fly ash characteristics and feed coal properties research report 73
COOPERATIVE RESEARCH CENTRE FOR COAL IN SUSTAINABLE DEVELOPMENT Established and supported under the Australian Government’s Cooperative Research Centres Program
FLY ASH CHARACTERISTICS AND FEED COAL PROPERTIES
RESEARCH REPORT 73
Authors: David French Jim Smitham
CSIRO Energy Technology
May 2007
QCAT Technology Transfer Centre, Technology Court Pullenvale Qld 4069 AUSTRALIA Telephone (07) 3871 4400 Facsimile (07) 3871 4444 Email: [email protected]
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DISTRIBUTION LIST CCSD Chairman; Chief Executive Officer; Manager TT&C; Files Industry Participants Australian Coal Research Limited ............................................................. Mr Mark Bennetts BHP Billiton Mitsubishi Alliance.............................................................. Mr Ross Willims .................................................................................................................... Mr Ben Klaassen .................................................................................................................... Dr Andre Urfer CNA Resources.......................................................................................... Mr Ashley Conroy CS Energy .................................................................................................. Dr Chris Spero Delta Electricity ......................................................................................... Mr Greg Everett Queensland Department of Mines & Energy............................................. Mr Bob Potter Rio Tinto (TRPL)....................................................................................... Mr Kevin Creagh Stanwell Corporation ................................................................................. Mr Howard Morrison Tarong Energy ........................................................................................... Mr Dave Evans The Griffin Coal Mining Co Pty Ltd ......................................................... Mr Jim Coleman Verve Energy ............................................................................................. Mr Ken Tushingham Wesfarmers Premier Coal Ltd ................................................................... Mr Patrick Warrand Xstrata Coal Pty Ltd................................................................................... Mr Colin Whyte .................................................................................................................... Mr Barry Isherwood Research Participants CSIRO ……............................................................................................... Dr David Brockway Curtin University of Technology …………………………………. ......... Prof Linda Kristjanson Macquarie University ................................................................................ Prof Jim Piper The University of Newcastle ..................................................................... Prof Barney Glover The University of New South Wales ......................................................... Prof David Young The University of Queensland ................................................................... Prof Don McKee
This page is intentionally left blank
Cooperative Research Centre for Coal in Sustainable Development QCAT Technology Transfer Centre Technology Court Pullenvale, Qld 4069 Telephone: (07) 3871 4400 Fax: (07) 3871 4444
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Disclaimer Use of the information contained in this report is at the user’s risk. While every effort has been made to ensure the accuracy of that information, neither Australian Black Coal Utilisation Research Limited (ABCUR) nor the participants in the CRC for Coal in Sustainable Development make any warranty, express or implied, regarding it. Neither ABCUR nor the participants are liable for any direct or indirect damages, losses, costs or expenses resulting from any use or misuse of that information. Copyright © Australian Black Coal Utilisation Research Limited 2007 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, whether electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of Australian Black Coal Utilisation Research Limited.
TABLE OF CONTENTS Page EXECUTIVE SUMMARY .........................................................................................vii 1. INTRODUCTION................................................................................................1 2. ISSUES ARISING FROM pf COMBUSTION WASTE MANAGEMENT/UTILISATION .......................................................................3 2.1 Introduction ....................................................................................................3 2.2 Waste Disposal/Management Issues ..............................................................3 2.2.1 Legislative Context.............................................................................3 2.2.2 Leaching and Water Quality ..............................................................4 2.2.3 Public perceptions..............................................................................4 2.2.4 Ash Stewardship “Cradle to Grave” .................................................4 2.3 Utilisation Issues ............................................................................................5 3.
2.3.1 Adequacy of Current Standards.........................................................5 THE KEY CHARACTERISTICS OF FLY ASH FOR MANAGEMENT AND DISPOSAL .................................................................................................8 3.1 Introduction ....................................................................................................8 3.2 Identification of the key characteristics..........................................................8 3.2.1 Physical characteristics .....................................................................8 3.2.2 Chemical characteristics..................................................................11 3.3 Summary.......................................................................................................13
4.
FEED COAL PROPERTIES AND KEY FLY ASH CHARACTERISTICS – CURRENT KNOWLEDGE............................................................................16 4.1 Introduction ..................................................................................................16 4.2 Broad Trends of Coal Type .........................................................................16 4.3 Broad trends of coal characteristics and physical properties of fly ash .......18 4.3.1 Detailed study of the effects of coal on fly ash properties. ..............21 4.4 Broad Trends of coal characteristics and chemical properties of fly ash .....21
5.
FEED COAL PROPERTIES AND KEY FLY ASH CHARACTERISTICS –KNOWLEDGE GAPS .....................................................................................32 5.1 Introduction ..................................................................................................32 5.2 Physical characteristics.................................................................................34 5.3 Chemical characteristics...............................................................................35 5.4 Discussion.....................................................................................................37
6. 7.
