CA1159762A - Desupersaturation of supersaturated aqueous calcium sulfate solutions - Google Patents
Desupersaturation of supersaturated aqueous calcium sulfate solutionsInfo
- Publication number
- CA1159762A CA1159762A CA000360536A CA360536A CA1159762A CA 1159762 A CA1159762 A CA 1159762A CA 000360536 A CA000360536 A CA 000360536A CA 360536 A CA360536 A CA 360536A CA 1159762 A CA1159762 A CA 1159762A
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- CA
- Canada
- Prior art keywords
- calcium sulfate
- vessel
- apex
- waters
- proximate
- 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
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/02—Softening water by precipitation of the hardness
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Removal Of Specific Substances (AREA)
Abstract
ABSTRACT
There is provided a process for desupersaturation of supersaturated calcium sulfate solution which comprises injecting solutions into an inverted truncated sub-stantially conical reaction vessel proximate to the apex thereof. Said vessel is provided with crystalline calcium sulfate, an entry port proximate to the said apex, an exit port proximate to the base and, in a preferred embodiment, a second exit port for the re-moval of excess calcium sulfate suspension. The size of the vessel, the amount of calcium sulfate charged and the rate and volume of injected supersaturate are predetermined to provide intimate contact between the supersaturate and the calcium sulfate charged while providing a volume adequate to permit sufficient set-tlement of the upper portions of the thus formed cal-cium sulfate suspension o that the treated waters may be drawn off at the top of said vessel through the first exit port in a form substantially free of suspended calcium sulfate.
The charged calcium sulfate provides seed cores for the crystallization of the dissolved calcium sulfate whereby the charged waters are desupersaturated.
A novel improvement in the otherwise conventional ap-paratus utilized, lies in the provision of a second exit port in the circumference of the vessel for the removal of calcium sulfate suspension to control the amounts thereof. Such a second exit port is suitably located in the lower portion of the vessel but above its apex.
There is provided a process for desupersaturation of supersaturated calcium sulfate solution which comprises injecting solutions into an inverted truncated sub-stantially conical reaction vessel proximate to the apex thereof. Said vessel is provided with crystalline calcium sulfate, an entry port proximate to the said apex, an exit port proximate to the base and, in a preferred embodiment, a second exit port for the re-moval of excess calcium sulfate suspension. The size of the vessel, the amount of calcium sulfate charged and the rate and volume of injected supersaturate are predetermined to provide intimate contact between the supersaturate and the calcium sulfate charged while providing a volume adequate to permit sufficient set-tlement of the upper portions of the thus formed cal-cium sulfate suspension o that the treated waters may be drawn off at the top of said vessel through the first exit port in a form substantially free of suspended calcium sulfate.
The charged calcium sulfate provides seed cores for the crystallization of the dissolved calcium sulfate whereby the charged waters are desupersaturated.
A novel improvement in the otherwise conventional ap-paratus utilized, lies in the provision of a second exit port in the circumference of the vessel for the removal of calcium sulfate suspension to control the amounts thereof. Such a second exit port is suitably located in the lower portion of the vessel but above its apex.
Description
~59762 BACKGROUND OF THE INVENTION
1. Field of the Invention The removal of calcium sulfate from supersaturated solutions thereof.
1. Field of the Invention The removal of calcium sulfate from supersaturated solutions thereof.
2. Description of Relevant Art The excess dissolved salt in a supersaturated solution may be precipitated by contacting said solution with suitable crystalization seeds. These seeds may be, but do not have to be initially of the same chemical composition as the dissolved solid. While this prin-ciple is one of the oldest in the field of physical chemistry, its application in industrial processes is often not simple since the speed of said desuper-saturation and the size of the particles thus precipi-tated vary enormously in accordance with somewhat un-predictable principles.
In the field of water treatment, the recovery of waters in cooling towers utilized in areas having poor water supply is an extremely important aspect of generation of electric power in such areas. In order to protect the condensers of such plants the mineral content of such cooling tower blowdown waters must be minimized.
' One particularly important contaminent has been found to be gypsum or calcium sulfate. In one of the puri-~ fication steps used for the demineralization of such -~ waters the blow down waters are subjected to reverse osmosis which gives rise to an effluent of relatively ~; ~ low mineral content and a second effluent of relatively high mineral content. The effluent of relatively high mineral content contains a substantial amount of cal-cium sulfate in a supersaturated state. Such super-saturation is reduced to saturation and the thus treated ::
~ waters are recycled through the reverse osmosis system.
