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Die Kohlenversorgung HollandsHoolwerff, Johan van, January 1934 (has links)
Thesis (Ph. D.)--Universität Zürich. / Includes bibliographical references (p. 12-14).
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Correlating laboratory and pilot scale reflux classification of fine coal / Izak Gerhardus Theron SmithSmith, Izak Gerhardus Theron January 2015 (has links)
The search for efficient and economical ways to beneficiate fine coal remains an active research area. Recent developments have shown that the reflux classifier can successfully be used on Australian coals, and based on that, a number of pilot plant investigations have been done in South Africa. While pilot scale units are usually used to test the applicability of a new technology on specific coals, a need exists to gather more fundamental data at a laboratory scale in order to save manpower, costs and time. This study has aimed at introducing a way to pre-test material prior to pilot plant trials in the design chain.
The study shows that a laboratory water only reflux classifier can be used as a density fractionator, which accurately produces washability data for coal – this was also investigated by Callen et al. (2008). There is also a linear correlation between density cut-point and fluid velocity within the plates. Only when looking at the model proposed in Walton (2011:68), does it become clear that the relationship is indeed slightly curved. Many investigations from laboratory and pilot tests accept the linear relationship, and describe it as slightly curved due to the settling being in the intermediate settling regime (Iveson et al., 2014; Galvin & Lui, 2011).
The separation procedures that produce two products – an overflow and underflow – compare well with fractionation results produced. Thus, fractionation results can generate washability data and predict batch separation operations. The laboratory reflux classifier setup is also dependent on particle size, where individual size ranges achieve e.p.m. values of 0.012 and 0.030, while the combined separation efficiency is 0.039.
It was, however, found that the respective laboratory scale reflux classifier that was designed and built was not suitable for continuous operation. The vertical fluidisation section was not high enough to enable a steady fluidised bed. This was necessary for density separation within the bed and to produce a significant pressure differential. It is also recommended to obtain a PID controller. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015
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Correlating laboratory and pilot scale reflux classification of fine coal / Izak Gerhardus Theron SmithSmith, Izak Gerhardus Theron January 2015 (has links)
The search for efficient and economical ways to beneficiate fine coal remains an active research area. Recent developments have shown that the reflux classifier can successfully be used on Australian coals, and based on that, a number of pilot plant investigations have been done in South Africa. While pilot scale units are usually used to test the applicability of a new technology on specific coals, a need exists to gather more fundamental data at a laboratory scale in order to save manpower, costs and time. This study has aimed at introducing a way to pre-test material prior to pilot plant trials in the design chain.
The study shows that a laboratory water only reflux classifier can be used as a density fractionator, which accurately produces washability data for coal – this was also investigated by Callen et al. (2008). There is also a linear correlation between density cut-point and fluid velocity within the plates. Only when looking at the model proposed in Walton (2011:68), does it become clear that the relationship is indeed slightly curved. Many investigations from laboratory and pilot tests accept the linear relationship, and describe it as slightly curved due to the settling being in the intermediate settling regime (Iveson et al., 2014; Galvin & Lui, 2011).
The separation procedures that produce two products – an overflow and underflow – compare well with fractionation results produced. Thus, fractionation results can generate washability data and predict batch separation operations. The laboratory reflux classifier setup is also dependent on particle size, where individual size ranges achieve e.p.m. values of 0.012 and 0.030, while the combined separation efficiency is 0.039.
It was, however, found that the respective laboratory scale reflux classifier that was designed and built was not suitable for continuous operation. The vertical fluidisation section was not high enough to enable a steady fluidised bed. This was necessary for density separation within the bed and to produce a significant pressure differential. It is also recommended to obtain a PID controller. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2015
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The influence of CO₂ on the steam gasification rate of a typical South African coal / Gillis J.D. Du Toit.Du Toit, Gillis Johannes Dekorte January 2013 (has links)
It is recognised that the reactions with steam and CO2 are the rate limiting step during coal gasification, and a vast number of studies has been dedicated to the kinetics of these reactions. Most studies were carried out by using a single reactant (CO2 or H2O), either pure or diluted with an inert gas. Research using gas mixtures of CO2 and steam and their effects on gasification kinetics have been undertaken but are limited.
