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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 distillation column and two or more fractions, enriched with some components and combined with others, are continuously withdrawn from the column.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 an important characteristic of the 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 of a 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.

1. Requirements for the design of distillation columns

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 (low cost, ease of maintenance, high performance, strength, corrosion resistance, durability, etc.) In addition, the following specific requirements for column design 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.

2. Classification of column devices

2.1 Classification depending on the relative motion of the phases

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 the steam flow interacts with the 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.

2.2 Classification of 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 plants. 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 the 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 load by liquid. 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.

To carry out the rectification process, devices are used various designs mostly columnar type. Based on the type of contact devices, a distinction is made between packing, disc and film devices. The scope of application of certain devices is determined by the properties of the mixtures being separated, productivity, etc.

Rice. 6.9.1. Column apparatus of the main types:

a - nozzle; b - disc-shaped; c - film; 1 - device body; 2 - distributor; 3 - restrictive grid; 4 - nozzle; 5 - support grid; 6 - plate; 7 - transfer device; 8 - contact surface.

Rice. 6.9.2. Basic flow patterns of steam and liquid in the contact zone:

a - counterflow; b - forward flow; c - cross current.

According to the method of organizing the relative movement of the contacting flows of liquid and steam, contact devices with countercurrent, co-current and cross-flow phase movement are distinguished (Fig. 6.9.2). Regardless of the flow pattern within an individual contact device (contact stage), as a rule, there is a counterflow of steam and liquid throughout the apparatus as a whole.

Packed Columns have found application in cases where it is necessary to ensure a small amount of liquid retention in the column, a small pressure drop, as well as for small-scale production. Types of packings were created (Pall rings, expanded metal, meshes, etc.) that turned out to be quite effective in large-diameter columns.

Main types of nozzles. The attachments are solids various shapes, which are loaded into the column body in bulk or laid in a certain way. The developed surface of the nozzles provides a significant contact surface between steam and liquid. Many design modifications of packed bodies are known, the main types of which are shown in Fig. 6.9.3.

Raschig rings made from various materials, which ensures their versatility practical use. However, Raschig rings have relatively low performance and relatively high resistance. The latter limits their use for vacuum processes. The various modifications of Raschig rings created - Pall rings, Borad rings and others made it possible to obtain better performance characteristics than with Raschig rings.

Rice. 6.9.3. Elements of irregular nozzles:

1-4 – Raschig, Lessing, Pall rings and rings with cruciform partitions; 5, 6 – round and triangular springs; 7, 9 – ceramic and stamped metal Intallox nozzles; 8 – Berl nozzle

Due to the need to create nozzles with low hydraulic resistance, various options regular laying of packed bodies, block packings, as well as packings made of meshes of various designs.

Regular ones include nozzles, the arrangement of elements of which in the volume of the column is subject to a certain geometric order, creating ordered channels for the passage of elements. Examples of such attachments are shown in Fig. 6.9.4.

Elements of a plane-parallel nozzle 1 can be made of boards, glass, metal plates or mesh.

Sulzer attachment 2 consists of alternating layers of corrugated mesh or perforated metal sheet, with the corrugations in adjacent layers turned in the opposite direction.

Goodlow nozzle 3 (sometimes called a Panchenkov nozzle) is a folded spiral of mesh stocking. Such twisted packages are stacked in layers in a column. The steam flow passes through them in the cracks between the mesh layers.

Inclined packet nozzle 4 are rectangular bags made of layers of stocking mesh laid in them, which are installed at an angle of 45-60° to each other (or vertically).

Rice. 6.9.4. Regular attachments:

1 – plane-parallel; 2 – Sulzer; 3 – Goodloe; 4 – batch with inclined sections

The main dimensional characteristics of nozzles are specific surface area and free volume. Under the specific surface of the nozzle f understand the total surface of all packed bodies per unit volume of the apparatus. The SI unit is m 3 /m 3 . The larger the specific surface area of ​​the nozzle, the higher its efficiency, but the greater the hydraulic resistance and the lower the productivity.

The free volume of the nozzle ε is understood as the total volume of voids between the nozzle bodies in a unit volume of the apparatus. The SI unit is m 3 /m 3 . The greater the free volume of the nozzle, the higher its performance, the less resistance and efficiency. As the size of the packed bodies increases, productivity increases, but at the same time the separation efficiency decreases.

Rice. 6.9.5. Liquid distributors:

7 – perforated plate; 2 – plate with pipes; 3 – plate with inclined jet reflectors; 4 – pressure mother liquor-sprayer

To prevent the liquid from spreading to the walls of the column, the packing is loaded into the column in separate layers with a height of 1.5 to 3 m. Distributors of various designs are installed between the layers of the packing (Fig. 6.9.5).

The nozzle is placed on supporting distribution grids and plates. The free cross-section of such devices should be as large as possible and approach the value of the free volume of the nozzle. For the nozzle to work effectively, the surface of the nozzle element must be well wetted by the liquid.

Packed Column Hydraulics. Depending on the steam and liquid loads of the column, the nature of the interaction between them changes, and this determines the maximum steam velocity in the packed column. At certain values ​​of steam and liquid loads, the amount of liquid retained in the nozzle and the hydraulic resistance of the nozzle layer sharply increase. This mode is called column flooding and is considered the upper limit of its stable operation.

Disc columns. In tray columns, steam (or gas) passes through a layer of liquid on a tray. In this case, the steam is split into small bubbles and jets, which high speed move in liquid. A gas-liquid system is formed, which is called foam. The operation of a disc column is shown in the figure.

Rice. 6.9.7. Main types of distillation plates:

I – lattice failure; II – mesh failure; III – sieve cross-flow; IV - cap (a, b, c - capsule, tunnel and grooved caps); V – from S-shaped elements; VI - valve (a, b, c, d); VII – jet (a, b); VIII - vortex (a - structure of the vortex element); 1 – column body; 2 – canvas (base) of the plate; 3 – holes for the passage of vapors; 4 – overflow pipes; 5 – drain segment pockets; 6 – drain plates (partitions); 7 – steam pipes; 8 – caps; 9 – valves; 10 – valve lift limiters; 11, 12 – shaped bends of the plate cloth; 13 – cuts of the vortex element; 14 – reflectors (p and g – directions of movement of steam and liquid)

The main designs of distillation plates are shown schematically in Fig. 6.9.7.

The simplest of them is lattice failure plate(Fig. 6.9.7, I), the canvas of which has geometrically ordered rows of slits (dimensions approximately 10 x 150 mm), through which steam passes upward, bubbling through a layer of liquid on the plate, and through which part of the excess liquid flows (falls) in streams onto the underlying plate.

