High Electrical Resistance Ceramics E-Book
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HIGH ELECTRICAL RESISTANCE CREAMICS Pond and fly ash waste materials generated by thermal power stations pollute the environment; this book demonstrates how the utilization of these materials minimizes environmental pollution and conserves land for cultivation. This book highlights the preparation of ceramics using pond/fly ash. Since the mullite phase formed by heat treatment improves the properties of ceramics, current investigations will perhaps be the first attempt to develop ceramics using pond ash. The properties of components made with these developed ceramics are found to be comparable to those made with porcelain. The extensively reviewed chapters of this book illustrate the current status of research on these materials. At the end of each of the 10 chapters, conclusions are drawn which will benefit researchers working in this area. Subjects discussed include: * The fundamentals of thermal power plant wastes; * Different production methods of ceramics and various characterization techniques; * The preparation of ceramics from fly ash and fly ash/kaolin composite; * The production of ceramics using pond ash; * The preparation and characterization of geopolymer from pond ash and the preparation of pond ash composite; * Production of ceramic matrix composite (CMC) using pond ash and pyrophyllite; * The preparation of ceramics using pond ash and k-feldspar mixture. Audience The book will be used by civil engineers in the construction and ceramic industries as well as the industrial waste sector. Researchers in materials science, structural, civil and electrical engineering, environmental science, and ceramic engineering, will also have interest. Industries that have an interest include construction, electrical, and ceramic industries as well as pollution and waste sectors.
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Table of Contents
Cover
Series Page
Title Page
Copyright Page
Preface
1 Fundamentals of Thermal Power Plant Wastes-as Ceramic Backbone
1.1 Introduction
1.2 Thermal Power Plant Wastes
1.3 Generation of Thermal Power Plant Ashes
1.4 Nature and Composition of Thermal Power Plant Ashes
1.5 Characteristics of Thermal Power Plant Ashes
1.6 Causes of Resistance in Insulator
1.7 Resistance Measurement
1.8 Different Methods for Resistivity Measurement
1.9 Resistance Temperature Detector (RTDs)
1.10 Platinum Resistance Thermometer (PRTs)
1.11 Thermal Power Plant Wastes (i.e., Coal Ash) Management
1.12 Literatures Survey on Thermal Power Plant Wastes-Based Ceramics
1.13 Conclusions
Acknowledgements
References
2 Ceramic Production Methods and Basic Characterization Techniques
2.1 Introduction
2.2 Characterization Techniques
2.3 Conclusions
Acknowledgements
References
3 High Resistance Sintered Fly Ash (FA) Ceramics
3.1 Introduction
3.2 Experimental Details
3.3 Conclusions
Acknowledgements
References
4 High Resistance Sintered Fly Ash/Kaolin (FA/CC) Ceramics
4.1 Introduction
4.2 Experimental Section
4.3 Preparation of Test Samples
4.4 Characterization Techniques
4.5 Results and Discussion
4.6 Conclusions
Acknowledgements
References
5 High Resistance Pond Ash Geopolymer Ceramics
5.1 Introduction
5.2 Experimental Details
5.3 Test Methods
5.4 Results and Discussion
5.5 Conclusions
Acknowledgements
References
6 High Resistance Sintered Pond Ash Ceramics
6.1 Introduction
6.2 Experimental Details
6.3 Conclusions
Acknowledgements
References
7 High Resistance Sintered Pond Ash/Kaolin (PA/CC) Ceramics
7.1 Introduction
7.2 Experimental Details
7.3 Results and Discussion
7.4 Conclusions
Acknowledgements
References
8 High Resistance Sintered Pond Ash/Pyrophyllite (PA/PY) Ceramics
8.1 Introduction
8.2 Experimental Section
8.3 Preparation of PA/PY Composite Materials
8.4 Test Methods
8.5 Results and Discussion
8.6 Conclusions
Acknowledgements
References
9 High Resistance Sintered Pond Ash/k-Feldspar (PA/k-FD) Ceramics
9.1 Introduction
9.2 Experimental Details
9.3 Preparation of PA/FD Sintered Materials
9.4 Test Methods
9.5 Results and Discussion
9.6 Conclusions
Acknowledgements
References
10 Applications, Challenges and Opportunities of Industrial Waste Resources Ceramics
10.1 Introduction
10.2 Different Ways of Utilization of Waste
10.3 Glass
10.4 Glass-Ceramic (GC)
10.5 Mullite
10.6 Wollastonite
10.7 Cordierite
10.8 Silicon Carbide
10.9 Silicon Nitride
10.10 Ceramic Membranes
10.11 Challenges
10.12 Opportunity
10.13 Conclusions
Acknowledgments
References
Index
Also of Interest
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Normal range of chemical compositions for Fly ash produced from diff...
