Kang Bed-stove: conversion of Hunter Silverfire TLUD Inverted Downdraft heater-stove

So the key insight I realized - duh - is I needed the stove below the actual "ground" heater - the Kang bed-stove heater system. This is the only way I can get "negative pressure." As you can see from putting the photos together - I am missing a 90 degree elbow that busted on me - actually I have a 4 inch one that might work - but anyway. I tried it with a straight shot and there was hardly any smoke leaking - unlike all my previous designs (all 2 of them before now).

So the above design then, instead of just a one straight duct pipe, has two pipes connected by the 90 degree elbow - so the exhaust eventually comes back out by the stove. That way I have two hitting pipes in the ground - that will be into an insulated tent-A frame. So with just the insulation it will be 50 degrees - under 3 feet of leaves. Then with the gasifier stove that will store the heat exhaust into the clay.

Gasifier Stove aka TLUD aka Chinese Burner is secret of alchemy!

So the other improvement - as I read up on this subject into the night - is you want to make sure that the "crimping" end of the duct pipe is facing up and away from the chimney. The main reason for this is because the smoke exhaust heat is being "pushed" up and away and so it's not going to leak nearly as much if it is push into the other pipe. So I had not done that when I tried it out - and as I said there was still much less leaking, due to the negative pressure. So with that crimping improvement then it should be able to handle being turned around again.

That way I can slow the exhaust down enough to get all the heat out of the exhaust. But at the same time I will not have any fire hazard - unless I get creosote build up but I can use my chimney sweep to clean the duct pipe. I'll have to take it out of the clay - but since the smoke is supposed to get very hot if the wood is dry, from the gasifier, then there should be less creosote. Also since the pipe is insulated into the clay - then it cools down less so less creosote.

O.K. so then to make sure I have no leaks - I will also get aluminum duct tape. Now normally I would not aluminum but since it is exhaust it is not as hot and its designed for hot temps. Also normally you don't want galvanized duct pipe - but since it is in the clay - then any zinc oxide fumes will get absorbed. Only with welding does the fire get hot enough to achieve the "boiling" point of zinc oxide - other wise you get melting of zinc but then it just oxidizes again back into a solid very quickly. So the Rocket Mass people say they just "burn off" the zinc by doing a couple outside burns and also again that the clay would absorb any zinc fumes.

But carbon monoxide leakage is still a big concern - despite these three precautions I am taking - of the negative pressure, the crimping on the inside of the pipes and the aluminum duct tape. So then I will get a battery operated carbon monoxide detector just to be safe, as a precaution. But the downward draft secret burns off the carbon monoxide:

 Combustion from the top creates a gasification zone, with the gas escaping downwards through ports located at the base of the burner chamber. The gas mixes with additional incoming air to provide a secondary burn. Most of the CO produced by gasification is oxidized to CO₂ in the secondary combustion cycle; therefore, gasification stoves carry lower health risks than conventional cooking fires.

But on the plus side - the duct pipes get hot from the heat and that is the whole point - to leverage the heat of the exhaust and use all that heat. As for the actual heat from the stove - I will have the stove in my water hole - and the point is then to heat the water hole, to make sure my water source does not freeze in the winter. So then also the stove will be outside of the insulated hut, which then means I don't have to worry about carbon monoxide from the stove itself smoking.

And so this is a dramatically different design than what I had considered before. But I did not really totally understand the TLUD stove mechanism. I kept studying it and realized in fact this TLUD design - pronounced T-LUD - is actually considered a key strategy for "sustainable" in "developing" countries. This T-LUD is also called a Chinese Burner but it was also called the "Inverted Down Draft" stove.

Now personally I much prefer the name Inverted Down Draft stove. Because, for example, I had made biochar in that big pit - you can see in the above photo - and the idea if you light it from above, like a TLUD - but then the oxygen gets pulled from below as the fire burns down - and so this cuts off the oxygen of the bottom wood, so that it remains a charcoal, burning without oxygen.

So it would appear that is how the TLUD works but now that is not quite it. So because you have the primary air on the bottom of the stove - in the Hunter its in the front of the stove, but also the back of the stove - and this pulls in the oxygen from below and that is the only source of oxygen for the wood's primary oxidation burn, since the wood has to burn in the down draft direction.

So even if you light a pile of wood from above it would still pull its oxygen from above but by then covering the top of the stove of the TLUD, that forces the oxygen to be relied on from below - hence the Inverted Down Draft name is more accurate. But they didn't stick with the name since it's more difficult to explain.

Who's they? Dr. TLUD. So this design won some award around 10 years ago and since then has taken off in being promoted around the world. But in reality it's called a Chinese Burner - the Chinese were using this gasification secret for who knows how long?

I tried to look that up. We know that Kang Bed-stoves go back to at least 1000 BCE. I am quite interested because to bring the fire down - as an "inversion" - is the secret of alchemy!

So then the carbon monoxide gets separated from the primary oxidation since the fire is now below the charcoal that is above, as the oxygen source is from the bottom of the stove.

This enables a much cleaner burn because then the oxygen from below is also rerouted up the side of the stove to come out the top as hot oxygen that ignites the carbon monoxide.

So then when the Hunter is working properly you see a blue flame at the "secondary" burner that is an inch and half down into the stove.

 Our stove lets air flow from in at the bottom and out at the top, which is either an inverted downdraft or an updraft, depending on how fancy you want to sound. But the fuel still burns from the top down, unlike the action in other wood stoves.

So this person is stating that TLUD and inverted downdraft mean the same thing.  Nope. Because the key concept of the downward draft is that the fire is being pulled down since the only oxygen source is from below.

You don't believe me?

Go to the source "inventor" of the terminology:

While technically accurate, the concept of an inverted downdraft was difficult to explain.

 Indeed it is! You want people to understand how the stove works - so use the accurate terminology and then allow people to realize that the concept is actually quite unique.

Just lighting a pile of wood from above is not the same as an inverted downward draft.

Therefore, the ability to add additional fuel while the stove is burning does not automatically mean that it is operating in the TLUD mode. What is happening to the newly input wood is that it is being pyrolyzed by the heat that is coming upward.

So in other words - just because you have an "updraft" does not mean it's an "inverted down draft"!!

 Therefore, it is not the same as the physical-chemical processes in the downward migrating pyrolysis front.

So then T-LUD to be "accurate" needs a qualifying additional phase:

  a process of “”top-lit updraft with migrating pyrolysis front”,

 So it's being pulled down because the oxygen is coming up from below, not from above.

So then there are lots of academic physics analysis of this secret of gasification burning - why? Because it is much more efficient in producing heat without any pollution - so you get more heat and less pollution. A great deal. Again the Chinese knew this secret a long time ago - thousands of years ago.

Now think about it - Shen is Fire and the whole key of alchemy is to get the Shen below the water - to create steam as qi energy. The Steam in this case is the highly charged gasification fumes that are then burned off from secondary oxygen from below.

So you put the Shen fire below the charcoal that is emitting the carbon monoxide fumes - and this separates the secondary burning of the fumes from the primary burning of the oxidation in the flame of the fire.