Influence of coal quality on combustion behaviour and mineral phases transformations

Abstract Coal is still an important resource for power generation. The combustion behaviour of various types of coal is dependent on its ash properties. These are the most important fuel characteristics in the design and operation of commercial boilers. The present study aims to evaluate the whole coal seam quality, coal ash behaviour, fundamental mechanisms, which more closely simulate the conditions of a pulverised coal-fired boiler. The authors formed seven representative samples from overall 126 band-by-band samples of Prajapara coal block (PCB) borehole of Ib valley coal basin, Odisha, India. Authors have carried technological, elemental and petrographical analysis of coal samples. The major oxides and minerals present in coal ash samples were characterised by inductively coupled plasma optical emission spectrometer (ICP-OES) and X–ray diffraction (XRD). The volatile matter (VMdaf) and ash (Ad) yields vary from 42.05–44.49 and 30.82–32.12 wt% respectively. The mean vitrinite reflectance ranges from 0.46 to 0.64%. Moreover, FactSage thermodynamics Model (FactSage 6.3) was used for understanding of the coal ash fusion behaviour in boiler operation and to predict the phase transformations that occur during the process of coal combustion which is a chemical thermodynamic models of oxide systems. FactSage provides mineralogical characteristics of coal which are in agreement with XRD analysis of coal. SiO2, Al2O3, K2O appears to influence positively fusion characteristics where as Fe2O3 and MgO have negative effect on it. The datasets provide information about the contribution of major oxides towards the ash fusion temperatures (AFT). The linear regression analysis of high temperature ash (HTA) composition and AFT indicate trend, which may be used to determine the predictive indices for slagging, fouling, and abrasion propensities during combustion practices.

[1]  Richard W. Bryers,et al.  Fireside slagging, fouling, and high-temperature corrosion of heat-transfer surface due to impurities in steam-raising fuels , 1996 .

[2]  X. Querol,et al.  Environmental impact of mineral transformations undergone during coal combustion , 1991 .

[3]  V. R. Gray Prediction of ash fusion temperature from ash composition for some New Zealand coals , 1987 .

[4]  Understanding thermal coal ash behaviour , 1983 .

[5]  Zihao Jiang,et al.  Relationship between coal ash composition and ash fusion temperatures , 2013 .

[6]  J. Qiu,et al.  Mineral transformation during combustion of coal blends , 1999 .

[7]  Gunnar Eriksson,et al.  FactSage thermochemical software and databases , 2002 .

[8]  S. Vassilev,et al.  A new approach for the combined chemical and mineral classification of the inorganic matter in coal. 2. Potential applications of the classification systems , 2009 .

[9]  S. Benson,et al.  Coal and coal ash characteristics to understand mineral transformations and slag formation , 2009 .

[10]  A. K. Pal,et al.  A Middle Triassic age for the Kamthi(Hingir)Formation of the Lower Gondwana Ib-Hingir basin, Orissa, India : New Palaeobotanical Evidence , 1992 .

[11]  G. R. Dunmyre,et al.  Investigation of the high-temperature behaviour of coal ash in reducing and oxidizing atmospheres , 1981 .

[12]  Geir Skjevrak,et al.  Sintering characteristics of sewage sludge ashes at elevated temperatures , 2012 .

[13]  Ravi Kumar,et al.  A Novel tool for assessing slagging propensity of coals in PF boilers , 2008 .

[14]  H. Marsh,et al.  Reactivity of coal macerals and lithotypes , 1988 .

[15]  A. Banerjee,et al.  Composition, mineral matter characteristics and ash fusion behavior of some Indian coals , 2015 .

[16]  N. Calos,et al.  Behaviour of selected minerals in an improved ash fusion test : quartz, potassium feldspar, sodium feldspar, kaolinite, illite, calcite, dolomite, siderite, pyrite and apatite , 1999 .

[17]  Cairncross,et al.  Mineralogical, petrographic and geological controls on coal ash fusion temperature from New Clydesdale Colliery, Witbank Coalfield, South Africa , 2000 .

[18]  Lihua Tang,et al.  Fusibility and flow properties of coal ash and slag , 2009 .

[19]  D. T. Liang,et al.  Agglomeration Characteristics of Sludge Combustion in a Bench-Scale Fluidized Bed Combustor , 2007 .

[20]  X. Querol,et al.  The behaviour of mineral matter during combustion of Spanish subbituminous and brown coals , 1994, Mineralogical Magazine.

[21]  S. Vassilev,et al.  Behaviour of inorganic matter during heating of Bulgarian coals: 1. Lignites , 2005 .

[22]  Liu Haifeng,et al.  Study on the ash fusion temperatures of coal and sewage sludge mixtures , 2010 .

[23]  Prediction of Ash Melting Behavior from Coal Ash Composition , 1979 .

[24]  L. Baxter,et al.  Chemical fractionation tests on south african coal sources to obtain species-specific information on ash fusion temperatures (AFT) , 2005 .

[25]  S. Vassilev,et al.  A new approach for the combined chemical and mineral classification of the inorganic matter in coal. 1. Chemical and mineral classification systems , 2009 .