Such a plate is very sensitive to changes in the liquid load, with changes in which from the calculated load by 20-30% the plate may either choke or not hold a layer of liquid on the canvas. The same effect will occur when the load fluctuates between pairs.

Hole wave plate(Fig. 6.9.7, II) is an improved lattice. Its canvas does not have cracks, but holes with a diameter of 10-15 mm. The cross-sectional profile of the canvas is sinusoidal. This allows you to separate the zones of preferential passage of steam (upper bends of the plate) and liquid drainage (lower bends of the plate). The layer of liquid on the plate is held above the top bends, so steam bubbles through this layer. The tray is designed for small-diameter columns and is used in gasoline stabilization columns and hydrocarbon gas separation columns.

Both plates ( I And II in Fig. 6.9.7.) are failures, and the column with such plates operates in counterflow mode of steam and liquid. The rest of those shown in Fig. 6.9.7 plates are cross-flow, i.e. the liquid on them does not move towards the flow of steam, but perpendicularly or at an angle close to a straight line.

Depending on the magnitude of the liquid load, its flow from plate to plate is carried out in one, two or more flows (Fig. 6.9.8).

Rice. 6.9.8. Diagrams of liquid flows on trays with overflow devices:

a – single-flow; b – two-flow; c – three-flow; g – four-flow; d – with annular movement of liquid; e – with unidirectional movement of liquid on adjacent plates; g, h – cascade type; and - with a crescent-shaped drain partition.

The simplest of this type of plates is sieve (hole) cross-flow plate. Its canvas has holes with a diameter of 4 - 12 mm over the entire area, except for two opposite segments where the drain pipes are located. These pipes are raised above the plate surface to a height of 20–40 mm (the height of the drain is the height of the bubbling layer of liquid on the plate), and their other (lower) end does not reach the plate surface by 30–50 mm. To prevent the flow of steam from entering the drain pipe, its lower end is immersed in a layer of liquid no more than 50 mm high, created by a support bar in front of the perforated part of the plate. The resulting water seal prevents vapor from entering the drain pipe. The overflow device can be not only in the form of drain pipes, but also in the form of a segmented partition (IV, rice. 6.9.7), which cuts off a segmental volume from the vapor space through which the liquid is poured from one plate to another.

In the drain pipes (or segment), the liquid level is usually higher than the level on the underlying tray by an amount that balances the hydraulic resistance of the tray. Therefore, the distance between the plates cannot be less than this column of liquid in the drain device.

On the other hand, the distance between the plates (plate pitch) is actually set taking into account the following factors:

· separation of liquid splashes from the steam flow emerging from the bubbling layer and, due to this, reduction of liquid entrainment to the overlying plate;

· Possibility of human access to the inter-plate space during repair and inspection of plates.

Based on these conditions, regulatory documents set the plate spacing depending on the column diameter from 300 to 900 mm.

Sieve plates (see Fig. 6.9.7, III) used in columns of small diameter (up to 2.0-2.5 m). Currently, variants of sieve plates are often used, the canvas of which is made of expanded metal. The vapor flow, passing through such a canvas, deviates from the vertical and, at the exit from the bubble layer, is directed at an angle of 40-60° to the horizontal. To intensify the operation of the plate along the path of the steam escaping from the bubbling layer, fender elements made from the same expanded sheet are installed obliquely. Hitting these elements, the vapor-liquid mixture is separated: the liquid flows like a film down the element into the bubbling zone, and the vapors pass through the cracks into the interplate space. Such plates have very low hydraulic resistance (0.1-0.2 kPa) and provide fairly high efficiency of mass transfer processes.

Rice. 6.9.9 Scheme of operation of a plate made of expanded metal:

1 – column body; 2 – walls of the drain pocket; 3 – plate cloth; 4 – fender elements made of expanded metal

The disadvantage of such plates (as well as other variants of the sieve plate) is that with the slightest non-horizontality or local bulges or dents in the plate cloth, it works unevenly over the entire area - liquid falls through at the underlying points, and steam escapes without bubbling at the overlying points. As a result, the efficiency of the plate decreases.

One of the oldest types of plates in terms of duration of use and still widespread is cap plate(see Fig. 6.9.7, IV) with round (capsule) caps. Its difference from the previous ones is the presence of a pipe at each hole for the passage of vapors 7 a certain height above which the cap is fixed 8 with slots for the passage of vapor along its entire lower edge. Such a device allows a stream of steam to be introduced into a layer of liquid on a plate parallel to its plane and split into many small jets. In addition, counter jets from adjacent caps collide and create turbulence in the intercap zone, resulting in increased tray efficiency. Indeed, in the vast majority of cases, the average efficiency In practice, such a plate turns out to be the largest - 0.6-0.8.

Exists big number modifications of the cap plate, differing in the design or shape of the caps. Three of these modifications are shown in Fig. 6.9.7 (IV, a; IV, b And IV, c).

The first of them is the plate with round caps described above. Such a plate is universal; it has found application in various columns - from gas separation columns to atmospheric and vacuum ones. In the latter, it is rarely used due to the high metal consumption of the plate and the complexity of manufacturing and installation.

Second modification (IV, b) – This is a plate with cast or stamped rectangular (tunnel) caps, used in the 1930-40s in columns of the Foster-Wheeler company (USA) to separate fuel oil into oil fractions.

Third modification (IV, c) – This is a grooved plate, the peculiarity of which is the absence of a plate cloth. Steel gutters are installed instead 2, between which gaps are formed for the passage of vapors. The slots are covered with caps 8, having slots along their edges, the length of each cap corresponds to the length of the gap between the gutters. The liquid moves along the gutters to the drain; and vapors bubble through the cracks of the caps.

In the 1960-70s, two new types of plates came to replace cap and grooved plates in oil refining - from S-shaped elements (V) and valved ( VI).

Originality S-shaped plates is that its canvas and caps form identical elements (in cross-section - S-profile), but each cap has slots for the passage of vapor on only one side, i.e. per unit bubbling area of ​​the plate, a steam flow is introduced into the liquid by a smaller (compared to a grooved plate) “front” of crushed jets. Unlike a grooved tray, the liquid on this tray moves across the tunnel caps, flooding them.

Trays made of S-shaped elements are very widespread in all columns, except vacuum ones (due to increased hydraulic resistance), due to low metal consumption, ease of manufacture (stamping) and installation, combined with high efficiency (average efficiency 0 .4–0.7).

