The boilers on the USS Midway (and I’m sure other ships) generate Saturated Steam
(486 degrees) and Superheated Steam (850 degrees) at 600 PSI. The superheated is used for the main turbines, the cats and for electrical generation.
My understanding, which is very basic, is that the hotter steam contains more energy. I don’t understand this. I could see where more psi would turn the turbines faster, but how does temperature factor into this?
Can someone explain (in layman’s terms) the relationship between hotter steam and more energy?
This is actually the easy part to understand. It takes energy (i.e. heat) to raise the temperature of saturated steam at 486 deg F to superheated steam at 850 deg F, therefore the superheated steam must contain more energy.
Basically, in a turbine, the steam drops in both pressure and temperature as it passes through the turbine. You can therefore extract more energy from higher pressure steam as well as higher temperature steam.
Steam expands and cools as it does work in the turbine. If condensation forms as a result of the cooling, it will damage the turbine. Super heating allows for more expansion and cooling before the point of condensation is reached, and so more energy can be extracted from the steam.
A turbine will not extract the latent heat of condensation. The turbine exhaust temp and pressure will be a function of the condencing water temp and pressure. The exhaust of a fully loaded turbine will be saturated steam.
A lot of Navy ships use M type of boilers with seperatly fired superheaters. There are time when the ship can be underway and and the superheaters not light. At these times turbines are only getting saturated steam and water inside the turbine is not a problem.
In simple terms the higher temp means that the same amount of steam will have a larger volume.
IMHO… THIS is a very good answer!
I say this from the point of someone that has virtually no working knowledge of steam powered warships or their peripheral power systems.
The explanation provided by yoyodyne makes perfect sense to me.
I don’t think this follows that simply. If I have a mass of steam at 486, and add energy to bring it to 850, the pressure will also increase. For a given volume, if the steam at 486 and at 850 are at the same pressure, the hotter steam must have less mass for them to have the same pressure. The energy per mass of steam will certainly increase, but it’s not clear that the energy per volume will increase.
Plus, the hotter steam can probably be used to cook lunch or make coffee or something (I have no idea, and it’d probably be horribly dangerous to try, so if you have a M type steam boiler with accompanied superheater at home, don’t try this)
But I was an electrician and only studied the steam cycle as a side qual. I’m sure Robby and Snnipe 70E know far more than I do.
Though I will add the 600 PSI had additional uses, reduced down to 150 PSI for the Ship’s Whistle and the water heaters in the heads as minor ones but a huge one was the Zap Evap that made nearly purified water. When the ships switched from bromide distillers to Zap Evaporators we ran into an odd problem; the new ice machines relied on the water itself to close the switch that shut the solenoid valve to cut off the water into the ice makers. The water from the Zap Evaps was nearly non-conducting. It took us 2 days to troubleshoot the problem but the Engineers at the manufacturer did send us a thank you for solving the problem.
Ship’s use to run out of water until the Zap Evaps were installed, then we never had the problem again.
It was a very small float switch instead. I forget where we scavenged it from but the manufacturing company was OK with the idea and sent us the parts for the rest of the ice machines.
