overfeed vs. underfeed stokers for Bituminous

I have an Anchor stoker, very simular to Will-Burt underfeed Bituminous Stokers.
The next advancment is the adition of the rotating ring around the grate shaped like a circle, breaks any clinker and keeps the grate burning clear. Prill, Coal King, ect.

I've heard of overfeed heads that went on units like mine these essentally replaced the wind box and twyers with a grate located below the auger with air coming from below, similar in concept to the KeyStoker line, feeding onto a sloped grate, except I have a 3" auger, instead of a pusher block. A cutaway view of the Liesure line looks similar to my underfeed, pushing up past a grate.

Found this abstact on the web http://www.ags.gov.ab.ca/publications/a ... EP_46.html I think I found the artical one night, discusing efficiancy and claiming better Nox output, I'm looking for the ash to fall off the grate and into a pit or drag chain, currently I need to clear ash from around my underfeed twyers twice a day, high ash coal, this always results in some coal and smoke getting out of the fire box, stinks up the garage ect.

Who has experiance with an overfeed stoker in the 30#/hr range with 7,500 BTU/lb coal ?
I'm thinking about building an overfeed head for my spare parts stoker, using grates form Hern Iron works or possibly KeyStoker, any sugestions on grates ?
I'm not talking about the Detroit moving grate overfeed stoker, those are million BTU and up.

Great project

I am surprised that it wasn't done in the past when this stuff was in demand - but then the price per ton was cheap so ????

Also wondering what Berlin might add to this Bit discussion.

Maybe you should ask Greg to move this project to the Bit forum for more interaction from those guys and it won't fall off the map as fast as it can in this popular section.

Any way - please keep us posted and take/post lots of pictures. My need for a bit boiler is trailing off - yet plans can change and I do have some parts laying around too.

found this last week

over feed system

claims will burn coal and by the design -- it might???

http://www.youtube.com/watch?v=bka1vBpE ... re=related

Thanks for moving this post, I questioned my choice of headings.

I looked at the BioBurner not sure it would like my six to eight shovels full of ash per day.

Not sure why but here is a picture of a underfeed stoker head, showing the center where coal comes into the fire and the circle of Twyres/grates, where the air is introduced.

Some Twyrs are missing

These are pictures of the more modern round grate

I want to try a grate similar to the round grate, but like I said rectangular like KeyStoker.

Overfeed (rotating grate or otherwise) stokers work well only with very low coke button coals such as some western and illinois basin coals. With your alaskan subbituminous coal something like that might work well, but the best design for small btu output units and low coke button, high ash coal is the prill style rotating ash ring/underfeed stoker. This will give you the benefit of being able to remove ash quickly via an ashpan and avoid some of the issues you mentioned. however, a better (much cheaper) solution to having smoke and soot in the garage when the loading door is open is to have a chimney develop proper draft to prevent it, raise the hight and/or increase the flow capacity at a given draft by enlarging the flue size. reducing the heat load via insulation etc. will also cut down on the frequency of ash removal, but with high ash/low btu coals ash removal will be frequent whether you remove it as a clinker or powder. the great thing about clinkering type stokers is that they substantially reduce the volume of ash if operated properly.

You caught me Subbituminous coal not just Bituminous.
I'm catching the heat off my boiler and plumbing in my garage.
I think I have plenty of draft, I have no smoke coming out the door I remove ash from, the smoke comes from the ash, as it has some coal in it and some red clinker.
When I remove ash I try to get the clinkers, and trim the pile, with the shovel till I'm down to just the red coals, probably about 20% clinker by volume.
The floor of my combustion chamber is firebrick and about 1" below the top of the Twyres, with about six inches of flat from the twyres to the boiler wall
This is a picture of the fire at rest, I let it go another eight hours or so, brfore I cleaned the ash out.

One load of coal I had made mostly clinker and I was able to sort of push the ash toward the twyres and pull it as clinker, haven't had a load like that since.
I'm going to try to learn more about coke button, or swelling index, of my coal, my clinkers are very weak, I can break them bare handed when cool.

Upon fruther inspection I'm using Sub-bitumious C coal and this is what I find on that

"Sub-bituminous coal is black; and as it is mined, it looks a great deal like the bituminous coal seen in coal yards. It contains from 15 to 30 percent moisture. The range of heating value of cub-bituminous “A” coal is the same as that of high-volatile “C” bituminous coal. Sub-bituminous coal is entirely non-coking. Like lignite, it weathers or slacks rapidly upon exposure to air and is subject to spontaneous combustion if not stored properly". From http://www.miningbasics.com/sub-bituminous-coal

The high volatile content I can attest to when hand firing, lots of white smoke if you added to much to fast.
Sub-bituminous C is aparently a non-coking coal and therfore no coke button number?

all coals will burn somewhat differently, but what i'm seeing in that last photo is not something that is typical of an underfeed clinkering stoker fuelbed. typically the tuyeres will be buried under 3-8" of ash and the clinker will be pulled from around the fuelbed with very little (usually no) fuel attatched. there should be ample loose ash left in the furnace at all times to insulate the fuelbed and provide the proper development of clinker. If the clinker is developing within or on top of the tuyeres the feed rate may be too low or the air setting too high.

Now we're talking.
I'll get some pictures, make some adjustments, get more pictures, one adjustment at a time.
My clinkers seam to form along the top ot the twyres and down the face toward the center of the pot.
Currently running at middle speed on cone pulleys and about a 1/16 inch gap on a 8 inch disk air regulator.
I will wait at least twenty four hours between adjustments.
I have boiler controls that start stoker at around 160F and shut down about 180F when there is a zone valve open, when no zone is calling for heat the boiler sits untill it reaches 140F and then it runs the stoker till about 150F
This low temp 140 -150F control also shuts the circulator pump down to prevent the boiler from getting cold and condensing water out of the flue gasses.

I've been thinking about adding a relay to hold stoker on till boiler reaches 180F each time it starts, currently the stoker stops when no zone is calling for heat, this would lengthen run times and maybe get hotter burn temperatures, my Kewanee boiler holds about 60 gallons of water.

Tonight I will move feed belt to high speed and monitor for soot or evidence of oxygen shortage, check in morning, and see results tomarrow night, too dark to see stack for smoke, and I'm at work during the day, Winter, short days .

Thank You Berlin.

Moved belt to high speed, I think this is 25# per hour.
Did laundry, took a shower, and did dishes, boiler has run constant for about one hour, blue flame at base, for about 1 inch, then yellow for 6-8 inches, no soot, stack looks clear in moon light, stack temp at boiler 245F
I'll look at it in morning, and tomarrow night will disturb the ash pile, hopfully we have made improvments.

it's been 21 hours, pulled one clinker about the size of a modern quart oil jug.
going for another 24 hours at this setting.

I pulled a quart size clinker at 24 hours, and now at 48 hours a two quart size clinker.

So far the only changes I've made is to speed up the feed and allow the ash to build up, so the clinkers form in the ash pile not on the twyers.

I think Saturday when I can see the stack in the light I will turn the air down some.

Temperatures outside -8F at night, 7F in the day. We need a penquin smilly face.

If the clinkers you are pulling out are forming around the outside of the tuyres and not over or down in the retort then you're doing good. You don't want to do anything to areas where the coal is still burning in or above the retort/tuyres. At the time the burning coal is pushed to the outer perimeter of the tuyres it should be completely burned to ash and hot enough to start to clinker. You'll still have some ash to clean out though.
How long does a full hopper last in that weather?

Just back from eight hour ambulance run but too wound up to sleep.

Tomarrow the Military is coming to town, I guess we are the closest town to a F-22 that went down, the operators that I mechanic for at the DOT are clearing fifty miles of the summer road to Paxon, out to a mud airstrip that will be used for staging.

I fish for clinker with a claw and pipe tool for grabbing clinkers, the last two clinkers didn't have the twyre shape on them so they are from within the ash pile, I pull them out and they are glowing red but definatly solid and not burning.

Short Bus wrote:Tomarrow the Military is coming to town, I guess we are the closest town to a F-22 that went down, the operators that I mechanic for at the DOT are clearing fifty miles of the summer road to Paxon, out to a mud airstrip that will be used for staging.

Hadn't heard about this until now. News on line says wreckage found but pilot missing..?