Contents
The heart of each RC is a drawer with a packing, and it is its capabilities that largely determine the performance of the column as a whole. For analysis, we agree that, as it should be during rectification, the tsarga has a height of the nozzle part of 150 cm and SPN 3,5 x 3,5 x 0,25 mm is filled into it, and the cube is filled by three quarters with 40% raw alcohol.
Theory
A 35-inch column can have sides with an inside diameter of 38 or 2 mm, and a 48-inch column can have 50 or 20 mm. The standard for today set of possible cubes: 30, 37, 50 and XNUMX liters.
The maximum separating capacity of the column is achieved at the pre-choke capacity, and it also provides the maximum selection rate at a given reflux ratio. Many novice distillers do not quite rightly equate pre-choke capacity with the performance of the column. In fact, rectification includes several stages, each of which takes time.
When choosing the column diameter and cube volume, it is important to understand how their combination will affect the labor intensity of the process and the amount of time spent on rectification.
Stages of rectification
1. Preparation of equipment for work. Assembly of equipment, pouring raw alcohol into a cube and other preparatory operations. Usually everything takes about 0,5 hours, T1 = 0,5.
2. Heating to a boil. If the heating element is chosen correctly, based on the ratio of 1 kW of power to 10 liters of bulk, then heating will take approximately 40 minutes or T2 = 0,7 hours.
3. Stabilization. This step takes 30 minutes to 1 hour. Let it be 45 minutes or T3 = 0,75 hours.
4. Selection of the head fraction. The time of selection of “heads” (T4) does not depend on the speed of selection. To remove all head impurities from the cube, it is necessary that each liter of the bulk evaporates at least once and visits the column. This requires applying 1 kW of heating power for each liter of absolute alcohol in the cube.
The operating power in Watts is numerically equal to the cross-sectional area of the column (S) in square millimeters.
The amount of absolute alcohol (AS) is determined based on the bulk volume (SS) and its strength.
T4 = AC / N (hours), where:
AC = 0,4 * CC (liter);
N = 3,14 * d2 / 4 / 1000 (kW);
d is the inner diameter of the column (mm).
From here we get:
Т4 = 510 * CC / d2 (hours), where:
SS – 40% bulk in liters,
d is the inner diameter of the column (mm2).
5. Selection of head restraints. This stage is necessary to clean the nozzle from the remnants of the head fraction. The number of head restraints depends on the holding capacity and volume of the nozzle. The holding capacity of SPN 3,5 x 3,5 x 0,25 is approximately equal to 150 ml of phlegm per 1 liter of nozzle. To wash it with high quality, you need to select 2-3 volumes, for calculations we will take – 2,5.
To select this volume at a rate of 0,5 l / h, it takes 2 hours. If you raise the speed to half the nominal, then 1,2 hours will be enough, regardless of the diameter of the side.
Too low a speed reduces the cleaning efficiency and the quality of the alcohol. But this is not about that now, for today’s task we will take the maximum selection time: T5 = 2 hours.
Sampling volume in liters:
Votb = 2,5 * 0,15 * Vn = 0,375 Vn, where:
Vn is the volume of the nozzle in liters.
If the withdrawal rate is taken equal to 0,5 l/h, then the withdrawal time is:
T5 = 0,75 * Vn.
If the withdrawal rate is equal to half the nominal rate, then considering that the nominal withdrawal rate Wnom in ml/h is numerically equal to the cross-sectional area of the column in mm2, head restraint selection time:
Т5 = (0,375 * Vн) / (0,5 * S) = 0,75 * Vн / S = 0,75 * L *S / S
T5 = 0,75 * L (hour), where:
L is the height of the column in meters.
When the head restraint removal rate is equal to half of the nominal one, the extraction time in hours is numerically equal to ¾ of the column height in meters, and does not depend on the column diameter or bulk volume.
6. Selection of commercial alcohol. The initial withdrawal rate in ml/h is numerically equal to the cross-sectional area of the column (S) in mm. By the end of the selection, to increase the phlegm number and increase the separating ability, we reduce the selection rate by 2.5 times. The average rate of selection of the “body” will be approximately one and a half times lower than the nominal one.
The volume of commercial alcohol is approximately 80% of the AS in bulk.
Hence the time of selection of the “body”:
Т6 = 0,8 * 0,4 *CC / (S / (1000 * 1,5)) = 480 * CC / S;
Т6 = 611 * CC / d2, where:
SS is the amount of 40% raw alcohol (l);
d – drawer diameter (mm).
7. Selection of “tails”. The number of “tails” is approximately equal to 10% of the volume of the AC in the cube. The extraction rate is approximately equal to half of the nominal.
