Monotube Boiler Idea

Moderator: csonics

Post Reply
User avatar
csonics
Anne from Little Britan
Anne from Little Britan
Posts: 232
Joined: Tue Nov 17, 2009 11:17 pm
Boat Name: No Boat Yet
Location: Roseville, MN
Contact:

Monotube Boiler Idea

Post by csonics » Wed Nov 18, 2009 4:52 pm

Posted on behalf of stevey_frac:

stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Thu Aug 13, 2009 8:16 am Post subject: Monotube Boiler Idea
Hi Guys!

I was thinking about an idea for a monotube boiler, and i'd like to see if you guys can spot any flaws in it.

I want to separate the heat exchanger from the combustion area. There are two reasons for this

1) I want to burn wood at temperatures hot enough, that even wood smoke burns, at least 1300 degrees, hopefully closer to 2000 degrees. The introduction of steam lines before everything has finished burning is detrimental to this process by cooling things off before combustion is complete.

2) I want to be able to completely and instantly shut off steam production for no load situations.

This creates a disadvantage in that I would not have any radiant heating of the steam lines, and all heat transfer must occur almost solely by convection heating. This could have the side effect of increasing the surface area of the heat exchanger more then could be cost effective. I haven't done the math on it.

In operation though, such a boiler would be safer. When I'm not using steam, i can shut off all exhaust past the heat exchanger and almost instantly stop steam production.
It would also be more fuel efficient. I can completely insulate the firebox and the heat exchanger areas. All heat radiating off the fire itself would hit the insulation, and be radiated back to wards the fire. I can also use the exhaust gas to heat the air going to feed the fire, extracting as much heat as possible from the exhaust gas to be reused. Ideal full load temperature would be 2000 degrees F. At these temperatures, Carbon monoxide and other exhaust gases burn, and release additional heat.

In order to achieve this, air has to be added to the exhuast after the fire itself in order to achieve secondary combustion. Such a system would also of necesity be of a forced draft design. You can also linearly vary steam output, by varying air in, although at low loads this could result in very poor combustion. At low loads, it might work better to allow some exhuast gasses to escape without going past the heat exhanger.

This system is more complicated, and may not even be feasible. I'm going to do some math on the size of the heat exchanger required tonight, and see where I land.
Back to top


farmerden
Warming the Engine


Joined: 19 Apr 2008
Posts: 70
Location: Shawnigan Lake,B.C.
Posted: Thu Aug 13, 2009 1:47 pm Post subject:
In theory you may be correct.I remember introducing a hot water coil into my wood furnace .It worked well -then I added the coil and all of a sudden I produced so much creosate [sorry I think that's spelt wrong!] that I had to clean the chimney once a week!! The amount of BTU's absorbed by the coil cooled the furnace temp so much that the excess gases were not burned off! In the real world I don't think one can create a perfect burn. Also you seem to think you will have surplus steam-in reality ,in little boats ,it would appear the boiler limits all H.P. production more than engine size. the bigger the boiler ,more steam and on and on! At least in my situation I use all the steam I can produce and free space limits the size of the boiler!! However keep workin' on the theory! Den
Back to top


mcandrew1894
Full Ahead


Joined: 11 Oct 2007
Posts: 149

Posted: Thu Aug 13, 2009 9:48 pm Post subject:
Should work....I can't comment on monotubes but your ideas on combustion are well placed, you should have enough firebox volume to combust the fuel before the gases touch a heating surface....I am concerned the physical size will be too big though,,,but keep at it what do I know...

Dave
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Fri Aug 14, 2009 8:01 am Post subject:
mcandrew1894 wrote:
Should work....I can't comment on monotubes but your ideas on combustion are well placed, you should have enough firebox volume to combust the fuel before the gases touch a heating surface....I am concerned the physical size will be too big though,,,but keep at it what do I know...

Dave


I also am concerned about the physical size. This idea may stay on the back burner for a while. I think it would work in theory, but in practice the size of the heat exchanger might make it prohibitive. I can't seem to find my old thermodynamics for engineers. My wife may have already packed it up in anticipation of our move. Eitherway i'll revisit it when i do find it, and work out the size of the monotube required.

