Gieseler Fluidity Research Articles

95/01197 The effect of selected additives and treatments on Gieseler fluidity in coals

95/01197 The effect of selected additives and treatments on Gieseler fluidity in coals

95/01200 Manufacture of binder-free pellets of low-rank coal

A two-stage study was undertaken to establish what effect, if any, perchloroethylene has on coal coking properties. Stage 1 was a kinetic study in which the Gieseler fluidity of samples of a high fluidity coal was measured over a 64-week period. Two of the samples were left untreated, with one stored in air and one immersed in water. The third sample was also stored in air, but was soaked in perchloroethylene for 2 h and then air dried immediately prior to fluidity testing. In Stage 2, seven different coking coals were studied, covering three different Australian coal measures and a wide range of coking rank. For each coal, a 40 kg clean coal composite was formed using laboratory water-based methods, a Reflux Classier for the 0.038–0.25 mm and 0.25–2.0 mm size fractions and a Mintek jig for the 2.0–16 and 16–50 mm size fractions. This 40 kg composite was then subdivided into four sub-samples. Samples A and B were coked immediately, whereas Samples C and D were stored in open trays at ambient conditions for a month before coking. Samples B and D were soaked in perchloroethylene for 2 h and then air dried prior to coke testing, whereas Samples A and C were left untreated. Coal properties were measured prior to coking, and after coking the NSC Coke Reactivity Index (CRI) and Coke Strength after Reaction (CSR) were measured.In Stage 1 it was found that storage under water was able to maintain the sample fluidity better than refrigerated storage. The combined Stage 1 and 2 results showed that perchloroethylene had a detrimental effect on the coking properties of many coals. Hence coking tests on clean coal composites formed using heavy organic liquids may often under predict a coal’s true coking properties. This could lead to many coal deposits being undervalued. Perchloroethylene had the largest detrimental effect on the fluidity, CRI and CSR of coals that started with relatively poor properties. Perchloroethylene had a negligible effect on coals with relatively good initial coking properties. There was no clear correlation with vitrinite reflectance. The three most seriously affected coals all had relatively high inertinite content. It is speculated that the higher porosity of inertinite might allow greater access and retention of perchloroethylene in the coal particles.The laboratory water-based methods were able to produce clean coal composites that matched the proximate, petrographic and coal swelling number properties of the coal preparation plant product. The dilatometer and fluidity results were lower than those of the coal preparation plant, but this can be explained by the up to three month delay between mining of the original sample and the coking of the composite. These delays were an unavoidable part of the research nature of this project and had nothing to do with the water based methods deployed. If these water-based methods of preparing clean-coal composites were to become standardized, then there is no reason why a well equipped coal testing facility could not receive a refrigerated bore core and produce a clean coal composite within the period of a week.

Application of Fourier self-deconvolution to the FT-i.r. characterization of coals and their N-methyl 2-pyrrolidinone extraction products

Analysis by Fourier transform infrared (FT-i.r.) spectroscopy of coals and their extraction products, i.e. extracts and residues, gives an insight into the chemical structure of the initial material and changes due to the separation procedure. High quality spectra are obtained for solids by diffuse reflectance FT-i.r. spectroscopy. They also provide rather broad overlapping bands which have to be manipulated to supply useful information. It is shown that Fourier self-deconvolution improves the qualitative and semi quantitative analysis of FT-i.r. spectra of the coals and their N-methyl 2-pyrrolidinone (NMP) extraction products. Several samples of coals (rank ranging from C (wt%, daf) 85.6 to 92.4) were studied. Four spectral regions were selected for discussion: 3100-2800 cm −1 ν(CH ar), ν(CH ali); 1750-1600 cm −1 ν(CO), ν(CC ar); 1260-1034 cm −1 ν(CO); 900-650 cm −1 γ(CH ar). Several ratios were calculated, including: [ν(CH ar)/ν(CH 2,CH 3)], [ν(CO)/ν(CC)], [ν(CO)/ν(CC)], [γ(CH)(1H)/Σγ(CH)], [γ(CH)(2,3H)/Σγ(CH)] and [γ(CH)(4H)/Σγ(CH)]. These data led to a comparison of the structural characteristics of the coals and of their extraction products. In each case the results are discussed in relation to the various trends observed in the samples, the possible relations with Gieseler fluidity of coals and the sizes of molecular orientations in the relevant cokes obtained by pyrolysis at 1000°C.

