Author Topic: Smokeless Outdoor Wood Boiler  (Read 10719 times)

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greenenergyexperimenter

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Smokeless Outdoor Wood Boiler
« on: October 14, 2014, 01:00:21 PM »
I've constructed a smokeless outdoor wood boiler for heating my house this winter. It is designed to work as is, but I am actively modifying it to achieve better efficiencies. Here's what it looked like right after I installed it:



Here's a close up on the door:



The firebox is fairly small, but due to heavy insulation and adequate air supply, combustion is smokeless. The drawback is 4 hours between load times for now:



The boiler is an inside out design. Instead of a firebox surrounded by a water jacket, I placed a vented tank in the back of the firebox:



Here's some numbers on the initial design:

Max inside temperature measured at 1246 *F and rising. My thermocouple is only rated to 1400, so I removed it before seeing how high it really gets in there.

Max outside temperature is 255 *F, most of it is 190 *F. This is an obvious place for improvement. I am very pleased with the effectiveness of the homemade insulation, however.

Max exhaust temperature is 343 *F. My goal is to get this down to 275.

Planned improvements:
1. Install a baffle on the top back portion of the tank. This was just done this morning and I will be testing its effectiveness throughout the day. Preliminary observations show it forces the flames to swirl around the tank better.

2. Install a heat reclaimer. This will use the heat from the body of the stove to preheat combustion air, putting that waste heat back into the fire.

3. Install a secondary air injection system. I'm getting smoke free combustion and a lot of blue flame in there, but I think adding preheated air at the end of the grate will boost things further.

4. Install firetubes in the boiler tank. I'm teaching myself how to weld, and I felt this was out of my reach at the time. I've got another tank that I will do this with when my skills improve.

5. Insulate the hydronic lines and possibly the heat reclaimer.

I hope you find this project entertaining. Let me know if you have other improvements you can think of. Questions are welcome too.

gww

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Re: Smokeless Outdoor Wood Boiler
« Reply #1 on: October 14, 2014, 02:07:22 PM »
I have no improvements but thank you for taking the time to post pictures.
gww

Mary B

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Re: Smokeless Outdoor Wood Boiler
« Reply #2 on: October 14, 2014, 06:41:00 PM »
what are you using for insulation?

greenenergyexperimenter

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Re: Smokeless Outdoor Wood Boiler
« Reply #3 on: October 14, 2014, 06:51:31 PM »
The insulation is a mix of 4 parts perlite, 1 part portland, and 1/4 part bentonite. If you have access to proper refractory cement and fireclay, I'd recommend using 4 parts perlite to 1 part refractory cement and 1/4 part fireclay.

To compensate for the less than desirable binder that I used, I allowed it to cure for a week before firing it. The first couple of fires were really small and served to drive away excess water.

So far, everything is holding up well. In the wood burning area, I applied a thin coat of fireplace mortar to give a more durable finish.

12AX7

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Re: Smokeless Outdoor Wood Boiler
« Reply #4 on: October 14, 2014, 08:04:05 PM »
Hello!

What are you using for a heat exchanger/pump.   Are you using water, or a anti-freeze mix?

greenenergyexperimenter

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Re: Smokeless Outdoor Wood Boiler
« Reply #5 on: October 14, 2014, 08:15:05 PM »
I've got a 3 speed circulator pump, the kind that comes with commercially made boilers. At some point, I'd like to replace it with a 12V pump and run it with my solar panels.

The exchanger is a 18"x18" triple pass model rated at 120,000 BTU. It is overkill for what I need, but it is a safety measure. Since the exchanger can remove more heat than the stove puts out in normal operation, there is never any danger of steam production.

I'd also like to put in hydronic radiators and ditch the exchanger/blower setup, but the cost is too much for me right now.

I keep the pump and blower on a computer UPS that I modified with forced air cooling and marine batteries. Not ideal, but it keeps things going during power outages.

I am using a antifreeze mix. I've used straight water in past projects, but I had a freeze that burst some pipes, so now I'm scared not to use antifreeze.  :-[

madlabs

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Re: Smokeless Outdoor Wood Boiler
« Reply #6 on: October 15, 2014, 07:51:22 PM »
Great project. Can we get some more pics, like the fan mounting? Fan specs? What type of tank did you start with for the firebox? What did you use for the inside tank? Any and all details, if you have the time.

Thanks!

Jonathan

gww

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Re: Smokeless Outdoor Wood Boiler
« Reply #7 on: October 15, 2014, 08:03:54 PM »
My old man made a living in the early eighties using hot water tanks and boxing around them.  I got one of them in my out building right now.  I think it is going to last forever.  Plain wood stove but still something to be proud of.
gww

greenenergyexperimenter

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Re: Smokeless Outdoor Wood Boiler
« Reply #8 on: October 16, 2014, 02:25:35 AM »
Great project. Can we get some more pics, like the fan mounting? Fan specs? What type of tank did you start with for the firebox? What did you use for the inside tank? Any and all details, if you have the time.

