Boiler design and Green Steam Engine

[sigurd]

PAR made me aware of the green steam engine (http://www.greensteamengine.com/) in this thread (http://www.boatdesign.net/forums/open-discussion/designing-boat-age-12-a-10068-18.html#post259767).
The engine gives 10hp at 125psi. The plans for it includes return pump.
Here (http://www.nearfutures.com/products.htm) is a turnkey version, with some graphs.
Here is a little discussion, with some mention of the engine: (http://www.energeticforum.com/renewable-energy/2835-friction-steam-boiler-3.html) Robert Green states that, "The plans and parts are for the 10HP version. The rpm's depend on the steam pressure. 3500-to 4000 is typical running a generator of about 5KW at around 100psi.
The discussion also contains some links pertaining to the use of a steam injector as water return pump.

I am going to find out whether the engine will be suitable for my boat. So I need to find out what sort of boiler I can use. I need it to be very compact and light.

Here are my initial thoughts.
Water pipe boiler from copper could be my easiest option.

I hope the boiler will be able to burn all sorts of junk.
I am intrigued by downdraft stoves, have made a few from tin cans.
The stratified downdraft gasifier (http://www.gengas.nu/byggbes/ix.shtml) dries the fuel before burned - they have tossed snow in the fuel compartment and it still did not stop the engine.
edit: the top loading of fuel is also a nice feature when stuffing the boiler down into a narrow hull.

Speculation: No matter what the boiler design, I was thinking that a main feature of any wood burner is that the primary combustion is kept at a very high temperature, in order to break down most tars and CO, as well as keeping the flame going even with wet or green wood. So that leads to an insulated combustion chamber, where the steam tubes are not exposed to the primary combustion heat. maybe.

Hoping for inputs.

[sigurd]

Here, trying to get all gases burnt before entering the chimney with the coiled boiler pipe.
Also the condenser heats primary and secondary air.
What I don't like about the stratified downdraft gasifier as in the gengas pages, is that due to the narrow fire tube, it can only burn rather small pieces, preferrably chips, which will not be available usually. So I am going to ponder a burner for normal logs.
Electric draft connected to a manometer may be the simplest way to keep pressure in the boiler constant?

[sigurd]

Here (http://www.dangerouslaboratories.org/genboiler.html) is a recipe for a monotube boiler.
Here (http://www.woodgas.com/gasification.htm) is an illustration of the downdraft gasifier. Mine should have the wood gas burning up before it enters the boiler chamber?

[sigurd]

According to this site (http://www.flyingkettle.com/japsite/boilers.htm) it is possible to build a boiler of 40 kg boiling 500kg steam per hour, powering a 50hp engine. Using ID 12mm and wall thickness 0.71mm, the 90m ss coil (the coil metal is not mentioned) weighs 18kg according to this (http://www.prochem.com.au/cache/6f6f60f078ed3dad284d3870f7e036da/Stainless_Steel_Tube.pdf).
Is that tube something like what I should look for?
Given 10hp at 8.6 bar, maximum continuous pressure 15 bar, what length pipe would be a good starting point? How much for the draft cooled condenser?
What is a good insulation material? Light, draws no water, moldeable/shapeable?

I changed the boiler to use centrifugal fan but then I drew it with air from a third engine piston injected to the stack.

[apex1]

Using ID 12mm and wall thickness 0.71mm, the 90m ss coil (the coil metal is not mentioned) weighs 18kg according to this (http://www.prochem.com.au/cache/6f6f60f078ed3dad284d3870f7e036da/Stainless_Steel_Tube.pdf).
Is that tube something like what I should look for?
Given 10hp at 8.6 bar, maximum continuous pressure 15 bar, what length pipe would be a good starting point?


