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    公开号:BE1019741A5
    申请号:E2010/0333
    申请日:2010-06-01
    公开日:2012-12-04
    发明作者:
    申请人:Electric Power Res Inst；
    IPC主号:
    专利说明:

    APPLICATION OF DISPERSIFIER FOR CLEANING RECYCLING ROADS OF AN ENERGY-GENERATING DEVICE DURING START-UP
    BACKGROUND OF THE INVENTION
    The present invention generally relates to a method for cleaning recirculation paths and more particularly to a method for cleaning recirculation paths for an energy-generating facility, whereby the supply of corrosion products is reduced, which can later lead to the fouling of the steam generator.
    Pollution of the steam generator (SG) due to the accumulation of corrosion products from the secondary system remains a major problem in the nuclear industry. Such fouling causes heat transfer losses, corrosion deterioration of pipes and internal components, level instabilities, and plant output reductions. Many features report that a significant fraction of the corrosion product transport to the steam generator takes place during start-up and use significant tools to reduce contamination caused by corrosion products.
    Today, many energy-generating installations use methods such as 'top-of-tube-sheet sludge lancing' (removal of slurry on tube casings with a (water jlans), dry-cleaning, soaking of advanced deposits with conditioning agent, treatment for minimizing deposition, applying a (water) ) lance between pipes, hydraulic cleaning of the upper bundle and bundle rinses to remove existing deposition material In addition, many nuclear installations perform a recirculation cleaning of the supply water system during initial start-up of the installation via a path that goes around the steam generators. cleaning method is the removal of existing corrosion products from the systems, which could otherwise be transported later to the steam generators.
    Unfortunately, the prior art only addresses treatment of the feed water that goes into the secondary side of the nuclear steam generator during operation. During operation, the accumulation of metal oxide deposits in a recirculating nuclear steam generator can be removed via pipe fracture. In a single-pass nuclear steam generator (OTSG), accumulation of metal oxide corrosion product cannot be avoided since only a small percentage of the corrosion products are transported with steam from the OTSG. Thus, the prior art is limited to recirculating steam generators. It is well known to those skilled in the art that sulfur species can accelerate deterioration of a PWR steam generator. Therefore, the prior art is limited to dispersants containing low concentrations of sulfur. Moreover, the prior art does not address contamination or corrosion product transport to a reactor of a BWR facility.
    SHORT SUMMARY OF THE INVENTION
    These and other shortcomings of the prior art are addressed by the present invention, which provides for additional corrosion products present in the recirculation paths, such as supply water and condensation systems, to be removed prior to start-up by adding dispersant during recirculation periods. This would promote the retention of iron oxides in suspension until they can be eliminated via drainpipes, condensate polishers, filter elements, etc. and would reduce the supply of corrosion products available for transport during operation.
    Furthermore, dispersants would require a significant reduction in the time required for cleaning the secondary system prior to power generation, a reduction in the stock deposits in the secondary cycle (which could otherwise be transported during buoyancy) and / or a significant reduction in provide the mass of corrosion products transported during operation early in the operating cycle (typically start-up pulses).
    According to an aspect of the present invention, a method for reducing corrosion product transport in an energy generating facility comprises the steps of selecting a chemical dispersant adapted to reduce the deposition of corrosion products in the recycle path; and using at least one chemical injector to inject the chemical dispersant into a fluid present in the recirculation path during cleaning of the recirculation path to increase corrosion product removal, wherein the chemical dispersant is a polymeric dispersant and wherein the polymeric dispersant is selected from the group consisting of PAA, PMAA, PMA: AA and PAAM.
    According to another aspect of the present invention, a method for re-entraining certain deposits in a recirculation path comprises the steps of selecting a chemical dispersant adapted to suspend corrosion products in the recirculation path; using at least one chemical injector to inject a predetermined amount of the chemical dispersant into a fluid present in the recirculation path; and circulating the chemical dispersant in the recirculation path for a predetermined amount of time to cause the chemical dispersant to mix with the fluid and suspend the corrosion products.