The low efficiency of trays made of S-shaped elements is partly due to the lower proportion of crushed vapor jets per unit bubbling area. Therefore, a combination plate of this type appeared, in which holes are located along the upper plane of the caps with a pitch of 100-120 mm rectangular section, blocked by valves that open in the direction of liquid movement. This increases the bubbling effect, reduces the hydraulic resistance of the plate and, as a result, increases its efficiency.

Valve trays(Fig. 6.9.7, VI) According to the principle of the device, they are closer to perforated ones, but unlike them, they allow you to adjust the flow area of ​​the holes for vapor. To do this, above each hole (diameter from 30 to 50 mm) there is a device (valve), which, depending on the amount of vapor under pressure, is raised (or rotated) above the hole, thus changing the flow area for the vapor.

However, there are many different designs of valve discs, differing in the design of the valves.

In Fig. 6.9.7, VI 4 most typical valve arrangements are shown: a, b – valves with upper lift limiters (A - turning, b – poppet valve rising vertically); c, d – valves with lower lift limiters - “legs” (V - with three legs of equal height; G - with three legs of different heights: one short and two long). Glitch valve (V) rises vertically under the pressure of steam until the bends of its legs rest against the canvas of the plate. In this case, the cross-section for the passage of vapors will be maximum, and the movement of vapors and liquids will be strictly cross-flow.

Rice. 6.9.10. Fragment of the section and operation diagram of the cross-flow valve plate:

a, b, c – side view of the section at low (counterflow), medium (crossflow) and increased (forward flow) load of the plate in pairs, respectively; d – top view of the valves; e – view of the valve from the side of the short leg; 7 – plate cloth; 2 – holes for valves; 3 – valves; 4 – short legs; 5 – long legs (arrows indicate the directions of movement of liquid and vapor)

A valve with different legs (Fig. 6.9.10) is initially lifted by the steam flow from the side of the short leg (since the center of gravity of such a valve is shifted towards the long legs) until it rests against the blade. In this position (Fig. 6.9.10, A) the vapor flow is introduced at an angle to the plane of the plate towards the moving liquid flow, i.e. The plate operates in countercurrent mode. With a subsequent increase in the amount of vapor, the valve rises from the side of the long legs (more precisely, it rotates around the stop point - the short leg), and when the planes of the valve and the plate blade become parallel (position "b" in Fig. 6.9.10), the plate, as in the case of the Glitch valve, operates in the cross-flow mode of liquid and vapor. If the amount of vapor continues to increase, the valve rotates further around the stop point and eventually rests against the blade with all three legs (" V" in Fig. 6.9.10), taking an inclined position in which the larger flow area for vapor is located along the flow of the liquid, i.e. the plate operates in this case as a direct flow.

Valve trays combine a number of advantages (low metal consumption, ease of assembly, uniform bubbling over a wide range of steam and liquid loads, etc.), which allowed them to become the most common type of tray, from the 1970s to the present. These trays are used in almost all types of oil refining columns - from gas separation to vacuum.

Jet plates(Fig. 6.9.7, VII) They are a canvas 3-5 mm thick, in which holes of various configurations are stamped with the petals bent at a certain angle. The most typical variants of such plates are shown in the figure: A - with bent petals in the form of rectangles with rounded corners, b – in the form of conical convexities (like a “prompter booth”) with holes in one direction. Bubbling on such trays occurs in a cross-co-current mode, in which the dynamic energy of the steam flow is used to intensify the movement of liquid along the tray.

Jet trays are designed for use in cases where the vapor flow load of the column is quite high, so they have found greater use in gas separation columns. Due to the introduction of vapor into the liquid layer at an angle to the plane of the plate, the entrainment of liquid droplets onto the overlying plate is significantly lower than with cross-flow plates.

Vortex plate(Fig. 6.9.7, VIII) – an example of a plate with intensive mixing of steam and liquid on the plate with reduced entrainment of droplets from it. On the canvas of such a plate, in circles with a diameter of 100-120 mm, holes with bent petals are stamped in radial directions (VIII, a), and in the center of these circles on studs there are bumper cups of the same diameter (100-120 mm), in the bottom of which there are 6-8 holes with a diameter of 5-6 mm. Such vortex elements on the canvas are arranged in a checkerboard pattern with a pitch of 140-180 mm.

The steam flow, passing through the slots at an angle of 40-60° to the plate plane, swirls in a mixture with the liquid flowing along the plate surface, and this vapor-liquid mixture, hitting the breaker cups, is separated above them. The vapor flow goes further into the inter-plate space, and the main part of the liquid falls into the cups and flows through the holes in them again into the zone of the vortex bubble layer.

Such a plate on a pilot scale showed low hydraulic resistance, combined with high mass transfer efficiency, which meets the basic requirements for vacuum column trays.

For all types of plates considered, the factors that determine their scope of application and operating efficiency are:

· hydraulic resistance;

· uniformity and intensity of bubbling over the plate area;

· the range of steam and liquid loads in which the plate operates normally (without liquid failure and intense droplet entrainment).

Tray distillation columns have little strengthening capacity and are traditionally used in the production of whiskey, cognac and other fine drinks. Not a large number of plates allows you to preserve the organoleptic properties of raw materials with high stability and productivity of the device.

Material

Because of their similarity, copper dish-shaped columns with viewing windows are called flutes, and those made in a glass body are called crystal. It is clear that these names are just marketing ploy and have nothing to do with the design itself.

Copper is not a cheap material, so the approach to its processing is careful. A copper flute from leading manufacturers is a work of art and a source of pride. The cost of the product can be absolutely any amount that the buyer is willing to spend.

Not much cheaper than a flute with a body made of of stainless steel, and the most budget option is in a glass case.

Design features and types of dish columns

The most widespread are modular column designs based on tees-branches or cylinders made of borosilicate glass. Naturally, this means a large number of unnecessary connecting parts and an inflated cost.

A simpler option is ready-made blocks for 5-10 plates. Here the choice is wider and the price is more reasonable. As a rule, this option is made in glass cases.

There are also very budget options - just inserts for existing drawers.

They can be assembled from components in any required quantity.

The design may be different, but if such dish-shaped columns are used with metal flasks, the clarity of the process is lost. It is much more difficult to understand in what mode the column operates, and for working with plates this is very important.

Simple silicone discs are used to seal each floor.

Naturally, this is less reliable than sealing gaskets in modular designs, but overall it works well.

As an alternative, there is a simplified modular design, where each floor is assembled from simple and inexpensive parts, and the entire structure is pulled together with studs.

The advantage of modular columns is, first of all, their maintainability and openness to modifications. For example, it is easy to supplement the column at the required level with an intermediate fraction selection unit and a fitting for a thermometer. All you have to do is change the plate.

