Mineral Matter In Coal Research Articles

Understanding the influence of acidic components (Si, Al, and Ti) on ash flow temperature of South African coal sources

Ash flow temperature is one property that specifically gives more information on the suitability of a coal source for combustion or gasification purposes. Therefore the chemistry and mineral interaction have to be understood in order to determine the suitability for fixed bed gasification purposes with regards to ash flow properties. Various authors ([Seggiani, M., 1999. Empirical correlations of the ash flow temperatures and temperature of critical viscosity for coal and biomass ashes. Fuel 78, 1121; Alpern, B., Nahuys, J., Martinez, L., 1984. Mineral matter in ashy and non-washable coals—its influence on chemical properties. Commun. Serv. Geol. Portugal 70 (2), 299]) have expressed the fusibility of coal ash as a function of the content of the principal oxides frequently found in coal ash, i.e. SiO 2, Al 2O 3, TiO 2, Fe 2O 3, CaO, MgO, Na 2O and K 2O. However, coal ash fusibility characteristics are difficult to determine precisely, partly because coal ash contains many components with different chemical behaviours, and may very from coal source to coal source. The purpose of this study is primarily to understand the effect and chemistry of the acidic components (Si, Al and Ti) of South African coal sources, as well as the manipulation or addition of these components to the coal sources, with the view to understand their effect on the ash flow properties. A representative coal blend as it is currently used for gasification purposes, as well as coal mixtures with the addition of pure SiO 2, Al 2O 3 and TiO 2, respectively, were prepared. The variation of the acidic components SiO 2, Al 2O 3 and TiO 2 varied from 1 mass% to 50 mass% to the coal blend. The particle size of the samples were representatively prepared to <1 mm and analyzed for ash flow temperature and ash composition as dependant variables according to ASTM D1857-87 and ASTM D2795-95, respectively. The raw data was then statistically evaluated by means of regression models. Results of the statistical evaluation of ash flow temperature and the ash elemental composition indicated that based on the 95% confidence interval Al 2O 3, Fe 2O 3, CaO, MgO, P 2O 5, as well as the SiO 2–Al 2O 3 ratio have a statistical significant effect on ash flow temperature. Regression trends of the coal and Al 2O 3, SiO 2 and TiO 2 mixtures indicated that Al 2O 3 has the biggest effect on the ash flow temperature. A shift towards increasing the Al 2O 3 concentration has a significant increasing effect on the ash flow temperature in the three-component system Al 2O 3–SiO 2–TiO 2 phase diagram. The ash flow temperature is the highest at the point where the Al 2O 3 concentration is maximized. The shifts in frequency of the absorption band associated with the 6s–6p electron transaction which relates to the basicity of a glass or slag also relates to the different effect of the individual acidic components on ash flow temperature. The shift can be considered as a measure of the electron donor power and is usually expressed in terms of the optical ( Λ) basicity. The ion–oxygen attraction and the stronger (more positive) value obtained for Al 2O 3 in comparison with TiO 2 and SiO 2 could be seen; and possibly explain why Al 2O 3 has a bigger influence and effect on increasing the ash flow temperature. It can be concluded from this experimental work with the emphasis on flow properties, that the acidic components Al 2O 3, SiO 2 and TiO 2 all have an increasing effect on ash flow temperature when added to the coal blends currently used for gasification. In addition to this general conclusion, it has also been confirmed that Al 2O 3 addition to the coal blend has the most significant effect towards increasing the ash flow temperature when compared to SiO 2 and TiO 2.

High-Yield Hydrogen Production by Steam Gasification of HyperCoal (Ash-Free Coal Extract) with Potassium Carbonate: Comparison with Raw Coal

Steam gasification of the HyperCoals (ash-free coal extracts) with the physical addition of 5.8%−6.0% K2CO3 was conducted at 1023 K on a thermogravimetric apparatus that was equipped with an on-line quadrupole mass spectrometer. The catalytic gasification of the HyperCoals demonstrated a much higher gasification rate than the catalytic gasification of the raw coals. Interactions of K2CO3 with mineral matter in the raw coal formed water-insoluble potassium compounds, such as potassium aluminosilicates, and reduced the catalytic activity, whereas no such negative reactions occurred for the HyperCoals. The steam gasification of the HyperCoals with K2CO3 was also determined to be favorable for the high-yield production of hydrogen. From these experimental results, the catalytic steam gasification of HyperCoal would potentially be a more efficient process for the production of hydrogen in the future.

Climate Controls on Stratigraphy: SEPM Special Publication No. 77

C. Blaine Cecil and N. Terence Edgar, Editors, 2003, SEPM, Tulsa, 275 p. (SEPM members; US $68.00; nonmembers; US $95.00) ISBN: 1-56576-085-9. Climate long has played the poor stepsister to tectonics in the realm of sedimentary geology, but Cecil and Edgar's special publication ( Climate Controls on Stratigraphy ) facilitates Cinderella's continuing debut from the dungeon. The mantra of the volume is the primary role that climate plays in stratigraphy, which is a distinct and deliberate departure from previous emphases on tectonic and eustatic roles. Having been raised on a steady diet of the primacy of tectonics over all other controls on sedimentation, I found this volume to be a refreshing departure, despite my occasional disagreements with the details. Cecil begins the volume with an executive summary in which he advocates the position that a better appreciation of climate's control on sedimentation will lead to better models for the distribution and development of fossil-fuel sources—and we'll reap a bonus of learning more about Earth's climate system. He also outlines the three-part organization of the volume, in which Part 1 provides the framework for climatic controls on sedimentation, Part 2 presents the data and interpretations used to study a single Pennsylvanian cyclothem across North America, and Part 3 captures additional climate-themed studies. The Introduction recounts the butterfly-like flight path of research that ultimately resulted in this volume, which emerged from the sustained efforts of a USGS group working on the origin of mineral matter in coal. Cecil et al.'s first efforts to predict coal composition using then-popular facies models failed, and subsequent study of supposed analogs within the modern environments of the Mississippi Delta, Florida Everglades, and Atlantic coastal swamps similarly failed. The epiphany for a new model arrived when T.L. Phillips and colleagues reintroduced the importance of climate as a control on …

Chemical fractionation tests on South African coal sources to obtain species-specific information on ash fusion temperatures (AFT)

Coals from the different sources used by Sasol vary substantially in terms of chemical and physical properties and directly relates to gasifier behavior. Due to the large variation in coal properties from various sources, detailed coal and feedstock characteristics are essential to predict gasification performance when a specific coal source is to be gasified. One property that specifically gives detail information on the suitability of a coal source [Alpern B, Nahuys J, Martinez L. Mineral matter in ashy and non-washable coals—its influence on chemical properties. Commun Serv Geol Portugal 1984; 299–317.] for gasification purposes is the ash fusion temperature (AFT). The AFT of a coal source indicates the extent to which ash agglomeration and ash clinkering are likely to occur within the gasifier. Ash clinkering inside the gasifier can cause channel burning, pressure drop problems and unstable gasifier operation. The principle aim of this paper is to obtain mineral species-specific information on ash properties and the specific affect on AFT. Chemical fractionation treatment resulted in coals having different mineral properties that can be used to explain the affect of specific minerals on the AFT of coal. The highest concentration and species of minerals were removed from the coal by acid leaching (HCl and HNO 3) where Al, Ca, Mg, Na and Fe were removed in high concentrations from the coal. An interesting finding in the ash composition of the coal after leaching was that the SO 3 concentration decreased from >2 mass % in the original coal sources to <0.3 mass % after the acid leaching. The AFT of coal after leaching increased to >1600 °C. Based on the 95% confidence intervals depicted the following components can be highlighted as having a statistical significant effect on the AFT: Al 2O 3, Fe 2O 3, CaO, MgO, P 2O 5 and SiO 2–Al 2O 3 combination. When mineral ratio was used, the best correlation coefficient ( R) with AFT was obtained with the dolomite ratio. This is in agreement with the results obtained from the correlations between the AFT and the ash composition where CaO and MgO resulted in the best correlation with AFT. Although the correlation ( R) of 0.81 is fairly similar to that of the individual correlations with CaO and MgO, the dolomite ratio also includes Fe, Na and K, which can have mineral interaction with the Ca and Mg and thus may be included in the ratio. Results presented in this paper again highlights the fact and confirmed work from other researchers [Slegeir WA, Singletary JH, Kohut JF. Application of a microcomputor to the determination of coal ash fusibility characteristics. J Coal Quality 7: 248–54.] that ash composition (elemental analyses) on its own does not explain AFT behavior or commercial performance of coal accurately.

