Building a boiler: Why no firetube boilers for coal?

Building a boiler: Why no firetube boilers for coal?

PostBy: coalisorganic On: Thu Jul 24, 2008 2:20 pm

I am in the "thinking" stages of building a coal automatic stoker boiler from (mostly) pre-existing parts and need advice. Ideally I would like to use a pre-existing firetube steel boiler that was originally oil fired for the pressure vessel. I can weld, but I don't want to weld a pressure vessel. Cost and availability of coal burning boilers are not very favorable for buyers this year. Wood pellets on the other hand are either being rationed or are out of stock.

I noticed that the designs of most coal stoker boilers seem to have a large open space (like a chamber) over the burning coal. This is the opposite of steel oil fired boilers, which are firetube style. The EFM 520 is all just flat plate, another one (the Harman I think) has some water tubes high up over the coal fire in addition to flat plates. Big open volumes continue all the way to the exit flue collar.

The hot-side blower forced boilers (Axman Anderson Anthratube and Coal Gun™ Coal Stoker Boiler do have narrower passages.

Why are these (natural draft, not hot-side fan forced) systems designed as they are (what is the main design requierment that is being met)? I suspect the big open spaces are there to avoid ash plugging in an applience that is never maintained. Or maybe flat plate boilers with no firetubes are just easier to build, and a firetube boiler would work but need to be kept clean/cleaned more often and be more expensive to build. What do you-all think?
coalisorganic
 
Stove/Furnace Make: none yet

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: LsFarm On: Thu Jul 24, 2008 2:37 pm

Unless you have fairly high velocity in the airflow in the boiler firebox, you do have fly ash accumulating on surfaces,, even vertical surfaces.. An Axeman Anderson, and the AHS boiler designs have a high velocity combustion fan that uses the ash the 'scrub' the heat exchanger areas clean, and with a lot of turbulence in the hot air 'beats' the heat into the heat exchanger surfaces.. a smooth, lazy airflow creates insulating 'laminar flow' layers of air that do not transfer heat as well as turbulent air.

The current boiler designs also need the airspace to allow the fire off of the coal bed to burn completely,, I read some interesting boiler design books, and some info about sizing a stoker to the boiler when converting a hand feed to a stoker feed.. one parameter is that you do not want to have FLAME touching the water jacket if you can help it.. this is why you have the large air volume in the combustion area.. I can't remember exactly what the reasoning was, but I think it was that if you see flame, the gasses are still burning,, just beyond the top of the flame is where the combustion is complete, and you will get the least deposits on the inside of the boiler..

The EFM and others are designed for easy cleaning.. the later EFM designs have a removable steel plate that allows you access to all the back of the heat exchanger area,, just some long handled 'bottle brushes' are what is needed [and a shop vac] to give it a good cleaning. with a round tube design, you need to somehow brush out the entire tube area, difficult without removing a water jacket, [not possible] or using jointed, extendable brushes.. and ANY horizontal surface will accumulate a thick layer of ash within weeks.. insulating that surface from the heat of the fire..

I'm sure you could figure out a way to make up a coal boiler from a stoker unit, and an existing tube-type boiler.. but I'd highly recommend looking at several made-for-coal boilers first..
I made my own boiler, and made lots of mistakes. I wish I knew then what I know now.. I could have saved a lot of money and aggravation.

hope this helps.. Greg L

.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: coalisorganic On: Thu Jul 24, 2008 3:29 pm

LsFarm,
Thanks for your reply. I have the book "Boiler operators guide" third edition by kohan and spring. I also have the Audel books on oil, gas and coal burners, but this book does not really talk about design from scratch.

What other books would you recomend?

Do you have a value for the reccomended boiler heat release rates for coal? For oil fired boilers from the "boiler operators guide" I have for the volumetric heat ratio 35 MBTU per cubic foot of furnace volume, and an effective projected radiant surface heat release rate of 180,000 BTU per Square foot of furnace radiant surface. I plan to stay well away from these or any other limits.

I have measured the distance from the top lip of an empty coal pot on an EFM 520 to the overhead steel plate and it is about 14 inches (not exact, I have the number written down somewhere). I am planning to leave at least that much space between my coal bed and the bottom boiler sheet. I am thinking of a sloped ramp firebed with air blowing thru holes underneath like in the alaska channing III stove and many others. This burn ramp would be in a "fire chamber" area below the boiler, but burning coal would never touch the sides, it would burn on the ramp. I plan to line my "fire chamber" with hi temp board insutalation and put a layer of half-thickness firebrick over that. The board insulation is very fragile and I want to protect it. The boiler would sit on top of this firebox. A volume for an ash drawer would be below the insulated "firebox" space.

