JP2006258601A - Probe for monitoring dew point corrosion and monitoring method of dew point corrosion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical probe for monitoring dew point corrosion capable of performing accurate electrochemical measurement by preventing gap corrosion. <P>SOLUTION: The probe 1 for monitoring dew point corrosion is equipped with a pair of electrode members 10 each of which has an electrode surface 11 exposed to a dew point corrosion environment and a holder 12 for holding a pair of the electrode members 10 in an adjacent state so as to embed them. A liquid junction forming part 16 for forming the liquid junction of dew condensation water between the electrode surfaces 11 is constituted in an acid dew point environment and the part 20 for covering the electrode members 10 of the holder 12 is constituted of a resin material having water repellency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a probe for monitoring acid dew point corrosion generated in an incinerator, a boiler, an economizer attached to a chemical plant, an air preheater, an exhaust heat recovery device, or a chimney, and a dew point corrosion monitoring method using the probe.

Sulfuric acid dew point corrosion is caused by sulfuric acid vapor generated by the oxidation of SO _{2 produced} by combustion of sulfur in the fuel and reaction with water vapor in the exhaust gas. The exhaust gas temperature in boilers and subsequent economizers, etc. It is likely to occur when it falls below the dew point of exhaust gas. Research on materials that can withstand such a corrosive environment is also underway, but there are still many unknown parts regarding the mechanism by which materials corrode, and it takes a lot of time and effort to evaluate and select materials. However, the material is not always used without problems in an actual corrosive environment. For example, an environment in which the material is actually used is simulated and an accelerated corrosion test is performed. However, the corrosion in the actual environment is not reproduced. If the specimen is exposed in an actual corrosive environment, it will be a long-term evaluation and it will not be possible to capture short-term changes in corrosion behavior.

As a method for preventing such sulfuric acid dew point corrosion, for example, Patent Document 1 discloses a technology for preventing sulfuric acid dew point corrosion by calculating the dew point from the exhaust gas temperature and the exhaust gas humidity and keeping the heat transfer tube temperature at or above the dew point. Is disclosed. There is no specific description of how to calculate the dew point from the temperature and humidity of the exhaust gas. In recent years, this has been calculated based on an empirical formula in the SOx—H ₂ O system. For example, when there is a large amount of SOx, such as petroleum combustion exhaust gas, and the dew point is governed by the SOx concentration, it is possible to control with relatively high accuracy by this method.

On the other hand, combustion boilers such as municipal waste and industrial waste contain more HCl than SOx, so it is necessary to consider the dew point in the SOx-HCl-H ₂ O system. No calculation formula is disclosed. This is because SOx reacts directly with H ₂ O to produce H ₂ SO ₄ , and even a small amount greatly contributes to an increase in dew point, whereas HCl only dissolves in H ₂ O. This is probably because the contribution to dew point rise is relatively small and has not been taken up as a major factor for dew point corrosion.

  In a waste combustion environment that contains a lot of HCl, a further problem is that the temperature at which the condensed phase is formed is reduced to a pure gas equilibrium due to the adhesion of highly deliquescent chloride salts on the surface of metal structural members. There is a possibility of shifting to a higher temperature side than the dew point calculated from. Therefore, in an environment containing a lot of HCl, such as a waste combustion environment, it may cause severe corrosion via the liquid phase at a higher temperature than the dew point calculated only from the gas composition and temperature. If the set temperature is determined with reference to, severe corrosion through the liquid phase may not be avoided.

  Therefore, as described above, instead of indirectly measuring the corrosiveness of the environment, a method of directly monitoring corrosion by an electrochemical method, which is implemented as a countermeasure to high temperature corrosion, can be considered. That is, by placing an electrochemical sensor with a pair of electrodes embedded in a holder made of an insulator in a corrosive environment, condensing corrosive gas between the electrodes to form a liquid junction, and measuring resistance and impedance Measure corrosivity. However, this is not a dry environment in which high temperature corrosion occurs, but a special situation in which corrosive liquid is condensed at a high temperature, and an appropriate sensor has not been developed and has not been put to practical use.

  Therefore, it is difficult to take effective measures against sulfuric acid dew point corrosion, and the present situation is that excessive maintenance is performed. Therefore, the economic loss due to anti-corrosion measures is considered to be extremely large. On the other hand, the economic loss caused by the trouble caused by the underestimation of the corrosion of the material is considerable.

