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© Copyright 2014Operator Generic Fundamentals Components - Demineralizers and Ion Exchangers.

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Presentation on theme: "© Copyright 2014Operator Generic Fundamentals Components - Demineralizers and Ion Exchangers."— Presentation transcript:

1 © Copyright 2014Operator Generic Fundamentals Components - Demineralizers and Ion Exchangers

2 © Copyright 2014Operator Generic Fundamentals 2 Introduction This course will explore how power plant components help maintain water quality and chemistry during nuclear power plant operations. Intro

3 © Copyright 2014Operator Generic Fundamentals 3 Terminal Learning Objective At the completion of this training session, the trainee will demonstrate mastery of this topic by passing a written exam with a grade of 80 percent or higher on the following Terminal Learning Objective (TLO): Explain demineralizer operation and its effect on power plant operations. TLO

4 © Copyright 2014Operator Generic Fundamentals 4 Enabling Learning Objectives for TLO 1 1.State the purpose of a demineralizer. 2.Describe the principles of demineralizer operation. 3.Describe the process of demineralizer regeneration. 4.Describe the following demineralizer conditions to include causes, hazards, and corrective measures as applicable: a.Excessive differential pressure b.Channeling c.Excessive temperature d.Breakthrough e.Leakage 5.Explain how demineralizer use affects pH. 6.Describe the decontamination factor and explain how it is calculated. 7.Describe plant evolutions that could affect demineralizer operation. 8.Explain the condition of a saturated demineralizer and the effect temperature has upon it. ELO

5 © Copyright 2014Operator Generic Fundamentals 5 ELO 1.1 – State the purpose of a demineralizer. Demineralizers and Ion Exchangers Purpose Demineralizers (ion-exchangers) used in nuclear power plants to: –Remove ionic impurities –Filter/remove small particles –Help control pH of water Hold ion exchange resins that remove dissolved impurities from fluids –Dissolved impurities generate corrosion problems and foul heat transfer surfaces –Ion exchange aids in pH control Classified into two groups: –Single-bed ion exchangers –Mixed-bed ion exchangers ELO 1.1

6 © Copyright 2014Operator Generic Fundamentals 6 Demineralizers and Ion Exchangers Purpose Demineralizers provide filtration and ion exchange for water going to steam generators ELO 1.1 Figure: Typical PWR

7 © Copyright 2014Operator Generic Fundamentals 7 Knowledge Check Demineralizers are used in nuclear plants to... (Select all that apply.) A.remove small particles. B.control the pH of water. C.remove ionic impurities. D.remove oil impurities. Correct answer are A, B, and C. Demineralizers and Ion Exchangers Purpose ELO 1.1

8 © Copyright 2014Operator Generic Fundamentals 8 Principles of Demineralizer Operation Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex solution Ionic impurities are removed and replaced with acceptable substitutes ELO 1.2 Figure: Resin Beads ELO 1.2 – Describe the principles of demineralizer operation.

9 © Copyright 2014Operator Generic Fundamentals 9 Ion Exchange Small resin beads complete ion exchange Resin beads are porous with many exchange sites for ion exchange Generally will contain exchangeable ions that are harmless such as H + or OH - ELO 1.2 Figure: Resin Beads

10 © Copyright 2014Operator Generic Fundamentals 10 Ion Exchange Anion Resins Exchange ions with undesirable negative ions OH - or hydroxyl ion is typically used in an anion resin Cation Resins Exchange with undesirable positively charged ions H 3 O + or hydronium is typically used in an cation resin ELO 1.2

11 © Copyright 2014Operator Generic Fundamentals 11 Reactions ELO 1.2

12 © Copyright 2014Operator Generic Fundamentals 12 Reactions ELO 1.2

13 © Copyright 2014Operator Generic Fundamentals 13 Principles of Demineralizer Operation Knowledge Check Anion resins contain _____________ ions while cation resins contain __________ ions. A.negative; positive B.hydronium; hydroxyl C.positive; negative D.negative; hydroxyl Correct answer is A. ELO 1.2

