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Condensate polishing Corrosion protection Final Report September 1996

E

Electric Power Research Institute

Condensate Polishing Guidelines

SINGLE USER LICENSE AGREEMENT

THIS IS A LEGALLY BINDING AGREEMENT BETWEEN YOU AND THE ELECTRIC POWER RESEARCH INSTITUTE (EPRI). PLEASE READ IT CAREFULLY BEFORE REMOVING THE WRAPPING MATERIAL. THIS AGREEMENT CONTINUES ON THE BACK COVER.

BY OPENING THIS SEALED REPORT YOU ARE AGREEING TO THE TERMS OF THIS AGREEMENT. IF YOU DO NOT AGREE TO THE TERMS OF THIS AGREEMENT, PROMPTLY RETURN THE UNOPENED REPORT TO EPRI AND THE PURCHASE PRICE WILL BE REFUNDED.

1. GRANT OF LICENSE

EPRI grants you the nonexclusive and nontransferable right during the term of this agreement to use this report only for your own benefit and the benefit of your organization. This means that the following may use this report: (I) your company (at any site owned or operated by your company); (II) its subsidiaries or other related entities; and (III) a consultant to your company or related entities, if the consultant has entered into a contract agreeing not to disclose the report outside of its organization or to use the report for its own benefit or the benefit of any party other than your company.

This shrink-wrap license agreement is subordinate to the terms of the Master Utility License Agreement between most U.S. EPRI member utilities and EPRI. Any EPRI member utility that does not have a Master Utility License Agreement may get one on request.

2. COPYRIGHT

This report, including the information contained in it, is owned by EPRI and is protected by United States and international copyright laws. You may not, without the prior written permission of EPRI, reproduce, translate or modify this report, in any form, in whole or in part, or prepare any derivative work based on this report.

3. RESTRICTIONS

You may not rent, lease, license, disclose or give this report to any person or organization, or use the information contained in this report, for the benefit of any third party or for any purpose other than as specified above unless such use is with the prior written permission of EPRI. You agree to take all reasonable steps to prevent unauthorized disclosure or use of this report. Except as specified above, this agreement does not grant you any right to patents, copyrights, trade secrets, trade names, trademarks or any other intellectual property, rights or licenses in respect of this report.

(continued on back cover)

Prepared by

BLACK & VEATCH, Kansas City, Missouri

M A T E R I A L L I C E N S E D

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TR-104422

Research Projects 2712-10, 2977, and 9003

Final Report, June 1996

Prepared by

B.A. Larkin (Black and Veatch) D.C. Gay (Black and Veatch) L.C. Webb (Black and Veatch) F. Pocock (EPRI Consultant) M. Sadler (EPRI Consultant)

S.G. Sawochka (NWT Corporation) D. Siegwarth (NWT Corporation) L. Wirth (Consultant)

G. Crits (Consultant) Project Managed by Black and Veatch 8400 Ward Parkway

Kansas City, Missouri 64114 Authors

L.C. Webb B.A. Larkin

Prepared for

Electric Power Research Institute 3412 Hillview Avenue

Palo Alto, California 94304 EPRI Project Manager R.B. Dooley

Applied Science and Technology, Strategic Research and Development

for

Fossil Power Plants, Generation Group

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

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DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS REPORT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM: (A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITH RESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS REPORT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNED RIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS REPORT IS SUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDING ANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THIS REPORT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSED IN THIS REPORT.

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iii

ABSTRACT

Guidelines are presented for condensate polishing in United States utility generating units, for both nuclear and fossil plants. A portion of these guidelines was published earlier as TR-101942 which was issued as an EPRI Nuclear Group Guideline. This portion is included in these guidelines along with new materials to more generalize the guidelines and to include economics of condensate polishing. The TR-101942 material has been edited somewhat, primarily for document format purposes, but the technical content remains the same.

Properly designed and operated condensate polishing systems can provide the best possible quality of feedwater to steam generators. High quality feedwater is important to long-term, reliable operation. This document describes fundamentals of ion

exchange, the application of ion exchange to feedwater treatment, and equipment used in condensate polishing. Operating and maintenance guidelines and information on the economics of condensate polishing are also presented as well as methodology to

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v

ACKNOWLEDGMENTS

The authors thank the following members of the EPRI Fossil Plant Cycle Chemistry Group for their review comments on the draft guidelines:

Al Aschoff Malcom Ball

Consultant Consultant

Greg Bartley Jim Bellows

Tennessee Valley Authority Westinghouse Power Corporation

Albert Bursik Frances Cutler

Consultant Southern California Edison

Phil Daniel Larry Dupree

B&W Carolina Power & Light

Dan Everson Tom Gilchrist

Wisconsin Power & Light Co. Tri-State G&T

Don Goldstrom Doug Hubbard

Salt River Project American Electric Power

Bud Herre Ronnie Jones

Pennsylvania Power & Light TU Electric

Otkar Jonas Ronnie Pate

Jonas, Inc. Georgia Power Co.

Jim Mathews Kevin Shields

Duke Power Co. Shepperd T. Powell Associates

Rob Peterson Terry Spaulding

Salt River Project PSI Energy

Jim Rice Steve Shulder

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EPRI Licensed Material

Dave Stamp George Verib

Northern Indiana Public Service Co. Ohio Edison

The authors wish to thank those who facilitated plant visits including: Mr. S. Ronnie Pate at Georgia Power Company, Mr. Carl Scheerer of Central Illinois Power Company, Mr. Mike Waddlington formerly of TU Electric Company, Ms. Francis Cutler of

Southern California Edison, and Mr. Vernon James of Public Service Company of Oklahoma. We also wish to thank all of those at the individual stations for providing supporting information during our visits. The authors also wish to thank those members of the EEI chemistry subcommittees and the EPRI International Cycle Chemistry Group who provided survey input to these guidelines.

The authors wish to thank those members of the Condensate Polishing Guidelines Committee, who participated in the development of TR-101942, Condensate Polishing Guidelines for PWR and BWR Plants. The authors also wish to acknowledge the participation of T. O. Passell, who was a project manager for the nuclear guideline as well as a participant in initiating this guideline and to Mr. Peter Millett who

subsequently took over for the Nuclear Power Group.

We also wish to thank Mr. David Shallberg of Black & Veatch for his work in developing the many economic calculations used in these guidelines.

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vii

SUMMARY

These condensate polishing guidelines have been developed to provide guidance for US utilities for the installation, operation, and management of condensate polishing

systems. These guidelines are applicable to both nuclear and fossil units. Condensate polishing can be an important tool in the maintenance of high purity feedwater, which is so important for long reliable life of steam cycle components.

These guidelines are based upon scientific principles and 30 years of experience with condensate polishing. These guidelines include material which was published earlier as TR-101942, which was issued as an EPRI Nuclear Group Guideline. This material is included in these guidelines along with new materials to broaden the applicability of the guidelines and to include economics of condensate polishing. The TR-101942 material has been edited somewhat, primarily for document format purposes, but the technical content remains the same.

Purpose and Scope

These guidelines provide scientific basis for condensate polishing and its applications in power plants. The guidelines give the novice the background information to

understand the basis of polishing. The more common methods of application are also explained so that the impacts of equipment design on performance can be understood. The economics of polishing are developed using actual applications as input. Real applications were used because of the myriad of factors that need to be defined to evaluate the economics of condensate polishing. Guidelines were developed which are applicable to both new and existing plants. Methodology is provided (a road map) for evaluation of condensate polishing for individual circumstances.

