Thermodynamic Analysis on Gas Turbine Unit

Transcription

1 Gas Turbine Exhaust Super Heater Economiser HRB Exhaust IJIRST International Journal for Innovative Research in Science & Technology Volume 2 Issue 02 July 2015 ISSN (online): Thermodynamic Analysis on Gas Turbine Unit R. Ram Babu Dr. K. Dilip Kumar Department of Mechanical Engineering Department of Mechanical Engineering Laki Reddy Bali Reddy College Of Engineering Laki Reddy Bali Reddy College Of Engineering Dr. P. Vijay Kumar Department of Mechanical Engineering Laki Reddy Bali Reddy College Of Engineering Abstract The present work is focused on evaluating the performance of a Gas turbine power plant by conducting energy and exergy analysis of each component of the system. The influence of various parameters namely compression ratio (rp), compressor inlet air temperature (AT) and turbine inlet temperature (TIT). The individual and interaction effects of the input parameters over the responses are presented and discussed. From the results it is observed that pressure ratio is the key influencing factor which affects the performance of the Gas Turbine plant. Keywords: Gas Turbine Power Plant, Compression Ratio, Inlet Air Temperature, Turbine Inlet Temperature I. INTRODUCTION Combined cycle Power plants are those which have both Gas and Steam Turbines supplying Power to the network. The idea of combined cycles has grown out of the need to improve the simple cycle efficiency by utilizing the waste heat in the turbine exhaust gases of Gas Turbine. The solution was found in using large quantity of energy leaving with the turbine exhaust to generate steam for a steam turbine Power Plant. The idea of combined cycle is not new, it has been proposed by as early as the beginning of this century. It was not however, until 1950 that the first plant was installed. This was followed by a rapid raise in the number of installations, especially in the 1970s. The first law and second law efficiency was found to decrease for any increase in ambient temperature (AT), the increasing the compressor pressure ratio has less improvement to first law and second law efficiency when it is over It is worthless to raise the compressor pressure ratio in order to increase the first law and second law efficiency when the compressor pressure ratio is over [1] Generator Steam Turbine Condenser Deaerator Condensate Extration Pump Boiler Feed Pump Air in Fuel Boiler Combustion chamber Generator Compressor Gas Turbine Turbine Wast Heat Recovery Boiler Fig. 1: General Layout of combined cycle power plant All rights reserved by 280

2 Pressure (P) Temperature (T) Thermodynamic Analysis on Gas Turbine Unit Use of exergy balance equation to the components of thermal power plant helps to determine total consumption of available work potential or exergy provided as the input to the system under consideration. The irreversibility involved in the component of any system can be quantitatively measured with the help of exergy loss. The analysis made in gives the idea of impact of the inlet temperature of the turbine on the exegetic competence and exergy destruction in gas turbine system [2].Higher the GTIT, higher is the efficiency and specific work. Inlet air-cooling by vapour compression cycle can increase the specific work output of combined cycle power plant. The analysis reveals that a higher TIT up to 1900K is possible to achieve higher performances of power cycles [3-4] 2 3 ADIABATIC Volume (V) Fig. 2: P-V Diagram and T-Diagram of Brayton Cycle Entropy (S) A. Description of plant The gas turbine power plant is an open cycle single shaft system located at Genting Lanco, Vijayawada. The power plant uses natural gas of low heat value (LHV). The system consists of an air-compressor (C), combustion chamber (CC) and a gas turbine (T). Fig. 3: Over view of Plant Table 1 Plant specifications S.No. Description Type 1 Make General Electric 2 Model Frame 9 E 3 Power Out put Kwh (Natural Gas) 4 No. of Turbine stages 03 5 No. of Compressor stages 17 6 Compressor Type Axial flow, Heavy duty 7 Flow control Inlet Guide vane modulated 8 No. of Combustion chambers 14 (reverse flow design) 9 Fuel Nozzles One for Combustion Chamber 10 Spark Plugs Two (electrode type Spring injected self-retracting type) in 13, 14 C.C. All rights reserved by 281

3 Thermodynamic Analysis on Gas Turbine Unit B. Gas Turbine Description Fig. 4: Cut way of GE9E Gas turbine The G.E. Gas turbine is an industrial heavy duty engine consisting of a 17 stage axial flow compressor, a combustion section with 14 combustor assemblies, and a 3 stage turbine. The single-shaft engine is mounted on a bed plate with a lube oil reservoir, pumps, and filters. The rotor is supported by three pressure lubricated tilting-pad journal bearing. A double-acting thrust bearing maintains axial shaft alignment. The nominal Turbine-Generator speed is 3000 rpm, (50 Hz). A horizontally split casing allows access to the engine internals for maintenance. The compressor and turbine blades are individually removable. The Fourteen combustors and its internals are removable. II. THERMODYNAMIC ANALYSIS A. Engineering Model: Each component on the accompanying sketch is analysed as a control volume at steady state. The turbine, compressor, pump, and inter connection heat recovery steam generation operating adiabatic. Kinetic and potential energy affected are negligible. They are no pressure drop flow through the combustor, heat-recovery steam generation, and condenser. An air-standard analysis is used for the gas turbine To=300K, p=100kpa. Energy Analysis Exergy Analysis 1) Energy Analysis Work done by the compressor = Specific heat of compressed air X (Compressor discharge temperature Compressor inlet temperature) W co = C pc (T 1 2 T 1 ) KJ/Kg Work done by the turbine = Specific heat of gases (Turbine inlet temperature Turbine exhaust temp.) W tu = C ptu (T 3 -- T 1 2 ) KJ/Kg Heat supplied by fuel (Q 1 ) = Specific heat of combustion chamber (Turbine inlet temperature Compressor discharge temperature) Q 1 = C pcc (T 3 T 1 2 ) KJ/Kg Heat released to atmosphere (Q 2 ) = Specific heat of exhaust gases (Turbine exhaust temperature ambient temperature) = C pex (T 1 4 T 1 ) KJ/Kg Shaft work = Turbine work Compressor work = W tu - W co III. OBSERVATIONS Table - 2 Performance at base load without evaporative cooler Specific gravity of gas Power output MW Nm 3 /Hr. GCV of Gas KJ/m kg/sec SHC of Gas KJ/Kg/ 0 C Gas fuel Temperature 40 0 C Ambient Temperature C Ambient pressure bar Turbine Inlet temperature c Exhaust Temperature c All rights reserved by 282

