AHS S130 Coalgun- Puffbacks & Explosions

franco b
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Post Tue. Dec. 04, 2012 2:22 pm

Yanche wrote:You need to understand the combustion process and how it's changed by raising or lowering the coal height in the "anthratube".
I think the maker needs to understand which apparently they don't, especially the properties of gasses and their combustion.

The silence of the maker in this thread is deafening.

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EarthWindandFire
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Post Tue. Dec. 04, 2012 3:25 pm

The Coalgun owners on this board should draft a letter to AHS and collectively submit a signed letter. In my opinion, only the unified voices of so many concerned owners will generate the needed response from AHS.

Yanche has explained, in great detail, the steps needed by owner(s) to get the attention from the manufacturer. If I were an owner, I would act immediately on Yanche's advice.

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KLook
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Post Tue. Dec. 04, 2012 4:39 pm

I think instead, you have hit on why Harman does not talk to owners at ALL. They expect their dealers to be trained and experienced with coal. Selling to even techy intelligent people is fraught with danger from the standpoint of liability. AHS is checking their disclaimer on professional installation now.

Kevin

macdabs
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Post Wed. Dec. 05, 2012 5:53 am

AHS called me back yesterday and I will be emailing pictures of the grate motor and the control box. I guess some changes have been made and he wants to look at what model I have.
Heard the same, could be the coal? Something clogged? Did I clean the furnace this year ? Did I loose draft? I explained I could run 4 ton without any issues and the temp outside could be 65* and never have an issue.
My draft is a 8" flue and I am using a digital manometer to verify the .02-.06 draft. The final answer is to lower the SV to 113 and 3 diff. way below than the manual recommendations. I guess he is also going to look into some of the changes they made on the newer models that the grate only ashes with the fan on and so many seconds before the fan shuts down. I guess what bothers me is the fact they act like they never had this happen before and it can be expected depending on the coal.

I guess I have no option but to lower the Sv and hope for the best. As others mentioned the manual leaves a lot ot be desired and tells you not to lower the SV below 120. My question is what more can you do ? I am using Blackshak coal ;Installed the best 8" stainless flue with a good draft that is monitored;The boiler is sitting in a brand new building and can burn 2 ton or more without any burp or issue. Works great for heat output and purs like a kitten the majority of the time. Then out the blue will blow everything apart :o .

I understand the learning curve of burning coal. If you got draft, good coal(Blackshak), settings as recommended, what more can you do? This is a design issue that needs to be addressed.
Mac

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Post Thu. Dec. 06, 2012 12:02 am

amen

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Post Thu. Dec. 06, 2012 4:52 am

The silence of the maker in this thread is deafening.
Sorry guys, this is a critical fault in my estimation and the reaction of the manufacturer puts them in Harman territory. I will never own one, even assuming I could master the Ph.D. in mechanical engineering required. If I get sick in the winter my wife or even a neighbor, has to operate whatever I buy. It just shouldn't be that hard. Look the fire power (IQ) on this thread and no absolutely fool proof fix? forgedaboutit.
Last edited by coalnewbie on Thu. Dec. 06, 2012 8:54 am, edited 1 time in total.

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blrman07
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Post Thu. Dec. 06, 2012 6:59 am

I said it before and I'll say it again. I do not put things in my house that have a propensity to explode without warning and without being abused.

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titleist1
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Post Tue. Dec. 11, 2012 8:58 am

anything new happening with AHS on this one?

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whistlenut
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Post Tue. Dec. 11, 2012 9:04 am

506 posts and the poor horse is still being flogged!!!! Painful.....and yes I burn in a few of them with no issues. It is NOT Rocket Science!!!!!!

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Yanche
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Post Tue. Dec. 11, 2012 10:26 am

You are correct it's not rocket science, but it is combustion science. And in my opinion a coal appliance manufacturer needs to explain it to the buyer/operator in the owners manual. Few do it well.

Hopefully "macdabs" will post the solution and the support he got from AHS finding a solution for his installation. We can all learn from it.

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EarthWindandFire
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Post Tue. Dec. 11, 2012 2:05 pm

I was gonna post a picture of a coal-fired Rocket for Doug but that would make fun of a serious situation.

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Post Wed. Dec. 12, 2012 5:29 am

I have not heard a word from AHS since I emailed him picture of the setup of the boiler.. Darren recommended lowering the SV to 113 and the grate timer from 5 to 3. I replaced my Baro for the second time and had the stove back on line since last Sat.

I went through two ton last time before the big bang so I guess time will tell if the setting changes keep the boiler from exploding again. I would say it is a matter of time before all AHS owners get a letter in the mail from the safety police... :sick: I doubt the problem will go away without a design change.

