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Introduction
Rectification(from Latin rectus - correct and facio - I do) - separation of homogeneous liquid mixtures into practically pure components, differing in boiling points, through repeated evaporation of liquid and condensation of vapor. This is the main difference between rectification and distillation, in which, as a result of a single cycle of partial evaporation-condensation, only preliminary separation of liquid mixtures is achieved. Flows of steam and liquid during the rectification process, moving in countercurrent, repeatedly contact each other in special devices - distillation columns. Part of the steam (or liquid) leaving the apparatus is returned back after condensation (for steam) or evaporation (for liquid). This countercurrent movement of the contacting flows is accompanied by processes of heat exchange and mass transfer, which at each stage of contact proceed to a state of equilibrium; at the same time, the ascending steam flows are continuously enriched with more volatile low-boiling component (LC), and the flowing liquid is less volatile - high boiling point (HC). Using the same amount of heat as during distillation, rectification allows one to achieve greater extraction and enrichment of the desired component or group of components. Rectification is distinguished between continuous and periodic. In the case of continuous rectification, the mixture to be separated is continuously fed into the distillation column and two or more fractions, enriched with some components and combined with others, are continuously removed from the column. The complete column consists of 2 sections - strengthening and exhaustive. The initial mixture (usually at boiling point) is fed into the column, where it is mixed with the extracted liquid and flows down the contact devices (plates or nozzle) of the exhaust section in countercurrent to the rising steam flow. Having reached the bottom of the column, the liquid stream, enriched with highly volatile components, is fed into the column cube. Here the liquid is partially evaporated by heating with a suitable coolant, and the steam again enters the exhaust section. The steam coming out of this section enters the strengthening section. Having passed through it, the steam, enriched with volatile components, enters the reflux condenser, where it is usually completely condensed with a suitable refrigerant. The resulting liquid is divided into 2 streams: distillate and reflux. Distillate is a product flow, and reflux goes to irrigate the strengthening section, through the contact devices of which it flows. Part of the liquid is removed from the bottom of the column in the form of a bottom residue. The ratio of the amount of reflux to the amount of distillate is denoted by R and is called reflux ratio. This number is important characteristic rectification process: the higher R, the higher the operating costs of the process. The minimum required heat and cold costs associated with performing any specific separation task can be found using the concept minimum reflux ratio. The minimum reflux ratio is found by calculation based on the assumption that the number of contact devices, or the total height of the nozzle, tends to infinity. If the initial mixture needs to be divided continuously into a number of fractions greater than two, then a serial or parallel-series connection of columns is used. At periodic rectification the initial liquid mixture is simultaneously loaded into the column cube, the capacity of which corresponds to the desired productivity. Vapors from the cube enter the column and rise to the reflux condenser, where they are condensed. IN initial period all condensate is returned to the column, which corresponds to the full irrigation mode. The condensate is then divided into reflux and distillate. As the distillate is selected (either at a constant reflux ratio or with its change), first the highly volatile components are removed from the column, then the moderately volatile ones, etc. The required fraction (or fractions) is selected into the appropriate collection. The operation continues until the initially loaded mixture is completely processed. Apparatuses used for rectification - rectification columns - consist of the column itself, where countercurrent contact of steam and liquid occurs, and devices in which evaporation of liquid and condensation of steam occurs - a cube and a reflux condenser. The column is a vertically standing hollow cylinder, inside of which plates (contact devices of various designs) are installed or a shaped piece of material - a nozzle - is placed. The cube and reflux condenser are usually shell-and-tube heat exchangers (tube furnaces and rotary evaporators are also used). The purpose of the trays and nozzle is to develop the interfacial surface and improve the contact between liquid and vapor. The plates are usually equipped with a device for overflowing liquid. As a packing for distillation columns, rings are usually used, the outer diameter of which is equal to their height. The most common are Raschig rings and their various modifications. In both packed and disc columns, the kinetic energy of steam is used to overcome the hydraulic resistance of contact devices and to create a dynamic disperse system of steam - liquid with a large interfacial surface. There are also distillation columns with mechanical energy supply, in which a dispersed system is created by rotating a rotor mounted along the axis of the column. Rotary devices have a lower pressure drop over height, which is especially important for vacuum columns. Calculation distillation column comes down to determining the main geometric dimensions of the column - diameter and height. Both parameters are largely determined by the hydrodynamic operating mode of the column, which, in turn, depends on the speeds and physical properties of the phases, as well as on the type of packing. Rectification is widely used both on an industrial, preparative and laboratory scale, often in combination with other separation processes such as adsorption. Extraction and crystallization. Rectification is also applicable for the production of individual fractions and individual hydrocarbons from petroleum feedstocks in the oil refining and petrochemical industries. Rectification is widely used in many industries: coke-chemical, wood-chemical, food, chemical-pharmaceutical industries, etc. Recently, rectification has become increasingly practical in connection with the solution of such important problems as the purification of substances and the isolation of valuable components from waste or natural mixtures. This includes the isolation of stable isotopes of a number of light elements. Rectification as a cleaning method has a number of undeniable advantages, among which the most significant is that the process does not require the introduction of agents that themselves can be sources of pollution.