    BRIEF DESCRIPTION OF THE DRAWINGS
    The subject matter considered as the invention can best be understood with reference to the following description, taken in conjunction with the accompanying drawings, in which the figures represent the following:
    Figure 1 is a diagram of dispersant use during long-term recirculation;
    Figure 2 is a graph showing magnetite concentration versus% transmittance;
    Figure 3 is a graph showing hematite concentration versus% transmittance;
    Figure 4 shows magnetite settling behavior with 100 ppm PAA (2kD);
    Figure 5 shows sedimentation behavior of magnetite with 10,000 ppm PAA (2kD);
    Figure 6 shows sedimentation behavior of hematite with 10,000 ppm PAA (2kD);
    Figure 7 shows magnetite settling behavior with 100 ppm PAA (5kD);
    Figure 8 shows sedimentation behavior of magnetite with 10,000 ppm PAA (5kD);
    Figure 9 shows hematite settling behavior with 10,000 ppm PAA (5kD);
    Figure 10 shows sedimentation behavior of magnetite with 100 ppm PAA (high molecular weight);
    Figure 11 shows sedimentation behavior of magnetite with 10,000 ppm PAA (high molecular weight);
    Figure 12 shows hematite settling behavior with 10,000 ppm PAA (high molecular weight);
    Figure 13 shows sedimentation behavior of magnetite with 100 ppm PMAA;
    Figure 14 shows sedimentation behavior of magnetite with 10,000 ppm PMAA; Figure 15 shows sedimentation behavior of hematite with 10,000 ppm PAA;
    Figure 16 shows sedimentation behavior of magnetite with 100 ppm PMA: AA Figure 17 shows sedimentation behavior of magnetite with 10,000 ppm PMA: AA; Figure 18 shows hematite settling behavior with 100 ppm PMA: AA; Figure 19 shows sedimentation behavior of magnetite with 100 ppm PAAM;
    Figure 20 shows sedimentation behavior of magnetite with 10,000 ppm PAAM; Figure 21 shows hematite settling behavior with 10,000 ppm PAAM; Figure 22 shows sedimentation behavior of magnetite with 100 ppm PAA: SA; Figure 23 shows magnetite settling behavior with 10,000 ppm PAA: SA; Figure 24 shows hematite settling behavior with 10,000 ppm PAA: SA; Figure 25 shows sedimentation behavior of magnetite with 100 ppm PAA: SS: SA; Figure 26 shows sedimentation behavior of magnetite with 10,000 ppm PAA: SS: SA;
    Figure 27 shows hematite settling behavior with 10,000 ppm PAA: SS: SA; Figure 28 shows magnetite settling behavior with 100 ppm PAA: AMPS; Figure 29 shows magnetite settling behavior with 10,000 ppm PAA: AMPS;
    Figure 30 shows hematite settling behavior with 10,000 ppm PAA: AMPS; Figure 31 shows magnetite settling behavior with 100 ppm PAMPS;
    Figure 32 shows sedimentation behavior of magnetite with 10,000 ppm PAMPS; Figure 33 shows sedimentation behavior of hematite with 10,000 ppm PAMPS Figure 34 shows sedimentation behavior of magnetite with 100 ppm PMA: SS; Figure 35 shows sedimentation behavior of magnetite with 10,000 ppm PMA: SS; Figure 36 shows hematite settling behavior with 10,000 ppm PMA: SS; Figure 37 shows the effects of dispersant candidates (10,000 ppm) on 10,000 ppm Fe 3 O 4 (magnetite) solution;
    Figure 38 shows dispersant candidate (10,000 ppm) fitness tests - extended duration;
    Figure 39 shows the effects of dispersant candidates (100 ppm) on 10,000 ppm Fe 3 C> 4 (magnetite) solution;
    Figure 40 shows dispersant candidate (100 ppm) - fitness tests - extended duration;
    Figure 41 shows the effects of dispersant candidates (10,000 ppm) on 10,000 ppm Fe 3 O 4 (hematite) solution;
    Figure 42 shows dispersant candidate (10,000 ppm) fitness tests - extended duration;
    DETAILED DESCRIPTION OF THE INVENTION
    Although the invention is discussed in connection with long-distance PWRs and recirculation, it should be taken into consideration that the invention is not limited to long-way recirculation and PWRs and other energy-generating facilities (such as a BWR) and with other recirculation paths ( ie short circulation path, steam and drainage systems) can be used. PWRs and long-term recirculation are used in this discussion for clarity and as examples only.
