ME 188 - Combined Brayton & Rankine Cycles

THE COMBINED BRAYTON AND RANKINE CYCLES

THE COMBINED BRAYTON AND RANKINE CYCLESReported by: Azher Roi Ferrer & Darryl Mathew TongsonME 188: Power Plant Engineering (THUV)Second Semester, A.Y. 2015-20161QUICK REVIEW: THE BRAYTON CYCLE

2/12/20162QUICK REVIEW: THE BRAYTON CYCLERegeneration!

2/12/20163QUICK REVIEW: THE BRAYTON CYCLEReheat!

2/12/20164QUICK REVIEW: THE BRAYTON CYCLEIntercooling!

2/12/20165QUICK REVIEW: THE BRAYTON CYCLEO_O!

2/12/20166QUICK REVIEW: THE RANKINE CYCLE

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QUICK REVIEW: THE RANKINE CYCLE

2/12/20168Reheat!QUICK REVIEW: THE RANKINE CYCLE2/12/20169Regeneration!

The Combined CycleCombines both the Brayton & Rankine cyclesTopping cycle: Brayton cycleBottoming cycle: Rankine cycleLink between the two cycles: waste-heat recovery boiler (WHRB) (aka Heat-Recovery Steam Generator, HRSG)WHRB: device that transfers the heat content of the flue gas (Brayton-cycle exhaust gases) to the water in the steam cycleWHRB: Economizer, Evaporator, Superheater

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A More Detailed Schematic Diagram of the Basic Combined Cycle (Unfired Boiler)

2/12/201611Combined Cycle Energy DiagramFuel Input (100%)Gas Turbine Output (38%)Radiation Losses (0.5%)Exhaust Energy (61.5%)Radiation Losses (0.3%)Radiation Losses (0.3%)Steam Turbine Output (21%)Condenser (30%)Radiation Losses (0.2%)2/12/201612Darryl, please explain how did you come up with these values.12Modifications of the Basic Combined CycleNOTE: Either the top cycle or the bottom cycle can be modified so that the new cycle can be called as a modification to the basic combined cycle.Supplementary FiringAdditional fuel combustion with exhaust gases to increase steam turbine outputFlexible operation due to varying power-to-heat-production ratio (AKA -ratio)Steam-turbine cycle remains operational in case something goes wrong in the gas-turbine cycleDecreases overall thermal efficiencyPlacement of HRSG with relation to the supplementary firing burner depends on duct velocities.Horizontal-firing from 500-3500 ft./minVertical Firing from 5004000 ft./min

2/12/201614Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Gjerde, Ed. Supplementary Firing of Gas Turbine Exhaust System14Multipressure BoilerUsed when exhaust gases are hotter than normal.2/12/201615

Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Darryl, please explain what is the normal temperature range of the exhaust gases.15Multipressure Boiler, Triple Pressure Boiler

2/12/2016Ibrahim, T. K., Rahman, M. M. Study on Effective Parameter of the Triple-Pressure Reheat Combined Cycle Performance.16Deaerator are the Tw1 to Tw2 processes. Mass effectively reduced due to elements being siphoned off.16Supercharged BoilerReplaces combustion chamber for gas turbineHigher energy inputSupposedly not a true combined cycle plant, due to no steam being generated.2/12/201617

Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Integrated GasificationPrimarily CO2 capture taken from other industrial processesinvolves partial oxidation of feed-stock (such as coal) and high-pressure, high purity oxygen to make syngasMore compact equipment compared to pulverized coal plants

2/12/2016Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Beer, Janos. High Efficiency Electric Power Generation; The Environmental Role.18

Integrated Gasification2/12/2016Beer, Janos. High Efficiency Electric Power Generation; The Environmental Role.19

Coal GasificationUses coal as fuelNeeds high pressure air and steamFlow rates usually inadequate

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Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Humid Air CyclePlants using this are also known as mixed/wet gas turbine plants.Combustion gases and steam mixed in certain proportions. (10%-15% steam in mass flow)Brayton and Rankine cycles parallel rather than serial in configuration

2/12/201621Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Pressurized Fluidized Bed CombustionFuel enters a hot, turbulent bed.Bed includes solid fuel particles (up to 3%)Temperatures around 800-900CHas better temperature control and heat transferHandling of solids within plant similar to handling fluidsHeat exchanging surfaces may experience erosionHigh variation in fluidization2/12/201622Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Oxy-Combustion Turbine Cycle SystemRankine cycle boiler process replaced with direct combustionRequires pure oxygen, needing large air separation unitsHigher efficiency for CO2 SeparationMostly for cleaning flue gas