Influence of Inherent Coal Mineral Matter on the Structural Characteristics of Graphite Materials Prepared from Anthracites

Anthracites with different mineral matter content and composition but similar organic matter compositionand, therefore, microtexturewere obtained by consecutive immersion in mixtures of organic liquids of increasing density from an anthracite with a low degree of graphitizability, thus reducing the characteristics of the anthracite that affect the graphitization process to the mineral matter. Graphite materials were then prepared by heating the anthracites in the temperature interval of 2400−2600 °C for the purpose of studying the influence of the anthracite mineral matter (amount and composition) on their ability to graphitize. The interlayer spacing (d002) and crystallite sizes (along the c-axis (Lc) and along the a-axis (La)), calculated from X-ray diffractometry (XRD), as well as the relative intensity of the Raman D-band (ID/It), were used to assess the degree of structural order of the materials. A progressive increase in this degree of structural order with increasing mineral matter content of the anthracite was observed. The catalytic effect of the mineral matter on the graphitization of the anthracites relies mainly on promotion of the growth of the crystallites along the basal plane. Reasonably good linear correlations between the mineral matter content and the La value of the material were attained. Among the different constituents of the mineral matter, the clay mineral illite and the iron carbonates ankerite and siderite were observed to be the main active catalyst compounds during the graphitization of anthracites. In addition to the amount and composition of the mineral matter, the distribution of the mineral matter also influences the graphitization process of the anthracite. A fine distribution in the organic matter, such as that in the case of the iron compounds, was observed to improve the catalytic effect of the mineral matter.

Evaluation of the collective washing of coals from the Soma region with different characteristics

Coal basins may have different coal formations. Therefore, different coal characteristics can be seen even in the same coal seam. The characteristics of the coal and the type of the mineral matter in coal are very important factors for the design of coal washing plants. The Soma coal region in Turkey has different coal formations which necessitate a careful blending of the coals prior to the washing plant. At present, Soma coals are being washed in a conventional heavy media plant. However, coals from different productions zones are fed to the plant without any blending. The clean products are also not blended to gain a consistent quality before sale. In this study, five different types of coal from the Soma region were washed together in the same washing plant. First, these coals were submitted to float–sink tests. Data derived from these tests were used for the evaluation of the plant trials. A novel method was used for the evaluation of the coal's washability and its probable effects on the performance of the coal washing equipment. As a result, experiments and evaluations show that the coal formations in the Soma region have significant differences in their characteristics which can impair the performance of the coal washing plant. Thus, washing these coals in the same plant under the same conditions needs blending or a special feeding programme.

Depolymerization Study of Pakistani Lignite Coal Influence of Pre‐treatments on Product Slate

AbstractInfluence of pretreatments, i.e., demineralization and pre‐soaking in some solvents on the yields of liquefied products obtained from hydro‐depolymerization of Pakistani coal in a pool of hydrogen has been discussed. Results of hydrogenation experiments demonstrated that demineralizing the coal sample prior to liquefaction caused the yields to decrease compared with the virgin coal samples. The contribution of mineral matter of coal has been evaluated by comparing the yields of liquid products of virgin and leached samples. Increase in the yields obtained from the hydrogenation experiments of swollen coal samples was not satisfactorily significant.

Production of carbon nanotubes from coal

We have demonstrated that the production of carbon nanotubes in large quantities is possible with inexpensive coal as the starting carbon source by the arc discharge technique. It has been found that a large amount of carbon nanotubes of good quality can be obtained in the cathode deposits in which carbon nanotubes are present in nest-like bundles. For the growth of carbon nanotubes, the buffer gas pressure in the reactor is one of the crucial factors. The mineral matter in raw coals may also play an important part in the formation process of carbon nanotubes.

Production of carbon nanotubes from coal

We have demonstrated that the production of carbon nanotubes in large quantities is possible with inexpensive coal as the starting carbon source by the arc discharge technique. It has been found that a large amount of carbon nanotubes of good quality can be obtained in the cathode deposits in which carbon nanotubes are present in nest-like bundles. For the growth of carbon nanotubes, the buffer gas pressure in the reactor is one of the crucial factors. The mineral matter in raw coals may also play an important part in the formation process of carbon nanotubes.

Determination of the Handleability of Power Coals and Factors Generating its Variability

The behavior of fine thermal coal during loading, transportation, unloading, and storage depends on such factors as moisture content, particle size composition, ash content, and mineralogical composition of coal mineral matter. The principles of the GIG method of determination of handleability index, developed at the Central Research Mining Institute (GIG) in Katowice, is described. Results of the handleability index measurements using the GIG method are presented, and the classification system of thermal coals based on such a handleability index is introduced and discussed.

Effect of demineralization on hydrogen transfer of coal with tritiated gaseous hydrogen

Roles of mineral matters and oxygen functional groups of coal on hydrogen transfer reaction with gaseous hydrogen were investigated by using a tritium tracer technique in a fixed-bed reactor system. Mineral matters in coal were removed by HCl or HCl/HF treatments. Alkali metals and a part of pyrite were removed by HCl treatment. SiO 2 and Al 2O 3 were removed only by HCl/HF treatment. A large part of pyrite was removed by HCl/HF treatment but about 20% of them still remained even after the treatment. It was observed that the efficiency of hydrogen transfer of coal decreased to some extent when cations and mineral matters were removed by HCl treatment. Further decrease in hydrogen transfer was observed after HCl/HF treatment. These results suggested that iron species from pyrite may catalyze the hydrogen transfer reaction with H 2 gas. Mineral matters assist the H-transfer to the carbon network of coal but does not promote hydrogen transfer to hydroxy groups.

Investigation on chemical structure of minerals in coal using 27Al MQMAS NMR

High-resolution two-dimensional 27Al multiple-quantum magic-angle-spinning (MQMAS) NMR, being capable of averaging the second-order quadrupolar interaction, was applied in order to characterize the mineral matter in coals that have been spotlighted recently in new approach to the coal utilization. Octahedral aluminum compounds which consist of kaolin and other mineral phases could be clearly distinguished by 27Al MQMAS method. As the total carbon percent increases, octahedral aluminum species tend to vary from kaolin. A combination of cross polarization and MQMAS, it being called as 1H→ 27Al CP/MQMAS, was also employed to evaluate chemical bonding between aluminum atom and hydrogen atom. As a result, the octahedral components containing the linkage of Al–O–H such as kaolin and excluding the Al–O–H bond were separated by this technique. MQMAS and CP/MQMAS are very effective in characterization of inorganic matter including quadrupolar nuclei, which are particularly well suited to the analysis of clay minerals with noncrystalline materials and present in coals while XRD is difficult to analyze the amorphous compounds.

04/00005 Influence of mineral matter in coal on decomposition of NO over coal chars and emission of NO during char combustion: Zhao, Z. et al. Fuel, 2003, 82, (8), 949–957

04/00005 Influence of mineral matter in coal on decomposition of NO over coal chars and emission of NO during char combustion: Zhao, Z. et al. Fuel, 2003, 82, (8), 949–957

04/00008 Methods for characterization of inorganic and mineral matter in coal: a critical overview: Vassilev, S. V. and Tascon, J. M. D. Energy & Fuels; 2003, 17,(2), 271–281

04/00008 Methods for characterization of inorganic and mineral matter in coal: a critical overview: Vassilev, S. V. and Tascon, J. M. D. Energy & Fuels; 2003, 17,(2), 271–281

Effect of inorganic matter on reactivity and kinetics of coal pyrolysis

Two Chinese coals, Shenfu subbituminous coal and Huolingele lignite, were used to investigate the effect of mineral matter in coal on reactivity and kinetic characteristics of coal pyrolysis. The experiments were carried out by using thermogravimetry to check the pyrolysis behavior of raw coal, HCl/HF demineralized coal and demineralized coal with inorganic matter (CaO, K 2CO 3 and Al 2O 3) added, respectively. The results showed that inherent mineral in coal had no evident effect on the reactivity and kinetics of coal pyrolysis. CaO, K 2CO 3 and Al 2O 3 all had a catalytic effect on the reactivity of coal pyrolysis, their effects were closely related to temperature region and coal types. The pyrolysis process of all the samples studied can be described by three independent first order kinetic model. Addition of inorganic matter the activation energy decreased and the characteristic temperature of coal changed.

The influence of mineral matters in coal on NO-char reaction in the presence of SO 2

The effect of mineral matter in char on NO-char reaction in the presence of SO 2 was studied by temperature programmed reaction and isothermal experiments. Three coals with different ranks and their demineralized samples were pyrolyzed in N 2 at 900 °C to prepare the chars. Different kinds of metals were loaded on the demineralized chars to compare their catalytic effect on NO conversion during NO-char reaction. The results show that the effect of mineral matter is closely related to the content of catalytically active components. More catalytically active components in mineral matter in the char, higher catalytic activity for NO-char reaction. While the inert components, such as Al 2O 3 and Si 2O 3, will abate the NO conversion. Besides the catalytic effect of active mineral matter, the reactivity of the char is another important factor to affect the NO conversion during NO-char reaction. With increasing coal rank, the resultant char shows lower activity for reduction of NO. The effect of SO 2 on the NO-char reaction is changed with temperature. At higher temperatures NO conversion is further enhanced by the reaction of NO–SO 2 and the increase in the amount of active sites due to the release of SO 2 chemisorbed on the char surface.