    Use of dispersant in nuclear power plants is nowadays merely an on-line addition, during operation, to the feed water which enters the secondary side of a nuclear steam generator for the purpose of minimizing the accumulation of metal oxide deposits in the nuclear steam generator, via pipe breakage removal, considered during continuous operation of the steam generator.
    In energy-generating facilities, long-term recirculation is used to remove corrosion products (mainly iron oxides and or oxyhydroxides) from the supply water and condensate systems prior to power generation. This reduces the mass of corrosion products transported to the steam generator, where corrosion products can settle, thereby aggravating tube corrosion and reducing thermal efficiency. Long and short recirculation loops for an energy-generating facility are generally shown in Figure 1 with reference numerals 10 and 11.
    With regard to long-way recirculation, the invention uses a method for injecting a dispersant in the long-way recirculation cleaning process, as proposed for a secondary train supply system from an installation outside the nuclear steam generator, wherein the water to be treated containing the dispersant will have no contact or limited contact (valve leakage) with the nuclear steam generator. The invention further comprises cleaning a secondary system from an installation outside the nuclear steam generator and thus removing metal oxides from the system before they can even enter the steam generator. In addition, the invention is applicable to plants with recirculating steam generators, plants with one-pass steam generators (i.e., independent of steam generator type), and BWRs with reactors.
    As described herein, the use of dispersants during long-term recirculation increases the effectiveness of corrosion product removal, thereby reducing either the mass that is ultimately transported to the steam generator or the time required for recirculation cleaning prior to power generation. reduced. Dispersant injection sites are generally shown in Figure 1 with reference numerals 12-14. Places of injection will be based on unit-specific designs; thus, a plant-specific assessment should be performed prior to injection of a dispersant.
    As shown, multiple sites can be used for injection. For example, one location may be just downstream of the purification equipment, so that the entire system is exposed to the chemical. However, alternative sites can be used to achieve significant cleaning benefits.
    In general, the inventive method comprises the injection of a chemical using chemical injectors 16-18 (such as dosing pumps), specifically a polymeric dispersant, such as, but not limited to, polyacrylic acid (PAA), in the feed water / condensate system during cleaning of the recirculation path. The injectors 16-18 can be existing injectors or new injectors installed for injection of the dispersant. The method comprises the injection of the chemical (which can take place on a once-occurring or continuous basis); recirculation of the system (which can be started prior to injection); and cleaning the system (using existing equipment).
    The choice of a specific chemical is a non-trivial matter, including evaluation of effectiveness and system compatibility. The speed and choice of the correct time of chemical injection can be adjusted to the individual unit, taking into account various factors such as the estimated charge of corrosion product, existing supply water / condensate system configuration and failure / start-up schedule.
    The dispersant works by effectively increasing the diameter of the corrosion product particles (i.e., reducing an effective density), thereby reducing the tendency of these particles to settle and facilitating entrainment of deposited material. These effects combine to increase the fraction of corrosion product that circulates with the water in the system, relative to the fraction retained on surfaces. The circulating corrosion product particles can be easily removed from the system by existing equipment (e.g. ion exchange resin beds for ion exchange, filters, etc.) or by system dumps. Because the chemical increases the suspension-retained fraction, its use increases the fraction that can be removed during cleaning, resulting in either removal of a larger mass, faster removal of the same mass, or both. In some cases, cleaning times are related to fault schedules. Specifically, the window during which recirculation can take place is fixed. For other units, cleaning is continued until a predetermined criterion (iron concentration, filter color, etc.) is reached. Addition of chemicals to obtain concentrations of suspended corrosion products would be beneficial in both of the aforementioned cases.
    Dispersant effectiveness is partially defined by the ability of the polymer to reduce particle settling rate. Rate of settling of particles was determined from the spectrophotometry data obtained from tests in which the transmittance of the solution was measured at different time intervals. The rate of settling of a particle in a given fluid (fluid) is a function of its density and diameter, as well as the density and viscosity of the fluid. Two Experiments without dispersant were therefore conducted to characterize the settling behavior of magnetite and hematite particles and to develop a conversion between the stated transmittance and the concentration of the deposition material in solution. This was done by measuring the percentage of light transmitted through the solution at different time intervals and correlating these measurements with the theoretically calculated concentration of deposition material after the same time period.
