CA2360517C - Carbon dioxide treatment of atmospheric cooling water - Google Patents
Carbon dioxide treatment of atmospheric cooling water Download PDFInfo
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- CA2360517C CA2360517C CA002360517A CA2360517A CA2360517C CA 2360517 C CA2360517 C CA 2360517C CA 002360517 A CA002360517 A CA 002360517A CA 2360517 A CA2360517 A CA 2360517A CA 2360517 C CA2360517 C CA 2360517C
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- water
- carbon dioxide
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- waters
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- 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
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
- C02F5/10—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances
- C02F5/12—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances containing nitrogen
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- 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
-
- 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
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/02—Non-contaminated water, e.g. for industrial water supply
- C02F2103/023—Water in cooling circuits
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- 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)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Preventing Corrosion Or Incrustation Of Metals (AREA)
- Physical Water Treatments (AREA)
- Food Preservation Except Freezing, Refrigeration, And Drying (AREA)
Abstract
The invention relates to a process for the treatment of atmospheric cooling waters circulating in a semi-open circuit recirculation loop comprising an atmospheric cooling device (2) equipped with means for the natural or forced convection of atmospheric air, a bleeding device (D) and a make-up water feed, (E), characterized in that carbon dioxide is introduced at at least one point in the said recirculation loop or in the said make-up water feed or in a bypass circuit provided on the said loop or the said feed for the purpose of the said introduction.
Description
Carbon dioxide treatment of atmospheric cooling water The present invention relates to a novel process for the treatment of atmospheric cooling waters.
It is commonplace in industry to resort to water circulation in order to cool a plant. The devices to be cooled are extremely varied in nature. They can be condensers, heat exchangers or chemical reactors.
The term "atmospheric cooling waters" is understood to mean that the said waters are at a given moment in contact with air, which brings about partial evaporation and/or entrainment of this cooling water.
Cooling water circuits can be classified into three categories:
- open circuits, in which the water which has been used for a cooling operation (hot water) is discharged to a river or to a drain, - closed circuits, in which the hot water is subsequently cooled by contact with a secondary fluid (air or water) and subsequently returns to the devices to be cooled without contact with air, - so-called semi-open circuits, in which the hot water is cooled by partial entrainment and/or evaporation in an atmospheric cooler before returning to the devices to be cooled.
Atmospheric cooling circuits or semi-open circuits are therefore cooling water circuits in which, at at least one point, a portion of the water to be cooled is removed by evaporation and/or entrainment by means of natural or forced convection of atmospheric air.
An example of such circuits is composed of cooling water circuits in which the water which has been used to cool a plant (hot water) arrives at the upper part of a cooling tower equipped with a packing and air convection means and passes through this cooling tower from the top downwards, the cold water
It is commonplace in industry to resort to water circulation in order to cool a plant. The devices to be cooled are extremely varied in nature. They can be condensers, heat exchangers or chemical reactors.
The term "atmospheric cooling waters" is understood to mean that the said waters are at a given moment in contact with air, which brings about partial evaporation and/or entrainment of this cooling water.
Cooling water circuits can be classified into three categories:
- open circuits, in which the water which has been used for a cooling operation (hot water) is discharged to a river or to a drain, - closed circuits, in which the hot water is subsequently cooled by contact with a secondary fluid (air or water) and subsequently returns to the devices to be cooled without contact with air, - so-called semi-open circuits, in which the hot water is cooled by partial entrainment and/or evaporation in an atmospheric cooler before returning to the devices to be cooled.
Atmospheric cooling circuits or semi-open circuits are therefore cooling water circuits in which, at at least one point, a portion of the water to be cooled is removed by evaporation and/or entrainment by means of natural or forced convection of atmospheric air.
An example of such circuits is composed of cooling water circuits in which the water which has been used to cool a plant (hot water) arrives at the upper part of a cooling tower equipped with a packing and air convection means and passes through this cooling tower from the top downwards, the cold water
- 2 -arriving at the lower part of the cooling tower subsequently being returned to the plant to be cooled.
Another semi-open circuit example is that of water recirculation circuits in which the heat exchanger which it is desired to cool acts as atmospheric cooler.
It is generally well known that a number of difficulties are inherent in cooling water circuits.
These difficulties arise from dirt, scale formation, corrosion phenomena and biological growths.
The invention is targeted at solving the specific problems posed by this third type of cooling water circuit.
The dirt is composed of matter capable of being deposited or of forming in a circuit. It can have several sources: the make-up water, the atmospheric air or the manufacturing operations in the plant.
Scale formation is related to the precipitation on the surfaces of the pipes of sparingly soluble calcium salts and possibly of silica. The main parameters controlling the precipitation of scale are the temperature, the rise in which generally decreases the solubility of the salts concerned, the concentration of the ions and the stirring.
The carbonate is the commonest cause of the formation of scale which can be chemically redissolved in operation.
Calcium sulphate, which has a maximum solubility at 40 C, can precipitate under cold conditions in the form of gypsum or under warm conditions in the anhydrous or hemihydrate form.
In addition to bacterial corrosion, microbial corrosion is a direct consequence of poor control of the microbiology in a water circuit. This results directly from biofilms, which decompose, resulting in a size such that the region in contact with the material is deprived of oxygen or encounters an acidic pH. As corrosion is one of the major risks for industry, it is
Another semi-open circuit example is that of water recirculation circuits in which the heat exchanger which it is desired to cool acts as atmospheric cooler.
It is generally well known that a number of difficulties are inherent in cooling water circuits.
These difficulties arise from dirt, scale formation, corrosion phenomena and biological growths.
The invention is targeted at solving the specific problems posed by this third type of cooling water circuit.
The dirt is composed of matter capable of being deposited or of forming in a circuit. It can have several sources: the make-up water, the atmospheric air or the manufacturing operations in the plant.
Scale formation is related to the precipitation on the surfaces of the pipes of sparingly soluble calcium salts and possibly of silica. The main parameters controlling the precipitation of scale are the temperature, the rise in which generally decreases the solubility of the salts concerned, the concentration of the ions and the stirring.
