SO2/ SO3 dew point 3

[Sandeep1970]

Can some one suggest any software or program or literature to calcu;ate the SO2/ SO3 dew point in the flue gas which contain water as well. Already used Pierce equation and similar graphs.

 

[dickwilber]

I have found two web sites of interest: 1) V.Ganapathy provides a set of formulas at

http://vganapathy.tripod.com/corros.html

and 2) an on-line acid dew point calculator is available at

http://www.jehar.com/dewpnt.htm

. The results from both of these compare closely with my previous experience.

However, there is a caveat with the use of these formulii: conditions within a combustion and gas exhaust system vary considerably over the gas stream and with time. To much reliance upon theoretical dew point calculations can result in unanticipated localized corrosion. One codifier of steel stacks suggests a safety allowance of 50 degrees F (28 degrees C). This is probably too conservative, but gives you an idea of the problem.

Another factor to keep in mind is that while these formulii predict the point at which acid droplets begin to condense out of the gases, the temperatures at which they fully re-evaporate when reheated may be somewhat higher. Early in my career, Robert Pierce (then with Pennwalt, later associated with Ohio State University) suggested that in some cases complete regasification may not occur until the gas temperatures reach something in the range of 500 degrees F (260 degrees C). Again, I don't believe that this figure is representative of the actual conditions we encounter, but the concept should be kept in mind.

Finally, a paper published in the late 80's suggested that the actual measured acid dew point for very low concentrations of SO3 in the gases (less than 10 ppm) varied significantly from the theoretical. Unfortunately, I can no longer find reference to that document.

 

[psdeshmukh]

we are facing H2SO4 dewpoint corrosion in WHRB at condensate
preheater section due to 0.3%S in HSD FIRING.We are looking
for proper neutralising chemicals ie Mg(OH)2,liq. ammonia etc.has anybody faced this type of problem.what action taken.We will be very much thankfull if anybody reply.

 

[Rich2001]

In Material Performance (NACE) in 1982 or 1983 had a article with the equations to calculate the ACID DEW POINT.

 

[Masami]

Hi, from Japan. In my area, it is used equation:
Dew point = 20log (SO3%) + (2Xmoisture + 184) where moisture is H2O% in flue gas
My clients are controlling metal temperature based on the SO3 concentration after economizer. (inlet temperature from gas airheater).. Hopefully, it will help.

 

[Masami]

Mg(OH)2 and NH4 injection is effective to control cold end corrosion.
2NH4 + SO3 + H2O ¨ (NH4)2SO4
SO3 in ppm can decide the volume of required NH4. By the way, it usually happens shortage of NH4, since some tends to react with SO2. Some extra ppm NH4 is required. Firstly, you need to check SO3ppm in the flue gas. Check pH value of sticking ash (probably lower than 2.0 as it might exist free H2SO4. In the meantime, Mg(OH)2 feeding requires high volume (either powder or liquid). If you are interested, let me know.

 

[Norberto]

Mr. Masami, in your dew point formula temperature used in Celsius degree?