ABOVE GROUND GEOTHERMAL ALLIED TECHNOLOGIES HEAT EXCHANGER DESIGN FOR MATERIALS RESEARCH Holger Heinzel HERA NZWC
Technologically Advanced Low Enthalpy Conversion Systems Knowledge Base Project context Expert design tool Material Knowledge Base Research Understanding and Modelling Scaling Mechanism Heat Transfer Performance Data Expander Technology Research Material Knowledge Base Research Research team - HERA Welding Centre - University of Canterbury Timeframe 01/10/2012-01/10/2016 Control Technology Research Standardised System Concepts Heat Exchanger Technology Development Turbo-Machinery Technology Development Control Systems Development
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
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 Factors influencing corrosion and scaling ph Temperature Velocity of flow Pressure Microbial growth Suspended Solid Material and Deposits 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 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 HCO 3 SiO 2 SO 4 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
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: 1 st test site Wairakei Geothermal Field 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
Geothermal test rigs Salton Sea, USA Gross Schoenebeck, Germany Soultz-sous-Forets, France Mammoth, USA
HX types Type of heat exchangers Shell and Tube / Plate / U-tubes Tube arrangements Straight / U-tubes Flow arrangements Counter flow / parallel flow / cross flow 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 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 4 temperature matrices: Geothermal brine Cooling fluid Wall temperature tube-side Wall temperature shell-side
Outlet temperature of brine [degc] HX Calculation results Example: Results for max brine flow rates Length of tube: 130 125 120 115 110 105 100 95 90 85 0 2 4 6 8 10 Length of tube [m] 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