EFFECT OF COAL PYRITE SURFACE OXIDA-TION ON COAL DESULFURATION BY FLOTA-TION AND METHODS OF PYRITE DEPRESSION

This paper discusses the hydrophobicity of the pyrite surface under different extents of oxidation. Experimental results demonstrate that pyrite is floatable only under initial oxidation of its surface, while the fresh unoxidized or deeply oxidized surface of pyrite is hydrophilic. In the tests an organic reductant C6H3(OH)3 was chosen as the pyrite depressant. It is highly efficient ,and the sulfur in flotation can be significantly improved.

Modeling and process optimization for microbial desulfurization of coal by using a two-level full factorial design

The microbial sulfur removal was investigated on high sulfur content (1.9%) coal concentrate from Tabas coal preparation plant. A mixed culture of ferrooxidans microorganisms was isolated from the tailing dam of the plant. Full factorial method was used to design laboratory test and to evaluate the effects of pH, particle size, iron sulfate concentration, pulp density, and bioleaching time on sulfur reduction. Statistical analyses of experimental data were considered and showed increases of pH and particle size had negative effects on sulfur reduction, whereas increases of pulp density and bioleaching time raised microbial desulfurization rate. According to results of designing, and regarding statistical factors, the optimum values for maximum sulfur reduction were obtained; pH (1.5), particle size (-180 μm), iron sulfate concentration (2.7 mmol/L), pulp density (10%) and bioleaching time (14 d), which leaded to 51.5% reduction from the total sulfur of sample.

Experimental research on Phanerochaete chrysosporium as coal microbial flocculant

The flocculation effect of the Phanerochaete chrysosporium on the coal slurry were studied by orthogonal experimental method in this study.The results of research show that the P.chrysosporium has a good effect on flocculating coal slurry.The optimum combination of the experimental is the P.chrysosporium,which is cultured in 2 days,mixed with 2 mL coagulant and 2 mL broth.The flocculant is a broken liquid with pH value of 6.The hightest flocculation ratio is 93.5%.The result of FTIR shows that the biological extraction of P.chrysosporium contains a lot of acidic polysaccharides that has the effect on flocculation.Microbial flocculant molecules and particles of coal slurry could be flocculated by‘‘absorption bridge’’.

Characteristics of dissolved inorganic carbon in produced water from coalbed methane wells and its geological significance

Based on long-term dynamic tracing of dissolved inorganic carbon(DIC)and stable carbon isotope(δ13CDIC)in produced water from 20 coalbed methane(CBM)wells in western Guizhou,the spatial-temporal dynamic variations ofδ13CDIC of the GP well group produced in multi-layer commingled manner were analyzed,and the relationship between the value ofδ13CDIC and CBM productivity was examined.The produced water samples of typical wells in the GP well group were amplified and sequenced using 16S rDNA,and a geological response model ofδ13CDIC in produced water from CBM wells with multi-coal seams was put forward.The research shows that:δ13CDIC in produced water from medium-rank coal seams commonly show positive anomalies,the produced water contains more than 15 species of methanogens,and Methanobacterium is the dominant genus.The dominant methanogens sequence numbers in the produced water are positively correlated withδ13CDIC,and the positive anomaly of v is caused by reduction of methanogens,and especially hydrogenotrophic methanogens.Vertical segmentation of sedimentary facies and lithology in stratum with multi-coal seams will result in permeability and water cut segmentation,which will lead to the segmentation ofδ13CDIC and archaea community in produced water,so in the strata with better permeability and high water cut,theδ13CDIC of the produced water is abnormally enriched,and the dominant archaea is mainly Methanobacterium.In the strata with weak permeability and low water cut,theδ13CDIC of the produced water is small,and the microbial action is weak.The shallow layer close to the coal seam outcrop is likely to be affected by meteoric precipitation,so theδ13CDIC of the produced water is smaller.The geological response model ofδ13CDIC in produced water from multi-coal seams CBM wells in the medium-rank coal reveals the geological mechanism and microbial action mechanism of theδ13CDIC difference in the produced water from the multi-coal seams CBM wells.It also provides effective geochemical evidence for the superimposed fluid system controlled by sedimentary facies,and can also be used for the contribution analysis of the produced gas and water by the multi-layer CBM wells.

Desulfurization kinetics of ZnO sorbent loaded on semi-coke support for hot coal gas

Zn-based sorbent （Z20SC） prepared through semi-coke support in 20 wt% zinc nitrate solution by high-pressure impregnation presents an excellent desulfurization capacity in hot coal gas,in which H2 S can not be nearly detected in the outlet gas before 20 h breakthrough time.The effects of the main operational conditions and the particle size of Z20SC sorbent on its desulfurization performances sorbent were investigated in a fixed-bed reactor and the desulfurization kinetics of Z20SC sorbent removing H2 S from hot coal gas was calculated based on experimental data.Results showed that the conversion of Z20SC sorbent desulfurization reaction increased with the decrease of the particle size of the sorbent and the increases of gas volumetric flow rate,reaction temperature and H 2 S content in inlet gas.Z20SC sorbent obtained from hydrothermal synthesis by high-pressure impregnation possessed much larger surface area and pore volume than semi-coke support,and they were significantly reduced after the desulfurization reaction.The equivalent grain model was reasonably used to analyze experimental data,in which k s=4.382×10-3 exp（-8.270×103/RgT） and Dep=1.262×10-4exp（1.522×104/RgT）.It suggests that the desulfurization reaction of the Z20SC sorbent is mainly controlled by the chemical reaction in the initial stage and later by the diffusion through the reacted sorbent layer.

Progress of the technique of coal microwave desulfurization

With the advantages of its fast speed,effective and moderate controllable conditions,desulfurization of coal by microwave has become research focus in the field of clean coal technology.Coal is a homogeneous mixture which consists of various components with different dielectric properties,so their abilities to absorb microwaves are different,and the sulfur-containing components are better absorbers of microwave,which makes them can be selectively heated and reacted under microwave irradiation.There still remain controversies on the principle of microwave desulfurization at present,thermal effects or non-thermal effects.The point of thermal effects of microwave is mainly base on its characters of rapidly and selectly heating.While,in view of non-thermal effect,direct interactions between the microwave electromagnetic field and sulfur containing components are proposed.It is a fundamental problem to determine the dielectric properties of coal and the sulfur-containing components to reveal the interaction of microwave and sulfur-containing compounds.However,the test of dielectric property of coal is affected by many factors,which makes it difficult to measure dielectric properties accurately.In order to achieve better desulfurization effect,the researchers employ methods of adding chemical additives such as acid,alkali,oxidant,reductant,or changing the reaction atmosphere,or combining with other methods such as magnetic separation,ultrasonic and microorganism.Researchers in this field have also put forward several processes,and have obtained a number of patents.Obscurity of microwave desulfurization mechanism,uncertainties in qualitative and quantitative analysis of sulfur-containing functional groups in coal,and the lack of special microwave equipment have limited further development of microwave desulfurization technology.

Advances in the chemical leaching (inorgano-leaching), bioleaching and desulphurisation of coals

Coal still remains an important source of power generation world over. Along with its usage, comes unwanted generation of noxious gas emissions, toxic metal releases into wastewater and other pollutants which ultimately lead to environmental concerns. So cleaning of coal through physical or chemical processes becomes utmost important. There are several coals which cannot be cleaned by physical beneficiation techniques to produce low ash cleaner coals. Such coals can be cleaned only through chemical cleaning techniques. The present paper reviews the chemical demineralisation and desulphurisation of coals over the years using various inorganic and organic acids, alkalis, oxidants, leachants and various acids and alkali-acid combinations to reduce the ash and sulphur contents in coals. As high as 90% demineralisation and desulfurization could be achieved with the use of these cheap inorganic acids as compared to the expensive solvents used for solvent extraction processes, a parallel approach of cleaning and refining coals.

TRACKING PYRITIC SULFUR DURING THE MICROWAVE- CHEMICAL DESULFURIZATION OF COAL USING MOSSBAUER SPECTROSCOPY

The transformations of pyrite in coal during the microwave-chemical treatment for desulfurization of coal was studied with Mossbauer spectroscopy of Fe. The results for phase analyses show that the selective dielectric heating by microwave energy can give rise to the thermal decomposition of pyrite FeS2 in coal to new phases, pyrrhotite Fe1-xS (0【x≤0.125) and troilite FeS which can be dissolved in dilute HC1 solution. Therefore the microwave irradiation combined with the acid washing treatment will be an effective method of desulfurization of coal.

Effect of impurities on desulfurization properties of limestone during coal gasification

In order to understand the function of calcium based sorbents on desulfurization during coal gasification and the effect of impurities on it, a series of tests using three different limestones and four kinds of different sodium salts and four kinds different chlorides were conducted by X ray diffraction and X ray photoelectron spectroscopy techniques. The structure of precursory compounds and pretreatment materials were examined by XRD. The binding energy and relative contents of sulfur, calcium and carbon, which exist in different forms in the residues after coal gasification, were measured by means of XPS. The existing forms of sulfur and calcium vary with impurities in limestone. Sodium or chloride play a promotive role on limestone desulfurization, but this promotion is affected by the chemical environment.

Effect and influence factors of sulfur removal in coal with fungus

The influence of coal desulfurization by fungus was experimentally studied. The results suggest that fungus can effectively remove inorganic and organic sulfur in coal, and main influences of desulfurization by fungus of pH value, temperature, coal slurry concentration and coal granularity were studied by orthodox experiment and the optimal experimental conditions are′as follows: pH value 6, temperature 45 ℃, coal slurry concentration 10% and coal granularity 100 μm. Under above conditions, fungus car remove up to 44.96% total sulfur and 54. 87% inorganic sulfur within two days, and their desulfurization rates will increase along with time. Compared with sulfolobas, desulphurization by fungus is steady and more effective, and has advantage of high speed.

Changes in sulfur form during coal desulfurization with microwave:Effect on coal properties

The changes in sulfur form in coal were analyzed by sulfur K-XANES(K-edge X-ray absorption near edge structures) spectra before and after the coal microwave desulfurization in a Na OH solution. After the desulfurization, the pyritic sulfur content of coal decreased significantly from 53.6% to 39.2%, while the sulfate sulfur content increased from 17.3% to 34.6%. Only a small amount of thiophene sulfur(20.1–16.1%) was removed. Some sulfur-containing components were oxidized to sulfate sulfur. Under the optimum conditions, the ash content decreased, while the volatile content increased. The calorific value of coal slightly decreased with a slight variation in the amplitudes. The overall structure of coal did not change significantly based on Fourier transform infrared(FTIR) spectral analyses. Thus, the desulfurization of coal with microwave irradiation in a Na OH solution did not significantly change the properties of coal.

Desulfurization of coal by an electrochemical-reduction flotation technique

The optimum conditions for sulfur removal from coal by electrochemical reduction flotation in an aqueous NaCl solution were determined from orthogonal experiments. The effect of electrolytic conditions on the desulfurization ratio was also studied. The electrochemical-reduction processed coal was examined by X-ray diffraction, Fourier transform infrared spectroscopy and wet chemical analysis. The results show that electrochemical reduction converts hydrophobic pyrite in Nantong coal into hydrophilic FeS and S2- and leads to an increase in the concentration of hydroxyl groups and aliphatic moieties and a corresponding decrease in carboxyl and carbonyl groups, which enhances the flotation desulfurization of the coal.

