Mini Rocket with forced induction

[gadget]

So...I've always wanted to build a rocket mass heater and needed some warmth while I cut wood for a kitchen remodel outside under my patio this winter. I had some firebrick but did not want to cut it since this is just a one season build. Came up with an interesting core just from staking the brick.

I did not use standard flue pipe for the exhaust and I do not recommend doing this. Especially do not ever use the snap together vent tubing for a flue. It will open up like a zipper if there is a chimney fire. With that said, I ended up using some extra down spout for rain gutter that I had. It has a robust seam but IT IS NOT FLUE PIPE so don't do what I do. With that said the flue pipe is very small so I added a blower on the end of the exhaust.

It lights very easy with the blower and runs fine. It puts out an OK amount of heat, to be expected for its small size. I burn lots of cardboard and typically have about a gallon of ash after 3-5 hours of burn. It never clogs or stalls since the blower will just pull the ash through.

Barrel temps average 500-750F If I keep up on the feeding. Exhaust goes from 280F at the barrel to 180F at the blower. Cob takes about 4-5hrs before heat show up at the skin. My cob is not very good and has lots of cracks. Warmup time is very quick.

Dimension are not very consistent for a rocket mass heater but with the blower it does not matter as much. It does not run or light very well with out the blower.

It was a fun build. I'm not a big fan of the rocket mass heater feed tube but I can appreciate the simplicity and performance of the design. It has its uses but I don't like the constant feeding. 

[Orange]

I guess it would work also without blower. Do you tkink it is possbile to have a chimney fire if the chinmey temps are low? I've found out that creosote’s auto-ignition point is at 451F / 233 C.

I partly use this type:

[gadget]

Jan 19, 2019 4:33:36 GMT -8 Orange said:

I guess it would work also without blower. Do you tkink it is possbile to have a chimney fire if the chinmey temps are low? I've found out that creosote’s auto-ignition point is at 451F / 233 C.

I partly use this type:

It does not work without the blower running, I tried it tonight full temp with good wood and the draft dies once I stopped the blower. The flue pipe is to small and the blower is a major restriction. It did work with the tiny flue pipe before I added the blower but if there was any wind it would blow back. It was also very hard to start. Now with the blower installed, it will not work without it running.

Thats some interesting pipe, what is it used for?

On the creosote build up, if you build a rocket mass heater correctly and burn good wood in it, you won't have any creosote or very little to worry about. Many have proven this. And yes that is low enough temperature for creosote to condense.

[gadget]

I did some testing burning lots of cardboard. As you can imagine the ash loading is very high. I had so much ash in the burn tunnel it was easily 90-95% full after about 5 hours of cardboard. It was having some drafting issues even with the draft blower. I took the blower apart to swap motors a week later and found lots of ash in the blower and the exit flue pipe.



What I found is that burning cardboard, fuel needs to be added about twice as often as wood. I was adding about every 8 minutes - a small stack of 3x5" pieces of cardboard. I would poke a breathing hole for air every once in a while to help air flow through the burned out cardboard.

a rocket mass heater is not a good platform for burning lots of cardboard though I believe one could design a heater that would work. It would need a large ash trap. Maybe Peters idea for a cyclone filter but it would need to be big. A fuel magazine so lots of cardboard could be added at once. It would need an air intake at the feed end so the cardboard didn't burn up all at once.
Maybe even blower help with the draft.

Someday, I will finish my firelog press and try some pressed cardboard firelogs

tonight i'm testing veggie oil fuel

[ronyon]

The size of the fire box on a batch rocket is constrained because the tested ratios get the right air for complete, efficient and clean burn.
If you add a blower like this to a batch box rocket, you might be able to have huge firebox with a relatively small riser and chimney, but still achieve the desired burn.
This would be great for burning cardboard and the like, because it is less energy dense than wood.
My day-dream forced draft burner would start with junked electric or gas double oven.
I put a huge firebox in the top oven and turn the bottom oven into a bell.
Yeah, I would go against gravity, for the sake of my back!

[gadget]

I can confirm, there seems to be less heat output with cardboard but it does burn clean.

Your converted oven with a lower bell would definitely work with a blower. I like the idea of repurposing an oven, should work good if it was lined well with ceramic insulation.

[gadget]

I wanted to add a second bell to see if I could capture more heat. I got a steel drum from work and filled it full of brake rotors. Inlet temp gets to about 300F and exit gets to about 120F after 4 hours. Top of the barrel was 200F and the sides went from 130F at the top down to about 50F at the bottom. I'm going to check it in the morning and see if its still warm. The exit pipe extends down to about 1/3 from the bottom. I wanted it lower but it just worked out easier where it ended up.

I was surprised how much more heat there was with this second bell. This is under a patio cover that is enclosed by a green house. Outside is about 30F and It brought the not fully insulated greenhouse up to about 50F, about a 5 degree improvement.

I'm thinking about taking off the first barrel and adding some tubing for heating some water. I have 6 - 55gallon barrels I can run warm water through.

[ronyon]

So cool!
An inspiring build.

I know you stress NOT to use the downspout like you do, but I can't help thinking what a great stealth chimney it could be!
Right up the side of the house,totally fitting in!