A cheaper option is columns with sieve trays. This does not mean that the quality of the product using them will be worse. But they require more precise control.

Failure plates are even cheaper, but their operating range is very narrow, so you need to be prepared to accurately control the heating with stabilized power sources. Basically, failure plates are used at the NSC.

The most common materials for making plates are copper, stainless steel and fluoroplastic. Any combination of them is possible. Copper and stainless steel are familiar materials, fluoroplastic is one of the most inert materials, comparable to platinum. But its wettability is poor.

If you compare a fluoroplastic plate with a stainless one, it will flood much faster.

The number of plates in the column is usually limited to 5 to obtain distillates with a strength of 88-92% and 10 for purified distillates with a strength of up to 94-95%.

Modular columns allow you to make a set of the required number of plates from various materials.

Difference between packed and tray column

“I have a packed column, do I need a tray column?” – this question sooner or later faces every distiller. Both columns implement heat and mass transfer technology, but there are significant differences in their operation.

Number of strengthening stages

The packed column operates in maximum separation mode at pre-flush power. By adjusting the reflux ratio, you can change the number of theoretical plates in a wide range: from zero to infinity (with the reflux condenser completely turned off and the column running on itself).

A plate column is characterized by a structurally specified number of separation stages. One physical dish has an efficiency of 40 to 70%. In other words, two physical plates give one stage of separation (strengthening, theoretical plate). Depending on the operating mode, the efficiency does not change enough to significantly affect the number of stages.

Holding capacity

The packed column with its low holding capacity makes it possible to clean the distillate well from the head fraction and somehow contain the tail fraction.

The plate column has an order of magnitude greater holding capacity. This prevents her from doing such a harsh cleaning of the “heads”, but allows her to keep the tails in great control. That is, align the distillate with chemical composition. Moreover, the more the distillate needs to be purified from impurities, the more plates need to be placed. Simple task, solvable practically. Once you find the optimal number of plates for yourself, you don’t think about it anymore.

Sensitivity to control inputs

The packed column is very sensitive to changes in water pressure in the dephlegmator or changes in heating power. A slight change in them leads to a change in the number of strengthening steps by several times or even tens of times.

The efficiency of the plates can change by a maximum of 1.5 times, and even then with a very large and targeted change in these parameters. It can be considered that a tuned tray column, from the point of view of separation ability, will practically not respond to ordinary small changes in water pressure or voltage.

Performance

The productivity of a packed column mainly depends on its diameter. Optimal diameter for modern nozzles it is 40-50 mm; with a further increase in diameter, the stability of the processes decreases. Wall effects and channel formation begin to manifest themselves. Disc-shaped columns do not suffer from such weaknesses. Their diameter and productivity can be increased to any required value. If only there was enough heating power.

Technological features of obtaining aromatic distillates

When using packed columns, to limit the degree of reinforcement, we are forced to use shorter frames and a larger packing. Otherwise, the esters that give the main flavor to the distillate will create azeotropes with impurities in the head fraction, and then quickly fly out of the still. We select the “heads” briefly, the “body” - at increased speed. As for the “tails”, the small number of nozzles and the short drawer do not allow the barnacle to be completely contained. It is necessary to proceed to the selection of tailing fractions earlier or to work with small vat bulks.

The dish-shaped column has a relatively high holding capacity, so there are no issues with holding the fusel. To select “heads” and “bodies”, 5-10 physical plates provide 3-5 levels of strengthening. This allows distillation to be carried out according to the rules of conventional distillation. Calmly, without the risk of depriving the distillate of aroma, select the “heads”, and when collecting the “body”, do not think about the premature approach of the “tails”. Fogging on the lower plates at the end of the selection will clearly indicate the need to change the container. The degree of cleaning can be set by changing the number of plates.

Five or ten plates are not enough to approach the level of purification of alcohol, but it is possible to meet the GOST requirements for distillate.

The use of plate columns when distilling fruit or grain raw materials, especially for further aging in barrels, greatly simplifies the life of the distiller.

Basics of choosing the design dimensions of trays for a column

Let's look at the designs of the most common plates for household purposes.

Failed plate

At its core, it is just a plate with holes that can be round, rectangular, etc.

Phlegm flows into relatively large holes towards the steam, which determines main drawback failing plates - the need for precise control of a given mode.

A slight decrease in heating power leads to the fact that all the phlegm falls into the cube, and an increase in power locks the reflux on the plate and leads to choking. These plates can operate satisfactorily in a relatively narrow range of load changes, where they are quite competitive.

The simplicity of the design and high performance of failure plates, along with heating heating elements with a voltage-stabilized power source, which is common in home distilling, has led to their widespread use for continuous mash columns (CBM), which, in combination with a body made of borosilicate or quartz glass, makes the column tuning simple and clear.

To calculate the number and diameter of holes, we proceed from the condition of ensuring bubbling. It was experimentally determined that the total area of ​​the holes should be equal to 15-30% of the area of ​​the plate (pipe cross-section). In the general case, for periodic BC, the base diameter of the holes is about 9-10% of the column diameter, allowing access to the working area.

The diameter of the holes of the failure plates for the NSC is selected based on the properties of the raw materials. If, when distilling sugar mash and wine, holes with a diameter of 5-6 mm are sufficient, then when distilling flour mashes, a hole diameter of 7-8 mm is preferable. However, trays for NSC have their own design features, since the vapor density changes significantly along the height of the column, the dimensions must be calculated for each tray separately, otherwise their operation will be far from optimal.

Sieve plate with overflow

If the diameters of the holes of the failure plate are made less than 3 mm, then even at a relatively low power the phlegm will be locked on the plate and without additional overflow devices it will flood. But a sieve plate equipped with such devices significantly expands its operating range.

Diagram of the sieve column device:
1 – body; 2 – sieve plate; 3 – overflow tube; 4- glass

Using overflow devices on these trays, the maximum level of reflux is set, which allows you to avoid early flooding and more confidently work with a high steam load. This does not prevent the phlegm from completely merging into the cube when the heating is turned off, and the column will have to be restarted from scratch, as is usual for all failed plates.

A simplified calculation of such plates is based on the following relationships:

• the total area of ​​the holes is 7-15% of the cross-sectional area of ​​the pipe;
• the ratio between the diameters of the holes and the pitch between them is about 3.5;
• the diameter of the drain tubes is approximately 20% of the diameter of the plate.

Water seals must be installed in the drain holes to avoid steam breakthrough. Sieve trays must be installed strictly horizontally to allow steam to pass through all openings and to prevent reflux from flowing through them.