CONCLUSIONS and RECOMMENDATIONS................................................38 REFERENCES ...................................................................................................39
iv
LIST OF TABLES Page
Table 1.1. Summary of the tasks to be undertaken within the coal by-product characterisation research activity and the outcomes. ..................................1 Table 2.1 Categorisation of fly ash usage for 2003 (after ADAA, 2005)......................3 Table 2.2 Classification of fly ash according to Australian standard AS3582.1 ...........5 Table 2.3 Examples of Australian Fly Ashes (Bucea et al, 1996) .................................6 Table 2.4. Comparison of Fly Ash Specifications for Concrete Use: Chemical Properties. Values are expressed in wt%. ...................................................7 Table 3.1. Significant characteristics which influence fly ash waste management and utilisation options (after Cope and Dacey (1984)). “P” indicates those characteristics which are of primary importance and “S” those which are of importance in the end use product for concrete manufacture...............................................................................................10 Table 3.2. Key characteristics for fly ash derived products (after Cope and Dacey, (1984), Sloss et al., (1996) and Clarke, (1992)). “P” indicates those characteristics which are of primary importance in selection of the material as “fit for purpose” and “S” those which are of importance in the end use product. ...........................................................15 Table 4.1 Comparison of the physical properties of Australian fly ashes derived from the combustion of A) sub-bituminous coals and B) bituminous coals (after Killingley et al., 2000). ..........................................................20 Table 4.2 Comparison of the surface properties of Polish fly ashes derived from the combustion of A) lignite and B) black coals (after Sarbak et al., 2004) .........................................................................................................21 Table 4.3: Average and standard deviation of ultimate, major oxide and minor element analyses of fly ashes from Kentucky power plants grouped by sulphur content (values in upper set, wt%; in lower set, ppm). After Hower et al (1996)...........................................................................24 Table 4.4 Trace element abundance in A fly ashes derived from combustion of sub-bituminous coals and B) of bituminous coals (after Ward & French, 2005). Differences are highlighted in red. ...................................25 Table 4.5 Chemical composition of Australian fly ash samples, inferred composition of mineral and glass fractions (after Ward & French, 2005). ........................................................................................................30 Table 5.1. Identification of knowledge gaps...............................................................33 Table 5.2. Current state of knowledge of influence of feed coal properties on key physical fly ash characteristics for Australian Coals. ...............................34 Table 5.3. Current state of knowledge of influence of feed coal properties on key chemical fly ash characteristics.................................................................36
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LIST OF FIGURES Figure 1.1. Schematic outlining the topics relevant to fly ash utilisation and the topics to be covered by the reports to be issued within task 6.1.5 ..............2 Figure 3.1. Strength at 28 days of mortar prisms made according to BS3892 Part 1 from a range of UK fly ash sources and fineness (Sear 2001).................9 Figure 3.2. Elements of environmental significance in fly ash...................................14 Figure 4.1 Relationship of coal source to fly ash major element chemistry for selected countries (after Cope and Dacey (1984)). ...................................17 Figure 4.2 Relationship of coal rank to fly ash major element chemistry (after Cope and Dacey (1984)). ..........................................................................18 Figure 4.3 Relationship of coal rank to fly ash major element chemistry with respect to the basic oxides (after Cope and Dacey (1984)).......................19 Figure 4.4. The variation of CaO content during the first three week sampling period. Range plot shows the mean, maximum and minimum values from the feed coal, a sampling location close to the furnace exit (EFA), from two automated fly ash collectors (NFA, OFA), the truck silo (TFA) and the bottom ash. (From Affolter et al, 1999) ....................22 Figure 4.5. Temporal variation of selected elements in A, feed coal and B, fly ash at a Kentucky power plant (From Brownfield, 2004).........................22 Figure 4.6 Relationship between A) quartz contents and B) iron-bearing minerals in fly ash and the LTA of the feed coal as determined by quantitative X-ray diffraction. Data points circled are discussed in the text.............................................................................................................29
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EXECUTIVE SUMMARY This report deals with the characterisation of fly ash from conventional pf power generation. This research is part of an on-going activity within program 6 (Waste management and utilisation) of the CCSD to fully characterise the key properties of waste streams from coal utilisation relevant to utilisation and environmentally safe disposal practices. The purpose of this document is to provide a brief overview of the present knowledge with respect to the relationship of feed coal properties to fly-ash characteristics that are relevant to issues of ash utilisation and disposal in order to identify the knowledge gaps and make recommendations for future research opportunities within the CCSD. This study deals only with the combustion byproducts of conventional pulverized fuel generation... The focus of this report will be on fly ash as fly ash generally constitutes the bulk (80-90%) of the combustion by-products of pf power generation with bottom ash making up the remainder. Australia is heavily reliant upon the use of coal for electric power generation with approximately 84% (including brown and black coal) of electricity being generated in this manner (ESAA, 2005). This reliance results in the annual production of approximately 13Mt (2003) of fly ash of which approximately 5.8Mt (44%) is utilized, the remainder going to ash disposal sites (ADAA,2005). Of the ash which is utilised, most goes into “under-utilisation” bulk fill applications such as mine site remediation and structural fill with only 28% being effectively utilised i.e. in a value-added application. Active research is being undertaken into more effective utilisation of fly ash e.g. use as aggregate or in soil remediation but, in the foreseeable future, there will be a need for ash disposal. Therefore, there is a need to understand the influence feed coal properties have on fly ash characteristics which are relevant to: 1. current utilisation, 2. identification of new utilisation opportunities and 3. management of ash disposal sites. A literature survey has been undertaken of the influence of coal properties on those characteristics of fly ash relevant to ash utilisation and waste management. The issues concerning fly ash utilisation and waste management have been outlined and the key characteristics of fly ash pertaining to these issues identified. The literature survey has further shown that there is little information available in the public domain detailing the chemical characteristics of Australian ashes and relationship to coal properties and it is clear that the role of other factors besides coal properties (such as boiler design, operation, particle collection technology and mill performance) needs to be properly investigated. The gap analysis of Table 5.1 shows how an escalating level of detail is required to move from a
vii
general marketing of Australian coals through to a detailed, project level specification and monitoring of key parameters. To position Australian coals and fly ashes in relation to world coals and markets, it is recommended that CCSD coal supply members and generators be approached to gather general data on coal mineralogy, trace elements, fuel ratio and, where there is an overlap between export coals and domestic consumption, details of major fly ash properties like particle size, unburnt carbon, free lime contents, pozzolanicity and quantitative mineralogy so that these can be compared to international standards and literature. To increase the potential for domestic consumption of fly ash it is recommended that regional studies (e.g. Upper Hunter, Low Hunter, Gladstone, Collie) of coal properties and fly ash properties be conducted with an emphasis on temporal variability and consistency and to examine if there will be any significant changes to coal sources over the next 10 years that could positively or negatively impact general fly ash properties. Any available data on particle size, area bulk density, permeability, compressive strength and shear strength should be compiled for ease of future reference. Other characteristics such as viscosity, moisture content, slurry pH and colour are of lesser importance and probably do not need to be considered at this stage. The greatest scientific ambiguity appears to arise around the influence of coal properties compared to plant operations e.g. low NOx burners on the level of unburnt carbon in fly ash. It is recommended that a project be scoped to investigate these phenomena at pilot scale or suitable plant scale. It is also recommended that contact be established with overseas researchers to continue to find opportunities to examine the use of coals in combustion and gasification technologies (e.g. the study of Font et al, 2005) and to use this knowledge in the selection of coals for the forthcoming CCSD pilot gasification trials.
