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Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K.

Energy and Exergy Analysis of Brayton-Diesel Cycle

Sanjay, Mukul Agarwal, Rajay

Abstract-- In this the energy and exergy analysis of a hybrid turbines has improved the efficiency of the simple-cycle operation more than 40%. gas turbine cycle has been presented. The thermodynamic developments, such as recuperation, mixed air steam characteristic of Brayton-diesel cycle is considered in order to turbines (MAST) are among the possible ways to improve the performance of gas turbine based power plants at establish its importance to future power generation markets. feasible costs. Significant work in the field of advanced gas Mathematical modeling of Brayton-diesel cycle has been done at turbine based cycles has been done by Abdallah, H. and component level. Based on mathematical modeling, a computer code Harvey, S [1], Alabdoadaim, M et.al [2], Arrieta, F. R. P [3], Yadav R [4], Bianchi, M [5] , Chiesa. et al.[6] , has been developed and the configuration has been subjected to Gabbrielli [7], Jonsson [8], Kuchonthara [9], thermodynamic analysis. Results show that, at any turbine inlet Heppenstall[10], Horlock [11], Waldyr [12], Lukas [13], temperature (TIT) the plant specific work initially increases with Poullikkas, A [14], etc. After reviewing recent technical papers by leading researchers Brayton-diesel cycle has been increase of ratio (r ), and but at very high values of r , it p,c p,c identified for detailed study. starts decreasing. For a fixed value of rp,c (more than 10) with the increase in TIT, plant efficiency and specific work both increase. II. NOMENCLATURE

The cycle is best suited for applications where power requirement -1. -1 cp = specific …………..(kJ-kg K ) ranges between 700-900 kJ/kg. The exergy analysis shows that gt = gas turbine . -1 maximum exergy loss of around 27% occurs in during h = specific ………(kJ kg ) -1 -1 in the plant. ΔH r = lower heating value……(kJ.kg K ) . -1 Index Terms— Diesel cycle, exergy, exergy loss, gas turbine cycle, m = mass flow rate……….. (kg s ) hybrid. Q = heat added/ removed during process I. INTRODUCTION rp = cycle pressure ratio p = pressure………………..(bar) With the increasing population of the world, the energy T = temperature……………(K) consumption will increase rapidly. While as the fossil are TIT = turbine inlet temperature (K) = combustor exit depleting and one can imagine the future energy crisis unless temperature some alternate cheap energy resources are developed. The W = specific work………(kJ.kg-1) increasing energy demand and depletion of fossil resources inevitably necessitate for the optimum utilization of exhaustible Greek symbols fossil fuel and non-renewable energy resources. In this effort, a hybrid gas turbine based power cycle has been conceived for ε = effectiveness ………..(%) achieving maximum utilisation of thermal energy associated with η = efficiency………………(%) the gas turbine exhaust. γ = ratio of specific heat at constant pressure and constant In regard to the simple-cycle gas turbine technology, the υ = ………(m3kg-1) major driver to enhance the performance has been the increase in process conditions (temperature and pressure) through Subscripts advancements in materials and cooling methods. On-going development and near term introduction of advanced gas a = air , ambient b = blade Dr. Sanjay . is with the National Institute of Technology, Jamshedpur c = compressor, coolant, INDIA in the Mech. Engg. Deptt. (phone: +91-657-2373813; fax: +91- 657-2373813; e-mail: [email protected] ). C = compression (Diesel Cycle) Mukul Agarwal, is with the Tata Consultancy Services, INDIA(e-mail: comb = combustor [email protected]). dc = diesel cycle Rajay, is with the Bharat Heavy Electricals Ltd. At Haridwar, INDIA as Senior Engineer (email: [email protected] )

ISBN:978-988-18210-1-0 WCE 2009 Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K.

