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 and optimization of Rankine cycles for

low temperature power generation

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 2

LOW BIN PROJECT

Objective of the projects

Development and demonstration of the ORC power plant with geothermal water temperature of 65-90°C 80°C

80°C

Our Objective

• Computer Modelling of the Rankine Cycle

• Optimization of the Rankine Cycle

Optimal Rankine Cycles

Low-Bin Final Workshop : Braunau 28 August

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

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 4

Cooling Heat Exchanger

( )1

ln /1 12

oo o io

i i o

UA r rA

A h kL hπ

=+ +

( )( )

25.03

725.0⎥⎥⎦

⎤

⎢⎢⎣

⎡

−

−=

wgf

ffgvo TTd

kghh

μρρρ

μρ⋅⋅

=

=

=

DuNu

DNukhi

Re

PrRe023.0 4.08.0

Overall heat transfer coefficient :

Laminar condensationon tubes surface :

Turbulent flow of the cooling water inside the

tubes :

Low-Bin Final Workshop : Braunau 28 August

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 5

Single phase flow

Liquid ⇒ Two Phase ⇒ Vapor

35.012.04124.02

,65Re

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛=

βcrP

fgl

e

ltpwf p

pL

hDkCh

0.2

23

/ , /

Re

0.074 1050Re Re

12

PrRe Pr

f

f

sp l g gw

u L

c

cSt

Nu StNu kh

L

ρμ⋅ ⋅

=

= −

= ⋅

= ⋅ ⋅⋅

=

Overall heat transfer coefficient for each phase:

Evaporation heat transfer –Two phase

Low-Bin Final Workshop : Braunau 28 August

Geothermal Heat Exchanger

/

/

/

/

1 1,1 1 1 1

11 1

sp l tp

sp l gw tp gw

sp g

sp g gw

U Ux xh ktit h h ktit h

U xh 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,

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 6

2p

wfm&

In order to optimize the Rankine cycle of the plant we had to define:

1.

The variables of the optimization

Rankine cycle optimization

Low-Bin Final Workshop : Braunau 28 August

1p

K.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

pumpswfinvgen

ground

pumpselectcycle mhh

NmhhQ

NN⋅−

−⋅−⋅⋅=

−=

21

54ηηη

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

Low-Bin Final Workshop : Braunau 28 August

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 8

ORC with temperature threshold of 80°C

Optimal solutions

Low-Bin Final Workshop : Braunau 28 August

1st

objective

2nd

objective

(m2)

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 9Low-Bin Final Workshop : Braunau 28 August

ORC with temperature threshold of 80°C

Optimal solutions

1st

objective

2nd

objective

(m2)

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 10

ORC with temperature threshold of 80°C

1.6Total length of the exchanger (m)

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

29Number of tubes0.8Width 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 Workshop : Braunau 28 August

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 11

Comparison between different temperature thresholds

Low-Bin Final Workshop : Braunau 28 August

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

K.C. Giannakoglou, Lab. Thermal Turbomachines, NTUA, Greece 12

Variable T = 80οC 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 8.8

Net electrical Power (kW) 172 277 332 336

Low-Bin Final Workshop : Braunau 28 August

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

and optimization of Rankine

cycles for

low temperature power generation