; : ~
~15~97fiZ
A generally accepted prior art apparatus is discussed and illustrated by Kosarik et al (Professional Engineer 47, 30 (october 1977)) and by Van Hoek et al (Desalina-tion 19, 471-479 (1976)). Such systems basically com-prise a settling tank or compartment containing solid calcium sulfate which may or may not be agitated.
The problem encountered with these systems is that - they require relatively long settling times and the calcium sulfate produced in the desupersaturation step is in the form of a sludge which is very difficult to dewater. It is therefore desirable to provide a method whereby the desupersaturation takes place rapidly and yields the precipitated gypsum in a good crystalline form which may be readily dewatered.
The sludge problem in the removal of supersaturates is not new. An interesting and successful approach in the removal of calcium carbonate in lime softening of water was developed and patented by Zentner, U.S.
Patent 2,259,717. In the Zentner process there is utilized an inverted truncated conical reaction vessel.
The high calcium bicarbonate containing waters together with solutions of certain reagent chemicals are in-; 25 jected into the vessel proximate its apex. This in-- jection is tangential, since the swirling effect pro-duced by tangential injection aids mixing without creating undesirabl~ forms of turbulence. A further feature of the Zentner process requires the provision of core particles, designated generally as granular contact materials, which may but need not be of the same chemical composition as is formed in the lime treatment of the injected waters.
; 2 ~IL159~62 In the Zentner process the bicarbonate present in the injected waters is converted into carbonate by the introduction of lime solution (calcium hydroxide).
This reaction raises the total carbonate level above the saturation point of the calcium carbonate ~nducing a temporary state of supersaturation which is ~hen reduced by the formation of the calcium carbonate coating upon added swirled sand granules. Due to the nature of calcium carbonate crystallization such particles continue to grow in the system by the formation of a substantially even coating of calcium carbonate on the sand granules.
While the high mineral content reverse osmosis effluent contains calcium sulfate in a state of supersaturation and does not req~Jire the addition of further chemicals ; to provide said state of supersaturation, the inventors herein p~stulated that the swirling granular aspect of the Zentner process might be useful in the desuper-saturation of supersaturated calcium sulfate solution.
;~ Unfortunately this postulate proved to be erroneous.
A review of the results obtained in such attempts show tha~ calcium sulfate, in contrast to calcium carbonate does not form an even coating upon the sand granules.
It was observed that the crystals which did form, broke off from the seed granules and formed very finely di-vided material having dewatering problems analogous to those shown by the sludges of the prior art.
SUMMARY OF THE INVENTION
; ~ ~ It has been found that by utilizing crystalline gypsum as the seed core in an inverted truncated reaction vessel, supersaturated calcium sulfate solutions can be readily reduced to saturation state with the concomitant .
~ 3 ' ' ' production of crystalline and readily dewaterable cal-cium sulfate precipitate when injected into said reac-tion vessel at or proximate to the apex thereof. It has been found that particularly desirable results may be obtained by injecting the supersaturate tan-gentially to the circumference of the reaction vessel at a location proximate to the apex thereof. The size of the reaction vessel therefor the amount added calcium sulfate crystals and the velocity and volume of super-saturate injection are so predetermined as to permit a settlement area at the top of the vessel so that the desupersaturated solution may be drawn off in a condition substantially free of any suspended calcium sulfate. ;It has also been found, contrary to the arrangements pr~sently utilized, that the optimum location of a second exit port for the removal of excess solid calcium sulfate is at a point proximate to but above the apex of the reaction vessel, prefer-ably between about three quarters to about one-half of the height of the cone above the apex.
In one particularly preferred embodiment of the process the formation of gypsum of desirable crystalline size and quantity is obtained by the periodic injection of a portion of the treated waters from the top of the reaction vessel into the entry port at the bottom or apex of the vessel. Such injection provides an alternation in the concentration of the injected waters and such alternation has been found to yield desirable results.
DESCRIPTION OF THE DR~WINGS
The sole figure is a schematic representation of the system of the present invention.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drawing may be considered as containing two parts.
Items 10 through 22 are substantially conventional and represent a typical source of supersaturated calcium sulfate solution and Items 24 through 34 represent the additional apparatus required to practice ~he present invention.
