Outdoor Wood Furnace Info
Outdoor Furnaces - Manufacturers with NON EPA-Certified Models Only => Home Made => Topic started by: binfordw on January 21, 2014, 12:39:27 AM
-
Hi, New here, been reading what I can.
I'm set to build a Gasifier boiler this year, and believe I have the basics figured.
What are some of the key elements that I need to focus on for a successful build? Anything I need to make sure I give extra thought?
-
Nozzle size, nozzle target refractory material, correct sizing of the heat exchanger, amount of primary intake air, and the amount of secondary intake air. Those are just a few perimeters that need to be engineered correctly. I think the biggest thing is that the technology is so new that there isn't that much engineering info out there for us DIYers to figure out some these things. If I was to build a Gasification boiler, I would find a factory built one sized to your needs and take some measurements and reverse engineer it. Just my 2 cents.
-
Nozzle being the port/ports in the bottom of burn chamber correct? If so these could be changed fairly easily after build was complete if they turned out to be too big/too small.
Airflow, primary (burn chamber air/pressure?) Secondary, (the airflow to mix with "smoke" to help re-burn right?) These could be adjustable and tweaked after build as well.
Size of heat exchanger- This is for airflow concerns? I agree this would need to be done pretty close to right the first time. Although, should be easy enough to copy a working stoves tube sizes.
What about the Target area refractory material? Just so it holds up to the heat?
Thanks so much for your input and suggestions. Hopefully I can get 99% of the questionable sections of this build figured out before I start, I'm feeling better about it the more and more I read for sure.
-
Nozzle size could be made large and reduced if needed along with primary and secondary intake air. On most Gasification boilers the main heat exchange is off the exhaust after the the secondary burn has occurred. So sizing of the exhaust heat exchange would be critical. Another thing to remember is the secondary burn chamber is exposed to over 2000 degrees. This is where the correct refractory comes into play. Most commercial Gasification boilers have replaceable refractory nozzles and targets. These are wear items that have to be replaced. Back around 2008 there was a guy about 60 miles from me that attempted to build a Gasification boiler and got it up and running but he only ran it for a couple months and then gave up on it because it kept burning itself up. Have you looked into a "Garn" style boiler? Its much larger but it is very simple compared to some of the modern Gasification boilers. I know there has been quite a few home built Garn style boilers and there very successful.
-
No I haven't heard about Garn type boilers.
It doesn't sound like a mystery to install the correct refractory to me. As long as one is aware of the temps and wear it will need to withstand, it shouldn't be an issue I wouldn't think.
When you say sizing of the heat exchange is critical- in what manner- just mainly speaking for efficiency? I realize it would need to be sized to handle the amount of exhaust/gases that need to pass through it of course. I also understand too big would not strip heat from it as well/ much at all.
I've read several postings that comment that gasifiers are too complex, high maintenance and possibly dangerous, but I have not yet really found out why. For instance, one post commented that he had made several boilers, and that one suffered a catastrophic meltdown when the owner tried to load it while drunk.
-
Please do research the Garn style boiler. A guy on here that goes by "petemoss" built a nice Garn style. There is almost a picture by picture build of a Gasification boiler by a member named "jackel440" that he built and got up and running but seems to have not been around since 2012 so I don't know how it worked out. Also do a Google search of Professor Dick Hill's stick wood furnace. It seems to be the very first gasification wood boiler designed on a government grant back in the late seventies. A company in Canada made it and sold if for a few years ,but the concept just didn't catch on. There are a few people that still have and run them and there have been a few that have built a couple.
Refractory isn't has simple has it sounds. There are many different types and molding,designing, and curing refractory is a art in itself. Refractory/firebrick wears or erodes almost everywhere it is used. Its just the nature of the beast. Also refractory doesn't like to be heated and cooled. This heating and cooling seems to take a lot of the durability out of it.
Sounds like you have a lot of research to do before you start to build. Don't worry I've been researching and lurking around since 2007 and still not ready to build yet.
-
Refractory can be had that has a high abrasion resistance, can also be had with a high resistance to thermal shock. It will cost more, but if it lasts longer is cost really a consideration then?
