Doble Boiler

Hi, I got the boiler running on propane. The blowoff valve worked good, kept the pressure at 600 psi.
Looked good, sounded good, I think I want to hook it to my multi rotor steam engine.
Movie [youtu.be]

So I hooked it up to the engine, made steam, the temp and pressure was going down. Than I noticed the propane pressure went from 70 PSI to 20 PSI.and frosted the tank. So I switched to gasoline and was unable to get a good burn.
I took the burner off the boiler and am going to see if I can figure it out.
Ooo Weee, and this is the fun part?
Don

The propane tanks typically frost up when used. The guys with the steam boats often put their propane tanks into their hot wells to keep them warm. Unfortunately, with a full propane tank, the expansion at times blows the tank's safety valve and often a fire results. Personally, for fire safety, I perfer to use kerosene or JP1. A lot safer. The fun starts when the assembly starts and the fun never quites. I have more fun driving a steam car than I do working on them. Both are fun though.

Ran the burner today, I was able to get good reliable combustion using my welding torch.
I am wondering how much of the gasoline is oxidizing in the atmosphere O2 outside of the burner. It is hard to tell because it is invisible. In the boiler it will only have the O2 from the blower.
I was increasing the gas flow and the air requirements for good combustion stayed about the same.
I started at 25 PSI gas pressure and went up to 100 PSI with the needle wide open. The more gas the more heat.
I feel most of the gas was burning out side the burner, so there is no way to tune it for the boiler.
Movie at [youtu.be]
Best, Don

Hi all,
So is combustion complete before it gets to the water tubes? Or does combustion continue through the coils to the end.of the boiler? Any ideas?
Don

Don-

You must have your combustion chamber set up in a way that ensures the combustion is complete before it hits the tubes. Otherwise you will get incomplete combustion and soot forming thruout your coil stack. It is possible you are "throwing away" some of your fuel...unburnt fuel blowing thru your flame without burning because you've already used all the O2 in the combustion air.

The combustion chamber must be designed in a way that encourages a long enough residence time within the chamber for the fire, so that combustion is complete before it exits and hits your tubes. You can increase the residence time in several ways. I've used a circular baffle positioned right in front of the fire, so that the fire hits it and has to pass around it causing turbulence. Mounting a swirler into the incoming combustion air to induce turbulence and good fuel/air mix is another way to to it.

It looks like the fire in your combustion chamber is blowing thru without staying long enough to get complete combustion. The design of the chamber itself will determine to a large extent how well the combustion goes. Turbulence within the combustion zone is the key to everything!

If you PM me-I can send you a coupla photos of combustion chambers I have designed/built that work quite well.

Good Luck!!

Chuk

Combustion should be complete before the heat goes through the water tubes. Combustion happening while going through the water tubes will result in sooting up the water tubes, thus insulating the water tubes from the heat. The same applies to the fire tube boilers. On our Stanleys, the flame is adjusted at the burner so that it has a proper blue color with a very small tip of yellow on the top of the flame. This flame all takes place below the lower tube sheet on a vertical fire tube boiler. The flame is adjusted by fuel pressure, jet size and how far the jets are located out from the mixing tubes.

I added a secondary air supply after the burner to control combustion. It may induce turbulence and more complete combustion. There is 16" from the burner outlet to the water tubes 14" wide, so room for combustion?
If you can`t see fire, red or blue does that mean there was complete combustion?

Don,

Look at an original Doble steam generator....a large portion of the unit is dedicated completely to combustion, before it passes over any generator tubing. The fuel / air enters tangentially at the top and swirls (just like Chuk was referring to), thoroughly mixing the fuel / air for complete combustion.

Jamison

G-day
I`ll run the boiler with the exhaust open till I get the mixture figured out than see the effect of closing down to 5" is.