Japanese Unexamined Patent Publication No. 63-21402 Japanese Patent Publication No.59-25456

The problem in the method of directly monitoring corrosion by the electrochemical method as described above is the durability and accuracy of the sensor. Sulfuric acid dew point corrosion is expected because the condensed phase generated by condensation of SOx-HCl-H ₂ O gas is expected to be a fairly strong acid environment, with insulation at high temperatures above 100 ° C and high acid resistance. It is necessary for the material to have properties.

  Also, when sulfuric acid dew point corrosion occurs, if the adhesion between the electrode and the insulator of the holder is poor, crevice corrosion occurs in the gap between the electrode and the holder, making accurate electrochemical measurement impossible. . On the other hand, sulfuric acid dew point corrosion is measured by forming a liquid junction between electrodes and measuring resistance and impedance. Therefore, if the wettability of the holder is poor, it becomes difficult to form a liquid junction between the electrodes. It is thought that chemical measurement becomes difficult.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a practical dew point corrosion monitoring probe and a dew point corrosion monitoring method capable of performing accurate electrochemical measurement while preventing crevice corrosion. And

  In order to achieve the above object, a dew point corrosion monitoring probe according to claim 1 embeds a pair of electrode members each having an electrode surface exposed to a dew point corrosion environment and the pair of electrode members adjacent to each other. A dew point corrosion monitoring probe comprising a liquid junction forming part that forms a liquid junction between the electrode surfaces in an acid dew point environment, and covering the electrode member of the holder The portion to be formed is made of a resin material having water repellency.

  In the first aspect of the invention, since the holder portion that covers the electrode member is made of a water-repellent resin material, the electrode member and the holder can be formed even when condensed water is generated on the holder surface in an acid dew point environment. Since it is difficult for dew condensation water to enter the gaps between the boundary portions, the occurrence of so-called crevice corrosion is suppressed, and the dew point corrosion tendency can be accurately measured by electrochemical measurement.

A dew point corrosion monitoring probe according to claim 2 is characterized in that, in the invention according to claim 1, the water-repellent resin material is a fluororesin.
In the invention described in claim 2, the fluororesin has heat resistance, acid resistance, and insulation, and has optimum characteristics as a material for the holder portion covering the electrode member. As the fluorine-based resin, a resin containing fluorine such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene / perfluoroalkoxy resin (PFA), or the like can be used.

The dew point corrosion monitoring probe according to claim 3 is the probe according to claim 1 or 2, wherein the electrode member is covered with the electrode member in order to improve the adhesion between the electrode member and the water repellent resin material. It is characterized in that fine irregularities are formed on the buried surface.
In invention of Claim 3, the adhesiveness between an electrode member and a water-repellent resin material is improved, and a crevice corrosion prevention effect further improves.
In order to improve the adhesion between the electrode member and the water-repellent resin material, the embedded surface of the electrode member may be coated and adhered to the embedded surface of the electrode member. The film may be coated with a liquid fluororesin material.

  The dew point corrosion monitoring probe according to claim 4 is the invention according to any one of claims 1 to 3, wherein a structure for suppressing adhesion of deposits to the electrode surface is provided. Features. You may comprise this adhesion suppression structure by providing water repellency to the surface of a holder. Moreover, you may comprise an adhesion suppression structure by forming an inclined surface in the surface of the said holder.

  A dew point corrosion monitoring method according to claim 5 is a method in which the dew point corrosion monitoring probe according to any one of claims 1 to 4 is disposed in an exhaust gas duct of a combustion facility and energized between the electrode surfaces. The dew point corrosion rate in the exhaust gas duct is measured.

  Electrochemical for measuring the dew point corrosion rate in the exhaust gas duct by disposing the dew point corrosion monitoring probe according to any one of claims 1 to 4 in an exhaust gas duct of a boiler and energizing between the electrode surfaces. The combustion equipment is configured by installing an automatic measurement device and an operation control device that controls the operation of the boiler based on the measurement result of the electrochemical measurement device and adjusts the dew point corrosion rate in the exhaust gas duct You may do it. As a result, the dew point corrosion rate in the exhaust gas duct is accurately measured while suppressing crevice corrosion by an electrochemical measurement device, and the operation of the boiler is controlled based on the measurement result, and the dew point corrosion rate in the exhaust gas duct is adjusted. Is done.