Combustion chamber Fuel

Compressor

Alternator Turbine

Air inlet

Exhaust

Heat exchanger

Diesel engine

Alternator

Fig. 1. Schematic of a Brayton-Diesel cycle

III. BRAYTON-DIESEL- CYCLE CONFIGURATION e = exit E = expansion (Diesel Cycle) The configuration identified for parametric study is built up f = fuel of various types of components. Preheating of the inlet air g = gas of a can sufficiently improve its performance. gen = alternator The gas turbine exhaust can be applied in order to increase gt = gas turbine the temperature of the air, which is extracted from the he = heat exchanger compressor and fed into the diesel engine. Subsequently, i = inlet, stage of compressor the engine outlet flow expands through the low-pressure in = inlet stage of the gas turbine as illustrated in Fig. 1. Main j = coolant bleed points components of this cycle are gas turbine, gas-to-gas heat net = difference between two values exchanger and diesel engine. The turbine exhaust is used to p = pressure heat up the air bled from the compressor, which goes into plant = brayton-diesel cycle plant diesel engine for further power generation. Modeling of all z = cooled row stage these components/elements that constitute the cycle configuration has been done. Modeling of these Acronym components are based on mass and energy balance across the boundary of each of these components. C = Compressor Modeling the various elements of a cycle and derived CC = Combustion chamber governing equations is detailed in the following section. GT = Gas turbine A. Modeling of Components

Modeling of various elements like working fluid/gas, compressor, combustor, and cooled gas turbine has been

ISBN:978-988-18210-1-0 WCE 2009 Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K.

done in the earlier work [15,16,17]. Following are a few of the V important equations of the model. 4 Expansion ratio, r = (7) T e V3 Enthalpy of air/gas, h = c (T ) dt (1) ∫ p To V 3 Cut –off ratio, r = (8) Compressor work, Wc = c V    2 mehe + (∑ mc, j hc, j − mc,i hc,i )+ mdc hdc (2) It is seen that rk=re.rc (9) Energy balance of combustor : m .ΔH η = (m h − m h ) (3) γ −1 f r comb g,e g,e a.in a.in comb T ⎡V ⎤ 1 The gas turbine work is the sum of the work done by all rows of 4 = 3 = bladings having open loop air-cooled blades. Process 3-4 ⎢ ⎥ γ −1 (10) T3 ⎣V4 ⎦ re = Σm (h − h ) + Σm (h − h ) W gt g.i g.az g.bz cooled g.i g.i g.e uncooled (4) T2 p2V2 V2 1 where ‘cooled’ and ‘uncooled’ in the equation represent rows of Process 2-3 = = = (11) blade requiring cooling and rows of blade not requiring cooling. T3 p3V3 V3 rc Heat exchanger is used to transfer heat from the heated stream to the colder stream flowing through it. The energy balance γ −1 equation of heat exchanger gives: T1 ⎡V2 ⎤ 1 Process 1-2 = ⎢ ⎥ = γ −1 m ⋅ c ⋅ε T − T = m ⋅ c ⋅ T − T T2 ⎣V1 ⎦ rk h p,h he [( he,h )i ( he,h )e ] c p,c [( he,c )i ( he,c )e ] (5) So where ‘h’ stand for hot stream and ‘c’ stands for colder stream. 1 T3 1 T1 = T2 . γ −1 = . γ −1 (12) B. Diesel Engine Cycle rk rc rk

Diesel engine works on diesel cycle comprises of two isentropic, As we know that one isochoric and one . For 1 kg of air in the cylinder, the efficiency analysis of the cycle can be made as Q m ⋅c (T −T ) T −T given below. η =1− 2 =1− v 4 1 =1− 4 1 The efficiency may be expressed in terms of any two of the  following three ratios Q1 m⋅cP (T3 −T2) γ (T3 −T2 ) (13)

p=c Now substituting the values from equation ( 7) , (8) , (9) , (10) in (13)

V=c γ T 1 1 rc −1 WE η Diesel = 1− . . (14) γ −1 Q1 γ rk rc −1

IV. RESULTS AND DISCUSSIONS WC Q2 For predicting the performance of the Brayton-diesel-cycle,

a computer code based on the modeling of various cycle

components discussed in the previous section has been

developed.

s For predicting the performance of the Brayton-diesel-cycle,

Fig. 2. T-s representation of ideal Diesel cycle mathematical modeling of various cycle components has

been discussed in previous section. Based on this modeling

a computer code in C++ language has been developed. V1 Results have been obtained for input data listed in Table I. , rk = (6) and the results obtained have been plotted using graphic V2 package ORIGIN 6.0. Based on results of exergy analysis, a Sankey diagram has been drawn for the cycle. The exergy distribution quantifies the losses in various elements of the cycle. The results (Design Monograms and Sankey diagrams) have been discussed.

