Calculation of Packing Fractionation Column

Contents

Task

Introduction

1. Status of the question

1.1 Rectification of double mixtures

1.2 Rectification of multicomponent mixtures

1.3 Cap Columns

1.4 Sieve Columns

1.5 Packing columns

1.6 Bubble columns

1.7 Operation of rectifiers

2. Description of operating principle of process diagram

3.Technological calculation

3.1 Initial data

3.2 List of permitted simplifications

3.3 Material Balance

3.4 Construction of phase diagram

3.5 Determination of working reflux number

4. To Define the Geometric Dimensions of a Column

4.1 Determination of column diameter

4.2 Determination of nozzle height

4.3 Column Height Determination

5. Hydraulic calculation

6. Thermal calculation

7. Calculation of shell and tube condenser

8. Heat Transfer Surface Calculation of the Dephlegmator

9. Pump Calculation and Piping Matching

Conclusion

Literature

Introduction

Rectification is one method of separating liquid mixtures based on the different distribution of the components of the mixture between the liquid and steam phases. Rectification columns consisting of the column itself, where there is countercurrent contact of steam and liquid, and devices in which liquid evaporation and condensation of steam - cube and reflux are carried out, are used as apparatus of employees for rectification. The column is a vertically standing hollow cylinder inside which so-called trays (contact devices of various designs) are installed or a shaped piece material is placed - a nozzle. The cube and dephlegmator are shell and tube heat exchangers (tubular furnaces and evaporator cubes are also used).

The purpose of the trays and the nozzle is to separate the interfacial surface and improve contact between liquid and steam. The trays are typically provided with a liquid overflow device. Rings whose diameter is equal to their height are commonly used as the packing of distillation columns.

In both packing and poppet columns, the kinetic energy of steam is used to overcome the hydraulic resistance of contact devices and to create a dynamic dispersion of steam-liquid with a large interfacial surface. There are also rectification columns with the supply of mechanical energy, in which a disperse system is created when the rotor installed along the axis of the column rotates. Rotary machines have a smaller pressure drop in height, which is especially important for vacuum columns.

According to the method, continuous and periodic rectification is distinguished. In the first case, the separated mixture is continuously fed to the distillation column, and two or more fractions enriched with one component and depleted with another are continuously withdrawn from the column. The complete column consists of two sections: reinforcing and exhaustive. The feed mixture (usually at boiling point) is fed to a column where it is mixed with the so-called recovered liquid flowing through the contact devices (trays or packing) of the exhaustive section countercurrent to the rising steam stream. Reaching the bottom of the column, the liquid is enriched with heavy volatile components. At the bottom, the liquid is partially evaporated as a result of heating by the supplied coolant,

and steam re-enters the exhaustive section.

After passing it, enriched with volatile components, steam enters the reflux condenser, where it is usually completely condensed with a suitable refrigerant. The resulting liquid is divided into two streams - distillate and reflux. Distillate is a product stream, and reflux is supplied to the irrigation of the strengthening section, through the contact devices of which it flows. Part of the liquid is withdrawn from the bottom of the column as a so-called bottom residue (also a product stream).

If the initial mixture is to be divided in a continuous manner into a number of fractions greater than two, then a sequential or parallel - sequential column connection is used.

During periodic rectification, the initial mixture is simultaneously loaded into the column cube, the capacity of which corresponds to the desired productivity. The vapors enter the column and rise to the reflux condenser, where they condense. In the initial period, all condensate is returned to the column, which corresponds to the complete reflux mode. The condensate is then divided into distillate and reflux. As the distillate is withdrawn (either at constant reflux or with its change, first volatile components are removed from the column, then medium volatile, and so on). The desired fraction (or fractions) is collected in a suitable collector. The operation continues until the initially charged mixture is fully processed.

The main areas of industrial application of rectification are the production of individual fractions and individual hydrocarbons from oil raw materials in the oil refining and petrochemical industries, in the chemical industry. Rectification is widely used in other sectors of the national economy: coke-chemical, forest-chemical, food, chemical-pharmaceutical industries.

1.3 Cap Columns

These columns are most common in distillation plants. This is a column of small diameter, consisting of trays, on each of which there is one cap of round section and a nozzle for steam passage. Edges of cap are immersed in liquid. This creates a hydraulic seal on the tray and the steam exiting the cap must pass through the liquid layer on the tray. Caps have holes or toothed slots for breaking steam into small bubbles, i.e. to increase surface of its contact with liquid.

