WELCOMETO PRESENTATION ON SUPERCRITICAL By BOILER 1 OPERATION TEAM APML,TIRODA Introduction to Supercritical Technology What is Supercritical Pressure ? Critical point in water vapour cycle is a thermodynamic state where there is no clear distinction between liquid and gaseous state of water. Water reaches to this state at a critical pressure above 22.1 MPa and 374 oC. 2 Rankine Cycle Subcritical Unit 3 1 - 2 > CEP work 2 - 3 > LP Heating 3 - 4 > BFP work 4 - 5 > HP Heating 5 – 6 > Eco, WW 6 – 7 > Superheating 7 – 8 > HPT Work 8 – 9 > Reheating 9 – 10 > IPT Work 10–11 > LPT Work 11 – 1 > Condensing 2 > CEP work 2 – 2s > Regeneration 2s .Rankine Cycle Supercritical Unit 1 .3 > Boiler Superheating 3 – 4 > HPT expansion 4 – 5 > Reheating 5 – 6 > IPT & LPT Expansion 6 – 1 > Condenser Heat rejection 4 . VARIATION OF LATENT HEAT WITH PRESSURE Absolute Pressure (Bar) Saturation Temperature (oC) 264 342 366 374 Latent Heat (K J/Kg.) 50 150 200 221 1640 1004 592 0 5 . WATER DENSITY STEAM 175 224 PRESSURE(ksc) 6 .Departure from Nucleate Nucleate boiling is a type of boiling that takes place when the surface temp is hotter than the saturated fluid temp by a certain amount but where Boiling heat flux is below the critical heat flux. Nucleate boiling occurs when the surface temperature is higher than the saturation temperature by between 40C to 300C. Supercritical Boiler Water Wall Rifle Tube And Smooth Tube 7 . Once Through System 8 .Natural Circulation Vs. 5710C To HP Turbine Mixer Header 4230C Separator 4620C To IP Turbine 5690C 5340C 5260C FRH FSH Platen Heater From CRH Line 3240C LTRH 4730C LTSH 4430C 3260C From FRS Line 2800C NRV 2830C Economizer Phase 1 Economizer Phase 2 Boiler Recirculation Pump Bottom Ring Header . Feed water flow. Drum less Boiler Feed water control by 1.Load demand 2.Feed water control In Drum type Boiler Feed water flow control by Three element controller 1.Water/Fuel ratio(7:1) 3.Ms flow 3.Drum level 2.OHD(Over heat degree) 10 . Difference of Subcritical(500MW) and Supercritical(660MW) 11 . Enthalpy Sp. Coal consumption Air flow. Dry flu gas loss Heat addition more More High High .COMPARISION OF SUPER CRITICAL & SUB CRITICAL DESCRIPTION Circulation Ratio SUPERCRITICAL (660MW) SUB-CRITICAL (500MW) Once-thru=1 Assisted Circulation=3-4 Natural circulation= 7-8 Three Element Control -Feed Water Flow -MS Flow -Drum Level 1 Feed Water Flow Control -Water to Fuel Ratio (7:1) -OHDR(22-35 OC) -Load Demand Nil Low Low Low Latent Heat Addition Sp. . DESCRIPTION SUPERCRITICAL (660MW) SUB-CRITICAL (500MW) Coal & Ash handling Pollution Aux.Continue. Power Consumption Overall Efficiency Low Low Low High (40-42%) High High More Low (36-37%) Total heating surface area Reqd Tube diameter Low (84439m2) Low High (71582m2) High 13 . Continue.. DESCRIPTION SUPERCRITICAL SUB-CRITICAL (660MW) (500MW) Material / Infrastructure (Tonnage) Start up Time Blow down loss Water Consumption Low 7502 MT Less Nil Less High 9200 MT More More More 14 . Water Wall Design 15 . WATER WALL ARRANGEMENT Bottom spiral & top vertical tube furnace arrangement Once through design feature is used for boiler water wall design The supercritical water wall is exposed to the higher heat flux Spiral tube wall design (wrapped around the unit) with high mass flow & velocity of steam/water mixture through each spiral Higher mass flow improves heat transfer between the 16 WW tube and the fluid at high heat flux. . SPIRAL VS VERTICAL WALL VERTICAL WALL Less ash deposition on SPIRAL WALL More ash deposition More fluid mass flow Less number of tubes wall Less mass flow More number of tubes More boiler height for same capacity No uniform heating of tubes and heat transfer in all tubes of WW Less boiler height Uniform heat transfer and uniform heating of WW tubes 17 . Furnace Arrangement SPIRAL TYPE VERTICAL TYPE 18 . Supercritical Sliding Pressure Boiler Water Wall Design Comparison of Vertical Wall and Spiral Wall 19 . 