The effect of selected additives and treatments on Gieseler fluidity in coals

The modification of Gieseler fluidity development in coals by various pretreatments is examined and clarified. These pretreatments include the addition of solvent extracts, preheating and quenching, addition of radical stabilizers and blending. The effect of each treatment is found to be dependent on the degree to which it satisfies the requirements of the hydrogen donor theory of fluidity development. This includes changes in behaviour which would otherwise be difficult to explain, such as the very different effect preheating has on the fluid properties of fresh and oxidized samples of the same coal. From a chemical viewpoint the components in blends are found to behave predictably. That this does not always translate into predictable fluidity development can be attributed to chemical differences between the components and the consequences these have for the fluidity development process as described by the hydrogen donor theory.

ＮＥＤＯＬ法液化残さの熱流動性と酸化改質

Themoplastic property of liquefaction residue produced at NEDOL lt/d Process Supporting Unit using Wandoan and Wyoming coals was studied by Gieseler plastometer under atmospheric and elevated pressure. Effect of air oxidation on thermoplasticity was also investigated. Gieseler fluidity of residue was successfully reduced to zero by air oxidation at 150°C. Pressure dependency of fluidity of oxidized residue was different from that of caking coal. Fluidity was more reduced under higher pressure. Photoacoustic FT-IR spectra were measured for oxidized residues. Oxidation of residues was also observed in-situ by diffuse reflectance FT-IR spectrometer equipped with controlled environment chamber. IR spectra obtained showed that oxidation reaction of residue seemed to be similar to that of coal. Increase in absorption at around 1700 and 3400cm-1 along with decrease in absorption at 2800 to 3050cm-1 was observed as oxidation reaction proceeds, indicating formation of carbonyl and hydroxyl groups and dehydrogenation from methylene group mainly in aliphatic compounds.

Further studies of Gieseler fluidity development in New Zealand coals

The hydrogen donor ability of fresh samples of a Webb coal with high Gieseler fluidity is shown to be greater than that of samples of the same coal after oxidation has caused a significant decline in fluidity. Model compounds containing hydrogen donor sites similar to those in coal are found to donate hydrogen when heated through a Gieseler temperature profile and to undergo oxidation at these sites under the conditions used to destroy fluidity in coals. The addition of sulphided metal catalysts is found to destroy Gieseler fluidity. The results support the theory that a major factor in fluidity development is a supply of donor hydrogens involved in the generation of low molecular weight ‘solvating’ species.

Use of fluorescence microscopy in the detection of low level oxidation in bituminous coals

Oxidation has a deleterious effect on the coking properties of bituminous coals. Interaction with the atmosphere markedly alters both the physical and chemical attributes of coal, thus reducing its value. Fluorescence microscopy offers a means by which these effects can be readily detected and quantified. Blue light excitation (450–490 nm) has been used to produce autofluorescence in vitrinite and inertinite macerals. Their fluorescence intensities, measured at 650 nm in both Australian Permian and German Carboniferous coals, were found to decrease with duration of exposure to air. This was observed in coals of different rank but was most pronounced in high volatile bituminous coals. By establishing a profile of fluorescence intensity levels in unoxidized coals over a wide rank range, it is possible using this technique to detect whether even minimal oxidation has occurred. A comparison with various carbonization tests showed that only Gieseler fluidity and dilatation were of similar sensitivity.

Oxidation studies of high fluidity coals

Highly fluid fresh bituminous coals were oxidised and four techniques (cross-link measurement, chloroform extraction, proton magnetic resonance thermal analysis (PMRTA) and FT-i.r. diffuse reflectance spectroscopy) were used to correlate Gieseler fluidity changes with chemical differences between the fresh and oxidised samples. The oxidised samples were found to have a depleted concentration of aliphatic CH bonds. During slow heating through the plastic temperature range, they developed less molecular mobility, and generated smaller amounts of chloroform extracts but underwent cross-link formation to the same extent and at the same rate as the fresh samples. The addition of a radical stabiliser greatly inhibited fluidity loss and restored fluidity to some oxidised samples. The results suggest that for Geiseler fluidity development, the capping of radicals derived from the coal structure during heating is a far more important factor than variations in cross-link formation.

