Digest - industrial safety. Laboratory distillation column Complex distillation columns

Goal of the work:

Study of the operation of a laboratory packed column periodic action at maximum (full) and working irrigation.

Determination of the number of stages of concentration change (theoretical plates) in the column under different operating modes.

Determination of the height of the nozzle equivalent to a theoretical plate (HETP).

Determination of irrigation coefficient.

Determination of the temperature of the top and bottom of the column.

1. Description of the laboratory setup

The laboratory installation (Figure 1) includes a packed column 1, a heating mantle 2, a return condenser - refrigerator 3 and a distillate refrigerator 4. Metal spirals are used as packing in the column. To ensure the adiabatic process of the rectification process, the column has lateral electrical heating 5. Inlatrom 6. The cube of the column 1, placed in a heating mantle, has a bottom sampler 7. A condenser is used to condense the vapor phase - a refrigerator 3. The distillate selection is regulated by a tap 8. The sampled distillate is cooled in the refrigerator 4 and receiver 9 arrives. To maintain atmospheric pressure in the column, air vent 10 is designed.

1- distillation column; 2 – heating mantle; 3 – return condenser – refrigerator; 4 – distillate refrigerator; 5 – lateral electric heating; 6 – LATR; 7 – sampler; 8 – tap; 9 - receiver

Figure 3 – Laboratory setup diagram

2. Experimental procedure.

An initial mixture containing NCC and VCC is prepared, 50 ml of the mixture is loaded into the column cube.

Start-up of the installation begins with the supply of water to the condenser - refrigerator. Then the heating mantle is turned on. After the mixture boils and irrigation appears in the lower part of the nozzle, the side heating is turned on. The intensity of the side heating is maintained such that a layer of liquid appears at the top of the nozzle. This phenomenon is called “flooding” of the column. “Choke” is necessary to wet the nozzle and, accordingly, intensify the mass transfer process. The side heating is then reduced until the set flow rate (number of drops per minute above and below the nozzle) is achieved. In this case, the layer of liquid located above the nozzle flows into the column cube. Side heating should be reduced gradually so that irrigation does not stop. If irrigation stops, then it is necessary to “flood” the column again. This sets the column mode corresponding to the full irrigation mode. The distillate is not selected.

After maintaining the full irrigation regime for 30-40 minutes, 3-4 drops of distillate and the residue are taken for analysis. Next, the operating mode is set with distillate selection at a speed of 6-10 drops per minute. After receiving 2.5 - 4 ml of distillate, 3-4 drops of distillate and the same amount of the residue are taken for analysis, and work on the column ends. The heating mantle and side heating stop. The supply of water to the refrigerator condenser stops 15-20 minutes after the heaters are turned off.

Four samples taken during the experiment (distillate and residue with full irrigation and operating mode of the column) are analyzed on a refractometer at 20 o C. Using the graphical relationship “refractive index - composition”, the NCC content in all samples is determined in volume fractions.

The results of the experiment are recorded in a journal. It must be kept in mind that the number of drops per minute above and below the nozzle are not necessarily equal to each other. However, they must be close and constant in time under steady-state operating conditions of the column.

Experimental data:

Full irrigation mode:

n dist = 1.392

n cube = 1.433

Volume fractions:

distillate – 0.95

cube – 0.56

Work mode:

Top of the column – 135

At selection – 18

n dist = 1.3925

n cube = 1.44

Volume fractions:

distillate – 0.92

cube – 0.51

3. Processing of experimental results

The volumetric compositions of the distillate and residue are converted to molar compositions.

With full irrigation:

During working irrigation:

Let's determine the reflux ratio:

Excess irrigation ratio:

According to the schedule we determine:

where

Number of stages with full irrigation – 15

During operating mode – 23

Packing height equivalent to one theoretical plate:

With full irrigation:

During operating mode:

Find the temperature of the top and bottom of the column:

With full irrigation: t 1 = 98.8 0 C and t 2 = 102.0 0 C

During operating mode: t 1 = 99.0 0 C and t 2 = 102.5 0 C

In operating mode, the number of theoretical plates is greater than in full irrigation, so the height of the nozzle is correspondingly smaller.

Laboratory work No. 5

“Study of the operation of failure-type lattice plates”

Goal of the work:

Study of the influence of hydrodynamic characteristics on the position of the dispersion point and the “flooding” point on a column model using an air-water system.

