Water tube boiler & fire seperation

[marinesteam]

I'm reviewing past posts on water tube boiler builds and have a few questions.

Is there a general rule of thumb regarding the placement of the grates in relation to the mud drums on a three drum WT boiler? What generally keeps the combustion material (coals) from building up against the mud drum / lower water tube area. Does one put a vertical row of fire brick between the outside perimeter of the grate and the mud drum or place the grate low and let whatever material lay against the mud drum (or some combination of grate perimeter containment and mud drum above?

Photos of your installation would be very helpful.

Thanks

Ken

[barts]

If you have the vertical space, I'd make sure the coals don't rest against the tubes, since this leads to quenching flames and producing soot, and when the fire is out and the boiler cold, it tends to hold moisture-attracting, possibly acid ash against the steel boiler.

Keep in mind that refractories such as Mizzou are readily cast in greased/painted wood molds into any desired shape.

- Bart

[Cyruscosmo]

Hey Bart

How well did that castable refractory hold up for you? Could it have been used with an IFB filler to make the whole unit lighter? Like say a couple inches of castable refractory in front of IFB?

Cyruscosmo

[barts]

How well did that castable refractory hold up for you? Could it have been used with an IFB filler to make the whole unit lighter? Like say a couple inches of castable refractory in front of IFB?

That's what I did... but the castable is heavy, and I got more of it in there due to some mold expansion than I planned on. The Mizzou backed w/ Fibrefrax/kaowool works really well; the Mizzou does a good job of protecting the wool, which is what does all the insulating.

I've not run the boat yet this year; that's coming up now.... but it worked well for all the steaming I did last year.

- Bart

[Lopez Mike]

Bart is designing his new boat so he doesn't love Otter any more. So fickle.

[PeteThePen1]

Hi

I imagine that this is way too late to be of interest, but one never knows.

Bart raised some good points about coals against the mud drums, but one that is worth raising since nobody else has done so is the implications for safety with copper steam generating tubes. The SBA was very concerned that the Blackstaff three drum pressure vessel with a high grate could lead to the coals being built up until they impinge upon the coils. The result could be over heating of the copper and ultimately failure. The problem with that design, so far as I can see, is that in many instances a strip is welded along the inside of the mud drums to make a support for the grate. Having played about with that design to try to create a 'pretty' casing, I can see why putting the grate at that point seems a good idea.

For Frances Ann's boiler, my decision to go for coal meant that I needed to create more combustion space since the Yarrow style pressure vessel steam generation pipes cross under the steam drum. As shown in the diagram below, I got the extra height needed by mounting the pressure vessel on fire bricks. To keep the coals off the mud drums I also installed a 2mm sheet along each side of the grate. That has, for the most part, kept stuff off the generating tubes, but 2mm was way too thin as the sheets have warped severely.



I would be interested to hear what other folk have done.

Regards


Pete

[barts]

Hi

I imagine that this is way too late to be of interest, but one never knows.

Bart raised some good points about coals against the mud drums, but one that is worth raising since nobody else has done so is the implications for safety with copper steam generating tubes. The SBA was very concerned that the Blackstaff three drum pressure vessel with a high grate could lead to the coals being built up until they impinge upon the coils. The result could be over heating of the copper and ultimately failure. The problem with that design, so far as I can see, is that in many instances a strip is welded along the inside of the mud drums to make a support for the grate. Having played about with that design to try to create a 'pretty' casing, I can see why putting the grate at that point seems a good idea.

For Frances Ann's boiler, my decision to go for coal meant that I needed to create more combustion space since the Yarrow style pressure vessel steam generation pipes cross under the steam drum. As shown in the diagram below, I got the extra height needed by mounting the pressure vessel on fire bricks. To keep the coals off the mud drums I also installed a 2mm sheet along each side of the grate. That has, for the most part, kept stuff off the generating tubes, but 2mm was way too thin as the sheets have warped severely.



I would be interested to hear what other folk have done.

Regards


Pete

This could be a good place to cast some Mizzou into shapes that would protect the mud-ring, and keep you from having to put metal in direct contact w/ flaming coal.
Custom cast shaped firebrick .
- Bart

[Mike Rometer]

These sheets may have warped for several reasons, most likely is uneven heating from the fire. A right-angle folded lip (15 - 20mm) top and bottom, would do plenty to resist such warping, 3 mm sheet would also help.