Spanish Lignite Research Articles

Flue gas analysis for biomass and coal co-firing in fluidized bed: process simulation and validation

Coal-conversion technologies, although used ubiquitously, are often discredited due to high pollutant emissions, thereby emphasizing a dire need to optimize the combustion process. The co-firing of coal/biomass in a fluidized bed reactor has been an efficient way to optimize the pollutants emission. Herein, a new model has been designed in Aspen Plus® to simultaneously include detailed reaction kinetics, volatile compositions, tar combustion, and hydrodynamics of the reactor. Validation of the process model was done with variations in the fuel including high-sulfur Spanish lignite, high-ash Ekibastuz coal, wood pellets, and locally collected municipal solid waste (MSW) and the temperature ranging from 1073 to 1223 K. The composition of the exhaust gases, namely, CO/CO2/NO/SO2 were determined from the model to be within 2% of the experimental observations. Co-combustion of local MSW with Ekibastuz coal had flue gas composition ranging from 1000 to 5000 ppm of CO, 16.2%–17.2% of CO2, 200–550 ppm of NO, and 130–210 ppm of SO2. A sensitivity analysis on co-firing of local biomass and Ekibastuz coal demonstrated the optimal operating temperature for fluidized bed reactor at 1148 K with the recommended biomass-to-coal ratio is 1/4, leading to minimum emissions of CO, NO, and SO2.

Supercritical gas extracts from low-quality coals: on the search of new precursors for carbon materials

This paper studies the chemical composition of several supercritical gas (SCG) extracts and its influence on the thermal behaviour under carbonisation conditions. The extracts were obtained from a Spanish lignite (Mequinenza), a low-quality coal from the point of view of energy applications. The lignite was treated with toluene, ethanol (EtOH) and tetrahydrofuran (THF) as solvents under different supercritical temperature and pressure conditions. The extracts display high aliphatic nature and enhanced concentrations of oxygen functional groups, aided by the contribution of hydrogenation and oxygen incorporation reactions occurring in the SCG extraction with EtOH and THF. Thiophenic compounds are also present in great concentrations derived from the exceptionally high organic sulphur content of the parent coal. The carbonisation of the extracts renders anisotropic material with fine mosaic texture, as a consequence of the significant thermal reactivity inferred by the aliphatic and oxygenated groups. The size of the mosaic increases with the temperature of the SCG extraction and varies with the supercritical solvent in the order: toluene<EtOH<THF.

Supercritical gas extracts from low-quality coals: on the search of new precursors for carbon materials

This paper studies the chemical composition of several supercritical gas (SCG) extracts and its influence on the thermal behaviour under carbonisation conditions. The extracts were obtained from a Spanish lignite (Mequinenza), a low-quality coal from the point of view of energy applications. The lignite was treated with toluene, ethanol (EtOH) and tetrahydrofuran (THF) as solvents under different supercritical temperature and pressure conditions. The extracts display high aliphatic nature and enhanced concentrations of oxygen functional groups, aided by the contribution of hydrogenation and oxygen incorporation reactions occurring in the SCG extraction with EtOH and THF. Thiophenic compounds are also present in great concentrations derived from the exceptionally high organic sulphur content of the parent coal. The carbonisation of the extracts renders anisotropic material with fine mosaic texture, as a consequence of the significant thermal reactivity inferred by the aliphatic and oxygenated groups. The size of the mosaic increases with the temperature of the SCG extraction and varies with the supercritical solvent in the order: toluene<EtOH<THF.

The influence of nitric acid oxidation of low rank coal and its impact on coal structure ☆

FT-i.r. was used to examine the behaviour of a Spanish lignite during its oxidative treatment with nitric acid with a view to assessing the different forms of sulphur reduction and the changes produced in the coal structure, as a result of the action of the reagent. Inorganic sulphur decreases rapidly and practically disappears, even under mild attack conditions (50 °C, 20% acid concentration). At first, organic sulphur undergoes a rapid decrease but more energetic conditions are required to maintain the reduction. Reduction may even reach 53% under such conditions. Unfortunately, energetic attacks (90 °C) lead to a high-level of coal organic matter solubilization and an increase in oxygen content. Basically, the oxygen appears as carbonyl group within the desulphurized coal. The nitric acid causes effective nitration of the coal, the nitrogen being incorporated especially as aromatic nitrogen. The substitution is easily produced (50 °C) when there are two adjacent aromatic hydrogens per ring. The isolated hydrogens in aryl- or polycyclic aromatic structures, are more resistant to attack under mild conditions but not so at 90 °C. As nitration progresses, more electrophilic molecules appear and aliphatic hydrogen tends to increase after initially decreasing under mild attack and increases more so under more energetic condition. This aliphatic hydrogen compensates for the decrease in aromatic hydrogen.

A study of sulfur functionalities in fossil fuels using destructive- (ASTM and Py–GC–MS) and non-destructive- (SEM–EDX, XANES and XPS) techniques

A set of Spanish coals and oil shales were studied using destructive and non-destructive techniques to identify the functionalities of the sulfur compounds. The selected samples included organic-sulfur-rich Spanish lignites mined in the Mequinenza, Utrillas and Calaf basins; calcareous source-rocks from Organyà and sulfur-rich oil shales from Ribesalbes. Using analytical pyrolysis coupled to gas chromatography–mass spectrometry, we estimated the ratio S org/C in these coals and oil shales, and compared them with those obtained by the ASTM method D2492. Also, a scanning electron microscope (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX) allowed the direct determination of organic sulfur content in coals. Two major non-destructive techniques, XANES and XPS, were used to investigate sulfur functionalities, such as pyritic, sulfidic, thiophenic, sulfoxide, sulfone, sulfonate and sulfate forms. The study shows that sulfur characterization in coal is not without difficulties and no method is exempt from problems and the introduction of possible artifacts.

Influence of temperature, catalysts and partial pressure of hydrogen on the co-processing of spanish lignites

Studies on coal-oil co-processing are one aspect of the research carried out in the field of coal liquefaction. The oil used in the process is likely to be a heavy petroleum residue due, in part, to the economic constraints of the process and, moreover, to the expected chemical compatibility. This project studies the influence of the kind of coal, vacuum residue, catalyst and temperature on the co-processing conversion and the quality of liquid products. The influence of partial pressure of hydrogen is studied. Two different Spanish lignites were co-processed with a typical commercial vacuum residue and in the presence or absence of solid catalysts. Two supported catalysts, one with 25% Fe, as oxide, and a second with 25% Fe plus 10% Mo, as oxides, were prepared. Prior to their utilization, the catalysts were sulphided. The range of temperatures studied was 350–470°C. Experimental results show that the temperature and the partial pressure of hydrogen are the most important variables. A maximum conversion and proportion of valuable liquid oil fraction was obtained between 375 and 425°C. Temperatures exceeding this range produce a negative value of conversion because of the retrograde recombination reactions of radicals and, consequently, a great increment in the gases formed. The comparison of the two lignites used, Berguedà and Utrillas, confirms the relation between the structural composition and the level of maximum conversion attained. The results obtained with catalysts suggest that their effect overlaps or competes with the compounds present in the ashes when the level of ashes is high. The only general conclusion about the use of Fe and Fe-Mo catalysts is that the amount of sulphur present in the oil fraction is lower than that obtained without catalyst. With respect to the effects of hydrogen partial pressure, the main conclusion refers to the comparison between the normal loading of solid reagents and 3/4 of this loading. A wide screening of temperatures was carried out with normal and with 3/4 loadings, and with the other loading only one temperature was checked. The lowest loading (highest H2 content) produced an increment in the conversions attained and a displacement of the region of maximum conversion toward lower temperatures.

Transport fuels from two-stage coal liquefaction

Four Spanish lignites and their vitrinite concentrates were evaluated for coal liquefaction. Correlationships between the content of vitrinite and conversion in direct liquefaction were observed for the lignites but not for the vitrinite concentrates. The most reactive of the four coals was processed in two-stage liquefaction at a higher scale. First-stage coal liquefaction was carried out in a continuous unit at Clausthal Universität at a temperature of 400°C at 20 MPa hydrogen pressure and with anthracene oil as a solvent. The coal conversion obtained was 75.41% being 3.79% gases, 2.58% primary condensate and 69.4% heavy liquids. A hydroprocessing unit was built at the Instituto de Carboqumica for the second-stage coal liquefaction. Whole and deasphalted liquids from the first-stage liquefaction were processed at 450°C and 10 MPa hydrogen pressure, with two commercial catalysts: Harshaw HT-400E (Co-Mo/Al2O3) and HT-500E (Ni-Mo/Al2O3). The effects of liquid hourly space velocity (LHSV), temperature, gas/liquid ratio and catalyst on the heteroatom liquids, and levels of 5 ppm of nitrogen and 52 ppm of sulphur were reached at 450°C, 10 MPa hydrogen pressure, 0.08 kg H2/kg feedstock and with Harshaw HT-500E catalyst. The liquids obtained were hydroprocessed again at 420°C, 10 MPa hydrogen pressure and 0.06 kg H2/kg feedstock to hydrogenate the aromatic structures. In these conditions, the aromaticity was reduced considerably, and 39% of naphtas and 35% of keroseno fractions were obtained.

Influence of Fe and FeMo high loading supported catalysts on the coprocessing of two Spanish lignites with a vacuum residue

The catalytic coprocessing of two Spanish lignites with a vacuum residue of petroleum has been studied. Two catalysts supported on γ-Al 2O 3, with loadings of 25% Fe 2O 3 and 25% Fe 2O 3/10% MoO 3, have been tested at temperatures from 400 to 425°C with an initial hydrogen pressure of 8 MPa. Results show that both catalysts improve the conversion of coal and upgrade the liquid product distribution. When a high ash lignite is used the catalytic effect of the own mineral matter overcomes the effect of added catalysts. The FeMo catalyst yields the highest coal conversion, oil production and desulphuration within the range of temperatures studied.

A spectroscopic study of structural changes occurring in supercritical gas extraction of a Spanish lignite with alcohols

Supercritical gas (SCG) extraction of a Spanish lignite was conducted with methanol and ethanol in a semicontinuous mode at temperatures between 250 and 350 °C and pressures up to 15.2 MPa. The resultant extracts and residues were characterized principally by FT-i.r. spectroscopy and n.m.r. to specifically provide information on the mode and extent of solvent incorporation via secondary reactions. FT-i.r. and n.m.r. revealed that alkylation and esterification reactions both occur to a significant extent. The extent of alkylation increases with increasing temperature and SCG extractions with 13C-labelled methanol demonstrated that the incorporated methyl groups are mainly bound to C atoms but also to O, S and N atoms. The extent of esterification is incomplete, as indicated by the presence of free carboxylic acids in both the chars and extracts, and decreases with increasing temperature due to the competing effect of decarboxylation reactions.

Influence of temperature and hydrogen partial pressure on the coprocessing of two Spanish lignites with a vacuum residue

This work studies the influence of temperature and hydrogen availability on the coprocessing of two high sulphur content Spanish lignites, with a petroleum vacuum residue. The experimental results show that temperature and partial pressure of hydrogen have a great influence on the conversion of coal and on the quality of oils formed. The conversion increases with temperature of reaction until a maximum is achieved. This maximum is between 400 and 420 °C depending on the reaction conditions. Beyond this maximum the conversion drops quickly, even producing negative results, due to recombination reactions. A higher hydrogen partial pressure induces a larger coal conversion but the maximum is achieved at lower temperatures. On the basis of these results, hydrogen transfer through aromatic compounds is proposed as the reaction mechanism of coprocessing.

