Chemical Engineering June 2015 - 52

Engineering Practice
Filtration and Separation During Chemical
Process Operations: Avoid Common Errors
The seven commonly made mistakes discussed here often lead to poor filtration and
separation performance and many associated problems
David Engel and Heath Burns
Nexo Solutions
Michael Sheilan
Sulphur Experts, Amine Experts Div.
F
or almost any chemical process
industries (CPI) plant,
contamination is a reality that
can cause numerous associated
- and often chronic - problems.
Some of the issues caused
by contamination include: foaming,
fouling, corrosion, solvent degradation
and losses, deposition, undesired
side reactions and impacts on
downstream process operations.
These problems invariably lead
to capacity reductions, efficiency
decay, inability to meet specifications,
equipment failures and, high
maintenance and operational costs.
Problems with contamination can
also lead to undesired environmental
discharges and loss of profitability.
Many of these detrimental effects
can be mitigated by the use of proper
contamination-control measures
and appropriate separation technologies,
such as chemical additives
and mechanical separators and filters.
This article focuses on proper
mechanical separation.
Mechanical separation in chemi0.7
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cal
process operations, as related
to contamination control, is generally
undertaken in the following areas of
the process:
* Feed stream - to remove contaminants
from a process stream
feeding a unit
* Effluent stream - to remove
contaminants from the process
stream leaving a unit
* Internal stream - To remove cotaminants
from a process stream
that recirculates (such as amine
solvents, glycol solvents and
many other recirculating process
solvents)
The predominant mechanisms
for contaminant separation are
as follows:
* Filtration - removes suspended
solids in a liquid or gas stream
* Coalescence - removes free
liquids and aerosols from a gas
stream or emulsions from a liquid
* Adsorption - captures dissolved
species, predominantly organic
components, from a gas or liquid
stream
Proper contamination control, prior
to any chemical process operation,
is essential to ensure plant stability,
performance and low operational
costs. This is often achieved when
there is a thorough understanding
of all inlet feed contaminants in
a gas stream. Such an understanding
will help to determine what separation
process and system should
be used.
Inlet contamination in chemical
- Differential pressure-F4002 - Flow-F4002
FIGURE 1. In this differential pressure trend for an automatic backwash system, note that the cycle times between backwashes
decrease over time, indicating that the contaminants are not being fully back-flushed off the filtration media. The red line is the flow
through the backwash filter, the blue line is differential pressure
52
process units can vary drastically,
and depends on a number of factors,
including the following:
* Feed contaminant types, concentrations
and variability
* Upstream processes for the feed
and carried-over contamination
* Transmission methods and equipment
used to take the feed material
to the unit
* Chemical additives used upstream;
along with a type and dosage
amounts
Particle filters are most commonly
used for removing suspended solids.
These devices are most commonly in
the form of disposable filters. These
can provide a very cost-effective
means of removing contaminants.
They also have the advantage of
physically removing the solids from
the process - unlike backwashfiltration
systems that typically recirculate
the backwash stream (including
contaminants) back to the front
of the plant for reprocessing. With
these systems,
errors in design,
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Chemical Engineering June 2015

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