CA2045195C - Steam stripping process for softening water - Google Patents
Steam stripping process for softening waterInfo
- Publication number
- CA2045195C CA2045195C CA 2045195 CA2045195A CA2045195C CA 2045195 C CA2045195 C CA 2045195C CA 2045195 CA2045195 CA 2045195 CA 2045195 A CA2045195 A CA 2045195A CA 2045195 C CA2045195 C CA 2045195C
- Authority
- CA
- Canada
- Prior art keywords
- water
- steam
- process according
- produced
- temperature
- 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 - Fee Related
Links
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 74
- 238000000034 method Methods 0.000 title claims abstract description 24
- 239000000463 material Substances 0.000 claims abstract description 9
- 238000001556 precipitation Methods 0.000 claims abstract description 8
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 24
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 12
- 239000003129 oil well Substances 0.000 claims description 7
- 238000010793 Steam injection (oil industry) Methods 0.000 claims description 6
- 235000017550 sodium carbonate Nutrition 0.000 claims description 6
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 6
- 238000000926 separation method Methods 0.000 claims description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 29
- 229910002092 carbon dioxide Inorganic materials 0.000 description 15
- 239000001569 carbon dioxide Substances 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 10
- -1 Mg++ ions Chemical class 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 3
- 239000010802 sludge Substances 0.000 description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910000019 calcium carbonate Inorganic materials 0.000 description 2
- 239000000347 magnesium hydroxide Substances 0.000 description 2
- 235000012254 magnesium hydroxide Nutrition 0.000 description 2
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 2
- 238000011045 prefiltration Methods 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000011780 sodium chloride Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000003643 water by type Substances 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 235000010216 calcium carbonate Nutrition 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002332 oil field water Substances 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 239000008234 soft water Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000004326 stimulated echo acquisition mode for imaging Methods 0.000 description 1
- 238000013022 venting Methods 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
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
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
- C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
Landscapes
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Paper (AREA)
- Removal Of Specific Substances (AREA)
- Physical Water Treatments (AREA)
Abstract
A steam stripping process for softening water comprises contacting said water with steam to bring said water to a temperature of at least substantially 190 °C, to strip CO2 from said water and to cause the precipitation of Ca++ and/or Mg++ from said water.
Subsequently sufficient alkaline material is added to bring the pH of said stripped water to at least substantially 10. Thereafter, precipitated Ca++ and/or Mg++ is separated from said water.
Subsequently sufficient alkaline material is added to bring the pH of said stripped water to at least substantially 10. Thereafter, precipitated Ca++ and/or Mg++ is separated from said water.
Description
204~19S
STEAM STRIPPING PROCESS FOR SOFTENING WATER
This invention relates to a steam stripping process for softening water. More particularly, the invention relates to a steam stripping process for softening "produced water" from an oil well.
Steam injection is practised in some oil fields to enhance the product of heavy, viscous crudes. Typically the produced waters are strongly saline solutions, which also contain dissolved Ca++ and Mg++ ions.
To protect the environment, and to avoid disposal problems, it is desirable to use the produced water as feed water for the steam generators which make the steam for the steam injection. Before the produced water can be used it must be softened, i.e., Ca++
and Mg++ ions must be removed: this is necessary to protect the steam generators from scale formation and subsequent burnout.
In US-A-4877536 and CA-A-1217986 softening processes are described in which the produced waters are stripped of carbon dioxide (CO2) with steam, thereby (i) converting bicarbonate ions (HCO3-) to carbonate ions (CO3--), which precipitates calcium, and (ii) converting HCO3- to hydroxyl ions (OH-), which precipitates magnesium. The advantage of these methods of water softening is that they are efficient for water that contains sodium chloride, whereas conventional ion exchange, or zeolite, softening processes become less efficient as the salt concentration increases, and become impracticable at salt concentrations above about 5000 mg/1. Furthermore, the steam stripping methods utilize HCO3-, which is already present in the produced water,thereby minimi~in~ any required addition of CO3-- and/or OH-.
In the above patents it is disclosed that if the produced water does not contain sufficient HCO3- to precipitate completely the Ca++ and Mg++ through the formation of CO3-- and OH-, then sufficient Na2CO3 and/or NaOH must be added to the feed water to effect the desired reactions during subsequent steam stripping. To produce soft water having less -~r ~ . .~
than 1 mg/l Mg++ and Ca++, as specified for steam generators, the outlet pH of the steam stripper must be at least about 10.0, and the temperature must be at least about 190C.
