Making Large Rocket Incinerator...could use some he!p

Hello,
This is my first post here. I live off grid in Hawaii and I am currently very motivated to make a large rocket incinerator . I attached a rough basic drawing. I am partially inspired by the one at the
SECMOL campus. ( https://www.linkedin.com/pulse/low-cost-high-temperature-waste-disposal-incinerator-prototype-rohit )

Mine is a bit different. I couldn't find the size of one at SECMOL but I think it seems a bit smaller than my planned one.

I have an idea they may simp!ify things . It does not have a closed trash opening with a separate air opening. The trash and air enter from the same vertical end . I have a stainless drum from a washing machine with extra holes in the end and I want to use that as a"fire grate" and to put the trash in. Those drums already make cleaner fires on their own because so much air gets in.

So I was thinking the feed chamber could be a few inches larger in diameter than the stainless drum. That would allow a huge air space around the drum with no trash clogging the airway. If done right, It seems to me this would eliminate the need for secondary air pipes like the SECMOL one needed to burn cleanly. It would also not need a cover over the burn chamber( except maybe while starting it or when it cools.)

I have many porous volcanic rock here to build it with of all sizes. Im not sure yet the best way to make it. I was thinking about making forms with rolls of chicken wire to help lay the stone around to make if easier to make uniform. I read commercial refractory mortar is probably my best bet for mortar, but I wanted ask people here since I do not have much experience making these. Then to make it insulated and reflect heat back, I am planning on putting on a coating of waterglass mixed with some perlite. Or is there better ways?

I just am not sure about the best dimensions. I read about the 1:2:3 general rule, but I  cannot seem to find info on the comparative diameter of the feed,  burn chamber, and riser. I have been assuming they are best being the same diameter, but is that rigbt?
I have people say " its not rocket science" but when I'm making some huge labor intensive incinerator, I dont want to guess at things. There must be an ideal size of the burn chamber and riser for this application. An incinerator does not need to conserve fuel, but just the opposite. And it needs to burn hot and clean. The rise is 14 feet tall, so that's the biggest challenge. I was thinking about just using a few of stove pipes side by side.
Should their square inch area be the same as the area of the horizontal burn chamber?
I don't understand what happens if its smaller ( like if I used just one or two stovepipes). Is that really bad? Or could it be better if it slows things down so the exhaust gases get to sit there a bit longer and get hotter and burn cleaner ( as long as it does not restrict oxygen too much)?

My stainless steel washing drum is 22" in diameter and 14" tall. So I was thinking the feed tube would be about 28" inner diameter. That would allow a 3 " wide gap all around the drum for airflow. That's just a guess though. I know there is a " best" air to fuel area ratio for the inlet. I dont think extra air injector pipes are needed if enough air gets in. I know the Demontfort incinerators have a secondary burn chamber that gets all the 02 it needs just from the intake, so I know it is possible.

If anyone could help me with the size if the riser and horizontal burn chamber, it would be much appreciated.

I would really like to know the opinion of people more experienced in this area even if they think its not a good idea.

Aloha
Pete

Hi Pete,
Welcome to Permies!

That is one huge J-Tube design you want to create.
I can tell you the dimensions for an 8" J-Tube, and you can enlarge them to suit your needs.
The feed tube is 8" x 8" and traditionally is 16" deep
The Burn tunnel is 8" x 8" and has a roof length of 12" or less.
The riser is 8" and up to 48" tall.

The feed tube and burn tunnel should have the same diameter; the riser can be larger if necessary.

That is a gigantic J-tube! The dimensions generally scale proportionally, though at such sizes, I don't know if anybody really knows how it will perform. As there is a lower limit around 4" where the combustion to surface area ratio causes excessive losses and reduced temperatures, there may also be an effect at much larger sizes where temperatures get so high that you approach blast furnace conditions, with temperatures far above 2000 F. I would absolutely expect even stainless steel to be degraded quickly, and perhaps even melt.

You will need to use only refractory materials in your core. I don't know how your lava rock behaves, though I suspect it will start melting by 2000 F. Also, temperatures around 2500 F or so cause nitrogen to burn, creating NO2 and similar compounds which are harmful. You really don't want temperatures much over 2000 F. The highest grade firebrick I know of is rated for 2600 F.

Generally, the feed tube is the lowest temperature zone, with the later burn tunnel and lower riser the hottest. I am not sure how air velocity through the core will scale; I don't think it will be fully linear, as in three times faster than in an 8" J-tube. Thus, there may not be an advantage in making a 14' tall riser aside from the chimney draft effect. I don't think the horizontal burn tunnel needs to be fully twice as long as the feed depth. 28" diameter as you show is so huge that I think you would need industrial engineering and materials to construct and operate it safely. Even 12 to 16" square would have a very large capacity and high temperatures for incinerating.

What kinds of material do you want to incinerate? What size is the largest thing you would need to put in? What volume per day would you be burning?

For the riser, it needs to be one single cross section, not split up, as that would introduce more friction and slow the system.

Rather than trying to hold the trash in a drum, I think it would work better to make a firebrick "grate" of closely spaced fins standing up some from the floor, with the slots following the airflow streamlines so they get swept out by the draft. What would be the minimum common size of items in the load? Spacing to hold most of those up would allow good flow around the load. Fins/slots running down the sides of the feed might work well to get airflow around the load without dead spots.

On studying the SECMOL incinerator article, I note that is only around maybe 10" diameter (hard to tell for sure). It achieved up to 2000 F (1100 C), with a rather crude construction. Note that the riser is entirely ceramic fiber, and the base is clay bricks which will get fired nicely at the temperatures they are achieving.

Do you have a good quantity of wood or other easily combustible material to sustain the incineration of more problematic or erratic materials? You would want a good clean hot burn going before introducing plastics.

I'm wondering if some controlled water injection would be a viable way of keeping the combustion temps in the "safe zone" on a monster like this. There are gasifiers and pyrolysis technologies that require the feedstock to have a high moisture content and they burn efficiently and super clean. The one that I'm most familiar with has stack gas temps peaking at about 1000 C.