Biodesulphurization of Hungarian lignite and sub-bituminous coal

The annual SO₂ emission is approx. 0.6 million tons in Hungary because of the high amount of sulphur in the power plant coals. Since Hungary has signed the European Environmental Agreement, the high sulphur emission has to be gradually reduced. To overcome the acid rain problem, the biodesulphurization of Hungarian power plant coals has also been started in Hungary. The R&D programe of biodesulphurization has been launched in 1990. According to our findings the biodesulphurization process is a suitable tool for reducing the pyritic sulphur content in lignite and sub-bituminous coal.     

Ion-solvent interactions - studies on the solvation of electrolytes in mixed solvents

In order to throw light on ion-solvent interactions, the solvation numbers of electrolytes in different mixed solvents (methanol + water and ethanol + water mixtures) have been determined using ultrasonic interferometer. The anomalies in the solvation number of cations (in aqueous solutions) like K⁺, Na⁺ and H⁺ are presented. The changes in the solvation numbers of electrolytes with increasing quantities of alcohol indicates some interesting features and are explained on the basis of:(i) decrease in the solvent molecules.(ii) structural re-arrangement.(iii) preferential solvation of cations and anions.(iv) Approximations in the determination of solvation numbers. The role of the solvents could hardly be explained in absence of a complete knowledge of the nature of solvation of electrolytes and particularly of ions. The subject has attracted considerable attention and the solvation number has been determined using different well-known techniques[1-4].In order to throw light on the ion-solvent interactions, we tried to determine the solvation numbers of different known electrolytes like HCl, NaCl and KCl in water, methanol + water and ethanol + water mixtures by the compressibility method using ultrasonic interferometer. The results are presented in this communication.     

Structural studies of coal extracts

The reductive alkylation of a medium-volatile bituminous coal was carried out using potassium and naphthalene in tetrahydrofuran, and using methyl, ethyl and butyl iodides to alkylate the resultant polyanion. The soluble products of the reductive alkylation reaction were isolated by extraction with n-pentane and benzene. The extracts were characterized by i.r. and ¹H n.m.r. spectroscopy, molecular mass and ultimate analyses.     

Modeling of oxy-fuel combustion for a western Canadian sub-bituminous coal

The motivation of this research is to develop practical oxy-coal combustion techniques in order to facilitate the conversion of coal-fired utility power plants so as to recover a CO₂ rich flue gas stream for use and/or sequestration. The objective of this study is to ascertain the applicability and accuracy of a modeling tool to assist with future pilot scale oxy-fuel combustion experiments and burner scale-up studies. Two modes of oxy-coal combustion, O₂ enriched air (OEA) and recycled flue gas (RFG), were experimentally tested in a 0.3 MW_th pilot-scale combustor using a western Canadian sub-bituminous coal. The computational fluid dynamic tool was utilized to model the combustion, heat transfer and pollutant formation characteristics of these test cases and to examine the impact due to changes in the combustion medium, burner swirl and burner configuration. The model provided insights for the observed variation in NO_x production among the test cases: the dramatic increase in the OEA mode, the drop at higher burner swirl settings and the surprisingly small reduction in the RFG mode. Overall the model results compared well with measured data in all test cases and established confidence in using the model to explore new design concepts for oxy-coal combustion.     

Oxidation of ash-free coal from sub-bituminous and bituminous coals in a direct carbon fuel cell

The present study proposes the production of ash-free coal (AFC) and its oxidation as a primary fuel in direct carbon fuel cells (DCFCs). The AFC was produced by the extraction of Arutmin sub-bituminous coal (AFC1) and Berau bituminous coal (AFC2) using polar solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). It was carried out at a temperature of around 202 °C under atmospheric conditions and using a microwave irradiation method. Using NMP as the solvent showed the highest extraction yield, and the values of 23.53% for Arutmin coal and 33.80% for Berau coal were obtained. When NMP was added to DMSO, DMA and DMF, the extraction yield in the solvents was greatly increased. The yield of AFC from a sub-bituminous coal was slightly lower than that from a bituminous coal. The AFC was evaluated in a coin-type DCFC with a mixture of AFC and carbonate electrolyte (3 g/3 g) at 850 °C. The AFC and gaseous H₂ fuels were compared using the electrochemical methods of steady-state polarisation and step chronopotentiometry. The DCFC ran successfully with the AFCs at 850 °C. The open-circuit voltages were about 1.35 V (AFC1) and 1.27 V (AFC2), and the voltages at 150 mA cm^?2 were 0.61 V (AFC1) and 0.74 V (AFC2).     

Optimization of the utilization of a sub-bituminous coal in conventional and form-coking

An attempt has been made to determine the extent to which a sub-bituminous coal can be utilized in the production of coke of metallurgical quality. It was established that coke of acceptable quality can be made from blends of up to 15% low-temperature sub-bituminous char and a high-volatile, high-fluidity coal. With partial agglomeration of the blend, the char constituent can be increased to about 30%. Formcoke of metallurgical quality can be made entirely from the coal by binderless briquetting of fluidized-bed char. It was shown that the strength and abrasion resistance of the formcoke is greatly influenced by the char preparation conditions and the post-briquetting heat treatment.     

Action of solvents on coal at low temperatures: 1. Low-rank coals

The dissolution behaviour of brown coals (67–75% C, daf) in pyridine, primary amines and aqueous KOH has been studied. The solubility in the last two solvents greatly depends on temperature, but in the first it is relatively temperature-independent. Pretreatment of the brown coals with aqueous HCl or with sodium ethanolate in ethanol leads to enhanced solubility. It is concluded that ester-bond breaking is necessary before extensive dissolution can take place. The solubility of brown coals in amines and aqueous KOH is found to increase with increasing carboxylic-acid group concentration in the coal. The solubility of Morwell brown coal in n-alkylamines at 180 °C increases with increasing length of the alkylchain in the solvent. The class of good solvents for brown coals is restricted to strong bases, because: 1. ester bonds have to be broken, 2. the acidic coal fragments have to be solubilized. Because of their capacity to break ester bonds these are so-called reactive solvents. Complete solvent recovery is impossible in the case of amines.     

Morphologies of anodic oxide films deduced from dissolution studies

Study of the chemical stripping of anodic oxide films on hafnium, zirconium, tungsten and aluminium has led to the deduction of the morphology of the respective oxides. Away from the boundary region hafnium oxide is a compact, smooth, homogenous and crystalline oxide. Zirconium oxide has a superficial disorder layer which constitutes about 17% of the entire film. Tungsten oxide deposits are composed of two defective partial layers the outer one being more disordered. Aluminium oxide is a porous film. A schematic representation of each film had been presented.     

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.     

Compositions of distillate recycle solvents derived from direct coal liquefaction in the SRC-I process: 1. Hydrocarbons

The qualitative and quantitative compositions of 260–427 °C distillate recycle solvents derived from direct liquefaction of subbituminous Wyodak coal and bituminous Kentucky $\text{9}\text{14}$ coal in the SRC-I process are discussed. A liquid chromatography method which involves a column switching technique was used to provide solubility characteristics and compound-class compositions. The hydrocarbon compounds, which accountfor> 60 wt% of the distillate recycle solvents, were further analysed using a unique combination of high-performance liquid chromatography (h.p.l.c.) and field ionization mass spectrometry (f.i.m.s.). Thirty homologous series were identified. Carbon number and distribution and concentration of the homologous series were determined. The h.p.l.c./f.i.m.s. method unravelled various hydroaromatic types which otherwise would be very difficult or impossible to determine.     

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%).     

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.     

Supercritical solvents. Carbon dioxide extraction of retained pyridine from pyridine extracts of coal

Pyridine extracts of coal are excellent models for studies of coal structure and reactions, but the pyridine that is retained is undesirable. A method is described, using supercritical carbon dioxide, for the removal of retained pyridine from pyridine extracts of Illinois No. 6 and Western Kentucky No. 9 coals.     

Fate of the chlorine and fluorine in a sub-bituminous coal during pyrolysis and gasification

The fate of the chlorine and fluorine present in a sub-bituminous coal from Indonesia during pyrolysis and gasification has been studied with fixed and entrained bed reactors. The rate profile for HCl evolved in the temperature programmed pyrolysis exhibits the main and shoulder peaks at 480 and 600 °C, respectively. Model experiments and subsequent Cl 2p XPS measurements show that HCl reacts with metal impurities and carbon active sites at 500 °C to be retained as inorganic and organic chlorine forms, from which HCl evolves again at elevated temperatures. It is suggested that the HCl observed in the coal pyrolysis may originate from the above-mentioned chlorine functionalities formed by secondary reactions involving the nascent char. In the CO₂ gasification of the 900 °C char at 1000 °C and 2.5 MPa, any measurable amounts of HCl and HF could not be detected even at a high conversion of 75 wt% (daf), suggesting the accumulation of these halogens in the residual char. When the coal is injected into an O₂-blown, entrained bed gasifier at 1200-1400 °C under 2.6 MPa, the partial oxidation proceeds to a larger extent at a higher O₂/coal ratio, whereas the chlorine and fluorine are enriched in the remaining char, and the extent of the enrichment at the latter stage of gasification is larger with the fluorine. The XPS measurements of the chars reveal the presence of the broad F 1 s peak, which can cover a wide range of binding energies attributable to inorganic and organic fluorine. The halogen enrichment during gasification is discussed in terms of secondary reactions of HCl and HF with char.     

Gasification of coals treated with non-aqueous solvents. 1. Liquid ammonia treatment of a bituminous coal

A Japanese bituminous coal was treated with liquid ammonia at temperatures up to 120 °C. Extract was separated from the treated coal by washing with benzene-ethanol mixture. The amount of extract was about 2% in a single treatment at 120 °C and some additional extract was obtained by successive treatments. Particles of the residue had cracks and showed an increase in surface area. The ammonia-treated coal was found highly reactive toward gasification with hydrogen at high temperature when catalysed by nickel.     

Structural analysis of tars from fluidized-bed pyrolysis of coal. 1. Gas-liquid chromatography of aliphatic and aromatic subfractions

The effect of pyrolysing gas composition on the low-molecular-weight aliphatic and aromatic components of fluidized-bed tars has been investigated. Two tars from the rapid pyrolysis of coal in a fluidized-bed were solvent-fractionated into oils, asphaltenes and benzene-insoluble materials. The aliphatic and low-molecular-weight aromatic subfractions of the oils were then analysed by glass-capillary column gas-liquid chromatography. The results show that pyrolysis in a more active atmosphere of char gasification gases is ‘deeper’, and, to some extent, similar to hydrogen-assisted pyrolysis; the yield of tar is higher, and the product has higher aromaticity and average molecular weight compared with pyrolysis in nitrogen-rich flue gases.     

Fusion temperatures of PFA from New Zealand sub-bituminous coals

The ash fusion temperatures of 20 analysed samples of pulverized fuel ash obtained from the Meremere coal-burning power station have been determined. It is shown that the fusion temperatures can be related to the acid-soluble calcium and iron oxide contents, and that it is possible to predict the softening and hemisphere temperatures of ash cubes with a precision of ca. 10 to 20 °C in either oxidizing or reducing atmospheres. Removal of the magnetic iron fraction from the PFA reduced both the softening and hemisphere temperatures by ca. 10 to 15 °C in an oxidizing atmosphere, and in a reducing atmosphere it increased the softening temperature by ca. 10 °C and the hemisphere temperature by ca. 30 °C.     

Initial solvation of coal with tetralin under liquefaction conditions

Secondary vitroplast, produced by treating a Liddell vitrinite concentrate with tetralin in a continuous flow, packed-bed microreactor under a nitrogen pressure of 13.8 MPa at 360, 410 and 460 °C, has been analysed by i.r. spectroscopy, gel permeation chromatography, solid state ¹³C n.m.r. and reflectance microscopy. Results showed that this intermediate in the liquefaction process had the same carbon aromaticity as the untreated vitrinite concentrate and that both its aromaticity and reflectance were independent of the temperature of formation. It was concluded that the initial solution of the vitrinite concentrate in tetralin involved no significant hydrogenation of the vitrinite.