14 © Copyright 2014Operator Generic Fundamentals 14 Resin Regeneration Contains cation or anion resin beads Generally two single-bed ion exchangers used in series –First is a cation bed –Second is an anion bed Impurities are replaced with –Hydrogen ions from cation bed –Hydroxyl ions from anion bed –Combine to form pure water Figure: Single-Bed Demineralizer ELO 1.3 – Describe the process of demineralizer regeneration. ELO 1.3

15 © Copyright 2014Operator Generic Fundamentals 15 Regeneration Resin bed becomes exhausted and not able to function at peak performance –Indicated by increased effluent conductivity –Resin exchange sites will run out of enough mobile ions –Impurities in outlet indicate resin exhaustion Restore resin bed ability to exchange ions Regeneration strips away impurities Chemicals used to reverse chemical process refreshing the resin bed for further use ELO 1.3

16 © Copyright 2014Operator Generic Fundamentals 16 Single-Bed Regeneration Three-Step Process 1.Backwash – Water is pumped into the bottom of the ion exchanger and up through the resin, fluffs resin, and washes out entrained particles 2.Regeneration – Uses an acid solution for cation units and caustic solution for anion units 3.Rinsing – Removes any excess regenerating solution ELO 1.3

17 © Copyright 2014Operator Generic Fundamentals 17 Mixed-Bed Regeneration More complicated than single- bed regeneration Regenerated in place Normal operation –Water enters through a distribution header at the top of vessel –Water exits through bottom of vessel Regeneration needed when effluent water conductivity increases ELO 1.3 Figure: Mixed-Bed Demineralizer Regeneration

18 © Copyright 2014Operator Generic Fundamentals 18 Mixed-Bed Regeneration Mixed-Bed Demineralizer Normal operation Regeneration Sequence Backwash Regeneration Slow rinse Vent and partial drain Final rinse ELO 1.3

19 © Copyright 2014Operator Generic Fundamentals 19 External Regeneration Some mixed-bed demineralizers are designed to be regenerated externally –Resins removed from the vessel, regenerated, and then replaced Resin is sluiced with water (sometimes assisted by air pressure) ELO 1.3

20 © Copyright 2014Operator Generic Fundamentals 20 External Regeneration Resins backwashed in cation tank to remove suspended solids and to separate resins Anion resins are then sluiced to an anion tank Two batches of separated resins are regenerated by the same techniques used for single-bed ion exchangers Then sluiced into a holding tank where air is used to remix them Demineralizer Regeneration Video Demineralizer Regeneration Video ELO 1.3

21 © Copyright 2014Operator Generic Fundamentals 21 Ion Exchange Knowledge Check When a mixed-bed demineralizer resin is exhausted, the resin should be replaced or regenerated because... A.ions previously removed by the resin will be released into solution. B.the resin will physically bond together, thereby causing a flow blockage. C.particles previously filtered out of solution will be released. D.the resin will fracture and possibly escape through the retention screens Correct answer is A. ELO 1.3

22 © Copyright 2014Operator Generic Fundamentals 22 Changes in Demineralizer Operation ELO 1.4 – Describe the following demineralizer conditions to include causes, hazards, and corrective measures as applicable: A.Excessive differential pressure B.Channeling C.Excessive temperature D.Breakthrough E.Leakage Under normal operations, demineralizers and ion exchangers are passive components that can process a portion of or total system flow No moving parts and therefore not subject to mechanical failures like a pump or motor, but internal components can fail or deteriorate and affect performance Susceptible to effects of temperature, flow rate changes, and chemical saturation ELO 1.4

23 © Copyright 2014Operator Generic Fundamentals 23 Changes in Demineralizer Operation Differential pressure (D/P) across the demineralizer is a valuable tool in assessing demineralizer operation Demineralizer filters suspend solids that cannot pass through the resin and retention element Differential Pressure More materials removed results in higher resistance to flow or D/P –Low D/P could indicate demineralizer operating at a reduced capacity –High D/P could indicate clogging or the flow rate is too high ELO 1.4

24 © Copyright 2014Operator Generic Fundamentals 24 High Flow Rate and Channeling Abnormally high flow rate could cause several problems –Lower retention element clearances are designed to hold the resin under normal conditions –Resin beads could be forced through retention element –Resin organic material could break down into small resin fines –Conductivity could suddenly increase at demineralizer outlet ELO 1.4

25 © Copyright 2014Operator Generic Fundamentals 25 High Flow Rate and Channeling Channels are developed under high flow rates –Reduces ion exchange effective surface area –Reduces mechanical filtration Creates a path of least resistance for fluid indicated by –Decrease in differential pressure –High outlet ion concentration and conductivity ELO 1.4

26 © Copyright 2014Operator Generic Fundamentals 26 Excessive Temperature Exchange resin sites start to break down above 140°F –Damaged resin smells like dead fish –High temperatures cause resin to release boron –Damaged resin increases the concentration of sulfate and organics in the effluent ELO 1.4

27 © Copyright 2014Operator Generic Fundamentals 27 Breakthrough and Leakage Breakthrough – Ionic impurities in outlet indicate resin exhaustion Leakage – Small amounts of impurities pass through demineralizer during normal operation ELO 1.4

28 © Copyright 2014Operator Generic Fundamentals 28 Changes in Demineralizer Operation Knowledge Check A sudden increase in conductivity of water at the outlet of a demineralizer will result from... A.increased demineralizer flow rate. B.reduced demineralizer inlet temperature. C.reduced demineralizer inlet conductivity. D.increased demineralizer effluent pressure. Correct answer is A. ELO 1.4

29 © Copyright 2014Operator Generic Fundamentals 29 Changes in Demineralizer Operation Knowledge Check – NRC Bank A condensate demineralizer differential pressure (D/P) gauge indicates 4.0 psid at 50 percent flow rate. Over the next two days, plant power changes have caused condensate flow rate to vary between 25 percent and 100 percent. Which one of the following combinations of condensate flow rate and demineralizer D/P, observed during the power changes, indicates an increase in the accumulation of corrosion products in the demineralizer? A.100 percent flow, 15.0 psid B.75 percent flow, 9.0 psid C.60 percent flow, 5.0 psid D.25 percent flow, 2.0 psid ELO 1.4

30 © Copyright 2014Operator Generic Fundamentals 30 Changes in Demineralizer Operation Knowledge Check – NRC Bank – SOLUTION To solve this problem, we must apply the pump law that flow rate is proportional to the square root of the D/P. Therefore, you have to plug in the expected D/Ps for each flow rate and find out which one exceeds the expected D/P. At 100 percent flow, the D/P should be: (100/50)^2×4=16 psid At 75 percent flow, the D/P should be: (75/50)^2×4=11.25 psid At 60 percent flow, the D/P should be: (60/50)^2×4=5.76 psid At 25 percent flow, the D/P should be: (25/50)^2×4=1 psid Only the 25 percent flow rate has a higher than the expected D/P, and therefore indicates that there is accumulation of corrosion products. Correct answer is D. ELO 1.4

31 © Copyright 2014Operator Generic Fundamentals 31 pH Effects on Demineralizer Use Measure of acidity or basicity of a solution Defined as cologarithm of activity of dissolved hydrogen ions (H + ) Hydrogen ion activity coefficients cannot be measured experimentally so they are based on theoretical calculations pH scale is not an absolute scale –Relative to a set of standard solutions whose pH is established by international agreement Figure: pH Scale ELO 1.5 ELO 1.5 – Explain how pH is affected by demineralizer use.

