ADS inclusion. No decision has been rendered yet, but you
might keep this in mind if you think you may use these
We currently apply one exception to our ADS guidelines.
The decision process for ADS inclusion is really based around
the activation energy, as well as the operating temperature
and its proximity to the onset of thermal cracking, which
is 850° F. We currently utilize a very mild, amorphous-like
hydrocracking catalyst system to increase volume swell in
diesel hydrotreating service. The activation energy of this
system is extremely low. In this case, ADS is optional as long
as the expected operating temperature is also low, relative
to 850° F.
Next I will discuss ADS activation. ADS triggers are de-
signed to provide the console operator sufficient time and
notification to gain control of the unit or manually initi-
ate depressurization. Time, in this case, is not a fixed clock
time. Rather, it is the effective time created between the
alarm and trip set points. Based on experience with early
implementations, we have a concern with false trips, so we
utilize redundant voting. One of our ADS triggers is loss of
recycle gas flow. For this, we use two-out-of-three voting.
High outlet-line temperature is another trigger. This is based
on two-out-of-two voting. For catalyst bed temperatures, we
only trigger the ADS from catalyst beds containing hydro-
cracking catalyst and only from the bed outlet temperatures.
For these locations, any two high temperature indicators
(TIs) at the same bed outlet will trigger the ADS.
Finally, ADS functionality: When the ADS trips, it will
depressurize the unit until all permissives are clear. For
CLG, the permissive for pressure is reducing the system to
50% of design. The CVX permissive for pressure is reduc-
ing to 25% of design. We use a 50° F. bandwidth on high-
temperature trips, so TIs have to drop 50° F. below their trip
temperature before the permissive will clear. Finally, 5 min
of continuous recycle compressor operation is required to
clear the associated permissive. If all of the permissives are
clear, then the ADS will stop depressurization. If all permis-
sives do not clear, depressurization will continue down to
the nitrogen header pressure.
My last point on ADS: The operator is generally in control of the depressurization process. Once all permissives
A California superior court recently cleared the way for Chevron Corp. to proceed with its long-planned, $1-billion project to modernize operations at its 257,000-b/d refinery in Richmond, Calif. (OGJ Online, Apr. 22, 2015). The project will replace some of the
refinery’s oldest processing equipment with technology meeting the broad spectrum of US air quality standards without changing
the basic operation or amount of crude the refinery can process. A main project component is replacement of the refinery’s existing
1960s-era hydrogen plant to enable more efficient and reliable processing of higher-quality hydrogen. Photograph from Chevron.