Can You Get Condensation Inside A Solid Fuel Boiler?

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: dave brode On: Sun Jan 15, 2012 11:13 pm

kstills wrote:
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?


Oct to 1st of June. My boiler room is very dry. There was no pitting in the firebox, just in the upper chamber where the condensation appeared to occur. All of the sections were pitted, and one finally leaked. The sections were apx 3/8" thick castings. Nice old boiler, made into scrap.

Dave
dave brode
 
Stoker Coal Boiler: Keystoker KAA-2
Hand Fed Coal Boiler: used to have a 5 section Red Square
Coal Size/Type: rice anthracite

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: qbwebb On: Mon Jan 16, 2012 12:44 am

coaledsweat wrote:
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.


Yes, but once the O2 disassociates doesn't it eventually get removed by the air scoop? I'm sure it takes a fare amount of time but if you regularly go above 153 and then draw down to say 120 eventually there shouldn't be any O2 left to be redissolved in the water, assuming your system is actually closed.
qbwebb
 
Stove/Furnace Make: Harman
Stove/Furnace Model: VF3000

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: qbwebb On: Mon Jan 16, 2012 12:59 am

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 sulfer 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.


In the case of a coal boiler, aren't you really balancing coal cost vs. electricity cost? Run your temps too high and delta T between water and flue gas is less, so less heat removed from combustion products and more coal used to reach setpoint, but also less electric used distributing heat from larger delta T between water and living space, but also more residual losses from boiler jacket. Run temps low and use more electric to distribute to the living space, but extract more precious BTU's from the exhaust gas.

If I ever built my own house I would install in floor radiant, conduction heat Xfer is the most efficient way to transfer heat and I could run fairly low temps to get the most heat from the coal flu gas. Right now I run about 150F, but my circ pump and large furnace heat heat exchanger draw out the BTU's in a hurry, to the point where a full fire will keep the water around 111-115 at steady state and I'm wasting electric blowing luke warm air into the living space, especially when its this cold. I think I am going to try installing an interrupt aquastat soon that stops the heat call if the temp drops below 125-130 to give the boiler a chance to recover.
qbwebb
 
Stove/Furnace Make: Harman
Stove/Furnace Model: VF3000

Visit Lehigh Anthracite

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: coaledsweat On: Mon Jan 16, 2012 10:10 am

qbwebb wrote:
coaledsweat wrote:
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.


Yes, but once the O2 disassociates doesn't it eventually get removed by the air scoop? I'm sure it takes a fare amount of time but if you regularly go above 153 and then draw down to say 120 eventually there shouldn't be any O2 left to be redissolved in the water, assuming your system is actually closed.

Wishful thinking. Once below 140* the water gets hungry and will draw O2 back into it. A sealed system may do a wonderful job of keeping water in but it can't keep O2 out.
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: qbwebb On: Mon Jan 16, 2012 10:53 am

I guess I don't understand the mechanism for this (I'm not saying it doesn't happen), O2 external to the plumbing is at an atmosphere and your H2O is at a positive pressure, how does O2 make it back in? Isn't the entire purpose of using Pex-Al-Pex or barrier pipe to "block" the O2 molecules from getting back in because the poly chains themselves in the Pex pipe are much too large?

Check out this curve (http://docs.engineeringtoolbox.com/docu ... _water.pdf) , the 40-50C region seems pretty linear wrt O2 solubility, is there really that big a difference between 130F & 153F? As steam up said in other heating appliances where high concentrations of H2O vapor are in the combustion gas I can see it being an issue, but maybe anthracite is the exception.
qbwebb
 
Stove/Furnace Make: Harman
Stove/Furnace Model: VF3000

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: coaledsweat On: Mon Jan 16, 2012 11:00 am

qbwebb wrote:I guess I don't understand the mechanism for this

Neither do I, but it happens with oil and gas fired appliances. No reason to think it any different with anthracite.
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: Yanche On: Mon Jan 16, 2012 1:05 pm

We think of hydronic heating systems as sealed systems. But in fact they are not. Not as sealed, as for example, a refrigerant system. While the larger water molecule can't get out other much smaller molecules have a path in and out. Places like, valve stem seals, pressure relief valve gasket, diaphram in your expansion tank, your makeup water regulator, automatic air vent, even the AL-PEX-AL at it's adapter. Does the amount of O2 that gets in or out make a difference? I don't know but the molecule level it's really not sealed. I've often wondered why designs have a make up water regulator. Why not just design it using components that don't leak, don't leak at the molecular level.

It's like old large food store refrigerant systems. They leaked like a sieve. I was at a seminar on HVACR compressors last week. One refrigerant service company tech talked about a local supermarket that leaked 1000-1200 lbs of R12 a year. They wouldn't pay to fix the leak, but would pay for the refrigerant. His favorite customer. With current regulations and refrigerant cost those days are long gone.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: Matthaus On: Mon Jan 16, 2012 1:22 pm

I have run one of our boilers in excess of a year at temperatures under 100* with no signs of corrosion on the firebox side of the pressure vessel. There is currently one of our 220 units running a very large radiant floor system (over 2,000' of 3/4" tubing in 90 cubic yards of concrete), the plumbing design (if you can call it a design) uses no mixing valve and therefore lets the boiler run at between 85* and 105*F. This unit is in the torture chamber to see what will happen, so far after over 10 tons of coal through the unit this year, no visible issues. As to whether it will suck the O2 into the pressure system at lower temps, ask me in a couple years after the boiler in question has been run extensively and then torn down.

