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Scavenged heat exchanger and burner

Posted by Arch-Tone 
Scavenged heat exchanger and burner
September 22, 2017 10:13AM
Scavenged this burner assembly and heat exchanger out of the metal recycling dumpster at my workplace. It's from a large swimming pool heater and has lots of neat parts like copper finned tubing, stainless steel burner assembly, temperature and pressure sensors, gas regulator and circuit, etc. Yeah....I know it's a "heater" and not a steam generator....built for lower pressure and temps / high volume....but I'm sure some of the parts could be reused for steam. Exchanger has a row of 9, staggered copper finned, straight tubes with cast iron manifolds on each end. The stainless steel burner assembly is probably the most steam friendly part here....made for natural gas but could be easily converted to propane. Here are some pictures...let me know what you guys think:


Re: Scavenged heat exchanger and burner
September 27, 2017 04:40AM
i tested the pool heater burners with propane....big orange flames from that thing. Would rather see blue flames, but it seemed to work fairly well and put out a lot of heat. I might use about 10 out of the 16 burners for the new lawn tractor boiler. Here's a link to the video:

Re: Scavenged heat exchanger and burner
September 27, 2017 07:19AM
Here I go again..smiling smiley

Yellow flame is too much fuel, not enough air. That was probably set up for natural gas which uses a much larger orifice as it is a lower pressure gas. There may be a chart on line to determine the correct size drill for propane based on what size they are now.

Re: Scavenged heat exchanger and burner
September 27, 2017 08:48AM
Thanks, Ron...,always appreciate you "tellin' it like it is". I noticed...especially in the slow motion part of the video...the fireball created about a foot above the burners when the valve was opened up suddenly...like you said, the flow is too "rich" and it is combusting mid air as it finally gets enough oxygen to do so...I might be wrong about that...just an observation.

So....is it the individual nozzles that are too oversized or does the propane flow need to be more restricted at the manifold (or both)? I noticed the individual burner nozzles are replaceable and threaded with 1/8" npt....I could replace them with 1/8" pipe plugs drilled out to the smaller orifice size for propane...or find direct replacements from the manufacturer.

What do you think of the flame pattern / distribution as far as adapting to heating a boiler?...I have in mind a rectangular Ofeldt (oops...I mentioned it again) style , natural circulating boiler design...similar in layout to the "marine type" Ofeldt (again), but with two vertical drums instead of the horizontal ones depicted. The fire would go underneath and ten of those burners would fit perfectly with what I have in mind. Or....am I just better off fabricating some burners from scratch?

Re: Scavenged heat exchanger and burner
September 27, 2017 09:37AM
Quote: "So....is it the individual nozzles that are too oversized"

Yes, more than likely, each one will have to be resized as each branch does it's own fuel/air mixing. The big manifold behind all of them simply supplies each one. Yes, you can make your own orifices or - Depending on how the orifice is made, the hole can probably be peened up over a mandrel by tapping with a hammer and then redrilling the proper size, common practice. Just looked, there are several Orifice conversion charts in Google images.

I don't know about the fireball above, but yellow flame is lack of oxygen. There is no way to fix that with fuel pressure, it's simply incorrect fuel to air ratio at the mouth of the branch or "mixing tube". We have the same issue with vaporizing fuel burners, orifice size is critical. We have different orifices for different driving- Parades type driving and shows where we have to go slow, detune with a smaller orifice and drop the fuel pressure. Too big of an orifice and we outrun the flow capacity of the mixing tube to draw adequate primary air and get yellow flame and sooting- problem you're having.

Would that work as a boiler burner? Sure will. No point is making what you already have. The burner you'd make would need orifices too smiling smiley You can probably modify the mixing tube length as well, shorten it up, but the closer the mouth is to the flame the better chance of a "backfire". Which in steam car speak isn't a pop or boom, it's when the fuel/air catches fire in the mixing tube or throat.

Re: Scavenged heat exchanger and burner
September 27, 2017 10:46AM

Good to hear that those burners are usable...they seem to be made out of high quality stainless and have the engineered taper to help equalize the pressure across the burner...not to mention the manifold that goes with it. I will try the peen and redrill technique you mentioned...and look up the orifice size as well.

I had the lawn tractor furnace "backfire" a few times...I had trouble igniting the torch and the cavities filled up with gas...sounded like a cannon going off. My 9 year old son thought that was the coolest thing and wanted me to repeat it...so I did. The neighbors were not quite as thrilled, however.

Hmmm...maybe use all of the burners for an automobile sized boiler spinning smiley sticking its tongue out...can these burners be modified to run on gasoline, with a vaporizer? Kinda scary to experiment with gasoline, though...I understand you preheat the vaporizer with something like propane and then switch to gas pressurized with an air tank...like Tony G's "De Lora". Perhaps Jeremy's statement about me making a steam car will come to fruition, after all. Not sure if the burner assembly has enough BTUs for that application....geez....sooo many questions...and I'm getting sidetracked...again

Re: Scavenged heat exchanger and burner
September 27, 2017 12:11PM
I also thought about converting a propane burner to gasoline. Theoretically all you would have to do is pass a vaporizer tube over the fire and feed that into the burner inlet, and change the jets.
Re: Scavenged heat exchanger and burner
September 27, 2017 12:44PM
Quote: "can these burners be modified to run on gasoline, with a vaporizer?"

