CA1056868A

CA1056868A - Dry channel liquid seal

Info

Publication number: CA1056868A
Application number: CA272,210A
Authority: CA
Inventors: John S. Zink; Robert E. Schwartz; Robert D. Reed
Original assignee: John Zink Co
Current assignee: Zinklahoma Inc
Priority date: 1976-02-25
Filing date: 1977-02-21
Publication date: 1979-06-19
Also published as: NL7701987A; DE2708009A1; GB1550276A; IT1082169B; FR2342439B1; FR2342439A1; JPS52110363A

Abstract

ABSTRACT OF THE DISCLOSURE

A liquid seal assembly for a gas flow system having a housing containing a water seal, a vertically directed cylindrical pipe for gas entry dipping into the water and a second smaller cylindrical pipe, coaxial with the first, also dipping below the water level. Communication between the annulus between the first and second cylindrical pipes to the inside of the second pipe, is by means of one or a plurality of nested annular cups. These are below the normal static water level and are thus filled with water whenever the pressure of incoming gas is below a selected value. As the pressure of the incoming gas increases, the water level is depressed until gas can flow through the U-shaped passage of one of the annular cups. If entering gas is not water saturated, it will pick up the water in the cup and, as flow continues, the cup then essentially becomes dry and there is no further loss of water from the bath. When the pressure again drops below the selected level, the water level in the seal rises and floods the cups so as to provide the water seal.

Description

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This invention lies in the field of gas handling equipment. More particularly, it is concerned with the control of back flow of gas in a gas system. Still more particularly it is concerned with the control of back flow of gas in a gas flare and in other applications of water seals.
In the prior art o~ liquid seals for gas flow passages, such devices have always used a large area of -water with a pipe for entering gas dipping into the water, such that as the gas pressure increases the water level in the pipe depresses until the bottom edge of the pipe i5 reached, after which flow of gas is possible under the edge of the pipe, and up through the water on the outside of the pipe~ Since the gas must flow upwardly through a column of water in the form of bubbles or thin streams, there is a turbulence which ~;
results in considerable oscillation of the water level in the seal, and thus can cause pressure surges which are transmitted upstream and downstream of the liquid !.;
seal. These surges cause considerable difficulty, and great effort has been expended in the past to find ; means for minimizing this turbulence and oscillation. ~ ;
Since the gas which flows to the outlet must always ~;~
bubble up through the water in the seal, and if the gas is not saturated at entry, there will be considerable loss of water, which must be replenished. This water loss can be quite signiicant, according to the gas volume and temperature as it passes through the seal.