Table 1.2 Typical composition of Class F Fly Ash, Class C Fly Ash, and Portlan...
Table 1.3 Chemical composition of Bottom Ash (BA) [19].
Table 1.4 Some typical physical properties of bottom ash [21].
Table 1.5 Chemical composition of Pond Ash (PA) [11].
Table 1.6 Chemical and physical characteristics of pond ash.
Chapter 3
Table 3.1 Different constituents with percentage of as-received NALCO fly ash ...
Table 3.2 Different set of sintered fly ash based materials preparation.
Table 3.3 Crystallographic parameters of sintered fly ash [27].
Table 3.4 Resistivity value of as-received fly ash and processed fly ash [27] ...
Chapter 4
Table 4.1 Chemical composition of fly ash and kaolin [15].
Table 4.2 Compositions (%) of fly ash/CC composite materials preparation (sint...
Table 4.3 Resistivity value of fly ash, kaolin, fly ash/kaolin composites prep...
Chapter 5
Table 5.1 Chemical composition of pond ash (PA) in percentage (%) [26, 27].
Table 5.2 PA based geopolymer mixtures (Three samples of same compositions).
Table 5.3 Compressive strength of PA based geopolymer (Treatment combinations-...
Table 5.4 Wave number and peak assignment of as-received PA and PAGP [28, 29].
Table 5.5 Resistivity value of pond ash geopolymer materials [radius=1.5 cm an...
Chapter 6
Table 6.1 Presence of constituents with percentage (%) of NALCO pond ash [37].
Table 6.2 Elements present (with percentage) in EDS images (Figure 6.4).
Table 6.3 Structural information of pond ash based samples.
Table 6.4 Resistivity value of pond ash based sintered samples [radius=1.5 cm ...
Chapter 7
Table 7.1 Constituents with percentage (%) of processed pond ash and Kaolin.
Table 7.2 Compositions (%) of pond ash/CC composite materials preparation.
Table 7.3 Resistance value of pond ash/Kaolin based samples [radius=1.5 cm and...
Table 7.4 Resistance value of pond ash/Kaolin based samples [radius=1.5 cm and...
Table 7.5 Resistance value of pond ash/Kaolin based samples [radius=1.5 cm and...
Table 7.6 Structural information of pond ash/Kaolin based composite.
Chapter 8
Table 8.1 Constituents with percentage (%) of processed pond ash and pyrophyll...
Table 8.2 Compositions (%) of pond ash/PY materials preparation.
Table 8.3 Electrical resistivity value of pond ash/pyrophyllite (PA/PY) based ...
Table 8.4 Structural information of pond ash/pyrophillite composite with diffe...
Chapter 9
Table 9.1 Constituents with percentage (%) of as-processed pond ash and feldsp...
Table 9.2 Compositions (%) of pond ash/k-FD materials preparation.
Table 9.3 Resistance values of pond ash (sintered) and sintered pond ash/ k-Fe...
Table 9.4 Structural information of pond ash/k-Feldspar based samples.
Chapter 10
Table 10.1 Name of waste used in the composition of tiles [10].
List of Illustrations
Chapter 1
Figure 1.1 Optical micrograph of Fly ash (a) [5] and SEM image of Fly Ash (b) ...
Figure 1.2 Optical image of Bottom Ash (a) [8] and SEM image of Bottom Ash (b)...
Figure 1.3 Optical image of Pond Ash (a) [11] and SEM image of Pond Ash (b) [1...
Figure 1.4 Generation of ash at the power plants [14].
Figure 1.5 Schematic diagram of a simple resister [47].
Figure 1.6 Schematic diagram for resistivity measurement [50].
Figure 1.7 Schematic diagram of two probes electrical resistivity measurement ...
Figure 1.8 Schematic diagram of four probes electrical resistivity measurement...
Figure 1.9 Schematic diagram of Van-der Pauw electrical resistivity measuremen...
Chapter 2
Figure 2.1 Schematic representation of linear two probe set-up.
Chapter 3
Figure 3.1 Morphological investigation of as-received fly ash (a), FA sintered...
Figure 3.2 EDS spectrum of fly ash sintered at 900 °C (a), 1100 °C (b), 1200 °...
Figure 3.3 XRD analysis of as-received NALCO fly ash [27].
Figure 3.4 (a) XRD pattern of fly ash sintered at 900 °C (Quartz Phase) [27]. ...
Figure 3.5 FTIR spectrum of sintered fly ash at different temperatures (1000 °...
Chapter 4
Figure 4.1 Sintered fly ash (60%)/kaolin (40%) composite preparation flow char...
Figure 4.2 XRD plot of kaolin (a), fly ash (b), sintered fly ash/kaolin compos...