    The concentration of deposition material in solution at each time period is determined as follows. The suspended particles (magnetite or hematite) can be given the approximate shape of spherical particles that settle in a low turbulence environment (low Reynolds number). Under these conditions, the settling rate is described according to the Stokes formula: gP2px (pp-Pf) = vt 18μ where Dp is the particle diameter; pp and pf are the densities of the particle and fluid, respectively; μ is the viscosity of the liquid; g is the gravitational constant; and vt is the settlement rate.
    A particle size distribution was predetermined (according to laser analysis of particle size) for magnetite and hematite deposition materials. Particle size measurements were made before and after a short period of ultrasonic wave treatment to ensure that the measurement was not affected by agglomerates. From the geometry of the spectrophotometer chamber, the settling rate of the largest particle that remains in solution can be determined for each time interval.
    The measurement of transmittance at each time point was plotted against the concentration of the appropriate control determined from the size distribution data and model of Stokes for Reynolds low number particle deposition. A relationship between transmittance and concentration was then found by adjusting the resulting curve to a tanh function. The point of zero transmittance predicted by this model was ~ 6500 ppm. This range corresponds to transmittances between 67% and 90.7% (the deionized water transmittance) for magnetite, and 78% and 90.7% for hematite. In both areas the curve can be described by a second order polynomial. The graphs of the relationships between transmittance and concentration for magnetite and hematite are shown in Figures 2 and 3, respectively.
    The purpose of adding dispersant is to reduce the settling rate, resulting in an apparent change in particle diameter and density. Effective particle size S is used to describe this apparent particle diameter and density and is defined as:
    S - D p, e (P p, e "P f) ~ 18VtU
    g where the subscript e indicates the "effective" or apparent value. A parameter describing the difference in apparent and actual particle sizes that is proportional to the settling rate can then be generated for each time point by comparing the "effective" particle size with the particle size corresponding to the observed concentration, according to the following equation :
    % Change = C - S C
    where C is the calculated particle size based on the observed transmittance in the absence of dispersant i, and Pp and Pf are the known densities of the deposition material and deionized water. The parameter C is given by the following equation: C - D p, calculated (p p, magnetite - Pf)
    The "% change" therefore refers to the percentage reduction in settling rate observed in the presence of a dispersant. The settling speed was used to resolve for "S". "C" was then determined using the settling rate of the control experiment in the current transmittance reading. The values for C and S were then used to determine the relative change in settling rate (% change).
    A number of general observations made during testing include: • At 100 ppm of dispersant (a ratio of dispersant: magnetite of 1: 100), the effectiveness of polymeric dispersants in dispersing magnetite typically increases with increasing particle size.
    • At 10,000 ppm dispersant, the settling rate of larger magnetite particles was increased by high molecular weight dispersants. High molecular weight dispersants can promote particle agglomeration at these concentrations.
    • For low molecular weight dispersants, the dispersant had the same order of effectiveness at both concentrations / dispersant-iron ratios.
    • All candidate dispersants except PAAM promoted the retention of hematite in the solution.
    • Sulfur-containing dispersants did not perform significantly better than the strict acrylic acid / methacrylic acid / maleic acid copolymers. Thus, sulfur-containing dispersants should be used in a limited manner because of concerns about compatibility of materials. This would eliminate much of the danger associated with potential dispersant access to the steam generator during this application (via leaking isolation valves, human error, etc.).
    Exemplary dispersants for use in recirculation pathways and the changes in the effective particle diameter (and therefore settling rate) in the presence of a polymeric dispersant are summarized in Table 1.
    Table 1
    The polyacrylic acid (PAA) effectively reduced the settling rate of magnetite particles with a size of -1-10 μπι by -20-50%. This polymer was also the most effective in dispersing hematite, which forms a major part of supply water system deposits.
    Three PAA candidates were evaluated. All three PAA candidates that were evaluated showed similar degrees of effectiveness in dispersing both magnetite and hematite. In particular, a low molecular weight polymer (2,000 Dalton), a low-moderate molecular weight (5,000 Dalton) and a high molecular weight polymer were evaluated.