Typically, a distillation column is made in the form of a cylinder filled with special distribution devices to create a contact surface between the liquid phase flowing down from above and the vapors rising towards it. The design of distillation columns is usually guided by the requirements for the design of any chemical apparatus (cheapness, ease of maintenance, high productivity, strength, corrosion resistance, durability, etc.) In addition, the following specific requirements for the design of the column must be taken into account:
The column must have maximum throughput capacity for the vapor and liquid phases;
Contact devices must provide maximum contact surface between phases with maximum mass transfer efficiency;
The column must operate stably and uniformly over its entire cross-section under a wide range of loads;
The hydraulic resistance of switchgears should be minimal. The desire to maximally satisfy these requirements, as well as the specific properties of the mixtures to be separated (heat generation, aggressiveness, coking, formation of thermopolymers, etc.), leads to a variety of types of distillation columns.
Features of the devices cross current and complete mixing is that the interaction of phases in these devices is carried out by bubbling the vapor phase through the liquid phase. Therefore, these groups are usually combined under the general name bubble columns; since steam bubbling through a layer of liquid occurs on plates-plates equipped with special devices for introducing steam and flowing liquid, these two groups of distillation columns are also called disc-shaped. Complete mixing columns differ from cross-flow columns mainly in the absence of overflow devices for liquid. The liquid drains onto the underlying plates through the same holes through which the steam rises. As a result of this, complete mixing plates are called failed. IN counter-flow and direct-flow columns steam flow interacts with liquid flowing in the form of a thin film over the surface of a special nozzle. Therefore, these two groups of distillation columns are usually combined under the general name film or packed. The most widespread are bubble columns. The working space of these columns is divided into sections formed by plates.
When quantitatively calculating the operation of distillation columns, the concept is used theoretical plate(a hypothetical contact device in which thermodynamic equilibrium is established between the flows of vapor and liquid leaving it, that is, the concentrations of the components of these flows are related to each other by a distribution coefficient). Any real distillation column can be associated with a column with a certain number of theoretical plates, the input and output flows of which, both in size and in concentration, coincide with the flows of the real column. Based on this, determine efficiency columns as the ratio of the number of theoretical plates corresponding to this column to the number of actually installed plates. For packed columns, the HETP value (height equivalent to a theoretical plate) can be determined as the ratio of the height of the packed layer to the number of theoretical plates to which it is equivalent in its separating action.
A) cap columns(Fig. a) are most often used in distillation units. Vapors from the previous plate enter the steam pipes of the caps and bubble through a layer of liquid in which the caps are partially immersed. When bubbling steam through a liquid, three bubbling modes are distinguished:
bubble mode (steam bubbles in the form of individual bubbles forming a chain near the wall of the cap);
jet mode (individual steam bubbles merge into a continuous stream);
torch mode (individual vapor bubbles merge into a common flow that looks like a torch).
The caps have holes or serrated slots that divide the vapor into small streams to increase the surface of its contact with the liquid. Overflow tubes serve to supply and drain liquid and regulate the liquid level on the plate. The main area of mass transfer and heat exchange between vapor and liquid, as studies have shown, is the layer of foam and splashes above the plate, created as a result of steam bubbling. The height of this layer depends on the size of the caps, the depth of their immersion, the speed of steam, the thickness of the liquid layer on the plate, the physical properties of the liquid, etc.
It should be noted that, in addition to cap plates, valve, grooved, S-shaped, flake, failure and other plate designs are also used. The advantage of cap-shaped trays is satisfactory operation in a wide range of liquid and steam loads, as well as low operating cost.
b) sieve plates(Fig. b) are used mainly for the rectification of alcohol and liquid air. The permissible liquid and steam loads for them are relatively small, and regulating their operating mode is difficult. Liquid and steam pass alternately through each hole depending on the ratio of their pressures. The plates have low resistance, high efficiency, operate under significant loads and are simple in design. Mass and heat exchange between steam and liquid mainly occurs at some distance from the bottom of the plate in a layer of foam and spray. The pressure and speed of steam passing through the mesh holes must be sufficient to overcome the pressure of the liquid layer on the plate and create resistance to its swelling through the holes. Sieve plates are necessary install strictly horizontally to ensure the passage of steam through all the holes of the plate, as well as to prevent liquid from dripping through them. Typically, the diameter of the holes of the sieve plate is taken in the range of 0.8-8.0 mm.
V) valve plates occupy a middle position between cap and sieve. Valve discs have shown high efficiency over significant load intervals due to the possibility of self-regulation. Depending on the load, the valve moves vertically, changing the open cross-sectional area for the passage of steam, with the maximum cross-section determined by the height of the device that limits the rise. The live cross-sectional area of the steam holes is 10-15% of the cross-sectional area of the column. The steam speed reaches 1.2 m/s. The valves are manufactured in the form of round or rectangular plates with top or lower lift limiter. Trays assembled from S-shaped elements ensure the movement of vapor and liquid in one direction, helping to equalize the concentration of liquid on the plate. The live cross-sectional area of the plate is 12-20% of the cross-sectional area of the column. Box-shaped cross section element creates significant rigidity, allowing it to be installed on a support ring without intermediate supports in columns with a diameter of up to 4.5 m.
