The Steamboating Forum

Hi,

I need some advice on penetration points for the upcomers on my boiler. My reading indicates that "drowned tube" is the way to go, but a friend of mine argued quite eloquently that if the steam is arriving through the water in the steam drum that it will be partially cooled down and therefore condensed etc.

I have included drawings that repesent the general configuration of the boiler, (missing grate tubes, etc etc).

Any help would be appreciated.

jon

As all of the water in your boiler will be the same temperature (once you have it boiling under pressure, anyway), the water in your drum will not cool or condense steam that is generated in the tubes. I believe that the only issues to be concerned with regarding tube arrangement is that they need to support efficient circulation in the tubes (to prevent overheating of tubes), and efficient mechanical separation of steam from water droplets in the drum (to prevent carryover).

Cheers,
Scott

If cool feedwater is introduced into the boiler drum, some of the steam coming in thru the generating tubes will condense, but this energy of condensation immediately heats up the feedwater, and temperatures are basically uniform. With good circulation throughout the boiler, temperatures are quite uniform, and some slight condensation of incoming cool feedwater is of little concern. Put a larger quantity of cool feedwater into the boiler, and water/steam temperature/pressure will go down, regardless of the location of the generating tube outlets.

Some boilers have the outlets of the generating tubes enter the drum at a high elevation, above the water level. This aids steam/water separation, and can reduce carryover of water into the steam pipe, but on initial firing, before steaming begins, the upper portions of the generating tubes can be overheated as they contain no water initially. The attached LIFU boiler picture from the beginning of the last century shows such an arrangement, and this boiler had to be started slowly to avoid overheating the tubes.

The boiler sketch you show seems to have downcomers that are too small to allow good circulation, they should probably be about double the size shown.

I'd also tie both mud drums together in the back of the boiler with another pipe.... which would be a great place to add feedwater, by the way.

- Bart

Hi Gents,

Thanks for the replies. I will move the penetrations down lower on the drum as was my original plan. As to the size of the downcomers, I had planned 2" mud drumd and 1" downcomers. The steam drum is oversized from the original plans because I didnt think a 6" drum would give me a long enough reserve.

Should I go with a larger mud drum/downcomer combination ? What would you recommend ? Bart, There will be seventeed 1/2" tubes welded in between the two mudrums and then a 1" tube at the back with an inlet for the feedwater. I was also thinking of putting another port for injuecting feed water on the steam drum in case I had an issue with the one on the grate tube. DO you think I am being paranoid ?

Also, are people typically running one or two safety valves ? Two seems wise, althought I dont want dueling safetys........but they are expensive....

thanks

jon

JonRiley56 wrote:Hi Gents,

Thanks for the replies. I will move the penetrations down lower on the drum as was my original plan. As to the size of the downcomers, I had planned 2" mud drumd and 1" downcomers. The steam drum is oversized from the original plans because I didnt think a 6" drum would give me a long enough reserve.

Should I go with a larger mud drum/downcomer combination ? What would you recommend ? Bart, There will be seventeed 1/2" tubes welded in between the two mudrums and then a 1" tube at the back with an inlet for the feedwater. I was also thinking of putting another port for injuecting feed water on the steam drum in case I had an issue with the one on the grate tube. DO you think I am being paranoid ?

Also, are people typically running one or two safety valves ? Two seems wise, althought I dont want dueling safetys........but they are expensive....

thanks

jon

Are the 17 tubes part of a water cooled grate?

I run with one safety. I haven't seen any boats with two.

- Bart

Hi Bart,

Yup, there are 18 water circulating grate tubes with the furthest one back being a 1" to accomodate the inlet for feedwater. How do I answer the question as to whether or not the downcomers are too small ? Should I be trying to match the volume of the downcomers with that of the upcomers ? If so, I am way to small. If I go to a larger downcomer I will likely have to make the mud drums larger as well since it will be harder to weld larger downcomers into the existing mud drum size.

I am beginning to wonder if I am taking the right approach, it is going to cost me a fortune to have this welded up. Maybe I should take another look at doing a silver soldered bent tube boiler using copper,

I am going to have 12 upcomers, each with 16 welds each, 18 grate tubes with two welds each, to endcaps to weld in, and about 10 penetrations to set up threadolets or nipples for........................

That is not counting the ~ 220 holes that will need to be bored to accept the various bits and pieces and all the pipe I need to cut.

jon

Jon "Steam Queen" runs two safetys -one 10 lb higher than the other. She has several methods of bilge pumping, two methods of fuel pumping [plus wood] If it's made by man it's going to wear out! And I have no intentions of breaking down at sea! Den
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Den.

Nice looking set up. It looks like you have the pressure reliefs coming off the same outlet from the boiler. Does that concern you at all ? Also, can I ask what you are doing for pumps ? I am struggling with what to use and where to source it for both a feedwater pump and a pump fpr the condensate circuit.

jon

jon No I not concerned .One of these safety's will handle the boiler quite fine-the second is overkill [maybe that was a poor choice of words] Here's a pic showing pump placement.[all these photos are in the achives of this site but I guess it's always good to refresh them once and a while Den
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