Bituminous Stoker/Lump Coal Grates

 
unhippy
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Post by unhippy » Tue. Sep. 01, 2015 4:31 am

Teddy wrote: Unhippy: I thought about a chain grate stoker but would like to keep this thing a lot less mechanically complicated. I was thinking that if the gap between the bottom edges of the side grates were big enough to allow clinkers to pass through to the ash auger, the ashes piled up on the auger would stop raw coal from "falling through". I thought that the bottom edge of the grates would sit on top of the trough the auger sits in. I could make the trough deep enough that the auger wouldn't get too hot. If need be, put a "clinker breaker" between the grates at the bottom operated from the outside? Again I would like to know what diameter an ash/clinker auger ought to be? 3"? 4"?
Coal needs primary air from directly underneath, having some of it sitting on top of ashes piled up on the auger will result the that coal directly above the auger not burning due to a lack of primary air.

Clinkers don't form in nice little lumps that will slide down the grates and into the ash auger.....if your firing hard your likely to end up with one stonking great clinker that takes up most of the grate surface

I think some of the problems you are having understanding how coal burns, is that you are trying to treat it like pieces of ultra-hard hardwood 2 inches across.....It has needs and burn characteristics that are totally different to wood.

The closest analogy I can come up with is the difference between tuning a high performance petrol engine and a high performance diesel engine....both have roughly the same type of parts in the same places, but the difference between them means they have to be treated totally differently.

Before you dismiss a travelling grate stoker out of hand, count up how many moving parts, actuators and timers etc you would have in anything you design or modify.....by the time you get clinker breakers and ash augers going it makes the chain-grate look pretty simple....and they can be run on natural draught if they are designed for it and the coal you have wouldn't need resized either.


 
Teddy
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Post by Teddy » Wed. Sep. 02, 2015 11:45 am

Thanks again Unhippy. I thought the almost vertical grates would mimic the conical pot grates of the underfeed stokers, the air comes in from the side not the bottom like through a horizontal grate. The coal just flows down in my proposed design instead of up like the conventional stokers. I'll know a lot more next week when I start to play with the Combustioneer.

I talked to Joe at Mark's Supply yesterday, he is the guy who modified an EFM to burn bit coal. He got a pot and auger setup up from Wyoming and can't remember the manufacturer's name. He said he would look for it for me. The only problem with it and with the Combustioneer, is the auger limits the coal size to 1.25". He said I should look for a 2.5" or 3" auger for my coal. Do you know of any? The pictures of coal feed augers on the inderfed stokers I have seen look shiny, like they are made of stainless steel. What are they made of? No body has answered my ash auger diameter question?

My coal has been sitting in a pile (not high enough for spontaneous combustion) outdoors for 2 years unprotected from the rain/snow. Does coal absorb moisture from the surroundings or does it have a certain moisture content from the mine which stays the same until you burn it? I was thinking I would put a large tarp suspended over it to keep snow off of it and protect it from rain. How important is this to do? I am sure that just the surface water on the coal even if the coal does not absorb water would reduce the efficiency of the burn.

If I end up building the burner and using the ash removal auger idea, do you know of a Motor Stokor or any other ash removal system that I could buy?

Can't wait to get home and burn some coal. Thanks again for all your help, this has been a great site to get educated. Teddy

 
unhippy
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Post by unhippy » Thu. Sep. 03, 2015 6:07 am

In the underfeed stokers the coal is pushed up and out over top of the air holes by the new coal being fed in from underneath any time the stoker is running.....what you are proposing would allow any coal that is in the middle of the burner to pass down thru without passing over any air holes, meaning it wouldn't get burnt properly .

All coals are different but No they generally won't absorb moisture.....however wet coal in an underfeed is actually not a bad thing as long as its not wet enough to clog and affect the feeding function (normally only a problem when running rice coal)

....the water turns to steam as the coal heats up before it gets hot enough to burn....this steam is then forced thru the char bed were it is cracked by contact with the hot carbon in the char bed into its base elements H2 &O2.......hydrogen is good fuel and oxygen helps improve the burn....most of the last generation of coal fired steam locomotives had steam injected into the underfire air to take advantage of this reaction

Some coals when left exposed to air will "slack down" or basically go crumbly and fall apart over time until if left outside in the elements for long enough you would have a pile of coal dust......the Bit coal I am running will do this over about a year.....if coal is kept damp it retards this action but doesn't stop it completely.....submerging coal in water stops the slacking down process entirely

Some other Bit coals are not affected by this process, the Bit coal I burned when I lived in another part of the country I used to get from a pile that had been mined about 20 years before and still looked like it had been dug up yesterday.

As far as I know the feed screws on underfeed stokers are just steel.....i have a pair of feed screws from an industrial sized stoker and they are definitely a steel of some kind altho it does cut like a wear plate steel.