What does the rate of buildup of the ash depend on? Just the lbs of coal burned and the coal ash content? I assume it is not sensitive to the boiler temperature. Not like burning wood, where creosote builds up on cool surfaces??

I would have access to the insides of the fire tubes from the top for cleaning, ash would fall down into the ash bucket. I would be able to clean the top flat surface as well. I will make sure to have a way to clean the bottom flat surface. The water jacket would not get in the way of cleaning any of the surfaces that combustion gas would touch.
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not to scale!!! boiler sketch.
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coalisorganic
 
Stove/Furnace Make: none yet

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Re: Building a boiler: Why no firetube boilers for coal?

PostBy: Sting On: Thu Jul 24, 2008 3:49 pm

simple vertical fire tube boiler design

not terribly efficient but it works

Are you using the old Tarm design - bought by Pinnical to make the Pb150?


http://www.pinnaclestove.com/sheets/pb150mn.pdf
This link is broken, either the page no longer exists or there is some other issue like a typo.


What do you plan to use / make for a stoker???

Very interested - how may I help
Sting
 
Other Heating: OBSO Lennox Pulse "Air Scorcher" burning NG

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: coalisorganic On: Thu Jul 24, 2008 6:09 pm

Sting,
Thanks for that link. I love users manuals. :D
I guess that is the idea, just with a carpet bed ramp feeder for coal and an ash door in the bottom.. Also that is a fire-tube boiler, and I want a fire-tube unit because I already have a new-ish steel firetube boiler in very good condition I would like to use for this.

For the stoker part I am thinking of using any of the carpet bed ramp burners (is that the right name?) Like the burner in this pic.

http://www.3cats.com/KeyStoker.htm

The different brands of burners each need their own shape of hopper and pusher, blowers, etc. I have lots of variety of motors/gearmotors and blowers available already so I am not too picky about which exact unit I get. I think my decision will be based on what I can get a hold of/buy, and with the rush and shortages of coal stoves right now I suspect I might have problems getting hold of new parts.

I would be real happy with a used burner unit, even if it needed work.

The only type of burner feeder design that I do NOT want is the harman underfeed ramp pusher (verti-flo coal feeder).

http://www.harmanstoves.com/doc/vf3000m.pdf
This link is broken, either the page no longer exists or there is some other issue like a typo.


This is really ironic/unfortunate because harman has the most easily found/best documented parts lists and price lists online. I have nothing against the design as part of a complete harman system, but I feel this type of burner is going to be harder/tricker/more-chance-for-unhappy-surprises for me to use because I will need a lot more force in my pusher block mechanism to raise the coal up, and also as shown in the pdf file the flame tends to burn towards the back where the coal inlet is and I worry a lot about a fire coming back into the hopper.

I think the (only?) stoker parts I want to buy (new) are the (non harman) equivalents of these two cast iron parts on page 22 of the harman pdf file liked above:

Item 1 Grate inserts
Item 2 Grate holder

or in this picture

http://www.keystoker.com/images/stoker%20parts%20breakdown.jpg
This link is broken, either the page no longer exists or there is some other issue like a typo.

I am looking for the A size (3 grate)
Item 1 stoker body
Item 2 + 3 side rails
Item 4 grate

The rest of the parts (hopper, pusher, etc) I can fabricate myself, unless they are so in-expensive that it just makes sense to buy them.

Here again if I could find a used burner unit complete I would buy it if not too expensive.

The electrical controls/over-temp/low-draft-warning/etc I can make up myself no problem.

I would love to be able to find a detailed parts list and price list for other carpet bed ramp burners, like the keystoker, or the alaska channing III, or other brands. I want to have an idea of what these parts are supposed to cost before I start calling around for them.
coalisorganic
 
Stove/Furnace Make: none yet

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: syncmaster On: Fri Jul 25, 2008 7:08 am

all these coal boilers go through a certification.
If you build your own... and it burns your house down I doubt the insurance co will pay.
syncmaster
 
Stoker Coal Boiler: harmanVF3000 Coal/oil option
Coal Size/Type: Rice
Stove/Furnace Make: VF3000
Stove/Furnace Model: Harman VF3000

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: Sting On: Fri Jul 25, 2008 7:25 am

if its in your own home and you made it your self and it burns you home down -- your covered :|

Thats what home owners insurance does - it covers you when YOU make stupid mistakes

and it covers you when others harm your house - but, the underwriter is paid back by litigation against said other...

Thats why you don't need a low pressure boiler license to pipe a boiler in your house basement but you do if its in your rental property or a dwelling of another.
Sting
 
Other Heating: OBSO Lennox Pulse "Air Scorcher" burning NG

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: Sting On: Fri Jul 25, 2008 7:32 am

Remember the boiler you picture has a water jacket all around the fire box - not like the vessel plunked on top in the design I sent.