G) cascading Venturi plates assembled from separate sheets, bent so that the direction of steam flow is horizontal. The channels for the passage of steam have a Venturi tube cross-section profile, which maximizes the use of steam energy and reduces hydraulic resistance. The flows of steam and liquid are directed in one direction, which ensures good mixing and phase contact. Compared to cap trays, the steam speed can be more than doubled. The design is flexible and does not allow liquid to leak and thereby reduce efficiency. The low holding capacity (30-40% compared to a cap plate) is a valuable feature when processing heat-sensitive liquids. The distance between the plates is selected within the range of 450-900 mm. Cascade trays are successfully used in installations where it is necessary to provide high velocities of steam and liquid.
d) grid plates made from stamped sheets with rectangular slots or assembled from strips. The need for a supporting structure is determined by the thickness of the metal and the diameter of the column. The distance between the plates is usually 300-450 mm. Better performance, compared to cap plates, at maximum loads.
e) wavy plates are made by stamping from perforated sheets 2.5-3 mm thick in the form of sine waves. The rigidity of the structure allows the use of thin metal. The direction of waves on adjacent plates is perpendicular. The depth of the waves is selected depending on the liquid being processed. Due to the greater turbulence of the liquid, the efficiency of the wavy plate is higher. And the risk of clogging is less than for a flat plate. Wave sizes increase with increasing design fluid load. The ratio of the wave height to its length is selected in the range from 0.2-0.4. The plates in the column are located at a distance of 400-600 mm from each other.
and) packed columns have become widespread in industry (see Fig. c). They are cylindrical devices filled with inert materials in the form of pieces of a certain size or packed bodies in the shape of, for example, rings, balls to increase the phase contact surface and intensify the mixing of the liquid and vapor phases.
A cap distillation column is an industrial device that is used primarily in the production of raw alcohol in large distilleries and vodka factories. Not everyone can use it under amateur conditions, much less do it with their own hands.
Factory cap column
This is not because its structure is too complex, but its manufacture requires special tools or high skill. Any qualified mechanic, or a person who knows how to work with basic hand-held power tools, can handle the construction of a cap column in a home workshop. All components of the cap column can be easily purchased in a store or online. It is not difficult to assemble them with your own hands using equipment that is available in any garage. With certain skills, many parts of the column can be made independently.
If you decide to build a moonshine still equipped with a cap column with your own hands, then you should remember that the dimensions of the device play a very important role here. If you violate the proportions, then instead of a cap-type distillation column you will get an ordinary distiller, which works even worse than a classically designed apparatus.
The bell-cap column operates on the principle of heat and mass transfer between steam rising from below, from the evaporator, and cooled reflux flowing down from above. Caps or plates serve to increase the contact area of heated steam and liquid. The number of points where steam turns into liquid and where the liquid re-evaporates depends on the number of plates. Alcohol-containing vapor condenses not only on the inner walls of the column, but also on the surface of the plates. They have the shape of a hemisphere, convexly facing upward.
Condensing on outer surface phlegm flows down through the overflow holes and falls onto the lower plate, heated to a higher temperature. Alcohol and other low-boiling fractions evaporate again, and liquids with higher high temperature boils (fusel oils and water) flow back into the evaporator, where they remain in the form of an aqueous solution.
When alcohol vapor passes through a column 50 centimeters high and 8-10 caps are installed inside it, the process of converting the liquid into steam and back occurs at least 30-40 times. This amount is called the cleaning factor. If you read in the characteristics of cap columns industrial production, which can be easily purchased on the Internet, that their purification ratio is 20 or 50, this does not mean that the alcohol becomes so many times purer, but characterizes only the features of the technological process.
Naturally, the higher the frequency, the better the quality of the alcohol, and the fewer impurities it contains. The ratio of the diameter and height of the column must be at least 1 to 8, this optimal sizes, both for industrial installations and for amateurs. Rising up the column, the steam is enriched with alcohol and impurities are removed from it, it is strengthened, which is why such columns are often called strengthening columns.
If you are going to distill the mash on a bell-shaped column, then you should remember that during the distillation process only the tails of the moonshine are cut off; to remove the heads - methyl alcohol, acetone, ether and aldehydes, you must use fractional distillation and select the estimated number of heads, as in the work in a conventional distiller. If you are distilling raw alcohol, the selection of heads is no longer required; they are removed at the stage of primary distillation.
It is very easy to maintain the temperature regime of distillation on a cap column - the temperature on the upper thermometer (near the outlet pipe from the column) should be 72-75 degrees Celsius. When re-distilling, the temperature can be raised to 78 C, the quality of the resulting raw alcohol will not deteriorate too much.
It’s not difficult to make a bell-shaped column with your own hands if you have one of the most difficult components to make - bell-shaped plates. You can buy them on the corresponding websites on the Internet. In most cases, plates are sold from China. But you don’t have to choose - the product is too specific and only a few workshops produce them. Making work plates yourself is quite difficult, but possible.
To do this, you will need copper or stainless steel plates, from which circles are cut equal to the internal diameter of the main pipe of the column. The column itself is made of glass, copper or stainless steel pipe, with a diameter of 8-10 mm and a length (height) of about 75 cm. Glass columns, offered by many manufacturers, are popular due to the fact that the bubbling process can be observed - this is a rather spectacular sight . But the material has little effect on the performance of the column.
