TLUD stove smokes; proposed modifications

My TLUD stove smoked quite a bit on startup, and again near the end of the cycle.

I've got some ideas to correct this, but I'd like to make sure I'm not going in the wrong direction.

For one thing, I didn't have alcohol to start it with and quickly get it up to heat; I think this was important.

My fuel bed was maybe an inch below the secondary air intake; I think it should have been lower to provide more of a chimney flow and give more room from preheating of the air rising along the sides.

My TLUD is about a 10 gallon; I'm wondering if a pipe coming up the middle and letting secondary air out at the same level as the secondary air intakes in the bucket rim would be a good idea.

If there is smoke, should I give it more primary air or more secondary air?

I know that the TLUD can do better then this, because my small version in a quart can worked perfectly.

Attached are some pictures.

UPDATED TO ADD: I dumped out the stove and most of the fuel was not charred at all. So, does this mean not enough primary air?

More pics; adding shavings and paper as a top layer. (Too restrictive of air?) I should add that once it really got going, it burned OK, though not great. And to get it going I had to keep adding more cardboard on top, so the smoke kept flaring; half an hour of fiddling, half an hour of steady burn.

An odd design! The bricks are your jacket to channel secondary air?
Most designs I have seen include a lid with a chimney.
The secondary air either enters through holes in the base of the chimney,or just under the lid.
I have seen one design that is single can divided into thirds. That had fuel in the bottom third, and secondary air inlets at the junction between the top and middle thirds.
So,by comparison,not a lot of space between your fuel and your secondary air.
To start the burn without lighter fluid,alcohol grease or some other accelerant, I suggest....charcoal.
Hear me out. A charcoal starter chimney can make a nice bed of red hot coals,with just paper as tinder. You already have the charcoal....

I've run a TLUD stove with a similar configuration. I've used it to produce biochar. My primary intake holes were larger than yours, but I'm not sure if that makes the difference. I did use a little 91% alcohol as a starter. The stove would smoke initially the first minute, but then I put on a flame restricter lid and the smoking instantly stops. I made the flame restricter out of a flat piece of sheet metal (from the skin of an old wash machine). The diameter of the hole, placed in the middle of the metal plate, was 1/3 the diameter of the top of the stove. I was using a metal garbage pail to hold the fuel. With the flame restricter in place, it never smoked.

I could only get about 40 burns out of a garbage pail before I had to replace it. I eventually made a TLUD out of an old propane cylinder tank with a cast iron BBQ grill bottom, but still used a flame restricter. The cylinder has lasted a long time.

William;

Yes, the bricks are the secondary air channel. I had the stainless steel garbage can hanging around, but no larger can for the outer channel. But I did have a bunch of bricks . . . About the space between fuel and secondary air; probably not enough. Your idea about starting with charcoal is interesting; so would you just put down some paper, get it burning, and then add charcoal, followed by the starter cone? I was wondering about soaking the charcoal in alcohol to get things moving.

Su;

I think I didn't have enough primary air; see update below. Your flame restrictor sounds like a good idea, it would ensure that all the air and smoke is well mixed and concentrated. What metal were your garbage pails made of?

UPDATE: I dumped out the stove and most of the fuel was not charred at all. So, does this mean not enough primary air?

The charcoal chimney looks like this:
https://goo.gl/images/kxIypv

Paper and charcoal go in to be lit,once the coals are red hot they are poured into the grill,or in our case,the tour.

Not enough primary air is right.  Here's how we fix this:

1) Get yourself big metal cone.  A funnel that is bigger in diameter than the can will work just fine.  Just make sure you don't choke down air flow too much.

2) Get rid of the bricks around the outside, just use 3 on the ground to lift the burn can up.

3) You need a better starter than alcohol, it just flashes off.  I use paint thinner (cheapest solvent out there).  Splash a couple ounces on the top of the TLUD, let it soak in a couple minutes and light 'er up.

4) When the top is burning vigorously, invert the cone/funnel and set it on top.  Flames may shoot out the top for the first minute or so, but soon it will settle down to pouring out copious amounts of white smoke (indicating the exhaust is mostly water vapor).

