Coalgun- Puff backs & Explosions

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Mon Feb 06, 2012 9:20 pm

I have never seen the thermocouple setup in an AHS, however, I am familiar w/ thermocouples in other applications. There is likely a resistance value for that "type" that could be used as a benchmark test reading that could be a clue to the integrity of the thermocouple junction itself.


Is it mounted in such a way that numerous puffbacks could cause misalignment or otherwise render it inaccurate?

Is it sheathed in some stainless steel cladding and mounted by way of some pipe threads and locking nuts to a bracket to hold firmly in the desired position/location?
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: ValterBorges On: Mon Feb 06, 2012 9:34 pm

Hope it's on right :roll:

1.
Image
IMAG0117 by ValterBorges, on Flickr

2.
Image
IMAG0121 by ValterBorges, on Flickr

3.
Image
IMAG0120 by ValterBorges, on Flickr
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Mon Feb 06, 2012 10:25 pm

Thanks Valter for posting pics. :) It helps to get better representation of how it is orientated in the AHS.

Note to all:
As far as accuracy goes, these thermocouples work on a millivolt level, so any connection in the entire circuit that is less than ideal will cause inaccurate readings at the measuring instrument.
The AHS has 3 connections...2 wire connections at instrument end and 1 at the "junction" at the opposite end near the grate.
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: ValterBorges On: Mon Feb 06, 2012 11:07 pm

McGiever wrote:any connection in the entire circuit that is less than ideal


Can you give some examples of less than ideal?
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Tue Feb 07, 2012 12:14 am

ValterBorges wrote:
McGiever wrote:any connection in the entire circuit that is less than ideal


Can you give some examples of less than ideal?


Loose terminal screw in instrument and junction end connection could become loose, cracked or separated.
As well, the lead wire could become grounded to boiler frame at some point.

BTW...there all many different cable insulation options available for many different applications.

Working at the millivolt level it takes very little to degrade the accuracy of the signal since the milivolts spans a very large temperature range as it is. The coal boiler only uses a very narrow portion of this overall range...like around a 30-35*F portion.

Type J (Fe/Cu-Ni) thermocouples are widely used in industry due to their high thermopower and low cost. This type of thermocouple has an operating temperature range from 0 oC to +760 oC.
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: ValterBorges On: Tue Feb 07, 2012 12:33 am

Any good replacement options out there within reasonable price?

How long do you thing these last in general?

Any simple way to test accuracy?
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Coalgun- Puff backs & Explosions

PostBy: titleist1 On: Tue Feb 07, 2012 8:35 am

McGiever wrote:Thanks Valter for posting pics. :) It helps to get better representation of how it is orientated in the AHS.

Note to all:
As far as accuracy goes, these thermocouples work on a millivolt level, so any connection in the entire circuit that is less than ideal will cause inaccurate readings at the measuring instrument.
The AHS has 3 connections...2 wire connections at instrument end and 1 at the "junction" at the opposite end near the grate.


Another note regarding accuracy with Thermocouples....

As I recall the lead length and resulting change in resistance also impacts the accuracy of thermocouples. So it would be better to not shorten or lengthen the leads that the thermocouple is mfg'ed with to make it work in your installation if at all possible.
titleist1
 
Hot Air Coal Stoker Stove: Harman Mag Stoker (old style) one in basement, one in workshop
Hand Fed Coal Stove: Harman Mark III on standby for long power outages
Coal Size/Type: Rice/Anthracite; Nut/Anthracite

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Tue Feb 07, 2012 12:02 pm

titleist1 wrote:
McGiever wrote:Thanks Valter for posting pics. :) It helps to get better representation of how it is orientated in the AHS.

Note to all:
As far as accuracy goes, these thermocouples work on a millivolt level, so any connection in the entire circuit that is less than ideal will cause inaccurate readings at the measuring instrument.
The AHS has 3 connections...2 wire connections at instrument end and 1 at the "junction" at the opposite end near the grate.


Another note regarding accuracy with Thermocouples....

As I recall the lead length and resulting change in resistance also impacts the accuracy of thermocouples. So it would be better to not shorten or lengthen the leads that the thermocouple is mfg'ed with to make it work in your installation if at all possible.


Well, not really so much, unless it is an extreme length. Controllers/Instruments have built in compensations for such a constant as fixed lengths...it's the variables ( like poor connections etc.) that make it get out of whack due to inability to compensate for those.

ValterBorges wrote:Any good replacement options out there within reasonable price?

How long do you thing these last in general?

Any simple way to test accuracy?


I think they are as good as any thing else out there in this application, no need to consider an other option.

They do last well if they are built and installed well to start with. That's where the accuracy part comes in.

