Sternwheeler boiler

[Bill Hudson]

Sandy and y'all interested,

Am separating this from the PS Pevensey thread so as not to run the Pevensey thread off course or aground.

Sandy said:
"I would suggest you would need a somewaht larger boiler for you 2 off engines (1/2" bore x 1 1/2" stroke) which are much the same size as the engines I am working on for the Bof L.
The boiler I am proposing for mine is the same style, but has a 4" OD barrel x 7-8" length and has a 2" OD centre flue with 2 rows of 10 water tubes (2 side by side with a 1/8" gap). The burner will be larger, having a ceramic element of 35mm OD, other than that the design is the same."

The original boiler I looked at and thought about using planned fit your latest design in size.  I had kind of put it aside because the size pushes the limits of my boat.  Many of these little boats (like the City of Eugene) had the boilers on the forward main deck.  After visiting the Portland i can see they can also be on a lower deck.  Opens me up to revisiting this boiler again.  

I don't have the drawings here but if I remember correctly it did not have as many tubes as you suggest.   Also the flue protrudes through the rear plate into a smoke chamber where the superheater coil is.  I like your design better as the flue is part of the heating surface.

Question :?:   :arrow:     How do you superheat the steam on this boiler?    :?: #2:  Is there information about ceramic heaters some where in PDs?  Heating the water is a whole new thing for me as I am used to the boiler with burner under it.  

Sandy, I really appreciate you and you willingness to share information.  Finding PD and you was a great find.   I have a very good friend who was a steam  engineer in a plant in Detroit.  He has built several steam boats.  He is a very good source too but not quite as up to date on somethings as you.  He is building a drifter using the V4 wobbler and boiler that was designed for it. He is going to electronics for boiler controls.

Thanks for you help,

Bill

[Bill Hudson]

Bill said:
"I like your design better as the flue is part of the heating surface."

To clarify, I meant that the "funnel flue" was internal thus being part of the heating surface rather than from the smoke box as in the boiler I was considering.

Bill

[sandy_ACS]

 :computer  

Hi Bill,

Good ploy on your part, Taking this away from the PS Pevensey thread, I agree it could get out of step quite easily.

Keeping the funnel uptake within the main barrel does, as you rightly say, increase the available heating surface, but it also reduces the water content (can't have it both ways) but, since water can be more easily added, (but not heated surface) I think it wins out.

Fitting a true superheater in this type of boiler is not at all easy, the best you can hope for is a steam dryer which can be added at the front end.

Make a suitable coiled tube which will pass down the funnel uptake into the front end of the main flue (just in front of the final water tube/s). This can be retained by the funnel when it is pushed into it's socket. A couple of small slots to clear the tube is all that is required.

Personally I do not think super heating is necessary (or desirable) for small, single expansion, engines. For larger compound expansion engines then there are benefits, but only where large ratios of expansion are required (such as in a triple expansion) and where low pressure condensers are also available. For the smaller engines then any perceived advantage is very quickly lost by the inevitably higher losses associated with smaller scale.

Superheating also brings with it a very much higher reliance on adequate lubrication (not always appreciated), and if the steam oil runs out in the lubricator then appreciable damage can be done in quite a short space of time...not so much of an issue where wet steam is concerned.
It can also destroy o-rings (where these are used as piston rings, or glands) and also cause rapid de-zincification of any bronze, and especially brass, engine components.

If space is a big problem in your hull, then it may be advantageous to go for a small Scott type boiler, (which can, if you still want one, have a true superheater easily fitted), this can produce a very much higher steam rate than any centre flue design and burners are less troublesome to organise/set up.

On the subject of Ceramic burners...I am prepared to be corrected here, but I don't think there has been any significant posting on this subject on PD's, at least not recently.

I am going to include a section on these burners in my Steam and Steam engines series, but this chapter will be some time yet, lots of other stuff to cover first.

Hope this helps a bit, but ask away if you need anything else... PD's are a great bunch, despite the Banter..and most of the guys are only to willing to help.

Keep us informed.

Best regards.

Sandy :computer  :vacat  

[Dave_Sohlstrom]

Sandy and Bill

Bills engines will be be 1/2x1 1/2 for his sternwheeler. I would like to build the steam tug Portland that Bill and I have posted some pictures of, she has engines of 26" bore and 9' stroke. In order for me not to be working with very small or very large engines I am thinking of modeling her at 3/8" = 1 foot.  This gives me a bore of .812 and stroke of 3.375. She originally had 2 boilers that feed main engines and aux. equip. Each boiler was 11' long 10' wide and 14' high. My scale boiler room will be approx. 4.5" wide and 12.75" long. I have been studying your Scott boiler design and a Scott boiler design in Model boilers and Boilermaking.  I have 27" of 3" copper tube and I am working on scoring a piece of 4".
Sandy would say that a single boiler that fits this boiler room would work well for these engines.

Dave

[sandy_ACS]

   :hmph  :hmmm    

Hi All,

Dave...the Scott design I posted, was adopted from the same book you have, I just altered it somewhat to bring it a bit more up to date and to be more suitable for Gas Firing......as for driving your engines....possibly pushing it a bit, but let me think about this one for a while....I will get back to you soon.

Best regards.

Sandy.    :computer  :computer  :hmmm  

[Dave_Sohlstrom]

Sandy:

Playing with my 3d cad I came up with this idea based on the 3" copper tube I have. Barrel is 9" long plus dome ends. Water tubes are .375" with 1" radius bends. I would need to increase my boiler room space a little to fit it into the model. What do you think?

Dave

Update

Changed my attachment to ver 2 of the boiler I am thinking of.

[sandy_ACS]

 

Hi PD's....Yes I am skiving off work.........    

got to have some time to play.

Dave,...I did some quick calculations on your engine requirements...I based them on 200rpm (off load speed) which should give you between 120 - 150 rpm on load.

You would require some 1400 cu ins steam per minute to achieve this with your engines.

This equates to 4 cubic ins water evaporated per minute per 100 sq ins heated surface.

The standard Scott design is capable of 2 cubic ins per minute so you would need 2 of these......not sure you would get more than 3 cubic ins per minute out of the slightly larger version you are looking at now.

The other problem would be how to fire the blooming thing....perhaps 2 x 6" x 2" wide ceramic burners...one from each end.....think about it.

just had the call for dinner, so better go, or I will be in the DOG house again.

Best regards.

Sandy.  

[Dave_Sohlstrom]

Sandy

Thank you for running the numbers. Now my problem is do I design one boiler that is big enough to do the job or two that will do the job. Two means two of everything. My question is how to control two sets of burners and feed pumps.  

If my numbers are correct for the design you see that I posted that boiler has about 162 sq in of surface area and if I follow your numbers I would need better than 200 to get the steam for the engines I would like to do.

Would a straight water tube boiler with Steam drum and Mud drum be a better idea but with the added difficulty of building one.

Dave