Presentation on theme: "TO PRESENTATION ON SUPERCRITICAL BOILER"— Presentation transcript:
1 TO PRESENTATION ON SUPERCRITICAL BOILER WELCOMETOPRESENTATION ONSUPERCRITICAL BOILERByOPERATION TEAM APML,TIRODA
2 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.
5 VARIATION OF LATENT HEAT WITH PRESSUREAbsolute Pressure(Bar)Saturation Temperature(oC)Latent Heat(K J/Kg.)5015020022126434236637416401004592
6 Departure from Nucleate Boiling 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 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.PRESSURE(ksc)DENSITYWATERSTEAM175224
7 Supercritical Boiler Water Wall Rifle Tube And Smooth Tube
9 5710CTo HP TurbineTo IP Turbine5690CMixer Header5340C4230C5260C4620CSeparatorFRHFSH4730CPlaten HeaterFrom CRH LineLTSH4430C3260CLTRH3240CNRVFrom FRS Line2830C2800CEconomizer Phase 1Economizer Phase 2BoilerRecirculation PumpBottom RingHeader9
10 Feed water controlIn Drum type Boiler Feed water flow control by Three element controller1.Drum level2.Ms flow3.Feed water flow.Drum less Boiler Feed water control by1.Load demand2.Water/Fuel ratio(7:1)3.OHD(Over heat degree)
11 Difference of Subcritical(500MW) and Supercritical(660MW)
12 COMPARISION OF SUPER CRITICAL & SUB CRITICAL DESCRIPTIONSUPERCRITICAL(660MW)SUB-CRITICAL(500MW)Circulation Ratio1Once-thru=1Assisted Circulation=3-4Natural circulation= 7-8Feed Water Flow Control-Water to Fuel Ratio(7:1)-OHDR(22-35 OC)-Load DemandThree Element Control-Feed Water Flow-MS Flow-Drum LevelLatent Heat AdditionNilHeat addition moreSp. EnthalpyLowMoreSp. Coal consumptionHighAir flow, Dry flu gas loss
13 Total heating surface area Reqd Continue..DESCRIPTIONSUPERCRITICAL(660MW)SUB-CRITICAL(500MW)Coal & Ash handlingLowHighPollutionAux. Power ConsumptionMoreOverall Efficiency(40-42%)(36-37%)Total heating surface area Reqd(84439m2)(71582m2)Tube diameter
14 Material / Infrastructure Continue..DESCRIPTIONSUPERCRITICAL(660MW)SUB-CRITICAL(500MW)Material / Infrastructure(Tonnage)Low7502 MTHigh9200 MTStart up TimeLessMoreBlow down lossNilWater Consumption
16 WATER WALL ARRANGEMENT Bottom spiral & top vertical tube furnace arrangementOnce through design feature is used for boiler water wall designThe supercritical water wall is exposed to the higher heat fluxSpiral tube wall design (wrapped around the unit) with high mass flow & velocity of steam/water mixture through each spiralHigher mass flow improves heat transfer between the WW tube and the fluid at high heat flux.
17 SPIRAL VS VERTICAL WALL SPIRAL WALLLess ash deposition on wallLess mass flowMore number of tubesMore boiler height for same capacityNo uniform heating of tubes and heat transfer in all tubes of WWMore ash depositionMore fluid mass flowLess number of tubesLess boiler heightUniform heat transfer and uniform heating of WW tubes
26 S. No. Parameter Sub Critical Super Critical 1Type of Boiler water treatmentLP and HP dosing. OrAll Volatile Treatment (Hydrazine + Ammonia)No HP dosingCombined water treatment (CWT).2Silica< 20 ppb in feed water and steam, < 250 ppb in boiler drumStandard value <15 ppb in the cycleExpected value <10 ppb in the cycle3pHfor feed, steam & condensate,9.0 – 10.0 for Boiler drum9.0 – 9.6 for AVT(All volatile treatment)8.0 – 9.0 for CWT(Combine water treatment)4Dissolved Oxygen (DO)< 7 ppb for feed.< 7 ppb for feed in case of AVT30 – 150 ppb for feed in case of CWT5Cation (H+) Conductivity<0.20 µS/cm in the feed & steam cycleStandard value <0.15 µS /cm in the cycleExpected value- <0.10 µS /cm in the cycle6(CPU)CPU is optionalCPU is essential for 100% flow.7Silica and TDS controlBy maintaining feed water quality andBy operating CBDBlow down possible till separators are functioning (upto 30% load).
27 Advantages of SC Technology I ) Higher cycle efficiency meansPrimarily– less fuel consumption– less per MW infrastructure investments– less emission– less auxiliary power consumption– less water consumptionII ) Operational flexibility– Better temp. control and load change flexibility– Shorter start-up time– More suitable for widely variable pressure operation
28 ECONOMY Higher Efficiency (η%) Less fuel input. Low capacity fuel handling system.Low capacity ash handling system.Less Emissions.Approximate improvement in Cycle EfficiencyPressure increase : % per barTemp increase : % per deg K
29 Increase of Cycle Efficiency due to Steam Parameters
31 Challenges of supercritical technology Water chemistry is more stringent in super critical once through boiler.Metallurgical ChallengesMore complex in erection due to spiral water wall.More feed pump power is required due to more friction losses in spiral water wall.Maintenance of tube leakage is difficult due to complex design of water wall.Ash sticking tendency is more in spiral water wall in comparison of vertical wall.
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