Construction Of Packed Distillation Column

INTRODUCTION
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.