Size of your firebox, bed of coal

LS,
I certainly admire your welding skills !! I did look at your pics but didn't put 2 and 2 together. As far as the crusted top of the coal is concerned I think I have found a partial solution, but it decreases burn time a little ( I think)
My boiler has a natural draft in the loading door ( for wood burning) and forced draft under the grates for coal. Both drafts are controlled with an aquastat that turns a motor and shuts both drafts off when desired temp is acheived. I can run either draft or both and the loading door draft has an arm that is adjustable. I have found that if I adjust the natural draft arm so it is still be open about a quarter inch when the boiler shuts down that allows enough draft into the firebox to burn off that pesky crust, to a dregree. BUT, this will also overfire the boiler if your not careful. I am still experimenting with this.
I think alot of my overfiring problems are coming from the mild temps outside. It is supposed to snow pretty good tomorrow and the next day so I will see how it works then.

Greg-

I have a hand fired Harman SF-250 rated at 120k btu's. The firebox is 26" long x 15..5" wide x 9" deep. You can not fill it level to 9" due to the door opening below the firebrick line.

It's been so darn warm, I too reduced the firebox 33% with busted pieces of firebrick. But the few times I have removed the filler brick & loaded it up, I easily obtained 350F air temps using the tiny 135 cfm blower. And yes, I see the highest temperatures when I have the yello/blue temps dancing 6-8" above the bed of coals. This only occurs when I have the ash door open and/or the draft wide open. Once I cut back on the draft and allow it to *simmer*, the outlet temp will reduce and it will stay constant for 6 to 8 and maybe 12 hours depending on how much coal I shoveled.

I have installed a firebox thermometer and will begin monitoring the actual temperature inside of the stove under various conditions. ( It was just reading nearly 1000F with the yellow/blue flames dancing high ).

Hope this helps.

ktm rider wrote:NEPA,
You say that your water temp sometimes goes as high as 220* ? WOW !! is that safe as for as your pipes are concerned.

There's a pressure release valve, if it gets too high it will relieve it. You should have on on your furnace as well, if you don't I'd suggest getting one. Any furnace/heater that uses water should have one.

Do you think if i raise my hi limit aquastat to say 205* that my pex would handle the heat. I can not recall the max temp it is designed for.

The hi is set at 180 on ours as I mentioned above. It will continue to go up after the furnace turns off since the fire has such a "head of steam". As I mentioned above especially if the furnace is no longer circulating the water. Generally it's in the 180 range in the winter, it's rare for it to go above 200. You can even get adjust circulate the water at a certain temp regardless of demand for heat or not....

Cap, where did you get your firebox thermometer? What does it look like and how is it set up? A wired lead going into the firebox from an outside meter?

Nepa,
I mean is that water temp safe for the pipes? as in the max temp allowed through the pipe. ( melting issue) I do have a pressure relief valve. I wouldn't put a fire in a $6,000 boiler without one, not to mention the explosion factor.
I have my circulating pump set up to run constantly. I burst my pipes 2 years ago when we got 54"of snow and I was snowed out for 5 days and the temp dropped to about zero. If I would have had my pump running I don't think I would have had a problem. I could be wrong though and I don't want to find out.

ktm rider wrote:Nepa,
I mean is that water temp safe for the pipes? as in the max temp allowed through the pipe. ( melting issue) .

It's all copper or steel pipe, there's not a piece of plastic tubing in this house except for the sewer. Again, that's an extreme, it rarely gets above 200.

Thanks again everyone, your input has been very helpfull.

So far I've learned that:

My 22"x24"x4-8" load of coal should be about 120-140,000 BTU and I could potentially double that by using all my firebox.

There is a peak heat initially tapering to a lower sustained heat output for a load of coal. I thought it would climb steadily and be hottest in the glowing bed of coals stage until the coal was close to being burnt up.

The other boilers in use are seeing 140* -160*or so as their sustained water temp, just like mine. And when the coal is burning down even with the blower running full time through a bed of hot coal the water temp can drop.

That a large load of coal bridges just like mine does.

And from the above information I may try:

I may make a new firebox front wall out of steel with an air passageway from the grate to the top with a lip to aim the air onto the top of the coal to see if it will burn off the crust. This should be a fairly easy thing to fabricate.

I may try to wire up my two speed combustion blower to run on high when the water temp drops below a setting. I'm not sure if I need a second aquastat or if my current one has a way to do this.

