Validation and Thermal Analysis of Combined Cycle Power Plant

(CCPP) Standalone and with Multi Effect Desalination with Thermal

Vapour Desalination (MED-TVC)

Nuri Eshoul1

, Brian Agnew1, Mohammed Al-Wesahi

2, Ratha Mathkor

1

1School of Mechanical and System Engineering, Newcastle University, UK

2Shinas College of Technology, Alqr, Oman

Abstract. A combined cycle power plant (CCPP) and multi effects desalination with thermal vapor

compression (MED-TVC) desalination plant were modelled using IPSEpro software package based on

operational duties and validated against Vender and measured data respectively. Relative differences between

the model result and vender data vary from 0.37% to 1.9% for CCPP and from 0.00 to 4.3% for MED-TVC

desalination with Kamali work [1]. Energy and exergy analysis were studied for the combined cycle power

plant alone and then combined with a MED-TVC. Exergy analysis showed coupling proposed MED-TVC

desalination with combined cycle power plant is not preferable option thermodynamically, due to low exergy

efficiency of such system. The study found also gas turbine units was the main contributor of the fuel exergy

destruction; it destructs about 39% on each GT, while MED-TVC was consuming only 0.23 %, which due to

low exergy in.

Keywords: Cogeneration, exergy efficiency, exergy destruction, exergy destruction ratio, MED-TVC.

1. Introduction.

This study which is loaded on a CCPP in zawya Libya examined the preform a combined CCPP – MED-

TVC plant. The result were validated against the work of Kamali [1] Choosing this type of power plant in

this study, because there are many advantages, such as when it coupled with MED-TVC the power reduction

will not affect too much and this plant located on the coast which encourage to couple with desalination plant.

Poura et al [2] carried out a thermodynamic and exergy-environmental analyses and mult-objective

optimization of a gas turbine power plant. Their result indicated an increase in compressor isentropic

efficiency, exergy efficiency and increase gas turbine isentropic efficiency, moreover improve the objective

function also preheat the inlet air temperature will improve the function and parameters. Kazerouri V. [3]

performed a parametric study based on an energy and exergy analysis of the Abbas oil refinery gas turbines.

He included inlet air conditions to the compressor, inlet fuel conditions to the computation chamber and

steam injection to the combustion chamber in his model. The results showed that as the ambient temperature

increases the exergy and energy decrease and power output decreases. Other research work mainly has

concentrated on simulating combined cycle thermal systems in hot climates using the commercially available

software IPSEpro. The cycles studied include a gas turbine with a heat recovery steam generator (HRSG) [4].

A Mehta et al [5], Investigated how to improve cogeneration plant efficiency and reduce the exergy

destruction, using existing power plant in Izmir- Turkey. Their result indicated that, to improve cogeneration

plant efficiency and reduce exergy destruction, some improvement should be made to the heat exchanger,

then the combustion chamber.

2. Plant Description

Corresponding author.

E-mail address: (N.M.M.ESHOUL1@NEWCASTLE.AC.UK).

20

2015 5th International Conference on Environment Science and Engineering

Volume 83 of IPCBEE (2015)

DOI: 10.7763/IPCBEE. 2015. V83. 4

Figure 1 shows the studied power plant; it has total power production of 468 MW (at 15 °C and 60%

relative humidity). The GT exhaust is directed to heat recovery steam generator (HRSG), which produces

high pressure stream (HP) to high pressure steam turbine [6] to produce further power, and low pressure for

Low pressure steam turbine (LP). On the other hand when the CCPP coupled with proposed MED-TVC

desalination plant part of low pressure steam extracted to MED-TVC ejector as shown in figure 1. This

steam is used to heat the seawater in the MED-TVC after leaving the ejector to the first stage of MED-TVC

and then return back to the power plant deaerator after mixing with the condensate that coming from turbine

condenser. The steam power is reduced when the CCPP coupled with desalination. Figure 5. Shows the

proposed MED-TVC plant which was validated with kamali result [1]. To build up the plant model

components IPSEpro software package was used at different operating scenarios [7, 8]. As can be seen in

figure 1. A combined cycle power plant was built and validated against vender data and it shows a good

agreement. Figures (2-4) show the validation results, which proved that the model was working properly and

the variation was lee than 5% was assessed by the calculation of relative difference between vender data (Xi)

and model result (Yi) [9].

N

ee

i

2

(1)

Where 100xx

yxe

i

iii

(2)

Table 2 shows the comparison between result obtained from MED-TVC model and kamali result [1]. As

can be seen a good agreement was found. To perform this study and achieves its aims, two different

scenarios were be examined. Running the Standalone combined cycle power plant, which produced only

power from GT, produce steam from the HRSG to generate power from steam turbine (ST). While scenario

two the combined cycle will couple with MED-TVC desalination plant to produce portable water, which

mean a part of steam produced from HRSG will extracted from steam turbine.

Fig. 1: Snapshot for CCPP model

21

Fig. 2: Effect of ambient temperature on GT power Fig. 3: Effect of ambient temperature on total power

33

34

35

36

37

10 15 20 25 30 35 40

Eff

icen

cy

( %

)

Ambient temperature ( C )

Eff. VenderEff. Model

Fig. 4: Effect of ambient temperature on plant efficiency

3. Methodology.

Total electrical power produced from the CCPP plant is the GT1, GT2 and ST output minus the

auxiliaries’ plant power consumption [4].

AuxSTGTnet WWWW (3)

The overall thermal efficiency of the standalone CCPP ( ) can calculated by;

100xxLHVm

W

gas

netI

(4)

Where is the gasm is the natural gas flow rate and is the lower heating value. When the power plant

is coupled to a thermal desalination plant the heat utilization factor can be calculated by;

LHVm

QWHUF

gas

TVCMEDnet

(%) (5)

Although, TVCMEDQ is the heat supplied to the ejector of the MED-TVC. Both products

TVCMEDnet QandW have the same units but are different in quality. Where, the Exergy is defined as a

maximum obtainable useful work when a stream is moved from its initial state to the dead state at the

environment temperature T0 and environment pressure P0 [10, 11].

The total exergy (ET) for any stream can be defined as;

KEPOCHPHT EEEEE (6)

Where KEandPOEPHEEE

CH

,,

, are the total of physical, chemical, potential and kinetic exergies

respectively. However, the specific exergy is the total exergy divide by the mass flow rate of the stream.

m

Ee T

T

(7)

22

Accordingly, the specific exergy is a sum of the exergies of a defined stream;

KEPOCHPHT eeeee (8)

Since the stream is assumed at rest relative to the environment, CHPOandee are considered negligible

[10, 12, 13]. While physical exergy of the stream is defined as;

000 ssThhePH (9)

Where h, and s are enthalpy (kJ/kg) and entropy (kJ/ (kg.k)) of the stream, h0, s0, T0. Moreover, to obtain the

chemical exergy of the stream with i components with x mass concentration the following equation is used

[14].

Gi

n

i

iCHOi

n

i

iCH xXRTeXe ln0 (10)

Where G is the change in free Gibbs energy which is negligible at low pressure gas mixture [15]. The

CHe is the standard chemical exergy of the stream composition and obtained from [10].

The exergy efficiency can be defined as a ratio of the network output to the fuel exergy to thermal

system;

in

usefulnet

IIE

EW

(11)

In the case of the cogeneration system, where useful heat beside the network can be used in other process,

exergy efficiency is obtained by [10].

in

usefuloutnet

IIE

EW

, (12)

Exergy destruction rate can be evaluated by two ways, either with respect to total input exergy of the fuel

totfuel

DD

E

Ey

,

(13)

Table 1: Summarize the Exergy analysis method of the studies on combined cycle power plant.

Equipment Efficiency (%) Exergy destruction (MW)

GT1

321 EEE

Wout

outWEEE 321

GT2

232221 EEE

Wout

outWEEE 232221

HPT

2926 EE

Wout

outWEE 2926

MPT

3028 EE

Wout

outWEE 3028

LPT

3231 EE

Wout

outWEE 3231

HRSG1 43

141375

EE

EEEE

75431312 EEEEEE

HRSG2 2423

40201825

EE

EEEE

242518244020 EEEEEE

Condenser 3632

2433

EE

ccpEE

35343233 EEEE

Deaerator 109

1411

EE

EE

1411109 EEEE

Stack ---

244 EE

Desalination MED-

TVC

--- 39191 EXETVC

23

Fig. 5: Multi effect desalination with thermal vapor compression plant (MED-TVC)

Table 2: A compression between Kamali et al [16] result and model result

Parameter, unit Kamali Result Model Result Variation %

Total distillate product, tone/day 1536 1536.192 0.0125

Seawater temperature °C 35 35 0

Motive steam, ton/day 200 200 199.504 0.247

Feed water temperature °C 39 39 0

NO. of effects 7 7 0

First effect temperature °C 67.5 67.521 0

Condenser temperature, °C 48 48.018 0.031

Steam pressure, bar 10 10 0

Boiler temperature °C 188 179.98 4.2

GOR 7.7 7.70 0

Table 3: Summarize the Exergy analysis method of the studies on MED-TVC plant.