Mac

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Post Wed. Dec. 12, 2012 10:53 am

:alone: :stretcher: :crutch: :bang:

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Yanche
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Post Wed. Dec. 12, 2012 1:57 pm

Mac, I'll try to help you get to a solution to your problems. First the AHS Coalgun is a good boiler and properly installed and operated will give good long term use. It along withe the A-A boiler is unique in the way it burns coal. Coal is burned in a tube, hence the term "Anthratube". When this method of burning coal was researched in the early 1940's there was nothing like it, in fact some of the experts at the time were surprised by the test results. A report was published in 1945 on the Anthratube. I've uploaded a copy. Much of the development work was done by Anthracite Industries, Inc. A company long gone. The report is somewhat technical but what I want you to understand is the concept of "fire height". By this I mean where the coal actually burns. This is important because if the "fire height" is in the wrong place problems result. The only way to control "fire height" is with the ashing grate. Stop the grate operating and the fire will burn higher. Stop it too long and you will have the fire burn it's way up the feed tube and you will have a hopper fire. Operate the ashing grate more and the "fire height" will be lower. Operate it too much and you will put burning coal in the ash bucket. Followed by raw coal.

So between these two extremes is where the "Coalgun" needs to operate. If you read the referenced report carefully you will see they determined the fundamental bed burning properties for Anthracite.

**Broken Link(s) Removed**

I'll quote from page 59 of the referenced report.

"As a result of the investigation of the fundamental properties of beds of burning Anthracite, it was shown that the thickness of the oxidation or intense burning zone in the bed depends depends upon the size of the fuel used. In general, it was found that Anthracite burns approximately 4 to 5 pieces deep. In other works, the oxygen in the air for combustion will pass a given amount of fuel surface before it is completely consumed."

Read and re-read this until you understand what it's saying and then think about the implications. First the burning coal is only 4 to 5 pieces deep, not much using Anthracite pea coal. Second all the oxygen in the combustion air sucked up by the combustion blower gets all used up. This is key to understanding "puff backs".

Let's think what happens when the "fire height" is just right, whatever that is. When the blower is running hot combustion gases are drawn into the boiler tubes heating the boiler water. Sufficient air flows thru the coal bed to support coal combustion. Next the blower stops. The inspection port opens. Fresh air with new oxygen enters, drawn in by both chimney draft and hot air rises principles. IF, the "fire height" was such that all the oxygen was used up AND combustion-able gases exist a "puff back" will occur. The oxygen for the "puff back" came in via the inspection port door. This is why minor "puff backs" are often heard when the combustion blower turns off.

So, what's the correct "fire height"? Seems to me it needs to be no lower than a few thickness of coal below the bottom of the inspection port. You should be able to see the burning coal when you look in thru the inspection port. If you do it means the coal combustion gases that didn't have enough oxygen to burn are on their way thru the boiler tubes. Sucked there by the combustion blower. Now when the blower stops and fresh air enters these unburnt gases are past a source of a flame which would ignite them. Adding fresh air has no effect and the open inspection port door just allows the natural chimney draft to work.

How to adjust "fire height"? It's changed by operating or stopping the ashing crank motor. It has nothing to do with the thermocouple controller temperature settings. The controller settings are used to maintain the position of the "fire height" oncee you get it to where it needs to be. Raising the "fire height" can be achieved by breaking the electrical connection to the grate motor. Clearly if it's not ashing the "fire height" will rise up in the "Anthratube". Conversely, applying power to the ashing motor will lower it. How you break or make the connections to the motor is up to you. I chose to put the motor in series with a switch. Normally the switch is closed. When I want to raise the "fire height" I open it. Since coal responds slowly you need to watch it, because if you forget it, you will have a hopper fire. Use caution.

You could use your thermocouple controller as an on-off switch. Just use extreme set points that either turn on or off the grate motor. Remember these are temporary set points only. Used solely for setting initial "fire height". Again pay attention. A wrong setting for too long could cause a hopper fire or an out of fire condition.

I hope this helps.

Bob
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Post Wed. Dec. 12, 2012 2:10 pm

I just want to supplement Yanche's post.

On my thermograte installation there is a separate switch for the grate operation that will stop grate operation but otherwise allow the unit to operate normally. This switch is normally ON but it can be used to stop grate operation at any time. The AHS instructions actually tell the operator to switch the grate off during unit start up to allow the fire to fully develop.

In my experience the appearance of where the fire level is when looking through the port varies depending on whether the unit has just operated on forced draft or whether a period of time has lapsed since the last forced draft operation.

I have had best operating experience when the burning coal level appears to be above the bottom of the port--WHEN VIEWED IMMEDIATELY AFTER A FORCED DRAFT BURN. On the other hand if the fire is viewed a considerable period after a forced draft burn very few ir no glowing coals will be visible.

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