CA1044132A - Foam suppression arrangement - Google Patents
Foam suppression arrangementInfo
- Publication number
- CA1044132A CA1044132A CA212,590A CA212590A CA1044132A CA 1044132 A CA1044132 A CA 1044132A CA 212590 A CA212590 A CA 212590A CA 1044132 A CA1044132 A CA 1044132A
- Authority
- CA
- Canada
- Prior art keywords
- water
- gas
- tower
- tray
- relation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Physical Or Chemical Processes And Apparatus (AREA)
- Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a heavy water process having a tower with a plurality of trays dividing the tower into communicating adjacent zones for the passage of water downwardly and H2S gas upwardly therethrough in counter-flow isotope exchanging relation, the presence of heavy foam is controlled by the provision of water sprays and H2S gas jets to break up heavy foam formations up their occurrence in the tower. The control of foam formation contributes to the stability of operation of the tower, so as to permit operation at a rate close to design production capacity.
In a heavy water process having a tower with a plurality of trays dividing the tower into communicating adjacent zones for the passage of water downwardly and H2S gas upwardly therethrough in counter-flow isotope exchanging relation, the presence of heavy foam is controlled by the provision of water sprays and H2S gas jets to break up heavy foam formations up their occurrence in the tower. The control of foam formation contributes to the stability of operation of the tower, so as to permit operation at a rate close to design production capacity.
Description
~ ; Case 2409 This invention is directed to a foam control apparatus, and in particular to a heavy water separation plant incorpcrating a foam suppression arrangement within a deuterium isotope exchange tower thereof.
In the operation of isotope exchange towers used in ~ the manufacture of heavy water which is required for the '~ operation of "Candu" type nuclear reactors, difficulty has ; been experienced in achieving design output from the plants, due to a number of factors. One ~uite important factor is the difficulty experienced in achieving rated flow within the isotope exchange towers, particularly the ~irst stage towers, which are very large and operate at high pressure and under i heavy tray loadings.
In t~ese towers ~ydrogen su phide (H2S) gas is ; bubbled upwardly through zones of the tower, while water flows ;' downwardly therethrough, passing transversely over the surfaces : of a large number of trays arranged in mutual parallel relation transversely of the tower, through which the gas is bubbled.
The water passes sequentially downwardly from tray to tray by i~
way of downcomer flow passages over weirs.
In order to effect the desired mass exchange it is necessary to obtain a compromise between the flow rates of gas upwardly and water downwardly, and t~e achievement of sufficient ~ -frothing necessary to effect the mass transfer, w~ile avoiding the creation of foaming to the extent that fluid flow is impeded and the mass transfer efficiency is disrupted. Foaming may ~ -take place, under uncontrolled conditions to the extent that ;
foam is recirculated with the gas.
The present invention provides a system for foam suppression, wherein the occurrence of foaming to an extent ~-to disrupt desired flow and mass transfer rates is suppressed by the use o~ ~ mixed g~s- and liquid spray. In addition to ' ~ '~' s,~ .
~" ' ... , .. ~,, .
: . , -~ . . .. .. . . .
~ f~ Case 2409 suppressing the formation of fo~m beyond desired limits, the mixed fluid spray further provides a balanced addition of water and H2S gas to supplement the throuyhput of the tower and to enhance the mass transfer activity within the respective tray zone.
Thus there is provided in a heavy water production plant having at least one pressure tower for the passaye of H2S gas and water in opposed coun~er flow relation therein, with a plurality of transversely extending perforated trays mounted in substantial mutually paralle]. relation and connected by downcomers for passage of water downwardly, defining flow zones wherein li~uid flows primarily transversely across the tray surface and gas flows upwardly through perforated portions of the tray surfaces, the improvement comprising a plurality of water nozzles and gas jets within at least some of the zones positioned to spray a respective fluid in foam dispersing relation towards the adjacent underlying tray, and pump means to circulate ~2S gas and waterrespectively to said jets and :~ nozzles at pressures in excess of the pressure within the tower, to supplement the fluid loading within the tower~
The provision of foam level de-tectors is con-templatedt whereby the need for the provision of foam suppression may be established, and the foam suppression system : -~operated on a non-continuous bas i5 .
Certain embodiments of the invention are described, reference being made to the accompanying drawings, wherein:
FIGURE 1 is a diagramatic representation of a tower :~ in diametrical sectional elevation I FIGURE 2 is a detail of a portion of the tower of .~ 30 Figure 1, and FIGURE 3 is a cross-sectional view of a mixing nozzle embodiment for use with the invention.