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If for example, 50,000 CFH of dry gas at 150 F. should pass through a seal built according to the prior art, the water saturation l~ss, that is, the loss of wa~er from the seal, would be 610 pounds per hour or 73 GPH. `This is not serious from th0 cost standpoint, but it does set up a liquid level control problem of some consequence, and the water loss is to be avoided if possible.
If the temperature should rise to 175~F., the water loss would be 1,104 pounds per hour or 132 GPH.
It is the primary object of the invention to provide a water seal that has the necessary protection of a water trap to preven~ the back flow of gas, while providing a dry passage for the forward flow of gas so long as the ~ `
pressure remains greater than a minimum selected value. -~
According to the invention, there is provided a dry channel liquid seal comprising:
(a) a first vertical cylindrical pipe open at its bottom and ha~ing :~
a gas inlet conduit through said pipe near the top;
(b~ a second cylindrical pipe coaxial with and of smaller transverse :
dimension than said first pipe, the annular space between the top of said first pipe and the second pipe closed, the bottom of said second pipe open with the upper end of said second pipe connected to a gas utilizing means;
; 20 Cc) a housing surrounding and spaced below the bot~om of said first and:~second pipes, and closed to the ~irst pipe near its ~op; ;
Cd~ means to partiall~ fill said housing with water to a selected static level; and (e) at least one annular U-shaped cup means supported below the bottom of said second pipe, with the outer and inner cylindrical walls of said cup extending up outside and inside respectively of said second pipe and said out- ~:
side wall terminating below said selected levelO
~n one embod~l~ent a ~e~tical c~lindrical pipe ~s immersed in a pool of water within a chamber .
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surrounding the first pipe. There is a second smaller pipe coaxial with the first pipe, the bottom edge of which is also immersed below the level of the water in the chamber. There are one or more annular cups which provide a U-shaped passage from the outside ~-to the inside of the second pipe. This cup, or cups, are immersed below the static water level, so that when the pressure is below a minimum value the cups are flooded with water and provide a proper trap against back flow of the gas. As the pressure of the entering ;
; gas increases, the water level in the first pipe is depressed until it reaches the level o~ the bottom of the second pipe, whereby gas can then flow be~ow the bottom edge of the second pipe, gas begins to flow and bubbles up through the water in the first cup. As gas continues to flow, it becomes saturated, and picks up water, so that as time goes on, the channel in the first cup becomes dry, and there is no further saturation loss of water to the flowing gas. As the pressure increases, the level is depressed farther, uncovering a second annular cup until gas begins to flow under the bottom of the first cup, within the second cup. As time goes on ~; the water~filling the second cup is absorbed by the ;~ partially saturated gas and a second dry channel is ~-provided, and so on. As long as the gas flow continues, ~; the channels remain dry and the level of water in the seal remains depressed. If the gas flow and its pressure decrease, the level of water may rlse to partially flood the second cup, permitting further flow of gas through ' ~ 4 ~
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the second cup, although the first cup may still be dry. If thegas pressure drops to zero the water level rises to the static level and floods all cups, so that a complete seal is then provided.
These and other objects and advantages of the invention and a better understanding of the principles and details of the invention will be evident from the following description taken in conjunction with the appended drawings in which FIGURE 1 represents a vertical cross-section through one embodiment of this invention.
FIGURES 2 and 3 indicate enlarged detail of the embodi-ment of Fl W RE 1.
FIGURE 4 illustrates a prior art design.
FIGURE 5 illustrates in greater detail the embodiment of FIGURE 1.
FIGURE 6 (which appears on the first sheet) illustrates another embodiment of the invention.
Referring now to the drawings and in particular to FIGURE l, there is shown in vertical cross-section one embodiment of this invention. It provides an entering pipe or conduit 12 through which gas flows in accordance with arrows 14 to pass into ~` the water seal, down through a first cylindrical pipe 16 which dips into a water pool 30 within a housing 24. The housing 24 is filled with water to a selected static level through a supply line 24a. There is a second cylindrical pipe 18 which is of ..~ .~ . ., smaller diameter and coaxial with the first pipe, and also with its bottom edge below the static level 28 of the pool of water 30.

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. . f, ................. - . .- - -S~B6~1 The second pipe is sealed to the first pipe at point 20 -so as to provide a support for the second pipe and also to close the annulus space 15. After passing through the seal the gas flows in accordance with arrows 37 vertically up through the pipe 18 to a flare, or other device, for utilization of the gas flow. Means such as the radial webs 21, 22 may be used to provide additional support of the second pipe 18 within the first pipe 16. ~ -The housing 24 comprises an outer cylinder with a base 25 and a conical top 26, which is welded to the ~-~
first pipe 16 at point 27 forming a space for the pool of water 30 having a static liquid surface 28 and a gas space 47 above the liquid. A pipe 46 communicates from the space 47 through the sidewall of the second pipe 18 into the space 19 within the second pipe. The pipe 46 has an upper portion of its surface 48 cut away as shown in FIGURES 2, and 3. As the gas flows in accordance with arrows 37 upward past the end 48 of the pipe 46, there will be a reduced pressure in the end of the pipe, which will be communicated to the space 47 so that the space 47 will be at or below atmospheric pressure.
Refer for a moment to FIGU~E 4, which is an illustration of the prior art. The conventional prior - art water trap comprises a housing for containing the water 30 having a bottom 25 and sidewalls (not shown).
Gas enters vertically downwardly in accordance with ' ~ .
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~rrows 31 inside of the pipe 18, and the static liquid level is indicated by the numeral 50. As the pressure of the gas 31A increases, the liquid level 50 will be depressed inside of the pipe 18 down to : :
a point 52 which is just at or below the bottom edge 17 of the pipe 18. When the level reaches 52, gas can flow over the surface 52 and under the end 17 of the pipe 18, and up through the column of liquid 56 outside of the pipe 18. The level of liquid 54 outside the pipe 18 is higher than the static level ~:
50 due to the pressure of the gas 31A. As gas continues to flow in accordance with arrows 31A, 55 and 57 down through the pipe 18, if the gas is not saturated, it will continue to saturate itself with the liquid in the volume 56. As liquid is removed, it will come from the body of the water pool and maintain the l~vel 54. In other words, in the prior art system, there is always a column of water through which the gas flow must ~ pass, either in the form of bubbles, or of thin threads 20 of gas, which vary in size and position and continuity, ` and cause turbulence and variation of the levels 52 and 54. As the level 52 oscillates up and down, it momentarily closes off the flow of gas 55 and can cause serious oscillation and surging of the gas in the pipes :
12 and 18. ~
Referring now to FIGURE 5 which is an enlarged .
view of the bottom portion of the pipes 16 and 18, it .
~: is seen that there is an annular cup 44, comprising an ;~
outer cylindrical wall 44A, an annular base 44B and an "