The objective of this study is to determine the effects of CO2 on the steam gasification rate of a typical Highveld seam 4 coal.
The South African medium ranked high volatile bituminous coal was charred at 950 °C. 2.0 g samples of ± 1 mm particles were analysed in a modified large particle thermo gravimetric analyser under various reactant gas concentrations. Experiments were conducted at atmospheric pressure (87.5 kPa) and temperatures from 775 to 900 °C, such that the conversion rate was controlled by chemical reaction. Reagent mixtures of steam-N2, steam-CO2 and CO2-N2 at concentrations of 25-75 mol%, 50-50 mol%, 75-25 mol% and 100 mol% were investigated.
Arrhenius plots for steam and CO2 gasification produced activation energy values of 225 ± 23 kJ/mol and 243 ± 32 kJ/mol respectively. The calculated reaction orders with respect to reagent partial pressure were 0.44 ± 0.08 and 0.56 ± 0.07 for steam and CO2 respectively.
Comparisons of the experimental data showed a higher reaction rate for the steam-CO2 mixtures compared to steam-N2 experiments. The semi empirical Wen model (m = 0.85) with an additive Langmuir-Hinshelwood styled rate equation predicted the mixed reagent gasification accurately. Reaction constants that were determined from the pure reactant experiments could directly be applied to predict the results for the experiments with mixtures of steam and CO2. The conclusion was made that under the investigated conditions steam and CO2 reacts simultaneously on different active sites on the char surface. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.
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The influence of CO₂ on the steam gasification rate of a typical South African coal / Gillis J.D. Du Toit.Du Toit, Gillis Johannes Dekorte January 2013 (has links)
It is recognised that the reactions with steam and CO2 are the rate limiting step during coal gasification, and a vast number of studies has been dedicated to the kinetics of these reactions. Most studies were carried out by using a single reactant (CO2 or H2O), either pure or diluted with an inert gas. Research using gas mixtures of CO2 and steam and their effects on gasification kinetics have been undertaken but are limited.
The objective of this study is to determine the effects of CO2 on the steam gasification rate of a typical Highveld seam 4 coal.
The South African medium ranked high volatile bituminous coal was charred at 950 °C. 2.0 g samples of ± 1 mm particles were analysed in a modified large particle thermo gravimetric analyser under various reactant gas concentrations. Experiments were conducted at atmospheric pressure (87.5 kPa) and temperatures from 775 to 900 °C, such that the conversion rate was controlled by chemical reaction. Reagent mixtures of steam-N2, steam-CO2 and CO2-N2 at concentrations of 25-75 mol%, 50-50 mol%, 75-25 mol% and 100 mol% were investigated.
Arrhenius plots for steam and CO2 gasification produced activation energy values of 225 ± 23 kJ/mol and 243 ± 32 kJ/mol respectively. The calculated reaction orders with respect to reagent partial pressure were 0.44 ± 0.08 and 0.56 ± 0.07 for steam and CO2 respectively.
Comparisons of the experimental data showed a higher reaction rate for the steam-CO2 mixtures compared to steam-N2 experiments. The semi empirical Wen model (m = 0.85) with an additive Langmuir-Hinshelwood styled rate equation predicted the mixed reagent gasification accurately. Reaction constants that were determined from the pure reactant experiments could directly be applied to predict the results for the experiments with mixtures of steam and CO2. The conclusion was made that under the investigated conditions steam and CO2 reacts simultaneously on different active sites on the char surface. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013.
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Evaluation of the reduction of CO2 emissions from a coal-to-liquids utilities plant by incorporating PBMR energy / M.M. GouwsGouws, Marizanne Michele January 2012 (has links)
Due to the constantly growing environmental concerns about global warming, there is immense
pressure on the coal-to-liquids (CTL) industry to lower carbon dioxide emissions. This study
evaluates the cogeneration of electricity and process steam, using coal and nuclear heat
obtained from a High Temperature Gas Cooled Reactor (HTGR) such as a Pebble Bed Modular
Reactor (PBMR), for the use in a CTL plant. Three different cogeneration processes were
investigated to resolve what influence nuclear cogenerated electricity and process steam would
have on the carbon dioxide emissions and the unit production cost of electricity and process
steam.
