JPH09271601A - Refluxing method of rectifying column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply, certainly and rapidly regulate the reflux ratio essential to a rectifying apparatus by an external signal. SOLUTION: A reflux ratio regulating mechanism is constituted by connecting a primary reflux device 11 and a secondary reflux device 18 up and down in series. The primary reflux device 11 is operated in a predetermined reflux ratio and a primary reflux soln. 8 is sent to a column and the remainder is sent to the secondary reflux device 18 to set the reflux ratio designated for the secondary reflux device 18 by the signal from the outside. The obtained secondary reflux soln. 24 is refluxed to the column in combination with the primary reflux device 8 and the remainder is obtained as a distillate 9. By this method, an average reflux ratio with a one cycle time is set to a predetermined value. The reflux ratio regulating mechanism can be operated by natural flow-down based on a slight head under a small amt. of a residence soln. and the cost of the whole apparatus becomes inexpensive with respect to capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the operation of a reflux ratio in a rectification apparatus which is frequently used in the field of chemical industry. The rectification device can be applied to both continuous type and batch type.

[0002]

2. Description of the Related Art A rectification apparatus is one of the unit operations in chemical engineering for the purpose of separating a mixture containing two or more components by distillation using a difference in boiling points to separate into fractions having a predetermined composition. . One of the factors that has a decisive influence on the separation performance is the theoretical plate number N provided in the rectification column main body, and the other is the reflux ratio R provided by the reflux ratio adjusting mechanism. N and R are both dimensionless numbers. The N value is determined at the planning and designing stage of the rectification column and remains unchanged after the completion of the equipment, while the R value depends on the composition of the stock solution supplied during operation and the specifications for its separation requirements. It is necessary to make adjustments and changes accordingly. For this purpose, the rectification device needs means for adjusting the reflux ratio in each case quickly and reliably as required.

FIG. 2 is an example of a flow sheet for explaining the role of the reflux ratio controller in the rectification device. In the figure, a condenser 5 and a reflux ratio adjusting mechanism 7 are provided on the upper part of the rectification tower / tower body 1, and piping lines 4, 6, 8 and 9 connecting these are shown. A packing layer 10 is provided in the interior of 1 for gas-liquid contact, and a reflux liquid distributor 3 provided in the column section 2 faces the packing layer 10 to direct the reflux liquid sent through a reflux liquid line 8. Evenly spread and descend while wetting 10 surfaces. On the other hand, steam rises between 10 and below,
Gas-liquid contact occurs through 10 surfaces at each point. Due to the countercurrent contact between the falling liquid and the ascending vapor, the light boiling components are driven up to the top 2 of the column 1 and discharged from the column steam line 4, while the falling liquid is the bottom of the 1. And reach the end of the system. The above is an example when a packed tower is used for 1. At this time, it is a matter of mixing components that the falling liquid is uniformly wetted on the surface of the packing material and the rising vapor is evenly contacted with the falling liquid. This is an essential condition for enhancing the retention effect.

As the internal structure of 1, there is a type called a tray tower in addition to a packed tower. This is because a plurality of trays are stacked in a tower, a liquid having a certain liquid depth is retained in each stage, and a vapor-liquid contact effect is generated when vapor rising in the liquid rises in the form of bubbles. The type is generally widely used.

In FIG. 2, as an indispensable element constituting the rectification column, in addition to 1, the condenser 5 for condensing and liquefying the distillate vapor passed through 2 and 4 and the liquid from the condensate line 6 are divided into two. A reflux ratio adjusting mechanism 7 is displayed for refluxing one through the reflux liquid 8 line to the reflux liquid distributor 3 inside 1 and recovering the other through the distillate liquid line 9. In FIG. 2, the positions of 5 and 7 are sufficiently higher than those of 3, and due to the drop,
The liquor of 8 is less than 8
A mechanism for naturally flowing down inside the is depicted. Depending on the mutual arrangement of 7 and 3, or due to the structure of 7 and 3, there is often a shortage of the head, and in this case, it is necessary to appropriately provide a liquid feed pump to secure the flow rate.

The present invention relates to 7 and can be applied to all rectification towers. Particularly, as shown in FIG. 2, a packed tower is used for 1 and reflux is carried out by gravity flow under a relatively low head. Its main purpose is to perform the remote control of the reflux ratio over a wide range, accurately and promptly by an external instruction.