    The low molecular weight polymer performed moderately well in dispersing both large and small particles. The dispersant was more effective at dispersing magnetite at the lower (1: 100) dispersant: iron ratio. The following results were specifically obtained: • At 100 ppm of dispersant: The settling time was increased by -40% for large particles and -17% for smaller particles. The results of this test are shown in Figure 4.
    • At 10,000 ppm dispersant: The settling time increased by -18%, with the exception of two isolated points with large particle sizes. The results of this test are shown in Figure 5.
    • Hematite dispersion: The dispersant increased hematite settling time by -50% over a wide range of particle sizes. The results of this test are shown in Figure 6.
    The low-molecular-weight polymer resulted in small improvements in an intermediate particle size range, but showed abnormal increases in settling rate at the extreme values. In total, this polymer appears to be less effective than the low molecular weight polymer. The following observations were made with these tests: • At 100 ppm: The dispersant increased sedimentation time by -10-20% for some particle sizes, but showed significant reductions in performance at other points. The results of this test are shown in Figure 7.
    • At 10,000 ppm: The dispersant increased sedimentation time by up to 50% for small particles, but had little effect on intermediate particle sizes. The settling time of the largest particles was greatly reduced. The results of this test are shown in Figure 8.
    • Hematite dispersion: The low-moderate molecular weight polymer increased the settling time of hematite by 50-70%. The results of this test are shown in Figure 9.
    The high molecular weight polymer performed well at a low concentration (100 ppm), but was less effective at 10,000 ppm.
    • At 100 ppm: The settling time increased by 18% to 50% with increasing particle size. The results of this test are plotted in Figure 10.
    • At 10,000 ppm: The settling time increased slightly (to around 20%) for smaller particles. But for larger particles, the settling time decreased by around 20%. The results of this test are plotted in Figure 11.
    • Hematite dispersion: The dispersant constantly increased the settling time over the tested particle distribution by approximately 100%. The results of this test are plotted in Figure 12.
    The generic polymethacrylic acid (PMAA) polymer also showed high efficiency at a concentration of 100 ppm. Unlike many of the dispersant candidates, it did not increase the rate of settlement and did not promote agglomeration; PMAA was equally effective at a high concentration (10,000 ppm). The polymer was moderately effective in dispersing hematite, with the settling rate falling by -60%.
    PMAA has been tested for boiler applications with moderate levels of efficiency. The PMAA used during this test program had a molecular weight of -6500 Dalton. The following observations were made.
    • At 100 ppm: The settling time increased by 19 to 50% with increasing particle size. The results of this test are plotted in Figure 13.
    • At 10,000 ppm: the settling time increased by 22 to 56%. A weak correlation was observed between the improvement of settling speed and the particle size. The results of this test are shown in Figure 14.
    • Hematite dispersion: although few data points were available, the settling time increased by -60% for all particle sizes. The results of this test are shown in Figure 15.
    Other polymers were also evaluated. Poly (acrylic acid: maleic acid) (PMA: AA) had a molecular weight of -3000 Dalton and had the following characteristics: • At 100 ppm: The presence of the dispersant increased the settling time by -30% for moderate to large particle sizes, but decreased the settling time of particles of -1 pm with almost 17%. The results of this test are shown in Figure 16.
    • At 10,000 ppm: The settling time was increased by -20% with the exception of the smallest particles (-1 pm), which showed a longer settling time. The results of this test are shown in Figure 17.
    • Hematite dispersion: A ~ 70% increase in settling time was observed at all data points. The results of this test are shown in Figure 18.
    The poly (acrylic acid: acrylamide) (PAAM) copolymer had an average molecular weight of ~ 200,000 Daltons, making it significantly larger than most of the candidates. PAAM was the only dispersant tested that did not effectively disperse in hematite.
    • At 100 ppm: The dispersant increased the settling time of small particles (diameter <2.5 µm) by 25-50%, but significantly reduced the settling time of particles with a diameter greater than 10 µm. The results of this test are shown in Figures 19.
    • At 10,000 ppm: Large increases in sedimentation rate were observed with particles with diameters> 4.5 µm. Little change in settling rate was observed for smaller particles. The results of this test are shown in Figure 20.