Thanks!

Jonathan

Thanks! The outer shell of the boiler is the inner tank of a hot water heater. The door is made from the top of that tank.

The inside tank came from a broken twin tank air compressor. I welded 3 half inch black iron pipes to it for the intake, vent, and output. The intake goes nearly to the bottom of the tank and the other two are welded up at the top.

Here's a picture of the heat exchanger as I was installing it with a bottle of homemade hopped cider for scale:



Here's what it looks like with the cover on it:



I plan to make a mock fireplace around it to spruce it up.  :)

Behind all that is a blower box I made from scrap wood. The blower is a 3 speed with a maximum output of 1200 CFM. I'll take a picture of the whole blower assembly soon and post it here.

My old man made a living in the early eighties using hot water tanks and boxing around them.  I got one of them in my out building right now.  I think it is going to last forever.  Plain wood stove but still something to be proud of.
gww

Man, that'd be a heck of a way to make a living!

keithturtle

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Re: Smokeless Outdoor Wood Boiler
« Reply #9 on: October 17, 2014, 12:28:04 AM »
"The drawback is 4 hours between load times for now:"

Set it up to burn pellets, but with the horizontal burn chamber I wouldn't know how without an auger

Turtle
soli deo gloria

madlabs

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Re: Smokeless Outdoor Wood Boiler
« Reply #10 on: October 19, 2014, 01:55:21 PM »
Green,

Thanks for the extra pics and I look forward to the blower pics. I am going to build a house with hydronic floor heating one of these days and will be doing an outside boiler for back up heating.

JOnathan

GoVertical

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Re: Smokeless Outdoor Wood Boiler
« Reply #11 on: October 28, 2014, 10:02:53 AM »
Greetings, great work. What is the average burn time of the stove burn between refills?

I am starting a similar smaller project.


I just found the info, about 4 hours.
Learn from the past, live in the present, plan for the future
kilroyOdin is not here ;)
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GoVertical

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Re: Smokeless Outdoor Wood Boiler
« Reply #12 on: October 28, 2014, 04:31:50 PM »
Hi, where did you get the heat exchanger?
Learn from the past, live in the present, plan for the future
kilroyOdin is not here ;)
SEMPER FEROX

greenenergyexperimenter

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Re: Smokeless Outdoor Wood Boiler
« Reply #13 on: October 28, 2014, 05:27:41 PM »
Thanks, GoVertical.

I bought the exchanger on Amazon, they are $109 shipped to your door.

Are you planning to use a rocket stove similar to the one on your recent thread?


GoVertical

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Re: Smokeless Outdoor Wood Boiler
« Reply #14 on: October 28, 2014, 07:03:33 PM »
Hi, yes. I am just starting with a small system for experimentation. I have a shop space in a outer building that is not heated. I will try it there first. Last year I was playing with steam engines and fabricated a small mono tube boiler. My main concern is safety. 
Learn from the past, live in the present, plan for the future
kilroyOdin is not here ;)
SEMPER FEROX

greenenergyexperimenter

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Re: Smokeless Outdoor Wood Boiler
« Reply #15 on: October 30, 2014, 10:05:32 PM »
I've now added a copper coil that creates two stages of heating. The cool side enters the coil, preheating the water before going into the boiler tank. The water finishes heating in the tank, where it then goes to the heat exchanger.

Here's what the coil looks like installed:



This modification works almost too well. I had a boil over when I first started the fire since I added too much kindling. The good news is that the vent system worked flawlessly.

Another good thing is that the temperature of the stovepipe above the coil has never measured over 250*F. This means I'm extracting almost all the usable heat from the exhaust.

gww

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Re: Smokeless Outdoor Wood Boiler
« Reply #16 on: October 30, 2014, 10:56:49 PM »
How will you handle freezing?  It looks like in the cold weather there would be lot of heat loss with the exposed pipes.  My dads is incased and insulated and then ran underground. 
Good luck
gww

greenenergyexperimenter

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Re: Smokeless Outdoor Wood Boiler
« Reply #17 on: October 30, 2014, 11:32:31 PM »
I'm using a antifreeze mix to prevent freezing. Now that I've gotten the two stage heating done, I plan to insulate the pipes as there is a calculated 1400 BTU an hour heat loss when it is really cold, less when warm. I'll use fiberglass insulation encased in reflectix. Moisture will be sealed out with aluminum tape.

I also plan to insulate the body of the stove as it is between 190* and 250*F.

gww

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Re: Smokeless Outdoor Wood Boiler
« Reply #18 on: October 31, 2014, 11:43:45 AM »
Thanks for the update.
gww