TLUD / RMH Hybrid?

Hi folks,
I was out playing with my various TLUD tin cans, and got to wondering if anyone has tried combining a TLUD with a rocket mass heater design for home heating purposes. The way I had envisaged it would be a sort of TLUD "cassette" that you would stick directly under a riser / barrel bell / manifold setup, and let it run as per the normal RMH protocol, then switch cassettes at the end of the burn. I came up with a few advantages & disadvantages - I'd appreciate any thoughts. Maybe someone has already done this...


The initial "cassette" I envisage is a 1gallon paint can with holes pierced in the bottom for the primary air (to support charring combustion & gasification) and more holes around the rim to allow ingress of secondary air (for combustion of gas).

Advantages:
* Easy design: avoid the core stuff - cassette plugs straight into riser
* incorporate wider range of feedstock - pellets, wood chips etc
* load and forget (batch system) so you can leave it running while you go and do stuff
* generate biochar as an end product (unless you let the biochar itself burn)
* remove ash in cassette
* can add a fan to the bottom to enhance primary gasification
* can seal cassette unit, so no smoke-back

Disadvantages:
* Batch system - need to change cassettes to keep going; can't just keep adding bits of stuff in
* Requires deeper build / higher (as opposed to taller) bell to accommodate bottom-loading of TLUD cassette
* biomass needs to be in chip or pellet form (not great for sticks unless you have a chipper)
* hot-changing requires a storage solution for the hot biochar
* Cassettes eventually burn out; need replaced (eg 1 gal paint tin)
* TLUDs can sometimes be tricky to start burning

I'm sure there are plenty of things I haven't thought of - probably more disadvantages than advantages. Grateful for the thoughts of you experts!
Thanks,
-Shane

Doing some further thinking about this; I think this potentially simplifies design quite a bit - you still need the manifold, but the elimination of a refractory burn tunnel in favour of a removable cassette may be worth entertaining. However, I'm thinking there may actually be a lot *more* combustion going on in the riser, so it might not last just as long as in a conventional RMH...

I was googling the idea of using a Tlud to "charge" a bench nor bell with heat, and this thread kept popping up so I ended up at your blog. Have you gone any further with this:http://answersingenes.blogspot.com/2011/09/tlud-experiment-hot-rocks.html?

Hi William,
No - I haven't made a great deal of progress on this yet - mainly due to time issues. I've sketched out a few concept designs, but I really need to get building. I think the key to it will be to have a good size of riser, and I also think it'll need the facility to throttle it down or up - TLUDs are in my experience, prone to going off a bit if you don't get the primary/secondary air balance right, particularly for the larger ones. Depends a lot on the fuel. I hope someone picks this up and runs with it - I'd be interested to see the results!
Cheers,
-Shane

Thanks the reply!
I hope to make my first tlud soon, I plan on going big by building It with a dryer drum.

Thinking big! I like it! Mind you, I would definitely recommend getting a feel for the territory by experimenting with a few smaller models - soup can TLUDs are fast and easy and you can make them in parallel to the larger project. Good luck!

(What are you using for feedstock?)

I have the same project, after I will have done my first main RMH!

I have seen the same advantages and drawbacks as you (well, you found more than I had! So thanks!)

I really have the good place for doing it, as I have a lot of room UNDER what I want to heat.
My 1st goal is char for the garden.
My 2nd goal is a batch fire that I will not charge after the start.

The drawback at the moment is the proper fuel.
I do not want to chip as it needs an extra machine I do not have.
And I want a ready-made fuel.

TLUD are mainly used with agriculture's wastes like rice husks, or coconut shells... and I do not have any.
I can light it with pine needles on top as a fast burning fuel starter.
Then I have a lot of pine cones.

But they make a nasty smoke, I don't know if this is possible.
How great would it be to burn this AND prevent fire propagation around!

I haven't tried it, but I would imagine that (dry) pine cones would make an excellent TLUD fuel - all the volatiles will burn off in the secondary burn. You might need a slightly larger reaction vessel than Alexis Belonio uses for his rice husks, otherwise maintaining a coherent pyrolysis front will be difficult, due to variations in cone spacing at the walls of the vessel. I'd suggest a vessel of at least 8in diameter (guessing here!) for cones of up to 2in long. However, this is worth experimenting with. In Ireland we have a lot of peat (turf); the smaller granules aren't a lot of use in a fire, but graded down to ~0.5 in (no dust or it chokes the fire) they burn extremely hot, and without that peaty smell, so I think we're getting a clean burn.

Mind you, if you live near a fir forest, I would think a RMH is the way to go. The big advantage of the RMH isn't so much the overall mass of wood it burns to run, but the grade of wood that you can use. I don't quite think Paul's figures of a *tenth* of the wood add up (I would love to be wrong, and maybe I am!), but I'd certainly be prepared to accept 25-30%, which is still OK. The heat from a lot of the small sticks that normally just gets radiated out quickly, and then "disappears" into the thermodynamic void when you're using an open fire is very efficiently made use of in the RMH, so you can burn crappy twigs that you normally wouldn't bother with, other than as kindling, and still get a great result. I'd be interested to see the pine cone thing in operation though!

Xisca Nicolas wrote:Then I have a lot of pine cones.
But they make a nasty smoke, I don't know if this is possible.
How great would it be to burn this AND prevent fire propagation around!

As far as I know, pine cones will burn beautiful in a J-tube rocket stove. The smoke which it is producing in a regular wood stove is from the high pine resin content. But that will be burn away in a properly built rocket heater. Since there is an abundance at your place, it would be sensible to build a stove just for that specific fuel.

I am long to get started because I have a lot of problems to solve at my place, but my project include more than 1 RMH!
There will be a RMH in the main place,
and then a TLUD / RMH in the second place when ready.
I must profit of the level difference for this TLUD under a RMH!

Peter Berg wrote:As far as I know, pine cones will burn beautiful in a J-tube rocket stove. The smoke which it is producing in a regular wood stove is from the high pine resin content. But that will be burn away in a properly built rocket heater. Since there is an abundance at your place, it would be sensible to build a stove just for that specific fuel.

Peter, a little RMH is already working at a friend's home, and she burns only pine, AND she has soot problem ! It is running black from the pipes connexions. She has no smoke back when she uses it, if this is the sign it is properly built...
If this is worth (not to be out Topic here) to open a new threat about pine and soot, I can do this and take pics of this rocket if my friend agrees.

Also, I do cook on my rocket heater with pine cones, and they do beautifully, I agree.
But they must be added often, more than wood.

The J shape is great for loooong twigs, even if I agree with Shane about the grade of wood we can feed the dragon!.
And I just don't see any better fuel HERE for the batch of a TLUD.
(And if I want to burn the "more useless" and use wood for compost.)

I have 2 good woods: almond and cistus monspellensis (jara in Spanish)
Then also pruning of orange and avocado, and some heather tree as a starter (no paper needed with it!).

Shane McKee wrote:I haven't tried it, but I would imagine that (dry) pine cones would make an excellent TLUD fuel - all the volatiles will burn off in the secondary burn. You might need a slightly larger reaction vessel than Alexis Belonio uses for his rice husks, otherwise maintaining a coherent pyrolysis front will be difficult, due to variations in cone spacing at the walls of the vessel. I'd suggest a vessel of at least 8in diameter (guessing here!) for cones of up to 2in long.

The second burn is definitely an advantage when burning resin!

Oops, I have pine cones up to 8 inches long....
That would be 32 inches as a diameter according to your ratio
I am going to search for Alexis Belonio, I did not hear about him before.

Thanks