US3595260A

US3595260A - Dip pipe unit for a flare system

Info

Publication number: US3595260A
Application number: US889428A
Authority: US
Inventors: Winfried Lotzmann; Gunter Hein; Helmut Possekel
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1969-01-03
Filing date: 1969-12-31
Publication date: 1971-07-27
Anticipated expiration: 1988-07-27
Also published as: DE1900272A1

Abstract

A dip pipe unit for a flare system comprising a normally closed hollow pressure vessel with a gas outlet disposed at the upper portion thereof and a partition dividing the interior of the lower portion into an inner and outer chamber, each of the chambers being open at the top and in communication with the interior of the inner chamber and the bottom of the inner chamber is substantially below the bottom of the outer chamber with a throttle line coupled to the bottom of both the inner and outer chambers for equalizing fluctuations in each of the inner and outer chambers.

Description

United States Patent Winlrled Lotzrnann Bad l-loennigen;

Gunter l-lein. Lechenich; llelmut Possekel, Wesseling, Rhineland, all 01, Germany [72] Inventors [21] Appl. No. 889,428

(22] Filed Dec. 31,1969

[45] Patented July '27, 1971 [73] Assignee Shell Oil Company New York, N.Y.

[32] Priority Jan. 3, 1969 [33] Germany [54] DIP PIPE UNIT FOR A FLARE SYSTEM 7 10 Claims, 7 Drawing Figs.

[52] U.S.Cl 137/251, 137/254 [51] Int. Cl F16k 9/00 [50] Field of Search 137/251,

Primary Examiner-Harold W. Weakley Aitarneys- Louis J. Bovasso and J. H. McCarthy ABSTRACT: A dip pipe unit for a flare system comprising a normally closed hollow pressure vessel with a gas outlet disposed at the upper portion thereof and a partition dividing the interior of the lower portion into an inner and outer chamber, each of the chambers being open at the top and in communication with the interior of the inner chamber and the bottom of the inner chamber is substantially below the bottom of the outer chamber with a throttle line coupled to the bottom of both the inner and outer chambers for equalizing fluctuations in each of the inner and outer chambers.

PATENTEDJULNIQTI 3.595.260

SHEET 1 OF 2 I FIG. 3

PATENTEO JUL2 719m SHEET 2 BF 2 lab FIG. 4

FIG. 7

FIG.5

DIP PIPE UNIT F OR A FLARE SYSTEM BACKGROUND OF THE INVENTION 1. Field of the invention The invention relates to flare systems, and, more particularly, to a dip pipe unit for providing a seal of the flare system of a processing plant.

2. Description of the Prior Art For a controlled discharge of their process gases, refineries and petrochemical plants have installed flare systems which must also be capable ofsmoothly carrying off the sudden waste gas surges occurring during operating disturbances and in emergencies. A flare system of this type generally consists of a collecting line system in which the gases to be flared are passed by way of a liquid separator having a dip pipe unit con nected beyond it to the flare which is designed as a high stack and/or as a ground-level flare and from which the gases can be flared in so far as they are combustible.

The functions of the dip pipe unit as such which is connected directly ahead of the flare are several in number.

It is a permanent safety device against flashback from the flare into the gas-collecting line system, especially when the flare gas effluent completely stops or is temporarily decreased during a blowoff. A prerequisite in this respect is a sufficient immersion.

By using different immersion depths in systems comprising several flares, it is possible to vary the quantities of gas to be discharged by way of the individual flares; thus, a high flare designed for maximum quantities of gas may have connected ahead of it a ground-level flare for smaller quantities of gas.

The immersion liquid used may be water or, if required, a glycol/water mixture.

Conventional designs of dip pipe units which have so far been used in practice have the following disadvantages:

During blowoff, the immersion liquid is affected during the whole period of the flaring operation by the quantity of gas involved, as a result of which a liquid funnel (cone) is formed. The effect of this is that droplets of liquid are entrained by the gas flowing through at high velocity and are discharged by way of the flare.