How To Use These Guidelines

These guidelines allow the user the greatest level of flexibility possible and apply to the widest variety of plant situations. There is flexibility in the effective use of these

guidelines. Users with little experience in condensate polishing can find valuable information in Chapter 1 about the fundamentals of condensate polishing. Users

considering the addition of condensate polishing to existing or new units can make use of the economic evaluation information in Chapter 3 and the road map information in Chapter 4. Those looking for water quality impacts of condensate polishing or

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EPRI Licensed Material

Outline

The contents of each chapter are briefly described below.

Chapter 1--Principles of Condensate Polishing

Chapter 1 describes the basics of condensate polishing, including the ion exchange reaction, important properties of ion exchange resin, and the application of ion exchange process to treat condensate. Much of this information was taken from the Nuclear Group Guideline, TR-101942. The impact of feedwater treatment chemicals is described. Several of the more common methods of regeneration and the basics of the equipment involved are introduced. The use of powdered resins and the application equipment are discussed.

Chapter 2--Water Chemistry Impacts

This chapter outlines the water chemistry requirements for several types of nuclear and fossil units, as well as some of the impacts of various applicable cycle chemistry options. Effluent quality of alternative condensate polishing systems are also addressed in this Chapter.

Chapter 3--Justification of Condensate Polishing

This chapter discusses the economic justification of condensate polishing systems and is generally based upon fossil plant information. The costs of polishing are evaluated using real plant economic factors. The capital and operating cost impacts are evaluated. Cost savings from the use of condensate polishing are also evaluated. Cost sensitivity analyses are evaluated to show the effects of variation of important parameters such as availability improvements, replacement power costs, the annual number of startups, and turbine efficiency improvements.

Chapter 4--Condensate Polisher Guidelines

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ix

Appendix A--Condensate Polishing Experience Summary

This appendix is a summary of the input received from utilities surveyed and visited. Most input was from fossil plants, but these were limited input from nuclear units.

Appendix B--European Practices

This appendix gives insight into the condensate polishing practices of European plants.

Appendix C--Economic Factors

This appendix gives the detailed economic factors used in the example economic evaluations.

Appendix D--Resin Information

This appendix outlines resin analyses and procedures recommended for the evaluation and maintenance of resin in condensate polishing systems. This information was taken extensively from the Nuclear Guideline, TR-101942. The information includes: resin analyses methods, regenerant specifications, and resin purchase specifications.

Appendix E--Contractor Regeneration

This appendix provides some insight to application of offsite, Contractor regeneration of condensate polisher resins and economic comparisons of this fairly new alternative.

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CONTENTS

1 PRINCIPLES OF CONDENSATE POLISHING ... 1-1 Basics ... 1-1 Resin ... 1-4 Physical Characteristics ...1-4 Resin Properties ...1-6 Deep Bed Resin Regeneration... 1-16

Cation Resin Regeneration ... 1-17 Anion Resin Regeneration ... 1-20 Resin Ratio... 1-21 Polisher Vessel Design... 1-23 Mixed Bed Service Vessels... 1-23 Polisher Operation... 1-31 Recycle ... 1-31 Service Cycle Termination ... 1-32 Flow Transients and Outages ... 1-33 Regeneration ... 1-33 Resin Transfers... 1-34 Resin Cleaning... 1-34 Mixed Bed Separation... 1-36 Resin Transfer from Separation Vessel ... 1-39 Resin Regeneration...1-39 Resin Mixing and Final Rinse ...1-46 Resin Transfer to Service Vessel ...1-46 Typical Resin Regeneration System... 1-47 Cation Regeneration Separation vessel... 1-47 Anion Vessel ... 1-51 Mix and Storage Vessel ... 1-51 Special Resin Regeneration Systems ... 1-51

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High Efficiency Separation Plants ... 1-51 Post Regeneration Resin Purification Technologies ... 1-58 Inert Resin... 1-61 Uniform Particle Resins... 1-62 Contractor Regeneration... 1-63 Regenerant Reuse ... 1-63 BWR Throwaway Resin ... 1-63 Cross-contamination... 1-63 Powdered Resin Filter Demineralizers ... 1-64 Filter Demineralizer System Design ... 1-64 Powdered Resin Filter Demineralizer Operation ... 1-73 References ... 1-82 2 WATER CHEMISTRY IMPACTS ... 2-1 Overview... 2-1 Fossil Stations ... 2-1 Nuclear Stations ... 2-2 PWR Recirculating Steam Generators... 2-5 PWR Once-Through Steam Generators ... 2-7 Justification for Condensate Polishing in PWRs ... 2-9 Boiling Water Reactors ... 2-10 Justification for BWR Condensate Polishing ... 2-12 Condensate Polishing Effluent Targets ... 2-13 Cycle Chemistry Effects ... 2-15 Benefits ... 2-15 Problems ... 2-17 System Effluent Quality... 2-19

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xiii Power Plant Features... 3-9 Condensate Polishing System Features ... 3-9 Cost of a Powdered Resin Condensate Polisher Installed as a Retrofit ... 3-11 Condensate Polishing System Operating Costs... 3-13 Operating Costs for a Mixed Bed Polisher Installed in a New Plant... 3-13 Operating Costs for a Powdered Resin Polisher Installed in a New Plant ... 3-15 Operating Costs for a Retrofit Mixed Bed Polisher... 3-17 Operating Costs for a Retrofit Powdered Resin Polisher ... 3-18 Benefit of Condensate Polishing ... 3-19 Boiler Blowdown... 3-21 Chemical Cleaning Frequency ... 3-21 Startup Time... 3-22 Improved Unit Availability... 3-22 Improved Turbine Efficiency... 3-22 Condenser Tube Leakage... 3-23 Boiler Tube Failures ... 3-23 Lower Fuel Costs ... 3-23 Condensate Polishing Economic Justification--Cost Versus Benefit ... 3-23 Cost Sensitivity to Availability and Replacement Power Cost ... 3-25 Sensitivity to Number of Starts per Year and Replacement Power Cost ... 3-25 Improved Turbine Efficiency... 3-34 Conclusion... 3-34 References ... 3-34 4 CONDENSATE POLISHER GUIDELINES ... 4-1 Rationale for Guidelines ... 4-1 Design Guidelines ... 4-1 Direct Polishing ... 4-2 Mixed Bed Polishing ... 4-3 Vessel Sizing... 4-3 Vessel Design ... 4-4 Vessel Design Features ... 4-5 Regeneration Vessels ... 4-7 Powdered Resin Polishing... 4-15 Vessel Sizing... 4-15 Backwash Systems ... 4-16

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EPRI Licensed Material Precoat Systems ... 4-17 Valves ... 4-17 Piping ... 4-17 Resin Strainers... 4-17 Operating Guidelines... 4-18 Mixed Bed ... 4-18 Mixed Bed Regeneration Systems... 4-20 Regeneration System Operations ... 4-24 Resin Cleaning... 4-29 Powdered Resin... 4-31 Resin Guidelines ... 4-34 Management Guidelines... 4-36 Wastewater Disposal... 4-36 Road Map for Condensate Polisher Justification... 4-38 References ... 4-46 A CONDENSATE POLISHING EXPERIENCE... A-1 Condensate Polishing Advantages/Justifications ...A-1 Mixed Bed Versus Powdered Resin ...A-2 Mixed Bed Advantages...A-3 Powdered Resin Advantages ...A-3 Equipment Sizing Criteria ...A-4 Equipment Sizing Criteria ...A-5 Mixed Bed Service Vessels...A-5 Regeneration Vessels, Typical, Three Tank System ...A-5 Equipment Design Features ...A-6 Bypass Valves...A-6

