Upper Freeport Research Articles

Two dimensional 1H magnetic resonance relaxometry-based analyses of Argonne premium coals

1H magnetic resonance (MR) is a useful technique for determining molecular structure of coals. Most previous MR studies were based on one-dimensional 1H magnetic resonance relaxometry. Two-dimensional (2D) 1H magnetic resonance relaxation correlation methods, T1–T2* and T1ρ–T2*, were used to evaluate Argonne premium coals, including Beulah-Zap (BZ), Wyodak-Anderson (WA), Pittsburgh #8 (PIT), Upper Freeport (UF), and Pochontas #3 (POC) coals as received. Samples were also measured after oxidization at low temperature (110 and 210 °C). From the 2D relaxation correlations, various hydrogen-containing components were distinguished and characterized. The change of hydrogen during low temperature oxidation was analyzed, and the hydrogen content estimated. The technique captured significant differences between low rank coals (BZ and WA) and high rank coals (PIT, UF, and POC). The order of T1/T2* ratios is aliphatic hydrogen > aromatic hydrogen > hydrogen- and oxygen-containing functional groups > moisture in BZ and WA coals. The PIT, UF, and POC coals mainly contain aromatic hydrogens. The T1–T2* and T1ρ–T2* spectra of BZ and WA coals change significantly during low temperature oxidation. Our new MR method provides new insight into coal behaviour.

Analysis of Thermal Behavior of Crystalline Minerals in Bituminous Coal Samples under Air and Argon Atmospheres.

The thermal behavior of ash components in two bituminous coal samples [Upper Freeport (the “UF”) and Illinois #6 (the “IL”)] was investigated under air and argon atmospheres in the temperature range of 800–1200 °C using thermal gravimetric–differential thermal analysis, X-ray diffraction transmission electron microscopy (TEM), and TEM–energy dispersive X-ray spectrometry measurements. The UF treated under air formed the needle-like crystals which were assumed to be mullite-related substances formed by transformation of andalusite, because the crystals are mainly composed of SiO2 and Al2O3. In contrast to the UF, the IL did not generate such crystals; however, when the IL was treated under air after carbonization under Ar, crystals appeared. The composition of the UF with an Al/Si ratio higher than that of the IL favored the formation of mullite-related substances, while the presence of lime in the IL inhibited the formation of mullite-related substances. Oldhamite was formed by the reaction of lime with sulfur at the carbonization of the IL under Ar and remained even at the successive air treatment. As lime was consumed, the formation of mullite-related substances was ceased to be inhibited under air after Ar treatment.

Mechanical performance of thermoplastic composites using bituminous coal as filler: Study of a potentially sustainable end‐use application for Appalachian coal

This study evaluated the utilization of bituminous coal from the Appalachian basin as filler material in high density polyethylene (HDPE) composites. Three coal types including Pittsburgh No. 8, Kittanning, and Upper Freeport were evaluated. The impact of coal (0–60 wt%) and coupling agent (0–3 wt%) content on flexure and tensile properties of the coal/HDPE composites was investigated. In addition, coal surface chemistry was analyzed using Boehm analyses and compared to pine wood flour. Composite flexure strength was maximum at 30 wt% coal, while tensile strength decreased with coal content. Addition of coupling agent to the composite had little to negative impact on mechanical properties. POLYM. COMPOS., 40:591–599, 2019. © 2017 Society of Plastics Engineers

Quantifying Curvature in High-Resolution Transmission Electron Microscopy Lattice Fringe Micrographs of Coals

The observation of high-resolution transmission electron microscopy (HRTEM) lattice fringe images for coals has aided the rationalization of structure and order. Within the hundreds of lattice fringes (edge-on view of the aromatic structures) in a typical micrograph, apparent curvature is common. Traditional image analysis approaches do not appropriately quantify curvature. Tortuosity is functional for the quantification of single-inflection-point smooth lines but poor for complex or undulating lines. Here we present an image analysis method that can identify the points of inflection, angles, and segment lengths that constitute curved lattice fringes. Four coals from the Argonne Premium suite (Pocahontas No. 3, Upper Freeport, Illinois No. 6, and Beulah-Zap) and example anthracites were examined, and curvature was present in 17–24% of the fringes. These curved fringes were further classified as having low ( 90°) on the basis of cumulative angle changes. For the A...