viii
1. INTRODUCTION This report deals with the characterisation of fly ash from conventional pf power generation. This research is part of an on-going activity within program 6 (Waste management and utilisation) of the CCSD to fully characterise the key properties of waste streams from coal utilisation relevant to utilisation and environmentally safe disposal practices. The tasks within this activity and the task outputs are outlined in Table 1.1 Table 1.1. Summary of the tasks to be undertaken within the coal by-product characterisation research activity and the outcomes. Task To review Australasian and international standards used for fly ash characterisation and classification and assess the relevance of international standards to Australian conditions. To review analytical techniques available for the characterisation of fly ash To develop a database of the characteristics of Australian fly ashes relevant to ash utilisation and disposal. Existing public domain information to be compiled and knowledge gaps identified. Collection and analysis of samples to address identified knowledge gaps
Outcome Report outlining the standards used for fly ash characterisation and classification and review of applicable analytical techniques.
Report presenting available public domain information on the characteristics of Australian fly ashes. Report on existing knowledge of influence of coal properties on fly ash characteristics. (This report) Report on preliminary analytical results for a suite of Australian fly ashes. Final report providing a comprehensive assessment of the characteristics of Australian fly ashes relevant to utilisation and waste management. Report on the characteristics of waste from transitional technologies based upon a literature review and analysis of a preliminary sample set.
To undertake a scoping study of waste from transitional technologies to assess potential environmental impacts arising from the introduction of such technologies. Further research on the environmental impact of the introduction of transitional technologies if required.
As illustrated in Fig. 1.1.that shows the topics covered by this and future reports, the purpose of this document is to provide a brief overview of the present knowledge with respect to the relationship of feed coal properties to fly-ash characteristics that are relevant to issues of ash utilisation and disposal in order to identify the knowledge gaps and make recommendations for future research opportunities within the CCSD. This study deals only with the combustion by-products of conventional pulverized 1
fuel generation. As fly ash generally constitutes the bulk (80%) of the combustion byproducts of pf power generation with bottom ash making up the remainder, the focus of the report will be on fly ash and, since flue gas clean–up technologies are not used in Australia, other waste streams such as flue gas desulphurisation wastes will not be considered.
Figure 1.1. Schematic outlining the topics relevant to fly ash utilisation and the topics to be covered by the reports to be issued within task 6.1.5 Australia is heavily reliant upon the use of coal for electric power generation with approximately 84% (including brown and black coal) of electricity being generated in this manner (ESAA, 2005). This reliance results in the annual production of approximately 13Mt of fly ash (2003 data) of which approximately 5.8Mt (44%) is utilised, the remainder going to ash disposal sites (ADAA, 2005). Of the ash which is utilised, most goes into “under-utilisation” bulk fill applications such as mine site remediation and structural fill with only 11% being utilised i.e. in high value-added cementitious application. Active research is being undertaken into more effective utilisation of fly ash e.g. use as aggregate or in soil remediation but, in the foreseeable future, there will be a need for ash disposal. Therefore, there is a need to understand the influence feed coal properties have on fly ash characteristics which are relevant to: 1. current utilisation, 2. identification of new utilisation opportunities and 3. management of ash disposal sites.
2
2. ISSUES ARISING FROM pf COMBUSTION WASTE MANAGEMENT/UTILISATION 2.1 Introduction As mentioned above, Australia currently produces 13 million tonnes/pa of pfcombustion by-products of which 46-13% is utilised (vide Table 2.1), the variation depending upon whether applications such as landfill are included in the definition of “utilisation”. Given that high volume uses for ash are unlikely to be identified in the near future, much of the ash will be going to waste repositories either as wet or dry disposal. Table 2.1 Categorisation of fly ash usage for 2003 (after ADAA, 2005) Underutilised Ash
Effectively Utilised Ash Usage Category Tonnes Utilised *106 Percentage Utilised
1.42
0.51
Beneficial UnderUse (mine utilised Ash site (ash ponds, remediation, etc) void backfill) 2.45 8.6
11
4
19
NonCementitious Applications
Cementitious Applications
66
Before the relationship of coal properties to fly ash characteristics can be considered, the issues relevant to fly ash utilisation and disposal need to be identified. Once the issues have been recognised, the key fly ash characteristics relevant to those issues can be identified and the influence of coal properties evaluated. The purpose of this section is to identify the significant issues which impact upon fly ash utilisation and disposal. 2.2 Waste Disposal/Management Issues 2.2.1 Legislative Context Within Australia, fly ash is currently classified as waste and the standards set by state legislation vary widely (Aynsley et al., 2003, Elliot and Zhang, 2003, Newcombe et al., 1998)). The legislative context of ash disposal has also been in a separate CCSD report (Riley, 2005) and is only summarised here. There is a move to have fly ash declared as a product and there is a need to provide the scientific data to form the basis of sound legislation for this initiative to proceed. With regard to current Australian Federal legislation, fly ash would have the potential hazardous characteristics of being Ecotoxic Leachate (capable of producing a leachate), Toxic or Poisonous. However, there is doubt on the relative importance of the characteristics due to incomplete scientific data on fly ash behaviour. Under current Federal legislation, the procedure is to initially identify if a material is a waste and if so is it
3
