Cinders

[Timm40]

Some of you more seasoned burners may know what is causing this......... I have noticed lately that I have coal cinder like ash left after a wood fire in my wood stove. I'm not talking about charcoal.........this is more like coal cinder and it seems to fuse together in plate size chunks. Only thing I am doing different is once a hot fire is going with good coal bed is to shut down the vents to just a small opening.......nice secondary effect on the fire.

 

[edthedawg]

I get the same thing - kinda hard but they crumble if you smack with a poker? And they don't glow hot in the late coaling stages, right? I chalk it up to just chemicals in the wood, the intense heat, and the ash buildup... I get it more in a thicker ash bed.

 

[Timm40]

I get the same thing - kinda hard but they crumble if you smack with a poker? And they don't glow hot in the late coaling stages, right? I chalk it up to just chemicals in the wood, the intense heat, and the ash buildup... I get it more in a thicker ash bed.

Same here......this is the first year I have ever seen that.....of course I'm running it more damped down then I ever have.

 

[Matt_W]

I have the same effect.
It seems to be more evident when I burn alot of locust. Maybe wood type?

 

[Timm40]

I have the same effect.
It seems to be more evident when I burn alot of locust. Maybe wood type?

Red and Chestnut Oak for me .....seasoned one calender year in full sun.

 

[Corey]

Something that may be of interest

Slagging Behavior of Wood Ash under Entrained-Flow Gasification Conditions
(broken link removed to http://gasifiers.bioenergylists.org/node/741)

Abstract

The overall objective of the work described in this paper was to determine the behavior of wood ash under entrained-flow gasification conditions. Experimental work in atmospheric and pressurized entrained-flow gasification simulators, combined with thermodynamic equilibrium calculations, has shown that wood ash is not prone to form a molten slag at typical operating conditions of (pressurized, dry-feed, oxygen-blown) entrained-flow gasifiers, in spite of the presence of a relatively high amount of low-melting alkaline elements. This appears mostly due to the formation of mainly high-temperature-melting compounds (e.g., CaO) and only a small fraction of Ca silicates, which are characterized by a lower melting temperature. Phosphor and silicon may contribute to creating a higher melt amount, whereas low-melting alkali metal compounds are mostly partitioned into the vapor phase. Experiments, as well as modeling work performed for three types of wood, have shown consistent results. Addition of a fluxing agent is a promising option to improve the slagging behavior of wood-based systems by reducing the melting point of the slag. Moreover, thermodynamic calculations have shown that slag recycle may represent a feasible option in order to obtain sufficient slag coverage of the refractory wall despite the low ash content of woody fuels (typically 1 order of magnitude lower than in coal). In the present work, the determination of slag viscosity, a parameter critical for continuous operation of a slagging gasifier, has been addressed as well. The results of modeling work, showing the inapplicability of predictive formulas developed in the past for coal slags to wood-based slags, underline that further work is required to allow for a quantitative assessment of the slag viscosity as a function of slag composition and temperature.

In summary, there are various compounds in wood ash which can melt to form a glassy/crunchy 'slag' or 'clinkers' like you observe. The relation of the high melting point compounds to low melting point compounds can determine what temperature this slag forms. Burning hotter or cooler and/or wood with different ratios of high/low melting compounds may change the slag formation, eliminate it, or enhance it.

The formation of the slag shouldn't be anything to worry about or any indication that something is 'wrong' with the combustion.

 

[jadm]

Corey- So how on earth did you find an article such as the one above??? I can't believe someone actually has done a study on it. I am constantly amazed and love all of these kind of tidbits that I run across here.

By the way, thanks for summarizing the article. I did read it and got the general gist of it but a lot of it went right over my head.

When I first got into wood burning it was about keeping warm at an affordable cost only. Now it is a whole new field of study and wonder at how amazing this world is. ;-)

 

[Timm40]

I don't what to say........thanks. I did find this though based on the word "clinker"
What is that melted rock-like stuff in my wood stove?
Lava-like pieces of rock in your wood stove are referred to as clinkers. Clinkers are the result of ash fusion, where noncombustible salts and minerals entrenched in the wood fibers liquefy and bond together. Clinkering is inherent with the burning of compressed wood, due to the the higher burning temperatures of the logs. Depending on the type of minerals and salts contained in wood fibers, ash fusion can occur from 1100 degrees to 2400 degrees Fahrenheit.

 

[Corey]

Perplexed - I just googled it! I think I looked for 'fused ash' or something similar. Thought maybe i might find some actual temps, but I ran across that article which seemed to suggest it would vary based on the ratios of the compounds originally in the wood.

Too bad we'd have to pay up to read the whole article, but the abstract hints at what is going on.