JP2014069097A - Method for removing marine organisms from heat exchanger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing marine organisms from a heat exchanger, capable of effectively depleting marine organisms adhered to the inner plane of the heat transfer tube, while suppressing the volume of microbubbles of a carbon dioxide gas dispensed into a heat transfer tube.SOLUTION: In a case where marine organisms adhered to the inner plane of the heat transfer tube 13 of the heat exchanger 12 are depleted, a body of sea water or fresh water including microbubbles of a carbon dioxide gas is dispensed intermittently into the heat transfer tube 13. The timing of the commencement of this intermittent dispensation coincides with the achievement of a control value set in advance as a result of the proliferation of the inlet-outlet pressure difference of the heat exchanger 12. Moreover, it is desirable to confine the pH of the microbubble-containing dispensation water and the dispensation period respectively to 6.5-6.9 and 1-7 days. Moreover, it is desirable to perform an ordinary washing operation such as backwashing, fresh water substitution, etc. during the microbubble dispensation stoppage period. Moreover, it is desirable to intermittently dispense the microbubble-containing dispensation water in a state where the dispensation of sea water into the heat exchanger 12 is being halted.

Description

  The present invention relates to marine organisms in a heat exchanger using carbon dioxide gas microbubbles in order to reduce marine organisms adhering to the inner surface of a heat transfer tube of a heat exchanger using seawater such as a condenser in a power plant, for example. It is related with the removal method.

  In heat exchangers using seawater, seawater is introduced into the heat transfer tube for a long time, so that marine organisms such as microorganisms, algae such as diatoms and green algae adhere to the inner surface of the heat transfer tube. In order to reduce such marine life from the inner surface of the heat transfer tube, a method has been proposed in which carbon dioxide gas is injected into the seawater to lower the pH of the seawater and prevent the attachment of marine life.

  This kind of marine organism adhesion prevention method is disclosed in Patent Document 1. That is, in this method, carbon dioxide gas is injected into seawater, and the pH of the seawater is lowered to 5-6. According to this method, the low pH seawater can suppress the adhesion of shells formed by hormonal action of larvae of marine organisms.

  A similar marine organism adhesion prevention method is disclosed in Patent Document 2. In this method, carbon dioxide gas is injected into seawater so that the mixing ratio of carbon dioxide gas to seawater is (0.1 to 4) / 100, and microbubbles of carbon dioxide gas are generated. 4 to 8.1. According to this method, the pH of seawater can be lowered to suppress the attachment of marine organisms, and the marine organisms adhering to the inner surface of the heat transfer tube can be scraped off by the carbon dioxide gas microbubbles.

Japanese Patent No. 3605128 JP 2010-43060 A

  In the conventional method for preventing adhesion of marine organisms proposed in Patent Documents 1 and 2 described above, marine organisms are introduced into the heat transfer tubes of the heat exchanger by injecting carbon dioxide gas into the seawater to lower the pH of the seawater. It is supposed to suppress adhesion. Both of them focus on preventing fouling in the heat transfer tube due to growth of larvae by suppressing the attachment of marine larvae to the heat transfer tube. If carbon dioxide gas injection stops even for a short time of about 1 hour, sea life larvae will adhere to the heat transfer tube during that time. Continuous injection is essential to avoid the blank period. For this reason, there has been a problem that long-term continuous injection becomes a requirement and a large amount of carbon dioxide is required.

  Therefore, an object of the present invention is to perform heat exchange that can effectively reduce marine organisms adhering to the inner surface of the heat transfer tube while suppressing the amount of carbon dioxide gas microbubbles injected into the heat transfer tube. It is to provide a method for removing sea life in a vessel.

  In order to achieve the above object, a method for removing marine organisms in a heat exchanger according to a first aspect of the present invention is a heat exchanger configured to inject seawater into a heat transfer tube and perform heat exchange. A method of reducing marine organisms adhering to the inner surface of the heat transfer tube, wherein seawater or fresh water containing carbon dioxide gas microbubbles is intermittently injected into the heat transfer tube.

  According to a second aspect of the present invention, there is provided a method for removing sea life in a heat exchanger according to the first aspect, wherein the start time of injection of seawater or fresh water containing microbubbles of carbon dioxide gas is attached to the inner surface of the heat transfer tube. This is characterized in that the pollution caused by the marine life increased and the inlet / outlet differential pressure of the heat exchanger has reached a predetermined control value.

  The method for removing marine organisms in the heat exchanger of the invention according to claim 3 is the pH according to the invention according to claim 1 or claim 2, wherein the seawater or fresh water containing the microbubbles of carbon dioxide gas is injected. Is 6.5 to 6.9, and the injection period is 1 to 7 days.

  The sea life removal method in the heat exchanger of the invention described in claim 4 is the invention according to any one of claims 1 to 3, wherein seawater or fresh water intermittently containing the microbubbles of carbon dioxide gas. During the period from the start of the injection to the start of the next intermittent injection, backwashing is performed to reversely flow seawater flowing through the heat transfer tube, or fresh water replacement is performed to replace the heat transfer tube with fresh water.

