Transformation of organic and inorganic sulphur in a lignite during pyrolysis: Influence of inherent and added inorganic matter

The transformation of organic and inorganic sulphur during pyrolysis of a Western Australian lignite has been studied using several complimentary techniques. The lignite contains high moisture, oxygen, volatile matter, organic sulphur and inherent inorganic matter. FTIR and solid state ¹³C TOSS NMR spectroscopic studies revealed that the high oxygen content is attributed to the oxygenated functional groups, which is saturated with organically bonded inherent inorganic matter. Sodium and chlorine are the dominant inorganic matter and present in the form of sodium chloride. TGA-MS studies of the raw lignite showed that SO₂ is the dominant sulphur-bearing gases evolved during the pyrolysis of the raw lignite. The effect of inherent and added inorganics was studied by comparing the amounts of various forms of sulphur retained in the chars of the raw lignite, the acid washed lignite and the acid washed lignite doped with sodium and kaolinite following pyrolysis in a fixed-bed reactor in nitrogen. Inherent inorganic matter was shown to reduce the decomposition of organic sulphur but has little effect on the decomposition of inorganic sulphur. Sodium helps the retention of sulphur in the chars between 400 and 500 °C while kaolinite has a better ability to retain sulphur above 600 °C.     

The transformation and fate of sulphur during CO2 gasification of a spent tyre pyrolysis char

The transformation and fate of sulphur (S) in a spent tyre pyrolysis char during CO₂ gasification were studied by following the S species and contents using X-ray photoelectron spectroscopy (XPS). The spent tyre pyrolysis char (particle size fraction ≤150 µm), without and with 1 M HCl acid washing to remove inorganic S, were gasified in a fixed bed reactor. The effect of temperature (850, 950, 1050 °C), reaction time (1, 2, 3, 6 h) and CO₂ concentration (33.3, 50.0, 66.7 vol% in N₂) on the S species in the char samples were investigated. The main S species in the spent tyre pyrolysis char were ZnS and aliphatic sulphide. After CO₂ gasification, aliphatic sulphide, thiophene, sulphoxide and sulphone became the dominant organic S while ZnS and CaSO₄ were the main inorganic S. The percentage of total S increased with increasing gasification temperature, time and CO₂ concentration. The content of organic S increased with increasing gasification temperature and time, while, the content of inorganic S decreased. Increasing CO₂ concentration had negligible effect on the content of organic S but led to significant reduction in the content of inorganic S since ZnS reacted with CO₂ to produce ZnO and SO₂. Aliphatic sulphide, sulphoxide and sulphone were shown to have transformed to more stable thiophene. ZnS decomposed to release S_X at > 900 °C while CaSO₄ reacted with CO and carbon to produce COS. Both S_X and COS reacted with the organic matrix in the char to form sulphoxide and sulphone.     

Correlation of Coal Calorific Value and Sulphur Content with 57Fe Mössbauer Spectral Absorption

Coal is the most abundant, most economical and widely distributed fossil fuel in the world today. It is also the principal form of reductant in the iron and steel industry. This study was undertaken to not only add to the growing use of Mössbauer spectroscopy application in industry but also to increase the chemistry and physics knowledge base of coal. Coal is 40 to 80 percent carbon with small amounts of sulphur and iron as pyrite and ferrous sulphate. The environmental concern associated with mining and burning of coal has long been a subject of investigation with emphasis on the sulphur content. We examined five ranks of coal: anthracite, Eastern bituminous, bituminous, sub-bituminous, and lignite. Relationships were investigated between the Calorific Value (CV) of coal and inorganic sulphur content, ⁵⁷Fe Mössbauer absorption, and ratio of pyrite (FeS₂) to FeSO₄. Twenty-eight samples of the five different types of coal had CVs ranging from 32,403 to 16,100 kJ/kg and sulphur concentrations ranging from 0.28 to 2.5 percent. CV appeared to be positively correlated with concentrations of sulphur and of iron–sulphur salts, although there appears to be little connection with the distribution of their oxidation states.     

A Modified Technique for the Preparation of SO2 from Sulphates and Sulphides for Sulphur Isotope Analyses

Abstract

A modified technique for the conversion of sulphates and sulphides to SO₂ with the mixture of V₂O₅—SiO₂ for sulphur isotopic analyses is described. This technique is more suitable for routine analysis of large number of samples. Modification of the reaction vessel and using manifold inlet system allows to analyse up to 24 samples every day. The modified technique assures the complete yield of SO₂, consistent oxygen isotope composition of the SO₂ gas and reproducibility of δ³⁴S measurements being within 0.10‰. It is observed, however, oxygen in SO₂ produced from sulphides differs in δ¹⁸O with respect to that produced from sulphates.     

Investigation of sulfur speciation in particles from small coal-burning boiler by XANES spectroscopy

Sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy was employed to study the speciation of sulfur in raw coal, ash by-product and fine particulate matter from a small coal-burning boiler. By means of least square analysis of the XANES spectra, the major organic and inorganic sulfur forms were quantitatively determined. The results show that about 70% of the sulfur in raw coal is present as organic and a minor fraction of the sulfur occurs as other forms: 17% of pyrite and 13% of sulfate. While in bottom ash, fly ash, and PM_2.5, the dominant form of sulfur is sulfate, with the percentage of 80,79 and 94, respectively. Moreover, a number of other reduced sulfur including thiophenic sulfur, element sulfur and pyrrhotite are also present. During coal combustion, most of organic sulfur and pyrite were oxidized and released into the atmosphere as SO₂ gas, part of them was converted to sulfate existing in coal combustion by-products, and a small part of pyrite was probably reduced to elemental sulfur and pyrrhotite. The results may provide information for assessing the pollution caused by small boiler and developing new methods for the control of SO₂ pollution.     

Effects of high pressure and temperature on carbon isotope compositions of some acyclic alkanes and preservation of organic matter

The effects of high pressure and temperature on carbon isotopic compositions of acyclic alkanes and the stability of the acyclic alkanes were experimentally investigated. The pyrolysis of lignite with water in a closed system was conducted at 400–700°C and 1–3 GPa. The carbon isotope data, variations of peak carbon and evident odd–even predominance of acyclic alkanes indicated that: (1) the high pressure retarded the maturation of organic matter and destruction of hydrocarbons, (2) n-C₁₂₊ hydrocarbons from biogenic sources could be preserved in the cool slab subducted into the upper mantle, and (3) some organic compounds might preserve the carbon isotope signals inherited from biogenic sources. The results favor tracing the origins of organic matter in mantle rocks and extraterrestrial organic matter in meteorites and the process of deep carbon cycle.     

TG–FTIR analysis on pyrolysis and combustion of marine sediment

In this paper, the pyrolysis and combustion of sediment have been compared using thermogravimetric analysis (TG) coupled with Fourier transform infrared spectrometry (TG-FTIR) analysis. The TG results showed that both the pyrolysis and combustion of sediment presented four weight loss stages, each. The evolving gaseous products during pyrolysis were H₂O, CO₂ and hydrocarbons, while combustion yielded considerable amounts of CO₂, in addition to H₂O, CO, CC, CO and NH₃. Comparing the pyrolysis and combustion TG-FTIR curves, it is possible to evaluate the effect of oxygen presence in the temperature range of 200–600 °C, which increases the volatilisation rate of organic matter in sediment. For the better detection of organic and inorganic matter in sediment by TG-FTIR analysis it is recommended to work in combustion mode of sediment.     

Application of Mössbauer spectroscopy for: (1) characterization of Egyptian Maghara coal; (2) evaluating the efficiency of different methods for coal desulphurization

Coal has been recently discovered in Maghara mine at Northern Sinai, Egypt. Coal samples have been collected from different depths and were measured by XRD, XRF, and MS, in order to characterize this type of coal. It has been found that the iron bearing minerals are mainly pyrite and different sulphates depending on the depth of the sample. The second part contains the application of desulphurization techniques to Egyptian coal which are: floatation (one step and two steps) chemical [(HCl+HNO₃), and Fe₂(SO₄)₃] and bacterial methods (Chromatium and Chlorobium species). The efficiency of each technique was calculated. A comparative discussion is given of each desulphurization method, from which the bacterial method has proved to be the most efficient one.     

