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HYDROGEN FLUORIDE

HYDROGEN FLUORIDE . CHEMICAL ENGINEERING DESIGN PRESENTATION 02/05/02. Hydrogen Fluoride Manufacture for the Semiconductor Industry. Important bulk chemical used as an intermediate for the production of refrigerants and solvents

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HYDROGEN FLUORIDE

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  1. HYDROGEN FLUORIDE CHEMICAL ENGINEERING DESIGN PRESENTATION 02/05/02

  2. Hydrogen Fluoride Manufacture for the Semiconductor Industry • Important bulk chemical used as an intermediate for the production of refrigerants and solvents • Development of the electronics industry means that it is becoming an increasingly important chemical, where it is used for etching silicon chips • Concerns over its transport and storage has led to an interest in small ‘point of use’ plants

  3. BASICS… • All processes follow the same basic chemistry H2SO4(l) + CaF2(s)2HF(g)+ CaSO4 (s) • Similar feed preparation, solids handling and separation • Producing 100te/yr of HF

  4. 3 PROCESSES WERE DEVELOPED • SOLID-LIQUID • Buss kneader and rotary kiln reactor • Simple separation scheme • SLURRY • Three-phase, co-current upflow reactor • Complex separation scheme with diluent recovery • SOLID-GAS • Fluidised bed reactor • Simple separation scheme

  5. BLOCK FLOW DIAGRAM FOR ALL PROCESSES HF PRODUCT All Processes Slurry AREA 600 HIGH PURITY UNIT AREA 400 SEPARATION SECTION AREA 300a SLURRY SEPARATION AREA 200 REACTOR SECTION AREA 300b SLURRY SOLIDS HANDLING AREA 100 FEED PREPARATION AREA 500 SOLIDS HANDLING CaF2 BY-PRODUCT

  6. PRESENTATION OUTLINE • AREA 100 – FEED PREPARATION • AREA 200 – SOLID-GAS REACTOR – SOLID-LIQUID REACTOR • AREA 400 – GENERAL SEPARATION • AREA 500 – SOLIDS HANDLING • AREA 300 + SLURRY PROCESS DIFFERENCES • AREA 200 – SLURRY PROCESS REATOR • AREA 600 – HIGH PURITY UNIT • HAZARDS AND SAFETY ANALYSIS • COST, CONCLUSIONS AND RECOMMENDATIONS

  7. AREA 100 - Feed Preparation • Fluorspar • Steam (2 and 10.6 bar) • Sulfur trioxide • Sulfuric acid • Diluent hexafluorobenzene (slurry only)

  8. Storage tank Fluorspar Steam (10.62 bar) Steam (2 bar) Sulfur trioxide Diluent Sulfuric acid Screw conveyor Lock hopper Lock hopper Steam boiler Main Reactor Main Reactor Steam boiler High purity unit Storage tank Vapouriser Main Reactor Storage tank Main Reactor Reactor gas absorber Storage tank Mixing vessel Sulfuric acid absorber

  9. Area 200: Solid-Gas Reactor • 3 Stage Fluidised Bed Reactor • Reaction 1 (Main) • CaF2(s) + H2SO4(l) 2HF(g) + CaSO4(s) • Reaction 2 (Heat) • SO3(g) + H2O(g) H2SO4(g) + Heat

  10. Operating Conditions/Performance 0.4m • Conversion of CaF2 = 99% • Temperature = 400oC • Pressure = 10 bar(a) • Acid : Spar Ratio = 1.15 • Residence Time (CaF2) =15 minutes 0.85m 2.75m 1.5m 0.1m

  11. H2SO4(l) ATOMISER FLUIDISED BED SECTION OF REACTOR SOLIDS FROM CYCLONE SOLID REACTANT (CaF2) 3 FLOW OF HOT GASES DISTRIBUTOR PLATE FLOW OF SOLIDS 2 FLUIDISED SOLIDS 1 WASTE SOLIDS (CaSO4) SO3(g) H2O(g)