The carbonate is the commonest cause of the formation of scale which can be chemically redissolved in operation.
Calcium sulphate, which has a maximum solubility at 40 C, can precipitate under cold conditions in the form of gypsum or under warm conditions in the anhydrous or hemihydrate form.
In addition to bacterial corrosion, microbial corrosion is a direct consequence of poor control of the microbiology in a water circuit. This results directly from biofilms, which decompose, resulting in a size such that the region in contact with the material is deprived of oxygen or encounters an acidic pH. As corrosion is one of the major risks for industry, it is
- 3 -generally preferable to operate at a higher pH, often of the order of 7.9 to 8.4, and at the same time to counter the risks of formation of scale of calcium sulphate, phosphate or carbonate type using sequester-ing and/or dispersing agents.
Conditions which are favourable to the growth of microorganisms and specifically of bacteria are encountered in a cooling water circuit when the pH
values are greater than 7 and when the temperature is greater than 25 C, which is often the case. The process for the formation of a biofilm is always the same.
Conventionally encountered microbial strains have a tendency to colonize the surfaces by secreting attaching filaments which allow the bacteria to adhere to the walls. The microorganisms, until then entrained by the fluid, then become attached and grow into colonies at all the points in a circuit. This is the first stage in the creation of a biofilm. Once attached, the bacteria have the distinguishing feature of secreting a mucopolysaccharide, which can represent a size several times that of the bacterium. This bacterial gel or slime then acts as protection for the colony of bacteria, which it will nourish by scavenging the particles necessary for microbial growth present in the waters. This phenomenon furthermore increases the size of the layers. This layer, which grows, furthermore results not only in progressive losses in thermal efficiency of the plants but also in an oxygen and pH gradient within the same biofilm. This gradient will bring about, on contact with the material, an anaerobiosis region representing conditions favourable for the growth of sulphate-reducing bacteria which produce hydrogen and are responsible for the sudden microbial corrosion which is well known in the industrial world. Control of the layers remains a problem if the scale and corrosion phenomena are present in the cooling circuit.
Conditions which are favourable to the growth of microorganisms and specifically of bacteria are encountered in a cooling water circuit when the pH
values are greater than 7 and when the temperature is greater than 25 C, which is often the case. The process for the formation of a biofilm is always the same.
Conventionally encountered microbial strains have a tendency to colonize the surfaces by secreting attaching filaments which allow the bacteria to adhere to the walls. The microorganisms, until then entrained by the fluid, then become attached and grow into colonies at all the points in a circuit. This is the first stage in the creation of a biofilm. Once attached, the bacteria have the distinguishing feature of secreting a mucopolysaccharide, which can represent a size several times that of the bacterium. This bacterial gel or slime then acts as protection for the colony of bacteria, which it will nourish by scavenging the particles necessary for microbial growth present in the waters. This phenomenon furthermore increases the size of the layers. This layer, which grows, furthermore results not only in progressive losses in thermal efficiency of the plants but also in an oxygen and pH gradient within the same biofilm. This gradient will bring about, on contact with the material, an anaerobiosis region representing conditions favourable for the growth of sulphate-reducing bacteria which produce hydrogen and are responsible for the sudden microbial corrosion which is well known in the industrial world. Control of the layers remains a problem if the scale and corrosion phenomena are present in the cooling circuit.
- 4 -Furthermore, closing a circuit has the immediate consequence of increasing the pH, which is one of the parameters favourable to bacterial growth and therefore to the formation of biofilms.
It is seen that the problems which exist in all cooling water recirculation circuits are found to be further increased in the case of semi-open circuits due to the recirculation in a loop of the water and the increase in the concentration of salts related to the partial evaporation of the water in this type of circuit.
Various means for protecting against the risks of scale formation and corrosion are already known.
Mention will be made, by way of example, of the so-called natural equilibrium process, which consists in adjusting the pH and the hardness of the circulating water so that it is at equilibrium (monitoring of the total alkalimetric assay (TAA), this assay reflecting the content of OH-, C032- and HC03- ions in the water).
This adjusting is carried out by introducing acidic or alkaline reagents and by limiting the level of concentration. This process is attractive in its simplicity but it has significant limits related mainly to the concentration of dissolved salts, which requires resorting to a significant extent to bleeding and thus to high consumptions of make-up water.
Recourse is also had to chemical additives for controlling scale which inhibit scale formation. They are specific reagents, for example synthetic organic polymers in the form of polyacrylates or of poly-phosphonates. These chemical additives have disadvantages. Thus, when these chemical additives are of polyphosphonate type, they increase the hardness of the water and thus the concentration of the salts.
Furthermore, these chemical additives are expensive.
Use is also made of agents intended to slow down the precipitations. Such agents are generally acids. However, when an acid is added, the hardness of
It is seen that the problems which exist in all cooling water recirculation circuits are found to be further increased in the case of semi-open circuits due to the recirculation in a loop of the water and the increase in the concentration of salts related to the partial evaporation of the water in this type of circuit.
Various means for protecting against the risks of scale formation and corrosion are already known.
Mention will be made, by way of example, of the so-called natural equilibrium process, which consists in adjusting the pH and the hardness of the circulating water so that it is at equilibrium (monitoring of the total alkalimetric assay (TAA), this assay reflecting the content of OH-, C032- and HC03- ions in the water).
This adjusting is carried out by introducing acidic or alkaline reagents and by limiting the level of concentration. This process is attractive in its simplicity but it has significant limits related mainly to the concentration of dissolved salts, which requires resorting to a significant extent to bleeding and thus to high consumptions of make-up water.
Recourse is also had to chemical additives for controlling scale which inhibit scale formation. They are specific reagents, for example synthetic organic polymers in the form of polyacrylates or of poly-phosphonates. These chemical additives have disadvantages. Thus, when these chemical additives are of polyphosphonate type, they increase the hardness of the water and thus the concentration of the salts.
Furthermore, these chemical additives are expensive.
Use is also made of agents intended to slow down the precipitations. Such agents are generally acids. However, when an acid is added, the hardness of
- 5 -the water is decreased, which results in an increase in the risk of corrosion.
Another solution is to attempt to limit the concentration of calcium and of magnesium and to resort to a prior softening process on the make-up water.
However, the investment in and the maintenance of this type of device are onerous.
In the case of semi-open circuits, it is well known that all the problems mentioned above are found to be accentuated by the phenomenon of concentration of the salts. Furthermore, as the removal of the heat in semi-open circuits takes place essentially by evaporation of pure water without dissolved salt, this results in:
- the need to resort to make-up water in order to compensate for the evaporation, - an increase in the salinity of the circulating water. In order not to exceed_ the solubility of some salts (for example, calcium carbonate), it is then necessary to dilute the circuit by bleeding.
Numerous documents are found in the literature in which carbon dioxide has been used to treat the water in circuits, either open circuits or closed circuits.
Thus, Patent FR 2,697,827 provides a process for descaling structures and for protecting structures against scale formation, which structures are in contact with scale-depositing water circulating in an open circuit.
Application WO 85-03697 employs carbon dioxide in the recovery of oils in flotation cells.
European Patent EP 0,380,299 discloses a process for reducing the corrosion in a water conveyance system which consists in using carbon dioxide. However, this document in no way relates to the specific problem of cooling water circuits and even less to semi-open cooling water circuits.
Another solution is to attempt to limit the concentration of calcium and of magnesium and to resort to a prior softening process on the make-up water.
However, the investment in and the maintenance of this type of device are onerous.
In the case of semi-open circuits, it is well known that all the problems mentioned above are found to be accentuated by the phenomenon of concentration of the salts. Furthermore, as the removal of the heat in semi-open circuits takes place essentially by evaporation of pure water without dissolved salt, this results in:
- the need to resort to make-up water in order to compensate for the evaporation, - an increase in the salinity of the circulating water. In order not to exceed_ the solubility of some salts (for example, calcium carbonate), it is then necessary to dilute the circuit by bleeding.
Numerous documents are found in the literature in which carbon dioxide has been used to treat the water in circuits, either open circuits or closed circuits.
Thus, Patent FR 2,697,827 provides a process for descaling structures and for protecting structures against scale formation, which structures are in contact with scale-depositing water circulating in an open circuit.
Application WO 85-03697 employs carbon dioxide in the recovery of oils in flotation cells.
European Patent EP 0,380,299 discloses a process for reducing the corrosion in a water conveyance system which consists in using carbon dioxide. However, this document in no way relates to the specific problem of cooling water circuits and even less to semi-open cooling water circuits.
- 6 -Patent FR 2,570,393 relates to a process intended to remove the incrustations in a closed water circuit by introducing pressurized carbon dioxide gas.
International Application WO 97/23414 discloses a process for the treatment of water intended to remove the volatile compounds which are found therein.
In the prior art, it was envisaged to use CO2 to treat the cooling water circulating in a semi-open circuit but this use was always carried out under highly specific conditions. This is because a person skilled in the art expected complete desorption of the dissolved COZ in the cooling tower and its removal into the atmosphere at this point. This ought to have rendered the use of CO2 uneconomic. This fear is mentioned in Patent US-A-4,547,294 and it is indicated therein that this problem of desorption of CO2 can only be avoided if chemical additives for controlling scale are introduced simultaneously with the CO2 into, the cooling waters. These chemical additives can be polymers or copolymers of maleic acid, polyphosphonates, phosphonic acid derivatives, aminophosphonic acid derivatives, polyacrylic acid and polymethacrylic acid derivatives, polyesters or poly-phosphates. The disadvantage of this implementation is that these chemical additives are expensive and are slowly removed in the cooling tower. It is therefore necessary to regularly re-add them, which increases the cost of their use.
The abstract of Japanese Patent JP-A-11028461 also discloses the injection of CO2 into the cooling water of an open circuit. However, the water used has to be softened beforehand by passing through an ion-exchange resin. As indicated above, the investment in and the maintenance of this type of device are onerous and not suited to semi-open circuits.
The aim of the present invention is to provide a simplified process for the treatment of the atmospheric cooling waters circulating in a semi-open
International Application WO 97/23414 discloses a process for the treatment of water intended to remove the volatile compounds which are found therein.
In the prior art, it was envisaged to use CO2 to treat the cooling water circulating in a semi-open circuit but this use was always carried out under highly specific conditions. This is because a person skilled in the art expected complete desorption of the dissolved COZ in the cooling tower and its removal into the atmosphere at this point. This ought to have rendered the use of CO2 uneconomic. This fear is mentioned in Patent US-A-4,547,294 and it is indicated therein that this problem of desorption of CO2 can only be avoided if chemical additives for controlling scale are introduced simultaneously with the CO2 into, the cooling waters. These chemical additives can be polymers or copolymers of maleic acid, polyphosphonates, phosphonic acid derivatives, aminophosphonic acid derivatives, polyacrylic acid and polymethacrylic acid derivatives, polyesters or poly-phosphates. The disadvantage of this implementation is that these chemical additives are expensive and are slowly removed in the cooling tower. It is therefore necessary to regularly re-add them, which increases the cost of their use.
The abstract of Japanese Patent JP-A-11028461 also discloses the injection of CO2 into the cooling water of an open circuit. However, the water used has to be softened beforehand by passing through an ion-exchange resin. As indicated above, the investment in and the maintenance of this type of device are onerous and not suited to semi-open circuits.
The aim of the present invention is to provide a simplified process for the treatment of the atmospheric cooling waters circulating in a semi-open
- 7 -circuit recirculation loop which employs the injection of C02r without the latter desorbing into the atmosphere and without the addition of chemical additives or the use of softened water.
The process according to the invention results from the observation that, in contrast to all expectation, it turns out that carbon dioxide, used alone, i.e. in the absence of chemical additives for controlling scale, in the treatment of water circulating in a semi-open circuit, desorbs markedly less than when the same circuit is treated solely with inorganic acids and makes it possible simultaneously to obtain better regulation of the pH, less fouling and a decrease in bleeding. This is because it has been demonstrated by the inventors of the present invention that the introduction of carbon dioxide, in complete or partial substitution for inorganic acids, makes it possible to markedly reduce the scale-formation phenomena.
Furthermore, the dispersing agents and inorganic acids conventionally employed generate inorganic sludges as a result of the salinity which they bring about. Such an effect is in no way observed with carbon dioxide, which releases only soluble bicarbonate ions. The present invention thus provides a process which makes it possible to reduce, indeed even eliminate, the various disadvantages of the processes of the prior art. This is because the inventors have shown that, by virtue of the addition of CO2 at a point in a water cooling circuit of semi-open type, it is possible to decrease the amounts of salt generated by the addition of scale inhibitor and of inorganic acids, which makes it possible to decrease the amount of make-up water while retaining the same level of concentration of salts. This is particularly advantageous since it is well known that, in order to save water, it is advantageous to look for the highest possible level of concentration of dissolved salts.
The process according to the invention results from the observation that, in contrast to all expectation, it turns out that carbon dioxide, used alone, i.e. in the absence of chemical additives for controlling scale, in the treatment of water circulating in a semi-open circuit, desorbs markedly less than when the same circuit is treated solely with inorganic acids and makes it possible simultaneously to obtain better regulation of the pH, less fouling and a decrease in bleeding. This is because it has been demonstrated by the inventors of the present invention that the introduction of carbon dioxide, in complete or partial substitution for inorganic acids, makes it possible to markedly reduce the scale-formation phenomena.
Furthermore, the dispersing agents and inorganic acids conventionally employed generate inorganic sludges as a result of the salinity which they bring about. Such an effect is in no way observed with carbon dioxide, which releases only soluble bicarbonate ions. The present invention thus provides a process which makes it possible to reduce, indeed even eliminate, the various disadvantages of the processes of the prior art. This is because the inventors have shown that, by virtue of the addition of CO2 at a point in a water cooling circuit of semi-open type, it is possible to decrease the amounts of salt generated by the addition of scale inhibitor and of inorganic acids, which makes it possible to decrease the amount of make-up water while retaining the same level of concentration of salts. This is particularly advantageous since it is well known that, in order to save water, it is advantageous to look for the highest possible level of concentration of dissolved salts.
- 8 -This level depends essentially on the risks of precipitation of the salts due to the lime/carbonic acid equilibrium in water. In point of fact, the currently existing solutions did not make possible a maximum level of concentration without a significant increase in the scale produced, limiting the heat exchange. The invention has made it possible, by virtue of the introduction of C02, to double the concentration of dissolved salt. Thus, the invention has made it possible to decrease the amount of make-up water by increasing the level of concentration of salts and without the appearance of scale, indeed even with a decrease in the thickness of scale existing before the injection of C02, up to its complete disappearance.
The introduction of CO2 makes it possible to decrease the pH by contributing carbonic acid and the soluble bicarbonates scavenge the calcium and magnesium ions, which no longer precipitate and no longer act as nutrient for the bacteria. The COz scavenges the Ca2+ ions of the scale dissolved by the acid and prevents it from precipitating or from being absorbed by the bacterial films.
It is possible, by virtue of the use of C02, to increase the concentration in the bleed by pushing back the solubility limit for the carbonates, it being known that there will in point of fact be doping by the COZ
less free CO2 desorbed after passage of the water through the atmospheric exchanger. Furthermore, the CO2 does not result in dissolved salts of sulphate type and therefore the solubility limit of the gypsum is pushed back.
The inventors have been able to demonstrate that this injection of CO2 can be carried out in a general way directly at any point in a preexisting semi-open circuit or in the water feed circuit for this circuit but that it can also be carried out on a bypass specifically provided on one or other of these circuits for the purpose of this introduction, it being possible
The introduction of CO2 makes it possible to decrease the pH by contributing carbonic acid and the soluble bicarbonates scavenge the calcium and magnesium ions, which no longer precipitate and no longer act as nutrient for the bacteria. The COz scavenges the Ca2+ ions of the scale dissolved by the acid and prevents it from precipitating or from being absorbed by the bacterial films.
It is possible, by virtue of the use of C02, to increase the concentration in the bleed by pushing back the solubility limit for the carbonates, it being known that there will in point of fact be doping by the COZ
less free CO2 desorbed after passage of the water through the atmospheric exchanger. Furthermore, the CO2 does not result in dissolved salts of sulphate type and therefore the solubility limit of the gypsum is pushed back.
The inventors have been able to demonstrate that this injection of CO2 can be carried out in a general way directly at any point in a preexisting semi-open circuit or in the water feed circuit for this circuit but that it can also be carried out on a bypass specifically provided on one or other of these circuits for the purpose of this introduction, it being possible
- 9 -for the aim of such a bypass to be, for example, better control of the amounts of COZ injected.
Thus, according to one of its essential characteristics, the invention relates to a process for the treatment of atmospheric cooling waters circulating in a semi-open circuit recirculation loop comprising an atmospheric cooling device equipped with means for the natural or forced convection of atmospheric air, a bleeding device and a make-up water feed, in which process carbon dioxide is introduced at at least one point in the recirculation loop or in the make-up water feed or in a bypass circuit provided on the loop or the feed for the purpose of the introduction and in which process no chemical additive for controlling scale is introduced into the waters.
The CO2 can be injected without distinction on the recirculation loop for the cooling water or on the inlet for the make-up water or on a bypass water circuit provided specifically in order to facilitate this introduction.
According to a particularly advantageous alter-native form of the invention, the carbon dioxide is introduced at the outlet of a water circulation pump, such as the pump of the recirculation loop or of the make-up water feed or of the bypass circuit. Good results were obtained if the carbon dioxide is introduced at a point in the process where the water exhibits a pressure of at least 1 bar.
'The carbon dioxide can be introduced in the liquid form or in the gaseous form. Recourse may also be had to mixtures of carbon dioxide and an inert gas, for example nitrogen. The combustion flue gases resulting from a boiler constitute an example of such a mixture.
As set out above, the carbon dioxide is advantageously used in substitution for inorganic acids conventionally used in the treatment of such a semi-open circuit, in particular in complete substitution
Thus, according to one of its essential characteristics, the invention relates to a process for the treatment of atmospheric cooling waters circulating in a semi-open circuit recirculation loop comprising an atmospheric cooling device equipped with means for the natural or forced convection of atmospheric air, a bleeding device and a make-up water feed, in which process carbon dioxide is introduced at at least one point in the recirculation loop or in the make-up water feed or in a bypass circuit provided on the loop or the feed for the purpose of the introduction and in which process no chemical additive for controlling scale is introduced into the waters.
The CO2 can be injected without distinction on the recirculation loop for the cooling water or on the inlet for the make-up water or on a bypass water circuit provided specifically in order to facilitate this introduction.
According to a particularly advantageous alter-native form of the invention, the carbon dioxide is introduced at the outlet of a water circulation pump, such as the pump of the recirculation loop or of the make-up water feed or of the bypass circuit. Good results were obtained if the carbon dioxide is introduced at a point in the process where the water exhibits a pressure of at least 1 bar.
'The carbon dioxide can be introduced in the liquid form or in the gaseous form. Recourse may also be had to mixtures of carbon dioxide and an inert gas, for example nitrogen. The combustion flue gases resulting from a boiler constitute an example of such a mixture.
As set out above, the carbon dioxide is advantageously used in substitution for inorganic acids conventionally used in the treatment of such a semi-open circuit, in particular in complete substitution
- 10 -for H2SO4 or HC1. Such a substitution makes it possible to decrease the pH of the water, releasing calcium ions originating from the dissolution of the scale. The addition of COz can thus be regulated by measuring the calcium hardness of the water treated. The CO2 can also be used in partial substitution for or in doping an inorganic acid, in particular in doping H2SO4 or HC1.
The CO2 is advantageously injected at doses such that as far as possible conditions of lime/carbonic acid equilibrium in the water are approached, that is to say conditions such that the precipitation of the carbonates is avoided. To this end, a person skilled in the art can either subject the amounts of CO2 injected to an operation of quantitative determination of the water, establishing a lime/carbonic acid balance in the water, or to a pH
measurement on the water, this pH being regulated at a set value close to the lime/carbonic acid equilibrium value, or to a measurement of the dissolved calcium ions.
The process of the invention makes it possible to completely dispense with the use of the scale-inhibiting chemical additives conventionally used.
The treatment of the invention applies to all cooling circuits of semi-open type. As emerges from the detailed description which will follow, the treatment of the invention applies to all types of semi-open circuits comprising an atmospheric cooling system. It also applies to circuits in which the cooling of the waters within the cooling loop is provided by an air heat exchanger.
Other characteristics and advantages of the invention will become apparent in the light of the description and example which follow, which are illustrated by Figures 1, 2 and 3.
Figure 1 diagrammatically represents a cooling water semi-open circuit of a heat exchanger.
The CO2 is advantageously injected at doses such that as far as possible conditions of lime/carbonic acid equilibrium in the water are approached, that is to say conditions such that the precipitation of the carbonates is avoided. To this end, a person skilled in the art can either subject the amounts of CO2 injected to an operation of quantitative determination of the water, establishing a lime/carbonic acid balance in the water, or to a pH
measurement on the water, this pH being regulated at a set value close to the lime/carbonic acid equilibrium value, or to a measurement of the dissolved calcium ions.
The process of the invention makes it possible to completely dispense with the use of the scale-inhibiting chemical additives conventionally used.
The treatment of the invention applies to all cooling circuits of semi-open type. As emerges from the detailed description which will follow, the treatment of the invention applies to all types of semi-open circuits comprising an atmospheric cooling system. It also applies to circuits in which the cooling of the waters within the cooling loop is provided by an air heat exchanger.
Other characteristics and advantages of the invention will become apparent in the light of the description and example which follow, which are illustrated by Figures 1, 2 and 3.
Figure 1 diagrammatically represents a cooling water semi-open circuit of a heat exchanger.
- 11 -Figure 2 diagrammatically represents a cooling water semi-open circuit of a heat exchanger which acts as atmospheric cooler.
Figure 3, given with reference to the example, shows the change in the pH measured at the inlet and at the outlet of the cooling tower in a process according to the invention, in comparison with a control process which does not resort to the use of CO2.
Figures 1 and 2 diagrammatically represent two types of cooling water semi-open circuit to which the invention in particular applies.
A person skilled in the art will have no difficulty in devising other alternative forms of semi-open circuits to which the invention also applies.
Figure 1 thus illustrates an example of a cooling water semi-open circuit of a heat exchanger 1, into which enters a hot fluid (arrow marked A) which it is desired to cool in order to exit a cold fluid (arrow B). The cooling of this heat exchanger is carried out by a semi-open circuit, in which the water which has been used to cool the fluid circulating in the heat exchanger (hot water) arrives via the pipe represented by the arrow C at the top of a cooling tower 2 comprising a packing 3. This cooling tower is equipped in its lower part with conventional air convection means, not represented, allowing circulation of air from the lower part to the upper part of the tower. During its circulation from the top downwards in the cooling tower, the water is subjected to a phenomenon of partial entrainment and/or evaporation related to the natural or forced convection of air in the tower. The part which is not evaporated or entrained during the circulation in the cooling tower is recovered at the lower outlet of the tower in a recovery tank 4. This tank is equipped with a bleeding device, represented by the arrow D, and is connected to a feed for making up with water represented by the arrow E. A pump 5 makes it possible to recirculate the
Figure 3, given with reference to the example, shows the change in the pH measured at the inlet and at the outlet of the cooling tower in a process according to the invention, in comparison with a control process which does not resort to the use of CO2.
Figures 1 and 2 diagrammatically represent two types of cooling water semi-open circuit to which the invention in particular applies.
A person skilled in the art will have no difficulty in devising other alternative forms of semi-open circuits to which the invention also applies.
Figure 1 thus illustrates an example of a cooling water semi-open circuit of a heat exchanger 1, into which enters a hot fluid (arrow marked A) which it is desired to cool in order to exit a cold fluid (arrow B). The cooling of this heat exchanger is carried out by a semi-open circuit, in which the water which has been used to cool the fluid circulating in the heat exchanger (hot water) arrives via the pipe represented by the arrow C at the top of a cooling tower 2 comprising a packing 3. This cooling tower is equipped in its lower part with conventional air convection means, not represented, allowing circulation of air from the lower part to the upper part of the tower. During its circulation from the top downwards in the cooling tower, the water is subjected to a phenomenon of partial entrainment and/or evaporation related to the natural or forced convection of air in the tower. The part which is not evaporated or entrained during the circulation in the cooling tower is recovered at the lower outlet of the tower in a recovery tank 4. This tank is equipped with a bleeding device, represented by the arrow D, and is connected to a feed for making up with water represented by the arrow E. A pump 5 makes it possible to recirculate the
- 12 -water collected in the tank 4 (cold water) to the heat exchanger.
In an alternative form, the cold water can also be subjected to an intermediate washing stage in a bypass circuit, represented as dashes (--), comprising a washing device 6 intended to remove the impurities due to the air, the water returning to the heat exchanger via a pump 7.
In such a process, it is possible to introduce the CO2 at different points. The CO2 can be injected without distinction on the loop at any point in the water loop or on the inlet for the make-up water. It is also possible to inject the CO2 at a point in a bypass circuit specifically provided for this purpose. An example of such a circuit is represented by a discontinuous line composed of a series of dots and dashes. The bypass is provided in this case on the recovery tank 4 situated at the base of the cooling tower 2. The circulation in this bypass circuit is provided by the pump B. Possible injection position examples are represented in the figure by the indication "CO2-->". However, the CO2 is preferably injected at the outlet of at least one of the pumps (5, 6 and/or 8) and in particular at the outlet of the pump for returning the waters from the tank to the heat exchanger.
Figure 2 represents an alternative form of the invention in which the heat exchanger to be cooled acts as an atmospheric cooler. In such a device, the heat gradient in the water is reversed with respect to the system represented in Figure 1.
More specifically, in the device represented in Figure 2, the heat exchanger 1, equipped with its inlet for hot fluid A and with its outlet for cold fluid B, is inside the cooling tower 1. The cold water arrives according to arrow C' at the upper part of the cooling tower 2 and cools the heat exchanger by descending to the base of the said tower in order to be collected in
In an alternative form, the cold water can also be subjected to an intermediate washing stage in a bypass circuit, represented as dashes (--), comprising a washing device 6 intended to remove the impurities due to the air, the water returning to the heat exchanger via a pump 7.
In such a process, it is possible to introduce the CO2 at different points. The CO2 can be injected without distinction on the loop at any point in the water loop or on the inlet for the make-up water. It is also possible to inject the CO2 at a point in a bypass circuit specifically provided for this purpose. An example of such a circuit is represented by a discontinuous line composed of a series of dots and dashes. The bypass is provided in this case on the recovery tank 4 situated at the base of the cooling tower 2. The circulation in this bypass circuit is provided by the pump B. Possible injection position examples are represented in the figure by the indication "CO2-->". However, the CO2 is preferably injected at the outlet of at least one of the pumps (5, 6 and/or 8) and in particular at the outlet of the pump for returning the waters from the tank to the heat exchanger.
Figure 2 represents an alternative form of the invention in which the heat exchanger to be cooled acts as an atmospheric cooler. In such a device, the heat gradient in the water is reversed with respect to the system represented in Figure 1.
More specifically, in the device represented in Figure 2, the heat exchanger 1, equipped with its inlet for hot fluid A and with its outlet for cold fluid B, is inside the cooling tower 1. The cold water arrives according to arrow C' at the upper part of the cooling tower 2 and cools the heat exchanger by descending to the base of the said tower in order to be collected in
- 13 -the tank 4. Here again, the water, during its circulation inside the tower 2 in which air circulates by natural or forced convection, is partially evaporated or entrained via the upper part of the cooling tower. The part which is not removed by evaporation and/or entrainment is recovered in the tank 4 equipped, as in Figure 1, with means for making up with water E and with bleeding means D. A pump 5 subsequently recirculates the water recovered in the tank 4 to the cooling tower.
In this case, as in the preceding one, the COZ
can be injected at any point in the loop for recirculation of the water or on the inlet for the make-up water or optionally on a bypass circuit provided specifically on one of these circuits. Here again, the injection can be carried out at various points on the semi-open circuit. Examples of positions for these injections are given material form in Figure 2 by arrows (C02-+). According to the preferred alternative form, the injection will take place at the outlet of the pump 5.
It transpired that, in all the cases where COZ
is injected into a cooling water semi-open circuit, the same advantages are observed. A person skilled in the art can, of course, inject the CO2 both at a point in a cooling water circuit or at a point in the circuit for injection of the make-up water but he can also, in an entirely equivalent way, provide an additional bypass circuit on one of these circuits, in order to result in better control of the amounts of CO2 injected and complete dissolution of this CO2.
Thus, it was noticed that the injection of CO2 at any point in the water recirculation loop or on the make-up water inlet or in a bypass circuit provided on one of these circuits makes it possible to greatly decrease scale formation and that very little CO2 dissolved in the loop desorbs in the aeration system, in contrast to what could be feared. In fact, on the
In this case, as in the preceding one, the COZ
can be injected at any point in the loop for recirculation of the water or on the inlet for the make-up water or optionally on a bypass circuit provided specifically on one of these circuits. Here again, the injection can be carried out at various points on the semi-open circuit. Examples of positions for these injections are given material form in Figure 2 by arrows (C02-+). According to the preferred alternative form, the injection will take place at the outlet of the pump 5.
It transpired that, in all the cases where COZ
is injected into a cooling water semi-open circuit, the same advantages are observed. A person skilled in the art can, of course, inject the CO2 both at a point in a cooling water circuit or at a point in the circuit for injection of the make-up water but he can also, in an entirely equivalent way, provide an additional bypass circuit on one of these circuits, in order to result in better control of the amounts of CO2 injected and complete dissolution of this CO2.