Т7 = 0,1 * 0,4 * CC / (S / (1000 * 2)) = 80 * CC / S;
Т7 = 102 * CC / d2.
8. Displacement of impurities from the column. This operation takes half an hour, T8 = 0,5.
9. Dismantling of equipment and cleaning of the premises. The least enjoyable stage, usually takes up to 1 hour, T9 = 1.
Total rectification time
Total time required for one rectification cycle:
T u1d T2 + T3 + T4 + T5 + T6 + T7 + T8 + T9 + TXNUMX;
0,5 + 0,7 + 0,75 + 510 * CC / d2 + 2 + 611 * CC / d2 + 102 * CC / d2 + 0,5 + 1.
Simplify and get:
T = 5,45 + 1223 SS / d2.
The volume of alcohol (Vc) obtained during this time is approximately equal to 0,8 of the AC in the cube, we will neglect the losses for irreparable “heads” and the remainder in the cube.
Vt = 0,8 * 0,4 * CC.
The productivity with which we can get alcohol per hour of work with the column can be calculated by the formula:
Pr uXNUMXd Vc / T.
Practical aspects of rectification
On the basis of the obtained model, we will try to answer the exciting questions.
1. The actual performance of the column, depending on its diameter and bulk volume (l/h).
The starting rate of “body” selection is much higher than the actual performance of the column. To think that with a nominal capacity of 2 ml/hour of a 1800-inch column, the distillation of 40 liters of raw alcohol with a strength of 40% can be completed in 9 hours is simply naive.
Taking into account all the necessary operations, the real performance will be almost 3 times less. The performance difference between 35 mm and 48 mm columns is not actually 800 ml/h, as it seems at first glance, but only 250 ml/h. And this is a lot, since the process takes more than one hour.
2. Working cycle time (hours).
The graph shows the effect of still volumes (X-axis) on the total rectification time (Y-axis) for different column diameters. The bulk is standard – three quarters of the volume of the cube. The unreasonableness of some configuration options becomes obvious. In order to assess how convenient it will be to use one or another option, consider the duration of the main operations.
3. Key work points requiring operator intervention.
3.1. Time from the beginning of the process to the end of the selection of “heads” or the first approach to the cube for changing containers.
3.2. Next, we select the head restraints for 2 hours at a speed of half the cruising (nominal). We approach the column and change the container, proceeding to the selection of the “body”.
3.3. The selection of the body will end and you will need to go to the column to change the dishes.
3.4. The selection of “tails” will take.
3.5. Then we approach the column and complete the work, which takes 1,5 hours.
conclusions
1. The larger the pile of the cube, the higher the real productivity. But you can’t increase it indefinitely. When the temperature in the cube reaches 90-92 degrees, the fusel and other intermediate impurities begin to massively leave the cube and accumulate in the nozzle. If the bulk is too large, then after accumulation in the lower part of the column, impurities will begin to rise higher and break through into the selection. We’ll have to switch to “tails” earlier. To obtain normal performance, the bulk should be more than 10 nozzle volumes, but less than 20 – so as not to miss the “tails”.
2. The optimal bulk volume of 40% SS during rectification is 15 packing volumes.
| Column diameter, mm | Nozzle volume, l | Bulk volume, l | |
| from | to | ||
| 35 | 1,44 | 14 | 29 |
| 38 | 1,7 | 17 | 34 |
| 48 | 2,71 | 27 | 54 |
| 50 | 2,95 | 30 | 59 |
With a minimum bulk, you can switch to the selection of “tails” at a bottom temperature of 96-97 degrees, with a maximum bulk – 92-93 degrees.
3. The duration of rectification increases with a decrease in the diameter of the column and an increase in the volume of a single bulk. But the use of large diameters of columns with a small bulk entails the production of a relatively large volume of recycled alcohol and a low yield of good.
4. Without automation tools that allow equipment to be left unattended for a long time, it is possible to use kits with a relatively short cycle time. This narrows down the range of possible options and explains the fact that many distillers simply do not select “tails” on their equipment or prefer to make NDRF – the forces are not unlimited.
5. In general, if the process takes more than 12-15 hours in total, automation is mandatory. At least the simplest one with a security block that allows you to signal a flood, a water outage or an increase in temperature in the TCA. If this is not possible, you should limit yourself to the minimum volume of cubes.
6. The obtained dependencies and graphs make it possible to make a qualitative and, to some extent, a quantitative analysis of various options for completing the RC. The main thing at the same time is not to forget about the need to compare them with the time that the distiller is ready to devote to a hobby.
The author of the article is IgorGor.