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Associate

Join Date: Jan 2008
Posts: 33

### Catalytic Converter

07/29/2012 3:37 PM

I am intending to buy a catalytic converter for an engine exhaust.

Catalytic converter manufacturers require the amount of SO2 at the exhaust in PPM.

Can someone please tell me how to calculate the PPM of SO2 from the following data?

Engine Power = 1980 bhp

BSFC = 7792 Btu/bhp-hr

Total exhaust heat = 4527 Btu/hr

Exhaust flow = 13713 lb/hr

H2S content of the inlet Natural gas is 800 PPM.

I need the amount of SO2 in PPM at the exhaust.

Assume worst case scenario that all the H2S gets converted to SO2.

Please let me know if any further information is required for this calculation.

Thanks!

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#1

### Re: Catalytic Converter

07/29/2012 4:44 PM

Send the converter manufacturer the information you presented here and tell them that if they want to sell you equipment they should figure it out.

If they have no one who can perform the calculation, or use your data to size the cat, go elsewhere.

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#2

### Re: Catalytic Converter

07/29/2012 7:26 PM

'.....

Engine Power = 1980 bhp

BSFC = 7792 Btu/bhp-hr

Total exhaust heat = 4527 Btu/hr

....'

.

Are you certain these are correct/close?

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#3

### Re: Catalytic Converter

07/29/2012 8:58 PM

The second was certainly wrong, it should be in gram/ kwh or equivalent. The third one means the engine output power is only A few watt! Not 1980 bhp.

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#5

### Re: Catalytic Converter

07/29/2012 9:24 PM

Correction, the engine power is only about 1 kw at best.

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Associate

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#6

### Re: Catalytic Converter

07/30/2012 12:12 AM

the third one: Total exhaust heat Btu/Hr = 4527x1000 = 4527000 Btu/hr

BSFC is 7792 Btu/Bhp-hr or 11027 KJ/KWh

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#4

### Re: Catalytic Converter

07/29/2012 9:07 PM

Your local diesel repair shop might have a portable engine exhaust gas analyzer, I would start there...

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#7

### Re: Catalytic Converter

07/30/2012 1:15 AM

Do you want to buy a converter for your engine or do you have to buy one?

Wanting one for an engine that large is going to be a very expensive and for the most part waste of time effort and money.

However if you have to buy one to meet some political emissions specs what the fine cost Vs what the converter going to cost?

Just trying to save you some money and efforts here.

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#8

### Re: Catalytic Converter

07/30/2012 2:25 AM

Client requirements -.-

Not much I can do about that!

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#9

### Re: Catalytic Converter

07/30/2012 3:53 AM

http://en.wikipedia.org/wiki/Stoichiometry

• H2S + 11/2O2 → SO2 + H2O.
• Molecular weight of H2S is 34g/mol.
• Molecular weight of SO2 is 64g/mol.

One needs to know the gas/air ratio both sides of the combustion process to work out the ppm of SO2 in the exhaust. Assume the natural gas is CH4, burning in air.

• CH4 + 2O2 + roughly 10 N2(inert) → CO2 + 2H2O↑ + roughly 10N2(inert), so there is no increase in the number of molecules as a result of combustion. Therefore the mole fraction of sulphur compounds in the exhaust is not diminished by any increase in molecules of the main fuel's combustion.

Therefore the maximum SO2 in the exhaust will be simply 800ppm x 64/34.

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#10

### Re: Catalytic Converter

07/30/2012 4:40 AM

Now that's more like it!

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#11

### Re: Catalytic Converter

07/30/2012 11:28 AM

Oooops! '10N2' should read '8N2', though it doesn't affect the outcome.

Got in very late last night.

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#12

### Re: Catalytic Converter

07/30/2012 1:15 PM

Yea, I was just going to say that.

Great information. I am amazed at the knowledge that shows up here.

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#13

### Re: Catalytic Converter

08/02/2012 4:49 PM

'....CH4 + 2O2 + roughly 10 N2(inert) → CO2 + 2H2O↑ + roughly 10N2(inert), so there is no increase in the number of molecules as a result of combustion. Therefore the mole fraction of sulphur compounds in the exhaust is not diminished by any increase in molecules of the main fuel's combustion.

.

Therefore the maximum SO2 in the exhaust will be simply 800ppm x 64/34.

....'

.

There is a problem with the above. While it is unclear whether the ppm H2S, provided by the OP, is based on volume, mass, or molarity (which does affect the outcome), the above calculation significantly overestimates probable exhaust SO2 concentrations.

Consider for a moment the following hypothetical...

62 grams of a mixture of steam (H2O) and CO2 ( in a 1 to 1 molar ratio) that also contains ~1506 ppm SO2 (assume ppm mass or ppm mole) at 15 psia and 250 F.,

280 grams of N2 at 15 psia and 250 F.

As expected there is no evidence of any significant reaction.

.

Will the SO2 concentration remain close to ~1506 ppm?

.

.

Hopefully you agree that the concentration SO2 will be much lower than 1506 ppm (800 * 64/32 ppm) regardless of whether you chose ppm mole or mass. even though no reaction occurred the SO2 concentration was diluted with the addition to N2.

.

The concentrations in this hypothetical are not much different from what the stoichiometric reaction you suggested above should yield. The concentrations should not remain static from the fuel to the exhaust.

.

I should note that you do qualify your statement with '...the maximum SO2 in the exhaust will be... ' which is technically true, since the actual concentrations will be around an order of magnitude lower. If this was your intention, then I simply misjudged what you were attempting to communicate. if not then I'm just noting a forgotten component of the otherwise helpful calculation you provided.