Equipment Calculation method Unit

Seawater pump Exergy in E2 –E1 MW

Brian pump Exergy in E6 – E7 MW

Distillate pump Exergy in E9 – E10 MW

Pumps input exergy in 1097612)75.0/1( EEEEEEx MW

Heating system exergy in E16 MW

Exergy in MW

Minimum separation factor = E6-A + E4-A + E12 -A MW

Exergy efficiency 10976121246 75.0/1/ EEEEEEXEEE AAA

%

Exergy destroyed in pumps 109761275.0/125.0 EEEEEEXX

MW

Exergy destroyed in condenser = E2 + E14 – E3 – E8 MW

Exergy destroyed in ejector = E15 + E16 –E17 MW

Exergy destroyed in effects E5+E17-E7-E13-E12-E11 MW

Exergy destroyed in products E9-E9-A MW

Exergy destroyed in brain disposal E6-E6-A MW

Exergy destroyed in condensate E2+E14-E3-E8 MW

24

4. Results and Discussions.

The results obtained from the two scenarios, standalone combined cycle power plant and CCPP coupled

with proposed MED-TVC desalination plant at T0 = 21.45 °C and P0 = 1.013 bar and sea water temperature

= 35 °C. The GT power are same since both units are running at full load for the two scenarios. In addition,

both HRGS production are also the same for scenario one and scenario two, as a result of that the steam `was

produced from the gas turbine exhaust. However, the LPT power was reduced by 32.5% when the part of the

steam extracted to MED-TVC desalination.

39

.93

39

.93

2.2

2

0.6

9

2.8

9

4.1

6

4.1

1

0.9

7

1.4

2

3.4

4

0.2

3Exer

gy d

estr

uct

ion

rat

io (

%)

Plant equipment

Fig. 6: Plant equipment exergy efficiency Fig. 7: Exergy destruction ratio on plant equipment

Tables 1 and 3 are showing the models simulation results of the thermodynamic properties of the

numbered streams in figures 1 and 5. These properties are used to perform the plant exergy estimated in the

two scenarios. During the calculation step, air streams physical and chemical exergies for both gas turbine

inlet are vanishes since they are at T=T0 and P=P0 [10]. Table 1 equations were used to calculate the

equipment exergy efficiency of CCPP which was found at level of 44.25% and exergy destruction ratio. It is

important emphasis the exergy efficiency of the MED-TVC desalination proposed was found at level 5.2%.

In addition, table 4 shows equations which were used to calculate equipment exergy destruction of MED-

TVC. Exergy efficiency for the two scenarios is calculated using equation 11. It was found on the two

scenarios exergy efficiency are 44.252% and 44.123% respectively. The reduction of exergy efficiency at

scenario two is due to less exergies efficiency of the MED-TVC unit which was only 5.2% [17]. Moreover,

the total power production was reduced by about 5%. Therefore, operating the combined cycle with thermal

desalination systems such as, MED-TVC is not preferable option from energetic analysis due to low exergy

efficiencies of such systems. This result was opposed with HUF, which found coupling the MED-TVC

desalination system of combined power plant achieved high heat utilization rose by about 18%. The exergy

analysis expanded more than obtaining the equipment that responsible for input fuel exergy destruction.

Figure 6. Shows the exergy efficiency of the plant equipment at the two scenarios. As can be seen from the

figure the exergy efficiency for plant main equipment such as GT, HRSG, HPT and LPT remains same at

different operating configurations because either they stayed at same operating condition, such as GT or the

change in component inlet exergy associated with it relatively same change in the output exergy that

responsible for input fuel exergy destruction. But the exergy efficiency of the deaerator has slight change

from 53.4% to 53.7 % due to the variation in return condensate flow from MED-TVC distillate. Although it

was observed exergy that the efficiency of the condenser was decreased by 6.5% but that is not significant

since the input exergy to condenser from the total fuel exergy was low. In addition, it was noticed that exergy

efficiency of the MED-TVC unit was 5.2 % [14]. However, the overall exergy destruction was to low 1.34

MW, due to very low exergy input about 1.42MW for MED-TVC distillation plant. To find the irreversibility

resource in the plant. Exergy destruction (MW) and exergy destruction ratio are obtained using equation 12

and 13. Table 6 shows the energy destruction of plant equipment at the two operating configurations.

Whereas figure 7 describes the exergy destructions ratio for various cogeneration plant equipment. It was

found on the two scenarios gas turbines and its component are the main source of plant exergy destruction, it

counts 24% at scenarios 1 and scenarios 2 [18-20].The study found also that rejected exergy to atmosphere

25

through the stack was at 3.4 % for scenario 1 scenario 2. The exergy destruction ratio of the plant equipment

is shown at figure 7. As can be seen GT has the highest exergy destruction ratio about 40%, followed by

HRGS 4.16%, while MED-TVC has only 0.23% due to low exergy in.

