Medium sized monotube boiler

[rangerssteamtoys]

I think you need to have the groove in the bender exactly the same as the OD of the tube. I've heard that filling a tube with sand can help prevent it from kinking when bent.

Thats a copper tube bender. We have some small ones 3/8" diameter but thats not 5/8" The copper tube bender is a very well designed bender, so if we can get a big one we might have something to work with.

 

[rangerssteamtoys]

SAND is the key. Kvom, you were a supporter in this but we had already tried it. I went out and tried a different process and it worked perfectly. A nice 6 1/4" diameter OD coil, I used about 6 feet of sand filled copper. Now I'm thinking about making a turn table for the pipe. I can attach a crank to the pipe and spin the pipe while someone holds the sand filled copper. Now how to fill up 60' of copper tubing?

 

[georgeseal]

Maybe a 60' step ladder :big: :big: :big: :big: :big:

 

[raym 11]

Don't forget the most important things.

Hydrostatic testing of completed boiler.

Calculation of Pressure Relief Valve sizing and pressure setting.

Ray M

 

[rangerssteamtoys]

Don't forget the most important things.

Hydrostatic testing of completed boiler.

Calculation of Pressure Relief Valve sizing and pressure setting.

Ray M

How do I calculate a pressure relief valve. I was going to use one from an air compressor.

As for the boiler, I have not made much progress. The valve tappet on my 2hp Briggs broke so its no good till I get another. But I have converted the 5hp Briggs, it gives quite a bit of power.

I figured the boiler needs to only go up about 70-80 psi max. Not the 150 I had hoped for, but its safer this way. My bigger and more powerful engine only need about 55 psi MAX that gives about 700-800 RPM. With steam I hope I can get more speed and more power.

Now for the question, can I make a monotube boiler only go up to 80psi max? To do this I would need a very small fire, right? Its getting to be the time to make the boiler that I have been putting off, getting technical; not something that I'm really good at.

 

[rangerssteamtoys]

Progress has been made. Today I coiled and soldered the tubing. Its about 50' of 1/2" in a 8" diameter, I will try to get some pictures.

Here is a problem that has occured though, the coils need to have an entry and exit and to do that I need to couple the copper tubing to some copper pipe. I have the couplers and know how but its just the saftey, one couple has to be next to the fire. I have some really good silver solder but am still worried, do you think that this will be OK?

Here is a coupler to connect the length of tubing together. The longer lenghts are closer to the fire, shorter ones are farther away

I added this piece of tubing on so the steam water in and steam out are next to each other. It will make it easier for me to plumb the boiler this way. There is less pipe needed and the tube acts as a preheater.

It basically goes right down the middle

I'm proud of what I have done, in all there is 53 feet of coil to be heated. I have some extra but it was getting close to not fitting in the outer shell.

Can anyone give some advice on how to hold the coils in the boiler???? I'm going to have a problem with that ???

 

[Florian]

Hi ranger(steamtoys)

1. I would put another tube into the boiler which has the inner Diameter of your coil minus 2 inches. This would make the fire go over your coil and i think it would make your boiler more efficient. -> If you don't have any idea what i mean, ill make a sketch. Of course, on the bottom you would need to fit a cone to the tube.
To fix your tube, you then could ad bolts from the outer tube to the inner one (if you are going to make such a tube) and then just have your coil supported by the bolts. And i would fix the coil where it enters the outer tube and where it leaves the outer tube.

2. Security-valves: I don't know if the security valve of a compressor is suitable for steam. Maybe the sealing is not for these temperatures. (If you want to use one.. check this first!)

Maybe you should couple the copper pipe with the tubing on the outside of your outer tube. But actually it should not get damaged if you always have some cold water being pumped into your tube-coil.
For Firing it, i think it would be best, if you make a circular tube burner using propane. (so you can adjust the fire to the steam consumption.

Florian

 

[raggle]

I'm late in this thread having joined you all only yesterday.

Seems there has been no activity here since July - did I miss something? Was there a loud bang or hiss out west?

I've been interested in flash steam boilers since I read a book borrowed from the library on Doble Steam Cars about 30+ years ago. Shortly after that, when I was making a good living chemically descaling boilers and other heat exchangers, I was called to a Stone's Generator for descaling. I was delighted to find that I could leave my pumps unused on the truck. I needed to ask the proprietor of the knitwear factory for a look at the manual.

