efficient design of homemade OWB

[tom in maine]

Dick’s paper is here:

(broken link removed to http://hotandcold.tv/wood) furnace.html

Make sure you use the whole line since this website seems to not underline the whole thing.

We found the missing pages.

Castable refractory needs to be cured. Either it sits for about 30 days unfired or it is slowly fired for longer periods at relatively low temps.
Read the labels if you purchase it.

 

[kuribo]

good castable refractory is not cheap. I wouldn't waste my time with the low budget variety if you hope to get any longevity at all out of it....

 

[tom in maine]

Dicks Hill's paper is an early version of his design. After he had sold the rights for household units, he developed a much larger version for a Maine Forest Service Nursery in Greenbush Maine. It looked the same but was much larger. If I remember correctly, at full fire it required 40 pounds of wood every 20 minutes. The wood was standard splits. I do not know if there was a paper published.

Trying to combust a whole log effciently is very difficult, the logs tend to be wetter and the log can form a char layer on its exterior slowing the burn. There were several outdoor boilers that advertised they could burn green logs, in theory they could but most of the heat went up the stack as CO and creosote with a lot of water vapor. Most states have banned them.

I actually inherited one of the Greenbush boilers. Sold it to a farmer who never paid for it in full.
I was glad to get rid of it since it was quite large.
Dick said that the guys who had to pitch the wood into it would try to mess it up since they did not like pitching wood into it all day long.

Apparently, they did work okay. I still have an ID fan for one of the units. It was big.

 

[boatboy63]

good castable refractory is not cheap. I wouldn't waste my time with the low budget variety if you hope to get any longevity at all out of it....

I will vouch for that. I paid about $1 per pound for Mizzou Castable Plus refractory. Bought it in 50# bags, but it is rated for 3000 degrees. I actually have more money spent in the refractory than any other item in my boiler. I recently saw a listing on ebay for refractory that was sold by the pallet in 5 gallon buckets for around $200. It consisted of about (10) 5 gallon buckets, but they were out of date. There is a recipe for making your own refractory here. https://www.hearth.com/talk/threads/54155/ I don't know the rating for it and that is the primary reason why I went ahead and bought something rated. When I finish my boiler, I don't want to stand back and say, "If only I had bought the good stuff."

 

[peakbagger]

One saturday during college, I got to feed the Greenbush boiler for a few hours. It was a nice design but it really needed an automatic stoker unless there were prisoners (or college students) available to feed it.

 

[woodburnerdave]

I will vouch for that. I paid about $1 per pound for Mizzou Castable Plus refractory. Bought it in 50# bags, but it is rated for 3000 degrees. ."

I agree with you, but need a clarification. If your castable refractory for $1 per pound was pure cement this is a cheap price. I'm looking at 80 cents a pound for a mix that is probably 75% sand, which puts pure cement in the price range of $2.40 per pound, which is expensive. Does anyone have an idea where I can pick up castable refractory cement for less than this price?

 

[boatboy63]

