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Sulfur dew point 3
- Thread starter kkanel
- Start date
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2
- #3
KKanel,
I read this site from home in the evenings, away from my reference material. I will look in a book I have, titled "Steam" published by B&W, the boiler manufacturer, and if it is not there, I will have to scratch my head as to where I might have anything.
In general, with sulfur bearing fuels, the flue gas in steam boilers is kept above the 300-350F range to stay above the sulfur dew point. The heat transfer equipment could get it much lower, but the sulfur won't allow it.
Now, I can't tell you if that is a function of the sulfur dew point itself, per se, or a function of maintaining an air preheater outlet temperature high enough, so as to keep the "resultant" temperature of the flue gas leaving the air pre heater, which in a high percentage of cases is a Ljunstrom, and the fresh air flow from seal leakage around the Ljunstrom wheel, which is 8% guaranteed for a new Ljunstrom right out of the box, and up to 25% for units that have been in service for lots of years.
In any case, it is to keep the resulting flue gas temperature above the sulfur dew point, to prevent back end corrosion. That sulfuric acid that results when the dew point is reached is brutal.
Also, while sulfur content is taken in fuel analysis as an average, or mean value, it is well known that the sulfur can vary all over the map. If your fuel is Natural gas, you are probably not talking about much. However, if your fuel is fuel oil, check your fuel analysis samples closely.
It is one of those things that I learned a long time ago how to do, and the answer was always just stay above 300 minimum, so I did not need to calculate it any more, and, forgot how. My first GTCC was dual fuel fired, and we had to add an economizer recirc circuit to the back end of the HRSG (that was before the name HRSG was coined) to maintain the flue gas at a higher outlet temperature when firing on fuel oil, because of the sulfur in the fuel oil.
If I find something, I will repost tomorrow nite.
rmw
I read this site from home in the evenings, away from my reference material. I will look in a book I have, titled "Steam" published by B&W, the boiler manufacturer, and if it is not there, I will have to scratch my head as to where I might have anything.
In general, with sulfur bearing fuels, the flue gas in steam boilers is kept above the 300-350F range to stay above the sulfur dew point. The heat transfer equipment could get it much lower, but the sulfur won't allow it.
Now, I can't tell you if that is a function of the sulfur dew point itself, per se, or a function of maintaining an air preheater outlet temperature high enough, so as to keep the "resultant" temperature of the flue gas leaving the air pre heater, which in a high percentage of cases is a Ljunstrom, and the fresh air flow from seal leakage around the Ljunstrom wheel, which is 8% guaranteed for a new Ljunstrom right out of the box, and up to 25% for units that have been in service for lots of years.
In any case, it is to keep the resulting flue gas temperature above the sulfur dew point, to prevent back end corrosion. That sulfuric acid that results when the dew point is reached is brutal.
Also, while sulfur content is taken in fuel analysis as an average, or mean value, it is well known that the sulfur can vary all over the map. If your fuel is Natural gas, you are probably not talking about much. However, if your fuel is fuel oil, check your fuel analysis samples closely.
It is one of those things that I learned a long time ago how to do, and the answer was always just stay above 300 minimum, so I did not need to calculate it any more, and, forgot how. My first GTCC was dual fuel fired, and we had to add an economizer recirc circuit to the back end of the HRSG (that was before the name HRSG was coined) to maintain the flue gas at a higher outlet temperature when firing on fuel oil, because of the sulfur in the fuel oil.
If I find something, I will repost tomorrow nite.
rmw
OK, so I lied. It has been more than several nights. But, I did finally get by the office, and could not find a calculation method per se in Steam, the B&W book, but in a book named, "Boilers-types, characteristics, and functions", by Carl D. Shields, a McGraw Hill publication, on page 272, there is a good discussion of the topic, and a graph of Acid Dew Point plotted against H2SO4 in dry gas, percent by volume, with plot lines for 5, 10, and 15% moisture. Edison Electric Institute, "Boilers, Economizers, Air Heaters, and Piping" is credited as the source.
What B&W Steam does have, however, which I believe might be useful for you, on page 19-12 of the 40th edition, is is two figures, both of which are associated with recuperative air heaters cold end metal temperature limits, plotted against % by wt. of Sulfur in fuel. There are different plot lines for NG, Oil, and Coal, PC, and cyclone.
If you can find either of these books, I think you could use the information for what you are seeking. At this point in the process, I don't think the gasses care if they came from a GT, or a combustion boiler.
