27. mecs chile roundtable urban legends and myths
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Octava Mesa Redonda de Plantasde Acido Sulfúrico
Sulfuric Acid Urban Myths and Legends
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A fictional tale that circulates widely, is told and retoldwith differing details, and is supposedly true.
An urban myth, also known as an urbanlegend, is
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Sources of Myth and Legend in an Industrial Setting
With limited process information, conjecture canbecome reality
Actual events are embellished (a good story spreadsfast!)
Opinion from a credible source becomes reality
Word of a bad experience filters through the industry
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Myth 1:
Which is Better?
> ?8% V2O5
7% V2O5
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A Little About The Makeup Of Catalyst
Catalysts are comprised of > 80% silica support . . .that comes from diatomaceous earths.
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Which Provides Great Surface Area For The Catalyst And GasTo Interact
Sil ica
Suppor t
Catalyst Extrudates: Pores Contain Active PhaseThat Becomes Molten atReaction Temperatures
Fractional Liquid LoadingTypically, 30 to 40% pore
volumes are filled.
Schematic of catalys t pores
Active phase
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The Myth Busting Machine
Adiabatic Integral Reactor
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The Myth Busting Machine
MultipleThermocouples
Gas samplingalong the lengthof the catalyst
bed
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Test Results
Catalysts A and B are identical in composition andmade at same time in our catalyst plant.
Which Catalyst is More Active?
Catalyst A Catalyst B
Particle size (mm) 0.074 –
11.6 0.074 –
11.6
Total pore Volume (cm3/g) 0.682 0.609
K/V ratio 2.9 2.9
V2O5 (wt%) 7.2 7.8
Fractional Liquid Loading 0.36 0.46
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The Data
62.6%
11.5% SO2, 9.5% O2,
420oC Inlet Temperature,100 SLFM
Adiabatic Integral Reactor Results
More act ive A
conta ins less
vanadium
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Theoretically Speaking
0
25
50
75
100
125
150
175
200
0.00 0.15 0.30 0.45 0.60 0.75
WV / FSO2, g V-s/mol
-r SO2,
mol/g V-s
475oC
MECS-A7.2 % V2O5
MECS-B7.8% V2O5
Reaction Rates Compared Using Differential Reactor Data
Catalyst A with less V sh ows
near ly twice react ion rate
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What Really Matters in Catalyst Design
• Catalyst activity arises from:
* Process conditions* Catalyst composition* Catalyst porosity
* Internal mass and heat transfer- diffusion, reaction & effectiveness factor
2D Catalyst Cro ss Sect ion3D Catalyst Cross Sect ion
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● The Most Active Catalyst Will Not Necessari lyContain Most Vanadium
● Many Factors Play Into Making The MostEffective Use of the Vanadium
Higher Vanadium Content ImprovesSulfuric Acid Catalysts Activity
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Myth 2: When it comes to mist, what
happens in the tower, stays in thetower
Mist Formation
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Competing SO3 Mechanisms in anAbsorber
Desired mechanism
Absorption of SO3 gas into the circulating acid
Reaction of absorbed SO3 gas with H2O in the liquid
Competing reaction
SO3 (g) + H2O (g) -> H2SO4 (mist)
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The Mist Busting Machine
VISIBLE
TOWER
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Vapor Pressure of H2O and SO3 Over H2SO4
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
0.7000
0.8000
99.999.599.098.598.097.597.096.596.095.595.0
% H2S)4
V a p o r P r e s s u r e ( m m H g )
SO3 tow er top
SO3 tow er botH2O tow er bot
H2O tower top
104 C
82 C
104 C
82 C
Mist Forms
H2Ovapor
SO3
Final Absorber Conditions
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Vortexing Can Cause Problems as Well
Gas Inlet Duct CFD Model
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Diffusion of H2O vapor and vortexing are significant andcan cause mist to migrate outside of the tower
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Myth No. 3:
A stick test is only qualitative and
doesn’t tell me much about what theproblem is.
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How do you relate spot size to the type of problem?
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Calibrate a Stick Test!
Air brush supplied finemist particles to stick
And the mist wasmeasured by a Welaslaser particle counter
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Measured Particle Size Distribution
0
2
4
6
8
10
12
14
16
0 . 2 3 7
0 . 2 5
5
0 . 2 7
4
0 . 2 9
4
0 . 3 1
6 0 . 3 4
0 . 3 6
5
0 . 3 9
2
0 . 4 2
2
0 . 4 5
3
0 . 4 8 7
0 . 5 2
3
0 . 5 6
2
0 . 6 0
4
0 . 6 4
9
0 . 6 9
8 0 . 7 5
0 . 8 0
6
0 . 8 6
6
0 . 9 3
1 1
1 . 0 7
5
1 . 1 5
5
1 . 2 4
1
1 . 3 3
4
1 . 4 3
3 1 . 5 4
1 . 6 5
5
1 . 7 7
8
1 . 9 1
1
2 . 0 5
4
2 . 2 0 7
2 . 3 7
1
2 . 5 4
8
2 . 7 3
8
2 . 9 4
3
3 . 1 6
2
3 . 3 9
8
3 . 6 5
2
3 . 9 2
4
4 . 2 1 7
4 . 5 3
2 4 . 8 7
5 . 2 3
3
5 . 6 2
3
6 . 0 4
3
6 . 4 9
4
6 . 9 7
8
7 . 4 9
9
8 . 0 5
8 8 . 6 6
9 . 3 0
6
0
20
40
60
80
100
120
140
160
180
Number of Particles
Cumulative Number of Particles
Mean = 0.4
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View of stick after spraying
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Comparing Acid Spray to Paint Spray Sticks
Acid
Paint
Paint
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Microscopic view of a paint large spot
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View of smaller spots
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Conversion of Droplet to Spot
Volume of mist droplet
4/3ΠR3
1 = 0.52 3
3 = 14 3
5 = 65 3
25 = 8,180 3
Diameter if a spot is 0.1 thick
ΠR2L1 = 2.5
3 = 15
5 = 30
25 = 325
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Microscopic View of Spots on the Stick
Paint Acid
Average Ø = 15 Average Ø = 15
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Smallest particle found
They do not impinge on the stick!!
Although a majority of the particlesare sub-micron…
1 droplet = 2.5 spot
Stick test >1
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A stick test is only qualitative…
With the proper calibration, the venerable stick testtakes on new meaning!
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Pop Quiz!
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Condensation or Mechanical Mist?
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Mechanical Re-entrainment problem
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Is there a problem here?
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What if the stack looked like this?
And the Gas Above the Mist Eliminators
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And the Gas Above the Mist Eliminatorslooked like this?
SO3 gas above tubesheetMist above tubesheet
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Clean 3 minute stick test
Sub-micron mist or trace SO3
Slight opacity in stack
Sub-micron mist or trace SO3
Clear gas above candles
SO3
Cause: SO3 slip due to an absorption problem
Summarizing the Data…
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Myth No. 4:
Can a sulfuric acid spillcause a fire?
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Trial 1: H2SO4 + C12H22O11 (sugar)
H2SO4 + C12H22O11 → 12C + 11H2O
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Trial 2: H2SO4 + C12H22O11 + KNO3 (rocket candy)
H2SO4 + C12H22O11 + KNO3 →
12C + 11H2O + KSO4 + H2O + NO2
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Trial 3: H2SO4 + C12H22O11 + Secret Sauce
6H2SO4 + C12H22O11 + 12KClO3 →
12CO2 + 17H2O + 6KCl2 + 6KSO4 +SO2
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Can a sulfuric acid spill cause a fire?
Yes, but you really have to try!
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