There were two diaphragm pumps in the system, operated by cams from the motor and controlled by electro solenoids which held the diaphragms still when needed. Neither got hot, the valves being at one end of a long-ish pipe and the diaphragm at the other, well away from the circulating steam coil. One pump fed the boiler, the other kept it circulating.

The basic principle is that the water is continuously circulated through the single coil which may be several hundred feet long, thus no steam pockets can develop. These would lead to "dry" areas which would be quickly burned by the fire, rather the fluid is water containing bubbles of steam. Near the top of the coils the fluid escapes into a centrifugal separator which also contains high and low water level sensors. Steam output from the top of this chamber is passed through a small number of coils in the flue in order to dry it and maybe give a little superheat.

In the foregoing I believe it is identical to the Doble's boiler, possibly even depending on Doble's patents.

The Doble car was fired by kerosene through a carburettor and could get 30 miles per US gallon. This was due in no small part to its excellent condensing system. 65% of the used steam was recycled, so its water tank could be quite small and there was no telltale cloud following it like those of the Whites and Stanleys.

The "compact" car that failed to get into production (concocted financial irregularities scuppered it so I believe) was to have a simple uniflow engine, unlike the DA one of the large cars, much as you have mentioned with your B&S engine. A good vacuum in the exhaust here would be a great advantage.

Doble Henschel ran steam locomotives in Germany for some years and the boilers found their way into diesel powered passenger trains for heating.

http://webserve.govst.edu/users/gaskrau/vapor.html

They seem to be more correctly referred to as vapour generators, but I remember being told they were used on board ship to power small auxiliary engines for pumping duties, etc.

To sum up, a flash plant should be an automatic unit with safety built in. Circulation of the water is essential, not just desirable. Overpressure, low (or high) water and over temperature of combustion outlet must ALL shut down the system.

I'm not sure of the use of copper pipe as a material, but probably fine for the circulated fluid. If you ever go the way of superheat those last couple of turns should be steel. After all, they won't suffer much scale.

I wish you well with the project. You have exactly the right attitude. Maybe it's a little on the large side for an experimental rig.

Ray

 

[taterfarmer]

hay, this about how far along i am on my monotube boiler

 

[Richard Hed]

hay, this about how far along i am on my monotube boiler

As for myself, I thimk a single tube is dangerous because of the steam bubbles building up and moving upward thru the tube. I thimk that several tubes coming from a base and moving upward to a manifold is less dangerous. If built right, it should have circulation built in.

 

[57mm_M18]

I'm late in this thread having joined you all only yesterday.

Seems there has been no activity here since July - did I miss something? Was there a loud bang or hiss out west?

I've been interested in flash steam boilers since I read a book borrowed from the library on Doble Steam Cars about 30+ years ago. Shortly after that, when I was making a good living chemically descaling boilers and other heat exchangers, I was called to a Stone's Generator for descaling. I was delighted to find that I could leave my pumps unused on the truck. I needed to ask the proprietor of the knitwear factory for a look at the manual.

There were two diaphragm pumps in the system, operated by cams from the motor and controlled by electro solenoids which held the diaphragms still when needed. Neither got hot, the valves being at one end of a long-ish pipe and the diaphragm at the other, well away from the circulating steam coil. One pump fed the boiler, the other kept it circulating.

The basic principle is that the water is continuously circulated through the single coil which may be several hundred feet long, thus no steam pockets can develop. These would lead to "dry" areas which would be quickly burned by the fire, rather the fluid is water containing bubbles of steam. Near the top of the coils the fluid escapes into a centrifugal separator which also contains high and low water level sensors. Steam output from the top of this chamber is passed through a small number of coils in the flue in order to dry it and maybe give a little superheat.

In the foregoing I believe it is identical to the Doble's boiler, possibly even depending on Doble's patents.

The Doble car was fired by kerosene through a carburettor and could get 30 miles per US gallon. This was due in no small part to its excellent condensing system. 65% of the used steam was recycled, so its water tank could be quite small and there was no telltale cloud following it like those of the Whites and Stanleys.

The "compact" car that failed to get into production (concocted financial irregularities scuppered it so I believe) was to have a simple uniflow engine, unlike the DA one of the large cars, much as you have mentioned with your B&S engine. A good vacuum in the exhaust here would be a great advantage.

Doble Henschel ran steam locomotives in Germany for some years and the boilers found their way into diesel powered passenger trains for heating.

http://webserve.govst.edu/users/gaskrau/vapor.html

They seem to be more correctly referred to as vapour generators, but I remember being told they were used on board ship to power small auxiliary engines for pumping duties, etc.

