Dephlegmator - Rectifier Design

Contents

Introduction

In a number of industries, chemical, petroleum, food and other industries, mixtures of liquids are obtained as a result of various technological processes, which must be divided into components

To separate mixtures of liquids and liquefied gas mixtures, the industry uses methods of simple distillation (distillation), vacuum and steam distillation, molecular distillation and rectification. Rectification is widely used in industry to completely separate mixtures of volatile liquids partially or wholly soluble in one another

The essence of the rectification process is the separation from the mixture of two or more liquids with different boiling points of one or more liquids in a more or less pure form. This is achieved by heating and evaporating such a mixture followed by multiple heat and mass exchange between the liquid and steam phases; as a result, part of the volatile component goes from the liquid phase to the vapor phase, and part of the less volatile component from the vapor phase to the liquid phase

Rectification process is carried out in rectification plant including rectification column, refluxer, cooler-condenser, initial mixture heater, distillate and bottom residue collectors. The reflux, condenser and heater are conventional heat exchangers. The main apparatus of the plant is a distillation column, in which vapors of distilled liquid rise from below, and liquid flows towards the vapors from above, supplied to the upper part of the apparatus in the form of reflux. In most cases, the final products are distillate (refluxed volatile component vapors exiting the top of the column) and bottoms (less volatile liquid component exiting the bottom of the column).

The rectification process can take place at atmospheric pressure, as well as at pressures above and below atmospheric pressure. Under vacuum, rectification is carried out when high-boiling liquid mixtures are to be separated. Elevated pressures are used to separate mixtures in a gaseous state at a lower pressure. The degree of separation of the liquid mixture into constituent components and the purity of the resulting distillate and bottoms depends on how developed the phase contact surface is, and therefore on the amount of reflux liquid (reflux) and rectification column arrangement.

In industry, cap, sieve, packing, film tubular columns and centrifugal film rectifiers are used. They differ mainly in the design of the internal device of the apparatus, the purpose of which is to ensure the interaction of liquid and steam. This interaction occurs by bubbling steam through a layer of liquid on trays (cap or sieve) or by surface contact of steam and liquid on a nozzle or surface of liquid flowing by a thin film

1 Analytical Overview

Distillation columns differ mainly in the design of an internal device for distributing liquid and steam phases. The interaction of liquid and steam is carried out in the columns by bubbling steam through the liquid layer on the trays or by surface contact of steam and liquid on the nozzle or on the surface of the liquid flowing with a thin film

Bubble columns of the poppet type are usually made in the form of round columns, along the height of which one or another tray structure is located, each of which has one contact stage. On each tray, depending on its design, direct flow, countercurrent flow, cross-current phases can be carried out with different degrees of liquid mixing from complete mixing to complete displacement. Poppet columns are used at temperatures from minus 40 ℃ to 200 ℃, atmospheric overpressure up to 2.5 MPa, as well as under vacuum at residual pressure not lower than 665 Pa

The trays can be divided into four groups:

Trays with cross contact of phases in which the movement of liquid and steam (gas) is carried out by cross current. These trays have special overflow devices for the flow of liquid from one tray to another, while steam does not pass through overflow devices. This group includes cap, sieve, valve and other trays

Dishes of failed type in which overflow devices are absent, so that steam (gas) and liquid pass through the same holes. On these trays, phase contact is carried out according to the scheme of complete mixing of the liquid. This group includes lattice (slot) failed trays, hole failed trays and tubular ones composed of pipes so that slots remain between them, through which steam (gas) and liquid move. The latter are used for non-thermal absorption, while cold water is passed through the pipes to remove the generated heat

Trays with unidirectional movement of steam (gas) and liquid, so-called ramjet. Steam (gas) leaves the holes in the direction of liquid movement on the tray. These trays usually have overflow devices. This group includes S-shaped valve, sieve and jet with baffle elements and other trays

The choice for lattice (failed) trays was made for the following reasons:

Simplicity of construction;

Low metal consumption;

High liquid throughput;

With sufficient width, the slits can be used to treat contaminated liquids leaving a precipitate on the tray;

In terms of efficiency, lattice (failure) trays are usually not inferior to overflow trays

Disadvantages include the narrow diapozone of stable operation and the difficulty of ensuring an even distribution of irrigation on the surface of the trays at the beginning of the process

2 Objectives and objectives of the course project

The purpose of the course project is to develop a continuous rectification plant for the separation of ethanol-water mixture under atmospheric pressure, as well as a detailed calculation and drawing of the reflux generator

Objectives of the course project: to achieve maximum productivity of the plant at optimal sizes and power consumption, as well as to achieve a high degree of separation of the mixture into components

Conclusion

In this course project, a distillation column was calculated to separate the ethyl alcohol-water mixture under atmospheric pressure. As a distillation column, an apparatus with lattice trays with a height of H = 4.2 m with a diameter at the top of the column Dc = 1.2 m and a diameter Dn = 1.4 m at the bottom is used. Total number of trays to be separated -

One-way shell-and-tube heat exchanger can be selected as reflux meter. The total heat exchange surface taking into account the reserve is 52 m2; length of heat exchange pipe is 6 m; diameter of heat exchange pipes 25 x 2 mm and diameter of casing pipe 400 mm

Introduction 3

1 Analytical Overview 5

2 Objectives and objectives of the course project 7

3 Process Diagram 8

4 Engineering calculations 10

4.1 Process Calculation 10

4.1.1 Material Balance 10

4.1.2 Determination of phlegm number. Working Line Equations 12

4.1.3 Determination of average physical values of vapor and liquid flows 14

4.1.4 Heat Balance 24

4.2 Selection of heating steam pressure 26

4.3 Hydraulic calculation 27

4.3.1 Calculation of operating speed and diameter of column 27

4.3.2 Calculation of hydraulic resistance of tray and splash 28

4.3.3 Column Height Calculation 32

4.4 Approximate calculation of heat exchangers 36

4.4.1 Calculation of bottoms cooler 36

4.4.2 Calculation of the feed heater 41

4.4.3 Calculation of evaporator cube 44

4.4.4 Calculation of distillate cooler 46

4.5 Deflegmator calculation 49

4.5.1 Indicative calculation 49

4.5.2 Detailed Calculation of Heat Transfer Process 52

Output 58

List of sources used 59

Appendix A 60