Standard Technical Features of BTG System for Supercritical 660 ...

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Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Units15.1 Number and TypeCHAPTER - 15BOILER FEED PUMPS15.1.1 2x50% capacity turbine driven feed pumps shall be provided for each unit fornormal working along with 1x50% capacity motor driven feed pump for startup purpose and to serve as standby. Alternatively, 3x50% MDBFPs shallalso be acceptable.15.1.2 The MD-BFP shall be driven by constant speed squirrel cage inductionmotor with hydraulic coupling between motor and main pump and boosterpump at other end of motor. TD-BFP shall be driven by variable speedturbine drive with suitable coupling between turbine and main pump andbooster pump at other end of turbine with a gear box for each TD-BFP.Booster pump of TD-BFP may, alternatively, be separately driven by anelectric motor as per standard practice of the OEM.15.1.3 Main pump shall be horizontal, centrifugal type, multistage, outer casingbarrel type, cartridge design with end rotor removal. Booster pump shall besingle stage, two bearing design and double suction impeller type. Overhungimpeller is not acceptable.15.2 Pump SizingDesign Criteria TDBFP MDBFPi) Design capacity & a) Combined flow of All conditionsdesign head2x50% Turbine driven prescribed inBoiler feed pumps to column for TDBFPbe based on 10% shall be required tomargin over feed flow be met by MDBFP,corresponding to as applicable.turbine V.W.O.condition, 1% makeup, The headdesign condenserpressure andcorresponding head.b) One TDBFP shall becapable of handlingflow and headcorresponding to 65%of rated unit load.developed byMDBFP shall becalculated in thesame way as donefor TDBFPs for allthe conditions sothat TDBFPs andMDBFPs can beoperatedparallel.in113
Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsii)Best efficiencypointCombined flow of 2x50%TDBFPs shall be based onTMCR requirementand corresponding head.iii) Emergency pointTwo turbine driven feedpumps to be capable ofgenerating the dischargepressure corresponding tosteam generator highestsafety valve set pressure at100% BMCR flow.Requirement ofemergency pointshall be met byMDBFP at 50Hz grid frequency.iv) Other Capabilities Combined flow of 2x50% TDBFP shall meet thefollowing:a) BMCR flow and head corresponding to ratedsteam pressure.b) V.W.O. output, 1% makeup, worst condenserpressure (MDBFP should meet thecorresponding requirement at 47.5Hz).v) Rated dischargeflow throughinterstage bleed offfor reheaterattemperationAs per 8% of maximum reheat steam flow forthe unit as a minimum.Note: Discharge flow of main pump not to include any seal flow, warm-upflow and balance drum leakage flow.15.3 Design Requirements15.3.1 Pumpsi) NPSH Margin: The ratio between NPSH (A) and NPSH (R) at 3%head drop for booster pump and main pump shall be not less than 2.5 atdesign point corresponding to lowest level of deaerator and maximumpressure drop across the suction strainer.ii)iii)iv)Trip Speed of TD-BFP: 10% above the design speed of the feed pump.Performance Curve: The characteristic curves of booster pump andmain pump should be continuously rising type with decrease in flowand shut off head shall be in the range of 115% to 130% of TDH atdesign point.Minimum Recirculation: The minimum flow of the booster pump andmain pump shall not be less than 25% of design flow. ON-OFF ormodulating type minimum recirculation valve with valve bodydesigned for about 40% of design flow shall be provided.114
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