It is an object of the present invention to provide an improved steam stripping process for softening water.
According to the present invention there is provided a steam stripping process for softening water, comprising contacting said water with steam to bring said water to a temperature sufficient to strip CO2 from said water and to cause the precipitation of Ca++ and/or Mg++ from said water; subsequently adding sufficient alkaline material to bring the pH of said stripped water to at least substantially 10; and thereafter separating precipitated Ca++ and/or Mg++ from said water.
Said separation is advantageously carried out by settling.
It is especially preferred that the water is produced water obtained from an oil well that has been subjected to steam injection.
The alkaline material is preferably Na2CO3 and/or NaOH.
Preferably the water is brought to a temperature of at least 185 C, more preferably at least 190C.
Desirably the stripping steam brings the water to a temperature in the range of from substantially 190C to substantially 200C. The skilled person will readily appreciate that the pressure can be m~int~ined at a suitable value to keep the water in liquid form.
The softened water may be converted to steam in a steam generator, and the steam can then be used in oil well steam injection.
X
The reactions that occur when the produced water is steam stripped to a temperature of 190C to 200C are as follows:
(i) bicarbonate is converted to carbonate in accordance with the reaction:
2HCO3- -------> H2O + CO2 + CO3 (1) (ii) carbonate is converted to hydroxyl in accordance with the reaction:
CO3-- + H2O -------> CO2 + 20H- (2) The CO3-- formed by reaction (1) and the OH- formed by reaction (2) precipitate Ca++
and Mg++ respectively by the reactions:
Ca++ + C03-- ------> CaC03 (3) Mg++ + 2(0H-) ------> Mg(OH)2 (4) Reaction (4) requires a pH of substantially 10 or more to effect sufficient precipitation of Mg++.
In practice, it can be calculated from chemical equilibria that the CO2 concentration in equilibrium with HCO3- and CO3- becomes smaller as the pH increases. For example, it has been calculated for a given oil field water originally CO~ g about 500 mg/l of HC03- that the CO2 partial pressure would decrease with increasing pH as follows:
TEMPERATURE/C ~ CO2 PART. PRESS./KPa 195 7.7 42 195 8.5 35 195 9.0 25 195 9.5 12 195 10.0 2.3 195 10.5 0.21 ,' ~ ~r .:~
- ` 2045195 It is clear from the foregoing that in order to obtain a pH of about 10 in the stripping step (i.e., sufficient to effect precipitation of Mg++) it is necessary for the stripping steam itself to contain virtually no CO2. However, in practice, the steam produced by oil field steam generators contains CO2 because the feed water contains some HCO3-and CO3--: this causes CO2 to be produced in the steam generator at its operating temperature of around 300C by reactions (1) and (2). In the example cited above, the steam contained about 3.0 KPa partial pressure of C02; and a pH of 10 could not be achieved in the stripping step, so that Mg++ would not precipitate.
In the present invention CO2 is stripped more effectively by not adding any alkaline agents (e.g., Na2CO3 and/or NaOH) prior to the stripping step. It has been found that if the stripping steam contains sufficient C2 to prevent the attainment of pH 10, then it is more efficient to add Na2CO3 (if required for Ca++ precipitation) and NaOH to achieve a pH of 10 or greater after the stripping step. In tests, it was found that the process according to the invention halved the required steam venting rate and halved therequired addition of NaOH.
Reference is now made to the accompanying drawing, which is a schematic diagram illustrating the method of softening water according to the invention.
A mixture of oil and water is removed from the oil well and passed through a de-oiling unit (not shown), which separates the oil from the water; in practice the water (known as "produced water") is a saline solution, which also contains Ca++ and Mg++ ions in solution.
After being separated from the oil, the produced water is passed to a de-oil tank 10 via line 12. The produced water is then fed to an oil pre-filter 14 via line 16; the oil pre-filter 14 removes oil that may not have been separated in the de-oiling unit. The filtered produced water is fed to a heat exchanger 18 via line 20, where it is pre-heated to a temperature of about 75 C. The pre-heated water is then fed to a steam stripper 22 - X
- ~ 2045195 via line 24; the pre-heating of the produced water reduces the quantity of steamrequired in the stripper 22.