    • Hematite dispersion: No significant change in sedimentation behavior was observed in the presence of 10,000 ppm PAAM. The results of this test are shown in Figure 21.
    The poly (sulfonic acid acrylic acid) (PAA: SA) copolymer had a molecular weight of <15,000 Daltons. The following observations were made.
    • At 100 ppm: A 20-50% improvement in settling time was observed. The increase in settling rate was greater for larger particles (~ 12 µm) and smaller for smaller particles (2-3 µm). The results of this test are shown in Figure 22.
    0 At 10,000 ppm: A small increase in settling rate (<20%) was observed for most particle sizes. The settling time decreased for larger (~ 12 µm) particles. The results of this test are shown in Figure 23.
    ° Hematite dispersion: A 30-60% increase in settling time was observed. The results of this test are shown in Figure 24.
    The poly (acrylic acid: sulfonic acid: sulfonated styrene) (PAA: SS: SA) polymer had the following characteristics.
    0 At 100 ppm: The settling time of magnetite increased by -40% for particles with diameters> 5 µm. A smaller increase in settling time was observed for smaller particles. The results of this test are shown in Figure 25.
    ° At 10,000 ppm: The settling time increased by -40% for particles with a diameter of 3-5 µm. Below 3 µm, the change in settling time decreased with decreasing particle size. The results of this test are shown in Figure 26.
    ° Hematite dispersion: an improvement of 40-80% of settling time was observed. The results of this test are shown in Figure 27.
    The poly (acrylic acid: 2-acrylamide-2-methylpropane sulfonic acid) (PAA: AMPS) copolymer had an average molecular weight of 5,000 Daltons and resulted in the following observations.
    ° At 100 ppm: The settling time increased by 18-42%, with a greater improvement in the dispersion of larger particles. The results of this test are shown in Figure 28.
    • At 10,000 ppm: The settling time increased by -30%, although less improvement was observed at the extreme values of the particle sizes investigated. The results of this test are shown in Figure 29.
    • Hematite distribution: The settling time generally increased by -40-60%. A greater (80%) improvement in settling time was observed with small particle sizes (-2 µm). The results of this test are shown in Figure 30.
    The poly (acrylamide-2-methylpropane sulfonic acid) (PAMPS) was the largest polymer tested, with an average molecular weight of 800,000 Daltons.
    • At 100 ppm: Little or no improvement in the settling rate was observed. The results of this test are shown in Figure 31.
    At 10,000 ppm: The settling rate increased with increasing particle size. At particle diameters above - 3.5 µm, the settling rate was greatly increased. The results of this test are shown in Figures 32.
    • Hematite dispersion: With the exception of the abnormalities observed at -8 pm, the settling time increased by 70 to 90%. The results of this test are shown in Figures 33.
    The poly (sulfonated styrene: maleic anhydride) (PMA: SS) copolymer had a molecular weight of -20,000 daltons.
    • At 100 ppm: The settling time of particles> -8 µm increased by -40%. Smaller particles needed -20% more time to settle. The results of this test are shown in Figure 34.
    • At 10,000 ppm: Improvements in settling time similar to those seen at 100 ppm were observed, the improvement decreasing with decreasing particle size. The results of this test are shown in Figure 35.
    • Hematite dispersion: The settling time increased by -30-68%. The results of this test are shown in Figures 36.
    Recirculation procedures at three typical energy-generating facilities were evaluated to provide a baseline for evaluating the use of dispersant during long-term recirculation cleaning. The following parameters were typical of the long-way recirculation for the three energy-generating facilities.
    • Flow rates for a long-way cleaning process of recirculation range from 2000-4000 gpm. This indicates that cycle times for use in cleaning long-cycle recirculation (ie, the time required for all fluid to pass through the long-path loop once) are in the order of -1-2 hours, depending on the fluid volume of the system. Consequently, the time period during which corrosion products must remain suspended in order to be removed from the secondary system is bound to approximately 1-2 hours.
    • The period of cleaning for recirculation generally lasts 1-2 days and is not based on the critical path. All three installations remain in long-term recirculation for a sufficient period of time to achieve constant iron removal.
    Start-up procedures are generally initiated from the long-way circulation cleaning process, i.e., there are no additional drains or flushes prior to buoyancy increase. Additional flushes may not be practical due to the establishment of a tight breakdown schedule. The majority of the system remains at or around ambient temperature for the duration of the cleaning period.
