Harder Theoretical Question. What's your opinion on my suggestion for the summer.

TeachMeSteam

So, I know the best way to prepare the steam boiler is to raise the temperature a bit so that the oxygen doesn't oxidize at the water level point. But that's because that's where oxygen comes in contact with the water and enters the water. So raising the water level will actually increase longevity of the tank. BUT, what about burning the oxygen off every 3 months or so? It'll get the house hot but do it when you're out for the day and close the doors so the steam boiler can get nice and hot and burn off the oxygen in the water. I'm assuming it won't do THAT much since oxygen is constantly going into and out of the surface of the water but it will probably help, no?

Why not just empty the steam tank completely for the summer? Clean it out and just empty it so there is no oxygen problem at all? (I read all of Dan's books but I forget. It's been a while.)

Fred

Draining the boiler completely will expose the entire block to oxygen and potential corrosion as the entire surface will be damp (have some moisture in it) and, as you say oxygen is always present in an open system.

Jamie Hall

Slight misapprehension there. Oxygen is in the air. The stuff is about 20% oxygen. It's also in fresh water. It's not in water which has been boiled.

Therefore... if you want to avoid corrosion of the iron to the extent possible (you can't avoid it completely) you would fill the boiler (some advocate up into the risers, some say nah why bother) and bring it up to a boil -- and then let it sit.

There is very little oxygen exchange between the surface of the still water and the air in the space above. Indeed, it is interesting to note that the air above the water in the boiler if it is left alone will be significantly depleted in oxygen; what oxygen was in there will have reacted with the iron rather early on. So you don't want to bring fresh air into the boiler if you can help it (which you will, if you run it at long intervals...).

TeachMeSteam

Jamie,

I know you have a lot of experience in this stuff but are you sure that there is not a lot of oxygen in the air above the water?

After the boiler cools down, the main vents open and oxygen rich air would come in until all the steam cools down. All the displaced steam would now be filled with oxygen air, wouldn't it? Wouldn't the air above the water be similar to the air composition as outside the boiler because the steam is what separated the other molecules but now they would be cool and have shrunk considerably. And after a few weeks, Brownian movement would lead to equilibrium which would make the composition of oxygen to be the same as the outside of the boiler, no?

Do you know specifically that the air above specifically would be devoid of oxygen or were you just guessing?

Thanks for your help.

Jamie Hall said:

Slight misapprehension there. Oxygen is in the air. The stuff is about 20% oxygen. It's also in fresh water. It's not in water which has been boiled.

Therefore... if you want to avoid corrosion of the iron to the extent possible (you can't avoid it completely) you would fill the boiler (some advocate up into the risers, some say nah why bother) and bring it up to a boil -- and then let it sit.

There is very little oxygen exchange between the surface of the still water and the air in the space above. Indeed, it is interesting to note that the air above the water in the boiler if it is left alone will be significantly depleted in oxygen; what oxygen was in there will have reacted with the iron rather early on. So you don't want to bring fresh air into the boiler if you can help it (which you will, if you run it at long intervals...).

Jamie Hall

I try very hard not to guess. Yes, when the boiler first cools down air -- 20% oxygen more or less -- is drawn into the pipes and, to a certain extent, the boiler. Once it is cool there is no interchange between the air in the pipes and the boiler and the atmosphere. Now... very roughly, that air weighs 0.1 pounds per cubic foot. Of that, a little more accurately, 0.017 pounds is oxygen. Now each pound of oxygen will react with 2 pounds of iron to form rust (very roughly). Suppose further that our hypothetical boiler has a steam space volume -- now full of air -- of 2 cubic feet (about 15 gallons). So. We have 0.034 pounds of oxygen in there, which will react (remarkably quickly, by the way) with 0.07 pounds of iron to form rust. The boiler weighs, let's say, 400 pounds.

Me? I'm not going to worry about 0.07 pounds of rust from a 400 pound boiler...

Now there are several items about this rather simplistic picture.

First, corrosion (rusting) tends to be highly concentrated by surface irregularities and small deposits of odd minerals -- so most of that rust will be formed in small areas, rather than uniformly. This is why corrosion can and does cause leaks, if allowed to continue.

Second, continuously replenishing the oxygen will allow the corrosion to continue, and eventually you may get enough of it to cause leaking. This is particularly true in thin sections -- such as some boilers today.

Third, and somewhat less obvious (except for those of us who have afflicted with confined space training): a space, as it might be a manhole or a steam drum or a pit with a rusting tank bulkhead in it, which has little or no air circulation, will be significantly depleted in oxygen, and if you go in there you may very well die. That can ruin your whole day...

