Volume
VI helps the user to avoid operational problems
or improve the performance of existing
crystallizers.
Volume
CR VI Part 1 Tailoring
of crystal size distribution.
The crystal
size distribution (CSD) of the product from a crystallizer
is obviously important, and the product requirements
may specify that a particular distribution must be achieved.
The crystal size distribution can also affect downstream
processing, solids and slurry transport, and the caking
and storage properties of the material. Achievement
of the correct crystal size can be vital for economic
production.
This guide
shows how to modify the product crystal size distribution
obtained from a working crystallizer; it also contains
a section concerning the design of new crystallizers.
Crystal size distribution problems are divided into
6 basic categories:
- Mean size too low.
- Mean size too high.
- Too many fines present.
- Too many large crystals present.
- Distribution too wide.
- Distribution varying erratically.
The guide
contains four sets of logic diagrams:
- Identification of the
basic problem category or categories.
- Identification of low
cost/short time scale solutions.
- Identification of medium
cost/medium time scale solutions.
- Identification of high
cost/long time scale solutions.
This report
also forms the basis of the CRYSES expert system.
Volume
CR VI Part 2 Encrustation
of crystallizers.
Wherever
high supersaturation is present in a crystallizer, encrustation
and fouling can occur. This will reduce crystallizer
performance by:
- Reducing heat transfer rates.
- Acting as nuclei sources.
- Reducing the working volume of the crystallizer.
- Causing physical damage
to the crystallizer if large crystal masses become
detached.
Six fouling
mechanisms are discussed - particulate deposition, scaling,
chemical reaction (corrosion), polymerization, biological
fouling and freezing. The prevention or minimisation
of fouling is a factor which should be considered when
designing or operating crystallizers. The report discusses
both aspects, providing guide-lines to both designers
of new crystallization equipment and operators of existing
equipment encountering fouling and encrustation problems.
Volume
CR VI Part 3 Attrition and
Breakage. This
report provides guidance on the control of attrition and
breakage during crystallization. The report contains sections
on characterisation of the impact of attrition on granular
solids, attrition behaviour in stirred and description
of attrition phenomena in terms of the particle size distribution.
The manual also contains extensive appendices on the more
fundamental aspects of attrition and breakage, attrition
testing methodologies and the role of fluid dynamics on
particle breakage.
Volume
CR VI Part 4 Chemical and Physical Purity.
This report provides a structured
approach to addressing crystal purity problems. It begins
by distinguishing between chemical impurity and physical
impurity (polymorphism and amorphous phases). It continues
with a review of the different mechanisms by which impurities
can be incorporated within the product, each mechanism
being illustrated with suitable examples from the literature.
The report then addresses troubleshooting; it lists potential
warning signs, indicates methods to identify, quantify
and locate impurities and suggests suitable remediation
options. The report ends with a section on purity in process
development which offers guidelines on how to improve
product purity in development through careful selection
of isolation conditions and design of the crystallization
process.
Volume
CR VI Part 5 Troubleshooting a Continuous Crystallization
Process. This
manual part on troubleshooting continuous crystallizers
is written from the practical experience gained through
many years of developing, commissioning and troubleshooting
continuous crystallization plant. The manual begins with
the identification of the problem and defining a problem
statement. This is followed by a practical approach to
specifying the crystallizer and associated plant and its
anticipated performance. The next step is the collection
of data to help quantify the actual performance of the
unit. This is focused around the construction of the heat
and mass balance and characterisation of the product stream.
The potential pitfalls in this process are identified
and strategies to help avoid them are given. Comparison
of the anticipated performance of the unit and its actual
performance should help to diagnose the problem more fully.
At this point the problem statement can be reassessed
and modified if necessary and a list of potential causes
can be drawn up and reviewed with the process "owner".
The potential solutions can then be considered and ranked
and an action plan formulated. An important issue at this
stage in the process is the management of the implementation
of the proposed changes and the expectations of the process
owner and operators. This should include the expected
response of the system to the proposed change, the perceived
probability of success and the next line of action to
be taken in the event of failure. The report ends with
some guidance on ensuring the problem is solved and does
not recur. The report is written to be used in a troubleshooting
situation and its style reflects this, it is not an academic
thesis, but rather a practical document designed to assist
those facing operational problems.
