotating shaft. This ideal cycle can operate in closed cycle

which is consisted of the following four reversible processes as shown in figure (1): 1-2 in a compressor unit – a

process of isentropic compression, 2-3 in combustion chamber unit – a process of addition of heat at constant

pressure, 3-4 in gas turbine unit- a process of an isentropic expansion, 3-4 in a heat rejection unit - a process at

constant pressure [1, 5]. All these processes of Brayton cycle are operated under steady-state conditions. The T-S

diagram of this cycle can be seen in Figure (2).

Figure 1. Schematic diagram of Brayton Cycle


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Figure 2. Brayton cycle of T-S diagram

Steam power cycle (The simple ideal Rankine cycle)

Steam power cycle follows thermodynamically an ideal cycle which is called Rankine cycle. This ideal cycle

operates in a closed cycle which is consisted of the following four reversible processes as shown in figure (3): 1-

2 in pump unit – a process of isentropic compression, 2-3 in boiler unit – a process of addition of heat at constant

pressure, 3-4 in steam turbine unit- a process of an isentropic expansion, 3-4 in a heat rejection condenser unit - a

process of at constant pressure. The T-S diagram of this cycle can be seen in figure (4) [1].

Figure 3. Thermodynamic schematic of Rankin cycle


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Figure 4. T-S diagram of Rankine cycle

Combined cycle

Combined cycle gas plant is a modified kind of power plant which is used to produce more electricity. This type

of power plants consists of a simple cycle gas turbine power plant (ideal Brayton cycle) in combination with a

second power plant steam turbine cycle (ideal Rankine cycle). The high temperature exhaust gases from the

topping process gas turbine plant are introduced to the bottoming steam cycle to produce steam. And then it can

be expanded in a second turbine producing additional power. This led to increase the overall plant efficiency and

net produced power. This combined cycle can be schematized thermodynamically as shown in figures (5) and (6)

[1].

Figure 5. Schematic of combined cycle


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Figure 6. T-S diagram of combined cycle

MATERIALS AND METHODOLOGY

Al-Khairat power plant specifications

This plant locates in Iraq in Kerbala city in Al-khairat town. It comprises of 10 of outdoor type of a simple gas

turbine units, Unit 2 GT43 - Frame 9E. These turbines were manufactured by General Electric Company, USA.

A design out power of each unit is 125 MW. A Crude Oil is currently used as a main fuel and the back-up fuels

are Light Distillate Oil, and Natural Gas. The main specifications and operating parameters of each unit are shown

in table (1).

Table 1. Actual field operating parameters data for Al-kayrat simple gas turbine cycle SGTC power plant

Operating parameters data Values and units of data

Inlet (Intake) Temperature of Air to compressor 15 oC

outlet temperature of air from compressor 322.8 oC

Relative humidity 60 %

Pressure Ratio of Compressor 10

Fuel Mass flow-rate 6 kg/s

Lower Heating Value of fuel, LHV 43300 kJ/kg

Temperature of inlet fuel gas 50 oC

Inlet temperature of flue gases to turbine Co 970

Exhaust temperature of gases from turbine (T4) 495.7 oC

Power required for compressor 105.26 MW

Power produced by turbine 186.68MW

Net power produced by SGTC 81.42 MW

Total net power 81.42 MW

Total thermal efficiency 31.3 %

Simulation package

In this study, an Aspen HYSYS software version-2016 was used to simulate a simple gas turbine cycle and

combined cycle. This software is a powerful engineering simulation tool that can be utilized for modeling and


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simulating most of the chemical, petroleum and power plant processes. It enables the engineer to build, design

and simulate these different processes chemical using most common devices and equipment such as chemical

reactors, mixers, pumps, separators, distillation columns and other devices. HYSYS is able to perform many of

the calculations of especially for chemical engineering, including those concerned with mass and energy balances,

vapor-liquid equilibrium, heat transfer, mass transfer, chemical kinetics and reactor design, and fractionation.

Also, this program has the power to produce results that approach a great deal of reality.