  The operation control device may have means for adjusting the temperature of the heat exchanger in the exhaust gas duct. Further, the operation control device may have means for neutralizing corrosive components in the exhaust gas in the exhaust gas duct. The probe for dew point corrosion monitoring may be attached to a heat exchanger in the exhaust gas duct. Further, the electrochemical measurement device may apply an AC voltage between the electrodes to measure the impedance between the electrodes, and analyze this to calculate the dew point corrosion rate.

  According to the first to fourth aspects of the invention, it is possible to provide a practical probe for measuring sulfuric acid dew point corrosion by preventing crevice corrosion and performing accurate electrochemical measurement.

  According to the fifth aspect of the present invention, the dew point corrosion rate in the exhaust gas duct is accurately measured while suppressing crevice corrosion, and by taking countermeasures based on this measurement result, the dew point of the component in the exhaust gas duct is determined. Corrosion can be prevented and stable and efficient operation can be performed.

  FIG. 1 shows the main part of a probe 1 for monitoring acid dew point corrosion according to a first embodiment of the present invention. Electrodes 10 and 10 comprising a pair of conductors and a disc-shaped holder 12 for supporting the electrodes 10 and 10 are shown. It consists of and. In this embodiment, the electrodes 10 and 10 are rectangular parallelepipeds having a substantially square planar shape as shown in the figure, and the holders 12 are exposed so that one surface thereof (electrode surface 11) is exposed adjacent to each other. Buried. The portion where the two electrodes 10 and 10 are opposed to each other on the holder surface 14 is a liquid junction forming portion 16 for forming a liquid junction of condensed water, and the distance w between the electrodes is set to 0.05 to 2.0 mm. Yes. Conductive wires 18 are connected to the electrodes 10 and 10 by spot welding or the like, and these conductive wires 18 are also protected by being covered with a material having the same function as the embedding material.

  In this embodiment, the holder 12 includes a covering portion 20 surrounding the electrodes 10 and 10 and a base portion 22 that supports the electrodes 10 and 10 together with the covering portion 20. The material of the covering part 20 is required to have heat resistance, acid resistance, insulation and water repellency, and the material of the base part 22 is required to have heat resistance and acid resistance. In each of these examples, a fluororesin is used. Specific characteristics required for heat resistance are that the probe 1 does not break or soften even at high temperatures, does not expand more than the electrode metal, or does not deform due to thermal contraction, impairs insulation, or does not adhere. And adhesion with the electrodes 10 and 10 is not lost. On the other hand, it is desirable that the function is not lost when the temperature is low. The fluororesin refers to a resin containing fluorine such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene / perfluoroalkoxy resin (PFA).

  When the probe 1 is manufactured, the surface on which the two electrodes 10 and 10 are embedded is provided with appropriate irregularities, and then coated with a fluorine-based resin to form the covering portion 20. It is embedded in the part 22 and manufactured. Examples of the method for imparting irregularities include processing using SiC abrasive grains, shot blasting using alumina, etching using a chemical solution, and sputtering. This makes it possible to improve the adhesion between the electrodes 10, 10 and the fluororesin constituting the covering portion 20, and to suppress crevice corrosion between the electrodes 10, 10 and the holder 12. Moreover, as a coating method, the method by electrodeposition coating, baking, etc. is suitable. In these methods, since it takes time to form the layer, it is not necessary to form the coating layer thick, and the minimum necessary thickness is sufficient.

  In the above example, the two electrodes 10 and 10 are integrated by the covering portion 20 and then embedded in the base portion 22, but as long as adhesion and dimensional accuracy can be ensured, as shown in FIG. The electrodes 10 and 10 may be individually coated and then embedded in the base portion 22 or may be directly embedded in the base portion 22 as shown in FIG. 3 or FIG. In that case, the material of the base portion 22 is also required to have insulation and water repellency. It should be noted that the electrode 10 or 10 may be preliminarily electrodeposited to avoid crevice corrosion.

  Electrodes 10 and 10 for electrochemical measurement are plates of two conductors (mainly metals) of the same material, and usually the same metal material used in an acid dew point corrosion environment is used. May be used intentionally with a higher or lower acid dew point corrosion resistance. These sizes are not particularly specified, but if the area is too small, accurate monitoring becomes difficult. Conversely, if the area is too large, corrosion will occur locally and the current density distribution will be uneven, making accurate electrochemical measurements. May be difficult. For example, when measuring AC impedance, if the electrode area is large and the current density distribution is non-uniform, the frequency dependence of the impedance becomes large, and accurate measurement cannot be performed. In addition, if the difference between the areas of the two electrodes is large, it may be difficult to accurately measure the reaction resistance, so it is desirable that the areas of the two electrodes be approximately equal.