Cap plates

If instead of holes in the plates we make steam pipes higher than the drain pipes and cover them with caps with slots, we will get a completely new quality. These plates will not drain the phlegm when the heating is turned off. The phlegm divided into fractions will remain on the plates. Therefore, to continue working, it will be enough to turn on the heating.

In addition, such trays have a structurally fixed layer of reflux on the surface; they operate in a wider range of heating powers (steam loads) and changes in the reflux number (from complete absence to complete return of reflux).

It is also important that cap plates have a relatively high efficiency - about 0.6-0.7. All this, along with the aesthetics of the process, determines the popularity of cap plates.

When calculating the structure, we proceed from the following proportions:

• the area of ​​the steam pipes is about 10% of the column cross-section;
• the area of ​​the slots is 70-80% of the area of ​​the steam pipes;
• drain area 1/3 of the total area of ​​steam pipes (diameter approximately 18-20% of the diameter of the pipe section);
• the lower plates are designed with a high level of reflux and a large cross-section of slots so that they act as retainers;
• The upper plates are made with a lower level of reflux and a smaller cross-section of the slots so that they act as separators.

Based on the graphs given by Stabnikov, we see that with a reflux layer of 12 mm (curve 2), the maximum efficiency is achieved at a steam speed of the order of 0.3-0.4 m/s.

For a 2” column with an internal diameter of 48 mm, the required useful heating power will be:

N = V * S / 750;

• V – steam velocity in m/s;
• N – power in kW, S – cross-sectional area of ​​the column in mm².

N = 0.3 * 1808 / 750 = 0.72 kW.

You might think that 0.72 kW defines little performance. Perhaps, given the available power, it is worth increasing the diameter of the column? This is probably correct. Common diameters of quartz glass for diopters are 80, 108 mm. Let's take 80 mm with a wall thickness of 4 mm, internal diameter 72 mm, cross-sectional area 4069 mm². Let's recalculate the power - we get 1.62 kW. Well, it’s better, for home gas stove fits.

Having chosen the column diameter and design power, we determine the height of the overflow tube and the distance between the plates. To do this, we use the following equation:

V = (0.305 * H / (60 + 0.05 * H)) - 0.012 * Z (m/s);

• H – distance between plates;
• Z is the height of the overflow tube (i.e. the thickness of the reflux layer on the plate).

The steam speed is 0.3 m/s, the height of the plate should not be less than its diameter. For the lower plates, the height of the phlegm layer is larger. Smaller for the top ones.

Let's calculate the closest combinations of plate heights and overflow, mm: 90-11; 100-14; 110-18; 120-21. Considering that standard glass has a height of 100 mm, for a modular design we choose a pair of 100-14 mm. Naturally, this is just our choice. You can take more, then the protection against splashing will be better with increasing power.

If the design is not modular, then there is more room for creativity. You can make the lower plates with a larger holding capacity of 100-14, and the upper with a larger separation capacity - 90-11.

We select caps from standard and available sizes. For example, plugs for 28 mm copper pipe, steam pipes - 22 mm pipe. The height of the steam pipe should be greater than that of the overflow pipe, say 17 mm. The gaps for the passage of steam between the cap and the steam pipe must have a larger cross-sectional area than that of the steam pipe.

The slots for the passage of steam in each cap must have a cross-sectional area of ​​about 0.75 of the area of ​​the steam pipe. The shape of the slots does not play a special role, but it is better to make them as narrow as possible so that the steam is broken into smaller bubbles. This increases the contact area between the phases. Increasing the number of caps also benefits the process.

Operating modes of a disk-type column

Any bubble columns can operate in several modes. At low steam velocities (low heating power), a bubble regime occurs. Steam in the form of bubbles moves through the reflux layer. The phase contact surface is minimal. As the steam velocity (heating power) increases, individual bubbles at the exit from the slots merge into a continuous stream, and after short distances, due to the resistance of the bubbling layer, the stream breaks up into many small bubbles. A rich foam layer is formed. The contact area is maximum. This is foam mode.

If you continue to increase the steam supply rate, the length of the steam jets increases, and they reach the surface of the bubbling layer without collapsing, forming a large amount of spray. The contact area decreases, the efficiency of the plate decreases. This is jet or injection mode.

The transition from one mode to another has no clear boundaries. Therefore, even when calculating industrial columns, only steam velocities are determined by the lower and upper limits of operation. The operating speed (heating power) is simply selected in this range. For home columns, a simplified calculation is carried out for a certain average heating power, so that there is room for adjustments during operation.

Those wishing to spend more accurate calculations I can recommend the book by A.G. Kasatkina “Basic processes and apparatus of the chemical industry.”

P.S. The above is not a complete methodology for calculating optimal sizes each plate in relation to any specific case and does not claim to be accurate or scientific. But still, this is enough to make a working dish column with your own hands or to understand the advantages and disadvantages of the columns offered on the market.

The invention relates to mass transfer equipment in the field of processing hydrocarbon raw materials, chemical and food products, in particular to devices for rectification, absorption of petroleum products, chemical and food products by separating products by boiling point in the process of mass and heat exchange between liquid and steam (gas), and can find application in oil refining, chemical, petrochemical, gas, Food Industry. The rectification column includes a housing with process fittings, trays with steam and overflow pipes, as well as height-adjustable bubble caps. The upper end of each overflow pipe is fixed in a plate with the possibility of axial movement of the pipe relative to the latter, and its lower end is equipped with a plate-shaped perforated disk, as well as a glass concentric to the overflow pipe and forming a water seal with it. Technical result: improving the quality and productivity of the column for target products, increasing the efficiency of the distillation column. 2 ill.

The invention relates to mass transfer equipment in the field of processing of hydrocarbon raw materials, chemical and food products, in particular to devices for rectification, absorption of petroleum products, chemical and food products by separating them by boiling point in the process of mass transfer between liquid and steam, and can find application in oil refining , chemical, petrochemical, gas, food industries.

A distillation column for separating a three-component mixture is known (patent 2234356), containing a vertical housing with plates and a longitudinal vertical partition that intersects part of the plates and divides the column body into vertical sectors. The column contains a reflux flow regulator and a vapor phase flow regulator.

A columnar apparatus with cap plates is known (patent 2214852). In that column apparatus with cap plates, the body is made of drawers; support rings are sandwiched between their bases, on which plates with elastic seals rest. The central supports are equipped with locks. The base of the plate is dome-shaped. All column elements are made of fluoroplastic and are designed for processing corrosive materials.