~alS~3t~8 inner annular wall 44C such that the pipe 18 can be inserted within the cup, providing a U-shaped channel for flow of the gas in accordance with arrows 32 for ;~
example.
There may be a second annular cup 42 having an outer cylindrical wall 42A, an annular base 42B and an inner wall 42C which is nested with the first cup 44, so as to provide a second U-shaped channel for the flow of gas in accordance with the arrow 34 for example.
- 10 There may be other annular cups, ox a third cup 40 which just has an outer cylindrical wall 40A and - the base 4OB nested with and surrounding the cup 42.
; All of these cups must be supported rigidly together. They can be so supported by means of radial webs 60, 62, 64, 66 and 68, for example, or by any other suitable manner of support.
The static level of liquid in the housing 24 is maintained by conventional means, which are well known in the art, at the level 28. The depth of penetration .:
of the bottom 17 of the pipe 18 below the level is set at a desired value. The top edge of the outer wall 44A
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is set at a selected level above the bottom 17 of the pipe 18. The inner wall is set at a second selected level~above the bottom of the pipe 18, and similarly for the other cups. Also the diameters of the outer ': . ::
and inner walls of each of the cups are designed so . . .
~- that the cross-sections of the U-shaped passages through all of the cups on the outside of the pipe 18 will be ' "; .. `",'' . ', ''~ ~, ''', ~''.. ,'''.~,''"' '` '. ,.~':

~5686~3 at least as great, and preferably greater than, the internal area of the pipe 18. Thus there will be no reduction in cross-section for flow of gas from the space 15 into the space 19, and up to the flare, or other using device.
Consider the static level of liquid 28 inside the housing 24 as the pressure of the gas 31 increases. ~ -The level will be depressed to a level such as 70A, at which time gas will then be free to flow through the first cup in accordance with arrow 32 under the bottom edge 17 of the pipe 18 and up inside of the inner wall 40C of the first cup, and into the space 19. As previously explained, as the gas flows, it will pick up water from the first cup 44 unti:L the space within the ~-first cup 44 will be dry and free of water. Thereafter, there will be no further turbulence or surging because the liquid water content of 44, which is the cause of turbulence and surging, will have been removed by the i flow of 32, as has been pointed out, and 44 is separate from 30. As the pressure increases further so that the level drops to 70B, then the bottom of the first cup becomes cleared of liquid and gas can begin to flow in accordance with arrow 34 through the U-shaped channel ; of the second cup 42 under cup 44 and into the space 19.
;~ As the pressure increases still further, so that ;
the level of water is dropped to the level 70C, then ;
gas can begin to flow in accordance with arrow 36 -through the third cup, which now provides gas through ~
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the full area of the pipe 18.
Referring back to FIGURE l, it is seen that as the level of water is depressed inside of the pipe 16, water must be increased in level outside of the pipe 16. If there was no opening to the space 47, the pressure of gas in space 47 would rise and prevent ~
the liquid from rising to the full level. Consequently, ~ -the bypass pipe 46 provides a means of maintaining in the space 47 a value of pressure which is at, or close to, atmospheric pressure. - -By reference again to FIGURE 4, it will be seen that as the in-flowing gas 31A flows down inside pipe 18, and up outside the pipe 18, the action of the water seal is that the level of water before gas flow can begin must be at the level 52 which is just at or below ~-the bottom 17 of the pipe 18. Then as gas flows, it must bubble up through the column 56 to the surface 54 outside of pipe 18, and thus can cause serious damage by oscillation and surging. Also, it can cause a serious loss of water, which must be replenished and which requires a careful level control.
In the embodiment which has just been described in connection with FIGURES 1 and 5, while the gas`inlet is shown to flow down through the annulus, through the U-shaped passages of the nested cups, and up the central pipe 18 through the space l9, it would be equally ` possible to arrange for the down flow through the pipe 18 and through the U~shaped passages of the nested cups, "~ ~and up the annulus between the pipes 16 and 18. Of ; ., ~ . ": ' ..j -- 10 -- ::.
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co,urse, it will be clear that the corresponding levels of the inner and outer walls would have to be reversed to what they are shown in FIGURE 5. However, this second embodiment which would involve flow down through the inside pipe and up through the annulus is not illustrated, but could well be designed on the basis of what has been described.
It will be clear that the embodiment described , provides a water seal which is fully protected by an opposing head of water to back flow of gas through the seal, after the pressure water surface and therefore surging of the gas upstream and downstream of the water seal. ,' ~
Specific dimensions of the apparatus shown in ` ,, FIGURE 5 have not been given since these will depend ',,' upon the situation for which the water seal is designed ' and can be signed in terms of variables which are known "
in accordance with the prior art devices. While three separate passages have been shown, one or more may be , used. Also, levels to which the water must be depressed ~ by gas pressure before the sùccessive openings of flow '`~ through successive cups, are designed in accordance with the conditions of gas flow as is well known in the " art.

