Propane burner for a monster of a furnace

What sort of air pressure should I be aiming for? My air compressor is pretty damn big, (Again blessed w/ my new shop)



and Jeff thank you for the videos that large moya is quite handsome I’m currently reworking my drawing to be more moya than brute

 

It only requires enough pressure to effectively blow the oil drop into the furnace and to provide turbulence, so some but not much. It's more about volume. A $10 yard sale leaf blower or shop vac exhaust should give you enough of both pressure and volume.

 

Didn't we have someone playing with air amplifiers some time back (probably AA). I know very little about them but if you really want to avoid a blower it may give you the CFM needed, or it may be an added complication, just thought I'd throw it out there (and maybe learn something!)

 

once again, it is not normal to have lots of free oil,
it's like the people on youtube claiming to make things super cheap, but they have 90% of the expensive parts and materials laying about . thats not reality
BTW 100Lb propane tanks are $150 , you get to use them for 10 years. not a huge issue for most ( yes handling them sucks, no argument there)


V/r HT1

 

To hot today to pour so I'm trying to catch up on my forums stuff. The efficiency of our furnaces with propane at non ferrous temperatures would be between about 8% on the 2400F range to about 12% on the 1500F aluminum range. The more combustion air used the lower the efficiency because the more air the lower the flame temp, energy transfer is the difference between flame temp and metal temp. Also the time it takes to get to melting temp is basically 0% efficiency as the heat is lost to the furnace mass with no work being done. The furnace being discussed would be very high in thermal mass losses. especially if not being used for multiple pours. My tilting furnace takes about 15 minutes to get to temp at full fire, that is almost the same amount of heat it takes to melt 75 lbs of aluminum. If 75 lbs was all i was going to melt that takes the overall efficiency from the 12% range down to a 4% My furnaces are low mass furnaces because of the wasted time factor.

Air compressors are high pressure low volume devices, you only use an air compressor when you need the high pressure like the air needed to atomize oil using the Delevan/Hago type siphon oil nozzles, for combustion air you would use a blower which is a low pressure high volume device. even then the volume must stay low enough the the velocity leaving the burner stays at the flame spread rate or the burner blows out.

Fuel type depends on the availability of the fuel, and the amount of fuel needed. I live in a primarily agricultural environment and waste oil is readily available. So that is what i use, even then I use propane as a stabilizing fuel until i get the furnace above ignition temp. This is mostly to keep the initial smoke down.

Art B

 

It would seem that with my delevan siphon setup burning waste oil, the furnace bore is actually the "burner". What we normally refer to as the burner is actually the fuel delivery device and it would never burn WMO as a standalone device or in a cold furnace. Fuels like kero or diesel do light up on their own in a cold furnace, but not super effectively, but good enough to get the furnace preheated. I dont know if it would light kero/diesel outside the furnace as I've never tried it nor have any reason to. Jason has mentioned that he lights his kwicky on jet in open air and then inserts it in the furnace so I guess it's possible that I could.

I've made the observation that once I get my furnace hot enough to burn WMO by preheating with propane or diesel, it takes quite awhile burning WMO to be able to really open it up to full tilt. The furnace's ability to fully combust increases as the bore temp increases. I'm never able to just start it up and leave it alone. Just as a reference, my furnace is 1" Mizzou backed up by 1.5" fireclay/sand so no insulation per se. Only some in the lid. So yes, it's a bit of a pig.

So i tune the furnace initially by watching the flame out of the exhaust as Yoda and others have previously described. About 4" out the hole, orange flame and no black. Then I adjust as the session proceeds and will finally top-out at full fuel (20psi fuel pressure (about 3 gal/hr), 25 lbs atomizing pressure) with my Kirby running flat out. The whole process takes about 1/2 hour and in that time can melt around 10 lbs of aluminum. By that time it's really ready to roll.

So now I'll get to the point. I'm having trouble wrapping my arms around the following quoted statement.

Is it excess air - air above and beyond what's necessary for complete combustion - that you are referring to? If so, then it is easy to understand. But is increasing air to support complete combustion along with more fuel in an increasingly hotter environment really make the flame colder?

 

it is excess air, you get flame temp increase with more air until you have complete combustion then the more air the cooler the flame temp because your using the btus to heat the excess air but it doesn't enter into the combustion process. any flame exciting the furnace after complete combustion is reached is wasted fuel,as there is no heat transfer to the metal outside of the furnace. if you measure the exhaust temp it will track the melt temp reasonable close, 2 or 300 degrees above melt temp until you start getting exiting flame then the exhaust temp will climbs towards flame temp quite fast. It is quite noticeable with oil and melting aluminum as the flame temp peaks at about 3600 NG or propane flame temp peaks at about 2900, the lower peak flame temp on NG or propane is why things need to be almost perfect to reach iron temps.

Art b

 

All the components of a flame must reach combustion temp before you have flame and BTUs coming from the process. fuel only burns in the vapor state never in the liquid state ( except magnesium then that is exothermic) so the BTUs needed must come from an outside source to vaporize the liquid and increase the oxygen,(combustion air) to ignition temp. this can be from a pilot, ignition arc,mechanical work of compression etc. It can take a substantial sized pilot to ignite a large burner. the burners in my titling furnace take almost 10000 BTUs for stable cold ignition. most of the commercial waste oil furnaces have a ceramic target that reaches stable ignition temps quite fast to prevent them from smoking on startup.

