Chemical Engineering August 2020 - 41

HOT
Polysilicon
rods
(~1,150ºC)
COLD
Power
Gas
applied for
resistive
heating
Gas inlet
SiHCl3+H2
(Trichlorosilane and hydrogen)
FIGURE 8. Through a long process of gaseous
deposition, ultra-pure polysilicon builds up on the
filaments
is made worse by regular cycling
of the reactor, allowing pressure
to drop to atmospheric when each
charge is completed. Any hydrogen
that migrates through the diaphragm
and into the fill fluid can
outlet
SiCl4
(H2)
(SiHCl3)
(HCI)
potentially bubble out and deform
the diaphragm.
Given the extreme process temperature,
an instrument to monitor
gas pressure is usually located on
the feed pipe, where the temperature
is much lower. Nonetheless,
with 5 bars pressure, conditions
are optimal for creating hydrogen
permeation able to cause instrument
failure. This calls for gold
coating on the diaphragm to minimize
permeability.
Multiple solution possibilities
Hydrogen service, as discussed
here, presents critical challenges
fully capable of causing instrument
failure. However, there are solutions
that can reduce the problem,
and often eliminate it entirely for all
practical purposes. For users, the
lesson should be that no challenge
must be tolerated over the long
term. Instrumentation companies
are generally very responsive to the
Author
Keith Riley is the national product
manager for Pressure and Temperature
at Endress+Hauser
(2350 Endress Place, Greenwood,
IN 46143; Phone:
317-5352169;
Email: keith.riley@endress.
com), a position he has held since
April 2008. Prior to this, he was a
product manager and regional
sales manager with L.J. Star Inc.,
as well as a product manager for Penberthy (Tyco
Valves). Overall, he has over 20 years of sales, marketing,
and instrumentation experience in the chemical
process industries.
needs of manufacturers and have
found many creative approaches to
solve or at least manage problems
that may have seemed unsolvable.
The answer is engaging the vendor
as a trusted partner, one with extensive
domain expertise and a full
portfolio of solutions.
■
Acknowledgment
All images courtesy of Endress+Hauser.
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CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM AUGUST 2020
39
13_CHE_0820_FR1_GSO_p35-39.indd 39
7/17/20 10:33 AM
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Chemical Engineering August 2020

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