2/12/2016Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Beer, Janos. High Efficiency Electric Power Generation; The Environmental Role.23Also handy in reducing NOx emissions.23External FiringA subset of externally fired gas turbinesHas been researched for over 5 decadesMost developments are for the steam turbine (bottoming) system

2/12/201624Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Hybrid Fuel-Cell Gas TurbineHigh-temperature fuel cells integrated with gas turbine, normally by replacing combustorHigh pressure operation of gas turbineElectricity additionally produced by fuel cell

2/12/2016Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation.Beer, Janos. High Efficiency Electric Power Generation; The Environmental Role.25An example Presented here is to run on Hydrogen and carbon monoxide gas reacting with a solid oxide fuel along the cathode-anode area.25PROBLEM SOLVINGAfter all, we like to see numbersPROBLEM 8.14 (Powerplant Technology by El-Wakil)A combined gas-steam-turbine power plant is designed with four 50-MW gas turbines and one 120-MW steam turbine. Each gas turbine operates with compressor inlet temperature 505R (280.556 K), turbine inlet temperature 2450R (1361.111 K), pressure ratio for both compressor and turbine 5, and compressor & turbine polytropic efficiencies of 0.87. The turbines have a mechanical efficiency of 0.96. The gases leaving the turbines go to a regenerator with an effectiveness of 0.87 then to a heat-recovery boiler. The turbine gases correspond to 200% theoretical air. The steam cycle has a turbine steam inlet at 1200 psia (8.27309 MPa) and 1460R (811.1111 K), one open feedwater heater (not optimally placed), where the feedwater goes to the heat-recovery boiler at 920R (511.111 K), condenser pressure 1 psia (6.89476 kPa), and turbine polytropic & mechanical efficiencies of 0.87 and 0.96, respectively. All electric generator efficiencies are 0.96. Supplementary firing at full load raises the gas temperature to 2000R (1111.111 K). Draw the schematic and T-s diagrams and calculate a) the required steam mass flow rate in the steam turbine in pound-mass per hour, b) the required air mass flow rate in each gas turbine in pound-mass per hour, c) the heat added in the gas cycle and in the supplementary firing at full load, d) the stack gas temperature in F, e) the cycle efficiency at full load, and f) the efficiency at startup when only one gas turbine is used at its full load with no supplementary firing or regeneration.Ignore the work required by the pump in the steam cycle. 2/12/201627PROBLEM 8.14 (Powerplant Technology by El-Wakil)Given:Gas Turbine CycleRating of Gas Turbines: 50 MWCompressor Inlet Temperature: 505R (280.556 K)Turbine Inlet Temperature: 2450R (1361.111 K)Pressure Ratio of Compressor (Exit-to-Intake Ratio): 5:1Pressure Ratio of Turbine (Exit-to-Intake Ratio): 1:5Polytropic Efficiency (both compressor & turbine): 0.87Mechanical Efficiency (turbine): 0.96Exit Temperature of Exhaust Gases after Supplementary Firing: 2000R (1111.111 K)Model of Working Fluid: Dry Air & Gas products when fuel is burned at 200% theoretical air

Given:Steam Turbine CycleRating of Steam Turbine: 120 MWTurbine Inlet Pressure: 1200 psia (8.27309 MPa)Turbine Inlet Temperature: 1460RNot optimally-placed open feedwater heaterFeedwater Temperature: 920R (511.111 K)Turbine Polytropic Efficiency: 0.87Turbine Mechanical Efficiency: 0.96Model of Working Fluid: Water at Liquid & Gaseous StatesGenerator Efficiency: 0.962/12/201628PROBLEM 8.14 (Powerplant Technology by El-Wakil)Required:Schematic DiagramT-s DiagramMass Flow Rate of Steam (lb-m/h)Mass Flow Rate of Gas Turbine Working Fluid (lb-m/h)Heat added to the combustors of the gas turbine cycles at full load (BTU/h)Heat added to supplementary firing at full load (BTU/h)Temperature of the gas going to the stack (F)Cycle efficiency at full loadEfficiency at startup when only one gas turbine is used at its full load with no supplementary firing or regeneration