The disadvantage of both of these columns is that, due to the rigid fastening of all elements of the cap plate, it is not possible to change such technological parameters as, for example, the thickness of the liquid layer on the plate and the difference in liquid levels under the caps relative to its level on the plate, which does not allows you to change the operating mode of the column in height depending on the changing properties of the processed products, i.e. influence the process of heat and mass transfer in the column.

A distillation column with cap plates is also known, for example, described in the book “Processes and Apparatuses”, D.A. Baranov, A.M. Kutepov, M., Academy, 2005, pp. 182, 183, in which the disadvantage of the above-mentioned columns according to patents is partially eliminated, so at least the caps are fixed with the ability to adjust their position in height.

The specified distillation column with cap-shaped plates, as the closest in technical essence to the proposed device, was adopted as a prototype.

However, the prototype is not without the disadvantages characteristic of known columns, namely, there is no possibility of adjusting the thickness of the liquid layer on the plate, and there is also no possibility of developing the interphase contact surface, which largely determines the efficiency of the heat and mass transfer process, i.e. efficiency of the column as a whole.

The purpose of the present invention is to eliminate the listed disadvantages and increase the efficiency of the column.

Essentially, the problem is solved due to the fact that the upper end of each overflow pipe is fixed in a plate with the possibility of axial movement of the pipe relative to the latter, and its lower end is equipped with a plate-shaped perforated disk, as well as a glass concentric to the overflow pipe and forming a water seal with it.

As a result of this technical solution, the vapor-liquid mixture passes through the steam pipe and the cap, bubbling through the cracks of the cap and contacting the liquid on the plate. The vapor-gas mixture goes to the overlying plate, and the excess liquid (heavy) fraction is drained through the overflow pipe into the water seal glass, from where it ends up on a perforated plate disk. Some of the liquid flows over the side of the disk, forming an annular film. The other part of the liquid in the form of drops and streams passes through the perforations in the disk and drains onto the underlying plate. The easily evaporating liquid, located on the plate in a film, drops, streams, evaporates and passes through the steam pipes to the overlying plate. Taking into account changes in temperature, liquid viscosity, composition and state of aggregation environment along the height of the column, you can adjust the ratio and height (gaps) between the steam pipes and caps, between the overflow pipes and the glasses of water seals with disc disks, and also, using the overflow pipes, change the height (and, accordingly, the bubbling resistance) of the liquid on the plate and the living cross-section for bottling vapors through the slots of the caps.

This allows you to optimize the process of dividing the processed product into specified fractions.

Figure 1 shows schematically lengthwise cut columns.

Figure 2 is view A, which shows on an enlarged scale trays with steam and overflow pipes, brackets with clamps and adjusting pins, steam caps, and water seals with disc discs.

The proposed distillation column consists of a housing 1, fitting 2 for the inlet of the vapor-liquid mixture, fitting 3 for the liquid outlet (heavy fraction) and fitting 4 for the vapor outlet (light fraction). In addition, the column contains plates 5 with steam pipes 6 and overflow pipes 7, as well as caps 8 and water seal cups 9, brackets 10 with clamps 11, pins 12, transverse strips 13 and perforated disks 14.

The proposed column works as follows. The initial vapor-liquid mixture is fed into the column through fitting 2. Vapors through steam pipes 6 enter the cavity of the caps 8, displace liquid from them through the slots of the caps 8, after which the steam mixture begins to bubble into the liquid layer outside the caps 8, and a lighter vapor-gas mixture enters onto the plate above. The heavy fraction condenses in this liquid on a plate, through overflow pipes 7 enters the water seal glass 9, overflows over the edges of the glass 9 and falls onto the perforated discs 14. The liquid then drains from these discs through the sides of the discs in the form of a film, as well as through the perforations of the discs in the form of drops and streams.

Equipping the lower ends of the overflow pipes 7 with disc-shaped overflow disks 14 provided a significant increase in the surface due to the outflow of liquid from these disks in the form of a film, drops and jets, which in turn increased the efficiency of the heat and mass exchange process in the column as a whole.

In case of clogging of steam caps and overflow pipes, it is possible to dismantle them and clean them from contaminants and then install them through hatches in the column body, which significantly reduces the time and labor costs for cleaning and Maintenance columns.

Thus, changing the height of the overflow pipe (and the liquid layer) on the plate, in combination with a perforated disc on the overflow pipe, made it possible to optimize the liquid level on the plate and significantly increase the interfacial contact surface on each plate, the total height of the liquid column (resistance) in the column , operating mode of the column in height, heat and mass transfer surface depending on the changing properties of the processed products (boiling point, liquid viscosity, mixture composition).

This makes it possible to separate products into clearer fractions and, accordingly, improve the quality of the target products. The advantages outlined above lead to a significant increase in the efficiency of the column.

A rectification column, including a housing with process fittings, trays with steam and overflow pipes, as well as height-adjustable bubble caps, characterized in that the upper end of each overflow pipe is fixed in a plate with the possibility of axial movement of the pipe relative to the latter, and its lower end is equipped with a disc-shaped a perforated disk, as well as a glass concentric with the overflow pipe and forming a water seal with it.

Similar patents:

The invention relates to the design of contact devices for absorption plates, rectification and other heat and mass transfer devices equipped with overflow devices, and can be used in the chemical, gas, petrochemical, food, energy, mining and related industries.

The invention relates to mass transfer equipment in the field of processing hydrocarbon raw materials, chemical and food products, in particular to devices for rectification, absorption of petroleum products, chemical and food products by separating products by boiling point in the process of mass transfer between liquid and steam (gas), and can find Application in oil refining, chemical, petrochemical, gas, food industries. The rectification column includes a housing with process fittings, trays with steam pipes and overflow devices, as well as caps with vertical slots. The horizontal edges of the cap slots are equipped with blades located with outside caps radially and horizontally. The technical result is to increase the efficiency of the mass transfer process in the distillation column as a whole. 3 ill.

The invention relates to an improved method for producing para-tert-butylphenol by alkylation of phenol with isobutylene on a heterogeneous sulfonic cation exchange catalyst, separation of the reaction mass containing phenol, para-tert-butylphenol, ortho-tert-butylphenol, 2,4-di-tert-butylphenol, high-boiling impurities, by vacuum rectification in two columns with the selection of phenol and ortho-tert-butylphenol in the form of a distillate. In this case, the reaction mass is subjected to rotary-film evaporation to separate high-boiling impurities from it, the commercial product is isolated in an additional distillation column in the form of a distillate, and on a vacuum line, uncondensed vapors of para-tert-butylphenol are captured by absorption, the bottoms of the commercial product separation column containing 2,4-di-tert-butylphenol and para-tert-butylphenol are recycled to the phenol alkylation step with isobutylene. The invention also relates to a device for implementing a method for producing para-tert-butylphenol. The method makes it possible to obtain a product with a high degree of purity and high yield. 2 n.p. f-ly, 1 ill.