Illustrated in FIGURE 6 is another embodiment of , the invention, in which the pipe or cylinder 16 is , ~ ' , absent and the series of vested annular cups 40, 42, 44 is replaced by a single cup 80 which surrounds the -bottom end 17 of the pipe 18. The rim of cup 80 .;
- 11 - ', 1~6~36~3 rises above the level 84 of the liquid. The cup 80 has an opening 82 in the bottom through which liquid can pass from the body of liquid 30 to the space inside the cup. -~
~as flow is from inlet pipe 86, in accordance - with arrow 88 into the chamber 94, down as arrow 89 into the cup 80, then as arrows 90 into space 19 inside pipe 18, as up as arrow 92 to the stack. Water carried out of the cup by flow 90 is replenished through opening 82.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and arrangement of components. It is understood that the ` ;~
invention is not to be limited to the specific embodiments set forth herein by way of exemp:Lifying the invention, but the invention is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element or step `; 20 thereof is entitled.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A dry channel liquid seal comprising:
(a) a first vertical cylindrical pipe open at its bottom and having a gas inlet conduit through said pipe near the top;
(b) a second cylindrical pipe coaxial with and of smaller transverse dimension than said first pipe, the annular space between the top of said first pipe and the second pipe closed, the bottom of said second pipe open with the upper end of said second pipe connected to a gas utilizing means;
(c) a housing surrounding and spaced below the bottom of said first and second pipes, and closed to the first pipe near its top;
(d) means to partially fill said housing with water to a selected static level; and (e) at least one annular U-shaped cup means supported below the bottom of said second pipe, with the outer and inner cylindrical walls of said cup extending up outside and inside respectively of said second pipe and said outside wall terminating below said selected level.

2. The seal as in claim 1 in which said first and second cylindrical pipes are circular cylinders.

3. The seal as in claim 1 in which said at least one annular cup has a higher inside cylindrical wall than outside cylindrical wall.

4. The seal as in claim 3 including at least a second U-shaped annular cup of greater radial dimension than that of said first cup and having its outer and inner cylindrical walls extending up outside and inside respectively of said first annular cup, the outside wall terminating at a level below the top of said first cup.

5. The seal as in claim 1 in which said at least one annular U-shaped cup comprises:
(a) an inner cylindrical wall of less diameter than said second pipe;
(b) an outer cylindrical wall of greater diameter than said second pipe and;
(c) a planar annular ring sealed to the bottom edges of said inner and outer walls.

6. The seal as in claim 1 including conduit means connecting the upper portion above said water level in said housing to the interior of said second pipe.

7. The seal as in claim 1 including three nested annular U-shaped cups surrounding the bottom end of said second pipe.

8. The seal as in claim 7 in which the static level of said liquid is above the top of each of said annular cups.