Ambient temperature affects the length of the burn.  On cold days, it may take me 6 hours to process a 55 gal. drum of wood.  On warmer days, maybe it will be done in 2 or 3 hours.  I'm thinking since your burn chamber is not that tall, it will go fairly quickly.

A trick to see how your burn is progressing is to throw a little water on the outside of the burn can.  It will quickly evaporate above the flame front, but lower, where it has wood and rising combustion air on the inside, it will take longer to evaporate.

John;

Thanks for the advice!

About the funnel; would it work to just use the flame reducer plate that Su talked about? Or could the funnel be use just until the flame got going? One of my goals is to boil water over the flame; cooking and outside projects. A tall cone would make this difficult. Is the purpose of the cone to act as a chimney? Should it go inside or outside the secondary air holes? (In other words, should it be drawing air through them or not?) If I added the cone, would I still need to poke more holes in the bottom of the can, or do I need both? Or if I poked holes, would I still need the cone?

Why should I remove the bricks? Would I need to replace them with something else to channel/ heat the secondary air? I'm not sure if the picture showed this, but there are air gaps in the bottom of the brick tower.

A lot of tluds don't use a larger container to channel/preheat secondary air.
Most of those that do seem to use a lid that concentrates(funnels) the woodgas(the flame concentrate Su described) and a chimney to provide draft.
The funnel is like both of these together ,and it should draw air through the secondary air holes.

I would consider putting your tlud in a pit. This would lower the whole shebang, and free up the bricks for building a walls on three sides of the tlud. Bridge the top of those walls with a grill.
Clearly the tlud would need a few inches clearance all around and below it so air could enter.
Set the body of the tlud entirely underground and you will have 2-3' of space beneath the grill that can be used for chimney.

William Bronson wrote:
Most of those that do seem to use a lid that concentrates(funnels) the woodgas(the flame concentrate Su described) and a chimney to provide draft.
The funnel is like both of these together ,and it should draw air through the secondary air holes.

Yes.  For my 55-gallon drum TLUD, I use two coffee cans stacked vertically as a chimney.  There is a rough hole cut in the lid of the drum, and the cans don't sit tight on the lid, so secondary air is drawn in there.  You have more than enough secondary air slots cut at the top; what you need to do now is improve the draw of air.  Any chimney that cuts down the cross-sectional area is going to do that.  Even if you take a piece of sheet metal and fasten a crude cone where the exit at the top is maybe 1/3 to 1/4 the diameter of the base (where it sits on the TLUD).  With the cone resting on the rim of the TLUD, it will suck in secondary air as it rises up the funnel/chimney.  As for heating the secondary air, I'm doubtful that is much of a factor.

Unfortunately,  a chimney that makes the TLUD draw well is not the same as one that will effectively heat a pot sitting above it.  If you do put it in a pit, as William says, then you may have better control of the heat coming out of the top of it and be able to make use of it.  If you come across an arrangement that makes biochar at the same time that you are making good barbecue, then you've got a winner.

Thanks for all the feedback!

So, for my next burn, I doubled the number of primary air holes in the bottom of the barrel, put a flame concentrator on top of it, and put a big can for a stack on top of the hole in the concentrator. The concentrator was made from a piece of scrap MgO cement board that I had hanging around, since I don't have any sheet metal currently. The burn was a huge success. Beautiful clean flames gushing out of the can, and no smoke. Even at the end of the burn, the flames just died down; there still was no smoke. Everything in the can was evenly and thoroughly charred. The charcoal was easy to crush and didn't leave a greasy residue on my fingers, so it was well done. I used alcohol soaked wood shavings for lighting it, and I can see what John meant about flashing off too fast; I'll use mineral spirits next time.

The one problem was that the MgO board had disintegrated by the end of the hour burn; it held together till I tried to remove it, then crumbled. I need to get some sheet steel.

The next step is to build an oven fired by this stove, so that I can use all the heat as I generate biochar for my yard and farm. If you have any thoughts on that, let me know!

Here are some pictures. You can see the can and the MgO board down inside the bricks; they are a temporary wind screen until I can get a bigger barrel.

This is a J -tube rocket exhausting into a junked wall oven.

