HYDROGEN FLUORIDE

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HYDROGEN FLUORIDE

• CHEMICAL ENGINEERING DESIGN PRESENTATION 02/05/02

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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

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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

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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

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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

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AREA 100 - Feed Preparation

• Fluorspar
• Steam (2 and 10.6 bar)
• Sulfur trioxide
• Sulfuric acid
• Diluent hexafluorobenzene (slurry only)

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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
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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

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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
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FLUIDISED BED SECTION OF REACTOR
SOLIDS FROM CYCLONE

SOLID REACTANT (CaF2)
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FLOW OF HOT GASES
DISTRIBUTOR PLATE
FLOW OF SOLIDS
2
FLUIDISED SOLIDS
1
WASTE SOLIDS (CaSO4)
SO3(g)
H2O(g)
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TOP SECTION OF REACTOR
HF (H2SO4) TO SEPARATION AREA 400

CYCLONE
SOLIDS
FLOW OF HOT GASES
FLOW OF SOLIDS
SOLIDS TO STAGE 3
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AREA 200 SOLID-LIQUID PROCESS REACTOR

• BFD
• PROBLEM
• LARGE SCALE SMALL SCALE
• INDUSTRY - KNEADER KILN
• THINK DIFFERENT!

H2SO4
HF
REACTOR

CaF2
CaSO4
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KNEADER

• DIRECT SCALE DOWN
• DIMENSIONS
• T 200C, P 10 bara
• HEATING
• DIRECT RESISTANCE
• ALTERNATIVE HEATING TAPE

5.21cm
25.25cm
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ROTARY KILN REACTOR

• WHY KILN?
• DIMENSIONS
• T 400C, P 10 bara
• PROBLEMS
• CONTAINMENT
• ROTATION
• HEATING

0.175m
0.699m
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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!

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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

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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
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T400 Reactor Gas Absorber
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E410 Partial Condenser
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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
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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
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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.

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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.

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

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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

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SIMPLIFIED BFD OF THE SLURRY PROCESS
Non-condensables
AREA 100
E300
E310
E320
T420
T430
AREA 200
H2SiF6
H2SO4
CaF2
D330
M360
AREA 600
D350
AREA 500
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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 30w/w CaSO4 in
  exit slurry

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Operating Conditions
Vapour Pressure Boiling point (oC)
17 203
20 212
25 230
30 248
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?
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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).
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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
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V/L sep
Gas disengagement drum
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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

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What Impurities are we Dealing With?

• 99.8 pure HF from Separations Section

Order of Decreasing Relative Volatility
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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
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Other Process Options

• An Ultrafiltration Device

• An Evaporator

• A Refrigerated Packed column

• Reusing the spent HF

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Hazards and Environmental Impact

• Hazards
• Materials Present
• Operating Conditions
• Location
• Scale of plant

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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

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Hazards and Environmental Impact

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

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CAPITAL COST ESTIMATION
2M
KEY
0M
Sol-Liq
Slurry
Sol-Gas
-1.5M
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RESULTS

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

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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

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CONCLUSIONS AND RECOMMENDATIONS

• INITIAL INVESTIGATION
• BUT! FURTHER ANALYSIS REQUIRED

SOLID-LIQUID PROCESS
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THANK YOU FOR LISTENING!

• QUESTIONS?