Boiler has trouble maintaining gassification

[traparatus]

Howdy, folks.

This question is regarding a Central Edge 550 gasification boiler. It's a pretty standard outdoor downdraft boiler with fire box up top and secondary combustion chamber on the bottom.

This boiler's burn cycle lasts about 10-12 minutes and happens every couple of hours. This brings the water up from 175f to 185f.

When the boiler initiates its burn cycle temperature in the lower chamber climbs steadily and when it reaches around 750f gasification begins. Around the same mark the boiler throttles down primary air and increases secondary air flow. Temperature in the reaction chamber continues to climb up to 1300-1400F at which point gasification stops rapidly and thick smoke starts bellowing out of the chimney. Temperature in the combustion chamber slowly drops all the way down to 750f.

Does anyone know what would cause this sudden stop of gasification? I'm burning pine, measured moisture content around 16%.

 

[hobbyheater]

Howdy, folks.

This question is regarding a Central Edge 550 gasification boiler. It's a pretty standard outdoor downdraft boiler with fire box up top and secondary combustion chamber on the bottom.

This boiler's burn cycle lasts about 10-12 minutes and happens every couple of hours. This brings the water up from 175f to 185f.

When the boiler initiates its burn cycle temperature in the lower chamber climbs steadily and when it reaches around 750f gasification begins. Around the same mark the boiler throttles down primary air and increases secondary air flow. Temperature in the reaction chamber continues to climb up to 1300-1400F at which point gasification stops rapidly and thick smoke starts bellowing out of the chimney. Temperature in the combustion chamber slowly drops all the way down to 750f.

Does anyone know what would cause this sudden stop of gasification? I'm burning pine, measured moisture content around 16%.

The boiler is up to temperature !

 

[traparatus]

The boiler is up to temperature !

Lol. Funny man.

On a serious note, no. Gasification stops mid burn cycle, well before water gets up to set temperature.

 

[maple1]

Maybe your dry pine is off gassing more than the boiler is able to burn? Have you tried smaller loads? Or an air passage is dirty?

 

[traparatus]

Maybe your dry pine is off gassing more than the boiler is able to burn? Have you tried smaller loads? Or an air passage is dirty?

Air passages are clean. Like I say, it does actually gassify. It just has trouble doing it for a long enough time.

I haven't considered the size of wood load as a potential factor. Will have to do a bit of experimenting with that. Mind you, there is only so much that I can do there. I kind of have to reload it with ~12hours worth of wood because of work schedule.

Thanks for the suggestion. I wish these boilers ran some sort of O2 sensor so I could actually tell what the mixture is in the combustion chamber.

 

[brenndatomu]

Maybe your dry pine is off gassing more than the boiler is able to burn? Have you tried smaller loads

This ^ ^ ^
You need less pine in a given load (as a percentage of the load) and larger pieces will not off-gas as rapidly either...and it might sound weird, but MC closer to 20% will give you less problem with this too. (not permission to burn green/wet wood though)

 

[traparatus]

This ^ ^ ^
You need less pine in a given load (as a percentage of the load) and larger pieces will not off-gas as rapidly either...and it might sound weird, but MC closer to 20% will give you less problem with this too. (not permission to burn green/wet wood though)

Burning wetter wood... Now, that's a solution I could get behind

It's kind of a problem for my area. Pine and spruce is what we got. There is no hard wood here. I'm going to try some larger splits, see how it gasifies.

 

[hobbyheater]

Lol. Funny man.

On a serious note, no. Gasification stops mid burn cycle, well before water gets up to set temperature.

185 F in a lot of boilers is up to temperature !

 

[brenndatomu]

185 F in a lot of boilers is up to temperature !

All of them, that I'm familiar with. I've heard of guys going to 190 in real cold weather, but that's about the upper limit on a solid fuel hydronic heater...asking for trouble going much higher.

 

[traparatus]

185 F in a lot of boilers is up to temperature !

It is set at 185F. That's not the problem. The boiler stops gassifying well before it gets up to set temperature, mid way through the burn cycle.

It doesn't shut down or stop the blower. It continues running, just the physical process of gassification in the combustion chamber stops and all the smoke gets pumped out of the chimney, unburnt.

 

[brenndatomu]

It is set at 185F. That's not the problem. The boiler stops gassifying well before it gets up to set temperature, mid way through the burn cycle.

It doesn't shut down or stop the blower. It continues running, just the physical process of gassification in the combustion chamber stops and all the smoke gets pumped out of the chimney, unburnt.

Yeah sounds like that pine gas is overwhelming the fire (rich) its kinda like pulling the choke out on your chainsaw when its already running and warmed up...just kills it. (might smoke some before it dies)

 

[all night moe]

A gasser is basically the same as an internal combustion engine.
Fuel, air, and spark.
Fuel is the wood gas.
Air is the secondary hot air, and some primary air.
Spark is the coal at the nozzle.

One of those are out of wack. An easy fix would be to try another fuel source. Say tiny bit of what you have on hand and some fir that is seasoned to below 20% MC. Could it be your coals are not enough, and/or hot enough from the fuel chosen?

 

[coolidge]

When I burn hemlock in my OWB the wood bridges over the nozzle and stops gassing.

 

[traparatus]

Thanks for all the replays, folks. I'm running a few test burns now, following some of the suggestions. It's going really well. I'm just waiting for a few more days worth of data to make sure and I'll share my findings.

 

[traparatus]

I'd like to provide an update to those interested.

As it was suggested by a few posters, extremely dry pine seems to off gas so rapidly as to completely overwhelm gassification process. To further complicate matters, all my firewood is split to very small size. That was done by design due to the fact that when I first inherited this boiler and tried using large splits, the fire would bridge constantly.

I ended up throttling the primary air way down. I also went back to large wood splits. Well, massive splits is a better way to describe it in a hope that this would slow down off gassing. On a suggestion from a poster in a different thread, I put one large split flat side down right over top of the secondary air charge tube to help prevent bridging. Between this and the sharp decrease in primary air, bridging has not been a problem at all.

I'm happy to say that feeding the boiler in this manner has resulted in continuous and very thorough gassification. There is no visible smoke coming out of the chimney after the first ~30 seconds of a burn cycle. There is always a gasification torch flame roaring in the combustion chamber.

Interestingly, temperatures in the combustion chamber don't climb as high as they used to. They get up to 1100-1200F and stay there for the duration of burn cycle. Mind you, aggressive gassification begins from right around 800F.

Most importantly, wood consumption has absolutely plummeted. I've ran the boiler in this manner for 4 days now and I estimate that wood consumption has dropped by about 30%. It's a remarkable difference. Big thanks to everyone who provided suggestions and advice.

 

[hobbyheater]

I'd like to provide an update to those interested.

I'm on the Island Port McNeill to be exact , were are you in the province?

 

[traparatus]

Up by Smithers. I lived in Port McNeill for about a year. Small world, right?