Using more coal at lower feed rate - Why?

Greta, you might have seen this before, but check these things from another posting. Is your unit new?


I went out with a dealer who couldn't fix a problem with lots of unburned coal in the ash in an old '50s efm stoker. Here's what we found:

1: The coal was a 60/40 mixture of barley/rice and resulted in a "tight" bed. The black spot at 3 teeth/5 air was at least 6" across. We set that at 5 feed/5 air after we made the other corrections.
2. The cleanout cover was not fully closed because the cover clamps were set too tight and the lever wasn't fully pushed back. There was air being pushed out of the bottom of the pot. The opening was about 20% of full open. There was ash all around the bottom of the ash door on the outside.
3. The ash door latch handle wasn't installed correctly and the ash door could move open and closed by about 3/4", with the latch in the locked position.
4. The draft at the fire door was zero because the barometric damper was corroded and not responsive to changes in draft. We set that to negative .02
5. The aquastat did not have the required 40 degree spread between low and high limit.

That was enough changes for one day and we haven't heard again from the man who would surely call if it wasn't working.

I've increased the feed rate to 7 from 6, as today's experiment. I looked back through my records and saw that i didn't leave the feed rate at 7 for a 24-hour period to evaluate it. I jumped impatiently from 8 to 6. We'll see how it goes...

How much air are you giving it?

Mike

The air is at 6, which gave me perfect fire the last time the feed rate was at 7. 8/7 also gave me a perfect looking fire, but too much unburnt coal, so i am starting with a feed rate of 7.

[Note: These comments are based on my experiences with 700 and 900 stokers. I've never specifically dealt with undersize coal in a 520, so I'll defer to others who have more direct experience.]

1. I wouldn't be bashful about giving it air, especially if your coal is tending towards undersize. For any given feed rate, your most efficient operation is going to be achieved with the air setting that gives the proper ash ring around the top of the stoker. With undersize coal, it wouldn't be surprising if your air setting needed to be high relative to the feed rate.
2. I'm not sure what your definition is of a "perfect fire". As you move toward max output, the fire may tend to get kind of rowdy - a bit loud and unruly. If you get something reminiscent of a blacksmith forge, you're doing ok. In the bigger units, if the fire really gets enough air, it can be more like someone left the engine from a jet fighter in your boiler, and they forgot to turn off the afterburner. As one of these units works harder to deliver more btu's, the "dancing ladies" run for cover, and you're left with more of a primal blast of fire. To make steam efficiently in your situation, I think that's what you want.

Good luck and please keep us posted.

Mike

Anyone know the biggest size coal which can be burned in a 700 efm? By using a bigger size do you get more btu's or not necessarily? I would appreciate your thoughts on this.

Joe

here's the simple answer, your house requires a certain amount of BTU's to maintain the temperature you desire. Fiddling with the settings will never solve how much coal you need to burn to keep your house warm. If your ash pan looks good with very little unburned coal and your chimney isn't blazing hot your doing fine. I burn 150 to 200 pounds a day easy heating 3000sq.ft

I've run a 700 stoker on rice and a 900 on buckwheat. The 700 running with rice had trouble putting out enough heat even running flat out. The 900 on buck isn't breaking a sweat and is carrying the load fine. I was going to try to burn buck in the 700 but the (non-EFM) boiler it was in crapped out before I had the chance.

In general, I think the bigger coal lets the air flow through the fire better, and helps to get the max output attainable. The auger won't move as much buck as it will rice in a given time, but at higher feed rates the bigger coal will burn better.

I'll leave it whistlenut to talk about the virtues of running stove coal through a 700, but I'd say if you're going to push the unit you'll get better results with buck than with rice.

Mike

I was using rice coal on my EFM 700 but I changed to buckwheat coal and now I don't know what I am doing wrong but I am unable to get the right settings in order for it to keep burning all night long. I restart it, change the settings, but I am wondering if by burning buckwheat which is bigger I might have to change the settings and increase the air or maybe less air. I have tried both ways, it begins to burn well, red hot, but within a couple of hours it chokes and turns off. I would truly appreciate any thoughts...I am frustrated. Could I have made a mistake switching to buckwheat? what I am I doing wrong?

From my experience I'd think the air setting should be lower with buck than with rice. If your fire is going out you might need to add a little burn time on your timer, or increase the frequency with which the timer kicks in. It probably also wouldn't hurt to check whether fly ash buildup may be interfering with your draft.

Good luck.

Mike