Chemical Engineering December 2020 - 30

considered. In effect, using such
internals may result in the creation
of tall, costly columns to accommodate
the elevated number of theoretical
stages required. Structured
packing (Figure 4)
is preferred in
FIGURE 4. Structured packing is selected in applications
that separate thermally sensitive compounds,
or those that have similar boiling points
Biorefineries usually involve some
diluted
process
aquedegree
of solids handling, and they
frequently
ous process streams with foulants.
Therefore, the separation equipment
should always be resistant to
solids and fouling while providing the
best efficiency possible. To address
these issues, trays are generally
used in front columns for biomass
removal and concentration, followed
by packed columns operated
under vacuum for the purification of
intermediate or end products.
Column trays have evolved over
the years to accommodate bioprocessing
feedstock. In particular, the
industry moved from generally having
no internals at all, as is the case
for flask- or pot-based processes,
to baffle trays, discs and donuts,
as well as sieves and V-grids. For
example, column trays with antifouling
properties (Figure 3) are
suitable for separation columns in
first- and second-generation biofuel
plants. Their outlet weirs are resistant
to fouling and the trays can also
be equipped with extra-large fixed
valves developed for severe fouling
applications.
Trays are also beneficial when vessel
walls need periodic inspection.
In this way, plants can reduce their
costs and the downtime associated
with repairs and maintenance, as
well as extend their replacement intervals,
reducing the overall environmental
impact.
Once the feed streams are free of
solids, mass-transfer efficiency becomes
the key factor to optimize,
and alternatives to trays should be
30
these applications.
In particular, structured packing
is the go-to choice when processing
thermally sensitive compounds
or when substances have similar
boiling points. This type of column
internal minimizes liquid holdup and
residence time, meaning that substances
can be processed without
undergoing any degradation.
It also allows columns to run at a
lower temperature, further protecting
the thermally sensitive feed.
Particularly, by featuring low liquid
flowrates (and higher vapor rates),
such a setup can operate at low
pressure. Also, since the packing's
open area is nearly as large as the
column's cross-sectional surface,
pressure drop is limited. This aspect
also makes structured packing
ideal for use in vacuum services,
where the pressure drop needs to
be low. These features also benefit
highly corrosive services or applications
where the feed may be
prone to foaming. Finally, the reduced
pressure drop also facilitates
heat-integration concepts that improve
the energy efficiency of the
overall process.
Similarly, the structured packing
can provide benefits in carbon capture
projects, because plants can
significantly reduce the size and the
pressure drop across their separation
column, thus reducing capital
expenditure (CAPEX) and OPEX. In
addition, the texture of certain types
of packing can offer more uniform
residence time, preventing microorganisms
from the fermentation process
accumulating on its surfaces,
which can lead to reduced equipment
service life.
Continuous improvements
In order to maintain optimum operational
conditions, as well as
maximize yields and energy efficiency,
businesses should conduct
regular servicing and maintenance
on their separation equipment and
seek the expertise of third-party
specialists when needed. In addition,
performance evaluations of
existing separations trains can reveal
opportunities for improvement.
The most suitable and effective revamp
strategies can be defined,
which are key to implementing appropriate
modifications to column
internals and mass-transfer components
and increasing overall column
capacity in biorefineries and
carbon-capture plants.
In order to run a successful bioprocessing
plant for the production
of biofuels and chemicals from
sustainable resources, waste or byproducts,
it is crucial to maximize
energy efficiency and cost. These
aspects can be addressed by developing
separation solutions based
on the ideal methodology, design
and components. In addition, it is
fundamental for businesses to keep
up with the latest technological advances
in order to intensify their processes
and maintain a competitive
edge. Holistic, proven solutions and
technological expertise can support
the entire lifecycle of a plant, from
development through to maintenance,
ensuring continuous process
optimization and reliability.
n
Edited by Mary Page Bailey
Authors
Thomas Raiser is a senior applications
manager at Sulzer Chemtech's
global bio-based chemicals
and renewables group in Switzerland
(Email: thomas.raiser@sulzer.
com). He has over 30 years of experience
in process and plant design
with focus on distillation and
membrane separations, sales and
process development in solvent
recovery, product purification and biofuels. He holds a
B.S.Ch.E. from the University of Applied Science in
Mannheim, Germany and a postgraduate study in business
engineering management from the University of
Applied Sciences and Arts Northwestern Switzerland.
Ramnik Singh is a senior applications
manager at Sulzer Chemtech's
global bio-based chemicals
and renewables group in California
(Email: ramnik.singh@sulzer.com).
He has over 20 years of combined
experience in process development,
research and development
and bioproducts scaleup in
pulp-and-paper and chemicals inthe
dustries.
He has a Ph.D. in environmental sciences from
the University of California at Berkeley.
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