Flue Temp on gasifiers

[Grover59]

Can any tell me what I should expect for an average flue temp. on my gassification boiler. I have a surface themometer on the pipe now and it reads most of the time around 200 to 220 if it goes in the idle mode it will go down to 150.

Steve

 

[slowzuki]

That sounds about right. As long as the interior stays above 140 F or so before it exits you shouldn't get condensation in the flue. My Jetstream (not quite a gasifier but similar) says when the interior flue temps climb to 400 F or so it is time to clean the heat exchanger tubes because they are fouled. I think the normal interior was supposed to be 300 F or so.

 

[Eric Johnson]

Thanks for the tip on hx maintenance indicators, Ken. I didn't know that, but it makes sense.

I know that the gas temp in most gasifier chimneys should be in the 200 to 300 degree range, but I'm not sure how to convert a surface reading into an estimate of the internal stack temp.

 

[slowzuki]

The conversion is not easy without doing it once with a pair of thermometers. My parents downstairs stove was about 600F outside was 800F inside but that obviously must scale somewhat with temperature.

 

[Tarmsolo60]

the booklet on my stss storage tank says constant flue temperatures of less than 300 degrees F are too low when turbulators are installed in the tarm.

 

[Eric Johnson]

The plot thickens.

I wonder if that's a draft issue. You'd almost think it would be the other way around, since the turbulators are supposed to slow down the gas and allow more heat into the pressure vessel. On the other hand, the turbs themselves are probably pretty hot, so maybe they're contributing the extra heat. Fundamentally, however, if lower exhaust temps mean greater efficiency and the turbulators provide better efficiency, then it should be the other way around.

I should measure mine. I have an old internal stack thermometer from a failed catalytic converter experiment around here somewhere. Drill one hole and I should be in business.

 

[brad068]

Hey guys,
Go to Wal-Mart and pick up one of them turkey thermometers. They are a analog gauge with @12" stem and are accurate with a range from 100* to 450* I think. I seen one being used by a master builder of home built gasification boilers, a.k.a. High E. I think they @ $5. Drill a hole and insert it into the middle of the exhaust stream. I found this to be the most accurate.

 

[slowzuki]

Turbulators don't make any heat Eric, all they do is force the gases to form turbulent flow in the tubes. This happens to add a flow resistance that slows down any draft system a bit but the volume of the flue gas also decreases as it cools just by nature of gases.

Lower temp exhaust gases do mean higher efficiency but you can't have condensation in your boiler or stack. Gasification is clean but it will still cause corrosion problems and if you don't have a drain all that condensate has to go somewhere.

Part of why the Garn shoots its exhaust out the side is likely due to this very reason. If it had a long stack you would need higher temps to prevent condensation. They can just fire it out at the dew point and let the water vapour dillute with drier surrounding air.

The plot thickens.

I wonder if that's a draft issue. You'd almost think it would be the other way around, since the turbulators are supposed to slow down the gas and allow more heat into the pressure vessel. On the other hand, the turbs themselves are probably pretty hot, so maybe they're contributing the extra heat. Fundamentally, however, if lower exhaust temps mean greater efficiency and the turbulators provide better efficiency, then it should be the other way around.

I should measure mine. I have an old internal stack thermometer from a failed catalytic converter experiment around here somewhere. Drill one hole and I should be in business.

 

[Eric Johnson]

I've used meat thermometers from the local grocery store, and they work great for monitoring pipe temps. Great tip, Garnification. I think I paid $25 for my add-on cat thermometer.

 

[Grover59]

A meat themometer is a great idea I'll get one tomorrow and drill a hole, I think that would be a better indications of the flue temp.

Steve

 

[WRVERMONT]

Hi All,
My Eko 60 with tubulators is at temp and running nicely with an exhaust temperature of about 300 degrees F. (Actual gas temp. I have a probe thermo.) Important in the beginning of the burn to keep exhaust temp up, no lower than 200. Once boiler is fully up to temp somewhere temps between 250 and 350 seem to be fine. Toward the end of a burn it is OK for exhaust temp to drop some because moisture, tar etc. has mostly been consumed. Some findings and thoughts.