  According to a fifth aspect of the present invention, there is provided a method for removing marine organisms in the heat exchanger according to the fourth aspect of the present invention, wherein after the intermittent injection of seawater or fresh water containing the microbubbles of carbon dioxide gas, the next intermittent injection is performed. The starting time is that after the base value indicating the inlet / outlet differential pressure of the heat exchanger after the backwashing or fresh water replacement has reached a predetermined primary control value, the seawater is injected and the inlet / outlet differential pressure of the heat exchanger is increased. Is the time when a predetermined management value is reached.

  The sea life removal method in the heat exchanger of the invention described in claim 6 is the invention according to any one of claims 1 to 5, wherein seawater or fresh water intermittent containing the carbon dioxide gas microbubbles The injection is performed with the seawater injection stopped and the heat exchanger isolated, and during the intermittent injection period, the replacement of the water in the heat exchanger with seawater or fresh water injection water containing microbubbles of carbon dioxide gas is continued. Alternatively, the heat exchanger is filled with injected water after the replacement is stopped.

According to the present invention, the following effects can be exhibited.
The method for removing marine organisms in the heat exchanger of the present invention is to intermittently inject seawater or fresh water containing carbon dioxide gas microbubbles into a heat transfer tube. With this configuration, the seawater attached to the heat transfer tube is effectively reduced by lowering the pH of the seawater while reducing the injection amount compared to the case of continuously injecting the carbon dioxide gas microbubbles into the heat transfer tube. be able to. That is, not only marine organisms attached to the inner surface of the heat transfer tube, that is, the larvae, but also grown marine organisms can be removed by the carbon dioxide gas microbubbles injected intermittently into the heat transfer tube.

  Therefore, according to the method for removing marine organisms in the heat exchanger of the present invention, marine organisms adhering to the inner surface of the heat transfer tube can be effectively suppressed while suppressing the amount of carbon dioxide gas microbubbles injected into the heat transfer tube. There is an effect that it can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing which shows typically the removal apparatus of the sea life in the heat exchanger of embodiment which actualized this invention. (A) is a conceptual graph showing the relationship between the number of days elapsed and the amount of marine organism adhesion (wet volume) in the marine organism adhesion test, and (b) is the number of days elapsed and marine life in the marine organism removal test. The conceptual graph which shows the relationship with the adhesion amount (wet volume). The graph which shows typically the relationship between an elapsed period (week) and wet volume. The graph which shows the relationship between elapsed days and the inlet / outlet differential pressure | voltage of a heat exchanger. The graph which shows the relationship between elapsed days and wet volume. The graph which shows the relationship between elapsed days and a dirt coefficient. The graph which shows the relationship between elapsed days and polarization resistance. The graph which shows the relationship between elapsed time and wet volume about the case of seawater. The graph which shows the relationship between elapsed time and wet volume about the case of fresh water. The graph which shows the relationship between elapsed time and a dirt coefficient about the case of seawater. The graph which shows the relationship between elapsed time and a soil coefficient about the case of fresh water. The graph which shows the relationship between elapsed time and polarization resistance about the case of seawater. The graph which shows the relationship between elapsed time and polarization resistance about the case of freshwater.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, in an equipment cooling water system of a power plant, a heat exchanger 12 is connected to a seawater line 11 that passes seawater as a heat exchange medium, and seawater is supplied to a heat transfer tube 13 in the heat exchanger 12. Heat exchange is performed by passing water. The heat transfer tube 13 is made of aluminum brass (aluminum / copper alloy). An iron ion supply device (not shown) is connected to the seawater, and iron ions are mixed into the seawater to form an iron coating as a protective coating on the inner surface of the heat transfer tube 13.

  A fresh water line 14 is connected to the sea water line 11 so that fresh water can be sent to the heat transfer pipe 13 of the heat exchanger 12 instead of sea water, and the inside of the heat transfer pipe 13 can be replaced with fresh water. The seawater line 11 and the freshwater line 14 are provided with valves 15 and 16, respectively, and switching between seawater and freshwater is possible by opening and closing the valves 15 and 16. Further, a water discharge pipe 17 is connected to the downstream side of the heat exchanger 12, and the water discharge pipe 17 is connected to a water discharge pit (not shown) via a valve 18.

  A microbubble supply line 19 for carbon dioxide gas is connected to a downstream side of the seawater line 11 from the connection portion of the fresh water line 14 via a check valve 20 and a valve 21. Seawater or fresh water is introduced into the microbubble supply line 19 from the outside via a flow rate adjusting valve 22 at a predetermined flow rate. The microbubble supply line 19 is provided with a carbon dioxide gas microbubble generating mechanism 23. An ejector-type microbubble generator 27 is installed in the microbubble generating mechanism 23, and the carbon dioxide gas supplied from the carbon dioxide gas cylinder 25 via the gas pipe 26 is microbubbled in seawater or fresh water. ing.