But could we be certain the exhaust is clean and not too hot?

How about this:
Fill the drum two thirds full with water.
Put 90 degree elbows on the exhaust and input, pointing opposite directions along the inside of the drum.
Like dust collector with water.
I bet you will capture a lot of the crap from burning cardboard before it ever reaches the blower, as it sounds the water before exiting the drum.
I wonder if a mister or fountain inside would further remove particulates,or would we ruin the blower with moisture?

It occurres to me that at low enough tempatures, shop vacs and bathroom fans be done viable blowers, and the can endure moisture.

Alternatively, if you brought your exhaust in to the side of the bell drum, you could stack a drum of water ontop of it.

With the blower you be able to fill the drum with marbles or steel wool or gravel, and pull the exhaust right through it, a giant filter that also captures heat.

[gadget]

Most down spout is a folded seem that can be pulled apart and this will give out if it gets to hot like in a chimney fire. I did however find some down pipe that had a small crimp every 1/4" on the seem that was stronger. Still not as good as real stove pipe but for this test rocket its fine.I believe stove pipe uses stainless steel rivets but I not 100% certain. Rain gutter pipe really is undersized even with a blower but if someone wanted to heat a very small place maybe it would work. With the blower, I'm probably getting the increase similar to a 4" pipe. Also, the blower allows for easy starting and the extra bell would not work without the blower.

The squirrel gauge blower I am using is typical for moving air through restrictions like ducting. It is more efficient at this then a blade style fan. Box(blade) fans do not work good pushing or pulling through restriction. A shop vac might work but it will probably use allot more power and be very noisy. I would use a duct blower since they are very efficient at what they do. A bathroom fan would also not be well suited since it is typically an open blade style fan.

Some of the newer furnaces use a blower similar to some thing like a shop vac style wheel but are very quiet. They are typically plastic and are also very efficient and move tons of air.

Furnace induction blowers are designed to see some heat, especially the metal ones. They are easy to find for next to nothing and use little power. This is your best choice.

[Orange]

Jan 20, 2019 19:39:07 GMT -8 gadget said:

Thats some interesting pipe, what is it used for?

On the creosote build up, if you build a rocket mass heater correctly and burn good wood in it, you won't have any creosote or very little to worry about. Many have proven this. And yes that is low enough temperature for creosote to condense.

it's a spiral galvanized vent pipe, not ideal but does the job.

[gadget]

So I checked the second barrel thats full of metal the next morning at it was slightly warmer then ambient. Im guessing it probably put out some heat for a couple of hours. Next I am going to pull off the first barrel and add a coil of aluminum tubing and try heating some water. I have 330 gallons of water in the green house in 6 55gallon drums. The patio is connected to the greenhouse. I have not heard of anyone using aluminum tubing before so we shall see what happens. If I can get those barrels up to say 100F maybe I can start using this greenhouse this winter.

[gadget]

My oh my....I decided I better tear the barrel off and take a look for buildup. I wanted to install some tubing for heating hot water so I took the barrel off yesterday and oh boy lots of build up.

I have been experimenting with burning vegetable oil and was concerned there may be some creosote deposits. I had some over fueling trying different was of getting the oil to burn well. There was a couple of over fueling episodes with solid black smoke coming out the exhaust. I was concerned the fire department might show up a couple of times. Anyway found lots of dry soot on the outside of the riser and a ton of ash from burning cardboard. What was more interesting was the normal water drip I get from the exit pipe near the blower changed from clear to a golden dark brown color. I have no doubt that continue use of veggie oil would cause a creosote build up condition in the system. 

Took the barrel off and found lots of carbon stuck to the side of the riser. Its to hot for the tars to collect with the carbon but I am sure further down the line where it is cooler there is creosote  formed. Since I have stopped running veggie oil, the drips of water from the exit flue has mostly cleared up.

It is my conclusion that rocket mass heaters are not suitable for burning oil, at least not without an atomizer in front of the burn tunnel. There just is not enough mixing and more importantly, not enough residence time in a rocket mass heater for oil. Plenty of heat and air but not enough time or mixing.



You can see the excessive buildup from burning veggie oil on the side and all that ash

Very dry soot, No tars collecting due temp of bricks



I also took a pic of the ash build up in the feed tube after 5+ hours of burning wood and cardboard together. There was barely a path for the airflow but it kept running along. The blower tries to keep a small path cleared for airflow. Since I have added the second barrel bell and changed motors on the blower, it does not draw as hard as before but it still works. This system could use a stronger blower. There was also lots of hot, unburned coal covered in ash the next morning. The large amounts of ash from the cardboard really clogs things up quick.

95% blocked. Amazingly it still made heat and worked. Still good steam out the exhaust


Bottom of the riser about 80-90% blocked

[Orange]

hey, but you don't have any insulation around firebox and riser?

[gadget]

Jan 30, 2019 9:17:57 GMT -8 Orange said:

hey, but you don't have any insulation around firebox and riser?

No insulation anywhere. I was almost tempted to wrap the riser while I had the barrel off but since this thing is getting torn down in a few months why use up insulation.

[Orange]

would be interesting to see if there would be so much carbon and ash if the whole thing was insulated.