The advantage of the packed column over the tray column is that the pressure loss of the vapor phase per theoretical stage of the column is small. This has the advantage that the column bottom temperature can be kept even lower when the high boiling point mixture is fractionally distilled under reduced pressure, which cannot be achieved in a tray column. Another feature of the packed column is that the amount of liquid retained per theoretical stage in the column is significantly smaller than in the tray column. According to the present invention, the amount of stagnant liquid existing in the pipes connecting them 5, 7 and 3 can be reduced accordingly. This property is particularly advantageous when used in a batch type rectification column to perform a high degree of separation between components. This is used in the field of so-called fine chemicals, including high-performance rectification towers in laboratories, such as pharmaceuticals, agrochemicals,
It is widely used and an important unit operation in the manufacturing process of fragrances and electronic materials.

As described above, the packed tower is superior to the tray tower in that the pressure loss per theoretical plate and the amount of retained liquid are low, but on the other hand, the surface of the packing is not uniformly wet. It means that it is easy to become. In order to prevent this, the reflux liquid irrigated from the reflux liquid distributor 3 to the upper end of the packed bed must be evenly distributed over the entire surface thereof. This uniformity is
It is necessary that the irrigation volume at each point in the tower be constant over time, and there should be no large fluctuations. If spatial,
When such unevenness of liquid wetting occurs on the surface of the packing material at each point in time, the gas-liquid contact effect is diminished, and the fractional distillation performance is greatly reduced.

[0009]

Various methods have been conventionally used for the reflux ratio adjusting mechanism essential for the operation of the rectification column. Many of these use a ratio control system of the flow rate by a complicated instrumentation method, so that a considerable amount of pressure loss is required for the flow of liquid, and the differential pressure for returning the reflux liquid to the column is further increased. If it is included, a liquid feed pump and piping are required. If these are included, the reflux device tends to be complicated and expensive, and the operator also needs a high degree of knowledge and attention. On the other hand, a reflux ratio adjusting mechanism 7 which enables the arrangement and piping of a low free fall type as shown in FIG. 2 and which is particularly suitable for a packed column has not been previously disclosed. The present invention is as follows when the problems and conditions to be solved by the present invention are listed.

Even if the state of the liquid to be discharged (liquid amount, temperature, physical properties, etc.) changes from 6 in FIG. 2, the flow rate ratios of 8 and 9 are always as specified by the reflux ratio and R specified from the outside. Be able to maintain. Incidentally, the reflux ratio R is defined as (flow rate of 8) / (flow rate of 9) as in the usual method.

The amount of retained liquid existing inside 7 and in lines 6 and 8 is small. In addition, the pressure loss during that period is small, and the reflux is carried out in the normal flow due to the normal head, and no pump or the like is required.

The reflux ratio of 7 is in a wide range (for example, R =
0.5 to 200) and it can be set and changed accurately and instantly by transmitting an electric signal from the outside to an arbitrary value.

The system must be able to operate under atmospheric pressure / reduced pressure / pressurization and under general temperature. In some cases, the structure should be such that moisturization by heating 7 and 6, 8 and 9 is easy to prevent the condensate from coagulating. Also, it is possible to easily procure the material that matches the processing liquid.

For each given R value, the ratio of the average liquid volume distributed in 8 and 9 within one cycle time must be able to correspond exactly. However, there is no limit to the flow rate fluctuation of 9 during one cycle, but for 8 the lower limit of the temporal fluctuation of the flow rate must be set to a value that is determined by the wetting of the filler.

As a matter of course, 7 and its peripheral accessories,
Installation costs such as piping and instrumentation costs are low.

[0016]

Next, the principle of the present invention and its means will be described with reference to FIGS.

FIG. 1 shows the internal arrangement of 7, in which a primary reflux device (body 11) and a secondary reflux device (body 18) are connected in series in the vertical direction. First, the condensate line 6
It penetrates through the center of the upper lid of 11 and enters the inside vertically, and its tip is connected to a closed liquid reservoir 12. A plurality of liquid ejection holes 13 are provided around the lower portion of 12 at appropriate intervals. The condensate that has flowed into 6 is ejected to the periphery from each 13 that is opened in the side wall of 12 as shown in the figure, but the total liquid amount L [kmol / h] is 13 holes diameter, 6 holes and 6 holes. It is determined by the drop H [m] between the liquid surface of 13 and 13. Since the relationship between the liquid flow rates L and H is shown by a known calculation formula, first, the standard value of the vapor flow rate V [kmol / h] in the column and the expected fluctuation range ΔV are set, and L is adjusted to V. Seeking
Next, the procedure is to determine H [m] to be adopted while taking the arrangements of 6, 7 and 3 into consideration, and calculate and determine the diameter and number of 13 according to this. The partition plate 15 is installed so as to divide the bottom part of 11 into two parts, and the top end thereof is in close contact (not welded) with the bottom part of 12. The liquid collects in any of the sections at the bottom depending on the injection direction of each 13, and one flows from the primary reflux liquid outlet 16 to 8 and the other flows down to the secondary reflux device via the primary distillate outlet 17. As described above, the condensate passing through 6 has a liquid amount L [kmol /
Corresponding to [h], a liquid surface H having a constant height is formed inside 6 to be in dynamic equilibrium, and due to the liquid pressure, a total amount L of liquid amount is jetted dispersedly. The distribution of this liquid amount L to both areas according to the primary reflux ratio R1 is determined by the hole diameter of each of the 13 holes, the number of holes, and their arrangement, but after the determination, V, L, or H, fluctuates. Also R1 itself is kept constant according to the initial decision value. Usually, 12 and 6 are joined by screwing etc., so if R1 needs to be changed, it can be easily converted to another 12 corresponding to it.

Next, the operation principle and means inside the secondary recirculation device 18 will be described with reference to FIG. 1 and FIGS. 3 and 4.
A liquid distribution funnel 19 is installed at the center of the inside of 18, and a rotary shaft 20 fixed to the funnel 19 extends horizontally to the left and right and penetrates through the bearing seal of the body of 18 and projects to the outside. Although 19 can perform a pendulum-like swinging motion to the left and right around 20, the center position coincides with the center line of the partition plate 21. The liquid discharged from 17 passes through the first distillate line 14, penetrates the upper lid of 18 and flows into the inside of 19 from above, and flows out from the funnel liquid outlet 25 as it is.
At that time, the following flow selection is made toward one of the two sections dividing the bottom of 18 by the inclined position of 19 and the partition plate 21 provided at the bottom. As shown in FIG. 1, FIG. 3, and FIG. 4, the stop position of 19 is that the axis of 20 is rotated ± 10 ° to ± 15 ° to the left and right by an external mechanism (not shown) at regular intervals. , Or when the whole amount of liquid advances to the right chamber due to the inclination of 19 as shown by the solid line in FIG. 3 and flows to the distillate line 9 from the secondary distillate outlet 22, or at the inclination of 19 as shown by the broken line Proceed to the room and from the second reflux liquid outlet 23, the same line
It flows down to 24, is combined with the primary reflux liquid flowing down through 16 and 8, and is refluxed to the tower. More than 7
The structure and operation of each of the two-stage reflux condensers constituting the above are described with reference to FIGS. 1, 3, and 4. At this time, the amount of liquid retained inside includes 12 and the internal liquid column of 6 pouring into it,
It is slightly seen from the pipe diameter. Others are only adherent liquids that wet the surfaces of vessel walls and other parts. Further, since the length of the pipe of 8 can be shortened by the entire arrangement, the amount of the retained liquid existing in the whole 6, 7, 8 can be greatly reduced.

As described above, in the secondary reflux device, 17
The inflowing primary distillate can be directed to the total distillate or the reflux liquid by giving the position of 19 to 20 from the outside at a rotation angle of 2 degrees. Such a swinging and rotating operation of the head 20 can be easily carried out by using an electromagnetic driving force or a commercially available servo mechanism such as a pneumatic cylinder. In addition, it is possible to easily carry out such a swinging operation at an arbitrarily set cycle by using various commercially available electric timers.

As the liquid distribution system for time-dividing one cycle in the secondary recirculation device, many systems other than the above-mentioned operation example 19 can be considered, but the point is that the secondary recirculation set by an external signal. R2 value of the ratio can be quickly responded and the line
Liquid flowing in from 17 is distributed on and off in a fixed cycle to line 24 and line 9 in a time-divided manner and reciprocally distributed.
Any type may be used as long as the value of R2 preset as the average value within the cycle time can be accurately realized.