03/02125 The influence of mineral matters in coal on the reaction of NO-char in the presence of SO 2: Chang, H. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2003, 48, (1), 306–307

03/02125 The influence of mineral matters in coal on the reaction of NO-char in the presence of SO 2: Chang, H. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2003, 48, (1), 306–307

The relationship between excluded mineral matter and the abrasion index of a coal

Predictions of the wear rates of components in grinding mills at pulverised coal-fired power stations are currently made using empirical relationships based on the ash content of the coals. However, modern coal characterisation techniques now allow the mineral inclusions in a coal that are responsible for the abrasive nature of the coal to be accurately characterised. Hence, there is scope to make improved predictions of wear based on a detailed knowledge of the mineral matter in a particular coal. It is first necessary, however, to understand the nature of the minerals and properties of the minerals in a coal that would contribute to abrasive wear. In this study known quantities of quartz, pyrite and slate have been added to a washed coal and the Abrasion Indices of the coal/mineral mixtures have been measured. The results show how the size, shape and hardness of excluded mineral matter contribute to the abrasive properties of a coal.

Occurrence and volatilization behavior of Pb, Cd, Cr in Yima coal during fluidized-bed pyrolysis ☆

The volatilization behavior of Pb, Cd, Cr and the influence of coexisting mineral matters were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 500 to 900 °C. The modes of occurrence of Pb, Cd, Cr in Yima raw coal and two char samples were determined using density fractionation, demineralization and sequential chemical extraction methods. Lead in Yima coal is mostly associated with mineral matter in various forms, mainly pyrite, sulfates and monosulfides. Large part of cadmium is associated with pyrite. Chromium in Yima coal is mainly associated with organic matter. Different trends are observed for various forms of trace metals during pyrolysis. Lead associated with pyrite, sulfates and carbonates, lead in water soluble and ion exchangeable forms, and cadmium associated with pyrite are all unstable under pyrolysis conditions. During Yima coal pyrolysis, the volatilities of lead and cadmium vary greatly with pyrolysis temperature, while chromium volatility in Yima raw coal only has slight changes over the temperature range (500–900 °C) studied. The volatility of Pb, Cd, Cr in demineralized Yima coal (YimaD) is much higher than that of Yima coal during pyrolysis. New thermally stable forms of Pb, Cd and Cr are formed during pyrolysis of Yima, whereas the sources of them are different. The interactions between chromium and its coexisting mineral matters in Yima coal retard its vaporization during pyrolysis.

Rare earth element sources and modification in the Lower Kittanning coal bed, Pennsylvania: implications for the origin of coal mineral matter and rare earth element exposure in underground mines

In this study, we examine the variations in rare earth elements (REE) from the Lower Kittanning coal bed of eastern Ohio and western Pennsylvania, USA, in an attempt to understand the factors that control mineral matter deposition and modification in coal, and to evaluate possible REE mixed exposure hazards facing underground mine workers. The results of this study suggest that the Lower Kittanning coal mineral matter is derived primarily from a clastic source similar to that of the shale overburden. While highly charged cations like silicon, aluminum, and titanium remained relatively immobile within the coal mineral matter, iron (primarily as pyrite) was added from nonclastic sources, either during deposition of the coal mire vegetation or subsequent to burial. Other mobile cations (e.g., alkali and alkaline earth elements) appear to have been added to and/or leached from the originally deposited clastic mineral matter. Most of the sulfur in the Lower Kittanning coal bed is bound as FeS 2 in the mineral matter, but a majority of samples contain a small excess of S that is most likely organically bound. In general, the total rare earth element content (TREE) in coal ash is greater than that in the shale overburden. If the primary source of mineral matter is the same as that for the overlying shale, then REE must have been enriched in the coal mineral matter subsequent to deposition. The total rare earth element content of Lower Kittanning coals correlates strongly with Si concentration ([TREE]≈0.0024 [Si]), which provides a threshold for evaluating possible mixed exposure health effects. Chondrite-normalized REE patterns reveal a shale-like light rare earth element (LREE) enrichment for the coal, similar to that of the shale overburden, again suggesting a primarily clastic REE source. However, when normalized to the shale overburden, most of the coal ash samples display a small but distinct heavy rare earth element (HREE) enrichment. We surmise that the HREE were added and/or preferentially retained during epigenesis, possibly associated with groundwater flow through the coal unit, but not necessarily in close association with the addition of iron. At least some of the “excess” HREE could be organically bound within the Lower Kittanning coal.