Describe the construction, operation and application of distillation equipment used in industry

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Outcome 2: Describe the construction, operation and application of distillation equipment used in industry

1.        describe the construction, operation and applications of common types of plate

column to include:-

a        bubble cap

Bubble cap trays have a riser, or chimney, fitted over each hole with a cap covering the riser.  There is a small gap between the riser and the cap to allow vapour travel through the trays.  The cap then diverts the vapour back onto the top of the tray so that it interacts with the liquid.

b        sieve trays

Sieve trays are constructed from sheets of a highly resistant material, then having holes drilled through it.  This allows the passage of vapour and liquid through it.  They are the most widely used system as they are simple, versatile, have a good capacity and are cost effective.

c        valve trays

Valve trays are sheets of resistive metal, containing lots of small sections that are raised and leaving a gap for vapour and liquid transfer and migration.

d        shower trays.

Shower trays do not have downcomers.  The level of liquid that they retain is determined by the pressure of rising vapours.

2.        explain the function of these main components of plate columns

a        plates/trays

Plates and trays are used in a distillation column to collect and remove any formed product.  As the product cools and condenses, it is collected on the trays and removed from the side of the vessel.  Different products condense at different temperatures, so maintaining a temperature gradient across the column is essential.

b        weirs

Weirs are in place to maintain a small level of liquid on each tray.  This is useful because as vapours and gases rise, some of them will condense when they pass through the liquid level on a tray at a certain temperature.  Overall, it makes the distillation process a little bit more efficient as product can be collected more readily.

c        downcomers.

A downcomer consists of an active area where mass-transfer takes place.  A downcomer is in place to move the liquid from tray-to-tray with an open area where vapour-liquid disengagement takes place and the vapour moves from tray-to-tray.  The purpose is to provide extra front’s where condensation can occur.

3.        explain the relative advantages and disadvantages of the plates listed in I above in terms of the following :-

a        weight

Bubble Cap:  The main disadvantage of the weight of bubble caps is that they can become detached if too much debris collects on and around them.  On the other hand, this is also an advantage because they are then automatically cleaning themselves before too much damage can be done such as lowering distillation rates.  The weight also limits the number that can be installed, and as such limits the efficiency.

Sieve Trays:  Lighter than bubble caps, but still heavy compared to shower trays.  No valves or caps to add weight.

Valve Trays:  The heaviest of all the tray types, weight to efficiency is very low.  The valves situated on the top of the tray add to the weight.

Shower Trays:  Lightest of all tray types, no valves or caps to increase weight and large holes which also lower the weight.

b        cost

Bubble Cap:  Bubble cap trays have very few advantages.  A major disadvantage when cost is involved is that they are expensive to purchase due to the materials and price of manufacture compared to the efficiency which is lower than a lot of other options.

Sieve Trays:  Again, high cost for the efficiency that is given.

Valve Trays:  Cheaper alternative to bubble caps and sieve trays, with a greater efficiency than the bubble caps.

Shower Trays:  Very cheap to purchase but do not last very long so overall the cost is quite high.  Very low efficiency for the cost.

c        installation

Bubble Cap:  There are two big advantages of bubble cap trays when installation or removal is required.  It can be done by just one person which would cut down on labour costs, and only requires a hammer or mallet to secure/unsecure them from the vessel.

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Sieve Trays:  Harder to install than bubble caps, needs two people to install.

Valve Trays:  Basically the same as a sieve tray, however installation time can be very lengthy if the valves do not come pre-fitted.

Shower Trays:  Easy installation, however time and cost come into consideration as they require replacing quite regularly.

d        liquid/vapour handling capacity

Bubble Cap:  Have an average handling capacity due to quite large surface area of each plate.  The problem that it does have is that it can only have small quantities of liquid surrounding each bubble or the liquid will ...

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