Electrochemical Water Processing E-Book

Ralph Zito

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 290

Veröffentlichungsjahr: 2012

Beschreibung

Even though most of the Earth's surface is covered with water, most of it is not directly usable for human consumption or applications. As the population increases and our general style of living standards increase, the importance useable water is becoming acute. This book addresses this issue with approaches to treating water sources that require removal of unwanted or dissolved substances. In particular, it covers various methods for removing dissolved ionic materials. There are numerous methods for accomplishing this end, and the book reviews most of them in some depth.

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Acknowledgements

Introduction

Chapter 1 Water Contaminants and Their Removal

1.1 Introduction

1.2 Technology, History, and Background

1.3 Application Areas: Electrochemical Technology Water Processing

Chapter 2 Basic Electrochemical and Physical Principles

2.1 Introduction

2.2 Acidity and Alkalinity, pH

2.3 Activity and Activity Coefficients

2.4 Equilibrium and Dissociation Constants

2.5 Electrode, or Half Cell Potential

2.6 Chemical Potential Definition

2.7 Concentration Potential

2.8 Equivalent Conductance

2.9 Free Energy and Equilibrium

2.10 Dissociation Constants

2.11 Ionic Conductance and Mobility

2.12 Osmotic Pressure

2.13 Diffusion (Flick’s Law)

Chapter 3 Systems Description: General Outlines of Basic Approaches

3.1 Electrodialysis

3.2 pH Control: Analytic Development

3.3 Biociding Technology

3.4 Ion Exchange Resin Regeneration System

3.5 Metals Reclamation

Chapter 4 Mathematical Analysis & Modeling Electrodialysis Systems

4.1 Electrodialysis: Descriptions and Definitions

4.2 Basic Assumptions and Operating Parameters

4.3 Parametric Analysis: Flow-Through Configuration

4.4 Flow-Through Design Exercises

4.5 Batch Process Analysis: Re-Circulating or Static Water Processing System

4.6 Design Exercises for Water Re-Circulation Systems

4.7 Cell Potential and Membrane Resistance Contributions

4.8 Diffusion Losses of Ions and Molecules Across Membranes

Chapter 5 System Design Exercises & Examples

5.1 Electrolytic Generation of Bromine and Chlorine: Design Procedures

5.2 Simple Estimate of Capital Equipment and Operating Cost of Electrochemical Desalination Apparatus

5.3 Cost Estimates Outline for an Electrodialysis De-ionizing System

Chapter 6 Applications Discussion

6.1 Demineralizer: Electrodialysis

6.2 Residential Water Softener

6.3 Electrical Water Processor Portable Design

Appendix A: Some Physical Constants and Conversion Factors

Appendix B: Conductance and Solubility

B.1 KCl Ionization Constants

Appendix C: Feeder Tube and Common Manifolding Losses

Appendix D: Variable Current Density

D.1 Current Density Variation

Appendix E: Mathematical Analysis: Water pH Control Cell and Ion Exchange Resin Regeneration

E.1 Analytic Approach

E.2 Special Case Evaluation - No Resins Present in System

E.3 Estimation of Resin Constants

E.4 Electrolytic Resistance of the System Water

E.5 Solution of the Simultaneous System Equations

E.6 Sample Solution of Operating System

Appendix F: Industrial Chlorination and Bromination Equipment Cost Estimates

F.1 Bromination Equipment List

F.2 Capital Cost Analysis

F.3 Operating Cost Analysis

F.4 Conclusions and Comments

References

Appendix G: Design Mathematics in Computer Format

G.1 Case A

G.2 Case B

G.3 Case C

Appendix H: Mathematics for Simple Electrochemical Biociding

Bibliography

Index

Also of Interest

Electrochemical Water Processing

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Preface

In recent years, the awareness of water needs and processing requirement has become an increasingly important topic. As the earth’s population increases the demand for “clean” water has become an even larger factor in residential as well as industrial and commercial costs. There are now almost no natural water sources that do not require some purification of one form or another to render them potable sources.