Personal computer

A laptop personal computer type - hp - core i7- window 10 with high specifications was used to run the Aspen

HYSIS software. This computer is highly compatible with this version of HYSIS program.

Simulation environment and assumptions

The following assumptions were made in the simulation of combined plant, The power plants for single turbine

cycle and proposed combined cycle were simulated with the following assumptions:

1) Peng Robinson was selected as a base property package for air, fuel, and exhaust gas, and ASME steam

table for water and steam.

2) According to the interested process, the following are the main components and elements for this

simulation: crude oil as C18H38, Oxygen O2, Nitrogen N2, CO2, CO, H2O.

3) The mole percent of Oxygen and Nitrogen in air composition are 21% and 79%, respectively.

4) The crude oil is fed at pressure of 30 bar and temperature of 50 oC.

5) The polytropic efficiencies for compressor and turbine units are 80% and 85%, respectively.

6) The efficiencies of compressor and turbines are adiabatic.

7) The chemical formula of crude oil is C18H38.

8) The mechanical losses and losses in each unit (turbine, compressor, boiler and HRSG adiabatic) were

neglected.

Flowcharts preperation for cycles simulation

According to the simulation environment and assumptions, a simple gas turbine cycle of Al-Khairat power plant

and proposed combined gas turbine cycle were separately simulated using Aspen HYSYS software. Their

simulated flow chart are presented in figurs below. According to thermodynamic cycle ( Brayton cycle ),

simulation environment and assumptions, the present simple gas turbine cycle of Alkayrat power plant was

modeled and simulated using Aspen HYSYS software as shown in the flow chart below figure (7). As shown in

thermodynamic cycle. it comprised of three main sections: air compressor, combustion reactor and gas turbine

unit. The percentage of pressure drop in combustion chamber is very little and there is no drop at inlet and outlet.

Atmospheric air introduces the compressor under field conditions ( Temprature, T1= 15 oC, Pressure, P1=

101.3kPa and Relative Humidity RH= 60 % ).

Figure 7. Flow chart of a simple gas turbine model using Aspen-HYSYS simulator.


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In addition, and according to thermodynamic cycle ( Brayton cycle + Rankine cycle as shown in previous section),

simulation environment and assumptions, the simulation of suggested combined gas turbine cycle CGTC for heat

recovery purposes was also modeled and built using the same simulator as shown in the flowchart below, figure

(8). As shown in thermodynamic cycle of combined gas turbine cycle, the exhuat gases from gas turbine of simple

cycle at 550 oC are passed through steam turbine cycle to recover a heat in boiler unit to produce steam which is

finally used as awork fluid in steam turbine unit additional power producing.

Figure 8. Flow chart of simulated combined cycle gas turbine plant model using Aspen- HYSYS simulator.

RESULTS AND DISCUSSION

Simulation performance parameters results

In this work the performance parameters result for both power plants SGTC and CGTC which were obtained from

simulation process are presented in table (2). For SGTC, it can be seen that a high validation was obtained for net

power produce. Error percentage of 4.15 % was obtained by simulation process where the actual net power for

Al-kayrat plant is 81.42 MW whereas 84.78 MW for simulation results. Also, it is 83.2 MW in simulated CGTC

power plant. In addition, the total thermal efficiency for actual and simulated plant are 31.3% and 31.91 %,

respectively. The error percentage is 2.6 %. These simulation results give an indication that an Aspen-HYSIS

software has a good reliability for simulation process for CGTC. For simulated CGTC power plant a good result

was obtained for both total net power and total thermal efficiency. As illustrated in table 3, the values are 125.85

MW and 47.23 %, respectively. The percentage increase in total net power is 54.6 % and 50.9 % for total thermal

efficiency. These percentages can be considered a reasonable result to utilize the waste energy and to improve the

power plant performance.

Table 2. Performance parameters results for present work three cases: 1) SGTC for Al-kayrat power plant actual

field data), 2) Simulated SGTC power plant, 3) Simulated CGTC power plant.

Results of performance

parameters

Al-kayrat power

plant actual data

(present plant)

Simulated SGTC

power plant (present

plant)

Simulated CGTC

power plant

(suggested plant)

Net power produced by SGTC

power plant only

81.4 MW

84.78 MW

83.2 MW


407

Net power produced by SSTC

power plant only

Nil

Nil

42.65 MW

Total Net Power 81.42 MW 84.78 MW 125.85 MW

Total Thermal Efficiency 31.3 % 31,91 % 47.23

Effect of compressor pressure ratio on thermal plant efficiency

The effect of compressor pressure ratio on total thermal efficiency for both simulated power plants SGTC and

CGTC are studied. From figure (9) it can be noticed that the total thermal efficiency increased gradually as

pressure ratio increase. For the same pressure ratio the thermal efficiency at 15 oC of inlet air temperature for

CGTC plant is higher than SGTC, 47.23 % and 31.3 % at 10 pressure ratio, respectively and approximately 50

% as increase percentage is obtained. Also, it can be seen that at low values of pressure ratio ranged between 1-5

the thermal efficiency is dramatically increased for both plants.

Figure 9. Plant efficiency vs compressor pressure ratio for SGTC and CGTC power plants

Effect of compressor pressure ratio on net power

The effects of the compressor pressure ratio on the net power of both plants SGTC and CGTC are shown in figure

(10). As illustrated in previous section (effect on thermal efficiency) it can be seen that the same trends were

obtained for this effect. Also, it can be noticed that at the same pressure ratio the net produced power for CGTC

plant is higher than SGTC plant, 125. 85 MW and 81.42 MW, respectively. There is no noticeable increase in the

net power for pressure ratios more than 10 especially for CGTC power plant.

0

10

20

30

40

50

60

0 2 4 6 8 10 12 14

Th

erm

al

Eff

icie

ncy

, %

Compressor Pressure Ratio

SGTC

CGTC


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Figure 10. Net power vs compressor pressure ratio for SGTC and CGTC power plants

Effect of inlet air temperature on plant efficiency

The effects of the inlet air temperature on the total thermal efficiency of both plants SGTC and CGTC are shown

in figure (11). It can be seen that the thermal efficiency for both plants decrease slightly as the air temperature

increase. At 15 oC (actual field operating data) the thermal efficiency of CGTC power plant is higher than SGTC

plant, 47.32 % and 31.3 %, respectively. The increase percentage is approximately more than 50%.

Figure 11. Plant thermal efficiency vs air inlet temperature for SGTC and CGTC power plant.

Effect of inlet air temperature on net produced power

The effects of the inlet air temperature on the total thermal efficiency of both plants SGTC and CGTC are shown

in figure (12). As shown in previous section 4.3, the effect of inlet air temperature on the net produced power has

the same trends for both plants. It can be seen that at 15 oC, the net produced power for both plants are 81.31 MW

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14

Net

Pow

er,

MW

Compressor Pressure Ratio

SGTC

CGTC

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70

Th

erm

al

Eff

icie

ncy

, %

Inlet Air Temp. oC

SGTC

CGTC


409

for SGTC power plant and 125.85 MW for CGTC. These results show that at the same inlet air temperature CGTC

plant produces higher power than SGTC plant around 54 %.

Figure 12. Net produce power vs inlet air temperature for SGTC and CGTC power plants.

CONCLUSIONS

This research study was objective to utilize the waste energy from Al-kayrat power plant to improve its

performance. This was done by using a heat recovery steam generator unit HRSG to make use the available energy

in the exhaust gases of a simple gas turbine unit. In this work two major performance parameters, total thermal

efficiency and net produced power were used. Aspen HYSYS simulator was used to model and build a combined

gas turbine power plant using simulation process. From the study results it can be concluded that:

1- A simulation process for a simple gas turbine unit by Aspen-HYSIS software gives a good validity. It

can be considered as a reliable simulator for such power plant process.

2- The total thermal efficiency and net produced power parameters are chosen as main performance

parameters for comparison.