1,2 - rotameter; 3 - compressor; 4 - distribution grid; 5 - pressure gauge;

6 - plate; 7 - column; 8 - control valve.

Figure 4 - Laboratory setup diagram

1 Methodology of work

Turn on the compressor, creating a small air flow through the model. The pressure drop is measured using pressure gauge 5 on the plate without irrigation in order to determine the resistance coefficient of the dry plate. Then reduce the air flow to).

Set the specified water flow rate using the rotameter and create a small air flow through the model. When the plate operates at a steady state, the resistance of the plate is measured, and the maximum value of the difference, which is observed at given flow rates of liquid and gas, and the height of the foam on the plate are measured. Then the air flow rate is slightly increased using the valve on the rotameter. With a new air flow rate, after 3-5 minutes of operation the plates again measure the difference and height of the foam. Record the flow of water and air when the tray initially comes into operation. Increase air flow. The data is entered into table 1.1

Table 1.1- Experiment results

2 Processing of experiment results

Determine the relative free cross-section of the plate using the formula:

Using the air flow rate, determine the air speed in the full cross section of the column

Let's calculate the resistance coefficients of a “dry” plate, taking into account that at air flow Q 2 = 0.007 m 3 /s plate resistance
=80 Pa

Using the pressure drop across the “dry” plate, determine the resistance coefficient of the “dry plate”:

Table 2.2 - Calculation results

We studied the influence of hydrodynamic characteristics on the position of the dispersion point and the “flooding” point on a column model using an air-water system. We calculated the pressure drop across the plate and compared it with the experimental value.

This step-by-step instruction- just one of the methods of distillation on a distillation (RK) or mash (BK) column, having mastered which you can obtain a highly purified product. However, for fruit, berry and grain distillates there are technological nuances, without knowledge of which instead aromatic drink it will be pure alcohol. Each type of nozzle has its own characteristics. Use the proposed method as a starting point for studying the operation of columns, practicing on sugar mash, or knowing that you will end up with rectified alcohol or a drink close to it.

Initial conditions. Raw alcohol is available - sugar mash distilled in a conventional distiller (moonshine still) and - RK or BK. In this case, the method of working on different types columns is almost identical, and the differences are described in the appropriate places in the instructions.

Technology of home rectification on RK and distillation on BK

1. Fill the cube with raw alcohol to no more than 3/4 of the height, making sure to leave at least 10-12 cm of vapor zone. However, it is also impossible to fill in too little, so that at the end of the distillation process, when there is almost no liquid left in the cube, the heating elements do not emerge (become bare).

The strength of the vat bulk should be about 40%. This value is related to the minimum reflux ratio required to achieve the selection of a given strength. As the strength of the vat bulk increases, the minimum reflux ratio decreases nonlinearly, reaching a minimum at a strength of about 45%. Therefore, if you start the process with a strength of 60%, you will have to reduce the reflux ratio down to 45% of the strength, and then increase it as the still alcohol content is further depleted. That is, first increase the selection from 60 to 45% of the pot strength, and then reduce it. As a result, rectification will not only be more difficult to manage, but will also take longer.

2 Turn on the heating element maximum power and bring the raw alcohol to a boil. The optimal power of the heating element for acceleration is 1 kW per 10 liters of bulk, then the time until boiling is 15 minutes for every 10 liters of bulk.

3. Shortly before the start of boiling, at a temperature of 75-80 °C in the cube, turn on the water supply. Once boiling begins, reduce heat to operating power. If the operating power is still unknown, reduce it to a level below the rated power by 200-300 W. Adjust the water supply so that the steam is completely condensed in the dephlegmator. The outlet water should be warm or hot. The column began to work for itself.

4. Monitor the values ​​on the thermometers in the column, wait for the readings to stabilize.

5. Determine the operating capacity of the column. To do this, after the temperatures have stabilized, check the pressure in the cube. You will need a pressure gauge up to 6000 Pa (0.06 kg/sq. cm, 400 mm water column), or a U-shaped differential pressure gauge; a pressure gauge from a tonometer will also work (if nothing else is available).

If the pressure is stable and does not increase, add heating power by 50-100 W. The pressure in the cube should rise and after 5-10 minutes stabilize at a new value. Repeat this operation until the pressure stops stabilizing and continues to increase, for example, after 20 minutes the increase continues. Remember the current readings - this is the power of the choke.