Gordy

Depends how you like your tea, or coffee:)

Destructive Myths: The Dissolved Oxygen Hypothesis
Part I: The Argument

There are a lot of myths and unfounded maxims surrounding the proper preparation of coffee and tea. Most are harmless, or, at worst, detrimental to beverage flavor. But one such myth has resulted in a massive waste of energy and water. I refer to this myth as the dissolved oxygen hypothesis.

The dissolved oxygen hypothesis states that, when brewing tea, one should always use freshly drawn water, and never reboil water in the kettle. The justification given is that water that has previously been boiled has less dissolved oxygen (DO). The result is that many tea drinkers are wasting enormous amounts of energy by dumping leftover hot water from their kettles.

The dissolved oxygen hypothesis rests on two premises: (1) that once-boiled water contains more dissolved oxygen than twice-boiled water; (2) that dissolved oxygen improves the flavor of tea. Both premises are demonstrably false.

Boiling itself does not remove dissolved gases. It is the change in temperature or pressure that affects the amount of gas that a liquid can hold (i.e., the solubility of a gas in a liquid). Solubility decreases as temperature increases. Assuming normal atmospheric pressure and composition, water at 0˚C can hold a maximum of ~15ppm DO, while water at 50˚C can only hold ~5ppm. Once the water reaches 100˚C, solubility is zero. Therefore, if you've brought water even close to a boil, you've removed virtually all the DO. What this means is that neither once-boiled nor twice-boiled water contain significant levels of DO, refuting premise (1).

Studies (Faust & Aly 1998, Pangborn & Bertolero 1972) have found that the level of DO in drinking water does not have a significant impact on its taste. It seems likely that the folk belief that DO improves water flavor results from the fact that running water (e.g., streams) is generally preferred to stagnant water (e.g., lakes), and is also higher in DO.

In principle, DO could soften the tannins in tea, just as decanting a bottle of red wine does. However, decanted wine contains much more DO, on account of its lower temperature, and wine is usually allowed to breathe for at least 15 minutes, compared to the 1-5 minutes that tea steeps for. Furthermore, tea drinkers can control the level of tannins in their cup via manipulation of steeping time, water temperature, and water/tea ratio. In short, a well-brewed cup has no need of oxidation.

Therefore, both premises that lead to the dissolved oxygen hypothesis are false. (1) Tea water does not contain a significant amount of DO, and even if it did, (2) there's no evidence that the level of DO has any impact on the flavor of the tea.

All argumentation aside, I simply cannot tell the difference between tea brewed with once-boiled water and tea brewed with twice-boiled water. I've done the tasting blind, more than once. In part, this post is a challenge to any believers in the dissolved oxygen hypothesis: try a blind triangle test. If you succeed in distinguishing tea made from once- and twice-boiled water, let me know.

All this is not to say that water is unimportant. Water is important. Alkalinity is important. Salt content is important. Minimal iron content is super important. Dissolved oxygen is not important.

Part II: Confounding Results

Here's the twist: I can easily distinguish between fresh tap water and water that has been boiled for an extended period of time. In the process of investigating the dissolved oxygen hypothesis, I boiled a small quantity of filtered water for 5 minutes, then refrigerated it until it matched the temperature of my tap water. I then drew some fresh filtered water, and tasted the two, blind.

There was a clear taste difference between the boiled and freshly drawn water. The freshly drawn water had a clean, crisp finish, while the boiled water had an off-putting twang to it. This was not a hard distinction to make.

I repeated the test using a different pot to boil the water, to make sure there weren't any contaminants in the first pot. Same result: the boiled water tasted worse than fresh water.

Given that DO does not have an impact on water flavor, what could explain the flavor impact of the 5 minute boil? Boiling can have a number of effects besides removing dissolved oxygen. It can also remove chlorine as well as concentrate dissolved minerals by reducing the water. But my water filter removes all detectable chlorine, and the short boiling time did not reduce the amount of water by an appreciable amount. Boiling can also remove calcium and bicarbonate ions (by precipitating temporary hardness), but my water is quite soft, and I have never noticed any scaling (which would indicate precipitation of temporary hardness.)

The only plausible explanation I can think of is that boiling the water would also have removed any dissolved CO2. Dissolved CO2 will form a small amount of carbonic acid, which can significantly lower the pH of very soft water (like mine). The fresh water would then have a lower pH than boiled water. Since most consumable liquids are at least slightly acidic, this might explain why the fresh water seemed to have a clean, crisp finish compared to the boiled water. This explanation predicts that less of a difference would be evident if more alkaline water were used, because alkalinity buffers against changes in pH.