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The invention relates to mass transfer equipment in the field of processing hydrocarbon raw materials, chemical and food products, in particular to devices for rectification, absorption of petroleum products, chemical and food products by separating products by boiling point in the process of mass and heat exchange between liquid and steam, and can find application in oil refining, chemical, petrochemical, gas, food industries

1) Rectification is widely used in industry for the complete separation of mixtures of volatile liquids that are partially or completely soluble in one another.

The essence of the rectification process comes down to the separation of one or more liquids in a more or less pure form from a mixture of two or, in general, several liquids with different boiling temperatures. This is achieved by heating and evaporating such a mixture, followed by repeated heat and mass transfer of m/d liquid and vapor phases; As a result, part of the highly volatile component passes from the liquid phase to the vapor phase, and part of the less volatile component passes from the vapor phase to the liquid phase.

The rectification process is carried out in a rectification plant, including a distillation column, a reflux condenser, a refrigerator-condenser, a heater for the initial mixture, and collectors for the distillate and bottoms. The reflux condenser, refrigerator-condenser and heater are conventional heat exchangers. The main apparatus of the installation is a distillation column, in which vapors of the 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 end products are a distillate (vapors of a highly volatile component condensed in a reflux condenser, escaping from the top of the column) and bottoms (a less volatile component in liquid form, escaping from the bottom of the column).

The rectification process can take place at atmospheric pressure, as well as at pressures above and below atmospheric. Rectification is carried out under vacuum when separation
subject to high-boiling liquid mixtures. Higher pressures are used to separate mixtures that are in a gaseous state at lower pressure. The degree of separation of a mixture of liquids into its constituent components and the purity of the resulting distillate and bottoms depend on how developed the phase contact surface is, and therefore on the amount of reflux liquid and the design of the distillation column.

Rectification can be carried out in a batch or continuous manner.

The main advantages of valve discs are the ability to provide effective mass transfer over a wide range of operating loads, simplicity of design, low metal consumption and low cost.

Valve trays are manufactured with disc and rectangular valves; The plates operate in the mode of direct-flow or cross-phase movement. In the domestic industry, the most common valve plates with disc valves are direct-flow valves. On the valve direct-flow plate (Fig.) there are holes in a checkerboard pattern in which self-regulating disk valves with a diameter are installed, capable of rising to a height of 6-8 mm when steam (gas) moves.

The disc valve is equipped with three guides located in plan at an angle of 45°; two of these guides are longer. In addition, special stops are stamped on the valve disk to provide an initial gap between the disk and the plate; this eliminates the possibility of the valve “sticking” to the plate (Fig. a, position I). With a small steam production, the light part of the valve rises (Fig., position II) and steam comes out through the gap between the valve and the plate cloth in the direction opposite to the direction of liquid movement along the plate. As the steam speed increases, the valve rises and hovers above the plate (Fig., position III); Now steam bubbles into the liquid through the annular slot under the valve. With a further increase in steam production, the valve takes a position in which steam exits in the direction of liquid movement, reducing the difference in liquid levels on the plate (Fig., position IV). In this case, the short guide is fixed in a special cutout on the edge of the hole, ensuring the specified position of the valve when it is lifted.

2) 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 an upper or lower lift limiter.

The limiting steam velocity is determined by the contact elements themselves, which clutter the internal cross-section of the column. Different contact elements have their own maximum steam velocity in the full cross-section of the column, which is in the range of 0.5...1.2 m/s. This is also the maximum throughput column, which is usually expressed by the mass flow rate of steam (kg/h) per unit area of ​​the total cross-section of the column (m"). Its value for different contact elements is in the range of 2000...7000 (kg/h)/m.

3 The material balance of the process is expressed by the general equation

hence the total consumption

and its specific consumption

In a real distillation column, equilibrium between the phases is not achieved and the real concentration is always less than the concentration of absorbed gas in the liquid that is in equilibrium with the incoming gas. It follows that the actual specific flow l must always be greater than the minimum value lmin.

The value of the specific minimum consumption of the absorbent can be determined by the formula:

The productivity of the column increases if you install an additional fitting to remove vapors from the cube. The performance of a distillation column, standing separately from the cube, strongly depends on the area of ​​the connecting fitting.

To increase productivity and range of stable operation, valve plates are made of ballast. Above the hole of the plate 1, lift limiters 4 are installed on special legs, and inside them, on the legs 7, there is a light valve 5 and ballast 2. To prevent the valve from sticking to the ballast, there are stops 3 and 6. At low gas output, the tray operates like a regular one with disc valves less weight; when the load increases, valve 5 rests against the ballast and works together with it as one weighted valve. The productivity of the column increases if you install an additional fitting to remove vapors from the cube. The performance of a distillation column, standing separately from the cube, strongly depends on the area of ​​the connecting fitting.

4 As the reflux ratio increases, the working line of the column moves away from the equilibrium line

Consequently, the number of contact plates is reduced, and the height of the column is also reduced.

At the same time, as the reflux ratio increases, the amount of reflux flowing down the column increases, therefore, more heating steam must be spent on its evaporation - energy costs increase - optimization.

5) Column flooding is an off-design mode of its operation. The column can remain in this state for no more than 30...60 seconds. During this time, the phlegm first fills the internal cavity of the distillation part of the column, then the reflux condenser, and then it is accidentally released from the column through the upper fitting of the reflux condenser. The choking of a column can easily be heard as a specific “gurgling” noise in the column. To avoid flooding of the distillation unit, you must strictly follow the operating recommendations. It is worth noting that flooding of the column can occur even at the rated (correct) process power supplied to the evaporation tank. There are only three reasons for this non-standard behavior of the column. The first reason is either clogging of the lower part of the column with foam, for example, from mash, or overfilling of the evaporation tank with the processed liquid. This is a direct violation of the operating instructions regarding filling the evaporation tank. The second reason is the increased voltage in the network (more than 230V), which leads to an increase in the thermal power of the technological heating element. The third reason is a strong decrease in atmospheric pressure or an attempt to operate the column in high mountains. This reason is worth paying special attention to.

6) 1 – container for the initial mixture; 2 – heater; 3 – distillation column (a-strengthening part, b-exhaustive part); 4 – boiler; 5 – reflux condenser; 6 – phlegm divider; 7 – refrigerator; 8 – distillate collection; 9 – collection of still residue; 10 – residue refrigerator.