Testing for our application only needs done by comparing temperature readings to a "good" liquid filled thermometer. If possible, best to compare it in a ice water bath at 32*F...if not possible, then use any temperature bath you desire.
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: Tue Feb 07, 2012 12:04 pm

A junction of dissimilar metals will produce an electric potential related to temperature. This is the principle that thermocouples use. There is nothing to calibrate in the thermocouple probe. It's just two pieces of known wire welded together. You can make your own. The difficult part is making an electronic instrument to measure the tiny voltage, especially in a harsh environment. Stray current ground loops are a particular problem.

Read more about how thermocouples work here:

http://en.wikipedia.org/wiki/Thermocouple

There are various methods to sheath the wire junction. Some methods protect it physically from the environment others improve the unwanted noise rejection. Read more about the different types of probes here:

http://www.omega.com/techref/themointro.html

The AHS coal gun uses the thermocouple as a control signal measuring device. There is no need to have it calibrated to absolute accuracy. It makes little difference if the reading the thermocouple electronics display is right or not. What's important is how it controls the height of the fire in the "stack" of ash, burning coal and unburnt coal.

It's far more important to understand how the thing you can set (lower set point, upper set point and hysteresis) influences the "stack". It's the control system that matters.

You can not use ordinary copper wire to lengthen a thermocouple. If you do you have introduced another thermocouple junction, the one between the copper wire and the thermocouple wire. You can shorten thermocouple wires but you must know how to reattach it to the special connector.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Coalgun- Puff backs & Explosions

PostBy: McGiever On: Tue Feb 07, 2012 12:31 pm

Yanche, I totally agree about the fire height/position is the only important factor, and temperature readout is whatever it is...and not all that important. :)

My previous postings were only to show that how well the thermocouples are installed may have allowed some unwanted variables and would account for some erratic reading.
The differences one might see when comparing settings to the manual or what other owners see in their installations has little meaning. However, a loose connection could be easily found and corrected...and would remove the erratic readings, more stable is more better.:)

McGiever wrote:My belief is, if one has "puffbacks" they must get the fire(hot coals) raised higher in their firepot.

What the digital display reads on the controller may not match the owners manual or even what other AHS owners settings are...keep adjusting lower to get the fire higher and the problem will be gone.


McGiever wrote:"rychw", You may have developed significant inaccuracies in your digital ashing controller...you just need to do as suggested and keep going lower...forget the read-out, do it by appearance of level in firepot...then you will be par w/ all the others as far as puffbacks. :idea:
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: ValterBorges On: Wed Feb 08, 2012 12:08 am



Reference Fire Height. Sv120, Boiler Temp 160.

Check out this video on YouTube:

http://www.youtube.com/watch?v=HeiuwqQJ ... ata_player
ValterBorges
 
Stove/Furnace Make: AHS
Stove/Furnace Model: S260

Re: Coalgun- Puff backs & Explosions

PostBy: Freddy On: Mon Oct 08, 2012 3:48 pm

It's been a while since anything added to this post, but a bit of news to add from my AHS buddy. He ended up adding a draft inducer... and still had the occasional boom. Toward the end of last year he made an accidental discovery. He removed the "tombstone" that covers the inspection (view port) door and for one reason or another it got left off. It took some time for him to realize it, but, he has not had one single puff back since it's been left off. He's wondering if the tombstone itself holds some methane? Anyway, if someone else that has the occasional puff back wants to remove their tombstone & see if it makes a difference, it would be an interesting experiment.

I think the only reason for the tombstone is perhaps to keep possible sparks at bay? I don't know, but, certainly don't try this experiment unless you deem it is safe for you do do so. My buddy Charlie's boiler has only concrete all around it, so no chance of fire. ( although I''m not sure that safety is the factory reasoning. I've had some spectacular puff backs & never had embers fly)
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Coalgun- Puff backs & Explosions

PostBy: Pacowy On: Mon Oct 08, 2012 3:59 pm

To the uninitiated, it might be a little disconcerting to learn, on the 28th page of a thread about boiler explosions, that some coal boilers are supplied with tombstones. Just sayin'. :lol:

Mike
Pacowy
 
Stoker Coal Boiler: H.B. Smith 350 Mills boiler/EFM 85R stoker
Coal Size/Type: Buckwheat/anthracite

Re: Coalgun- Puff backs & Explosions

PostBy: Freddy On: Mon Oct 08, 2012 7:25 pm

Pacowy wrote:it might be a little disconcerting... that some coal boilers are supplied with tombstones.


LMAO No more than the building that airplanes aim for being called "the terminal". ;)
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Coalgun- Puff backs & Explosions

PostBy: Yanche On: Mon Oct 08, 2012 9:40 pm

As I understand the "tombstone" cover, it was an improvement over the previous design. The need is to keep the flapper door from being damaged when a severe "puff back" occurs. The first design was simple a horizontal bar, one that went across the lower part of the flapper door, restricting travel. I had my boiler upgraded to the "tombstone" when I had it back at the factory for other mods. My secondary theory on the benefit of the "tombstone" is it creates additional idle draft. With the flapper door ajar, air heated by the front surface of the boiler rises creating a draft. I fully acknowledge it may be so small it doesn't make a difference at all.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea