Structural characterization of filter cake solids from a solvent-refined coal process (SRC-1)

A study has been undertaken to characterize the structural aspects of the solids that have been recovered from solvent refined coal (SRC-I). Both the mineral matter as well as the organic materials are characterized through the utilization of various analytical techniques: chemical analysis, X-ray techniques, optical microscopy and electron microscopy studies, surface area measurements, density gradient separation, electron spin resonance, magnetic susceptibility and ESCA studies. A comparison is being made of the solids from this particular process with solids derived from another SRC process. Some of the main findings of this study include the following. Major minerals are pyrrhotite and α-quartz. Organic inerts consist of fusinite, semifusinite, micrinite and macrinite. The least dense fraction is essentially organic, while the high density fraction contains much of the pyrrhotite. The e.s.r.-free-radical measurements show that the solids contain few reactive species.     

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.     

Effect of coal liquefaction conditions on the trace element content of the soluble non-volatile product

Analysis of 18 trace elements via inductively coupled plasma atomic emission spectrometry has been performed on ‘in-house’ coal-derived non-volatile products. Analyses were conducted in a pyridine matrix to determine the effect of various conversion parameters on metal content. Four subbituminous coals (Wyodak 1–4) and one bituminous coal (Indiana V) were employed in conjunction with both non-basic (tetralin) and basic (1,2,3,4-tetrahydroquinoline) model process solvents. Trace metal data on solvent-refined coals as a function of feed coal, process solvent, reaction time, reaction temperature and extraction solvent are reported. Few trends in metal concentration are apparent on changing various liquefaction parameters. Metal concentrations are, however, approximately one to two orders of magnitude higher in pyridine soluble SRC relative to toluene soluble SRC. The majority of soluble metals, it is therefore suggested, are in the form of coordination complexes rather than true organometallics in SRC. Information regarding the effective molecular size of metal-containing species has been obtained via size exclusion chromatography with specific metal detection. Subtle changes are observed in the effective molecular size of metal-containing materials using different liquefaction parameters. For example, a greater fraction of each metal appears to be bonded to larger ‘sized’ molecules in pyridine soluble fractions than in toluene soluble fractions.     

Effects of coal cleaning on the short contact time liquefaction of Illinois No. 6 coal

This study was carried out to determine the effect of coal cleaning by oil agglomeration and sink-float methods on yields from short contact time liquefaction of Illinois No. 6 coal. The runs were made in a continuous unit using SRC-II distillates as process solvent. Measured yields included hydrogen (consumption), hydrocarbon gas, distillate oil, SRC (the pyridine-soluble portion of the residue) and insoluble organic matter, the pyridine-insoluble organic residue. The solubility of product SRC in hexane, toluene and pyridine was also determined. The principal finding was that coal cleaning by density methods reduced the yield of IOM obtained in subsequent liquefaction and this is attributed to the removal of inert components from the feed coal. In addition, cleaning which significantly reduced pyrite content of the feed coal also reduced the yield of distillate oil and tended to give a less soluble SRC during liquefaction. Deep cleaning by gravity methods gave the lowest IOM, but reduced pyrite content to the point where distillate oil was consumed rather than produced. Oil agglomeration reduced total ash to 50% of that in the run-of-mine coal, but left the pyrite level in the coal high. The relevance of these results to two-stage liquefaction is discussed.     

Effect of mineral matter on coal self-heating rate

Adiabatic self-heating tests have been conducted on subbituminous coal cores from the same seam profile, which cover a mineral matter content range of 11.2-71.1%. In all cases the heat release rate does not conform to an Arrhenius kinetic model, but can best be described by a third order polynomial. Assessment of the theoretical heat sink effect of the mineral matter in each of the tests reveals that the coal is less reactive than predicted using a simple energy conservation equation. There is an additional effect of the mineral matter in these cases that cannot be explained by heat sink alone. The disseminated mineral matter in the coal is therefore inhibiting the oxidation reaction due to physicochemical effects.     

Fourier Transform Infrared study of mineral matter in coal. A novel method for quantitative mineralogical analysis

A novel method for the quantitative determination of mineral matter in coal is reported. The low-temperature ash of coal is analysed by means of absorbance spectral subtraction of individual components. The spectra of individual minerals, stored in digital form on computer memory, are multiplied by appropriate weighting factors and subtracted from the spectrum of the low-temperature ash, so that the characteristic bands of the mineral are removed. Provided that the weight of each mineral in the infrared beam is known then the weight fractions can be determined from the weighting factors. Successive subtraction starting with the most strongly absorbing components reveals the minor or less strongly absorbing species, which could not previously be determined by infrared spectroscopy. The analysis of several mixtures and of the low-temperature ash of various coal samples is reported.     

Characterization and catalytic activity of coal mineral matter: 2. Hydrodesulfurization of thiophene

Intrinsic catalytic activity was evaluated for nine low-temperature ash samples (LTAs) from U.S. coals, a sample of SRC solids, and reference constituents of coal for the hydrodesulfurization (HDS) of thiophene. A pulse micro-reactor, gas-chromatograph system was used to determine conversion by measuring the C₄s produced at 673 K. Activity ranking placed Kentucky Homestead as the best HDS catalyst by a factor of 14.3 times the activity of the lignite, which gave the lowest conversion. SRC solids from a Pittsburgh seam coal were evaluated and showed moderate HDS activity. This activity was similar to that of the mineral matter of two other Pittsburgh seam coals (Ireland and Bruceton). The catalytic activity of the LTAs was much smaller than measured conversions using a commercial cobalt molybdate catalyst. The SRC solids gave the highest hydrogenation activity (HA) of all the LTAs tested. The LTAs were found to be very poor hydrogenation catalysts. The worst HDS catalysts, lignite, gave the highest HA while Kentucky No. 11 had the lowest HA activity. More than 95% of the products were butenes or 1,3-butadiene. Surface area for the LTAs increased after catalyst testing, and the HDS activity correlated strongly with surface area while hydrogenation activity showed no such correlation. Favorable element correlations showed potassium to be the most favored for predicting HDS activity. The potassium in the LTAs was present as illite or feldspar. Results are also given for several reference clays and a synthetic mixture of mineral matter constituents.     

Ash deposition of a Spanish anthracite: effects of included and excluded mineral matter

This study has been undertaken to provide an insight into the effects of mineral matter distributions in coal on the nature of boiler slags formed during the combustion of a high ash Spanish anthracite. Three density fractions were prepared, and the light and heavy fractions were combined to give a sample containing mainly excluded mineral matter. The mineral matter in the medium density fraction was predominantly included. Slag deposits were prepared in the laboratory from the whole coal, the light+heavy and medium density fractions. The coal with excluded mineral matter was found to produce a slag similar in nature and chemistry to the whole coal ash deposit. The coal with included mineral matter produced a vitreous, iron-rich deposit. The deposits were compared with slags, obtained from a Spanish power station boiler, burning a blend containing the same anthracite.     

Influence of petrographic and mineral matter composition of coal particles on their combustion reactivity☆

Combustion at programmed temperature in a thermobalance is a rapid technique, which monitors coal burning characteristics and has shown its utility to classify coals according to their combustion performance. However, combustion profiles are affected by different coal properties and characteristics such as particle size, rank, maceral composition and mineral matter content, whose separate effects are difficult to determine. The objective of this work was to ascertain the influence of coaly and mineral matter composition and distribution on burning profiles as determined by thermogravimetric analysis, by using coals of different rank, and fractions of these coals obtained by density separation. Five coals ranging in rank from lignite to anthracite and with variable mineral matter content and composition were used in this study. Density fractions were separated from each coal to obtain samples with different organic/mineral matter proportions. Some of the factors influencing coal combustion profiles are widely recognised as the negative effect of increasing both rank and inertinite content on the reactivity. The favorable effect of mineral matter content on the reactivity has shown to be related to the maceral size within the density fractions and the intimate association organic/mineral matter that favors the diffusion of the reacting gas. Catalytic effects of the mineral matter could not be demonstrated.     

Catalytic effect of mineral matter constituents in a North Assam coal on hydrogenation

The catalytic effect of the mineral matter constituents as estimated in the ash samples prepared from the various specific gravity fractions of a North Assam coal sample on hydrogenation has been studied. Both iron and titanium present in coal have a catalytic effect on hydrogenation. Pyritic as well as organic sulphur present in the coal appear to be responsible for formation of the catalytically active form of iron sulphide from the iron present in the coal mineral matter. Of the aluminosilicates, kaolinite, which is the major component of coal mineral matter, was found to influence the conversion of coal to gas and benzene-soluble products under the conditions of hydrogenation.     

A formula for the mineral matter to ash ratio for low rank coals

Existing formulae relating mineral matter to ash yield of coal, which assume that all the mineral matter is separate from the coal, do not apply to low rank coal because part of the mineral matter is bound in the coal substance. A mineral matter/ash formula is derived for low rank coal that allows the calculation of the ratio of mineral matter to ash for a sample of any coal the basic properties of which have been determined. The formula requires a modification to the procedures previously developed for calculating basic properties of low rank coals. Basic properties and the parameters determining the mineral matter to ash ratio are presented for New Zealand sub-bituminous Waikato coals.     

Graphical methods for determination of the mineral-matter-free properties of coal and the mineral matter/ash ratio

Mean values of the mineral-matter-free specific energy, volatile matter and moisture content of coal, together with the mineral matter/ash ratio and the mineral matter moisture content, can be obtained from linear regression analyses of the appropriate analytical quantities against ash yield for grouped coal samples from geographical areas. The results can be used to assess rank and quality variations and the determined mineral matter/ash ratio can be used to correct individual analyses to a mineral-matter-free basis.     

煤中矿物质对神府煤快速液化的影响

利用共振搅拌反应器研究了煤中矿物质对神府煤高温快速液化的影响。原料煤经酸洗去除煤中大部分矿物质,脱灰率可达84．83％。脱灰后的煤在490℃进行加氢液化,结果表明,煤中矿物质的降低对神府煤高温快速液化有较大的影响,尤其影响了煤的初始高活性,煤转化率及液化产物的产率都降低,且煤中矿物质的降低会使矿物质自催化作用减弱,影响了神府煤液化产物质量。     

Effect of coal minerals on the thermal treatment of aromatic ethers and carbonyl compounds

To elucidate the effect of mineral matter in coal on coal liquefaction, the thermal decomposition of some model compounds of coal structure, aromatic ethers and carbonyl compounds, has been carried out in tetralin solvent and in the presence of coal ash obtained by low temperature combustion. The conversion of benzyl phenyl ether and dibenzyl ether was considerably enhanced; alkylated products such as benzyltetralin were obtained. The conversion of phenoxyphenanthrene and phenoxynaphthalene also was increased to some extent in the presence of coal ash. These effects can be attributed to the acidic components of coal minerals, because silica-alumina has shown the same effect, which is suppressed by quinoline. The addition of coal ash increases the yield of hydrocarbon from the corresponding aromatic carbonyl compounds by reduction. This effect is attributable to iron sulphide.     

Inherent mineral matter in coal and its effect upon hydrogenation

The problems associated with assessing the catalytic effects of inherent mineral matter in coal during hydrogenation are discussed in detail. Preliminary results obtained from various relative density fractions of a South African high-mineral-matter coal are reported. Inert matter has been added in an attempt to minimize the complicating effects of agglomeration of the coal particles in order to gain a greater understanding of the relative importance of maceral versus mineral content of the coal during hydrogenation. It is difficult to determine any ‘catalytic effect’ of mineral matter in coal during hydrogenation since the mineral matter appears to be acting in a physical capacity as an internal diluent, reducing agglomeration of the coal particles. This decrease in agglomeration allows more effective diffusion of hydrogen to the sites of bond rupture and products away from the coal particles as well as maintaining a higher overall surface area for reaction.     

The nature of solids accumulated during solvent refining of coal

Solids accumulated in the reactor of a solvent-refined coal (SRC-1) pilot plant during processing of three coals were studied using optical microscopy and X-ray diffraction. A classification system was devised for each of the two groups of components: organic materials and mineral matter. The various organic components were classified by the extent of change from the original coal macerals, and by optical properties of different semi-cokes and other organic phases. Minerals were divided into four groups: those unchanged from the original coal; minerals which were physically degraded; minerals which were chemically or crystallographically transformed; and those minerals formed during processing of a subbituminous coal. Gold-tube carbonization experiments were performed on SRC to determine the conditions under which retrogressive reactions occur to form mesophase semi-coke. Autoclave experiments were designed to investigate the recrystallization of pyrite as pyrrhotites, and to determine the causes of carbonate-mineral formation in the reactor. Calcium carbonate was found to crystallize from the interaction of ion-exchangeable calcium and carbon dioxide, which are available when low-rank coals are processed.     

‘Solubility parameters’ in coal and coal liquefaction products

‘Solubility parameter’ spectra have been used in polymer research to determine the characteristics of cross-linked polymer systems. Cross-linked systems are not soluble in any solvent. Instead, solvent is imbibed by the cross-linked polymer and causes it to swell. The ‘solubility parameter’ of the solvent which causes maximum swelling is identified as that of the cross-linked material. Coal can be thought of as having some characteristics of a cross-linked system^1,2. That is, when immersed in a solvent with which it interacts, it will swell. In addition, coal contains extractable material. If coal is regarded as a ‘multipolymer’, this extractable matter can be thought of as the uncross-linked portion of the coal. Swelling spectra have been taken for untreated coal and coal from which some extractable matter has been removed, which partly suppresses swelling. This extractable matter can be thought of as similar to the uncross-linked coal molecule. Its structure can therefore be used to model the coal matrix itself, to determine the coal structure without using destructive chemical methods to break the coal apart. Dissolution spectra for both the coal extract and the coal liquefaction products from the PAMCO and Synthoil processes were taken. A set of mixed solvents with effective ‘solubility parameters’ ranging from 14.3 to 47.9 MPa^1/2 (7.0 to 23.4 hildebrands) was used. The behaviours of the coal extract and coal liquid products show striking similarities, leading us to believe that molecules similar to those found in liquefaction products already exist in the virgin coal and that hydrogenation products reflect the properties of the starting material.     

Selectivity improvement in the SRC process

The selectivity for hydrodesulfurization over hydrogenation has been examined in a new short residence time catalytic two-stage SRC process, which has the potential of producing a low-sulfur solid SRC product to meet the newly proposed EPA new point source emission standards (NPSES). In the first stage of the process, residence time and hydrogen consumption are minimized through the use of an inexpensive mineral catalyst (SRC residue ash) that has been treated under a combustion environment to improve its selectivity for hydrodesulfurization over hydrogenation. The second stage of the process involves hydrotreating the filtered liquid product with a commercial Co-Mo-Al catalyst, before splitting into a solid SRC and solvent recycle by distillation. Several process variables — such as type of coal, catalyst, temperature, hydrogen partial pressure, and reaction time — have been examined to provide information on hydrogen consumption, product distribution, sulfur removal, SRC yield and solvent quality. The results show that the ash of SRC residue can be used to selectively catalyze desulfurization over hydrogenation in SRC processing. Selectivity for desulfurization in two stage hydrodesulfurization of coal is improved by using high reaction temperatures, short residence times, the ash of SRC residue as a first stage catalyst, and Co-Mo-Al as a second stage catalyst. Two stage catalytic SRC processing is more selective for hydrodesulfurization than catalytic or non-catalytic single stage SRC processing.     

Correlation between the content of volatile matter and mineral matter in hard coals

If coal is heated to 900 °C, in the absence of air the organic coal substance and the associated mineral matter are decomposed. The analytically determined volatile-matter yield includes the volatile decomposition products of both the coal substance and the minerals. The correlation between mineral matter and ash and the volatile-matter yield is derived, and its accuracy shown by evaluation of test results. Methods are proposed for calculating a value for the volatile matter dmmf for coals of a particular mine. Various formulae for calculating the volatile matter of coals to dmmf basis are critically considered. Finally, a generally applicable equation for calculating dmmf volatile matter is derived which can be used for classification.     

A mathematical model of ash formation during pulverized coal combustion

A mathematical model of ash formation during high-rank pulverized coal combustion is reported in this paper. The model is based on the computer-controlled scanning electron microscope (CCSEM) characterization of minerals in pulverized coals. From the viewpoint of the association with coal carbon matrix, individual mineral grains present in coal particles can be classified as included or excluded minerals. Included minerals refer to those discrete mineral grains that are intimately surrounded by the carbon matrix. Excluded minerals are those liberated minerals not or at least associated with coal carbon matter. Included minerals and excluded minerals are treated separately in the model. Included minerals are assumed to randomly disperse between individual coal particles based on coal and mineral particle size distributions. A mechanism of partial-coalescence of included minerals within single coal particles is related to char particulate structures formed during devolatilization. Fragmentation of excluded minerals, which is important particularly for a coal with a significant fraction of excluded minerals, is simulated using a stochastic approach of Poisson distribution. A narrow-sized sample of an Australian bituminous coal was combusted in a drop-tube furnace under operating conditions similar to that in boilers. The particle size distribution and chemical composition of experimental ash were compared to those predicted with the model. The comparisons indicated that the model generally reflected the combined effect of coalescence of included minerals and fragmentation of excluded minerals, the two important mechanisms governing ash formation for high-rank coals.