Biodesulphurization of coal: behaviour of trace elements

The purpose of this study is to show how the different size fractions of coal are affected during a process of biodesulphurization in a packed column and to examine the repercussions of the process on the elimination of certain heavy and trace elements. The total desulphurization obtained in 51 days is about 25 wt%, as only pyritic sulphur is attacked. The greatest reduction in sulphur content was for the 1-0.5 mm fraction although the lowest actual sulphur content was found in particles of under 0.125 mm, where it dropped from 1.76 to 1.17 wt%. The most important changes in the metal content were decreases in Ni, Cu, Zn, As, Cr, Co and Sr, mainly in the smaller sizes.     

Modification of sub-bituminous coal by steam treatment: Caking and coking properties

A Chinese sub-bituminous Shenfu (SF) coal was steam treated under atmospheric pressure and the caking and coking properties of the treated coals were evaluated by caking indexes (G_RI) and crucible coking characterizations. The results show that steam treatment can obviously increase the G_RI of SF coal. When the steam treated coals were used in the coal blends instead of SF raw coal, the micro-strength index (MSI) and particle coke strength after reaction (PSR) of the coke increased, and particle coke reactivity index (PRI) decreased, which are beneficial for metallurgical coke to increase the gas permeability in blast furnace. The quality of the coke obtained from 8% of 200 °C steam treated SF coal in coal blends gets to that of the coke obtained from the standard coal blends, in which there was no SF coal addition in the coal blends. The removal of oxygen groups, especially hydroxyl group thus favoring the breakage of the coal macromolecules and allowing the treated coal formation of much more amount of hydrocarbons, may be responsible for the modified results. The mechanism of the steam treatment was proposed based on the elemental analysis, thermo gravimetric (TG) and FTIR spectrometer characterizations of the steam treated coal.     

Biodesulphurization as a complement to the physical cleaning of coal

Physical and biological processes have been combined with a view to reduce the sulphur and ash content of finely ground coal. The coal used was a semianthracite from the North Spain Coal Field. A sample of several kg in a coal/water suspension with a w/w concentration of 15% was subjected to a physical treatment combining cyclone and flotation separation processes. Representative samples were taken from each of five size fractions: original feed and the physical separation products, which were screened through water into sub-samples classified by particle size. Each fraction from the physical separation and the screening was analysed for ash and sulphur. The elimination yield of the hydrocyclone was 22% of ash and 21% of sulphur. The figure for ash raised to 41% when the hydrocyclone and flotation equipment were both used, with no change in sulphur elimination. In turn, the biodesulphurization treatment applied in addition to the two processes raised the respective yields to 59 and 42%. The change in the calorific value of the coal was hardly significant, while sulphur emissions, expressed as g S/GJ were reduced by 51%. Additionally, an assessment was made of the thermal behaviour of the various samples from the physical and biological treatment by means of programmed temperature combustion analysis carried out by a thermogravimetric equipment.     

Biodepyritisation of coal

This review provides a detailed summary of the recent and past research activities in the area of biodesulfurisation of coal. It provides information about microorganisms important for biodesulfurisation of coal, with the emphasis on Thiobacillus ferrooxidans. The review presents an insight into various methods of desulfurisation of coal combining physical and biological methods. Also, there are discussions on coal structure, distribution, mechanism and kinetics of pyrite oxidation and jarosite precipitation. Finally, areas requiring further research are identified. Copyright © 2003 Society of Chemical Industry     

Removal of sulfur from Assam coal by bacterial conditioning and froth flotation

Reduction of sulfur by bacterial leaching from a high sulfur‐bearing coal sample from Assam was attempted. Flotation of the sample with light diesel oil could not depress the pyrite and also the Thiobacillus ferrooxidans was found to be ineffective in leaching the sulfur from the flotation concentrate. Conditioning of the same coal sample with Thiobacillus ferrooxidans was found to assist in selectively depressing the pyrite, thereby reducing nearly 60% of the pyritic sulfur present in the sample. © 1999 Society of Chemical Industry     

