CONSTRUCTION OF PACKED DISTILLATION COLUMN
This is an abstract on the construction of a packed distillation column. A packed distillation column is used in the separating process distillation that is the separation of two miscible liquids.
It was constructed by marking out the dimension of the column, condenser, pot, using steel rule scriber, oxyacetylene flame was used for cutting after which the work piece were center punched and drilled using the drilling machine. At last they were folded, shaped, welded tested, finished and painted.
This construction was done with the following specifications, 650, 220, 188 for height, external and internal diameter of column respectively.
For condenser, 650, 120, 114 for height, external and internal diameter respectively. For boiler pot, 450, 240, 236 for height, external and internal diameter respectively all in mm dimension.
It was generally required that stainless steel be used totally for the construction as the standardized Material but due to tits cost, galvanized metal was used. Using the constructed packed distillation column, a fermented palm wine can be distilled to collect gin as the distillate. In comparing the standardized distillation column with the Oni constructed it was rated 80% due to cost of materials (galvanized of construction used. But the standard material of construction that was supposed to be used is stainless steel.
At the end of the construction the cost was (N9, 000). Nine thousand Naira from the direct labour condenser etc. the cost is as a result of economy situation in Nigeria.
The aim of this project is to construct a packed distillation column. The separation of liquid mixtures into their several components is one of the major operations in the chemical and petroleum industries, and distillation, the most widely used method of achieving this end, is the key operation of the oil refinery. Throughout the chemical industry the demand for puner products, coupled with a relentless pursuit of greater efficiency, has necessitated continued research into the techniques of distillation. The operation is restricted to situations when components distribute themselves between liquid and vapour phases. The vapour phase is generated by the addition of heat and separation is enhanced by the differences in the vapour pressure of the components, hence their boiling points.
Packed columns are generally used for distillation, gas-absorption and liquid-liquid extraction. They ensure continuous contact of liquid and gas in both counter-current and concurrent flows and are essentially, vertical columns which have been filled with packings or devices of larger surface. The liquid is distributed over and trickles down through the packed-bed, exposing a large surface to contact the gas, while the gas or vapor moves upwards counter-currently. In some gas-absorption columns, concurrent flow is used.
The packings for the tower should offer the following characteristics: –
1. Provide for larger interfacial surface between liquid and gas.
2. Posses desirable fluid characteristics.
3. Be chemically inert to fluids being processed.
4. Have structural strength to permit easy handling and installation.
5. Represent low cost
6. Should be light in weight.
There are two major types of packings arrangements:
a. Random and
b. Regular packings.
The performance of a packed column is dependent on the maintenance of a good liquid and gas distribution throughout the packed-bed and this is an important consideration in packed column design.
A packed distillation column is similar to a plate column with the plates replaced. Be packed sections but in process industries they are considered more economically than plate columns for the following reasons: –
a. For columns less than 0.6m (2.0 ft) diameter, packings are usually cheaper than plates unless alloy-metal packings are required.
b. Acids and many other corrosive materials can be handled in packed columns because construction can be of ceramic, carbon, or other resistant materials.
c. Packings often exhibit desirable efficiency drop characteristics for critical vacuum distillations.
d. Liquids ending to form may be handled more readily in packed columns because of the relatively low degree of liquid agitation by the gas.
e. Holdup of liquid can be quite low in packed columns, an advantage when the liquid is thermally sensitive.
Conditions unfavourable to packed columns are:
a. If solids are present in the liquid or gas plate columns can be designed to permit easier cleaning.
b. Some packing materials are subject to easy breakage during insertion into the column or resulting from thermal expansion and contraction.
c. High liquid rates can often be handled more economically in plate columns than packed columns.
d. Cooling coils can be incorporated more readily into plate devices.
e. Low liquid rates lead in complete welting of column packings, thus decreasing contacting efficiency.
f. Packed columns exhibit narrower operating ranges than cross-flow plate columns.
However, the packed tower is a cylindrically vertical column operating with top and bottom flow allowances. Provisions are made for packing support, packing restrainers, packing entrainment eliminators liquid distributor etc. the cost and choice of materials of construction are also important considerations in this project as they go along way to influence the safety and efficiency of the equipment and also dictate its service-life for distillation in packed towers,
It is normally a practice to increase the calculated height of packing by 40 per cent to allow for liquid maldistribution and wetting problems.
1.1 HISTORICAL DEVELOPMENT
Distillation seems to have been mentioned firstly by a man called Aristotle (384 – 322BC), he coined it when he described seawater being evaporated to make drinking water. The Romans and Alexandrians (from Alexandria, Egypt) distilled pure wood resin to condense the oil of turpentine (tarps), which boiled off. These processes make use of air – coded condensing arms (outlet from the boiling vessel), which also allowed the most volatile component to escape. It was probably the Arabians who first used a water-cooked arm, and using this method discovered various oils (natural plant oils, used mostly as flavouring or perfume) by distilling plant juice. Later the chemists, using a distillation apparatus known as an Alembic, were able to prepare a relatively pure nitric acid and other mineral acids.
The preparation of alcoholic beverages by distillation has taken place since antiquity. Distillation has taken place since antiquity. Distilled alcohol, probably discovered in Italy in the early twelfth century, was at first used as a medicine.
Distillation is a method used in separation of mixture and the separation of mixture is one of the major processes of the chemical industries and distillation is the most widely used method of achieving this end.
Thus the basic requirement for a separation of components by distillation is that the composition of the vapour be different from the composition of the liquid with which it is in equilibrium. If the vapour composition is the same as the liquid composition distillation processes will not effect a separation. But in a case where the vapour composition is greater than the liquid, composition, and distillation process will effect a good separation and a difficult one is affected if the vapour composition is less than that of the liquid.
In practice, distillation may be carried out either by two principal methods. The first method is based on the production of a vapour by boiling the liquid mixtures to be separated and condensing the vapour without allowing any liquid to return to the still. There is then no reflux. The second method is based on the return of part of the condensate to the still, under such conditions that this liquid returning is brought into intimate contact with the vapour on their way to the condenser. It is known as rectification with reflux.
Distillation is defined as the process involved in the conversion of a substance into a vapour that is subsequently condensed to liquid form. The operation may be employed to separate liquidours from terminated materials or of pure water from the salt in seawater on in the separation of two or more liquids having different boiling points as in the separation of gasoline, fuel oil and lubricating oil form petroleum.
Packed column for gas-liquid contacting are used extensively for absorption operations and, to a limited extent, for distillations. Usually the columns are filled with randomly oriented packing material but in some cases the packing may be carefully positioned. The packed column is characteristically operated with counter flow of the phase.
A typical column consists of a cylindrical shell containing a support plate for the packing material and a liquid distributing device designed to provide effective irrigation of the packing devices may be added to the packed bed to provide redistribution of liquid that might channel down the wall. Several beds may be used in the same column shell.
Many packings are commercially available, each possessing specific advantages for liquid gas contacting from the aspects of cost, surface availability, interface regeneration, pressure drop, weight, and corrosion resistance. The packed bed is usually formed by dumping packing elements into the column (“dumped packing”) and allowing them to form a random arrangement. For most application, the less expensive dumped packings are used, and typical packing elements. For distillation in packed towers, it is normally practicable to increase the calculated height of packings by 40 percent.
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