hazardous as defined under the Basel Convention. If fly ash is to be used as a byproduct then scientific evidence needs to be provided as to its non-hazardous nature. Under New South Wales and Western Australian legislation (vide Aynsley et al. 2003 for details of relevant Federal and state legislation), the generators of pollution and waste are held accountable for the cost of containment, avoidance and abatement. The potential issue for power generators is the possible long-term contamination of the environment from ash disposal sites due to trace element leaching which may also have impacts upon future land use following power station closure. Currently there is little scientific data on the long-term effect of ash disposal practices to identify if there is a potential risk and what management strategies may be appropriate. Much of current Australian legislation has been imported or follows international trends and appears to lack any firm scientific basis given the frequently varying requirements between various State regulations and the need has been identified for the provision of scientific data to assist in the future development of Australian legislation. 2.2.2 Leaching and Water Quality The major issue associated with ash disposal is the possible effect upon water quality arising from ash leachates. Although there appear to be few problems in the short term management of ash repositories, the long term effects of current disposal practices are largely unknown. Community and industry attitudes are now changing with the consequence that the environmental effects of industry practices are being considered within time frames of hundreds of years rather than decades (and in the mining industry, periods of a thousand years have been seriously discussed (Milnes, 2002)). The changing attitudes have implications for long term risk management with possible changes in legislative requirements and the consequent cost of legislative compliance. 2.2.3 Public perceptions Community perceptions can influence the development of legislation and these perceptions can be based upon inadequate information (Rossiter at al., 2003). An example of such attitudes is a series of articles which appeared in the Sydney Morning Herald in May, 2002 (Ryle, 2002a, b, c, d, e, f: Delaney & Ryle, 2002) dealing with the utilisation of industrial waste, principally for agricultural applications, which highlighted the existing strong negative perceptions in the community with respect to the utilisation of industrial waste products. 2.2.4 Ash Stewardship “Cradle to Grave” Another issue which is emerging is the potential interest from Japan to return ash to the country from which the feed coal was purchased, most likely as a treated ash for soil conditioning (pers. comm. C. Heidrich and Tokyo Embassy staff and discussions at Japan-Australia Coal Research Workshop, 2004). As coal blending is widely practiced in Japan, the returned ash is unlikely to be a “pure” Australian coal ash but could contain ash derived from Chinese, Indonesian or South African coals the behaviour of which in such a blend is unknown. In addition, the effect of any conditioning upon the environmental behaviour of the ash and soil-ash interaction is unknown. Although there is likely to be a significant lead time before such practices are widely adopted, with the need to address issues such as community and industry attitudes, research is required to identify likely environmental issues and their remediation before such a practice become commonplace.
4
2.3 Utilisation Issues 2.3.1 Adequacy of Current Standards With respect to the utilization of pf combustion by-products the two issues which need to be addressed are: 1. The adequacy of current specifications and standards with regard to the properties of Australian fly ash and the critical properties. 2. The identification of data is required to assist in the identification of future uses of pf by-products. Current classification of fly ashes for utilisation mostly is based upon the ASTM classification (ASTM, 1999) which recognizes the following two categories: 1. Type F Si+Al+Fe.contents >70%, derived from anthracite, bituminous and some sub- bituminous coals. 2. Type C Si+Al+Fe.contents >50%, CaO contents may be >10%, derived from lignite/sub-bituminous coals; ash is self-hardening. This classification reflects the broad subdivision of US coals in the bituminous and higher rank coals of the eastern states and the lower rank western coals with associated high calcium contents. Although widely used (Sloss et al., 1996, Smith, 2005), the ASTM classification may not be directly applicable to or adequately reflect the variability found in Australian fly ashes both with respect to chemistry and mineralogy. In Australia three grades of fly ash are recognised within AS3582.1 (SAA, 1998) as shown in Table 2.1. Data from Bucea et al (1996) provides some data for Australian fly ashes from three states (Table 2.3). Table 2.2 Classification of fly ash according to Australian standard AS3582.1 Grade Fine Medium Coarse
Fineness (% Minimum Mass passing a 45um sieve) 75 65 55
Loss on Ignition (% maximum) 4.0 5.0 6.0
Moisture content (% maximum)
SO3 Content (% maximum)
1.0 1.0 1.0
3.0 3.0 3.0
Due to the variability of fly ash, doubts have been raised as to the suitability of the current classification schemes which may be overly simplistic and fail to take into account other important characteristics such as mineralogy (vide discussion in Sloss et al., 1996). Also, many of the current classifications have been developed for the use of fly ash in concrete and cement and thus may not be applicable for other end uses. A need has been identified for an overall rating system which would be useful for all potential end-users of fly ash (Sloss et al., 1996).
5
Table 2.4 is a comparison of various national specifications for the use of fly ash in concrete. Two points are immediately obvious; firstly the variation in the identity of the critical factors e.g. SiO2 vs Si+Al vs Si+Al+Fe and secondly, where the same category is used the variability of acceptable values e.g. Na2O contents which vary from 1.5 wt% in Denmark and the United States to 6.0 wt% in France. Research has indicated that some of the requirements of the various standards may be too prescriptive such as those governing particle size and LOI values (Cope and Dacey, 1984). Table 2.3 Examples of Australian Fly Ashes (Bucea et al, 1996) Ash Pt Augusta Pt Augusta face Eraring Kwinana Hopper 1 Kwinana Hopper 2
Fineness (10% passing 45um sieve) 72.5 86.0 92.0 86.9 77.2
Loss on Ignition (%) 0.3 0.3 1.3 1.8 3.8
6
Moisture content (%)
SO3 Content (%) 0.4 0.5 0.2 0.2 0.2
Table 2.4. Comparison of Fly Ash Specifications for Concrete Use: Chemical Properties. Values are expressed in wt%. Australia
Austria
Canada
France
Europe
Japan
Netherlands
Spain
United Kingdom
Standard
AS3582.1
Onorm B3320-8
CAN/CSAA 23.5-M86
PR P18.50188
EN450
JIS A6201-92
UNE83-41587
BS Pt1
Moisture Loss on Ignition SiO2 SiO2+Al2O3 SiO2+Al2O3+Fe2O3 MgO CaO(total) CaO(free) Water-soluble Na2O Na2O+K2O Na2O equivalent Available alkalis SO3 Cl Glass
FLY ASH CHARACTERISTICS AND FEED COAL PROPERTIES
RESEARCH REPORT 73
Authors: David French Jim Smitham
CSIRO Energy Technology
May 2007
QCAT Technology Transfer Centre, Technology Court Pullenvale Qld 4069 AUSTRALIA Telephone (07) 3871 4400 Facsimile (07) 3871 4444 Email: [email protected]
This page is intentionally left blank