Figure 4.3 FTIR of fly ash (a), sintered fly ash/kaolin composite (b) [15].
Figure 4.4 FESEM images of fly ash (a), Kaolin (b), sintered fly ash/kaolin co...
Figure 4.5 EDS analyses of fly ash (a), kaolin (b), sintered fly ash/kaolin co...
Figure 4.6 TGA plot of fly ash/kaolin composite (60:40) [15].
Figure 4.7 Dielectric plot of fly ash/kaolin composite (C) [15].
Chapter 5
Figure 5.1 Schematic diagram of preparation process of GP from pond ash.
Figure 5.2 XRD patterns of: (a) As-received NALCO pond ash, (b) Pond ash based...
Figure 5.3 HRTEM image of PA (lower magnification, a), HRTEM image of PA (high...
Figure 5.4 HRTEM image of PA based GP curried at 70 °C for 24h (lower magnific...
Figure 5.5 FESEM image of PA (a), EDS of PA (b), PA based GP curried at 70 °C ...
Figure 5.6 Nitrogen adsorption/desorption isotherms of pond ash (a) and pond a...
Chapter 6
Figure 6.1 Optical image of pond ash (a) and dextrin (b).
Figure 6.2 (Scheme 6.1) Flow chart for preparation of sintered pond ash based ...
Figure 6.3 Morphological investigation of as-processed pond ash (a), pond ash ...
Figure 6.4 EDS spectrum of as-processed pond ash (a), sintered PA at 900 °C (b...
Figure 6.5 XRD pattern of unsintered pond ash and sintered pond ash (indicated...
Figure 6.6 FTIR spectra of pond (sintered at 1300 °C).
Figure 6.7 Nitrogen adsorption/desorption isotherms of pond ash (a) 1100 °C si...
Chapter 7
Figure 7.1 Optical image of pond ash (a), Kaolin (b) and Dextrin (c).
Figure 7.2 Flow chart for preparation of sintered pond ash/kaolin based compos...
Figure 7.3 XRD pattern of pond ash (a), PA(60%)/CC(40%) composite (b), PA(70%)...
Figure 7.4 Optical image of pond ash/CC (60%-40%) based composite.
Figure 7.5 PA (a), Kaolin (b), PA/kaolin (lower magnification, c), PA/kaolin (...
Figure 7.6 EDS spectrum of pond ash/Kaolin (60:40) composite.
Figure 7.7 TEM images of pond ash (a) and pond ash (60%)/kaolin (40%) sintered...
Figure 7.8 SAD profile of pond ash (a) and pond ash (60%)/kaolin (40%) sintere...
Figure 7.9 Sintered pond ash (a) and pond ash (60%)/kaolin (40%) composite (b)...
Chapter 8
Figure 8.1 Optical image of pond ash (a), Dextrin (b) and pyrophyllite (c).
Figure 8.2 Flow chart for preparation of sintered PA/PY (50:50) composite mate...
Figure 8.3 FTIR spectrum of pond ash (60%)/pyrophillite (40%) composite.
Figure 8.4 Pond ash (a), sintered pond ash (b), pond ash-pyrophillite (60-40 (...
Figure 8.5 Pond ash (60%)/pyrophillite (40%) composite.
Figure 8.6 Pond ash (a), pyrophillite (b), pond ash (60%)/pyrophillite (40%) w...
Figure 8.7 EDS spectrum of pond ash/pyrophyllite (60:40) composite sintered at...
Figure 8.8 TEM image of raw pond ash (a) and PA/PY (60:40) composite sintered ...
Figure 8.9 SAD pattern of raw pond ash (a) and PA/PY (60:40) composite sintere...
Chapter 9
Figure 9.1 Optical image of pond ash (a), dextrin (b), and k-feldspar (c).
Figure 9.2 (Scheme 2) Flow chart for preparation of sintered pond ash/k-Feldsp...
Figure 9.3 Pond ash (a), k-Feldspar (b), Pond ash /k-FD(50:50, c), Pond ash/k-...
Figure 9.4 Optical micrograph of pond ash/k-FD composite.
Figure 9.5 FESEM image of pure PA (a), Pure k-feldspar (b), PA/k-feldspar comp...
Figure 9.6 EDS spectrum of pond ash/k-feldspar (60:40) composite sintered at 1...
Figure 9.7 HRTEM image (a) and SAD pattern (b) of pond ash.
Figure 9.8 TEM image (a) and SAD pattern (b) of pond ash/k-Feldspar (60/40) co...
Figure 9.9 FTIR spectrum of Feldspar (a), pond ash (b), and pond ash/k-Feldspa...