If there is a 50 mm column and a SPN 3.5 nozzle, then the last non-increasing pressure (in mm of water column) will be approximately equal to 20% of the column height in millimeters. If the pressure is 30-40% of the height of the column, this means that the phlegm is stuck, and then the process of choking continues. With a less dense nozzle with less holding capacity, the choking power will be higher.

If there is no pressure gauge, they are guided by the sounds of the column - when choking, the column may begin to sway, gurgling can be heard, increased noise, spontaneous emissions of alcohol through the communication tube with the atmosphere or into the refrigerator during steam sampling are also possible. For the first time, without experience, it is difficult to determine the flooding of the column, but it is possible.

After determining the power of the reflux, turn off the heating and wait a few minutes for the phlegm to flow into the cube. Turn on the heating at a power 10% less than the cold one. Wait until the temperature and pressure in the cube stabilize. If everything is in order, then this will be the operating power of the column.

If the operating power is much lower than the nominal one, this means that the nozzle or the supporting elements of the nozzle are not packed correctly into the column: the nozzle is too compacted, there may be a tangle, there are pockets of reflux concentration where steam stops it, flooding the column. In this case, you need to disassemble the column, pour in the nozzle, straighten out the confusion, then reassemble it and repeat the adjustment process.

The operating power of the column is determined once. In the future, the obtained value is used constantly, occasionally making adjustments.

With correctly selected operating power, the pressure in the cube will be the same every time. It does not depend on the diameter of the column and is usually 3.5 – 150-200 mm of water for the SPN packing. Art. for each meter of nozzle height, for SPN 4 - 250-300 mm of water. Art., for other attachments the value will be different.

When searching for operating power, you can also focus on the following practical data: for an etched heptagonal SPN 3.5, the operating power in Watt is approximately equal to 0.85-0.9 of the cross-sectional area of ​​the pipe in millimeters. If SPN 4 is used, the coefficient increases to 1.05-1.1. For less dense nozzles the coefficient will be higher.

6. After stabilizing at operating power, let the column work for itself for 40-60 minutes.

7. Set the selection of “heads” at a speed of 50 ml/hour for a 40 mm column, for 50 mm – 70 ml/hour, for 60 mm – 100 ml/hour, for 63 mm – 120 ml/hour. Provided that SPN is used.

The time for selecting “heads” is determined based on the volume of the bulk: 12 minutes (0.2 hours) for each liter of 40% raw alcohol. It must be remembered that this is not distillation on a conventional apparatus with a coil - in the columns there is a separation into fractions and their sequential output to the selection in a concentrated form.

Recommendations such as 3-5% of absolute alcohol are average values, but no one has canceled them, and precise control of the end of the selection of “heads” is done based on the smell of the output. It should be remembered that the time and speed of selecting “heads” are unrelated quantities. If you select the “heads” at twice the speed, they will simply end up in a less concentrated form.

General principle: when selecting any fraction, you cannot take more from the column than enters the selection zone. This will prevent disruption of the separation of fractions along the height of the column.

8. Changing the extraction rate is carried out only by adjusting the water supply to the reflux condenser for columns with steam extraction above the reflux condenser. If the column has liquid extraction, then simply a withdrawal valve.

The heating power should always remain constant; this ensures stability in the amount of steam supplied to the column and the operation of the column as a whole.

9. Select headrests - this is second-grade alcohol, slightly contaminated with head fractions. Its quantity is equal to 1-2 volumes of alcohol held by the nozzle in the column (150-500 ml). In essence, the nozzle is washed to remove any remaining “heads” and intermediate fractions accumulated in the column. To do this, the selection is set at 1/3 of the nominal level (about 500 ml/hour). Second grade alcohol is suitable for re-distillation.

10. Go to the “body” selection: set the initial selection speed equal to the nominal or slightly higher. The nominal speed (ml/hour) is numerically approximately equal to the operating heating power (in W). For example, if the operating power is 1800 W, then the initial rate of “body” selection is 1800 ml per hour. Towards the end of the selection, the power is reduced to 600 ml/hour,

11. Monitor the process using thermometer readings and pressure in the cube. There are several methods. The simplest one is to navigate by the temperature difference between the lower (20 cm from the bottom of the nozzle) and middle (at half or 2/3 of the column height) thermometers. After the start of the “body” selection, the difference between these readings should not change by more than 0.3 degrees. As soon as the difference increases by more than the accepted value, you need to reduce the sampling rate by 70-100 ml.

