catalytic converter

Hi,   Been doing a lot of research about Rocket Stoves to heat a large shop.  Please bear with me.

Seems to me the difference between a Rocket stove and Rocket Mass is Rocket for instant heat and Mass is for longer heat release?

catalytic converter:  appears a rocket stove is just a modified wood stove with a massive catalytic converter that, in theory, will not plug or burn out?
Wood Stove catalytic converter will melt down if fired over 500F  where as fire brick will take about 2000 to 3000F.

Rocket stove vs wood:
Wood stove dissipate heat directly from the wood fire where as a Rocket stove  dissipates heat after fire / smoke has gone thru the heat riser (catalytic converter)?  
Heat dissipates off the 55 gallon drum.  I don't like that description, sounds cheap, Going to call it the Primary Heat Exchanger.
Primary heat exchanger can be made from lot of things, 55 gallon drum, air tank, fuel tank, etc. Just has to be metal?

From what I read, the top of Primary heat exchanger should be about 2" above the Heat Riser.  Seems like a thin barrel that close to the heat riser would burn thru?  Basically the sheet metal is getting hit with about +1000F steam of air.
Should a person mount a fire brick to the top inside of the Primary Heat Exchanger to take the brunt of the heat to spread out the the hot gases?

Flue gas should be about 110F to 140F  seems to be general consensus.
How do you control that?  Seems only way to control flue temperature would be to control how  much wood you feed at a time?

Also found something called a Batch Rocket Stove.
Which is what I'm leaning towards.
To me is a modified wood stove using the catalytic converter properties of the heat riser and Primary Heat Exchanger

Granted this takes away from the basic simple non power rocket stove but.....
lets just say you are building the Batch Rocket Stove for maximum heat recover, minimum wood usage. ( which would be my case)
Inflation driving cost of everything thru roof.   NW Montana cord of fir/ lodge pole is running $275 to $300 a cord. Well, they call a pickup load a cord.  Too old to cut my own.

Add a Secondary heat exchanger that has heat pipes running thru it.
Add a variable frequency drive fan blowing air thru the Secondary heat exchanger to maintain about 125F flue temperature.
Install a type K probe into flue.
Would need a Raspberry PI to control VFD.
Would greatly increase the complexity but you could maintain max heat recovery.
Being you have a Raspberry PI, might as well put a type K temperature probe in the heat riser ( inside a heat brick) Use that to control damper for secondary air to riser. Maintain a set temperature in fire brick
Could also control primary air damper to control main burn/ gassification of wood.
Being a Batch Rocket Stove, you could load it up and would burn overnight or at least an extended period of time with no one there.
Monitor and add some safety control.   text you if something goes out of wack.  Some basic HMI to your phone over wifi

The Rocket stove just needed some Rocket Science... Ar ar ar

$64,000 question.  Would it be worth it?
Cost at least $1000 to add the PI and VFD

Thoughts?

Good Morning Neighbor;
Welcome to the wonderful world of rocket science!
Really sucks what they think a load of shitty wood is worth during winter.
I buy mine by the long log load.  
I still have to cut it and move it to the wood sheds but I can do this right at home on my schedule.

Now on to your questions.
I'll start by giving you my opinion of your final question.
No, not worth the money to set up that kind of testing.
If you had all the equipment on hand, it would be fun to see what numbers you came up with.
Buying that equipment is very cost prohibitive.
The innovators have done extensive testing and fine-tuned their designs to run as cleanly and efficiently as possible while storing that heat in a mass.

Now let's talk about rocket stoves.  Boy scouts build them, ice fishermen build them, and their most handy use is for cooking/ boiling water.
Rocket mass heaters are for storing and slow release of heat.

A rocket stove/RMH riser is only similar to a catalytic in temperature.  
It is a short wide open insulated chimney where the temperatures run from 1800F to over 2000F.
These temps like in a catalytic, burn the particulates resulting in very little ash.
Unlike a catalytic, the RMH sends its heat to a storage area to harvest as much as possible before allowing it to leave your nice warm home.
Ideally, the exhaust chimney temps are 140F minimum,  I like mine between 150-180F.
Below 140F condensation can become a problem.

Next is the barrel or the "primary heat exchanger" as you named it.
It is commonly made with metal to enjoy instant radiant heat before sending that heat into a mass.
It does not need to be metal at all.  Brick bells are becoming very common in rmh construction.
A steel plate is sometimes added to have access to the riser and to provide quick radiant heat.

J-tube RMH needs 3" minimum between the riser and lid.  
My 8" J-Tube when up to full burn had an 8" glowing orange spot that was right at 1100F. That same barrel is still in use today.
A batch box ideally will have 12" or more.