If the water impurities are ionic in nature, i.e., inorganic salts such as sodium chloride, calcium chloride, or iron sulfate, or inorganic acids such as sulfuric and hydrochloric etc., then the most effective method of moving these components about is by electrochemical means. Most substances dissolved in water do not lend themselves to be removed by filtration, as usually such ionic materials have been leached out of the ground supply. If the contaminants are non-ionized organic substances in solution, then there must be other means for their removal, and we will not treat the subject of their removal by chemical, distillation or filtration means.

The technology that will be described here is well known but it is hoped that some of the quantitative and systems fabrication aspects covered here will contribute to the increasing practicality of electrochemical methods in water treatment applications. Much of the methods discussed here are a direct outgrowth of our research and development work in energy storage. Electrode design and construction methods for single and multiple cell devices were first addressed in the development of energy storage cells and multi-cell modules.

As the title of this book indicates, the following pages represent a summary of the results of a number of years of R&D effort directed to a better understanding of some basic processes for water treatment as well as the development of practical methods for design of useful hardware. The information contained herein is presented in an informal manner, in much the same fashion that it was generated in the laboratory studies. It is sincerely hoped that this compendium of technical notes will add meaningfully to the body of information associated with electrochemical approaches to water treatment, and will encourage others to pursue these avenues more intensively.

Except for the review of some very basic mathematical relationships associated with chemical and physical processes, involving electric potential, molecular diffusion and solution pH, all of the material presented in this book is original.

The major purpose of this book is the presentation of a body of analytical and design information that the reader may find useful in the exploration of electrochemical technology as applied to water processing. Hopefully, the contents of this text will encourage and promote further development of electrochemical processing systems for consumer as well as industrial and commercial applications.

In our attempt to accomplish this end, the book has been organized into three main sections. They are:

1. General description of electrochemical processing and their application areas

2. Mathematical analysis of operating systems for design and optimization purposes

3. Design examples and procedures.

Most of the experimental work on various water treatment projects was done at GEL/TRL during the period between 1978 and 1988.

A short introduction to some very important and basic concepts is included at the beginning of the book and in Chapter 2 as a convenient review for the reader. The Appendices are also offered for some additional analytical and ancillary application information, without disrupting the arguments and descriptions in the main portion of the text.

The thread of the discussions to follow is to first identify the nature of the technology and to describe its various formats and uses. Then the book proceeds to develop an approach to mathematically treat the essential parameters associated with the principle mechanisms of ionic transport, electrolysis and diffusion. These developed mathematical tools are then applied to the preliminary design of a number of systems, serving as exercises for those that wish to carry on with their application in practical water processing problem-solving.

The fundamental equations that evolve in the analyses are listed in a reasonably convenient and accessible form so that the reader can place them into appropriate computer software programs for easy solution and graphing of data. I have tried to establish an obvious rationale throughout the book to minimize confusion and the obscuring of direction and purpose.

The Technology Research Laboratories, Inc. sponsored most of the analytical and experimental developments presented in the following pages. Some of the laboratory hardware and prototype systems were part of development projects funded by other industrial organizations for evaluation purposes.

Our purpose in writing this book is to present sufficient basic applications and information about electrodialysis so that the reader is able to develop his own designs and approaches to solving water management problems. We will treat a number of forms of electrochemical water treatment from pH control to desalination along with their many application potentials.

This book is concerned with the development of the basic principles and engineering design aspects of electrochemical water processing. The intent in writing this volume is to serve as handbooks for the further development of related products. It should provide most of the necessary physical and chemical background to enable the reader to proceed with his own mathematical computations and engineering designs and mathematical computations. He should be able to arrive at sizes, performance characteristics and some preliminary cost factors on the basis of the information presented in this volume.

No attempt is made in this book at covering the entire field of water treatment or reviewing the various competitive technologies associated with these methods. There are many excellent texts that have treated these subjects extensively, and have reviewed and summarized the work of numerous other investigators. There have been many texts that present excellent reviews of the state of the art in electrodialysis, reverse osmosis, filtration and distillation systems.