In the steam stripper 22 the produced water is contacted with steam to bring thetemperature thereofto about 190 - 200C; typically the pressure in the stripper would be of the order of 1000 KPa. The steam enters the stripper 22 via the line 26 at a temperature of about 300C. It is preferred that the steam is sprayed into the produced water as the water flows downwardly through the stripper. In the stripper 22 the steam strips CO2 from the produced water; during this process, reactions (1) to (4) above take place causing the precipitation of Ca++ and Mg++. CO2, together with uncondensedsteam, pass out through the top of the stripper via line 28. The stripped produced water passes out through the bottom of the stripper through line 30.
If the pH of the stripped produced water is below substantially 10, and the stripping steam has too large a CO2 partial pressure to permit precipitation of sufficient Mg++ (or even Ca++), then an alkaline material from container(s) 32 can be mixed with line 30 via line 34. It may be, in certain circumstances, that the amount of alkaline material needing to be added is zero. The alkaline material would typically be Na2CO3 to precipitate Ca++, and NaOH to precipitate Mg++. A pH meter (not shown) may monitor the pH of the stripped produced water in line 30 as it leaves the stripper 22 and may provide data to a flow control device (not shown) that can adjust the addition of NaOH
to m~int~in a pH above substantially 10.
The stripped produced water is passed to a settling tank 36 where the Ca++ and Mg++ are removed (as CaCO3 and Mg(OH)2 respectively) in the form of a sludge via line 38. It is possible to provide a sludge mixer (not shown) at the bottom of the tank 36, and also a sludge recirculation system (not shown) can be provided; these features can help to reduce the quantity of silica in the water. In addition, anti-scale chemicals may be added to the tank 36, to help prevent scale from depositing on the surface thereof.
Finally, it is possible for the stripper 22 and settling tank 36 to be formed as a single ., y ,~".
. ~
unit; in this embodiment the alkali material would be added to the produced water after it had passed through the stripping part of the appal~us.
The softened produced water is removed from the tank 36 via line 40, and is fed to the heat exchanger 18 where it is cooled by the pre-filtered produced water in line 20. The cooled softened produced water is then fed via line 42 to filtration and polishing equipment indicated by reference 44, where any solids carryover from the settling tank 36 is removed. The softened produced water is subsequently passed to a head tank 46 via line 48.
Water is taken from the head tank 46, as required, and fed to a steam generator 50 via line 52. Steam generator 50 produces steam that is fed to an oil well for steam injection via line 54. It will be noted that a part of the steam in line 54 is diverted via the line 26 for use as feed steam in the stripper 22; approximately 20% of the flow in the line 54 is diverted to the stripper 22.
It will be appreciated by the person skilled in the art that modifications may be made to the embodiment described with reference to the drawings, within the scope of theappended claims.
STEAM STRIPPING PROCESS FOR SOFTENING WATER
This invention relates to a steam stripping process for softening water. More particularly, the invention relates to a steam stripping process for softening "produced water" from an oil well.
Steam injection is practised in some oil fields to enhance the product of heavy, viscous crudes. Typically the produced waters are strongly saline solutions, which also contain dissolved Ca++ and Mg++ ions.
To protect the environment, and to avoid disposal problems, it is desirable to use the produced water as feed water for the steam generators which make the steam for the steam injection. Before the produced water can be used it must be softened, i.e., Ca++
and Mg++ ions must be removed: this is necessary to protect the steam generators from scale formation and subsequent burnout.
In US-A-4877536 and CA-A-1217986 softening processes are described in which the produced waters are stripped of carbon dioxide (CO2) with steam, thereby (i) converting bicarbonate ions (HCO3-) to carbonate ions (CO3--), which precipitates calcium, and (ii) converting HCO3- to hydroxyl ions (OH-), which precipitates magnesium. The advantage of these methods of water softening is that they are efficient for water that contains sodium chloride, whereas conventional ion exchange, or zeolite, softening processes become less efficient as the salt concentration increases, and become impracticable at salt concentrations above about 5000 mg/1. Furthermore, the steam stripping methods utilize HCO3-, which is already present in the produced water,thereby minimi~in~ any required addition of CO3-- and/or OH-.
In the above patents it is disclosed that if the produced water does not contain sufficient HCO3- to precipitate completely the Ca++ and Mg++ through the formation of CO3-- and OH-, then sufficient Na2CO3 and/or NaOH must be added to the feed water to effect the desired reactions during subsequent steam stripping. To produce soft water having less -~r ~ . .~
than 1 mg/l Mg++ and Ca++, as specified for steam generators, the outlet pH of the steam stripper must be at least about 10.0, and the temperature must be at least about 190C.
It is an object of the present invention to provide an improved steam stripping process for softening water.
According to the present invention there is provided a steam stripping process for softening water, comprising contacting said water with steam to bring said water to a temperature sufficient to strip CO2 from said water and to cause the precipitation of Ca++ and/or Mg++ from said water; subsequently adding sufficient alkaline material to bring the pH of said stripped water to at least substantially 10; and thereafter separating precipitated Ca++ and/or Mg++ from said water.
Said separation is advantageously carried out by settling.
It is especially preferred that the water is produced water obtained from an oil well that has been subjected to steam injection.
The alkaline material is preferably Na2CO3 and/or NaOH.
Preferably the water is brought to a temperature of at least 185 C, more preferably at least 190C.
Desirably the stripping steam brings the water to a temperature in the range of from substantially 190C to substantially 200C. The skilled person will readily appreciate that the pressure can be m~int~ined at a suitable value to keep the water in liquid form.
The softened water may be converted to steam in a steam generator, and the steam can then be used in oil well steam injection.
X
The reactions that occur when the produced water is steam stripped to a temperature of 190C to 200C are as follows:
(i) bicarbonate is converted to carbonate in accordance with the reaction:
2HCO3- -------> H2O + CO2 + CO3 (1) (ii) carbonate is converted to hydroxyl in accordance with the reaction:
CO3-- + H2O -------> CO2 + 20H- (2) The CO3-- formed by reaction (1) and the OH- formed by reaction (2) precipitate Ca++
and Mg++ respectively by the reactions:
Ca++ + C03-- ------> CaC03 (3) Mg++ + 2(0H-) ------> Mg(OH)2 (4) Reaction (4) requires a pH of substantially 10 or more to effect sufficient precipitation of Mg++.
In practice, it can be calculated from chemical equilibria that the CO2 concentration in equilibrium with HCO3- and CO3- becomes smaller as the pH increases. For example, it has been calculated for a given oil field water originally CO~ g about 500 mg/l of HC03- that the CO2 partial pressure would decrease with increasing pH as follows:
TEMPERATURE/C ~ CO2 PART. PRESS./KPa 195 7.7 42 195 8.5 35 195 9.0 25 195 9.5 12 195 10.0 2.3 195 10.5 0.21 ,' ~ ~r .:~
- ` 2045195 It is clear from the foregoing that in order to obtain a pH of about 10 in the stripping step (i.e., sufficient to effect precipitation of Mg++) it is necessary for the stripping steam itself to contain virtually no CO2. However, in practice, the steam produced by oil field steam generators contains CO2 because the feed water contains some HCO3-and CO3--: this causes CO2 to be produced in the steam generator at its operating temperature of around 300C by reactions (1) and (2). In the example cited above, the steam contained about 3.0 KPa partial pressure of C02; and a pH of 10 could not be achieved in the stripping step, so that Mg++ would not precipitate.
In the present invention CO2 is stripped more effectively by not adding any alkaline agents (e.g., Na2CO3 and/or NaOH) prior to the stripping step. It has been found that if the stripping steam contains sufficient C2 to prevent the attainment of pH 10, then it is more efficient to add Na2CO3 (if required for Ca++ precipitation) and NaOH to achieve a pH of 10 or greater after the stripping step. In tests, it was found that the process according to the invention halved the required steam venting rate and halved therequired addition of NaOH.
Reference is now made to the accompanying drawing, which is a schematic diagram illustrating the method of softening water according to the invention.
A mixture of oil and water is removed from the oil well and passed through a de-oiling unit (not shown), which separates the oil from the water; in practice the water (known as "produced water") is a saline solution, which also contains Ca++ and Mg++ ions in solution.
After being separated from the oil, the produced water is passed to a de-oil tank 10 via line 12. The produced water is then fed to an oil pre-filter 14 via line 16; the oil pre-filter 14 removes oil that may not have been separated in the de-oiling unit. The filtered produced water is fed to a heat exchanger 18 via line 20, where it is pre-heated to a temperature of about 75 C. The pre-heated water is then fed to a steam stripper 22 - X
- ~ 2045195 via line 24; the pre-heating of the produced water reduces the quantity of steamrequired in the stripper 22.
In the steam stripper 22 the produced water is contacted with steam to bring thetemperature thereofto about 190 - 200C; typically the pressure in the stripper would be of the order of 1000 KPa. The steam enters the stripper 22 via the line 26 at a temperature of about 300C. It is preferred that the steam is sprayed into the produced water as the water flows downwardly through the stripper. In the stripper 22 the steam strips CO2 from the produced water; during this process, reactions (1) to (4) above take place causing the precipitation of Ca++ and Mg++. CO2, together with uncondensedsteam, pass out through the top of the stripper via line 28. The stripped produced water passes out through the bottom of the stripper through line 30.
