Fine-grained Coal Research Articles

Fluidization characteristics of loaded vibrating fluidized bed and dewatering and deashing effect of moist fine-grained coal

ABSTRACT The influence of a thermal vibrating fluidized bed on the dewatering and deashing effect of moist fine-grained coal was investigated by digital image processing and signal analysis methods. Comparative analysis results of the pressure signals of a loaded vibrating fluidized bed indicated that high or low gas velocity and strong or weak vibration conditions easily caused the formation of numerous irregular bubbles and contributed to violent fluctuations in the bed. An interaction between gas velocity and vibration energy was found, with vibration energy being the dominant factor influencing the bubble behavior at low gas velocities. Moreover, at high gas velocities, the advantages arising from vibrations were weakened. Under the condition of f = 20 Hz, A = 2 mm, v = 18 cm⋅s−1, the contact efficiency between the gas – solid two phases was higher, and the pressure fluctuation of the bed became more stable. Under this condition, the ash content of clean coal and the moisture removal rate were 11.76% and 83.54%, respectively. Finally, comparison and analysis of the influence of different parameters on the calorific value of clean coal revealed that the influence of each parameter on heat generation of the selected product was found to be in the following order: f > A > V > T.

Impacts of vertical variation of coal seam structure on hydraulic fracturing and resultant gas and water production: A case study on the Shizhuangnan Block, Southern Qinshui Basin, China

Hydraulic fracturing plays a vital role in the development of coalbed methane (CBM). Coal seam structures can, however, affect the fracturing operations, further affecting gas and water production from the coal seam. Within the research area—the Shizhuangnan Block, Southern Qinshui Basin, China—three types of coal body textures are relevant, including original, cataclastic, and granulated structure. This research describes the impacts of different coal seam types on fracturing operations and gas and water production. The results show that different types of coal seams have different impacts on hydraulic fracturing and the resultant production of gas and water. The coal seams are classified according to the vertical variation characteristics of the coal seam structures. The first type of coal seam (Type I) only develops the original and cataclastic coal structure. The effects of fracturing reconstruction for Type I are good. A high degree of coal breakage and fracture formation is observed. Gas production from CBM wells in Type I coalbeds is usually high because the water in the coal reservoir can be discharged smoothly at an early stage. The second type of coal seam (Type II) develops an additional layer of granulated coal compared with Type I. During the fracturing process, breakage of the coal seam is obvious, and the granulated coal can easily produce fine-grained coal that can block the pores and fractures, which causes an increase and fluctuation of oil pressure and can affect the effectiveness of fracturing. The gas production curve from CBM wells in Type II coal seams is mostly bimodal and water production depends on whether the pulverized coal blocks the pores and fractures. The third type of coal seam (Type III) develops two additional layers of granulated coal compared with Type I, with a greater proportion of granulated coal present. A low degree of coal breakage and fracture formation is observed, and fractures are easily blocked by pulverized coal. The effects of fracturing reconstruction for Type III are bad. Forming an effective seepage channel in this type of coal seam and extending the fracture to the far end is difficult. The gas production from CBM wells in Type III coal seams is usually low, and water production is generally low during the whole drainage period.

Study on fluidization characteristics and drying characteristics of fine coal in thermal vibration separation fluidized bed

By studying the fluidization characteristics of the granular bed in the separation process of fine coal, this paper explores the effect of coal particles on the distribution and evolution of the fluidization behavior of the bed, and analyzes the separation and drying characteristics of fine coal. The results indicated that the stable value of pressure drop curve of bed with medium particles is larger than that of mixed particle bed of medium and coal. Meanwhile, with the increase of the coal particle size, the stable value of pressure drop gradually decreases, as well as the drying rate of lignite increases first and then decreases with the increase of gas velocity, vibration frequency and amplitude. Contrarily, the drying time of fine-grained coal decreases and then increase with the increase of vibration amplitude. Under the conditions of N = 1.4, f = 20 Hz, A = 2 mm, the contact efficiency between the gas–solid phases is good, and the bed pressure fluctuation is stable. After the separation of −6 + 3 mm and −3 + 1 mm fine coal, the ash content of clean coal is 13.4 % and 9.1 % respectively, and the gangue ash reached 43.7 % and 63.5 % respectively. With the increase of gas velocity, vibration frequency and amplitude, the activation energy Ea of fine coal drying process decreases first and then increases, and then the activation energy Ea in the separation process of fine coal is the lowest under the conditions of N = 1.4, f = 20 Hz, A = 2 mm.