[0021]

As described above, the first aspect of the present invention
The secondary and secondary reflux devices themselves have a known structure. However, it will be described below how they function and exhibit excellent effects by combining these as a series two-stage reflux ratio adjusting mechanism configured as described above. First, the vapor amount V [kmol / h] rising in the tower keeps an almost constant value and flows from 4 to 5 where it is condensed and liquefied to form a liquid amount L [kmol / h].
As shown in FIG.
It is assumed that there is a relationship of L. However, this is not a requirement of the invention, and 6 may be a partial condensation type. First
When the secondary reflux ratio is fixed to R1 and set, the primary reflux liquid amount constantly flowing from 6 to 8 and the primary distillate liquid amount to 17 are as follows. Amount of primary reflux liquid = L (R1 / (R1 + 1)) ··· (1) Amount of primary distillate liquid = L / (R1 + 1) ··· (2) Primary from 14 When the secondary reflux ratio is R2, the distillate is divided as follows as a time average amount in one cycle. Secondary reflux liquid volume = (L / (R1 + 1)) (R2 / (R2 + 1)) ... (3) Secondary distillate volume = (L / (R1 + 1)) / (R2 + 1) ...・ (4) Therefore, the primary and secondary are combined, and the total amount of reflux liquid = L (R1 × R2 ＋ R1 ＋ R2) / ((R1 ＋ 1) (R2 ＋ 1)) ・ ・ ・ ・ (5) If the time-averaged reflux ratio in one cycle combining the secondary is RR, from (5) and (4), RR = (total reflux liquid amount) / (secondary distillate amount) = (R1 + 1) x R2 + R1 ... (6)

That is, the total average reflux ratio RR within the time is, when the primary reflux ratio R1 is initially set as a parameter,
As shown in equation (6), it can be displayed as a primary equation with the secondary reflux ratio R2 as a variable. This means that when implementing the present invention, an instrumentation system with a sequence controller having a simple arithmetic expression can be used. When R1 and R2 are determined, RR is calculated by the equation (6), while the upper limit value RMAX and the lower limit value RMIN of the instantaneous reflux ratio in the cycle are
It is calculated as follows from the equations (1) and (2). Maximum instantaneous reflux liquid amount = L, RMAX = L / 0 = infinity, that is, total reflux ... (7) Minimum instantaneous reflux liquid amount = L (R1 / (R1 + 1)), RMIN = (R1 / (R1 + 1)) / (1 / (R1 + 1)) = R1 ··· (8) Therefore, the fluctuation range of the reflux liquid amount and the reflux ratio in one cycle is the fluctuation range of the reflux liquid amount = L / (R1 + 1), of the corresponding reflux ratio. Variation range = 1 / (R1 + 1) (9) By using equations (6) to (8) in this way, wetting of the filling material is ensured along with the RR necessary for the prescribed component separation. Therefore, if the minimum amount of reflux liquid required is known, RMIN can be found from equation (8), and the corresponding R1 can be set.

The operation of the two-stage in-line reflux mechanism of the present invention has been described above, and the method for determining the reflux ratios R1 and R2 of each stage has also been described. When this method is compared with the normal one-step method, the effect is clear. First of all, the fixed reflux ratio corresponding to R1 specified in advance will be selected only for the first stage reflux device,
It cannot be operated outside this, which is out of the question. Next, the use of only the second-stage reflux condenser is nothing but the method widely used in the past for experimental or small-scale equipment. However, this means that the total reflux and total distillation are repeatedly performed by the on / off signal from the timer during one cycle where the time is set, and the reflux liquid amount follows this, so The irrigation volume fluctuates greatly, uniform gas-liquid contact cannot be expected, and the separation performance deteriorates. In particular, in the region where the reflux ratio is low, for example, R = 0.5 or less, the reflux interruption time increases and the separation performance deteriorates significantly. In a normal on / off one-stage reflux ratio control system, in order to smooth the fluctuation of the reflux liquid amount and bring it close to a constant average value, a device such as providing a liquid reservoir in the middle of 8 has been devised. , And the like, since the retention amount of the reflux liquid increases and the separation performance decreases (in the case of a batch system),
The effect of the present invention cannot be obtained.

