HCl in the stack

[fvincent]

What are the main sources of HCl in flue gases condensate downstream a wet FGD system?

How can I calculate the concentration of HCl in the stack condensate given the Cl content of fuel, of process water (used for lime milk preparation) and of calcium sulfate (cake)and given the water condensation mass rate on the stack (per sq meter)?




fvincent
Figener S/A

 

[aybee]

if you are asking what I think you are , it will start to corrode when the gas reaches the dew point. If the stack is lined it will go behind the lining and corrode there even though the temperature of the gas is above the dew point at that location..once it gets behind it is insulated , cools down - corrodes

 

[fvincent]

Aybee,

Thanks for your answer

The saturated gases come from a wet FGD and so are clearly below H2SO4 dew point, so that an acid mist is carried by these gases.

The stack is not insulated so that we can expect water condensation depending on the rate of heat transfer to outside air.

My question refers to HCl presence: how can we calculate the HCl (or in general, chlorides) in the condensate, according to Cl content of fuel, lime slurry and sulfate cake (considering that filtrate is sent back to lime slurry preparation?



fvincent
Figener S/A

 

[aybee]

Sorry, cant answer that question but just to cheer you up the H2S04 will creat sulphuric acids or sulphonic (a chemist will telll you which but I think they are generally polythionic ie multi varieties..all corrosive)which will eat the steel when in low concentration and warm-hot,can also cause SCC of the welds so if you can get in and check them out do so

 

[martinwhelan]

I would think the calculated concentration of HCl is irrelevent as the concentration will increase over time as you have downtime which allows vaporisation of the diluting medium (water).

You should either select suitable chloride resistant materials if the stack is unlined - anything from Corten through to the special high nickel alloys, or if your stack is insulated you might be wise to line it with one of the proprietry products available specially for this purpose and suitable for temps up to about 200°C (stack wall temp, not process gas temp).
Hope this helps!

 

[DeltaCascade]

Note: HCl is more volatile than water and will vaporize moreso than water.

 

[EdStainless]

And remember that the acids can condense over a wide temperature range (just look at their boiling curves).
The problem with any acid, not just HCl and H2SO4, is that it isn't the total amount that controls the corrosion. It is the location that happens to have enough present.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[DeltaCascade]

On the original question, for what it may be worth:

For HCl calculation I guess you could assume that all chlorides in fuel burn to form HCl. Not sure to what extend that would be true, without testing, but it would be a worst case. Now, you calculate vol or wt% HCl in the flue gas.

Then for HCl-water liquid phase in equilibrium with HCl-Water-Air vapour phase, get water-concentration vs temperature and vs pure-component-partial-pressure-data. Liquid-concentration vs vapour-pressure equilibrium data is avaialble at Vulcan Chemicals web site, for example, i believe (they sell HCl). etc. Assume liquid-vapour equilibrium and from there assume ideal gas, as an approximation. From the % volume or % wt HCl in vapour (PV=nRT) that you calculated above, calculate %wt HCl in liquid phase (for your specified tempeture). A good chemical thermodynamics book or even Perry's handbook could help in review of Dalton's Law (? in vapour phase, partial pressure of a pure component represents the volume concentration of a pure component if i recall correctly), etc, which is used in the calculations. Then you could estimate HCl content in condensate at a given temperature (keeping EdStainless's comment in mind! when specifying temperature)

Good luck.