HEAT EXCHANGER DESIGN FOR MATERIALS … EXCHANGER DESIGN FOR MATERIALS RESEARCH Holger Heinzel HERA NZWC Project context ase Expert design tool Material Knowledge Base Research Understanding

ABOVE GROUND GEOTHERMAL ALLIED TECHNOLOGIES

HEAT EXCHANGER DESIGN FOR MATERIALS RESEARCH

Holger Heinzel HERA NZWC

Project context Kn

ow

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ase

Expert design tool

Material Knowledge Base Research

Understanding and Modelling Scaling Mechanism

Heat Transfer Performance Data

Expander Technology Research

Control Technology Research

Tech

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Ad

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Enth

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Sys

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s Standardised System Concepts

Heat Exchanger Technology Development

Turbo-Machinery Technology Development

Control Systems Development

Material Knowledge Base Research Research team - HERA Welding Centre - University of Canterbury Timeframe

01/10/2012 - 01/10/2016

Research Aim

What material performs best for any given application in the AGGAT environment ?

Objectives Identification and characterisation of

• standard and novel materials and • surface modifications

for components within an ORC plant

Built up industry capability to manufacture and deliver equipment and sample materials required for the research and consulting services.

Performance parameters

• Corrosion performance • scaling • heat transfer • thermal and corrosion fatigue • ability to fabricate • economic • sustainability

Above Ground Geothermal Technologies Workshop 2014

Material selection

Goal: best performance at minimal life cycle cost

Required: • performance criteria for components in

AGGAT environment Pathway:

• Identify material solutions through research and testing

In geothermal binary plant: • Heat exchanger main challenge:

• geothermal brine • organic medium


Common problems

Fouling and Scaling

• is the accumulation of unwanted material on solid surfaces to the detriment of function – Fouling

caused by coarse matter

– Scaling

crystallization of solid salts, oxides and hydroxides

Corrosion

• is the gradual destruction of material, usually metals, by chemical reaction with its environment


Influencing factors / Effects Effects on corrosion/scaling on Heat exchanger • Reduced (thermal) efficiency • Reduced flow • Induced under-deposit

corrosion • Increased use of cooling water • may induce vibrations Turbines • Reduced efficiency • Increased probability of failure

Factors influencing corrosion and scaling

• pH • Temperature • Velocity of flow • Pressure • Microbial growth • Suspended Solid Material and

Deposits

Minimize fouling and corrosion • Selection of low corrosive material • Specification of surface condition • Selection of coating


Primary fluids Chemical composition of geothermal brines (worldwide incl. NZ)

Country Name Type degC pH Li Na K Rb Cs Mg Ca B HCO3 SiO2 SO4 Cl

- Seawater 4 7.8 0.2 10560 380 0.13 <0.1 12700 400 5 140 2710 19000

Colombia Ruiz acid spring 62 1.2 0.3 280 224 0.37 0.04 155 214 8 154 10670 1350

Colombia Ruiz neutral spring 94 8 3.8 610 78 0.56 0.62 5.1 48 19 175 180 41 100

Guatemala Zunil well 300 8.4 8.1 1030 210 1.90 2.00 0.01 11 45 150 890 61 1700

Mexico Araro spring 92 8.1 6.6 705 50 0.43 1.12 0.3 30 75 63 230 135 1010

NZ Maui well 130 7.5 3.6 7880 440 0.71 0.08 48 190 15 630 36 18 12600

NZ Morere spring 47 7 4.6 6700 84 0.10 0.00 80 2360 57 30 27 <3 15800

NZ Ngawha spring 80 7.2 10.4 910 64 0.29 0.60 1.4 11 850 330 150 446 1290

NZ Ngawha well 230 7.1 10.9 880 75 0.30 0.75 0.1 3 895 310 285 26 1240

NZ Wairakei spring 99 7.7 14.5 1220 140 2.30 2.10 4.5 30 43 30 320 30 2100

NZ Wairakei well 240 8.5 10.7 1170 167 2.20 2.00 0.01 20 26 5 590 35 1970

NZ Waitangi Soda spring 49 7.3 1.7 285 24 0.11 0.07 8.9 17 3 365 176 48 365

NZ White Island spring 98 0.6 2.9 5910 635 5.40 0.36 3800 3150 160 <1 4870 38700

Solomon Is. Paraso spring 56 5.6 1.8 1210 178 0.74 0.09 26.6 289 16 6 150 205 2340

