Thermoeconomic Analysis Of Combine Cycle Power Plant

Thermoeconomic Analysis Of Combine Cycle Power Plant

Thermoeconomic Analysis Of Combine Cycle Power Plant Kirit L. Kachhelaa (ShriSadVidyaMandal Institute of Technology, Bharuch, Gujarat) Dr. R. G. Kapadia(ShriSadVidyaMandal Institute of Technology, Bharuch, Gujarat)

Abstract

In this research paper thermoeconomic analysis of the combine cycle power plant is carried out. The aim of this new methodology is to find out Exergy Production Cost (EPC) of the combine cycle power plant under study. The exergy analysis of this plant is carried out with the simulator software Cycle-Tempo. Exergy analysis shows that maximum exergy destruction occurs in the combustion chamber followed by gas turbine, LP steam turbine, compressor, Heat Recovery Steam Generator (HRSG) and condenser. HP steam turbine is having maximum exergetic efficiency while combustion chamber is having second highest exergetic efficiency among all components. Pressure ratio of compressor and gas turbine, turbine inlet temperature and mass flow are considered as decision variables for calculating capital cost of components and Exergy Production cost. With the help of thermoeconomic analysis EPC of plant comes 6.315 Rs/kWh.

1. Introduction

   Generally, the performance of thermal power plants is evaluated through energetic performance criteria based on first law of thermodynamics, including electrical power and thermal efficiency. In recent decades, the exergetic performance based on the second law of thermodynamics has found as useful method in the design, evaluation, optimization and improvement of thermal power plants. The exergetic performance analysis can not only determine magnitudes, location and causes of irreversibilities in the plants, but also provides more meaningful assessment of plant individual components efficiency. These points of the exergetic performance analysis are the basic differences from energetic performance analysis. Therefore, it can be said that performing exergetic and energetic analyses together can give a complete depiction of system characteristics. Such a comprehensive analysis will be a more convenient approach for the performance evaluation and determination of the steps

   towards improvement [1-3].Combined Cycle Power Plants (CCPP) and related technologies have been mature enough due to almost three decades of experience and implementation in power production eld. The development of heat recovery steam generators (HRSG) with more than one pressure level and with reheating sections meets the need to exploit better the enthalpy available at the gas turbine exhaust, reducing the exergy losses in heat exchange between hot gases and water [4,5].

   The design of CCGT power plants is commonly complex due to the presence of two different power cycles which are coupled through the heat recovery steam generator (HRSG). As common practice, gas and steam turbines are selected within a set of commercially available ones, while the HRSG is the only component of a combined cycle which can be tailored specically for each gas turbine unit and for each specic plant. Improvement of the HRSG for a combined cycle can be conducted by many approaches [6].

   Thermoeconomics is nowadays a powerful tool to study and optimize an energy system. In its application led is the evaluation of utility costs as products or supplies of production plants, the energy costs between process operations or of an energy converter. Those costs are applicable in feasibility studies, in investment decisions, on comparing alternative techniques and operating conditions, in a cost-effective section of equipment during an installation, an exchange or expansion of an energy system [7].Exergetic production cost (EPC) is a new method developed for the analysis of thermal systems. The developed technique has as objective to find out total operating costs of the plant (EPC), assuming a xed rate of electricity production and process steam [8].

   The objective function is to find out thermoeconomic analysis of combine cycle power plant with Exergy Production cost of the product of the plant. Pressure ratio of compressor and gas turbine, turbine inlet temperature and mass flow are considered as decision variables for calculating capital cost of components and

   Nomenclature

   m mass flow rate (kg/s)

   E energy (kJ/kg)

   Ex exergy (kJ/kg)

   e exergy of matter (kJ/kg)

   h enthalpy (kJ/kg)

   s entropy (kJ/kg*K)

   Q heat (kJ)

   W work (kJ)

   PEC purchase equipment cost ($/kW) P pressure (MPa)

   T temperature (0C)

   f annuity factor

   CP construction period

   k annuity factor (years)

   c specific cost value ($/kWh)

   Pele purchased electricity cost ($/kWh) H operation hour (h)

   Z equipment cost rate ($/h)

   ri rate of inflation (%)

   efficiency

   maintenance factor

   Ep power developed (kW)

   Subscripts

   i inlet

   o outlet

   0 atmospheric conditions

   k component

   d destruction

   ac air compressor

   cc combustion chamber

   gt gas turbine

   HRSG heat recovery steam generator st steam turbine

   gen generator

   cond condenser

   ex exergy based

   el electricity

   s steam

   req required

   p product

   x constituent

   Superscript

   ph physical

   ch chemical

   Exergy Production cost. Those parameters areselected because of their effect over the power generated and the purchase costs of the components. The EPC equation is developed as a function of these operating parameters.

2. Methodology

   Assumptions were made for calculations are system operates in steady state, ideal gas equations are applied to air and combustion products, complete combustion reaction.

   1. Thermodynamic analysis

Fig.1 shows the process flow diagram of the combine cycle power plant under consideration. Thermodynamic

Fig-1: layout of combine cycle power plant

= ( + )

analysis of plant considered following balances like mass, energy and exergy. The parameters and data are based on actual plant data for 660 MW combine cycle power plant being installed by National Thermal Power co. Ltd, Bharuch, India.

= 0 0 ( 0 ) 4. Exergy efficiency of power plant,

For steady state process, the mass balance for control volume system,

= 1.

= 1 (, ) 5.

,

The energy balance for control volume system,

+ = + 2.

The exergy balance for control volume system,

, + 1 0 = , + + , 3.

2.2 Economic analysis

In this method, cost associated with purchase and operating cost of each component. The expression for purchase cost of components and amortization factor are presented here [9], but some coefcients were adapted to quotation made by manufacturers. The new coefcients also take into account installation, electrical

Where,

=

equipment, control system, piping and local assembly.

= 75 , ln[ , ] 6.

Table-1.

Input parameters
, /	465.5	,	583
, /	491.7	, ,	156.58

Input parameters
, /	465.5	,	583
, /	491.7	, ,	156.58

0.9

,

,

= 48.75 1 + exp (0.018

26.4)

0.997 ,

,

,

7.

, / 1

[ , ] 1.33 5

= 1536 ln , 1 + exp (0.036

,

0.92

,

,

[ , ] 67.3 1.06

54.4) 8.

= 4745 + 11820 +

log , ,

658 9.

,

,

= 6000 0.7 10.

= 60 0.95 11.

= 1773 12.

,

, ,0C 1069 , $/ 22.01

, ,	7	, $.	7.9
	0.6	,	8000
	0.6

, 660

Table-2

Natural gas composition

Component Mole (%) CH4 81.39

N2 14.82

= [

= [

+ 1

1 +

1

1

]1

13.

C2H6 3.01

C3H8 0.78

Total 100

= 1 + + (1 + ) 14.

100 100

= , + , +

15.

Where,

4. Results and discussion

The exergy analysis of combine cycle power plant is carried out with the help of the software Cycle- Tempo [10]. Fig-2 shows the exergy destruction from

= ( + + + + ) +

,

= ( ) +

16.

17.

different components of the plant. Results shows that maximum exergy destruction occurs in combustion chamber which followed by gas turbine, LP steam turbine, compressor, Heat Recovery Steam Generator

,

(HRSG) and condenser. It is interesting to observe that

1. Case study

   The present method is applied to 660 MW combine cycle power plant being installed by National Thermal Power co. Ltd, Bharuch, India. This plant has three gas turbine unit and one steam turbine unit. This steam turbine unit has two types of steam turbine; one is high pressure and second is low pressure turbine. Water type cooling tower is used to condense steam coming out of low pressure steam turbine.

   condenser is having least exergy destruction.

   Fig-2: exergy destruction from components of plant

   Fig-3 shows the exergetic efficiency of components of plant. It is observed that HP steam turbine have highest exergetic efficiency while condenser is having lowest

   exergetic efficiency. It is very interesting to observe that though combustion chamber and gas turbine have maximum exergy destruction but it have second and third highest exergetic efficiency respectively.

   Fig-4 shows the effect of amortization period on EPC (Rs/kWh). From fig-3 and 4 it can be observed that EPC in both cases decreased as amortization period

   7

   EPCe1

   EPCe1

   EPCe1

   6

   EPCe1 [Rs/kWh]

   EPCe1 [Rs/kWh]

   5

   4

   3

   Fig-3: Exergetic efficiency of components of plant

   Economic analysis is carried out with help of the software EES by generating code in this software. The result of purchase equipment cost and one year calculation of EPC is shown in the table-3.

   Table-3

   Result for k = 1 and in = 8%

   1.134 , ($/) 4427

   2

   1

   1 2 3 4 5 6 7 8 9 10

   k

   Fig-5: effect of amortization period on EPC (Rs/kWh)

   1. Conclusion

      , ($	1.286 682.5	, ($ /) , ($	21.45 be improve. Combustion chamber have highest exergy 4.338 efficiency. In the economic analysis, the method
      /) , ($/)	4.796	/) , ($/)	66988	developed to find out EPC is very good tool to carry out economic analysis of the combine cycle power
      , ($/)	1693	, ( /)	6.315	plant.The advantage of this method is its lowest computational time, because it is a direct algebraic
      , ($ /)	7603				method, easy to handle and to change its parameters. The study was applied to combine cycle systems and

      , ($	1.286 682.5	, ($ /) , ($	21.45 be improve. Combustion chamber have highest exergy 4.338 efficiency. In the economic analysis, the method
      /) , ($/)	4.796	/) , ($/)	66988	developed to find out EPC is very good tool to carry out economic analysis of the combine cycle power
      , ($/)	1693	, ( /)	6.315	plant.The advantage of this method is its lowest computational time, because it is a direct algebraic
      , ($ /)	7603				method, easy to handle and to change its parameters. The study was applied to combine cycle systems and

      It is observed that there is significant amount of loss ofexergy from components of the power plant which should be reduced so that power produced by plant can

      destruction but it also have second highest exergetic

      The variation in EPC as a function of amortization period is shown in fig-4.

      EPCexe

      EPCexe

      EPCexe

      EPCexe

      EPCexe

      EPCexe

      EPCexe

      EPCexe

      70000

      60000

      EPCexe [US$/h]

      EPCexe [US$/h]

      50000

      40000

      30000

      20000

      10000

      1 2 3 4 5 6 7 8 9 10

      k

      Fig-4: effect of amortization period on EPC (US$/h)

      cost of electricity produced comes 6.315 Rs/kWh.

   2. References

1. NatererGF, Regulagadda P, Dincer I,Exergy analysis of a thermal power plant with measured boiler and turbine losses, Applied Thermal Engineering 2010,pp. 970976.

2. Rosen MA, Energy- and exergy-based comparison of coal-fired and nuclear steam power plants, International Journal of Exergy 2001, pp. 180192.

3. Ganapathy T, Alagumurthi N, Gakkhar RP, Murugesan K,Exergy analysis of operating lignite red thermal power plant, Journal of Engineering Science and Technology Review, 2009, pp. 123130.

4. J.H. Horlock, Combined power plants e past, present, and future, ASME Journal of Engineering for Gas Turbines and Power, 1995, pp. 608-616.

[5]R. Kehlhofer, B. Rukes, F. Hannemann, F. Stirnimann, Combined Cycle Gas &Steam Turbine

Power Plants, third ed. PennWell Corporation, USA, 2009.

1. Alessandro Franco, Analysis of small size combined cycle plants based on the use of supercritical HRSG, Applied Thermal Engineering, 2011, pp. 785- 794.

2. Silveira JL, Balestieri JAP, Almeida RA, Santos AHM, Thermoeconomic analysis: a criterion for the selection of cogeneration systems. 1996 International Mechanical Engineering Congress and Exposition, ASME Symposium on Thermodynamics and Design, Analysis and Improvement of Energy Systems, 1996, pp. 240253.

3. J.L. Silveira, C.E. Tuna, Thermoeconomic analysis method for optimization of combined heat and powersystems part-1, Progress in Energy and Combustion Science, 2003, pp. 479-485.

4. Schwarzenbach A, Wunsch AK, Flexible power generation systems and their planning, 1989, ABB Review 6/89.

5. Cycle-Tempo release 5.0, 2006, Delft University of Technology. www.cycle-tempo.nl

6. A. Bejan, G. Tsatsaronis, M. Moran, Thermal Design and Optimization, Wiley, New York, 1996.

7. T.J. Kotas, The Exergy Method of Thermal Plant Analysis,Butterworths, London, 1985.