32 © Copyright 2014Operator Generic Fundamentals 32 pH Effects on Demineralizer Use Exchanged mobile ions from resins are H + and OH - –Affect pH of fluid undergoing exchange –Basic solutions will have an excess of OH - ions –Acidic solutions will contain excess H 3 O + In mixed-bed demineralizers containing both resins, pH effect cancels In mixed-bed, a different type of cation resin is used to counteract canceling effect Lithium form cation resin used with anion to form mixed-bed resin Mobile Li + given up does not counteract OH - thereby increasing pH pH of solution can be controlled by ion exchange ELO 1.5

33 © Copyright 2014Operator Generic Fundamentals 33 pH Effects on Demineralizer Use Knowledge Check A mixed-bed demineralizer contains resins that exchange positive ions for H + ions and exchange negative ions for OH - ions. What is the effect on effluent pH? A.The H + ions and the OH - ions cancel each other and result in a neutral pH. B.The H + ions are dominant and decrease pH. C.The OH - ions are dominant and raise pH. D.pH is not affected by either H + or OH - ions. Correct answer is A. ELO 1.5

34 © Copyright 2014Operator Generic Fundamentals 34 Decontamination Factor Decontamination (also called demineralization) factor is used for determining when resin bed is exhausted Decontamination factor (DF) is inlet conductivity divided by outlet conductivity To determine percentage of impurities removed, divide amount of impurities (conductivity) removed by ion exchanger by amount of impurities (conductivity) entering the ion exchanger ELO 1.6 ELO 1.6 – Describe decontamination factor and how it is calculated.

35 © Copyright 2014Operator Generic Fundamentals 35 Example – Decontamination Factor What is the DF and percent of impurities removed for an ion exchanger with condensate of 20 μmho/cm entering and 0.4 μmho/cm exiting? ELO 1.6

36 © Copyright 2014Operator Generic Fundamentals 36 35μmho/0.3μmho = 117 Decontamination Factor = 117 (35-0.3) μmho removed)/(35 μmho in) =0.99 x 100 percent impurities removed = 99 percent Demonstration – Decontamination Factor A demineralizer has been in service for 60 days. When first placed in service, the decontamination factor was 200. Currently, the inlet and outlet conductivities are: 35 μmho/cm entering 0.3 μmho/cm exiting What is the decontamination factor now, what percent impurities are removed, and would you recommend regeneration? ELO 1.6

37 © Copyright 2014Operator Generic Fundamentals 37 Demonstration – Decontamination Factor The demineralizer is removing 99 percent of the inlet contaminants. Although the decontamination factor has decreased to about 55 percent of the original value, it is still effective at removing unwanted ions. The demineralizer should remain in service. Normally, demineralizers are replaced or regenerated when the DF is 25 or less. ELO 1.6

38 © Copyright 2014Operator Generic Fundamentals 38 Decontamination Factor Knowledge Check – NRC Bank The decontamination factor for ionic impurities of a demineralizer can be expressed as... A.inlet conductivity minus outlet conductivity. B.outlet conductivity minus inlet conductivity. C.inlet conductivity divided by outlet conductivity. D.outlet conductivity divided by inlet conductivity. Correct answer is C. ELO 1.6

39 © Copyright 2014Operator Generic Fundamentals 39 Plant Evolutions that Affect Demineralizer Operation During plant heatup or cooldown, coolant purification system's inlet temperature can vary greatly –May change suspended solids in coolant system and in turn affect performance of resin bed Crud burst is a release of a large amount of corrosion products in reactor coolant system Operational events cause large amounts of solids to become suspended within system Oil contamination is another potential hazard for demineralizers ELO 1.7 ELO 1.7 – Describe plant evolutions that could affect demineralizer operation.

40 © Copyright 2014Operator Generic Fundamentals 40 Crud Burst Crud burst is a release of a large amount of corrosion products in reactor coolant system Operational events cause large amounts of solids to become suspended within system Events that may cause a crud burst: –Reactor scrams –Cooldown –Heatup –Reactor coolant pump starts/stops Evolutions will tax demineralizer with excessive corrosion products, resulting in increased pressure drop across demineralizer Effluent should be monitored during cleanup efforts ELO 1.7

41 © Copyright 2014Operator Generic Fundamentals 41 Temperature Resin beads susceptible to damage at elevated temperatures Exchange sites break down around 140°F Proper procedures must be followed to ensure resin remains intact Damaged resin will give off an odor similar to dead fish ELO 1.7