Distillation column 3 has a cylindrical body, inside of which contact devices in the form of plates or packings are installed. From bottom to top of the column, vapors move, entering the lower part of the apparatus from boiler 4, which is located outside the column, i.e., it is remote (as shown in Figure 3), or is located directly under the column. The steam, which is almost pure HC at the exit from the reboiler, becomes increasingly enriched in the low-boiling component as it moves upward and leaves the upper plate of the column in the form of almost pure HC, which almost completely passes into the vapor phase on the steam path from the reboiler to the top of the column. Therefore, with the help of a boiler, an upward flow of steam is created. The vapor passes through a layer of liquid on the bottom plate. The evaporation of liquid on the plate occurs due to the heat of steam condensation. The vapors are condensed in a reflux condenser 5, cooled by water, and the resulting liquid is divided in a divider 6 into distillate and reflux, which is sent to the upper plate of the column. Consequently, with the help of a reflux condenser, a downward flow of liquid is created in the column. In the reflux condenser 5, either all the vapors coming from the column, or only a part of them corresponding to the amount of reflux returned to the column, can be condensed. In the first case, part of the condensate remaining after separation of the reflux condensate is a distillate (rectified product), or upper product, which, after cooling in refrigerator 7, is sent to the distillate collector 8. In the second case, the vapors not condensed in the reflux condenser are simultaneously condensed and cooled in refrigerator 7, which with this type of operation it serves as a condenser-refrigerator for the distillate.

The liquid coming out of the bottom of the column (close in composition to VC) is also divided into two parts. One part, as indicated, is sent to the boiler, and the other - the remainder (lower product) after cooling with water in refrigerator 10 is sent to collection 9.

7) The materials for the manufacture of steel welding machines are semi-finished products supplied by the metallurgical industry in the form of sheets, long and shaped rolled products, pipes, special forgings and castings.

Materials must be chemically and corrosion resistant in a given environment with its operating parameters, have good weldability and appropriate strength and plastic characteristics under operating conditions, allow cold and hot machining, and also have the lowest possible cost and be non-scarce.

The following factors must be taken into account:

Operating conditions (pressure and temperature of the working medium, the degree of its corrosiveness), the nature of the load application (static, low-cycle, cyclic):

Mechanical characteristics of the material under given operating conditions;

Cost of material (taking into account the economical use of scarce alloying elements);

For example, if the device contains an aggressive environment, then all elements in contact with it (body, cover, flange) are steel X18N10T, all others (support) are steel 3

8) In recent years, when reconstructing disc distillation columns, disc contact devices are most often replaced with packed ones. This is explained by the fact that the packed column provides a lower pressure drop across the height of the apparatus, a wider range of stable operation, higher efficiency, and, consequently, higher separation capacity, etc. Also, for uncontaminated liquids, sieve trays can be installed, because . They have a greater range of stable operation.

9) High vertical devices include all devices whose height relative to the zero mark (relative to the Earth's surface) is more than 10 meters, which are installed in the open air. If the device is located in a workshop, then it is designed to tip over if its height is more than 5 diameters.

Rollover calculation includes:

1) Calculation of the hull based on current loads;

2) Calculation of the body for capsizing at a minimum load without filling;

3) Calculation of the skirt support for crushing;

4) Calculation of the support ring for bending.

1 – body; 2 – skirt support; 3 – support ring; 4 – foundation bolt

From the action of the wind load, an overturning wind moment arises, which tends to tear the support away from the foundation, hence the first dangerous section. The second dangerous section is the welding area between the body and the supporting shell.

Purpose of calculation: determine the force caused by the wind, i.e. wind load, its wind moment and the dimensions of the support of the fundamental ring and the need to install fundamental bolts. The problem is solved using the method of calculating the flexibility of a rigidly fixed rod.

Calculation procedure:

1. Wind loads act on the apparatus in the horizontal plane. At the same time, they cause bending and overturning wind moments. When calculating, the entire height is divided into sections of 10 m. The center of mass is applied in the middle of each section. When exposed to wind, the center line deviates from the equilibrium position, forming an elastic line. At the same time, in each section there is also a deviation of the centers of mass. Elastic forces tend to return the system to an equilibrium position. In this case, a phenomenon similar to oscillations of an elastic system occurs.

2. Wind moment: (1)

3. Wind load:

4. According to the found MV:

- according to the minimum weight for capsizing

Calculation of foundation bolts. If by condition negative, this means that the wind moment is greater than the moment from the weight. Therefore, it is necessary to install foundation bolts. If the value positive, then 4-8 M36 bolts.

According to the maximum weight for compression of the support shell

Determination of the thickness of the support ring. Checking the weld seam, checking the stability of the shape of the support shell from the weight of the apparatus.

The stability of the support shell is checked from the condition:

– permissible axial compressive force

If the shell is loaded with internal excess pressure. The wall thickness is determined by the formula:
,

Where S– minimum shell thickness, including allowance for corrosion; P– design pressure, including hydrostatic pressure; D– internal diameter, excluding allowance for corrosion; φ – weld/base material strength ratio; [σ] – maximum permissible tensile stress at design temperature, kg/cm 2 ; C– structural increase, see

The permissible external pressure is determined by the formula: ,

where [P] p – permissible external pressure within the limits of plasticity; [P] E – permissible external pressure within the elasticity limits.

, ,

where E is the elastic modulus of the shell at the design temperature; n y – stability safety factor; l – design length of the hull (length of the cylinder part + 1/3 of the height of the convex part of the bottoms).

1. Horizontality of the plates (determined using a level, or by the intensity of bubbling in different areas of the plate);

2. Disc seals

Preparing the device for repair: 1) Deviation from factory provision, installation of plugs; 2) Removal of product residues; 3) Steaming, washing, products

One of the most frequently damaged parts of a column is the supply and discharge pipes. This part may have the following defects:

– crack at the welding site of the flanges;

– abrasive wear;

– deformation of the sealing surface.

These defects are eliminated as follows:

– we eliminate the crack by cutting for welding, welding the crack and grinding the welded crack;

– abrasive wear is eliminated by cutting out the damaged part, grooving the pipe from the ends for welding, welding the pipe and grinding the welded surface;

– deformation of the sealing surface is eliminated by cutting off the flange, then turning the sealing surface, grooving for welding, welding the flange and grinding the welded surface.

– Bulges in the body are removed using a sledgehammer.

If the diameter is up to 800 mm, then the apparatus is prefabricated (from drawers) - the drawers are disassembled and elements requiring repair are removed.

If the diameter is more than 800 mm, the device is all-welded, then the elements must be dismountable. They are disassembled, removed and repaired.

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