Also I asked to buy just the stoker as you pictured - and they said no - have to buy the whole appliance

I am still holding out for a bit boiler better sized for my load - than the huge engine I have in the shed

BTW -- there is nothing wrong with the Harmon design -
Sting
 
Other Heating: OBSO Lennox Pulse "Air Scorcher" burning NG

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: coalisorganic On: Fri Jul 25, 2008 9:25 am

Remember the boiler you picture has a water jacket all around the fire box - not like the vessel plunked on top in the design I sent.

I am confused and do not understand exactly what you mean, could you please rephrase that?
I am thinking of a vessel plunked on top.. That is what my sketch is meant to show, but it is a bad picture.
In my sketch the firebox is a sheetmetal box with no top or bottom. it lined on all 4 sides with hi-temp insulation as backing insulation and firebrick on top of that as hot face insulation. The fire-tube boiler is plunked on top of this firebox. I intend to leave enough space between the burn grate and the underside of the vessel to make sure the flame does not touch the vessel.

Thanks for the tip on trying to buy a stoker, that helps. Can you recall who you tried to buy from (was it a manufacturer or a dealer)and which brand you tried to get?

I plan to do extensive run testing on this unit outside, using a car radiatior with blower as the thermal load. I would make up a forced draft with barometric damper for the tests. I would also check out-of-coal/low-coal behaviour to see if the unit wants to burn back into the hopper. I am thinking of having a temperature sensor at the hopper base to detect this problem if it happens in operation.

I am certainly not just going to slap something together and light it indoors.
coalisorganic
 
Stove/Furnace Make: none yet

Re: Building a boiler: Why no firetube boilers for coal?

PostBy: coal berner On: Fri Jul 25, 2008 2:16 pm

coalisorganic wrote:Sting,
Thanks for that link. I love users manuals. :D
I guess that is the idea, just with a carpet bed ramp feeder for coal and an ash door in the bottom.. Also that is a fire-tube boiler, and I want a fire-tube unit because I already have a new-ish steel firetube boiler in very good condition I would like to use for this.

For the stoker part I am thinking of using any of the carpet bed ramp burners (is that the right name?) Like the burner in this pic.

http://www.3cats.com/KeyStoker.htm

The different brands of burners each need their own shape of hopper and pusher, blowers, etc. I have lots of variety of motors/gearmotors and blowers available already so I am not too picky about which exact unit I get. I think my decision will be based on what I can get a hold of/buy, and with the rush and shortages of coal stoves right now I suspect I might have problems getting hold of new parts.

I would be real happy with a used burner unit, even if it needed work.

The only type of burner feeder design that I do NOT want is the harman underfeed ramp pusher (verti-flo coal feeder).

http://www.harmanstoves.com/doc/vf3000m.pdf
This link is broken, either the page no longer exists or there is some other issue like a typo.


This is really ironic/unfortunate because harman has the most easily found/best documented parts lists and price lists online. I have nothing against the design as part of a complete harman system, but I feel this type of burner is going to be harder/tricker/more-chance-for-unhappy-surprises for me to use because I will need a lot more force in my pusher block mechanism to raise the coal up, and also as shown in the pdf file the flame tends to burn towards the back where the coal inlet is and I worry a lot about a fire coming back into the hopper.

I think the (only?) stoker parts I want to buy (new) are the (non harman) equivalents of these two cast iron parts on page 22 of the harman pdf file liked above:

Item 1 Grate inserts
Item 2 Grate holder

or in this picture

http://www.keystoker.com/images/stoker%20parts%20breakdown.jpg
This link is broken, either the page no longer exists or there is some other issue like a typo.

I am looking for the A size (3 grate)
Item 1 stoker body
Item 2 + 3 side rails
Item 4 grate

The rest of the parts (hopper, pusher, etc) I can fabricate myself, unless they are so in-expensive that it just makes sense to buy them.

Here again if I could find a used burner unit complete I would buy it if not too expensive.

The electrical controls/over-temp/low-draft-warning/etc I can make up myself no problem.

I would love to be able to find a detailed parts list and price list for other carpet bed ramp burners, like the keystoker, or the alaska channing III, or other brands. I want to have an idea of what these parts are supposed to cost before I start calling around for them.

PM Memeber Scrapper 23 jr he has all types and style stoker units EFM's Keystoker Yellowflame Losch he also will be abel
to Answser & Help you in your design
coal berner
 
Stoker Coal Boiler: 1986 Electric Furnace Man 520 DF
Stove/Furnace Make: Electric Furnace Man
Stove/Furnace Model: DF520

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