Benson type boiler project

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Steam Captain
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Benson type boiler project

Post by Steam Captain » Mon Nov 19, 2018 12:28 am

Hello everyone from the land of efficiency (at least that is what the stereotype says ;) )

Until now, I've been immersing myself into all the old books I could find on flea markets and in antique stores to understand steam engines. Eventually, my focus shifted to the boiler. I already wrote in another post, that I intend to work through several stages to reach my goal of an own steam boat.
Now, I am building a water tube boiler. I always pindered about the pro's and con's of a flash boiler and I decided I would definitely settle for water tubes like a flash boiler, but I still wandered about having a steam drum. I still don't know. A benson-type boiler seems amazing in principle. Besindes the feed pump, there would also be an additional circulating pump, that doesn't work against the boiler pressure, but only needs to overcome the resistance of the water tubes. This nice feed would make it theoretically possible to alter the circulation per steam ratio (I'm sure there is a proper term for that, but I think you will understand it ).
There are some pictures out there about the Belleville boiler and I was thinking of that general appearance. Since all the plates holding all the tubes would be a real challenge, I thought to have the main tube bundle like this:

Image

I am talking about the bundle right behind the three parallel coils in the front. So, it looks like instead of having let's say 100 straight tubes ending in 100 drilled holes & soldered in 100 times for each side, 10 tubes start in one big register tube, go to and fro 10 times and end in another register tube, reducing the amount of holes by factor 10.
For the 2 register tubes, where the 10 water tubes would start and end in, I thought of using a square tube of 20mm / 3/4" and for the water tubes 6mm/ 1/4" diameter copper tubing. Since I would not want to work with more than 10bar/140psi, a square tube would be no problem.

For the pumps, I was thinking of using brass pipe fittings and a stainless steel plunger.

Let's see how it develops. It will not be a high speed project, since I am very busy, but I will continue step by step.
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Re: Benson type boiler project

Post by Steam Captain » Sun Jan 20, 2019 3:15 pm

Finally one step further, I am at the step to build the aforementioned tube stack. My task right now is to find what the smallest diameter is, that the copper tubes can be bent into safely without too many fails. Now, I have bult a wooden bending block to try out the bending. After this is done now, my next step is to get fine sand to fill the tubes with. What plays into my hands, is the fact, that the main bundle will not consist of one single, very long tube, but of roughly a dozen parallel tubes. That way, the tubes can be handled much easier.
As the picture above shows, there are 4 elements spread ofer the lengh of the tube bundle, whose function is to hold the tube bundle together. If it was intended or not is hard to say, but these elements would also support a longitudinal stream of hot gasses striking over the tubes orthogonally.

I like the boiler designs with several cylindrical tube bundles of different diameters stacked inside each other with the gas stream flowing up and down them successively. But I wanted to go with an overall simple water tube boiler design, that can be easily modified and changed, if it doesn't meet the expectations.
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Re: Benson type boiler project

Post by cyberbadger » Mon Jan 21, 2019 1:43 am

What fuel are you considering using with your design?

With what I see in the picture I think you will have an issue with soot unless you use some really clean burning fuel.

Soot is a common battle with solid fueled steamboats. It's horrible stuff, it accumulates and it can really hamper heat transfer as soot is a good insulator.

-CB
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Re: Benson type boiler project

Post by Steam Captain » Mon Jan 21, 2019 9:46 am

I will use wood/coal/brikets as fuel, I think 90% of the time wood. Soot still is something of an undiscovered country for me, considering this scale of steam propulsion. So, I'd rather go the careful way and provide for enough space.
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Re: Benson type boiler project

Post by cyberbadger » Mon Jan 21, 2019 8:04 pm

I would suggest thinking about how you plan to remove soot. Make sure to think about what brushes/scrapers you are going to use and that you can feasibly get into all the areas for a good cleaning when the boiler is not fired. When the boiler is being fired, some folks employ a steam lance.

Steam lances are a personal choice, some folks think they are a bit dangerous. It's just basically a wand with a nozzel that is connected via on a steam hose to the boiler and you can stick the nozzel end of the lance into the firebox and blow steam to try and remove soot. The dangers of a steam lance are that 1) It gets very hot, make sure you are wearing gloves and provide an insulated handle on the lance. 2) Don't point it at living things. 3) Watch for falling soot, ash, burning embers. :)

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Re: Benson type boiler project

Post by Steam Captain » Tue Jan 22, 2019 7:37 am

From the beginning on, I had easy maintenance in mind. Thus, easy access and modularization is my aim. I had in mind to design a boiler, whose components can be dismantled easily to exchange them with better versions or to replace damaged elements. The main bundles will be accessible permanently by sheet metal hatches. So, brushing the soot off the tubes will be easy.
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Re: Benson type boiler project

Post by Steam Captain » Sun Jun 23, 2019 8:06 pm

Because the name Benson-type boiler is very misleading die to several facts - namely Benson boilers are usually associated with supercritical systems, which I will not run my system with for many a reason; and Benson does only describe a boiler type so far, as it creates supercritical steam, and even that is not exclusive - I decided to conclude this thread at this point and open another one. Also, because a lot of things have changed in the conceptual outlay of the boiler. Especially because a solid-fired drum-less boiler is a subject I don't want to pursue right now.

Follow me on my path of experimentation to the following forum thread :arrow:

viewtopic.php?f=8&t=2171
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