Benefits and dangers of boiler refractory, this weeks video.

RayWohlfarth

In this video, i talk about what refractory is and what it does. I also talk about the dangers it poses when disturbed after the burner fired on it.

https://www.youtube.com/watch?v=i9bePVMsdHM

retiredguy

You should record this video and distribute it to every commercial/industrial boiler service company in the world. This was a very informative video with information that everyone should listen to and study. My only complaint is; Where were you and this information when I got into the business in 1972. I definitely could have used it back then. Thanks Ray for the video.

EBEBRATT-Ed

Agree with @retiredguy. I did a fair amount of refractory work and I started in "73" one year after he did.

I know I sucked in more bad crap then anyone should although I didn't do refractory every day.

Thanks for the video Ray,

At this point I will skip it though

RayWohlfarth

@retiredguy Thank you so much. What an awesome compliment.

@EBEBRATT-Ed We all did dumb things back then. I remember knocking asbestos pipe insulation off with a hammer Thanks

Bob Harper

Great info. Ray and thank you for putting this together. I would add a few thoughts: An appliance or machine has design parameters. These are for performance but also durability and safety. When you think about the effects direct flame impingement can have on the durability and integrity of steel, you see a cascade of undesirable effects. Once a toehold of erosion or damage has begun on the refractory, failure at that point will accelerate. As soon as material is lost, you no longer have the designed thickness of material. This means the designed R value protecting the underlying steel is less, thus that steel will begin seeing temps. in excess of design, which will hasten failure. Less refractory results in more heat transfer at a point location. This reduces combustion efficiency. If you allow it to progress to direct flame impingement, you'll be producing a lot of CO but the steel will begin to fail. The differential heating of the flame target versus adjacent steel will create increasing stresses in the steel and welds, which eventually can lead to failure. At high temperatures, steels can change their chemical makeup and become other alloys. For instance, around 800-850C you can get intergranular corrosion in various alloys, especially stainless steels. The steel becomes sensitized, and you get chromium carbides forming at the grain boundaries. The 'stainless' steel then can 'stain' or rust and you will see pitting and corrosion.

Another aspect of refractories is the heat signature of the combustion chamber. Once you wander from the design, you stress points not intended or designed to take it. You get incomplete combustion added to offset or differential stresses in the steel, which shortens the life of the appliance. The same applies to the type of refractory. Fireclay firebricks can be of various chemical compositions for various applications. Not all firebrick are the same. Then you can have insulating firebrick, such as volcanic pumice. Again, each different type or make will have varying R values. High mass firebrick have a high specific heat meaning they absorb and store a lot of heat. Conversely, insulation brick store very little heat. Both affect the firebox temperatures. You may need to insulate the firebox to protect the underlying material from high heat while focusing heat back unto itself for higher efficiency. Likewise, firebrick can protect against flame impingement but do conduct more heat to the backing steel yet still release radiant heat back into the fire. It depends upon what you're trying to accomplish. Many woodstoves will use firebrick in the main combustion chamber to protect the steel from flames but use insulating refractories in the upper secondary combustion chamber where need to keep it very hot but don't need to protect the steel from direct contact and rather actually do want heat transfer.

In short, I'd say use and maintain only the refractories as designed.

RayWohlfarth

thank you very much You answered many questions I had

EBEBRATT-Ed

All true. Hard fire brick absorb heat and store it but protect the other surfaces from direct heat. Insulating brick more or less keep the heat from passing through thus "insulating brick"

They both will heat up and reflect heat back into the fire to aid combustion although insulating brick do this better.

Hard fire brick generally can take more heat and for longer periods of time and will last longer. Insulating brick is fine for residential and comes in several different temperature selections starting at I think 2000 deg on the lower end.

Sometimes in larger boilers hard brick is used facing the fire with insulating brick behind it to get the best of both worlds