Dave, I don't know if it will help you or not, but I am attaching the .pdf for my refractory. I also noticed when I dug up the email, I paid $48 for a 55# bag of this.
Edit, can't post .pdf so I will c/p the file.
II I
Product Data 02/09: 5976
Page 1 of 2
MIZZOU® CASTABLE PLUS
Description: 3000°F High-Alumina Castable
Features: • Excellent resistance to numerous slags.
• Resists vitrification.
• Shows expansion rather than shrinkage at high temperatures.
• Superior resistance to spalling.
• High strength throughout its entire temperature range.
Uses: • Combustion chambers.
• Low-temperature incinerators.
• Air heaters, boilers, and burner blocks.
• Aluminum furnace upper sidewalls and roof regions.
• Forge furnaces and iron foundry ladles.
Chemical Analysis: Approximate (Calcined Basis)
Silica (SiO2) 32.6%
Alumina (Al2O3) 60.6%
Iron Oxide (Fe2O3) 1.2%
Titania (TiO2) 2.2%
Lime (CaO) 2.6%
Magnesia (MgO) 0.3%
Alkalies (Na2O+K2O) 0.5%
Physical Data (Typical)
Maximum Service Temperature 3000°F (1650°C)
Material Required 141 lb/ft3 (2.26 g/cm3)
Bulk Density
After 220°F (105°C)
After 1500°F (815°C)
lb/ft3 (g/cm3)
145 (2.32)
141 (2.26)
Modulus of Rupture
After 220°F (105°C)
After 1500°F (815°C)
After 2000°F (1095°C)
After 2500°F (1370°C)
lb/in.2 (MPa)
1,200 (8.3)
800 (5.5)
600 (4.1)
1,100 (7.6)
Cold Crushing Strength
After 220°F (105°C)
After 1500°F (815°C)
After 2000°F (1095°C)
After 2500°F (1370°C)
lb/in.2 (MPa)
5,500 (37.9)
3,500 (24.1)
3,000 (20.7)
4,000 (27.6)
Permanent Linear Change
After 220°F (105°C)
After 1500°F (815°C)
After 2000°F (1095°C)
After 2500°F (1370°C)
After 2900°F (1595°C)
-0.1%
-0.2%
-0.2%
+0.9%
+2.8%
Product Data
Page 2 of 2
MIZZOU® CASTABLE PLUS
Thermal Conductivity
At 400°F (205°C)
At 800°F (425°C)
At 1200°F (650°C)
At 1600°F (870°C)
At 2000°F (1095°C)
At 2400°F (1315°C)
Btu·in/hr·ft2·°F (W/m·°C)
7.8 (1.12)
7.7 (1.11)
7.6 (1.10)
7.5 (1.08)
7.4 (1.07)
7.4 (1.07)
Particle Size
Maximum Grain Size 4 Mesh (Tyler)
Less than 5%
Note: The test data shown are based on average results on production samples and are subject to normal variation on individual tests. The test
data cannot be taken as minimum or maximum values for specification purposes. ASTM test procedures used when applicable.
Mixing and Using Instructions (Water calculated at 8.337 lb/gallon) 55 lb bag 1000 lb bag 1500 lb bag
Water Required—Vibration Casting (Weight 8.6%)
Pounds
Gallons
Liters
4.7
0.6
2.1
86.0
10.3
39.0
129.0
15.5
58.5
Water Required—Hand Casting/Pouring (Weight 9.1%)
Pounds
Gallons
Liters
5.0
0.6
2.3
91.0
10.9
41.2
136.5
16.4
61.9
Working Time 20 minutes
For detailed mixing and using instructions, contact your ANH representative or visit www.anhrefractories.com.
Heatup/Dryout Schedule
See ANH Dryout Schedule 2—PLUS Rated Castables and Gunning Castables.
Installation Guidelines
See ANH Installation Guidelines CC-1—Conventional Castables—Standard.
Shelf Life (Under Proper Storage Conditions) 365 days

 

[Duetech]

I will vouch for that. I paid about $1 per pound for Mizzou Castable Plus refractory. Bought it in 50# bags, but it is rated for 3000 degrees. ."

I agree with you, but need a clarification. If your castable refractory for $1 per pound was pure cement this is a cheap price. I'm looking at 80 cents a pound for a mix that is probably 75% sand, which puts pure cement in the price range of $2.40 per pound, which is expensive. Does anyone have an idea where I can pick up castable refractory cement for less than this price?

Here are a couple links for castable refractory
(broken link removed to http://www.ebay.com/itm/130343615133?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649)

(broken link removed to http://www.ebay.com/itm/130343614933?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649)

 

[boatboy63]

I will vouch for that. I paid about $1 per pound for Mizzou Castable Plus refractory. Bought it in 50# bags, but it is rated for 3000 degrees. ."

I agree with you, but need a clarification. If your castable refractory for $1 per pound was pure cement this is a cheap price. I'm looking at 80 cents a pound for a mix that is probably 75% sand, which puts pure cement in the price range of $2.40 per pound, which is expensive. Does anyone have an idea where I can pick up castable refractory cement for less than this price?