Guide
Cover Page
Series Page
Title Page
Copyright Page
Preface
Table of Contents
Begin Reading
Index
Also of Interest
WILEY END USER LICENSE AGREEMENT
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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
High Electrical Resistance Ceramics
Thermal Power Plants Waste Resources
Muktikanta PanigrahiRatan Indu Ganguly
and
Radha Raman Dash
This edition first published 2023 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2023 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data
ISBN 978-1-394-19993-8
Cover image: Pixabay.ComCover design by Russell Richardson
Preface
The pond and fly ash generated by thermal power stations are waste materials which pollute the environment. Dumping these materials on land spoils its cultivability. Therefore, the present challenge for scientists and researchers is the fruitful utilization of these materials. This will serve the dual purpose of minimizing environmental pollution and conserving land for cultivation.
The major constituents of fly ash (FA), pond ash (PA), and bottom ash (BA) are SiO2, Al2O3, and Fe2O3. Their composition, however, will depend on the nature of coal used by thermal power plants. The present problems associated with these materials can be solved by minimizing power generation through thermal routes with alternative power generation methods such as solar energy, nuclear energy, wind energy, hydraulic electricity, etc. However, in reality, due to increasing urbanization and industrialization, power requirements are also increasing, which are being met by thermal power generation plants. Hence, the production of these materials (FA/PA/BA) is inevitable. Therefore, investigations are currently being conducted in an effort to utilize pond and fly ash to produce a novel material called ceramics, in which kaolin/pyrophyllite/feldspar are mixed with pond/fly ash. These thermal power plant waste-based ceramics can replace porcelain-based ceramics. Since permanent ceramic components can be developed using these wastes, it is no wonder why some scientists are trying to develop ceramics utilizing them.
This book highlights the preparation of ceramics using pond/fly ash. Since the mullite phase formed by heat treatment improves the properties of ceramics, current investigations will perhaps be the first attempt to develop ceramics using pond ash. The properties of components made with these developed ceramics are found to be comparable to those made with porcelain. Since evidence has shown the formation of mullite after heat treatment, systematic investigations are being carried out to understand phase transformation during thermal treatment. Upon the performance of these materials above ambient temperature being evaluated, results have indicated the possible replacement of porcelain with these newly invented ceramics prepared with pond ash.
The extensively reviewed chapters of this book illustrate the current status of research on these materials. At the end of each of the 10 chapters, conclusions are drawn which will benefit researchers working in this area. Chapter 1 discusses the fundamentals of thermal power plant wastes, which are the backbone of ceramics. Different production methods of ceramics and various characterization techniques are discussed in Chapter 2. This will help new researchers to progress in further development of new ceramics from waste on a laboratory scale. Chapter 3 describes the preparation of ceramics from fly ash. The preparation of ceramics from fly ash/kaolin composite is discussed in Chapter 4; and Chapter 5 is devoted to the production of ceramics using pond ash. Chapter 6 describes the preparation and characterization of geopolymer from pond ash; and the preparation of pond ash composite (pond ash and kaolin) is described in Chapter 7. Chapter 8 deals with the production of ceramic matrix composite (CMC) using pond ash and pyrophyllite, while Chapter 9 discusses the preparation of ceramics using pond ash and k-feldspar mixture. The book concludes with a discussion of the applications, challenges and opportunities regarding ceramics from industrial waste resources in Chapter 10.
The Authors
June 2023
1Fundamentals of Thermal Power Plant Wastes-as Ceramic Backbone
Muktikanta Panigrahi1*, Ratan Indu Ganguly2 and Radha Raman Dash3
1Department of Materials Science, Maharaja Sriram Chandra BhanjaDeo University, Balasore, Odisha, India
2Department of Metallurgical Engineering, National Institute of Technology, Raurkela, Odisha, India
3CSIR-National Metallurgical Laboratory, Jamshedpur, Jharkhand, India
Abstract
The chapter has provided extensive reviews on production of fly ash/pond ash/ bottom ash globally. Properties of different minerals present in fly ash are discussed. By adjustment of chemical composition of fly ash, useful dielectric materials can be developed by proper treatment. Since compositions of pond ash, bottom ash, and fly ash depend on resource material like coal, therefore, judicial selection of compositions and their adjustment is very important for developing dielectric materials.
Keywords: Energy, thermal power point waste, fly ash, bottom ash, pond ash, ceramics, electrical resistance measurement, two point method, four point method, Van-der Pauw method, thermal waste managements
1.1 Introduction
Energy is the backbone of a country. Sustainable development and growth of industries largely depend on energy. Therefore, it plays a vital role for the economic development of a nation. A developing country like India is still dependent on natural reserves like coal. Even in the 21st century, coal is the first choice as a fuel for electricity generation [1]. In any coal based thermal power plants, Coal fly ash generated is considered to be a by-product [2]. Presence of fly ash in air (in micro fine level) affects human health. However, residual burnt product i.e. ash is considered to be a waste. Dumping of ash into a pond saves air pollution but at the same time it causes water pollution. Additionally, some of the undesirable elements such as Sb, As, Pb etc cause problems for living creatures in water.
