Can steam be produced from very hot water

dopey27177

JUMPER asked a very interesting question

I wonder if there's a district heating system anywhere that circulates very hot water to produce steam in the buildings the system serves?

Jakes reply is

To: Jumper

The answer is not likely or a yes and no.

Iceland has geothermal hot water and circulates this through district heating.

No need for steam. Super heated hot water is piped into the buildings for heating and domestic hot water production. Although there may process plants in iceland

For a utility or factory to super heated water to then through a heat exchanger is extremely costly.

There may on site power plants that use the super heated water to produce steam to operate generators.

Have not seen a plant like this, but taking pressurized hot water (220 and above) when entering a flash tank at atmospheric pressure the water will flash into steam.

Example: Let say you steam pressure at 10 psi, that is steam at 240 degrees F.

You would need a vessel (flash tank) with a relief valve set above your desired steam pressure to contain the steam. The piping leaving the vessel will go to the point of need.

The only place you can get this is from a very large geothermal source like yellows tone park or some places in California.

Or:

In 1969, the Laxá Power Company constructed the country´s first geothermal power plant in the Lake Mývatn area, the 3 MW Bjarnarflag plant (now upgraded to 5 MW). Now owned by the National Power Company, Landsvirkjun, this plant is still producing steam for district heating, electricity and waters for the geothermal spa on Lake Mývatn. Nearby, the Landsvirkjun operates the Krafla geothermal power plant that came online in 1977 with 30 MW installed capacity, with another 30 MW added in 1997. There are five other geothermal plants situated around the country; the 75 MW Svartsengi owned by HS Orka, 120 MW Nesjavellir station owned by Reykjavík Energy, 2 MW at Húsavík owned by Húsavík Energy, 100 MW at the Reykjanes plant owned by HS Orka, and the 213 MW Hellisheiði Power Plant owned by Reykjavík Energy. The 90 MW Theistareykir Geothermal Project has been added in the northeast, not far from Krafla, with the first unit of 45 MW in 2017 and the second 45 MW in 2018.

Jake

Steamhead

Yes, it definitely is possible.

Remember the infamous Three Mile Island near-meltdown? That reactor, a Babcock & Wilcox model 177, circulated water at something like 2,100 PSI through the reactor core, then ran it through heat exchangers (called "boilers" in that application) which caused water on the low-pressure side to not only boil, but to be superheated to run the turbines that powered the generators. The designers thought the water in the reactor loop could never exceed 700°F, so the computer was not programmed to read anything higher. The resulting lack of accurate information was one factor that led to the accident.

There's a very good book about that accident called "The Warning: Accident at Three Mile Island" by Mike Gray and Ira Rosen, from which I obtained the details above. Like @DanHolohan , they present the technical details so they're easy to understand, and the writing is as good as any thriller novel. You can find copies on eBay or Amazon.

EBEBRATT-Ed

There is a hospital in Springfield, MA Mercy Medical Center (built around 1970) that uses high temperature hot water. I forgot the exact temp and pressure but it's around 500 psi at the boilers and 450 degrees.

The send the hot water to unfired steam generators basically a steam boiler with a coil in it. The boiler has a gauge glass, safety valve pump controls etc just like any steam boiler.

They generate steam for the laundry and for steralizing etc. Most all the heat is hot water

dopey27177

The basic question is:

I wonder if there's a district heating system anywhere that circulates very hot water to produce steam in the buildings the system serves?

Not done in situ but done in district heating. District heating is where the water is produced in a central location and sent to off site locations to produce steam for use.

Jake

Steamhead

Sounds to me like that would be inherently dangerous. In order to get the water hot enough, the system must be pressurized enough so the water is well above steam temperature at atmospheric pressure (assuming the usual steam-heating pressures in the building). If a pipe breaks, the water is now superheated for the lower pressure resulting from the broken pipe, and will expand 1700 times as it flashes to steam- BOOOOOM!

EBEBRATT-Ed

@Steamhead

The boom factor is a possibility.

If I am not mistaken they pressurize the expansion tanks with a tank of nitrogen. I did some work there a few years back. At the pressure they run small leaks show up quickly. Pretty much all the piping is welded and it's all schedule 80 except some smaller threaded stuff.

Interesting that because it is hot water (and not steam) the State of Ma. does not require a licensed boiler operator, but the hospital in it's wisdom has them on site 24/7.

It's the only HTHW system I have ever seen or herd of.

It's been on line since around 1970 and I don't think they have had any disasters. They keep it in good shape but the whole plant is 50 years old now. Original boilers and burners they can burn gas or oil