  The microbubble generator 27 mixes microbubbles in the seawater or fresh water of the microbubble supply line 19. A pH sensor 29 is connected downstream of the microbubble generator 27 in the microbubble supply line 19 so as to detect the pH of seawater or fresh water containing carbon dioxide gas microbubbles. When the valve 21 of the microbubble supply line 19 is opened, seawater or fresh water containing microbubbles of carbon dioxide gas is supplied from the microbubble supply line 19 to the seawater line 11, and is supplied to the heat transfer tube 13 of the heat exchanger 12. It is supposed to be sent.

  When seawater or fresh water containing microbubbles of carbon dioxide gas is sent from the microbubble supply line 19, the valves 15 and 16 provided in the seawater line 11 and the freshwater line 14 are closed, and the seawater line 11 And the water flow from the fresh water line 14 is stopped. In this state, seawater or fresh water containing microbubbles of carbon dioxide gas is sent from the microbubble supply line 19 to the heat exchanger 12 at a predetermined pH and flow rate.

  In addition, it is preferable that the diameter of the microbubble of carbon dioxide gas is several micrometers-several tens of micrometers. When the size of the microbubbles is excessively large, the surface area of the microbubbles is reduced, the function expression of the microbubbles is reduced, and the bubbles are liable to float and the dispersibility is deteriorated. Since it falls, it is not preferable.

  FIGS. 2A and 2B are conceptual diagrams showing the behavior of the amount of marine organisms adhering to the heat transfer tubes 13 of the heat exchanger 12. As shown in FIG. 2A, when seawater is introduced into the heat transfer pipe 13 of the heat exchanger 12 from the seawater line 11 and heat exchange is performed, and the heat exchange is continued for a long time under a certain condition. Marine organisms (marine organisms) such as plankton and algae adhere to the inner surface of the heat transfer tube 13. The amount of adhesion increases as the number of elapsed days increases.

  FIG. 2 (a) shows the amount of adhesion when seawater is continuously injected into the heat transfer tube 13 in the initial state where no marine organisms adhere. 1-1 is a case where normal seawater is injected, and the amount of adhesion gradually increases as the number of days increases. 1-2 is a case of continuously injecting seawater containing carbon dioxide gas microbubbles, but the increase in the adhesion amount is moderate compared to 1-1, but the increase does not stop. Even when low pH seawater is injected, the amount of attachment increases because a certain amount of larvae that can adapt to the low pH environment exists among the larvae of the larvae that adhere to the heat transfer tube 13 and adhere to it. The larvae have grown.

  On the other hand, as shown in FIG. 2B, when the valve 21 of the microbubble supply line 19 is opened and seawater or fresh water containing microbubbles of carbon dioxide gas is introduced into the heat transfer tube 13, the low pH of the microbubbles The amount of marine organisms attached to the inner surface of the heat transfer tube 13 gradually decreases due to the action.

  FIG. 2B shows the amount of adhesion when seawater and fresh water containing microbubbles of carbon dioxide gas are continuously injected into the heat transfer tube 13 in an initial state where marine organisms are attached and fouled. 2-1 shows a gradual decrease in the attached amount of marine organisms that can be removed with carbon dioxide gas microbubbles. When the heat exchange medium is seawater, as shown in 2-2, in addition to the attached amount of the gradually decreasing curve of 2-1, marine organisms contained in the injected seawater are attached and the attached amount is obtained. The attached marine life is expected to be the same as the 1-2 marine life.

  When the amount of decrease in the gradually decreasing curve 2-1 of the amount of marine organisms that can be removed with carbon dioxide gas microbubbles decreases with the passage of days, the influence of the amount of marine organisms contained in the injected seawater is relative. The amount of sea creatures as a whole draws a gradual increase curve 2-2 at the inversion time. Therefore, even if microbubbles of carbon dioxide gas are continuously injected into the heat transfer tube 13, the attached amount of marine organisms increases after the inversion time. When the amount of attached marine organisms increases, the pressure difference (differential pressure) of seawater at the entrance / exit of the heat exchanger 12, that is, the entrance / exit of the heat transfer tube 13, increases. For this reason, the magnitude of the differential pressure at the inlet / outlet of the heat transfer tube 13 (inlet / outlet differential pressure) can be used as an index of the fouling of the heat exchanger 12. When the inlet / outlet differential pressure of the heat transfer tube 13 increases, backwashing in which seawater flows in the reverse direction in the heat transfer tube 13 or fresh water replacement for replacing the heat transfer tube 13 with fresh water is performed.

  On the other hand, when the injected water is fresh water, since the seawater is not contained in the injected water, the attached amount of the sea life can be shown by a gradually decreasing curve of 2-1. The gradual decrease during low pH seawater injection shown in 2-1 is due to the following reason. The target for removal is grown sea life, and generally it is more resistant to environmental changes than sea life at the larval stage, but it has grown because it was not experienced in a low pH environment during the growth period. Even in the case of marine organisms, there were marine organisms with relatively low resistance to a low pH environment, and the number of marine organisms was very large with a large amount of marine organisms accumulated. For this reason, there are a certain amount of sea creatures that can be removed, and these are gradually reduced by removing them intensively.