3- A combined gas turbine cycle power plant shows a higher performance parameters compared to a single

gas turbine cycle power plant. 54.6% as increase percentage was achieved for net produced power and

50.9% for total thermal efficiency Practically, these results can be utilized to improve the performance

of present Alkayrat power plant by adding a heat recovery steam cycle unit to get a combined gas turbine

power plant.

4- For both power plants there is no significant effect of compressor ratio on total thermal efficiency. So it

is preferable to work at 10. The same conclusion can be applied for net produced power.

5- For both power plants there is no high effect of inlet air temperature on total thermal efficiency and net

produced power of plants. It is better to work under ambient condition.

REFERENCES

[1] M.A.B. Yunus, and A. Cengel, “Thermodynamics: An Engineering Approach”, 5th Edition. 2004.

[2] Definition of Gas Turbine Accessed on 23/04/2012 from McGraw Hill dictionary of Science at

http://www.thefreedictionary.com/gas+turbine.

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70

Net

Pow

er,

MW

Inlet Air Temp. oC

SGTC

CGTC


410

[3] J. Manninen and X.X. Zhu, “Optimal Gas Turbine Integration to the Process Industries,” Ind. Eng. Chem.

Res., Vol. 38, Pp. 4317–4329, 1999.

[4] J.M. Robles, “Simulation of a Gas Power Plant”.

[5] Z. Liu and I.A. Karimi, “Simulating combined cycle gas turbine power plants in Aspen HYSYS,” Energy

Convers. Manag., Vol. 7, No. 6, Pp. 1213–1225, 2018.

[6] H.A. Saddiq, S. Perry, S.F. Ndagana, and A. Mohammed, “Modelling of Gas Turbine and Gas Turbine Exhaust

and its Utilization as Combined Cycle in Utility System,” vol. 6, no. 4, Pp. 925–933, 2015.

[7] E.N. Achimnole, E.K. Orhorhoro, and M.O. Onogbotsere, “Simulation of Gas Turbine Power Plant Using

High Pressure Fogging Air Intake Cooling System,” Vol. 5, No. 5, Pp. 16–23, 2017.

[8] H.J. Kadhim, T.J. Kadhim, and M.H. Alhwayzee, “A Comparative Study of Performance of Al-Khairat Gas

Turbine Power Plant for Different Types of Fuel A Comparative Study of Performance of Al-Khairat Gas

Turbine Power Plant for Different Types of Fuel,” 2020.

[9] A. Altaie, M.R. Hasan and F.L. Rashid, "Numerical Heat Transfer and Turbulent Flow in a Circular Tube

Fitted with Opened Rings Having Square Cross Section", Journal of Basic and Applied Scientific Research,

Vol. 4, No. 11, Pp. 28-36, 2014.

[10] R.F. Lafta, A. Arkan, H.R. Moayed, "Numerical Investigation of Heat Transfer Enhancement in a Circular

Tube Using Ribs of Separated Ports Assembly", European Scientific Journal, 2014.

[11] A. Altaie, M.R. Hasan and F.L. Rashid, "Numerical Investigation of Heat Transfer Enhancement in a

Circular Tube with Rectangular Opened Rings", Bulletin of Electrical Engineering and Informatics, Vol. 4,

No. 1, Pp. 18-25, 2015.

[12] A. Altaie, M.R. Hasan, and F.L. Rashid, "Heat Transfer Enhancement in a Circular Tube Using Ribs with

Middle Arm", Elixir International Journal, 2015.

[13] A. Altaie, M.R. Hasan, F.L. Rashid, "Numerical Investigation in a Circular Tube to Enhance Turbulent Heat

Transfer Using Opened Rings-Triangular Cross Section", Journal of Babylon University/ Engineering

Sciences, 2015.

[14] F.L. Rashid, M.W. Al-Jibory, and H.Q. Hussein, "Cooling Enhancement in Gas Turbine Blade Using Coated

Circular Ribs with a New Nanocomposite Material", Patent (5092), 2017.