4 holes with a diameter of 1-1.5 mm are made in the cut out disks and copper or stainless steel tubes about 1.5 cm high are inserted into them. They serve to pass steam from the bottom up. Two holes are made along the edges of the disk. Their diameter is about 10 mm. Tubes are also inserted into them, but smaller in height - 1.5-0.8 cm. The joints of the tubes and disks are soldered.
Copper plates for column
Caps are placed on the ends of the middle tubes so that they touch the surface of the disk. Top part The tubes are perforated around the perimeter with holes 1-2 mm in diameter to allow steam to escape. The more there are, the better. The lower edges of the caps are sawed to a height of 0.5 cm. They should be 2 mm below the cut of the side tubes.
It is difficult to make classic hemispherical caps, so you can make them cone-shaped or glass-shaped. They can be secured to the steam pipes with self-tapping screws or couplings. The plate assembly represents one working element. In a column of the specified height there must be at least 5 of them, maximum - 8.
To make it more convenient to insert the plates into the column and remove them for cleaning, they are placed on a pin with a diameter of 5-8 mm and secured with nuts at an equal distance from each other. The upper edge of the column is connected to the refrigerator by a steam line flow type. Thermometers are installed at the top of the column and on the cube. To make it more convenient to install and remove the plate assembly from the body, the top of the column is made in the form of a screw cap. The steam outlet pipe is installed below the thread level by 1-1.5 cm.
Video on how to make a cap column:
Steam from the cube with mash rises up and fills the space above the first plate through the steam pipes. There it condenses and settles as a liquid on its surface. When its level becomes higher than the slots on the caps, steam breaks through the liquid and, due to the bubbling phenomenon, removes the remaining alcohol vapor from it and rises up, entering another plate. There the process is repeated.
When the level of phlegm on the plate rises above the cut of the pouring tube, it flows down into the cube. As the steam rises, it becomes richer in alcohol and, after passing through the last plate, is almost completely freed from impurities.
A cap-shaped distillation column works most effectively when re-distilling moonshine obtained in a conventional moonshine still, but primary mash can also be distilled on it. True, the process will go quite slowly.
Distillation column (fractionation column)- a cylindrical vertical apparatus equipped with internal heat and mass transfer devices and auxiliary units, designed to separate two-component or multicomponent liquid mixtures into fractions, each of which contains substances with a similar boiling point.
Distillation columns are divided into:
by the number of products received:
Simple rectification columns ensure the separation of the initial mixture (raw materials) into two products: rectificate (distillate), removed from the top of the column in a vapor state, and the residue (lower liquid rectification product)
Complex Distillation columns separate raw materials into more than two products. There are complex columns with the selection of additional fractions from the column in the form of side straps and columns in which additional products are selected from special stripping columns (stripping).
by purpose:
1) for atmospheric and vacuum distillation of oil and fuel oil
2) for secondary distillation of gasoline
3) for stabilization of oil, gas condensates, unstable gasolines
4) for fractionation of refinery refineries, oils and natural gases
5) for distilling off solvents in oil purification processes
6) for separation of tube furnace products and catalytic processes for processing petroleum feedstock and gases, etc.
by pressure value:
these are columns in the upper part of which the pressure is slightly higher than atmospheric (0.1...0.2 MPa). The pressure at the bottom of the column, as a rule, depends on its resistance internal devices and can significantly exceed atmospheric. Such columns are used for the distillation of stabilized or stripped oil into fuel fractions and fuel oil.
operate under vacuum (or deep vacuum). In other words, the pressure in them is lower than atmospheric (a vacuum is created), which makes it possible to reduce the operating temperature of the process and avoid decomposition of the product. Such columns are intended for fractionating fuel oil into vacuum (deep vacuum) gas oil or narrow oil fractions and tar.
are used in the stabilization or topping of oil, stabilization of gas gasolines, petroleum distillation gasolines and secondary processes, and fractionation of refinery or associated petroleum gases.
according to the operating principle:
are used in low-capacity installations when it is necessary to select a large number of fractions and have high separation clarity. The feedstock is poured into the cube to a height equal to 2/3 of its diameter. Heating is carried out with silent steam. During the first period of operation of the distillation unit, the most volatile component of the mixture, for example, benzene head, is selected, then components with a higher boiling point (benzene, toluene, etc.). The highest boiling components of the mixture remain in the cube, forming a bottom residue. At the end of the rectification process, this residue is cooled and pumped out. The cube is again filled with raw materials and rectification is resumed. The periodicity of the process results in greater heat consumption, lower labor productivity and less efficient use equipment.
Installations with continuous columns do not have the disadvantages of periodic columns. In such columns, the heated raw material is introduced into a distillation column, where it is separated into liquid and vapor phases. As a result of rectification, isopentane is selected from the top of the column as the main product and n-pentane as the residue from the bottom of the column.
according to the method of interstage fluid transfer:
1) with transfer devices (with one, two or more)
2) without transfer devices (failure type)
according to the method of organizing contact between the vapor-gas and liquid phases:
These columns are used, for example, for the separation of heavy water. The plates are conical shields with an inclination angle of 40°. Fixed plates 4 are attached at the periphery to the body of the column 1, movable plates 3 are attached in the center to the shaft 5 and rotate with it. Rotating plates alternate with stationary ones. Every 1.5 m in height, the shaft is covered by ball bearings 6 operating without lubrication. For ease of installation, the column is assembled from frames (parts / on flanges). The phlegm descends from above along the stationary plate 4 and at the center overflows onto the underlying rotating plate 3. Under the influence of centrifugal force, the phlegm moves along the rotating plate up to its periphery and, in the form of a continuous annular film, overflows onto the stationary plate. The vapors move countercurrently over the phlegm.
