Coalgun- Puff backs & Explosions

Re: Coalgun- Puff backs & Explosions

PostBy: Rob R. On: Sun Feb 10, 2013 8:57 am

Just an observation from someone looking through the glass - What has AHS actually done to try and correct this problem?
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: Coalgun- Puff backs & Explosions

PostBy: lsayre On: Sun Feb 10, 2013 9:02 am

Rob R. wrote:Just an observation from someone looking through the glass - What has AHS actually done to try and correct this problem?


So far they keep telling me to lower my ashing SV and/or decrease my hysteresis. I think I've gone as far as they are willing to take me with these settings. They have also suggested that I try a different coal (or try blending my coal), since Harmony has too high a percentage of volatiles, and so little ash (perhaps this is because it is so dense due to fusing into clinkers, or perhaps it is a combination of clinkering and truly low ash content). Both low ash "volume" and high volatiles are apparently considered major negatives for the AHS. A certain volume of ash is always needed to keep the fire high in the tube, else detonations, and the higher volatiles contribute to increased detonation intensity.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Sun Feb 10, 2013 10:49 am

With the 130M Axeman-Anderson the fire column/tube is 11" dia. and ashing cycle is done w/ an Anthrastat temp. switch combined w/ an adjustable linkage to select the number of *clicks* to control the ashing speed/fire position...this would be much like what *rychw* is doing w/ his slowing down of the ashing motor's speed on a 130S AHS.
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek

Re: Coalgun- Puff backs & Explosions

PostBy: Yanche On: Sun Feb 10, 2013 11:33 am

lsayre wrote:
Rob R. wrote:Just an observation from someone looking through the glass - What has AHS actually done to try and correct this problem?

They have also suggested that I try a different coal (or try blending my coal), since Harmony has too high a percentage of volatiles, and so little ash (perhaps this is because it is so dense due to fusing into clinkers, or perhaps it is a combination of clinkering and truly low ash content). Both low ash "volume" and high volatiles are apparently considered major negatives for the AHS. A certain volume of ash is always needed to keep the fire high in the tube, else detonations, and the higher volatiles contribute to increased detonation intensity.

But I'm burning the same UAE Harmony mine coal with a % time control without serious problems. Adjust the thermocouple controller all you want, it's not going provide a solution. The thermocouple sensor is the wrong place and the logic of the control system is incomplete.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Coalgun- Puff backs & Explosions

PostBy: lsayre On: Sun Feb 10, 2013 11:52 am

Yanche wrote:But I'm burning the same UAE Harmony mine coal with a % time control without serious problems. Adjust the thermocouple controller all you want, it's not going provide a solution. The thermocouple sensor is the wrong place and the logic of the control system is incomplete.


Are you ashing for 2 minutes out of every 10? Does your cycle timer remember its place if a firing cycle runs for only 6-7 minutes, or does it reset after each fan cut-off?

Example: Boiler fires for 6 minutes. Does your boiler subsequently ash 2 minutes into the next firing cycle (ashing 2 minutes out of every 10 minutes of cumulative firing)? Or does it start counting time all over again instead and ash only if the firing cycle extends beyond 8 minutes (with ashing beginning at the 8 minute mark)? Or does it do something different from these two options?

My last two firing cycles were of 9 minutes and 8 minutes in duration.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Coalgun- Puff backs & Explosions

PostBy: Yanche On: Mon Feb 11, 2013 1:02 am

As previously posted in this thread:

"My boiler ashing is controlled by a ten minute cycle timer. It is powered only when the combustion blower is running. I have it set to 1.5 minutes. So the ashing grate moves 1.5/10 % of the time the combustion blower is running. My fire height is near the top of the "Anthratube". I'm burning UAE pea coal and I have no puff backs."

Because the timer motor is not powered when the blower turns off, it remembers it's previous state. If it was ashing and didn't finish, it will start again when the blower is next powered.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Coalgun- Puff backs & Explosions

PostBy: lsayre On: Mon Feb 11, 2013 6:48 am

Yanche wrote:As previously posted in this thread:

"My boiler ashing is controlled by a ten minute cycle timer. It is powered only when the combustion blower is running. I have it set to 1.5 minutes. So the ashing grate moves 1.5/10 % of the time the combustion blower is running. My fire height is near the top of the "Anthratube". I'm burning UAE pea coal and I have no puff backs."

