Monotube Boiler Design – Radical Thinking

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Tony
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Monotube Boiler Design – Radical Thinking

Post by Tony » Wed Aug 30, 2017 5:43 pm

For many years I have been building and developing various monotube boiler designs including a couple of Lamont ones, some with a moderate degree of success others were very unsatisfactory! There were none that I was entirely satisfied with.
My last one was probably about the best. This was a Lamont boiler using a pump I designed myself located in the bottom of the drum. It was driven by a long shaft through a seal in the top end plate coupled to a DC motor. The seal caused a few problems but I managed to solve them eventually. One advantage of this system is that the steam exits from behind a spinning baffle disc attached to the shaft near the top giving remarkably dry steam. When it was working properly the system worked well producing a good quantity of dry steam at 120 PSI from 20ft of 10mm copper tube and a 15Kw gas burner. However, there were various reliability problems with the pump, and access to it was difficult as it meant a complete strip down of the drum. The whole set-up is also heavy and complex.
I was considering going back to a basic simple monotube again using the experience gained with recent designs, but then I had an idea!
The problem with any monotube boiler is that it is unstable. Because the passage of water/steam through the coil is slow (especially through the first part of the coil) steaming is poor so a long length of tube is required compared to a Lamont. This leads to slow response times for controlling and consequent instability.
Now, it might be possible to take advantage of this instability and design a system that was deliberately unstable. If there were 2 of these (i.e. 2 separate monotubes) one could be fed into the other in such a way that they would oscillate, it would probably be necessary to fit non-return valves in various places and possibly supply the feed water alternately to encourage it to oscillate. This would give a system which had rapid flow in both directions enabling a shorter length of tube to be used for satisfactory steaming. The temperature gradient along the length of the coils would also be much less and consequently overall control should be easier.
What does everyone think?
Has it been tried before and failed? (like most of my Eureka ideas!)
Comments would be much appreciated.
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Re: Monotube Boiler Design – Radical Thinking

Post by cyberbadger » Wed Aug 30, 2017 10:35 pm

Tony wrote:The problem with any monotube boiler is that it is unstable.
I would say that they are difficult to match their steam ourput to steam consumption. With essentially almost no buffer that is hard to do.

Keep in mind that consumption can change for a lot of reasons that may be out of your control - eg no insulation on the engine and suddenly a lot of wind cooling it, A changing engine load from say choppy waters maybe not so noticable with a VFT but a big deal with no buffer from a monotube.
Tony wrote:Now, it might be possible to take advantage of this instability and design a system that was deliberately unstable. If there were 2 of these (i.e. 2 separate monotubes) one could be fed into the other in such a way that they would oscillate, it would probably be necessary to fit non-return valves in various places and possibly supply the feed water alternately to encourage it to oscillate. This would give a system which had rapid flow in both directions enabling a shorter length of tube to be used for satisfactory steaming. The temperature gradient along the length of the coils would also be much less and consequently overall control should be easier.
What does everyone think?
I see where you are going, but I think it will be very hard to pull off. Don't let anybody discourage you if really want to try it, but expect difficulty at best.

Can some sort of a steam drum be added to a monotube boiler?

-CB
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Re: Monotube Boiler Design – Radical Thinking

Post by Lopez Mike » Thu Aug 31, 2017 12:14 am

Seems like a bunch of trouble for a pretty small increase in efficiency.

How about taking the liquid fuel and injecting in right on top of the piston at the top of the stroke. You let in a bunch of air near the bottom of the stroke and the air gets so amazingly hot as it is compressed that the instant the fuel is put in there it burns.

This could be combined with the uniflow principle thus letting the burned gasses escape through ports at the bottom of the stroke.

The possiblities are endless. I don't know why no one has thought of this before. It completely bypasses all this converting of the energy of the flame into evaporating water with all the losses inherent.

Oh well. Probably some German has thought of it in the nineteenth century.

