Hot well size

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fredrosse
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Re: Hot well size

Post by fredrosse » Tue Jun 20, 2017 12:35 pm

Not to change the thread subject, but for boiler layup:

I have a steel feedwater tank which is piped directly into the feed pump suction, then continuing into the boiler/economizer. When finished with an outing, I run the highest safe level in the boiler, about 85% full, and kill the fire. The boiler cools down, forms a vacuum (if valves and pump packings are tight) and sucks from the feedwater tank until the boiler is completely full of water. This allows a small amount of oxygenated water into the boiler, but is far better than having air over the normal liquid level of an idle boiler.

If I am going to layup for a week or a month, then I run live steam into the feedwater tank until all of this water is brought to a rolling boil, which drives out all of the dissolved gasses, especially Oxygen. Then on cooldown, the water that is in the feedwater tank is already free of dissolved oxygen, and what gets sucked into the boiler is essentially deaerated.

Depending on valving, similar layup should be available for condensing boats that have a reserve feedwater tank, and a path to the feed pump bypassing the hotwell.
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Re: Hot well size

Post by DetroiTug » Tue Jun 20, 2017 1:04 pm

Quote: " The boiler cools down, forms a vacuum (if valves and pump packings are tight) and sucks from the feedwater tank until the boiler is completely full of water."

That is exactly how I shut down the Locomobile steam car. Most steam car folk store their cars this way. It laid full of water last winter all closed up and I fired it up a few weeks ago and blew down several times, no rust, just some black - whatever it is. Our water tanks er daytanks go around the boiler so the water is heated thereby removing oxygen. I kept watching the sight glass for anything rust colored and it was clear. The winter before I simply emptied it the best I could cold before disassembly. On first firing last year, small rust flakes appeared in the glass. The shell is 3/8" thick so I wasn't too concerned.

On the tug, I pull the most of the fire leaving a thin bed of embers, then blow down completely, then leave all the valves open. I pull out of the lake and don't want to leave that in there for an extended period unfired. Some bodies of water I've been on like the Detroit river (which is actually pretty clean now), I'm very leery of for boiler water.

Knock on wood, but both methods albeit two different scenarios seem to be working.

-Ron
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Re: Hot well size

Post by Lopez Mike » Tue Jun 20, 2017 3:14 pm

I think that's a good point about the oil film inhibiting gas transfer. I have no oil film so it doesn't help me.

I've thought about a lid on the well but I find that being able to see what is going on has been very helpful in catching changing conditions especially malfunctions.

I wonder what that black stuff is made of? When I discard my hot well filters it has penetrated perhaps half way through the three layers of Oilsorb sheet. Ring and bore wear? Some sort of erosion of the boiler shell? Maybe I'll hang a magnet in the well.

I am thinking more about replacing my copper ball float with a flat wood or plastic one. I'm not sure why I've not seen this before.
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Re: Hot well size

Post by DetroiTug » Tue Jun 20, 2017 3:37 pm

Quote "I wonder what that black stuff is made of? When I discard my hot well filters it has penetrated perhaps half way through the three layers of Oilsorb sheet. Ring and bore wear? Some sort of erosion of the boiler shell?"

Probably the latter. It wouldn't be piston and cylinder etc wear on mine as I'm not condensing. My guess is it is mill shale on the steel breaking loose over time. I blow down until it's clean then blow down again later and more black stuff. It could be some sort of mineral in the water cooking down over time. By it going through layers of filter says it's very small whatever it is. When I remove my cylinder heads on both engines, one on city water, one on river water , there is a thin film of black residue as well, which I attribute to the oil.

-Ron
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Re: Hot well size

Post by RGSP » Tue Jun 20, 2017 4:16 pm

The black stuff is magnetite, Fe3O4, i.e. black iron oxide, which is the normal oxidation product of iron in contact with hot water without much oxygen dissolved in it. Oxygenated water produces Haematite, Fe2O3, which is the normal red rust. The full chemistry of it is more complicated than I've implied, but the above is still true. Incidentally, magnetite dust is surprisingly heavy, and in circulating hot water systems always collects at low points.

The good news is that commercial inhibitors for hot water based domestic heating systems (common in England) are very effective at minimising magnetite production from hot water passing through pressed steel radiators (which can otherwise block small bore copper tubes, and cause excess circulating pump wear), and so presumably the things sold as boiler water inhibitors are similarly good.
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Re: Hot well size

Post by Lopez Mike » Tue Jun 20, 2017 5:29 pm

I knew that someone on here would know.

From the small volume of this stuff that I am filtering out I would surmise that it will be a while before my boiler suffers much. There is a small bit that discolors the first spurt of water when I blow down. A light film on the bottom of the hot well. And what collects in the filter.

What would we do without something to worry about?

In the next few weeks I'll be doing some steaming and will start the investigation by varying the hot well level and recording any significant change in the feed water temperature. Science (or what passes for it around here) marches on!
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Re: Hot well size

Post by DetroiTug » Tue Jun 20, 2017 5:48 pm

Well, there ya go.. Magnetite. It's never very much, just a small bit of black when I blow down after a days running. On the tug I can't see it as the exit is submerged. I'm always watching for red coloring in the water.

-Ron
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Re: Hot well size

Post by RGSP » Tue Jun 20, 2017 7:06 pm

DetroiTug wrote:Well, there ya go.. Magnetite. It's never very much, just a small bit of black when I blow down after a days running. On the tug I can't see it as the exit is submerged. I'm always watching for red coloring in the water.

-Ron
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Re: Hot well size

Post by cyberbadger » Tue Jun 20, 2017 10:48 pm

The boiler treatment I use Terlyn LSB, which is amine based, helps develop and maintain a coat of magnetite on the interior surfaces of the boiler. This is considered desirable because it inhibits further rust/corrosion.

On the smokstak.com forums somewhere there are pretty pictures of the inside of some traction engines boilers that have used this treatment and they are coated inside in a grey to black layer. State boiler inspectors are pleased to see boilers with this layer inside and have complemented the consistent owners who keep up with blowdowns and the water treatment..

-CB
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Re: Hot well size

Post by Lopez Mike » Sun Jun 25, 2017 7:58 am

I went out for a short shakedown around the bay with my new feed water temperature gauge installed. The old one had been an automotive accessory type and the lowest it read was 140F. My new one reads down to 30F. I have been assuming that the temperature was just low enough that it wouldn't get on scale. Wrong.

When I backed the rig down the ramp the gauge read in the high sixties. About the same as the air temperature. To my dismay, after a half an hour of running the feed water temperature stabilized at 78F. Big deal.

I didn't have time for any experiments but there is little question that there is room for improvement.

I checked the new gauge with ice water and boiling water so I'm fairly certain that it's reading properly. I can't imagine that I can cut down the volume of the hot well enough to raise the temperature and still hold any water at all. Certainly not enough for a reserve.

Time for the new feed water heater project.
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