Cleaning of fine asphaltite by oil agglomeration process

ABSTRACT In Turkey, asphaltite deposits are located in the Southeastern Anatolia region in the form of fleets around the Sirnak province and its environs. According to the research, although the lower thermal values of Sirnak asphaltites are between about 11–24 MJ/Kg, the ash contents are between 35% and 55% and the total sulfur rates are between 3% and 8%. Asphaltite with high-ash content ratios can be cleaned by applying coal preparation and enrichment methods and made into high-quality energy raw materials with higher calorific value. Most fine-grained coals are disposed of without use or any economic consideration and cause environmental pollution. The oil agglomeration method, which is one of the methods of ore enrichment used to clean very fine coals, can be applied for coal samples. In this study, chemical and sieve analyzes of asphaltite samples taken from the Seguruk and Avgamasya mine sites operating within the borders of the Sirnak province were carried out and oil agglomeration enrichment method was applied with different types of oil and ash content were reduced. Under the conditions determined, the ash content of the Seguruk asphaltite sample called sample-A was reduced from 45.14% to 19.91% and the ash content of the Avgamasya asphaltite sample called Sample-B was reduced from 43.65% to 18.72%.

A Novel Approach of Bulk Strength Enhancement through Microbially-Mediated Carbonate Cementation for Mylonitic Coal

Mylonite coal is known to be highly tectonically deformed coal and is a result of crushing original coal into fine-grained coal under multiple tectonic events. Because of its granular nature and the resultant inferior mechanical property, the borehole stability during both drilling and gas drainage is challenging due to unpredictable failures. This study explored a potential approach to enhance the bulk strength of mylonitic coal via microbiologically-mediated CaCO3 cementation which effectively increases the cohesion of the fine coal particles through the bio-cementation process. The experimental results indicated that the mechanical strength was significantly enhanced after a short period of biotreatment with 12 cycles of biotreatment yielding a maximum stiffness of 32 KN/mm and maximum uniaxial compressive strength of 9.3 MPa. The strength evolution behavior demonstrated that the macroscopic failure behavior of mylonite coal evolves from plastic failure to brittle failure as the increase of bio-treatments. The results from XRD indicated that the generated CaCO3 crystals mainly occurs in the form of calcite and vaterite. Imaging by SEM further indicated the cementation process for CaCO3. The generated CaCO3 precipitation first occurs on random spots on the particle surfaces, and then occupies the interstitial space until particle-particle bonds are generated.

Research on the Production of Composite Fuel on the Basis of Fine-Grained Coal Fractions and Biomass—The Impact of Process Parameters and the Type of Binder on the Quality of Briquettes Produced

This paper presents the partial results of a study on obtaining compacted fuel from fine-grained coal fractions and biomass. The aim of the study was to determine the impact of selected parameters of the extrusion process and the applied binder (mechanical durability and density of the products). The fuels were formulated using the extrusion process. Raw materials used in the research were: Fine-grained coal (flotation concentrates), biomass (hydrolytic lignocellulose), and a wide spectrum of organic and mineral binders and their compositions. During the investigations, the variable factors were the following: Extrusion pressure, preparation of the mixtures for extrusion (mixing time and temperature of the mixture), composition of the extruded mixtures (share of fine-grained coal and biomass and type of binder). It was found that it is possible to extrude mechanically durable briquettes from mixtures containing fine-grained coal products and biomass. Under the conditions of the experiment, the most favorable mechanical durability was characterized by briquettes containing in their composition 90% of coal and 6% of biomass (in relation to the dry state). The briquettes with the most favorable physico-mechanical properties were obtained using organic binders—Starch (based on wheat and potato starch) and cellulose derivatives.

