Instructables

Gravity fed pellet burner

Picture of Gravity fed pellet burner
Hi, 

This is my gravity fed pellet burner.

The air intake and the feeding rate can be adjusted depending on the intensity of heat needed.

Set to the minimum feeding rate,  i get over 8 hrs of heat with a 40 pound bag of wood pellets.

Together the rocket stove and the burner work better then i expected,  

Wood pellet are cheap and easy to find.  

Since wood pellets are made from recycled wood, i guess this is somme kind of green way to heat my garage..


 
 
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Step 1: The perforated plate is the key to success

- Pellets will fall on the perforated plate, slide down and form a pile. Fire wil waken the pile and make it crash.  This will allow other pellets to fall into the burner.  This process will continue as long as there are pellets in the container.

- The angle of the perforated plate is about 45 degres.  The holes act in two ways, they allow air to feed the fire and hold the pellets as they fall.  After a few minutes of burning the plate is red hot and every pellet that comes in contact with it quickly ignite.   

- The space between the plate and the interior side of the square tube il about 1/4 inche so air can get in at all time. 

You  can see it work there:

 http://www.youtube.com/watch?v=rEosHNLZJek&feature=g-upl&context=G2e8c2daAUAAAAAAAAAA

This burner could be install on different kind of heat exchanger device, it could just be an extension of the square tube ending to a chimney.  



Any questions???


Step 2: New burner...

This is the new burner i made.  Bigger holes and less steal.  This model provides a better airflow... 

Step 3: Video

Made this video on how to ignite the pellet burner... 

Cheers!!

https://www.youtube.com/watch?v=jpNxeTdrGXE&feature=g-crec-u
Finnish-guy8 months ago
(removed by author or community request)
Removed my design pictures and related comments. In my opinion, the modifications to the original design I shared here, were too close to some commercial solutions. I found this after I released my comments here.
Seniortrader (author)  Finnish-guy8 months ago
your design is very interesting, it's the answer to the ash problem. Another problem will occur as your burner will work for hours. The pellet intake to the burner is a possible path for the flames. When there is not enough pellets, air can pass trough and the flames will then go both ways, in the heat exchanger and in up in the pellet container. I'm working on a pellet valve design witch will block the pellet intake when the pellet level get to low. Tank you for shearing your design every visitors on this page will apreaciate
cube1229 months ago
Im Finninsh guy nr.2, and im allso building tentstove (sorry my english) i had problems with you burner design, because i think i made it too tight (ari dont pass anywhere else ), pellets bocked "down air intake that size is abut 1cm" and result was great smoke and unburned pellets. Next i make stop vertically longer that pellets stay on that (allso drilled), and cut upper side on the stop about 5mm so air can go over the stop.
I'm using 8mm pellets and 8mm holes 100x100 tube

When i looked your design it's not so tight so air can get sides
Seniortrader (author)  cube1229 months ago
Hi, be sure to create an air flow through the system by heating the chimney before lighting the wood pellets. I used a propane torch. Simply heat the air inside the chimney to create this stream of air. The burner must receive as much air as possible, adjusting the intensity of the flame is done by adjusting the amount of pellets entering the burner. With some pictures i could help you more! Cheers!
Igniting is no problem... I ment that afther while about 1hour when the holes is blocked by ash and air can't get thru "stop" and my case it can't get sides either.
I think your system works because "stop" is very loose and air can get sides and over" im not sure but i find out today when i make modifications...
ficko609 months ago
Hi,
i would like to make such a stove. But i have a few questions. First, the little holes in the plate (through which the pellet falls), how wide are they (in mm), and how large are the pellets? Also the burner (square tube) where the pellet fall in through the perforated plate, is this burner deep in the chimney and if yes, how deep? What are the dimensions of the burner? Is the burner conected to any tubes inside the chimney, if yes to which tube?
And also is there anything inside the chimney or is it empty? Does the chimney have any isolation inside on the wallas?

It would be great if i could ask you anything else if i need help. Thank you very much.

Best regards,
M.T.
Seniortrader (author)  ficko609 months ago
Hi, i think most of your questions could find answers on my second instructable the rocket stove mass heater witch is more like a rocket stove without much mass. If you have any questions after viewing this i will be please to help you!

Cheers! ST
Hi,

I tried a couple of different stops and I came into same conclusion as you. If the stop is open enough not to form too much ash on the plate, it gives only marginal help during the ignition phase. After about 30 minutes of operation, the stop seems to lose its purpose as you state.

First I used too small diameter for the feeder outlet. That made the feeding unreliable and too pulse-like, which also made the rolling worse. It seems the minimum diameter for reliable feeding is about 57mm with D8mm pellets. That results about 3lbs / h pellet consumption without any air block at the air intake.

Your design just work as it is. It could not be any simpler and still it has all what is needed.