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xv Powdered Resin...A-11 Operation of Regeneration Facilities...A-12 Bead Resins...A-14 Condensate Polisher Problems...A-18 Bead Resin Systems...A-21 Powered Resin Systems ...A-22 Improvements ...A-22 Wastewater Disposal and Miscellaneous Issues ...A-24 In-Place Regeneration ...A-24

B EUROPEAN PRACTICES... B-1 United Kingdom ...B-1 Ireland ...B-2 Germany...B-2 Other European Countries...B-3 In-Place Regeneration...B-3 References ...B-4 C ECONOMIC FACTORS... C-1

D RESIN INFORMATION ... D-1 Method A--Perfect Bead Content ... D-1 Applications... D-1 Principle ... D-1 Procedure ... D-1 Calculations... D-2 Method B--Exchange Capacity of Hydroxide Form Anion Resin ... D-2 Application ... D-2 Reference ... D-2 Principle ... D-2 Method C--Trace Metals Determination... D-3 Application ... D-3 Principle ... D-3 Reagents... D-4 Sample Preparation ... D-4 Reagent Blanks... D-5

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Procedure ... D-5 Method D--Cation Resin Organic Extractables... D-5 Application ... D-5 Principle ... D-5 Procedure ... D-5 Calculations... D-6 Method E--Anion Resin Exchange Kinetics Assessment ... D-6 Application ... D-6 References... D-6 Principle ... D-6 Procedure ... D-6 Calculations... D-8 Method F--Resin Cross-Contamination ... D-11 Reference ... D-11 Cation Resin in Bulk Anion Exchanger ... D-11 Anion Resin in Bulk Cation Resin ... D-11 Method G--Determination of Chloride, Sulfate and Sodium Impurities Exchanged on Bead Resin ... D-12

Summary... D-12 Reference ... D-12 Procedure ... D-12 Calculations... D-12 Sodium Content of Cation Resin ... D-13 Summary... D-13 Reference ... D-13 Procedure ... D-13 Calculations... D-13

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xvii Principle ... D-15 Procedure ... D-15 Method J--Water Leachable Impurities in Powdered Resin Fiber Filter Aid ApplicationD-15

Principle ... D-15 Calculations... D-16 Resin Purchase Specifications... D-16 Bead Resin ... D-17 Powdered Resin... D-18

E CONTRACTOR REGENERATION...E-1 Overview...E-1 Process...E-1 Economic Evaluation ...E-2 Disadvantages...E-4

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xix

LIST OF TABLES

Table 1-1 Data Relating To US Standard Screen Scale... 1-6 Table 1-2 Cation Resin Sodium Selectivities at Low Sodium Concentration... 1-15 Table 1-3 Ion Exchange Resin Capacities... 1-16 Table 1-4 Degree of Regeneration to Achieve Sodium and Chloride Leakages of 0.3

ppb with Ammonia as a pH Control Additive... 1-40 Table 2-1 Cycle Chemistry Limits... 2-3 Table 2-2 Once-Through Unit Cycle Chemistry Limits... 2-4 Table 2-3 Maximum Allowable Impurity Level in Recirculating Steam Generator

Polished Condensate Calculated from EPRI Action Level 1 Blowdown Chemistry Guidelines ... 2-7 Table 2-4 Maximum Polished Condensate Impurity Levels in OTSG PWRs Based on

EPRI Guidelines ... 2-8 Table 2-5 Maximum Impurity Levels in BWR Polished Condensate Based on EPRI

Guidelines ... 2-11 Table 2-6 Condensate Polisher Effluent Limitations--Comparison Tables... 2-14 Table 3-1 Cost of a Mixed Bed Condensate Polishing System Installed With a New

Power Plant (440 MWe)... 3-2 Table 3-2 Total Installed Cost of Alternate Service Vessel Configurations ... 3-5 Table 3-3 Cost of a Powdered Resin Condensate Polishing System Installed With a

New Power Plant (440 MWe) ... 3-6 Table 3-4 Total Installed Cost of Alternative Powdered Resin Equipment... 3-7

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Table 3-5 Cost of a Mixed Bed Condensate Polishing System Installed as a Retrofit (360 MWe) ... 3-7 Table 3-6 Total Installed Cost of Alternative Service Vessel Configurations... 3-11 Table 3-7 Cost of a Powdered Resin Condensate Polishing System Installed as a

Retrofit (360 MWe)... 3-12 Table 3-8 Total Installed Cost of Alternate Powdered Resin Equipment ... 3-13 Table 3-9 First Year of Cost of Operation for a Mixed Bed Condensate Polishing

System Installed with a New Plant (440 MWe) ... 3-14 Table 3-10 First Year Cost of Operation for a Powdered Resin Condensate Polishing

System Installed with a New Plant (440 MWe) ... 3-16 Table 3-11 First Year Cost of Operation for a Mixed Bed Condensate Polishing System

Installed as a Retrofit (360 MWe)... 3-17 Table 3-12 First Year Cost of Operation for a Powdered Resin Condensate Polishing

System Installed as a Retrofit (360 MWe)... 3-18 Table 3-13 First Year Benefits for a Condensate Polishing System Installed with a New

Plant (440 MWe) ... 3-20 Table 3-14 First Year Benefits for a Condensate Polishing System Installed as a Retrofit

(360 MWe) ... 3-20 Table 3-15 Major Fixed Assumptions... 3-24 Table 4-1 Ion Exchange Resin Regeneration ... 4-28

Table 4-2 Typical Powdered Resin Precoat Materialsa

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LIST OF FIGURES

Figure 1-1 Typical Mixed Bed Condensate Polishing System... 1-2 Figure 1-2 Typical Powdered Resin Polishing System ... 1-3 Figure 1-3 Typical Structure of Hydrated Gel Type Cation Resin... 1-5 Figure 1-4 Typical Cycle Location for Condensate Polishing Systems ... 1-8 Figure 1-5 Filter Demineralizer Differential Pressure Behavior (Source: Reference 10)1-11 Figure 1-6 Effect of Selectivity on Ion Movement Through Ion Exchange Beds ... 1-13 Figure 1-7 Cation Resin Regeneration with Sulfuric Acid (Source: Reference 19)... 1-18 Figure 1-8 Elution of Sodium From Cation Resin (Source: Reference 15) ... 1-19 Figure 1-9 Elution of Sodium and Ammonium Ions from *% DVB Cation Resin (Source:

Reference 20)... 1-20 Figure 1-10 Regeneration of Type I Chloride from Anion Resin with Sodium Hydroxide (Source: Reference 22)... 1-22 Figure 1-11 Typical Spherical Condensate Polisher Vessel with Parallel Lateral

Underdrain... 1-24 Figure 1-12 Typical Spherical Polisher Vessel with Convex Support Plate ... 1-25 Figure 1-13 Typical Spherical Polisher Vessel with Wedge Wire Screen Underdrain 1-26 Figure 1-14 Typical Cylindrical Polisher Vessel with Drop Leg Underdrain ... 1-27 Figure 1-15 Typical Cylindrical Polisher Vessel with Parallel Lateral Underdrain ... 1-28 Figure 1-16 Adverse Effects of Fluidizing Resin ... 1-30 Figure 1-17 Condensate Polisher Recycle... 1-32

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Figure 1-18 Ultrasonic Resin Cleaner (Source: Reference 27)... 1-36 Figure 1-19 Example of Condensate Polisher Resin Bed Expansion as a Function of

Backwash Temperature and Flow Rate (Source: Reference 29) ... 1-38 Figure 1-20 Condensate Polisher Operating Time to Amine Breakthrough (Source:

Reference 20)... 1-41 Figure 1-21 Sodium Leakage for Cation Resin (Source: Reference 31) ... 1-43 Figure 1-22 Chloride Leakage for Anion Resin (Source: Reference 31) ... 1-44 Figure 1-23 Effect of Storage on Mixed Bed Sulfate Release (Source: Reference 18) ... 1-45 Figure 1-24 Conventional Regeneration Procedure... 1-48 Figure 1-25 Interface Isolation Regeneration System ... 1-53 Figure 1-26 Bottom Transfer Regeneration System ... 1-54 Figure 1-27 Resin Cleaning, Sizing, and Separation System ... 1-56 Figure 1-28 Ammonium Sulfate Density Separation System ... 1-57 Figure 1-29 Caustic Flotation Regeneration Process... 1-58 Figure 1-30 Ammonia Wash Regeneration Procedure ... 1-60 Figure 1-31 Regeneration with Inert Resin... 1-62 Figure 1-32 Top Tubesheet Polisher Vessel (Source: Reference 41)... 1-65 Figure 1-33 Bottom Tubesheet Polisher Vessel (Source: Reference 41)... 1-67

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xxiii Figure 1-39 Precoat Chloride Removal Efficiency (Source: Reference 40)... 1-76 Figure 1-40 Precoat Sodium Removal Efficiency (Source: Reference 40) ... 1-77 Figure 1-41 Hydrogen Form Precoat Sodium Removal Efficiency... 1-79 Figure 3-1 Sensitivity to Availability and Replacement Power Cost: New Plant Mixed

Beds ... 3-26 Figure 3-2 Sensitivity to Availability and Replacement Power Cost: New Plant Mixed

Bed--Ammonia Cycle ... 3-27 Figure 3-3 Sensitivity to Availability and Replacement Power Cost: Powdered Resin

Condensate Polisher for a New Plant ... 3-28 Figure 3-4 Sensitivity to Availability and Replacement Power Cost: Retrofit Plant

Mixed Beds... 3-29 Figure 3-5 Sensitivity to Availability and Replacement Power Cost: Retrofit Plant

Mixed Bed--Ammonia Cycle... 3-30 Figure 3-6 Sensitivity to Availability and Replacement Power Cost: Powdered Resin

Condensate Polisher for a Retrofit Plant ... 3-31 Figure 3-7 Sensitivity to Number of Startups: New Plant Condensate Polisher ... 3-32 Figure 3-8 Sensitivity to Number of Startups: Retrofit Plant Condensate Polisher ... 3-33 Figure 3-9 Sensitivity to Reduced Turbine Efficiency Losses: New Plant Condensate

Polisher ... 3-35 Figure 3-10 Sensitivity to Reduced Turbine Efficiency Losses: Retrofit Plant Condensate

Polisher ... 3-36 Figure 4-1 Typical Booster Loop Polishing Diagram... 4-4 Figure 4-2 Regenerant Reuse Diagram ... 4-10 Figure 4-3 Anion Exchanger Resin Kinetics--New Resin (Source: Reference 9)... 4-13 Figure 4-4 Anion Exchange Resin Kinetics--Used Resin (Source: Reference 9)... 4-14 Figure 4-5 Equilibrium Sodium Capacity as a Function of pH ... 4-24

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Figure 4-6 In-Bed Sodium Concentrations Profile (Source: Reference 10) ... 4-25 Figure 4-7 Roadmap for Condensate Polisher Justification... 4-40

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1-1

1

PRINCIPLES OF CONDENSATE POLISHING

Both fossil and nuclear plants make great demands on the purity of the water used for steam generation. Condensate polishing improves the quality of feedwater by using ion exchange to remove soluble species and filtration to remove insoluble species.

Basics

Condensate polishing uses ion exchange processes to treat cycle condensate being returned to the boiler as feedwater. Ion exchange resin temperature limitations require the treatment system to be located in the lower temperature areas of the cycle.

Condensate polishing is accomplished by treating condensate with ion exchange resin. In the United States, polishing is generally accomplished by using either mixed bed or powdered resin systems. Outside the United States more extensive treatment is used with a wider variety of processes, including cartridge filtration, single resin polishing, cation bed prefilters, and combination systems. In Europe, filtration is often applied ahead of mixed bed units, and there has recently been some increased in and use of filtration in United States plants.

Mixed bed systems normally use a mixture of bead type strong acid cation resin and strong base anion resin. The resin is contained in service vessels which treat the

condensate at a relatively high specific flow rate (high rate per ft3

(l/s) of resin) as the higher rates improve filtration and reduce the number of vessels and the amount of resin required. Normally, several vessels are used in parallel. When exhausted, the resin is generally transferred to external regeneration vessels for cleaning and regeneration. Usually a spare charge of resin is stored in one of the regeneration vessels. A schematic of a typical mixed bed condensate polishing system is shown on Figure 1-1.

Powdered resin polishing uses finely ground ion exchange resins as precoat material. The precoat material is deposited in a thin layer upon septa, which are contained in a service vessel. The condensate is passed through the precoat for both filtration and ion exchange. Once the precoat is exhausted of ion exchange or filtration capacity, the precoat is removed from the septa by backwashing. The spent powdered resin precoat is then discarded. Figure 1-2 schematically shows a typical powdered resin condensate polishing system.

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Principles of Condensate Polishing

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1-3 Figure 1-2 Typical Powdered Resin Polishing System

Condensate polishing requires properly designed equipment, properly selected resin, well trained operators, and a comprehensive surveillance and monitoring program in order to maximize the potential benefits of condensate polishing. Each of these

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Principles of Condensate Polishing

Resin

An important component in condensate polishing is the resin used in the ion exchange process. Modern day ion exchange resins generally used for condensate polishing are synthetic organic polymer skeletons functionalized to provide ion exchange capability. Condensate polisher ion exchange resins typically are produced from

styrenedivinylbenzene (SDVB) copolymers. The SDVB copolymer consists of

polystyrene chains with divinylbenzene crosslinking between the styrene chains. The SDVB copolymer-based ion exchange resin has the advantage over most other synthetic polymers from a stability and capacity standpoint. The resin properties such as

hardness, swell, capacity, oxidation resistance, and organic leachables can be modified

by variation in the divinylbenzene crosslink content1

.

Two types of ion exchange resins are normally used in condensate polishers: strong acid cation resin and strong base anion resin. These resins are synthesized by adding the appropriate functional group to the copolymer aromatic ring. Cation resin is formed by adding a sulfonic acid group. The maximum suggested operating temperature for hydrogen form cation resin is 80 to 105°C (180 to 220°F) for condensate polishing applications. A quaternary ammonium exchange site is formed on the copolymer to form strong base anion resin. Type 1 anion resin is normally used for condensate polishing applications because of its temperature stability. The recommended temperature limit is 60°C (140°F).

Physical Characteristics

Studies of the initial SDVB resins indicated that they had essentially homogeneous crosslinked polyelectrolyte gel structures with ion exchange sites distributed

throughout the particle as illustrated on Figure 1-3. The pore structures of these gel resins are determined by the distances between the polymer chains and crosslinks under any particular set of operating conditions. The pore structure, which has quite ill-defined, small diameter pores (<30 angstroms), generally is considered to be comprised

of molecular type pores2

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1-5 Figure 1-3 Typical Structure of Hydrated Gel Type Cation Resin

The copolymer substrate for ion exchange resins is synthesized as small spheres within a predetermined particle size range. Condensate polishing resin beads generally are in the 50 to 16 mesh range (0.3 to 1.2 mm diameter). (Table 1-1 shows the relation between mesh, mm, and microns.) The copolymer bead may be synthesized with either the gel or macroporous structure. Cation and anion resins can be produced from the copolymer by sulfonation or amination, respectively, of the polymer beads.

Powdered resins are made by grinding bead resins. The bead resins are ground to less than 200 US mesh particles (0.07 mm diameter). Gel type 8 and 10% crosslinked resins normally are ground to produce powdered resins used for condensate polishing applications.

Several of the major resin manufacturers have developed manufacturing techniques which allow them to produce ion exchange resin beads with a narrow particle size distribution range. The primary advantage claimed for these resins is better separation of mixed resins.

Ion exchange resins can be purchased in several different ionic forms. Hydrogen form cation resins and hydroxide form anion resins should be used for mixed bed condensate

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Principles of Condensate Polishing

polishers. Hydroxide form anion resin and either hydrogen or amine form cation resin are recommended for powdered resin polishers.

Resin Properties

The generic cycle diagram on Figure 1-4 shows the typical location of condensate polisher systems in the steam cycle feedwater train. The condensate polisher system serves two purposes. The resins remove suspended solids (primarily corrosion products of steam cycle materials of construction) by filtration and remove dissolved solids by ion exchange.

Filtration. Suspended solids in the condensate are primarily corrosion products. These are predominately iron oxides but also include other metal oxides, such as nickel and copper oxides. Ion exchange resins, either powdered resin precoats or deep bed mixed bead resins act as effective filters. The highly charged surfaces of anion and cation exchange resins make the resins a considerably more effective filter than uncharged media such as sand, charcoal, or other media. The mechanisms by which they remove particles of iron oxides are complex and have been intensely studied.

Table 1-1

Data Relating To US Standard Screen Scale

Sieve Opening Size Sieve (mesh)

Number Millimeter Inches Microns

10 2.0 0.0787 2000

12 1.68 0.0661 1680

14 1.41 0.0555 1410

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1-7 Table 1-1

Data Relating To US Standard Screen Scale

45 0.35 0.0138 350 50 0.297 0.0117 297 60 0.250 0.0098 250 70 0.210 0.0083 210 80 0.177 0.0070 177 100 0.149 0.0059 149 120 0.125 0.0049 125 140 0.105 0.0041 105 170 0.088 0.0035 88 200 0.074 0.0029 74 230 0.062 0.0024 62 270 0.053 0.0021 53 325 0.044 0.0017 44 400 0.37 0.0015 37

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1-9 beads influenced the filtration process. Corrosion product particle surface charge

generally is positive in low to neutral pH solutions and negative in high pH solutions and electrokinetic potentials for anion and cation resin are positive and negative,

respectively5

. The results suggest that boiling water reactor (BWR) corrosion products in neutral condensate are attracted to cation resin while pressurized water reactors (PWR) and fossil corrosion products in alkaline condensate are attracted to anion resin. Other

work33 suggests that magnetite from all volatile treatment (AVT) cycles is attracted to

cation resin while hydrated iron oxides bridge both cation and anion resins. Work at a PWR with cation-mixed bed system shows that 90% of the iron crud under startup

conditions is removed by the cation beds9

. Regardless of the mechanisms, experience has shown that mixed bed resins are effective filters.

In-depth filtration is obtained in condensate polisher deep beds because the flow rate is sufficiently high to avoid filtration only on the inlet surface of the bed. In-depth

filtration increases the particulate filtration capacity of the bed to a given pressure drop across the bed.

Corrosion product removal efficiencies for approximately 3 ft deep mixed resin fossil and PWR condensate polishers, using all-volatile treatment (AVT), are in the range of 60

to 90% for iron, copper, and nickel4, 6

. The cation to anion resin ratio for PWR and fossil stations generally is 2 to 1 by volume (approximately 4 to 1 equivalence ratio) to

maximize the time required for the pH additive to exhaust hydrogen form cation resin (hydrogen cycle operation).

Decreasing resin bead size improves filtration but also increases bed pressure drop. Condensate polisher resin vendors normally recommend 16 to 40 U.S. mesh (1.19 to 0.42 mm) cation resin and 20 to 50 US mesh (0.84 and 0.30 mm) anion resin. These mesh sizes give a reasonable compromise between pressure differential and properties important for ion exchange, such as kinetics, hydraulic separation, etc. Pilot studies showed little difference between gel and macroporous resins for filtration of fossil

station corrosion products4. The same study indicated that uniform particle size resin

filtration performance in fossil plant condensate polishers was essentially the same as

other resin systems4

. The filtration efficiency for crystalline corrosion products in alkaline fossil and PWR station condensate does not appear to be affected significantly by the type of condensate polisher resin. Fossil and PWR stations with deep bed

polishers usually emphasize ion exchange more than filtration when selecting resins. Condensate and feedwater systems of BWRs are constructed of all-ferrous materials and operate at neutral pH with oxygen present. Consequently, most BWRs have a

significant amount of amorphous iron oxide along with the other forms of iron7.

Amorphous iron is more difficult to remove than crystalline corrosion products because

it is removed by adsorption on resin bead surfaces rather than filtration7

. Maintenance of the 2 ppb feedwater iron concentration guideline value at US BWRs is difficult

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new, potentially useful 6% crosslinked cation resin with different morphology than that of a typical gel resin has recently been developed which shows promise of improved

BWR corrosion product removal efficiencies8

. However, release of sulfur bearing compounds from such resins may limit use of currently available resins.

During post-outage plant startups or cycling operation at fossil and PWR stations, significant quantities of amorphous corrosion products may be present in the steam cycle. Startup operation with hydrogen form cation resin should improve amorphous corrosion product removal. Reduced polisher flow rates permit time for adsorption of amorphous corrosion products on the resin surfaces and may improve removal

efficiency9. However, station evaluation is necessary because the nature and quantity of

corrosion products differ from one station to another.

Powdered Resin Precoat Filters. Condensate filter demineralizers (FDs) are excellent filters when properly precoated. A good FD precoat also operates as a depth filter (body as opposed to surface). Initially, the precoat has high porosity and strong electrostatic activity. Corrosion product particles smaller than the precoat pores enter the precoat layer and are electrostatically adsorbed by the ion exchange resin. Most filtration occurs in the body of the precoat and the removal efficiency is superior to bead resin because

of the large resin surface area and small precoat pore size.10

As particulates are adsorbed in the precoat and cation resin is exhausted by ion exchange, the resin electrostatic charge is neutralized and cation resin pH increases. The precoat then separates into

smaller floc clumps and precoat porosity decreases.10

Eventually the loss of porosity and corrosion product oxide precipitated in the resin interstices because of increasing pH, prevents particulates from entering the precoat, and they are trapped on the surface of the precoat layer. The surface filtration blinds the precoat surface and pressure drop

across the filter rapidly increase. A typical operating curve is shown on Figure 1-5.10

Powdered resin condensate polisher vendors generally recommend a 20 to 25 psi differential pressure endpoint.

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1-11 Figure 1-5 Filter Demineralizer Differential Pressure Behavior

(Source: Reference 10)

The precoats on FDs are more effective for iron removal than are deep beds, but the thin precoat provides only limited ion exchange capacity. Particulate corrosion product removal efficiencies of 80 to 99% for iron and copper are similar for fossil and PWR

polishers6, 11. Generally, corrosion product removal for BWRs, which maintain neutral

pH in the presence of dissolved oxygen, improves with increasing cation to anion resin ratio in the precoat5, 10

. Cation to anion resin ratios (dry weight basis) recommended by resin vendors vary between 2 to 1 and 4 to 5 (chemically equivalent). In some cases, a resin/cellulose fiber mixture or a resin precoat with fiber overlay is used to improve FD

run lengths and reduce precoat cracking12. Ion exchange fibers currently are being used

as an alternative at some plants.

Ion Exchange. Strong acid cation resins are comparable in acid strength to hydrochloric

acid and will form stable ionic bonds with most cations13

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resins are comparable to sodium hydroxide and will form stable bonds with most

anions13. The only exceptions are ions with complex structures or organic ions which are

too large or are hindered from entering the interior of the resin particles. However, not all bonds between the resins and different ions are of equal strength. All ion exchange resins have preferences for different ions which are referred to as resin selectivities.

Selectivity. At concentrations below one-tenth normal, divalent ion selectivity is higher than that for monovalent ions. Trivalent selectivity is the highest. A qualitative example of strong acid cation resin selectivity in decreasing order is as follows:

Fe+++ >Ca++ >Fe++ >Ni++ >Cu++ >Mg++ >K+ >NH4 +

>Na+ >H+

The selectivity of resins for the morpholinium ion generally is less than for ammonium ion and varies with resin type.

Similarly, for Type I strong base anion resin: SO4 = >CO3 = >NO3 >Cl- >HCO3 > CHOO- >CH3COO >F- >OH

-These selectivities, which are for low flow rate operation, may not be apparent for high flow rate condensate polishers because of ion exchange kinetic effects.

The effect of selectivity on the movement of ions through cation and anion exchange beds at low flow rates is shown on Figure 1-6. The lower selectivity ions exchanged on the resin are replaced by the ions with higher selectivity ions so that the ions form bands on the resin as the resin bed exhaustion progresses. As the resin bed exhaustion proceeds, the ions with lower selectivity move further along the bed in the direction of the flow path. For beds with nonuniform flow across the surface of the resin bed, the resin exhausts faster in the area of high linear flow (and is therefore exposed to higher amounts of exhausting ion) than for the lower flow areas (Figure 1-6b). Ion exchange in mixed beds is more complicated since exhausting either the anion or cation component influences the performance of the other resin. Also, kinetics become important at condensate polishing flow rates and will have an effect on the ion distribution in the

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1-13 Figure 1-6 Effect of Selectivity on Ion Movement Through Ion Exchange Beds The selectivity coefficient is used to express the relative affinity for exchange of two ions by ion exchange resin. For example, the following shows the exchange of sodium ions by hydrogen form cation resin:

Na+ +RH↔H RNa+ (eq. 1)

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K [RNa][H ] [RH][Na ] 1.5 H Na = = + + (eq. 2)

Similarly, expressions for other exchange reactions can be developed, such as the one describing sodium-ammonia exchange in ammonia form operation:

K RNa][NH RNH ][Na NH Na 4 + 4 + 4 = = [ ] [ ] 0 8. (eq. 3) K [RCl][OH ] [ROH][Cl ] 1.7 OH Cl == − (eq. 4) where:

Kyx = Equilibrium coefficient for ion exchange of “x” ions on “y” y

form resin Rx = Concentration of “x” ion on the resin, eq/L

H+

= Solution hydrogen ion concentration at equilibrium, eq/L Na+

= Solution sodium ion concentration at equilibrium, eq/L

NH4

+

= Solution ammonia ion concentration at equilibrium, eq/L

Cl- = Solution chloride ion concentration at equilibrium, eq/L

OH

= Solution hydroxide ion concentration at equilibrium, eq/L

Typical sodium selectivity coefficients relative to hydrogen, ammonium, and morpholinium are given in Table 1-2. Cation resin hydrogen and sodium-organic amine selectivities increase with increasing cation resin crosslinkage and

decrease with increasing sodium exchanged on the resin14,15,16

. In addition, the sodium-morpholinium selectivity of 20% crosslinked resin increases with increasing solution

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1-15 Table 1-2

Cation Resin Sodium Selectivities at Low Sodium Concentrationa

Sodium Selectivity Coefficient for Indicated Type of Resina

Resin Ionic Form 8% Gel 10% Gel 12% Macro 20% Macro

Hydrogen 1.5 1.5 1 to 2.2 2 to 4

Ammonium 0.8 0.8 0.8 0.8

Morpholinuim -- 1.0 2 to 3 12 to 35

a

References 15 and 16.

Capacity. Either gel-type or macroporous bead resins can be used in condensate polishers, as listed in Table 1-3. Cation resin wet volume capacities vary between 1.65 and 2.1 meq/ml. Macroporous resins generally exhibit the lower capacities because the resin beads are 10 to 30% pores, by volume. Similarly, the anion resin capacities range from 0.8 to 1.1, with the macroporous form usually having the lower capacities.

The new resin capacities are important for polisher systems that replace exhausted resins with new resins. The higher capacities generally should decrease resin

replacement frequency, although capacity is not always the controlling factor. When resins are regenerated, the recovery of hydrogen or hydroxide capacity achieved during regeneration (operating capacity) is more important than initial, new resin capacity. Operating capacities are dependent on the quantity of regenerant used, the resin type, and contaminant loading.

Kinetics. Bead resin kinetic performance will deteriorate with extended use because of contaminant accumulation on the bead surfaces and capacity degradation. Resin bead fouling may be a problem for regenerated resins and for BWR resins which are cleaned regularly but not regenerated. Since powdered resins are used only for one cycle, powdered resins are not subject to long-term fouling and capacity loss problems. Anion resins are susceptible to loss of strong base capacity (salt splitting capacity) as well as fouling by organics and iron. These effects reduce the usable capacity and increase anionic slip through the bed. At the normal condensate polisher design flow

rate of 50 gpm/ft2

(2040 liters/m2

-min), anion resins are operating near their kinetic limit17

. Therefore, it is important that the best available resin is used, and the resin

performance is tested regularly. Accumulation of organic or iron foulants on anion resin beads also increase bead density, making the anion resin more difficult to separate from

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the cation resin prior to mixed bed regeneration. However, the major difficulties in separation of cation and anion resins relate to equipment design and operation. Iron oxides removed by the condensate polisher sometimes can accumulate on cation resin beads. This surface fouling degrades cation kinetics and possibly filtering

efficiency. Vigorous scrubbing and backwashing during regeneration or thorough ultrasonic cleaning will minimize corrosion product fouling. Cation resin kinetics generally do not degrade as fast as anion resin kinetics and, therefore, usually are not a serious problem. Decrosslinking of cation resin as it is oxidized in continued service and/or incomplete polymerization during the manufacturing process can be a source of organic sulfonates which foul the anion resin. Regular testing of cation and anion resin is important to identify possible problems and to determine the advisability of resin replacement.

Deep Bed Resin Regeneration

Ion exchange of condensate impurities eventually will exhaust the resin capacity sufficiently that resin replacement or regeneration is required. BWRs in the United States currently replace exhausted deep bed polisher resin with new resin. Fossil and PWR station normally regenerate exhausted cation and anion resins with sulfuric acid and sodium hydroxide, respectively. PWR plants normally regenerate the polisher beds at the ammonia or amine break on those stations employing volatile amines. This is in order to maintain low steam generator impurity levels. Drum boiler fossil station

polisher effluent impurity levels are somewhat less restrictive so that operation through the cation resin transition from hydrogen to ammonium form is practiced at some stations. The operation of the regeneration systems is covered in Chapter 4. The following discussion is limited to resin concerns.

Table 1-3

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1-17 Table 1-3

Ion Exchange Resin Capacities

Type Cross Linkage Ionic Form Capacity, meq/mL

Anion Resins Gel -- OH 1.1 Porous Gel OH 1.0 Macroporous -- OH 0.8-1.0

Cation Resin Regeneration

Sulfuric acid normally is used to regenerate cation resin to the hydrogen form. Some foreign plants use hydrochloric acid which removes corrosion products from the resin more effectively than does sulfuric acid. However, plants designed for sulfuric acid regeneration cannot use hydrochloric acid without some changes in regeneration

system materials18

. Resin vendors recommend sulfuric acid concentrations of 4 to 10% by weight. As shown on Figures 1-7 and 1-8, elution of sodium from cation resin

becomes more difficult with increasing divinylbenzene crosslinking 15, 19

. Similarly, the difficulty of regenerating ammonium form resin increases with crosslinkage.

Consequently, gel type cation resins with 8 to 10% crosslinkage require less acid to recover a given capacity than macroporous resins with 12 to 20% crosslinking. Typical curves for the regeneration of sodium and ammonium form cation resin are

given on Figure 1-920. Regeneration efficiency decreases with increasing fraction of

hydrogen form resin and decreases rapidly above approximately 10 lb acid/ft3

. More complete removal of ionic contaminants leads to longer polisher service cycles and lower ionic leakage.

Low sodium leakage can be easily achieved during hydrogen cycle operation. However,

ammonium cycle operation requires very low resin sodium contamination21

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1-19 Figure 1-8 Elution of Sodium From Cation Resin (Source: Reference 15)

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1-21 removed. In this process, the sodium hydroxide solution also functions as the anion resin regenerant.

Chloride elution curves for various new, Type I strong base anion resins are shown on Figure 1-2022

. Chloride is difficult to remove from Type I anion resin. In some instances, a two-stage displacement regeneration is used for anion resin to remove chloride. The chloride is displaced with either sulfate or carbonate. The sulfate or carbonate form resin is then conventionally regenerated with sodium hydroxide. This is a method typically used by resin suppliers to convert chloride form resin to hydroxide form resin. Sulfate removal efficiency increases with increasing sodium hydroxide regenerant concentration23.

Resin Ratio

The relative quantity of cation and anion resin in mixed bed polishers commonly is expressed as a volume ratio. The equivalence and weight ratios depend on the

characteristics of the particular resins. The volume ratio can be converted to equivalence ratio by multiplying the resin volume by the wet volume capacities for specific resins. Similarly, weight ratios are calculated by multiplying the volume of resin times density. In plants using amines for condensate and feedwater conditioning, such as fossil units and PWRs, the operating time to ammonia breakthrough decreases with increasing pH and increases with cation resin operating capacity and cation to anion resin ratio. In this case, a 2 to 1 cation to anion volume ratio appears to offer a reasonable compromise between run length and anion exchange efficiency. This ratio, on a chemical equivalence basis, may be as high as 4:1 to allow a longer period of operation prior to exhaustion of the cation resin to amine. For example, for a station operating with ammonia for pH

control, a cation to anion resin volume ratio of 2:1, a bed flow rate of 50 gpm/ft2 (2040

liters/m2

-min) and a 3 ft (0.9 meter) deep bed, exhaustion of the cation resin by

ammonia leads to ammonium breakthrough in 11 to 15 days at pH 9.0 and 3 to 4 days at pH 9.4.

In systems equipped with cation beds followed by mixed beds, the pH control additive and cation impurities are removed by the upstream cation bed, thus requiring primarily anion impurity removal by the mixed bed. Therefore, a mixed bed cation to anion

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1-23 In neutral water systems like BWR systems, only condensate impurity ions need to be removed, a 1 to 1 equivalence ratio is normally used. In this case, a chemically

equivalent resin ratio (cation to anion resin volume ratio of approximately 2 to 3) is preferred for ionic removal, but other resin ratios may be selected to improve corrosion product removal. When other than a chemically equivalent bed is employed, extreme caution is needed to prevent development of highly acidic or caustic chemistries in the reactor vessel during periods of significant condenser in-leakage.

In BWRs, the resins are used on a throw-away basis; i.e., the resins are replaced prior to or subsequent to reaching kinetic, pressure drop or exhaustion limits. However, the resins are intermittently cleaned, generally with an ultrasonic resin cleaner (refer to Figure 1-18) to remove suspended corrosion products and resin fines, thereby minimizing long-term pressure drop buildup.

Recommended resin ratios are summarized in Chapter 4.

Polisher Vessel Design

Mixed Bed Service Vessels

A schematic of a typical mixed bed condensate demineralizer system and associated regeneration equipment was shown on Figure 1-1. In this approach, condensate is passed through a 3 to 4 foot deep bed of 20 to 50 mesh bead resin to remove ionic and particulate impurities. Process vessels may be spherical or cylindrical. The condensate

flow rate generally is maintained at 40 to 60 gpm/ft2 (1630 to 2450 L/m2-min) of bed

cross-sectional area.

Examples of typical polisher vessels are shown on Figures 1-11 through 1-15. The distributors and underdrains shown in these figures generally can be used with either cylindrical or spherical vessels. Key design features of the vessels are discussed below.

Influent Water Distribution. Water distribution is affected by both the inlet distributor and the underdrain. The function of these is to provide uniform water flow across the surface area of the resin bed and thus uniform flow throughout the resin volume. The

condensate flow of about 50 gpm/ft2 (2040 L/m2-min) through the bed must be

distributed to prevent jets and eddies that fluidize the resin. The inlet distributors shown in Figure 1-11 and 1-13 should provide reasonable influent water distribution. The distributors shown on Figure 1-12, 1-14, and 1-15 potentially can cause jets and eddies which can fluidize the top of the resin bed. However, it should be noted that the minor turbulence caused by some distributors is dampened by the water column above the bed.

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Figure 1-11 Typical Spherical Condensate Polisher Vessel with Parallel Lateral Underdrain

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1-25 Figure 1-12 Typical Spherical Polisher Vessel with Convex Support Plate

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1-27 Figure 1-14 Typical Cylindrical Polisher Vessel with Drop Leg Underdrain

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Figure 1-15 Typical Cylindrical Polisher Vessel with Parallel Lateral Underdrain Resin fluidization allows particulate matter to penetrate into the bed and causes nonuniform flow over the bed area because of pressure drop variations through different depths of compacted resin. Only the packed resin will act effectively to filter particulate matter and remove ionic contaminants. Areas of high flow cause premature leakage of impurities. Figure 1-16 illustrates two different, adverse geometries caused by resin fluidization.