Fluidity of coal residues after extraction with mixed solvents

The Gieseler fluidity of coal residues after their extraction with mixed solvents was investigated for four bituminous coals to elucidate the effect of low molecular weight extractable substances on the plasticity of coals. The maximum fluidity was found to decrease with an increase in extraction yield. At a low extraction yield, bulk softening was predominantly affected by the softening behaviour of low molecular weight substances originally present in coal, while the softening of pyrolytic products became dominant at a higher extraction yield. The resolidification temperature and the plastic range also decreased as the extraction yield increased. For a coal containing a higher concentration of extracts, the plastic range tends to increase. Three petroleum pitches were used as model compounds of the extracts. By addition of pitches to the residues of one coal, the maximum fluidity was shown to increase and the maximum fluidity temperature was found to be related to the pitch aromaticity. The role of the extracts in coal fluidity is discussed.

Caking properties of coal residues after extraction with mixed solvents

The caking properties of nine bituminous coals were measured after their soluble parts were extracted with mixed solvents. The extraction yields of the soluble components could be arbitrarily controlled up to ≈60 wt% at room temperature by varying the composition of the mixed solvents. The variations of the crucible swelling number (CSN) and Roga index with the extraction yield were classified into four patterns. Pattern 1: both CSN and Roga index decrease rapidly with extraction yield; i.e. all the soluble parts act as ‘caking components’. Pattern 2: CSN and Roga index remain constant for ≈10 wt% of extraction yield, followed by rapid decreases. Pattern 3 (Shin-Yubari coal): CSN is invariant with extraction yield; even after low molecular weight materials are extracted, caking components may be produced from the residue during heat treatment. Pattern 4 (Zao Zhuang coal): CSN increases with extraction yield up to 28% and then begins to decrease. The presence of a maximum CSN, and the observations for Gieseler fluidity, suggest that there is an optimum fluidity for swelling character. Soxhlet extraction with chloroform revealed that the chloroform soluble substances, which have often been regarded as ‘caking components’, in fact form only a fraction of the caking components.

Effect of aerial oxidation of coking coals on the technological properties of the resulting cokes

A study has been made using four coking coals to determine the influence of aerial oxidation on their plastic properties and on the technological properties of the resulting cokes. Samples of each coal, at different degrees of oxidation, were subjected to the Audibert-Arnu dilatation and Gieseler fluidity tests. In both processes a progressive decrease of dilatation and fluidity was observed. In the initial steps of oxidation of the parent coals, a slight influence on the mechanical properties of the cokes was observed but in all cases a strong degradation was suddenly produced. The reactivity of the cokes obtained increases with the degree of oxidation of the parent coals.

A comparison of various characterization techniques for low-temperature oxidation of coal

A comparative survey is presented of the kind of information furnished by a number of techniques used for characterizing coal oxidation. Although this phenomenon influences the different coal conversion processes, emphasis is placed on the loss of coking ability on oxidation. Six different coals ranging from subbituminous to semianthracite were studied. Measurements of plastic properties (Gieseler fluidity, Arnu swelling and free swelling index) and of mechanical resistance of the resulting cokes served to quantitatively evaluate the oxidation degree of bituminous coals. These four techniques provide a set of methods useful over a broad range of oxidation degree, Gieseler plastometry being the most sensitive in the early steps while determination of coke abrasion index worked better in the case of the most oxidized coals. Infrared Photothermal Beam Deflection Spectroscopy permitted the identification of the chemical changes associated with coal oxidation. Bands in the 1800-1700 cm −1 region were ascribable to different types of carbonyl groups (anhydride or ester, carboxylic acid). Also, ionized carboxylate groups were detected after oxidation. However, no formation of ether functional groups was detected. It is concluded that infrared spectroscopy still gives poor information on the subtle changes associated with initial oxidation steps, but that the joint use of techniques providing both, quantitative and structural types of information, offers a powerful combination of methods to fully characterize coal oxidation phenomena.