Bioleaching of molybdenum from coal liquefaction catalyst residues

It has been shown that the bacterium Thiobacillus ferrooxidans can solubilize MoS₂ from coal liquefaction catalyst residues. The MoS₂ is formed during the liquefaction process from a molybdenum catalyst precursor. MoS₂ is insoluble; in order to be recovered and reused, it must be converted to a soluble form. T. ferrooxidans can oxidatively solubilize the molybdenum in MoS₂ to molybdate, in which form it can be recovered as a soluble or HCl extractable material. Bioleaching experiments show that with a starting cell concentration of 1.0 × 10⁷ cells ml⁻¹, or greater, a significant amount of the molybdenum in the residue was solubilized. These experiments indicate that the amount of molybdenum biologically solubilized from the liquefaction residues is dependent on inoculum size, with all strains of T. ferrooxidans tested having equal ability, and on the particle size of the residue. An important factor in the solubilization of MoS₂ by T. ferrooxidans is the inhibitory effect of molybdate. Literature reports that as little as 10 ppm molybdate is inhibitory to growth or ferrous iron oxidation. However, leachates containing in excess of 70 ppm molybdenum (equivalent to 116 ppm molybdate) were generated as a result of bioleaching of the liquefaction residue. When cells from previous leaching experiments were used to inoculate flasks containing fresh media and additional liquefaction residue, the bacteria were able to bioleach the fresh residue. Recent experiments have focused on the ability of T. ferrooxidans to produce protective agents in the leachate that minimize the inhibitory effects of molybdate. We found that production of the protective factor(s) did not depend on previous exposure of the cells to molybdenum or liquefaction residue.     

Energy-efficient coal dewatering using liquefied dimethyl ether

In this study, we dewatered sub-bituminous coal mined in Warra, Indonesia, by using liquefied dimethyl ether (DME); no heating was required in this dewatering process. We achieved this dewatering both in a laboratory-scale experiment and using previously developed bench-scale equipment. We also examined the properties of the coal before and after dewatering and measured the amount of energy required by the equipment. We found that the maximum water extraction efficiency of liquefied DME was 98.3%. Further, the properties of the coal did not change after the dewatering treatment. The wastewater obtained by dewatering can be treated by existing wastewater treatment technologies. The energy consumed by the bench-scale equipment was 2069 kJ/kg-water; thus, this dewatering process using liquefied DME was confirmed to be effective and energy efficient.     

Research issues in combustion and gasification of lignite

This paper presents an overview of the combustion and gasification research sponsored by the CRC for Clean Power from Lignite. This research is focused on two distinct areas, gasification of lignite for use in advanced gas turbine cycles and the utilisation of de-watered lignite in existing boilers. Fluid bed gasification is at the centre of a suite of technologies being developed for advanced power generation cycles using Victorian and South Australian lignite, the latter being particularly difficult to utilise on account of its high sodium and sulphur contents. Gasification research at Adelaide is focused on obtaining fundamental reactivity data under gasification conditions to validate and to further develop an existing fluid bed gasification model. The sodium and sulphur in the SA fuel present a special challenge and a considerable part of the research effort is devoted to developing techniques to manage these components. The team is utilising two small gasifiers, one batch and one continuous for this work and is about to commission a new 200-mm continuous fluid bed gasifier. Utilisation of de-watered lignite in existing boilers represents a significant fuel change, similar to the changes from coal to oil (1950-1960s) and oil to natural gas (1970-1980s), which did not occur smoothly. Researchers at Adelaide are currently developing mathematical and physical models for lignite-fired boilers, which, together with the lessons from the past, will equip the industry for the changes with minimum disruption.     

Mineralogical and elemental composition of fly ash from pilot scale fluidised bed combustion of lignite, bituminous coal, wood chips and their blends

The chemical and mineralogical composition of fly ash samples collected from different parts of a laboratory and a pilot scale CFB facility has been investigated. The fabric filter and the second cyclone of the two facilities were chosen as sampling points. The fuels used were Greek lignite (from the Florina basin), Polish coal and wood chips. Characterization of the fly ash samples was conducted by means of X-ray fluorescence (XRF), inductive coupled plasma-optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), particle size distribution (PSD) and X-ray diffraction (XRD). According to the chemical analyses the produced fly ashes are rich in CaO. Moreover, SiO₂ is the dominant oxide in fly ash with Al₂O₃ and Fe₂O₃ found in considerable quantities. Results obtained by XRD showed that the major mineral phase of fly ash is quartz, while other mineral phases that are occurred are maghemite, hematite, periclase, rutile, gehlenite and anhydrite. The ICP-OES analysis showed rather low levels of trace elements, especially for As and Cr, in many of the ashes included in this study compared to coal ash from fluidised bed combustion in general.     

