CRES Rankine Cycles Optimizing

8/6/2019 CRES Rankine Cycles Optimizing

http://slidepdf.com/reader/full/cres-rankine-cycles-optimizing 1/13

NATIONAL TECHNICAL UNIVERSITY OF ATHENS

Laboratory of Thermal Turbomachines

Kontoleontos Evgenia

EFFICIENT LOW TEMPERATURE

GEOTHERMAL BINARY POWER

Centre for Renewable Energy Sources

Low-Bin Final Workshop : Braunau 28 AugustLOW-BIN PROJECT

Computer modelling andoptimization of Rankine cycles for

low temperature power generation





K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 3

Cooling Heat Exchanger

shell and tube condenser

Modelling Rankine Cycle’s Components

Modelling of the condenser

Modelling of the heat exchanger

Geothermal Heat Exchanger

plate heat exchanger (PHE)

with corrugated parallel plates

Development of a software which uses the fluids’

properties and provides us with the thermodynamic properties of each point on the Rankine Cycle.

Optimization of the

Rankine cycle

Low-Bin Final Workshop : Braunau 28 August

R134a




Cooling Heat Exchanger

( )1

ln / 1 1

2

o

o o io

i i o

U A r r A

A h kL hπ

=

+ +

( )

( )

25.03

725.0

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

−

−=

wg f

f fgv

o

T T d

k ghh

μ

ρ ρ ρ

μ

ρ ⋅⋅=

=

=

Du

Nu D

Nuk h i

Re

PrRe023.04.08.0

Overall heat transfer

coefficient :

Laminar condensation

on tubes surface :

Turbulent flow of the

cooling water inside the

tubes :





Single phase flow

Liquid⇒ Two Phase⇒ Vapor

35.012.04124.02

,

65Re

⎟⎟ ⎠

⎞⎜⎜⎝

⎛ ⎟⎟ ⎠

⎞⎜⎜⎝

⎛

⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎟⎟ ⎠

⎞⎜⎜⎝

⎛ =

β cr P

fgl

e

ltpwf

p

p

L

h

D

k C h

0 .2

2

3

/ , /

R e

0 .0 7 4 1 0 5 0

R e R e

12

P r

R e P r

f

f

sp l g gw

u L

c

cS t

N u St

N u k h

L

ρ

μ

⋅ ⋅

=

= −

= ⋅

= ⋅ ⋅

⋅=

Overall heat transfer

coefficient for each phase:

Evaporation heat transfer –Two phase


Geothermal Heat Exchanger

/

/

/

/

1 1,

1 1 1 1

1

1 1

sp l tp

sp l gw tp gw

sp g

sp g gw

U U x x

h ktit h h ktit h

U x

h ktit h

= =Δ Δ

+ + + +

=Δ+ +



• the pressure of the liquid working fluid at the pump outlet,

•the pressure of the liquid working fluid at the pump inlet,

• the mass flow rate of the working fluid in the cycle,


2 p

wf m&

In order to optimize the Rankine cycle of the plant we had to define:1. The variables of the optimization

Rankine cycle optimization


1 p


http://slidepdf.com/reader/full/cres-rankine-cycles-optimizing 7/13K.C. Giannakoglou, Lab. Thermal Turbomachines, TUA, Greece 7

Rankine cycle optimization

2. The objectives of the optimization :• MaximizeMaximize net overall efficiency of the plant

• MinimizeMinimize

the cost of the plant

( )( )gwgwgw

pumpswf invgen

ground

pumpselect cycle

mhh N mhh

Q N N

⋅−

−⋅−⋅⋅=

−=

21

54η η η

Minimize both Exchangers’

surface

using the EASY software code (Evolutionary Algorithm System)by National Technical University of Athens

http://velos0.ltt.mech.ntua.gr/EASY





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ORC with temperature threshold of 80°C

Optimal solutions


1st

objective

2nd

objective

(m2)


http://slidepdf.com/reader/full/cres-rankine-cycles-optimizing 9/13K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 9Low-Bin Final Workshop : Braunau 28 August


Optimal solutions

1st

objective

2nd

objective

(m2

)



K.C. Giannako lou Lab. Thermal Turbomachines NTUA Greece 10


1.6 Total length of the exchanger (m)

5.5Length of the condenser (m)520Number of plates

29Number of tubes0.8 Width of the plate (m)

1.3Diameter of the tube (cm)1.43Length of the plate (m)

Shell and tube condenserP.H.E. -

plate heat exchanger

Parameter Value

p2 (kPa) 1876

mgr

(kg/sec) 60

mR134a

(kg/sec) 18.5

ΔΤH

(°C) 15

ΔΤC

(°C) 5

R134a pump power (kW) 30

Cooling water flow (kg/sec) 164.5

Surface of the condenser (m2) 2158

Surface of the heat exchanger (m2) 597

Total H.E. surface (m2) 2755

Net conversion efficiency 5.77

Net Electrical Power (kW) 217

Low-Bin Final Worksho : Braunau 28 Au ust



Comparison between different temperature thresholds


Temperature threshold at 80, 100, 120,140 °C



Variable T = 80 οC T = 100οC T = 120οC T = 140οC

P2

(bar) 16.24 26.51 29.98 29.98

mgeothermal

(kg/sec) 60 60 60 60

mR134a

(kg/sec) 18.5 17.5 16 16

R134a pump power (kW) 22 47 53 53

cooling water flow

(kg/sec)

167 161 159 161

Condenser surface (m²) 1647 1629 1831 1785

Surface of the PHE (m²) 445 397 154 83

Total H.E. surface (m²) 2092 2026 1986 1867

Net conversion efficiency 4.6 7.3 8.7 8.8Net electrical Power (kW) 172 277 332 336


Comparison between different temperature thresholds



NATIONAL TECHNICAL UNIVERSITY OF ATHENS

Laboratory of Thermal Turbomachines

Kontoleontos Evgenia

EFFICIENT LOW TEMPERATURE

GEOTHERMAL BINARY POWER

Centre for Renewable Energy Sources

Low-Bin Final Workshop : Braunau 28 AugustLOW-BIN PROJECT

Computer modelling andoptimization of Rankine cycles for

low temperature power generation

Documents

CRES Rankine Cycles Optimizing