In packed columns, contact between gas (steam) and liquid occurs on the surface of special packed bodies, as well as in the free space between them.
The nozzle is a body made of inert materials, it is designed to create a larger contact surface between the liquid flowing down it and the rising flow of vapors and intensively mix them. The nozzle is usually made of corrosion-resistant material (ceramics, porcelain, glass).
The nozzle is placed on plates equipped with two openings of two types: small - for the drainage of irrigation (reflux) and large - for the passage of vapors. The nozzle layer is divided into several small layers 1-1.5 m high, separating them with free space.
The smaller the packing rings, the better the contact between vapor and reflux, but the higher hydraulic resistance movement of vapors in the column. At a certain limiting value of the load of the packed column, i.e. at a high velocity of vapor or liquid, it can be observed “choking” of the nozzle, when the flow of liquid stops and its ejection from the column begins. The main disadvantage of packed columns is the formation of “dead” zones in the packing, through which neither vapors nor reflux pass, which worsens the contact between mass-exchange phases and reduces the separation efficiency.
The designs of nozzles used in industrial equipment for oil and gas refining and petrochemistry can be divided into two groups - irregular (bulk) and regular nozzles.
Used as irregular (bulk) nozzles solids of various shapes, loaded into the body in bulk. As a result, a complex spatial structure is formed in the column, providing a significant phase contact surface.
Among the nozzles poured into bulk, Raschig rings, which are sections of pipes whose height is equal to the outer diameter, are widely used. The low cost and ease of manufacturing of Raschig rings make them one of the most common types of attachments. Along with smooth cylindrical rings made of metal, ceramics or porcelain, nozzles with a ribbed outer and (or) internal surfaces. To intensify the mass transfer process, designs of cylindrical nozzles with partitions have been developed. 
Nozzle from Raschig rings (1 - separate ring; 2 - rings in bulk; 3 - regular nozzle)
Another ring attachment, the Pall rings, has now found industrial use. When making such rings, two rows of rectangular cuts are made on the side walls, offset relative to each other, the petals of which are bent inside the nozzle. The design of Pall rings, compared to Raschig rings, allows for increased throughput and reduced hydraulic resistance.
The saddle known as Intallox saddles is the most common ceramic saddle today. Its surface is part of a torus. Intallox saddles have mechanical strength, ensure uniform placement of the nozzle and good self-distribution of the liquid. 
In disk columns, contact between phases occurs when steam (gas) passes through a layer of liquid located on a contact device (plate).
Distillation column plate It is a horizontal partition in a column; on a plate there is a layer of liquid flowing down the column (irrigation), through which vapors rising from below bubble.
In the book Skoblo A.I., Molokanov Yu.K., Vladimirov A.I., Shchelkunov V.A. “Processes and Apparatuses of Oil and Gas Refining and Petrochemicals” column apparatuses are divided into disc, packed and film devices based on the type of internal contact devices (the authors of this publication include film devices in which the phases are in contact on the surface of a thin film of liquid flowing down a vertical or inclined surface).
The purpose of the article is to analyze the theoretical and some practical aspects of the operation of a home distillation column aimed at producing ethyl alcohol, as well as to dispel the most common myths on the Internet and clarify points that equipment sellers are “silent” about.
Rectification of alcohol– separation of a multicomponent alcohol-containing mixture into pure fractions (ethyl and methyl alcohols, water, fusel oils, aldehydes and others) having different boiling points, by repeated evaporation of the liquid and condensation of steam on contact devices (plates or nozzles) in special counter-flow tower devices.
From a physical point of view, rectification is possible, since initially the concentration of the individual components of the mixture in the vapor and liquid phases is different, but the system tends to equilibrium - the same pressure, temperature and concentration of all substances in each phase. When in contact with a liquid, the steam is enriched with highly volatile (low-boiling) components, and the liquid, in turn, is enriched with non-volatile (high-boiling) components. Simultaneously with enrichment, heat exchange occurs.
Schematic diagram The moment of contact (interaction of flows) of steam and liquid is called the process of heat and mass transfer.
Due to the different directions of movements (steam rises up and liquid flows down), after the system reaches equilibrium in the upper part of the distillation column, it is possible to separately select practically pure components that were part of the mixture. First, substances with a lower boiling point (aldehydes, ethers and alcohols) come out, then those with a high boiling point (fusel oils).
State of balance. Appears at the very boundary of phase separation. This can only be achieved if two conditions are simultaneously met:
The more often the system comes into equilibrium, the more effective is the heat and mass transfer and separation of the mixture into individual components.
As you can see in the graph, from a 10% alcohol solution (mash) you can get 40% moonshine, and the second distillation of this mixture will yield a 60-degree distillate, and the third – 70%. The following intervals are possible: 10-40; 40-60; 60-70; 70-75 and so on up to a maximum of 96%.