This loss of sealing liquid must be made up again and in the case of a glycol/water mixture considerable costs are involved. The liquid funnel which is being formed collapses again and again, and this gives rise to pulsation, causes an upsurge in the gas column in the flare and produces the familiar picture of a pulsatingly burning flare; this has the effect of increasing the noise level. In the case of prolonged blowoffthe gas can entrain so much sealing liquid from the dip pipe unit, that the remaining quantity of sealing liquid is no longer sufficient to provide a safe seal against flashback into the gascollecting line system.

Because of their great volume the cohventional dip pipe units require large quantities of immersion liquid. Accordingly, after each flaring operation considerable quantities of sealing liquid for the dip pipe unit must be replenished.

lf several plant units are connected to a common flare system, the corresponding number of dip pipes must likewise issue into a common dip pipe unit. This involves the risk of mutual interference of the dip pipes of the various units; in this case the safety seal may be impared or even be completely eliminated, for example on account of liquid losses.

It has already been proposed to reduce the liquid loss by surrounding the dip pipe by a partition wall which is open at the top and extends into the liquid underneath the lower end ofthe dip pipe. During blowoff only the liquid within the partition wall is displaced, so that it is possible to prevent the liquid cone form collapsing again and again.

Summary of the Invention it is an object of the invention to provide a dip pipe unit which contains a comparatively small volume of sealing liquid and in which pulsation and consequently increased noise during flaring do not occur, while retainingthe function of a safe seal against flashback even under extreme operating conditions, i.e., also during and after the sudden flaring of large quantities of gas.

According to the been this object is achieved in that the dip unit is designed as a closed pressure vessel having a gas outlet in the upper part thereof, which vessel is divided by a partition wall into an inner and an outer space which are open at the top and contain sealing liquid, above which spaces there is a com mon gas space in the upper part of the pressure vessel, at least one gas-supplying dip pipe extending into the inner sealing liquid space, characterized in that the two sealing liquid spaces are closed at their bottom ends and are interconnected by means of a throttle line, the bottom of the outer space being located above the bottom of the inner space.

The construction of the dip pipe unit according to the invention permits a small pressure chamber of the vessel, and this is of particular importance in the case of great immersion depths. A small volume of the vessel also means a small quantity of immersion liquid and consequently low installation and operating costs, especially in the case of expensive immersion liquids such as glycol.

The arrangement of the inner space ensures that during blowoff there is always a small quantity of liquid of a certain height which, as a result of static pressure, is available for refilling the dip pipe space. If desired, an auxiliary vessel for the storage of sealingliquid may be installed between the throttle line and the outer space.

As soon as the dip pipe unit starts operating, the liquid is collected in the outer space; the connecting line operates as a throttling section (damping) to equalize any fluctuations.

The throttle line is preferably provided with a throttling element, for example, a throttle valve or control valve.

This provision permits the regulation of the backflow of immersion liquid into the inner space by means of the throttle valve and loss of liquid can thus be effectively avoided.

The throttle valve may also be operated by way of an on/off function" as a remote-control shutoff element.

According to the invention, several dip pipes from various gas-discharging units may be included in a dip pipe unit, without there being mutual interference of the dip pipes, even at differently set immersion depths.

To this end, the dip pipe unit has been so designed that several dip pipes extend into the inner space, the inner space being divided by separating elements into such a number of sections that each dip pipe extends into a separate section, and that the bottom end of at least one of the sections is connected with the outer space by a throttle line. The immersion depths of the separate units may be different (back pressure exerted by different units).

The advantages of a dip pipe unit with multiple connection are that only one dip pipe unit is required so that the capital expenditure is low; moreover, the required space is limited, while the maintenance and operating costs are low. 7

BRIEF DESCRIPTION OF THE DRAWING FIG. 6 is a cross-sectional view of a dip pipe unit showing a modification of the unit of FIG. 4 and 5; and

DESCRIPTION OF THE PREFERRED EMBODIMENT The clip pipe unit according to FIG. 1 consists of a cylindrical pressure vessel 1 with a gas outlet 2. The vessel is provided with a partition wall 13, by means of which the liquid space is divided into an outer space (annular space) 4 and an inner space 5. The two spaces are open at the top and communicate with a common gas space 6 in the upper part of the vessel 1.

A dip pipe 7 is arranged concentrically in the vessel 1 and extends into the inner liquid spaces; the immersion depth is determined by the pressure head (water column) which is required under the operating conditions and must be overcome in order to start the blowoff. A throttle line 8 connects the two

liquid spaces

4 and 5.

The bottom 9 of the outer space is arranged considerably higher than the bottom 10 of the inner space. The dip pipe is provided with a baffle plate 11, by means of which the upflowing gas/liguid mixture is deflected sideways and demixed. The outer space my be provided with a sieve palate 12 to stabilize the liquid surface. The throttle line 8 contains a valve 13 by means of which the liquid flow through the throttle line can be regulated. The pressure vessel is located on a welded-on skirt (not shown). The operation of the unit is as follows: in the absence of flare gases the dip pipe unit has a constant liquid seal; the liquid surface is at the level indicated by 14.

The beginning of the blowoff is shown in FIG. 1. The gas pressure has overcome the static pressure of the liquid column in the inner space 5 and the gas flowing through the liquid entrains drops of liquid from the inner space. The entrained liquid is primarily separated by the baffle plate 11 and passed into the outer annular space 4 and the gas flows by way of the gas outlet 2 to the flare (not shown). The inner space 5 and the outer annular space 4 are in communication with each other by way of the throttle line 8 so that a controlled liquid exchange can take place. If the unit is adequately provided with measuring and control devices (not shown), automatic operation is possible.

In the case oflarge quantities of flare gas, the interior space no longer contains sealing liquid since the through-flowing gas empties the lower part of the inner space by entraining the sealing liquid present therein, which is subsequently separated off by means of the baffle plate in the outer annular space. In this way, the flare gas can freely flow out without undesirable pulsation occurring.

As soon as the lower end of the dip pipe 7 has been exposed and the inner annular space no longer contains any liquid, there is no longer any static excess pressure available (equalization of pressure). Owing to the dynamic pressure, the inner space is kept free of liquid. Small quantities of liquid which may find their way to the bottom of the inner space through the throttle line are immediately entrained by the gas, separated again in the gas space and then passed into the outer annular space.

If the amount of flare gas diminishes or the blowoff is completed, the liquid immediately flows back through the throttle line 8, whereupon the original immersion depth and thus the flashback seal is restored. The valve 13 in the connecting line 8 is always open and only serves to control the flow.

The embodiment shown in FIGS. 2 and 3 represents a dip pipe unit with multiple connection. In so far as the same reference numerals have been used as in FIG. 1, they refer to corresponding elements. By way of example, three dip pipes (7a, 7band 70) have been provided which are arranged in the form of a circle and have different immersion depths. The inner space is divided into separate sections (5a, 5band St) for each dip pipe by radially arranged partition walls (30, 3band 3c). The gas outlet 2 is arranged centrally and the baffle plate 11 encloses the three dip pipes.

The throttle lines (80, 8band 80) issue into each of the sections (50, Sband 50). It is advisable to provide each of the lines (8a, b, and 80) with a throttling element to prevent a rapid backflow of liquid from the adjoining sections (Saand 5b) when only one of the pipes (for example 70) is supplied with gas, in which case, when there are large quantities of gas described above, the relevant section (for example 5c) contains no longer any sealing liquid.