2/12/201629PROBLEM 8.14 (Powerplant Technology by El-Wakil)Schematic Diagram

T-s Diagram

2/12/2016Source: I drew the schematic & T-s diagrams. +10 points for effort!30PROBLEM 8.14 (Powerplant Technology by El-Wakil)2/12/201631PROBLEM 8.14 (Powerplant Technology by El-Wakil)Thermodynamic states:State 6T6 = 2000RrP6 = 211.6h6 = 15189.3 BTU/lbm-molNet work done:wGT = h4 h5A = CP(T4 T5A) = 0.24(2450 1782.782213) = 160.1322689 BTU/lb-mwGC = h2A h1 = CP(T2A T1) = 0.24(842.1130824 505) = 80.90713978 BTU/lb-mwBC = wGT wGC = 79.22512912 BTU/lb-mwnet = wBCMG = (79.22512912)(0.96)(0.96) = 73.013879 BTU/lb-m

2/12/2016The values of the properties were obtained via REFPROP.32NOTE: We cant directly subtract the hs in computing the turbine work because we dont know how many moles of fuel were burned in the combustor.32PROBLEM 8.14 (Powerplant Technology by El-Wakil)2/12/20163333PROBLEM 8.14 (Powerplant Technology by El-Wakil)STEAM TURBINE CYCLE ANALYSISState 10P10 = 1200 psiaT10 = 1460Rh10 = 1501.3 BTU/lbms10 = 1.6314 BTU/lbm-RState: Superheated vaporState 11ST11 = 920Rs11S = s10h11S = 1252.9 BTU/lbmP11 = 159.15 psiaState: Superheated vapor

State 11Ah11A = h10 + T(h11S h10) = 1285.192 BTU/lbmState 12SP12 = 1 psias12S = s10h12S = 911.08 BTU/lbmT12S = 561.36RState: Saturated Mixture (x12S = 0.81176)State 12Ah12A = h10 + T(h12S h10) = 987.8086 BTU/lbmState 13Saturated Liquidh13 = 69.769 BTU/lbmv13 = 27.884 in3/lbms13 = 0.13271 BTU/lbm-R2/12/201634NOTE: For reporting convenience, we have skipped double interpolation and instead, we found the properties using REFPROP.34PROBLEM 8.14 (Powerplant Technology by El-Wakil)STEAM TURBINE CYCLE ANALYSISState 14s14 = s13 = 0.13271 BTU/lbm-RP14 = P11 = 159.15 psiah14 = 70.242 BTU/lbmState 15Saturated LiquidP15 = P14h15 = 335.80 BTU/lbmv15 = 31.357 in3/lbms15 = 0.52042 BTU/lbm-RState 9State: Subcooled Liquids9 = s15P9 = P10 = 1200 psiah9 = 339.29 BTU/lbm2/12/201635NOTE: If you dont have REFPROP, use the integral of v dP (v13 times P14 P13) in order to compute for the work required by the pump, and then compute h14 by equating the enthalpy difference to the work input.35PROBLEM 8.14 (Powerplant Technology by El-Wakil)2/12/201636NOTE: If you dont have REFPROP, use the integral of v dP (v13 times P14 P13) in order to compute for the work required by the pump, and then compute h14 by equating the enthalpy difference to the work input.36PROBLEM 8.14 (Powerplant Technology by El-Wakil)2/12/201637NOTE: If you dont have REFPROP, use the integral of v dP (v13 times P14 P13) in order to compute for the work required by the pump, and then compute h14 by equating the enthalpy difference to the work input.37IMPROVEMENTS TO THE COMBINED CYCLEWithin the recent 5 years2/12/201638InnovationsOptimization with carbon dioxide (CO2), supercritical in the Brayton Cycle and transcritical in the Rankine cycle. (published 7 July 2015)Improvement on fuel consumption with integration of solar energy (published 17 January 2016)Increased efficiency and operation range via supercharging (published 24 January 2015)Increased efficiency by optimization and use of inlet cooling system (published 22 November 2014)

2/12/201639CO2 OptimizationSimple and recompressing CO2 cycles considered in topping and bottoming cycleGenetic Algorithm used to maximize efficiencyModified Supercritical CO2 Cycles with bottoming transcritical CO2 Cycles have thermal efficiency increases of 10.12% in combined recompression and 19.34% in simple configurations compared to original values