To sum up, a flash plant should be an automatic unit with safety built in. Circulation of the water is essential, not just desirable. Overpressure, low (or high) water and over temperature of combustion outlet must ALL shut down the system.

I'm not sure of the use of copper pipe as a material, but probably fine for the circulated fluid. If you ever go the way of superheat those last couple of turns should be steel. After all, they won't suffer much scale.

I wish you well with the project. You have exactly the right attitude. Maybe it's a little on the large side for an experimental rig.

Ray

 

[57mm_M18]

I don't know if this link will work properly. I sometimes have issues with digital systems. Anyway, here is a link to some drawings of the single tube boiler being discussed here.

http://kimmelsteam.com/henschel.html

 

[Steamchick]

How do I calculate a pressure relief valve. I was going to use one from an air compressor.

As for the boiler, I have not made much progress. The valve tappet on my 2hp Briggs broke so its no good till I get another. But I have converted the 5hp Briggs, it gives quite a bit of power.

I figured the boiler needs to only go up about 70-80 psi max. Not the 150 I had hoped for, but its safer this way. My bigger and more powerful engine only need about 55 psi MAX that gives about 700-800 RPM. With steam I hope I can get more speed and more power.

Now for the question, can I make a monotube boiler only go up to 80psi max? To do this I would need a very small fire, right? Its getting to be the time to make the boiler that I have been putting off, getting technical; not something that I'm really good at.

Hi Ranger.. I have just picked-up on this one, as I have been busy with life, odd jobs and other threads.... But I have just spotted your "boiler" ideas and discussion. Please forgive me if I seem to be "teaching Grandma how to boil the kettle" - but there are a few MUSTS - as suggested by ElGringo, Richard, Ray and others who probably know more than I do.
But here are some MUSTS - taken from the ASME Regulation: Incidentally, before anyone gets a bit "gung-ho" about my quoting a Regulation and says it doesn't apply to them, please put your sensible head on and ask yourself if you want a boiler to blow up and kill you or your loved ones... Actually, Regulations are Law in the countries to which they apply, but I don't care about anyone breaking their laws, as long as they don't break hearts.... Steam is flippin dangerous! - Hence Boilers and equipment need PROPER control.
The simple rules (I won't just quote Regulations, but here's common sense as well...).

1. A Boiler shall be properly designed: - I,E, Calculations for strength, sizes of materials, heating and safety valve sizes, etc. And if you don't know how to do it, get a real professional design and use that. (NOT just something someone gave you of a boiler that "does the job", but one with a certified engineer's name to it. As you have made a coil, I suggest you get the calculations done before doing anything else - so you do not do any wasted work but have a good boiler.
2. The Regs talk about the Maximum pressure for a silver soldered copper boiler as being based on material taking a max. stress of 3000psi. - which is based on the Maximum allowable stress at 400deg.F. (205 deg.C). Beyond that temperature, the copper and silver solder are simply not good enough. - So you need to calculate what pressure you can permit for your various tube diameters and wall thicknesses. Take a sample of the bent tube as per your coil and cut it carefully into some pieces, then check the minimum thickness of the copper that has been stretched (and thinned) by the bending process, Including any proprietary bends or other components. You must use the THINNEST of the measured wall thicknesses in any calculations - and even then be generous to be safe. You cannot know the thinnest point of a coil that is in effect 50ft long, so make allowances for the process having some areas thinner than others. Also, I am assuming it is seamless tube? - You can't use seamed tube in boilers according to my understanding of UK Regs. Common "plumbing" pipe is OK for water up to 100deg.C or 212 deg F. for the pressure it says on the label. BUT at the temperature for 80psi you want to HALVE that pressure to avoid over-stressing the copper tube - according to the Regulations. So, unless the tube is factory approved for 160psi or over for domestic water supply, then scrap it and get heavier gauge tube that is good for well over 200psi "domestic temperature" water... Then think about temperature of your superheater, and maybe use better material than copper for that?
3. Incidentally, Lead or tin soldered joints will fail in a boiler to steam above about 15psi NWP. - And you want 80psi NMP!! So don't use ANY soft solder on your boiler.
4. Safety valves: The safety valve needs to be capable of preventing over-pressure when the fire is at its maximum. So you need a good understanding of what fuel, how much fuel and air can be supplied, and the total heating area of the boiler so you can calculate how much steam - at 84psi the safety valve needs to be capable of venting. Don't just fit one off your compressor. Steam is NOT air and although "at lift" the safety may do the same job, it is doing a different job to limit the pressure of the HOT steam compared to Cold compressed air. Gas flow through the valve, and all that. I have proprietary safety valves for air and they perform differently with steam - and vice-versa with the steam safety valves. So now I make my own STEAM designed safety valves - which work nicely - without over-pressure during the safety certification test, and without washing the garage roof when they blow!
5. There is a lot more... but I think you should digest this lot and others' comments first before you make anything else?