42 © Copyright 2014Operator Generic Fundamentals 42 Oily Water Oily water is another hazard for demineralizer resin beds Oil will affect exchange sites and render the resin ineffective Oil will create a film on the resin beads that will block or inhibit resin exchange sites from performing their intended function since oil is an organic compound ELO 1.7

43 © Copyright 2014Operator Generic Fundamentals 43 Plant Evolutions that Affect Demineralizer Operation Knowledge Check – NRC Bank A nuclear power plant was operating at steady-state 100 percent power when the reactor coolant system experienced a large crud burst. After ten minutes, the operators began to record parameters for the in- service reactor coolant purification ion exchanger. Assuming no additional operator actions, what trend will the recorded parameters show during the next few hours? A.Increasing flow rate through the ion exchanger B.Increasing pressure drop across the ion exchanger C.Increasing ion exchanger inlet water conductivity D.Increasing ion exchanger outlet water conductivity Correct answer is D. ELO 1.7

44 © Copyright 2014Operator Generic Fundamentals 44 Plant Evolutions that Affect Demineralizer Operation Knowledge Check – NRC Bank Prior to a scheduled nuclear power plant shutdown, the reactor coolant system was chemically shocked to induce a crud burst. What effect will this have on the purification demineralizers? A.Decreased radiation levels around the demineralizers B.Increased flow rate through the demineralizers C.Decreased demineralizer outlet conductivity D.Increased pressure drop across the demineralizers Correct answer is D. ELO 1.7

45 © Copyright 2014Operator Generic Fundamentals 45 A demineralizer is saturated when the resin beads are loaded with positive or negative ions –Biases resin so it will have a reduced affinity for certain ions –Occurs based on exposure of ion exchanger to an overabundance of either hydroxyl or hydronium ions Saturating a resin bed effectively changes the affinity for ions of the whole bed and can be used to buffer changes in coolant chemistry Saturated Demineralizer ELO 1.8 – Explain the condition of a saturated demineralizer and the effect temperature has on it. ELO 1.8

46 © Copyright 2014Operator Generic Fundamentals 46 Boron Saturation During lower temperatures, the borate ion bonding to the resin exchange sites contains three boron atoms, while at higher temperatures only contains one atom Lower temperature resin will remove more boron and is more efficient Lowering the temperature of influent may increase the affinity for a particular ion such as boron If temperature is increased, boron is released due to changed affinity Operation of a demineralizer in a PWR using boron in solution must take this into account Changing efficiency of resin affects coolant pH, boron in solution, and consequently reactivity and power ELO 1.8

47 © Copyright 2014Operator Generic Fundamentals 47 Lithium-Saturated Demineralizer In PWR's, reactor coolant chemistry is maintained slightly basic to inhibit corrosion A pH of approximately 6.8 can be achieved by maintaining a balance between boron and lithium concentrations At beginning of core life, boron concentration is high; to balance pH, must maintain the lithium concentration high Lithium hydroxide added to maintain pH value in alkaline range If ion exchanger was not saturated with lithium, it would rapidly remove Li + and release H + ELO 1.8

48 © Copyright 2014Operator Generic Fundamentals 48 Saturated Demineralizer Knowledge Check – NRC Bank A nuclear power plant is operating at 70 percent steady-state power level when the temperature of the reactor coolant letdown passing through a boron-saturated mixed-bed ion exchanger is decreased by 20°F. As a result, the boron concentration in the effluent of the ion exchanger will ____________ because the affinity of the ion exchanger for boron atoms has __________ inlet conductivity minus outlet conductivity. A.decrease; increased B.decrease; decreased C.increase; increased D.increase; decreased Correct answer is A. ELO 1.8

49 © Copyright 2014Operator Generic Fundamentals 49 Crossword Puzzle It’s crossword puzzle time! Summary

