Prill combustion air

Changed the subject title to more accurately reflect where this thread has lead us.

Greg and Yanche: Those are all good ideas. I have choices, from making a bigger gearbox pulley fit, to turning a smaller motor pulley, to using a different motor to drive the gearbox altogether.

One plus for using a different motor is that I could save electricity. The current motor that turns the gearbox and combusion fan takes over 5 amps at 115 VAC. The distribution fan pulls over 2 amps. When everything is running, I'm probably at about 8 amps. That adds up. Yes, it's still cheaper that natural gas or oil, but if the stove run's at 50%, that's about $30 per month. Maybe that means I'm too cheap if that amount of electricity bothers me.

I'm guessing I could about half those amps. Less than an amp for the combustion blower and maybe a couple amps for the stoker motor, and the two amps for the distribution blower. I have a 115 VDC, 5+ RPM gearmotor I could try, I just don't have a motor controller for it. If I could rig up a PWM controller for it, it could be variable speed. I could remove the Prill/Wil-burt gearbox altogether.

Greg - thanks for the offer on the smaller motor pulley. Yes it's a 5/8" bore with keyway. 1-3/4" is the smallest I can order. My dad has a couple lathes that I can use. But I'm thinking that with a 5/8" shaft and a keyway, I can't get much smaller that that. Measurements for pulleys are ODs, so with about 1/2" of belt x 2, plus the shaft and keyway, I don't think 1" is possible. I'm fairly certain I need to half the rpms of the auger, so I don't think the motor pulley will do it. If you find something smaller, let me know.

Gotta decide between notching the coal bin for a bigger gearbox pulley, making a jackshaft, or trying a different motor. Hmmm....I'm thinking jackshaft or gearbox pulley is the quickest and cheapest. But the DC gearmotor could save me electricity in the long run. Now you guys got a little insight into how my brain works. I'm a civil engineer, and just always analyze everything to death. Drives my wife nuts.

Steinke

Steinkebunch:

I didn't realize that the one motor did the stoking and the blower,so I didn't suggest the right

cure. The best and least expense would be to,as others have said,separate the two functions

and you would have many alternatives for each.

I would keep what you have for the coal feeder and add a cycle timer to better able control

the feed so you would get a complete burn and very little wasted coal in the ash pan.You don't

have to even use the timer when there is a large call for heat,but on warmer days you could tweak

it for those conditions.

I also would add a small blower for the air supply so that you have a steady air stream for the

combustion air,a small shutter on the blower allows fine tuning.

With this setup all kinds of conditions and coal could be dealt with and even a little power would

be saved by not running the huge blower all the time by the timer feeding and letting the coal

burn before the next stoke cycle.


Bigbarney

OK - after spending some time over the holiday making a jackshaft, I tried it out today. I slowed the feed rate to about 1/4 what I had before (jackshaft has a 6" pulley and a 1-3/4" pulley). I used two 1/2" bore flange bearings. Welded two flanges onto a 6" length of pipe, inserted a 1/2" shaft, installed the locking collars, milled a flat spot on the shaft for the pulley set screws, and added a way to adjust the belt tension. See pic below.

However, I think I went too far. It is about 35 degrees today. This morning, before I installed the jackshaft, the stove would run for about 5 mintues, then idle for 10 minutes to keep the house at 75 degrees. Now, it is running constantly, (it hasn't shut off for about 2 hours now), and is just keeping the house a steady 75.

The fire is much smaller, just barely extending to the heat exchange tubes. Below, I attached one photo of the fire with the old feedrate (about 1 rpm on the auger). Then I attached a photo after the install, about 1/4 rpm.

I think I need something in between. I'll try a different size pulley on the jackshaft and report back.

It did seem to take care of the fire in the smokepipe however.

The fire looks much better with no sign of carbon rich flames only a nice clean hot fire.

Probably a little fine tuning and you'll have a hot burn and clean too.

Can you see less soot inside the flue pipe?

BigBarney

Too soon to tell how much the soot is reduced. I guess I should clean the smokepipe now and see how fast it builds up again.

I changed the pulley sizes a little again. I'm now at about 1/2 an RPM, or 1/2 the original pre-jackshaft speed. Seems like it's stoking about 70% of the time now, under the same temperature conditions. Still seems like it's running too long for this mild weather.

Maybe a suggestion earlier in this post was correct - the factory setting was OK. Maybe I should focus more on trying to get better secondary burn.

I did adjust my combustion air some again. I opened it up quite a bit more, and my blower air temp rose about 10 degrees. But I noticed it was then pushing a little smoke into the hopper, so I backed it off until I saw no more smoke in the hopper.

Steinke

It would be interesting to see what some hot secondary air would to with that fire/flames.. I'm betting it would look like a big Propane or Mapp gas torch.