Due to advancement in technologies, environmental pollution is enhanced. In addition, there is global warming which affects the climate and environment. Therefore, the Government is making policies to control pollution by consuming wastes for development of useful products.
Financial support need be sanctioned to develop value-added products from these wastes i.e., fly ash, bottom ash and pond ash.
Based on their mineralogical properties, these materials can be used for developing tiles, zeolite, geopolymer, etc.
In the present chapter discussion has been made on coal-based thermal power plants, ash production, properties, and utilization.
1.2 Thermal Power Plant Wastes
Due to rapid urbanization and industrialization in developing countries [3], natural reserves are being exhausted to be increasing demand for production of energy. In 21st century, coal is the prime choice for generating electricity. During electricity production in thermal power plants, Coal ash is produced as waste [2]. Waste increases environmental pollution. It is to ensure that sustainable growth and development of urban cities need a receptive, innovative, and productive environment for a better quality of life.
1.3 Generation of Thermal Power Plant Ashes
Fly ash is generated from thermal power plant and steam producing plants [4]. Normally, coal is blown with air in ignition chamber. Quickly, it is heated where there is formation of liquid which causes deposit of mineral. However, the pipe gas and creating the liquid mineral builds up to solidify and structure slag. Coarse particles present in coal stay back in bottom of the heating chamber and suspended particles are blown with air to the atmosphere. This hot blown air contains fine particles of minerals with unburnt carbon are passed through an electrostatic precipitator where particles get settles. These are called fly ash [4]. Liquid minerals form which solidifies resulting slag.
Optical image and SEM image of Fly Ash is shown in Figure 1.1.
Ash stored in a heating chamber is a non-combustible residue. It is likely that some traces of combustibles are embedded in clinkers. Clinkers are to be stick to hot side walls of a coal-burning furnace. Clinkers fall by themselves into bottom hopper of a coal-burning furnace and are cooled. The above portion of ash is known as bottom ash [7]. Optical image and SEM image of Bottom Ash is shown in Figure 1.2.
Pond ash [10] is a waste collection of ash from burning chamber of boilers. In short, it can be defined as wet disposal of fly ash mixed with bottom ash. Pond ash is obtained from in large ponds or dykes as slurry. Pond ash is increasing in an alarming rate. Its production ash is posing threat to our environment. Therefore, sustainable management of these materials has become a thrust area in engineering research. Optical image and SEM image of Pond Ash are shown in Figure 1.3.
Figure 1.1 Optical micrograph of Fly ash (a) [5] and SEM image of Fly Ash (b) [6].
Figure 1.2 Optical image of Bottom Ash (a) [8] and SEM image of Bottom Ash (b) [9].
Figure 1.3 Optical image of Pond Ash (a) [11] and SEM image of Pond Ash (b) [12].
Grading of coal is made on the basis of ash content [13]. Usually, coal used in thermal power stations, contains ash in the ranges 30-40% (with the average ash content around 35%). However, for metallurgical industries, different grade coal is used. Metallurgical coal should contain low amount of ash and high clerking index. Generation of ash at the power plants is shown schematically in Figure 1.4.
Figure 1.4 Generation of ash at the power plants [14].
1.4 Nature and Composition of Thermal Power Plant Ashes
Micron-sized Fly ash particle is collected as flue gas from gases of coal fired plants during the production of electricity by electrostatic precipitators. Table 1.1 describes composition of coal (Bituminous, Subbituminous, and Lignite). It is revealed from Table 1.1 that major constituents of coal are silica, alumina, iron oxide, and lime. However, other constituents (magnesia, sulphur oxide, sodium oxide, and potassium oxide) are comparatively less than 10%.
In Fly ash [14], Elements with major percentages are silica, alumina and iron, whereas minor percentage elements are sodium, potassium, titanium, etc. Also, large amounts of non-combustible impurities (i.e., limestone, shale, dolomite, feldspar and quartz) are main constituents of coal ash obtained from thermal power plant. Chemical composition of fly ash using different types of coal is shown in Table 1.1.
ASTM C618 classifies fly ash into two classes i.e., Class F fly ash and Class C fly ash (Table 1.2). This classification is based on amounts of content i.e., calcium, silica, alumina, and iron (Table 1.2). Chemical properties of fly ash are largely depends on its chemical compositions and occurrence of this minerals [15].
Table 1.1 Normal range of chemical compositions for Fly ash produced from different coal types [14].
S. no.
Component
Bituminous
Subbituminous
Lignite
1
SiO
2
(%)
20–60
40–60
15–45
2
Al
2
O
3
(%)
5–35
20–30
20–25
3
Fe
2
O
3
(%)
10–40
4–10
4–15
4
CaO (%)
1–12
5–30
15–40
5
MgO (%)
0-5
1-6
3-10
6
SO
3
(%)
0-4
0-2
0-10
7
Na
2
O (%)
0-4
0-2
0-6
8
K
2
O (%)
0-3
0-4
0-4
9
LOI
0-15
0-3
0-5
Table 1.2 Typical composition of Class F Fly Ash, Class C Fly Ash, and Portland cement with their ASTM standard.
Components
Class F Fly Ash
Class C Fly Ash
Portland cements
Typical*
ASTM C-618
Typical**
ASTM C-618
Typical***
ASTM C-150
SiO
2
48.0
---
37.3
---
20.25
---
Al
2
O
3
24.3
---
21.4
---
4.25
---
Fe
2
O
3
15.6
---
5.7
---
2.59
---
SiO
2
+ Al
2
O
3
+ Fe
2
O
3
87.9
70.0 (min.%)
64.3
50.0 (min. %)
---
---
CaO (Lime)
3.2
---
22.4
---
60.6
---
MgO
---
---
---
---
2.24
6.0 (max.%)
SO
3
0.4
5.0(max.%)
2.5
5.0(max.%)
---
3.0 (max.%)
Loss of Ignition (LOI)
3.0
6.2 (max.%)
0.4
6.0 (max.%)
0.55
3.0 (max.%)
Moisture content
0.1
3.0
0.1
3.0
---
---
Insoluble residue
---
---
---
---
---
0.75
Available alkalis as equivalent Na
2
O
0.8
1.5
1.4
1.5
0.20
---
Class F fly ash
Class F fly ash is generated from coal containing less than 7% lime (CaO). It is pozzolanic in nature [16]. Because of pozzolanic behaviour, Class F fly ash is used as a cementing agent, such as Portland cement. Class F ash contains alkaline activator such as sodium silicate and alkali and therefore, it can form a geopolymer. Geopolymer is a cementitious material.
Class C fly ash
Class F fly ash is obtained from burning of lignite or sub-bituminous coal in thermal power stations. Class F fly ash has self-pozzolanic behaviour. Since, it contains higher amount of limes [16]. Therefore, it does not require an activator for producing cementitious materials. Also, alkali and sulfate contents are generally higher in Class C fly ashes. Composition of Class F Fly Ash, Class C Fly Ash, and Portland cement is presented in Table 1.2.
Coal bottom ash is coarse and granular, nature. Bottom ash is collected from bottom of furnaces. Usually, a coal-burning furnace is a dry in nature. Out of 100% ash, 20 percent of ash is dry bottom ash. They look is a dark grey, granular, porous, sand size 12.7 mm (½ in). They usually is collected in a water-filled hopper locked at the bottom of the furnace [17].
Main constituents of bottom ash are silica, alumina, and iron, whereas calcium, magnesium, sulphates. However, alkali constituents such as Ca, Mg, Na, and K are present in a trace amount. Also, it contains very less amount of sulphur. Table 1.3 presents a chemical analysis of bottom ash. If bottom ash is produced from burning of lignite or sub-bituminous coals, it has higher percentage of calcium if compared with bottom ash produced from burning of anthracite or bituminous coals. Bottom Ash show corrosive properties because of salt content and low pH value. Corrosively indicator tests normally used to evaluate bottom ash are pH, electrical resistivity, soluble chloride content, and soluble sulfate content. Bottom ash is found to be non-corrosive if pH exceeds 5.5 and electrical resistivity is greater than 1,500 ohm-centimetres. Other criterion for defining non-corrosive nature is soluble chloride content. If bottom ash is less than 200 parts per million (ppm) soluble chloride content or less than 1,000 parts per million (ppm) soluble sulfate content, then it is non – corrosive [18].
Table 1.3 Chemical composition of Bottom Ash (BA) [19].
Raw materials
SiO
2
Al
2
O
3
CaO
MgO
Fe
2
O
3
TiO
2
Cr
2
O
3
MnO
P
2
O
5
C
LOI
Bottom Ash
68.0
25.0
1.66
0.02
2.18
1.45
0.00
0.00
0.00
0.0
1.69
Microstructural aspect of Bottom ash show angular particles with a very porous surface texture. Bottom ash particle size is ranging between sizes of fine gravel to fine sand with very low percentages of silt-clay sized particles.
Specific gravity of dry bottom ash is depends on its chemical composition. If unburnt carbon is more, then specific gravity value is lower. Bottom ash with a low specific gravity has a porous or vesicular texture. They easily degrade under loading or compaction [20]. Table 1.4 indicates some typical physical properties of bottom ash.
