On Thu, 27 Sep 2007 13:54:13 -0000, "jim.isbell"
wrote:

On Sep 22, 10:39 pm, OldNick wrote:
On Sat, 22 Sep 2007 10:55:52 -0500, Brian Whatcott
wrote stuff
and I replied:

But what is the cheap source of getting the vacuum? I figured there
had to be a vacuum, although it was not said. But how do you get it?


Gravity.


Wishful thinking. Where are you going to get the feedwater containing
no noncondensible gasses in solution? In all real distillation plants
a continuosly operating vacuum pump is required to maintain vacuum and
prevent the condensers from filling with noncondensible gasses. There
is no way you are going to eliminate the vacuum pumps with any kind of
inverted tube arrangement.

For reasonable efficiency real distillation plants are multi-stage,
where the latent heat of condensation from one stage is used to boil
feedwater in the next stage, with up to 5 stages being used in larger
plants (in the days before reverse osmosis made them uneconomical by
comparison). Sucessive stages operate at lower pressures, and
corresponding lower temperatures. The 1100 or so BTU required to boil
one pound of water can thus boil up to 5 pounds of water instead.

You still need enough thermal gradient to get the heat to flow through
all those heat exchangers. By using low thermal differentials between
the hot and cold ends you either reduce capacity to a pittance or
require huge and expensive heat exchangers, in either case not
competitive. TANSTAAFL.