Refractory Thermo Shock

[hobbyheater]

The argument has been made that water returning to boiler has to be kept over 140 degrees or you will thermo-shock the steel in the boiler.
In the wood gasification boiler I believe it also possible to thermo-shock the refractory component. Now I have a very small cross section of this field to base this conclusion on, the operation of my own Jetstream, two other Jetstreams and a recent post " Gasification Chamber Refractory" where a unit is seeing refractory cracking after only three years of use.
On the Jetstream I have operated for nearly 30 years, its refractory is nearing the end of its life. Over the years I have seen refractory damage when the boiler water has reached high limit and has shut the blower off with a full charge of wood. There has been a fairly consistent pattern. Any time the blower would shut down at maximum fire and I would find small pieces of refractory when cleaning out the fly ash. When I have sized the finale charge of wood correctly and the storage tank has achieved its desired temperature so that the fire goes out with no cycling of the blower, I have seen no damage.
The two other Jetstreams that I have knowledge of. One worked with no heat storage at all it and went through its original and a second refractory liner inside of five years. The other had heat storage, but the heat exchange to the tank did not work properly, so the blower would constantly cycle on and off. This unit also had a very short life.
My conclusion is at least with the Jetstreams, is if the unit is run where the blower cycles, the preheated blower air that accelerates the burn and elevates burn chamber temperatures also creates a consistent refractory temperature and if this air is instantly cut off, the temperature in the burn chamber is momentarily elevated causing thermal shock to the refractory.

 

[ISeeDeadBTUs]

You are kidding, right? You got 30 years out of the refractory and you want to find a way of firing that will lengthen its life?!?!!

 

[hobbyheater]

You are kidding, right? You got 30 years out of the refractory and you want to find a way of firing that will lengthen its life?!?!!

Thankyou for your input. The point that I was trying to make was that a lot of importance has been placed on not thermo shocking the metal components of your boiler but very little has been said about caring for the refractory side. If by making myself look foolish or greedy so I can create some disscussion on this topic, I'm happy to look that way. :cheese:
I have recently completed a face lift to the refractory of the Jetstream and after 10 weeks of operation, no cracks as of yet. This repair may add another 5-10 years to its life. In this part of the woods, freight costs very often exceed that of the expensive materials needed to do the repair.

https://www.hearth.com/econtent/index.php/forums/viewthread/84031/ This is the thread where I described my latest refractory base repair.

 

[maple1]

You got 30 years out of the refractory and you want to find a way of firing that will lengthen its life?!?!!

Where did he say that?

 

[ISeeDeadBTUs]

the refractory in my GW didn't crack for at least 6 or 7 days :long:

Is your Jetstream a one piece refractory, B4 the cracks I mean?

 

[Gasifier]

hobbyheater. I am guessing here, so go with me for a minute. Does the temperature of the air coming into the boiler air intake make a big difference. For instance, my boiler is inside in the basement. The air in the basement is generally 72-76 degrees when boiler is running. The boiler takes it's air right in from the basement, about a foot and a half off of the floor. Some people have their boiler taking air in from outside. I do not know, but I think some of them heat the air as it comes in, and I do not know if that works fast enough or not. Can you discuss this, and maybe others can tell us how theirs is done and chime in on there temperature, if they know their temperatures as they come into boiler if they are pre-heating, etc. Interesting thread. Thanks.

 

[hobbyheater]

the refractory in my GW didn't crack for at least 6 or 7 days :long:

Is your Jetstream a one piece refractory, B4 the cracks I mean?

The first picture is of a bare refractory liner. It weighs between 600-700 lbs.
The second picture is a complete base surrounded by insulating vermiculite. The round section is the burn chamber and the rectangular section would be under the smoke tubes that pass up through the heat exchanger. The blower air is preheated as it passes through the back section of the base before it enters the burn chamber.

 

[hobbyheater]

hobbyheater. I am guessing here, so go with me for a minute. Does the temperature of the air coming into the boiler air intake make a big difference. For instance, my boiler is inside in the basement. The air in the basement is generally 72-76 degrees when boiler is running. The boiler takes it's air right in from the basement, about a foot and a half off of the floor. Some people have their boiler taking air in from outside. I do not know, but I think some of them heat the air as it comes in, and I do not know if that works fast enough or not. Can you discuss this, and maybe others can tell us how theirs is done and chime in on there temperature, if they know their temperatures as they come into boiler if they are pre-heating, etc. Interesting thread. Thanks.

The first picture is of the original blower housing where it would have been mounted on the back of the boiler heat exchanger. The blower motors ( vacuum cleaner motors) in this configuration were short lived. They just swallowed too much abrasive dust from the boiler.