Pond ash [22] is obtained from wet disposal of fly ash mixed with bottom ash. Since it is obtained from large ponds or dykes as slurry. It is called pond ash. Pond ash is being generated at an alarming rate. Therefore, its sustainable management has become the thrust area in engineering research. Pond ash is relatively coarse and dissolvable in alkalis. Since it is obtained from water, and hence it’s pozzolanic reactivity becomes low. Due to less pozzolanic effect, it is not preferred as replacement of cement in concrete. Optical image and SEM image of Pond Ash is shown in Figure 1.5.
There is a possibility to use pond ash for making burnt clay bricks. In bricks production at brick manufacturing plants, pond ash is mixed with clay to manufacture bricks using conventional methods. Usually, green bricks are fired (traditional way) to produce brick products. Different tests (i.e., tolerance in dimension, water absorption, compressive strength, initial rate of absorption and weathering) are performed to evaluate performance of bricks. Ash ponds use gravity to settle out large particulates from power plant waste water. This technology does not treat dissolved pollutants [23]. Ponds generally have not been built as lined landfills, and therefore chemicals in the ash can leach into groundwater and surface waters, accumulating in the biomass of the system [24−26]. Chemical composition of pond ash is presented in Table 1.5. Physical characteristics of pond ash are indicated in Table 1.6.
Table 1.4 Some typical physical properties of bottom ash [21].
S. no.
Different type physical property
Physical property value
Reference
1
Specific gravity
2.1 - 2.7
6 (bottom ash)
2
Dry unit weight
720 - 1600 kg/m3
6 (bottom ash)
3
Plasticity
(45 - 100 lb/ft3)
6 (bottom ash)
4
Absorption
none
4 (bottom ash)
Table 1.5 Chemical composition of Pond Ash (PA) [11].
Raw materials
SiO
2
Al
2
O
3
CaO
MgO
Fe
2
O
3
TiO
2
Cr
2
O
3
MnO
P
2
O
5
C
LOI
Pond Ash
62.8
28.3
0.7
0.58
3.85
1.84
0.04
0.03
0.32
1.15
0.5
Table 1.6 shows chemical and physical characteristics of pond ash obtained from other regions. There is difference in composition of pond ash (Table 1.5). Alumina and silica content (Table 1.5) is 91%, whereas chemical composition of pond ash (Table 1.5) is 79 %. The other major constituent (Table 1.5) is Iron oxide (Fe2O3) and TiO2. Both the compounds are higher percentage in Table 1.5. Other important feature of Table 1.5 is higher percentage of alkali content.
It is concluded that type of coal, performance of generating facility, variety collection, disposal & storage methods, coal burning temperature, and peak load demand in thermal stations, etc are controlled properties of pond ash. Physical, chemical, and mineralogical characteristics of pond ash play an important role in different sectors. Therefore, use of pond ash has to done judicially depending on the nature of applications.
Table 1.6 Chemical and physical characteristics of pond ash.
Chemical characteristics [
11
]
Physical characteristics [
27
]
Parameters
Concentration (% by wt.)
Parameter
Pond ash
SiO
2
59.007
Al
2
O
3
19.551
Specific gravity @ 27°C
2.0675
Fe
2
O
3
15.350
Fineness (m2/kg)
73.78
TiO
2
3.158
Hydraulic conductivity @ 27°C
0.992
K
2
O
1.271
Dry density, γd (g/cc)
0.848
CaO
1.151
Void ratio
1.435
Mn
2
O
3
0.197
1.5 Characteristics of Thermal Power Plant Ashes
Specific gravity is an important physical property that is needed to use coal ashes in different applications, particularly geotechnical areas [28]. Generally, specific gravity of coal ashes varies from 1.6 to 3.1. Variation of specific gravity causes many factors such as gradation, particle shape and chemical composition. Low specific gravity coal ashes may be due to the presence of a large number of hollow cenospheres. Hollow cenospheres entraps air, and also varies in chemical composition (particularly iron content) in coal from which it is obtained.
Fly ash has usually higher specific gravity compared to pond and bottom ashes (obtained from the same locality). When the particles are crushed, they show a higher specific gravity compared to the uncrushed portion of the same material [29].
Specific surfaces [28] of coal ashes are important characteristics and supports to understand their physical and engineering behaviour. Coal ashes are primarily silt/sand-sized particles and their specific surface is expected to be very low.
Surface area of particles is important because it may control total adsorption capacity but not necessarily the desorption rate. Surface areas of fly ash particles generally vary inversely with the particle size. Smaller the particle size, larger the surface area [30].
