JPS6222642B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the fractional distillation of near-boiling components, particularly those found in heavy water production, using an improved method and apparatus for concentrating heavy water-containing liquids by fractional distillation.
A dual temperature concentrator system for producing concentrated deuterium is described in US Pat. No. 4,008,046. Similarly, various fractional fractionation apparatus systems are well known, including the rectifier tube apparatus of US Pat. No. 2,999,795.

Generally, a stream of heavy water with a concentration of 30% by weight (all percentages below are weight%, hereinafter omitted) is 99.7% by weight.
1.052 and 90% at 54°C (130〓) if this fractionation was carried out under reduced pressure.
To improve the separation factor, which fluctuates during this time by 1.030 °C (195〓), requires over 300 equilibration steps. Usually two to four fractionation columns are used for this purpose, operating at a given low pressure with respective condensers and reboilers. Therefore, they cannot function as a series of separate sections of a fractionation column to reduce their respective operating pressures. Increasing the operating pressure in such a series of sections reduces the separation factor to such an extent that an increase in the number of backflow and equilibration stages cancels out the savings in equipment and utilities.

In the present invention, a method and apparatus for fractional distillation of closely boiling components of a multicomponent system are provided, the apparatus comprising at least two fractionation columns with multiple equilibrium stages, and comprising a downstream fractionation column. The vapor from the column is compressed and sent to the bottom of the preceding fractionation column, and the liquid bottom stream from any of the columns except the last is sufficiently expanded to carry the resulting liquid-vapor mixture into the next fractionation. It is configured to be carried to the top of the tower. This configuration eliminates both the need to pump a liquid bottoms stream to the next fractionation column as well as the need for a reboiler for the preceding fractionation column. In a particularly preferred embodiment, the compressed overhead vapor stream exchanges heat with the liquid stream extracted from the preceding fractionation column before being introduced into the lower part of the fractionation column.

In order to facilitate the explanation of the method and apparatus of the present invention, reference is made to the fractional distillation of heavy water/water system in heavy water production as shown in the figure. It should be understood that it can be applied to various multi-component systems with close boiling components such as methylpentane, n-pentane/2-methyl butane, etc. In this text, the term "proximate boiling of a multicomponent system" refers to a component system in which the difference in boiling point of each component is less than -12°C (10〓).

Next, in the drawing, two fractionating columns forming a plurality of equilibrium stages (not shown) are collectively indicated at 10 and 12. For illustrative purposes, these fractionators constitute the last two fractionators of a heavy water concentration plant that uses four fractionators to concentrate a 30% heavy water stream to a concentration of approximately 99.7%. are doing. in general,
Such a fractionation column has the same or similar temperature and pressure in both its upper and lower parts, i.e. from 40 mmHg to 400 mm in the upper part.
Temperature pressure from 37℃ (100〓) to 87℃ (190〓) in Hg, 82℃ in lower part from 400mmHg to 850mmHg
(180〓) to 104℃ (220〓) temperature and pressure operation. Later columns are operated at lower pressure levels. The fractionating column 10 is provided with a feed line 14, an overhead steam line 16, a liquid outlet line 18 and a lower steam line 20. In the fractionating column 12,
A reboiler 28 is provided having a feed line 22, an overhead steam line 24, a liquid outlet line 26 as well as an inlet line 30 and a steam line 32 for introducing reboiled vapor into the lower portion of the fractionation column 12.
Outlet line 26 is in fluid communication with the suction side of pump 34 and the pump discharge side is in fluid communication with line 36.

The lower steam line 20 of the fractionating column 10 is connected to a heat exchanger 38 and a compressor 4 having a compression ratio of 1.5 to 10.
It is in fluid communication with the overhead vapor line 24 of the fractionation column 12 through the discharge side of the column 12 . The liquid outlet line 18 is provided with a restriction orifice 42 at a height "d" from the bottom of the line 18 and in fluid communication with the feed line 22 of the fractionation column 12 via a heat exchanger 38.

During operation, a partially concentrated heavy water flow e.g. 90%
A stream containing heavy water is passed through line 14 to fractionator 1.
0 and sent into countercurrent contact with the vapor introduced by line 20 into fractionation column 10 .
The liquid bottom flow in line 18 is drawn out and passed through the squeeze orifice 42 where it is at least about 0.35 kg/cm ²
A pressure drop of (5 psi) vaporizes approximately 3% of the liquid, which is sufficient to raise the liquid-vapor mixture produced at the top of column 12, thus requiring pumping to transfer this flow. removed. To ensure the maintenance of the vapor portion of such liquid-vapor mixture, the liquid-vapor mixture is passed through a heat exchanger 38 and compressor 40.
heat exchange with the superheated steam stream in line 24 after compression.

Orifice 42 is located at a height "d" of at least 1.5 meters (5 feet) from the bottom of outlet line 18 and is sized to be self-venting. The liquid level is automatically maintained in line 18. Thus, as the liquid level in line 18 falls below the level of orifice 42, some of the liquid is evaporated before reaching orifice 42, thereby restricting the flow through orifice 42. Accordingly, a liquid level is automatically maintained in the effluent line 18 of the fractionation column 10 to meet the designed pressure drop requirements of the system. The liquid bottom stream from the fractionating column 10 is transferred to the fractionating column 1.
2, the height of the fractionator 10 is reduced, which eliminates liquid wave requirements at the bottom of the fractionator 10 with savings in heavy water inventory.

A stream of vapor liquid containing 98% heavy water in line 22 is sent to fractionation column 12 in countercurrent contact with reboiling vapor in line 32, and the resulting concentrated heavy water product (99.7% heavy water) is pumped to pump 32. By line 2
6 and sent to a storage facility (not shown) via a line 36.

In accordance with the present invention, the compressor 40 overcomes the pressure increase and maintains a low operating pressure for the fractionating columns 10 and 12, resulting in savings in steam and cooling water that do not substantially add to the cost of compressor power. ie, the omission of a condenser for the overhead in line 24 of fractionation column 12 that is reevaporated in the reboiler for fractionation column 10.

EXAMPLE An example of the method and apparatus follows. 7.515 Kg (16,700 lbs) of 90% heavy water per hour flows through line 14 at a temperature of 87°C at the bottom.
(190〓) is sent to a fractionating column 10 operating at a pressure of 425 mmHg. An overhead stream of 6,840 kg (15,200 lb) per hour is withdrawn from fractionator 12 via line 24 at a temperature and pressure of 52° C. (126° C.) and 100 mm Hg;
Compressor 40 compresses the compressed overhead stream to 218°C before passing it to heat exchanger 38.
(425〓) and introduced into the fractionating column 10 as a vapor stream in line 20. The underflow of line 18 with a heavy water content of 98% at 6930 Kg (15400 lbs) per hour is squeezed through orifice 42 and then into line 22.
is passed through a heat exchanger 38 before entering the fractionation column 12 as a vapor-liquid mixture. A stream of heavy water with a concentration of 99.7% is withdrawn by line 36 at a rate of 95 kg (213 lbs) per hour.

Although the foregoing describes preferred embodiments of the invention, it is understood that many more features are within the scope of the invention. For example, a squeeze orifice may be replaced with a liquid leveling device, but it must be noted that the use of a liquid leveling device increases on-site time and therefore increases liquid inventory. Additionally, the use of insulation around the transfer lines eliminates the need for heat exchangers in each vapor-liquid line. Furthermore, if more than two fractionation columns are operated in series at the same or similar pressures, similar compressor and conduit assemblies as described above may be provided for such fractionation columns. Thus, vapor from any downstream fractionator in the series can be compressed and sent to the bottom of the preceding fractionator in the same series, and one of the optional fractionators in the series The liquid bottom stream from the main column, except in the case of the last column, is configured so that it can be sufficiently expanded to carry the resulting liquid-vapor mixture to the top of the next fractionation column.

[Brief explanation of the drawing]

The accompanying drawings schematically illustrate the fractionation method and apparatus according to the invention. 10, 12: Fractionation column, d: Head, 14: Feed line, 16, 24: Overhead steam line,
18, 26: Liquid outflow line, 28, 38: Heat exchanger, 40: Compressor, 42: Squeezing orifice.

Claims (1)

[Scope of Claims] 1. A method for fractionating closely boiling components of a multi-component system, comprising sequentially passing the multi-component system through at least two fractionating columns operated in series at the same pressure, In the above-mentioned method, in which the high-boiling components of the system are drawn out as a liquid from the last fractionating column, and the low-boiling components are separated from the fractionating column as vapor, (a) one column other than the last one of the series of columns; withdrawing a liquid bottoms stream from the column and expanding said liquid bottoms stream sufficiently to send the produced liquid-vapor mixture to the top of the next fractionation column; (b) any one of said series of fractionation columns other than the first one; (c) introducing the compressed vapor stream of step (b) into the lower part of the fractionating column immediately before the fractionating column from where the vapor stream was drawn and compressed; fractional distillation method. 2. The method of claim 1, wherein the compressed vapor stream of stage B is cooled before being introduced into the immediately preceding fractionation column. 3. A method according to claim 1 or claim 2, wherein the liquid withdrawn from said one column is expanded by direct heat exchange with said compressed vapor stream before being sent to said next column. 4 Any one of claims 1 to 3
the method according to paragraph 1, wherein said expansion is at least
Method carried out in a 1.5 m (5 ft) liquid head. 5 Any one of claims 1 to 4
3. The method according to item 1, wherein the multicomponent proximity boiling system is a heavy water/aqueous solution. 6 Any one of claims 1 to 5
In the method described in paragraph 1, the fractionating column is 50 mm
37℃ (100〓) to 87℃ at Hg or 500mmHg
(190〓) top column temperature and pressure and 400mmHg to 850mmHg from 82℃ (180〓) to 104℃ (220℃).
〓) Method of operating at bottom temperature and pressure. 7 Apparatus for fractionating close-boiling components of a multicomponent system in a plurality of fractionation columns, at least two of which are arranged in series and operated at the same working pressure for the purpose of fractionation. a liquid conduit is provided in said apparatus to convey a liquid bottoms stream from the penultimate column to the top of said last fractionation column, and a vapor conduit is provided in said apparatus to draw a vapor stream from the top of said last fractionation column. , compressing the vapor stream in the fractionator, in which the high boiling components of the multicomponent system are withdrawn as liquid from the last fractionation column and the low boiling components of the multicomponent system are withdrawn as vapor; and a device for introducing the compressed vapor stream from any downstream column in said series into a preceding fractionation column in said series. 8. A fractionator according to claim 7, further comprising a heat exchanger for the liquid conduit and a conduit for cooling the compressed vapor stream. 9. A fractionator according to claim 7 or claim 8, wherein said liquid conduit is provided with a throttling orifice having a head level of at least 1.5 m (5 feet). 10. The apparatus according to any one of claims 7 to 9, wherein there are more than two fractionating columns, and furthermore, said almost last fractionating column and a preceding fractionating column. A fractionator with a compressor device in the steam conduit between the column and the column.