The first process investigated utilises coal as combustion medium and an extraction/condensing
steam turbine, together with the thermodynamic Rankine cycle, for the cogeneration of
electricity and process steam. This process was used as a basis of comparison for the nuclearbased
cogeneration processes.
The second process investigated utilises nuclear heat generated by a HTGR and the same
power conversion system as the coal-based cogeneration system. Utilising a HTGR as a heat
source can decrease the carbon dioxide emissions to approximately zero, with a 91.6%
increase in electricity production cost. The last process investigated is the nuclear-based
closed cycle gas turbine system where a gas turbine and Brayton cycle is coupled with a HTGR
for the cogeneration of electricity and process steam. It was found on technical grounds that
this process would not be viable for the cogeneration of electricity and process steam. The unit production cost of electricity and process steam generated by each process were
determined through an economic analysis performed on each process. Overall it was found that
the CTL industry could benefit a great deal from utilising nuclear heat as a heat source. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.
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Evaluation of the reduction of CO2 emissions from a coal-to-liquids utilities plant by incorporating PBMR energy / M.M. GouwsGouws, Marizanne Michele January 2012 (has links)
Due to the constantly growing environmental concerns about global warming, there is immense
pressure on the coal-to-liquids (CTL) industry to lower carbon dioxide emissions. This study
evaluates the cogeneration of electricity and process steam, using coal and nuclear heat
obtained from a High Temperature Gas Cooled Reactor (HTGR) such as a Pebble Bed Modular
Reactor (PBMR), for the use in a CTL plant. Three different cogeneration processes were
investigated to resolve what influence nuclear cogenerated electricity and process steam would
have on the carbon dioxide emissions and the unit production cost of electricity and process
steam.
The first process investigated utilises coal as combustion medium and an extraction/condensing
steam turbine, together with the thermodynamic Rankine cycle, for the cogeneration of
electricity and process steam. This process was used as a basis of comparison for the nuclearbased
cogeneration processes.
The second process investigated utilises nuclear heat generated by a HTGR and the same
power conversion system as the coal-based cogeneration system. Utilising a HTGR as a heat
source can decrease the carbon dioxide emissions to approximately zero, with a 91.6%
increase in electricity production cost. The last process investigated is the nuclear-based
closed cycle gas turbine system where a gas turbine and Brayton cycle is coupled with a HTGR
for the cogeneration of electricity and process steam. It was found on technical grounds that
this process would not be viable for the cogeneration of electricity and process steam. The unit production cost of electricity and process steam generated by each process were
determined through an economic analysis performed on each process. Overall it was found that
the CTL industry could benefit a great deal from utilising nuclear heat as a heat source. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.
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The effects of chemical and physical properties of chars derived from inertinite–rich, high ash coals on gasification reaction kinetics / Gregory Nworah OkoloOkolo, Gregori Nworah January 2010 (has links)
With the increasing global energy demand and the decreasing availability of good
quality coals, a better understanding of the important properties that control the
behaviour of low–grade coals and the subsequent chars in various utilisation
processes, becomes pertinent. An investigation was therefore undertaken, to study the
effects of chemical and physical properties imparted on chars during pyrolysis on the
subsequent gasification reaction kinetics of typical South African inertinite–rich, high
ash Highveld coals. An attempt was made at following these changes in the transition
from coals to chars by a detailed characterisation of both the parent coals and the
respective chars. These changes were determined using various conventional and
advanced techniques, which included among others, carbon crystallite analysis using
XRD and char carbon forms analysis using petrography.