20 . Ash accumulation on walls Vertical water walls Spiral water walls 21 . Super Critical Boiler Materials 22 . Advanced Supercritical Tube Materials (300 bar/6000c/6200c) 23 . 000 Nos T11. T22 T22.000 Nos 24 .Material Comparison Description Structural Steel Water wall 660 MW Alloy Steel T22 500 MW Carbon Steel Carbon Steel SH Coil RH Coil LTSH Economizer Welding Joints (Pressure Parts) T23.Super 304 H T12 SA106-C 42.T11 T11 Carbon Steel 24. T91 T91. T91. Steam Water Cycle Chemistry Controls 25 . Parameter No.5 for feed.0 – 10.9. steam & condensate.0 for Boiler drum < 7 ppb for feed.0 for CWT(Combine water treatment) < 7 ppb for feed in case of AVT 30 – 150 ppb for feed in case of CWT Standard value <0.15 µS /cm in the cycle Expected value.0 . Standard value <15 ppb in the cycle < 250 ppb in boiler drum Expected value <10 ppb in the cycle 9.20 µS/cm in the feed & steam cycle 9.S. 9.10 µS /cm in the cycle 4 Dissolved Oxygen (DO) Cation (H+) Conductivity 5 6 7 26 (CPU) CPU is optional CPU is essential for 100% flow. Or All Volatile Treatment (Hydrazine + Ammonia) Super Critical No HP dosing Combined water treatment (CWT). <0. 2 < 20 ppb in feed water and steam. Silica and TDS By maintaining feed water quality Blow down possible till separators are control and functioning (upto 30% load).<0.0 – 9.0 – 9. By operating CBD . 1 Type of Boiler water treatment Silica pH 3 Sub Critical LP and HP dosing.6 for AVT(All volatile treatment) 8. control and load change flexibility – Shorter start-up time – More suitable for widely variable pressure operation 27 .Advantages of SC Technology I ) Higher cycle efficiency means Primarily – less fuel consumption – less per MW infrastructure investments – less emission – less auxiliary power consumption – less water consumption II ) Operational flexibility – Better temp. •Low capacity ash handling system.005 % per bar Temp increase : 0.ECONOMY Higher Efficiency (η%) •Less fuel input. •Less Emissions. Approximate improvement in Cycle Efficiency Pressure increase : 0.011 % per deg K 28 . •Low capacity fuel handling system. 75 566 / 566 538 / 566 580 / 600 HP / RH outlet temperature [deg.26 3.64 2.78 0 241 175 538 / 538 5.81 4.42 1.47 600 / 620 0.37 2.79 3.77 5.74 2.76 3.74 4. C] 29 .Increase of Cycle Efficiency due to Steam Parameters Increase of efficiency [%] 10 9 8 7 6 5 4 3 2 1 0 300 Pressure [bar] 6.44 1. Btu / kw-hr Subcritical 34 .9.41 9. %* Plant Efficiency.300 Plant Efficiency.000 .8. % Fuel Consumption/Total Emissions including CO2 34% Base 37% Base-8% 41% Base-17% 30 * HHV Basis . vs.37 10.200 .Sub.200 Supercritical 37 . Supercritical Cycle Impact on Emissions Plant Efficiency. Maintenance of tube leakage is difficult due to complex design of water wall. Metallurgical Challenges More complex in erection due to spiral water wall. More feed pump power is required due to more friction losses in spiral water wall.Challenges of supercritical technology Water chemistry is more stringent in super critical once through boiler. 31 . Ash sticking tendency is more in spiral water wall in comparison of vertical wall. THANK YOU .