Sorry sigurd, I step in a bit late.
The principle of your boiler design looks a bit strange to me, would have to go in deep to make a proper statement.
Airdraft is never sufficient for a condenser of useable size, must be raw water.
Stainless and copper are not suitable for the piping intended. The one melts away, the other has a corrosion problem. Mild steel is the choice.
I just had a brief look at the site you linked to and found already several points I seriously doubt.
Do´nt mix 500kg of water with 500kg of steam.
The pressure given (15 bar) is by far too high for the little 2cyl. engine on cont.duty. I guess 10bar is more likely what she will stand. IF that!
And it´s not neccessary to go that high with pressure. Just manufacture the engine with a larger cyl. diameter and have the same power output at lower pressure.
Maybe I can find the time (or steel it) next week, to give you some better recommendations. What is the installation for? Which type of vessel has to be propelled?

Regards
Richard

[sigurd]

6m proa. 200-500kg.

I will try to keep the burner and boiler less than 40cm in width and pretty low, 50cm?

Ok. After it has heated the draft, the condenser can boil seawater.

[apex1]

6m proa. 200-500kg.



some sketches?

[sigurd]

Sorry sigurd, I step in a bit late.
The principle of your boiler design looks a bit strange to me, would have to go in deep to make a proper statement.
please do.
Airdraft is never sufficient for a condenser of useable size, must be raw water.
Stainless and copper are not suitable for the piping intended. The one melts away, the other has a corrosion problem. Mild steel is the choice.
ok
I just had a brief look at the site you linked to and found already several points I seriously doubt.
Care to elaborate?
Do´nt mix 500kg of water with 500kg of steam.
I don't understand. When you boil 1kg water it becomes 1kg steam?
And it´s not neccessary to go that high with pressure. Just manufacture the engine with a larger cyl. diameter and have the same power output at lower pressure.
I would like that, to get more torque, maybe longer stroke as well - and possibly put a lid on the cylinder opening; the same valve opening that feeds one cylinder's "top chamber" could feed the other's "bottom chamber" - adding some tensile loads to the piston rods and cylinder universal joints may not require any upsizing.

Regards
Richard

I'll see if i can do a sketch.

[sigurd]

Here. Tail and wands are things I want to try. Not necesary at first. Steering is also done by moving kite tow point.

[sigurd]

Hello

I found a design that seems clever - it is called a Lamont boiler (http://www.steamautomobile.com/northea/lamont.html).
more on it: http://www.geocities.com/MotorCity/Shop/3589/newboiler2-11-2004.html

A comparison vs some other boilers were done, a Stanley, a White and a Doble. Much more could be evaporated with the Lamont per tube surface area, and was said to be safer and more durable due to being flushed all the time. Sounds like he had difficulty finding a proper circulation pump. Suggestion? (http://steamfittings.co.uk/asp/d-no.asp?ProductID=116&Process=1)

ps. I updated the first post with some more links about the engine.

pps. Regarding the pics. Not sure what is required for the overflow from the injectors. Probably it has to be fed back to the low pressure feedwater tank/condenser. Possibly lossy and requiring a larger condenser. The average injector has a 13 to 1 ratio, that is, 1 lb. of steam will deliver 13 lbs. of water into the boiler. (http://www.smokstak.com/forum/showthread.php?t=45128)

ppps. Found some lightweight refractory blankets. (http://www.anvilfire.com/sales/pages/kaowool_index.htm) Kaowool is rated for 1100C continuous. Is that enough?

[sigurd]

Found a great looking boiler - powering a 100kw engine in 40x40cm, 50kg.
Getting some papers on it from SAE and SACA

[apex1]