[15] M.W. Al-Jibory, F. Lafta, R. Hasan, and Q. Hussein, "Heat Transfer Augmentation in Gas Turbine Blade

Rectangular Passages Using Circular Ribs with Fins", Journal of University of Babylon, Engineering Sciences,

Vol. 26, No. 1, 2018, Pp. 247-258.

[16] M.W. Al-Jibory, F.L. Rashid and S.M. Talib, "Numerical Investigation of Heat Transfer Enhancement in

Ribbed Elliptical Passage", Journal of Engineering and Applied Sciences, Vol. 13, No. 17, Pp. 7223-7234,

2018.

[17] F.L. Rashid, H.N. Azziz, and E.Q. Hussein, "Heat Transfer Enhancement in Air Cooled Gas Turbine Blade

Using Corrugated Passages", Journal of Petroleum Research & Studies, Vol. 20, Pp. 52-69, 2018.

[18] A.M. Wahhab, R. Farhan, L. Alais, and S.M. Abu, "An Experimental and numerical investigation of heat

transfer enhancement using annular ribs in a tube", IOP Conference Series: Materials Science and Engineering,

Vol. 433, No. 1, Pp. 012057, 2018.

[19] F.L. Rashid, M.W. Al-Jibory, and S.M. Talib, "Numerical Investigation of Heat Transfer Augmentation in

Elliptical Passage with Different rib Geometries and Aspect Ratios", International Journal of Mechanical

Engineering and Technology, Vol. 9, No. 13, Pp. 1390-1409, 2018.

[20] M.W. Al-Jibory, F.L. Rashid, and S.M. Talib, "An experimental Investigation of Heat Transfer Enhancement

in Elliptical Passage Fitted with Different rib Geometries", International Journal of Mechanical Engineering

and Technology, Vol. 9, No. 13, Pp. 1033-1048, 2018.


411

[21] F. Lafta, H. Qahtan, and M.W. Al-Jibory, "Heat Transfer Augmentation in Gas Turbine Blade Passages",

LAP LAMBERT Academic Publishing, 2019.

[22] A.H. Nadhom, R.F. Lafta, and H.H. Qahtan, "Simulation and Modeling of Tower Diesel Power Station in

Samawah Using Finite Element Method with MATLAB and COMSOL Programs", IOP Conference Series:

Materials Science and Engineering, Pp. 671, 2020.

[23] A.M. Wahhab, R.F. Lafta, and T.S. Mahdy, "Review on Cooling Enhancement of Different Shape Gas

Turbine Ribbed Blade with Thermal Barrier Coating", International Journal of Scientific Research and

Engineering Development, Vol. 3, No. 1, Pp. 313-329, 2020.

[24] A.M. Wahhab, R.F. Lafta, and H.H. Qahtan, "Review of Heat Transfer Enhancement in Air-Cooled Turbine

Blades", International Journal of Scientific & Technology Research, Vol. 9, No. 4, Pp. 3123-3130, 2020.

[25] H.H. Qahtan, A.M. Wahhab, R.F. Lafta, "Heat Transfer Enhancement of Gas Turbine Blades Using Coated

Ribs with Nanocomposite Materials", Journal of Mechanical Engineering Research and Developments, Vol.

43, No. 6, Pp. 09-22, 2020.

[26] R.F. Lafta., A. Ahmed, and H. Ahmed, "Geothermal Energy for Electricity Generation", British Journal of

Science, Vol. 3, No. 2, 2012.

[27] R.F. Lafta, N.O. Hani, and H. Ahmed, "Energy output of geopressured geothermal reservoir for electricity

generation", British Journal of Science, Vol. 3, No. 2, 2012.

[28] O. Amir, R.F. Lafta, and A.H. Fadhil, "Design of Circular Collector Solar Chimney Electric Power

Generation", Journal of Energy Technologies and Policy, Vol. 3, No. 6, 2013.

[29] R.F. Lafta, H.E. Qasem and A.H. Nadhom, "Design of Solar Chimney with Spherical Collector for Electricity

Production", Eastern Academic Journal, Pp. 101109, 2015.

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