On Wed, 2003-11-05 at 13:11, David Weinshenker wrote:
> Still, it's good to know that pure stuff (in any decent strength) is available
> at all... with any continuous-freezing process, there may be limiting issues
> with solutes concentration. (It's _going_ to lower the freezing point and thus
> limit the effective extraction fraction; the question is how much, how soon, and
> with how much other impact on crystallization characteristics... don't know the
> answer to that one yet.)
I doubt it will lower the freezing point a detectable amount. Our
solute levels, even in the sparge product made from the 50% Solvay food
grade, are measured in a few tens of parts per million. It takes
something just over 1% salt to lower the freezing point of water 1
degree Kelvin, so I don't think we will have that kind of problem.
> Also, even with an evaporative concentrator, it's going to be difficult to make
> really high concentrations (independent of solutes issues) - our large-scale
> sparger trials, so far, seem to indicate a "point of diminishing returns"
> somewhere around 80%. We see ways to possibly improve things, but I am not
> abandoning freezing processes yet.
Actually, that point of diminishing returns is a result of the physics
of the process. It happens when the concentration of the vapor coming
out of the column reaches 50%. That happens around 85%, more or less. I
don't think our sparger is as efficient as it could be, but there's not
a whole lot to wring out with a single stage. Multiple stages could
drive the practical concentration levels higher, and eliminate
contaminants in the process.
-p
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