As for an ash auger..... in the boiler I am lining up to build I will use a 2" auger driven by a 1 rpm pellet stove motor that I will wire in parallel with the main stoker drive motor.

As for an off the shelf ash removal system, I have no idea.....
lol half the time when I build something its because I don't know that there is a off the shelf set up available......the other half of the time I do know there is a off the shelf set up available and "NO WAY am I paying THAT for THAT!!!!".......as my wife put it....."i'm shacked up with a cheapskate armed with a welder"......i kinda like to think of that as a backhand compliment....
Last edited by unhippy on Thu. Sep. 03, 2015 8:39 am, edited 2 times in total.

 
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McGiever
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Post by McGiever » Thu. Sep. 03, 2015 7:09 am

teddy, ask Mark, If it was a Prill Stoker that was from Wyoming?

:idea: Member *bksaun* modified a auger to remove his Bit coal ashes from his under-fed Bit Stoker, have you seen?. :idea:

 
Teddy
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Post by Teddy » Tue. Sep. 15, 2015 7:58 pm

McGlever - I asked him and it was a Prill Stoker.

I drove to KY and picked up the Combustioneer. It had coal in it and when I got home, it started right up when I poured a few ounces of kerosene in it and lit it. After it ran for a while I shut it off. The next day I removed all the coal and ashes from the combustion chamber, burner, auger, and hopper. The auger is 3" OD, 2.625" ID, the auger flight is 2.125" OD with a 3/4" shaft. The firepot is about 5" ID at the top and tapers down and is about 5" tall and then there is the 3" OD auger hole under that. There are two rings of air holes in the firepot, the first ring is 1" down from the top and the second is 2" down. There are 12 holes in each ring and the top ring has about twice the area as the second ring. The fire pot has about a 7.5" OD and only sticks up about an inch above a firebrick/ceramic/? horizontal surface. The OD of the surface or ID of the combustion chamber is around 15". There is a firebrick cylindrical wall that goes up about 9" above the surface. The air carrying heat exchanger tubes are about 6" above the wall. There is a small amount of secondary air that comes in through a few holes in the door in the side of the combustion chamber. You clean out the ashes and klinkers by opening the door and scraping them out into a small box under the door. I guess that in normal use you would do this when it was going through it's "down time".

After taking all the dimensions, I loaded it up with "my" coal and the auger had no problems with it. I would hear some crunching noises from time to time, but it fed my coal. The high fire shut off safety worked as I was firing it up with 100-% new, un coked coal and it got very hot. Once it got to a normal burn, it burned fairly cleanly. I say fairly because even though it looked clean coming out of a short 6 foot stack, I could see smoke about 20 feet away as it cooled. Also I experimented by throwing a small amount of new coal on top of the firepot while it was going and as you all predicated, it put off some smoke until the volatiles burned out. I just wonder if it had really hot secondary air and more combustion chamber volume (hot residence time) before hitting the heat exchanger, that the smoke could be burned where it is supposed to be - in the combustion chamber? The reason this concerns me is that somehow I would like to solve the problem that this burner has and I am afraid all the stokers have, that is that when it goes to sleep mode, it smokes for a while. Maybe this isn't a problem. If we could stop the auger and keep the air going for a while, then when the air is turned off it might not smoke?

I put a thermocouple in the hottest part of the burn and it recorded 1830 F. Just 4 or 5" above this, the temp had dropped to less than 1400 F. You believe that if we could get the combustion temp to where all the crap was being burnt, like 1800 F for about 0.8 seconds, we will make tons of klinkers. I hope I can find the time to do this experiment. I have no problem using a bottom feed stoker, but would like to disconnect the auger from the air to try and control smoke better.

So, the reasons for not wanting to use the Combustioneer burner- 1. Manual ash removal. 2. Smokes during down time. 3. auger and air connected. 4. poor combustion chamber design I believe.

Do any other bit burners address these problems? Thanks again for your insights, Teddy

 
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Post by McGiever » Tue. Sep. 15, 2015 8:40 pm

Here is a link to *bksaun's* Gentleman Janitor stoker beneath a EFM boiler thread.
He did add an ash auger near the end or was it shortly after he got it burning.

Hybrid Boiler Project

 
chubs
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Post by chubs » Wed. Sep. 16, 2015 1:09 pm

heres a link about mod. to the combustioneer
Combustioneer Model 77 Stoker Pics Etc.
I would search the site for combustioneer, thers alot of imfo. on them


 
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Post by Teddy » Wed. Sep. 16, 2015 3:29 pm

Thanks McGlever and Chubs. I have been reading these threads for the last few hours including the 14 page one on the GJ/EFM marriage, can't wait to see that one burn this weekend. My goal is to 1. burn the Illinois coal that I have 2. have automatic augered ash removal 3. Have minimal smoke production during off time. For item 1, I do not know if my Combustioneer feed auger with it's 2.125" OD flight in a 2.625" ID tube will do too much grinding of my coal. I guess I need to burn a bunch more coal in it to answer that one, however this week I am stuck in TN for a week and can't do anything other than research. For 2 the Combustioneer chamber is not condusive to augering out ashes. I ordered a 3.5 OD flight auger to play with if I come up with another burner setup or just jerk the Combustioneer firepot out of the housing.