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1-29

resin exhaustion across the bed50. Resin capacity is lost when laterals are significantly

above the bottom of the resin bed as on Figure 1-15. In addition, underdrains with insufficient distribution capability cause high local velocities near takeoff points. These high local velocitions result in stagnant areas which lead to some decreased effluent water quality and resin utilization.

When exhausted resin is transferred to the regeneration system, complete resin removal from the polisher vessel is essential. Laterals or nozzles above the polisher vessel resin support, if not properly designed, can impede the removal of resin. Upflow of water through the underdrain, coupled with a supply of water to the vessel walls from a nozzle or distribution ring, will sluice the resin to the transfer pipe so that complete transfer of the exhausted resin can be achieved. If necessary, the vessel can be partially refilled and air sparged while draining to assist in the transfer.

Sight Glasses. Sight glasses are highly desirable to permit observation of the key steps in the condensate polisher operation. Proper water distribution and complete resin transfer can be verified only by viewing the inside of the polisher vessel. Clear

observation of the inside of the vessel can be accomplished only by internal lighting or light directed through one sight glass while one looks through another. However, some field experience indicates that site glass cracking and corrosion product deposition on the glass can be problems. Additionally, it is difficult to install proper sight glasses for high-pressure systems. Sight glass installation should assure that a smooth surface is maintained inside the service vessel; otherwise, resin may be trapped in the sight glass housing.

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1-31 the polisher vessel, although this is rarely used. Limited consideration has been given to the use of nitrogen rather than air in new installations to reduce anion resin exposure to carbon dioxide and to minimize the potential for resin contamination by oil.

Polisher Operation

Full flow rather than partial flow polishing is the most common and preferred approach to condensate polishing. Although pretreatment normally is not used, some stations have precoat or fixed media filters installed upstream of the mixed beds to improve corrosion product removal. In some PWRs and in many foreign fossil units, a cation resin bed is installed upstream of the mixed beds. The cation resin bed serves as a corrosion product prefilter and improves the ion exchange efficiency of the mixed bed by removing the pH control additive upstream of the mixed bed.

In some plants, polisher systems are designed only for partial condensate flow (20 to 30% of full power flow rate) and are used primarily to reduce suspended solids (corrosion products) and dissolved solids during startups. In other cases, only one or two beds of a full flow system are operated during normal power operation to control secondary cycle pH and minimize impurity levels.

Recycle

Prior to placing the vessel into service, the polisher vessel should be given a slow rinse to remove air-saturated water containing high ionic contaminant concentrations. This water should be discharged to waste if possible. After the slow rinse and before return to service, a recycle pump (Figure 1-17) should be used to recirculate condensate through the vessel for a fast rinse at least one half of the normal operating flow rate. A more typical practice is the use of recycle only, which has proved to be acceptable. Impurities released from freshly regenerated mixed beds, when they are put into service, generally are the result of ion exchange taking place in a resin layer at the

bottom on the bed24, 25

. The high flow rate recirculation system will transfer these contaminants to the top of the polisher bed, if recycle is routed back to the initiating vessel. Thus, chemistry transients caused by inadequately rinsed resins at the beginning of a new service cycle are minimized. Flushing and compaction of the resin bed during the fast rinse also improves initial particulate impurity removal, and reduces particulate release. Alternatively, a high flow rate recirculation to the hotwell provides similar benefits; however, the contaminants are distributed to all beds instead of returning to the same bed.

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Figure 1-17 Condensate Polisher Recycle

Polisher outlet water is used for the high flow rinse, when a local recycle pump is used, the rinse can continue for an extended time without exhausting the cation resin with

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1-33 an impurity leakage endpoint such as silica, sodium, or chloride, or to a specific

throughput. Operation past the transition from the hydrogen to ammonium form resin increases sodium and chloride concentrations and should be used only where stations have installed specific equipment or operational features to allow such operation. In all cases, the polisher bed service cycle should be terminated when bed effluent quality approaches the water quality limits (described in Chapter 2) or at the maximum allowable bed differential pressure.

BWR stations in the United States currently do not regenerate mixed bed resins. The resins are periodically cleaned and returned to service. The beds are taken out of service for cleaning according to time, volume throughput, or differential pressure. The resin cleaning cycle varies with polisher system operating parameters and is plant specific.

Flow Transients and Outages

Compaction of the resin bed during operation varies with bed flow rates as a result of pressure differential. The collection of particulate corrosion products in the bed further increases the pressure drop. The resin bed can expand with decrease in flow rate

allowing the corrosion products to penetrate deeper into the bed or be released in the effluent. Polisher bed flow changes, such as those which occur when a vessel is being added or removed from service or during condensate flow rate changes associated with power transients, should be made as slowly as possible.

During outages, all vessels containing resin should be filled with demineralized water. Cleaning and regeneration of the resin beds is optional during short outages but should be performed during major outages. Resin beds used for shutdown chemistry control in nuclear units generally should not be used during startup unless the resin is

regenerated or replaced. During refueling and extended maintenance outages, sampling the resins for analysis is recommended.

After a bed has been out of service, it must be rinsed by recycle to an acceptable effluent conductivity before being put in service. Resin regeneration or replacement is required if acceptable rinse conductivity cannot be achieved or if effluent purity is unacceptable in service.

Regeneration

This discussion of regeneration is based upon the conventional system external regeneration in three regeneration vessels. Variations from this conventional arrangement are discussed later.

The conventional regeneration system consists of three vessels: the cation

regeneration/resin separation vessel, anion regeneration vessel, and resin mix and storage vessel. Resin regeneration is initiated by transfer of exhausted resin from the

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polisher vessel to the cation vessel. After the resin is cleaned by air scrubbing or passing the resin through an ultrasonic resin cleaner (URC), it is backwashed to remove residual corrosion product particulates and resin fines and to hydraulically separate the anion resin from the cation resin. (Separation can be achieved since the anion resin has a lower density than the cation resin and is purchased with a smaller average particle size.) After separation, the anion resin is transferred to the anion vessel for caustic

regeneration, and the cation resin is acid-regenerated in the cation vessel. After the regenerated cation and anion resin fractions are rinsed with demineralized water, they are transferred to the resin mix and storage vessel. After air mixing, the mixed resin bed is rinsed to a low effluent conductivity and stored. When required, this bed is used to replace an exhausted resin bed in one of the process vessels. Each of these operations are described in more detail in the following section.

Resin Transfers

Resin transfers are accomplished by fluidizing the resin with high purity water and sluicing the resin to specially designed vessels in which resins are cleaned, separated, and regenerated. Complete resin transfer from the service vessel to the resin separation vessel is extremely important. In general, following bulk sluicing of the resin, an

additional step transferring the last of the resin from the service vessel is undertaken. This may be accomplished by using special spray nozzles or by splashing water in the service vessel. A high degree of completion of transfer is desirable in order to have the best effluent quality and resin capacity. Plants with the most stringent water quality requirements and planning to operate beyond amine breakthrough will need to achieve the higher levels of resin transfer completeness, e.g., >99.99%. Plants with less stringent effluent quality needs and operating only in the hydrogen cycle can be successful with achieving less complete resin transfers.

Resin Cleaning

Suspended solid present in the condensate are primarily corrosion products which collect on the surface of the resin beads. The corrosion products must be removed to

References

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