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THERMO-ECONOMIC ANALYSIS OF ZEOTROPIC MIXTURES AND PURE WORKING FLUIDS IN ORGANIC RANINKE CYCLES FOR WASTE HEAT RECOVERY 3rd International Seminar on ORC Power Systems, Brussels (Belgium) Florian Heberle and Dieter Brggemann Introduction

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SLIDE 1

3rd International Seminar on ORC Power Systems, Brussels (Belgium)

THERMO-ECONOMIC ANALYSIS OF ZEOTROPIC MIXTURES AND PURE WORKING FLUIDS IN ORGANIC RANINKE CYCLES FOR WASTE HEAT RECOVERY

Florian Heberle and Dieter Brüggemann

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SLIDE 2

Introduction

Zeotropic mixtures as working fluids in ORC power systems

Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann
  • Zeotropic mixtures are potential working fluids for ORC power systems.
  • The temperature-glide at phase change leads to temperature match with

heat source and sink. Compared to pure components lower irreversibilities and higher efficiency is obtained.

  • In the context of a thermo-economic evaluation, a reduction of heat transfer

characteristics due to additional mass transfer resistance has to be taken into account for zeotropic mixtures.

  • A comparison to pure working fluids is performed to clarify, if the efficiency

increase overcompensates the additionally required heat transfer surface.

12.10.2015 Page 2

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SLIDE 3

Page 3

Introduction

General approach

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 3

Boundary conditions / Fluid selection Simulations / Second law analysis Design of key components Cost estimation / Economic evaluation

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SLIDE 4

Page 4

Boundary conditions

Parameter Value mass flow rate of heat source ṁHS 10 kg/s

  • utlet temperature of heat source THS,in

80 °C inlet temperature of cooling medium TCM,in 15 °C temperature difference of cooling medium ΔTCM 15 °C maximal ORC process pressure p2 0.8∙pcrit isentropic efficiency of feed pump ηi,P 75 % isentropic efficiency of turbine ηis,T 80 % efficiency of generator ηG 98 %

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 4

  • Subcritical and saturated cycle
  • Heat input of 3 MW by pressurized water

at 6 bar and 150 °C

  • Additional boundary conditions:

H H

cooling water

injection drill hole production drill hole

5 4 3 2 1

evaporator

ORC - working fluid geothermal water

preheater generator turbine condenser pump

H H

cooling water

injection drill hole production drill hole

5 4 3 2 1

evaporator

ORC - working fluid geothermal water

preheater generator turbine condenser pump

heat transfer medium cooling medium

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SLIDE 5

Page 5

Fluid selection

Investigated working fluids

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 5

  • Pure fluids: R245fa, isobutane, isopentane
  • Zeotropic mixture: isobutane/isopentane

 Composition is varied in discrete steps of 10 mole-%

20 40 60 80 100 2 4 6 8 10 12 14

temperature glide (K) mole fraction of isobutane (%)

@ condensation @ evaporation

isobutane/isopentane

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SLIDE 6

Page 6

Simulations / Second law analysis

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 6

  • The minimal temperature difference in the evaporator and condenser are

chosen as independent design variables in order to identify the most cost- efficient process parameters.

  • Pressure and heat losses are neglected in the pipes and components.
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SLIDE 7

Page 7

Simulations / Second law analysis

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 7

  • The minimal temperature difference in the evaporator and condenser are

chosen as independent design variables in order to identify the most cost- efficient process parameters.