4 Compressor Discharge pressure bar Compressor Discharge temperature c Table - 3 Performance at base load with evaporative cooler Power output MW Nm 3 /Hr GCV of Gas KJ/m 3 SHC of Gas Gas fuel Temperature Ambient Temperature Ambient pressure Turbine Inlet temperature Exhaust Temperature Compressor Discharge pressure Kg/sec KJ/KG/ 0 C 40 0 c c bar C c bar Thermodynamic Analysis on Gas Turbine Unit Compressor Discharge temperature c 1) Exergy Analysis The maximum useful work potential of a system at the specified state is called exergy. Exergy is a composite property depending on the state of the system and surroundings. Hence I concentrate to analyze on operating conditions of a closed system i.e., compressor, Combustion chamber, Gas Turbine. The exergy content of a system after neglecting K.E And P.E is given by Ex = (h-h0)-t0(s-s0) Table 4 State state h(kj/kg) S(KJ/kg.K) Compressor exergy Destruction Ed =mg To (s 2 -s 1 ) =mt 0 (s 2 -s 1 -R In p 2 /p 1 ) = [(100)(300)( )]- [(8.314/28.97) In(100/1200)]1/103 =2.83MW Turbine exergy destruction Ed =mgt0 (S4-S3) =mt0 (s4-s3-r In p4/p3) =[(100.87)(300)( )-(8.314/28.97) In (100/1200)][ 1/103] =3.42MW IV. RESULTS AND DISCUSSIONS Fig. 5: Variation of plant efficiency with Turbine inlet temperature. All rights reserved by 283

5 Thermodynamic Analysis on Gas Turbine Unit The variation of plant efficiency with increase in turbine inlet temperature is indicated in this plot. When the turbine inlet temperature is increases the output of the gas turbine increases. Hence increase in plant efficiency. Fig. 6: Variation of thermal efficiency with pressure ratio. The variation of thermal efficiency with increase in pressure ratio is indicated in this plot. When the pressure ratio is increases, it ultimately increases thermal efficiency of plant. But there is a certain limit to increasing pressure ratio. Within the limit only we observe increase in thermal efficiency. Fig. 7: Influence of ambient temperature on energy extraction and utilization This plot indicates the influence of ambient temperature and energy utilization and extraction, As the ambient temperature increases, heat energy i,e extracted energy goes on decreases where as the utilized heat energy of gases to that of steam production is more at 30 C compared to other two cases. Fig. 8: Percentage of heat utilized to ambient temperature All rights reserved by 284

6 Thermodynamic Analysis on Gas Turbine Unit This plot indicates influence of percentage of heat utilized to the ambient temperature as the ambient temperature increasing the heat utilization is increases because as the ambient temperature increases HRSG inlet gas temperature is increases, hence heat extraction also increases. The percentage of heat utilization is increasing with respect to the increase of ambient temperature. Fig. 9: Influence of total exergy to that of ambient temperature This plot indicates influence of total exergy to that of ambient energy, where the gas side exergy is goes on decreasing with respect to the ambient temperature, the total exergy of steam production in case of 30 c is less compared to other. V. CONCLUSIONS The effect of operating parameters on first law and second law efficiency of gas turbine plant performance was investigated. The first law and second law efficiency was found to decrease for any increase in ambient temperature (AT) The increasing the compressor pressure ratio has less improvement to first law and second law efficiency These parameters and the need for plant optimization will be necessary for optimum values of operating parameters that offer the best plant performance. REFERENCES [1] V. Tara Chand, B. Ravi Sankar and M. Ramanjaneya Reddy (2013), First Law and Second Law Analysis of Gas Turbine Plant. International Journal of Mechanical Engineering and Research. ISSN No , Volume 3, Number 4 (2013), pp [2] M.K.Pal, H.Chandra and A.Arora (2014), Second Law Analysis of Gas Based Thermal Power Plant to Improve Its Performance. International Journal of scientific research and management (IJSRM) Volume 2 Issue 3 Pages [3] A.kumar, S.S kachhwaha and RS Mishra (2014), Steady state thermal analysis of gas turbine power plants at higher temperatures. International Journal of Mechanical Engineering and Research. ISSN No , Volume 3, Number 4 (2013), pp [4] A.K.Tiwari, Mohd Islam, M.N.Khan,Thermodynamic analysis of combined cycle power plant A.K. Tiwari et. al. / International Journal of Engineering Science and Technology Vol. 2(4), 2010, All rights reserved by 285