The blowdown waters from cooling tower 10 are lead through transfer line 20 into the reverse osmosis unit 14. Connected to line 20 through branch pipe 18 is a source of pH adjustment 12. The reverse osmosis unit 14 comprises the segment 16 from which a substan-tially mineral-free effluent is exited through outflow pipe 17 and a high mlneral content segment 19 from which the supersaturated calcium sulfate solution is exited through outflow pipe 22. The actual reaction apparatus, that is to say the truncated inverted conical vessel suitably of COnical angle of about 20 through about 25 degrees utilized in the present invention is represented by sector A of a vessel 30. In the preferred embodiment, inflow pipe 22 enters reactor 30 at entry port 24 proximate apex 25, as shown in the illustration. Preferably the inflow pipe 22 is tangential to the circumference of a section of the cone taken at the polnt of entry 24.
:
The remaining sector8 B and C of reactor vessel 30 are illustrated as bcing cylindrical. The shape of these sectors is not important to the present invention and is used to increase the volume of the vessel.
The conical form of sector A may, if desired, be continued to the top of the reactor vessel 30. Proximate to ~ the top of reactor vessel 30 is a first exit port 28 !~ ~ 35 connected through exlt line 29 to transfer line 20.
Leading from exit pipe 29 is transfer pipe 32 controlled by valve 34 leading to supersaturate inflow pipe 22.
: , , .
:~597~2 A second exit port 26 is provided proximate to but above apex 25 in sector A of reactor 30. Connected to second exit port 26 is second outflow pipe 33.
In the operation of the process, crystalline ~alcium sulfate, suitably 40-50 mesh (U.S. standard si~eves) is charged to reactor 30 to a level not higher than the indicated interface of sectors B and C of reactor 30. Supersaturated calcium sulfate, suitably reverse osmosis reject is injected into entry port 24 through inlet pipe 22. The injection of these waters swirls the calcium sulfate in reactor 30, bringing about further crystallization on the previously charged seed core.
The swirling effect in the lower sector A of reactor 30 diminishes as the water passes upwards through the vessel. It has been found suitable to inject waters at a rate which would provide a flow of about 6 to about 12 gallons per square foot of area in sector B.
In sector B the calcium sulfate crystals are found -~ ~ as a suspension of a decreasing density with respect to height, while sector C is substantially free of suspended calcium sulfate.
It will be understood by those skilled in the art that ; the designation of sector A, B, and C of reactor 30 is purely a matter of illustrative convenience and is not intended to specify or delineate strict boundary lines.
The desupersaturated waters are drawn off through exit port 28 and recycled into the reverse osmosis system through outflow pipe 29. It is our surprising observation that in contFast to the swirling motion near the apex of the cone, a circumferential downdraft is noticed at levels above 1/2 to 1/4 of the cone height above - . " ~
" . . . . . .
~1~976~:
the apex where the reactor is entirely conical or 1/2 to 1/4 at the combined height of A and B in the reactor shwon in Figure 1.
In one embodiment of the present invention it has been found useful to "pulse" the concentration of supersat~rate in reactGr 30. Thus, supersaturate is injected into entry port 24 for a predetermined time period. Thereafter the supersaturate is diluted by saturated solution drawn off from exit pipe 29 through branch pipe 32 controlled by valve 34, for a further predetermined period. It has been found that this concentration pulsing prevents excessively rapid build up of calcium sulfate crystals in sector A of reactor 30.
The amount of calcium sulfate in the reactor is con-trolled by drawing off the calcium sulfate crystals through the second exit port 26 which is preferably located at a point above the apex 25 which is between 25-50% of the height of the cone (section A), where a totally conical reactor is employed or at a point between 25-50% of the combined height of sections A
and B of the reactor shown in Figure 1. It has been found that drawing off the crystals at such a level is more efficient than drawing them off at the apex 25 and leads to the formation of more readily dewater-able calcium sulfate crystals than the methods in the prior art which taught that the product should be drawn off through apex 25. While drawing off the crystals at these levels is preferred the invention is not limited thereto since the crystals could be removed at points above or below these levels. The thus obtained crystal-' line calcium sulfate is then dewatered, suitably by ; ~ strainin~, by methods well known in the art.
:,.
.''' ' .
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:, - " -Example 1 There is utilized a twenty inch top diameter Spiractor of approximately 25 apex angle. The Spiractor is filled about two-thirds full with gypsum crystals of 5 approximately 45 mesh (US standard sieve) saline solu-tions containing sodium chloride and sulfate in con-centrations as set forth below were passed through the Spiractor. The calcium levels of the influent and effluent after certain given time periods of operation 10 are measured and the removal shown.
Rcduction of Calcium Levels (mg/l as CaC03) Across 20"0 Spiractor flow rate 12 gpm Date 2/10 2/15 2/17 Influent Ca 3650 3775 3800 Mg 3900 4025 4000 Cond. x 103 mho 37.9 42.0 43.0 S04 approximately 7500 Effluent Cà 3250 3275 3300 Mg 3900 3975 4000 Cond. x 103 mho 37.B 41.3 43Ø
Removal Ca 400 - 500 500 Gypsum removed/ ND 1.64 1.72 day-cu.ft.
NDcnot determined , Registered Trademark ., ~ - .
~5~2 Example 2 In a similar test using a 24 inch diameter Spiractor the change in calcium and sulfate content when passed through the fluidized seed bed at 12 gpm was as follows:
S
Reduction of Calcium Levels ~ ~mg/l as CaC03) .Across 24"0 Spiractor flow rate 12 gpm Date . 3/21 3/22 Influent Ca 4200 3400 Mg 3050 3100 Cl . 13400 13300 Effluent Ca 3500 2900 Mg 3050 . 3100 Cl 13400 13300 : Removal Ca 700 . 500 Cypsum removed/
day-cu.ft. ND ND
ND=not determined ;~
'i ::j :j~ 9 ~ ~ .
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Example 3 In accordance with the procedures in Example 2, super-saturated solution was circulated through the Spiractor 24 hours a day for 468 hours of continuous operation.
The level of the settled gypsum in the Spiractor increased by 21 inches during this time. The flow rate utilized was 15 gallons per minute comprising 2.4 gallons per minute of influent of the type utilized in Example 1.
The remainder comprising saturated but not supersaturated recirculated Spiractor effluent.
Example 4 A feed containing 1,500 ppm calcium chloride and 1,500 ppm sodium sulfate was passed through a tubular reverse osmosis process. This represents a calcium sulfate concentration of approximately 50% of concentration.
The reverse osmosis system operates to produce 90~ re-covery of water. Thus, a concentration factor of ten time yields an effluent of 14,300 ppm calcium sulfate which is 4.5 times saturation value. This reverse osmosis effluent was utilized as the Spiractor influent in the 468 hour operation set forth above, the effluent from the Spiractor operation being utilized by in part, for the feed for the reverse osmosis system. No clogging of the reverse osmosis membrane during this operation was noted.
:~
.
' ': 10 ' ; :
In the field of water treatment, the recovery of waters in cooling towers utilized in areas having poor water supply is an extremely important aspect of generation of electric power in such areas. In order to protect the condensers of such plants the mineral content of such cooling tower blowdown waters must be minimized.
' One particularly important contaminent has been found to be gypsum or calcium sulfate. In one of the puri-~ fication steps used for the demineralization of such -~ waters the blow down waters are subjected to reverse osmosis which gives rise to an effluent of relatively ~; ~ low mineral content and a second effluent of relatively high mineral content. The effluent of relatively high mineral content contains a substantial amount of cal-cium sulfate in a supersaturated state. Such super-saturation is reduced to saturation and the thus treated ::
~ waters are recycled through the reverse osmosis system.
; : ~
~15~97fiZ
A generally accepted prior art apparatus is discussed and illustrated by Kosarik et al (Professional Engineer 47, 30 (october 1977)) and by Van Hoek et al (Desalina-tion 19, 471-479 (1976)). Such systems basically com-prise a settling tank or compartment containing solid calcium sulfate which may or may not be agitated.
The problem encountered with these systems is that - they require relatively long settling times and the calcium sulfate produced in the desupersaturation step is in the form of a sludge which is very difficult to dewater. It is therefore desirable to provide a method whereby the desupersaturation takes place rapidly and yields the precipitated gypsum in a good crystalline form which may be readily dewatered.
The sludge problem in the removal of supersaturates is not new. An interesting and successful approach in the removal of calcium carbonate in lime softening of water was developed and patented by Zentner, U.S.
Patent 2,259,717. In the Zentner process there is utilized an inverted truncated conical reaction vessel.
The high calcium bicarbonate containing waters together with solutions of certain reagent chemicals are in-; 25 jected into the vessel proximate its apex. This in-- jection is tangential, since the swirling effect pro-duced by tangential injection aids mixing without creating undesirabl~ forms of turbulence. A further feature of the Zentner process requires the provision of core particles, designated generally as granular contact materials, which may but need not be of the same chemical composition as is formed in the lime treatment of the injected waters.
; 2 ~IL159~62 In the Zentner process the bicarbonate present in the injected waters is converted into carbonate by the introduction of lime solution (calcium hydroxide).
This reaction raises the total carbonate level above the saturation point of the calcium carbonate ~nducing a temporary state of supersaturation which is ~hen reduced by the formation of the calcium carbonate coating upon added swirled sand granules. Due to the nature of calcium carbonate crystallization such particles continue to grow in the system by the formation of a substantially even coating of calcium carbonate on the sand granules.
While the high mineral content reverse osmosis effluent contains calcium sulfate in a state of supersaturation and does not req~Jire the addition of further chemicals ; to provide said state of supersaturation, the inventors herein p~stulated that the swirling granular aspect of the Zentner process might be useful in the desuper-saturation of supersaturated calcium sulfate solution.
;~ Unfortunately this postulate proved to be erroneous.
A review of the results obtained in such attempts show tha~ calcium sulfate, in contrast to calcium carbonate does not form an even coating upon the sand granules.
It was observed that the crystals which did form, broke off from the seed granules and formed very finely di-vided material having dewatering problems analogous to those shown by the sludges of the prior art.
SUMMARY OF THE INVENTION
; ~ ~ It has been found that by utilizing crystalline gypsum as the seed core in an inverted truncated reaction vessel, supersaturated calcium sulfate solutions can be readily reduced to saturation state with the concomitant .
~ 3 ' ' ' production of crystalline and readily dewaterable cal-cium sulfate precipitate when injected into said reac-tion vessel at or proximate to the apex thereof. It has been found that particularly desirable results may be obtained by injecting the supersaturate tan-gentially to the circumference of the reaction vessel at a location proximate to the apex thereof. The size of the reaction vessel therefor the amount added calcium sulfate crystals and the velocity and volume of super-saturate injection are so predetermined as to permit a settlement area at the top of the vessel so that the desupersaturated solution may be drawn off in a condition substantially free of any suspended calcium sulfate. ;It has also been found, contrary to the arrangements pr~sently utilized, that the optimum location of a second exit port for the removal of excess solid calcium sulfate is at a point proximate to but above the apex of the reaction vessel, prefer-ably between about three quarters to about one-half of the height of the cone above the apex.
In one particularly preferred embodiment of the process the formation of gypsum of desirable crystalline size and quantity is obtained by the periodic injection of a portion of the treated waters from the top of the reaction vessel into the entry port at the bottom or apex of the vessel. Such injection provides an alternation in the concentration of the injected waters and such alternation has been found to yield desirable results.
DESCRIPTION OF THE DR~WINGS
The sole figure is a schematic representation of the system of the present invention.
:
~ 4 '~
' '76Z
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drawing may be considered as containing two parts.
Items 10 through 22 are substantially conventional and represent a typical source of supersaturated calcium sulfate solution and Items 24 through 34 represent the additional apparatus required to practice ~he present invention.
The blowdown waters from cooling tower 10 are lead through transfer line 20 into the reverse osmosis unit 14. Connected to line 20 through branch pipe 18 is a source of pH adjustment 12. The reverse osmosis unit 14 comprises the segment 16 from which a substan-tially mineral-free effluent is exited through outflow pipe 17 and a high mlneral content segment 19 from which the supersaturated calcium sulfate solution is exited through outflow pipe 22. The actual reaction apparatus, that is to say the truncated inverted conical vessel suitably of COnical angle of about 20 through about 25 degrees utilized in the present invention is represented by sector A of a vessel 30. In the preferred embodiment, inflow pipe 22 enters reactor 30 at entry port 24 proximate apex 25, as shown in the illustration. Preferably the inflow pipe 22 is tangential to the circumference of a section of the cone taken at the polnt of entry 24.
:
The remaining sector8 B and C of reactor vessel 30 are illustrated as bcing cylindrical. The shape of these sectors is not important to the present invention and is used to increase the volume of the vessel.
The conical form of sector A may, if desired, be continued to the top of the reactor vessel 30. Proximate to ~ the top of reactor vessel 30 is a first exit port 28 !~ ~ 35 connected through exlt line 29 to transfer line 20.
Leading from exit pipe 29 is transfer pipe 32 controlled by valve 34 leading to supersaturate inflow pipe 22.