. .
,' . .
;,. .. ....... .
.: .
'~ , -':',: .
: ~ .
3~ Case 2409 n Figure l the arrang~ment 10 includes a tower 11 designed to operate at a pressure in the order of 300 p.s.i.
The tower 11 contains a plurality of trays 12 in stacked spaced relation ~herein. Each tray 12 has a perforated, gas permeable portion 13.
Feed water enters the top of the tower 11 by way of inlet feeds 15, and H2S gas is illustrated as recirculating from the top of the tower a~ ouklet 21 ~y way o~ a pipe 22 connecting with a compressor 14, from whence the gas passed to the inlet 31 located at the bottom of the tower ` Each tray 12 is served from the tray above by a downcomer 17 or plurality of downcomers 17 by which water passed from ~ray to tray. On the upper surface of each tray 12 an annular weir 33 regulates the rate of flow of water across the respective tray 12. The depth of liquid on the tray is governed by an annular outlet weir 18 bounding the respective downcomer 17 leading to the adjoining lower tray 12. Fach tray 12 is provided with an impermeable surface portion co-operating with the respective downcomer 17, and the active portion 13 of the tray 12~ is perforated, as is well known in the ar~, for ~ ~
~ the controlled passage of gas upwardly therethrouyh. - ;
; In accordance with~the present invention a water : --supply 34 connected to pump 37 provides a supply of feed water -;
at a suitahle temperature by way of inlet 26 to a riser 39 located within the towar, at a pressure in excess of tower ;
internal pressure. The riser 39 is shown chain dotted for purposes of claxity. A control ~alve 48 provides regulation o~ water ~low. Similarly, a gas supply line 42 from the pipe ~ -', 22 conne~ts wi-th a compressor 50 to supply gas at a pressure 1 30 in excess of tower pr~sure, by way of inlet 46 to a gas riser 49. The gas riser 49 is skLown irL dotted line formation for purposes of distinction and clar:ity, in Figures l and 2. A
. " .
i ,;, , ... . ,., . ,, ~ , -: , . . : :, :: . .: , , ,. ~
,.. ~ ; :: . . . . . .
: . . :, :,, . : . , : : ~
.: : . . . :
~ Case 2409 gas flow colltrol valve 47 is provided.
The zones between at least some of the trays 12 are each serviced by a water header 51 and a gas header 53.
A number of mixing nozzles 23 (See Figures 2 and 3) are located in spaced relation above the surface of the respective under-lying tray 12. Each nozzle 23 (see ~igure 3) has a gas inlet 24 and a water inlet 25 leading to coaxial outlet jets 55 and 57 respectively. The jets 55, 57 serve to mix the water and ~ ~2S gas as a high velocity jet, with the H2S gas usually `- 10 serving to energize the water, thus providing a high velocity ; water spray for impingement on the foam to be controlled.
~; While illustrated as a single unitary temperature system for a complete tower, it will be understood that the presently disclosed system may be modified where desirable, ;~ such as for purposes of temperature zoning to provide combined gas and water jets at suitable temperature and pressure com-;; patible with respective zone conditions within the tower.
~ The particular arrangements of nozzles 23 in the ; different tray zones of the tower is made in accordance with :
functional requirements. It is known in at least one existing plant to have a foam building to an extent to cause upward foam carry over from tray to tray with the gas flow, to the extent that foam may even be entrained into the gas exit 21 and re-; circulated through the compressor 14. It is contemplated that at some levels, such as the top tray, that the dispersive sprays may even be operated continuously. ~wing to the '! provision of a combined gas and water dispersive spray the extent of dilution of the working fluids may be minimized.
One experimental use, using a spray noæzle according , 30 to the invention located to spray gas and water into a downcomer,significantly reduced the foam height both within the downcomer and also across the surfa~e of the tray served by the downcomer.
,; , . . .
, , .
Case 2409 f~-The s~stem herein disclosed has the particular characteristic of re~uiring a minimum of penetrations through the wall of the tower 11. In view of the usual 3 inch plate thic~ness and the corrosive nature of H2S gas, this affords particular advantage to the s~stem~
_ 5 _ .
' .
,, , . ,, ,. ~ . . .. . . ... . .
, -.. , .. : .. : ~ .- . . . .
In the operation of isotope exchange towers used in ~ the manufacture of heavy water which is required for the '~ operation of "Candu" type nuclear reactors, difficulty has ; been experienced in achieving design output from the plants, due to a number of factors. One ~uite important factor is the difficulty experienced in achieving rated flow within the isotope exchange towers, particularly the ~irst stage towers, which are very large and operate at high pressure and under i heavy tray loadings.
In t~ese towers ~ydrogen su phide (H2S) gas is ; bubbled upwardly through zones of the tower, while water flows ;' downwardly therethrough, passing transversely over the surfaces : of a large number of trays arranged in mutual parallel relation transversely of the tower, through which the gas is bubbled.
The water passes sequentially downwardly from tray to tray by i~
way of downcomer flow passages over weirs.
In order to effect the desired mass exchange it is necessary to obtain a compromise between the flow rates of gas upwardly and water downwardly, and t~e achievement of sufficient ~ -frothing necessary to effect the mass transfer, w~ile avoiding the creation of foaming to the extent that fluid flow is impeded and the mass transfer efficiency is disrupted. Foaming may ~ -take place, under uncontrolled conditions to the extent that ;
foam is recirculated with the gas.
The present invention provides a system for foam suppression, wherein the occurrence of foaming to an extent ~-to disrupt desired flow and mass transfer rates is suppressed by the use o~ ~ mixed g~s- and liquid spray. In addition to ' ~ '~' s,~ .
~" ' ... , .. ~,, .
: . , -~ . . .. .. . . .
~ f~ Case 2409 suppressing the formation of fo~m beyond desired limits, the mixed fluid spray further provides a balanced addition of water and H2S gas to supplement the throuyhput of the tower and to enhance the mass transfer activity within the respective tray zone.
Thus there is provided in a heavy water production plant having at least one pressure tower for the passaye of H2S gas and water in opposed coun~er flow relation therein, with a plurality of transversely extending perforated trays mounted in substantial mutually paralle]. relation and connected by downcomers for passage of water downwardly, defining flow zones wherein li~uid flows primarily transversely across the tray surface and gas flows upwardly through perforated portions of the tray surfaces, the improvement comprising a plurality of water nozzles and gas jets within at least some of the zones positioned to spray a respective fluid in foam dispersing relation towards the adjacent underlying tray, and pump means to circulate ~2S gas and waterrespectively to said jets and :~ nozzles at pressures in excess of the pressure within the tower, to supplement the fluid loading within the tower~
The provision of foam level de-tectors is con-templatedt whereby the need for the provision of foam suppression may be established, and the foam suppression system : -~operated on a non-continuous bas i5 .
Certain embodiments of the invention are described, reference being made to the accompanying drawings, wherein:
FIGURE 1 is a diagramatic representation of a tower :~ in diametrical sectional elevation I FIGURE 2 is a detail of a portion of the tower of .~ 30 Figure 1, and FIGURE 3 is a cross-sectional view of a mixing nozzle embodiment for use with the invention.
. .
,' . .
;,. .. ....... .
.: .
'~ , -':',: .
: ~ .
3~ Case 2409 n Figure l the arrang~ment 10 includes a tower 11 designed to operate at a pressure in the order of 300 p.s.i.
The tower 11 contains a plurality of trays 12 in stacked spaced relation ~herein. Each tray 12 has a perforated, gas permeable portion 13.
Feed water enters the top of the tower 11 by way of inlet feeds 15, and H2S gas is illustrated as recirculating from the top of the tower a~ ouklet 21 ~y way o~ a pipe 22 connecting with a compressor 14, from whence the gas passed to the inlet 31 located at the bottom of the tower ` Each tray 12 is served from the tray above by a downcomer 17 or plurality of downcomers 17 by which water passed from ~ray to tray. On the upper surface of each tray 12 an annular weir 33 regulates the rate of flow of water across the respective tray 12. The depth of liquid on the tray is governed by an annular outlet weir 18 bounding the respective downcomer 17 leading to the adjoining lower tray 12. Fach tray 12 is provided with an impermeable surface portion co-operating with the respective downcomer 17, and the active portion 13 of the tray 12~ is perforated, as is well known in the ar~, for ~ ~
~ the controlled passage of gas upwardly therethrouyh. - ;
; In accordance with~the present invention a water : --supply 34 connected to pump 37 provides a supply of feed water -;
at a suitahle temperature by way of inlet 26 to a riser 39 located within the towar, at a pressure in excess of tower ;
internal pressure. The riser 39 is shown chain dotted for purposes of claxity. A control ~alve 48 provides regulation o~ water ~low. Similarly, a gas supply line 42 from the pipe ~ -', 22 conne~ts wi-th a compressor 50 to supply gas at a pressure 1 30 in excess of tower pr~sure, by way of inlet 46 to a gas riser 49. The gas riser 49 is skLown irL dotted line formation for purposes of distinction and clar:ity, in Figures l and 2. A
. " .
i ,;, , ... . ,., . ,, ~ , -: , . . : :, :: . .: , , ,. ~
,.. ~ ; :: . . . . . .
