Regenerative Rankine Cycle

The Regenerative Rankine Cycle Presented by David Willis

Objectives • Brief overview of Regenerative Rankine Cycle • Basic plant layout including: – – – – –

Steam Generator Turbine Generator and Main Engine Condensers Condensate Pump Moisture Separator Condenser and Fresh Water Drains – First Stage Feed Heater – DFT – Main Feed Pumps and Booster Pumps

• Calculations and Examples • Review • Q&A

The Regenerative Rankine Cycle

Temperature Entropy Diagram

Isobaric Heat Transfer (via Steam Generator) (Steam Generator) • Energy added in Steam Generator: •7 to 8: Isobaric heat addition •qIN=(h8-h7) •T8=480 F P8=565.5 psig •h8=1204.6 Btu/ lbm •s8=1.4524 Btu/ lbm R

Isentropic Expansion of Steam (Energy Extracted via Turbine Generator) •8 to 9: Isentropic expansion (Steam turbine) •Work done on Turbine: •wT=(h1-h2) •Note:20% of steam Bled off to FSFH

Isobaric Heat Rejection (via Condenser) 9 to 1: Isobaric heat rejection P1=.5 psia T1=80 F •Heat Rejected in Condenser •qOUT=(1-y)*(h9-h1) •s9=s8=1.4524 Btu/lbm R •x=(s9-sf)/ssf = (1.4524-.09332)/1.9423 = .7 or 70% •h9=hf+x*hfg= =48.09+.7*1048.3= 781.9 Btu/lbm •h1=48.09 Btu/lbm qOUT=(1-.2)*(781.9-48.09)= 587.05 Btu/lbm

Isentropic Compression (via Centrifugal Pump) 1 to 2: Isentropic compression (Pump) •Work of the Pump •wP=υ(Pout-Pin) •υ=specific volume =.016073 ft3/lbm •P2= 60 psig •P1=.5 psia •wP =.22 Btu/lbm •h2=h1+ wP=48.31 Btu/lbm

Isobaric Heat Addition in Moisture Separator Drain Cooler

•T2= 80 F T3= 100 F •Cp = 1 Btu/ lbm F •h3=h2 + Cp*∆T =48.31 + (20*1)= 68.31 Btu/ lbm

Isobaric Heat Addition in Air Ejector Condenser •T3=100F T4=120F •h4=h3 + Cp*∆T •h4=68.31 + (20*1)= 88.31Btu/lbm

Isobaric Heat Addition in First Stage Feed Heater •T4=120F T5=170F •h5=h4 + Cp*∆T •h5=88.31 + (50*1) = 138.31 Btu/ lbm

De-aerating Feed Tank •Temp. Raised to approximately 280 F at 45 psig •T6=280F T5=170F •h6=h5 + Cp*∆T •h6=138.31 + (110*1)= 248.31 Btu/ lbm •Tsat @ 45 psig=292.73 F •hsat=262.25 Btu/ lbm

Main Feed Booster Pump and Main Feed Pump 6 to 7: Isentropic compression Work of the Pump •wP=υ(Pout-Pin) •υ=specific volume=.017 ft3/lbm •P7= 600 psig •P6=45 psig •wP =1.75 Btu/lbm •h7=h6+ WP= 250.06 Btu/lbm

Isobaric Heat Transfer (via Steam Generator) 7 to 8: Isobaric heat addition (Steam Generator) • Energy added in Steam Generator: •qIN=(h8-h7) •T8=480 F P8=565.5 psig •h8=1204.6 Btu/ lbm •qIN=1204.6-250.06 = 954.54 Btu/lbm

Calculations • Work output of the cycle (Steam turbine), wT and work input to the cycle (Pump), wP are: wP = (h2-h1) + (h7-h6) wT = ? • Heat supplied to the cycle (boiler), qin and heat rejected from the cycle (condenser), qout are: qin = (h8-h7) qout = (h9-h1) • The net work output of the cycle is: – wNET= wT - wP • The thermal efficiency of a Rankine cycle is: – ήth= wNET/ qIN=1-(qout/qin)

Calculations ƒqout= (1-.2)(781.9 - 48.09) = 587.05 Btu/lbm ƒqin= 1204.6 – 250.06 = 954.54 Btu/lbm ƒηth= 1 - (qout/qin) = 1- ( 587.05 / 954.54 ) = 38.

Review •Types of Regeneration looked at: •Moisture Separator Drain Cooler •Air Ejector Condenser •First Stage Feed Heater •De-Aerating Feed Tank •Efficiency of Regenerative Rankine Cycles •Conceptual Questions

Questions