How Much Max 'Measured' Coal Can Your Stoker Push Per Hour?

 
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lsayre
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Post by lsayre » Sun. Oct. 12, 2014 7:50 am

If you have ever measured the maximum delivery of coal that your stoker can give (in pounds per hour), would you mind sharing what you found? Only actual measured delivery is of interest here, not the manufacturers specs.


 
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Post by lsayre » Sun. Oct. 12, 2014 10:12 am

In asking this I'm trying to establish an honest output BTUH rating for the various stokers.

I would do this by:

Max output BTUH = Max lbs. stoked per hour x 12,300 BTU's/Lb. x 0.80
(where the 0.80 factor is added to account for 80% efficiency)

Drop 0.80 from the equation and you have max input BTUH.

 
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Post by Rob R. » Sun. Oct. 12, 2014 10:37 am

I have verified EFM's rating of 10 lbs per hour of rice coal on 4 teeth of feed. 2.5 lbs per hour per tooth of feed...it will run a maximum of 10 teeth, but I have not verified the output or even confirmed that it can product a satisfactory ash ring at that output.

 
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Post by Lightning » Sun. Oct. 12, 2014 10:42 am

I'm gonna venture to say that at maximum feed rate there will be an excessive amount of un burnt coal being pushed off the plate. Or isn't this the case?

 
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Post by lsayre » Sun. Oct. 12, 2014 10:44 am

Rob R. wrote:I have verified EFM's rating of 10 lbs per hour of rice coal on 4 teeth of feed. 2.5 lbs per hour per tooth of feed...it will run a maximum of 10 teeth, but I have not verified the output or even confirmed that it can product a satisfactory ash ring at that output.
The EFM 520 is truly a heat monster! If it can properly burn 25 lbs. per hour that equates to 307,500 input BTUH, and around 246,000 output BTUH.

 
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Post by lsayre » Sun. Oct. 12, 2014 10:45 am

Lightning wrote:I'm gonna venture to say that at maximum feed rate there will be an excessive amount of un burnt coal being pushed off the plate. Or isn't this the case?
If that is so, then what is really needed is the maximum lbs. per hour that a stoker can both push and properly burn.

 
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Post by McGiever » Sun. Oct. 12, 2014 10:51 am

It's tricky to actually gauge input lbs. when not drawing coal from a "hopper" or "batch bin".
I'm referring to bulk bins. ;)

And, yes, if one thows hot coals into the ash bucket the figures can get out of hand. :funny:


 
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Post by lsayre » Sun. Oct. 12, 2014 10:54 am

McGiever wrote:It's tricky to actually gauge input lbs. when not drawing coal from a "hopper" or "batch bin".
I'm referring to bulk bins. ;)

And, yes, if one thows hot coals into the ash bucket the figures can get out of hand. :funny:
That is why to do this one must push coal that is not burning and then weigh it from the ash tub to compute max lbs. pushed per hour. That makes being able to determine if it can properly be consumed at that rate of feed a tad more difficult.

 
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Post by Pacowy » Sun. Oct. 12, 2014 2:30 pm

lsayre wrote:
Rob R. wrote:I have verified EFM's rating of 10 lbs per hour of rice coal on 4 teeth of feed. 2.5 lbs per hour per tooth of feed...it will run a maximum of 10 teeth, but I have not verified the output or even confirmed that it can product a satisfactory ash ring at that output.
The EFM 520 is truly a heat monster! If it can properly burn 25 lbs. per hour that equates to 307,500 input BTUH, and around 246,000 output BTUH.
The original recommended max firing rate on an S-20 in a 520 was 20 lb/hr, which equates to 10 teeth on buck or 8 teeth on rice. EFM no longer recommends buck for this unit, and I think there are threads on the forum started by people who had problems when they tried to run one flat out on rice. However, 8 teeth/20 lb on rice seems doable.

I have verified that my 85R feeds buck at approximately the claimed rate of 5 lb/tooth. I've only tested up to 12 teeth; it will feed up to 17 teeth, or 85 lb/hr. It's pretty much just loafing at 12 teeth, so I'm pretty sure it would run ok at the claimed max rate as long as decent buck is used.

I don't really follow the application of the 80 percent figure. If you assume that there is 10 percent unburned coal included in the "ash" when the stoker is run at optimal feed/air settings, the heat released by the stoker in operation would be 0.9 x firing rate x assumed btu/lb as received. That would be the gross input BTU's for the boiler. The boiler itself typically might be something like 80% efficient, so the boiler output would be approximately 0.8 x 0.9 x firing rate x btu/lb.