Very nice job on the fabrication of the jackshaft.. on my Iron fireman I have a three shiv pulley setup, so I can 'hop' the belt from one ratio to another. Maybe you can finds some similar tripple pulleys so you can adjust the feed without swapping the actuall pulleys and belts. ?

Greg L

I hear you on the step pulleys. It would be nice.

I've been thinking about how to add heated secondary air. Got some ideas. Think I'll try suspending a steel disk over the pot first to see how it acts. Berlin has the opinion that a disk or ceramic board above the pot will do just as well or better than hot secondary. He seems to usually hit the nail on the head, based on what I've learned over the past few years burning coal.

Thanks everyone for the help. I'll keep you posted

You're right about Berlin and I've been waiting for him to post about the changes you've made. Really want to hear his take.

It shouldn't be too tough to suspend a piece of 1/4" or 3/8" plate over the fire, but don't get it too close or it will load up with soot.. and you want to make it so you can vacuum off or sweep off the top of the plate as well.

Greg L..

there are places online where you can buy ceramic fiber board relatively inexpensively. ceramic fiber will reflect heat to the coal bed much more effectively than steel although steel would work slightly, perhaps; but uncooled steel will also sag and warp in a short amount of time. a 7" disc of 1/2" ceramic fiber board (just like the material used in oil furnace "firebowls") suspended above the fire with a 2" hole cut in the center to allow a minimum buildup of flyash. it should be suspended about 4" below the airtubes in the firebox.

secondary air preheated or not may not work well for two reasons. bituminous coal loaded into a hand fired stove has a very rich air/fuel mixture above it after the intial loading. this allows the preheated air introduced into the fuel rich furnace to have the "blowtorch" effect. without the fuel rich air the additional secondary combustion will be almost nonexistant. the stoker should also not be producing fuel rich air inside the furnace. the stoker should be running lean; there should already be slightly more air available than is needed. the ceramic disc will work because it allows the flame temp to be increased to the point that hard to combust hydrocarbons will breakdown and combust more thoroughly using the adaquate air already supplied by the stoker blower. unnecessary and excessive secondary air will reduce the efficiencey of the furnace by reducing residence time of the furnace gasses and thus heat transfer.

based on what i see in your pic, you still need considerably more air. the fire should not be burning lazily as it is. i've attatched a pic of my bituminous stoker with the perfect amount of air/fuel. the firebox will usually have a thin layer of soot that will burn off during each firing, but be reapplyed after each shutdown when the coal smoulders for a minuite or two. Note the bright AND vigorous yellow/white flame.

Wow Berlin - that's enough technical info to make my head spin. I'll take it as "don't try the secondary air, go for the ceramic board".

I tried suspending a metal disk over the fire last night, but it doesn't seem to help much.

Web hits are pretty low when it comes to fiber board. Seems that soldering and kiln sites have some. Most sell in larger quantities, but a few below show smaller boards for sale.

Any idea which product would be most suitable at the following link? They have soft boards, hard boards, honeycomb board, etc.

http://www.contenti.com/products/soldering/soldering-boards.html

also a link here too: http://www.progresstool.com/cat_soldering_board__block_all.cfm

Other sources anyone knows of?

Tempted to try a piece of ceramic tile, but it would probably just crack.

Thanks,

Steinkebunch

McMaster-Carr has a selection of various refractory materials that would work, but it doesn't look like you'll get off cheap due to the sizes offered. I wonder if you could weld up an angle iron frame and fill it with some regular stove firebricks? Might not last forever, but it would give you a way to find out if it helps.

Chris

The steel disc will work well,it is used by many European stove manufacturers for many

years with great success.It is critical that it be placed at the proper height from the fire,it

has be right at the tip of the inner hot flame at full burn to do its work.It should get red

hot when operating at peak efficiency.You may have to rig a way to hold in that position

to reflect the heat back against the burning pot.


BigBarney

I tried a few different things tonight:

I went back down the the slowest feed rate (1/4 RPM) with a steel disc above the fire. It was 10 degrees out, 75 in the house. The stove ran constantly, and the house temp was dropping. I had the combustion air plate wide open. The flames did not look too impressive either. Not bright yellow or white. Stove blower air was 115 degrees. I just don't think I'm feeding enough coal this way.

I then went back to no jackshaft, about 1 RPM. I left the air disc wide open. There were major flames in the firebox, and the steel disc above the fire was cherry red. Stove blower air was 180 degrees (too hot) and there were flames in the chimney. I then throttled back on the combustion air, but it did not seem to change much.

It seems to me that I need to be somewhere in between.

Maybe I'll get some castable refractory and make a thick disk out of that to suspend over the fire.

Thanks for all the help. I'll just keep playing with it.