Special cases: if there is only one thermometer, act in exactly the same way, focusing on changes in its readings. For the lower one - a change of 0.3 degrees, for the upper one - 0.1 degrees. It's less exact method, since it is sensitive to changes in atmospheric pressure.

If there are no thermometers in the column at all, they focus on the change in temperature in the cube - reduce the selection by 6-10% after increasing the temperature in the cube by every degree. This is a good method that allows you to stay ahead of the temperature rises in the column.

12. After selecting half of the “body”, more and more often it is necessary to reduce the selection speed. When the temperature in the cube rises above 90 °C, fusel and other intermediate impurities leave the cube and accumulate in the nozzle. To cut them off more clearly, before reducing the selection, you can let the column work for itself for several minutes, then resume selection after the temperature difference returns to its previous level, naturally reducing the selection rate. This will make it possible to more clearly cut off the “tails” by creating an alcohol buffer in the selection zone.

13. When the selection decreases by 2-2.5 times relative to the initial one, the temperature regularly leaves the operating range, with the temperature in the cube being 92-93 °C. These are signals for the bookmaker that it’s time to move on to selecting “tails”. On the RK, due to the greater holding capacity, when loading less than 20 volumes of nozzle, selection can be continued up to 94-95 °C, but often the process is stopped, saving time and nerves.

Change the container, set the sampling speed to approximately half or 2/3 of the nominal one. Although these are “tails”, you need to try to take a minimum of impurities. Select up to 98 °C cubed. The "tails" are suitable for the second distillation.

14. Rinse the column. After selecting the “tails,” let the column work for itself for 20-30 minutes, during which time the remaining alcohol will collect at the top, then turn off the heating. The alcohol flowing down will wash the nozzle.

You also need to periodically steam the nozzle, removing any remaining fusel oils. This can be done by driving the raw alcohol “to dryness”, then continuing the selection at a decent speed until an odorless distillate comes out. The second method is to pour into a cube clean water and steam the column.

Laboratory work.

Study of the rectification process

Goal of the work:

study of the rectification process ethyl alcohol on a periodic installation,

calculation of the number of theoretical plates,

coefficient determination useful action distillation column.

Basic information

Rectification is the process of separating liquid homogeneous mixtures through the mutual exchange of components between liquid and vapor obtained by evaporation of the mixture being separated. This process is based on the different volatility of the components that make up the mixture, i.e. on the difference in their boiling points at the same pressure.

The rectification process is carried out in columns, which are vertical cylindrical devices with contact devices. The most widely used in industry distillation columns, in which cap, sieve and failure plates are used as contact devices. In a distillation column, flows of vapor and liquid that are nonequilibrium in composition pass towards each other. The steam in the column goes from bottom to top, and the liquid flows from top to bottom. As a result of contact interaction, the vapor is enriched with a more volatile (low-boiling) component, and the liquid is enriched with a less volatile (high-boiling) component. The developed phase contact surface on the plates is formed by bubbles and jets of vapor as it repeatedly passes (bubbling) through layers of liquid.

The main task of rectification plants in the food industry is to obtain rectified alcohol with an alcohol concentration of at least 96% with a minimum content of foreign impurities from 40% raw alcohol. It is known that ethyl alcohol dissolves well in water, forming a binary water-alcohol mixture with varying alcohol content. Boiling point of 100% ethyl alcohol (t bale =73.8°C at a pressure of 760 mmHg. Art.) differs significantly from the properties of distilled water, and this difference is used when separating the components of various alcohol-containing materials to obtain high-concentration alcohol. There are molar, mass and volume concentrations of alcohol. Traditionally, the food and chemical industries use the concept of volumetric concentration as the ratio of the volume of dissolved liquid to the volume of the entire solution. This value is expressed as a percentage and is designated as % vol. or in fractions of m 3 /m 3 , l/l, ml/ml. Due to differences in the densities of alcohol (ρ = 0.790 g/ml) and water (ρ = 1.000 g/ml) and their thermal expansion characteristics, volumetric and weight concentrations do not always translate correctly into each other.