Art b

 

Thanks for the clarification

Pete

 

Here are some rough numbers to play with.
- A Air compressor Piston pump, generally produce about 4 CFM per horsepower up to 90-110 psi. My5 horsepower air compressor Max's out around 17 CFM.
- Most high-quality blowers can produce about 380 CFM (and 10 to 20 inches water column airlocked. My 5 hp dust collector pull's 1950 CFM at 6 inch diameter and the air is moving over 160 km an hour with 2 to 4 inches of water column.
- My big furnace blower (5.5 hp) has a maximum recommendation of 4.8 psi at the blower, with a maximum capacity 220 CFM through a 2 inch pipe minimal length. I'm only running it at 50% of the speed and 25% of the FLA.
- I also have a little portable blower. This thing draws 12 A from 120 V single phase. But at the end of all this plumbing piping and hoses I might be lucky to get 30 CFM at the torch tip.

I think it was mentioned earlier on in this thread but you do need CFM at the end of the torch. This is true. Some air CFM does come from torch tips that use solid liquid fuel that use pressurized air from an air compressor in a syphon nozzle tip. A syphon nozzle tip usually shears the fuel into a mist. Most liquid fuels have a viscosity that is too low, so sometimes pumping or pressurizing the fuel needs to take place.

In my situation, I need to warm up my WVO to above 40°C, and I pressurize the fuel container with a very small air compressor to 40 psi. But my fuel delivery lines are 3/16 ID. (I seen some guys using garden hoses with gravity feed).

I use a miniaturized air compressor to pressurize my fuel. The compressor is out of a refrigerator. My blower does the rest of the work.... Yes, I have a small air compressor and small blower. (But I also have a big blower and a big air compressor.) If I'm close to the home shop, I'll use the big machines.

This next part might get a little confusing as I have two torches. I have set up my torches to burn about 80 mL per minute. My aluminum melts are taking me about 20-30 minutes from a cold start up to melt 8 pounds. I can easily double the air and fuel ratio with my set up, but I don't think my furnace is big enough. I pushed my furnace to these numbers and I have about a 3 foot flame coming out the exhaust. Maybe my attitude might change when the clock is running and I'm doing cast iron.

The thing about too much air cooling a furnace, I have done this.... Had a good burn where I'm having orange/White flames 4 to 8 "out of the exhaust and then I juice up the air. Very quickly the furnace cools down and the flame pushes out.

 

I suggested this years ago as a possible idea back on AA years ago and was shot down (in flames), possibly quite rightly on a hobby scale furnace. How are the commercial 'targets' constructed?

 

they are basically a piece of Kaowool that is saturated with a ceramic mix and probably something similar to Sodium Silicate then fired to the 2500 range. The furnace linings are Kaowool saturated with SS to stabilize them. the picture that I included is from a waste oil furnace service company that sells on Ebay.

 

if my understanding is correct the air flow increase is due to the coanda effect that has to due with fluids following a curved surface at high velocity and generating a low pressure laminar flow parallel to the the high velocity fluid stream. the problem in using it in our furnaces is that it is affected by back pressure to a large degree. amplifiers don't work with much more ducting then 50 ft. an elbow in the ducting will almost kill the effect.
My first experience with coanda effect was with turning vanes in HVAC duct work elbows. a square throated/ radiased heeled elbow had the same pressure drop as a square heeled elbow but with a radiased throat it cut the pressure drop in half. as the coanda effect pulled they air around the elbow with very little turbulence after the elbow, with radiased turning vanes you could reduce the drop in an elbow to 5 to 10% of a square elbow.

Art B

 

I did wonder about back pressure/resistance. I can't see the point in over complicating things if a blower will suffice

So they are a consumable piece? All be it cheap and easy, makes sense.

 

I've had issues with various nozzle designs having a spray angle wider than 90 degrees and hitting the walls of the tuyere. I can exploit this spray cone by lining my 4" tuyere with a layer of refractory to form a slight nozzle and have a hot surface for the spray to vaporize off. The nozzle fires into the furnace chamber and I had noticed an improvement in performance by withdrawing the nozzle about four inches back into the tuyere pipe. At first I thought it was tuning the length of the flame but now I think the spray was hitting the hot refractory surface where the tuyere enters the furnace.

 

hey fellas, so after a lot more reading and playing around with a few things i ended building a dave allen delvan siphon nozzle burner, and boy is she hot, i used a hago delvan 1gph siphon nozzle and a corded leaf blower capable of 450 cfm. Last night got her going full blast. I used 15lbs of copper as a test material but was unable to bring the furnace up to copper temps after an hour and a half, The crucible/frurnace walls were glowing a light orange yellow color as was the copper but i couldnt get any hotter. Im realizing that i might have an insulation issue in the furnace body. There was no shortage of heat so clearly keeping the whole thing properly zipped up might be the next task.

Been reading about blue-ram this morning? thinking about adding another layer of refractory of some sort on the interior of furnace (walls and lid) but not sure exactly how to move forward.

as always any and all advice would be greatly appreciated

C

 

Really? Ran it on propane for about twenty min heat up the walls, then added the diesel. 1 gph for a little over an hour, Running diesel, became frustrated at the end and added propane into the mix to see if it would make a difference. About twenty mintues after that I got rained out.

If it makes a difference I was running 40 psi through the siphon nozzle.

Ty Kelly