DISTRIBUTION LIST CCSD Chairman; Chief Executive Officer; Manager TT&C; Files Industry Participants Australian Coal Research Limited ............................................................. Mr Mark Bennetts BHP Billiton Mitsubishi Alliance.............................................................. Mr Ross Willims .................................................................................................................... Mr Ben Klaassen .................................................................................................................... Dr Andre Urfer CNA Resources.......................................................................................... Mr Ashley Conroy CS Energy .................................................................................................. Dr Chris Spero Delta Electricity ......................................................................................... Mr Greg Everett Queensland Department of Mines & Energy............................................. Mr Bob Potter Rio Tinto (TRPL)....................................................................................... Mr Kevin Creagh Stanwell Corporation ................................................................................. Mr Howard Morrison Tarong Energy ........................................................................................... Mr Dave Evans The Griffin Coal Mining Co Pty Ltd ......................................................... Mr Jim Coleman Verve Energy ............................................................................................. Mr Ken Tushingham Wesfarmers Premier Coal Ltd ................................................................... Mr Patrick Warrand Xstrata Coal Pty Ltd................................................................................... Mr Colin Whyte .................................................................................................................... Mr Barry Isherwood Research Participants CSIRO ……............................................................................................... Dr David Brockway Curtin University of Technology …………………………………. ......... Prof Linda Kristjanson Macquarie University ................................................................................ Prof Jim Piper The University of Newcastle ..................................................................... Prof Barney Glover The University of New South Wales ......................................................... Prof David Young The University of Queensland ................................................................... Prof Don McKee
This page is intentionally left blank
Cooperative Research Centre for Coal in Sustainable Development QCAT Technology Transfer Centre Technology Court Pullenvale, Qld 4069 Telephone: (07) 3871 4400 Fax: (07) 3871 4444
Feedback Form To help us improve our service to you may I ask you for five minutes of your time to complete this questionnaire. Please fax or mail it back to me, or, if you would prefer, give me a call. ATTENTION
MANAGER TECHNOLOGY TRANSFER
FAX NO
07 3871 4444
FROM
NAME: .................................................................................................................................. COMPANY:............................................................................................................................
REPORT TITLE: AUTHORS:
FLY ASH CHARACTERISTICS AND FEED COAL PROPERTIES D. FRENCH, J. SMITHAM
DATE
...............................................................................
Would you please rate our performance in the following areas by ticking the appropriate box:
The Research
Agree
Neutral
Disagree
Don’t Know
This work has achieved its research objectives This work has delivered to agreed milestones This work is relevant to my organisation Communication of progress has been timely & useful
The Report The report is well presented The context of the report is clear The content of the report is substantial The report is clearly written and understandable This product is good value
Any further comments which would assist us in better serving your future requirements?: …………………………….…………………………………………………………………………………………… …………………………………………………………………………….…………………………………………… Are there any people you would like to add to our distribution list?: ………………………………………………………………………………………………………….……………… ………………………………………………………………………………………………………………….…....... Thank you for your response
Disclaimer Use of the information contained in this report is at the user’s risk. While every effort has been made to ensure the accuracy of that information, neither Australian Black Coal Utilisation Research Limited (ABCUR) nor the participants in the CRC for Coal in Sustainable Development make any warranty, express or implied, regarding it. Neither ABCUR nor the participants are liable for any direct or indirect damages, losses, costs or expenses resulting from any use or misuse of that information. Copyright © Australian Black Coal Utilisation Research Limited 2007 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, whether electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of Australian Black Coal Utilisation Research Limited.
TABLE OF CONTENTS Page EXECUTIVE SUMMARY .........................................................................................vii 1. INTRODUCTION................................................................................................1 2. ISSUES ARISING FROM pf COMBUSTION WASTE MANAGEMENT/UTILISATION .......................................................................3 2.1 Introduction ....................................................................................................3 2.2 Waste Disposal/Management Issues ..............................................................3 2.2.1 Legislative Context.............................................................................3 2.2.2 Leaching and Water Quality ..............................................................4 2.2.3 Public perceptions..............................................................................4 2.2.4 Ash Stewardship “Cradle to Grave” .................................................4 2.3 Utilisation Issues ............................................................................................5 3.
2.3.1 Adequacy of Current Standards.........................................................5 THE KEY CHARACTERISTICS OF FLY ASH FOR MANAGEMENT AND DISPOSAL .................................................................................................8 3.1 Introduction ....................................................................................................8 3.2 Identification of the key characteristics..........................................................8 3.2.1 Physical characteristics .....................................................................8 3.2.2 Chemical characteristics..................................................................11 3.3 Summary.......................................................................................................13
4.
FEED COAL PROPERTIES AND KEY FLY ASH CHARACTERISTICS – CURRENT KNOWLEDGE............................................................................16 4.1 Introduction ..................................................................................................16 4.2 Broad Trends of Coal Type .........................................................................16 4.3 Broad trends of coal characteristics and physical properties of fly ash .......18 4.3.1 Detailed study of the effects of coal on fly ash properties. ..............21 4.4 Broad Trends of coal characteristics and chemical properties of fly ash .....21
5.
FEED COAL PROPERTIES AND KEY FLY ASH CHARACTERISTICS –KNOWLEDGE GAPS .....................................................................................32 5.1 Introduction ..................................................................................................32 5.2 Physical characteristics.................................................................................34 5.3 Chemical characteristics...............................................................................35 5.4 Discussion.....................................................................................................37
6. 7.