Hi all,
Crashed my trike, fixed my trike, tested my boiler.
After increasing the size of the jet at the end of the burner tube (wide open 1/4" I got much hotter fire making 600psi 442F steam. That is a bit less than saturated for 600psi at 486F. So a lot of hot water?
To make super heated steam I need more heat or less water flow. The water flow is a little less than 1 gal/min or about 50 gallons /hr. Is this a lot? I have been having difficulty slowing the pump (pressure washer) as it shuts off after being restricted past a point. I think I could bleed off some of the incoming water to reduce the flow to the boiler. And 40psi fuel pressure, up from 20psi will give me more control through the needle valve.
Best regards, Don

Hi Don,

There's no real answer to "is that a lot?", it depends on the burner, engine demand and so on...it could be too little if the engine needs more steam than that in order to perform effectively.

The easiest way to regulate a piston pump is a bypass back to the pump suction or the feed water tank ... basically a tee in the line after the pump discharge with a needle valve on the leg of the tee connected to the feed tank. Or....if your pump is actuated by a pulley, chain or gear, you can just reduce the driving ratio.

Regards,

Ken

Hi ken,
How much water does a Doble use flat out?
I set up a bleed valve that goes to a bucket see pic.
I am reducing the flow to 2 qts/min
Don

Hi Don,

I would have to estimate, but a Doble probably consumes something on the order of 4 gallons a minute, at absolute full power. Let's say full power is 100 HP, the engine is drawing about 25 lbs/hp-hr (longer cutoff), that's 2500 lbs/hr. Divide by 60 minutes per hour to get about 40 lbs per minute. Divide by 8 lbs/gal (roughly) and figure about 5 gals per minute. There's some plus or minus involved here.

Hi all,
I insulated the boiler and did more testing.See pic.
I got the temperature up by giving it more gas flow and more air.
By looking in the spark plug hole in the burner I could see that the color was blue, as it expands into the after burner chamber there is a orange color to the flame. As I turned up the gas the closer to the water tubes the red flame got. I was trying to keep carbon off the tubes. So I was slowly turning up the gas till the colored flames got to the tubes. I wasn`t getting enough heat still so I gave it more gas ( flames licking the tubes) Heat wise it loved it, the steam output went up a lot at once and the temperature went up rapidly, It responded very well to 600psi 700F than I shut it off.because the temperature was going up very fast. It seams I need more water flow, less bypass water.
Don



Edited 1 time(s). Last edit at 11/27/2019 11:47AM by donmaguire1.

Keep in mind that the combustion in a coil monotube has different optimization from the flame plume in a typical Stephenson locomotive boiler, where radiant uptake is an important part of the steam generation. When combustion is complete, the resulting gas is transparent and therefore has transmission peaks (some in the infrared region) and not a smooth blackbody emission spectrum like excited vaporized carbon.

The problem with adjusting flame length in a typical monotube is that the more 'luminous flame' you can get around a tube, the greater the potential heat transfer (at Stefan-Boltzmann fourth power of luminous temperature) BUT the more likely that a relatively cold tube, for example one with even fairly preheated feedwater, will quench luminous combustion -- this is where the black carbon of soot comes from. If you wonder why some designs put thermal barrier coatings on the outside of some parts of a tube nest, precluding early quench is one reason.

The presumptive answer to a couple of Don's questions is to get a good, accurate spot-reading IR thermometer -- I prefer the kind with a small 'laser designator' showing the point of aim even at distance. This will give you a reading of combustion gas temperature in the IR emission range even if the gas is transparent; holding a small coupon of refractory metal or ceramic in the gas flow will give you a re-radiant target if not.

