Can You Get Condensation Inside A Solid Fuel Boiler?

Stoker Coal Boilers automatically feed the coal and have controls and pumps just like any conventions boiler. They are intended to be used as a primary heat and often have domestic hot water coils as an added bonus. They can be set up independently or in dual sytem with your existing oil/gas boiler. They can accommodate both hot water base board or steam plumbing.
kstills
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Post Sat. Jan. 14, 2012 10:30 am

I've been told no, I've read on here yes.

Verdict?

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WNY
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Post Sat. Jan. 14, 2012 10:35 am

Not any different from any other boiler, if you get down below the dew point, it will condense. I think around 120-130 degrees? I think thats why they tell you not to run below 140 degrees, so it doesn't condense.
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Post Sat. Jan. 14, 2012 11:14 am

it doesn't have anything to do w/ the fuel it's the dew point temp appox 130 so 140 is a good temp to shoot for this is the return h2o

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Post Sat. Jan. 14, 2012 11:22 am

Well then, time to up the high and low limits. :)

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Post Sat. Jan. 14, 2012 11:37 am

kstills wrote:Verdict?
Running a boiler under 140* is asking for trouble. Oxygen disassociates from water at around 153*. At 130* you are feeding your boiler to the forces of nature.
Nothing is impossible for people who don't have to do it themselves.

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Post Sat. Jan. 14, 2012 11:45 am

make sure you have a bypass to tempe rthe return h2o

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Post Sun. Jan. 15, 2012 1:45 pm

This is a highly techinical question. In pure theory, coal combustion will not condense like gas and oil combustion. Why, because coal is carbon and when combined with oxygen will result in carbon dioxide. (C + O2 => CO2 (12 kg C)+(32 kg O) => (34 kg CO2) ). Gas and oil are hydrocarbons. When hydrogen is combusted, you get water. (2 H2 + O2 => 2 H2O (4 kg H)+(32 kg O) => (36 kg H2O) ) So, in pure theory, coal will not condense to form water.

However, real world issues are that coal is neither 100 percent pure carbon nor perfectly dry. Therefore, any moisture in the coal that is evaporated during combustion, could condense if there was sufficiently cool enough combustion chamber walls.

The sulfur in the coal is combusted to form sulphur dioxide. (S + O2 => SO2 (32 kg S) + (32 kg O) => (64 kg SO2) ) While the sulphur will not condense until really low temperature, it could combine with the water to form sulphuric acid. (H2SO4). This would attack any metal surface over time.

Another problem is that any water temperature below 140 deg. F., is not very useful for heat. Another topic of concern would be on of thermal shock on cast iron equipment. ( not so much of a concern for welded steel boilers).

So, in conclusion, the rule of thumb of 140 deg. f return may not be as hard and fast for coal, but is a good number to stick with.

Note - wood is a different animal, more moisture content and creosote problems.
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kstills
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Post Sun. Jan. 15, 2012 1:59 pm

steamup wrote:This is a highly techinical question. In pure theory, coal combustion will not condense like gas and oil combustion. Why, because coal is carbon and when combined with oxygen will result in carbon dioxide. (C + O2 => CO2 (12 kg C)+(32 kg O) => (34 kg CO2) ). Gas and oil are hydrocarbons. When hydrogen is combusted, you get water. (2 H2 + O2 => 2 H2O (4 kg H)+(32 kg O) => (36 kg H2O) ) So, in pure theory, coal will not condense to form water.

However, real world issues are that coal is neither 100 percent pure carbon nor perfectly dry. Therefore, any moisture in the coal that is evaporated during combustion, could condense if there was sufficiently cool enough combustion chamber walls.

The sulfur in the coal is combusted to form sulphur dioxide. (S + O2 => SO2 (32 kg S) + (32 kg O) => (64 kg SO2) ) While the sulphur will not condense until really low temperature, it could combine with the water to form sulphuric acid. (H2SO4). This would attack any metal surface over time.

Another problem is that any water temperature below 140 deg. F., is not very useful for heat. Another topic of concern would be on of thermal shock on cast iron equipment. ( not so much of a concern for welded steel boilers).

So, in conclusion, the rule of thumb of 140 deg. f return may not be as hard and fast for coal, but is a good number to stick with.

Note - wood is a different animal, more moisture content and creosote problems.
Ok, since you used numbers......lol.

If I run a continuous circulation at lower temps, I won't have to worry (much) about condensation and I can run lower water temps which would result in savings on fuel?

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Berlin
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Post Sun. Jan. 15, 2012 5:05 pm

steamup wrote:This is a highly techinical question. In pure theory, coal combustion will not condense like gas and oil combustion. Why, because coal is carbon and when combined with oxygen will result in carbon dioxide. (C + O2 => CO2 (12 kg C)+(32 kg O) => (34 kg CO2) ). Gas and oil are hydrocarbons. When hydrogen is combusted, you get water. (2 H2 + O2 => 2 H2O (4 kg H)+(32 kg O) => (36 kg H2O) ) So, in pure theory, coal will not condense to form water.

However, real world issues are that coal is neither 100 percent pure carbon nor perfectly dry. Therefore, any moisture in the coal that is evaporated during combustion, could condense if there was sufficiently cool enough combustion chamber walls.

The sulfur in the coal is combusted to form sulphur dioxide. (S + O2 => SO2 (32 kg S) + (32 kg O) => (64 kg SO2) ) While the sulphur will not condense until really low temperature, it could combine with the water to form sulphuric acid. (H2SO4). This would attack any metal surface over time.

