Sulfur Retention Research Articles

Energetics of anhydrite, barite, celestine, and anglesite: a high-temperature and differential scanning calorimetry study

The thermochemistry of anhydrous sulfates (anglesite, anhydrite, arcanite, barite, celestine) was investigated by high-temperature oxide melt calorimetry and differential scanning calorimetry. Complete retention and uniform speciation of sulfur in the solvent was documented by (a) chemical analyses of the solvent (3Na2O · 4MoO3) with dissolved sulfates, (b) Fourier transform infrared spectroscopy confirming the absence of sulfur species in the gases above the solvent, and (c) consistency of experimental determination of the enthalpy of drop solution of SO3 in the solvent. Thus, the principal conclusion of this study is that high-temperature oxide melt calorimetry with 3Na2O · 4MoO3 solvent is a valid technique for measurement of enthalpies of formation of anhydrous sulfates. Enthalpies of formation (in kJ/mol) from the elements (ΔHfo) were determined for synthetic anhydrite (CaSO4) (−1433.8 ± 3.2), celestine (SrSO4) (−1452.1 ± 3.3), anglesite (PbSO4) (−909.9 ± 3.4), and two natural barite (BaSO4) samples (−1464.2 ± 3.7, −1464.9 ± 3.7). The heat capacity of anhydrite, barite, and celestine was measured between 245 and 1100 K, with low- and high-temperature Netzsch (DSC-404) differential scanning calorimeters. The results for each sample were fitted to a Haas-Fisher polynomial of the form Cp(245 K < T < 1100 K) = a + bT + cT−2 + dT−0.5 + eT2. The coefficients of the equation are as follows: for anhydrite a = 409.7, b = −1.764 × 10−1, c = 2.672 × 106, d = −5.130 × 103, e = 8.460 × 10−5; for barite, a = 230.5, b = −0.7395 × 10−1, c = −1.170 × 106, d = −1.587 × 103, e = 4.784 × 10−5; and for celestine, a = 82.1, b = 0.8831 × 10−1, c = −1.213 × 106, d = 0.1890 × 103, e = −1.449 × 10−5. The 95% confidence interval of the measured Cp varies from 1 to 2% of the measured value at low temperature up to 2 to 5% at high temperature. The measured thermochemical data improve or augment the thermodynamic database for anhydrous sulfates and highlight the remaining discrepancies.

Sulfur self-retention in ash a grain model approach

A developed overall model for sulfur self-retention in ash during coal particle combustion is presented in the paper. The total sulfur content in char, after devolatilization, is evaluated using a derived correlation. It is assumed that sulfur retention during char combustion occurs due to the reaction between SO2 and the active part of the Ca in the form of uniformly distributed CaO grains. Parametric analysis shows that the process is limited by solid diffusion through the product layer formed on the CaO grains and that the most important coal characteristics which influence sulfur self-retention are coal rank, content of sulfur forms, molar Ca/S ratio and particle radius. The model predicts relatively well the levels of the experimentally obtained values of SSR efficiencies, as well as the influence of temperature, particle size and the surrounding conditions.

Catalytic behavior of alumina-promoted sulfated zirconia supported on mesoporous silica in butane isomerization

Alumina-promoted sulfated zirconia was supported on mesoporous molecular sieves of pure-silica MCM-41 and SBA-15. The catalysts were prepared by “direct impregnation” of metal sulfate onto the as-synthesized MCM-41 and SBA-15 materials, followed by solid state dispersion and thermal decomposition. Measurements of XRD and nitrogen adsorption isotherms showed that the structures of resultant materials retain well-ordered pores, even with ZrO2 loading as high as 50 wt%. The characterization results indicated that most of the promoted sulfated zirconia were well dispersed on the internal surface of the ordered mesopores. The catalytic behavior of the alumina-promoted sulfated zirconia supported on mesoporous silica was studied in n-butane isomerization. The supports of mesoporous structures led to high dispersion of sulfated zirconia in the meta-stable tetragonal phase, which was the catalytic active phase. The high performance of alumina-promoted catalysts was ascribed to the sulfur retention by alumina.