Raman spectra of crystalline double sulphates

Raman spectra of single crystals of K₂M(SO₄)₂ · 6 H₂O where M=Mg, Zn, Ni or Co have been recorded for the first time usingλ 2537 as the exciting radiation. The corresponding five single sulphates have also been studied. Interesting results concerning the substitution of magnesium, zinc, nickel or cobalt in the double sulphate lattice on the sulphate frequencies are observed. The lattice spectra of these double sulphates are analysed group theoretically and discussed in relation to the lattice spectra of the corresponding individual sulphates. Certain new results concerning the Raman spectra of the individual sulphates have also been obtained and in the case of CoSO₄ · 7 H₂O the spectrum has been recorded for the first time.     

Raman spectra of crystalline double sulphates Part II. Ammonium double sulphates

Raman spectra of single crystals of (NH₄)₂M(SO₄)₂·6 H₂O whereM=Mg, Zn Ni or Co have been recorded using λ 2537 excitation. Interesting results concerning the substitution of the divalent atoms in the double sulphate lattice on the sulphate and ammonium frequencies are observed. The spectra of these double sulphates are discussed in the light of the known crystal structure details and in relation, to the spectra of the corresponding potassium double sulphates, reported recently by the author. The Raman spectrum of NaNH₄SO₄·2 H₂O has also been recorded for the first time and the results obtained are also included.     

The combined effect of H2O and SO2 on CO2 uptake and sorbent attrition during fluidised bed calcium looping

The effect of steam and sulphur dioxide on CO₂ capture by limestone during calcium looping was studied in a novel lab-scale twin fluidised bed device (Twin Beds – TB). The apparatus consists of two interconnected batch fluidised bed reactors which are connected to each other by a duct permitting a rapid and complete pneumatic transport of the sorbent (limestone) between the reactors. Tests were carried out under typical calcium looping operating conditions with or without the presence of H₂O and/or SO₂ during the carbonation stage. Carbonation was carried out at 650°C in presence of 15% CO₂, 10% steam (when present) and by investigating two SO₂ levels, representative of either raw (1500?ppm) or pre-desulphurised (75?ppm) typical flue gas derived from coal combustion. The sorbent used was a reactive German limestone. Its performance was evaluated in terms of CO₂ capture capacity, sulphur uptake, attrition and fragmentation. Results demonstrated the beneficial effect of H₂O and the detrimental effect of SO₂ on the CO₂ capture capacity. When both species were simultaneously present in the gas, steam was still able to enhance the CO₂ capture capacity even outweighing the negative effect of SO₂ at low SO₂ concentrations. A clear relationship between degrees of Ca carbonation and sulphation was observed. As regards the mechanical properties of the sorbent, both H₂O and SO₂ hardened the particle surface inducing a decrease of the measured attrition rate, that was indeed always very low. Conversely, the fragmentation tendency increased in presence of H₂O and SO₂ most likely due to the augmented internal stresses within the particles. Clear bimodal particle size distributions for in-bed sorbent fragments were observed. Microstructural scanning electron microscope and porosimetric characterisations aided in explaining the observed trends.     

Simultaneous detection of SO2, SO3 and H2O using QCL spectrometer for combustion applications

We demonstrate a high-sensitivity laser-based spectrometer for simultaneous detection of sulphur dioxide (SO₂) sulphur trioxide (SO₃) and water for coal-fired combustion applications. The spectrometer is based on a quantum-cascade laser (QCL) operating at 7.16 μm, capable of measuring all three components simultaneously in a single frequency sweep. An optical multipass cell having a total path length of 9.1 m is used at increased temperature and at low pressure to ensure reliable measurement of highly reactive SO₃ and adequate separation of overlapping spectral features, respectively. Detection limits for SO₂ and SO₃ are 0.134 and 0.0073 ppm, respectively, when employing a 20-s sampling time.     

Electrical conductivity of binary sulphates of lithium sulphate

To engineer lithium sulphate based material with high ionic conductivity at lowest possible temperature, the electrical conductivity of binary sulphates of Li₂SO₄ with Na₂SO₄, K₂SO₄, MgSO₄, ZnSO₄ and Ag₂SO₄ has been measured in the temperature range from 513 K to 773 K. The results are interpreted on the basis of different phases present therein. Li₂SO₄:Ag₂SO₄(40:60) mol % has high ionic conductivity = 2.17×10^-3(ohm cm)^-1 at 606 K which could be utilized in power sources.     

Fundamental investigation into characteristics of particulate matter produced from rapid pyrolysis of biochar in a drop-tube furnace at 1300 °C

This paper reports the emission characteristics of leaf and wood biochar (LC500 and WC500) pyrolysis in a drop tube furnace at 1300 °C in argon atmosphere. The char yields at 1300 °C are ～ 65% and ～ 73% respectively for LC500 and WC500. Over 60% Mg, Ca, S, Al, Fe and Si are retained in char after pyrolysis at 1300 °C. The retentions of Na and K in the char from LC500 pyrolysis are lower than those in the char from WC500 pyrolysis due to release via enhanced chlorination as a result of much higher Cl content in LC500. Particulate matter (PM) with aerodynamic diameter of < 10 µm (i.e. PM₁₀) from LC500 and WC500 pyrolysis exhibits a bimodal distribution with a fine mode diameter of 0.011 µm and a coarse mode diameter of 4.087 µm. The PM₁₀ yield for LC500 pyrolysis is ～ 8.2 mg/g, higher than that of WC500 pyrolysis (～2.1 mg/g). Samples in PM_1-10 (i.e. PM with aerodynamic diameter 1 µm – 10 µm) are char fragments that have irregular shapes and similar molar ratio of (Na+K + 2Mg+2Ca)/(Cl+2S+3P) as the char collected in the cyclone. In PM₁ (i.e. PM with aerodynamic diameter < 1 µm), the main components in sample are inorganic species, and carbon only contributes to ～5% and ～8% the PM₁ produced from rapid pyrolysis of LC500 and WC500, respectively. Na, K and Cl are main inorganic species in PM₁, contributing ～ 98.8% and ～ 97.5% to all inorganic species. Na, K and Cl from rapid pyrolysis of biochar have a unimodal distribution with a mode diameter of 0.011 µm. In PM_1–10, Ca is the main inorganic specie, contributing to ～71.2% and ～65.3% to all inorganic species in PM_1–10 from pyrolysis of LC500 and WC500, respectively.     

The Application of SF6 in the Geochemical Research

For mass spectrometric measurements of δ³¹S, pure sulphur hexafluoride was prepared quantitatively from different mineral sulphides by the reaction with elemental fluorine under pressure. The results of δ³¹S measurements on SF₆ samples were confirmed by comparison of δ³¹S values with the classical method leading to SO₂. Numerous mass spectrometric measurements of SF₆ and SO₂ with regard to the experimental conditions of the synthesis, the influence of background, memory effect, and adsorption were made. The measurements of small isotopic variations of sulphur with SF₆ has advantages in comparison to the SO₂ technique. The method described can be successfully used for routine work.     

Origin of salt mixtures and mixed salts in atmospheric particulate matter

The atmospheric particulate matter contains components of natural and anthropogenic origin, some of them are sulphates and nitrates. Considering the usual occurrence of many ions in the atmosphere and the presence of water, the generation of salt mixtures and mixed salts is possible as a consequence of dissolution–precipitation processes within water droplets, e.g., in fog or haze. This contribution presents the Raman spectroscopic study of the sodium–potassium nitrate system, which generates a salt mixture of both compounds. A phase transition of a KNO₃ crystal within a single solution droplet was observed. Additionally, we postulate the atmospheric generation of the mixed salt Na₃(NO₃)(SO₄)·H₂O (darapskite) by dissolution–precipitation processes, because Na⁺, SO₄^2–, and NO₃^– can be usually found in the atmosphere. The polarized Raman spectra of synthetic darapskite are reported. Copyright © 2011 John Wiley & Sons, Ltd.     

Characteristics of chars formed during rapid pyrolysis of biomass model components at high temperature