Role of pH on CO2 sequestration in coal seams

The effect of acidic or basic pre-treatment on the adsorption capacity of CO2 on coals was investigated. Argonne Premium Pocahontas No. 3, Upper Freeport, Pittsburgh No. 8, Lewiston–Stockton, Blind Canyon, Illinois No. 6, Wyodak, and Beulah–Zap coals were washed in weak solutions of H2SO4 and NaOH to the pH values of 10, 7, and 2, after an initial washing in acidic water. Attempts to treat the Wyodak and Beulah–Zap coals were unsuccessful because the base treatment after the initial acid treatment resulted in a suspension which could be separated neither via filtration through a 45μm filter nor centrifugation. Equilibration took several days in some cases, although the as-received coal had been ground to 150μm. Acid washing preferentially removed Ca (calcite) and Mg. Aluminosilicate clays were not notably removed. Iron was removed in significant amounts only after base treatment, possibly after it was converted to hematite. The adsorption capacity of CO2 on the acid treated coals was higher than both the base treated and untreated coals. The difference in adsorption capacities for acid and base treated coals was related to the pore sizes and mineral matter removal from the coals, where the calculated average pore size was higher for acid treated coals than for the base treated coals. It is concluded that the pH decrease due to CO2 dissolution in cleat water is favored in coal seam sequestration, which resulted in an increase in storage capacity of coals.

Sequence stratigraphy of fluvially-dominated strata of the Mid-Late Pennsylvanian Conemaugh Formation, Central Appalachian Basin

Sequence stratigraphic analysis of nonmarine, fluvially-dominated strata is particularly challenging compared to paralic and marine sequences due to rapid facies changes and limited lateral continuity of key beds. The Conemaugh Formation of central West Virginia is a prime example of this type of stratigraphic interval. This study describes the stratigraphy and sedimentary facies from 68 outcrops in the lower 100m of the Mid-Late Pennsylvanian, nonmarine Conemaugh Formation in this area. Facies identified include 1) fluvial–upper estuarine channel sandstones, 2) crevasse splay channel and sheet sandstones, 3) lacustrine shale, mudstone, and claystone, 4) lacustrine/palustrine limestone, 5) paludal coal and carbonaceous shale, and 6) hackly mudstone and claystone paleosols.Mature, polygenetic, high-chroma calcic vertisols and calcisols are the regionally developed interfluvial sequence boundaries (IFSBs) of seven fourth-order sequences (major cyclothems) between the Upper Freeport and Harlem coal horizons. Initial paleosol development occurred under well-drained conditions and strongly seasonal, semiarid–arid climate approaching and during glacial maxima at a time of minimal accommodation space on the interfluves. Subsequent rising water table associated with rising base level occurred as interglacial sea level rose and the climate became less seasonal and more humid. This initially led to deposition of thin, carbonaceous mud and peat followed by lacustrine and palustrine limestones. The presence of spirorbid microconchids indicates that the lakes were at least intermittently connected to the sea, which reached to within 50–80km of all outcrops in the study during five transgressions. The tops of these limestones represent maximum flooding surfaces. They are overlain by coarsening–upward lake-fill sequences formed during high accommodation on the interfluves during the HST. A nonmarine sequence stratigraphic model and a polygenetic paleosol model are proposed for the Conemaugh in central West Virginia. This study underscores the importance of recognizing regionally developed IFSB paleosols and microconchid limestones in correlation and sequence stratigraphic analysis.

Characteristics of Wetland Soils Impacted by Acid Mine Drainage

Abstract A proposed section of Appalachian Corridor H, an interstate highway that begins at I-79 near Weston, WV, and will continue east to I-81 at Strasburg, VA, will pass through an area of the Beaver Creek watershed that was previously mined for the acid-producing Upper Freeport coal. Beaver Creek flows into the Blackwater River after flowing out of Canaan Valley. Partially reclaimed spoils from past mining activities are generating acid mine drainage. Wetlands adjacent to the spoils support plant communities that appear to be naturally treating the drainage. To better understand the chemical and physical functions within the wetlands and to assist the West Virginia Division of Highways in constructing wetlands for mitigating environmental damage, we described the soils of the mine-drainage-impacted wetlands (Narrow Wetland, Iron Pond, and Railroad Grade) and took samples for subsequent laboratory analyses. For comparison, we also described and sampled unimpacted soils in Elder Swamp, which is an adjac...

S-XANES analysis of thermal iron sulfide transformations in a suite of Argonne Premium Coals: A study of particle size effects during pyrolysis

A suite of four bituminous Argonne Premium Coal Samples, namely Pittsburgh#8 (P8), Blind Canyon (BC), Upper Freeport (UF), and Illinois #6 (IL6), were pyrolyzed according to the Easy Ro kinetic model (Burnham and Sweeney, 1989) to Ro=4.3 and iron sulfide thermal transformations were tracked by the use of S-XANES (Sulfur X-ray Absorption Near Edge Structure.) It was shown that the pyrite transformed first to pyrrhotite by Ro=1.5, and then started to transform to troilite by Ro=2.4. Some Argonne Coals displayed evidence of structural instability. In addition, particle size effects were examined. Pyrolysis was performed on not-ground (large-particled) coal samples, which were subsequently ground to micron-size particles before data collection. S-XANES was also collected for the not-ground post-pyrolysis IL6 coal to show the effect of the extent of reaction on the surface of the particles as opposed to the bulk. It was found that the pyrite-to-pyrrhotite transformation in large particles of IL6 coal proceeded from the surface of the particle and progress inward, consistent with the shrinking core model. A scheme for determining particle size based on organic sulfur content was also developed for a coal model consisting of a 50/50mol% mixture of pyrite and Maya petroleum vacuum resid asphaltene for a range of known particle sizes. Lastly, the behavior of both marcasite (a polymorph of pyrite) and pyrite in a coal model was investigated for large (~100μm) and small (~5μm) particles. The marcasite proved to be less structurally stable than pyrite for the large particles, with an abrupt transformation to a mixture of pyrrhotite and troilite, and an abrupt drop in aliphatic sulfur content, indicating consequent H2S generation at Ro=2.4. This transformation is much less pronounced for pyrite at the same point in pyrolysis.

Fine Structure Evaluation of the Pair Distribution Function with Molecular Models of the Argonne Premium Coals

The pair distribution function (PDF) is one means of evaluating the atomic spatial arrangements of coals. Analysis of PDF based on X-ray diffraction data provides structural information on turbostratic crystalline parameters that can be utilized to further characterize coal structure. With coalification, expectations are of limited growth in aromatic stacking and a slight growth in the aromatic cluster size over the lignite to medium-volatile bituminous range. The PDF can be also used to construct and validate atomistic representations for carbonaceous materials including coal. Here, the PDF was evaluated with molecular slice models of several Argonne Premium coals (Beulah-Zap, Illinois No. 6, Upper Freeport, Pocahontas No. 3), also a non-Argonne Hon Gai anthracite, and compared to experimental observations. Atomistic representations were generated directly from high-resolution transmission electron microscope (HRTEM) lattice fringe images. The Fringe3D approach populates aromatic moieties matching the distributions of fringe: length, layers per stack, interlayer spacing, and orientations to produce an aromatic slice model of limited depth. Perl scripts incorporated appropriate aliphatic and heteroatom components. This approach creates atomistic representations with greater ease, improved accuracy, and reduced computational expense than other construction approaches. The constructed coal models were partially geometry-optimized to achieve realistic bond lengths but without displacement of coal molecules enabling the distribution of fringe length, stacking, and orientations to be duplicated in 3D modeling space. The resulting coal slice models, devoid of cross-links, captured a distribution of turbostratic crystalline dimensions with an average cluster size of about 1 nm, an average interlayer spacing ranging between 0.37 and 0.39 nm, and an average stacking number of ∼2–3 in accordance with HRTEM and XRD data for Argonne coals. These structural models were used to predict PDFs and to evaluate the fine detail of the frequency spectra via examination of intermolecular and intramolecular contributions. There was good agreement between predicted and experimental observations. Analysis of the simulated intermolecular PDF contribution showed strong intensities with increasing coal rank in agreement with the growth in the stacking number and stack height observed from low- to high-rank coals. The simulated intramolecular PDF contribution showed shorter peak amplitudes for low-rank coals in comparison to high-rank coals in agreement with the increase in stack width as coal rank increases. To further examine these contributions, lattice models composed of pyrene molecules were also constructed via Fringe 3D and manipulated to directly investigate the effect of aromatic orientation distributions and stacking on the simulated PDF. Peak intensities of simulated intermolecular PDFs at the average interlayer spacing increased with the degree of alignment (ϕ) according to g(r)interd002 = 0.0014ϕ2 + 0.0107ϕ + 4.2784. This result was consistent with the slight increase in the stacking number observed from low- to high-rank coals with a more dramatic transition for anthracite.