Structural characteristics and geochemical significance of humic acids isolated from three Spanish lignite deposits

Three Spanish lignites of similar low maturity level taken from different deposits and their humic acid (HA) fractions have been characterized by chemical and spectroscopic methods. Some remarkable differences were found in the HA contents, as well as in the distribution of humic and fulvic fractions among the parent lignites. These differences, however, are not reflected by spectral or chemical distinguishing features. The results suggest that lignin-derived materials contributed to the formation of the lignite deposits.

Activated carbon columns as adsorbents of gallic acid from aqueous solutions: Effect of the presence of different electrolytes

Adsorption of gallic acid by activated carbons from aqueous solutions has been studied. Activated carbons were prepared from agricultural by-products and Spanish lignites. All carbon series were characterized by N 2 and CO 2 adsorption, mercury porosimetry, and water density. The adsorption processes have been carried out under both static and dynamic conditions. Adsorption isotherms obtained at 298 K were fitted by the Langmuir's equation. In the case of dynamic adsorption some characteristics of the beds, such as breakthrough volume, adsorption capacity at different breakthrough values, and height of the mass transfer zone, were calculated from the breakthrough curves, which were obtained by pumping a solution of the acids through the beds at a constant rate. Adsorption capacity was related to the pore volume of the activated carbons accessible to water. When other electrolytes were present in the gallic acid solutions, the adsorption capacity was enhanced and the rate of the adsorption process was lowered.

Effects of petrographic composition and sulphur in liquefaction of Spanish lignites

The behaviour in hydroliquefaction (H 2, tetralin, 400 °C) of four Spanish lignites with different petrographic composition and a similar ash content was studied and the nature of the derived oils was evaluated. Vitrinite and/or vitrinite plus exinite contents and percentages of total and organic sulphur correlate with conversion yields. Maceral composition does not appear to influence the nature of the derived oils.

Steam gasification of a lignite char catalysed by metals from chromium to zinc

The effect of various metals on the gasification rate and the composition of the evolved gases during steam gasification of a Spanish lignite char have been studied. Among the metals studied Ni showed the highest carbon conversion, although at steady-state conditions Fe was the best catalyst. However, neither metal increased reactivity up to the value corresponding to that of the original char. However, in the presence of H 2 in the steam flow Ni increased the reactivity up to a value similar to that obtained with the original char, and it behaved as a gasification catalyst suppressing the water gas shift reaction.

DIRECT HYDROGENATION OF A SPANISH LOW RANK COAL. THE EFFECT OF PROCESS VARIABLES

ABSTRACT The effect of operating conditions on the liquefaction behaviour of a Spanish lignite was studied using a 250 ml stirred autoclave, and the following operating conditions (except otherwise specified): 400 °C, 1 hour, 3.5 MPa initial (cold) H2 pressure, 400 rpm and 40 g/10 g tetralin/coal charge. The liquefaction products were fractionated into oils, asphaltenes, preasphaltenes and solid residue using pentane, toluene and THF as extractive solvents The influence of temperature was explored in the 300–475 °C range, observing little further improvement in liquefaction yields over 400 °C, and retrogressive reactions over 450 °C. The effect of time was studied from 0 to 180 minutes and was concluded that 1 hour is an appropriate period for liquefying a black lignite, since there is little further conversion for longer times. The influence of pressure and gas type was studied using 0, 3.5 and 7.0 MPa initial (cold) pressure of H2 and of N2, and the effect of stirring using 0 and 400 rpm. Little influen...

Comparison of activated carbons prepared from agricultural raw materials and spanish lignites when removing chlorophenols from aqueous solutions

Activated carbons obtained from agricultural by-products and Spanish lignites, as well as a commercial one, have been used to study the removal of ortho- and metachlorophenol from aqueous solutions, both under static and dynamic conditions. Results obtained show that although both isomers are adsorbed to the same extension, the interaction of metachlorophenol with the surface of the carbon is stronger than in the case of the other isomer. Characteristics of the carbon beds have been related with the textural characteristics of the adsorbents. Thus, it has been found that the pore volume accessible to water is an important parameter determining the yield of the removal process. The bed characteristics have been studied as a function of type of activated carbon, particle size, concentration, and pH of the solutions. The efficiency of these activated carbons to remove orthochlorophenol is higher under static conditions than under dynamic ones.

Hydrodesulfurization of a High Organic Sulfur Spanish Lignite with Impregnated Nickel Sulfate

Abstract The removal of sulfur from Mequinenza (Spanish) lignite was investigated by hydrodesulfurization reactions. This lignite has an unusually high sulfur content, 9.9% (dry basis) of which about 90% is organic sulfur. The lignite was impregnated with nickel sulfate prior to reactions, at various levels of nickel loading. The reactions were performed in bench-scale microautoclave reactors in 6.9 MPa hydrogen at 250-325° C for 1 hour. The best result was the removal of 63% of the sulfur in the lignite, achieved with 1.5% nickel loading at 325° C. Compared to reactions without impregnated catalyst, the addition of nickel sulfate enhances the hydrodesulfurization at all reaction temperatures, and improves the selectivity to H2S. A high selectivity to H2S minimizes the formation of organic sulfur compounds in by-product liquids

Desulphurisation of a spanish lignite via low temperature supercritical gas extraction

Supecritical gas (SCG) extraction of a high sulphur Spanish lignite with methanol has been conducted at temperatures between 250 and 350°C and the resultant extracts have been characterised by GC/MS and other appropriate techniques. Char prepared at 350°C contained 40% less organic sulphur than the initial coal but a similar reduction in organic sulphur content was achieved by pyrolysis at 500°C. Thus the extent of desulphurisation is influenced primarily by thermal processes rather than by the nature of the SCG. Nevertheless, the methanol had a significant impact on product distribution; it was incorporated into the extracts and residues as both methyl ethers and esters and decomposed to generate hydrogen in situ, some of which was transferred to the lignite.

Comparative performance of impregnated molybdenum-sulphur catalysts in hydrogenation of Spanish lignite

Hydrogenation of a Spanish lignite of 12% sulphur content was conducted using three molybdenum-containing catalysts impregnated into the lignite: ammonium tetrathiomolybdate, a sulphided ammonium heptamolybdate, and molybdenum disulphide. The conversions to liquids and hydrodesulphurization were investigated for a series of residence times and temperatures. At 275 °C, the ammonium salts provide no greater conversion or sulphur removal than obtained in the absence of catalyst, because these salts have not decomposed to an active catalyst at this temperature. However, lignite impregnated with molybdenum disulphide does experience greater conversion and desulphurization than lignite reacted without catalyst. At 325 °C, the lignite impregnated with the ammonium salts gives conversions and desulphurization substantially superior to that achieved with molybdenum disulphide or without catalyst. This is attributed to the superior dispersion that can be achieved by impregnation using a solution of a soluble salt rather than a slurry of the insoluble disulphide. The best conversions, liquid yield, and desulphurization are achieved using impregnated sulphided ammonium heptamolybdate.

Size exclusion chromatography of pyrolysis and hydropyrolysis tars from Spanish low rank coal

The molecular weight distributions of tars obtained from a Spanish lignite by pyrolysis and hydropyrolysis at 500–700 °C have been determined by size exclusion chromatography (SEC) using tar fractions as calibration standards. Two peaks, at 400–500 amu and 250–280 amu were observed in the chromatograms of all the tars studied, but their relative intensities varied with the pyrolysis temperature and atmosphere. The variations appear to be related to thermal cracking at higher temperatures.