Sure I'll send some pictures once I figure out how to upload them here.
I made a direct copy of your design, and I have to say I'm positively surprised how well it works! So far I have made about ten trial burns with different settings. The movable 45deg angle plate assy seems to be functioning well for adjusting the pellet feeding. I used constant pellet volume, and so far I have been able to variate the burning time between 45mins and 2 hours.

Only disadvantage in the design I can see is the fact that at least in my unit, the pellets seem to roll quite far away from the plate towards the exhaust. Those pellets are not probably burning optimally. Have you considered / tried to make some kind of stopper to the lower edge of the perforated plate to prevent that?

My intention is to integrate the burner to a rocket stove and use it for heating up my 12-person Swedish army tent (In Finland you can get those tents relatively cheap nowadays). In order to make as light construction as possible, I want to leave the mass around the central-pipe away . Does anyone have any opinion does that cause any problems?
Seniortrader (author)  Finnish-guy1 year ago
Hi Finnish-guy,

Glad you like the design! I thought about adding a stop but I immediately had a problem with the ash.

After some time of operation, the ash that accumulates at the bottom of the burner will act as a stop and it will become so hot in there that the pellets that have rolled foreword will burn quickly ..

Youre idea of using the burner in a rocket stove is the main reason why i did it that way. The only thing you have to care about is that this burner will work fine only if the air draft is good enough.

I would realy like to see some pics of that stove you will build.

Cheers!!!
Seniortrader (author) 1 year ago
Hy Badjo2,

It will work fine with any solid fuel that will act like wood pellet. It has to be able to flow down from the tank to the burner and form a pile. Corn could be a good fuel. I would like it very much if you could post your prototype even if it does not past the test... i'm working on a new desing to..

Cheers!
Badjo21 year ago
+++GREAT JOB+++Perfect 'Add-on"  for many Rocket mass heaters or stoves. Just the airflow gate - cut two 3.2mm (thickness of cutting disc) equal slots on the vertical sides,+-5mm from the edge and insert 3mm plate. Sliding the plate in or out regulates the airflow very fine and you do NOT need to "hold" it in position. Did you try using anything different then wood pallets.  At the moment I am working on "Weld free" 3 pieces "Rocket".- BBQ,oven and stove. I shall post all details as soon as it past the tests.
Cheers 
      Victor
JasonInSD1 year ago
Nice work.I built a similar RMH stove a few years ago. In place of your ramp, I had a wedge shapes stainless steel mesh that the pellets would drop onto. In a 4 car insulated garage, I was hard pressed to burn 40lbs in a 10-14 hr burn. I did not regulate pellets, only the air from below. I am currently working on a smaller version that hopefully won't overheat the space as much.
Seniortrader (author)  JasonInSD1 year ago
I think the only way to adjust the heat with pellet heating is by ajusting the flow of pellets in the burner. The airflow must be constent and sufficient to obtain the most complete combustion possible. Hope to see pics of your new stove soon!!

Cheers!
Atar1 year ago
I am planning to build a rocket stove mass heater and this looks like an amazing invention to feed your RMH. The only thing is, I would like to have a bit bigger burn chamber for when I am not using pellets. I saw in your other instructable that you basically use the same diameter square 'pipe' but this is a bit small for my liking. All the rest off it seems amazingly well designed! And I like the fact I could get back into welding again, no need for firebricks. Just weld it!

My question is: would it be possible to attach a bigger 'burn chamber' for regular wood? I'm thinking: dumpsterdived cargo-pellets cut up small with a chainsaw.

I would end up making a cob bench though, something like described in here:
http://www.richsoil.com/rocket-stove-mass-heater.jsp

I like the idea of sitting on a heat mass battery, reading a book :)

Thanks for the inspiration!
Seniortrader (author)  Atar1 year ago
Hi,

The exhaust must be at least the same size as the input and the pipe from the inlet to the end of the central chimney must have the same dimension. Your rocket stove will work best when you put small size peices of dry wood in it. When the fire intensity is not high enough you will get smoke witch is not an environment-friendly way to make heat.

If you make your stove would you be kind enough to send me a link to you're stove.. Thank you!

ST.

Seniortrader (author)  Seniortrader1 year ago
I ment a link to your photos...
Jerrod j1 year ago
Hello just seen your stove good design. I was thinking that if you mounted your burner a bit higher, and the burn site closer to your heat chamber then your ash may be swept into the bottom of it by the air flow. This way the ash would store on the bottom of the chamber and you would't need to clean it out as much.
Seniortrader (author)  Jerrod j1 year ago
Hi,

To get the best performance possible, the burner should be placed at the base of the central chimney of the stove. Even if it was placed above, the air flow would not be sufficient to carry the havier ashe particles to the inside of the stove.

I light the stove for less than one day at the time and let it go out every night. Cleaning the heat chamber is very easy and gives me the opportunity to check that everything is in good condition.

Cheers!
scbron1 year ago
great design.

two questions.

what happens to the ash? Does it end up clogging the intake and reducing the airflow. How often do you have to clear it out and do you have to put out the fire to clean it out. It looks like you have to open the air gate and pull the ramp out to clean the ashes. Am I not getting it right?

Also, how do you determine and control the correct airflow?

Thanks for sharing your elegant design.
Seniortrader (author)  scbron1 year ago
Hi,

This stove does not produce much ash. One reason is that the wood pellets have a low moisture content and an other is due to the intensity of the heat in the burner. However, i clean the heat chamber by taking the grate out of it just the way you say it. I have to do it after every 40 pounds of pellets. The way the grate is made makes it very easy to take out and back in even if the stove is hot. I made a container with a stove damper to stop the flow of pellets in the burner. Now i can stop the pellets to fall in the burner whenever i need to.

The burner makes a very nice sound, like a rocket.. When i close the front door i hear this typical rocket sound and adjust it to the level where i know it is at the maximum heat. For all rocket stoves more heat equal less smoke. I could let the door open and let the burner take the air it need.

Cheert



IMG_0516.JPG
achong02 years ago
Hey, how have you managed to get the flow of the gravity fed pellets to be off to one side? in your pictures it looks like the pipe you are filling with the pellets is directly above the burning chamber. Does this not just burn the whole lot at one go?

I am not quite sure how you have managed to get the burning and the ventilation separate from the feed tube.

Thanks
Seniortrader (author)  achong02 years ago
HI, look at the grate, it has a 45 degree angle and ti can't go all the way in the burning chamber. The feeding pipe end inside the burning chamber make's it stop in the minimum burning rate position. This is wy the pellets are going from the feeding pipe to the inside of the burning chamber. Prior to lightning the fire inside the burner it is important to build a good air flow to the exaust pipe outside the garage. The flames will follow the airflow to the inside of the stove. In the feeding pipe the pile of pellets prevents air from passing through the feeding tank and that make's it impossible for the flames to catch in the pellet tank above the burning chamber.

I hope to have answer your questions !!!

ST
kretzlord2 years ago
awesome idea!!! One question, how do you adjust the flow of pellets? From what i see, it seems like you move the grate in or out to change the flow rate. Is this correct?
Seniortrader (author)  kretzlord2 years ago
Hi, thank you!

Yes this is the way to ajust the flow of pellets. When closed all the way, it is still burning but at the minimum rate. This is the setting i use for long time burning.

I also use the front door to ajust the air flow...

Cheers!

jimvoth2 years ago
may i ask, is the air convection or pushed mechanically? and... how does one start this heater? :)

love it... i want to learn more.
Seniortrader (author)  jimvoth2 years ago
Hi, Before lighting the fire, I heat the chimney with a propane torch for about 10 seconds. This induces a movement of air in the stove to the outside. Then I light the fire in the burner with a small amount of wood. It's always best to use small stick of wood than larger blocks. When i use the gravity pellet burner, after heating the chimney i place a small piece of fire starter juste below the burner and let it start by it self. There must be a much better scientific explanation for this phenomenon ...

I used this stove all winter in my garage with the pellet burner and I'll do it again the next winter.

Cheers!!

ST
canucksgirl2 years ago
I see how this project would work very well with your other instructable for the "Rocket Stove Mass Heater".

Very cleaver design. :)
Seniortrader (author)  canucksgirl2 years ago
HI! After two week of testing and great heat in the garage, i have decided to make another one for my hunting camp. This time, the gravity pellet burner will be made directly on the heat chamber. Winter is here with day temps down to -20C and i get all the heat i need to work in the garage.

In the coming days I will show the stove to the local fire department. I hope to get there approval and maybe convince others to convert there oil or electric furnace to a gravity pellet stove...

Cheers!
Seniortrader (author)  Seniortrader2 years ago
Already had an answer from the local fire department. All heating device have to meet CSA standards. Otherwise, the stove must be installed with a clearance of more than 48 inches. This standard applies to Quebec and probably all Canada. If you decide to fab one you should first talk to your local fire department. This heating device could void your home insurance.

Well, i had a lot of fun makin it and share it with Instructables members, now i have to take the decision to get it out or to keep it in and move it to à 48 inches clearance in my 16 X 24 feet working space!!!!

When you had mentioned you were going to speak to the Fire Dept. I had my suspicions... I understand the rule, but if the design is done properly (or some safety measures were put in place), I think this could still be a safe and effective design.

I found what you created very interesting (that and the Rocket Stove Mass Heater) and will share the projects with my father. He has a hunting cabin as well, and although they have a heater in the main cabin, they may be interested in this.

Thanks for sharing your work!
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