[26]  Evgueni Jak,et al.  Predicting coal ash slag flow characteristics (viscosity model for the Al2O3-CaO-'FeO'-SiO2 system) , 2001 .

[27]  A. Georgakopoulos,et al.  Ash Deposition in a Pulverized Coal-Fired Power Plant after High-Calcium Lignite Combustion , 2004 .

[28]  M. Keyser,et al.  Influence of discard mineral matter on slag–liquid formation and ash melting properties of coal – A FACTSAGETM simulation study , 2014 .

[29]  A. Pelton,et al.  Coupled experimental and thermodynamic modeling studies for metallurgical smelting and coal combustion slag systems , 1999 .

[30]  Saimir A. Lolja,et al.  Correlation between ash fusion temperatures and chemical composition in Albanian coal ashes , 2002 .

[31]  T. Zeng,et al.  Iron transformations during combustion of Pittsburgh no. 8 coal , 2009 .

[32]  S. Vassilev,et al.  Relationships between chemical and mineral composition of coal and their potential applications as genetic indicators. Part 2. Mineral classes, groups and species , 2010, Geologica Balcanica.

[33]  V. Bouška Geochemistry of coal , 1981 .

[34]  C. W. Bailey,et al.  Index for Iron-Based Slagging for Pulverized Coal Firing in Oxidizing and Reducing Conditions , 2000 .

[35]  S. Vassilev,et al.  Occurrence, abundance and origin of minerals in coals and coal ashes , 1996 .

[36]  R. Creelman,et al.  Relation between Coal Mineral Matter and Deposit Mineralogy in Pulverized Fuel Furnaces , 2013 .

[37]  Evgueni Jak,et al.  Prediction of coal ash fusion temperatures with the F∗A∗C∗T thermodynamic computer package ☆ , 2002 .

[38]  Prashant Singh,et al.  The Petrology of Coals from the Rampur Seam-IV and the Lajkura Seam, Ib River Coalfield, Mahanadi Valley, Orissa, India , 2013 .

[39]  J. Unsworth,et al.  Combustion studies by thermogravimetric analysis: 1. Coal oxidation , 1986 .

[40]  E. Hippo,et al.  Combustion characteristics of selected whole coals and macerals , 1992 .

[41]  C. Ward,et al.  Occurrence of non-mineral inorganic elements in low-rank coal macerals as shown by electron microprobe element mapping techniques , 2007 .

[42]  S. Goswami Marine influence and incursion in the Gondwana basins of Orissa, India: A review , 2008 .

[43]  H. Brink,et al.  A mechanistic study of the formation of slags from iron-rich coals , 1996 .

[44]  S. Koyama,et al.  Effect of Coal Ash Composition on Ash Fusion Temperatures , 2010 .

[45]  S. Goswami,et al.  Pteridophytes from Lower Gondwana formations of the Ib River Coalfield, Orissa and their diversity and distribution in the Permian of India , 2006 .

[46]  J. C. V. Dyk,et al.  Mineral matter transformation during Sasol-Lurgi fixed bed dry bottom gasification – utilization of HT-XRD and FactSage modelling , 2006 .

[47]  B. T. Rhodes,et al.  An Empirical Study of the Relation of Chemical Properties to Ash Fusion Temperatures , 1975 .

[48]  Nevin Selçuk,et al.  Investigation of ash deposition in a pilot-scale fluidized bed combustor co-firing biomass with lignite. , 2009, Bioresource technology.

[49]  Kunihiro Kitano,et al.  Influence of mineral and chemical composition of coal ashes on their fusibility , 1995 .

[50]  Junying Zhang,et al.  Mineralogy, Chemical Composition, and Microstructure of Ferrospheres in Fly Ashes from Coal Combustion , 2006 .

[51]  V. Christina,et al.  Relationships Between Chemical and Mineral Composition of Coal and Their Potential Applications As Genetic Indicators.Part 1. Chemical Characteristics , 2010 .

[52]  G. Huffman,et al.  Correlation between ash-fusion temperatures and ternary equilibrium phase diagrams , 1981 .

[53]  M. Öhman,et al.  Slagging Characteristics during Combustion of Cereal Grains Rich in Phosphorus , 2007 .

[54]  Z. Dong,et al.  Application of the FactSage to Predict the Ash Melting Behavior in Reducing Conditions , 2006 .

[55]  J. Cashion,et al.  Mössbauer analysis of iron phases in brown coal ash and fireside deposits , 1984 .

[56]  Marek Pronobis,et al.  Evaluation of the influence of biomass co-combustion on boiler furnace slagging by means of fusibility correlations , 2005 .

[57]  C. Ward,et al.  Occurrence of non-mineral inorganic elements in macerals of low-rank coals , 2010 .

[58]  V. K. Saxena,et al.  Petrographic controls on combustion behavior of inertinite rich coal and char and fly ash formation , 2014 .

[59]  K. Thomas,et al.  Temperature-programmed combustion studies of coal and maceral group concentrates , 1997 .

[60]  W. Sage,et al.  Relationship of Coal-Ash Viscosity to Chemical Composition , 1960 .