Now I understand the intended use, and have to disappoint you, verry sorry Sigurd, thats not a way to choose for you.
The Lamont is a very effective and proven system. But Boy you´re going to install a bomb right under your Bu..t.
Condensed water injection is the cheapest way to feed the boiler, pumps are much dearer and heavier. But you know already, that the system you are planning here, will anyway be in the 25.000€ ballpark (to name the lower level)?
Are you shure that this is what you are going for? The engine is about 250€ or so! A larger Boiler (saturated vapor, 14 bar) for a 10hp cont. output at the engine crank, will end up in the 10.000€ already. Downsizing is possible by overheating only, and that means (as a rule of thumb) half the size, double the cost! Thats valid for the boiler only! Pumps and piping etc. have to become more rigid too.
It is possible, no doubt, but IMHO not worth thinking about. This little engiine is at home in the low pressure world, landbased and with easy to make, easy to maintain boiler system.
The SES boiler shown above looks quite promising, but I estimate the cost for such a system (closed loop) at about 50.000€ upwards.
And there is another piont, nobody tells you in advance: the time to heat such a system before you can run it full power, is several hours! The lighter the boiler, the smoother (but a bit faster) you can preheat! Otherwise internal tension will crack the plumbing with an impressive, but fatal, bang.
Sorry again, would have enjoyed to provide better and more constructive advice.
Regards
Richard

[sigurd]

Now I understand the intended use, and have to disappoint you, verry sorry Sigurd, thats not a way to choose for you.
The Lamont is a very effective and proven system. But Boy you´re going to install a bomb right under your Bu..t.

Are you referring to the separator/standing pipe? I think a decent separator can be made with large size T-fitting, like in one of the above links - or a larger dia pipe with screwed connections to the smaller dia. The point would be to recirculate the water to use less tube and be sure there is no dry tube close to the highest heat. Such a fitting would be much much stronger than the boiler tube, and would not neceserily be in contact with external heat. Do you still maintain it would be risky? Could you please elaborate.

Condensed water injection is the cheapest way to feed the boiler,

it would work for the recirculator as well? how would you plumb it, especially overflow?

pumps are much dearer and heavier. But you know already, that the system you are planning here, will anyway be in the 25.000€ ballpark (to name the lower level)?

no I had no idea. I have not yet found many of the parts that would be needed. Short summary: Refractory, a length of finned tube, unfinned tube, a big T fitting, a few small T fittings and some other fittings, some manual valves, a safety valve, a manometer, thermometer, water level meter, one or two injectors or pumps, and a control system acting on said -meters to adust feed pump and fuel supply. It is hard for me to imagine anything even in the order of magnitude that you are suggesting. Time might tell.

Are you shure that this is what you are going for?

No, I am investigating the possibility. I am getting the papers for the SES boiler, to see what can be learned and if it is possible to make a scaled down version.

The engine is about 250€ or so! A larger Boiler (saturated vapor, 14 bar) for a 10hp cont. output at the engine crank, will end up in the 10.000€ already. Downsizing is possible by overheating only, and that means (as a rule of thumb) half the size, double the cost! Thats valid for the boiler only! Pumps and piping etc. have to become more rigid too.
It is possible, no doubt, but IMHO not worth thinking about. This little engiine is at home in the low pressure world, landbased and with easy to make, easy to maintain boiler system.
The SES boiler shown above looks quite promising, but I estimate the cost for such a system (closed loop) at about 50.000€ upwards.
And there is another piont, nobody tells you in advance: the time to heat such a system before you can run it full power, is several hours! The lighter the boiler, the smoother (but a bit faster) you can preheat! Otherwise internal tension will crack the plumbing with an impressive, but fatal, bang.

bang interest me. As far as I have seen, people recommend small diameter water tube boilers for safety. Getting recirculation to work without a large steam/water separator will reduce the volume and thus reduce the likelyhood of getting boiled when it ruptures. Worst would be if there was metal shrapnel flying all over. It should not be necesery to put plumbing in the external heat, if this is a problem.

Sorry again, would have enjoyed to provide better and more constructive advice.
Regards
Richard

There are numerous questions that remains unanswered before I can decide whether it is worth building a boiler, or what sort. Some of them are in this thread. What, E50 000? Could you break it down roughly?

