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ABOVE GROUND GEOTHERMAL ALLIED TECHNOLOGIES
HEAT EXCHANGER DESIGN FOR MATERIALS RESEARCH
Holger Heinzel HERA NZWC
Project context Kn
ow
led
ge B
ase
Expert design tool
Material Knowledge Base Research
Understanding and Modelling Scaling Mechanism
Heat Transfer Performance Data
Expander Technology Research
Control Technology Research
Tech
no
logi
cally
Ad
van
ced
Lo
w
Enth
alp
y C
on
vers
ion
Sys
tem
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
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
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
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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
Above Ground Geothermal Technologies Workshop 2014
Material test facility
Test material performance under conditions similar to ORC plant
– Chemical composition of brine
– Physical conditions (Temp, pressure)
– Flow conditions
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
Geothermal test rigs
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
HX calculations II
4 temperature matrices:
• Geothermal brine
• Cooling fluid
• Wall temperature tube-side
• Wall temperature shell-side
Above Ground Geothermal Technologies Workshop 2014
• 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
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014
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
Above Ground Geothermal Technologies Workshop 2014