On 13/02/2021 10:43, newshound wrote:
On 12/02/2021 23:57, Fredxx wrote:
On 12/02/2021 21:00, newshound wrote:
On 12/02/2021 14:40, The Natural Philosopher wrote:
On 12/02/2021 11:24, Andy Burns wrote:
Jethro_uk wrote:

Especially the possibility for desalination - plonk a few of these
around
the parts of the world that need water and consider the electricity a
handy by product

Isn't the electricity /used/ to do the desalination?

Actually no.

the waste heat does that.

Boil some seawater, channel the steam through a condenser (cooled by
more seawater) and voilÃ*! - fresh water

You would probably build it just for that, since steam is what comes
out of a PWR.

I havn't seen any sums for that. IIRC reverse osmosis is remarkably
low-energy and low capital cost compared to distillation.

You might think so, but if you have oodles of low grade heat it might
become cost effective.

I heard it was a high energy process. Either way lower than distillation.

Sorry, just can't see it. Not sure I can even see a large scale solar
still with photovoltaic pumps working for coastal deserts. Otherwise
someone would be doing it.

You need a source of salt water, not normal in a desert.

Your low grade heat from a power station operated in the usual way isn't
going to evaporate water quickly. Then you need massive condensers to
collect it, pumping seawater through them to keep them cool with the
associated pumping and pipe friction losses.

Low grade heat could be 100+C, enough to boil water.

Given you can heat incoming water by the condensate much of the energy
can be reclaimed. That would make condensers more manageable and a power
station would normally need a condenser of some size.

In a combined electricity/desalination plant it *might* make sense to
take bled steam from the HP turbine outlet to do the evaporating, this
still has a decent energy density so your plant volume (and hence
capital cost) is lower for a given throughput.

You only need a little higher than 100C to boil water. HP steam can be
up to 600C, and there are many stages to a generating turbine to bleed
steam off, I might suggest nearer the low pressure exhaust side.

Of course if you want a higher temperature exhaust it means the turbine
could be a few stages shorter and correspondingly cheaper.

I suspect that reverse osmosis would still make better commercial sense.