Cheers!
Steve Grinwis
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Fri Aug 14, 2009 8:10 am Post subject:
farmerden wrote:
In theory you may be correct.I remember introducing a hot water coil into my wood furnace .It worked well -then I added the coil and all of a sudden I produced so much creosate [sorry I think that's spelt wrong!] that I had to clean the chimney once a week!! The amount of BTU's absorbed by the coil cooled the furnace temp so much that the excess gases were not burned off! In the real world I don't think one can create a perfect burn. Also you seem to think you will have surplus steam-in reality ,in little boats ,it would appear the boiler limits all H.P. production more than engine size. the bigger the boiler ,more steam and on and on! At least in my situation I use all the steam I can produce and free space limits the size of the boiler!! However keep workin' on the theory! Den


What i'm concerned about is things like, warming up by the docs, and such with respect to part load operation. There won't be a lot of water in the boiler at any time!
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Thu Sep 17, 2009 2:21 pm Post subject:
Hello again guys.

After checking with the authorities, i've found that regulation of small steam launches under 1000 HP for non-commercial use is surprising lax.

So i'm going to continue with this plan.

I need to find / build a boiler feed water pump. It would have to be electrically driven, so that I can control it's speed. It's for this monotube boiler, and i'm going to go with a fairly small tube to improve water velocity and with it heat transfer. This means that the water pump is very important. A failure of the water pump means it's likely that the boiler is about ready to burn through.

I'm using stainless steel line, probably 3/8". It's rated to 1500 PSI and

The water pump will step up and down to keep the temperature of the steam at the output at some fixed temperature. Probably around 300 degrees. Slighty superheated. Throttling will be accomplished by stepping up and down blower fans on the wood fired. All of this will be accomplished via micro-controller, and completely transparent to the operator.

As per the woodfired monotube boiler on the SL Alba, the water pump will be in constant operation when the boiler is fired up. Even when the boat is sitting still. Excess steam will be diverted directly to the condenser. I'm hoping I can find a three way lever valve that will let me slowly engage the engine by leaking steam to the engine side to warm it, then gradually engage the engine, and route less steam directly to the condensor. I haven't explained that very well, but I hope you can figure out what I mean.

Anyways to do this, i really need a reliable pump. I've even though of having two separate pumps in operation at all times so that when a pump fails, the other will get me home without blowing anything up. In theory anyways. All the commercial pumps i've seen are either high flow, low pressure designs, like car water pumps, or the other end of the extreme, where they can provide water at 10000 PSI and are then justifably very expensive.

Not sure if this is asking for help or just providing an update. If anyone knows of one, i'll be sure and listen though!

In other news, I'm waiting for the construction of the Reliable Steam Salty to see how she looks in real life. But i've also been looking at the boats from Selway Fisher. I must say, the Edwardian 26 looks might fine. The wife also likes that design, so that helps too!

-Steve
Back to top


P.F.Cuthbert@Classicfm.ne
Steam on Deck


Joined: 24 Nov 2007
Posts: 52
Location: Cheshire, UK
Posted: Sun Sep 20, 2009 2:23 pm Post subject:
Steve

If you like the idea of the Edwardian 26, have a look at the SBA Register http://www.steamboat.org.uk/register/index.htm. You should find several examples of that design, somewhat modified:

Ursula
Anabelle II
Sans Son

There are probably others, but I cannot bring them to mind just now.

Regards

Pete
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Thu Sep 24, 2009 7:03 am Post subject:
I looked at those. They are some mighty fine looking boats.

I'm going to order the study plans and take a closer look at the layout.
Back to top


fredrosse
Just Starting Out


Joined: 26 Sep 2007
Posts: 19
Location: Philadelphia, PA USA
Posted: Sun Oct 04, 2009 10:31 pm Post subject:
Feedwater pumps are easily gotten from small pressure washers. They are rated for a few thousand PSI discharge pressure, but work very well forcing feedwater into a launch boiler at 100 PSI, more or less. Discharge flow rate is directly proportional to pump RPM. Here in PA, a 3 horsepower, 3600RPM pressure washer costs about $275, and is rated at 2000 PSI with a flow of 2 US Gallons per minute (1000 pounds per hour). Running this pump at 10% speed (360 RPM) will give 100 pounds per hour feed flow, about right for a small launch.
Back to top


barts
Lighting the Boiler


Joined: 02 May 2009
Posts: 32
Location: Menlo Park, CA
Posted: Mon Oct 05, 2009 2:06 pm Post subject:
One approach you may wish to consider is a Lamont boiler; the heated surface is monotube but there's a external drum which contains water and steam. Circulation through the coil is maintained by a circulation pump, which takes water from the drum and routes it back into the drum. The circulation rate should be about 5x the steam production rate, and the tubes sized to get turbulent flow - which is what disturbs the boundary
layer at the tube wall and provides the high heat transfer rates.

This approach provides the high steam production per unit of surface area typical of monotube boilers, but avoids the controllability issues inherent in most monotube systems; this boiler can be run as a normal watertube. Note that the circulation pump design needs to cope w/ boiler conditions, but the actual pressure drop across the pump is only a few psi.