50 © Copyright 2014Operator Generic Fundamentals 50 Demineralizers and Ion Exchangers Summary Demineralizers hold ion exchange resins and transport water through the resins to filter and ionize water –Demineralization is used to remove dissolved contaminants. –Dissolved impurities can generate corrosion problems and decrease efficiency due to fouled heat transfer surfaces –Ion exchangers are generally classified into two groups: o Single-bed ion exchangers have resin of either cation or anion exchange sites o Mixed-bed ion exchangers contain both anion and cation resin Regeneration – Sustained operation leads to resin exhaustion –Increased effluent conductivity is indication of resin bed exhaustion –Breakthrough describes point when impurities in outlet or effluent of demineralizer indicate resin exhaustion –Regeneration entails backwash, regenerating solution of acid or caustic, and rinsing cycles TLO 1 Summary

51 © Copyright 2014Operator Generic Fundamentals 51 Demineralizers and Ion Exchangers Summary Principles of operation –Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex solution –Removes ionic impurities, replaces them with acceptable substitutes –Small resin beads serve as vehicle to complete ion exchange within demineralizer –Anion resins exchange ions with undesirable negative ions, typically using OH - or hydroxyl ions –Cation resins exchange ions with undesirable positive ions and typically use H 3 O + or hydronium ion TLO 1 Summary

52 © Copyright 2014Operator Generic Fundamentals 52 Demineralizers and Ion Exchangers Summary Changes in demineralizer operation –D/P – More materials removed, higher resistance to flow or D/P –Low D/P could indicate demineralizer operating at reduced capacity; high D/P could indicate clogging or flow rate too high –A flow rate that exceeds design rate could force resin beads through retention element o Can result in a sudden increase in conductivity and channeling of resin which reduces ion exchange and mechanical filtration –Resin beads in a demineralizer resin bed susceptible to damage at elevated temperatures, will begin to break down around 140°F –Eventually, resin bed will be exhausted and unable to function at peak performance; increased effluent conductivity is common indication o Breakthrough describes when impurities indicate resin exhaustion o Leakage when small amounts of impurities or unwanted ions pass through during normal operation o Larger amounts of leakage indicate imminent breakthrough TLO 1 Summary

53 © Copyright 2014Operator Generic Fundamentals 53 Demineralizers and Ion Exchangers Summary pH effects on demineralizer – The pH scale measures acidity or alkalinity (how basic) of substance –H + and OH - exchanged ions results from IX process –More basic solutions will have an excess of OH - ions, acidic solutions will contain excess H 3 O + –In mixed-bed resin, pH tends to cancel out, so lithium is used as cation resin –Controlling combination of resin used can control pH of water Decontamination factor – guide to determine when resin bed exhausted –DF is inlet conductivity divided by outlet conductivity Plant evolution can affect demineralizer operation –Crud burst releases large amounts of corrosion products –Oil contamination renders resin ineffective at ion exchange Demineralizer saturation – Demineralizer can become "saturated" when resin beads loaded with positive or negative ions; essentially biases resin so it will have a reduced affinity for certain ions TLO 1 Summary

54 © Copyright 2014Operator Generic Fundamentals 54 Summary Now that you have completed this module, you should be able to demonstrate mastery of this topic by passing a written exam with a grade of 80 percent or higher on the following TLOs: 1.State the purpose of a demineralizer. 2.Describe the principles of demineralizer operation. 3.Describe the process of demineralizer regeneration. 4.Describe the following demineralizer conditions to include causes, hazards, and corrective measures as applicable: a.Excessive differential pressure b.Channeling c.Excessive temperature d.Breakthrough e.Leakage Summary

55 © Copyright 2014Operator Generic Fundamentals 55 Summary 5.Explain how pH is affected by demineralizer use. 6.Describe the decontamination factor and how it is calculated. 7.Describe plant evolutions that could affect demineralizer operation such as crud burst. 8.Explain the condition of a saturated demineralizer and the effect temperature has on it. Review the objectives and conduct directed questioning to assure comprehension. Review topic for any areas where retention needs improvement. Summary


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