These electrodes 10 and 10 are preferably fixed with an insulator while maintaining a distance w between the electrodes of 0.05 to 2.0 mm in order to easily form a liquid junction between the electrodes due to condensed water or the like. If the distance between the electrodes is smaller than 0.05 mm, it is difficult to maintain the distance with high accuracy and there is a risk of conduction between the electrodes.
This is because if the distance is longer than mm, a liquid junction may not be formed between the electrodes even if condensed water is generated.

  In the probe 1 configured as described above, the electrodes 10 and 10 are embedded and protected in a fluororesin having heat resistance, acid resistance, and insulation. Furthermore, since the fluorine-based resin has water repellency, it is difficult for dew condensation water to enter the gap between the electrodes 10 and 10 and the holder 12, preventing crevice corrosion and accurate electrochemical measurement. In addition, due to the action of the water-repellent surface, ash accumulation on the probe surface can be suppressed and stable measurement can be performed even when used in an environment where incineration ash is likely to accumulate, such as an economizer after the waste combustion boiler. There is also an advantage.

  In this probe 1, since a material having water repellency is used as a material for filling between the electrodes, there is a tendency that the condensed water does not easily form a liquid junction in the liquid junction forming portion 16, and therefore it has not been used in this application. . However, according to the experience of the inventors etc., it is considered that the distance between the electrodes is kept at 0.05 to 2.0 mm, so that it is sufficiently practical. In this configuration, the surface roughness may be increased by surface processing of the resin surface of the liquid junction forming portion 16 between the electrodes, that is, unevenness may be imparted.

  Next, a liquid junction formation promoting structure for facilitating the formation of a liquid junction in the liquid junction forming unit 16 will be described with reference to FIG. In FIG. 2A, the liquid junction formation promoting structure 24 </ b> A is formed by forming minute irregularities on the resin surface of the liquid junction forming portion 16, that is, the portion between the electrodes of the holder 12. That is, the surface roughness of this portion is increased. The step of increasing the surface roughness may be performed during molding or may be performed after molding. The roughness of the surface can be appropriately determined by experiments or the like. As a result, the surface area of the liquid junction forming portion 16 increases and the flow of the dew condensation water is prevented and held, so that it becomes easy to form a liquid junction. Therefore, electrochemical measurement that accurately reflects the concentration of the component to be measured in the environment to be measured can be performed, and the dew point corrosion rate can be accurately measured.

  Further, in FIG. 2B, a U-shaped liquid junction forming groove 24 </ b> B is formed on the resin surface in the portion between the electrodes of the holder 12. The liquid junction forming groove 24 </ b> B does not open on the side surface of the holder 12. This makes it easy to form a liquid junction by holding condensed water in the groove. In FIG. 2C, a V-shaped liquid junction forming groove 24 </ b> C is formed on the resin surface in the portion between the electrodes of the holder 12. The cross-sectional shape of these grooves can be appropriately adopted, but it is necessary to prevent the electrode 10 from being exposed in the grooves.

In addition, in FIG. 2D, the pole surface 11 is a V-shaped inclined surface 24D where the liquid junction forming portion 16 is low. The inclination angle theta ₁ of the inclined surface 24D is suitably determined based on experiments or the like. FIG. 2B is particularly effective when the electrode surface 11 is installed facing upward. In this way, by making the liquid junction forming part 16 partially hydrophilic or having a shape in which the liquid easily accumulates, the performance as a probe for acid dew point corrosion monitoring is improved while taking advantage of water repellency. Can do.

3 to 4 show a probe 1 according to another embodiment of the present invention, which prevents deposits from accumulating on the measurement surface of the probe 1. As described above, since the holder 12 is formed of a fluorine-based resin, accumulation of incineration ash and the like on the probe surface can be suppressed, but in order to further improve the prevention effect, in this embodiment, The portions other than the electrodes 10 and 10 on the measurement surface, that is, the surface of the holder 12 are inclined surfaces 14A and 14B. When the electrode surface 11 is installed upward, as shown in FIG. 3, the inclined surface 14A is lowered as it goes outward from the electrode surface 11, and when installed downward, as shown in FIG. The inclined surface 14B is made higher than the electrode surface 11. The inclination angles θ ₂ and θ ₃ of the inclined surfaces 14A and 14B are appropriately determined based on experiments and the like. In addition, the holder surfaces 14, 14 </ b> A, and 14 </ b> B may be as smooth as possible, and surface coating or the like may be performed as necessary.

  FIG. 5 shows a boiler control system in which the probe 1 of the present invention is installed in a boiler economizer 30. The upstream side of the economizer 30 is connected to an exhaust gas duct of the combustion furnace, and the downstream side of the economizer 30 is connected to an exhaust gas treatment device such as a dust collector. The economizer 30 includes a heat transfer pipe 34 disposed in the exhaust gas duct 32, an economizer temperature control device 36 that adjusts the temperature of the heat transfer pipe 34 by controlling water supply to the heat transfer pipe 34, and an operation system of the economizer 30 or the boiler. A system controller 38 for controlling is provided. The economizer temperature control device 36 exchanges data and instruction signals with the system control device 38.

  The probe 1 constitutes a probe device 3 together with an impedance measurement device (electrochemical measurement device) 2. The probe 1 has a communication tube 4 attached to the holder 12 and is disposed in the vicinity of the heat transfer tube 34 of the economizer 30. Conductive wires 18 from the electrodes 10 and 10 are connected to the impedance measuring device 2 through the communication tube 4, and the output thereof is further input to the system control device 38. At the time of measurement, an AC voltage is applied between the electrodes 10 and 10 by the impedance measuring device 2, the measured impedance is subjected to frequency analysis to obtain a reaction resistance and a solution resistance, and the acid dew point corrosion rate is calculated therefrom.

  A corrosion mitigation device 40 for spraying an ammonia solution and neutralizing condensed water is provided at a predetermined location of the economizer 30 or the boiler. This includes a spray header 44 having a spray nozzle 42, a pipe 46 communicating with an ammonia solution source (not shown), a pump 48 and a flow rate adjusting valve 49 provided in the pipe 46. The operation of the pump 48 and the flow rate adjusting valve 49 is controlled by an instruction from the system controller 38.

  In this example, the heat transfer tube 34 is cooled by a heat medium, but the probe 1 is not cooled. Therefore, the temperature of the probe 1 is higher and dew point corrosion is less likely to occur than the heat transfer tube 34. Therefore, by disposing the probe 1 at a low temperature location on the downstream side of the heat transfer tube 34 or by embedding it in the heat transfer tube 34 and cooling it, dew point corrosion can easily occur at the same temperature state as the heat transfer tube 34. Alternatively, when the material of the heat transfer tube 34 is stainless steel, dew point corrosion occurs more than the heat transfer tube 34 as the material of the electrodes 10, 10, such as using general carbon steel as the electrodes 10, 10 of the probe 1. You may make it employ | adopt an easy thing. Furthermore, in order to obtain more detailed information, a temperature measurement sensor may be installed in the probe 1 or in the vicinity thereof.

  FIG. 6 is a flowchart showing a control method of the boiler control system of this embodiment. In this example, the upper limit value of the dew point corrosion rate is set to avoid an excessive dew point corrosion rate, and the lower limit value of the dew point corrosion rate is also set so that the corrosion mitigation device 40 does not operate excessively. First, in step 1, the initial value of the spray amount of the ammonia solution is set according to past data, the type of the combusted material, and the like. In step 2, an alternating voltage is applied between the electrodes 10 and 10 to measure the impedance between the electrodes, and this is analyzed to calculate the dew point corrosion rate. This dew point corrosion rate is monitored at a preset time pitch. In step 3, it is determined whether or not the dew point corrosion rate is equal to or lower than the allowable upper limit value. If NO, the corrosion rate is excessive. Therefore, in step 4, the spray amount of the ammonia solution by a predetermined pitch amount determined in advance. Increase. And it drive | operates in the state until predetermined time passes in step 7. FIG.

  In step 3, if the dew point corrosion rate is equal to or lower than the allowable upper limit value, it is further determined in step 5 whether or not it is equal to or lower than the allowable lower limit value. . In the case of YES, the corrosion mitigation device 40 seems to be operating excessively, so in step 6, the spray amount of the ammonia solution is reduced by a predetermined pitch amount determined in advance. And in step 7, it drive | operates in the state until predetermined time passes, and after progress of predetermined time, the process of step 2-step 7 is repeated. By performing such a control process, it is possible to reduce the cost by reducing the amount of sprayed ammonia solution as much as possible while maintaining the corrosion rate of the heat transfer tube 34 within an allowable range.

  In addition, dew point corrosion can be avoided by the same control when using a compound that forms a stable sulfide such as slaked lime or alkali metal salt instead of ammonia. Such a corrosion mitigating device 40 can also be used under conditions where condensation is unavoidable when the device is started and stopped. For example, in a fluidized bed furnace, slaked lime is sprayed into the fluidized bed when starting up to perform desulfurization in the bed, dew point corrosion is controlled by temperature control after steady operation, and control by desulfurization in the bed is performed again when stopped. To do.

  FIG. 7 shows a probe apparatus 3A having a probe 1A according to another embodiment of the present invention, which is provided with a mechanism for independently controlling the temperature. That is, in addition to the pair of electrodes 10 and 10 for measuring the dew point corrosion tendency, a temperature measuring electrode 50 such as a thermocouple is embedded in the holder 12A. These electrodes 10, 10, 50 are all provided so as to protrude to the back side of the holder 12 </ b> A. The portions of the electrodes 10 and 10 for dew point corrosion measurement and the configuration of the holder 12A are the same as those of the above-described embodiment, and the temperature measurement electrode 50 is well known, so the description thereof is omitted. . The back surface side of the holder 12A is covered with a cover 54 that forms a sealed heat medium space 52, and a connecting pipe 4A for circulating a heat medium such as air or water to the heat medium space 52 is attached thereto. Yes. As shown in FIG. 8, a cooling gas supply pipe 62 connected to a cooling gas source 56 such as a compressor or a gas cylinder through a valve 58 or a flow meter 60 is inserted into the communication pipe 4A. Conductive wires 18 from 10, 10, 50 are also led out through this and connected to the impedance measuring device 2.

  FIG. 8 shows an economizer 30 having a boiler control system using the probe 1A shown in FIG. 7. Unlike the control system shown in FIG. 5, an electrode temperature control device 64 that controls the temperature of the electrodes 10 and 10 of the probe 1A. Is provided. The electrode temperature control device 64 outputs a signal for adjusting the opening degree of the flow rate adjustment valve 58 based on the measurement signal from the temperature measurement electrode 50. In this embodiment, the corrosive environment of the heat transfer tube 34 is judged more directly and accurate control is performed, and the materials of the electrodes 10 and 10 have the same corrosion behavior characteristics as the heat transfer tube 34. Is preferred.

  In this boiler control system, by obtaining the relationship between the temperature in the exhaust gas duct 32 and the corrosion rate, the dew point of the exhaust gas in the exhaust gas duct 32 is judged in real time, and the temperature of the heat transfer tube 34 is determined from this measured dew point. Control to maintain slightly above. This process will be described with reference to the flowchart of FIG. First. In step 1, the temperature-corrosion rate relationship in the exhaust gas duct 32 of the economizer 30 is measured. This is done as follows.

  First, an instruction signal for adjusting the temperature of the electrodes 10 and 10 to a predetermined measurement start temperature is issued from the system controller 38 to the electrode temperature controller 64. The electrode temperature controller 64 adjusts the cooling gas flow rate, for example. Adjust to that temperature. When it is confirmed that the temperature has reached the target temperature, the impedance measuring device 2 applies an AC voltage between the electrodes 10 and 10 and measures the impedance between the electrodes. Further, the measured value is subjected to frequency analysis, and the reaction resistance and the solution resistance are obtained separately. Based on this, the acid dew point corrosion rate is calculated. Next, an instruction signal for changing the temperature of the electrodes 10 and 10 at a predetermined pitch is issued from the system controller 38 to the electrode temperature controller 64, and the electrode temperature controller 64 similarly adjusts the temperature of the electrodes 10 and 10. Then, the acid dew point corrosion rate is measured by the impedance measuring device 2 at that temperature. In this way, measurement in a predetermined temperature range is repeated, and for example, the relationship between temperature and corrosion rate as shown in FIG. 10 is obtained (step 2).

FIG. 10 shows the results of measuring the corrosion rate in a gas environment containing water vapor: 30%, SOx: 300 ppm, HCl: 3000 ppm. The temperature was varied between 150 ° C. and 230 ° C. at 10 ° C. intervals. At each temperature, an alternating current of 10 mV amplitude was applied between the electrodes 10 and 10, and the impedance was measured at two points of a high frequency of 10 kHz and a low frequency of 10 mHz. The resistance Rs of the solution formed at the dew point is measured from the high frequency impedance, and the value corresponding to the polarization resistance of the corrosion reaction is obtained by subtracting the value of the high frequency impedance from the low frequency impedance. FIG. 10 shows the obtained relative corrosion rate (reciprocal of polarization resistance 1 / R _p ) and solution conductivity (reciprocal of solution resistance 1 / Rs) with respect to temperature.

Next, in step 3, the system controller 38 estimates the dew point from the relationship between the obtained temperature and the corrosion rate, and further determines the temperature of the heat transfer tube 34, that is, the operation target temperature of the apparatus. For example, in the example of FIG. 10, the acid dew point of this system is between 180 ° C. and 190 ° C., and it can be seen that acid dew point corrosion occurs when set to 180 ° C. or lower. The target operating temperature is determined in consideration of various factors such as heat recovery efficiency in addition to the corrosion rate. For example, if the value of (1 / Rr), which is considered to have a correlation with the corrosion rate, is 10 ⁻³ or more and there is no practical problem, 190 to 195 ° C. can be set as the operation target temperature, If strictly controlled, the target operating temperature is 200 ° C or higher.

  Next, in step 4, the economizer 30 is controlled so that the temperature of the heat transfer tube 34 becomes the operation target temperature determined in step 3. As this control method, either a method of adjusting the amount of heat generated in the boiler or a method of adjusting the amount of cooling water flowing through the heat transfer pipe 34 of the economizer 30 may be adopted.

  Next, in step 5, the temperature of the probe 1A is adjusted to the same temperature as the apparatus operating temperature, and in step 6, the dew point corrosion rate is monitored. Here, since the probe 1A is under the same conditions (gas component, temperature, material) as the heat transfer tube 34, more accurate measurement data can be obtained. Next, in step 7, the system controller 38 determines whether or not the measured / calculated corrosion rate is within an allowable range.

  If it is not within the allowable range, the operation target temperature of the apparatus is increased by a predetermined pitch in step 9 until the same loop is repeated a predetermined number of times N. Then, the process returns to step 4 to operate the apparatus at the new operation target temperature, and the corrosion rate is measured in steps 5 and 6. After repeating Step 4 → Step 5 → Step 6 → Step 7 → Step 8 → Step 9 N times, the process returns from Step 8 to Step 1 to re-examine the relationship between temperature and corrosion rate, and newly set the operation target of the apparatus. Determine the temperature and control.

  In step 7, if the corrosion rate is within the allowable range, the process returns to step 6 and measures the corrosion rate after a predetermined time has elapsed (step 10) until the same loop is repeated a predetermined number of times N '. After step 6 → step 7 → step 9 → step 10 → step 6 is repeated N ′ times, the process returns from step 9 to step 1 to re-examine the temperature-corrosion rate relationship and newly set the operation target temperature of the apparatus. Decide and control.

  As described above, in the boiler control system, in the temperature control of the economizer 30, the temperature of the probe 1A is independently changed to measure the dew point temperature of the exhaust gas, and the operating temperature of the apparatus is determined based on the measured dew point temperature. Yes. Therefore, it is possible to grasp the operating temperature that directly corresponds to the tendency of dew point corrosion, in which various factors act in a complicated manner, and to operate the equipment, and to protect the equipment from corrosion and perform sufficient heat recovery to improve energy efficiency. Can be improved.

  Moreover, in the boiler control system of this embodiment, the process of calculating the dew point temperature (step 1 to step 3) and the process of measuring and feeding back the corrosion rate at the operating temperature for fine adjustment (after step 5). Therefore, it is possible to cope with both a long-cycle cycle change and a short-cycle cycle change, thereby enabling safer and more efficient device operation. Of course, even if these are carried out independently, it is possible to perform control utilizing the respective features.

  Of these, the process of measuring the dew point temperature (Step 1 to Step 3) changes the temperature of the probe 1A, and therefore requires a certain amount of time, and during that time, measurement at the operating temperature of the apparatus is not possible. Therefore, two probes 1A are provided in parallel, and the temperature is individually controlled, so that the measurement is performed in parallel, and the operating temperature may be controlled by combining the control by the dew point temperature calculation step and the feedback adjustment step. . Further, the probe 1 </ b> A that performs measurement at the operating temperature of the apparatus may be embedded in the heat transfer tube 34. Moreover, you may use together the corrosion mitigation apparatus 40 which was demonstrated in FIG.

  FIG. 11 illustrates another use of this control system. The corrosion rate is monitored, and the life of the apparatus is obtained based on this data. In this embodiment, if the corrosion rate data when the temperature of the probe 1A is the same as the apparatus temperature is accumulated and integrated with time as shown in FIG. 11A, the estimated corrosion amount with high accuracy is obtained. Is calculated.

Data collection and accumulation are not necessarily continuous. As shown in FIG. 11B, when the corrosive environment such as the economizer 30 periodically changes depending on the operation cycle or the like, the estimated amount of corrosion (ΔW) during a certain fixed period (Δt). ) Can be calculated as an integral value of the corrosion rate curve. Here, when the allowable corrosion amount is Wa, the device life LT can be obtained by the equation (1).
LT = Wa × Δt / ΔW (1)

  When the predicted device life is shorter than the required life, it is possible to extend the device life by taking appropriate anticorrosion measures. For example, if the time zone during which the corrosion rate is high corresponds to the time zone during which the device is stopped, the corrosion rate may be reduced by heating the device to prevent condensation even when the device is stopped. Good. In addition, when the operation of the apparatus is stopped, an appropriate anticorrosion measure such as sufficiently purging the corrosive gas becomes possible.

It is (a) top view and (b) sectional view showing a probe for dew point corrosion monitoring of an embodiment of this invention. (A) thru | or (d) is sectional drawing which shows the probe for dew point corrosion monitoring of other embodiment of this invention, respectively. It is (a) top view and (b) sectional view showing a dew point corrosion monitoring probe of further another embodiment of this invention. It is (a) top view and (b) sectional view showing a dew point corrosion monitoring probe of further another embodiment of this invention. It is a figure which shows the structure of the control system of the boiler using the probe for dew point corrosion monitoring of this invention. It is a flowchart which shows the control process of the control system of the boiler of FIG. It is (a) top view which shows the probe for dew point corrosion monitoring of other embodiment of this invention, (b) It is sectional drawing. It is a figure which shows the structure of the control system of the boiler using the probe for dew point corrosion monitoring of FIG. It is a flowchart which shows the control process of the control system of the boiler of FIG. It is a figure which shows the example of the measurement result using the probe for dew point corrosion monitoring of FIG. It is a graph which shows the example of how to use the control system of the boiler of FIG.

Explanation of symbols

1,1A Probe 2 Impedance measuring device (electrochemical measuring device)
10 Electrode (electrode member)
DESCRIPTION OF SYMBOLS 11 Electrode surface 12,12A Holder 14A, 14B Inclined surface 16 Liquid junction formation part 20 Covering part 22 Base part 24A Liquid junction formation groove 24B Inclined surface 30 Economizer 32 Exhaust gas duct 34 Heat exchanger tube 36 Economizer temperature control device 38 System control device 40 Corrosion mitigation device 50 Temperature measurement electrode 56 Cooling gas source 58 Flow rate adjustment valve 64 Electrode temperature control device

Claims (5)

A pair of electrode members each having an electrode surface exposed to a dew point corrosive environment;
A holder for embedding and holding the pair of electrode members adjacent to each other,
A dew point corrosion monitoring probe comprising a liquid junction forming part that forms a liquid junction of condensed water between the electrode surfaces in an acid dew point environment,
A dew point corrosion monitoring probe, wherein a portion of the holder covering the electrode member is made of a resin material having water repellency.   2. The dew point corrosion monitoring probe according to claim 1, wherein the water repellent resin material is a fluororesin.   The fine unevenness | corrugation is formed in the to-be-embedded surface of the said electrode member in order to improve the adhesiveness between the said electrode member and the said water-repellent resin material, The Claim 1 or Claim 2 characterized by the above-mentioned. Dew point corrosion monitoring probe.   The dew point corrosion monitoring probe according to any one of claims 1 to 3, further comprising a structure for suppressing adhesion of deposits on the electrode surface. The dew point corrosion monitoring probe according to any one of claims 1 to 4 is disposed in an exhaust gas duct of a combustion facility, and the dew point corrosion rate in the exhaust gas duct is measured by energizing between the electrode surfaces. A dew point corrosion monitoring method characterized by

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