A comparison of the results obtained from grinding in a stirred media mill lignite coal samples treated with microwave and untreated samples

Various studies have been carried out on the effect of microwave-treatment on grinding different types of coal. However, the effect of microwave treatment on grinding coal samples −3.35 mm in size which can be considered to be fine is still under investigation. The purpose of this paper is to make contributions to these studies conducted. In the study, lignite coal samples with pyritic sulphur and 25% structural moisture were crushed below −3.35 mm particle size using jaw and cone crushers and then classified into three different mono size groups by Russel sieve. For a complete removal of the structural moisture from the lignite coal, a microwave application with 600 W needs approximately 35% more energy consumption than that with 850 W. The untreated coal samples and the ones treated with microwave at 850 W were ground for 5, 15, 30, 60, 120 s in a stirred media mill. The breakage rates of microwave-treated coal increased and accordingly the ground products of microwave-treated coal yielded finer particles than −106 μm as compared to untreated coals. The untreated and microwave-treated feed coals of −3350 μm and −1180 μm particle sizes were ground for 2 min in the stirred media mill. It was found that the increases in the rate of weight percentages for −106 μm particle size fraction after 2 min of grinding of untreated and microwave-treated feed coals of −3350 μm and −1180 μm were found to be 15.81% and 2.69%, respectively. Moreover, Hardgrove Index (HGI) test results of lignite coal showed that the HGI index value increased by approximately 23% after microwave treatment with 850 W.     

Trigeneration integrated with absorption enhanced reforming of lignite and biomass

A technical investigation of an innovative trigeneration integrated with absorption enhanced reforming (AER) of lignite and biomass is carried out using the ECLIPSE process simulator. The system includes an internal combustion engine, an AER gasifier, a waste heat recovery and storage unit and an absorption refrigerator. The whole system is operated in the following sequence: The AER gasifier is used to generate hydrogen using lignite and biomass; the hydrogen generated is used to run the engine which drives a generator to produce electricity. Additionally, the heat recovery unit collects waste heat from the engine and is used to supply hot water and space heating. Furthermore, the waste heat is used to operate the absorption refrigerator. The electricity, heat and cooling can be used to meet the energy requirements for the households in a village, a resident building or a commercial building, or a supermarket. Within the study, the effects of lignite mixed with three different types of biomass (straw, willow and switch grass) on the system performance are investigated and the results are compared. The results show that it is feasible to use an AER system to reform the low quality fuels lignite and biomass to generate a cleaner fuel - hydrogen to replace fossil fuels (diesel or natural gas) and to fuel an engine based trigeneration system; the system works with high efficiencies and with a potential of carbon capture from the sorbent-regeneration process that would benefit the environment.     

Prospects for biodesulfurization of coal: mechanisms and related process designs

Recent developments in microbiological desulfurization of coal are reviewed. Microbiological removal of organic sulfur from coal remains to be proven conclusively, but is under active study for petroleum biodesulfurization. Microbiological removal of pyritic sulfur from coal is well established in the laboratory and recent efforts have been aimed at scale-up designs and process considerations. Microbiological depyritization may be as inexpensive as other forms of advanced coal desulfurization but it has not been tested on a large scale. Processes based on ‘indirect’ bioleaching of pyrite from coal may also have applications. Other forms of sulfur in coal, such as elemental sulfur, are usually quantitatively insignificant, but nonetheless can be removed microbiologically. Thermophilic bacteria remove pyritic sulfur from coal at faster rates than mesophilic bacteria, in part due to faster abiotic rates of pyrite oxidation at elevated temperatures. Future work in biological desulfurization of coal should include studies on treatment of waste coal or refuse material.     