Mike

 
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Post by lsayre » Sun. Oct. 12, 2014 4:16 pm

Pacowy wrote:I don't really follow the application of the 80 percent figure. If you assume that there is 10 percent unburned coal included in the "ash" when the stoker is run at optimal feed/air settings, the heat released by the stoker in operation would be 0.9 x firing rate x assumed btu/lb as received. That would be the gross input BTU's for the boiler. The boiler itself typically might be something like 80% efficient, so the boiler output would be approximately 0.8 x 0.9 x firing rate x btu/lb.

Mike
Mike, I'm in full agreement that something closer to 65%-70% overall efficiency is more long term realistically sustainable, but everyone seems to yell at me if I go below 80%, so I have learned to conform.

 
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Post by Pacowy » Sun. Oct. 12, 2014 6:56 pm

Personally, I'm more comfortable conforming with the numbers than with other peoples' misconceptions. If they need to get used to the idea that some of the BTU's are going out with the ash and some are going up the stack, so be it.

Mike

 
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Post by oliver power » Mon. Oct. 13, 2014 3:17 am

I believe the Kaa-2 would be a nice little boiler to get your answer. Last winter, there was a spell where it ran flat out, around the clock. It was at it's max, and still maintaining house temp. Another turn on the adjustment would have been pushing burning coal to, and off the end of the grate. I didn't keep track of coal used. But it seams as if I dumped 1-5/8, or 1-3/4 five gallon pails in the hopper every 24 hours. Boiler temp was pulled just below design temp of 180*.

 
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Post by Rob R. » Mon. Oct. 13, 2014 9:22 am

Pacowy wrote: The original recommended max firing rate on an S-20 in a 520 was 20 lb/hr, which equates to 10 teeth on buck or 8 teeth on rice. EFM no longer recommends buck for this unit, and I think there are threads on the forum started by people who had problems when they tried to run one flat out on rice. However, 8 teeth/20 lb on rice seems doable.
Somewhere I have some old EFM 520 literature that says rice is recommended, but buck may be used at reduced feed rates. That also follows my own experience when was heating my pool and burning buck. The highest feed rate that the stoker could handle with continuous operation was 6 teeth. Once I went to 7 or 8, it would push the fire out of the pot, regardless of the air setting. It behaved like there simply wasn't enough time to burn the buck in that size firepot. It would run fine in an on/off pattern, but if the load was increased enough to make the stoker run flat-out it would push the fire out.

Larry, attached you will find a table out of an old Van Wert brochure.

 
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Post by Pacowy » Mon. Oct. 13, 2014 12:26 pm

Rob R. wrote: Somewhere I have some old EFM 520 literature that says rice is recommended, but buck may be used at reduced feed rates. That also follows my own experience when was heating my pool and burning buck. The highest feed rate that the stoker could handle with continuous operation was 6 teeth. Once I went to 7 or 8, it would push the fire out of the pot, regardless of the air setting. It behaved like there simply wasn't enough time to burn the buck in that size firepot. It would run fine in an on/off pattern, but if the load was increased enough to make the stoker run flat-out it would push the fire out.
I think in your example there may be 2 different factors at work. I believe an S-20 will only move about 2 lb/tooth with buck vs. 2.5 lb/tooth with rice due to voids that arise when the buck tries to move through the tight quarters of an S-20 feed tube. So at 6 teeth you already are at a "reduced feed rate" of approximately 12 lb/hr with buck as opposed to 15 lb/hr with rice. The unit is able to blow more air into the pot with buck due to lower resistance; if it's not burning completely I would suspect you might have been using a "hard burning" (i.e., burn rate relatively insensitive to supply of excess air) as opposed to a "free burning" coal. All of the EFM units that can burn both sizes - and feed them at the same rate - can burn equal or higher teeth settings using buck vs. rice (because more air flows through the fire with buck), and equal or higher teeth settings using free burning vs. hard burning coal.

Mike

 
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Post by mdrelyea » Mon. Oct. 13, 2014 12:45 pm

McGiever wrote:It's tricky to actually gauge input lbs. when not drawing coal from a "hopper" or "batch bin".
I'm referring to bulk bins. ;)
Tricky, but not impossible. Count the number of revolutions on the feed auger. Run it into a 5 gallon bucket. Count the number of revolutions needed to fill the bucket, weigh the bucket and then divide by the number of revolutions. Once you know how many lbs/revolution then you only need to track the number of revolutions with some sort of counter.


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