In the construction shown in FIGS. 4 and 5, two gas-supplying systems are connected to the dip pipe unit. One dip pipe 17a has the form of a double-walled tube with lateral inlet and is arranged concentrically around the central dip pipe 17. Allowance is made for variations in diameter between the double-walled tube and the outer wall of the vessel by the incorporation of a compensator 19 in the supply line within the vessel.

A separating element 16 in the form of a top-hat" which is open at the top divides the interior into a central portion 15 and an annular space 15a. The function of this separating element is to divide the blowoff zone of the two dip pipes; it ensures that as soon as one of the dip pipes starts operating the other retains a sufficient liquid seal.

The remaining elements of this embodiment are indicated by the same reference numerals as are used in FIG. 1 to FIG. 3.

The operation of this dip pipe unit is as follows:

When there is no gas supply, the liquid level 14, is equal in all communicating spaces. When gas is supplied, for example through a line 18, the annular space 15aempties when there is an increased gas supply. In the central portion 15, the liquid level remains at the upper edge of the cylindrical separating element 16.

When gas is supplied through a dip pipe 17, the space 15 is emptied when there is an increased gas supply. In the annular space 15a there is still liquid at the upper edge of the cylinder of the separating element 16. If, moreover, gas is similarly supplied through line 18, the whole inner space and I5) is emptied.

The connection of each of the sections to the outer annular space by means of a throttle line ensures that each section if filled up again with sealing liquid independently of the other sections on completion of the gas supply from the outer annular space.

FIGS. 6 and 7 show a variant of the dip pipe unit with quintuple connection.

The constructional features, detailed descriptions and the mode of operation correspond to the description given for FIGS. 4 and 5.

In this embodiment, the cylindrical part of the separating element 16 extends upwards to the upper end of the inner space so that liquid can no longer flow over the upper edge of the cylinder. The connection between the various spaces is provided by branching the throttle line in a manner similar to that of the embodiment shown in FIGS. 2 and 3.

A connection for five systems is obtained by dividing the annular space into four sections (15b, 15c, 15d and 15s) by partition walls (16b, 16c, 16d and 162); each compartment is connected with a gas supply line (18b, 18c, 18d, and 18e) provided with a compensator (19b, 19c, 19d and 19e). In this embodiment and by way of example, the immersion depth of the central dip pipe 17 has been selected greater than the other connections. The throttle line splits into a central line 8a and four branch lines (8b, 8c, 8d and 8e), each line issuing into one of the separated spaces (15, 15b, 15c, 15d and 15c); if desired, these branches may be provided with a separate throttling element, forexample a throttle valve. The doublewalled tube is likewise divided into four parts (17b, 17c, 17d and 17e), each part issuing into one of the sections (15b15c, 15d and 15e).

The foregoing embodiments are given only by way ofexample; it is of course possible to provide combinations of the constructions shown such as, for example, the construction shown in FIGS. 2 and 3 with the construction shown in FIGS. 6 and 7. It will be understood that component parts can also be used and are interchangeable in all constructions shown, such as for example sieve plates which are indicated only in FIG. 1, and various immersion depths of the dip pipes. Furthermore, the partition walls between various sections need not have the same height as the partition wall between the inner and the outer space, the height of .the upper edge of which is deter mined by the maximum liquid level in the outer space; the upper edge of the partition wall is preferably lO0-20O mm, above the maximum liquid level in the outer space.

We claim as our lnvention:

1. A dip pipe unit for a flare system comprising:

a normally closed hollow pressure vessel; 1

a gas outlet disposed at the upper portion of said pressure vessel communicating with the interior thereof for removing gas therefrom;

partition means disposed internally of said pressure vessel dividing the interior of the lower portion of said vessel into an inner and outer chamber, each of said chambers being open at the top and closed at the bottom thereof;

the upper portion of said vessel above said chambers forming a gas chamber communicating with the top of each of said inner and outer chambers;

a dip pipe extending downwardly through said vessel into the interior ofsaid inner chamber and communicating therewith for supplying gas thereto;

the upper portion of said dip pipe extending out of said vessel and adapted to be coupled to a gas supply;

the bottom of said inner chamber being substantially below the bottom of said outer chamber; and,

throttle means coupled to the bottom of both of said inner and outer chamber for equalizing fluctuations in each of said inner and outer chambers.