Why then wouldn't removing dissolved CO2 from water also affect tea flavor? Well, the amount of dissolved CO2 in tap water is not enough to have a significant impact on the pH of any solution much stronger than pure (soft) water. A full explanation of this phenomenon would require an in-depth discussion of pH buffering, but this is why the pH of a brewer's mash depends much more on the alkalinity than the pH of the source water.

Even if small amounts of dissolved CO2 did affect the flavor of tea, heating water close to boiling will remove virtually all dissolved CO2, just as it removes DO. For brewing tea, coffee, or any other hot beverage, dissolved gases are irrelevant.

Jamie Hall

@Gordy -- I love it!

rbeck

I don't understand this. I don't know how inside the boiler will be any less oxygen that the air outside the boiler. The system is not a closed vessel due to air vents etc. Oxygen cannot be 20% outside the boiler and less inside the boiler unless there is an air seal, can it? Most steam systems have pressure vents that will vent air and suck air in. Shouldn't the higher oxygen blend with lower oxygen volume. However small there are still air currents in the piping and boiler due to surrounding temperature changes in the piping and boiler with no boiler operating. The temperature changes would come from cooler floors warmer ceilings and drafting between the sections themselves. No vent damper is 100% sealed when closed.

Jamie Hall

No, the vents aren't 100% sealed. However, the area of the opening is very small, and the pressure differences are also very small. The total air exchange, while not zero, is small enough that the air in the boiler itself -- distant from any vents -- will be seriously depleted in oxygen (it won't be quite zero) within a matter of days.

Gordy

Exposed surface area verses depth of the water is a big factor in how much available O2 will be reabsorbed.

It’s not like the water will be disturbed, and mixed during the off season.

I wonder if a shot of liquid solar blanket for swimming pools would do the trick. Skim it upon heating season fire up. It may not last that long.

TeachMeSteam

Gordy,

I wasn't sure but were you just stating an interesting but irrelevant topic or was what you said had something to do with the discussion. I'm sorry. I couldn't tell.

Gordy said:

Depends how you like your tea, or coffee:)

Destructive Myths: The Dissolved Oxygen Hypothesis
Part I: The Argument

TeachMeSteam

Jamie,

When I was reading about the wet fire sprinkler systems, just the small air pockets themselves were sufficient enough to causes enough corrosion to lead to significant leaks. Thus, the absolute requirement that the air pockets must be removed in wet fire sprinkler systems.

I'm guessing you don't need that much oxygen to react just at the water line that leads to corrosion that leads to those pin holes.

I know the traditional way for the last 100 years is to raise the water line and then boil off the oxygen but I'm starting to think that this traditional way might be incorrect. Of course, I'm very far from sure. I'm just putting my hypothesis out there so people can just think about it. I think Brownian movement is stronger than people think - the oxygen above the water will constantly be at the same oxygen content as outside the boiler due to the main vents, despite the smallness of the size of the vent. This is just total speculation on my part....

Jamie Hall said:

I try very hard not to guess. Yes, when the boiler first cools down air -- 20% oxygen more or less -- is drawn into the pipes and, to a certain extent, the boiler. Once it is cool there is no interchange between the air in the pipes and the boiler and the atmosphere. Now... very ...

Gordy

Mother Nature always try’s to maintain balance. High to low pressure, hot to cold, the same goes for oxygen depleted water. If there is oxygen available in the system it will be reabsorbed into the oxygen depleted water if the two can meet.

Hydronic systems fight this same battle, except hydronic systems are closed systems. However oxygen can, and will egress into the system through many different points. Through pex if not O2 barrier, bladders on expansion tanks, faulty air vents etc.

Your biggest battle is just thinner walled modern heat exchangers that can’t afford to lose as much material as the old ones before failure.

The tea, coffee, tidbit actually has some information to offer. As to the effects of boiling water.
I’m a Moka pot guy who loves espresso with a shot of Grappa.

Jamie Hall

Protecting boilers -- or anything else -- from corrosion is actually amazingly tricky. There are very good oxygen scavengers available for the purpose -- but many if not all of them are based on hydrazine compounds, which really require paying attention and are not the sort of thing I'd want in a domestic or even general commercial or public building setting. They are useful, however, in power boilers where a leak is not just an inconvenience. Google SS Norway boiler explosion...

Back in the day, @Gordy , I was an Irish coffee guy... but that was a long long time ago!

bobbob

Huh...? I am so glad that I don't like tea, and abhor coffee