BATH-TYPE VAPORISER-CONDENSER FOR A METHOD OF CRYOGENICALLY SEPARATING A NATURAL GAS STREAM

Abstract

A method of cryogenically separating a natural gas supply stream into a gas which contains the most volatile compounds of the supply stream, and a liquid product which contains the heaviest compounds of the supply stream, including the following steps: at least partially condensing a natural gas supply stream in a first heat exchanger system; introducing the liquid product into a fractionation column in order to obtain, in the bottom of the fractionation column, a liquid produce that contains the heaviest compounds of the supply stream and, at the top of the fractionation column, a distillate that is at least partially condensed; introducing, at a stage in the upper part of the absorption column, the gaseous phase of the condensed distillate as a supply stream for the absorption column; where the distillate is condensed in a bath-type vaporizer-condenser installed in a casing mounted on the fractionation column.

Claims

1.-5. (canceled)

6. A process for the cryogenic separation of a natural gas feed stream into a gas containing the most volatile compounds of the feed stream and into a liquid product containing the heaviest compounds of the feed stream, comprising at least the following stages: Stage a): at least partial condensation of a natural gas feed stream in a first heat-exchange system; Stage b): introduction of the at least partially condensed stream resulting from stage a) into an absorption column at an introduction level located in the lower part of said absorption column, said absorption column producing, at the top, a gas stream containing the most volatile compounds and, at the bottom, a liquid product; Stage c): introduction of the liquid product resulting from stage b) into a fractionation column in order to obtain, in the fractionation column bottom, a liquid product containing the heaviest compounds of the feed stream and, at the fractionation column top, an at least partially condensed distillate; Stage d): introduction, at a level located in the upper part of the absorption column, of the gas phase of the condensed distillate resulting from stage c) as feed stream of the absorption column; wherein the distillate resulting from stage c) is condensed in a bath vaporizer-condenser installed in a shell surrounding the fractionation column.

7. The process as claimed in claim 6, wherein the bath vaporizer-condenser contains at least one heat exchanger fed with refrigerating fluid by the liquid product resulting from stage b).

8. The process as claimed in claim 6, wherein the liquid phase of the condensed distillate resulting from stage c) is used as reflux at the top of the fractionation column.

9. The process as claimed in claim 6, wherein no pump is necessary for setting up said reflux.

10. A unit for the cryogenic separation of a natural gas feed stream utilizing the process as defined in claim 6, wherein a pipe connects the top of the fractionation column to a heat exchanger surmounting said fractionation column, which heat exchanger is itself placed in a shell provided for a bath formed predominantly of hydrocarbons.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0025] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0026] FIG. 1 illustrates a schematic representation of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In the FIGURE, a feed stream of natural gas 1 is introduced into a main heat exchanger 2 in order to be cooled. The gas thus cooled 3 is partially condensed and introduced into a phase separator 4. The gas phase 5 at the phase separator 4 top is introduced into a turbine 6 in order to recover the expansion energy and to condense a portion of the stream 5, and is then introduced into an absorption column 7 comprising a lower part 7 and an upper part 7. The liquid phase 8 at the phase separator 4 bottom is introduced after expansion 9 into the absorption column 7. The absorption column produces a liquid 10 at the column bottom and a residual gas 11 at the column top. The liquid 10 is reheated in a heat exchanger 12 in which it is partially evaporated. The stream thus reheated 13 is subsequently introduced into the main exchanger 2; this introduction 13 is thus strongly a two-phase introduction.

[0028] At the absorption column 7 top, the residual gas 11, which contains only the products more volatile than ethane, is reheated in the main heat exchanger 2; the stream which results therefrom 14 is subsequently compressed and sent to a treatment unit A.

[0029] The stream 13 at the heat exchanger 2 outlet resulting from the bottom of the absorption column 7 is introduced into a fractionation column 15.

[0030] This column 15 produces, at the bottom 16, a reboiled liquid product 18 using a reboiler 17 in order to obtain a liquid rich in propane and depleted in ethane.

[0031] A gas 20 is produced at the fractionation column 15 top 19. This gas 20 is condensed in the heat exchanger 12 and the product 21 which exits from this exchanger 12 is introduced into a phase separator 22. The gas phase 23 at the top of the phase separator 22 acts as reflux in the absorption column 7. The liquid 25 at the bottom of the phase separator 22 acts as reflux 26 at the top of the fractionation column 15. A pump is not necessary to pump the liquid 25. This arrangement with the use of a bath vaporizer-condenser exhibits the advantage of being very easy to control while integrating the exchanger and the fractionation column and without using a pump (thermosiphon scheme).

[0032] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.