27. MECS Chile Roundtable Urban Legends and Myths

7/21/2019 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



The Myth Busting Machine

MultipleThermocouples

Gas samplingalong the lengthof the catalyst

bed



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



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



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



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



● 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!



MECS and Lewis Pumps Hopes

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27. MECS Chile Roundtable Urban Legends and Myths

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