If I'm trying to burn a fuel with a moisture content of about 50% and an ash content of about 33%, can I expect to achieve gasification with a "clean" emmission. At best I've gotten it down to a white "fluffy" smoke. Is that simply because of the water content or what? Thanks for any input.
Ash content in relation to smoke
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jebatty
Minister of Fire
Excuse me if I misunderstand you, but I think you are using inconsistent terms with an illogical conclusion. First, home wood gasification boilers require wood moisture content between about 20% and a high of 30%, although drier than 20% is satisfactory.
Your statement of "ash" content confuses me. How do you know this? I've burned hardwood and softwood in my gasification boiler, and after about an 8 hour burn, I have about 1 cup of ashes -- my guess is that it's about 1% by weight. If you are ending up with 30% ash, you must be burning something close to "sand." There is very little ash with home gasification systems burnng wood. And if you are burning fuel with a stated ash content of 30%, you should take your price x 0.7 to determine the price for a good fuel.
Now, I feel confident that one could engineer a gasification system to burn 50% moisture content fuel with high unburnable material (ash), but I'm wondering what this is? refuse? or what? certainly not a wood fuel.
As to a white fluffy smoke, my call is that if the temperature is above 20F, you should be seeing no "smoke" at all in a typical home wood gasification system. Water vapor at and above this temp should not condense to visible "smoke.". Below about 20F, and as outside temp gets colder, you may see some white, light, whispy "smoke," but nothing denser, except on start-up or after an idle period.
This may not help you any, but your questions do not fit my experience.
Your statement of "ash" content confuses me. How do you know this? I've burned hardwood and softwood in my gasification boiler, and after about an 8 hour burn, I have about 1 cup of ashes -- my guess is that it's about 1% by weight. If you are ending up with 30% ash, you must be burning something close to "sand." There is very little ash with home gasification systems burnng wood. And if you are burning fuel with a stated ash content of 30%, you should take your price x 0.7 to determine the price for a good fuel.
Now, I feel confident that one could engineer a gasification system to burn 50% moisture content fuel with high unburnable material (ash), but I'm wondering what this is? refuse? or what? certainly not a wood fuel.
As to a white fluffy smoke, my call is that if the temperature is above 20F, you should be seeing no "smoke" at all in a typical home wood gasification system. Water vapor at and above this temp should not condense to visible "smoke.". Below about 20F, and as outside temp gets colder, you may see some white, light, whispy "smoke," but nothing denser, except on start-up or after an idle period.
This may not help you any, but your questions do not fit my experience.
The fuel is used mushroom compost (saw dust, straw, horse manure and chicken litter).
We're actually using a Goliath 180. Typically we burn wood scraps, but we're running a test with
the mushroom compost.
We messed around for a couple of hours yesterday trying to burn this stuff and it smoked most of
the time. Now I understand that we're playing with a commercial boiler, but none-the-less it
still uses the same principles as a residential boiler.
I've made the assumption that if the boiler is smoking then three things could be happening:
(Please correct if I'm wrong)
A. The combustion chamber isn't hot enough to ignite the smoke.
B. The smoke to fresh air ratio is off - need more secondary air.
C. Due to the high ash content (10 or more times that of wood) we are seeing more exit the boiler
Now I have another question - when burning a fuel with a higher moisture content; when gasifying your fuel,
does the H20 break down into H and 02 or does it simply remain H20 in a steam form?
Thanks again for any input.
Mike
We're actually using a Goliath 180. Typically we burn wood scraps, but we're running a test with
the mushroom compost.
We messed around for a couple of hours yesterday trying to burn this stuff and it smoked most of
the time. Now I understand that we're playing with a commercial boiler, but none-the-less it
still uses the same principles as a residential boiler.
I've made the assumption that if the boiler is smoking then three things could be happening:
(Please correct if I'm wrong)
A. The combustion chamber isn't hot enough to ignite the smoke.
B. The smoke to fresh air ratio is off - need more secondary air.
C. Due to the high ash content (10 or more times that of wood) we are seeing more exit the boiler
Now I have another question - when burning a fuel with a higher moisture content; when gasifying your fuel,
does the H20 break down into H and 02 or does it simply remain H20 in a steam form?
Thanks again for any input.
Mike
I think you'll find those questions a bit more theoretical than the focus of this group but I'll take a stab. I believe some large commercial garbage burners can handle nearly 50% moisture. They can't light off on it though, it has to be slowly introduced once the combustion chamber is up to temp. Even then you will probably lose control alot and drop the temps too much to sustain it. You may find you can't extract any heat from the boiler with this much moisture in the fuel. It may only produce enough heat to vapourize the water.
I can't imagine the ash content is actually that high. Have you had a lab do some test samples? More ash exiting the boiler is usually due to velocities inside, what fill config are you using? Does your boiler have a baghouse or cyclone? How many kW is it rated for?
The last question is, some of it does. Often fuel moisture in large burners is adjusted (by picking fuel streams ie the wet conveyor or dry conveyor) to reduce peak temps and reduce NOx emissions, if there is NOx that means H2O can be ripped apart too. At low moisture, high enough temps can be reached that some H20 is torn apart. This is more studied in wood gas gasifiers. I have no clue how big of effect it is in a heating gasifier.
I can't imagine the ash content is actually that high. Have you had a lab do some test samples? More ash exiting the boiler is usually due to velocities inside, what fill config are you using? Does your boiler have a baghouse or cyclone? How many kW is it rated for?
The last question is, some of it does. Often fuel moisture in large burners is adjusted (by picking fuel streams ie the wet conveyor or dry conveyor) to reduce peak temps and reduce NOx emissions, if there is NOx that means H2O can be ripped apart too. At low moisture, high enough temps can be reached that some H20 is torn apart. This is more studied in wood gas gasifiers. I have no clue how big of effect it is in a heating gasifier.
Nofossil
Moderator Emeritus
I think what happens with high moisture content is two things:
1) Vaporizing the water absorbs a percentage of the heat generated during primary combustion, cooling the wood gas and making it harder to ignite.
2) The steam generated by vaporizing the water is a wonderful fire suppressant, diluting the otherwise flammable gas/air mixture.
1) Vaporizing the water absorbs a percentage of the heat generated during primary combustion, cooling the wood gas and making it harder to ignite.
2) The steam generated by vaporizing the water is a wonderful fire suppressant, diluting the otherwise flammable gas/air mixture.
That makes sense to me - the moisture is "smothering" my fire. So the compost will either have to be mixed with very dry fuel prior to burning, or dried to a moisture content less than 30% - any other options I may have missed?
Thanks.
Mike
Thanks.
Mike
jebatty
Minister of Fire
A local ethanol plant installed a commercial gasification boiler system which supposedly was designed to burn green biomass (tree tops, branches, etc.), and the system failed to operate as intended. I understand the technology to involve moving the biomass at a measured rate from the top of the burn chamber to the bottom gasification portion which would allow the biomass to dry out during the burn to permit gasification at the bottom. Lots of blame is being thrown aboutas to why it failed, but I can appreciate the engineering issues when dealing with high moisture content material.
Yes. one other thing. Burning manure and chicken litter will volatolize ammonia, which will corrode your carbon steel. I agree with those saying high moisture content is not good . Adding more draft will increase the smoke and speed up the burn, with no appreciable increase in btu's. Lastly, your ash may not be true ash, but rather unburned fuel. There is a difference. true ash has no more heating value and will not re-ignite.
I haven't confirmed the ash content - I actually picked the 33% up off an article from someone else trying to do the same thing - it seemed that some outfits in the UK are trying to minimize mushroom waste and get the heat value out of it.
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