  • Pressure and heat losses are neglected in the pipes and components.
  • Second law efficiency:

where and T0 = 15 °C; p0 = 1 bar

G Pump Fans net II HS HS HS

P P P P η E m e     

HS

e h h T (s s )    

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SLIDE 8

Page 8

Design of key components

Preheater and evaporator – Predefined design specification

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 8

  • Shell and tube heat exchanger for preheater and evaporator (TEMA-E-type)
  • Inner diameter of the tubes:

di = 0.02 m

  • Wall thickness of the tube:

s = 0.002 m

  • Maximum flow velocities (VDI Heat Atlas): ul = 1.5 m/s and ug = 20 m/s
  • Squared layout:

do Pt 1 22

t

  • P

. d 

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SLIDE 9

Page 9

Design of key components

Preheater and evaporator – Heat transfer correlations

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 9

  • Shell side (preheater, evaporator)

Single phase; pressurized water: Kern (1950)

  • Tubes side (preheater)

Single phase; pure fluid & mixture: Sieder and Tate (1936)

  • Tubes side (evaporator)

Two phase; pure working fluid: Steiner (2006) Two phase; zeotropic mixture: Schlünder (1983)

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SLIDE 10

Page 10

Design of key components

Air cooled condenser – Predefined design specification

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 10

  • A tube bank staggered arrangement is considered.
  • Cross-flow heat exchanger with finned tubes.
  • Layout:

d dF pF tF

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SLIDE 11

Page 11

Design of key components

Air-cooled condenser – Heat transfer correlations

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 11

  • Air side

Single phase; air: Shah and Sekulic (2003)

  • Tubes side

Single phase; pure fluid & mixture: Sieder and Tate (1936) Two phase; pure working fluid: Shah (1979) Two phase; zeotropic mixture: Bell and Ghaly (1973), Silver (1964)

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SLIDE 12

Page 12

Cost estimation

Purchased equipment costs (PEC) of the major components

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 12

  • PEC in US $ for ambient operating conditions and a carbon steel construction
  • Equipment cost data according to Turton et al. (2003)

 

2 10 1 2 10 3 10

log log log PEC K K (Y) K (Y)   

component Y; unit K1 K2 K3 Pump (centrifugal) kW 3.3892 0.0536 0.1538 Heat exchanger (floating head) m2 4.8306

  • 0.8509

0.3187 Heat exchanger (air cooler) m2 4.0336 0.2341 0.0497 Turbine (axial) kW 2.7051 1.4398

  • 0.1776
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SLIDE 13

Page 13

Cost estimation

Purchased equipment costs (PEC) of the major components

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 13

  • PEC in US $ for ambient operating conditions and a carbon steel construction
  • Equipment cost data according to Turton et al. (2003)
  • Consideration of inflation and the development of raw material prices
  • Total investment costs (TCI) of the ORC modul according to Bejan et al. (1996)

 

2 10 1 2 10 3 10

log log log PEC K K (Y) K (Y)   

component Y; unit K1 K2 K3 Pump (centrifugal) kW 3.3892 0.0536 0.1538 Heat exchanger (floating head) m2 4.8306

  • 0.8509

0.3187 Heat exchanger (air cooler) m2 4.0336 0.2341 0.0497 Turbine (axial) kW 2.7051 1.4398

  • 0.1776

 

2014 2001 2014 2001 k , k ,

PEC PEC CEPCI / CEPCI  

2014

6 32

k ,

TCI . PEC  

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SLIDE 14

Page 14

Economic evaluation

Economic boundary conditions and parameters

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 14

  • Economic boundary conditions

parameter lifetime 20 years interest rate ir 4.0 % annual operation hours 7500 h/year Cost rate for operation and maintenance 0.02∙Z̈CI Costs for process integration CPI 0.2∙PECtotal Power requirements of the air-cooling system 5 kWe/MWth Electricity price 0.08 €/kWh

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SLIDE 15

Page 15

Economic evaluation

Economic boundary conditions and parameters

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 15

  • Economic boundary conditions
  • Calculated economic paramters

costs per unit exergy (Bejan et al.) specific investment costs

parameter lifetime 20 years interest rate ir 4.0 % annual operation hours 7500 h/year Cost rate for operation and maintenance 0.02∙Z̈CI Costs for process integration CPI 0.2∙PECtotal Power requirements of the air-cooling system 5 kWe/MWth Electricity price 0.08 €/kWh

F ,tot F ,tot k P,tot k P,tot P,tot P,tot

(c E Z ) C c E E   

tot,ORC net

C SIC P 

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SLIDE 16

Page 16

Results

Minimization of costs per unit exergy – R245fa

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 16

  • Minimal costs per

unit exergy are identified for each working fluid.