Next, FIG. 3 conceptually compares the case where seawater or fresh water containing microbubbles of carbon dioxide gas in the present embodiment is intermittently injected into the heat transfer tube 13 and the case where the conventional continuous injection is performed. FIG. That is, FIG. 3 is a diagram showing the relationship between the elapsed period (weeks) and the wet volume in the heat transfer tube 13 (cc / cm ² : the volume of marine organisms including moisture attached per 1 cm ^{2 of the} heat transfer tube area). The solid line represents the case of intermittent injection, and the alternate long and short dash line represents the case of continuous injection. Here, the wet volume is one of the parameters indicating the fouling in the heat transfer tube 13 and is an index of the same kind as the amount of attached marine organisms.

  As shown in FIG. 3, in the case of intermittent injection, seawater or fresh water containing microbubbles of carbon dioxide gas is transmitted after the elapse of two weeks until the wet volume corresponding to the control value of the inlet / outlet differential pressure of the heat exchanger 12 is reached. Inject into heat tube for 1 week and repeat for 12 weeks. For this reason, microbubbles are injected four times in 12 weeks, that is, 4 weeks. On the other hand, in the case of continuous injection, carbon dioxide gas microbubbles are injected into the heat transfer tube 13 for 12 weeks. Therefore, when the same removal effect is obtained for marine organisms, the amount of carbon dioxide gas used can be reduced to 1/3 in the case of intermittent injection compared to the case of continuous injection.

  The injection start time of the intermittent injection of seawater or fresh water containing the microbubbles is when the contamination by marine organisms adhering to the inner surface of the heat transfer tube 13 increases and the inlet / outlet differential pressure of the heat exchanger 12 reaches a predetermined control value. Is preferred. In this case, it is possible to appropriately determine the start timing of intermittent injection based on the inlet / outlet differential pressure that is an index of fouling.

  Furthermore, the interval between intermittent injections can be increased by combining normal cleaning (backwashing, fresh water replacement, etc.) between intermittent injections and subsequent intermittent injections, rather than repeating only intermittent injections. The amount of carbon dioxide gas used can be reduced. For example, by performing intermittent injection twice in 12 weeks and performing normal cleaning in the meantime, the amount of carbon dioxide gas used can be reduced to 1/6 compared to the case of continuous injection. However, normal cleaning such as backwashing and fresh water replacement tends to reduce the removal effect (cleaning effect) by repeated execution, so it is necessary to set the combination appropriately based on the experience of operating the equipment. is there.

  As shown in FIG. 4, for example, normal cleaning (replacement with fresh water) is performed, the effect is reduced, and the base value 30 of the inlet / outlet differential pressure after cleaning increases to reach a primary management value of a predetermined base value 30. Then, when seawater is injected and the inlet / outlet differential pressure of the heat exchanger 12 reaches a predetermined control value (secondary control value), carbon dioxide gas microbubbles are injected into the heat transfer tube 13 for cleaning. It is also effective to carry out and restore the performance of the heat exchanger 12. As a result, intermittent injection of carbon dioxide gas microbubbles and normal cleaning work together, and the opportunity for carbon dioxide gas microbubble injection can be further reduced, contributing to a reduction in the amount of carbon dioxide gas used. .

The period setting conditions in the conceptual diagram of FIG. 3 are as follows.
1) Period of intermittent injection: 1 week (about 170 hours)
2) Cleaning interval until the next intermittent injection: 2 weeks The interval of intermittent injection in low pH seawater is equivalent to the initial cleaning interval (about 2 weeks) of normal cleaning using fresh water (fresh water replacement). There is no significant difference in the reduction rate of the wet volume between the low pH seawater of Table 1 and the fresh water of Table 2.

3) Period of continuous injection: 4 weeks As shown in FIG. 5, the rate of increase in wet volume is about half that of normal seawater in low pH seawater, so the period is the cleaning interval in normal seawater. It was set to 4 weeks, which is twice that of 2). Moreover, after that, it was set as what fell to the wet volume equivalent after cleaning by cleaning, such as backwashing.

  Here, marine organisms when carbon dioxide gas microbubbles are injected into seawater using a new pipe of heat transfer tube 13 and low pH seawater adjusted to pH 6.9 and normal seawater (about pH 8) are passed for a long time. The adhesion behavior of is shown. The index indicating the fouling of the heat transfer tube 13 includes a wet volume and a fouling coefficient, and the results of measuring these are shown in FIGS. 5 and 6, respectively.