[0024]

[Example] The tower body 1 is composed of a packed tower, and the instantaneous lower limit of the reflux liquid amount is used to secure the wetting of the surface of the packed material and prevent the deterioration of gas-liquid contact efficiency. Judge from the table and set to L / 2. If this condition is entered in equation (8), R1 = 1
Becomes Substituting R1 = 1 into equation (6) gives RR = 2 × R2 + 1. At this time, if the value of RR required for separation is given, R2 is uniquely determined correspondingly. Required RR
To make the values 1, 2, 3, 5, 10 R2 is 0,0.
It should be 5, 1.0, 2.0, 4.5. At this time, it is impossible to suppress the RR to a low value of 1 or less, but in a normal rectification column, even if such a low RR value is calculated to be optimal, it is set to 1 and operated. do it. Even if there is a slight decrease in the processing capacity, the separation performance is improved on the contrary, so there is practically no problem. When the reflux mechanism of the present invention is applied to the actual design of a rectification column, according to the common sense of general chemical engineering, the ascending vapor amount V and the descending liquid amount L in the column consider the balance between N and R, Select a range such as RR ≧ 2, V ≒ L,
From an economic perspective, it is wise to prevent both N and RR from increasing extremely. In this case, the application of equation (4) is R1 = 1
It is expected that R2 ≧ 0.5 before and after, and the liquid-gas ratio (L / V) at the upper end of the packing in the column will be 1.0 and 1/2 at the maximum from equations (7) and (8). Even at the lowest value, the separation performance does not deteriorate due to insufficient wetting of ordinary packing materials. In addition, such a variation width of L / V usually occurs during one cycle time of 10 seconds to 60 seconds, and as the liquid descends in the packed bed, the flow rate is further smoothed, so that the column Considering the whole area of, the effect of the fluctuation of the falling liquid L in the column due to the on / off fluctuation of R2 can be neglected.

[0025]

The present invention is constructed with the contents described above, and the effects described below can be expected.

In the paragraph number "0009", six items of problems to be solved are listed from "0010" to "0015", but from "0016" to "002".
As described in "3", the present invention can generally satisfy these requirements.

The present invention can be applied regardless of whether the rectification column is a continuous type or a batch type. Further, it can be applied regardless of whether the structure of the tower body is a packed tower or a tray tower.
As shown in FIG. 2, it is particularly advantageous to connect the condenser 5 to the top 2
In this case, the reflux ratio adjusting mechanism 7 of the present invention is installed in the upper part of the column, and the reflux liquid is allowed to flow down to the column by a drop without using a pump or the like.

The operation of 7 can be controlled completely unattended by a fixed signal of R1 and a remote signal of R2 from an electric timer or the like. As a mode for carrying out the invention, as shown in the figure, a small and light pendulum type funnel 19 is provided in the inside of 7 only to perform a periodic swinging motion once every few seconds or tens of seconds. , A structure without any other moving parts is possible. This shows the durability and ease of maintenance of the device.

[Brief description of drawings]

FIG. 1 is an arrangement sectional view showing an example of a reflux ratio adjusting mechanism showing an embodiment of the present invention.

FIG. 2 is a flow sheet showing one embodiment of use of a reflux ratio adjusting mechanism in a general rectification column.

FIG. 3 is a vertical cross-sectional view showing the operation of the secondary reflux ratio in FIG.

FIG. 4 is a plan view of the AA cross section of FIG. 3 seen from above.

[Explanation of symbols]

 1 Fractionation tower / column 14 Primary distillate line 2 Tower top 15 Partition plate 3 Reflux liquid distributor 16 Primary reflux liquid outlet 4 Top vapor line 17 Primary distillate outlet 5 Condenser 18 Secondary reflux body 6 Condensate line 19 Liquid distribution funnel 7 Reflux ratio adjusting mechanism 20 Center of rotation axis 8 Reflux liquid line 21 Partition plate 9 Distillate line 22 Secondary distillate outlet 10 Packing layer 23 No. Secondary reflux liquid outlet 11 Primary reflux tank body 24 Secondary reflux liquid line 12 Liquid reservoir 25 Funnel liquid outlet 13 Liquid ejection hole

Claims (1)

[Claims] 1. A liquefied vapor from a rectification column is liquefied by a condenser, and is then distributed into a reflux liquid and a distillate according to a predetermined flow rate ratio, and the former is refluxed to a distillation column to give a predetermined component. In obtaining a distillate having a composition, a reflux ratio adjusting mechanism is configured by connecting a primary reflux device and a secondary reflux device in series,
In the primary reflux device, the total amount of liquid from the condenser is fixed and divided into two parts in a predetermined ratio, one is sent to the column as the primary reflux liquid, and the rest is sent to the secondary reflux device. A liquid is divided into two by a time division type distribution system under a predetermined ratio by a signal given from the outside, one is sent to the column as a secondary reflux liquid, and the rest is recovered as a distillate outside the system. A method for refluxing a rectification device.