  12. TOP SECTION OF REACTOR HF (+H2SO4) TO SEPARATION AREA 400 CYCLONE SOLIDS FLOW OF HOT GASES FLOW OF SOLIDS SOLIDS TO STAGE 3

  13. AREA 200: SOLID-LIQUID PROCESS REACTOR • BFD • PROBLEM • LARGE SCALE SMALL SCALE • INDUSTRY - KNEADER & KILN • THINK DIFFERENT! H2SO4 HF REACTOR CaF2 CaSO4

  14. KNEADER • DIRECT SCALE DOWN • DIMENSIONS • T = 200°C, P = 10 bara • HEATING • DIRECT RESISTANCE • ALTERNATIVE – HEATING TAPE 5.21cm 25.25cm

  15. ROTARY KILN REACTOR • WHY KILN? • DIMENSIONS • T = 400°C, P = 10 bara • PROBLEMS • CONTAINMENT • ROTATION • HEATING 0.175m 0.699m

  16. SOLUTIONS FOR KILN… • PRESSURE VESSEL • ENCOMPASS KILN • CONTAIN ALL PRODUCT • ROTATION • MAGNETIC DRIVE • BALL BEARINGS • ALCOMAX • MICROWAVES • HEAT POLAR LIQUID (AND HENCE PROCESS) • COAXIAL CABLE AND ANTENNA • HIGHLY EFFICIENT BUT COSTLY!

  17. SUMMARY • BASIC BFD • REALISABLE PROCESS SECTION • KNEADER • SCALE DOWN • DIRECT RESISTANCE HEATING • ROTARY KILN • CONTAINED IN PRESSURE VESSEL • ROTATED BY MAGNETS • HEATED WITH MICROWAVE UNIT

  18. Area 400 - Separation Section To atmosphere Reactor Gas Absorber T400 Sulfuric Acid Absorber T420 Condenser E410 Water Absorber T430 From Reactor Area 200 To High Purity Section Area 600 To disposal HF Recycle

  19. T400: Reactor Gas Absorber

  20. E410: Partial Condenser

  21. Area 400 - Separation Section To atmosphere Reactor Gas Absorber T400 Sulfuric Acid Absorber T420 Condenser E410 Water Absorber T430 From Reactor Area 200 To High Purity Section Area 600 To disposal HF Recycle

  22. T420: Sulfuric Acid Absorber • Function: To remove the HF from the vapour feed to the column. • Operating conditions highly favour absorption. • Packed bed construction. • High integrity design. 667 mm 33 mm

  23. T430: HF Recycle & Water Absorber • Recycle: The HF absorbed is recycled along with a quantity from the high purity section to the reactor gas absorber. • Cooling, pressure reduction, pumping and heating are the operations carried out in the recycle of the HF. • Water Absorber: Absorption of remaining HF and conversion of SiF4 to H2SiF6.

  24. Summary • Main stages in the separation section: • (1) Cooling of the reactor gases. • (2) Condensation of the HF passing to the high purity section. • (3) Absorption of remaining HF. • (4) Recycle of the HF.

  25. Area 500 - PFD Solids Handling From Reactor To Separations Compressor P530 Lock-hoppers LH500A/B Cyclone Dust Collector Screw Conveyor S510 TK520A/B Storage Hopper Solids To Disposal

  26. Lock-hoppers LH500A/B Solids In 80 mm LH500A 140 mm 43 mm Hopper Gates 90 mm LH500B 150 mm 70 mm Solids to S510

  27. Storage Hopper TK520A/B Air Out Hot Solids In Cold Air In Cold Air Out Cold Air Injection Jacket of Cold Air Air Injection Distributor Solids Outlet

  28. THE SLURRY PROCESS • H2SO4 + CaF2 2HF + CaSO4 + INERT DILUENT • aids mixing of reactants • improves heat transfer during reaction • Lower operating temperature • comparable or lower residence times • NOT PRACTICAL ON A LARGE SCALE