The separation of alcohol from a water-alcohol mixture must be carried out at a boiling point corresponding to the concentration of the mixture and constant vapor pressure above the mixture. At a pressure of 760 mm Hg. Art. The boiling point of water-alcohol mixtures of different concentrations decreases almost continuously from 100 °C at an alcohol concentration of 0% to 78.3 °C at 100%. The exception is a certain concentration region near the azeotrope point (94.6%), where the boiling point becomes slightly lower than the boiling point of 100% alcohol (Fig. 1). Azeotropic or nonseparately boiling mixtures are those in which the vapor is in equilibrium with the liquid and has the same composition as the boiling mixture.

Figure 1 – Temperature dependence of saturated aqueous-alcoholic

steam at a pressure of 760 mm Hg.

Separation of such mixtures by rectification is impossible, since condensation of vapors produces a liquid of the same composition as the original mixture, which is called “ethyl alcohol - rectified.” Its boiling point is 78.15 °C, and the alcohol concentration, set State standard Russian Federation - from 96 to 96.4%. In this case, the density of the condensed liquid at 20 °C is 8.12 g/ml, the vapor density at 760 mm Hg. - 1.601 g/ml, and specific heat vaporization - 925 J/g.

To obtain rectified alcohol, installations are used continuous action(Fig. 2). In them, raw alcohol and superheated water vapor are mixed at the bottom of the distillation column and water-alcohol vapor with a temperature of 94 ° C is converted.

The initial mixture is stored in storage tank 3, from which pump 9 through filter 11 is supplied to pressure tank 4. From pressure tank 4, the initial mixture flows by gravity through a rotameter into a heater located in cube 2, where it is heated by the bottom residue. The temperature of the initial mixture after heating is determined by the thermometer reading. In distillation column 1, the heated initial mixture is supplied to 7, 9 or 11 plates, counting from the top. The column has 12 sieve trays with segmented drainage devices. The inner diameter of the column is 200mm.

Figure 2 – Schematic diagram industrial installation continuous action using heating steam

1 – Distillation column; 2 – cube; 3 – storage tank; 4 – pressure tank; 5 – reflux condenser; 6 – distillate collection; 7 – bottoms refrigerator; 8 – collection of still remains; 9 – pump; 10 – rotameter; 11 – filter

From the lower plate, the liquid flows into the evaporator cube 2, which has a coil inside, heated by steam. The heating steam condensate from the coil is discharged into the sewer through a condensation pot. The flow of heating steam is regulated by a valve, and the pressure is determined by a pressure gauge. In the evaporator cube, part of the liquid is converted into steam, and the other is removed as a still residue. The bottom residue passes through the refrigerator 7, where it is cooled with water, and enters the collector 8. From the collector 8, the bottom residue is returned to the storage tank 3. The collectors 6, 8 and the annulus of the reflux condenser 5 are connected to the atmosphere, which ensures the operation of the column under atmospheric pressure. From the top plate of the column, steam enriched with the low-boiling component enters the reflux condenser 5, which is also cooled with water. Water flow is measured by a rotameter, and its temperature at the inlet and outlet is measured by thermometers. The liquid formed in the reflux condenser after complete condensation of the steam is divided into two parts. One in the form of reflux is supplied to irrigate the column, and the other is taken in the form of distillate, which enters collection 6 and is then sent to storage tank 3. The amount of reflux and distillate is measured by rotameters.

The column is equipped with samplers for liquid from the plates, reflux, distillate, liquid in the still, as well as samplers for steam entering the plate and leaving the foam layer. Steam samplers are equipped with pipe-in-pipe heat exchangers in which steam samples are condensed and the condensate is collected in separate containers. Temperature sensors are installed on each tray of the column, operating in conjunction with a secondary device. Knowing the temperature of the liquid on the plates allows one to determine the temperature profile along the height of the column.

Description experimental setup

Real work involves studying the process of rectification of ethyl alcohol in a laboratory installation with an electric heater (9) and periodic filling of alcohol-containing raw materials, the operation diagram of which is shown in Figure 3. The installation consists of an evaporation cube (1), a distillation column (2) vertically installed on its lid, and electric heater (9).

Figure 3 – Schematic diagram of a laboratory distillation unit with an electric heater and periodic filling of the evaporation tank with a water-alcohol mixture.