褐煤制浆和配煤制浆技术

基于中国煤炭资源状况及褐煤难成浆的特点,提出采用配煤制浆的方法来提高制浆浓度。分析了国内外褐煤和配煤制浆技术的研究现状,同时介绍了国内褐煤制浆技术的发展。研究发现:现有的配煤技术多采用煤质较好的原煤和褐煤,应寻求更多的现有资源和褐煤配煤制浆来提高煤浆浓度,尤其是热值不低却未被充分利用的煤炭资源,如煤炭液化废渣、沥青等,以充分利用煤炭资源,保护环境。     

Combined effects of pressure and ion-exchangeable metallic species on pyrolysis of Victorian lignite

A set of ion-exchanged samples prepared from Loy Yang lignite was pyrolyzed in a wire-mesh reactor at elevated pressures from 1 to 36 bar. The tar yields from the pyrolysis of H-form (acid-washed) sample at a fast heating rate of 1000 °C s⁻¹ were drastically reduced by increasing pressure to 6 bar and then remained unchanged with further increase in pressure to 36 bar. This behavior of the tar yield was in sharp contrast to that from the raw lignite which showed a minimum with increasing pressure. The sensitivities of the tar yields to changes in the heating rate were also suppressed by increasing pressure. The tar yields from Ca-form and Na-form samples (prepared by ion-exchanging Ca and Na on the H-form sample, respectively) were not very sensitive to changes in the heating rate and pressure up to 11 bar. At 20 bar, the tar yields from the Na-from sample nearly doubled whereas from the Ca-form sample nearly halved compared to those respective values at 1 bar. Although increasing pressure is thought to cause changes in the intra-particle mass transfer processes of volatile precursors, the rate of formation of volatile precursors tends to dictate the kind of mass transfer process responsible for the release of volatiles. Therefore, depending on the pyrolysis condition, bulk diffusion or forced flow would dominate the mass transfer processes for the release of volatiles. The introduction of cations is thought to result in irreversible changes in the lignite structure and not only control the process of formation but also the amount of volatile precursors and in turn alter the effects of pressure. Valence and catalytic activity of cations seem to play important roles in determining pyrolysis products distribution at elevated pressures.     

褐煤制气化水煤浆实验研究

为提高褐煤制气化水煤浆的制浆浓度,采用传统制浆工艺与分级研磨制浆工艺分别对某化工企业提供的3种煤样进行水煤浆成浆性实验,并在此基础上进行配煤制浆实验。结果表明:东明煤、扎赉诺尔煤、宝矿提质煤传统制浆工艺的最高浓度分别为48.54%、51.76%、56.08%,分级研磨制浆最高浓度分别为51.72%、54.82%、59.21%,3种煤样分级研磨制浆工艺水煤浆浓度提高3%以上。按照东明煤、扎赉诺尔煤质量比1∶1或东明煤、宝矿提质煤质量比2∶1配煤时所制水煤浆浓度分别为53.12%、54.21%,满足水煤浆浓度设计要求。     

氧化亚铁硫杆菌的培养及氧化性能测定

研究了自行选育的氧化亚铁硫杆菌的生长特性。结果表明：我们自行选育培养的脱硫自养菌氧化亚铁硫杆菌,在特定条件下具有快速高效将Fe^2＋转化为Fe^3＋的功能,通过氧化亚铁硫杆菌生长因素的研究,确定了其生长的最佳条件,即在细菌处于对数生长期时,按10％接种量接种,调节培养液pH为2．5左右,30℃时振荡培养,氧化亚铁硫杆菌的生长活性最佳。通过考察培养过程中Fe^3＋浓度的变化,测定了不同接种量时氧化亚铁硫杆菌的氧化性能参数μ。     