  • In case of R245fa

cp,total minimal for ΔTPP,E = 1 K and ΔTPP,C = 13 K.

  • Corresponding

LCOE = 106.6 €/MWh

TPP,E (K)

8 9

1 0

1 1

1 2

1 3

1 4

1

2 3

4 5

6

56

57

5 8

5 9

6

TPP,C (K)

costs per unit exergy (€/GJ)

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SLIDE 17

Page 17

Results

Costs per unit exergy – Variation of working fluids

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 17

7 8 9 10 11 12 13 14 15 16 50 52 54 56 58 60 62 11 12 13 14 15 16 17 18 19 50 52 54 56 58 60 62 isobutane/isopentane

isobutane isopentane costs per unit exergy (€/GJ)

TPP,C (K)

R245fa

30/70 70/30 90/10 10/90

costs per unit exergy (€/GJ)

TPP,C (K)

50/50

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SLIDE 18

Page 18

Results

Costs per unit exergy – Variation of working fluids

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 18

7 8 9 10 11 12 13 14 15 16 50 52 54 56 58 60 62 11 12 13 14 15 16 17 18 19 50 52 54 56 58 60 62 isobutane/isopentane

isobutane isopentane costs per unit exergy (€/GJ)

TPP,C (K)

R245fa

30/70 70/30 90/10 10/90

costs per unit exergy (€/GJ)

TPP,C (K)

50/50

 Most cost-efficient parameters for the investigated fluids and compositions.  Here, ΔTPP,E is chosen according to the cost minimum.

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SLIDE 19

Page 19

Results

Most cost-effective parameters depending on fluid selection

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 19

parameter isobutane R245fa isopentane isobutane/isopentane (90/10) Atotal (m2) 1043.4 1039.8 1065.4 1005.9 ΔTPP,E (K) 1.2 1.0 1.0 2.0 ΔTPP,C (K) 14.0 13.0 13.0 15.0 PG (kW) 387.8 345.9 331.0 366.4 PPump (kW) 60.1 21.6 12.1 41.4 ηII (%) 30.3 30.0 29.4 30.0 PECtotal,ORC 450,585 439,328 442,292 440,779 SIC (€/kW) 1,162 1,270 1,336 1,203 cp,tot (€/GJ) 52.0 56.8 59.8 53.8

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SLIDE 20

Page 20

Results

Most cost-effective parameters depending on fluid selection

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 20

parameter isobutane R245fa isopentane isobutane/isopentane (90/10) Atotal (m2) 1043.4 1039.8 1065.4 1005.9 ΔTPP,E (K) 1.2 1.0 1.0 2.0 ΔTPP,C (K) 14.0 13.0 13.0 15.0 PG (kW) 387.8 345.9 331.0 366.4 PPump (kW) 60.1 21.6 12.1 41.4 ηII (%) 30.3 30.0 29.4 30.0 PECtotal,ORC 450,585 439,328 442,292 440,779 SIC (€/kW) 1,162 1,270 1,336 1,203 cp,tot (€/GJ) 52.0 56.8 59.8 53.8 1061.4 1.0 13.0 54.0

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SLIDE 21

Page 21

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 21

Sensitivity analysis regarding thermodynamic and economic parameters

  • 20
  • 10

10 20 45.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5 65.0

costs for O&M interest rate

costs per unit exergy (€/GJ) deviation from standard boundary conditions (%)