-
Built a gasification boiler based on the design of the p&m opt 250. One thing I can say is have your plans well laid out before you start and prepared to spend a lot of hours on your build. Took myself and my welder about three months of weekends and some evenings to complete this build but well worth the time.
My unit heats about 3000sq.' home and a 36 x 50 shop. The unit recovers very quickly, never smokes. and stack temps run 240 to 260 under full burn as long as the unit is clean. My firebox is lined with a double layer of firebrick on the floor and one row upright against the wall(9"). The slot in the bottom of the primary is about 3/4" wide by 8" long. The secondary burn chamber is the most difficult part to line.
My chamber being 18"w and 10" h x 40"deep was a challenge to line as I placed a double layer on the bottom, single layer on top,(underside of primary), and single layer on sides and mortar all in with high heat mortar. Burn chamber and heat exchangers were all fabbed together and pressure tested before inserting in to water jacket and then welded front of jacket on. Burn chambers and heat exchange completely surrounded on all sides by water. Double return and supply extend 3/4 and 1/4 into tank respectively. Unit has been running 13 months now successfully and wish I had done this many years ago.
(previous 5 yr average was $4000yr on propane) ran unit thru summer as well to heat hot water and pool burning poplar and whatever lo btu wood I had around.
One change I would make if I had to do it again would be to feed the air introduction tubes through a bigger pipe sleeve so they wouldn't be in direct contact with the water jacket. Think this may help with creosote issue in the airtubes in higher idle times. As of late I have not had this issue with higher burn times and probably drier wood supply.
Any questions or specifics you may want to know about just ask and I will try to help you out
-
Nice job with thinking before building Renoman, you hit the nail right on the head, let me ask you a question, starting from the idea on a napkin to where you are now, labor included how much do you think you have invested
-
Renoman, how about some pics of this beast?
-
labor included how much do you think you have invested
Oh you never include labor!!
-
Can anyone elaborate on the importance of proper heat exchanger size?
As for refractory, I will do some searching. As long as I design the secondary chamber to allow access to change the target area out, I think that will take care of any concerns there.
I plan on modeling my boiler in CAD, and just CNC cutting the panel and parts from the model.
-
"allow access to change the target area out"
Hey,,,,,,, how about putting the whole secondary on a slide out? Just like an ash pan?
-
Nice job with thinking before building Renoman, you hit the nail right on the head, let me ask you a question, starting from the idea on a napkin to where you are now, labor included how much do you think you have invested
Well I guess if I would include labour I would probably have as much invested as a new unit. But that being said
I am the type of person who enjoys the challenge and really enjoy building stuff. Most of my days are spent either at work or at work in the shop working on different projects so I didn't track hours persay for expensing them but just as rough project time.
All said and done I have $9600 into all the materials to build the boiler, the slab (9' x 13" x 8"), the underground lines, the trench, the water hx, the furnace hx, sidearm in shop and the circ pumps. Also enclosed the boiler in a small enclosure plus some wood storage.
My payback should be fairly quick as my propane average use before was $4000 a yr. May have been $5000 or better this year with as cold as it has been!
-
Can anyone elaborate on the importance of proper heat exchanger size?
Not sure what the engineering is on that exactly but I know you don t want to restrict your air flow back too much.
As the air moves through the chambers and around corners it naturally loses velocity so you would want enough tubes to allow the heat to travel thru easily enough but many tubes of smaller sizes increase surface area contact to the water jacket thus allowing maximum heat extraction. Mine has six 2" tubes off of the secondary chamber about 30" long and ten 2" tubes travelling horizontally 36" back to front and then 10 more front to back then exits out 6" stack. That gives a total of 75' of tube immersed in the water jacket to extract the heat from.
I run the boiler at 195 with 8* dif and when it is clean my stack temp 1" above where it exits the water jacket will be 240* so I think it is pretty much extracting every btu it can. On cold days I have icicles hanging off my chimney cap!!
-
I wondered when you said you based yours off a P&M 250, if you did the extra runs of heat exchanger tubes- front to back. I have been doodling mine up in CAD, with just the rear upright tubes so far. Having the 2 extra sets front to back would add a good bit more labor, parts, and more stuff to clean. Do you feel its worth having in the end?