Controlling exhaust temp is easier than you think.
An RMH burns wide open,  all the time,  the idea is you only burn a few fires and then just enjoy the heat with no fire.
The only time you close the primary intake on a batch box is after it is nothing but coals.
A J-Tube can have the feed tube partially blocked with firebricks to assist with getting a roaring fire or to prevent smoke back.
Then totally closed after the fire is out to prevent a draft from pulling the heat out of your mass.

Welcome to Permies Allen!
Our conventional wood fired range cooker had a catalyst to ensure clean burn - basically as far as I can tell it was something (a bit of metal I think) that created a hot spot in the exhaust to help the burn. Well it burnt out - the catalyst that is. Completely gone in about 5 years use. My hubby is a combustion engineer and modified the firebox slightly to introduce some swirling to improve the burn and we certainly get no visible smoke after the fire is running hot, but nothing like as clean as a RMH (I want!). The riser does create that 'catalyst' hot spot and is made of refractory materials which should last a long time. There's a fair amount of info on this, some materials last longer than others so do your research.
The good thing about RMH is that you can play with them yourself (build them, mend them, modify them), but I understand it's better to start with a well tested design rather than doing too much different initially. I like the simplicity - no moving parts, no electric controls, and am looking forwards to building my first one.

Everything I researched so far points to the Rocket stove being very efficient.

First I'll have to get a Batch rocket stove set up.
Then work on a secondary barrel with heat pipes.
Being for shop, not to concerned about mass.  Just want efficient instant heat without having to burn a whole forest.


I do have some spare VFD's and 3 phase 1/2 HP motors ( I have some odd hobbies)
Should have a Raspberry PI sitting around too.
To play with fan speed and flue temp.

That stuff has all doubled in price is 2022.
Electronic are almost impossible to get.  Order some wifi stuff 8 months ago and still in back order.
May have to switch brands and models.

I find it easier to research and ask question, plan for future expansion before start cutting and welding.

thomas rubino wrote:Good Morning Neighbor;
Snip

Now on to your questions.
I'll start by giving you my opinion of your final question.
No, not worth the money to set up that kind of testing.
If you had all the equipment on hand, it would be fun to see what numbers you came up with.
Buying that equipment is very cost prohibitive.
The innovators have done extensive testing and fine-tuned their designs to run as cleanly and efficiently as possible while storing that heat in a mass.

Snip

I don't know a lot about RMH, but our woodstove has a catalytic converter and it's not as user-friendly as I expected.  It takes a lot of fussing to get it to burn within the right range - and that range is very small.  Getting that secondary burn is tricky and there is so much to do around the farm, I don't want to be fussing with the woodstove every half hour.  Most of the others in the neighbourhood who have this kind of stove also have the same problem.  

That said, it does produce less ick on the chimney than a regular wood stove or fireplace.  

So yes, Catalytic converter woodstoves are more efficient than a brick fireplace in real-world conditions.  But don't expect to be able to live life and get anywhere near the kind of efficiency they do out of it in the test settings.  

I know nothing about catalytic converters.

I just want to give you some of my thoughts.

heat your home with 80% to 90% less wood
exhaust is nearly pure steam and CO2 (a little smoke at the beginning)
the heat from one fire can last for days
you can build one in a day or two
folks have built them spending less than $20
less CO2 than natural gas or electric heat
if you buy the wood, it costs less to operate than natural gas

https://richsoil.com/rocket-stove-mass-heater.jsp

I understand there are several designs, though to me a simple explanation is that a rocket stove is an rmh without the mass.

Here are some threads that you or others might find of interest:

https://permies.com/t/208938/Batch-Channel-Pros-Cons

https://permies.com/t/206644/Batch-rocket-mm-bell-Project

https://permies.com/t/191801/Building-Ultimate-Rocket-Mass-Heater

Hi Allen;
As you are wanting to heat a shop here is a rebuild on my 7" batch box shop stove.
Double barrels for instant radiant heat and a large brick bell to hold that heat when the shop doors are opened to move equipment.
https://permies.com/t/181421/Batch-box-rebuild

Welcome Allen,

Allen Jangula wrote:
- - - -
Being a Batch Rocket Stove, you could load it up and would burn overnight or at least an extended period of time with no one there.

I just want to say this is conventional wood stove thinking.  A RMH must run wide open for a fast hot (1500°F) fire to make that rocket after burner work.  If you choke the air off the rocket cools and you don't have the smoke burning in the rocket.  A large 8" batch rocket only burns about an hour on a full load of wood.  Example shop heater.
https://m.youtube.com/watch?v=1hNgT_PvEd8
Tom

FWIW, many, if not most, VFDs have built in inputs and control loops that could take an input from a temperature sensor and control to a setpoint.