High-Pressure Adsorption of Pure Gases on Coals and Activated Carbon: Measurements and Modeling

High-pressure gas adsorption of pure methane, nitrogen, and CO2 were measured on five coals of varying rank and an activated carbon. All measurements were conducted at 328.2 K and pressures to 13.8 MPa using a volumetric method. The adsorption isotherm data are for dry Beulah Zap, Illinois no. 6, Pocahontas, Upper Freeport, and Wyodak coals and Filtrasorb (F-400) activated carbon. At about 7 MPa pressure, the ratio of excess adsorptions for N2/CH4/CO2 varied from about 1/1.9/2.8 for Pocahontas coal to 1/2.1/5.9 for Beulah Zap coal. A distinct maximum in excess adsorption was observed for CO2 on each coal between 6 and 8 MPa. For activated carbon at 7 MPa, the ratio of excess adsorptions for N2/CH4/CO2 was 1/1.5/2.3, which is consistent with our earlier data on this activated carbon at a different temperature (318.2 K). The isotherm measurements have expected experimental uncertainties that vary from 1 to 7% for the adsorption of the three gases. The simplified local-density (SLD) model was fit to describe...

Dissolution and Dispersion of Coal in Ionic Liquids

In “good” solvents such as pyridine, coal particles swell and fracture to some degree as soluble material is extracted, but they remain as more-or-less coherent particles. It is shown here that certain ionic liquids (ILs) are capable of solubilizing, disintegrating, and dispersing certain coals as very fine particles to a remarkable extent. The solubility of two coals, a Powder River Basin coal and an Illinois No. 6 coal, also increased significantly in IL/N-methyl pyrrolidinone (NMP) and IL/pyridine mixtures, relative to the solubility of the coals in NMP and pyridine. A third coal, Upper Freeport, gave yields that were lower than those obtained in pyridine alone. This coal may be anomalous in its behavior. It is suggested that many if not most coals are densely cross-linked networks where a portion of soluble material remains trapped, even upon swelling in good solvents, which fracture and only partially fragment coals at ambient temperatures. Certain ILs fragment and disperse some coals to a much greater extent, however, apparently releasing much of this trapped material.

Effect of Solvent Pretreatments on the Aggregation Behavior of Upper Freeport Coal

Upper Freeport (UF) coal was pretreated with various solvents with or without additive tetracyanoethylene (TCNE), and the residues were further extracted and characterized by Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) measurements in this study. It was found that pretreatments of UF coal by N-methyl-2-pyrrolidinone (NMP) with TCNE and CS2/NMP mixed solvent (4:1 by volume) gave almost the same extraction yields. However, the two soluble residues RNT and RCN, which were obtained from the extraction of UF coal with NMP + TCNE and the CS2/NMP mixed solvent (4:1 by volume), respectively, demonstrated quite different extraction yields in the CS2/NMP mixed solvent (1:1 by volume). FTIR indicated that a large amount of the −OH groups was extracted by NMP + TCNE solvent extraction. An endothermic peak at 350 °C in the difference DSC thermogram of RNT had been observed as that seen in UF raw coal. However, this endothermic peak at 350 °C in the difference DSC thermogram of RCN disappeared. The results show that the aggregation states of the two residues RNT and RCN are different. RNT with a less aggregated state gave a much higher extraction yield in CS2/NMP mixed solvent (1:1 by volume) than that of RCN. The mechanism of the effect of solvent pretreatments on the aggregation behavior of coal was discussed.

Reconnaissance spatial analysis of the hydrogeology of closed underground coal mines

A method is demonstrated to employ combined mapping and field techniques to unravel complexities in the hydrogeology of flooded and unflooded underground coal mines of shallow (120 m, 400 ft) depth. For a study area in the Appalachian coal basin, underground mines, coal outcrop, coal structure, and mine-drainage discharge locations were mapped onto an integrated geographic information system platform. The Upper Freeport coal seam (Allegheny Group) in the study area is relatively shallow (120 m, 400 ft), with many closed free-draining mines and numerous discharges. The mapping of coal outcrop and structure was accomplished using (1) high-resolution aerial orthophotographs, (2) digital outcrop polylines, and (3) a coal-bottom structure surface created by geospatial interpolation of point data mostly abstracted from original mine maps. Mapping results integrated with field measurements of mine-water discharge allow inference of likely pool locations and potential interconnections between underground workings, which are not apparent from mine maps alone. The results are reconnaissance level in that the interpreted pool locations and depths are unconfirmed by drilling or water level measurement; therefore, any action based on such results should be preceded by fieldwork to confirm hypotheses offered by the reconnaissance analysis. Nonetheless, such a preliminary interpretation of hydrogeological conditions based on little or no subsurface (well) water level information may be highly useful for both interpreting subsurface conditions and for planning future research. The technique is based on a combination of mine mapping, digital analysis of geologic structure, and surface reconnaissance fieldwork. Results are directly applicable to areas of reclamation of shallow coal mining where mine closures have resulted in an uncontrolled discharge of mine drainage.

Increase in Extraction Yields of Coals by Water Treatment: Beulah-Zap Lignite

In a previous paper, we have reported that water pretreatments of Argonne premium coals, Pocahontas No. 3 (PO), Upper Freeport (UF), and Illinois No. 6 (IL) at 600 K increased greatly the room-temperature extraction yields with a 1:1 carbon disulfide/N-methyl-2-pyrrolidinone (CS{sub 2}/NMP) mixed solvent. In this paper, the water treatment of Beulah-Zap (BZ) lignite has been carried out and the results obtained were compared with those for the three bituminous coals above. The extraction yields of BZ with CS{sub 2}/NMP increased from 5.5% for the raw coal to 21.7% by the water treatment at 600 K. Similar to the other three coals, the water treatments at 500 K gave little increase in the yields. The larger decrease in oxygen content and hydrogen-bonded OH and the increase in the methanol swelling ratio by the water treatment suggest that the yield enhancements for BZ are attributed to the removal of oxygen functional groups and the breaking of hydrogen bonds to a greater extent than that for IL. From the characterizations of the treated coals and the extraction temperature dependency of their extraction yields, it is suggested that, for high-coal-rank coals, PO and UF, the breaking of noncovalent bonds such as {pi}-{pi} interactionsmore » between aromatic layers and hydrogen bonds is responsible for the extraction yield enhancements. 14 refs., 3 figs., 2 tabs.« less

Effect of coal extracted with NMP on its aggregation

Tow-step extraction of Upper Freeport (UF) coal, i.e. exhaustive extraction with N-methyl-2-pyrrolidinone (NMP) solvent and subsequent extraction with the CS2/NMP mixed solvent (1:1 by volume) with or without additive was compared with the direct extraction of UF coal with the CS2/NMP mixed solvent (1:1 by volume) with or without additive. It was found that there is almost no difference of extraction yields between the two-step extraction and direct extraction with or without additive. The result show that NMP can only give external extraction to extract the outside fractions of coal particles, and this will not cause the new aggregation formed in the coal molecules. The interactions between coal molecule and additive are responsible for the extraction yield enhancement by additive.

Recovery of clean coal from polymer flocculated raw coal slurry

The recovery of fine clean coal from waste streams using column flotation is recognized as an efficient and economical technique. However, due to the low percent solids (≈3% by weight) found in these fine waste slurries, the flotation columns have low capacities and are, thus, underutilized. In this study, a 3% (by weight) solids suspension of Upper Freeport coal was flocculated with polymers and concentrated to 10% (by weight) solids. The flocculated slurry was then floated using 250 git No. 2 fuel oil and 250 git MIBC, which provided a clean coal with 12% ash at an 80% yield. The results showed that flocculated coal could be floated effectively. Zeta potential and contact-angle data showed that the presence of polymer on the surface of the coal did not affect its hydrophobicity, and in some cases it improved the hydrophobicity as indicated by larger contact angles.

Determination of the Glass-Transition Temperature of a Coal Extract, Using a Polymer Blend Methodology

The glass-transition temperature (Tg) of pyridine-soluble extracts obtained from Upper Freeport (UPF) coal was investigated. Previous studies have suggested that such a transition, if it exists, might occur at high temperatures and is probably masked by other transition processes. In this study, we used differential scanning calorimetry (DSC) experiments to calculate that the glass transition of the UPF coal extract occurs at ∼194 °C. This Tg value was obtained using an extrapolation of observed Tg values of miscible blends of the coal extract and poly(4-vinylpyridine) (P4VPy). UPF extract/P4VPy blends were prepared as a series that had a UPF extract content of 10−85 wt %. DSC thermograms of all blends exhibited a single Tg value at a temperature higher than that of pure P4VPy. The Tg values of the blends were dependent on the composition of the coal extract. Using the Kwei equation, which describes the relationship between blend composition and Tg, the Tg value of the coal extract was calculated.

Interactions of Organic Liquids with Coals: Analysis by Solid-State 13C Nuclear Magnetic Resonance

We analyzed the solid-state 13C cross-polarization/magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectra of three types of coal samples that had been immersed in toluene or n-hexane for 1 h. The coal samples were from the United States (Upper Freeport (UF) reserve, 86 wt % carbon, and Wyodak (WY) reserve, 75 wt % carbon), and Australia (Yallourn (YL) reserve, 65 wt % carbon). The spectra of toluene- and n-hexane-immersed UF and n-hexane-immersed WY coals were identical to the spectra of the corresponding fresh coals: sorbed molecule peaks were not observed, which indicates that almost all the molecules in these coals were in a mobile state. The spectra of toluene- and n-hexane-immersed YL coal and toluene-immersed WY coal showed peaks for toluene and n-hexane, demonstrating that some of the molecules were bound relatively strongly to the coal. The C-1 carbon of toluene was not observed in the CP/MAS NMR spectra of toluene-immersed YL and WY coals, so it is possible that the toluene molec...

Increase in Extraction Yields of Coals by Water Treatment

The effect of water treatment at 500 and 600 K on solvent extractions of Pocahontas No. 3 (PO), Upper Freeport (UF), and Illinois No. 6 (IL) coals was investigated. All the coals used show that the water treatments at 600 K increased the extraction yields greatly in the extractions with a 1:1 carbon disulfide/N-methyl-2-pyrrolidinone (CS2/NMP) mixed solvent, NMP, or 1-methylnaphthalene (1-MN). However, the water treatments at 500 K and the heat treatments at 600 K without water gave only a slight increase in the yields. Characterizations of the water-treated coals were performed using ultimate and proximate compositions, Fourier transform infrared analysis, solvent swelling, nuclear magnetic resonance relaxation time, and viscoelasticity behavior. The swelling degree in methanol and toluene was increased by the water treatment at 600 K, suggesting that crosslinks become loosened by the treatment. The results of infrared analysis and the extraction temperature dependency of the extraction yields with NMP and 1-MN suggest that the loosening of π−π interactions, and of both π−π interactions and hydrogen bonds, are responsible for the yield enhancements for PO and UF coals, respectively. However, for IL coal, which exhibited a decrease in oxygen content and the amount of hydrogen-bonded OH, suggesting the occurrence of some chemical reactions, the yield enhancements may be due to the relaxation of hydrogen bonds and the removal of oxygen functional groups, such as the breaking of ether bonds.

An Inter-laboratory Comparison of CO2 Isotherms Measured on Argonne Premium Coal Samples

Adsorption isotherms, which describe the coal's gas storage capacity, are important for estimating the carbon sequestration potential of coal seams. This study investigated the inter-laboratory reproducibility of carbon dioxide isotherm measurements on dry Argonne Premium Coal Samples (Pocahontas No. 3, Upper Freeport, Illinois No. 6, Wyodak-Anderson, and Beulah Zap). Four independent laboratories provided isotherm data for the five coal samples at temperatures of either 22 °C or 55 °C and pressures up to 7 MPa. The differences among the data sets in this study appeared to be rank-dependent in that the data among the laboratories agreed better for high-rank coal samples than for low-rank coal samples. A number of parameters such as sample size, equilibration time, and apparatus dimensions were examined to explain the rank effect, but no trend could be found that explained the differences. The variations among the data are attributed to different procedures for removing moisture to obtain the “dried” coal.