The flow and discharge of liquid, as well as the height of the liquid on the tray, is controlled by overflow tubes, which are located at diametrically opposite ends of the tray; therefore, liquid flows on adjacent trays in mutually opposite directions.

1.4.Sieve Columns

Columns of this type consist of a vertical cylindrical body with horizontal trays, in which a significant number of small holes are drilled, evenly distributed over the entire surface of the tray. Overflow tubes are used to drain the liquid and adjust its level on the tray. Lower ends of tubes are immersed in cups on plates lying below and form hydraulic gates. Steam passes through the holes of the tray and is distributed in the liquid in the form of small jets; only a certain distance from the bottom of the tray forms a layer of foam and splash - the main area of ​ ​ mass exchange and heat exchange on the tray.

1.5 Packing columns

In such columns, an annular nozzle is usually used. The most common rings are 25 × 25 × 3 mm. In the reinforcing column, the amount of liquid is less than the amount of rising vapors per the amount of distillate withdrawn, in the exhaustive column the amount of liquid is more than in the reinforcing column by the amount of mixture introduced.

An uneven distribution of the liquid across the column may result in an insufficiently clear separation of the components, especially when the diameter of the column is large. The low hydraulic resistance of the packing columns is significant only when rectified in vacuum.

Packed distillation columns are used mainly of small diameter (up to about 1 m), as well as in vacuum distillation and for the separation of chemically aggressive substances.

1.6 Bubble columns

They are used with cap, screened and failed plates. The significant resistance of bubble columns during distillation is usually not significant (except for the distillation process in vacuo), since it causes only a slight increase in pressure and, therefore, the boiling point at the bottom of the column and is not associated with additional energy consumption.

Bubble columns are the most common rectifiers due to the ability to separate components in them with any degree of clarity. Most often, columns with cap trays are used. Columns with screened and failed trays are used when separating non-contaminated liquids in installations operating with constant load.

1.7 Operation of rectifiers

In the operating distillation column, the number of trays or the height of the nozzle is constant. The main conditions for achieving the required degree of separation of components during rectification are: supply of the corresponding amount of heat to the column cube and its supply for irrigation of the required amount of reflux. Both conditions are inextricably linked. By changing the supply of heat in the cube and the supply of reflux, it is possible to regulate the operation of the column.

Typically, the degree of separation of the components is controlled by the temperatures at the bottom and top of the column. The temperature at the bottom of the column should correspond to the boiling point of the residue, the temperature at the top of the column should correspond to the boiling point of the distillate. In addition, other control methods are used.

If, for example, the HC content in the distillate is high (the temperature at the top of the column is above normal), it is necessary to increase the reflux supply to the column. At the same time, however, the previous amount of heat supplied in the cube will not be enough and the excess reflux will not evaporate in the cube, but will go to the residue, in which, thus, the content of NC will increase. Therefore, simultaneously with the increase in the reflux supply, it is necessary to increase the heat supply so that the temperature at the bottom of the column does not become below normal.

The reflux supply is controlled by changing the distillate extraction: at partial condensation by adjusting the amount of water supplied to the reflux condenser, at complete condensation with the help of a valve on the distillate extraction line.

Regulation of the rectification process is also carried out by changing the amount and composition of the supplied mixture.

When the amount of mixture changes, the capacity of the plant changes and the heat supply in the cube and the reflux supply must be adjusted accordingly. The change in the composition of the mixture has a significant effect. If, for example, the NC content of the mixture is reduced, then its content in the distillate will also decrease; therefore, the temperature at the top of the column will rise. To maintain the required composition of distillate, it is necessary to reduce its selection.

The withdrawal of the residue is usually controlled so that the level of liquid in the cube is constant. If, due to an increase in the supply of the mixture or an increase in the BK content in it, the level of liquid in the cube increases, then the residue extraction should be increased.

Conclusion

In this course project, as a result of engineering calculations, a rectification plant was calculated for separating a binary mixture of water-ethylene glycol with a nozzle, diameter D = 0.5 m, height H = 29.6 m, in which a nozzle of ceramic Rashig rings measuring 50x50x3 mm is used, the distance between which h = 0.5 m. The column is operating normally.

A heat exchanger was also approximately selected: for heating the initial mixture, a reflux meter was calculated. A corpse pipe was also calculated to supply the initial mixture, pumps were selected.