If you can't find the books, post back with some specifics as to % sulfur in the fuel, temps, and fuel types, and I will read the curves, and give you a grouping of results.
Good Luck,
rmw
What B&W Steam does have, however, which I believe might be useful for you, on page 19-12 of the 40th edition, is is two figures, both of which are associated with recuperative air heaters cold end metal temperature limits, plotted against % by wt. of Sulfur in fuel. There are different plot lines for NG, Oil, and Coal, PC, and cyclone.
If you can find either of these books, I think you could use the information for what you are seeking. At this point in the process, I don't think the gasses care if they came from a GT, or a combustion boiler.
If you can't find the books, post back with some specifics as to % sulfur in the fuel, temps, and fuel types, and I will read the curves, and give you a grouping of results.
Good Luck,
rmw
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1
- #5
Go to and then to Process submenu on the left side of the page. Click on Acid Dew Point of Flue Gas menu and you will get good details.
Regards,
Eng-Tips.com : Solving your problems before you get them.
Regards,
Eng-Tips.com : Solving your problems before you get them.
RMW!
Thanks for the undeserved star. I always enjoy your insights in other forums and my joy doubled in getting a star from experts like you.
Though I have been a member in this forum since my joining eng-tips.com, I occasionally peek in here as the activity in this forum is very dull.
PS: The owner of the website I mentioned above (Mr Jack Hardy, as I remember) is also a member of eng-tips.com and mentioned about the site couple of times here.
Regards,
Eng-Tips.com : Solving your problems before you get them.
Thanks for the undeserved star. I always enjoy your insights in other forums and my joy doubled in getting a star from experts like you.
Though I have been a member in this forum since my joining eng-tips.com, I occasionally peek in here as the activity in this forum is very dull.
PS: The owner of the website I mentioned above (Mr Jack Hardy, as I remember) is also a member of eng-tips.com and mentioned about the site couple of times here.
Regards,
Eng-Tips.com : Solving your problems before you get them.
Quark,
When I got there, I recognized that I had been there before, although on that occasion, without a particualr "quest" in mind, I did not dig in and really examine all the site had to offer. Now that I have, I see it as a really good site, and you deserve the star for bringing it to the attention, (again) of KKanel, and myself.
rmw
When I got there, I recognized that I had been there before, although on that occasion, without a particualr "quest" in mind, I did not dig in and really examine all the site had to offer. Now that I have, I see it as a really good site, and you deserve the star for bringing it to the attention, (again) of KKanel, and myself.
rmw
athomas236
Mechanical
Need to be careful about applying some acid dewpoint correlations as they are based on fired boiler experience and hence not directly applicable to HRSG. This is because of much lower sulphur contents of gas and higher O2 contents of HRSG's.
If you put SO3 content as zero into forumula and get the water dewpoint corresponding to whatever water content you input then its a good correlation. Most do not do this.
For HRSG's burning fuel gas with 10ppm sulphur acid dewpoint is 81C, with 100ppm sulphur acid dewpoint is 93C.
Between these points interpolate on a log10 scale for sulphur and a linear scale for temperature.
Regards,
athomas236
If you put SO3 content as zero into forumula and get the water dewpoint corresponding to whatever water content you input then its a good correlation. Most do not do this.
For HRSG's burning fuel gas with 10ppm sulphur acid dewpoint is 81C, with 100ppm sulphur acid dewpoint is 93C.
Between these points interpolate on a log10 scale for sulphur and a linear scale for temperature.
Regards,
athomas236
- Thread starter
- #11
Athomas, the use of the two points with interpolation in between seems a nice way to go. Do these values refer to ppm on a per volume basis or per mass?
Are these two temperatures verified somehow? At 1st glance they seem a bit high!
1ton : thanks
Are these two temperatures verified somehow? At 1st glance they seem a bit high!
1ton : thanks
athomas236
Mechanical
kkanel
Have checked graph and yes it is a straight line over the range mentioned with scales as linear for trmperature and log10 on ppm sulphur in gas. PPM is by volume.
Temperatures verified only in the sense that they come from an internationally renowned American GT supplier.
athomas236
Have checked graph and yes it is a straight line over the range mentioned with scales as linear for trmperature and log10 on ppm sulphur in gas. PPM is by volume.
Temperatures verified only in the sense that they come from an internationally renowned American GT supplier.
athomas236
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