public defence of master’s dissertation by p.j. yekoladio€¦ · conclusions &...

P u b l i c D e f e n c e o f M a s t e r ’ s d i s s e r t a t i o n

b y

P . J . Y e k o l a d i o

S u p e r v i s o r s : P r o f T . B e l l o - O c h e n d eP r o f J . P . M e y e r

D e p a r t m e n t o f M e c h a n i c a l &A e r o n a u t i c a l E n g i n e e r i n gU n i v e r s i t y o f P r e t o r i a

THERMODYNAMIC OPTIMIZATION OF SUSTAINABLE ENERGY SYSTEM:

APPLICATION TO THE OPTIMAL DESIGN OF HEAT EXCHANGERS FOR

GEOTHERMAL POWER SYSTEMS

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Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Introduction

Geothermal energy, an alternative energy source for electric power generation: Economic competitiveness Operational reliability Environmentally friendly nature

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Energy conversion systems

Drilling techniques

Reservoir stimulation

Resource exploration and extraction

Part1:Optimal geometry of

coaxial HE

Part 2:Thermodynamic

optimization of ORC

Current Research Activities

This Research

Thesis

Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Research methodology

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Sensitivity analysis

Energy & Exergy

analysisEntropy

Generation Minimization

analysis

Performance analysis

Irreversibility (or exergy loss)

analysis

Optimization model

Heat transfer & fluid flow

analysis

ScopeModel

validation

Research methodology

Flow chart of the simulation procedure

Optimization tool:Optimization tool:Engineering Equation Solver (EES)

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Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Optimal geometry of coaxial HE

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Operating variables:11.

2.

3.

3

Variables to be optimized:

5.

4.

2 5

4

Optimal geometry of coaxial HE

Objective functions: Heat transfer and fluid flow analysis

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Optimal geometry of coaxial HE

Objective functions: Entropy Generation Minimization (EGM) analysis

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Optimal geometry of coaxial HE

Optimized functions:

Optimal diameter ratio

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Pressure loss at lower extremity of well to be neglected for

Optimal geometry of coaxial HE

Optimized functions:

Optimal geothermal mass flow rate

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Where

Where

Optimal geometry of coaxial HE

Optimal geothermal mass flow rate

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(a) Variation in temperature gradient (b) Variation in geothermal resource temperature

Optimal geometry of coaxial HE

Outer diameter of the heat exchanger

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(a) Variation in temperature gradient (b) Variation in geothermal resource temperature

Optimal geometry of coaxial HE

Maximum First- and Second-law efficiency

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(a) Maximum First-law efficiency (b) Maximum Second-law efficiency

Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Organic binary fluids:

Dry: Isobutane & n-pentane

Wet: R152a

Isentropic: R123

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Thermodynamic performance of organic fluids

Thermodynamic performance of organic fluids

Effect of organic binary fluid’s properties on the ORC operating conditions

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(a) Effect of fluid’s boiling point temperature

(b) Effect of fluid’s vapour specific heat capacity

Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Performance analysis of ORC

Organic Rakine Cycles (ORC)1. The Simple ORC

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Performance analysis of ORC

2. The ORC with an internal heat exchanger (IHE)

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Performance analysis of ORC

3. The ORC with an open feed organic heater (OFOH) or the “Regenerative ORC”

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Performance analysis of ORC

4. The ORC with an OFOH & IHE or the “Regenerative ORC with an IHE”

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Performance analysis of ORC

Energy analysis with respect to To: First-law efficiency

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(a) Tgeo = 110oC (b) Tgeo = 160oC

Performance analysis of ORC

Exergy analysis with respect to To: Second-law efficiency

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(a) Tgeo = 110oC (b) Tgeo = 160oC

Performance analysis of ORC

Energy & Exergy analysis with respect to xin: First- & Second-law efficiency

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(a) Tgeo = 110oC (b) Tgeo = 160oC

Performance analysis of ORC

Performance analysis of the ORCs: Cycle net power output

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(a) Tgeo = 110oC (b) Tgeo = 160oC

Performance analysis of ORC

Irreversibility analysis of the ORCs: Overall plant exergy loss

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(a) Tgeo = 110oC (b) Tgeo = 160oC

Performance analysis of ORC

Sensitivity analysis of the ORCs: Variation with TE , TC & Tgeo

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Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Optimized solution

Optimal operating conditions

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(a) Optimal turbine Tin (b) Utilization ratio

Optimized solution

Energy and Exergy analysis with respect to To

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(a) Optimal first-law efficiency

(b) Optimal second-law efficiency

Optimized solution

Energy and Exergy analysis with respect to xin

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(a) First-law efficiency (b) Second-law efficiency

Optimized solution

Performance & Irreversibility analyses

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(a) Minimum overall plant irreversibility

(b) Maximum cycle power output

Content

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Introduction

Research Methodology

Optimal geometry of coaxial HE

Thermodynamic performance of organic fluids

Optimized solution

Conclusions & Recommendations

Performance analysis of ORC

Conclusions & Recommendations

With respect to Tgeo: Optimal operating conditions to increase almost linearly. Maximum cycle power output to increase exponentially.

With respect to the organic binary fluids: Organic fluids with higher Tbp to be preferred for the basic type of ORCs;

e.g.: n-pentane. Organic fluids with lower Cpv more suitable for the regenerative ORCs;

e.g.: isobutane.

With respect to the ORCs configurations: Basic types of ORC to yield maximum cycle power output. The addition of an IHE and/or OFOH to improve significantly the

effectiveness of the conversion of the available geothermal energy into useful work.

Regenerative ORC to be preferred for high-grade geothermal heat. Regenerative ORC with an IHE to yield maximum thermal efficiency.

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The end