I'm going to move the rear partition back about 8-10" and load more coal to see if I can maintain a slightly higher water temp for the cold temperatures this week. The fire will be 22"x ~32" x 4-8" Maybe 180K BTU?

I may just heap the coal higher and see if it will burn OK when it is 10"-12"deep in the center. I will probably bridge easier piled like this but I will find out.

Learning more every day, Thanks for the help.

Greg L

Most PEX is rated for a maximum of 200f. There is some PEX that is rated for up to 250f. It should be marked on the side of the pipe what its maximum temperature and pressure is. Pex is not an ideal material for use as distribution pipe for a coal boiler. If used, it should have a tempering valve that does not allow the max temp to exceed its rating.

Kirk

KTM, do a Google search for your PEX tubing I think it is rated for several pounds of pressure and around 250* I'm using Kitec tubing which has a welded aluminum tube with Pex type plastic on the inside and outside, it can handle a lot of pressure and heat, But my boiler is an open system, so there is no pressure buildup. So far I've not seen over 190* water temperature.

Richard [Coalman] I do get some small klinker in my ash pan. I will next week let the fire burn down enough to see what has acumulated on the top of the grate. But I have noticed that I have a lot less when I don't try to burn the 'fines'. The 'fines' seem to have an ability to weld themselves into some impressive hunks of rock.

My new boiler has wider slots in the grates so I see much more small 'klinker' in the ash than with the old boiler. In the old boiler it collected it on top of the grate and eventually couldn't get enough air through to the fire. So far this doesn't seem to be a problem with the new boiler.

When I get back home next week I'll post a photo of a few of my 'super klinkers'

Richard, does your Van Wert owners manual have a sketch or diagram of the auger and firebox?? if so could you scan and email it to me, sounds interesting. It is working very well for you, how many years did you say your boiler has been in continous use??

Thanks again. Greg L

Greg, I think that your problem may be one of heat exchanger design. Remember, one thing you are buying with an EFM or Keystone stoker boiler is their design. It sounds to me that the only time you are getting a good heat transfer to the water is when the stack temp. is quite high w/ a "roaring" fire. Also, water content is an issue, whether too much or too little. How is your boiler(actually water stove as it isn't pressurized) controlled? Do you have a low limit?
I guess what I'm getting at is this- adding a stoker to your unit may not make any difference.

Hi Oilman, I have the low limit on the aquastat set at about 145-150*. Any temp below that the combustion fan will run.

I have very low stack temps, the highest I have seen is 250* with a big fire and the water temp over 160* and the combustion blower running.

With a stable water temp at 155* or so, and the combustion blower off, and a big enough fire that a strong natural draft is pulling through the combustion blower, I see around 180* flue temps. I'm transfering a lot of heat to the water. I think the stove holds about 150 gallons with another 50-80 in the pipes and plate exchangers.

Take a look at the photo of the firebox below. You can see that I have two layers of crosstubes transfering water from guide channels in the waterjacket across the firebox as well as in the smoke/vent channel above the first row of crosstubes. The entire box you see here is surrounded by 4" of water, water enters into the box at the top, flows down both sides, is picked up by the shaped inlets of the crosstubes, transfered across, down the guide channel and into the next cross tube, then behind the firebrick in the firebox and out the back of the waterjacket to the house.

I looked at several designs of stoves and boilers and my heat exchanger surface area is greater than most compared to the fire size.

I actually thought when I designed it that I was getting a little carried-away with heat exhanger area. If I were burning only wood I'd be having a creosote build-up problem with all the water cooled surfaces for the smoke to condense on. With coal I'm only getting fly ash on the inside of the boiler.

With a big fire I'm seeing surface temps on the crosstubes above the firebox of 370*. {laser thermometer} The water will start to boil pretty quick if I shut off the circulating pump and stop the water flow.

But with a 'mature' coal bed, glowing red and a 1-2" blue flame dancing above it, I'm seeing only 140-160* flue temps and the inside of the firebox temps are 80-90* lower. The firebrick around the bed of coals is still 600*+, it sends my laser thermometer off scale. If I have a large heat demand from the house, even with the combustion blower running, I can only maintain about 140* with a mature bed of coals.

So I'm just going to have to learn to balance the size of the pile of coal I load in against the heat demand of the house based on outside temperature and wind. My old farmhouse is not very tight.