Three of the four original coals were characterised as Bituminous Medium rank C
(coals B, C and C2), while coal D2 was found to be slightly lower in rank
(Bituminous Medium rank D). The coals were rich in inertinites (> 54 vol. %, mmb
with coal C2 having as high as 79 vol. %, mmb) and high in ash content (> 26.7 wt. %,
db) and cabominerite and minerite contents (26 – 39 vol. %, mmb). The inertinitevitrinite
ratios of the coals were found to range from 1.93 to 26.3.
Characterization results show that both volatile matter and inherent moisture content
decreased, while ash, fixed carbon and elemental carbon contents increased from
coals to chars, indicating that the pyrolysis process was efficient. Elemental hydrogen,
oxygen and nitrogen contents decreased, whereas total sulphur contents increased
from coals to chars. This reveals that the total sulphur contained in the char samples
was associated with the char carbon matrix and the minerals. Hydrogen–carbon and
oxygen–carbon ratios decreased considerably from coals to chars showing that the
chars are more aromatic and denser products than the original coals. Despite the fact
that mineral matter increased from coals to chars, the relative abundance of the
different mineral phases and ash components did not exhibit significant variation
amongst the samples. The alkali index was, however, found to vary considerably
among the subsequent chars. Petrographic analysis of the coals and char carbon forms
analysis of the chars reveal that total reactive components (TRC) decrease while the total inert components (TIC) increase from coals to chars. The 0% gain in TIC
observed in char C2 was attributed to its relatively high partially reacted maceral char
carbon forms content. Total maceral reflectance shifted to higher values in the chars
(4.43 – 5.28 Rsc%) relative to the coals (1.15 – 1.63 Rsc%) suggesting a higher
structural ordering in the chars. Carbon crystallite analyses revealed that the chars
were condensed (smaller in size) relative to the parent coals. Lattice parameters: interlayer
spacing, d002, increased, while the average crystallite height, Lc, crystallite
diameter, La, and number of aromatic layers per crystallite, Nave, decreased from coals
to chars. Carbon aromaticity generally increased whereas the fraction of amorphous
carbon and the degree of disorder index decreased from parent coals to the respective
chars. Both micropore surface area and microporosity were observed to increase while
the average micropore diameter decreased from coals to chars. This shows that blind
and closed micropores were “opened up” during the charring process.
Despite the original coal samples not showing much variation in their properties
(except for their maceral content), it was generally observed that the subsequent chars
exhibited substantial differences, both amongst themselves and from the parent coals.
The increasing orders of magnitude of micropore surface area, microporosity, fraction
of amorphous carbon and structural disorderliness were found to change in the
transition, a good indication that the chars’ properties varied from that of the
respective parent coals.
Isothermal CO2 gasification experiments were conducted on the chars in a Thermax
500 thermogravimetric analyser in the temperature range of 900 – 950 °C with varying
concentrations of CO2 (25 – 100 mol. %) in the CO2–N2 reaction gas mixture at
ambient pressure (0.875 bar in Potchefstroom). The effects of temperature and CO2
concentration were observed to be in conformity with established trends. The initial
reactivity of the chars was found to increase in the order: chars C2 < C < B < D2, with
char D2 reactivity greater than the reactivity of the other chars by a factor > 4.
Gasification reactivity results were correlated with properties of the parent coals and
chars. Except for the rank parameter (the vitrinite reflectance), no significant trend
was observed with any other coal petrographic property. Correlations with char
properties gave more significant and systematic trends. Major factors affecting the
gasification reactivity of the chars as it pertains to this investigation are: parent coal vitrinite reflectance, and: aromaticity, fraction of amorphous carbon, degree of
disorder and alkali indices, micropore surface area, microporosity and average
micropore diameter of the chars.
The random pore model (chemical reaction controlling) was found to adequately
describe the gasification reaction experimental data (both conversions and conversion
rates). The determined activation energy ranged from 163.3 kJ·mol–1 for char D2 to
235.7 kJ·mol–1 for char B; while the order of reaction with respect to CO2
concentration ranged between 0.52 to 0.67 for the four chars. The lower activation
energy of char D2 was possibly due to its lower rank, lower coal vitrinite reflectance
and higher alkali index. The estimated kinetic parameters of the chars in this study
correspond very well with published results in open literature. It was possible to
express the intrinsic reactivity, rs, of the chars (rate of carbon conversion per unit total
surface area) using kinetic results, in empirical Arrhenius forms. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2011.