  • Low influence of

ir and CO&M (maximal deviation: 2.9 %)

working fluid: isobutane

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SLIDE 22

Page 22

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 22

Sensitivity analysis regarding thermodynamic and economic parameters

  • 20
  • 10

10 20 45.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5 65.0

costs for O&M interest rate cost factor

(here: TCI = 6.32 PEC)

costs per unit exergy (€/GJ) deviation from standard boundary conditions (%)

·

  • Low influence of

ir and CO&M (maximal deviation: 2.9 %)

  • Cost factor for

estimation of TCI with medium relevance (maximal deviation: 6.7 %)

working fluid: isobutane

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SLIDE 23

Page 23

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 23

Sensitivity analysis regarding thermodynamic and economic parameters

  • 20
  • 10

10 20 45.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5 65.0

costs for O&M costs for process integration interest rate cost factor isentropic efficiency

  • f turbine

costs per unit exergy (€/GJ) deviation from standard boundary conditions (%)

  • Low influence of

ir and CO&M (maximal deviation: 2.9 %)

  • Cost factor for

estimation of TCI with medium relevance (maximal deviation: 6.7 %)

  • High sensitivity for

ηi,T and CPI (maximal deviation: 19.7 %)

working fluid: isobutane

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SLIDE 24

Page 24

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 24

Sensitivity analysis regarding thermodynamic and economic parameters

  • 20
  • 10

10 20 45.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5 65.0

costs for O&M costs for process integration interest rate cost factor isentropic efficiency

  • f turbine

costs per unit exergy (€/GJ) deviation from standard boundary conditions (%)

  • Low influence of

ir and CO&M (maximal deviation: 2.9 %)

  • Cost factor for

estimation of TCI with medium relevance (maximal deviation: 6.7 %)

  • High sensitivity for

ηi,T and CPI (maximal deviation: 19.7 %)

working fluid: isobutane

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SLIDE 25

Base case (Bejan et al.) Cost factor 4.31 (Bejan et al.) Grass roots costs (Turton et al.)

10 20 30 40 50

costs per unit exergy (€/GJ)

  • Cost estimation - method for TCI

Page 25

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 25

Ongoing refinements of the thermo-economic model working fluid: isobutane

2014 BM ,k BM ,k k ,

C F PEC  

2014

4 31

k ,

TCI . PEC  

BM ,tot BM ,k

C CB   1 18 0 5

BM ,tot BM ,tot

TCI . C . C    

Grass roots costs: FBM,k: Bare module cost factor corrected for material and pressure > 1 atm

2014

6 32

k ,

TCI . PEC  

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SLIDE 26

Page 26

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 26

Ongoing refinements of the thermo-economic model

B a s e c a s e ( B e j a n e t a l . ) C

  • s

t f a c t

  • r

4 . 3 1 ( B e j a n e t a l . ) G r a s s r

  • t

s c

  • s

t s ( T u r t

  • n

e t a l . ) C

  • s

t d a t a

  • f

U l r i c h e t a l .

10 20 30 40 50

costs per unit exergy (€/GJ) working fluid: isobutane

  • Cost estimation - method for TCI
  • Cost estimation - database

working fluid: isobutane Chemical Engineering Process Design and Economics, A Practical Guide. 2nd Edition,

  • G. D. Ulrich and
  • P. T. Vasudevan,

2004; Process Publishing.

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SLIDE 27

Page 27

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 27

Ongoing refinements of the thermo-economic model

parameter isobutane R245fa isopentane isobutane/isopentane ηi,T (%) 78.5 80.6 80.2 78.8 rdηi,T (%)

  • 1.88

0.75 0.25

  • 1.50

SP (-) 0.0486 0.082 0.0729 0.0508 NS (-) 0.0759 0.0768 0.0767 0.076 Dmean (mm) 130.5 220.1 195.7 136.7 cp,tot (€/GJ) 52.20 59.05 56.69 54.02 rdcp,tot (%) 0.38