Keep on, as it is an interesting project. - Maybe it is mentioned earlier - and I haven't read everything yet (life is too short!) - but what dimensions are the bore and stroke and max. revs for running your engine? - That is the STARTING point to design a boiler... too many people start off guessing the size of boiler and end up too small - more wasted work. I buy those boilers and re-fit them. - People think my boilers are a bit large, but they won't be short of steam - and they perform as the calculations predict.
Ask when you need more information.
Cheers!
K2

 

[Steamchick]

Hi again Ranger, I forgot to mention that the Hydraulic test pressure for your boiler with NWP = 80psi shall be at least 204psi according to ASME regulations.
Min. Test value = NWP x 1.3 x Stress value for cold/stress value for temperature at NWP.
I.E. 80 x 1.3 x 6700/3418 = 204psi: So use 205psi min test value.
IF you are sure your tubing is good enough material (by reference to the maker's data on application and Normal working Pressure - then halved by calculation to see if it is OK for >80psi... and after checking any thinning from the bending...):
I suggest you do a 20 to 30psi air-leak test on your tube before progressing further, as you have some joints in it. Hold air for >15mins without pressure dropping, and check all joints with soapy water for bubbles all through the 15 mins. ANY bubble forming in the 15 mins must be fixed. Then repeat at 50psi, then 70 psi, then in 10 psi intervals up to 120psi. If you can do it in a bath - with the tube full of air but immersed under water - then bubbles may be easier to spot than soap bubbles. But you need to be able to examine all the way around all the joints and watch for 15 mins as a small leak may take that long to show a single bubble. Trust me - I did it as a job.
When definitely leak free with air, completely fill the boiler with water, all openings sealed and pump water to >205psi and hold for 15 mins. Only then should you bother making anything else...
But if the tubing isn't good enough on calculation, beforehand, don't bother even testing it. Use it for something else and not the planned steam boiler.
Did I suggest it is an "interesting" job?
K2

 

[Steamchick]

Hi Guys. I just spotted the dates on the postings while reading this one from start.... Seems I am 12 years late joining the party!
Ranger - Are you still around? - Hope you made a boiler and it worked safely. You had a couple of good guys as mentors while you were making that rig - including your Dad - from what I read.
As a few of us have just been joining this old thread, perhaps you can bring us up to date with your life, the universe, or anything?

Taterfarmer - is that Montana? If so, the ASME code is applicable to you. It seems you are doing something similar - making a tube boiler - so please ask if you want some help (from the UK!). I'll try my best.

Cheers!
K2

 

[taterfarmer]

copper tubing wasn't holding up to temperature or pressure i was reaching for. i now have 20ga. stainless steel 1/2" tubing .

on the construction of a vertical flash boiler :: anyone kno whether its better to inject water from the top or bottom of the coil?
..
in my research it seems different people have different preferences...

 

[Richard Hed]

copper tubing wasn't holding up to temperature or pressure i was reaching for. i now have 20ga. stainless steel 1/2" tubing .

on the construction of a vertical flash boiler :: anyone kno whether its better to inject water from the top or bottom of the coil?
..
in my research it seems different people have different preferences...

I would say if the water is hot when injected, that it wouldn't matter where you injected it, however, if the water is cold, I would thimk it would be best to inject it at the bottom

 

[Asm109]

Given that the OP has not been on the site since 2010, I don't think any updates will be forthcoming.

 

[Steamchick]

Maybe the adjudicator can move all 2020 posts from n to Taterfarmer to his other thread on this boiler?
K2

 

[Steamchick]

For best efficiency, cold water injected at the cold end should maximise heat exchange. But what burner and hot-end temperature do you expect?
What pressure will you have as NWP? Normal Working Pressure equals the point at which you will reduce fire and NOT EXCEED during normal useage. Even though you may run at a lower pressure, NWP is the pressure for designing and rating the boiler, safety valves, control system, etc. For safety, you must follow the regulations. (ASME). I'm sure it is law in USA and affects (possibly negates) your insurance.
K2