  29. DILUENT SELECTION • HEXAFLUOROBENZENE (C6F6) • Originally 1,2,4-trichlorobenzene • suspected carcinogen • Criteria for new diluent • Inert under reaction conditions • boiling point higher than reactor temperature • less hazardous than TCB • cost comparable to TCB • Operating pressure raised so product separation easier

  30. SIMPLIFIED BFD OF THE SLURRY PROCESS Non-condensables AREA 100 E300 E310 E320 T420 T430 AREA 200 H2SO4 H2SiF6 CaF2 D330 M360 AREA 600 D350 AREA 500

  31. HF gas + diluent vapour Solid spar Liquid acid Liquid diluent (recycle) Solid calcium sulfate + liquid diluent SLURRY REACTOR - 3-phase continuous reactor able to achieve 99% conversion of calcium fluoride in the presence of a diluent. • acid 15% in excess • amount of diluent used based on 30%w/w CaSO4 in exit slurry

  32. Operating Conditions Op. temp = 200oC Op. Pressure = 20bara - Reactants’ residence time = 80 mins Key issue: how to ensure good mixing between the reacting materials (i.e. acid and solid spar) and keeping the solids in suspension?

  33. Configuration - 3-phase co-current upflow reactor column - height-to-diameter ratio to be determined - critical gas velocity for solid suspension (small variation with reactor height-to-diameter ratios).

  34. Gas, Liquid and Solid holdups - gas residence time estimated as 5 seconds. - vary with column height-to-diameter ratios. - with H/d ratio = 10, Column diameter = 24cm; height = 300cm - vapour recirculation (1 part to separation , 3 parts recirculated) - slurry recirculation - heated by heating tapes (over 90% heating done in Reactor vessel) - Gas disengagement vessel

  35. Vapour Recirculation Reactor L/S sep Feed stream + diluent recycle HF recycle Slurry recirculation V/L sep Gas disengagement drum

  36. Why a High Purity Unit? • Build-up of Contaminants • Ionic & Particulate Materials Damage Wafers • This Reduces Yield & Increases Cost • Advances in Technology • Impurities to be in region of Parts per Billion

  37. SiF4 CO2 SO2 HF H2SO4 As2O3 Metals What Impurities are we Dealing With? • 99.8% pure HF from Separations Section Order of Decreasing Relative Volatility

  38. Process Flowsheet for Area 600 To Recycle Partial Condenser Partial Condenser Partial Condenser Ion Exchange Mechanism HF from Separations 1st Packed Column 2nd Packed Column HF Storage Tank

  39. Other Process Options • An Ultrafiltration Device • An Evaporator • A Refrigerated Packed column • Reusing the spent HF

  40. Hazards and Environmental Impact • Hazards • Materials Present • Operating Conditions • Location • Scale of plant

  41. Hazards and Environmental Impact • Materials • HF and H2SO4 • very hazardous to humans and the environment, particularly aquatic life. • Operating Conditions • High temperatures and pressures • Location • within another manufacturing facility • Plant design and safety features

  42. Hazards and Environmental Impact • Construction Materials • Hastelloy C2000 • Stainless steel • Carbon Steel • Equipment Design • large design margins • Process safety features • Alarms and trips

  43. CAPITAL COST ESTIMATION £2M KEY: £0M Sol-Liq Slurry Sol-Gas £-1.5M

  44. RESULTS • As can be seen, the Solid Liquid Process is the most economically attractive of the three

  45. WHICH PROCESS…? • REACTOR COMPLEXITY • Solid-Liquid ü • Solid-Gas û • Slurry û • SEPARATION COMPLEXITY • Solid-Liquid ü • Solid-Gas ü • Slurry û • EVALUATION OF CAPITAL COSTS • Solid-Liquid ü • Solid-Gas û • Slurry û

  46. CONCLUSIONS AND RECOMMENDATIONS • INITIAL INVESTIGATION… • BUT! FURTHER ANALYSIS REQUIRED SOLID-LIQUID PROCESS

  47. THANK YOU FOR LISTENING! QUESTIONS?

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