79. Enhancement in Sulfur Retention of Calcium-Loaded Coal by Ultrasonic Treatment (UST)

79. Enhancement in Sulfur Retention of Calcium-Loaded Coal by Ultrasonic Treatment (UST)

The influence of water-soluble and acid-soluble inorganic matter on sulphur transformations during pyrolysis of low-rank coals

Temperature-programmed pyrolysis (TPP) experiments are conducted on several samples prepared from a South Australian Bowmans coal, viz. raw, water-washed, acid-washed and Ca++ and Na+ ion-exchanged acid-washed samples, to study the influence of the physically absorbed (water-soluble) and organically bound (acid-soluble) inorganic matter on sulphur transformations during pyrolysis. Changes in sulphur forms between 200 and 900°C were monitored according to Australian Standards, wet chemical analysis of chars. Interpretation of sulphur transformation was aided by scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). During TPP, raw Bowmans coal is observed to evolve less sulphur than the treated coals between 400 and 500°C. Water-soluble sulphates above other water-soluble inorganics, are found to contribute to the sulphur retention by suppressing the decomposition of organic sulphur in the same temperature region. Acid-soluble inorganics are observed to increase the retention of sulphur between 500 and 600°C. Chemical analysis did not detect a corresponding formation of sulphides, suggesting that the presence of acid-soluble inorganics suppressed the decomposition of organic sulphur between 500 and 600°C. SEM-EDX and iDXi X-ray mapping of TPP chars removed at 800 and 900°C revealed that sulphur does interact with the organically-bound inorganics. Na interacts with silica and forms highly concentrated constituents in char particles during pyrolysis. Both types of inclusions were found to contain highly concentrated areas of sulphur. Calcium becomes enriched in the char to initiate decomposition of organic sulphur and form calcium sulphide in the char prepared between 800 and 900°C.

Circulating fluidized bed combustion in the turbulent regime: modelling of carbon combustion efficiency and sulphur retention

A model has been developed considering the hydrodynamic behaviour of a turbulent circulating fluidized bed, the kinetic of coal combustion and sulphur retention in the riser. The hydrodynamic characteristics of the turbulent fluidization regime were integrated together with the kinetic submodels of char combustion and sulphur retention by limestone. From the combustion of a lignite and an anthracite with limestone addition in a hot CBF pilot plant of 20 cm internal diameter and 6.5 m high, the effect of operating conditions such as temperature, excess air, air velocity, Ca/S molar ratio, coal and limestone particle size distributions on carbon combustion efficiency and sulphur retention were studied. The experimental results were compared with those predicted by the model and a good correlation was found for all the conditions used.

Experimental research on two-stage desulfurization technology in traveling grate boilers

In order to promote the desulfurization efficiency of calcium-based sorbents during coal combustion in traveling grate boilers, the influences on sulfur removal of the thermal conditions and the sorbents were discussed in this paper. It was found that the SO 2 concentration first rises, then declines along the traveling grate and reaches the peak near the midpoint of the grate. The fluctuation of the SO 2 concentration over time in the flue gas is mainly affected by the flame temperature. When the particle size of the sorbents decreases from 75 to 0.1 μm, the sulfur removal efficiency will increase slightly. A reasonable Ca/S molar ratio is about 2 when sorbents are blended with the coal on the grate and its further increase has little benefit to desulfurization. A new, so-called two-stage desulfurization process — sulfur capture firstly in the coal bed and secondly in the combustion gas — is suggested as it can greatly promote the sulfur removal efficiency up to 70∼80%. By X-ray powder diffraction analysis, some thermal stable phases were identified in the sulfur retention cinder obtained from the on-grate process.