Don't the flights look all worn out? Maybe it used to be 2.25" OD instead of 2.125" that it is now? Do you think I should try to find a bigger feed auger than this for my "big" bit coal like 2.5" or 2.75" or 3" OD flights? Which would be the best firepot to use for the it coal, I want it to be small like the combustioneer around 5" ID at the top? EFM, Motor Stokor, something else that can accept or be modified to accept the bigger feed auger?

Thanks again.

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20150910_131924.jpg

Combustioneer 77B feed auger and square air feed tube

.JPG | 76.4KB | 20150910_131924.jpg

 
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Post by Teddy » Thu. Sep. 17, 2015 4:00 pm

I am stuck in TN this week without cell service and of course not able to play with my burner. I was inspired by reading Stoker Don's Gentleman Janitor project and have decided that I should try to accomplish my goals using recycled stoker parts like he did. So I was able to make a call today (land line) to Joe at Marks Supply to price out an EFM firepot. Since it isn't designed for bit coal and has an 11" top ID, I think I want to stay with my Combustioneer firepot that has a 5" top ID. When I asked Joe what size feed auger would be best for my Illinois coal, he told me to give Henry a call at Maertens Mfg who makes bit burning furnacers and boilers. As I mentioned before, I hear crunching noises while feeding my coal and I am thinking I need to make the feed auger bigger. Joe said the Prill auger he used for the bit coal was 3" ID with a 2.5" OD flight. It worked well with his Wyoming coal. Henry uses a 3" OD flight in a 3.5" ID tube for his North Dakota sub bit/lignite fuel. Henry gave me some great ideas on the design of the feed auger and I may have him make it for me. Unfortunately the smallest firepot Henry makes is designed for 175,000 Btu/Hr - way bigger than I need in Southern Missouri. So unless anyone has another firepot for me to buy and play with, I will be playing with the Combustioneer.

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20150910_131818_Burst01.jpg

my Combustioneer firepot

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carlherrnstein
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Post by carlherrnstein » Fri. Sep. 18, 2015 3:02 pm

Contact these guys http://www.jonmargear.com/coal-and-wood-stokers/ they just bought the rights to make will burt stokers and replacement parts. Last year a brand new auger for my 77B was $130 from will burt.

 
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Post by Teddy » Fri. Sep. 18, 2015 7:29 pm

Thank you very much. I will contact them.

 
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Post by carlherrnstein » Sat. Sep. 19, 2015 11:07 am

I should have mentioned that some crunching is normal. I suggest you check the oil in the gearbox, the last thing you want to do is replace all the gears in there. It takes normal stinking 80-90 axle oil.

Do you have a owners manual? I can send you one in a digital format. Also a combustioneer will fuse the ash into a clinker. So you will need a clinker tong, and probably a poker to break the clinkers up in to smaller pieces, to get them out the door.

 
Teddy
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Post by Teddy » Sat. Sep. 19, 2015 1:18 pm

I have already downloaded the manual and read it from cover to cover - thank you for the offer. I will check the oil when I get home. Why is it prone to making clinkers? Even the manual says that one should clean out the clinkers at least once a day. I don't know if you saw it but I did measure the temp in the hottest part of the fire and it was over 1800 F. The manual calls for using coal with an ash fusion temp from 2100 to 2450 F. I haven't run my furnace long enough to see what it does produce in the way of clinkers. Do the flights of my feed screw look too worn out?

 
Teddy
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Post by Teddy » Sat. Sep. 19, 2015 1:22 pm

Maybe it is because it holds the ash up in the hot combustion chamber until you clean it out that it makes clinkers. If it dropped the ash to an ash bin below the combustion chamber, like some of the other burner designs, it might not make so many clinkers??? What do you think?

 
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Post by carlherrnstein » Sat. Sep. 19, 2015 3:09 pm

Once you have it up and running you will understand. The fresh coal comes up from the bottom and turns to coke, the coke continues to burn as it fuses into a mass that is being consumed and turned to ash/clinker but, is replenished from beneath by more coke. I hope I have been able to describe the burn, I'm not real good with words.

Basically the formation of clinker is not all at once, just like the formation of ash it is gradual. Coke on the top of the fire might have a layer of clinker on top of it that is being built by the fire.

What do you have against clinkers anyway? They are worlds easier to remove than loose ash.


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