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Revision as of 19:43, 10 September 2013

Due date(s): 18 September 2013 (at class)
Nuvola mimetypes pdf.png (PDF) Assignment questions

<rst> <rst-options: 'toc' = False/> <rst-options: 'reset-figures' = False/> Assignment objectives


.. |micron| replace:: :math:`\mu \text{m}`

There are several viewpoints we can use to understand separation processes. One is to consider them based on the mechanism being exploited; another is to consider them based on separations of solids, liquids and gases from various combinations of each other.

.. question:: :grading: 10

#. Identify the mechanism (principle of separation) by which the components are being separated in the following instances. For example, when concentrating orange juice in an evaporator, we are exploiting the difference in *volatility* between water, and the complex aqueous compounds that make up the juice.

#. Apart from the mechanism used, also identify the separating agent in each instance, and state whether it is an MSA or ESA.

*Unit operations to consider*:

* Crystallization * Adsorption * Steeping (brewing) tea * Using `monoethanolamine <http://en.wikipedia.org/wiki/Ethanolamine>`_ in a `carbon dioxide scrubber <http://en.wikipedia.org/wiki/Carbon_dioxide_scrubber>`_ * Flotation (mining industry)

.. answer:: :fullinclude: no

* Crystallization uses * Adsorption: * Steeping (brewing) tea exploits the different solubilities of the materials. The solvent, water, is the MSA. * MEA CO2

.. question:: :grading: 10

Give actual example(s) of where the following mechanism (principle of separation) could be used to split components from a given feed stream. State the name of a unit operation that exploits this mechanism to cause the separation. *For example*, the first answer could be "Petrochemical industry: naphtha from heavy gas oil; distillation column".

* Relative volatility * Evaporation * Condensation of liquid phase * Relative solubility * Particle size differences

.. answer:: :fullinclude: no

* Density differences are used during centrifugation. For example a wastewater stream with solids and liquids could be separated into an outlet stream of water and another of solids/cake in a centrifuge.

* Particle size differences are used during size exclusion chromatography. A mixture of proteins and excipients can be separated into a purified protein stream and a mostly excipient stream.

* Solubility differences could be used in a supercritical fluid extractor, using liquid carbon dioxide. The coffee bean feed is separated into a stream containing decaffinated beans, and the supercritical stream contains the dissolved caffeine, which is then recovered and separated further.

* Mobility differences are exploited in gel electrophoresis. A feed of mixed proteins is separated into purer protein outlet streams.

* Charge differences are used in electrostatic precipitation. For example an air-dust feed stream can be cleaned to an air stream and a concentrated dust stream.

* Phase changes are used in many separating units, e.g. freeze-drying (lyophilisation). e.g. foods can be separated into dried food and a water stream.

* Magnetism is used in a magnetic separator to isolate iron-bearing material from the gangue.

.. question:: :grading: 8

Describe what the following separators do (be a bit more adventurous than just using Wikipedia in your research)

* mechanical deboner * flotation column * pressure swing adsorption * evaporator

.. question:: :grading: 10

Dust particles, assumed to have a spherical shape, with diameter of 500\ |micron| are falling in an air stream that is at 405K. The particles have a density of 1530 :math:`\text{kg.m}^{-3}`; what is the terminal settling velocity?

The density of air at this temperature is 0.83 :math:`\text{kg.m}^{-3}` and viscosity of air is approximately :math:`\mu = \displaystyle \frac{C_1 T^{1.5}}{C_2 + T}` where :math:`C_1 = 1.46 \times 10^{-6}~\text{kg.m}^{-1}\text{.s}^{-1}\text{.K}^{-0.5}` and :math:`C_2~=~110.4~\text{K}`.

.. question:: :grading: 10

In this flowsheet for converting sugar cane to raw sugar from King's textbook, *Separation Processes*, identify 5 separation unit operations.

For each unit operation, describe:

(a) the principle being exploited to create the separation (b) the ESA and/or MSA being added.

Also, watch the `video on the sugar process again <http://www.youtube.com/watch?v=ZBOou6cahtw>`_ [1] to visualize the size of these units.

.. image:: ../figures/examples/sugar-flowsheet/King-Separation-Processes-Sugar-flowsheet.png :align: center :scale: 90%