[apex1]

Yes naturally, Sigurd, if I find the time.
But just a few words, you know that every boiler has to be certified, DNV I think in your case. Read: every single piece has to be too! Every seam welded by DNV approved welder / boilermaker. The burner unit is´nt just a Burner from central heating, etc. etc.
If you know what "aircraft certification" or "approval" means and how much that means in price comparison, you have a rough idea about additional cost over just plumbing items! Every single piece of stuff is miles away from affordable.
Regards
Richard

[sigurd]

didn't know you have to certify it. As little as possible welding I wanted anyway - screwing fittings seems more appropriate.
For the gas producer I was thinking a couple of insulated paint cans. Would function adequate I think. The burner system in the SES could be modified to use producer gas.
10k Euro is already way beyond what I can afford - don't bother with the 50k breakdown. I have to find out a way to do it cheaper or not do it.

[sigurd]

You can see that somebody made an SES for 2000 dollar. Still a bit much for me but mine would be smaller. About the cert. rules, he didn't have to certificate it but rules are different everywhere.
http://www.steamautomobile.com/ForuM/read.php?1,13015,13016#msg-13016
2/5 down the page.
Google is certainly not my friend when it comes to finding tubing prices.
One of the links in that discussion shows steel tubing at 4dollar per foot, thereabout. Pretty expensive stuffs.

[apex1]

Sigurd,
you MUST certify even if you do not want to use it in the public! Screw fittings usually get no approval. 10k € is the absolute minimum for a simple coal or oil fired "scottish" type of steam launch boiler, the most common and simple type.
some links:
http://www.deutscher-dampfbootverein.de/flohmarkt/index.html
http://www.steamboat.org.uk/
http://www.prestonservices.co.uk/boilers.htm
just ordinary, old fashioned stuff
the boiler type you are going for is far above those rates.

EDIT: did just read across the site you linked to, but even they are in the 10k$ region for homemade units without cert. needed!
In EU as in most countries you MUST. And believe me I have a clue about this subject, I had about 15 Boiler revisions and three new built boilers, in my museums ships.

Regards
Richard

[sigurd]

huh? I just told you, 2000 usd - 70 bar, 540kg/hour. read my last post, and the discussion (chuk is the one with the SES)!

(edit: You removed the part about screw fittings not getting approval?) What, screw fittings less reliable?

I think the old fashioned stuff is costlier, it doesn't use water tube, means a lot of welding, and it has much more volume so is much more dangerous when exploded.

Edit - thanks for the preston link. They have some injectors that look appropriate. (the boilers all look like they would sink my boat)

[sigurd]

I thought about a separator. As per the lamont, there
is an economizer, a generator and superheater coil.
However, this separator replace the normal superheater
- though it doesnt have to.
There is an inner and an outer coil. These need not be
cone shaped as in the rendering. Most probably they
could be cylinder shaped as well.
There are several connecting pipes between the two
coils.
Steam from the generator is admitted to the bottom of
the inner coil. Any water present will be forced
through the connecting pipes, due to gravity and
centrifugal force. Once inside the outer coil, it
will run downwards due to gravity, and down into
a chamber which will contain the water level meter.
The water from the economizer will also be admitted
to the top of this chamber.
On the bottom of the chamber is an exit to the
recirculation pump, pumping water to the generator.
Steam to the engine is taken from the top of the inner
separator coil.

I think this separator might separate quite reliably,
even with accelerations and at odd angles.
It also has a low volume, and is made from light tube
and fittings.

[apex1]

Sigurd I agree that there are many intelligent approaches possible, and some well proven too, I just do´nt see any sense in such a steam engine installation in a light boat.
It might be possible to make a boiler at half the amount I estimated, but even that is far above any lightweight Diesel. Let alone the annual inspection.
Do´nt get me wrong, I´m not fighting the principle, quite the opposite. I am going to install the very same engine as a generator in a off grid retreat on Bali. Solar powered, low pressure, much similar to PAR´s installation. Just different battery management and sizing, cos off grid.