Because the timer motor is not powered when the blower turns off, it remembers it's previous state. If it was ashing and didn't finish, it will start again when the blower is next powered.


Thanks much Yanche!
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Coalgun- Puff backs & Explosions

PostBy: macdabs On: Mon Feb 11, 2013 4:39 pm

Keep your fingers crossed the Puff -Back season will start soon as the warmer weather arrives and the boilers sit idle during the day while running hard at night. The perfect storm for puff back seems to be more during the mild days... :o :o

I do not want to jinx myself since I have been running without any puff backs and did a mid winter cleaning two weeks ago . I have to admit I have been a little nervous in the boiler room during the ash cycle and I hear the coal dropping in the hopper. :oops: My wife calls my boiler "The Boom Box".. LOL :lol: :lol:
macdabs
 
Stoker Coal Boiler: AHS 260
Coal Size/Type: Pea
Other Heating: Pellet,oil
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Coalgun- Puff backs & Explosions

PostBy: Bob On: Mon Feb 11, 2013 4:44 pm

Yanche wrote:In my opinion it's a defective design. One of the fundamental principles of a control system is that the control sensor be strongly related to the variable you are trying to control. Such is not the case here.


I'm not so sure the design is defective.

First the AA uses the same design--a temperature probe to sense ash temperature-- for control of ashing and neither you nor anyone else so far as I know say the AA design is defective. I simply don't see how the use of more modern temperature sensors and control could be considered a defective design. I am aware that it has been suggested that selection of an alternate thermocouple may be desirable--but is there any reason to believe the thermocouple selection is causing puff backs?

Second, I see no evidence that there has been a complete examination of the boilers that experience the problem to rule out sample variation in the construction of the boilers or a defective component or electrical connection problems. Without these steps I think it is entirely premature to conclude that the design is defective. I do think it is fair to be critical of AHS for the failing to step in and help the owners having problems with a careful step by step approach to identifying the problem and eliminating it.

I agree that direct measurement of temperatures in the column of coal/ash as you suggest could be an improvement--but it seems to me it would be more expensive to implement--both in manufacturing of the basic boiler and for the additional components required along with a more complex controller and that it may not be necessary based on the long history of success of a simple temperature probe in the AA boiler.
Bob
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea/Anthracite

Re: Coalgun- Puff backs & Explosions

PostBy: franco b On: Mon Feb 11, 2013 6:10 pm

It seems to me Freddy pin pointed the problem and fixed it with a more graduated and simple shut down of the air supply. Why go off on tangents? The excessive accumulation of unburned gas at certain times and conditions is the problem. The question I would have is, does Freddy's fix burn the gas or just dilute and exhaust it? The problem Yanche alludes to might be another problem entirely.
franco b
 
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

Re: Coalgun- Puff backs & Explosions

PostBy: Yanche On: Mon Feb 11, 2013 7:33 pm

Bob wrote:I'm not so sure the design is defective.

First the AA uses the same design--a temperature probe to sense ash temperature-- for control of ashing and neither you nor anyone else so far as I know say the AA design is defective. I simply don't see how the use of more modern temperature sensors and control could be considered a defective design.

If you look at the measurement characteristics of the A-A temperature sensor and the AHS thermocouple, there is a world of difference. The A-A sensor is basically a bi-metal snap switch-like sensor. It integrates temperature changes and has a slow to respond characteristic. A thermocouple, on the other hand, is a tiny sensor, and does not integrate temperatures at all. It's response to change is instant. The electronics amplifies the milli-volt thermocouple voltages to something useful, also includes a hysteresis function, which allows a similar integration-like capability. But it's really different and in my opinion not what's needed. As has been pointed out many times none of us has the engineering data for a definitive answer. I still stand by my opinion, that it's not the right design.