Probably. From what I understand there is nothing detrimental about the apertures of a burner other than making them too large and allowing flame to jump inside. Some are simply holes, some are narrow slots, some use a jet looking fitting etc. So your burner should work on gasoline and even Kerosene, but it would take some designing and refining. There could be an issue where the mixing tube size would be a limiting factor, one fuel type versus another. i.e. Kerosene likes lots of primary air, which means a larger mixing tube. The burner branches you have were designed for a certain number of BTU on propane or natural gas, and there may only be a small increase by using hotter fuels like Gasoline and Kerosene and that limitation is in the mixing tube diameter / amount of primary air.

Quote: "Kinda scary to experiment with gasoline, though."

It demands respect, and like many things, it is as safe as it is understood and handled. For testing, a large pressurized tank is not needed, a 1 pound propane cylinder could be modified for a fuel tank and another modified as an air tank. Work in small quantities to mitigate the danger. And obviously take it outside away from any sort of dwellings etc, never fire a steam car up inside a garage etc. That is one of the reasons I like Kerosene versus Gasoline is the lower volatility in regard to combustion, and too Kerosene is around 12% hotter than Gasoline by volume so it is worth the effort in working out the extra difficulty in vaporization. And the difference is notable, Tony burns Gasoline and I burn Kerosene in virtually the same burner, mine puts out quite a bit more heat, he and I have both remarked on that. shooting the exhaust with infrared etc. Before proceeding, do some research ask questions and start out with something close and then work from there. Designing a burner vaporizer is not a place to learn how they work.

Quote: ".I understand you preheat the vaporizer with something like propane and then switch to gas pressurized with an air tank...like Tony"

He is the only one I know or heard of that does it that way and it works really well. He helped me with my car and urged me to set mine up the same way. I decided to take a more traditional route with two vaporizing fuel systems in series. My burner uses white gasoline for the pilots and then they vaporize the Kerosene for the main burner. My pilots are Optimus Nova All fuel camp stoves which start up very easily and preheat themselves. One of the drawbacks with using propane, is you never really know how much you have - and you have to carry a propane tank aboard. He runs his whole burner on propane and preheats everything and then switches over to gasoline. It's very easy and fast start up. Some of the Stanley guys as I understand it, use piped in Propane or hexanes to preheat the vaporizer on their pilot to start up, then introduce gasoline, some use propane only for the pilot. Many different ways of doing it, each with advantages and disadvantages.

I mentioned he runs his whole burner on propane, he can run his car like that if he runs out of gasoline, but he said hes lucky if it will go faster than walking speed, which is a good example of the propane versus gasoline for heat.

Re: Scavenged heat exchanger and burner
September 27, 2017 01:39PM
The safety of gasoline largely depends on burner design. For example, I have no worries about pushing gasoline through a nozzle because there is no air mixed with the gasoline. The flame can only jump back to the nozzle and it extinguishes when it hits the pure gasoline mass. In the case of a nozzle, the only real danger is that your pressure and hole diameter are such that you are dribbling fuel rather than atomizing it. Fortunately, you can check this without actually lighting a fire ... just run some fuel and see if you get a nice, even cloud.

More care is needed with a perforated or slitted flameholder through which a fuel/air mix is passed before ignition. If the flame propagates back through the flameholder it will ignite the fuel/air mix on the back side. Even then, however, the situation is controllable. Trust me, I proved this experimentally a number of times. If the unit is fairly well built, it can take a decent backflash ignition. The main thing to remember is to limit the volume of fuel/air mix that can possibly accumulate. If the volume of a perfect fuel/air ratio is not capable of producing a destructive detonation (and this takes some work when running at atmospheric pressure) then it is likely that you will never even reach that condition as most probably the fuel/air mix will be either rich or lean when running under the kind of conditions that permit back flash.
Re: Scavenged heat exchanger and burner
September 27, 2017 02:49PM
Hey fellas, maybe this link will be of use. It shows the size orifices needed for natural gas or LPG according to pressure and btu output.
[www.joppaglass.com] /burner/lowp_chrt.html (delete the spaces between as for some reason the preview clips the last part of the address
So depending on how many btu's output the burner is meant to output you can figure what size orifice to use . I hope this helps.
The tractor project is looking good!
Re: Scavenged heat exchanger and burner
September 27, 2017 06:01PM
Well...it took me about 1/2 hr and I got the burners to make super hot, nice and blue flames. The secret...I simply tapped and installed a 7.5 size stainless steel pressure washer nozzle inside the reducer coupling and drilled some holes in the side of the coupling to make it a venturi...to draw in more air. Luckily...I did not have to mess with the individual nozzles. I still have to tweak the amount of air being drawn in the venturi...but it's doing the job. Here is the new video:


Nozzle used:

Edited 2 time(s). Last edit at 09/27/2017 06:20PM by Arch-Tone.

Re: Scavenged heat exchanger and burner
September 27, 2017 06:42PM
That's pretty slick. It's definitely one way to get more air.

Although I think it is diluting the gas with air. Less BTU per cubic foot.

Re: Scavenged heat exchanger and burner
September 27, 2017 07:16PM
Thanks...I'm thinking of putting a small valve...maybe a needle valve, like the type used on refrigerator water lines...on the reducer to control the amount of air drawn in. It seemed to have the best flames when all the ports I drilled were loosely covered by the tape and just a little bit of air was seeping through the gaps. With a small valve I should be able to duplicate that and fine tune it as needed.
Well...looks like I can get 2 usable burner assemblies out of this thing....a 10 burner for the tractor and a 6 burner for something else. I have a flash steam bicycle system I'm designing...don't think it will work for that, though.

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