Coal fired boiler overheating

davidbez

I have a Trianco coal fired boiler which works well most of time. However in very strong, prolonged winds ie force 6 or above it has overheated the complete system to boiling point. On shutting it down, including the fan, it continues to burn fiercely. The only way to stop it is to declinker to remove any embers. Anyone any suggestions as to cauise and more importantly a cure?

Intplm.

Sounds like you have a new source of draft feeding that fire.
Has anything changed on the boiler? Any recent work done on it?
Has the chimney changed?
You might have a crack or hole on the combustion chamber or your chimney may need some work?
Have you looked for or considered any of those things?

Jamie Hall

Coal fires are very sensitive to draught. You are just seeing the effect of excessive draught through the chimney in strong winds. Back in the day, coal fires were controlled by controlling the intake draught. You should have intake dampers on the firebox (not exhaust or breaching dampers) and while it is unlikely that they ever were airtight, they might be close. If the fire is running away, the first step is to close them completely; any induced or forced draught fans should also be off, obviously.

A warning on this: if the intake dampers are closed, carbon monoxide levels will skyrocket. Be sure your breaching and chimney are really truly sound -- if not, you shouldn't be running it anyway, of course. Therefore, if there happens to be a damper on the breaching, leave it open. Last thing you want is combustion fumes in your house.

The next step, if that doesn't get things under control, is to drop the fire, as you have noted. If at all possible, do this first with the shaker grates, with all the doors closed. Then rake the fire out through the ash pit and dispose of the embers outside, safely.

As an additional point. I presume this thing is for hot water? You should also have a dump tank and a circulating pump with enough capacity to keep it from boiling while you get the beast under control. You want enough water to absorb the maximum output of the beast, without boiling, for a couple of hours.

davidbez

Thanks for your reply. I do deal with the problem as you suggest. The boiler is not just for providing hot water but for central heating as well. There is an expansion tank as you state.
Both boiler and chimney are well maintained. The event referred to is rare, but rather scary. Could it be that air is being sucked through the system by the strong wind lowering the pressure rather as we might blow across a bottle top to produce a sound or it downdraught? If so would a cowl of some sort help?

kevinj_4

Do you have any pics? Does it have a barometric?

Jamie Hall

"air is being sucked through the system by the strong wind lowering the pressure" -- exactly what is happening. And it is scary, no argument with that! I had assumed it was providing space heating as well as domestic hot water (sometimes very hot! Do you have a mixing or tempering valve?).

The expansion tank is not a substitute for the dump tank. The dump tank is much larger. It needs to be around 250 to 300 gallons for each 100,000 BTUh maximum fire output of the boiler, and should have its own circulator -- possibly with a high limit aquastat on the boiler (circulator on at 190). The tank itself need not be pressurized; you can use a heat exchanger such as might be found in an indirect hot water tank.

You could consult with a really good chimney person on the cowl; it might help -- it might also make things much worse...

@kevinj_4 mentions a barometric damper. I honestly can't recommend one for a coal fired unit, as the CO levels get to be really high when the intake dampers are closed, and any openings in the breaching -- such as a barometric -- would just plain scare me.

kevinj_4

Jaime, I guess we are guessing without seeing the install info.

A lot of the old units had barometrics when I started.

Somehow you need to control the draft at the breech.

Even the modern wood / coal furnace in my shop calls for a barometric & .05 max at the breech.

leonz

davidbez said:

I have a Trianco coal fired boiler which works well most of time. However in very strong, prolonged winds ie force 6 or above it has overheated the complete system to boiling point. On shutting it down, including the fan, it continues to burn fiercely. The only way to stop it is to declinker to remove any embers. Anyone any suggestions as to cauise and more importantly a cure?

=====================================================

OK two things here,

What model trianco solid fuel boiler do you have??

Are you using a power venter???? A power venter will also allow the fire to become too large and create a runaway with a high wind condition.

First, If you do not have a barometric damper correctly adjusted for the coal boiler to prevent excess draft through the coal grates you will have the issue with too much fire due to a high wind condition creating a run away fire as you describe.

You need to have a chimney cap installed to prevent this from occurring again and when you have the barometric damper installed in your flue pipe FOLLOWING THE MANUFACTURERS DIRECTIONS EXACTLY is required.

The fastest way to do this is use Tee's the size of your flue pipe to install the Barometric damper and any new flue pipe.

Solid_Fuel_Man

You need a dump zone. An aquastat somewhere on the boiler or strap-on on the supply piping very close to the boiler. This will run a zone or zones to prevent a boil-over.

As has been said the draught needs to be investigated as well.

hot_rod

a dump zone could also be a length of fin tube, or a hydronic fan coil, unit heater, etc. If you do not have the room for a large dump tank.

A dump tank allows you to extract that energy and use it later.

If it is running away due to a draft issue, address that first, then add a dump if you still have more fire than load.