 

[bbb123]

I just checked mine its 250 1 hour into morning burn I'll check in another hour with full burn going im sure its over 400. I dont have my turbulators in I was having a problem at end of summer getting boiler to burn right. Turns out after I ripped it apart (stack, checked chimney, cleaned tubes) the bottom ceramic was broke. Make NOTE they dont burn good then.

 

[bbb123]

full burn its upto 550 guess i better get my turbulators back in.

 

[Tarmsolo60]

I turned down my primary air adjustment quite a ways and and dropped the stack temp 200 degrees. It's now about 400 and am getting what I think is a better flame. before with the secondary air adjustment I couldn't see the difference in the flame, just the velocity of it. Now I can see the difference, I was blowing alot of heat up the chimney. going to clean it today and check out the temps again. boiler seems to heat up and gasify much quicker, it all make sense now..DUH. my book says primary air shouldn't need to be adjusted, well let me tell you I think it does. I'm pleading ignorance because this is the only gasification boiler I have ever owned or even seen.

 

[Jim Post]

I have a probe thermometer in my flue pipe that typically reads between 300 - 400 degrees when the boiler is firing. If it gets to 600 I know it's time to clean my heat exchanger. When I first got the tarm fired up we were seeing temps between 600 - 800 degrees regularly....due to not fully closing the bypass damper...with the damper locked, a running temp over 600 screams "Clean Me". On the tarm, cleaning the heat exchanger is just a matter of brushing out the tubes and smoke box....I thought it was pretty dusty work the first time I did it, so I cut a piece of cardboard to fit in the lower door with my shop vac hose stuck through it. With the shop vac on, it cuts the dust remarkably. Just make sure the boiler has cooled enough to prevent a vac meltdown.

 

[Tarmsolo60]

I have a probe thermometer in my flue pipe that typically reads between 300 - 400 degrees when the boiler is firing. If it gets to 600 I know it's time to clean my heat exchanger. When I first got the tarm fired up we were seeing temps between 600 - 800 degrees regularly....due to not fully closing the bypass damper...with the damper locked, a running temp over 600 screams "Clean Me". On the tarm, cleaning the heat exchanger is just a matter of brushing out the tubes and smoke box....I thought it was pretty dusty work the first time I did it, so I cut a piece of cardboard to fit in the lower door with my shop vac hose stuck through it. With the shop vac on, it cuts the dust remarkably. Just make sure the boiler has cooled enough to prevent a vac meltdown.

bypass damper had always been tightly shut and I was still seeing 600 with a clean boiler, thats when I went for the primary air adjustment. as for the cardboard cut out, I just stick my vac hose down one of the heat exchanger tubes while brushing, same end result, no cardboard to deal with.

 

[Jim Post]

The cardboard in the lower door just provides a temporary seal while letting the vac pull all the fly ash down. I guess having one less thing to keep track of while perched over my tarm appeals to me ....but whatever having the vac going really cuts the dust.

 

[Grover59]

I did finally find a themometer that I can insert into the flue, I got it at a hardware store, and it is used to make candy, the meat thermometers only went up to 220 this one goes to 450. I drilled a hole in the pipe, I have an 8" flue and the stem on the thermometer is about 6" works great. The temp went up to about 400 deg, because I was just getting the boiler fired up and had the bypass open. As soon as I closed the bypass and it started to burn the gases the temp quickly went down to 320 and stayed there. When the boiler went into the idle mode the stack temp lowered to 150, I watched it on the next cycle on, and it went back to about 320 once everything got back up to temp. So based on what I have seen so far there is about a 100 degree difference from surface temp to actual gas temp.

Steve

 

[bbb123]

I cleaned mine and put turbulators back in yesterday now gas temp at 400. How often do the Tarm owners clean them?