Why steam rises from San Francisco streets
secretsanfrancisco.com
secretsanfrancisco.com
In my city the boilers run at 600psi.(Not near any salt water, however if we decided to use it if we could, removing all the impurities from the feed-water would be to expensive. At our psi the feed-water must be clean and deaerated to protect the boiler tubes.)
I'm a plant operator so I don't fix leaks in the field, these steam leaks are just that, small leaks that develop in the steam supply piping or the condensate return piping. (True, some lines aren't insulated properly in the maintenance boxes, so you do get some pulverized condensate.)
The steam generated from the main plant is used for all kinds of applications. Heating of course, whether live steam or heating water using a heat exchanger. Also it is used to power steam turbine chillers to create chill water, which cools a significant amount of office buildings and manufacturing plants. (These chillers use refrigerant, usually 134a, to cool down the water being pumped through them, which is then pumped to where the cooling process is needed. Sometimes these pumps are steam driven, but are usually electric motor driven. Water temp leaving the chiller is usually 38 degrees, but may be around 42 by the time it arrives to where it is used.)
My plant uses natural gas to create steam. Many electrical generating power plants still use coal or nature gas to heat treated water to create the steam to spin the turbines which spin generators to create the electricity. (Sorry, I’m not a very good writer.)
There are many other applications for steam boilers, and no matter what they are, there’s always the threat of leaks. The cleaner the system, whether steam of water, the better the chances of not corroding the piping. This is done by using chemical treatments to destroy the oxygen or rust inhibiters.
I couldn't help thinking of the fictional weapon used against Godzilla:
Had no idea you could make a steam powered air conditioner.
How is it more economical to have enough leaks that people start talking about it instead of doing proper maintenance? Especially since this situation seems fairly unique, I've never seen this outside the US, and could only name San Francisco and New York as places where this happens. So what discourages maintenance in those places compared to everywhere else?
My natural gas supplier for example (which is used primarily for heating where I live) routinely raises prices and always flouts state law. My only option would be to discontinue use of natural gas, which would cost me even more money.
Doing proper maintenance requires opening the streets, which is expensive and causes confusion and delay, so there's some amount of acceptable leak before it's a good idea to fix it. There's always a chance of finding unmapped critical infrastructure when you dig, which adds more risk. Plus, when you fix it, you lose the street cred.
This reminds me that in Paris you can pretty often see water flowing on the street, it seems that the Paris water supply has a tendency to leak that I just don't see in other towns (but then, i am really walking for kilometers through the city when visiting paris so maybe I just have more opportunities to spot leaks).
https://parisianfields.com/2012/03/11/a-most-unusual-water-s...
I’d think there would be some sort of safety system for venting pressure. Or even condensation around the hot pipes (which seems to be why the same thing happens in New York which also has a steam network)
All of the above could work too.
https://web.archive.org/web/20160811170408/http://www.coned....
This can be a large portion, e.g. in older systems from the days when fuel was cheap, and pollution wasn't a topic.
Modern systems attempt to recover exhaust heat, and can be 90-ish% efficient.
There's a more obvious argument that leaking steam into the streets is a waste of heat, but that still depends on your goals. You might like having warmer streets.
You're thinking of forced hot air systems, but these do not vent combustion exhaust into living space. There are fuel remnants and combustion byproducts in the exhaust which would smell bad, and kill people.
Combustion exhaust, and all of the heat it contains, goes up the chimney and is lost. The living space air is heated by proximity to the combustion chamber, but circulates in a separate closed loop.
Also, in a forced hot water system, there is no air circulation at all. 100% of the air involved is heated and goes straight up the chimney.
Aside: Some people call FHW systems "boilers" instead of "furnaces", but this seems to vary by region. Where I'm from, "boilers" are steam systems only -- which seems reasonable, since water is not boiled in a FHW system.
> Also, in a forced hot water system, there is no air circulation at all. 100% of the air involved is heated and goes straight up the chimney.
Without disputing your other points, this isn't right. I'm not thinking of any particular style of system. The point of every heating system is to release heat into the air. The problem people experience is that the air they occupy is too cold, and the solution is to heat that air. The point of a system that circulates hot water through your building, or your apartment, or anywhere, is that the hot water will release heat into the air there. Heating the air is the only goal regardless of whether the system involves circulating any air.
The point that you can lose heat by venting hot combustion waste to the external atmosphere is well taken.
So when I said that 100% of the air involved in a forced hot water system is used for combustion and exhausted, I mean the air at the furnace, not the air that is indirectly heated in the living space.
Agreed that the goal is to heat the living space though, including the air. A forced hot air system does that directly (pushing heated air into living space), and forced hot water does so indirectly (pushing hot water into radiators in living space, which heat the air by convection).
Radiant floor heat is another example where there's no air at the heat source.
This kind of argument works for power stations, but it doesn't work for heat because it's obviously not more efficient to heat 13 miles of piping in addition to your building rather than just burning stuff in your building.
The rest (almost 30%) goes up the chimney, or radiates out from the furnace itself. It's heat, thermodynamically speaking, but it is not useful heat.
(Some is also lost to light energy, and some fuel is not fully-combusted. These account for a small but measurable loss.)
The water is still plenty hot enough for steam to form in leaks, so there's perhaps some factor that makes leaks more tolerable in steam systems? Different corrosion concerns perhaps, air leaking in is less corrosive?
In college I would walk past a steam stack on campus every day, because I could see it was always on the verge of making rings (pretty much any cylinder with steam or smoke passing through it or around it is, I've seen rings from incense, boiling rice [the cylinder here is the column of steam bubbles], dropping food coloring into water - if you look for them you start finding them. The craziest example I've seen, which works much like the food coloring, is an airplane contrail.). I thought if I kept it up, one day the wind would blow in just right right way and there would be a beautiful train of rings.
I never did see it. But on a hot day[1], I saw the steam settle into the narrow alley next to the building. It formed into a tiny roll cloud, about six feet long. I watch it stunned for about fifteen seconds, and then it dispersed.
[1] I'm pretty sure it was a hot day, what I remember clearly was that it was an unusual temperature. I surmise the air was very warm and so the steam was denser than the air. But it may have been a cold day and the steam cooled and then sank, unfortunately I can't say for sure because I didn't write it down.
It can be both very cold and very hot here.
This can also just dump steam directly into the sewer. Get a real steam guy to repair and optimize your steam heating system!
Any reason why they couldn't use ocean water?
It would probably be cheaper to just convert to another heat source all together.