I welcome an design explanation of either the A-A or AHS system by anyone. Temperature design set points, for rising and falling temperatures, hysteresis values, CO concentrations that cause or do not cause puff backs. Even if you don't have numbers, just explain how it's supposed to work. Is the idle draft what is expected to clear out the CO boom-boom mix? Etc.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Coalgun- Puff backs & Explosions

PostBy: steamup On: Thu Feb 14, 2013 6:24 pm

My opinion is as follows:

The anthrastat is simply a device to make the boiler more effiecient. You only ash once the coal is burnt and the ash has cooled to set point. In the AA130's case, that is 140 degrees. You drop below 140, you ash until you go above 140. I do not know the span of the device but for most mechanical thermostats it could be anywhere from 1 to 8 degrees F.

What has to do with puff backs is ashing rate and amount. Too much ashing in relation to the firing rate, and the fire level drops creating more air and fresh coal volume in the combustion chamber, then ka-boom (technical term). Too little ashing rises the fire level to a point of chocking the fire. The right fire level is the key.

The reason for the explosions is not CO but fresh coal. Anthracite has 5 to 10 % volitiles. Put fresh coal in a hot zone and the first thing that happens is the volitiles bake off. This happens when the blower stops on the boiler. The only air drawn in is from natural draft. The excess heat rises and bakes the fresh coal releasing the volitiles. If your fire is too low, there is more volume of un-baked coal in the combustion chamber. This coal bakes, give off volitiles at a rate that overwhelms the natural draft's ability to draw them off. You hit the Lower Explosive Level (LEL) of the volitiles and then Ka-boom. There is also more air between the coal when the fire is low. That makes the Ka-boom even bigger.

No matter how you control it, the key is to match the firing rate and the ashing rate such that the fire level remains constant. The AA anthrastat acts as a limit if you are ashing too fast and hot coals start down the plate.

If ashing doesn't have a temperature input, you have no way to know if you are ashing right. The ashing rate has to be linked to the burn rate, more you burn, more you ash. If you were to ash at the end of a burn cycle with a timer, then the problem is under light load you cycle more and then ash more but burn less coal. Visa versa when under heavy load. Yanche has linked his timer to the blower such that he has it set to match his burn rate.

If you were to ash simply with a thermocouple or thermostat, then you again ash too much as it doesn't know when the blower shuts off and reduces the fire. It must be set to kill ashing when the blower shut off.

Again, just my view on things from operating my AA-130.
Last edited by steamup on Thu Feb 14, 2013 6:27 pm, edited 1 time in total.
steamup
 
Stoker Coal Boiler: Axeman-Anderson AA-130, Keystoker K-6
Hand Fed Coal Boiler: HS Tarm 502 Wood/Coal/Oil
Coal Size/Type: pea, buck, rice

Re: Coalgun- Puff backs & Explosions

PostBy: lsayre On: Thu Feb 14, 2013 6:52 pm

It is my understanding that all of the newer AHS Coal Guns (or at least the UL Listed ones) will only ash when the blower motor is running. Mine was made in October of 2009, and it is made that way. It only ashes when the blower (fan) is running, and when the ash grate temperature hits 95 degrees (shutting off ashing at 100 degrees).

Last year with Blaschak coal I initiated ashing at 120 degrees, with ashing shutting off at 130 degrees.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Coalgun- Puff backs & Explosions

PostBy: rychw On: Sat Feb 16, 2013 10:43 pm

I had another big explosion last night so I reduced the grate motor speed to 30%. I hope that the slower speed will prevent too much coal being added to the tube too fast. If I continue to have explosions, I'm going to install the timer system that Yanche has been using. Again, I feel that the thermo ash system is flawed as installed and programmed. The ash temperature is far less important than the tube temperature and the timing and method of adding coal is flawed. There should be a method of removing the coal gas before it ignites. Just some thoughts.
rychw
 
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea
Stove/Furnace Make: AHS
Stove/Furnace Model: 130

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Sat Feb 16, 2013 11:24 pm

I came across the info on the Percentage Timers I believe that are used on the AHS Coal Guns and thought I'd share. :)

Paragon Timer.pdf
(28.56 KiB) Downloaded 12 times
Select:BBcode: [nepafile=40604]Paragon Timer.pdf[/nepafile]
JW Series.pdf
(578.23 KiB) Downloaded 13 times
Select:BBcode: [nepafile=40605]JW Series.pdf[/nepafile]
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek