JP2016022458A - Injection water production system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection water production system stably operable even in the case a chlorine base bactericide causing self-decomposition is used.SOLUTION: Provided is an injection water production system comprising a bactericide storage tank 2 and a pump 21 of adding a chlorine base bactericide to seawater; a residual chlorine concentration sensor 4 of measuring the concentration of the residual chlorine in the seawater added with the chlorine base bactericide by the bactericide storage tank 2 and the pump 21; a reducing agent storage tank 6 and a pump 7 installed in the poststage of the residual chlorine concentration sensor 4 and adding a reducing agent of dechlorinating the residual chlorine in the seawater to the seawater added with the chlorine based bactericide; an RO membrane 10 capable of obtaining the injection water by the penetration of the seawater added with the reducing agent by the reducing agent storage tank 6 and pump 7; and an arithmetic control device 42 of controlling the addition amount of the chlorine based bactericide by the bactericide storage tank 2 and pump 21 based on the residual chlorine concentration measured with the residual chlorine concentration sensor 4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an injection water production system.

  There are primary sampling methods, secondary sampling methods, tertiary sampling methods, etc. in the method of extracting crude oil from underground oil reservoirs. The primary sampling method is a method of producing crude oil using natural waste oil energy. Specific examples of the primary sampling method include self-pulverized oil and artificial oil (such as pump oil). The secondary sampling method is a method of sampling by artificially applying oil drainage energy to the oil layer. A specific example of the secondary sampling method is a water flooding method in which water (pressed water) is injected to recover the oil reservoir pressure and increase the amount of oil production after production declines by the primary sampling method. Furthermore, the tertiary collection method is generally a collection method applied after secondary collection. Specific examples of the tertiary sampling method include chemical attack and thermal attack.

  Among these, in the secondary sampling method, when the geology of the oil layer is composed of fine and compacted particles, it is desirable to remove the number of fine particles in the injected water as much as possible. Therefore, in such a case, a reverse osmosis membrane (hereinafter referred to as “RO membrane”) is used, and fresh water from which the number of fine particles has been removed as much as possible may be pressed into the oil layer. However, fresh water obtained by desalinating seawater may be used in offshore oil fields or the like in which press-fed water cannot be obtained from the vicinity of the oil extraction site.

  In desalination facilities, sand filtration devices, ultrafiltration membranes (UF membranes), microfiltration membranes (MF membranes), etc., for removing obstructive substances that block the RO membrane in the pipes that are supplied to the RO membrane In some cases, microorganisms and shellfish derived from the collected seawater may breed. Therefore, in order to prevent this, a disinfectant may be injected into the seawater taken. At this time, there is a case where the disinfectant is supplied to the surface of the intake pump from the sea near the intake pump for the purpose of preventing propagation of shells and the like on the surface of the intake pump in the sea.

  For example, hypochlorous acid is used as the disinfectant. The amount of hypochlorous acid added (the amount used) is, for example, the amount of the product added so that the target concentration is obtained when added to seawater based on the hypochlorous acid concentration of the product purchased from the pharmaceutical manufacturer. Is calculated. Then, the calculated addition amount of hypochlorous acid is added to the seawater. At this time, a certain amount of hypochlorous acid is supplied so that the discharge amount from the product tank becomes the calculated addition amount.

  However, hypochlorous acid deteriorates the RO membrane. Therefore, a dechlorination treatment is usually performed by adding a reducing agent such as sodium bisulfite (hereinafter, SBS) in a piping line in front of the RO membrane. Then, the state of dechlorination treatment is monitored by an oxidation-reduction potentiometer (ORP meter). If residual chlorine is detected, the high-pressure pump installed for high-pressure filtration of the RO membrane is stopped to prevent the RO membrane from being deteriorated, and the entire desalination facility is stopped.

  As a technique for sterilizing seawater, a technique described in Patent Document 1 is known. In Patent Document 1, a ballast water supply line that connects a water intake and a ballast tank, and an aquatic organism in a liquid that is disposed in the line and taken from the water intake, are electrically or mechanically killed. And a chemical supply device that is connected to the line and supplies a sodium hypochlorite aqueous solution to the line for killing aquatic organisms in the liquid taken from the intake port. A ballast water treatment system is described. And the said chemical | medical solution supply apparatus connects with the 2nd water intake different from the water intake which the said ballast water supply line connects, and electrolyzes the liquid withdrawn from the said 2nd water intake, and hypochlorous acid It is described to generate sodium.

JP 2013-39516 A

  When fresh water is injected at an offshore crude oil mining site, seawater that becomes fresh water by the RO membrane is often taken from the vicinity of the offshore crude oil mining site. In addition, the concentration of turbidity including organic matter in seawater varies depending on the wind direction, tidal current, and the like. In particular, it has been confirmed that turbid substances constantly change in shallow waters. Therefore, since the added hypochlorous acid is consumed by the turbid components in the changing seawater, the effective chlorine concentration is also greatly changed, and it is difficult to control the concentration of hypochlorous acid in the seawater.

  Hypochlorous acid is an inexpensive and powerful sterilizing (oxidizing) agent, but it is an unstable substance and gradually decomposes itself during storage at room temperature, losing sterilizing power. That is, it is known that the concentration of effective components for sterilization (effective chlorine concentration) is lowered by the self-decomposition of hypochlorous acid, which is a weak acid. In particular, the self-decomposition easily proceeds as the temperature increases. Therefore, depending on factors such as the chemical storage period and storage temperature, the concentration displayed by the chemical manufacturer at the time of delivery and the hypochlorous acid concentration during actual use may differ greatly.

  In relation to this, the “Guidelines for the handling of sodium hypochlorite for water supply (Q & A) commissioned by the Ministry of Health, Labor and Welfare“ FY2007 Commission on Standards for Water Supply Chemicals, etc. ” Is described. In this document, a stock solution having an effective chlorine concentration of 13% is about 12% after one month at a temperature of 20 ° C., and a stock solution having an effective chlorine concentration of 13% is 10% after one month at a temperature of 30 ° C. It is described that at a temperature of 35 ° C., a stock solution having an effective chlorine concentration of 13% becomes more than 7% after one month. Thus, hypochlorous acid decomposes particularly quickly when the storage temperature is high, and the effective chlorine concentration rapidly decreases.

  This self-decomposition mainly proceeds in a container filled by a chemical manufacturer or in a hypochlorous acid stock solution tank (bactericide storage tank) provided in the facility. Therefore, although the actual concentration is constantly changing, the amount of hypochlorous acid added is fixed, so that the concentration of hypochlorous acid in seawater varies.

  Furthermore, since consumables used at offshore crude oil mining sites are transported by ship, there is a possibility that supply will be delayed due to the weather. Therefore, an excessive amount of hypochlorous acid is stocked, and the storage period becomes longer, so that the problem of self-decomposition inside the storage tank becomes even greater.

And a new subject arises by the above subjects.
The seawater to which the disinfectant is added is then supplied to the RO membrane (reverse osmosis membrane). However, if residual chlorine is contained in the seawater supplied to the RO membrane, the RO membrane is deteriorated by residual chlorine. Therefore, a reducing agent such as SBS (sodium bisulfite) is added at the front stage of the RO membrane, and dechlorinated seawater is supplied to the RO membrane. Here, in order to grasp the effect of dechlorination, an ORP meter (oxidation-reduction potentiometer) is often provided upstream of the RO membrane after the addition of the reducing agent. When a high oxidation-reduction potential due to residual chlorine is detected by the ORP meter, the operation of the system is stopped and the RO membrane is protected. Thereby, the arrival of residual chlorine to the RO film is suppressed, and the deterioration of the RO film is prevented.

  On the other hand, in order to perform a stable operation, it is generally performed to increase the reducing agent (SBS or the like) added in the upstream stage of the RO membrane to a chemical reaction equivalent or more. Specifically, for example, the reducing agent (SBS) may be set to about 2 to 5 times, preferably about 3 times or more the reaction equivalent of the bactericide (hypochlorous acid) to be added. However, excessive administration of the reducing agent is not preferable from the viewpoint of the global environment and cost.

  The present invention has been made in view of these problems, and the problem to be solved by the present invention is that even when a self-decomposing chlorine-based disinfectant is used, the RO membrane is prevented from deteriorating and can be stably operated. Is to provide a simple injection water production system.

  As a result of intensive studies to solve the above problems, the present inventors have provided a measuring device for measuring the residual chlorine concentration in the front stage of the RO membrane, and control the amount of the reducing agent to be added based on the measured residual chlorine concentration. Then, it discovered that the said subject could be solved.

  According to the present invention, it is possible to provide a pressurized water production system that can be stably operated even when a chlorine-based disinfectant that self-decomposes is used.

It is a systematic diagram of the injection water production system of a 1st embodiment. It is a control flow performed in the injection water production system of 1st Embodiment. It is a systematic diagram of the injection water production system of 2nd Embodiment. It is a control flow performed in the injection water production system of 2nd Embodiment. It is a systematic diagram of the injection water production system of 3rd Embodiment.

  Hereinafter, a form for carrying out the present invention (this embodiment) will be described with reference to the drawings as appropriate.

  FIG. 1 is a system diagram of a press-fit water production system 100 according to the first embodiment. Hereinafter, the “pressed water production system” may be abbreviated as “production system”. First, the configuration of the production system 100 will be described. In the following embodiment, hypochlorous acid is given as a specific example as a bactericidal agent (chlorine-based bactericidal agent).

  The production system 100 includes a pump 1 for taking seawater from the ocean, a bactericide storage tank 2 for storing a bactericidal agent (including hypochlorous acid) for addition to seawater, and a pump 21 for adding bactericidal agent to seawater. A static mixer 3 (static mixer) that statically mixes the added bactericide and seawater, an RO membrane 10, and a pump 9 (high pressure pump) for allowing the RO membrane 10 to pass seawater. ing.

  In addition, the production system 100 adds a reducing agent storage tank 6 in which a reducing agent (sodium bisulfite (SBS)) for neutralizing a bactericidal agent in seawater is stored, and the reducing agent is added to the seawater in front of the RO membrane 10. The pump 7 is provided. Furthermore, the production system 100 includes a residual chlorine concentration sensor 4 that measures residual chlorine concentration (hypochlorous acid concentration) in seawater, and an oxidation-reduction potential that measures the acid value reduction potential of seawater after the addition of a reducing agent. And a sensor 13.

  Among these sensors, as the residual chlorine concentration sensor 4, for example, a sensor using the principle of the amperometric method or a sensor using the principle of the polarographic method can be applied. The polarographic method is a method in which when the residual chlorine is reduced on the electrode surface, the residual chlorine concentration is measured based on the value of the current flowing between the electrodes. Among these, in the production system 100, a sensor using the principle of the polarographic method is installed. By using such a sensor, in-line continuous measurement becomes possible, so that continuous monitoring can be performed.

  Further, the production system 100 is provided with an arithmetic control device 42 that controls the driving of the pump 21 based on the residual chlorine concentration measured by the residual chlorine concentration sensor 4. By performing drive control of the pump 21, the addition amount of the bactericide added to the seawater is controlled. In addition, the production system 100 is provided with filters 5, 8, 11 for removing foreign substances in the flowing seawater or fresh water, and a pump 12 for press-fitting the injected water.

  Although not shown, the arithmetic and control unit 42 includes a CPU, a ROM, a RAM, an HDD, an I / F, and a monitor. Then, the program recorded in the ROM or HDD is executed by the CPU, whereby the arithmetic control device 42 is realized.

Next, the outline of the production method of the injection water in the production system 100 is demonstrated.
First, seawater is taken from the ocean by a pump 1 (raw water pump). A disinfectant is added from the disinfectant storage tank 2 to the taken-in seawater. As described above, this disinfectant contains hypochlorous acid.
Note that the disinfectant is preferably added after the pump 1, but it may be in the vicinity of the pump 1.

Seawater to which the disinfectant is added is sufficiently mixed in the static mixer 3. The static mixer 3 is a static mixer without a drive unit, and is also called a line mixer. The static mixer 3 can sufficiently mix the disinfectant and seawater by generating turbulent flow in the seawater to which the disinfectant is added. Further, the maintenance of the static mixer 3 is easy, and since there is no drive unit, there is an advantage of energy saving, and since it is small in size, there is an advantage of saving space.
From the viewpoint of preventing adhesion of shells and the like to the pump 1, when the bactericide is sufficiently mixed with seawater in the pipe, such as when the bactericide is added in the vicinity of the pump 1 in the ocean, the static mixer 3. Does not need to be installed.

  The residual chlorine concentration sensor 4 measures the concentration of residual chlorine in the seawater with respect to the seawater sufficiently mixed with the bactericide in the static mixer 3. Here, “residual chlorine” refers to the concentration of bactericide involved in the sterilization of seawater, that is, the total amount of free residual chlorine and combined chlorine. In the production system 100, the disinfectant is added so that the residual chlorine concentration in the seawater measured by the residual chlorine concentration sensor 4 is preferably about 0.2 ppm to 5 ppm, more preferably about 0.5 ppm to 2.5 ppm. Added.

  Here, as described above, the effective chlorine concentration of hypochlorous acid contained in the disinfectant in the disinfectant storage tank 2 varies depending on the temperature or the like. Therefore, in the production system 100, the pump 21 is controlled based on the residual chlorine concentration measured by the residual chlorine concentration sensor 4, and the addition amount of the bactericide is controlled. A specific control method will be described later with reference to FIG.

  The seawater after the residual chlorine concentration is measured is supplied to the filter 5, and turbid components in the seawater are removed. The filter 5 is a UF membrane (ultrafiltration membrane), an MF membrane (microfiltration membrane) or the like, but may be a sand filtration device or the like. Next, the reducing agent (SBS) from the reducing agent storage tank 6 is added to the seawater from which the turbid components have been removed, and if necessary, it is sufficiently mixed by a mixer (not shown). By adding a reducing agent, seawater dechlorination (oxidation power neutralization) is performed. Since the oxidizing power is neutralized, oxidative deterioration of the RO membrane 10 is prevented.

  Whether or not neutralization has been performed by the addition of the reducing agent is subsequently confirmed based on the oxidation-reduction potential measured by the oxidation-reduction potential sensor 13. That is, in the production system 100, when the oxidation-reduction potential measured by the oxidation-reduction potential sensor 13 is about 175 mV to 200 mV, it is determined that the residual chlorine has been neutralized to an allowable range.

  Seawater in which the oxidizing power is neutralized passes through the filter 8 and is supplied to the RO membrane 10 by a pump 9 (high pressure pump). In RO membrane 10, fresh water is obtained because the supplied seawater permeates. In the production system 100, the fresh water obtained here is usually 100 μS / cm or more, preferably 500 μS / cm or more as the electric conductivity. That is, since the electric conductivity required for normal drinking water level fresh water is about several tens to 100 μS / cm, the production system 100 uses fresh water under a condition that is looser than the RO membrane for obtaining drinking water level fresh water. Should be obtained.

  Then, the obtained fresh water is further transferred to a pump 12 (press-in pump) through a filter 11 installed as necessary in order to cope with a desired water quality condition, and is pressed into the oil layer as press-fed water. Although the filter 11 can be omitted, in the case of injecting an oxygen scavenger (chemical) into the subsequent stage of the RO membrane 10, it is effective for removing contaminants derived from the oxygen scavenger (chemical). is there.

  In addition, although illustration was abbreviate | omitted in FIG. 1, the tank which stores seawater and fresh water temporarily can be installed between each apparatus. In addition, a feed pump can be installed as necessary.

  FIG. 2 is a control flow performed in the injection water production system (production system 100) of the first embodiment. The control flow shown in FIG. 2 is performed during steady operation. The flow shown in FIG. 2 is performed by the arithmetic and control unit 42 (see FIG. 1) unless otherwise specified.

  When the seawater to which the bactericidal agent is added flows, the residual chlorine concentration sensor 4 measures the residual chlorine concentration in the seawater (step S101). Then, the arithmetic and control unit 42 determines whether or not the measured value of the residual chlorine concentration is not less than 0.2 ppm and not more than 5 ppm (step S102).

  As a result of the determination, when the residual chlorine concentration is less than 0.2 ppm, the discharge amount (addition amount) from the pump 21 that is a pump to which the bactericide is added is increased by 5% (step S103). That is, when there is almost no residual chlorine in seawater, that is, when there is almost no residual chlorine, the self-decomposition of hypochlorous acid in the disinfectant storage tank 2 has progressed considerably. As a result, the amount of the sterilizing agent in the sterilizing agent storage tank 2 is increased.

  In addition, hypochlorous acid is consumed more than expected by organic components derived from turbid components in seawater, although autolysis of the bactericide in the bactericide storage tank 2 has hardly progressed. Residual chlorine concentration in seawater may drop to less than 0.2 ppm. Therefore, even in such a case, the addition amount of the bactericide is increased in order to perform sufficient sterilization.

  When the residual chlorine concentration is 0.2 ppm or more and less than 5 ppm, the discharge amount of the pump 21 is maintained as it is (step S104). This is because the self-decomposition of hypochlorous acid in the sterilizing agent storage tank 2 is within the expected range, and it is judged that sufficient sterilization is possible by the hypochlorous acid in the sterilizing agent.

  Furthermore, when the residual chlorine concentration is 5 ppm or more, the discharge amount from the pump 21 that is a pump for adding the bactericide is reduced by 5% (step S105). That is, in this case, it is considered that the self-decomposition of hypochlorous acid in the disinfectant storage tank 2 has hardly progressed, and is not self-decomposing than the assumed degree of self-decomposition. Therefore, in this case, since the bactericidal agent contains a sufficient amount of hypochlorous acid, it is judged that there is no problem even if the addition amount of the bactericidal agent is reduced, and the addition amount of the bactericidal agent is reduced. .

  Further, when a new sterilizing agent (product) is replenished in the sterilizing agent storage tank 2, the residual chlorine concentration in the sterilizing agent in the sterilizing agent storing tank 2 increases. For this reason, the residual chlorine concentration of the added bactericide increases compared to the residual chlorine concentration before replenishment, and in this case, the addition amount is reduced by 5%.

  Then, after the control or maintenance of the discharge amount of the pump 21 is completed, the arithmetic and control unit 42 waits for a predetermined time (step S106). Here, the “predetermined time” is a time for adjusting the interval until the residual chlorine concentration is measured again after controlling the discharge amount. As a guideline, the disinfectant supplied by the pump 21 reaches the residual chlorine concentration sensor. As a guideline, it may be 2 to 5 times as long as the time required to do this (the time for staying in the pipe). Thereafter, the control flow of FIG. 2 is repeated again every predetermined time (step S106 described above), and the discharge amount of the pump 21 is feedback-controlled according to the residual chlorine concentration after adding the bactericidal agent.

  In FIG. 2, the change rate of the discharge amount of the pump 21 is 5%, but the change rate is not limited to this value. That is, the change ratio may be any predetermined value within a range of about 1% to 20%, for example, and is preferably an arbitrary predetermined value within a range of about 3% to 10%.

  Further, the “predetermined time” in step S106 is not limited to the “three times” time. That is, for example, it is preferable to set an arbitrary predetermined value within a range of about 1 to 10 times the time during which seawater stays in the pipe between the addition of the bactericide and the measurement. Preferably, it is an arbitrary predetermined value within a range of about 2 to 7 times.

  Further, in FIG. 2, the discharge amount of the pump 21 is maintained when it is 0.2 ppm or more and 5 ppm or less, but the present invention is not limited to this. Therefore, for example, it is also preferable that the discharge amount of the pump 21 be maintained when it is 0.5 ppm or more and 2.5 ppm or less.

  In the production system 100, the addition amount of the bactericide is controlled according to the residual chlorine concentration. Therefore, it can suppress that residual chlorine becomes an excessive amount. Thereby, the oxidation-reduction potential measured by the oxidation-reduction potential sensor 13 becomes a relatively small value. Therefore, the stop of the production system 100 due to the oxidation-reduction potential showing an abnormal value is suppressed. Therefore, the growth and adhesion of microorganisms and shells in seawater can be sufficiently prevented, and the operation of the production system 100 can be performed stably.

  Furthermore, since it can suppress that residual chlorine becomes an excessive amount, the quantity of the reducing agent used for neutralization of residual chlorine can be suppressed. Thereby, the cost reduction of a reducing agent can be aimed at. Moreover, compared with the case where it continues adding a predetermined amount of bactericides, the usage-amount of a bactericide can be reduced and the usage cost of a bactericide can be reduced by controlling the addition amount based on a residual chlorine concentration.

  The production system 100 is particularly suitable for use under conditions where the air temperature exceeds 35 ° C. (for example, installation in such an area), or conditions under which daily temperature changes or annual temperature changes are large. is there. Under these conditions, hypochlorous acid tends to self-decompose (deteriorate), and the concentration change of the sterilizing agent in the sterilizing agent storage tank easily proceeds. Therefore, if the production system 100 is installed under these conditions, even when the concentration of the bactericide changes greatly, the influence of the fluctuation can be absorbed and the production system 100 can be operated stably.

  Furthermore, as described above, hypochlorous acid is consumed by turbid components. Therefore, when taking seawater in which turbid components tend to fluctuate, the residual chlorine concentration may fluctuate depending on the amount of turbid components. However, even in such a case, the addition amount of the bactericide is controlled based on the residual chlorine concentration (that is, the amount of turbid components is small and large). Therefore, the production system 100 can be stably operated even in a place where the sea water quality fluctuation is large.

[2. Second Embodiment]
Next, the injection water production system (production system 200) of the second embodiment will be described with reference to FIGS. The production system 200 is basically the same as the production system 100 shown in FIGS. 1 and 2. Therefore, in the following description, the same reference numerals are assigned to the same components as in the water production system 100, and redundant descriptions are omitted.

  FIG. 3 is a system diagram of the injection water production system (production system 200) of the second embodiment. In the production system 200, unlike the production system 100 of FIG. 1, a bactericidal agent-added seawater storage tank 14 is provided between the filter 5 and the filter 8. The seawater (including the bactericidal agent) in the bactericidal agent-added seawater storage tank 14 is supplied to the electrolyzer 22 by the pump 24. In the electrolyzer 22, seawater is electrolyzed by the current from the DC power supply device 23, and hypochlorous acid is generated. And hypochlorous acid generated in the electrolyzer 22 is added to the taken-in sea water as a bactericidal agent (chlorine bactericidal agent).

That is, in the production system 100 of FIG. 1, the addition amount of the bactericide is controlled by the drive control of the pump 21. However, in the production system 200 of FIG. 3, by controlling the current supplied to the electrolyzer 22, the current density of the electrode plate installed in the electrolyzer 22 is also controlled so as to reduce the amount of hypochlorous acid generated. Control, thereby controlling the amount of hypochlorous acid added.
The current density of the electrode plate is a value obtained by dividing the DC current value supplied from the DC power supply device 23 by the electrolysis area of the electrode plate disposed in the electrolysis device 22.

The electrolyzer 22 is supplied with seawater (mainly an aqueous solution containing sodium chloride) from which turbid components have been removed by the filter 5, and generates hypochlorous acid by electrolysis. The pair of electrodes composed of a cathode and an anode provided in the electrolyzer 22 is not particularly limited as long as it can generate hypochlorous acid from seawater, but a noble metal such as platinum and / or iridium is titanium. An electrode plate coated on a metal plate such as a carbon plate or a carbon electrode plate is applicable. However, considering the electrode maintenance and the life of the electrode plate, the former electrode plate is preferable.
In the present embodiment, the electrolysis device 22 has a pair of electrodes (that is, a plurality of anode plates and a plurality of cathode plates) as described above, but only a pair of electrodes. It may be provided.

The DC power supply device 23 supplies a current used for electrolysis in the electrolysis device 22. The supplied current value is not particularly limited as long as hypochlorous acid can be generated. Specifically, for example, as the current density of the current supplied to the electrode plate, preferably ^{0.5mA / cm 2 ~100mA / cm 2} , more preferably ^{1mA / cm 2 ~50mA / cm 2} . An appropriate amount of hypochlorous acid can be generated by controlling the current density of the electrode plate disposed in the electrolyzer 22. As a result, the residual chlorine concentration measured by the residual chlorine concentration sensor 4 is included in the range of 0.2 ppm to 5 ppm (preferably 0.5 ppm to 2.5 ppm), and the amount of reducing agent used is also particularly appropriate. It will be a thing.

  FIG. 4 is a control flow performed in the injection water production system (production system 200) of the second embodiment. The control flow shown in FIG. 4 is performed during steady operation. The flow shown in FIG. 4 is performed by the arithmetic and control unit 42 (see FIG. 3) unless otherwise specified.

  First, similar to the control flow in the production system 100, the residual chlorine concentration is also measured in the production system 200 (step S101). Next, the arithmetic and control unit 42 determines whether or not the measured value of the residual chlorine concentration is not less than 0.2 ppm and not more than 5 ppm, similarly to the control flow in the production system 100 (step S102).

  As a result of the determination, when the residual chlorine concentration is less than 0.2 ppm, the current value supplied from the direct current device 23 to the electrolysis device 22 increases by 2.5% (that is, the current density of the electrode plate is also 2.5%). (Step S203). That is, when there is almost no residual chlorine, hypochlorous acid is almost consumed by the turbid component of seawater, and thus sterilization may be incomplete. Therefore, in this case, in order to increase the amount of hypochlorous acid generated and added, the current density of the electrode plate is increased by the supplied current.

  If the residual chlorine concentration is 0.2 ppm or more and less than 5 ppm, the current value supplied to the electrolysis device 22 is maintained (that is, the current density of the electrode plate is also maintained) (step S204). This is because the residual chlorine concentration is within a predetermined range, so that hypochlorous acid is not consumed by the turbid component to a predetermined concentration or less and sterilization is performed to a desired degree. This is because that.

  Further, when the residual chlorine concentration is 5 ppm or more, the current value supplied from the DC current device 23 to the electrolysis device 22 is reduced by 2.5% (that is, the current density of the electrode plate is also reduced by 2.5%). (Step S205). That is, since there is an excess amount of residual chlorine, there is a possibility that it cannot be sufficiently neutralized by the reducing agent in the subsequent stage. Therefore, in this case, the amount of hypochlorous acid generated and added is suppressed by electrolyzing seawater by reducing the current density of the electrode plate with the supplied current.

  Then, after the control or maintenance of the current density is completed, the arithmetic and control unit 42 waits for a predetermined time similarly to the control flow in the production system 100 (step S106). Thereafter, the control flow of FIG. 4 is repeated again every predetermined time (step S106 described above), and the current density of the electrode plate is determined by the current supplied to the electrolyzer 22 according to the residual chlorine concentration after addition of the bactericide. Is feedback controlled.

  In FIG. 4, the change rate of the current value and current density is 2.5%, but the change rate is not limited to this value. That is, the change ratio may be any predetermined value within a range of about 0.5% to 10%, for example, and is preferably an arbitrary predetermined value within a range of about 1% to 5%.

  In the production system 200 shown in FIGS. 3 and 4, the current density of the electrode plate to the electrolyzer 22 is feedback-controlled based on the residual chlorine concentration (hypochlorous acid concentration). Therefore, when the amount of hypochlorous acid added is small because there are few turbid components, control is performed to reduce the current density of the electrode plate to the electrolyzer 22.

  When the feedback control is not performed, since the current density of the current supplied to the electrode plate of the electrolysis device 22 is set higher, the amount of hypochlorous acid generated in the electrolysis device 22 also increases. And it exists in the tendency for the lifetime of an electrode plate to become short. Specifically, noble metals (platinum, iridium, etc.) coated on the surface of the electrode plate are likely to elute as the current density increases.

  However, by performing the control in the production system 200, it can be avoided that a current having a high current density is continuously supplied to the electrode plate. Thereby, it is possible to perform sterilization by generating a desired amount of hypochlorous acid by supplying a current at a high current density when necessary, while suppressing the consumption of the expensive electrode plate.

  Moreover, in the production system 200, since it is not necessary to separately prepare hypochlorous acid, the operating cost can be reduced. Furthermore, since the cost of sterilizing agent procurement and inventory management become unnecessary, cost reduction can be achieved in this respect as well.

[3. Third Embodiment]
Next, referring to FIG. 5, a press-fit water production system (production system 300) according to a third embodiment will be described. A production system 300 shown in FIG. 5 is basically the same as the production system 100 shown in FIG. Therefore, in FIG. 5, the same code | symbol shall be attached | subjected about the same thing as the water production system 100, and description of the overlapping content is abbreviate | omitted also in the following description.

  FIG. 5 is a system diagram of the injection water production system (production system 300) of the third embodiment. In the production system 300, in addition to the apparatus configuration of the production system 100, a temperature sensor 43 for measuring the temperature of the internal germicide is provided for the germicide reservoir tank 2. The temperature sensor 43 is connected to the calculation control device 42.

  In the production system 300, similarly to the production system 100 described above, the amount of fungicide added is controlled based on the residual chlorine concentration measured by the residual chlorine concentration sensor 4. However, in the production system 300, the addition amount determined by the production system 100 is corrected based on the temperature of the sterilizing agent stored in the sterilizing agent storage tank 2, and then becomes the corrected amount. The pump 21 is controlled. That is, in the production system 300, the addition amount of the bactericide is controlled based on two pieces of information, that is, the residual chlorine concentration measured by the residual chlorine concentration sensor 4 and the temperature measured by the temperature sensor 43.

  As described above, autolysis of hypochlorous acid is considered to occur mainly due to the change of the temperature of the sterilizing agent inside the sterilizing agent storage tank 2. Therefore, if the temperature of the disinfectant inside the disinfectant storage tank 2 is high, the self-decomposition rate is considered to be fast, and the concentration of hypochlorous acid in the added disinfectant is considered to be low. On the other hand, if the temperature of the disinfectant inside the disinfectant storage tank 2 is low, the rate of autolysis is considered to be slow, and the concentration of hypochlorous acid in the added disinfectant is considered to be maintained. .

  Therefore, in the production system 300, when the temperature of the bactericide measured by the temperature sensor 43 is high (for example, 30 ° C. or higher), a predetermined amount (for example, 10%) is added to the addition amount determined by the production system 100. The pump 21 is controlled as the amount of the added germicide to be added. On the other hand, when the temperature of the disinfectant measured by the temperature sensor 43 is low (for example, less than 30 ° C.), an amount obtained by subtracting a predetermined amount (for example, 10%) from the addition amount determined by the production system 100 is obtained. The pump 21 is controlled as the amount of the bactericide to be added.

  By performing such control, the degree of self-decomposition of hypochlorous acid contained in the disinfectant inside the disinfectant storage tank 2 is predicted, and the residual chlorine concentration after addition is more reliably determined by the reducing agent. Can be reduced. In addition, the amount of disinfectant and reducing agent used is more appropriate, and the global environment can be maintained and costs can be reduced.

[4. Modified example]
Although three specific examples of the present embodiment have been described above, the present embodiment is not limited to the above contents. In other words, the embodiment can be implemented with appropriate modifications.

  For example, the temperature sensor 43 described in the third embodiment may be applied to the first embodiment as described above, but may be applied to the second embodiment. When the temperature sensor 43 is applied to the second embodiment, for example, the temperature of seawater in the electrolysis device 22 may be measured to estimate the degree of decomposition of hypochlorous acid.

  For example, in the first embodiment, hypochlorous acid is used as the bactericidal agent, but any chlorinated bactericidal agent may be used. Furthermore, in the second embodiment, hypochlorous acid is generated by electrolysis of seawater, but other chlorine-based disinfectants may be generated.

  Further, the first embodiment and the second embodiment may be combined. That is, the bactericide storage tank 2 and the electrolysis device 22 may be provided side by side, and a bactericide such as hypochlorous acid may be added.

  Moreover, in 2nd Embodiment, although the mixture of seawater and a disinfectant was once stored in the disinfectant addition seawater storage tank 14, these mixtures do not need to be stored. That is, the disinfectant-added seawater storage tank 13 and the pump 24 are omitted, and the electrolysis apparatus is operated by the action of the gravity that is applied to the mixture directly through the filter 5 or the water pressure of the flow in the direction from the filter 5 to the filter 8. 22 may be supplied. At this time, the mixture supplied to the electrolyzer 22 is branched from the flow of the mixture supplied to the filter 8 and the like. And a flow control valve etc. are suitably provided so that the supply amount of the mixture to the electrolyzer 22 may be controlled.

2 Disinfectant storage tank (disinfectant addition device)
3 Static mixer (static mixer)
4 Residual chlorine concentration sensor (residual chlorine concentration measuring device)
6 Reducing agent storage tank (reducing agent addition device)
7 Pump (reducing agent addition device)
10 RO membrane (reverse osmosis membrane)
21 Pump (disinfectant addition device)
22 Electrolysis device (electrolysis device)
23 DC power supply (power supply)
42 arithmetic and control unit 43 temperature sensor 100 injection water production system 200 injection water production system 300 injection water production system

Claims (8)

In the injection water production system that produces injection water for crude oil production using fresh water obtained by permeating seawater through a reverse osmosis membrane,
A disinfectant addition device for adding a chlorine-based disinfectant to seawater;
A residual chlorine concentration measuring device for measuring a residual chlorine concentration in seawater to which a chlorine-based disinfectant is added by the disinfectant adding device;
A reductant addition device for adding a reductant for dechlorinating residual chlorine in the seawater to the seawater to which the residual chlorine concentration measuring device is installed, and to which the chlorine-based disinfectant is added;
A reverse osmosis membrane that obtains the injected water by allowing seawater to which a reducing agent has been added by the reducing agent addition device to pass through;
An injection water production system comprising: an arithmetic control device that controls an addition amount of a chlorine-based disinfectant by the disinfectant addition device based on a residual chlorine concentration measured by the residual chlorine concentration measurement device. . The chlorine-based disinfectant is hypochlorous acid,
2. The injection water according to claim 1, wherein the disinfectant adding device adds the chlorine-based disinfectant to seawater so that a concentration of hypochlorous acid in seawater is 0.2 ppm to 5 ppm. Production system.   3. The injection water production system according to claim 1, wherein the residual chlorine concentration measuring device is a sensor using a principle of a polarographic method.   The injection water production system according to any one of claims 1 to 3, wherein a static mixer is provided between the disinfectant addition device and the residual chlorine concentration measurement device. An electrolysis apparatus in which a cathode and an anode are provided with a pair of electrodes, and current is passed through the pair of electrodes to electrolyze seawater to obtain a chlorine-based disinfectant;
A power supply device that is connected to the one or more electrodes and allows a current to flow through the one or more electrodes; and
The chlorine-based disinfectant obtained in the electrolyzer is added to seawater by the disinfectant adding device as the chlorine-based disinfectant, according to any one of claims 1 to 4. Injection water production system. The power supply device, as the current density of the electrode plate by a current flowing through said one or more pairs of electrode plates is ^{0.5mA / cm 2 ~100mA / cm 2} , Tsuryu a current to the one or more pairs of electrode plates The press-fed water production system according to claim 5, wherein:   The arithmetic and control unit determines a current density of the electrode plate based on a current supplied from the power supply device to the electrolysis device based on the residual chlorine concentration measured by the residual chlorine concentration measuring device, and the determined current density The injection water production system according to claim 5 or 6, wherein the amount of the chlorine-based disinfectant added is controlled by controlling the current density with the current supplied from the power supply device. . A sterilizing agent storage tank connected to the sterilizing agent adding device and storing a sterilizing agent added to seawater by the sterilizing agent adding device;
A temperature sensor for measuring the temperature of the germicide in the germicide storage tank,
The arithmetic and control unit is configured to add a chlorine-based disinfectant added by the disinfectant adding device based on a residual chlorine concentration measured by the residual chlorine concentration measuring device and a temperature of the disinfectant measured by the temperature sensor. The press-fit water production system according to any one of claims 1 to 7, wherein

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