CONCLUSIONS and RECOMMENDATIONS................................................38 REFERENCES ...................................................................................................39
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LIST OF TABLES Page
Table 1.1. Summary of the tasks to be undertaken within the coal by-product characterisation research activity and the outcomes. ..................................1 Table 2.1 Categorisation of fly ash usage for 2003 (after ADAA, 2005)......................3 Table 2.2 Classification of fly ash according to Australian standard AS3582.1 ...........5 Table 2.3 Examples of Australian Fly Ashes (Bucea et al, 1996) .................................6 Table 2.4. Comparison of Fly Ash Specifications for Concrete Use: Chemical Properties. Values are expressed in wt%. ...................................................7 Table 3.1. Significant characteristics which influence fly ash waste management and utilisation options (after Cope and Dacey (1984)). “P” indicates those characteristics which are of primary importance and “S” those which are of importance in the end use product for concrete manufacture...............................................................................................10 Table 3.2. Key characteristics for fly ash derived products (after Cope and Dacey, (1984), Sloss et al., (1996) and Clarke, (1992)). “P” indicates those characteristics which are of primary importance in selection of the material as “fit for purpose” and “S” those which are of importance in the end use product. ...........................................................15 Table 4.1 Comparison of the physical properties of Australian fly ashes derived from the combustion of A) sub-bituminous coals and B) bituminous coals (after Killingley et al., 2000). ..........................................................20 Table 4.2 Comparison of the surface properties of Polish fly ashes derived from the combustion of A) lignite and B) black coals (after Sarbak et al., 2004) .........................................................................................................21 Table 4.3: Average and standard deviation of ultimate, major oxide and minor element analyses of fly ashes from Kentucky power plants grouped by sulphur content (values in upper set, wt%; in lower set, ppm). After Hower et al (1996)...........................................................................24 Table 4.4 Trace element abundance in A fly ashes derived from combustion of sub-bituminous coals and B) of bituminous coals (after Ward & French, 2005). Differences are highlighted in red. ...................................25 Table 4.5 Chemical composition of Australian fly ash samples, inferred composition of mineral and glass fractions (after Ward & French, 2005). ........................................................................................................30 Table 5.1. Identification of knowledge gaps...............................................................33 Table 5.2. Current state of knowledge of influence of feed coal properties on key physical fly ash characteristics for Australian Coals. ...............................34 Table 5.3. Current state of knowledge of influence of feed coal properties on key chemical fly ash characteristics.................................................................36
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LIST OF FIGURES Figure 1.1. Schematic outlining the topics relevant to fly ash utilisation and the topics to be covered by the reports to be issued within task 6.1.5 ..............2 Figure 3.1. Strength at 28 days of mortar prisms made according to BS3892 Part 1 from a range of UK fly ash sources and fineness (Sear 2001).................9 Figure 3.2. Elements of environmental significance in fly ash...................................14 Figure 4.1 Relationship of coal source to fly ash major element chemistry for selected countries (after Cope and Dacey (1984)). ...................................17 Figure 4.2 Relationship of coal rank to fly ash major element chemistry (after Cope and Dacey (1984)). ..........................................................................18 Figure 4.3 Relationship of coal rank to fly ash major element chemistry with respect to the basic oxides (after Cope and Dacey (1984)).......................19 Figure 4.4. The variation of CaO content during the first three week sampling period. Range plot shows the mean, maximum and minimum values from the feed coal, a sampling location close to the furnace exit (EFA), from two automated fly ash collectors (NFA, OFA), the truck silo (TFA) and the bottom ash. (From Affolter et al, 1999) ....................22 Figure 4.5. Temporal variation of selected elements in A, feed coal and B, fly ash at a Kentucky power plant (From Brownfield, 2004).........................22 Figure 4.6 Relationship between A) quartz contents and B) iron-bearing minerals in fly ash and the LTA of the feed coal as determined by quantitative X-ray diffraction. Data points circled are discussed in the text.............................................................................................................29
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EXECUTIVE SUMMARY This report deals with the characterisation of fly ash from conventional pf power generation. This research is part of an on-going activity within program 6 (Waste management and utilisation) of the CCSD to fully characterise the key properties of waste streams from coal utilisation relevant to utilisation and environmentally safe disposal practices. The purpose of this document is to provide a brief overview of the present knowledge with respect to the relationship of feed coal properties to fly-ash characteristics that are relevant to issues of ash utilisation and disposal in order to identify the knowledge gaps and make recommendations for future research opportunities within the CCSD. This study deals only with the combustion byproducts of conventional pulverized fuel generation... The focus of this report will be on fly ash as fly ash generally constitutes the bulk (80-90%) of the combustion by-products of pf power generation with bottom ash making up the remainder. Australia is heavily reliant upon the use of coal for electric power generation with approximately 84% (including brown and black coal) of electricity being generated in this manner (ESAA, 2005). This reliance results in the annual production of approximately 13Mt (2003) of fly ash of which approximately 5.8Mt (44%) is utilized, the remainder going to ash disposal sites (ADAA,2005). Of the ash which is utilised, most goes into “under-utilisation” bulk fill applications such as mine site remediation and structural fill with only 28% being effectively utilised i.e. in a value-added application. Active research is being undertaken into more effective utilisation of fly ash e.g. use as aggregate or in soil remediation but, in the foreseeable future, there will be a need for ash disposal. Therefore, there is a need to understand the influence feed coal properties have on fly ash characteristics which are relevant to: 1. current utilisation, 2. identification of new utilisation opportunities and 3. management of ash disposal sites. A literature survey has been undertaken of the influence of coal properties on those characteristics of fly ash relevant to ash utilisation and waste management. The issues concerning fly ash utilisation and waste management have been outlined and the key characteristics of fly ash pertaining to these issues identified. The literature survey has further shown that there is little information available in the public domain detailing the chemical characteristics of Australian ashes and relationship to coal properties and it is clear that the role of other factors besides coal properties (such as boiler design, operation, particle collection technology and mill performance) needs to be properly investigated. The gap analysis of Table 5.1 shows how an escalating level of detail is required to move from a
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general marketing of Australian coals through to a detailed, project level specification and monitoring of key parameters. To position Australian coals and fly ashes in relation to world coals and markets, it is recommended that CCSD coal supply members and generators be approached to gather general data on coal mineralogy, trace elements, fuel ratio and, where there is an overlap between export coals and domestic consumption, details of major fly ash properties like particle size, unburnt carbon, free lime contents, pozzolanicity and quantitative mineralogy so that these can be compared to international standards and literature. To increase the potential for domestic consumption of fly ash it is recommended that regional studies (e.g. Upper Hunter, Low Hunter, Gladstone, Collie) of coal properties and fly ash properties be conducted with an emphasis on temporal variability and consistency and to examine if there will be any significant changes to coal sources over the next 10 years that could positively or negatively impact general fly ash properties. Any available data on particle size, area bulk density, permeability, compressive strength and shear strength should be compiled for ease of future reference. Other characteristics such as viscosity, moisture content, slurry pH and colour are of lesser importance and probably do not need to be considered at this stage. The greatest scientific ambiguity appears to arise around the influence of coal properties compared to plant operations e.g. low NOx burners on the level of unburnt carbon in fly ash. It is recommended that a project be scoped to investigate these phenomena at pilot scale or suitable plant scale. It is also recommended that contact be established with overseas researchers to continue to find opportunities to examine the use of coals in combustion and gasification technologies (e.g. the study of Font et al, 2005) and to use this knowledge in the selection of coals for the forthcoming CCSD pilot gasification trials.