Second picture is the same blower mounted so it can draw outside air through a duct in the basement wall. I'm now getting double the life out of these motors. I had to put a gate valve in the pipe leading to the boiler to dump some of the air. The same blower motor mounted in this configuration generated too hot of a fire. The refractory, instead of being a nice orange color, was starting to pass from yellow to white. So I have drawn the conclusion that the incoming air temperature does make a difference to the temperature of the fire. The base and the heat exchanger are both uninsulated, so the temperature in the boiler room can hit 90F degrees but the air drawn in from the outside is 30-40F degrees through most of the winter months.

Third picture - the air as it gets to the boiler, splits with half going up to the draft inducer and half going down to the back of the base and the combustion air tube where it is preheated as it passes through the back section of the heat exchanger before it gets to the burn chamber.

Fourth picture - the draft inducer port in the first section of smoke pipe leaving the boiler.

Fifth picture - the end of a six hour burn.

 

[barkeatr]

MY GASSERs gas chamber is built/formed by fire brick. Cracks are built in.

 

[stee6043]

I guess I'll weigh-in, if only knee deep.

First, based on your inital post it sounds like you may be suggesting that after the fan is shut off the temperature in the refractory would temporarily increase. I do not believe this is physically possibly. Where would this increase in heat come from? In order for the refractory to increase in temperature, even if temporarily, it must be absorbing heat from something, somewhere. The refractory itself cannot produce energy.

Now if you are proposing that the "lower chamber proper" is temporarily increasing in temperature in the absence of air flow - this seems possible. But again, in most downdraft boilers the refractory "should" be the hottest part of the boiler. If this is the case and the air flowing through the lower chamber is in effect cooling everything else, it should be "everything else" that increases in temperature when the fan shuts off. And the refractory can only begin to cool in absence of air flow.

The only way the refractory could increase in temperature in the scenario you are proposing is if there is something of higher temp from which it is transfering heat when the fan shuts down. And I believe in a properly operating downdraft gasser you will not find anything hotter than the refractory, anywhere.

Just my two cents!

 

[hobbyheater]

[quote author="stee6043" date="1323814899"



Now if you are proposing that the "lower chamber proper" is temporarily increasing in temperature in the absence of air flow - this seems possible. [/quote]

Thank-you. You have made the point of what I was trying to get at.
Your system has adequate heat storage and should see very little cycling of its blower therefore lessening the potential for thermal shock of its refractory.

 

[ISeeDeadBTUs]

I've got way more questions than time, but a few . . .

1) Not really a question . . . please tell us you are not a salesman for Jetstream

2) The refractory in your pictures. . . is that an original from the factory? or a replacement you made?

3)If you made the refractory, care to share some details?

4)Since your wife does most of the work on your posts can you ask her to post some pics from the island? I have never been able to make it there during previous visits to Seattle/Vancouver.

Jimbo

 

[hobbyheater]

I've got way more questions than time, but a few . . .

1) Not really a question . . . please tell us you are not a salesman for Jetstream

2) The refractory in your pictures. . . is that an original from the factory? or a replacement you made?

3)If you made the refractory, care to share some details?

4)Since your wife does most of the work on your posts can you ask her to post some pics from the island? I have never been able to make it there during previous visits to Seattle/Vancouver.

Jimbo

1 No, I'm not a salesman for Jetstream, just can't afford anything else !
2 The refractory pictures - both are factory.
3 Had considered making a mold of the liner to make my own base, but that plan got scratched two months ago when I purchased a complete unit off of eBay that had never been used.
4 I will ask the good wife to do a post on The Perfect Picture of "Vancouver Island Alpine".
5 Question. Should she have here her own handle?

 

[Gasifier]

Question. Should she have here her own handle?

No. :lol: Your identity on Hearth.com will change forever. :lol: It will not be same after that. :lol:

 

[maple1]

The best summer of my life was spent on Vancouver Island in 1990 - my last summer job as a University student. I walked across that Island & back again, and then some, from Parksville thru Port Alberni to Bamfield, then back out to PA & across to Ucluelet & Tofino. Then back across to Parksville, with a side trip to Campbell River. Amazing memories - had a great group of 8 East Coasters to share it with. We had to make do with West Coast beer, but that was OK.

Sorry, back to the topic....

 

[heaterman]

I've got way more questions than time, but a few . . .

1) Not really a question . . . please tell us you are not a salesman for Jetstream

2) The refractory in your pictures. . . is that an original from the factory? or a replacement you made?

3)If you made the refractory, care to share some details?

4)Since your wife does most of the work on your posts can you ask her to post some pics from the island? I have never been able to make it there during previous visits to Seattle/Vancouver.

Jimbo

1 No, I'm not a salesman for Jetstream, just can't afford anything else !
2 The refractory pictures - both are factory.
3 Had considered making a mold of the liner to make my own base, but that plan got scratched two months ago when I purchased a complete unit off of eBay that had never been used.
4 I will ask the good wife to do a post on The Perfect Picture of "Vancouver Island Alpine".
5 Question. Should she have here her own handle?

Why yes of course!!

It would logically be hobbyheaterette

We would welcome her aboard.