Thus, it was noticed that the injection of CO2 at any point in the water recirculation loop or on the make-up water inlet or in a bypass circuit provided on one of these circuits makes it possible to greatly decrease scale formation and that very little CO2 dissolved in the loop desorbs in the aeration system, in contrast to what could be feared. In fact, on the
- 14 -contrary, the C02 added makes it possible to prevent the desorption of a large amount of C02 in the heat exchanger. It therefore proves to be advantageous in all the cases to inject C02 into a semi-open circuit since the desorption of the free C02, in view of the results, is not proportionally related to the level of dissolved C02. Thus, it can be demonstrated that the desorption of free C02 in the condensers and air coolers is greater during the use of inorganic acids alone than when they are coupled with an injection of CO2 or replaced completely by C0Z. This is because it transpired that the water is in a less unstable state during its passage in the atmospheric cooler, the desorption of C02 no longer being excessive and the precipitation decreasing. Furthermore, it turned out that it is not necessary to maintain a C02 partial pressure in the atmospheric air circulating in the tower by further addition of C02, as might have been expected.
The process according to the invention there-fore makes it possible, without increasing the salinity of the water circulating in the circuit, to decrease the scale of the bleeding and, consequently, to increase the level of concentration, which makes it possible to achieve considerable savings and an increase in productivity.
The invention applies to all types of cooling water circuit of semi-open type.
It proves to be particularly advantageous in the case of the treatment of the cooling waters of a nuclear power station. Nuclear sites are generally constructed close to water courses in order to provide an additional supply of water which allows the losses by evaporation in the air coolers and the bleeds needed for the discharge of concentrated salts in the circuits to be compensated for. The flow of make-up water should generally be conditioned by chemical treatment, in order to limit the risks of scale formation in the
The process according to the invention there-fore makes it possible, without increasing the salinity of the water circulating in the circuit, to decrease the scale of the bleeding and, consequently, to increase the level of concentration, which makes it possible to achieve considerable savings and an increase in productivity.
The invention applies to all types of cooling water circuit of semi-open type.
It proves to be particularly advantageous in the case of the treatment of the cooling waters of a nuclear power station. Nuclear sites are generally constructed close to water courses in order to provide an additional supply of water which allows the losses by evaporation in the air coolers and the bleeds needed for the discharge of concentrated salts in the circuits to be compensated for. The flow of make-up water should generally be conditioned by chemical treatment, in order to limit the risks of scale formation in the
- 15 -circuits. The type of treatment depends on the quality of the water and on the nature itself of the water course used. Generally, the use of sulphuric acid in the make-up circuit is restricted by legislation in force relating to the content of dissolved salts. It is conventional to use dispersing agents of polyacrylate type in such a case. Tests carried out by the inventors of the present invention have shown that CO2 can be used either in complete substitution for H2SO4 or in addition to treatment by H2SO4. The advantage of the complete substitution of H2SO4 by COZ is that the injection of CO2 makes it possible to decrease the pH
without modifying the TAC by contributing equilibrating COZ, it being possible for the concentration of carbonate to be thus reduced, and the formation of scale. The use of CO2 in addition to H2SO4 makes it possible to dope the acidification of the waters in the circuit while observing the discharge standards which restrict the use of acid. The decrease in the phenomenon of scale formation makes possible, in this case, a significant increase in electricity production.
Other advantages result from the complete or partial substitution of HZSO4 by CO2, in particular economic advantages related in particular to the fall in the delivery costs for acidifying agents. Another advantage is the fact that the use of CO2 which is dissolved in the bicarbonate form greatly decreases saline pollution. Another advantage is the improvement in the safety of personnel since the COZ can be stored in the anhydrous form and since it is a noncorrosive neutral gas, which consequently makes it possible to extend the lifetime of the plants. Furthermore, another advantage economically is that the injection is carried out without recourse to rotary equipment of the acid metering pump type.
The same advantages could be observed in various types of plant, in particular on aqueous ammonia/water units using exchangers.
without modifying the TAC by contributing equilibrating COZ, it being possible for the concentration of carbonate to be thus reduced, and the formation of scale. The use of CO2 in addition to H2SO4 makes it possible to dope the acidification of the waters in the circuit while observing the discharge standards which restrict the use of acid. The decrease in the phenomenon of scale formation makes possible, in this case, a significant increase in electricity production.
Other advantages result from the complete or partial substitution of HZSO4 by CO2, in particular economic advantages related in particular to the fall in the delivery costs for acidifying agents. Another advantage is the fact that the use of CO2 which is dissolved in the bicarbonate form greatly decreases saline pollution. Another advantage is the improvement in the safety of personnel since the COZ can be stored in the anhydrous form and since it is a noncorrosive neutral gas, which consequently makes it possible to extend the lifetime of the plants. Furthermore, another advantage economically is that the injection is carried out without recourse to rotary equipment of the acid metering pump type.
The same advantages could be observed in various types of plant, in particular on aqueous ammonia/water units using exchangers.
- 16 -Furthermore, the example which follows is given purely by way of illustration of the invention and relates to the treatment of such a cooling water circuit.
EXAMPLE
Use is made, in this example, of a plant of the type of that described in Figure 2.
The evaporative condenser is composed of a tower 2, inside which is installed the heat exchanger to be cooled which acts as atmospheric cooler in the said tower.
The power of the exchanger is 1,556,000 kcal/h, i.e. 1,244,800 frigories/h.
100 kg/h of COZ are injected on the lift side of the recirculation pump 5.
The make-up with water is 4.6 m3/d.
The water bleed is 11.3 m3/h.
A comparative test in every respect equivalent but not comprising injection of CO2 has made it possible to show that the injection of CO2 under the conditions of this test makes it possible to triple the maximum level of concentration of salts and to eliminate scale formation in the exchanger.
The water bleed changes to 5 m3/h.
The make-up with water is decreased by 50%.
No redeposition of scale is observed.
The scale present before the injection is dissolved and disappears (via the bleed).
Figure 3 gives the pH of the water at the bottom and at the top of the cooling tower in the case respectively of the test according to the invention in the presence of CO2 injected after the pressure pump and in the case of a control test.
The pH at the top is maintained at the equilibrium value, whereas the pH at the bottom approaches the initial pH of the make-up water. A
gradient is established during the exchange but the
EXAMPLE
Use is made, in this example, of a plant of the type of that described in Figure 2.
The evaporative condenser is composed of a tower 2, inside which is installed the heat exchanger to be cooled which acts as atmospheric cooler in the said tower.
The power of the exchanger is 1,556,000 kcal/h, i.e. 1,244,800 frigories/h.
100 kg/h of COZ are injected on the lift side of the recirculation pump 5.
The make-up with water is 4.6 m3/d.
The water bleed is 11.3 m3/h.
A comparative test in every respect equivalent but not comprising injection of CO2 has made it possible to show that the injection of CO2 under the conditions of this test makes it possible to triple the maximum level of concentration of salts and to eliminate scale formation in the exchanger.
The water bleed changes to 5 m3/h.
The make-up with water is decreased by 50%.
No redeposition of scale is observed.
The scale present before the injection is dissolved and disappears (via the bleed).
Figure 3 gives the pH of the water at the bottom and at the top of the cooling tower in the case respectively of the test according to the invention in the presence of CO2 injected after the pressure pump and in the case of a control test.
The pH at the top is maintained at the equilibrium value, whereas the pH at the bottom approaches the initial pH of the make-up water. A
gradient is established during the exchange but the
- 17 -limitation of the desorption of COZ amazingly prevents scale formation, even at the bottom of the column, where the pH is highest.
Claims (8)
1. Process for the treatment of atmospheric cooling waters circulating in a semi-open circuit recirculation loop comprising an atmospheric cooling device (2) equipped with means for the natural or forced convection of atmospheric air, a bleeding device (D) and a make-up water feed (E), characterized in that waters is non-softened and carbon dioxide is introduced without addition of chemical additives at at least one point in the recirculation loop or in the make-up water feed or in a bypass circuit provided on the loop of the feed for the purpose of the introduction.
2. Process according to claim 1, characterized in that the carbon dioxide is introduced at the outlet of a pump (5, 7, 8) for circulation of the waters.
3. Process according to claim 1 or 2, characterized in that the carbon dioxide is introduced at a point in the process where the water exhibits a pressure of at least 1 bar.
4 Process according to any one of claims 1 to 3, characterized in that the carbon dioxide is introduced in the gaseous form.
Process according to any one of claims 1 to 4, characterized in that at least a portion of the carbon dioxide injected is composed of a mixture of carbon dioxide and an inert gas.
6. Process according to any one of claims 1 to 3, characterized in that the carbon dioxide is introduced in the liquid form.
7 Process according to any one of claims 1 to 6, characterized in that the cooling of the waters within the recirculation loop is provided by an atmospheric cooling system
8 Process according to any one of claims 1 to 7, characterized in that the cooling of the waters within the cooling loop is provided by an air heat exchanger.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR99/14732 | 1999-11-23 | ||
| FR9914732A FR2801300B1 (en) | 1999-11-23 | 1999-11-23 | CARBON DIOXIDE TREATMENT OF ATMOSPHERIC COOLING WATER |
| PCT/FR2000/003252 WO2001038237A1 (en) | 1999-11-23 | 2000-11-22 | Carbon dioxide treatment of atmospheric cooling water |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2360517A1 CA2360517A1 (en) | 2001-05-31 |
| CA2360517C true CA2360517C (en) | 2007-05-08 |
Family
ID=9552444
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002360517A Expired - Lifetime CA2360517C (en) | 1999-11-23 | 2000-11-22 | Carbon dioxide treatment of atmospheric cooling water |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1152985A1 (en) |
| CA (1) | CA2360517C (en) |
| FR (1) | FR2801300B1 (en) |
| WO (1) | WO2001038237A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8153010B2 (en) * | 2009-01-12 | 2012-04-10 | American Air Liquide, Inc. | Method to inhibit scale formation in cooling circuits using carbon dioxide |
| DE102013006504A1 (en) | 2013-04-16 | 2014-10-16 | Messer Group Gmbh | Method for avoiding deposits in cooling water circuits |
| NL2010885C2 (en) * | 2013-05-29 | 2014-12-02 | Stichting Dienst Landbouwkundi | Cooling water. |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3925523A (en) * | 1973-11-12 | 1975-12-09 | Marley Co | Opposed air path wet-dry cooling tower and method |
| DE2638983A1 (en) * | 1976-08-30 | 1978-03-02 | Kurt Dipl Chem Dr Dannhaeuser | Direct-contact water cooling tower - using sump water level to control water purge rate and maintain concn. |
| US4444675A (en) * | 1981-07-16 | 1984-04-24 | Mechanical Equipment Company, Inc. | Alkaline scale abatement |
| DE3135783A1 (en) * | 1981-09-10 | 1983-05-19 | Ekkehard Dipl.-Ing. 7302 Ostfildern Bretting | Combined drying and wet cooling tower |
| US4547294A (en) * | 1982-02-18 | 1985-10-15 | Mechanical Equipment Company, Inc. | Alkaline scale abatement in cooling towers |
| HUT39482A (en) * | 1984-09-19 | 1986-09-29 | Budapesti Mueszaki Egyetem | Process and equipment for acid-free elimination of scale |
| JPH1128461A (en) * | 1997-07-10 | 1999-02-02 | Kurita Water Ind Ltd | Method for suppressing corrosion of metal in water system |
-
1999
- 1999-11-23 FR FR9914732A patent/FR2801300B1/en not_active Expired - Lifetime
-
2000
- 2000-11-22 EP EP00981459A patent/EP1152985A1/en not_active Withdrawn
- 2000-11-22 WO PCT/FR2000/003252 patent/WO2001038237A1/en active Application Filing
- 2000-11-22 CA CA002360517A patent/CA2360517C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| WO2001038237A1 (en) | 2001-05-31 |
| CA2360517A1 (en) | 2001-05-31 |
| FR2801300A1 (en) | 2001-05-25 |
| EP1152985A1 (en) | 2001-11-14 |
| FR2801300B1 (en) | 2001-12-28 |
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