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1. INTRODUCTION This report deals with the characterisation of fly ash from conventional pf power generation. This research is part of an on-going activity within program 6 (Waste management and utilisation) of the CCSD to fully characterise the key properties of waste streams from coal utilisation relevant to utilisation and environmentally safe disposal practices. The tasks within this activity and the task outputs are outlined in Table 1.1 Table 1.1. Summary of the tasks to be undertaken within the coal by-product characterisation research activity and the outcomes. Task To review Australasian and international standards used for fly ash characterisation and classification and assess the relevance of international standards to Australian conditions. To review analytical techniques available for the characterisation of fly ash To develop a database of the characteristics of Australian fly ashes relevant to ash utilisation and disposal. Existing public domain information to be compiled and knowledge gaps identified. Collection and analysis of samples to address identified knowledge gaps
Outcome Report outlining the standards used for fly ash characterisation and classification and review of applicable analytical techniques.
Report presenting available public domain information on the characteristics of Australian fly ashes. Report on existing knowledge of influence of coal properties on fly ash characteristics. (This report) Report on preliminary analytical results for a suite of Australian fly ashes. Final report providing a comprehensive assessment of the characteristics of Australian fly ashes relevant to utilisation and waste management. Report on the characteristics of waste from transitional technologies based upon a literature review and analysis of a preliminary sample set.
To undertake a scoping study of waste from transitional technologies to assess potential environmental impacts arising from the introduction of such technologies. Further research on the environmental impact of the introduction of transitional technologies if required.
As illustrated in Fig. 1.1.that shows the topics covered by this and future reports, the purpose of this document is to provide a brief overview of the present knowledge with respect to the relationship of feed coal properties to fly-ash characteristics that are relevant to issues of ash utilisation and disposal in order to identify the knowledge gaps and make recommendations for future research opportunities within the CCSD. This study deals only with the combustion by-products of conventional pulverized 1
fuel generation. As fly ash generally constitutes the bulk (80%) of the combustion byproducts of pf power generation with bottom ash making up the remainder, the focus of the report will be on fly ash and, since flue gas clean–up technologies are not used in Australia, other waste streams such as flue gas desulphurisation wastes will not be considered.
Figure 1.1. Schematic outlining the topics relevant to fly ash utilisation and the topics to be covered by the reports to be issued within task 6.1.5 Australia is heavily reliant upon the use of coal for electric power generation with approximately 84% (including brown and black coal) of electricity being generated in this manner (ESAA, 2005). This reliance results in the annual production of approximately 13Mt of fly ash (2003 data) of which approximately 5.8Mt (44%) is utilised, the remainder going to ash disposal sites (ADAA, 2005). Of the ash which is utilised, most goes into “under-utilisation” bulk fill applications such as mine site remediation and structural fill with only 11% being utilised i.e. in high value-added cementitious application. Active research is being undertaken into more effective utilisation of fly ash e.g. use as aggregate or in soil remediation but, in the foreseeable future, there will be a need for ash disposal. Therefore, there is a need to understand the influence feed coal properties have on fly ash characteristics which are relevant to: 1. current utilisation, 2. identification of new utilisation opportunities and 3. management of ash disposal sites.
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2. ISSUES ARISING FROM pf COMBUSTION WASTE MANAGEMENT/UTILISATION 2.1 Introduction As mentioned above, Australia currently produces 13 million tonnes/pa of pfcombustion by-products of which 46-13% is utilised (vide Table 2.1), the variation depending upon whether applications such as landfill are included in the definition of “utilisation”. Given that high volume uses for ash are unlikely to be identified in the near future, much of the ash will be going to waste repositories either as wet or dry disposal. Table 2.1 Categorisation of fly ash usage for 2003 (after ADAA, 2005) Underutilised Ash
Effectively Utilised Ash Usage Category Tonnes Utilised *106 Percentage Utilised
1.42
0.51
Beneficial UnderUse (mine utilised Ash site (ash ponds, remediation, etc) void backfill) 2.45 8.6
11
4
19
NonCementitious Applications
Cementitious Applications
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Before the relationship of coal properties to fly ash characteristics can be considered, the issues relevant to fly ash utilisation and disposal need to be identified. Once the issues have been recognised, the key fly ash characteristics relevant to those issues can be identified and the influence of coal properties evaluated. The purpose of this section is to identify the significant issues which impact upon fly ash utilisation and disposal. 2.2 Waste Disposal/Management Issues 2.2.1 Legislative Context Within Australia, fly ash is currently classified as waste and the standards set by state legislation vary widely (Aynsley et al., 2003, Elliot and Zhang, 2003, Newcombe et al., 1998)). The legislative context of ash disposal has also been in a separate CCSD report (Riley, 2005) and is only summarised here. There is a move to have fly ash declared as a product and there is a need to provide the scientific data to form the basis of sound legislation for this initiative to proceed. With regard to current Australian Federal legislation, fly ash would have the potential hazardous characteristics of being Ecotoxic Leachate (capable of producing a leachate), Toxic or Poisonous. However, there is doubt on the relative importance of the characteristics due to incomplete scientific data on fly ash behaviour. Under current Federal legislation, the procedure is to initially identify if a material is a waste and if so is it