    The duration of the dispersant candidate tests was initially set to 10 minutes. This period is considered to be typical of the recirculation time during the cleaning of the long road. During long-way recirculation, the system volume undergoes tumor once every 10 minutes to 1 hour (depending on flow rate and system volume). Additional mixing can take place as the current passes through elbows, T-pieces, expanders, etc., thereby enhancing particle suspension. In some areas, the flow can be turbulent, further enhancing particle suspension. In the sedimentation experiments conducted, iron oxide particles covered a maximum distance of 2.17 cm to settle on the bottom of the cuvette; this distance is significantly smaller than the average radius of typical supply water and condensate pipes. A typical suspended particle would therefore have a greater distance to settle, thereby reducing the likelihood of early particle deposition.
    Because the duration of an application with respect to long-distance recirculation is much shorter (in the order of a few days), at lower temperatures (layup temperatures), and at less critical means than the steam generators, the use of higher concentrations is dispersing agent or more chemically active dispersing agents acceptable.
    Since one of the purposes of this dispersant application is to extend the time that iron oxide particles spend in suspension, a relatively high deposition concentration (10,000 ppm) was used. The experiments performed focused on the suspension of either magnetite (Fe 3 O 4) or hematite (Fe 2 O 3) at a concentration of 10,000 ppm. In the results, the degree of settling is measured by determining the light absorption of the suspension, i.e. the rate of settling is determined by the rate at which the brightness of the suspension increases. The list of candidate dispersants and their properties is shown in Table 2. The raw data from all tests carried out are included in Tables 3 to 7. Table 3 shows the results for a magnetite: dispersant ratio of 1: 1 (10,000 ppm); Table 4 shows the results for a ratio of magnetite: dispersant of 1: 100; Table 5 shows the results for a ratio of magnetite dispersant of 1: 1000; Table 6 shows the results for a hematite: dispersant ratio of 1: 1 (10,000 ppm); and Table 7 shows the results for a magnetite: dispersant ratio of 1: 1 (100 ppm).
    Table 2
    Table 3
    Table 4
    Table 5
    Table 6
    Table 7

    An initial dispersant concentration of 10,000 ppm was selected to provide a ratio of dispersant iron oxide of 1: 1. The results of these tests are shown graphically in Figure 37. Several tests were allowed to continue beyond the initial 10-minute interval. The results of these tests are shown in Figures 38.
    Because a 10,000 ppm dispersant concentration may not be practical (due to compatibility of materials, costs, etc.), the effectiveness of the candidate dispersants was also evaluated at 100 ppm and 10 ppm dispersant concentrations (corresponding to iron oxide dispersant ratios) 1: 100 and 1: 1000, respectively). The results of the suitability tests with 100 ppm of dispersant are shown in Figures 39. Several tests were allowed to continue for a longer period of time; these results are shown in Figure 40.
    In some areas of the secondary system, in particular areas of the supply water system that experience relatively low temperatures during normal operation, deposits are mainly composed of hematite (Fe2C> 3). The effectiveness of candidate polymers in dispersing hematite was therefore evaluated. The results of dispersant suitability tests performed with 10,000 ppm of hematite are shown in Figure 41. As before, later tests were continued for a longer period of time; the results of these tests are shown in figure 42.
    Compatibility of dispersant material was also evaluated to assess the feasibility of using dispersant in a secondary system. The dispersants were tested with various materials such as nickel-based alloys, carbon steel and low-alloy steel, stainless steel, elastomers, ion exchange resins, copper alloys, titanium and titanium alloys, and graphite materials.
    As a result, it was determined that the following guideline should be applied for an initial industrial installation application test.
    • A dispersant concentration of 1 ppm is recommended as a starting point for an initial installation application. The concentration can be gradually increased within the interference window or with subsequent applications as data from the actual installation response becomes available.
    • It is recommended that the dispersant be supplied via a dosing pump to avoid overflow. The site of injection should be: a) far enough upstream of the condenser to allow adequate mixing, and b) downstream of the condensate polishers to maximize the contact time of the dispersant with corrosion products and to prevent local areas of higher concentration of dispersant come into contact with the resins.