I think I'll stay with my African Queen clone.
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Re: Monotube Boiler Design – Radical Thinking

Post by dhic001 » Thu Aug 31, 2017 9:30 am

Monotubes aren't that hard provided you have good fire control, which really means liquid fuel rather than solid. The trick is to have a variable stroke set up on the engine driven feed pump to allow it to be set perfectly to match the demand of the engine. Once it has been set up in action it shouldn't change. A good hand pump is needed to get things running initially, and a water separator is needed on the output of the coil, but otherwise its relatively simple. If you are getting wet steam coming out of the monotube you are putting too much water in, if its too dry, there isn't sufficent water. Once the engine is warm and under load, the steam consumption to water feed ration won't change, so by setting the stroke correctly on the pump, it will stay in balance nicely. Certainly has on the Monotubes that my friends have built here.
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Re: Monotube Boiler Design – Radical Thinking

Post by RGSP » Thu Aug 31, 2017 11:05 am

Lopez Mike wrote:Seems like a bunch of trouble for a pretty small increase in efficiency.

How about taking the liquid fuel and injecting in right on top of the piston at the top of the stroke. You let in a bunch of air near the bottom of the stroke and the air gets so amazingly hot as it is compressed that the instant the fuel is put in there it burns.

This could be combined with the uniflow principle thus letting the burned gasses escape through ports at the bottom of the stroke.

The possiblities are endless. I don't know why no one has thought of this before. It completely bypasses all this converting of the energy of the flame into evaporating water with all the losses inherent.

Oh well. Probably some German has thought of it in the nineteenth century.
Well, we know one did, because they tell us so, though in fact the German patent was for injecting coal dust into a cylinder, not oil. An Englishman from Bradford had demonstrated a compression ignition oil engine about 5 years earlier, and like everyone else, I can't remember his name.
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Re: Monotube Boiler Design – Radical Thinking

Post by DetroiTug » Thu Aug 31, 2017 1:02 pm

"If there were 2 of these (i.e. 2 separate monotubes)"

I think it would be half as much trouble with each for the same load and the sum being the same amount.

One of the big issues with a monotube, is they have virtually no natural internal circulation as the coils are typically very near horizontal, don't believe that? Try running one on it's side with the coils vertical. The water simply doesn't know which way to go, steam is created where it isn't supposed to be, and they end up belching water occasionally. A fix for this is the Lamont design and/or a continual running feedpump and it is reliant on a constant demand to balance it all. The best remedy is a column reservoir typically associated with the Lamont design which serves as a reserve and also separator, but it involves the circulation pump that no one can seem to find or build successfully.

If the coil is angled five degree upwards throughout it's height, this will promote natural reliable internal circulation, although this shortens the coil length and reduces heating surface, remedy is to add more coils connected to the drum. Eventually arriving at the Ofeldt design or some variant of it.

-Ron
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Re: Monotube Boiler Design – Radical Thinking

Post by Mike Cole » Thu Aug 31, 2017 2:36 pm

[quote="

Oh well. Probably some German has thought of it in the nineteenth century.

I think I'll stay with my African Queen clone.[/quote]


I think you will find it was no German but a man called Herbert Akroyd-Stuart 2 years before the German fella.
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Re: Monotube Boiler Design – Radical Thinking

Post by TahoeSteam » Mon Sep 11, 2017 4:14 am

You need a temperature and pressure controlled bypass, either mechanical or electrical... less feed equals less steam production, but also dryer/hotter steam.. more feed equals more steam, but also wetter.. a separator and a superheater or de-superheater and a lot of tuning... it can be done and made to run extremely reliably, albeit with lots of engineering and tinkering. The work William Grosjean did to build the boat I inherited from him is a testament to this.
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Re: Monotube Boiler Design – Radical Thinking

Post by Metaltrades01 » Tue Sep 26, 2017 1:25 pm

[quote="dhic001"]Monotubes aren't that hard provided you have good fire control, which really means liquid fuel rather than solid. The trick is to have a variable stroke set up on the engine driven feed pump to allow it to be set perfectly to match the demand of the engine. Once it has been set up in action it shouldn't change.

I have always had an interest in Mono's, bit of a fan of Doble's.
is that change the stroke "on the run" or stop and change.?
What type do you do you use.?
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Re: Monotube Boiler Design – Radical Thinking

Post by dhic001 » Thu Sep 28, 2017 10:27 am

The ones we've set up have been stop and change. Simply done by having an adjustable position eccentric to allow the stroke of the pump to be altered. Once you've got it set correctly, it doesn't ever get changed, unless you make some significant change to the steam consumption (ie alteration to the engine, load characteristics etc).
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