Theoretically, to obtain pure alcohol, 9-10 consecutive distillations are required on a moonshine still. In practice, distilling alcohol-containing liquids with a concentration above 20-30% is explosive, and due to the large expenditure of energy and time, it is not economically profitable.
From this point of view, rectification of alcohol is a minimum of 9-10 simultaneous, stepwise distillations that occur on different contact elements of the column (nozzles or plates) along the entire height.
| Difference | Distillation | Rectification |
| Organoleptics of the drink | Preserves the aroma and taste of the original raw materials. | The result is pure alcohol, odorless and tasteless (the problem has a solution). |
| Output strength | Depends on the number of distillations and the design of the apparatus (usually 40-65%). | Up to 96%. |
| Degree of fractionation | Low, substances even with different boiling points mix, this cannot be corrected. | High, pure substances can be isolated (only with different boiling points). |
| Ability to remove harmful substances | Low or medium. To improve quality, a minimum of two distillations are required, with at least one of them being divided into fractions. | High, at the right approach All harmful substances are cut off. |
| Alcohol losses | Tall. Even with the right approach, you can extract up to 80% of the total amount while maintaining acceptable quality. | Low. Theoretically, it is possible to extract all ethanol without loss of quality. In practice, at least 1-3% losses. |
| Complexity of technology for implementation at home | Low and medium. Even the most primitive apparatus with a coil is suitable. Equipment improvements are possible. The distillation technology is simple and straightforward. A moonshine still usually does not take up much space when in working order. | High. Special equipment is required, which cannot be manufactured without knowledge and experience. The process is more difficult to understand; preliminary at least theoretical preparation is required. The column takes up more space (especially in height). |
| Danger (compared to each other), both processes are fire and explosion hazards. | Thanks to the simplicity of the moonshine still, distillation is somewhat safer (subjective opinion of the author of the article). | Due to complex equipment, when working with which there is a risk of making more mistakes, rectification is more dangerous. |
Distillation column– a device designed to separate a multicomponent liquid mixture into separate fractions based on boiling point. It is a cylinder of constant or variable cross-section, inside of which there are contact elements - plates or nozzles.
Also, almost every column has auxiliary units for supplying the initial mixture (raw alcohol), monitoring the rectification process (thermometers, automation) and distillate selection - a module in which the vapor of a certain substance extracted from the system is condensed and then taken out.
One of the most common home designs Raw alcohol– a product of distillation of mash using the classical distillation method, which can be “poured” into a distillation column. In fact, this is moonshine with a strength of 35-45 degrees.
Reflux– steam condensed in the dephlegmator, flowing down the walls of the column.
Reflux ratio– the ratio of the amount of phlegm to the mass of the distillate taken. There are three streams in an alcohol distillation column: steam, reflux and distillate (the final goal). At the beginning of the process, the distillate is not withdrawn so that enough reflux appears in the column for heat and mass transfer. Then part of the alcohol vapor is condensed and taken from the column, and the remaining alcohol vapor continues to create a reflux flow, ensuring normal operation.
For most installations to operate, the reflux ratio must be at least 3, that is, 25% of the distillate is taken, the rest is needed in the column for irrigating the contact elements. General rule: the slower the alcohol is sampled, the higher the quality.
They are responsible for repeated and simultaneous separation of the mixture into liquid and vapor, followed by condensation of the vapor into liquid - achieving a state of equilibrium in the column. All other things being equal, the more contact devices there are in the design, the more effective rectification is in terms of purifying alcohol, since the surface of phase interaction increases, which intensifies the entire heat and mass transfer.
Theoretical plate– one cycle of leaving the equilibrium state and achieving it again. To obtain high-quality alcohol, a minimum of 25-30 theoretical plates is required.
Physical plate- a really working device. The vapor passes through the layer of liquid in the plate in the form of many bubbles, creating a large contact surface. In the classical design, the physical plate provides approximately half of the conditions to achieve one equilibrium state. Consequently, for normal operation of a distillation column, twice as many physical plates are required as the theoretical (calculated) minimum - 50-60 pieces.
Nozzles Often, plates are installed only on industrial installations. In laboratory and home distillation columns, nozzles are used as contact elements - specially twisted copper (or steel) wire or dishwashing mesh. In this case, the reflux flows in a thin stream over the entire surface of the nozzle, providing maximum contact area with steam.
Nozzles made from washcloths are the most practical There are a lot of designs. The disadvantage of homemade wire attachments is possible damage to the material (blackening, rust); factory analogues are free of such problems.
Material and sizes. The column cylinder, nozzles, cube and distillers must be made of food-grade, stainless, safe when heated (expands evenly) alloy. In homemade designs, cans and pressure cookers are most often used as a cube.
The minimum length of the pipe of a home distillation column is 120-150 cm, diameter is 30-40 mm.
Heating system. During the rectification process, it is very important to control and quickly adjust the heating power. Therefore, the most good decision is heating using heating elements mounted in the lower part of the cube. Heat input through gas stove not recommended because it does not allow you to quickly change the temperature range (high inertia of the system).
Process control. During rectification, it is important to follow the column manufacturer’s instructions, which must indicate operating features, heating power, reflux ratio and model performance.