I was thinking that a stoker fire is amost always in the 'roaring fire' stage since it is being fed fresh coal and pushing off the burnt up coal. Where with my batch fed fire, the fresh coal burns through the max heat stage and burns on into the mature stage leaving a bed of coals and lots of residual heat but nothing like what a fresh 2-4" layer of coal would produce.

I have shoveled some of the hot coals out of the fire during the 'roaring fire' stage and they keep burning, self sustaining in the shovel When I remove a shovel-full of coal from a 8 hour old mature fire, the coals act like they have no life left in them, and will very soon cool off and just become embers or ash.

I'm still learning about firing this boiler, about coal and getting a sustained, controled fire. I think with a bigger load of coal, as long as it won't over fire the boiler from natural draft I may be able to still have a hot fire after 8-10 hours.

I'll find out next week with the high demand from the house I suspect the combustion blower will run a lot more and the coal will burn down quicker while trying to maintain 150* water.

Maybe I'm just pulling a lot of BTU's out of the boiler??

Thanks for the input, it provokes fresh thought and ideas.

Greg L

NEPAForum Admin wrote: Again, that's an extreme, it rarely gets above 200.

Edit: let me clarify this a little further.... 220 I stated before is rare and needs a particular set of circumstances. Specifically it needs to run for quite a while then have the heat demand cut off as well. Another example would be if we were to shut it down for maintenance which is usually in the spring or summer. When you restart it the temp can escalate that high if you let it. Once it hits the 140 it will stop running but at that point in time there is such a large fire it will go well past the 200 mark. We don't allow that to happen because we get it going moderately and shut it down for an hour or so to let the water get tempered. As I mentioned above normal operating temps are in the 170 range. Really depends on the season... Even time of day. One issue many people will come across is keeping the furnace going in the spring. You get a demand for heat over the night and early morning and it gets hot... in the meantime it heats up outside... There's no water circulating so the furnace may not run for hours and it goes out. Ours is set so that hi setting overides the timer so if it's above 180 it won't run regadless of what the situation is.

LsFarm wrote:
Richard, does your Van Wert owners manual have a sketch or diagram of the auger and firebox?? if so could you scan and email it to me, sounds interesting. It is working very well for you, how many years did you say your boiler has been in continous use??

No sorry I don't have anything like that, ours has been in use for 25 years now. The one in my Grandmothers has been in use for well over 30 years. I have customers that have furnaces in there 50's and even longer, as I stated in another thread the key to longevity of a stoker of this type is to keep them running constantly. It's a simple well built machine as most are with little to break. The only thing we have ever replaced is the motors and pumps.

The oldest ones I have seen in operation were a brand call Losch. They have a very simple set similar to what you see on todays stoker stoves. The one I have actually seems a little over complicated to me and has many more moving parts than I prefer.

Ls, I am also using the Kitec red pipe with the aluminum lining. Good to know it won't melt when I overfire my boiler.

KTM: just an idea, if you can find a ceiling-suspended shop heater that uses hot water with a fan, you could use this heater in your detached garage as the heat dump instead of over heating your house.

It would take a little plumbing and rewiring to set it up, but it would remove a lot of BTU's from the water and heat the garage instead of the house.

About the pipe, is your boiler pressurized? Do you know the max pressure before the relief valve opens??

Take a look at some of the exposed pipe and see if it has the max temp and pressure printed on it. I'd go look at mine but it's in Michigan and I'm in Seattle tonight.

The Kitec pipe is the best out there that I know of.

Do you have a line drawing or diagram of the fire box and heat exchanger in your boiler?? If so can you scan it and email it to me, I'd be interested to see the design.

Greg L

Ls,
I have thought about the suspended heater idea. I just got this boiler hooked up a few weeks ago in my garage that was just completed a week before that. I think I will do that next year to heat the garage.
Yes my boiler is pressurized. it usually operates around 14-16 PSI the relief valve is det to 30 lbs. But even when the boiler overfired the PSI never went past 20 psi.
It shouldn't really be that hard at all to pipe or wire the heater into the garage. I just have one simple wire that runs from the hi limit aquastat to my air handler inside the house. No big deal really. I could just suspend the heater close to my boiler. woundn't be too bad.

I don't really have any diagrams for my boiler. Check out their website, there might be some interesting info on there.
http://www.alternateheatingsystems.com/ ... oilers.htm