2. The dip pipe unit in claim 1 wherein the upper part of the gas chamber is provided with a baffle plate above the top of each ofsaid outer and inner chambers.

3. The dip pipe unit ofclaim 1 wherein the outer chamber is provided with at least one sieve plate at its top thereof.

4. The dip pipe unit of claim 1 wherein a plurality of dip pipes extend into the inner chamber, the inner chamber being divided by partition walls into such a number of sections that each dip pipe extends into a separate section, and that the bottom end of at least one of the sections is connected with the outer chamber by said throttle means.

5. The dip pipe unit of claim 4 wherein a plurality ofsaid dip pipes are arranged in the form of a circle within the inner chamber and that said partition walls are provided in radial arrangement so that each dip pipe extends into a separate section of the inner chamber.

6. The clip pipe unit of claim 4 wherein at least two dip pipes are provided with one dip pipe being arranged as an annular tube around the other dip pipe, the outer wall of the annular tube forming the partition wall between the inner and the outer chamber, and a separating element being provided between the two dip pipes.

7. The dip pipe unit of claim 6 wherein the separating element divides the inner chamber into two substantially concentric, liquid chambers, the two liquid chambers being conn ected by said throttle means.

8. The dip pipe unit of claim 6 wherein the annular tube is divided into several chambers with each of said several chambers of said annular tube communicating with a gas inlet tube.

9. The clip pipe unit of claim 8 wherein the gas inlet tubes communicating with the annular tube having a pressure compensator between the annular tube and outer wall of the pressure vessel.

10. The dip pipe unit of claim 4 wherein the dip pipes have varying immersion depths within said vessel.

Claims

1. A dip pipe unit for a flare system comprising: a normally closed hollow pressure vessel; a gas outlet disposed at the upper portion of said pressure vessel communicating with the interior thereof for removing gas therefrom; partition means disposed internally of said pressure vessel dividing the interior of the lower portion of said vessel into an inner and outer chamber, each of said chambers being open at the top and closed at the bottom thereof; the upper portion of said vessel above said chambers forming a gas chamber communicating with the top of each of said inner and outer chambers; a dip pipe extending downwardly through said vessel into the interior of said inner chamber and communicating therewith for supplying gas thereto; the upper portion of said dip pipe extending out of said vessel and adapted to be coupled to a gas supply; the bottom of said inner chamber being substantially below the bottom of said outer chamber; and, throttle means coupled to the bottom of both of said inner and outer chamber for equalizing fluctuations in each of said inner and outer chambers.

2. The dip pipe unit in claim 1 wherein the upper part of the gas chamber is provided with a baffle plate above the top of each of said outer and inner chambers.

3. The dip pipe unit of claim 1 wherein the outer chamber is provided with at least one sieve plate at its top thereof.

5. The dip pipe unit of claim 4 wherein a plurality of said dip pipes are arranged in the form of a circle within the inner chamber and that said partition walls are provided in radial arrangement so that each dip pipe extends into a separate section of the inner chamber.

6. The dip pipe unit of claim 4 wherein at leaSt two dip pipes are provided with one dip pipe being arranged as an annular tube around the other dip pipe, the outer wall of the annular tube forming the partition wall between the inner and the outer chamber, and a separating element being provided between the two dip pipes.

7. The dip pipe unit of claim 6 wherein the separating element divides the inner chamber into two substantially concentric, liquid chambers, the two liquid chambers being connected by said throttle means.

9. The dip pipe unit of claim 8 wherein the gas inlet tubes communicating with the annular tube having a pressure compensator between the annular tube and outer wall of the pressure vessel.