-
I would think the more heat exchanger area the better, in this day of making it cheaper and charging more, if P&M thought they could do away with those tubes and not effect efficiency they would have already.
-
Can anyone elaborate on the importance of proper heat exchanger size?
. Mine has six 2" tubes off of the secondary chamber about 30" long and ten 2" tubes travelling horizontally 36" back to front and then 10 more front to back then exits out 6" stack.
All of your heat exchange tubes are 2"?
Is the goal to allow more volume in the heat exchange tubes the farther away from the secondary chamber you get? Or is it also possible to use the same area of tube from the secondary chamber all the way to the exit stack with no ill effects?
-
Sorry- I have quite a few questions I'm currently needing to solve!
Firebrick- I need to settle on a type early on so I can dimension the secondary chamber off of the brick sizes, Anyone have a specific type to look into- or a website that offers them?
-
yes all tubes are 2"
I would definitely do all the runs in fact maybe even a few more. I think the goal is to have the surface area to dissipate the heat in to the water. Given my stack temps are 240 I think it is pretty close but once they r a bit dirty it could be an advantage to have a few more runs to keep the efficiency up.
I purchased my bricks and high heat mortar from patene building supplies her in Ontario. Not sure on the grade of the firebrick but so far no sign of any deterioration. I believe they were 2" x 4" x 9" and around $3 a piece but in would have to check on that to be sure.
-
Think there may be something to not making the secondary chamber too big as well. think you want to keep that brick fairly close to that flame so it retains high temps that r produced there to keep the gasification happening quickly on the call for heat. to large of an area may cause reduced temps and sluggish start up of gasification. Not sure just a theory on my part. You may want to research what others are using for sizing on their secondarys.
-
So your tube volume steps up, 6 2" tubes to 10 2" tubes. My current drawing uses six 3" tubes. If/when I add a front/back run, I will probably use a smaller tube, but add quantity to have a bit higher internal surface area than the six 3" tubes.
Good to hear you have had good luck using what sounds to be pretty standard firebrick. I have looked briefly, but have not seen a lot of variety commonly sold to the public.
-
I slapped some quick skins on my current drawing, just so it made a little more sense. I will probably make lots of changes as I go, but this is the main plan so far.
The orange 8" is my bypass tube. I need to add a shutoff in the final chamber for it, which will probably require enlarging the final chamber to fit the mechanism.
If I can get this all drawn up right, the good part is I have a cnc plasma table at home, so cutting the parts and assembly should be pretty easy.
(http://i6.photobucket.com/albums/y218/Binfordw/boilerpic2.jpg) (http://s6.photobucket.com/user/Binfordw/media/boilerpic2.jpg.html)
(http://i6.photobucket.com/albums/y218/Binfordw/boilerpic1.jpg) (http://s6.photobucket.com/user/Binfordw/media/boilerpic1.jpg.html)
-
If I can get this all drawn up right, the good part is I have a cnc plasma table at home, so cutting the parts and assembly should be pretty easy.
Will you be my new best friend? Or if you prefer you could just adopt me.
-
lookin good so far binford. thinking you may want to raise or spread that heat exchange a bit so u can
access those vertical tubes a little easier for brushing them out.
Any ideas on your airbox and air feeds for the primary and secondary?
-
If I can get this all drawn up right, the good part is I have a cnc plasma table at home, so cutting the parts and assembly should be pretty easy.
Will you be my new best friend? Or if you prefer you could just adopt me.
I'd be happy to, but I'll take a stab at it and say you don't live anywhere near Indiana!
-
lookin good so far binford. thinking you may want to raise or spread that heat exchange a bit so u can
access those vertical tubes a little easier for brushing them out.
Any ideas on your airbox and air feeds for the primary and secondary?
I will have to raise the "lid" on the final pass exchange tubes anyway I think, to allow room for the bypass close-off mechanism- that will add a little extra room. The tubes will be a straight shot, with door access at both ends for cleaning.