00/03561 Circulating fluidized bed combustion in the turbulent regime: modelling of carbon combustion efficiency and sulfur retention

00/03561 Circulating fluidized bed combustion in the turbulent regime: modelling of carbon combustion efficiency and sulfur retention

Combined Alkyl and Sulfonic Acid Functionalization of MCM-41-Type Silica: Part 1. Synthesis and Characterization

Single-step synthesis of well-ordered MCM-41 materials containing simultaneously alkyl (methyl or propyl) and 3-mercaptopropyl groups has been carried out by hydrothermal treatment of gels containing a mixture of dodecyl and hexadecyltrimethylammonium surfactants. A wide range of synthesis conditions has been studied in order to optimize the pore arrangement and to vary the alkyl/mercaptopropyl ratio of the product. A number of characterization techniques suggest that the anchored organic fragments lined the wall channels of the MCM-41 in a close-packed configuration. The mercaptopropyl groups can be oxidized with hydrogen peroxide to sulfonic acid with a high retention of sulfur and no loss of methyl groups.

00/01509 Characteristics of sulfur retention in ashes of Chinese coals used for power generation

00/01509 Characteristics of sulfur retention in ashes of Chinese coals used for power generation

Comparison of sulphur retention by coal ash in different types of combustors

During coal combustion, a part of the total sulphur in coal will be retained as solid compounds in ash. In the present paper, the retention of sulphur by ash of typical Chinese coal used for electric power generation was correlated with the contents of alkaline elements relative to sulphur in the parent coal. Comparison was performed among the capabilities of sulphur retention by coal ashes in laboratory ashing procedure, pulverised coal-fired combustor and fluidised bed combustor (FBC). It was shown that calcium plays a dominant role in sulphur retention of laboratory-prepared ash and the sulphur retention percentage increases with the increase of Ca/S molar ratio of the parent coal, while the contributions of other elements are limited. The sulphur retention behaviour in pulverised coal-fired combustor is significantly different from that in laboratory ashing procedure. The contribution of calcium is reduced markedly, while the roles of the other alkaline elements are obviously enhanced. Using the literature data from foreign coals, it was found that the sulphur retention in FBC is comparable with that in laboratory ashing procedure. It was suggested from the results obtained in this study that the sulphur retention of laboratory-prepared ash can be applied to fluidised bed combustion because the behaviour of calcium is similar to that of lime in FBC.

Assessment of Catalyst Deactivation Model for Sulfur Retention in Fluidized Bed Combustors

An improved version of a combustion-desulfurization model for fluidized bed combustors burning high ash and sulfur content low quality lignite in its own ash with the addition of limestone is presented. The desulfurization model considers sulfur retention by both limestone and ash and is based on first order catalyst deactivation where the kinetics of desulfurization is described by two rate constants; one for the initial surface reaction, the other for the rate of pore plugging or deactivation. The accuracy of the complete model with experimentally determined deactivation rate constants was tested by applying it to a 0.3 MWt AFBC test rig and comparing its predictions with measurements. Comparisons show that (he model produces reasonably accurate predictions of sulfur retention provided that the rate constants are determined experimentally under the fluidized bed combustor operating conditions.

Partitioning behaviour of some toxic volatile elements during stoker and fluidised bed combustion of alkaline sub-bituminous coal

During coal combustion, the partitioning behaviour of the volatile toxic trace elements, boron, arsenic and selenium, is influenced by the highly alkaline nature of a typical New Zealand industrial sub-bituminous coal, and the combustion regime (underfeed stoker or fluidised bed) used to burn it. A significant amount of boron is retained in the bottom ash of the underfeed stoker, and some arsenic and selenium retention is also encountered. Mercury partitioning is not influenced by the combustion regime or alkalinity, although the fly ash generated from the stoker combustion appears to possess a significant mercury capture capability. Over 60% sulphur retention may be achieved, without additive, for fluidised bed combustion. Some of the chemical and physical factors responsible for the above partitioning behaviours are identified.