As a historical note: the actual effect of Besler tubes was analyzed in unrelated chemical-engineering research in the mid-1980s, and it turns out to have something to do with uptake from transparent combustion gas in firetubes. As I suspected, the Besler tubes act as passive re-radiators; any attempt to use them for feedwater heat or other convenient use of the enthalpy in the convection section is likely a mistake at best. One effect of the tube is to constrict the gas flow in a firetube to an annular region with relatively good flow characteristics (compared, say, to a Stanley nest of multiple tubes with small aspect ratio). The combination of convection and conduction in laminar flow adjacent to the Besler tube heats it, and the tube surface re-radiates as a good approximation to a blackbody -- now at a virtual right angle (it is somewhat refracted by the transparent gas) to the inside wall of the firetube. This I think explains the reported substantial heat-transfer improvement the Beslers reported for their experiments with this sort of arrangement.

I am making a new monotube boiler tubing array 600 ft of tubing, no connectors, no welding.
I made some aluminum plates with slots in them so when the first row is full you go through the slot in the separator discs than to the hub to start a new row. I made 4 of these discs and wound 100ft 3/8" .049 "ss I only used 3 discs. There is a clear 4 1/2" hole in the middle that I will block off.
See pics
Don
.

Hi all,
Made a tubing bender, 1/2" od, see pic, it works good.
Took the old tubing out of the boiler, it had a good coat of carbon on it.
I could bend the 3/8" tubing through continues multiple rows. The 1/2" tubing would kink a bit so i made individual rows and connected them together with compression fittings. The final array has 225ft of 3/8" tubing and 200ft of 1/2" tubing.

Don, what type of material is the tubing you are using made from? I have had trouble finding tubing in lengths shorter than 1000 feet or more except at very short lengths and high prices. At the moment unfortunately I can't afford anything but once I am again able to I do want to do more than draw out ideas on paper.
Thanks and best of luck to you!

Steve, I have been getting the stainless steel tubing from ebay in 100ft roles for $45.
Don

Hi all,
I tested the new boiler configuration.
The best I could get was 600 psi at 568F.
The combustion exhaust temp was 486F, I think that is a bit high.
A short vid, [www.youtube.com]
Don

How many SQ Ft of surface area do you have after the combustion area?

Drawing is one of mine about 30 years ago. Never did build it.
Rolly

Hi Rolly,
I have 48 sq ft surface on the tubing.
Don

Don
You really haven’t given us much to go on, but my 25 foot boat ran between 375 F and at about full firing rate at eight knots she’d run about 475 F,
I could push her to 500 RPM and 550 F and she would not go more then the eight knots.

My 35-foot boat Tryall ran at 600 F, all the time, Commercial Bryan 15 HP 300 PSI 5 Gal of oil per H, water tube boiler. I added a superheater and economizer to her. Tubes had two much spacing between them, they were designed to be replaceable.
Rolly

Hi, Don
On Your pictures it is seen rather wide central hole in the coil stack. Seems like You did not buffle it and this passage works and lifts exgaust gases temperature. Need to be clogged all through the length of the coils layout like on Rolly's picture.

Serge

There is a 4 1/2" hole in the meddle of the stack with a 4" tube with a plate welded at the fire end.
Don

Well, so may be the blowby goes another way. May be there is too big spacing between the tubes in the last section of tube stack within the row in the coil and so lower heat transfer coefficient. (Exessive passage area for gases and so lower velocity because cooler gases have bigger dencity) By the way, Abner Doble marked in his notebooks that without packing along outer shell of tube stack, performance of the boiler was worse than with packing due to the blowby... Heat transfer area of Your boiler is more than adequate, so it is something wrong with heat transfer.

Good luck,
Serge

Serge,
I think the answer is more tubing, more surface in the boiler.
I can`t move the stacks closer together because of the crossover portion spaces the coils by the thickness of the tubing. So 1/2" rows would have 1/2" spacing..
3/8 tubing will have a 3/8" spacing.
Don

½ tube diameter between tubes and arranged in turbulent flow is more to the norm for good heat transfer.
75% more then laminar flow.
This is the arrangement I used when I built my Derr boiler.


Rolly

Besler used a similar arrangement on a 200 HP generator.

Rolly

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