ISBN:978-988-18210-1-0 WCE 2009 Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K.

Table I. Input data for analysis for Brayton-Diesel Cycle 830 Component Parameters 825 Gas property cp= f(T) 820

Enthalpy h= ∫ cp(T) dT 815 Ambient condition Ta=288K 810 Pa=1.013 bar Relative humidity=60% 805

Inlet section ∆ploss=1 percent of entry 800

pressure 795 Compressor Isentropic efficiency (ηc)=86% 790 Mechanical efficiency 785 (ηm)=98%

Plant Specific work (kJ/kg)) 780 Combustor ∆ploss=2% of entry pressure

ηcc=98% 775 Fuel Natural gas 770 0 1020304050 (LCV)f=42000 kJ/kg Fuel inlet pressure = 110% of Cycle pressure ratio Fig. 4. Effect of r on plant specific work at TIT=1500K compressor exit pressure p,c Gas turbine Isentropic efficiency (ηt)=86% Mechanical . efficiency(ηm)=98% Exhaust pressure=1.08 bar 45 Heat exchanger ∆p =2% of entry pressure loss Effectiveness(εrec)=92% 44 Temperature gain in Heat exchanger=100K Diesel engine Compression ratio=5 43 Cut off ratio=2.5

Alternator Efficiency (ηalt)=98.5% 42

Overall plant efficiency,Overall %

41 45.0 4540 35 30 44.5 25 40 44.0 20 0 1020304050

(%) Cycle Pressure ratio

43.5 15 Fig. 5 Effect of r on plant efficiency at TIT=1500K p,c 43.0 42.5 10 K Results show that at TIT less than 1600K and upto rp,c=15, 0 42.0 0 4 the specific work increases with increase in r . At values 1 p,c K = 0 41.5 T 0 of TIT higher than 1600K, specific work increases with I 5 K 0 T 1 0 K 0 K TIT, till value of r is less than 20, beyond which specific 6 p,c 41.0 1 0 0 7 0

1 8 work reduces with increase in TIT. At any TIT value of the 1

Overall plant effeciency 40.5 plant efficiency increases with increase in rp,c upto a certain value, when after the plant efficiency curve loops back. 40.0 r =5 pc This design monogram can be used to select the operating 39.5 parameters for the brayton-diesel cycle plant depending on 740 760 780 800 820 840 860 880 Specific work(kJ/kg) required plant capacity. Fig. 3. Influence of TIT and r on plant efficiency Most of the gas turbines today operate at a TIT of 1500K, p,c and specific work Brayton-Diesel cycle hence performance of the configuration at this value of TIT is shown in Fig. 4 and Fig. 5. Fig. 4 shows the effect of pressure ratio on plant specific work for the configuration. Fig. 3. shows the variation of specific work and plant efficiency The graph shows the range of pressure ratio over which the with pressure ratio (rp,c) and turbine inlet temperature (TIT). cycle can operates and also the optimized value of specific work for the selected TIT. Fig. 5 shows the effect of

ISBN:978-988-18210-1-0 WCE 2009 Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K.

Fig. 6. Exergy flow diagram for Brayton-Diesel cycle

pressure ratio on plant efficiency for the configuration. The V. CONCLUSIONS graph shows the range of pressure ratio over which the cycle operates and also the optimized value of plant The brayton-diesel cycle is a gas turbine hybrid cycle and efficiency for the selected TIT. its thermodynamic analysis has been carried out to ascertain Fig. 6. shows the exergy flow at rp,c =25 and TIT=1700K its potential as a energy conversion system. From the among various components of the configuration. Diesel analysis following conclusions can be drawn: engine has the exergy of about 52.4% while gas turbine 1) Brayton-Diesel cycle provides the maximum exergy is about 8.55% because the bleeding from the available energy (about 60%) compressor has been done at 5 bar, so mass flow of 2) Braton-Diesel cycle gives maximum work output working fluid through the diesel engine is very large in between 840-875 kJ/kg. comparison of gas turbine. Exergy loss in combustion Thus the cycle is found to be useful as a energy conversion chamber of is about 3.10%, because in cycle and performance in the above mentioned range. turbine working fluid handled is lesser than in Diesel engine. Also the combustion process in Diesel engine exhibits an exergy loss of about 22.70%. This configuration has lower exergy loss (about 2.33%), because the exhaust gas heat has been recovered considerably well in the heat exchanger at the exit of turbine. Unaccounted exergy losses are about 4.61%.