Estimating historical anthropogenic global sulfur emission patterns for the period 1850–1990

It is important to establish a reliable regional emission inventory of sulfur as a function of time when assessing the possible effects of global change and acid rain. This study developed a database of annual estimates of national sulfur emissions from 1850 to 1990. A common methodology was applied across all years and countries allowing for global totals to be produced by adding estimates from all countries. The consistent approach facilitates the modification of the database and the observation of changes at national, regional, or global levels. The emission estimates were based on net production (i.e., production plus imports minus exports), sulfur content, and sulfur retention for each country's production activities. Because the emission estimates were based on the above considerations, our database offers an opportunity to independently compare our results with those estimates based on individual country estimates. Fine temporal resolution clearly shows emission changes associated with specific historical events (e.g., wars, depressions, etc.) on a regional, national, or global basis. The spatial pattern of emissions shows that the US, the USSR, and China were the main sulfur emitters (i.e., approximately 50% of the total) in the world in 1990. The USSR and the US appear to have stabilized their sulfur emissions over the past 20 yr, and the recent increases in global sulfur emissions are linked to the rapid increases in emissions from China. Sulfur emissions have been reduced in some cases by switching from high- to low-sulfur coals. Flue gas desulfurization (FGD) has apparently made important contributions to emission reductions in only a few countries, such as Germany.

99/02163 Investigation of sulfur retention and the effect of inorganic matter during pyrolysis of South Australian low-rank coals: Telfer, M. A. and Zhang, D. K. Energy Fuels, 1998, 12, (6), 1135–1141

99/02163 Investigation of sulfur retention and the effect of inorganic matter during pyrolysis of South Australian low-rank coals: Telfer, M. A. and Zhang, D. K. Energy Fuels, 1998, 12, (6), 1135–1141

99/01026 Oil-gas potential of Jurassic strata in northern margin of Qaidam basin : Wang, M. et al. Shiyou Kantan Yu Kaifa, 1997, 24, (5), 20–24. (In Chinese)

Sulfur X-ray Absorption Near Edge Structure Spectroscopy (S-XANES) was used to quantify the thermal transformations of organic and inorganic sulfur forms in pyrite-containing Type II kerogens and kerogen chars after open system pyrolysis for a series of well-defined times and temperatures. These results are compared to identical experiments conducted on the same kerogens treated to be pyrite-free. No significant differences were found in the thermal transformations of organic sulfur between the pyrite-containing and pyrite-free kerogen. The loss of aliphatic sulfur forms occurs early (equivalent Ro < 1.5%) while there is a relative increase in thiophenic sulfur over aromatic sulfide at higher maturity (Ro > 1.5%). In pyrite-containing kerogens, the complete conversion of pyrite (FeS2) into pyrrhotite (Fe1−xS) occurs by a laboratory equivalent Ro = 1.5%, followed by the conversion of pyrrhotite into troilite (FeS) at higher maturity. The availability of hydrogen from hydrocarbons generated from kerogen accelerates the initial decomposition of pyrite resulting in pyrrhotite and H2S evolution. H2S evolution up to Ro = 2.4% corresponds to the sulfur loss associated with pyrrhotite and troilite formation and aliphatic sulfur loss, indicating that sulfur from pyrite results almost exclusively in H2S evolution with no significant incorporation and retention of sulfur into the organic matter of the kerogen chars under the current set of open system pyrolysis conditions.

99/01307 Roles of alkaline elements in sulfur retention by ashes from Chinese coals used for electric power generation : Sheng, C. and Xu, Y. Ranshao Kexue Yu Jisho, 1998, 4, (1), 99–103. (In Chinese)

99/01307 Roles of alkaline elements in sulfur retention by ashes from Chinese coals used for electric power generation : Sheng, C. and Xu, Y. Ranshao Kexue Yu Jisho, 1998, 4, (1), 99–103. (In Chinese)

99/00732 Industrial experience on the development of the molten carbonate fuel cell technology

