"Richard Clark" wrote in message
...
On Thu, 11 Nov 2010 18:17:16 -0500, "Barry" wrote:

But if you have ever worked with a Fourdriner machine that
is not controlled well, i.e. the thickness varies with time due to any
number of variables,

I have. That and a year's worth of studying paper process chemistry
for precision (sic) measurement of K and Kappa.

It has been about 30 years ago, but I remember that while Kappa is
related to the amount of lignin remaining in the pulp after cooking,
every wet end process had its own peculiar measurement. I worked on the
online measurement of Kappa for several solvent pulping processes that
were to produce dissolving pulp for Eastman's cellulose ester process.
Once the vendor that supplied our pulp got wind that we were researching
solvent pulping, they quickly dropped their price and raised their
quality enough that we halted work on our own pulping processes. One
process we were considering involved the use of supercritical CO2. We
never got beyond early pilot plant work on this.

I fully understand the {sic} in your statement.

When it gets down to what you describe as "not controlled well" that
is more the definition of a Paper Mill that is destined for bankruptcy
before the end of one week - if not a weekend. I've seen the
production floor flood with product when the process encounters a
bottle neck. The production pipeline is enormous with a lot of
intertia.

I have toured quite a few paper mills over the years with both Kraft and
caustic pulping. I never really got to see one of the large continuous
digesters though. We had a small caustic plant that used hardwoods in
town with us. The odors were interesting - mercaptans by them and the
occasional butyric acid spill by us.

I always wonder how long the cellulose acetate business will last. While
cigarette smoking is declining in the US, increasing demand from China
seems to more than make up for the loss.

Going back to the original TDR discussion, probably the most interesting
use I ever put one through was in diagnosing thermocouple problems in our
coal gasifier. I saw that the platinum-rhodium thermocouples had water
in them. We finally got a metallurgist to do an "autopsy" on one of the
thermocouples pulled out during a shutdown. When we broke open the
thermocouple, water ran out. We saw a buildup of salts from the
Saureisen cement at exactly the place that I predicted. Water was
diffusing in through a silicon carbide protection tube and an Inconel
sheath.
Of course the gasifier operated at high temperature and pressure. A
Nastran simulation of the thermowell showed that the temperature at that
point was low enough for condensation to occur. Some extra insulation on
the external flange solved that problem!

73, Barry WA4VZQ

How the heck did we get off topic this far? :-)