ISBN:978-988-18210-1-0 WCE 2009 Proceedings of the World Congress on Engineering 2009 Vol II WCE 2009, July 1 - 3, 2009, London, U.K.

REFERENCES 13. Lukas, H., “Survey of alternative gas turbine engine 1. Abdallah, H. and Harvey, S.,( 2001) “Thermodynamic and cycle design,” EPRI Report AP-4450, Research analysis of chemically recuperated gas turbines,” Int. J. Project 2620-2, February 1986. Therm. Sci. Vol 40, pp. 372-384. 14. Poullikkas, A., “An overview of current and future 2. Alabdoadaim, M. A., Agnew, B., and Potts, I., (2006) sustainable gas turbine technologies,” Renewable and “Performance analysis of combined Brayton and Sustainable Energy Reviews, 9, pp409-443, 2005 inverse Brayton cycles and developed configurations,” 15. Sanjay, Onkar Singh, B.N Prasad, 2008, “Influence of Elsevier, Applied Thermal Engineering, 26, pp. 1448- Different Means of Turbine Blade Cooling on the 1454. Thermodynamic Performance of Combined Cycle” 3. Arrieta, F. R. P. and Lora, E. E. S.,(2005) “Influence Applied Thermal Engg. of ambient temperature on combined cycle power plant [doi:10.1016/j.applthermaleng.2008.01.022] performance,” Applied Energy, 80, pp 261-272. 16. Y. Sanjay, Onkar Singh and B.N. Prasad, Energy and 4. R Yadav, Pawan K .Dwivedi. (2004) “Thermodynamic exergy analysis of steam cooled reheat gas–steam evaluation of Humidified air turbine (HAT) cycles”, combined cycle, Applied Thermal Engineering 27 ASME paper No. GT2004 – 54098. (2007) 2779 -90. 5. Bianchi, M., Montenegro, G., Peretto, and Spina, P. R., [doi:10.1016/j.applthermaleng.2007.03.011] (July 2005) “A feasibility study of inverted Brayton 17. Sanjay, Onkar Singh, B.N Prasad, “Thermodynamic cycle for gas turbine repowering,” Journal of Modeling and Simulation of Advanced Combined Engineering for Gas Turbine and Power, Vol. 127, pp. Cycle for Performance Enhancement”, Proc. IMechE 599-605. Vol. 222 Part A: J. Power and Energy, 6. Chiesa, P., Lozza, G., Macchi, E., and Consonni, S., [DOI: 10.1243/09576509JPE593] “An assessment of the thermodynamic performance of mixed gas-steam cycles: Part B-Water-injected and HAT cycles,” Journal of Engineering for Gas Turbine and Power, Vol. 117, pp 499-508, July 1995 (ASME Paper No. 94-GT-424). 7. Gabbrielli, R. and Singh, R, (October 2003) “Thermodynamic performance analysis of new gas turbine combined cycles with no emissions of carbon dioxide,” (ASME Paper No. 2002-GT-30117), Journal of Engineering for Gas Turbine and Power, Vol. 125, pp 940-946, 8. Jonsson, M. and Yan, J., (2005) “Humidified gas turbines – a review of proposed and implemented cycles,” Energy, 30, pp. 1013-1078. 9. Kuchonthara, P., Bhattacharya, S., and Tsutsumi, A.,( 2003) “Combination of solid oxide fuel cell and several enhanced gas turbine cycle,” Journal of Power Sources, 124, pp. 65-75. 10. Heppenstall, T.,( 1998) “Advanced gas turbine cycles . for power generation: a critical review,” Applied

Thermal Engineering, 18, pp 837-846. 11. Horlock, J. H., “The evaporative gas turbine (ECT) cycle,” ASME Paper No. 97-GT-408, 1997 12. Waldyr L. R. Gallo.,”A comparison between the heat cycle and other gas turbine based cycles: efficiency, specific work and water consumption.

ISBN:978-988-18210-1-0 WCE 2009