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The effects of chemical and physical properties of chars derived from inertinite–rich, high ash coals on gasification reaction kinetics / Gregory Nworah OkoloOkolo, Gregori Nworah January 2010 (has links)
With the increasing global energy demand and the decreasing availability of good
quality coals, a better understanding of the important properties that control the
behaviour of low–grade coals and the subsequent chars in various utilisation
processes, becomes pertinent. An investigation was therefore undertaken, to study the
effects of chemical and physical properties imparted on chars during pyrolysis on the
subsequent gasification reaction kinetics of typical South African inertinite–rich, high
ash Highveld coals. An attempt was made at following these changes in the transition
from coals to chars by a detailed characterisation of both the parent coals and the
respective chars. These changes were determined using various conventional and
advanced techniques, which included among others, carbon crystallite analysis using
XRD and char carbon forms analysis using petrography.
Three of the four original coals were characterised as Bituminous Medium rank C
(coals B, C and C2), while coal D2 was found to be slightly lower in rank
(Bituminous Medium rank D). The coals were rich in inertinites (> 54 vol. %, mmb
with coal C2 having as high as 79 vol. %, mmb) and high in ash content (> 26.7 wt. %,
db) and cabominerite and minerite contents (26 – 39 vol. %, mmb). The inertinitevitrinite
ratios of the coals were found to range from 1.93 to 26.3.
Characterization results show that both volatile matter and inherent moisture content
decreased, while ash, fixed carbon and elemental carbon contents increased from
coals to chars, indicating that the pyrolysis process was efficient. Elemental hydrogen,
oxygen and nitrogen contents decreased, whereas total sulphur contents increased
from coals to chars. This reveals that the total sulphur contained in the char samples
was associated with the char carbon matrix and the minerals. Hydrogen–carbon and
oxygen–carbon ratios decreased considerably from coals to chars showing that the
chars are more aromatic and denser products than the original coals. Despite the fact
that mineral matter increased from coals to chars, the relative abundance of the
different mineral phases and ash components did not exhibit significant variation
amongst the samples. The alkali index was, however, found to vary considerably
among the subsequent chars. Petrographic analysis of the coals and char carbon forms
analysis of the chars reveal that total reactive components (TRC) decrease while the total inert components (TIC) increase from coals to chars. The 0% gain in TIC
observed in char C2 was attributed to its relatively high partially reacted maceral char
carbon forms content. Total maceral reflectance shifted to higher values in the chars
(4.43 – 5.28 Rsc%) relative to the coals (1.15 – 1.63 Rsc%) suggesting a higher
structural ordering in the chars. Carbon crystallite analyses revealed that the chars
were condensed (smaller in size) relative to the parent coals. Lattice parameters: interlayer
spacing, d002, increased, while the average crystallite height, Lc, crystallite
diameter, La, and number of aromatic layers per crystallite, Nave, decreased from coals
to chars. Carbon aromaticity generally increased whereas the fraction of amorphous
carbon and the degree of disorder index decreased from parent coals to the respective
chars. Both micropore surface area and microporosity were observed to increase while
the average micropore diameter decreased from coals to chars. This shows that blind
and closed micropores were “opened up” during the charring process.
Despite the original coal samples not showing much variation in their properties
(except for their maceral content), it was generally observed that the subsequent chars
exhibited substantial differences, both amongst themselves and from the parent coals.
The increasing orders of magnitude of micropore surface area, microporosity, fraction
of amorphous carbon and structural disorderliness were found to change in the
transition, a good indication that the chars’ properties varied from that of the
respective parent coals.