Some of the specific terms and physical constants employed in the analytic approaches are covered in Chapter 2. However, it is assumed that the reader is familiar with the basic concepts of physical chemistry and elementary inorganic chemistry. For those who are not so well versed in these scientific disciplines, the resultant equations developed in Chapter 4 and elsewhere in the book are still useable for purposes of calculating the design parameters for the water processing devices under discussion.

TRL, Inc. has performed the background work, a portion of which is covered by this book, over a ten-year period. The author, with over 35 years of research and development experience in related technical areas, has been principle investigator in most of the work represented in these pages.

Water treatment with the minimal use of chemical reagents will increasingly become the goal of most systems in the future. In some instances, the elimination entirely of chemical agents is possible.

A family of systems that provide means for controlling pH, biocide level and dissolved solids concentration in water have been studied as a result of the many years of electrochemical developments in the energy storage area at TRL. A larger portion of our attention here is devoted to the direct removal of dissolved, ionized materials in water via electrochemical (electrodialysis) separation.

As a final comment, it is important to note that this book is concerned primarily with methodology rather than the specifics of any one design or system configuration. Very little empirical data or materials’ properties information is contained herein. The specifics of component characteristics such as membranes, electrodes, and materials properties will be treated in another reference that is presently in preparation. This future text will also contain some empirical data on system performance as well as design and fabrication methods.

Many application possibilities are still available that are eminently suitable to electrochemical techniques.

I would like to express my sincere appreciation to Donald Morris, who performed many of the experiments and prototype design and fabrication, and for his invaluable assistance in organizing this information. Much of the discussion on biociding processes, and especially the sections that treat large-scale industrial water cooling systems was prepared by Catherine Middelberg as part of an application study at TRL, Inc.

Special gratitude is due to my wife, Min, for her encouragement and endurance with the labors of organizing the technical material for these volumes.

Ralph Zito

Port Orange, FL

January, 2011

Acknowledgements

The work represented as a summary of laboratory investigations, as well as the design, building and field testing of potentially viable and useful water treatment products took place over a period of a few years at TRL, Inc. in Durham, NC.

A number of different talents of various individuals participated in critical manners to bring about the net results contained in this book. Only a few of these people can be credited here. It required not only some scientific perceptivity, but also engineering and fabrication know-how to persistently pursue these projects. It is hoped that some of these developments and knowledge gained by the activities of these people will be useful to others in the commercializing of systems in the future. Generally, water must be treated in some manner due to the many problems that beset its use in applications where “uncontaminated water” is critical to our civilization.

Among the numerous contributors to this project, I would like to particularly cite Dale Jones for his steadfast support in overcoming some difficult situations, Don Morris for his unparalleled contributions to design and hardware fabrication. And many thanks to Patricia Pearson and Sara Tortora who provided order to the laboratory; orderly enough to maintain the necessary continuity for any work to succeed with a staff of usually over a dozen individual contributors. Also, without their imposed discipline and encouragement we almost certainly would not have completed these tasks.

Introduction

Water has been in plentiful supply on this planet since it long ago cooled down and the oceans were formed. Despite the fact that over 70% of the Earth’s surface is covered by water, the water needed for various life sustaining purposes is either unavailable at the required locations, or it is too contaminated for practical use.

Obtaining fresh water is almost invariably a costly endeavor. The natural pools and lakes have gone to a great extent, relatively free of contaminants, and scattered everywhere in the communities of this country. High population densities coupled with increased demands and pollution by industry and residents have left these idyllic scenes far behind us. Now, we must either transport water from a few remaining sources at higher elevations such as melting snow on mountains or lakes at or near mountaintops.

Roman cross country aqueduct.

The ancient Romans took advantage of such sources in Europe by building aqueducts (viaducts) to provide water to remote farms and villages by gravity feed. They spanned obstructions and valleys with gradually diminishing height to sustain the driving force of the mass of water being transported. There was little expense beyond the initial capital investment of the masonry, and of course, some continuing maintenance costs. These facilities were durable and had very long lives, as is evidenced by their existence today as functioning water lines.

Today, we must resort to other transportation mechanisms other than gravity. Now, pipelines with water pumps are more common, but trucking and shipping is even used in some areas where water is critical. Such means of provision are quite costly.