Be shure I would be the first to follow a senseful, new steam technology for yachts. I was preserving steamers for some 15 years, not for nostalgic reasons only. And you know me as a promoter of steam technology, but
for safety reasons, I´ll never recommend a "cutting edge" boiler installation without class. approval. Remember, one litre of water gives 1,600 litres of steam and you will have several litres circulating.
If your vessel capsizes, or a wave enters the fire grate / burner, which does´nt seem sooo unlikely, every sort of boiler will explode instantly.

Regards
Richard

[sigurd]

Either you or the people who did build a SES boiler for 2000 (there is more than one in that thread that agrees it is a realistic price) don't know what you are talking about - or more likely the difference stems from sourcing different parts, different paperwork, outsourcing work etc.
Repeating myself, that is a very much larger boiler than I need, which means the tube will cost much less and it will be much lighter.

Glad to hear you are going to try to make the engine work.
What do you intend for the cylinder support universal joint?

A diesel is not really comparable in this (my) situation because it cannot burn wood. A producer gas driven petrol engine is the easy alternative. It will be noisy, and includes a thousand parts, including a gear train. A small petrol as a concequence is not very reliable, has a short life span and often repair requires some obscure hard to find part. As of now I have got a 6hp outboard that does a good job. "Gasifying" it might require a means of lubricating the cylinders - probably not very difficult.
I suspect the torque of the GSE could be multiplied without adding a lot of structure. This would make large, efficient propellers possible with no gear train. Flapping propulsion seems also extremely well suited to steam cylinders.

I heard what you said about the heat and size. I understood it like a high pressure boiler (which means higher temperature water) will be smaller and lighter for the same power. I don't see why the principle of the Green engine is restricted to lower pressure - pipes, valves, fittings and cylinders would have to be stronger. Maybe there are more issues like water hammering in the cylinders, lubrication requirements etc. that I know little about.

Your point about the cold water shock on the hot pipes is a good one, which needs to be properly adressed. Obviously the air intake will be ducted to prevent it. I suspect an ICE will die just as much if you pour water into its cylinders while running - but they probably have worked out how to prevent it by clever ducting. Quite unrelated, I used to have an old 6hp 1cyl crank started yanmar diesel. One time the boat sank. When I had hauled it up and pumped the boat, I cranked it up without further ado (there is a decompressor on these engines to make cranking easier). The first few turns, it spitted out the water in the cylinders, then it started. I don't remember if I drained the sump first or not. Seem to remember it spitted some water from the sump overflow too. I like those diesels.

[sigurd]

I´ll never recommend a "cutting edge" boiler installation without class. approval. Remember, one litre of water gives 1,600 litres of steam and you will have several litres circulating.

I have not found out about the class. approval yet. Have sent a request to DNV.
About the water volume, I think as little as possible would be nice but i cannot estimate how much. The SES used finned tubes, decreasing the volume, and also I don't think it had any high pressure reservoir. If I need one, I can probably use more small dia tube, which will slow the expansion after rupture. So the expansion won't be faster than opening a valve full tilt to the atmosphere. It should be possible to test this by filing a weak point in the tube, fire up the boiler and leave the area? Repeat until it blows and see the amount of destruction.
Adding forced circulation will reduce the needed economizer area so there may be even less volume.

For the water level sensor, going to an indicator and the feedpump/injector control cirquit, electrodes inserted in the pipe is what I am thinking about now. Resistance between the electrode and steel pipe will decrease when submerged. I do not know if electroplating of the electrode is a concern, there was some trick mentioned to avoid it - using an AC "symmetrical source current wave" - not sure I understand the principle of that. There would have to be a sense current going there and there could be issues with galvanic corrosion of the pipe if it is not properly done, but these things are used in commercial boilers. For reducing false reading due to accelerations and temporary odd angles, sloshing should be inhibited. Maybe steel wool inserted to parts of the tube.

For controlling a feedwater injector, I am also reading about an interesting concept where water overflow will clog the injector.

For adding recirculation to the SES boiler, I am looking into canned electrical pumps. Solenoid pumps also seem good for this? Also it just occurred to me that perhaps a pop-pop engine with check valves could be used for this purpose.