As shown in FIG. 5, when a new pipe of the heat transfer pipe 13 is used, microbubble injection of carbon dioxide gas into seawater, and low pH seawater adjusted to pH 6.9 and normal seawater (about pH 8) are passed for a long time. The wet volume (cc / cm ² ) of marine organisms adhering to the inner surface of the heat transfer tube 13 was measured. In FIG. 5, ◇ indicates the case of normal seawater, and □ indicates the case of low pH seawater. As a result, with respect to the wet volume after passing water for about 20 days, the increase rate of the wet volume was about ½ in the case of low pH seawater compared to the case of normal seawater. For this reason, it turns out that low pH seawater has the effect of relieving adhesion of marine organisms. However, the wet volume has continued to rise gradually without stopping the attachment of marine life. If this state persists, the inlet / outlet differential pressure of the heat exchanger 12 will eventually rise to the control value, but in that case, it is necessary to lower the inlet / outlet differential pressure by another measure such as backwashing.

  The inlet / outlet differential pressure of the heat exchanger 12 does not have much influence as resistance to water flow and there is no expression as the inlet / outlet differential pressure when the wet volume of marine organisms adhering in the heat transfer tube 13 is small. As the pressure increases, the resistance increases and appears as an inlet / outlet differential pressure. In actual operation, the state of fouling is determined based on the inlet / outlet differential pressure of the heat exchanger 12 that can be monitored during operation, and the heat exchanger 12 is cleaned when a predetermined control value of the inlet / outlet differential pressure is reached. Do.

In addition, as shown in FIG. 6, the soil coefficient (m ² K / W) was measured according to a conventional method for low pH seawater having a pH of 6.9 and normal seawater (about pH 8). The contamination coefficient is the reciprocal of the heat transfer coefficient (W / m ² K). In FIG. 6, ◇ indicates the case of normal seawater, and □ indicates the case of low pH seawater. In the case of the fouling coefficient, as with the wet volume, the increase rate of the fouling coefficient was moderate at about 1/2 in the low pH seawater, but the increase itself has not stopped.

  In recent years, the use of titanium having corrosion resistance is increasing as the material of the heat transfer tube 13, but aluminum brass is often used even today. In the heat exchanger 12 using an aluminum brass tube, in order to prevent corrosion and thinning of the inner surface of the heat transfer tube 13 through which the seawater flows, iron ions are injected into the flowing water to protect the iron in the heat transfer tube 13. In many cases, a coating is formed to prevent seawater from directly contacting the inner surface of the heat transfer tube 13. In a low pH environment, it acts in the direction of promoting the dissolution of the protective film in the heat transfer tube 13, and therefore, when carbon dioxide gas injection is prolonged, the formation of the protective film may be insufficient. There is a concern that the soundness of the heat transfer tube 13 may be hindered.

As a method for determining the state of the protective coating in the heat transfer tube 13, there is a measurement of polarization resistance (electric resistance between the inner surface and the outer surface of the heat transfer tube 13). If the measured value of the polarization resistance is 20000 Ω · cm ² or more, it is judged that the formation of the protective film is good and the long-term operation thereafter is possible. However, this measurement requires the heat transfer tube 13 to be extracted, and the heat transfer tube 13 being used in an actual machine cannot be measured. For this reason, in actual operation, management of the formation of the protective coating in the heat transfer tube 13 is performed by continuously injecting iron ions of a predetermined concentration for a certain period from the time when the sea water flow of the heat exchanger 12 is started.

  Using a ferroco pipe (aluminum brass pipe pre-applied with a protective coating) as the heat transfer pipe 13, low pH seawater and normal seawater (about pH 8) adjusted to pH 6.9 by injecting microbubbles of carbon dioxide gas into seawater for a long time In the case of passing water, iron ions were respectively injected, and the state of adhesion of iron ions to the heat transfer tube 13 was confirmed. When iron ions adhere to the inside of the heat transfer tube 13, the electrical resistance (polarization resistance) between the inner surface and the outer surface of the heat transfer tube 13 increases.

Therefore, as shown in FIG. 7, the polarization resistance (Ω · cm ² ) was measured for normal seawater and low pH seawater according to a conventional method. In FIG. 7, ◇ indicates the case of normal seawater, and □ indicates the case of low pH seawater. As a result, in the case of normal seawater, an increase in the polarization resistance value was confirmed, and it was confirmed that an iron protective film was gradually formed. However, in the case of low pH seawater, an increase in the polarization resistance value was confirmed. It was judged that the protective film was not sufficiently formed. For this reason, in a long-term low pH environment, even if the polarization resistance value initially satisfies 20000 Ω · cm ² , the dissolution of the protective coating proceeds, resulting in poor film formation and the soundness of the heat transfer tube 13. It may be a hindrance.

  5 and 6, as described above, a result of continuously injecting microbubbles of carbon dioxide gas for a long period using a new pipe of the heat transfer pipe 13 is shown. The focus is on suppressing the attachment of marine life larvae to the inner surface of the heat transfer tube 13, but from this result, the increase in both the wet volume and the soil coefficient has not been stopped. This shows that even when the pH is lowered by injecting microbubbles of carbon dioxide gas, the larvae are not completely prevented from attaching, and a certain amount of larvae that can adapt even in a low pH environment continues to adhere. ing. For this reason, since the carbon dioxide gas is continuously injected over a long period of time while the effect of mitigating the attachment speed of larvae of marine organisms, it is considered that the burden on the use of carbon dioxide gas increases. Therefore, it is possible to rationalize the amount of carbon dioxide gas used by improving the continuous injection method.

  Based on the above, in this embodiment, the microbubble injection method is not continuous injection but intermittent injection. As described above, even the larvae of marine organisms cannot completely suppress adhesion by continuous injection of carbon dioxide gas microbubbles. Under such circumstances, intermittent infusion is expected to be more adaptable to environmental changes than larvae because sea life is considered to be growing during the period when injection is stopped. The Including this, a test was conducted to confirm the effect of intermittent injection.

  As shown in FIG. 8 and FIG. 10, in this test, sea water was continued for about two months to cultivate sea life, and from that state, carbon dioxide gas microbubbles were injected for 7 days (about 170 hours), Wet volume and soil coefficient were measured. As shown in these figures, it was possible to confirm the removal effect of sea life by microbubble injection of carbon dioxide gas with respect to the wet volume and the soil coefficient. Specifically, it was confirmed that the wet volume decreased by about 20% from the initial value in a low pH seawater environment as shown in Table 1 below. Table 1 shows the initial value of wet volume, the value after 7 days, and the difference (Δ) between normal pH and low pH (pH 6.9, 6.7 and 6.5) of normal seawater. The percentage (%) of the difference to the value is shown.

As shown in FIGS. 9 and 11, the same test as described above was also performed in a fresh water environment. As a result, both the wet volume and the soil coefficient showed a tendency to decrease by injecting microbubbles of carbon dioxide gas, and the removal effect of sea life was confirmed. As shown in Table 2 below, the wet volume was confirmed to be about 20% lower than the initial value, although a measurement error was observed in some wet volume data at pH 6.5.

  In Table 2, normal seawater pH 8.0 and low pH (pH 6.9, 6.8, 6.7, 6.5 and 6.3), the initial value of wet volume, the value after 7 days, and their difference In addition to (Δ), the percentage (%) of the difference from the initial value was shown.

From the above test results, the ratio of the difference between the wet volume corresponding to the management value of the inlet / outlet differential pressure and the wet volume corresponding to the inlet / outlet differential pressure after cleaning in FIG. It is estimated to be about 20%.

Next, as shown in FIG.12 and FIG.13, the influence on the protective film in the heat exchanger tube 13 accompanying microbubble injection | pouring of a carbon dioxide gas was confirmed using the ferroco pipe in seawater environment and freshwater environment. . As shown in FIG. 12 in the case of seawater and in FIG. 13 in the case of fresh water, if the injection period is limited to 7 days (about 170 hours), the polarization resistance value should be 20000 Ω · cm ² or more at pH 6.5 or more. It was confirmed that the heat transfer tube 13 can be maintained and the soundness of the heat transfer tube 13 can be maintained. The lower limit of pH 6.5 is a value that can maintain soundness even with an aluminum brass tube, and there is no problem even if it is applied to a titanium tube with excellent corrosion resistance. In the case of an aluminum brass tube, it is considered that the margin of polarization resistance value will be reduced after the microbubble injection of carbon dioxide gas. Therefore, iron ions are injected immediately after the operation to recover the polarization resistance value. It is desirable to plan.

  From the above results, even in the case of growing marine organisms, low pH seawater within 7 days is not experienced in a low pH environment and is accumulated in large quantities in the heat transfer tube 13 and has a large population. It was found that seawater could be removed efficiently with this water injection. In FIG. 2 (b), this corresponds to the range of the time continually decreasing before the inversion time in the curve 2-2.

  Since the injection period by intermittent injection of microbubbles is effective within a relatively short period of 7 days or less, for a system having a spare heat exchanger 12, the heat exchanger 12 to be cleaned is temporarily in an isolated state. It is possible to operate after stopping water flow and cleaning. When the heat exchanger 12 is isolated, the amount of water to be used can be greatly reduced and water can be easily secured, unlike the case of passing water, so that not only seawater but also fresh water can be easily used.

Here, as an example, the plant auxiliary water cooling system heat exchanger 12 (rated flow rate: 2000 m ³ / hr) was isolated and then injected with microbubbles of carbon dioxide gas in fresh water for 7 days. The amount of carbon dioxide gas used in the case of removal of carbon dioxide was estimated. That is, the isolation range (volume) around the heat exchanger 12 is set to 100 m ³ . The carbon dioxide gas required for the isolation range is 4 m ³ when the gas-liquid ratio of the fresh water having an initial pH of about 7.5 to about 6.5 is reduced to 4%. In order to perform reliable replacement, no matter how many times 100 m ³ of water is passed, if the capacity of a standard size carbon dioxide cylinder is about 15 m ³ , only a few cylinders are required. For this reason, the apparatus for supplying carbon dioxide gas can be reduced in size.

  Here, when microbubble injection of carbon dioxide gas is performed, the low pH seawater is discharged into the sea area. Water quality regulation values (public water quality standards) are set in the sea area, and it is necessary to consider that the pH is 7.8 or higher. As a method of recovering the pH value of seawater to the water quality regulation value, there is a method of recovering dilution by mixing with a large amount of normal seawater. In this case, in order to recover the seawater at pH 6.5 to pH 7.8, when the pH of normal seawater is 8.2, it is necessary to mix and dilute with seawater about 40 times as much as the water flow rate of the heat exchanger 12. Become. For this reason, in the heat exchanger 12 in an operating state, it is necessary to secure seawater that satisfies this capacity regardless of continuous injection and intermittent injection.

On the other hand, in the case of intermittent injection after performing isolation as described above, the following occurs. When the seawater in the isolated heat exchanger 12 is replaced with low pH water, it is assumed that the pH 6.5 low pH seawater is replaced at a speed of 10 m ³ / hr. In this case, the pH becomes 8.11 due to the mixed dilution of the heat exchanger 12 in operation with seawater at pH 8.2 with 2000 m ³ / hr of seawater. The pH of the seawater has a natural fluctuation of about ± 0.1 from the average pH depending on the time. If the pH average value of the seawater is 8.2, the lower limit side of the natural fluctuation is pH 8.1.

As described above, by limiting the discharge rate of fresh water containing carbon dioxide gas to 10 m ³ / hr or less, not only the water quality regulation value but also the range of the pH of natural fluctuations by dilution with operating units in the same system It is also possible to fit inside. Therefore, it becomes easy to secure seawater to be diluted.

Next, an effect | action is demonstrated about the removal method of the sea life in the heat exchanger 12. FIG.
Now, when seawater is introduce | transduced in the heat exchanger tube 13 of the heat exchanger 12 from the seawater line 11 and heat exchange is continued, the marine organisms contained in seawater will adhere to the heat exchanger tube 13 inner surface. When the inlet / outlet differential pressure of the heat exchanger 12 due to adhesion of marine organisms reaches a predetermined control value, the valve 15 is closed, the valve 21 of the microbubble supply line 19 is opened, and carbon dioxide gas is introduced into the heat transfer tube 13. Inject seawater or fresh water containing microbubbles. Thereafter, injection of carbon dioxide gas microbubbles and seawater flow after the injection stop are repeated, and microbubbles are intermittently injected into the heat transfer tube 13. At this time, when an increase in the inlet / outlet differential pressure occurs during the period in which the injection of microbubbles is stopped and seawater is running, an existing cleaning method such as backwashing may be performed.

In seawater or fresh water containing microbubbles, hydrogen ions (H ⁺ ) are generated by the reaction between carbon dioxide (CO ₂ ) and water (H ₂ O), and the pH of seawater or fresh water decreases, but pH 6.5- The injection amount of carbon dioxide gas is adjusted to be between 6.9. As a result, contaminants due to adhesion of marine organisms such as a biological film formed on the inner surface of the heat transfer tube 13 are peeled off and removed from the inner surface of the heat transfer tube 13. In intermittent injection of low pH water, it is considered that sea life larvae grow during the period when the injection is stopped and the resistance to environmental changes is strong. Can be removed from the inner surface. That is, when the number of marine organisms who have not experienced a low pH environment during the growth process increases to some extent, exposure to the low pH environment causes a decrease in the amount of adhesion at a certain rate, and the inner surface of the heat transfer tube 13 is separated. . By providing an interval between intermittent injections, the injection effect is improved by preventing the growing sea life from experiencing and adapting to a low pH environment.

  In this way, when the inlet / outlet differential pressure of the heat exchanger 12 reaches a predetermined control value, seawater or fresh water containing microbubbles of carbon dioxide gas is intermittently injected into the heat transfer tube 13, so that the heat transfer tube It is possible to efficiently remove marine organisms attached to the inner surface.

The effect obtained by the above embodiment is described collectively below.
(1) In this embodiment, seawater or fresh water containing microbubbles of carbon dioxide gas is intermittently injected into the heat transfer tube 13 of the heat exchanger 12. For this reason, by the said micro bubble, the pH of seawater can be lowered | hung and the marine organism adhering to the heat exchanger tube 13 inner surface can be decreased. That is, it is possible to remove the low-pH injection water by acting on the marine organisms that have adhered to and grown on the inner surface of the heat transfer tube 13 during the microbubble injection stop period.

Therefore, according to this embodiment, the marine organisms adhering to the inner surface of the heat transfer tube 13 can be effectively reduced while suppressing the injection amount of the carbon dioxide gas microbubbles injected into the heat transfer tube 13. Play.
(2) Since the injection mode of the carbon dioxide gas microbubbles is intermittent injection that repeats injection and stop, and the injection period is limited, the progress of dissolution of the protective coating on the inner surface of the heat transfer tube 13 made of aluminum brass is suppressed. The polarization resistance value can be maintained.

Therefore, the operation of the heat exchanger 12 can be continued in a stable state for a long time while maintaining the soundness of the protective coating of the heat transfer tube 13.
(3) Seawater or fresh water containing microbubbles of carbon dioxide gas starts to be injected at a control value in which the contamination by marine organisms attached to the inner surface of the heat transfer tube 13 increases and the inlet / outlet differential pressure of the heat exchanger 12 is determined in advance. It is time to reach. Therefore, marine organisms attached to the inner surface of the heat transfer tube 13 can be removed by a simple method based on the inlet / outlet differential pressure, which is an index of fouling.
(4) The pH of injection water for injecting seawater or fresh water containing microbubbles of carbon dioxide gas was set to 6.5 to 6.9, and the injection period was set to 1 to 7 days. For this reason, while being able to remove the marine organisms adhering to the inner surface of the heat transfer tube 13 by the low pH injection water, the removal effect of the marine organisms can be effectively exhibited in a short period of 7 days or less.
(5) Back washing or fresh water replacement is performed during the period from the intermittent injection of seawater or fresh water containing microbubbles of carbon dioxide gas to the start of the next intermittent injection. Therefore, the injection interval of carbon dioxide gas microbubbles can be extended, and the injection amount of microbubbles can be further reduced.
(6) After intermittent injection of seawater or fresh water containing microbubbles of carbon dioxide gas, the timing of starting the next intermittent injection indicates the inlet / outlet differential pressure of the heat exchanger after the backwashing or freshwater replacement. When the base value reaches the predetermined primary management value, seawater is injected and the inlet / outlet differential pressure of the heat exchanger reaches the predetermined secondary management value. In this case, the timing for starting the next intermittent injection can be easily and easily determined from the primary management value and the secondary management value based on the inlet / outlet differential pressure of the heat exchanger, and the removal operation of the sea life can be performed. It can be done appropriately and effectively.
(7) The intermittent injection of the microbubble injection water is performed in a state where the seawater injection is stopped and the heat exchanger 12 is isolated, and the water in the heat exchanger 12 is injected with the microbubble injection water during the intermittent injection period. The replacement is continued or the heat exchanger 12 is filled with injected water after the replacement is stopped. Thus, by isolating the heat exchanger 12 and performing intermittent injection, it is possible to easily lower the pH of the heat transfer tube 13 and more effectively reduce marine life adhering to the inner surface of the heat transfer tube 13. At the same time, it is possible to save the water injected into the microbubbles.

It should be noted that the embodiment described above can be modified and embodied as follows.
The microbubble supply line 19 is directly connected to the heat exchanger 12 without going through the seawater line 11 and configured to inject seawater or fresh water containing microbubbles of carbon dioxide gas directly into the heat transfer tube 13. May be.

  -You may comprise so that the injection amount and injection | pouring speed | velocity | rate of the microbubble of the carbon dioxide gas in the said heat exchanger tube 13 may be increased with the rise in temperature. For example, the amount of microbubbles injected into the heat transfer tube 13 and the injection speed may be increased in summer than in winter.

  12 ... heat exchanger, 13 ... heat transfer tube, 30 ... base value.

Claims (6)

A method of reducing marine organisms adhering to the inner surface of the heat transfer tube of a heat exchanger configured to inject seawater into the heat transfer tube to perform heat exchange,
A method for removing sea life in a heat exchanger, wherein seawater or fresh water containing microbubbles of carbon dioxide gas is intermittently injected into the heat transfer tube. The start time of the injection of seawater or fresh water containing the microbubbles of carbon dioxide gas is when the contamination by marine organisms adhering to the inner surface of the heat transfer tube increases and the inlet / outlet differential pressure of the heat exchanger reaches a predetermined control value. The method for removing marine organisms in the heat exchanger according to claim 1, wherein: The pH of injection water for injecting seawater or fresh water containing microbubbles of carbon dioxide gas is set to 6.5 to 6.9, and the injection period is set to 1 to 7 days. Item 3. A method for removing sea life in the heat exchanger according to Item 2. During the period from the intermittent injection of seawater or fresh water containing the microbubbles of carbon dioxide gas to the start of the next intermittent injection, backwashing or reverse replacement of the seawater flowing through the heat transfer pipe with fresh water The method for removing marine organisms in a heat exchanger according to any one of claims 1 to 3, wherein fresh water replacement is performed. After the intermittent injection of seawater or fresh water containing the microbubbles of carbon dioxide gas, the timing of starting the next intermittent injection is a base value indicating the inlet / outlet differential pressure of the heat exchanger after the backwash or the replacement of fresh water. The heat exchanger according to claim 4, wherein after reaching the predetermined primary management value, seawater is injected and the inlet / outlet differential pressure of the heat exchanger reaches a predetermined management value. Sea life removal method. The intermittent injection of seawater or fresh water containing microbubbles of carbon dioxide gas is performed with the seawater injection stopped and the heat exchanger isolated, and during the intermittent injection period, seawater or fresh water containing microbubbles of carbon dioxide gas The replacement of water in the heat exchanger with the injected water is continued, or the heat exchanger is filled with the injected water after the replacement is stopped. A method for removing sea life in a heat exchanger.