The only alternative to transporting water of good quality to other places of need is a purification or decontamination process of some sort. These methods, too, are costly depending upon the extent of processing necessary and the source of materials and energy. As in the case of transportation, energy for separation is necessary to produce useable water from contaminated sources. There are only a limited number of mechanisms that can be employed to remove unwanted substances from water, whether they are dissolved or simply as particulate matter in suspension. In the latter case, filtration of one form or another or sedimentation can solve these problems.

For those materials that are in solution, other methods must be employed, such as reverse osmosis, electrodialysis, or the old standby, distillation. Both distillation and RO will remove all solid matter in solution regardless of whether they are organic in nature, or inorganic, ionic materials. Distillation is the oldest method in existence, but it can be quite inefficient in terms of energy required per unit quantity of condensed water produced. Maintenance of boilers and evaporators can also be costly because of the solids left behind. The same is true for ED systems whose micro-porous membranes can become clogged with solid matter.

ED is a cleaner system in the sense that no solids are collected as such, but the process will only remove substances that produce ions when dissolved so that they will respond to electrical forces for the separation process. Hence, ED is limited to removing only inorganic materials. Depending upon the nature of the situation one or more of these systems might be employed in treating a single body of water.

It should be kept in mind that a minimum amount of energy is required to extract dissolved materials at the very least equivalent to their heats of solution. However, in practical systems that amount of energy is usually quite small compared to the dissipative factors of electrical resistance in ED devices, and mechanical resistances of RO devices. Desalination of sea water presents the greatest of all problems because of the very high concentrations of salt involved. Depending upon the form of energy available at a particular location where the fresh water supply is a problem, one of the preceding approaches is usually employed. If, for example, solar energy or cheap fuels are in great supply, distillation may very well be the method used in that location. Desalination should be receiving greater attention as a means of providing “fresh water” especially because seawater is so plentiful, and the demands are increasing so rapidly. The future will undoubtedly bring more conservation measures, but we may still be hard-pressed for better solutions to this ever-increasing problem.

In recent years, especially, many devices and gadgets have been offered for sale on the open market, claiming to be capable of “purifying” water for drinking and cooking purposes. Some of these offered products are, indeed, genuine and perform as advertised. Products such as those based upon the use of ion exchange resins and distillation are based upon real science.

However, numerous electrical devices on the market do not perform the tasks of which vendors claim they are capable. For example, ineffective devices include those that supposedly operate on the basis of some sort of magnetic field imposed on the water system via coils of wires that “polarize” or otherwise change the character of ionic species. These products are not based upon any known mechanism that would, in fact, separate unwanted materials in the water supply, or prevent mineral deposits from accumulating on the insides of pipes or hot water tanks in home or industrial water systems.

There are some simple rules that one can follow to determine whether these proffered products do indeed operate. One should consider the amount of energy required to remove a given quantity of maters, i.e., dissolved substances, from a given volume of water. Generally one can employ such simple estimates to determine the probability of successful operation. Most of these important issues are covered thoroughly in the text to follow.

There isn’t much question about the importance of water in every facet of our lives, specifically the necessity for good quality water. The issues covered here are largely concerned with the removal of unwanted dissolved substances in water—substances that are ionic and are usually inorganic salts, acids and bases of soluble materials. The most common of these is salt, i.e. sodium chloride, because of its abundance and global availability. Various competing methods for removing materials of this nature are reviewed, but the main emphasis is electrochemical approaches such as electrodialysis. Much of the book is an analysis of the performance, efficiency and configurations of these types of systems. Some information is provided about the materials of construction, but the main theme of the book is analytic in format.

Chapter 1

Water Contaminants and Their Removal

1.1 Introduction

This book is intended both as a tutorial presentation of basic principles of electrochemical water processing as well as a short working manual for the design and operation of electrochemical deposition cells and for electrodialysis devices.

Water quality for direct and indirect human uses has always been an important concern in the past, and continues on into the future. With the ever-increasing concentrations of population centers and the demands of the industry, that concern is growing continuously throughout the world.