Thermodynamic Analysis of Desulfurization of Fine Coal by Electrochemical Reduction Flotation

Problems in desulfurization of coal by electrochemical reduction is analyzed and calculated. The result shows that 1 ) the △rGm function of the reaction of pyrite into FeS and the modifying reaction decreasing the oxygenous functions on coal surface is smaller than zero in a spontaneous reaction, and greater than zero in a non-spontaneous reaction; 2) the △rGm value can be adjusted by pH and the dosage of electrolyte to make it be greaterthan zero , which is favorable for the modifying reaction and useful for desulfurization of coal. The research has provided a theoretical foundation for determining reasonable technical parameters of desulfurization。

Fractal desulfurization kinetics of high-sulfur coal

The pore structure characteristics of high-sulfur coal from Wansheng in Chongqing have been studied by a nitrogen adsorption method (BET). The effects of grinding and pre-treating with nitric acid on the inorganic sulfur content of coal have been investigated. Organic sulfur in coal pretreated with nitric acid was desulfurized by using propylene-glycol-KOH (PG-KOH). Fractal kinetic properties of these two desulfurization procedures were investigated by using fractal geometric theory. The results show that both the specific surface area and pore volume increased with the decrease in particle diameter. The microspore surface of coal had fractal characteristics; the fractal dimension was 2.48. The sulfur content decreased with the decrease in particle diameter by grinding. After pretreatment with nitric acid, the desulfurization ratio (DFR) of inorganic sulfur increased to over 99% and the DFR of total sulfur to over 70%. The desulfurization procedure of inorganic sulfur had fractal kinetic characteristics; its reactive fractal dimension was 2.94. The organic sulfur desulfurization procedure by PG-KOH was also tallied with fractal kinetic properties; the reactive fractal dimension was 2.57. The effect of temperature on the desulfurization ratio of organic sulfur can be described with an Arrhenius empirical equation. The rate constant, pre-exponential factor and the activation energy of the reaction increased with the decrease in particle diameter.

Research on Factors Affecting Flotation and Desulfurization of Coal by Electrochemical Method

Influence of factors such as potential of electrolyte, electrolyzing time, concentration of electrolyte, and pH value on flotation and desulfurization of coal was researched. The result shows that the electrochemical reduction can enhance the desulfurization effect and increase the yield of clean coal under certain conditions. So it is an effective method.

Factors Influencing Conversion of Pyritic Sulfur in Coal by Microwave Irradiation

The high sulfur coal from southwest of China was used to examine the influence of different factors such as irradiation time, particle size of coal, and leachant (Na2CO3, NaOH and CuCl22H2O)on the conversion rate of pyrite to pyrrhotite by microwave irradiation. Single factor experiment was performed firstly, then orthogonal test method was used to explore these factors. The result shows that the optimal treating conditions for the conversion are a treatment time of 3 min, a particle size from 0.086 mm to 0.102 mm, and a favorable leachant of sodium hydroxide. Under these conditions the conversion rate of pyrite can reach 45.7 %.

THE APPLICATION OF REVERSE FLOCCULATION METHOD IN HIGH SULFUR COAL DESULFURIZATION

The reverse flocculation method for removing pyritic sulfur from high sulfor coals has been conceptually beveloped and investigated. The tentative tests on China high sulfur coals have shown that this advanced physical separation techaique can be very efficient in coal desulfurization, provided the process parameters are properly optimized. Under the circumsances of acquiring high coal recovery, the total sulfur rejection with four kinds of coal samples normally falls in tbe range 57% to 71 % by one-step reverse flocculation, and within the range 40% to 59% by one-step normal flocculation process.

AN ADVANCED COAL DESULFURIZATION PROCESS──SELECTIVE FLOCCULATION

Selective flocculation is an idea separation method to separate ultrafine pyrite from coal. A number of selective flocculation separation tests under different conditions have been done and the results are very encouraging. The results also show that desulfurization and deashing can be finished simultaneously in selective fIocculation process. It is an advanced coal desulfurization process.