Chunks of carbon

[Brokk]

This has happened twice so far, so now I'm going to ask about it.

On two occasions, my pellet stove has generated a chunk of carbon. It looks a little like pummice and it's just a large solid chunk 1"x1"x2", perhaps larger. I find it sitting in the burn grate. Today I noticed it because my pellets were backing up into the chute. They were all "on fire", or at least red and the flame looked all weird. Instead of going straight up, it was kind of angled forward. So I took a closer look, realized the pellets were backing up the chute and started the shutdown process. When it finished, it looked like ash was piled up into the grate, but it really was just a large solid chunk of ash? carbon? I'm not sure. It didn't look like it was burning.

The first time I found one about a week back, it was during startup. It kept failing to start and after 3 attempts I took a closer look and noticed this chunk in the burn grate. It was blocking the lighting process and preventing the pellets from catching fire properly. After removing it the stove started up with no further issues.

Both times this happened I had been running the stove aggressively on feed rate 4, then powered down (the first time) or just turned it down to feed rate 2 (this last time).

Any thoughts on what this is, what causes it or how to prevent it?

Brokk...

 

[LIpelletpig]

What is the make and model of your pellet stove and what type of pellets are you burning?

 

[BadDad320]

I believe what you are discribing is known as a clinker. I usually flip them out of the burn area into the ash area or bust them up.....

 

[Xena]

This has happened twice so far,
so now I'm going to ask about it.

On two occasions, my pellet stove has generated a chunk of carbon.
It looks a little like pummice and it's just a large solid chunk 1"x1"x2", perhaps larger.
Any thoughts on what this is, what causes it or how to prevent it?

Brokk...

I do believe this is what is referred to as a clinker.
Some pellets may do this. Whenever I've had pellets
that do, I scrape the burnpot more frequently.
Should be fine.

 

[BadDad320]

A clinker is ash that has become fused together from heat..... Kind of like sand into glass.......

 

[sydney1963]

Clinker, nothing to worry about. Just scoop them out of your burn pot.

 

[Brokk]

Glad to hear this is normal. So there is no particular condition that causes it? Nothing to prevent it?

Brokk...

 

[SmokeyTheBear]

Depending upon the quality of the pellets and your stove you may be able to reduce the number and size of the sintered ash clumps you are getting.

The moisture and ash content along with the air flow through and the temperature in your burn pot determine clinker formation rates if any.

Low ash fuel greatly reduces the formation rate of clinkers.

In addition if there is enough air flow to blow the ash out of the burn pot clinkers are stopped from forming.

Moisture aids the formation of clinkers.

That fused mess is basically fused carbon silica (fused charcoal sand).

 

[Brokk]

Ah, that makes sense then. I was having issues with too much air flow and recently shut mine down as far as it would go. It helped the flame out immensely, but this is the likely side effect. It had never happened before that.

Brokk...