Another problem is that any water temperature below 140 deg. F., is not very useful for heat. Another topic of concern would be on of thermal shock on cast iron equipment. ( not so much of a concern for welded steel boilers).

So, in conclusion, the rule of thumb of 140 deg. f return may not be as hard and fast for coal, but is a good number to stick with.

Note - wood is a different animal, more moisture content and creosote problems.
Dewpoint is determined by humidity and temp, which, as steamup has mentioned, coal will have a vastly lower amount of moisture/humidity in its flue gas. condensation with coal anthracite or bit is almost a non-issue unless your coal is dripping wet when it's fired into the boiler.
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Post Sun. Jan. 15, 2012 5:37 pm

Berlin wrote:
steamup wrote:This is a highly techinical question. In pure theory, coal combustion will not condense like gas and oil combustion. Why, because coal is carbon and when combined with oxygen will result in carbon dioxide. (C + O2 => CO2 (12 kg C)+(32 kg O) => (34 kg CO2) ). Gas and oil are hydrocarbons. When hydrogen is combusted, you get water. (2 H2 + O2 => 2 H2O (4 kg H)+(32 kg O) => (36 kg H2O) ) So, in pure theory, coal will not condense to form water.

However, real world issues are that coal is neither 100 percent pure carbon nor perfectly dry. Therefore, any moisture in the coal that is evaporated during combustion, could condense if there was sufficiently cool enough combustion chamber walls.

The sulfur in the coal is combusted to form sulphur dioxide. (S + O2 => SO2 (32 kg S) + (32 kg O) => (64 kg SO2) ) While the sulphur will not condense until really low temperature, it could combine with the water to form sulphuric acid. (H2SO4). This would attack any metal surface over time.

Another problem is that any water temperature below 140 deg. F., is not very useful for heat. Another topic of concern would be on of thermal shock on cast iron equipment. ( not so much of a concern for welded steel boilers).

So, in conclusion, the rule of thumb of 140 deg. f return may not be as hard and fast for coal, but is a good number to stick with.

Note - wood is a different animal, more moisture content and creosote problems.
Dewpoint is determined by humidity and temp, which, as steamup has mentioned, coal will have a vastly lower amount of moisture/humidity in its flue gas. condensation with coal anthracite or bit is almost a non-issue unless your coal is dripping wet when it's fired into the boiler.
That's good news, for me at least, and appears to be a little understood benefit of burning coal.

Maybe it needs a sticky...?

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Post Sun. Jan. 15, 2012 6:06 pm

I believe the question was can you water vapor condensing in the boiler or flue when Running at low stack temps and that has been well covered. I find that when my mini-boiler is out and cold, humidity from the summer air condenses on the cool iron inside and out which causes rust. :mad: In theory the sulfur could react with the condensation exacerbating the problem. I use the mini-boiler to heat the water in a 77 gallon indirect and only run it about 8 hours every 3 days or so. Basically as needed.
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Post Sun. Jan. 15, 2012 6:40 pm

I ruined a very nice 5 section cast iron boiler by running the water temps too low [bit coal, iron fireman stoker]. I ran it 130-140* spring/fall, maybe 160 in cold winter. I thought that I was saving money. It was pristine when I put it into use. It took 17 years, but the apx 3/8" casting were deeply pitting in the upper section.

When cleaning the upper chamber, I did notice that the fly ash was stuck onto the metal, like it was glued on. Not until I joined this group that I learned what was happening.

Dave
I love my Kaa-2. It replaced a small 5 section Red Square, and Iron Fireman, burned bituminous for 20 yr.

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Post Sun. Jan. 15, 2012 6:55 pm

dave brode wrote:I ruined a very nice 5 section cast iron boiler by running the water temps too low [bit coal, iron fireman stoker]. I ran it 130-140* spring/fall, maybe 160 in cold winter. I thought that I was saving money. It was pristine when I put it into use. It took 17 years, but the apx 3/8" casting were deeply pitting in the upper section.

When cleaning the upper chamber, I did notice that the fly ash was stuck onto the metal, like it was glued on. Not until I joined this group that I learned what was happening.

Dave
Did you run it in the summer, or did you shut it down?

And if you shut it down, did you observe good practice for keeping it dry?

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Post Sun. Jan. 15, 2012 8:18 pm

dave brode wrote:I ruined a very nice 5 section cast iron boiler by running the water temps too low [bit coal, iron fireman stoker]. I ran it 130-140* spring/fall, maybe 160 in cold winter. I thought that I was saving money. It was pristine when I put it into use. It took 17 years, but the apx 3/8" casting were deeply pitting in the upper section.

When cleaning the upper chamber, I did notice that the fly ash was stuck onto the metal, like it was glued on. Not until I joined this group that I learned what was happening.

Dave
Bit coal has lower carbon and higher volatiles. The volatiles (coal tars) will condense at lower temperature and cause a problem. Not as big of a problem with anthracite. Personally, running any boiler temperature setpoints below the 150 to 160 deg. range(on call for heat) is not a good idea, unless the boiler was designed for condensing operation such as the modern gas and oil boilers. I have my K-6 idling at 140 + on the low side of the aquastat. High side setting is 180.
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Post Sun. Jan. 15, 2012 8:34 pm

I ran my EFM at 140 degrees (max) for part of the summer...after about a month I noticed some funky deposits on the inside of the firebox. It looked like flyash, but was peeling off in small pieces rather than the dusty ash I was used to. I cleaned it out and bumped the aquastat to 160 degrees...after that there was just a light layer of dusty ash that was easily brushed off. I can't say what caused the deposits in the firebox, but whatever it was hasn't returned since the boiler has been allowed to run at higher temperatures.

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