(81e) Introduction to Troubleshooting Distillation Columns

In all chemical plants and refineries there generally is not enough instrumentation in the
right places in
our processes. During the design phase, decisions were made between knowing more
about the process,
which means buying more instruments, and saving capital funds. When a problem appears
with the
operation of a vessel, there are always gaps in the knowledge of what is happening due to
a lack of
instruments in the places where knowledge is not routinely required. Process engineers
and operations
personnel need to know what is happening so they can take corrective action. When
knowledge is
missing, they often take actions that make matters worse.
For distillation and separation processes Chemical Engineers have historically relied upon
plant process
measurements such as low rates, temperatures, and pressures and model or simulation
results for data
with which to solve troubleshooting or re-design problems. An array of on-line diagnostic
services are
available that can provide additional data offering real-time information on how pieces of
process
equipment are actually operating. The most common application is Gamma Scanning. This
test is
primarily applied, but not necessarily limited to, distillation or separation columns. Gamma
scans
provide a density profle of the internal process of operating distillation columns and other
process
vessels. The density profle can be used to diagnose the hydraulic operating conditions of
mass transfer
devices such as damage to internals, fooding, degree of entrainment or weeping, liquid
levels on trays
and distributors, liquid distribution through packed beds, etc. The presenter will show case
studies
where scanning revealed vital process information that helped solve an operating problem,
or helped
make a revamp/re-design successful. Additional derivatives from gamma scanning of
detecting flow
distribution patterns will be demonstrated. The ThruVision Scan technique is a specialized
horizontal
gamma scan used to generate a topographic profile of the internal cross-sectional density
of process
equipment. This profile is useful for the detailed study of liquid flow distribution through
packed
columns as well as having applications beyond distillation columns. A hybrid application
involving tracers
and scanning on fixed bed catalytic reactors will also be discussed.