: , , .
:~597~2 A second exit port 26 is provided proximate to but above apex 25 in sector A of reactor 30. Connected to second exit port 26 is second outflow pipe 33.
In the operation of the process, crystalline ~alcium sulfate, suitably 40-50 mesh (U.S. standard si~eves) is charged to reactor 30 to a level not higher than the indicated interface of sectors B and C of reactor 30. Supersaturated calcium sulfate, suitably reverse osmosis reject is injected into entry port 24 through inlet pipe 22. The injection of these waters swirls the calcium sulfate in reactor 30, bringing about further crystallization on the previously charged seed core.
The swirling effect in the lower sector A of reactor 30 diminishes as the water passes upwards through the vessel. It has been found suitable to inject waters at a rate which would provide a flow of about 6 to about 12 gallons per square foot of area in sector B.
In sector B the calcium sulfate crystals are found -~ ~ as a suspension of a decreasing density with respect to height, while sector C is substantially free of suspended calcium sulfate.
It will be understood by those skilled in the art that ; the designation of sector A, B, and C of reactor 30 is purely a matter of illustrative convenience and is not intended to specify or delineate strict boundary lines.
The desupersaturated waters are drawn off through exit port 28 and recycled into the reverse osmosis system through outflow pipe 29. It is our surprising observation that in contFast to the swirling motion near the apex of the cone, a circumferential downdraft is noticed at levels above 1/2 to 1/4 of the cone height above - . " ~
" . . . . . .
~1~976~:
the apex where the reactor is entirely conical or 1/2 to 1/4 at the combined height of A and B in the reactor shwon in Figure 1.
In one embodiment of the present invention it has been found useful to "pulse" the concentration of supersat~rate in reactGr 30. Thus, supersaturate is injected into entry port 24 for a predetermined time period. Thereafter the supersaturate is diluted by saturated solution drawn off from exit pipe 29 through branch pipe 32 controlled by valve 34, for a further predetermined period. It has been found that this concentration pulsing prevents excessively rapid build up of calcium sulfate crystals in sector A of reactor 30.
The amount of calcium sulfate in the reactor is con-trolled by drawing off the calcium sulfate crystals through the second exit port 26 which is preferably located at a point above the apex 25 which is between 25-50% of the height of the cone (section A), where a totally conical reactor is employed or at a point between 25-50% of the combined height of sections A
and B of the reactor shown in Figure 1. It has been found that drawing off the crystals at such a level is more efficient than drawing them off at the apex 25 and leads to the formation of more readily dewater-able calcium sulfate crystals than the methods in the prior art which taught that the product should be drawn off through apex 25. While drawing off the crystals at these levels is preferred the invention is not limited thereto since the crystals could be removed at points above or below these levels. The thus obtained crystal-' line calcium sulfate is then dewatered, suitably by ; ~ strainin~, by methods well known in the art.
:,.
.''' ' .
:
,;, :.
:, - " -Example 1 There is utilized a twenty inch top diameter Spiractor of approximately 25 apex angle. The Spiractor is filled about two-thirds full with gypsum crystals of 5 approximately 45 mesh (US standard sieve) saline solu-tions containing sodium chloride and sulfate in con-centrations as set forth below were passed through the Spiractor. The calcium levels of the influent and effluent after certain given time periods of operation 10 are measured and the removal shown.
Rcduction of Calcium Levels (mg/l as CaC03) Across 20"0 Spiractor flow rate 12 gpm Date 2/10 2/15 2/17 Influent Ca 3650 3775 3800 Mg 3900 4025 4000 Cond. x 103 mho 37.9 42.0 43.0 S04 approximately 7500 Effluent Cà 3250 3275 3300 Mg 3900 3975 4000 Cond. x 103 mho 37.B 41.3 43Ø
Removal Ca 400 - 500 500 Gypsum removed/ ND 1.64 1.72 day-cu.ft.
NDcnot determined , Registered Trademark ., ~ - .
~5~2 Example 2 In a similar test using a 24 inch diameter Spiractor the change in calcium and sulfate content when passed through the fluidized seed bed at 12 gpm was as follows:
S
Reduction of Calcium Levels ~ ~mg/l as CaC03) .Across 24"0 Spiractor flow rate 12 gpm Date . 3/21 3/22 Influent Ca 4200 3400 Mg 3050 3100 Cl . 13400 13300 Effluent Ca 3500 2900 Mg 3050 . 3100 Cl 13400 13300 : Removal Ca 700 . 500 Cypsum removed/
day-cu.ft. ND ND
ND=not determined ;~
'i ::j :j~ 9 ~ ~ .