Here are a couple links for castable refractory
(broken link removed to http://www.ebay.com/itm/130343615133?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649)

(broken link removed to http://www.ebay.com/itm/130343614933?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649)

Shipping to my location is $77 for 1 bag. Dave lives 1 state north of me so I don't see where it would be worth it. Check out this link (broken link removed to http://www.ebay.com/itm/130427938990?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) For $200, you could get over 1000 pounds of the stuff and have a nice roadtrip too. :>

 

[bigburner]

Didn't read whole post, but I looked for a long time for fire brick and castable. I ended up finding a company that did boiler work [big stuff] and they had a warehouse full of products [there are hundreds] and a bunch of information on the use of the ones I wanted. My vote is there is one of these companies in every major city [still lots of boilers out there] I would search this route. I do remember buying fire brick at less then half the old price, units were a custom size but that didn't matter to me I was just piling them up any way.

 

[woodburnerdave]

Check out this link (broken link removed to http://www.ebay.com/itm/130427938990?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) For $200, you could get over 1000 pounds of the stuff and have a nice roadtrip too. :>

What a great link!! I will drive up to this place next week and pick up the half ton. That's only 20 cents a pound for the mix whereas the best local price I could find was about 75 cents a pound. Now I can pour my boiler 4" or 5" thick instead of 3". I intended to put some high strength reinforcing steel in the mix (either 6x6, #10 gauge or #3 rebar), but now I can cast this stuff thick enough that the reinforcement won't be necessary.

You just saved me a lot of money, this is just a few hours from me. Thanks so much.

 

[Gasifier]

Hi wodburnerdave,
boatboy63 is right about the galvanized pipe and the process he refers to is electrolysis. Electrolysis will dissolve stell as fast or faster than aggressive rust. Not a good element for a boiler. Sounds like a big project and I wish the best to you. Many very experienced people frequent this forum and you will learn loads to prevent extending your learning curve. Keep us posted please!

Quick question for you guys about galvanized. My boiler installers used a 24 gage galvaized flue pipe to go from my Wood Gun's exhaust to my S.S. chimney inside my basement. Would this cause any problems? Should I switch that to regular black exhaust pipe? We filled cracks with that red/orange high temp. caulk. What do you think? If it is going to create a problem I will change it. Thanks for your time.

 

[Duetech]

Hi wodburnerdave,
boatboy63 is right about the galvanized pipe and the process he refers to is electrolysis. Electrolysis will dissolve steel as fast or faster than aggressive rust. Not a good element for a boiler. Sounds like a big project and I wish the best to you. Many very experienced people frequent this forum and you will learn loads to prevent extending your learning curve. Keep us posted please!

Quick question for you guys about galvanized. My boiler installers used a 24 gage galvaized flue pipe to go from my Wood Gun's exhaust to my S.S. chimney inside my basement. Would this cause any problems? Should I switch that to regular black exhaust pipe? We filled cracks with that red/orange high temp. caulk. What do you think? If it is going to create a problem I will change it. Thanks for your time.

My experience with galvanized and exhaust says pull out the galvanized as it is very prone to corrosion where creosote is invlolved. 24 ga is so thin you could be leaking exhaust gases in a single season. 16 or 18 ga black would definitely be a better choice.

 

[boatboy63]

Check out this link (broken link removed to http://www.ebay.com/itm/130427938990?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) For $200, you could get over 1000 pounds of the stuff and have a nice roadtrip too. :>

What a great link!! I will drive up to this place next week and pick up the half ton. That's only 20 cents a pound for the mix whereas the best local price I could find was about 75 cents a pound. Now I can pour my boiler 4" or 5" thick instead of 3". I intended to put some high strength reinforcing steel in the mix (either 6x6, #10 gauge or #3 rebar), but now I can cast this stuff thick enough that the reinforcement won't be necessary.

You just saved me a lot of money, this is just a few hours from me. Thanks so much.

Glad I could be of assistance. Would have replied sooner, but computer took a crap Saturday morning and had to get another. Don't know if it makes any difference, but in the 3rd pic, it does say on the outside that it is supposed to be used by 3/18/11. Don't really know if it will make any difference or not, but just wanted you to know. Guess that is why it is so cheap.

 

[maple1]

Hi wodburnerdave,
boatboy63 is right about the galvanized pipe and the process he refers to is electrolysis. Electrolysis will dissolve steel as fast or faster than aggressive rust. Not a good element for a boiler. Sounds like a big project and I wish the best to you. Many very experienced people frequent this forum and you will learn loads to prevent extending your learning curve. Keep us posted please!

Quick question for you guys about galvanized. My boiler installers used a 24 gage galvaized flue pipe to go from my Wood Gun's exhaust to my S.S. chimney inside my basement. Would this cause any problems? Should I switch that to regular black exhaust pipe? We filled cracks with that red/orange high temp. caulk. What do you think? If it is going to create a problem I will change it. Thanks for your time.

My experience with galvanized and exhaust says pull out the galvanized as it is very prone to corrosion where creosote is invlolved. 24 ga is so thin you could be leaking exhaust gases in a single season. 16 or 18 ga black would definitely be a better choice.

I'd also consider or check out stainless flue pipe - if it's a short run it won't cost all that much, then you should be set for a long time. I think 24ga. galvanized is the last thing I would put in.

 

[Duetech]

+1 stainless (but remeber stainless does not mean it won't rust...creosote and water are very agressive and exhaust is often laden with steam)

 

[benjamin]

Check out this link (broken link removed to http://www.ebay.com/itm/130427938990?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) For $200, you could get over 1000 pounds of the stuff and have a nice roadtrip too. :>

What a great link!! I will drive up to this place next week and pick up the half ton. That's only 20 cents a pound for the mix whereas the best local price I could find was about 75 cents a pound. Now I can pour my boiler 4" or 5" thick instead of 3". I intended to put some high strength reinforcing steel in the mix (either 6x6, #10 gauge or #3 rebar), but now I can cast this stuff thick enough that the reinforcement won't be necessary.

You just saved me a lot of money, this is just a few hours from me. Thanks so much.

I haven't followed the whole thread but I wanted to point out that the buckets of mortar are for laying up firebrick and are probably premixed. Not sure if they would/could word for casting or not.

 

[sixmenn]

Hey all. I know it's been a while since this thread was active, but I'm very curious as to the status of your project, woodburner.

I have had a very similar project in the works for some time. In case it isn't too late to chime in:

1. Instead of using poured concrete (spalling issues; too much moisture near too much heat), my plan was to lay concrete blocks as the walls, and at any structural bearing points to fill the voids in the blocks with poured concrete. I'd then fill the rest of the voids with sand (cheap) and line the inside of the building with firebrick. I found firebrick to be expensive, though, so like you I've looked into other alternatives like refractory cement, which as you know is also very expensive. Recently I stumbled onto ceramic fiber board and am wondering whether it might be both less expensive and easier to install. Check it out here (some companies I researched will even custom-form sizes and shapes for you):

(broken link removed)

2. I'd like to make a gasification unit, but fear I'll spend far too much time and money trying to get it to work right. My idea instead is to have the exhaust exit the burn room through the rear of the burn room through an opening in the burn room near the floor. My thinking is that a) this will allow the unburned fuel to rise in the refractory-lined burn room where it will ignite in the vicinity of the suspended water tanks (see point #3 below), thereby realizing at least some gain from the burning of the gases, and b) only the coolest exhaust in the burn room will exit the burn room.

3. For water tanks (see attachment), my plan was to support three 120 gallon vertical-style propane tanks inside the block building at the ceiling, giving me 360 gallons of water to heat, and approximately 141 sq ft of surface area on the tanks ( Central Boiler claims their 393 gallons of water in their system is exposed to 119 sq ft of heat). Propane tanks are between 3/16 and 1/4 inches thick and already have numerous openings in them for plumbing. The water path would circulate from one to the other, then the other before exiting the structure. Also similar to you, I was first going to route my return water through 2" steel pipes criss-crossed in the room in the rear where the exhaust goes prior to venting out through the chimney. In order to "fine-tune" it, I was going to install shutoffs so I could either bypass this room with my return water, or gate it back as necessary.

Like woodburner, I'd love to hear whether my ideas have merit or I'm totally out to lunch. Please feel free to shoot holes in my project!

Colin

 

[bigburner]

You have several issues, as drawn. First the heat HX is going to cool the fire, second open the door for reload, smoke will poor out the door with out a bypass, third there needs to a re burn chamber/dome. That said up draft glassifiers work well, not many many moving parts. The heat transfer for you tanks will be poor [like an OWB] At a glance look at the "green-wood" fire box its all refractory, the draw back with the design is the HX, now take your tanks and add some fire tubes in two of them route the flue gases out of the fire box and threw the tanks then out the chimney. There will lots opinion here, this is mine. I currently run a system that has a very large fire box like yours, it's 40 inches wide 60 deep and 84 inches tall, the top is arched refractory and the flue gases burn up there, then the exhaust travels threw the back wall down into refractory tubes 12x12 on either side [by pass in the middle] then travels threw a fire tube HX. I use a fan on a timer for reloads, It will bring the fire box back up to temp, when it shuts off is when the magic happens, burns like a forage [super hot] I obliviously can put big pieces in there and to see a 24" round glowing to a point to where you think you could see threw it. Amazing, it's pretty cool. It's all about the refractory! Research will show you that all the big boys use lots of it.

 

[bigburner]

Sorry I for got to mention the concrete, my boiler is setting on poured concrete with the fire box inside, I inch air gap between the concrete and fire brick it did not spall, because it was baked slowly and the moisture escaped. It will get to 500F on the out side, that's sound warm but bad things don't happen until over a 1000 if cured correctly and heated and cooled slowing. Mine is a monster[boiler] and weight is about 20,000 lbs, I traded the wall for hunting privileges. doing it again I would build my fire box first. then a steel frame to set the fire tubes tanks on then frame the whole thing with steel studs and lot of rock wool insulation, pole bard steel if it's out side. None of this is cheap, might better just buy a Garn.

 

[sixmenn]

You have several issues, as drawn. First the heat HX is going to cool the fire, second open the door for reload, smoke will poor out the door with out a bypass, third there needs to a re burn chamber/dome. That said up draft glassifiers work well, not many many moving parts. The heat transfer for you tanks will be poor [like an OWB] At a glance look at the "green-wood" fire box its all refractory, the draw back with the design is the HX, now take your tanks and add some fire tubes in two of them route the flue gases out of the fire box and threw the tanks then out the chimney. There will lots opinion here, this is mine. I currently run a system that has a very large fire box like yours, it's 40 inches wide 60 deep and 84 inches tall, the top is arched refractory and the flue gases burn up there, then the exhaust travels threw the back wall down into refractory tubes 12x12 on either side [by pass in the middle] then travels threw a fire tube HX. I use a fan on a timer for reloads, It will bring the fire box back up to temp, when it shuts off is when the magic happens, burns like a forage [super hot] I obliviously can put big pieces in there and to see a 24" round glowing to a point to where you think you could see threw it. Amazing, it's pretty cool. It's all about the refractory! Research will show you that all the big boys use lots of it.

Thanks for the reply. I appreciate your insights. I have a few questions to make sure I understand what you're saying:

1. What does HX stand for and how will it cool the fire?
2. I've looked at a few boilers and don't remember seeing a bypass on them to prevent smoke coming out the door. Won't opening the door just introduce fresh air and kindle the fire? With fresh air coming in, won't the smoke naturally escape out the chimney due to the draft effect?
3. Do you have plans for your design? Can you post pics?
4. How often do you lhave to load your boiler?

Thanks again!

 

[sixmenn]

Sorry I for got to mention the concrete, my boiler is setting on poured concrete with the fire box inside, I inch air gap between the concrete and fire brick it did not spall, because it was baked slowly and the moisture escaped. It will get to 500F on the out side, that's sound warm but bad things don't happen until over a 1000 if cured correctly and heated and cooled slowing. Mine is a monster[boiler] and weight is about 20,000 lbs, I traded the wall for hunting privileges. doing it again I would build my fire box first. then a steel frame to set the fire tubes tanks on then frame the whole thing with steel studs and lot of rock wool insulation, pole bard steel if it's out side. None of this is cheap, might better just buy a Garn.

When you say 500F on the outside, is that the outside of the concrete, on in the air space?

The building method you describe sounds similar to what I plan to do. You're saying you would first build the firebox (out of steel and refractory??), then support the fire tubes and tanks on a steel frame (can you describe the tube/tank design a bit?), then build the insulating and cosmetic shell around the outside. Is that right?

Thanks again, bigburner