  • 1.25
  • 0.19

0.41

 Tool for prediction of the performance of low reaction, axial turbine stages

 P. Klonowicz, F. Heberle, M. Preißinger, D. Brüggemann: Significance of loss correlations in performance prediction of small scale, highly loaded turbine stages working in Organic Rankine

  • Cycles. Energy, vol. 72, pp. 322-330, 2014
  • Cost estimation - method for TCI
  • Cost estimation - database
  • Turbine model
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SLIDE 28

Page 28

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 28

Ongoing refinements of the thermo-economic model

parameter isobutane R245fa isopentane isobutane/isopentane ηi,T (%) 78.5 80.6 80.2 78.8 rdηi,T (%)

  • 1.88

0.75 0.25

  • 1.50

SP (-) 0.0486 0.082 0.0729 0.0508 NS (-) 0.0759 0.0768 0.0767 0.076 Dmean (mm) 130.5 220.1 195.7 136.7 cp,tot (€/GJ) 52.20 59.05 56.69 54.02 rdcp,tot (%) 0.38

  • 1.25
  • 0.19

0.41

 Tool for prediction of the performance of low reaction, axial turbine stages

 P. Klonowicz, F. Heberle, M. Preißinger, D. Brüggemann: Significance of loss correlations in performance prediction of small scale, highly loaded turbine stages working in Organic Rankine

  • Cycles. Energy, vol. 72, pp. 322-330, 2014
  • Cost estimation - method for TCI
  • Cost estimation - database
  • Turbine model
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SLIDE 29

Page 29

Results

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 29

Ongoing refinements of the thermo-economic model

parameter isobutane R245fa isopentane isobutane/isopentane ηi,T (%) 78.5 80.6 80.2 78.8 rdηi,T (%)

  • 1.88

0.75 0.25

  • 1.50

SP (-) 0.0486 0.082 0.0729 0.0508 NS (-) 0.0759 0.0768 0.0767 0.076 Dmean (mm) 130.5 220.1 195.7 136.7 cp,tot (€/GJ) 52.20 59.05 56.69 54.02 rdcp,tot (%) 0.38

  • 1.25
  • 0.19

0.41

 Tool for prediction of the performance of low reaction, axial turbine stages

 P. Klonowicz, F. Heberle, M. Preißinger, D. Brüggemann: Significance of loss correlations in performance prediction of small scale, highly loaded turbine stages working in Organic Rankine

  • Cycles. Energy, vol. 72, pp. 322-330, 2014
  • Cost estimation - method for TCI
  • Cost estimation - database
  • Turbine model

Input for cost estimation

  • Consideration of pressure losses
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SLIDE 30

Page 30

Conclusions

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 30

  • In this study, isobutane leads to the lowest specific costs of the product.
  • For the mixture (isobutane/isopentane) a mole fraction of 90 % isobutane

leads to the lowest specific costs of the product.

  • In contrast to geothermal applications, where the exploitation plays the major

cost role, the mixture does not lead to the most cost efficient system for the considered WHR case study.

(cf., F. Heberle and D. Brüggemann: Thermoeconomic Analysis of Hybrid Power Plant Concepts for Geothermal Combined Heat and Power Generation. Energies 2014, vol. 7, Issue 7, pp. 4482-4497, 2014)

  • The isentropic efficiency of the turbine and the cost for process integration

are the most sensitive parameters concerning the economic evaluation.

  • More detailed cost estimation for the axial turbine and a consideration of

pressure losses will be implemented.

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SLIDE 31

Page 31

Acknowledgements

The authors gratefully acknowledge financial support from

12.10.2015 Thermo-economic analysis of zeotropic mixtures and pure working fluids in ORC for WHR -

  • F. Heberle and D. Brüggemann

Page 31

“Fluid mixtures for efficiency increase of Organic Rankine Cycles in selected applications” (Grant no. 1713/12-1 and -2)

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SLIDE 32

www.zet.uni-bayreuth.de

Thank you

Florian Heberle and Dieter Brüggemann