A high performance titanium sheet for plate type heat exchanger

Transcription

1 A high performance titanium sheet for plate type heat exchanger October 6 th 2010 DAISUKE HAYASHI Titanium Marketing & Technical Service Section KOBE STEEL, LTD. 1

2 Contents The small thermal energy conversion, such as OTEC Requirements to material for PHE Press formability development with Pre-coated titanium The technology to improve the thermal efficiency of vapor heat exchanger 2

3 What s the OTEC? Ocean Thermal Energy Conversion (OTEC) is the power generation system with an extremely low emission of carbon dioxide. 3

4 Principles of OTEC Technology There is a temperature difference of over 20 degrees Celsius in the ocean. 4

5 Principles of OTEC Technology 2Turbine 5Warm seawater pump 1Evaporator 3Condenser 6Cold seawater pump 4Working fluid pump One major characteristic of OTEC is the use of a working fluid such as ammonia with low boiling point. 5

6 Heat exchanger of Evaporator and Condenser A cross section of tubular Heat effective range Fluid A cross section of plate channel Heat effective range Fluid PHE can improve heat transfer efficiency. Shell & tube heat exchanger Plate heat exchanger Titanium Plate Heat Exchanger is the best. 6

7 OTEC Roadmap Power Generation Output [MW] C.Y Hawaii (U.S.A.) 1) France 2) 200 Japan 3) ) The Hawaii Clean Energy Initiative 2) IFREMER 3) New Energy and Industrial Technology Development Organization Demand of titanium is estimated to be 18,000 MT/1000MW 7

8 Requirements to material for PHE Thermal resource is Seawater. A working fluid is Ammonia. Vapor pressure in plate channels is about 15MPa. Plates are manufactured by Press forming. Temperature Difference is small. Requirements High corrosion resistance Higher Strength with Good formability High heat transfer rate Solution Titanium Pre-coated Gr.2 titanium Design optimization of material & PHE 8

9 Press formability development with Pre-coated titanium 9

10 Lubricant for Press forming Comparison of usual lubricant method oil film Press formability Not good Good Dimensional accuracy of products Good Not good Productivity Good Not good Pre-coated? Good Good Good Erichsen value(mm) Material Grade ASTM G1 Thickness 0.8mm Finish 2B without lubricant oil film(p.e.) Lubricant and press formability of Titanium Sheet 10

11 Design concept of coating Hard to break after severe forming Enough thin for forming accuracy Easily removed after forming 11

12 Contents of pre-coat layer Contents mass % Roll Acrylic Resin 80 1) holds sufficient adhesive strength. 2) maintains enough flexibility to severe deformed surface. 3) Dissolves easily into alkaline solution. Silica ~10 1) gives moderate hardness Polyolefin wax ~10 1) leads to low static/dynamic friction. Pre-coat layer contains no harmful metal and organic chemicals. 12

13 Stretch formability of Pre-coated titanium Height to Failure (mm) kN with Press Oil Pre-coated with Polyethylene film 150kN Blank Holder Force Pre-coated titanium shows excellent formability compared to one with polyethylene film as lubricant. 13

14 Evaluation method thickness:0.5mm A of formability In practical size die How to Score (Index for Press-formability) 500 A A-A Cross section A Convex A 14.9mm Concave Forming Height :4.5mm Radius of beams :3.4mm Pitch between beams :14.9mm 1.Evaluation Points and their number 1 Apex:18 (Concave) 18 (Convex) 2 Ends of beams :56 2.Scoring at each point(e) 4 : No Crack 3 : Necking 2 : Severe Necking 1 : Small Crack 0 : Large Crack ΣE 1,2 100 Score(%)= ( ) 14

15 Press formability Good formability Score (%) in practical size die with Press oil Pre-caoted Conventional CP titanium for PHE Gr.1 Gr Tensile Strength (MPa) 20% stronger pre-coated titanium has same excellent press formability as a conventional CP titanium for PHE using press oil as a lubricant. 15

16 Removable coating layer by alkali cleaner Removal rate of coating layer/ % Weak Alkali Cleaner Strong Alkali Cleaner Dipping time / sec Only 60 sec. dipping in alkali cleaner can remove pre-coating layer perfectly. 16

17 Technology to improve the thermal efficiency of vapor heat exchanger 17

18 Improvement process 1. Elucidating and characterizing the behavior of ammonia on a compact plate evaporator, a type of PHE Because the boiling heat transfer performance of ammonia has not yet been elucidated. 2. Design optimization of material & PHE 18

19 Experimental apparatus Working fluid side frame Hot Water Warm heat source side frame Plate Sight Glass T.C. holes Working fluid (Tbulk) Twall 100 Working fluid 100 l2 T2 Urethane tube Plate l1 T1 Hot water Thermocouple sheath Spacer Test plate

20 Local boiling heat transfer Local heat transfer coefficient h loc [W/(m 2 K)] Ammonia Z= Ammonia / water mixture G = 7.5 kg/m 2 s G = 10 kg/m 2 s G = 15 kg/m 2 s q av =20 kw/m 2 P abs =0.8 MPa quality x [-] Comparisons of local heat transfer coefficient on quality at different mass flux 20

21 Visualization Z=1.0 Z=1.0 Quality 0.28 Quality 0.63 Z=0.9 Z=0.9 Flow direction Quality 0.26 Quality 0.66 G = 10kg/m 2 s, q av = 20kW/m 2, P abs = 0.7MPa 21

22 Conclusions KOBE STEEL has been developing the high performance titanium for PHE of small thermal energy conversion. Pre-coated titanium for good formability Titanium with high heat transfer coefficient ( under development ) There is a possibility to apply these technologies to the conventional heat exchanger. 22

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