Isothermal CO2 gasification experiments were conducted on the chars in a Thermax
500 thermogravimetric analyser in the temperature range of 900 – 950 °C with varying
concentrations of CO2 (25 – 100 mol. %) in the CO2–N2 reaction gas mixture at
ambient pressure (0.875 bar in Potchefstroom). The effects of temperature and CO2
concentration were observed to be in conformity with established trends. The initial
reactivity of the chars was found to increase in the order: chars C2 < C < B < D2, with
char D2 reactivity greater than the reactivity of the other chars by a factor > 4.
Gasification reactivity results were correlated with properties of the parent coals and
chars. Except for the rank parameter (the vitrinite reflectance), no significant trend
was observed with any other coal petrographic property. Correlations with char
properties gave more significant and systematic trends. Major factors affecting the
gasification reactivity of the chars as it pertains to this investigation are: parent coal vitrinite reflectance, and: aromaticity, fraction of amorphous carbon, degree of
disorder and alkali indices, micropore surface area, microporosity and average
micropore diameter of the chars.
The random pore model (chemical reaction controlling) was found to adequately
describe the gasification reaction experimental data (both conversions and conversion
rates). The determined activation energy ranged from 163.3 kJ·mol–1 for char D2 to
235.7 kJ·mol–1 for char B; while the order of reaction with respect to CO2
concentration ranged between 0.52 to 0.67 for the four chars. The lower activation
energy of char D2 was possibly due to its lower rank, lower coal vitrinite reflectance
and higher alkali index. The estimated kinetic parameters of the chars in this study
correspond very well with published results in open literature. It was possible to
express the intrinsic reactivity, rs, of the chars (rate of carbon conversion per unit total
surface area) using kinetic results, in empirical Arrhenius forms. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2011.
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The influence of potassium and calcium species on the swelling and reactivity of a high-swelling South African coal / Anna Catharina CollinsCollins, Anna Catharina January 2014 (has links)
Alkali compounds were added to a South African coal with a high swelling propensity and the behaviour of the blends were investigated. A vitrinite-rich bituminous coal from the Tshikondeni coal mine in the Limpopo province of South Africa was used. To reduce the influence of the minerals in the coal, the coal was partially demineralized by leaching with HCl and HF. The ash content of the coal sample was successfully reduced from 17.7% to 0.6%. KOH, KCl, K2CO3 and KCH3CO2 were then added to the demineralized coal in mass percentages of 1%, 4%, 5% and 10%. The free swelling indices (FSI) of the blends were determined and the samples were subjected to acquisition of TMA and TG-MS data. Addition of these potassium compounds to the demineralized coal reduced the swelling of the vitrinite-rich coal. From the free swelling indices of the various mixtures, it was concluded that the potassium compounds reduce the swelling of the coal in the following order of decreasing impact: KCH3CO2 > KOH > K2CO3 > KCl. From dilatometry experiments done on the blends with the 10% addition of potassium compounds, it was seen that with the addition of potassium compounds to the demineralized coal, a reduction in dilatation volume was obtained. The influence of the potassium compound in decreasing order: K2CO3> KOH> KCH3CO2> KCl. An increase in the softening temperature was observed for the demineralized coal-alkali blends. Thermogravimetric analyses were performed on the demineralized coal-potassium blended samples (<75 μm). These samples were pyrolyzed under a nitrogen atmosphere to a maximum temperature of 1200 °C using a heating rate of 10 °C/min. The relative reactivity for each of the blends with the different wt% addition was determined. From these results it was seen that KCH3CO2 increased the relative reactivity, whereas the KOH, KCl and K2CO3 showed an inhibiting influence. The attached mass spectrometer provided information on the low molecular mass gaseous products formed in the various temperature ranges as the thermal treatment proceeded. From the mass spectroscopy results, it was found that the potassium compounds decreased the temperature at which maximum evolution of H2 takes place. Thermomechanical analyses were performed on the 10 wt% addition of the potassium compounds to the demineralized coal. During TMA analyses, the sample was heated to 1000 °C using a heating rate of 10 °C/min. From the TMA result obtained it was clear that the addition of KCl did not have an influence on the swelling of the demineralized coal. All results are discussed. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014
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