Vanuatu Yasur spring 99 8.8 0.3 1210 73 0.16 0.01 0.3 17 21 75 270 280 1690

min 47 0.6 0.3 285 24 0.1 0.004 0.01 3 3 5 27 18 100

avg. 124 7 6 2286 171 1 1 306 475 171 181 275 516 6223

max 300 8.8 14.5 7880 635 5.4 2.1 3800 3150 895 630 890 4870 38700

Each location poses a challenge in its own rights

Highly variable Above Ground Geothermal Technologies Workshop 2014

Material solutions

Material selection • Plan carbon / low alloy steels • Stainless steel • Ti and Ti alloys • Nickel based alloys • Copper alloys • Tantalum & Zirconium • Al and Al alloys • Fibre reinforced materials

Coatings • Epoxy coatings

– Ceramic filled

• Polymer coatings • Phenolic resin • Inorganic and composite coatings • Metal coatings

Manufacturing option • Pipe welded from narrow strip

material


Material test facility

Test material performance under conditions similar to ORC plant

– Chemical composition of brine

– Physical conditions (Temp, pressure)

– Flow conditions


Design objectives

Test material performance under conditions similar to ORC plant • Chemical composition of brine // Physical

conditions //Flow conditions

Replicate standard HX design • Standard material dimensions • Standard material shapes

Cooling of brine to less than 80 °C - arsenic or antimony sulphide scaling Allow different materials to be tested simultaneously


Test rig: 1st test site

Geothermal brine

Temperature °C 135

Pressure bar 4-5

Chemistry

pH 8.5 @ 18 ºC

Barium mg/l 0.004

Boron mg/l 25

Bromide mg/l 4.7

Calcium mg/l 16.8

Chloride mg/l 1850

Potassium mg/l 184

Silica (as SiO2) mg/l 559

Sodium mg/l 1130

Sulphate mg/l 39

Antimony (Screen level) mg/l 0.11

Arsenic (Screen level) mg/l 4.3

Cooling water

Type Grey water

Temperature °C enviro

Wairakei Geothermal Field


Geothermal test rigs


Gross Schoenebeck, Germany

Soultz-sous-Forets, France

Salton Sea, USA

Mammoth, USA

HX types

• Type of heat exchangers

– Shell and Tube / Plate /…

• Tube arrangements

– Straight / U-tubes

• Flow arrangements

– Counter flow / parallel flow / cross flow


U-tubes

Straight tubes

Plate heat exchanger

HX calculations I

Calculation steps

Fluid temperatures, fluid properties, geometry

Reynolds numbers

Nusselt numbers

Heat transfer coefficients

Temperature drop

Simplifications

• Single pipe

• Heat transfer coefficient constant over tube length

• Fluid properties of brine similar to normal water

• No axial heat transfer over tube length

• Mathcad Express Excel sheet

• Iterative process


HX calculations II

4 temperature matrices:

• Geothermal brine

• Cooling fluid

• Wall temperature tube-side

• Wall temperature shell-side


• Shell and Tube HX with baffles – Cross- and Counter-flow zones

• Half HX-model (symmetric)

• Sectioning into finite volumes

• Separate wall-temperature calculation in each baffle area

• GNU-Octave

HX Calculation results


Example: Results for max brine flow rates

85

90

95

100

105

110

115

120

125

130

0 2 4 6 8 10

Ou

tle

t te

mp

era

ture

of

brin

e [

de

gC

]

Length of tube [m]

Length of tube:

Temperature of geothermal brine

Temperature of cooling fluid

Material test rig

• Shell and Tube Heat exchanger (small scale)

• Single pass of hot brine

• Vertical arrangement

• Brine in tubes • Cooling water in shell


Test rig: Instrumentation Adjustment of flow(s) through HX Monitoring and Recording of Process Data

• Pressure • In and Out

• Temperature • Hot/cold side • In /Out

• Flow • Hot/cold side • In /Out


Summary

Customized field test rig designed to investigate materials performance in the AGGAT environment

Comparative analysis of 19 tubes of different materials

Design optimized for increased likelihood of scaling

Results will benefit design of AGGAT components


Documents

HEAT EXCHANGER DESIGN FOR MATERIALS … EXCHANGER DESIGN FOR MATERIALS RESEARCH Holger Heinzel HERA NZWC Project context ase Expert design tool Material Knowledge Base Research Understanding