    • For the proposed initial application with 1 ppm (for example), addition of dispersant should be started 36 hours after the establishment of long-term recirculation. Data from these three installations investigated indicate that the majority of easily removable corrosion products have been eliminated by this time. The exact choice of the time of addition of dispersant is somewhat flexible. If possible, the cleaning solution should be sampled prior to dispersant injection to ensure that the iron concentration prior to dispersant injection is <100 ppb. The injection schedule is based on maximizing the effectiveness of a limited dispersant injection. In future applications where the concentration of dispersant is increased or initially higher, injection may be performed later.
    If it is expected that the cleaning period of long-distance recirculation is less than 36 hours, the dispersant injection should be started earlier, and at least 8 hours before feed water is introduced into the steam generators. This will allow the fluid to flow hot into the condenser to undergo at least 4-fold tumover, giving the dispersant ample time to act on any dispersible material and potentially to be removed by the capacitor polishers.
    • An overview of compatibility with an installation-specific system must be completed prior to performing dispersant application during the long-way recirculation cleaning process to ensure that the addition of dispersant has no unintended or unplanned consequences. Specifically, the effect of significantly increased charge deposition on the condensate polishers and the potential effect on flow measurement devices must be considered.
    The foregoing has described a method for cleaning recirculation paths for an energy-generating device. Although specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications may be made thereto without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best way to practice the invention are provided for the purpose of explanation only and not for the purpose of limitation.
    权利要求:
    Claims (12)
    [1]
    A method for reducing corrosion product transport in an energy generating facility, comprising the steps of: (a) selecting a chemical dispersant adapted to reduce the deposition of corrosion products in the recirculation path; and (b) using at least one chemical injector to inject the chemical dispersant into a fluid present in the recirculation path during the cleaning of the recirculation path to increase removal of corrosion product; wherein the chemical dispersant is a polymeric dispersant and wherein the polymeric dispersant is selected from the group consisting of PAA, PMAA, PMA: AA and PAAM.
    [2]
    The method of claim 1, further comprising the step of performing a plant-specific assessment to determine compatibility of chemical dispersant with the energy-generating device.
    [3]
    The method of claim 1, wherein the step of selecting a chemical dispersant comprises the steps of: (a) determining the ability of the chemical dispersant to reduce particle settling rate; and (b) determining the compatibility of the chemical dispersant with materials present in the energy generating device.
    [4]
    The method of claim 3, wherein the settling rate is determined by measuring a transmittance of a solution of chemical dispersant and fluid present in the recirculation path.
    [5]
    The method of claim 1, further comprising the step of determining an injection rate for the recirculation path.
    [6]
    The method of claim 5, wherein the injection rate is determined by factors selected from the group consisting of an estimated corrosion product loading, existing system configuration, and failure and start-up schedule.
    [7]
    The method of claim 1, further comprising the step of subjecting the recirculation path to recirculation.
    [8]
    The method of claim 1, further comprising the step of removing the corrosion product from the recirculation path.
    [9]
    The method of claim 1, further comprising the step of removing the dispersant from the recirculation path.
    [10]
    The method of claim 1, further comprising the step of subjecting the recirculation path to recirculation for a predetermined amount of time prior to injection of the chemical dispersant to remove easily removable corrosion products from the recirculation path prior to injection of the chemical dispersant.
    [11]
    The method of claim 1, wherein the at least one chemical injector is placed at a predetermined location to allow adequate mixing with and allow maximum contact time between the chemical dispersant and the corrosion products.
    [12]
    A method for re-entraining existing deposits in a recirculation path, comprising the steps of (a) selecting a chemical dispersant adapted for suspending corrosion products in the recirculation path; (b) using at least one chemical injector for injecting a predetermined amount of the chemical dispersant into a fluid present in the recirculation path; and (c) circulating the chemical dispersant in the recirculation path for a predetermined amount of time to allow the chemical dispersant to mix with the fluid and suspend the corrosion products.
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    同族专利:
    公开号 | 公开日
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US5864596A|1996-07-10|1999-01-26|Commonwealth Edison Company|Polymer dispersants and methods of use in a nuclear steam generator|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    US18325209P| true| 2009-06-02|2009-06-02|
    US18325209|2009-06-02|
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