Hot well size

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Lopez Mike
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Hot well size

Post by Lopez Mike » Sat Jun 17, 2017 7:02 pm

My hot well temperature seldom gets high enough to do much of anything towards getting rid of any dissolved oxygen that it might pick up through the exposed surface. The only time the return water from the condenser gets at all hot enough is at full throttle for a longish run. I don't want to cut down the size of my condenser as it is about right for hard running.

Since the float level is adjustable might I set it for a lower level and thus reduce the water volume and possibly raise the temperature?

I can find nothing in my literature about deciding how much water to carry in a hot well. I suppose that running it too low might narrow my safety margins in the case of a plumbing failure.

Or might I look into insulating the sides and bottom of it? I could glue on some foam from a sleeping pad.

Thoughts?
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Mike Rometer
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Re: Hot well size

Post by Mike Rometer » Sat Jun 17, 2017 7:37 pm

Mike, logic might suggest that insulating could be the best solution due to the stated risk of lower water content. Reality might find that a combination of both be better.

Further thought wonders what would then be the outcome of a long full throttle run?
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Re: Hot well size

Post by DetroiTug » Sat Jun 17, 2017 9:53 pm

Mike,

Did you ever add an economizer? That should take care of it instead of trying to control the temperature out of the condenser?

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Re: Hot well size

Post by Lopez Mike » Sun Jun 18, 2017 12:30 am

If by an economizer you mean a feed water heater that takes heat from the engine exhaust, I have all the bits and it's my next project of any significance.

I have run the beast wide open for about twenty minutes in a race and you could still stick your finger in the well without any discomfort even though the water from the condenser was giving off some steam.

The well is 5" x 14" and the water typically is regulated at about 6-8" deep. Call it two gallons. This with a 3 x 4 single running 400 r.p.m at maybe 120 p.s.i.

Insulating will be my first move. Why insulate the steam pipe and not the well?

And speaking of insulating stuff, does anyone have a half way elegant way to insulate a 3/8" copper pipe? Feed water temps not steam temps.

I just installed a new feed water temperature gauge and I plan on changing things one at a time.
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Re: Hot well size

Post by DetroiTug » Sun Jun 18, 2017 12:37 am

""does anyone have a half way elegant way to insulate a 3/8" copper pipe?""

Clothes line. It takes a while to install, but it works. Inexpensive too.

Once you install the economizer, you'll see a marked improvement in plant performance. The hotwell temp will be irrelevant. Due to your automatic water tending, the boiler is seeing little and often on the feedwater, the economizer works really well like that.

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Re: Hot well size

Post by Lopez Mike » Sun Jun 18, 2017 3:03 am

I suppose I could paint it after I wrap it on. Some sort of gloss paint. These boats are so filthy.

I tried some clothes line on my steam pipe and it wasn't all cotton and the plastic part melted. Total mess. Then I wrapped it with some fiberglass insulation and wrapped some all cotton cord over that. My workmanship leaves something to be desired. There must be a better way. The pipe is 5/8 copper and has an S bend in it.

Barbie does some sort of marlin spike seamanship stuff on their boat but I suspect that my extra thumbs may interfere with that route as well.

You can buy hard shell stuff for bigger pipes but I haven't seen it for little pipes.
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Re: Hot well size

Post by fredrosse » Sun Jun 18, 2017 4:57 am

In large USA steam plants, the standard is 3 minutes supply at maximum power. In Canada, 5 to 8 minutes is the norm. How much water to carry in a hotwell should not change the steady-state temperature, which is determined entirely by the condenser character, which in your case results in sub-cooled water, which can absorb Oxygen.

The amount of Oxygen absorbed by the water depends on:
The temperature of the water exposed to atmospheric air, higher temp = less O2 absorbed.
The surface area at the air/water interface, smaller area = less O2 absorbed.
The time of air exposure to the water in the hotwell to ambient air, less time = less O2 absorbed, but that is basically a constant value for our steamboats and cannot be manipulated by the engineer.

A method of avoiding the hotwell picking up O2 is to heat the condensate to saturation, near 212 F, with live steam. however this will almost certainly lead to problems with the feed pump not having good suction conditions if it sucks 212 F water. A solution here is to have a partition between the cool condensate (at the bottom of the hotwell), and the hot condensate (at the top level of the hotwell), so that the feed pump sucks from the cool condensate, and the upper portion of the hotwell, the part exposed to direct contact with atmospheric O2, is maintained near 200F, with a very small live steam bleed into the hotwell upper level water.

Insulating the entire hotwell helps in this process, however many feed pumps will experience trouble if the incoming feedwater from the "hotwell" is too hot. A compromise is usually appropriate.
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Re: Hot well size

Post by Lopez Mike » Sun Jun 18, 2017 5:05 am

Good info. Thanks Fred.

I would seem as though a smaller well would run warmer as the water would spend less time in storage and thus cool down less.

As far as getting the water too hot and having the pump cavitate, I have a long, long way to go before that problem might arise!
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Re: Hot well size

Post by steamboatjack » Sun Jun 18, 2017 7:44 am

The usual recommended temperature for the hotwell is “above 85C” as this will remove most of the oxygen, however as Fred points out above this can lead to pump suction problems.
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Re: Hot well size

Post by Lopez Mike » Sun Jun 18, 2017 1:57 pm

Thanks Jack.

I'm at maybe 50C or less now so it would have to be a lot warmer before I got into any pump problems. Also, my well is perhaps a foot above the pump suction so I have that going for me.
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