Permeability or Hydraulic Conductivity (K) is often used interchangeably for same property. Coefficient of permeability or hydraulic conductivity (K) takes into account of fluid properties, whereas intrinsic permeability (k) only refers to effectiveness of porous medium alone [31]. They are related by following equation 1.1;
Fluid is actually flowing through the void spaces, not particulate matter. Therefore, porosity can have a controlling influence on permeability. Porosity is a value that portrays the amount of voids in a sample which is representative of water bearing capacity. Porosity is usually represented by ‘n’. It is determined by calculating the ratio between volumes of voids and total volume multiply by 100 (to express as percent). Obviously, porosity and permeability can be affected by compaction (density) since this reduces amount of void space for a given total volume. Normally, higher porosity samples will have a higher hydraulic conductivity. Fly ash compacted in a laboratory to 95 % maximum density can achieve a permeability of 1 × 10-5 cm/sec. A higher density results in a lower permeability. This is beneficial since a low permeability will restrict leachate from migrating away from the site.
When fly ash is used to change soil for plant growth, the hydraulic conductivity in the soil increases upto 10 to 20 percent by volume of fly
ash. Beyond this point, hydraulic conductivity of soil decreases. This seems to be a pozzolanic reaction occurring in fly ash which tends to cement in contact with water.
Density is also affected by compaction. In a bituminous coal fly ash, a 95 percent maximum density (1.3 g/cm3) is achieved [28]. Since fly ash generally has a low bulk density, fly ash addition to soil reduces the bulk density of soil.
Grain size distribution [32] is indicated by well graded/poorly graded, fin/course, etc. It helps in classifying coal ashes. Coal ashes are predominantly silt sized with some sand-size fraction. Leonard’s and Bailey [33] have reported the range of gradation for fly ash and bottom ashes which can be classified as silty sands or sandy silts.
In Indian coal ashes, fly ashes consist predominantly of silt-size fraction mixed with some clay-size fraction. Pond ashes consist of a silt-size fraction with some sand-size fraction. Bottom ashes are coarser particles consisting predominantly of sand-size fraction mixed with some silt-size fraction. Based on the grain-size distribution, coal ashes can be classified as sandy silt to silty sand. They are poorly graded with coefficient of curvature ranging between 0.61 and 3.70. Coefficient of uniformity is in the range of 1.59-14.0.
Free swell index [34] is a tool to identify swelling behaviour of soils. Free swell test method has been proposed by Holtz and Gibbs to estimate swell potential. Sridhar et al. [35] have modified the definition of free swell index itself to take care of the limitations. 70% coal ashes show negative free swell index which is due to flocculation. Since clay-size fraction in coal ashes is very less, and hence, free swell index is negligible. Index properties [28] are extensively used in geotechnical engineering practice.
Percussion cup and fall cone methods are popular to determine the liquid limit of fine-grained soils. In Percussion cup method, it is very difficult to cut a groove in soils of low plasticity. It has a tendency to slip rather than flow. Fly ashes are not studied because of their non-plastic nature. In cone penetration method, fly ash is not been studied because of variation of water content in the cup with depth. So, it is very difficult to get a smooth surface of fly ash in the cup.
A new method, Equilibrium water content under Ko stress method has been found to determine liquid limit of coal ashes except class C fly ashes. This method is simple, reasonably error free, less time consuming and good reproducibility.
Chemical properties of coal ashes greatly influence an environmental impact. It may arise due to their use/disposal/engineering properties. The adverse environmental impacts include contamination of surface and sub-surface water with toxic heavy metals, loss of soil fertility around the plant sites, etc. which is present in coal ashes. Hence detailed studies of these ashes include their chemical compositions, morphologies studies, pH, presence of total soluble solids, etc are essential [28].
Chemical compositions determine the possible applications of coal ash in different sectors. Particularly, Indian coal ashes satisfy chemical requirements for their use (as a pozzolanic). According to ASTM classification, only Neyveli fly ash can be classified as Class C fly ash and all other coal ashes fall under Class F [28].
pH [36] of aqueous medium affects physico-chemical properties. Further, mobilization of trace elements in aqueous medium regulates solubility of hydroxide and carbonate salts which depending upon pH of aqueous media. Fly ash has higher pH values in comparison to pond and bottom ashes. This is because of the presence of higher amounts of free lime and alkaline oxides. Since coal ashes are nearly alkaline. Therefore, it can be used in reinforced cement concrete. This will be safe against corrosion.
Presence of soluble solids is an important aspect and has greatly influenced engineering properties. Further, solubility of nutrient elements like calcium, magnesium, iron, sulphur, phosphorus, potassium and manganese enhance crop yield to a great extent. Soluble solids range is found to be 400-17600 ppm (for fly ashes), 800 - 3600 ppm (for pond ashes), and 1400 - 4100 ppm (for bottom ashes), respectively.
Strength of fly ash generally improves with time due to pozzolanic reactions [37