This paper reports char formation and inherent inorganic transformation during rapid pyrolysis of various biomass model components under simulated pulverized fuel (PF) conditions at 1300 °C. A drop-tube furnace with a novel double-tube configuration was deployed to achieve direct determination of char yield. The results show that rapid pyrolysis of xylan and water-washed lignin (W-L) under the conditions results in char yields of 3.4 wt.% and 12.6 wt.%, respectively, while no char was founded during rapid pyrolysis of water-washed cellulose (W-C). After loading K₂CO₃ into the W-C (i.e. KW-C) and W-L (i.e. KW-L), the char yields increase to 2.1 wt.% and 15.6 wt.%, respectively. The retentions of Na and S are low in chars after pyrolysis. After rapid pyrolysis, W-L and KW-L chars have higher retentions of AAEM species than xylan, W-C and KW-C chars. Micromorphology analysis shows char particles formed after rapid pyrolysis of all biomass components have a cenospheric structure and a rough surface with many bubbles and pores, demonstrating strong melting processes. For xylan and KW-L, the abundant inorganics accelerate char formation with swelling and reduce the extent of particle shrinkage, resulting in char particles with apparent sizes bigger than the parent feedstock particles. Oppositely, for KW-C and W-L that have low contents of inorganic species, the pyrolyzing particles experience significant shrinkage, resulting in formed char particles with apparent sizes that are much smaller than feedstock particles.     

Regional and temporal (1992–2004) evolution of air-borne sulphur isotope composition in Saxony,southeastern Germany,central Europe†

The isotopic composition of air-borne sulphur was investigated in Saxony, Southeast Germany – a region with formerly very high atmospheric SO₂ concentrations. In addition, data from various authors were compiled for different Saxonian locations, spanning from 1992 to 2004, i.e., a time of decreasing SO₂ concentrations in the atmosphere. There were no obvious temporal changes in the mean δ³⁴S value of bulk precipitation. However, the variability of monthly mean δ³⁴S values decreased. The mean sulphur isotope composition of sulphate from bulk precipitation after the year 2000 converges in Saxony towards 4–5‰, with similar values for different locations. Mean values of different forms of sulphur show the following enrichment order: δ³⁴S of SO₂ < δ³⁴S of weathering crusts ≤δ³⁴S of sulphate from bulk precipitation ≤δ³⁴S of dust. Judging from local differences on sulphate crusts and corresponding isotope values of sources, the δ³⁴S value of SO₂ as well as for crusts mainly reflects local point sources. The mean δ³⁴S value of bulk precipitation represents more regionally well-mixed SO₂ sources and is therefore an ideal tool for monitoring regional atmospheric change.     

Optical and electrical properties of some sulphates doped with cobalt

Doubly ionized cobalt ion which has a ⁴F ground state exhibits several optical bands in orthorhombic sulphates. In view of the low symmetry, many degenerate states split and at low temperature (77°K) well resolved bands have been observed which enable the detailed calculation of the crystal field parameters in orthorhombic symmetry.Electrical conductivity measurements in pure potassium and ammonium sulphates show only the extrinsic unassociated region while in cobalt doped crystals, extrinsic as well as association regions are observed. Three distinct regions with slopes 0·86, 1·2 and 0·5 eV are obtained in cobalt doped K₂SO₄.X-irradiated pure crystals give two prominent bands at 2200 and 3300 Å which are attributed to SO₃^? and SO₂^?. Divalent cobalt doped crystals give additional bands at 2100 and 3100 Å. These bands are attributed to Co⁺ in different surroundings. Three ESR lines with ‘g’ values 2·042, 2·02 and 2·004 are obtained in support of the assignments.     

Experimental and modeling study of H2S formation and evolution in air staged combustion of pulverized coal

High-concentration H₂S formed in the reduction zone of pulverized coal air-staged combustion can result into the high temperature corrosion of water wall tube of boiler, so it is of great importance to accurately predict H₂S concentration for the safe operation of boilers and burners. H₂S formation and evolution depends on two steps: the sulfur release from coal conversion and gas-phase reactions of sulfur species. In this study, the sulfur release characteristics from the pyrolysis of 17 coals, including 5 lignite, 9 bituminous coals and 3 anthracites, are investigated in a drop tube furnace (DTF). Sulfur release model is developed to describe the relationship between sulfur release and coal types. A global gas-phase reaction mechanism of sulfur species composed of ten reactions is used to calculate and predict the formation and evolution of H₂S, COS and SO₂ in the reduction zone of pulverized coal air-staged combustion. A wide range of air-staged combustion experiments of 17 coals are conducted in the DTF at different temperatures and stoichiometric ratios to validate the developed model. The results show that the prediction errors of sulfur species, including SO₂, H₂S and COS, are within ± 30%, which indicates that the developed prediction model of sulfur species is of great assistance for CFD modeling of actual engineering application.