The main part of the installation is composite column, which is divided into upper (3) and lower (2) distillation parts. Top part includes a condensing device (4), a cooler (5), an alcohol selection regulator (6) and a system of pipes connecting them (10). During rectification, cooling water constantly flows in countercurrent into the condenser (4) and heat exchanger (5), made according to the “pipe-in-pipe” scheme. In the upper part of the evaporation tank, manometric tube leads are made to measure the pressure of the generated steam and the pressure drop in the column.

Unlike industrial distillation columns with cap, sieve and failure plates in laboratory columns ultra-small diameter (10-30mm) as contact elements, the most widely used are “Sulzer” type nozzles made of stainless corrugated mesh or spiral prismatic springs made of stainless steel. The process of heat and mass transfer on such contact elements occurs continuously along the entire height of the column, and a state of equilibrium equivalent to one theoretical plate occurs after steam overcomes a certain layer, the height of which is associated with the height of the theoretical plateVTT or transfer unit heightVEP . This height is usually estimated in millimeters, which makes it easy to evaluate the effectiveness of a particular nozzle byVEP . So when internal diameter columns of 30 mm, the BEP of the spiral-prismatic nozzle is 15-30, and for the “Sulzer” nozzle used in our case, 20-25 mm. However, even with a column diameter of 40 mm, their efficiency is virtually the same andVEP is 25-30 mm. Thus, for packed columns, the height of the transfer unit strongly depends on the diameter of the column and increases rapidly as it increases. Therefore one of promising directions improving energy efficiency industrial equipment is its miniaturization and use large quantity contact elements.

Safety requirements

To be completed laboratory work students are admitted only after undergoing instructions on labor protection and fire safety in the laboratory and at the workplace.

In accordance with them, before starting the installation, you need to familiarize yourself with its structure and external inspection to check the serviceability of the distillation column, evaporation tank, pipelines, shut-off valves, electrical appliances; presence of grounding, serviceability protective shutdown, electrical and thermal insulation.

The installation should be started in the presence of a training foreman and under his direct supervision.

To avoid flooding of the distillation column and emergency release of hot reflux, strictly follow the recommendations for the procedure for carrying out laboratory work.

When working on the installation, exercise caution and accuracy. Remember that during operation some of its elements and devices have a temperature of about 100 about S.

Work order

Familiarize yourself with the diagram of the laboratory setup and the location of instruments. Compose its description and prepare tables for recording test results.

Fill the evaporation tank 3/4 full with raw alcohol with a concentration of no more than 45%.

Completely block the distillate selection with its selection regulator.

Check the correct assembly and tightness of the pipe system.

Connect the inlet and outlet of cooling water to the water supply network and make sure that the series connection of the heat exchanger of the discharged condensate and the condenser itself are correctly connected in order to operate in counter-flow mode of the coolant.

* The complete time to prepare the installation for operation takes from 5 to 20 minutes, depending on work skills, the need to refill the evaporation tank, clean it, the duration of connection to the water supply network, etc.

Connect the stand to a 220 V network and turn on the power supply.

Connect the automated stand toUSBcomputer connector and run the program Start → Programs →MeasLAB→ “Rectification” (Figure 5). For a more detailed introduction to working with software, open the description of the “Software Operation Guide”.

Turn on VK 1 heater operation switch to the starting mode of 1 kW.

After stabilizing the readings of the measuring instruments, launch the computer system for automatic measurement (Figure 5) of process parameters and turn on the heating of the evaporation tank, and according to the readings of the instruments, monitor changes in the temperature of the liquid and vapor-gas environment.

Figure 5 – Appearance"Rectification" program

Monitor the consistent flow of steam generated in the evaporation tank into the distillation column and condenser; the beginning of vapor condensation and distillate formation. Record the boiling point of the solution, the temperature and pressure of the vapor-gas medium in the evaporation tank, total quantity energy spent on heating the liquid, installation design and heat loss in environment and enter the obtained data into table 1.

Fully open the distillate selection regulator and count the number of drops entering the alcohol receiver in 20 seconds.

Set the reflux ratio to at least 4, setting the distillate selection regulator to a 5-fold reduced number of drops for the same time.