In my opinion there is no real benefit to running an Anthracite Coal boiler under 140*F (except to make up for poor designs as in the system above), however if you think it provides benefit to you and you are using one of our units at low temps, please keep us posted on the results.
Matthaus
 
Stoker Coal Boiler: Leisure Line WL110 Dual Fuel, natural gas
Hot Air Coal Stoker Stove: Leisure Line Lil' Heater (rental house)
Coal Size/Type: Rice and Buckwheat Anthracite

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: kstills On: Mon Jan 16, 2012 2:10 pm

Matthaus wrote:I have run one of our boilers in excess of a year at temperatures under 100* with no signs of corrosion on the firebox side of the pressure vessel. There is currently one of our 220 units running a very large radiant floor system (over 2,000' of 3/4" tubing in 90 cubic yards of concrete), the plumbing design (if you can call it a design) uses no mixing valve and therefore lets the boiler run at between 85* and 105*F. This unit is in the torture chamber to see what will happen, so far after over 10 tons of coal through the unit this year, no visible issues. As to whether it will suck the O2 into the pressure system at lower temps, ask me in a couple years after the boiler in question has been run extensively and then torn down.

In my opinion there is no real benefit to running an Anthracite Coal boiler under 140*F (except to make up for poor designs as in the system above), however if you think it provides benefit to you and you are using one of our units at low temps, please keep us posted on the results.



Poor design (raises his hand).... :P

The issue came up because to overcome the system I currently have (better than a 1/4 ton of water, radiation output far in excess of heat loss even for the Antartic) I'm considering going to a constant circulation setup driven by an ODR. From the bits I understand about this right now, that would mean there would be times that the system would be running close to or below the condensation point of a normal boiler.

It's been difficult to determine online how much an issue this would be, but I'm still searching. So I figured I would poll the community here and see where that took me. So far, I'm back where I started. :)
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: Rob R. On: Mon Jan 16, 2012 2:49 pm

:secret:

You can run the boiler at a different temperature than the radiation.

Do some reading about this product: http://flopro.taco-hvac.com/products/Pr ... tegory=184
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: kstills On: Mon Jan 16, 2012 4:03 pm

Rob R. wrote::secret:

You can run the boiler at a different temperature than the radiation.

Do some reading about this product: http://flopro.taco-hvac.com/products/Pr ... tegory=184



Ah, interesting.

So, say I loop my 12 gallon LL110k with my 40gallon GE in order to increase the overall mass of heated water in the system (the GE would act as a resevoir only). I could conceivably add two zones to the house coming off that loop with seperate circulators, and using these valves on each zone in combination with the ODR I would be able provide my constant circulation to those big ass radiators I have?
kstills
 
Stoker Coal Boiler: WL 110
Stove/Furnace Make: Leisure Line

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: qbwebb On: Mon Jan 16, 2012 6:17 pm

Yanche wrote:We think of hydronic heating systems as sealed systems. But in fact they are not. Not as sealed, as for example, a refrigerant system. While the larger water molecule can't get out other much smaller molecules have a path in and out. Places like, valve stem seals, pressure relief valve gasket, diaphram in your expansion tank, your makeup water regulator, automatic air vent, even the AL-PEX-AL at it's adapter. Does the amount of O2 that gets in or out make a difference? I don't know but the molecule level it's really not sealed. I've often wondered why designs have a make up water regulator. Why not just design it using components that don't leak, don't leak at the molecular level.

It's like old large food store refrigerant systems. They leaked like a sieve. I was at a seminar on HVACR compressors last week. One refrigerant service company tech talked about a local supermarket that leaked 1000-1200 lbs of R12 a year. They wouldn't pay to fix the leak, but would pay for the refrigerant. His favorite customer. With current regulations and refrigerant cost those days are long gone.


I wonder what plumbing approach designers of in floor radiant systems take wrt O2 intrusion when planning geothermal systems? I imagine the water temps on them don't get all that hot, do they keep a water reservoir at elevated no O2 intrusion temps, then a plate heat hx to the in floor radiant heat fluid?

Even if a system has spots where O2 can intrude I just don't see what the driving force is as long as your running a positive pressure or not continually losing water and have to auto fill with cold water filled with dissolved O2.

I think your best efficiency is where standby losses are minimal @ the lowest possible temp balanced with the cost of using electric to distribute the heat to the living space as long as your not destroying your boiler with either O2 intrusion internally or corrosive condensation on the firebox side. Somewhere there must be data on the rate of internal oxidation vs. concentration of dissolved O2 in water for alloy steels.
qbwebb
 
Stove/Furnace Make: Harman
Stove/Furnace Model: VF3000

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: SMITTY On: Mon Jan 16, 2012 6:26 pm

Matthaus wrote: ...... This unit is in the torture chamber to see what will happen, so far after over 10 tons of coal through the unit this year, no visible issues. .......

I own a torture chamber that guarantees failure of anything made of metal. If your interested you can set one of the units up here free of charge. :P :D

Image

Image
SMITTY
 
Stoker Coal Boiler: Patriot Coal - custom built by Jim Dorsey
Hand Fed Coal Stove: Harman Mark III (not currently in use)
Coal Size/Type: Rice / Blaschak anthracite
Other Heating: Oil fired Burnham boiler

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: lsayre On: Mon Jan 16, 2012 6:43 pm

What is (or rather was) that thing in the upper photo?
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (It has been fixed!)

Re: Can You Get Condensation Inside A Solid Fuel Boiler?

PostBy: SMITTY On: Mon Jan 16, 2012 6:51 pm

That's the front firebrick retainer on the Harman Mark III after 3 seasons. ;)
SMITTY
 
Stoker Coal Boiler: Patriot Coal - custom built by Jim Dorsey
Hand Fed Coal Stove: Harman Mark III (not currently in use)
Coal Size/Type: Rice / Blaschak anthracite
Other Heating: Oil fired Burnham boiler

Visit Lehigh Anthracite