Starting such a boiler requires that the circulation be started beforehand; this will mean typically either an electric or a manual pump (I've seen both).

- Bart
_________________
-------------------
Bart Smaalders
S.L Otter
Menlo Park, CA
Back to top


87gn@tahoe
Full Ahead


Joined: 23 Feb 2009
Posts: 148
Location: South Lake Tahoe, CA
Posted: Mon Oct 05, 2009 9:44 pm Post subject:
hey Bart, did you see how well Jim Tangeman's Lamont worked at B&W?

I missed seeing it run.
_________________
Wesley Harcourt
-S.L. Wayward Belle (Mr. Grosjean was/is a genius.)
-S.L. George H. Sandin (Father's boat. Cut my teeth on that one.)
-'64 Buick Riviera
-'65 Buick Special WAGON
Back to top


barts
Lighting the Boiler


Joined: 02 May 2009
Posts: 32
Location: Menlo Park, CA
Posted: Tue Oct 06, 2009 10:15 am Post subject:
87gn@tahoe wrote:
hey Bart, did you see how well Jim Tangeman's Lamont worked at B&W?

I missed seeing it run.


I missed it as well; the hull developed a significant leak so he pulled it out of the water early . We talked for a while; it runs well, he said. Jim runs the circulation pump manually while firing up; the circulation pump is reciprocating w/ a 1/4" drive rod and a 7/8" bore to minimize gland leakage.

- Bart
_________________
-------------------
Bart Smaalders
S.L Otter
Menlo Park, CA
Back to top


stevey_frac
Lighting the Boiler


Joined: 28 Jul 2009
Posts: 37

Posted: Wed Oct 07, 2009 8:52 am Post subject:
barts wrote:
One approach you may wish to consider is a Lamont boiler; the heated surface is monotube but there's a external drum which contains water and steam. Circulation through the coil is maintained by a circulation pump, which takes water from the drum and routes it back into the drum. The circulation rate should be about 5x the steam production rate, and the tubes sized to get turbulent flow - which is what disturbs the boundary
layer at the tube wall and provides the high heat transfer rates.

This approach provides the high steam production per unit of surface area typical of monotube boilers, but avoids the controllability issues inherent in most monotube systems; this boiler can be run as a normal watertube. Note that the circulation pump design needs to cope w/ boiler conditions, but the actual pressure drop across the pump is only a few psi.

Starting such a boiler requires that the circulation be started beforehand; this will mean typically either an electric or a manual pump (I've seen both).

- Bart


I've looked at the lamont. There are two things I don't like about it.

1) That pump has to be able to survive very high temperatures. Much higher then i think any sealing material likes to work at.

2) It's inherently less safe, if only because there is more boiling water involved. The reason why it's easier to control, is because there is more reserve capacity to smooth things out for you. My monotube is only going to have about half a litre of boiling water in it at any time. And that stainless steel tubing is rated to run over 1000 PSI with a decent safety factor.

Plus, I am an engineer, and i'm looking forward to building the controller!
Back to top


richard orr
Just Starting Out


Joined: 13 Nov 2009
Posts: 7

Posted: Sat Nov 14, 2009 11:35 am Post subject:
when you suggest introducing pre-heated air after the fire,do you mean introducing it into the convection area of the boiler? I had a simular idea about dumping the heated air out of the fire box and bypassing the economizer. this set-up would be fairly easy. it would not get rid of heat in the radiant area but would deny heat to the economizer and thus reduce overall heat
Back to top


richard orr
Just Starting Out


Joined: 13 Nov 2009
Posts: 7

Posted: Sat Nov 14, 2009 12:23 pm Post subject:
barts wrote:
One approach you may wish to consider is a Lamont boiler; the heated surface is monotube but there's a external drum which contains water and steam. Circulation through the coil is maintained by a circulation pump, which takes water from the drum and routes it back into the drum. The circulation rate should be about 5x the steam production rate, and the tubes sized to get turbulent flow - which is what disturbs the boundary
layer at the tube wall and provides the high heat transfer rates.

This approach provides the high steam production per unit of surface area typical of monotube boilers, but avoids the controllability issues inherent in most monotube systems; this boiler can be run as a normal watertube. Note that the circulation pump design needs to cope w/ boiler conditions, but the actual pressure drop across the pump is only a few psi.

- Bart


I am building a double acting circulation pump for a Lamont style boiler. I am assumong that the pressure on the intake side will help push the water on the output side of the pump, making the power reouired to operate the pump negligeable. Correct? I imagine that the same kind of packing that is used in the packing chamber of the steam chest would suffice. Correct?
Post Reply