: . . :, :,, . : . , : : ~
.: : . . . :
~ Case 2409 gas flow colltrol valve 47 is provided.
The zones between at least some of the trays 12 are each serviced by a water header 51 and a gas header 53.
A number of mixing nozzles 23 (See Figures 2 and 3) are located in spaced relation above the surface of the respective under-lying tray 12. Each nozzle 23 (see ~igure 3) has a gas inlet 24 and a water inlet 25 leading to coaxial outlet jets 55 and 57 respectively. The jets 55, 57 serve to mix the water and ~ ~2S gas as a high velocity jet, with the H2S gas usually `- 10 serving to energize the water, thus providing a high velocity ; water spray for impingement on the foam to be controlled.
~; While illustrated as a single unitary temperature system for a complete tower, it will be understood that the presently disclosed system may be modified where desirable, ;~ such as for purposes of temperature zoning to provide combined gas and water jets at suitable temperature and pressure com-;; patible with respective zone conditions within the tower.
~ The particular arrangements of nozzles 23 in the ; different tray zones of the tower is made in accordance with :
functional requirements. It is known in at least one existing plant to have a foam building to an extent to cause upward foam carry over from tray to tray with the gas flow, to the extent that foam may even be entrained into the gas exit 21 and re-; circulated through the compressor 14. It is contemplated that at some levels, such as the top tray, that the dispersive sprays may even be operated continuously. ~wing to the '! provision of a combined gas and water dispersive spray the extent of dilution of the working fluids may be minimized.
One experimental use, using a spray noæzle according , 30 to the invention located to spray gas and water into a downcomer,significantly reduced the foam height both within the downcomer and also across the surfa~e of the tray served by the downcomer.
,; , . . .
, , .
Case 2409 f~-The s~stem herein disclosed has the particular characteristic of re~uiring a minimum of penetrations through the wall of the tower 11. In view of the usual 3 inch plate thic~ness and the corrosive nature of H2S gas, this affords particular advantage to the s~stem~
_ 5 _ .
' .
,, , . ,, ,. ~ . . .. . . ... . .
, -.. , .. : .. : ~ .- . . . .
Claims (5)
1. A heavy water production plant having at least one pressure tower for the passage of H2S gas and water in opposed counter-flow relation therein, with a plurality of transversely extending trays including perforated surface portions and mounted in substantial mutually parallel relation and connected by downcomers for passage of water downwardly from tray to tray, defining flow zones wherein liquid flows transversely across the perforated surface portions and downwardly through the downcomers, and gas flows upwardly through the perforated tray surfaces, a plurality of water nozzles and gas jets within at least some of the zones positioned to spray the respective fluid in foam-dispersing relation towards the adjacent underlying tray, and pump means to circulate H2S gas and water respectively to said jets and nozzles at pressures in excess of the pressure within the tower, to supplement the fluid loading within the tower.
2. The plant as claimed in claim 1 wherein said water nozzles and gas jets are combined to provide mixing nozzles, each having an inner jetpipe for passage of H2S gas therethrough, and an outer annular nozzle connected with a water supply for the passage of water therethrough, said water and gas providing a high velocity spray of water droplet and gas in combined relation.
3. The plant as claimed in claim 1 or claim 2, including fluid flow control means mounted in flow regulating relation with said pump means to regulate the flow of fluids passing through said pump means.
4. The plant as claimed in claim 1 or claim 2 wherein said respective fluids are sprayed into a said downcomer.
5. The plant as claimed in claim 1 or claim 2 wherein said respective fluids are sprayed over said tray.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA212,590A CA1044132A (en) | 1974-10-29 | 1974-10-29 | Foam suppression arrangement |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA212,590A CA1044132A (en) | 1974-10-29 | 1974-10-29 | Foam suppression arrangement |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1044132A true CA1044132A (en) | 1978-12-12 |
Family
ID=4101491
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA212,590A Expired CA1044132A (en) | 1974-10-29 | 1974-10-29 | Foam suppression arrangement |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1044132A (en) |
-
1974
- 1974-10-29 CA CA212,590A patent/CA1044132A/en not_active Expired
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