As far as air, not yet. Hopefully that should be pretty easy, small box with fan mount and block off "damper" mechanism, and tube running to topside of primary burn box, and one into secondary. Although I'm not real certain where to put the air in the secondary, I will need to look that up.
You guys have been great help so far, I'm really starting to get excited about this build now.
-
If I can get this all drawn up right, the good part is I have a cnc plasma table at home, so cutting the parts and assembly should be pretty easy.
Will you be my new best friend? Or if you prefer you could just adopt me.
I'd be happy to, but I'll take a stab at it and say you don't live anywhere near Indiana!
Bet I do, North Liberty Indiana to be exact.
Was cold enough yesterday the straight truck tried to gel up twice yesterday delivering hay, also had the loader tractor try to gel up as well.
-
Ah just barely Indiana by the looks of it! I'm about 4 hours south in Greensburg. It has been cold here for sure. We have some decent snow/drifting today, but the temps are warmer, seems like high 20's.
-
Some pics of my build:
(http://i512.photobucket.com/albums/t321/ajmrenovations/phonepics217_zps946df1e4.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/phonepics217_zps946df1e4.jpg.html)
-
(http://i512.photobucket.com/albums/t321/ajmrenovations/phonepics222_zps8bed35e9.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/phonepics222_zps8bed35e9.jpg.html)(http://i512.photobucket.com/albums/t321/ajmrenovations/phonepics232_zpsefd553c4.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/phonepics232_zpsefd553c4.jpg.html)
(http://i512.photobucket.com/albums/t321/ajmrenovations/phonepics227_zpsa9fdc8c5.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/phonepics227_zpsa9fdc8c5.jpg.html)
(http://i512.photobucket.com/albums/t321/ajmrenovations/phonepics234_zps646fc647.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/phonepics234_zps646fc647.jpg.html)
(http://i512.photobucket.com/albums/t321/ajmrenovations/73fc0d44-80ee-401a-a195-2be27a6d72df_zps8c980c74.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/73fc0d44-80ee-401a-a195-2be27a6d72df_zps8c980c74.jpg.html)(http://i512.photobucket.com/albums/t321/ajmrenovations/woodboiler_zps6428474e.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/woodboiler_zps6428474e.jpg.html)
-
(http://i512.photobucket.com/albums/t321/ajmrenovations/woodboiler_zps6428474e.jpg) (http://s512.photobucket.com/user/ajmrenovations/media/woodboiler_zps6428474e.jpg.html)
-
Nice pics, thanks for sharing.
So the square tubes are your air for the burn box and the secondary chamber right?
How is your secondary chamber laid out? Is it open, or does it route gases to the front and then back using firebrick to separate the space?
Is your nozzle at the back of the burn box?
-
Looking good, keep the pics coming!
-
yes the squares tubes are the primary and secondary air feeds. The primary feeds up over the top of the fire and the secondary branches out to both sides, down the walls to feed in under the firebrick where at that point I cut a hollow in the brick with four veins to feed out at the slot. The slot is in the middle of the firebox which seems to work very well for even burns in the firebox.
The secondary is mainly open except that I had to put a wall down the center with bricks to support the ceiling layer. this also seems to work well to spread the heat and the ash tends to move to the front and build there before filling the back end. All in all the performance of it seems to be virtually troublefree but I don't have experience with any others either.
-
Renoman, did you place a layer of steel in the bottom of your firebox over the refractory brick like jackal440 did on his or is your wood in direct contact with the top of the secondary burn chamber? I've been debating this, have even thought about using a double layer on top of the secondary and just letting the wood in the primary rest right on it to help with heat transfer. My thinking is the coals will help to retain heat in the secondary to allow quicker gasification? Also if damage was to occur from wood hitting the brick or cleaning it'd be a lot easier to change the top layer out than any of that actually involved in the secondary chamber.
-
yes there is a steel bottom in the primary burn with the slot cut in in a little larger than what I made with the
brick and the high heat mortar. 2 layers of 2" thick brick on top of the steel on primary side and one layer 2"
brick on the under side of the steel forming the firebrick top of the secondary. So far no deterioration in any of the brick that
I have noticed.