When steam and reflux of low-boiling components of the bottom liquid accumulate in the upper part of the column, a slow and consistent selection of these substances into the receiving tank is organized using a manually controlled distillate selection regulator, followed by their identification using computer records of the temperature of the vapor entering the condenser and taking into account the actual atmospheric pressure.

After the release of low-boiling components, the longest period of work begins on the rectification of ethyl alcohol itself, which is carried out at a reflux ratio of at least 3 and replacing the receiving container with a new one. In this case, it is important to prevent the column from flooding, the onset of which can be determined by the appearance of characteristic pulsations in the recording of the pressure drop in the column and the appearance of “gurgling” sounds during operation of the installation. The distillate selection is set correctly if, 5-15 minutes after stopping the selection, the vapor temperature in the upper part of the column has not decreased.

At the stage of obtaining the main product, measure traditional ways using a portable thermometer, a measuring container and a computer stopwatch and enter into the table the values ​​of slowly changing distillation parameters:

flow rate of water cooling the heat exchanger and reflux condenser;

temperature of water entering the heat exchanger;

water temperature at the outlet of the heat exchanger;

temperature of water entering the reflux condenser;

temperature of water leaving the reflux condenser.

Complete the selection of food alcohol when the temperature of its vapor exceeds 0.1 above 78.3 °C.

Selection of tail fractions of impurities contained in the feedstock. This does not imply changing the column settings, but only replacing the receiving tank. The selection of tail fractions is completed when the steam temperature in the condenser reaches about 82-85 °C.

After finishing work, turn off the heater of the evaporation tank (button BK1). After the column has cooled, stop supplying water to the condenser and heat exchanger. Switch off the measurement system and digital measuring instruments on front panel installations.

Disconnect the unit from the electrical network.

After draining the bottom residue and cleaning the evaporation tank, return the installation to its original state.

Process the received data and enter its results in Table 1.

Determine the number of theoretical plates of the distillation column and compare the total height of 3 drawers with the result obtained.

Answer control questions and draw independent conclusions about the work performed.

Slowly changing process parameters

Flow rate of water cooling the heat exchanger and reflux condenser ___ l/s

Temperature of water entering the heat exchanger ___ 0 WITH

Water temperature at the heat exchanger outlet ___ 0 WITH

Temperature of water entering the reflux condenser ___ 0 WITH

Water temperature at the outlet of the reflux condenser ___ 0 WITH

Table 1. Results of measurements and calculations.

Name of parameters and units of measurement

Current values ​​of monitored parameters

Average value

1. Heating the feedstock to boiling point

Heating time until liquid begins to boil, min

Temperature of the initial mixture after heating, 0 C,

Temperature of steam and reflux in the condenser, kPa

2. Initial period of rectification. Selection of head fractions

Pressure of the vapor-gas mixture at the inlet of the column, kPa

Electric Energy, released by the heater, number of counter pulses

3. The main period of rectification of ethyl alcohol

Evaporation time of low-boiling fractions, min

Liquid boiling point, °C

Temperature of steam and reflux in the column, kPa

Steam temperature in the condenser, kPa

Pressure of the vapor-gas mixture at the inlet of the column, kPa

Pressure of the distillate column in a hydrostatic density meter, kPa

Consumption of sampled distillate, number of drops per 20 seconds

Electrical energy released by the heater, number of counter pulses

4. The final period of rectification. Selection of tailing fractions

Evaporation time of low-boiling fractions, min

Liquid boiling point, °C

Temperature of steam and reflux in the column, kPa

Steam temperature in the condenser, kPa

Pressure of the vapor-gas mixture at the inlet of the column, kPa

Pressure of the distillate column in a hydrostatic density meter, kPa

Consumption of sampled distillate, number of drops per 20 seconds

Electrical energy released by the heater, number of counter pulses

Bottoms concentration X w , %

Distillate concentration X w, %

Processing of experimental data

For the average values ​​of the parameters of the main stage of rectification, the molar concentrations of alcohol in the initial mixture X are calculated by volume F and distillate X p . Recalculate the consumption of the original mixtureFand distillate R in moles. From the material balance equations of the column, the flow rate and concentration of the bottom residue are found using the equations

W= F – P, X w =(FX F – PX p )/ W,

Where F, P, W-consumption of the initial mixture, distillate, bottoms, kmol/s;

X f . X p . X w -compositions of the initial mixture, distillate, bottoms, mol. shares.

Determine the reflux ratioR– ratio of reflux flow to distillate flow and calculate the amount of steamG, climbing the column. Knowing the magnitudeGand column diameter (D at = 20 mm), determine the steam velocity in the free section of the column w. The steam velocity in the column can also be calculated by determining the amount of steam from the equation heat balance reflux condenser (this calculation can be used as a test calculation).

Based on reference data, an equilibrium curve is drawn on graph paper.y= f(x) on y-x diagram(Figure 5) and mark on the x-axis the concentration values ​​of the initial mixture X

f– the ratio of the consumption of the initial mixture to the consumption of the distillate.

Calculate the segment , which is cut off by the working line of the top of the column on the ordinate axis (Figure 6). Through point A (x p = y p ) and the resulting segment draw the working line of the upper part of the column. Through point D (x w= y w ) and point C draw the working line of the bottom of the column. Between the equilibrium and operating lines, steps of concentration changes are constructed (Figure 6). Each stage corresponds to one theoretical plate. Having determined the number of theoretical stepsn T , and, knowing the number of real plates in the columnn, find the average efficiency of the plate using the equation

The efficiency of the plate depends on the hydrodynamic conditions and physical and chemical properties steam and liquid.

When the column operates on its own, the distillate is not selected, i.e. reflux ratio is infinity . In this case, the working line of the column coincides with the diagonal.

Control questions

What process of separating substances is called rectification? What differences are used? physical properties separated substances?

Which mixtures are called azeotropic or continuous boiling mixtures? Why can't they be separated using rectification?

Why does the standard set the concentration of rectified alcohol equal to %. What additional requirements apply to this product?

How is a distillation column constructed? What devices are used in it as elements to increase the contact interaction of the phases moving in the column?

What causes flooding of the distillation column? How can it be detected and prevented?

How does a distillation column work when the reflux ratio is zero? How does the degree of purification and concentration of the resulting ethyl alcohol change?

Which of the substances contained in alcohol-containing raw materials are considered low- or low-boiling: aldehydes, acetones, heavy alcohols, methyl alcohol, fusel oils? Which of them are distilled immediately after the release of rectified alcohol?

Why does the selection of food alcohol end when its vapor temperature reaches 0.1 higher and not lower than 78.3 ° C?

Literature

Bogdanov Yu.P., Zotov V.N., Koloskov S.P. etc. Handbook on alcohol production. Equipment, means of mechanization and automation. - M: Light and food industry, 1983, 343 p.

Devyatykh G.G., Elliev Yu.E. Introduction to Theory deep cleaning substances. – M. Nauka, 1981. – 320 p.

We offer laboratory distillation columns made of glass or stainless steel (mixed designs are possible). Glass distillation columns are assembled on the basis of German borosilicate glass LENZ (the glass catalog can be downloaded from our website - see the CATALOGS section). We offer ready-made solutions, which can be modified taking into account the wishes of the customer.

In the distillation column, constant mass and heat exchange occurs between rising vapors and descending condensate. Due to such contact, it is possible to obtain a product of high purity, free from impurities. Laboratory distillation columns, as a rule, are assembled on the basis of borosilicate glass (up to 10 l). Semi-industrial distillation columns are made of stainless steel and special alloys.

Laboratory distillation columns have a spherical evaporation tank (cube) from 1 liter to 10 liters. The length of the column itself is limited by the height of the ceiling; it can consist of several sections and have product selection from several plates. The column has a mirror vacuum jacket, which provides thermal insulation of the contents. By default, bulk type columns are offered, laboratory columns disc type are rarely supplied due to more high cost and less efficiency.

For attachment we offer Raschig glass rings or spiral-prismatic steel attachment. Metal nozzle more effective due to the large contact surface, but if it is necessary to exclude contact of the product with metal, Raschig glass rings are used.

The reflux flow is controlled manually; in this case, the user adjusts the degree of opening of the reflux outlet valve so that it chokes and part of the reflux is returned to the column. When a column is equipped with a reflux modeler with a pneumatic or electric valve, the operation of the column can be set via a controller. In this case, the operator just needs to set the reflux ratio, and the controller will open/close the valve at the right time.

The distillation column can be installed on the chemical reactor in front of the condenser. In this case, it is possible to immediately synthesize and distill off the solvent (or product) with purification.