Fluidization and separation characteristics of gas–solid separation fluidized bed with wet coal

Raw coal is usually sorted using a gas–solid separation fluidized bed in a dry environment. However, when wet coal is sorted, the moisture carried by the coal causes the fluidized environment in the gas–solid separation fluidized bed to become extremely complex. In the present study, the mechanism whereby moisture is transferred to the medium particles was examined, the phenomenon that the coal and medium particles were subject to an agglomeration mechanism was found. The surface bonding properties of coal are affected by the particle size, moisture content, and the relative motion of the coal and medium particles, which is determined by the formula for calculating the bridging force. The effect of the moisture content on the fluidization characteristics is such that an increase in the water content exacerbates the agglomeration of the media particles, especially once the water content exceeds 1%, with channel flow and local collapse occurring in the fluidized bed (e.g. Sp = 0.33 in the axial direction), which adversely affects the sorting. Through a study of the coal surface adhesion and sorting, it was revealed that the critical amount of external moisture for the effective separation of coal falls with the particle size. For medium- and fine-grained coal, the critical moisture content can be as low as 2% and 1%, while the value can be as high as 4% for the coarse-grained coal.

Laboratory and Statistical Analysis of Chosen Concentrating Table Technological Parameters Influence on Coal Sludge Enrichment Process

AbstractConcentrating tables are a group of one of the oldest and most precise gravitational concentrators with a broad spectrum of application. They were used mainly for the anthracite enrichment process in the domestic coal industry. Conducted research prove that they can be also used for the enrichment of fine grained coals types. The article discusses the results of coal sludge enrichment using WILFLEY concentration tables, as the results obtained show that coal sludge enrichment using these concentration tables allows for the production of coal concentrates and half-products of satisfying quality parameters, the ash content of which varies between several and a dozen or so percent. The reciprocal connection between the actual contents and enrichment process has been determined based on a dependency analysis between the changing characteristics. The correlation analysis allowed for an evaluation of the dependencies between the technological parameters of the enrichment process and the obtained qualitative-quantitative parameters results, which allows the given mineral enrichment process to perform correctly. The enrichment process of the studied sludge has been performed using the most unfavorable construction parameters i.e. using sulcate plate, its inclination angle remained at 6°, furthermore studied material has not been hyphenated.

Stratified Sampling to Define Levels of Petrographic Variation in Coal Beds: Examples from Indonesia and New Zealand

DOI: 10.17014/ijog.3.1.29-51Stratified sampling of coal seams for petrographic analysis using block samples is a viable alternative to standard methods of channel sampling and particulate pellet mounts. Although petrographic analysis of particulate pellets is employed widely, it is both time consuming and does not allow variation within sampling units to be assessed - an important measure in any study whether it be for paleoenvironmental reconstruction or in obtaining estimates of industrial attributes. Also, samples taken as intact blocks provide additional information, such as texture and botanical affinity that cannot be gained using particulate pellets. Stratified sampling can be employed both on ‘fine’ and ‘coarse’ grained coal units. Fine-grained coals are defined as those coal intervals that do not contain vitrain bands greater than approximately 1 mm in thickness (as measured perpendicular to bedding). In fine-grained coal seams, a reasonable sized block sample (with a polished surface area of ~3 cm2) can be taken that encapsulates the macroscopic variability. However, for coarse-grained coals (vitrain bands >1 mm) a different system has to be employed in order to accurately account for the larger particles. Macroscopic point counting of vitrain bands can accurately account for those particles>1 mm within a coal interval. This point counting method is conducted using something as simple as string on a coal face with marked intervals greater than the largest particle expected to be encountered (although new technologies are being developed to capture this type of information digitally). Comparative analyses of particulate pellets and blocks on the same interval show less than 6% variation between the two sample types when blocks are recalculated to include macroscopic counts of vitrain. Therefore even in coarse-grained coals, stratified sampling can be used effectively and representatively.

Mechanism of Overpressure Formation in Deeply Burial Sandstone

Overpressure is often encountered in the Jurassic tight and the overpressure is closely associated with gas generation. The pressure transfer from the over-pressurized mudstones to adjacent tight sandstones might occur through overpressure induced-fractures. The fine-grained coal containing Jurassic sandstone is sensitive to compaction, and the porosity decreases dramatically with the increase of overlying load. As gas migrates into the tight sandstones, it must overcome the capillary pressure which is greater than the hydrostatic pressure. The gas charging pressure in the tight sandstone must be higher than the capillary pressure, resulting in an overpressure buildup within the tight sandstones. Gas shows, low permeability and strong diagenesis in the overpressure of the tight sandstone system have been observed. Additionally, capillary seals are identified as playing an important role in the mechanism of the overpressure formation in tight sandstone reservoirs. Overpressure might be a driving force to create induced fractures in the interval, which has applications for crossing-formation migration and gas accumulation.

