Can You Get Condensation Inside A Solid Fuel Boiler?
Posted: Sat. Jan. 14, 2012 10:30 am
I've been told no, I've read on here yes.
Verdict?
Verdict?
Using anthracite or bituminous coal for residential and commercial heating.
https://coalpail.com/coal-forum/
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.kstills wrote:Verdict?
Ok, since you used numbers......lol.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.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.
That's good news, for me at least, and appears to be a little understood benefit of burning coal.Berlin wrote: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.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.
Did you run it in the summer, or did you shut it down?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.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