CHEMICAL AND PHYSICAL STRUCTURAL STUDIES ON TWO INERTINITE-RICH LUMP COALS. Nandi Malumbazo A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philoso- phy in the School of Chemical and Metallurgical Engineering at the University of the Witwatersrand. Johannesburg, 2011 DECLARATION I, Nandi Malumbazo, declare that the thesis entitled: “CHEMICAL AND PHYSICAL STRUCTURAL STUDIES ON TWO INER- TINITE-RICH LUMP COALS” is my own work and that all sources I have used or quoted have been indicated and ac- knowledged by means of references. Signature: ……………………………………………………………….. Date:………………………………………………………………………… Page i ABSTRACT ABSTRACT Two Highveld inertinite-rich lump coals were utilized as feed coal samples in order to study their physical, chemical structural and petrographic variations during heat treat- ment in a packed-bed reactor unit combustor. The two feed lump coals were selected as it is claimed that Coal B converts at a slower rate in a commercial coal conversion process when compared to Coal A. The reason for this requires detailed investigation. Chemical structural variations were determined by proximate and coal char CO2 reactiv- ity analysis. Physical structural variations were determined by FTIR, BET adsorption methods, XRD and 13C Solid state NMR analysis. Carbon particle type analysis was con- ducted to determine the petrographic constituents of the reactor generated samples, their maceral associations (microlithotype), and char morphology. This analysis was undertaken with the intention of tracking the carbon conversion and char formation and consumption behaviour of the two coal samples within the reactor. Proximate analysis revealed that Coal A released 10 % more of its volatile matter through the reactor compared to Coal B. Unburnt carbon in the ash bed zone was ob- served for both coal samples (Coal A and B), and it was attributed to incomplete carbon conversion. Coal char CO2 reactivity analysis showed that indeed Coal A is more reac- tive than Coal B. Page ii ABSTRACT Qualitative FTIR analysis showed that both coals follow similar trends when exposed to high temperatures. Coal structural characterization revealed that Coal A has higher sur- face area when compared to Coal B. XRD analysis revealed that Coal A has less aromatic crystallites and lower Lc values compared to Coal B. It was observed that the coal struc- tural properties of Coal A became more ordered and aligned at lower temperatures (289 0C), whereas Coal B starts at higher temperatures (693 0C). 13C Solid state NMR results showed that Coal B is more aromatic than Coal A implying that it is difficult to gasify/combust Coal B. Petrography analysis showed that Coal A has 34.6 vol % reactive macerals of which 78 % is from liptinite and vitrinite contents. Coal B has 53.6 vol % of reactive macerals of which 49 % was from liptinite and vitrinite, the other 51 % is from reactive semifusinite and inertodetrinite. The 49/51 split between reactive maceral value for Coal B may explain the lower reactivity compared to Coal A. Coal B appeared to produce more inert char particles, ran at higher temperatures in the ash bed because of its aromatic richness than Coal A. This was also attributed to the fact that Coal B has higher inertinite content than Coal A. The allocation of parent coal samples to “reactive” and “inert” macerals gave more in depth results that were able to show a possible rea- son behind reactivity difference occurring during the coal conversion process and sup- port the structural analysis results obtained for these parent coal samples. The reactiv- ity difference of these parent lump coal samples appears to be greatly influenced by the chemical reactions (structure) of these samples more than the kinetic reactions (pres- sure, temperature, reaction rates etc.) of these samples. Page iii DEDICATION I dedicate this work to my son Hlumelo and my husband Mvuselelo Mathebula. Page iv ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I would like to extend my gratitude to the following: God almighty for guiding me throughout my studies and making my dreams come true. To my ancestors for opening doors and guiding me throughout the difficulties of my varsity life. My ancestors from maternal side: Oonkomo, Oogolela, Oomasikela, Ooyongwane, Oomntungwa, Oomalinga, Oomasikane, Oonkumbuzo. My ancestors from my paternal side: Oonyawuza, Oo- faku, Oompondo, Oondayeli, Uziqelekazi uhlamba ngobubende, OoDakile. To my parents (Mrs. Bukelwa Malumbazo-Ndayi and Mr. Makwedinana Ndayi) for giving me this life and raising me to be the person that I am today. To my siblings Thabiso Malumbazo, Zikhona “titi” Malumbazo and Yanga Ndayi, I was doing this to motivate you guys to continue with your studies no matter what. To my husband Mvuselelo Mathebula for his encouragement and motivation for me to study this far. To my supervisors, Prof. Wagner and Prof. Bunt for your constant guidance, support and pa- tience to develop my skills in coal research and also for believing in me. To Sasol for financial assistance and to the following people working at Coal processing Tech- nologies Prof. J. van Heerden, Dr. D. van Niekerk, Ms. H. Assumption, Mr Ben Ashton, Dr. R. Coet- zer, Mr. S. Duplessis and Dr. B. Hlatshwayo for your constructive support and always avail your- selves when I needed your help. To my close friends and Carbon and Coal Group colleagues for always putting a smile on my face whenever I need it, you know who you are. Page v CONTENTS Contents Chapter 1 ............................................................................................................................................ 1 1. INTRODUCTION.................................................................................................................................. 1 1.1 Background and motivation of the study......................................................................... 1 1.1.1 Coal Structure ............................................................................................................................. 2 1.2 Research Questions .................................................................................................................. 4 1.3 Aim and Objectives of the study .......................................................................................... 5 1.4 Scope of the thesis..................................................................................................................... 6 Chapter 2 ............................................................................................................................................ 7 2. LITERATURE REVIEW ...................................................................................................................... 7 2.1 Origins and Formation of Coal ............................................................................................. 7 2.2 Geological Occurrence and uses of Coal in South Africa ............................................ 9 2.2.1 South African Coalfields ....................................................................................................... 11 2.3 Classification of Coal ............................................................................................................. 13 2.4 Coal Structure .......................................................................................................................... 15 2.4.1 Analytical methods utilized for the Coal Structural Studies. ................................. 17 2.4.1.1 Fourier Transform Infrared Spectroscopy (FTIR) studies for Coals .................. 18 2.4.1.2 X-ray powder diffraction studies for Coals .................................................................. 21 2.4.1.3 13C Solid State Nuclear Magnetic Resonance Spectroscopy studies for Coals. 26 2.4.1.4 BET Adsorption studies for Coals .................................................................................... 29 2.5 Coal petrography .................................................................................................................... 30 2.5.1 Macerals ..................................................................................................................................... 34 Page vi CONTENTS 2.5.1.1 Liptinite ...................................................................................................................................... 35 2.5.1.2 Vitrinite ...................................................................................................................................... 36 2.5.1.3 Inertinite .................................................................................................................................... 36 2.5.2 Microlithotypes ....................................................................................................................... 38 2.5.3 Mineral Matter ......................................................................................................................... 40 2.6 Coal Conversion ...................................................................................................................... 40 Chapter 3 .......................................................................................................................................... 45 3. EXPERIMENTAL METHOD .......................................................................................................... 45 3.1 Origin of the feed coal samples ........................................................................................