It occurs to me that a junk oven could be a great tlud.
Insulated,cheap and fire resistant,pop a hole in the top for a chimney and rig a valve to control primary air.
Stack your feedstock on the bottom rack,add fine mesh if needed,say for grasses or woodchips. I imagine the oven rolled on its back for loading.
Lighting the top of the feedstock evenly would be a challenge,but closing the oven door and lighting it via the chimney hole might work.

I have an oven I scored in order to build a rocket oven like the one in the diagram. It has a double skin, with insulation in between. Imagine if you removed the insulation and used that space for preheated secondary air.

I haven't taken apart a double oven yet,but it might be possible to build a tlud in the bottom oven and exhaust it into the top one.

I have been searching the literature for optimal chimney length but there seem to be no rules of thumb or ratios.

In a rocket stove, so much of the action seems to count on an insulated heat riser. Would tluds benefit from insulated  heat risers?

William, that is really  interesting. I was thinking more along the lines of a classic earth bread oven, but a scrapped oven would be easier. One potential problem; I was thinking of something with a high mass, so that it could be fired, the biochar unit removed, and then the food placed in the oven, through which the hot gasses had been rising during the burn. With a low mass scrapped oven this would not work.

Could I add a bunch of bricks to the bottom of the oven? Or could the food be cooked while the burn was going on? Would the waste gasses have any effect on the food?

I think I'm going to try out the oven. I actually have a dead wall oven. And I think that some heavy cast iron cookware, some to hold the food and some full of sand lower down, could provide the needed thermal mass, while lowering the air temperature. I'd need to be really sure the fuel was clean though, before cooking over it. And that none of the cans, etc. outgass anything.

Another question; could I melt the insulation etc. in the oven? I'd strip the electronics out of course. I wonder if the spot where the bulb goes in the back could be used for the exhaust pipe.

All this will be done outside, of course!

One potential use for residual heat after a burn could be drying food; or wood chips for the next TLUD burn!

Though I don't know yet how my TLUD will work with wood chips. I hope it works well with them, since cutting and splitting scrap wood to size for a burn is a pain.

I doubt the insulation will melt,but you could replace it with:
-Portland concrete. It may fail due to the heat,but it will still be encased,and thus still provide thermal mass.
-RapidSet Cement All.  A calcium aluminate cement, it will take the heat just fine. Mix with Perlite in a 1/7 ratio,add rock wool fibers to the water for extra toughness.
-Rock wool insulation.Good to 2000°F. Nuf' said.
-Dirt,rocks sand etc. It will shrink up under heat, but you can just add in more. This mix  could also be benefit from fibers and/or fluffy aggregate.

One more thing. I just bought a set 4 of stainless steel nesting stock pots at Harbour Freight ,for less than 5 bucks each.
Should prove durable and not off gas.

Hello William,

The rock wool insulation is a good idea; I have some leftover from building projects.

Are you planning to punch holes in the stock pots for a TLUD? Or are they for cooking in?

My next experiment with this, before the oven, is to load it with shredded cardboard. I'm worried about getting a giant and uncontrollable tower of flame. How can I damp down the burn without making it smokey?

The stock pots are for tluds. When I bought them my wife was concerned I was adding to our kitchen gear-
I am not sure my tlud plan made her feel any better😏

Confession time: I have only made one tlud so far, and the poor performance gas driven me to read and prepare obsessively for the next one.

For example, I believe choking down on the primary air will control your cardboard burn,but only from research,not experience.
Note, if the process is working as it should, the cardboard will convert to char,and then the char will burn. When the pyrolysis of the cardboard is complete and the char has begun to burn,the flames should turn from red to blue- or so they say. I always quenched mine too soon,and thus I am not a  first hand witness to the tale tell blue flame .😳

Your work has inspired me to push forward on my own mad schemes,so thank you for inspiring me to get back out of the armchair  and into the game!

Well, I will just have to try it and see then. I will cut down the primary air.

To shred the cardboard, I'm planning to fold a big piece multiple times, clamp it to a work bench with half an inch sticking over the edge, and then saw strips off. It will (hopefully!) be a lot easier then using a scissors or utility knife. I do have a paper shredder, but it makes heavy weather of a few sheets of paper, so it will be no help.