Using more coal at lower feed rate - Why?

Hello. I have been running a DF520 since last January for my 3700 sq. foot house and have switched to Blaschak coal this month of December, so I found that the coal quality improved and I was able to lower my feed rate from 9 to 6; however, i am using more coal now than i was before to keep the house 2 degrees less-warm (i had the thermostat at 68 last winter and have it at 66 now). For example, last January on a day when the temps ranged from 9-27, i added 5 bags to the hopper. The day before yesterday, when the temps ranged from 9-28, i added 7 bags to the hopper. Andi have been consistently using 6-7 bags a day all December when last year, the most i added in one day was 5 bags, on the coldest days. Now, logic tells me that i should be using less coal at a lower feed rate, not more. The coal i used last year was of an unknown brand, bagged by the coal guy. I never weighed a bag, but he said they were 40 lb. bags. Even if they were 40+ lbs, even 50, that's 250 lbs. a day last year compared to 7 x 40 lbs. now. So, the stoker is running longer, a lot longer if all these bags have been 40 lbs., but i should be using less coal not more! Does anyone have any suggestions? I could increase the feed rate, but then i'd go back to having unburnt coal in the ashcan and that's wasteful in another way.

Three possibilities. The Blaschak has less BTU per pound, the inside of the boiler needs ash deposits cleaned off the surfaces, or your draft is too high, requiring an adjustment of the barometric damper. Should be negative .02 at the fire door and negative .04 at the smokepipe. A Dwyer Mark II meter would be helpful.

I would also look at the system as a whole. You say you were happy with using 200 lbs a day . you should not need to use 200 lbs a day for 3700 sf. I use about 70 on the coldest days heating 2500 sf and that will be about 74 downstairs 66 upstairs. There has to be something up with the system. At 200-250 lbs a day it would be cheaper to burn oil around here. I would look at your settings and compare with other users of the DF520.

Wow, I'm heating a 150 year old 4400sf farm house in a windy part of upstate NY and my high setting has never exceeded a feed rate of 6, I'm running 5 right now with the air at 4.5 , last year I burned 10 ton in 165 days, if my math is right that's 121.21 lb a day average, when the wind is blowing 30mph and it's -15 below I might burn 250lbs in one day. 520s rule

Glenn

It's damned cold and windy.....keep that daily log to reflect back upon. You will sort it out. I understand that you are doing updates on insulation, etc. Staying warm is the major objective here...the fuel economy will work itself out soon.

I have kept a daily log since i started the system up on Jan. 10, 2009 - that's how i know what i know about last year's temps and usage versus right now. I'm creating enough steam pressure to heat my radiators and my house, but i am using more coal than before. That's what i can't figure out. The CO2 is 11.5%; the baro is negative .05 at the smoke pipe, the net stack temp is about 430-450 when the unit is running. All the numbers are where they should be EXCEPT coal usage. I'm generating less ash with the Blaschak coal, but using more of it. Doesn't make sense. The dealer had no answers so he suggested i post here. Until i figure it out, i'll just keep loading the hopper.

What are recommended draft readings for a 900?

stoker-man wrote:Three possibilities. The Blaschak has less BTU per pound, the inside of the boiler needs ash deposits cleaned off the surfaces, or your draft is too high, requiring an adjustment of the barometric damper. Should be negative .02 at the fire door and negative .04 at the smokepipe. A Dwyer Mark II meter would be helpful.

All else being equal, and that is fuzzy as you did not know the weight of the bags previously. But assuming equal weight,
I would bet on lower BTU coal.

Stoker-man, given that i am able to lower the feed rate with the Blaschak, it seems that the Blaschak coal burns better than last year's and the draft is fine - checked this past week by the plumber, who installed the unit. That leaves ash deposits on the inside. The unit was cleaned in August - should it need to cleaning again now? How do i tell if there's enough ash deposits that it needs cleaning exactly?

P.S. Last year's coal was hand-bagged by the coal guy who delivered. He brought me 50 bags per ton and said they were 40 lbs., so unless he was in the business of giving away coal, i figured each bag weighed 40 lbs.

P.P.S. Draft is negative .05 at the smokepipe. Is that good enough?

The draft is fine. You'd need to know the current stack temp and see if it's similar to the one in August which would indicate an insulating effect of the ash. That assumes the use of Blaschak in August.

It's easier to figure if you burned more oil because oil is 140K BTU per gallon where coal can vary.

Is everything in your system exactly the same as last year? All circulation loops functioning the same? No changes in the house or the way it's used?

I wasn't using Blaschak in August; still using the old coal until December and that's when my coal usage jumped which is why i started the other thread on the Coal Stokers forum, to figure this out. Nothing in the house, its systems, or the way i use them has changed. Is there any "rule" that one should clean the unit after x-ton of coal is burned in it? Or, as with everything else, does it "depend" on the coal used? I was under the impression that a once a year cleaning would be enough. I cleaned the pot itself before xmas - shut it down, cleared all/any blocked holes and started it back up. There are ash deposits, certainly, but the plumber said it was fine until spring.

I also posted a reply in the other thread with more detail. The short form is I think you need to maintain the high feed rate to make steam efficiently. People with hot water systems can frequently save coal by bringing down the feed rate. However, to get heat out of a steam system you need to put in a critical mass of btu's (to get to a boil) and then run the system at a comparatively high temperature until the need for heat is satisfied. I have a bigger version of your boiler, and a bigger heating load, but from my experience I bet your system will make steam more efficiently if you run it at a high feed rate (as long as you still get a proper ash ring). At a higher feed rate, your boiler should run for a shorter period of time.

A second possible issue is that Blaschak may be giving you "smaller" rice than you were using before. Air flow through a stoker is generally better when the pieces of coal are bigger. To get max output and not too much unburned coal, you might want to look carefully at the actual sizes of the rice coal available from different sources.

Mike

Mike, hello and thank you for posting here. I don't remember seeing your post in the other forum. I was using rice before, but had to screen that coal because of irregular sizes, so it's possible that the Blaschak is more consistently small than what i was using before. I don't have too many choices for getting coal delivered to me where i am, that i know of, but that's something i can explore when i need more (i bought a truckload for the season already). Besides cleaning the unit again, which i wouldn't think i need to do, increasing the feed rate again is all i can think of to do also. I just have to find the right settings so that i don't revert to the previous problem i had - too much unburnt coal in the ashcan! I'll try this over the weekend - hopefully, i can figure this out before i am away on a business trip for 2 weeks. Otherwise, i'll continue to waste coal which annoys the crap out of me!

I think some coal users get carried away with the completeness of the burn as being the only important measure of efficiency, but if you can get the heat you need by burning 5 bags/day with 15% waste (at a high feed rate) rather than 7 bags/day with 5% waste (at a low feed rate), I'd vote for the 15% waste, at least until you can get deeper into the piece size issue.

In addition to the size of the rice coal, I recall that the 520 has been decreed a "multi-fuel" boiler. Maybe Stoker-man or other users would know whether there are any fuels you could blend with your Blaschak that would improve your airflow.

Mike