5. Conclusion

This paper was carried out to build, validate and assessment the thermal analysis of existing combined

cycle power plant and proposed MED-TVC desalination plant using IPSEpro software by using energy and

exergy analysis. The result showed that the CCPP model has good result with vender data. Moreover, the

proposed MED-TVC model also has a good agreement with measure data Kamali et al. The study noticed

that the energy analysis represented in electrical efficiency and heat utilization factor was lacking on

evaluating cogeneration power and water plant performance due to different of plant output product, either in

quality or quantity. However, the exergy showed a powerful tool on estimating plant performance and

pinpointing sources of exergy destruction among plant equipment. The exergy analysis showed coupling

proposed MED-TVC desalination with combined cycle power plant is not preferable option

thermodynamically, due to low exergy efficiency of such system. The study found also gas turbine units was

the main contributor of the fuel exergy destruction; it destructs about 40% on each GT, while MED-TVC

was consuming only 0.23 %, which due low exergy in.

NOUENCLATURE

E Rate exergy flow in stream (MW) e Specific exergy of stream (kJ)

G Gibbs energy (kJ) h Enthalpy of the stream (J/kg)

P pressure of the stream (pa) S Entropy of the stream (kJ/kg.k)

T Temperature of the stream (°C) Y Exergy destruction ratio

Greek Symbols

ɳ Efficiency of fuel chemical exergy ξ Coefficient of fuel chemical exergy

Subscripts

0 Dead state CH Chemical

I Component Ii Exergy

D Destruction KE Kinetic energy

PH Physical PO Potential

T Total stream X Mass fraction

6. References

[1] Kamali, R.K., et al., Thermodynamic design and parametric study of MED-TVC. Desalination, 2008. 222(1–3): p.

596-604.

[2] Ahmadi Pouria and D. Ibrahim, Thermodynamic and exergonevironmental analysis, and multi-objective

optimization of a gas turbine power plant APPLIED Thermal Engineering, 2011. 31.

[3] Kazerouni, V. and G. Karimi, Energy and exergy analysis of a recuperative gas turbine with steam injection: a

parametric study. Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy,

2013: p. 0957650912467452.

[4] Al - AlWeshahi A. Mohamed, et al., Validation of simulation model for cogeneration power and water

desalination plant. International journal of modeling and optimization, 2013. 3.

[5] Mehta Parth, N., N. Mehta, and C. Panchal, Exergy Analysis of a Cogeneration Plant. Exergy, 2014. 1(3).

[6] Al-Hawaj, O.M. and H. Al-Mutairi, A combined power cycle with absorption air conditioning. Energy, 2007.

32(6): p. 971-982.

[7] Sim Tech Simulation Technology, I.P.S.M.M.D.K., second ed. Sim Tech, Austria, 2005.

[8] Tech, S., Simulation Technology, IPSEpro Simulation Desalination process Library Manual,. Sim Tech, Austria,

2005(second ed. ).

[9] Dubey, S. and G. Tiwari, Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water

heater. Solar Energy, 2008. 82(7): p. 602-612.

26

[10] Bejan, A. and M.J. Moran, Thermal design and optimization. 1996: John Wiley & Sons.

[11] I. Dincer, M.A.R., Exergy, Energy, Environment and Simulation Development,, Exergy Elsever, Oxford, 2007.

firs ed.

[12] Kotas, T.J., The exergy method of thermal plant analysis, 1985. London ao: Butterworths.

[13] I. Dincer, M.A.R., Exergy,, Thermal Energy Storage Systems and Applications, . 2011. second ed., John Wiley &

sons, Oxford.

[14] Vosough, A., et al., Exergy concept and its characteristic. International Journal of Multidisciplinary Sciences and

Engineering, 2011. 2(4): p. 47-52.

[15] Ahmadi, P. and I. Dincer, Thermodynamic analysis and thermoeconomic optimization of a dual pressure

combined cycle power plant with a supplementary firing unit. Energy Conversion and Management, 2011. 52(5): p.

2296-2308.

[16] Kamali, R. and S. Mohebinia, Experience of design and optimization of multi-effects desalination systems in Iran.

Desalination, 2008. 222(1): p. 639-645.

[17] Al-Weshahi, M.A., A. Anderson, and G. Tian, Exergy efficiency enhancement of MSF desalination by heat

recovery from hot distillate water stages. Applied Thermal Engineering, 2013. 53(2): p. 226-233.

[18] Ameri, M., P. Ahmadi, and S. Khanmohammadi, Exergy analysis of a 420 MW combined cycle power plant.

International Journal of Energy Research, 2008. 32(2): p. 175-183.

[19] Cihan, A., O. Hacıhafızoglu, and K. Kahveci, Energy–exergy analysis and modernization suggestions for a

combined‐cycle power plant. International journal of energy research, 2006. 30(2): p. 115-126.

[20] Shi, X. and D. Che, Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat

recovery and utilization system. International journal of energy research, 2007. 31(10): p. 975-998.

27