98/04312 Reactor for burning or gasification of fine-grained coal

98/04312 Reactor for burning or gasification of fine-grained coal

The Delights of Memory, II: Doss

(The lights rise on the freight yards in Mesa City. On one side, we see a field heaped with fine-grained coal, and, beyond that, on the same side, a small adobe bungalow used as a resthouse and office for railroad men. In the accessible interior of this bungalow, there are: an old woodstove; wall lockers; a plain rectangular table; some straightbacked, wooden chairs; a few railroad lanterns hung on the wall behind a square, heavy oak desk; a water pitcher with a glass draped over its spout; an old axe, and a poster with the rules of the resthouse. Upstage, toward the center, a well-appointed private car sits, on a track, in state. Beyond this, there is the vague outline of a large adobe building, the city train station.

A comparison of methods for the determination of the pyritic sulfur content of coal

The accurate determination of the concentration of inorganic sulfur in coal is of major environmental importance. With few exceptions, unless the coal is weathered, the inorganic sulfur present within the coal is iron disulfide minerals, chiefly pyrite and to a lesser extent, marcasite. The accuracy of the presently used ASTM procedure for the determination of iron disulfide sulfur can be questioned because various quantities of the mineral grains encapsulated by the coal matrix are not available to the acid-leaching reaction utilized in the procedure. The goal of this study was to test this hypothesis and to devise a procedure which would give analytical results in agreement with a matrix-independent analytical procedure, namely Mossbauer spectroscopy. The concentration of inorganic sulfur was determined for a suite of coal samples varying in sulfur abundance by the ASTM D2492 procedure on two particle sizes of coal, −60 mesh and −220 mesh. The coal samples were subjected to low-temperature ashing and the resultant ashes were leached with 0.5 N hydrochloric acid. The total weight loss from the ashing process was made up by adding sulfur-free spectrographic grade carbon and the sulfur content of the mixture was determined using a LECO 1R32 sulfur analyzer. The inorganic sulfur contents as determined by the three methods were then compared to the sulfur concentrations as calculated from the iron disulfide abundance as determined by Mossbauer spectroscopy. The data show that the sulfur analysis using ASTM D2492 and the −60 mesh coal sample is unsatisfactory. Acceptable sulfur data can, however, be determined using the ASTM method and −220 mesh coal. The best comparison of data was obtained with the sulfur content obtained by the LECO analysis of the acid-leached low-temperature ash. These results strongly suggest a significant error in inorganic sulfur analysis due to the encapsulation of iron disulfide grains within the organic matrix of the coal when a procedure is used based upon the leaching of the coal sample. The problem can be minimized by utilizing fine-grained coal (−325 mesh) and essentially eliminated by utilizing an hydrochloric acid-leached low-temperature ash.

Thermodynamics and kinetics of coal gasification in a liquid iron bath

The thermodynamics and kinetics of the Molten-Iron-Pure-Gas (MIP) process used for coal gasification have been analyzed. In the MIP process, oxygen, fine-grained coal, and fluxes are injected into a liquid iron bath to produce a high temperature gas consisting of CO and H2 plus a liquid basic slag. The sulfur is transferred from the coal to this slag. Computer calculations bearing in mind test conditions were used to determine equilibrium conditions as well as mass and energy balances; these indicated that the MIP process is technically feasible. The kinetics of the gasification process have been investigated by analyzing and assessing the basic reactions for a bottom-blowing MIP reactor. A comparison of all relevant reactions reveals that the dissolution of carbon in iron is the rate-determining step of the process. The bath turbulence induced by the injected gas and by the product gas results in intense mixing and dispersion of the reactants and their intermediate products. These phenomena create extremely large mass-transfer surfaces and extend the retention time of the reactants in the liquid iron bath. This results in high conversion rates relative to the volume of the MIP reactor.