~i~i9~7{iZ
Example 3 In accordance with the procedures in Example 2, super-saturated solution was circulated through the Spiractor 24 hours a day for 468 hours of continuous operation.
The level of the settled gypsum in the Spiractor increased by 21 inches during this time. The flow rate utilized was 15 gallons per minute comprising 2.4 gallons per minute of influent of the type utilized in Example 1.
The remainder comprising saturated but not supersaturated recirculated Spiractor effluent.
Example 4 A feed containing 1,500 ppm calcium chloride and 1,500 ppm sodium sulfate was passed through a tubular reverse osmosis process. This represents a calcium sulfate concentration of approximately 50% of concentration.
The reverse osmosis system operates to produce 90~ re-covery of water. Thus, a concentration factor of ten time yields an effluent of 14,300 ppm calcium sulfate which is 4.5 times saturation value. This reverse osmosis effluent was utilized as the Spiractor influent in the 468 hour operation set forth above, the effluent from the Spiractor operation being utilized by in part, for the feed for the reverse osmosis system. No clogging of the reverse osmosis membrane during this operation was noted.
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Claims (8)
1. A process of treating waters to reduce the calcium sulfate concentration in waters containing concentra-tions of calcium sulfate above saturation concentration by contacting said waters with crystalline calcium sul-fate characterized by the steps of:
a) providing an inverted truncated substantially conical vessel having an entry port proximate the apex thereof and an outlet port proximate the top of said vessel;
b) charging crystalline calcium sulfate into said vessel;
c) injecting said waters containing supersaturated concentrations of calcium sulfate into said vessel through said entry port; and d) removing the excess treated waters through said outlet port.
a) providing an inverted truncated substantially conical vessel having an entry port proximate the apex thereof and an outlet port proximate the top of said vessel;
b) charging crystalline calcium sulfate into said vessel;
c) injecting said waters containing supersaturated concentrations of calcium sulfate into said vessel through said entry port; and d) removing the excess treated waters through said outlet port.
2. A process in accordance with Claim 1 wherein said entry port is disposed proximate said vessel apex in a manner to cause said water to flow upwardly with a swirling motion within said vessel.
3. A process in accordance with Claim 1 whereby said water inflow rate is sufficient to maintain the calcium sulfate in that degree of suspension so that the waters at the exit port are substantially free of suspended calcium sulfate.
4. A process in accordance with Claim 1 further in-cluding the additional step of recycling a portion of said treated outflow water through said entry port.
5. A process in accordance with Claim 1 further in-cluding the additional step of removing a predetermined amount of calcium sulfate from said vessel during the operation of the process.
6. A process in accordance with Claim 5 wherein said calcium sulfate is removed as a suspension from the apex of the vessel.
7. A process in accordance with Claim 5 wherein said calcium sulfate is removed as a suspension from a level in said vessel proximate to but above the apex of the said conical vessel.
8. A process in accordance with Claim 7 wherein said removal level is at a distance above the apex thereof of between about 25% and about 50% of the height of said conical vessel.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7597479A | 1979-09-17 | 1979-09-17 | |
| US75,974 | 1979-09-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1159762A true CA1159762A (en) | 1984-01-03 |
Family
ID=22129104
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000360536A Expired CA1159762A (en) | 1979-09-17 | 1980-09-17 | Desupersaturation of supersaturated aqueous calcium sulfate solutions |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS5645825A (en) |
| CA (1) | CA1159762A (en) |
| DE (1) | DE3034898A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3305800A1 (en) * | 1983-02-19 | 1984-08-23 | Philipp Müller, Nachf. Eugen Bucher GmbH & Co., 7000 Stuttgart | Waste water treatment process |
| US5538641A (en) * | 1994-12-29 | 1996-07-23 | Global Environmental Solutions, Inc. | Process for recycling laden fluids |
-
1980
- 1980-09-12 JP JP12615180A patent/JPS5645825A/en active Pending
- 1980-09-16 DE DE19803034898 patent/DE3034898A1/en not_active Withdrawn
- 1980-09-17 CA CA000360536A patent/CA1159762A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5645825A (en) | 1981-04-25 |
| DE3034898A1 (en) | 1981-04-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |