Gravity Pellet Boiler

[tom in maine]

I have been noodling over the concept of a batch fed pellet boiler. The idea is to use a gravity fed burner (no augers) to burn a batch of pellets at one setting and dump all the energy into storage.
It would be simple, unpressurized to keep cost down and basically function somewhat like a stickwood boiler.

Since these projects usually require time and money and I usually do not have both at the same time, it has been a little while getting it together.

What I have right now is a unit that works, without smoke, and a relatively low stack temp, 340F.
Am still testing it, but the boiler is relatively small and light and inexpensive. It has to be lit manually, but being pellets it takes about a half minute to get it going with a torch or fire starter.

Here is a brief video of the burner. Will show more as I get testing done. Right now, it delivers 50,000 btus/hr.
It does have an ID fan to keep the fire going in the right direction and not burn into the fuel tube.

 

[Karl_northwind]

Y'know, I've been thinking about this exact thing as well. I was thinking about being able to load the burner and fuel store (1 bag?) into the upper combustion chamber of the boiler, light and walk away. later in the day, you can just pour in another bag, light with torch, push the GO button and you're set for the evening.

do you have any other video or pics?

 

[tom in maine]

Nothing yet. Am running some more tests today.

 

[NE WOOD BURNER]

Tom,
I wonder if a hopper system similar to the EFEL coal hopper would work best for batch burning pellets.

Not sure if the whole batch would burn but sure does work great for pea coal.

 

[PassionForFire&Water]

FYI: No electric pellet stove: http://www.wisewaypelletstove.com/

 

[Karl_northwind]

FYI: No electric pellet stove: http://www.wisewaypelletstove.com/

I remember seeing this on youtube I think, the exhaust temps were way high for a pellet stove. 700-800 F if I recall.

 

[tom in maine]

The burner part is pretty easy to build. There are several stoves out there that use hoppers and gravity feed. I have not seen any stack temps, but 7-800F is certainly too high. I have spent a LOT of time over the years, starting with Dick Hill, messing with heat exchangers for boilers as well as hx for tanks.
Heat exchangers are the important part. As most of you know, anyone can build an unpressurized or pressure tank. Getting heat in and out of them in a way that is most useful for the application can be tricky. A coil of 3/4" copper is not ideal in most cases. Wood and pellet devices, although different animals, also need effective heat exchangers that are easy to maintain and are cost effective.

We ran the boiler again today. Stack temp was a bit higher, about 370F. (a bit too high for me, but nothing crazy) The unit was delivering up to about 80k btus.
I did not run it long. We are busy and playing with fire should probably wait for the weekend.
And I have not tied it to anything to dump the heat, so I just have a tank full of hot water steaming away in our shop.

It was nice in there, though...

 

[maple1]

Update has been made to my 'People I wish I was neighbors with' list....

 

[tom in maine]

Nice of you to say that. Put Dick Hill on that list ahead of me. He's a lot more fun!

 

[NE WOOD BURNER]

So I zeroed in on your hopper at first.

Now I see you claim "No smoke". Is that truly no smoke and 0 exhaust?

you should read about Clessie Cummins and about the many times he had no money, but kept moving forward with his many inventions.

Dick Hill From UMO?

 

[tom in maine]

Hopper is just a crude stand in for the real thing. I wanted something quick and potentially leaky, hoping to induce fire or smoke to come back into the living space. The ID fan prevents that. When the ID fan is off and the fire has been established, there is no smoke spillage, even when the hopper is empty and active fire is still going. A sealed hopper would be made.

No smoke that I can see. I need to pick up a new combustion analyzer. The one I had needed a new O2 sensor and I am going to try one that does not have one.
My ad hoc test was holding filter paper over the exhaust stream for a minute and looking for any deposits and smelling it (Large proboscis).
There is a little smoke in the initial three-five minutes and then nothing visible, just heat waves. Not a real test, but decent for now.
I am only a couple days into actually running this.

Although most of my work has been with stick wood, pellets seem to be a much simpler fuel to get "right" and tested to sell.

Yes, Dick Hill from UMO. He just did a piece for a local paper comparing the cost of stick wood vs. NG and guess which fuel won..
At age 95, he still is engaged in experiments and writing.
His regimen is eating a low fat diet, taking a half aspirin every day and living in a state of constant outrage.

 

[NE WOOD BURNER]

Ah yes, I read some of his work in my days @ UMO.

Keep @ it.
"speculation is the route to accumulation"

Do you have a link to his article?

 

[tom in maine]

No link to the article, but here it is:
As the resident manager of a multi-family household I constantly experiment with alternate heating systems. All of the tenants are graduate students in some technical program at the University. Their cooperation with my slip-shod alternatives is tolerated. One unit had been heated for decades with a system I had installed included a fan coil in combination with some large- diameter Vulcan radiation. This system was inadequate along with being noisy. Between tenants I had a professional install a Pensotti Steel Panel—the hot water was supplied by a natural gas boiler.

With the new tenant’s indulgence thermocouples were placed in seven locations to monitor performance. We found great difficulty in the establishment of a steady state. The outside temperature would change; the thermostat would force an oscillation in inside temperature, etc.

In the midst of much data, we found a 30 minute stretch where everything seemed to be constant. The boiler operated for ten minutes. The boiler rating is 70,000 Btu per hour. Our living unit was using energy at the rate of 23 thousand Btu per hour. With natural gas at $2 per therm, our housing unit heating cost was about fifty cents per hour. (It was very cold outside)

This same housing unit included a masonry stove which I had constructed decades ago. We shut off the heat from the gas boiler and constructed a fire in the masonry stove. After crude equilibrium had been established we set aside thirty pounds of 20% moisture fire wood. With careful stoking—don’t let the room temperature overshoot—we burned that wood in nine hours.. If I can do the conversions correctly, that is about 0.0007 cords per hour. With fire wood at $220 per cord we could heat the space for about 15 cents per hour.

WOW! Fifty cents for gas heat and fifteen cents for wood heat! But lookout. The boiler is in one end of the building and the circulator pumps are in the other end. We calculated that 40% of the heat that we charged to heating the apartment (based on running time of the boiler) was lost outside of the heated envelope of the apartment. That energy was not really lost as it is inside the total building envelope. This data will not be submitted to peer review.

My tenants, Lu Wang and his wife Yan, were excited with the wood option. It is difficult to “sit-around” a Pensotti wall panel, but wood stove can warm your mittens and your cup of tea. The radiant heat from a wood stove just “feels” better. I wonder what my tenants say when they communicate with their parents back in China. They must open the statement with: “You’re not going to believe this….”

I have trouble believing it too. Natural gas is a very versatile resource: plastics, motor fuel fertilizer, etc. Why do we squander it in home heating when wood is rotting all over Maine?

 

[tom in maine]

I have minimal reserves of firewood left and after running some more tests in my shop, just heating a tank and letting it cool off, I decided yesterday to
bring the pellet boiler to my house.
I disconnected the wood boiler and slid it out of the way. Brought the pellet unit home. Most stuff we make is built for me (skinny weakling) to handle.
Since it weighs about 50#, I lugged it down the basement and set it in place.
Came home at 4pm. Had it running a little after 5pm. The 350g tank was 118F. I stopped it (by letting it run out of pellets) at 6:32pm. The tank was 170F.
Used about a half bag of pellets. Stack temp was about 300F. Flow rate was a bit low, only 4.15 gpm, so the delta T was running around 40.
At the end of the burn, there were bubbles in the flow meter although there was no audible boiling.

All was good, with one exception. The thing howls and reverberates. It needs some sound deadening. I stayed with it while it ran for the first time in a lawn chair with my iPad.
Shut the damned oil off. Good times.

 

[BoilerMan]

I've been following this Tom and it looks pretty interesting!

TS

 

[Karl_northwind]

Numbers thanks for posting numbers!! 80,000 btu, half a bag in an hour and a half sounds really nice rate for most of us. I want one for my 200 gallon softtank!

 

[kopeck]

Always tinkering eh?

Figure out a way to integrate a HWHP and you might have something here!

Seriously though this is pretty interesting. I wish I had the guts to just start trying things.

K

 

[tom in maine]

No snow, just wind here.
Started up the pellet boiler. Left my torch at work the other day and worked out this routine for lighting the boiler.

 

[DZL_Damon]

Do you have pictures of the whole unit Tom? Perhaps a conceptual drawing? Or is that a conflict of interest for future development?!

 

[tom in maine]

There is a picture above. Click on it. It is larger than it appears.

 

[Karl_northwind]

Fire tube or water tube?