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hazardous as defined under the Basel Convention. If fly ash is to be used as a byproduct then scientific evidence needs to be provided as to its non-hazardous nature. Under New South Wales and Western Australian legislation (vide Aynsley et al. 2003 for details of relevant Federal and state legislation), the generators of pollution and waste are held accountable for the cost of containment, avoidance and abatement. The potential issue for power generators is the possible long-term contamination of the environment from ash disposal sites due to trace element leaching which may also have impacts upon future land use following power station closure. Currently there is little scientific data on the long-term effect of ash disposal practices to identify if there is a potential risk and what management strategies may be appropriate. Much of current Australian legislation has been imported or follows international trends and appears to lack any firm scientific basis given the frequently varying requirements between various State regulations and the need has been identified for the provision of scientific data to assist in the future development of Australian legislation. 2.2.2 Leaching and Water Quality The major issue associated with ash disposal is the possible effect upon water quality arising from ash leachates. Although there appear to be few problems in the short term management of ash repositories, the long term effects of current disposal practices are largely unknown. Community and industry attitudes are now changing with the consequence that the environmental effects of industry practices are being considered within time frames of hundreds of years rather than decades (and in the mining industry, periods of a thousand years have been seriously discussed (Milnes, 2002)). The changing attitudes have implications for long term risk management with possible changes in legislative requirements and the consequent cost of legislative compliance. 2.2.3 Public perceptions Community perceptions can influence the development of legislation and these perceptions can be based upon inadequate information (Rossiter at al., 2003). An example of such attitudes is a series of articles which appeared in the Sydney Morning Herald in May, 2002 (Ryle, 2002a, b, c, d, e, f: Delaney & Ryle, 2002) dealing with the utilisation of industrial waste, principally for agricultural applications, which highlighted the existing strong negative perceptions in the community with respect to the utilisation of industrial waste products. 2.2.4 Ash Stewardship “Cradle to Grave” Another issue which is emerging is the potential interest from Japan to return ash to the country from which the feed coal was purchased, most likely as a treated ash for soil conditioning (pers. comm. C. Heidrich and Tokyo Embassy staff and discussions at Japan-Australia Coal Research Workshop, 2004). As coal blending is widely practiced in Japan, the returned ash is unlikely to be a “pure” Australian coal ash but could contain ash derived from Chinese, Indonesian or South African coals the behaviour of which in such a blend is unknown. In addition, the effect of any conditioning upon the environmental behaviour of the ash and soil-ash interaction is unknown. Although there is likely to be a significant lead time before such practices are widely adopted, with the need to address issues such as community and industry attitudes, research is required to identify likely environmental issues and their remediation before such a practice become commonplace.
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2.3 Utilisation Issues 2.3.1 Adequacy of Current Standards With respect to the utilization of pf combustion by-products the two issues which need to be addressed are: 1. The adequacy of current specifications and standards with regard to the properties of Australian fly ash and the critical properties. 2. The identification of data is required to assist in the identification of future uses of pf by-products. Current classification of fly ashes for utilisation mostly is based upon the ASTM classification (ASTM, 1999) which recognizes the following two categories: 1. Type F Si+Al+Fe.contents >70%, derived from anthracite, bituminous and some sub- bituminous coals. 2. Type C Si+Al+Fe.contents >50%, CaO contents may be >10%, derived from lignite/sub-bituminous coals; ash is self-hardening. This classification reflects the broad subdivision of US coals in the bituminous and higher rank coals of the eastern states and the lower rank western coals with associated high calcium contents. Although widely used (Sloss et al., 1996, Smith, 2005), the ASTM classification may not be directly applicable to or adequately reflect the variability found in Australian fly ashes both with respect to chemistry and mineralogy. In Australia three grades of fly ash are recognised within AS3582.1 (SAA, 1998) as shown in Table 2.1. Data from Bucea et al (1996) provides some data for Australian fly ashes from three states (Table 2.3). Table 2.2 Classification of fly ash according to Australian standard AS3582.1 Grade Fine Medium Coarse
Fineness (% Minimum Mass passing a 45um sieve) 75 65 55
Loss on Ignition (% maximum) 4.0 5.0 6.0
Moisture content (% maximum)
SO3 Content (% maximum)
1.0 1.0 1.0
3.0 3.0 3.0
Due to the variability of fly ash, doubts have been raised as to the suitability of the current classification schemes which may be overly simplistic and fail to take into account other important characteristics such as mineralogy (vide discussion in Sloss et al., 1996). Also, many of the current classifications have been developed for the use of fly ash in concrete and cement and thus may not be applicable for other end uses. A need has been identified for an overall rating system which would be useful for all potential end-users of fly ash (Sloss et al., 1996).
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Table 2.4 is a comparison of various national specifications for the use of fly ash in concrete. Two points are immediately obvious; firstly the variation in the identity of the critical factors e.g. SiO2 vs Si+Al vs Si+Al+Fe and secondly, where the same category is used the variability of acceptable values e.g. Na2O contents which vary from 1.5 wt% in Denmark and the United States to 6.0 wt% in France. Research has indicated that some of the requirements of the various standards may be too prescriptive such as those governing particle size and LOI values (Cope and Dacey, 1984). Table 2.3 Examples of Australian Fly Ashes (Bucea et al, 1996) Ash Pt Augusta Pt Augusta face Eraring Kwinana Hopper 1 Kwinana Hopper 2
Fineness (10% passing 45um sieve) 72.5 86.0 92.0 86.9 77.2
Loss on Ignition (%) 0.3 0.3 1.3 1.8 3.8
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Moisture content (%)
SO3 Content (%) 0.4 0.5 0.2 0.2 0.2
Table 2.4. Comparison of Fly Ash Specifications for Concrete Use: Chemical Properties. Values are expressed in wt%. Australia
Austria
Canada
France
Europe
Japan
Netherlands
Spain
United Kingdom
Standard
AS3582.1
Onorm B3320-8
CAN/CSAA 23.5-M86
PR P18.50188
EN450
JIS A6201-92
UNE83-41587
BS Pt1
Moisture Loss on Ignition SiO2 SiO2+Al2O3 SiO2+Al2O3+Fe2O3 MgO CaO(total) CaO(free) Water-soluble Na2O Na2O+K2O Na2O equivalent Available alkalis SO3 Cl Glass