The thermometer allows you to accurately control the process of fraction selection It is very difficult to control the rectification process without two simple devices - a thermometer (helps determine the correct degree of heating) and an alcohol meter (measures the strength of the resulting alcohol).
Performance. It does not depend on the size of the column, since the higher the drawer (pipe), the more physical plates are inside, therefore, the better the cleaning. Productivity is affected by heating power, which determines the speed of steam and reflux flows. But if there is an excess of supplied power, the column choke (stops working).
The average productivity of home distillation columns is 1 liter per hour with a heating power of 1 kW.
Effect of pressure. The boiling point of liquids depends on pressure. For successful rectification of alcohol, the pressure at the top of the column must be close to atmospheric - 720-780 mmHg. Otherwise, as the pressure decreases, the vapor density will decrease and the evaporation rate will increase, which may cause the column to flood. When too high blood pressure the evaporation rate drops, making the device ineffective (there is no separation of the mixture into fractions). For supporting correct pressure Each alcohol rectification column is equipped with a communication tube with the atmosphere.
About the possibility of homemade assembly. In theory, a distillation column is not very complex device. The designs are successfully implemented by craftsmen at home.
But in practice, without understanding the physical foundations of the rectification process, correct calculations of equipment parameters, selection of materials and high-quality assembly of components, the use of a homemade distillation column turns into a dangerous activity. Even one mistake can lead to fire, explosion or burns.
In terms of safety, factory-made columns that have passed tests (have supporting documentation) are more reliable, and also come with instructions (which must be detailed). The risk of a critical situation comes down to only two factors - proper assembly and operation according to the instructions, but this is a problem with almost all household appliances, and not just columns or moonshine stills.
The cube is filled to a maximum of 2/3 of its volume. Before turning on the installation, be sure to check the tightness of the connections and assembly, shut off the distillate selection unit and supply cooling water. Only after this can you start heating the cube.
The optimal strength of the alcohol-containing mixture fed into the column is 35-45%. That is, in any case, distillation of the mash is required before rectification. The resulting product (raw alcohol) is then processed in a column, obtaining almost pure alcohol.
This means that a home distillation column is not a complete replacement for a classic moonshine still (distiller) and can only be considered as an additional purification step that better replaces re-distillation (second distillation), but neutralizes the organoleptic properties of the drink.
To be fair, I note that the majority modern models Distillation columns are designed to operate in moonshine still mode. To switch to distillation, you just need to close the connection to the atmosphere and open the distillate selection unit.
If both fittings are closed at the same time, the heated column may explode due to overpressure! Don't make such mistakes!
On industrial installations continuous action, the mash is often distilled immediately, but this is possible due to its gigantic size and design features. For example, the standard is a pipe 80 meters high and 6 meters in diameter, in which many times more contact elements are installed than on distillation columns for the home.
Size matters. The capabilities of distilleries in terms of still cleaning are greater than with home rectification After switching on, the liquid in the cube is brought to a boil by the heater. The resulting steam rises up the column, then enters the reflux condenser, where it condenses (reflux appears) and returns in liquid form along the pipe walls to the lower part of the column, on the way back coming into contact with rising steam on plates or nozzles. Under the action of the heater, the reflux becomes steam again, and the steam at the top is again condensed by the reflux condenser. The process becomes cyclical, with both streams continuously in contact with each other.
After stabilization (steam and reflux are sufficient for equilibrium), pure (separated) fractions with the lowest boiling point (methyl alcohol, acetaldehyde, ethers, ethyl alcohol), at the bottom - from the highest (fusel oils). As selection proceeds, the lower fractions gradually rise up the column.
In most cases, a column in which the temperature does not change for 10 minutes is considered stable (selection can begin). total time warming up – 20-60 minutes). Until this moment, the device works “on itself,” creating flows of steam and reflux that tend to equilibrium. After stabilization, the selection of the head fraction begins, containing harmful substances: ethers, aldehydes and methyl alcohol.
A distillation column does not eliminate the need to separate the output into fractions. As in the case of a conventional moonshine still, you have to assemble the “head”, “body” and “tail”. The only difference is the purity of the output. During rectification, the fractions are not “lubricated” - substances with boiling points close to, but at least a tenth of a degree different in, do not intersect, therefore, when the “body” is selected, almost pure alcohol is obtained. During conventional distillation, it is physically impossible to separate the yield into fractions consisting of only one substance, no matter what design is used.
If the column is brought to optimal mode work, then there are no difficulties in selecting the “body”, since the temperature is stable all the time.
During rectification, the lower fractions (“tails”) are selected based on temperature or smell, but unlike distillation, these substances do not contain alcohol.
Return of organoleptic properties to alcohol. Often, “tails” are required to return the “soul” to rectified alcohol - the aroma and taste of the original raw material, for example, an apple or grapes. After the process is completed, a certain amount of the collected tailings is added to pure alcohol. The concentration is calculated empirically by experimenting with small quantity product.
The advantage of rectification is the ability to extract almost all the alcohol contained in the liquid without losing its quality. This means that the “heads” and “tails” obtained in a moonshine still can be processed in a distillation column and produce ethyl alcohol that is safe for health.