Co-liquefaction of lignite and sawdust under syngas

Individual and co-liquefaction of lignite and sawdust (CLLS) under syngas was performed in an autoclave and the effects of temperature, initial syngas pressure, reaction time and ratio of solvent to coal and biomass on the product distribution of CLLS were studied. Sawdust is easier to be liquefied than lignite and the addition of sawdust promotes the liquefaction of lignite. There is some positive synergetic effect during CLLS. In the range of the experimental conditions investigated, the oil yield of CLLS increases with the increase of temperature, reaction time (10-30 min) and the ratio of the solvent to the feedstock (0-3), but varies little with the increase of initial syngas pressure. Accordingly, the total conversion, the yield of preasphaltene and asphaltene (PA + A) and gas, changes by the difference in operation conditions of liquefaction. The gas products are mainly CO and CO₂ with a few C₁-C₄ components. The syngas can replace the pure hydrogen during CLLS. The optimized operation conditions in the present work for CLLS are as follows: syngas, temperature 360 °C, initial cold pressure 3.5 MPa, reaction time 30 min, the ratio of solvent to coal and sawdust 3:1. Water gas shift reaction occurs between CO in the syngas and H₂O from coal and sawdust moisture during the co-liquefaction, producing the active hydrogen which increases the conversion of liquefaction and decreases the hydrogen consumption.     

Effects of glycerol on the minimization of water readsorption on sub-bituminous coal

The presence of water in coal presents a technological challenge for its industrial use in energetic processes. Water tends to negatively affect the coal quality and its net heating value (NHV), in addition to affecting its transportation costs. Therefore, this study aims to investigate the effects of glycerol and temperature on water adsorption onto systematically modified coals. A Colombian bituminous coal sample was used as support for being modified with glycerol. The virgin coal and modified coal were characterized by nitrogen adsorption at 77?K (S_BET), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (C–H–N elemental), and thermogravimetric analysis (TGA). The results showed that the water uptake decreased as the amount of glycerol on the coal surface increased. The optimum concentration of 8?wt% of glycerol impregnated on the coal minimized water adsorption. Over a range of water activity evaluations, this amount of glycerol (C8) reduced water adsorption by approximately 60% compared with nonimpregnated coal (C0). As expected, water uptake decreased with increasing temperature. These results are reflected in the NHV with an increase of 17% for the C8 sample compared with the other samples evaluated. The Talu and Meunier model was used to fit the experimental adsorption isotherms, and the mean square root error (MSRE%) was lower than 10%. The isosteric heat of sorption (IHS) for coal tends to decrease as the amount of adsorbed water increases. In addition, the value of IHS decreases as the concentration of glycerol increases due to the blocking of polar adsorption sites present on the coal surface, which are the main regions of low uptake of adsorbed water. Additionally, the Gibbs free energy was found to have negative values, which corroborates the spontaneous adsorption process.     

Distribution of inorganic and organic substances in the hydrocyclone separated Slovak sub-bituminous coal

A low-rank Slovak sub-bituminous coal from the Handlová deposit was physically treated by washing in a water-only cyclone with the goal to find the separation effect for inorganic (mainly Fe-bearing minerals) and organic substances (humic acids, diterpanes). A high-quality coal product with the ash content in the dry matter of 9.02% and carbon content of C^d = 68.12% at a mass yield of 29.51% was obtained using the water-only cyclone processing. At first, the physically treated coal samples were detailed characterized by XRD, ⁵⁷Fe Mössbauer spectroscopy, FT-IR and HR-TEM. In addition to non-crystalline organic coal components, inorganic compounds belonging to silicate minerals (kaolinite, muscovite and quartz) as well as to Fe-bearing sulphide minerals (pyrite) were identified in the sub-bituminous coal by XRD. ⁵⁷Fe Mössbauer spectroscopy detected the presence of iron carbonate (siderite), iron-containing clay mineral and two sulphur-containing minerals (pyrite, jarosite) in the untreated coal. On the other hand, only one Fe-bearing mineral, (pyrite) was found in the washed coal. Effect of the physical separation is also demonstrated in FT-IR spectra, where the peak at 1040 cm⁻¹ representing the silicate component in the untreated sample is not detectable in the washed coal sample. Presence of extractive organic substances, i.e. humic acids and tetracyclic diterpane (16α(H)-phyllocladane), in the hydrocyclone products is also evidenced. It was confirmed that the isolated diterpenoic compound is attendant in the washed product with the lowest ash content and it is assimilated with the organic part of coal. Surprisingly, humic acids were found in the highest concentration in the slurry that has the highest content of ash (63.14%).