2/12/201640Wang, Xurong, Ph.D., Jiangfeng Wang, Pan Zhao, Ph.D., and Yiping Dai. "Thermodynamic Comparison and Optimization of Supercritical CO2 Brayton Cycles with a Bottoming Transcritical CO2 Cycle."40Solar Integration with minimal modifications to plant designMaximum incremental power output given design solar irradiance limited to 19 MW, possible to go higher with larger steam turbinesSolar radiation-to-electrical efficiency about 24-29%Lower thermal efficiency compared to power boosting, due to efficiency drop of gas turbine at reduced loads.Reference Plant is a Natural Gas Combined Cycle plant located in Priolo Gargallo, Sicily, Italy. Analysis was done by simulation with plant data.2/12/201641Manente, Giovanni. "High Performance Integrated Solar Combined Cycles with Minimum Modifications to the Combined Cycle Power Plant Design."Supercharged Natural Gas Combined Cycle PlantHigher efficiencies in compression with addition of compressor stageAble to operate at part-load equal to 47.8% with an efficiency of about 49%, compared to original cycle at 70% with 48% efficiency3.5% efficiency increase compared to the non-modified cycleReference Plant generating power at 397.8 MW2/12/201642

Without SuperchargerWith Supercharger K1Barelli, Linda, and Andrea Ottaviano. "Supercharged Gas Turbine Combined Cycle: An Improvement in Plant Flexibility and Efficiency."Optimization of Fog Inlet Air Cooling System Using Genetic AlgorithmIncrease in power output by 17.24%, Energy efficiency increase by 3.6% and thermal efficiency increase by 3.5%Leads to cheaper electricitySusceptible to humid airCleaner byproducts2/12/201643Ehaaei, Mehdi et.al. Optimization of Fog Inlet Air Cooling System for Combined Cycle Power Plants using Genetic Algorithm.

ReferencesEl-Wakil, M. M. Powerplant Technology. New York: McGraw-Hill Primis Custom Pub., 2002. Print. Potter, Merle C., and Craig W. Somerton. Thermodynamics for Engineers. 3rd ed. N.p.: McGraw-Hill Education, 2014. Print. Yahya, S. M. Turbines Compressors and Fans. 4th ed. New Delhi: Tata McGraw-Hill Education Pvt, 2011. Print. Rao, Ashok D. Combined Cycle Systems for Near-zero Emission Power Generation. Oxford, UK: Woodhead Pub., 2012. Print. Wang, Xurong, Ph.D., Jiangfeng Wang, Pan Zhao, Ph.D., and Yiping Dai. "Thermodynamic Comparison and Optimization of Supercritical CO2 Brayton Cycles with a Bottoming Transcritical CO2 Cycle." ASCE Library. ASCE, 7 July 2015. Web. 23 Jan. 2016. http://dx.doi.org.ezproxy.engglib.upd.edu.ph/10.1061/(ASCE)EY.1943-7897.0000292Manente, Giovanni. "High Performance Integrated Solar Combined Cycles with Minimum Modifications to the Combined Cycle Power Plant Design." ScienceDirect. Elsevier, 7 Jan. 2016. Web. 23 Jan. 2016. http://dx.doi.org/10.1016/j.enconman.2015.12.079 Barelli, Linda, and Andrea Ottaviano. "Supercharged Gas Turbine Combined Cycle: An Improvement in Plant Flexibility and Efficiency." ScienceDirect. Elsevier, 2 Jan. 2015. Web. 23 Jan. 2016. http://dx.doi.org/10.1016/j.energy.2015.01.004Ehaaei, Mehdi et.al. Optimization of Fog Inlet Air Cooling System for Combined Cycle Power Plants using Genetic Algorithm. ScienceDirect. Elsevier, 22 Nov. 2014. Web. 23 Jan 2016. http://dx.doi.org/10.1016/j.applthermaleng.2014.11.032Ibrahim, T. K., Rahman, M. M. Study on Effective Parameter of the Triple-Pressure Reheat Combined Cycle Performance. THERMAL SCIENCE. N.p. n.d. 7 Feb 2016. http://www.doiserbia.nb.rs/img/doi/0354-9836/2013/0354-98361100143I.pdfBeer, Janos. High Efficiency Electric Power Generation; The Environmental Role. MIT Energy Initiative. Massachusetts Institute of Technology, 1967. Web. 7 Feb 2016. https://mitei.mit.edu/system/files/beer-combustion.pdfGjerde, Ed. Supplementary Firing of Gas Turbine Exhaust System ASME Digital Collection. Asme,1967. 10 Feb 2016. http://proceedings.asmedigitalcollection.asme.org.ezproxy.engglib.upd.edu.ph/proceeding.aspx?articleid=2288605&resultClick=1

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