Each design has a maximum speed of steam movement, after which the flow of reflux in the cube first slows down and then stops altogether. The liquid accumulates in the distillation part of the column and “flooding” occurs - the cessation of the heat and mass transfer process. There is a sharp pressure drop inside, and extraneous noise or gurgling appears.
Reasons for flooding of the distillation column:
Multi-cap plate with round caps - the most common (Fig. 7.68). She has metal sheet with holes for steam pipes that are attached to the canvas.
Caps are installed above the nozzles, most often with a diameter of 60 and 80 mm. The caps have slots with a height of 15, 20 or 30 mm. To create the required level of liquid, overflow tubes, which are located along the diameter, or segmented overflow partitions are used. The slots of the caps must be immersed in the liquid, so the overflow tubes and partitions protrude above the plate to a certain height. Steam enters through the steam pipe, passes through the slots and bubbles through the layer of liquid. When steam and liquid interact, a finely porous foam is formed and components are exchanged between the phases. There is a cross flow of liquid and vapor on the plate. These plates belong to the group of bubble contact devices. The liquid flows down from plate to plate through overflow devices (glasses). Steam passes towards you from bottom to top.
Cap contact devices have a wide range of stable operation, a relatively high efficiency (0.5-0.7), but have high hydraulic resistance and can be used for processing pure liquid. The disadvantage is also the significant metal consumption and complexity of manufacturing.
Single cap plate works similarly to a multi-cap. Single cap trays work well in small diameter columns. As the diameter increases, their efficiency decreases.
Multi-cap trays are used in the columns of distillation plants: epuration, alcohol, fusel, final purification. They are also used in the concentration part of distillation plants to produce raw alcohol. IN modern installations epuration columns have 39-40 multi-cap plates, and alcohol columns have 71 - 74.
The mash columns of the distillation plant and the depletion part of the distillation plant column are equipped with single-cap trays. They can be used to distill mash and other liquids that contain suspended solids.
Mesh plate is one of the simplest disc contact devices (Fig. 7.69.). This is a perforated metal disk with holes with a diameter of 2-12 mm, which are placed on the plane of the plate along the vertices of equilateral triangles. The plate is fixed horizontally in the column. To maintain a certain level of liquid in small-diameter columns, overflow tubes are used, the lower ends of which are immersed in solid glasses. In larger diameter columns, segmented overflow partitions are used. The steam that rises in the column passes through the holes of the plate and is distributed in the layer of liquid in the form of bubbles and streams. In this case, mass transfer occurs between the phases. Mesh plates have a larger free cross-section (the plane of the holes) than cap plates, which is why their steam output is 30-40% higher than cap plates. The liquid level on the plate is maintained by a certain pressure in the column. When the pressure decreases, liquid can flow through the holes along the entire plane of the plate or its individual parts, which impairs mass transfer. This can also happen if the plates are not positioned accurately (misaligned).
Mesh plates are effective, easy to manufacture, have low metal consumption, but require precise horizontal installation.
Mesh plates are used in mash columns large diameter(> 1400 mm).
Failed contact plates.In these plates, steam and liquid pass through the same holes, therefore they have a larger free cross-section than mesh ones (12-20%). These structures do not require overflow devices and have a large working area.
Lattice failure plates are made from steel or copper sheets 3-5 mm thick. Slots are stamped or milled with a width of 2-6 mm and a length of 60-200 mm. On adjacent plates, the slots are mutually perpendicular. Such plates are simple in design, they throughput more liquid than mesh ones, but they have a narrow range of stable operation. Lattice failure plates are recommended for use in mash columns.
Scale plate(Fig. 7.70) is made of a metal sheet in which arched scales are stamped in a checkerboard pattern. The tilt angle is 15-20°. Changing the free section of the plate (recommended 8-15%) is achieved by changing the number of flakes. The plate has recessed inlet and outlet segments. An overflow pipe is attached to the drain segment. The flow of steam that moves in the column changes the direction of movement when passing through the scales, the slots of which are directed towards the movement of the liquid. The directed steam flow increases the speed of the liquid, which moves upward towards the drain. In the operating jet mode, steam intensively turbulizes the liquid flow, a significant part of the vapor-liquid mixture rises above the plate and moves in the interplate space. Scale-shaped plates operate at high steam velocities and little splash removal, and have high efficiency (efficiency 0.5-0.7).
This type of plates is recommended for use in mash columns with a diameter of more than 1.4 m when distilling mash from crushed grain and potato raw materials. Brass Column with scaly plates characterized wide range stable operation, 20-40% greater productivity compared to typical mash columns, helps improve the quality of alcohol.
Valve trays. The metal flat plate of the plate has round or square holes which are closed by valves. Disc and rectangular valves are manufactured accordingly (Fig. 7.71). When steam moves from bottom to top in the column, the valves rise slightly, steam passes through the slot that has formed and comes into contact with the liquid that is on the plate. As the amount of steam increases, the valve rises higher. The flow area increases, but the speed of steam does not change. The valve lift height is 6-8 mm and is limited by a limiter bracket. The valve trays are also equipped with overflow devices and can operate in modes with cross-flow and direct-flow phase interaction. In the latter case, the valves have stops of different lengths.
On modern stage Valve trays are used to equip mash and evaporation columns. In rectification plants for the processing of secondary winemaking raw materials and the distillation of oil miscels, vortex contact devices are used.