Comparative sensitivity of various analytical techniques to the low-temperature oxidation of coal

A number of analytical techniques were used to investigate the low-temperature oxidation of a high-volatile and a low-volatile bituminous coal. Two oxidation treatments were used: stockpiling at a size of < 3 mm out of doors, and treating in moist air at < 420 μm in a laboratory retort maintained at 50 °C, 65% r.h. 57Fe Mössbauer spectroscopy and computer-controlled scanning electron microscopy (CCSEM) were used to investigate the oxidation of included minerals; diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and electron spectroscopy for chemical analysis (ESCA) were used to examine maceral oxidation; and the alteration of several technological properties (Gieseler plasticity, free swelling index and coke reactivity) was also monitored. Gieseler fluidity was by far the most sensitive of these measurements to the early stages of oxidation, while the Mössbauer measurement of the oxidation of pyrite to sulphates or oxyhydroxides was the second most sensitive indicator of oxidation for the coals investigated. DRIFT and ESCA exhibited significant features derived from oxygen functional groups in macerals only after the oxidation was severe enough to have nearly destroyed the plasticity. However, band ratio techniques appear promising as a method of enhancing the sensitivity of DRIFT to oxidation.

Effect of oxidative weathering on the thermoplastic and liquefaction behaviors of four coals

Using a Gieseler plastometer to measure the thermoplastic behavior, a systematic study of the change in fluid properties with progressive oxidative weathering of three high volatile A bituminous and one low volatile bituminous coal was performed. The degree of fluidity was found to decrease rapidly with initial oxidation and then more slowly with additional oxidation. The effect of oxidation on liquefaction behavior also was studied. A level of oxidation, which significantly reduced Gieseler fluidity, had no detrimental effect on the liquefaction conversion determined as ethyl acetate soluble material, of three of the four coals tested.

Characterization of vitrinite concentrates: 3. Correlation of FT-i.r. measurements to thermoplastic and liquefaction behaviour

Measurements of aliphatic C–H content by FT-i.r. have been correlated to the plastic properties and liquefaction behaviour of a set of coals and vitrinite concentrates obtained from the Lower Kittaning seam. It has been found that for vitrinites a measure of total aliphatic C–H content correlates with Gieseler fluidity, displaying an abrupt change over a narrow range of aliphatic C–H content. Liquefaction conversion does not correlate with FT-i.r. measurements of total aliphatic C–H content but does correlate with the intensity of a band that is a measure of CH 2 content. These results confirm the general relationship between the mechanism of liquefaction conversion and plastic development, but also suggests there are some subtle differences.

Further studies of coal oxidation

The low-temperature oxidation of coal has been investigated by Fourier transform infrared spectroscopy (FT-i.r.). Samples were oxidized at 140 and 60 °C for intervals of a few hours to days. These FT-i.r. results were correlated to changes in the thermoplastic properties of the coal measured by a Gieseler plastometer. The loss of Gieseler fluidity as a function of oxidation time corresponds to loss of aliphatic CH groups. Curve-resolving methods were used to distinguish between various C = 0 functional groups. At both oxidation temperatures there was an overall increase in carbonyl and carboxyl groups, but in different relative proportions depending on the oxidation temperatures.

Effect of cleavage of ether linkages on physicochemical properties of coals

Coals of different rank were treated with naphthalene anion in tetrahydrofuran. It was found that, as in the case of coal of 87.8% C (daf), large amounts of unreactive oxygen bonds, possibly of the ether type, were cleaved. Cleavage of these ether linkages led to a lowering of the melting point and, in some types of coals, to a large increase in dilatation and a substantial increase in Gieseler fluidity.

Oxidation studies on coking coal related to weathering. 3. The influence of acidic hydroxyl groups, created during oxidation, on the plasticity and dilatation of the weathered coking coal

A high-volatile bituminous coal possessing a high Gieseler fluidity and large dilatation was subjected to slight oxidation in air under chosen conditions. The resultant ‘oxycoal’ was treated with various chemical reagents in order to determine to what extent the original caking properties of this coal, as measured by Gieseler fluidity and dilatation, could be restored. Treatment with aqueous barium hydroxide or barium acetate solutions succeeded in doing so to a considerable degree. It is tentatively concluded that certain acidic hydroxyl groups formed in the course of oxidation are indirectly responsible for the deterioration of fluidity and dilatation — possibly via condensation reactions involving the hydroxyl groups — during subsequent pyrolysis of oxycoal. The presence of carboxyl groups appears to have no effect.

Comparative tests of Gieseler fluidity of coals

Comparative tests of Gieseler fluidity of coals