Textile dyeing sludge (DS) was pyrolysed using an auger pyrolyser under microwave irradiation. It showed the non-condensable gas yield was increased as reactor temperature increased and the char yield decreased with temperature. The condensate and oil yields reached maximum at 650 °C (i.e. 12.86 wt% and 0.84 wt%, respectively). The content of C, H and N in DS and sludge char (SC) decreased with temperature while S increased. The SC and sorbents (e.g. CaO) showed positive effects on sulfur retention. The maximum BET surface area of 91.9 m2/g was observed for SC at 550 °C. Addition of catalysts such as CaO and Fe decreased pyrolysis oil yield and increased the H2 yield. Oxygenates were mainly formed at 450–650 °C. The relative content of aromatic compounds in the pyrolysis oil increased as temperature increased, up to 88.38% (GC–MS area) at 750 °C. Heterocyclic aromatic compounds containing nitrogen accounted for 20%–58% of the pyrolysis oil. The H2 content increased from 25.39 vol% without catalyst to 64.17 vol% with addition of 30 wt% CaO. As concentration in DS and SC was beyond the control standards for forestland use in China and should be further treated and disposed. The electricity consumption for pyrolysing DS of 60 wt% water content were 0.76–2.59 kWh/kg wet DS in the temperature range of 450–750 °C and auger speed range of 1–9 rpm. Higher pyrolysis temperature and lower auger speeds increased electricity consumptions.

DIETARY DEFICIENCY OF CYSTINE AND METHIONINE IN RATS ALTERS THIOL HOMEOSTASIS REQUIRED FOR CYANIDE DETOXIFICATION

Nutritional status is an important factor in modulating the metabolic fate of xenobiotics. Sulfur amino acid (SAA) deficiency has been proposed as a risk factor for human neurological diseases among protein-poor populations subsisting on the cyanophoric plant cassava. Female Sprague-Dawley rats were used to develop and define a model of SAA deficiency for use in future studies examining cassava-related neurotoxicity. Rats were kept in metabolic cages for 7-21 d and fed a balanced diet (BD) of known composition or a comparable diet selectively deficient in methionine and cystine (SAA-free diet). Animals fed the SAA-free diet failed to thrive, lost body weight, excreted porphyrinic materials, and showed a steep and persistent reduction of urinary inorganic sulfate. In contrast, animals on the BD gained body weight and maintained baseline output of urinary inorganic sulfate. Urinary thiocyanate excretion did not differ between groups, but plasma thiocyanate concentrations reached double that in SAA-deficient rats. Increased plasma thiocyanate suggests mobilization of sulfur amino acids from endogenous sources. Liver glutathione and blood cyanide concentrations were similar in animals on the BD and the SAA-deficient diet. In summary, a diet free of methionine and cystine results in increased retention of inorganic sulfur as thiocyanate and a near absence of inorganic sulfur excretion in urine.

Pyrolysis of coal maceral concentrates under pf-combustion conditions (II): changes in heteroatom partitioning as a function of rank

Differences between maceral types with respect to heteroatom partitioning during pyrolysis under conditions representative of pf-combustion have been investigated. Pyrolysis experiments have been carried out in a wire-mesh reactor; maceral concentrates and whole coals have been heated at 5000°C s −1 to 1500°C, in atmospheric pressure He. The proportion of N-retention in chars was found to increase from about 10 to 60% in the 75–95% elemental-C range, irrespective of maceral composition. However, char-N retention by inertinites was slightly less than that for vitrinites; retention by liptinites was clearly less than that for vitrinites. The general trend for sulfur retention was similar: for vitrinite and inertinite concentrates, sulfur retention increased from about 30 to 60% over the 72–95% elemental-C content interval. Once again, retention in liptinites was considerably lower—between 5 and 15%—for the three samples used in the study. Ash contents of the present set of samples suggest that it would not be realistic to discuss the present set of sulfur retention data in terms of organic sulfur alone. The work outlined above lead to several tentative conclusions, pinpointing areas where new structural work is required.