If the pH of the stripped produced water is below substantially 10, and the stripping steam has too large a CO2 partial pressure to permit precipitation of sufficient Mg++ (or even Ca++), then an alkaline material from container(s) 32 can be mixed with line 30 via line 34. It may be, in certain circumstances, that the amount of alkaline material needing to be added is zero. The alkaline material would typically be Na2CO3 to precipitate Ca++, and NaOH to precipitate Mg++. A pH meter (not shown) may monitor the pH of the stripped produced water in line 30 as it leaves the stripper 22 and may provide data to a flow control device (not shown) that can adjust the addition of NaOH
to m~int~in a pH above substantially 10.
The stripped produced water is passed to a settling tank 36 where the Ca++ and Mg++ are removed (as CaCO3 and Mg(OH)2 respectively) in the form of a sludge via line 38. It is possible to provide a sludge mixer (not shown) at the bottom of the tank 36, and also a sludge recirculation system (not shown) can be provided; these features can help to reduce the quantity of silica in the water. In addition, anti-scale chemicals may be added to the tank 36, to help prevent scale from depositing on the surface thereof.
Finally, it is possible for the stripper 22 and settling tank 36 to be formed as a single ., y ,~".
. ~
unit; in this embodiment the alkali material would be added to the produced water after it had passed through the stripping part of the appal~us.
The softened produced water is removed from the tank 36 via line 40, and is fed to the heat exchanger 18 where it is cooled by the pre-filtered produced water in line 20. The cooled softened produced water is then fed via line 42 to filtration and polishing equipment indicated by reference 44, where any solids carryover from the settling tank 36 is removed. The softened produced water is subsequently passed to a head tank 46 via line 48.
Water is taken from the head tank 46, as required, and fed to a steam generator 50 via line 52. Steam generator 50 produces steam that is fed to an oil well for steam injection via line 54. It will be noted that a part of the steam in line 54 is diverted via the line 26 for use as feed steam in the stripper 22; approximately 20% of the flow in the line 54 is diverted to the stripper 22.
It will be appreciated by the person skilled in the art that modifications may be made to the embodiment described with reference to the drawings, within the scope of theappended claims.
Claims (10)
1 A steam stripping process for softening water, comprising contacting said water with steam to bring said water to a temperature sufficient to strip CO2 from said water and to cause the precipitation of Ca++ and/or Mg++ from said water;
subsequently adding sufficient alkaline material to bring the pH
of said stripped water to at least substantially 10; and thereafter separating precipitated Ca++ and/or Mg++ from said water.
subsequently adding sufficient alkaline material to bring the pH
of said stripped water to at least substantially 10; and thereafter separating precipitated Ca++ and/or Mg++ from said water.
2. A process according to claim 1, in which the alkaline material is Na2CO3 and/or NaOH.
3. A process according to claim 1 or 2, wherein said water is brought to a temperature of at least 185°C.
4. A process according to claim 1 or 2, wherein said water is brought to a temperature of at least 190°C.
5. A process according to claim 1 or 2, in which the water is brought to a temperature between substantially 190°C and substantially 200°C.
6. A process according to claim 1 or 2, in which the water is produced water from an oil well.
7. A process according to claim 6, in which said softened water is converted to steam in a steam generator.
8. A process according to claim 7, in which said steam produced by said steam generator is used in the steam injection of an oil well.
9. A process according to claim 8, in which part of said steam produced by said steam generator is used in the stripping of said water.
10. A process according to claim 1 or 2, wherein said separation is carried out by settling.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2045195 CA2045195C (en) | 1991-06-21 | 1991-06-21 | Steam stripping process for softening water |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2045195 CA2045195C (en) | 1991-06-21 | 1991-06-21 | Steam stripping process for softening water |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2045195A1 CA2045195A1 (en) | 1992-12-22 |
| CA2045195C true CA2045195C (en) | 1997-05-06 |
Family
ID=4147878
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2045195 Expired - Fee Related CA2045195C (en) | 1991-06-21 | 1991-06-21 | Steam stripping process for softening water |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2045195C (en) |
-
1991
- 1991-06-21 CA CA 2045195 patent/CA2045195C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2045195A1 (en) | 1992-12-22 |
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