Sulfur Retention Research Articles

Holocene interaction of maritime and continental climate in Central Europe: New speleothem evidence from Central Germany

Abstract Central European climate is strongly influenced by North Atlantic (Westerlies) and Siberian High circulation patterns, which govern precipitation and temperature dynamics and induce heterogeneous climatic conditions, with distinct boundaries between climate zones. These climate boundaries are not stationary and shift geographically, depending on long-term atmospheric conditions. So far, little is known about past shifts of these climate boundaries and the local to regional environmental response prior to the instrumental era. High resolution multi-proxy data (stable oxygen and carbon isotope ratios, S/Ca and Sr/Ca) from two Holocene stalagmites from Blesberg Cave (Thuringia) are used here to differentiate local and pan-regional environmental and climatic conditions Central Germany through the Holocene. Carbon isotope and S/Ca and Sr/Ca ratios inform us on local Holocene environmental changes in and around the cave, while δ18O (when combined with independent records) serves as proxy for (pan-)regional atmospheric conditions. The stable carbon isotope record suggests repeated changes in vegetation density (open vs. dense forest), and increasing forest cover in the late Holocene. Concurrently, decreasing S/Ca values indicate more effective sulfur retention in better developed soils, with a stabilization in the mid-Holocene. This goes in hand with changes in effective summer infiltration, reflected in the Sr/Ca profile. Highest Sr/Ca values between 4 ka and 1 ka BP indicate intensified prior calcite precipitation resulting from reduced effective moisture supply. The region of Blesberg Cave is sensitive to shifts of the boundary between maritime (Cfb) and continental (Dfb) climate and ideally suited to reconstruct past meridional shifts of this divide. We combined the Blesberg Cave δ18O time series with δ18O data from Bunker Cave (western Germany) and a North Atlantic Oscillation (NAO) record from lake SS1220 (SW Greenland) to reconstruct the mean position of the Cfb-Dfb climate boundary. We further estimate the dynamic interplay of the North Atlantic Oscillation and the Siberian High and their influence on Central European climate. Repeated shifts of the Cfb-Dfb boundary over the last 4000 years might explain previously observed discrepancies between proxy records from Europe. Detailed correlation analyses reveal multi-centennial scale alternations of maritime and continental climate and, concurrently, waning and waxing influences of Siberian High and NAO on Central Europe.

Bottom ash characteristics and pollutant emission during the co-combustion of pulverized coal with high mass-percentage sewage sludge

A municipal and a coal-coking industrial sludge (MS and CS) were separately co-combusted with bituminous coal at a sludge mass ratio (SMR) of 10%–50%. Quartz, larnite, gehlenite, mayenite, and calcium sulfate were formed during co-combustion. Slight or medium slagging was predicted to occur when slagging tendency was assessed based on the mineral components and fusion temperature of the ash. The SO2 emission peak at the devolatilization stage increased with increasing SMR of MS but only slightly changed with increasing SMR of CS. SO2 emission at the char combustion stage was suppressed due to the sulfur retention effects of sludge ash. NO, HCN, and N2O were the main emission forms of N-containing gases. With increasing SMRs of MS and CS, HCN emissions became increasingly prominent, whereas NO showed only a slight increase and even decreased. In addition, the volatilization percentages (VP) of Cd, Zn, Cr, and Ni decreased. By contrast, the VP of Pb increased when coal was combusted with CS because Pb was considerably influenced by high Cl. The concentrations of Cd, Cr, Ni, Pb, and Zn in the bottom ashes were determined and satisfied China's threshold limit value for landscaping land application or soil amendment.

Poly(ionic liquid)–zinc polyoxometalate composite as a binder-free cathode for high-performance lithium–sulfur batteries

A polyoxometalate–ionic polymer composite was utilized as highly stable and efficient catalyst for high performance Li–S battery cathode with high utilization of sulfur and capacity retention.

Intensified approach for desulfurization of simulated fuel containing thiophene based on ultrasonic flow cell and oxidizing agents

Intensified desulfurization of simulated crude fuel containing thiophene has been investigated using ultrasonic flow cell in combination with oxidizing agents such as peracetic acid, hydrogen peroxide (H2O2) and Fenton reagent at ambient conditions. The effect of thiophene loading, recirculation flow rate and the oxidant loading on the extent of desulfurization has been studied at 1 L capacity. Combination of ultrasound and hydrogen peroxide at optimized loading of 8% resulted in higher extent of desulfurization (38%) as compared to only ultrasound (17%). Higher degree of enhancement in extent of desulfurization (57% as the actual value) was observed for combination of ultrasound and peracetic acid at loading of 10%. Significant increase in extent of desulfurization was obtained for the combination of ultrasound and Fenton reagent (2 g/L FeSO4 + 10% H2O2) with actual extent being 87%. The conventional approaches of only hydrogen peroxide and only Fenton without ultrasound resulted in much lower extent of desulfurization as 22 and 40% respectively confirming the synergism for the combined process involving ultrasound. Maximum desulfurization extent as 96% was obtained for the approach of ultrasound combined with Fenton reagent at 2 g/L of FeSO4 and 15% H2O2 addition in three stages and 80 min of treatment time. The analysis of treated samples using HPLC spectra revealed that no other by-products or unwanted chemical species were formed during the treatment. The process intensification benefits have been clearly established in terms of much higher extent of desulfurization for combined approaches with the final sulfur content below minimum limit (5 ppm) whereas most of the conventional desulfurization approaches (without ultrasound) resulted in sulfur retention up to 10 ppm in final treated fuel.

Pyrolysis of textile dyeing sludge in fluidized bed: Characterization and analysis of pyrolysis products

Fluidized bed pyrolysis (FBP) of textile dyeing sludge (DS) was carried out in a benchtop unit. The FBP char (FC) yield decreased and non-condensable gas yield increased with increasing temperature. The minimum FC yield (73.47 wt%) and maximum non-condensable gas yield (24.10 wt%) were found with addition of kaolin at 850 °C. The maximum condensates yield was observed at 650 °C (i.e. 3.52 wt%) without additives. Catalysts reduced condensate yield and promoted decomposition of macromolecules (e.g. siloxane and dichloroacetic acid allyl ester). DS and FC contained small amounts of heavy metals (e.g. Zn, Ni, Pb, Cr and Cu) and a better sulfur retention ability of CaO at higher temperatures (e.g. 650–850 °C) was observed. The surface morphology of FC was improved significantly with increasing temperature and catalysts addition. CO2, CO and CH4 yields in non-condensable gases increased with temperature and the addition of CaO led to the highest yields of CO (5.46 wt%), H2 (0.35 wt%) and CH4 (1.22 wt%) at 850 °C and the lowest yield of CO2 (0.45 wt%) at 450 °C. Higher temperature promoted release of nitrogen, sulfur and chlorine and catalysts promoted release of nitrogen from DS. Kaolin and Ca-bentonite enhanced release of sulfur, whereas CaO showed good sulfur retention capacity.

Theoretical Modeling of the Electrochemical Lithiation Processes of Lithium-Sulfur Battery Cathodes Based on Sulfur/Graphene-Nanosheets Composites

The theoretical energy density of 2.5 kWh/kg of sulfur, plus its low-cost availability and environmentally friendliness, makes of lithium-sulfur (Li-S) batteries one of the most promising alternatives to fulfill the need of energy storage devices for high energy-demanding applications such as electric vehicles and smart grids. However, the successful commercialization of Li-S batteries is still challenged by the low utilization of sulfur, linked to its poor electronic/ionic conductivity and its continuous irreversible dissolution into the electrolyte in the form of long-chain lithium-polysulfides. So far, the mixing of sulfur with carbon has led to its better physical confinement and chemical sequestration in the cathode. However, the details of the sulfur-carbon interaction and its effects on the electrochemical lithiation processes during battery cycling are still largely unknown. Here we aimed at characterizing the structure of sulfur/graphene-nanosheets composites (SC composite) and understand its effects on the electrochemical lithiation processes during battery cycling. Reactive molecular dynamics (ReaxFF) calculations provided information on the cathode microstructure and the bulk reduction products upon lithiation. Ab initio molecular dynamics simulations (AIMD) along with density functional theory (DFT) optimizations, yield details of the effects of different electrolyte compositions on the SC composite capabilities for retention of sulfur and the polysulfide formation paths. We elucidated that a stronger sulfur-carbon interaction not only contributes to a better electronic conductivity but also leads to an alternative sulfur reduction path without the formation of long-chain polysulfides, which might help to explain the improved cycling stability observed in sulfurized polyacrylonitrile composites reported in the literature. In addition, we observed that different electrolyte compositions might be beneficial too by allowing an easier recovery of S-C bonds upon charging. We believe the results from this work can contribute to improving the synthesis methodologies of sulfur-carbon composites leading to a more rapid commercialization of lithium-sulfur batteries.

Insights into sulfur cycling at subduction zones from in-situ isotopic analysis of sulfides in high-pressure serpentinites and ‘hybrid’ samples from Alpine Corsica

Devolatilisation of serpentinites at depth in subduction zones contributes significant quantities of sulfur and other redox sensitive elements to the sub-arc mantle. However, the fate of sulfur in subducted serpentinites is poorly constrained. Textures of sulfur-bearing phases in subducted serpentinites are rarely studied, yet provide important information on the changes to sulfur distribution throughout the subduction cycle and as a result of fluid infiltration. δ34S values of sulfides provide constraints on sulfur sources, the redox state of sulfur in the host mineral, and on processes that have occurred subsequent to sulfide crystallisation, including interaction with oxidised or reduced fluids. Therefore, it is possible to use δ34S values in subducted serpentinites to constrain the redox state of sulfur in sulfides and subduction zone fluids. Furthermore, the proximity of serpentinites to ocean crust and metasediments may influence enrichment or depletion of 34S during subduction relative to serpentinites distal to such lithologies.This study investigates the redox state, the likelihood of sulfur addition to the sub-arc mantle from serpentinite dehydration, and the distribution of sulfur within subducted serpentinites and ‘hybrid’ mafic/ultramafic rocks from Alpine Corsica. The techniques utilised include petrographic analysis, in-situ sulfur isotopic analysis and trace element analysis of sulfides hosted in these rocks. All sulfides investigated have high δ34S values of 1.9–15.5‰, which suggests that mantle-derived sulfur (δ34S ~0.1‰), was not the sole source of sulfur. The highest δ34S values are recorded in pyrites of a hybrid mafic/ultramafic sample. High δ34S values are preserved in sulfides attributed to prograde metamorphism, and is most consistent with the retention of sulfur derived from hydrothermal sulfate reduction on the seafloor. However, a shift towards higher δ34S values in sulfides associated with the advanced stages of exhumation suggests that late stage exhumation enables enhanced access to slab-derived fluids bearing oxidised sulfur (SO42− or SO2). Such fluids may have been derived from the devolatilisation of serpentinite at greater depth, or from other lithologies.

Promoting effect of H2S on the performance of ZrO2 and La2O3-ZrO2 catalysts in biomass gasification gas clean-up

Use of the syngas produced by biomass gasification is rendered unviable because of impurity compounds, whose efficient removal is key to the feasibility of gasification concepts. Tars present in the biomass gasification gas can be efficiently oxidized by ZrO2 catalysts. H2S has been shown to increase the oxidation activity on ZrO2 and most notably on La2O3-ZrO2. Gasification gas clean-up experiments were performed at 600–800 °C to study the beneficial effect of H2S on naphthalene and toluene conversions. During time-on-stream with repeated doses of H2S on ZrO2, cumulative and strong H2S adsorption was observed as the conversion of toluene and naphthalene increased during the first H2S doses and stabilized towards the end. Therefore, a limited capacity of the catalyst to adsorb H2S was suggested, which is the origin of sulfur tolerance. Activity enhancement with H2S occurs most notably on La2O3-ZrO2 and towards naphthalene oxidation. XPS characterization of the used catalysts showed sulfur retention on the La2O3-ZrO2 but not on pure ZrO2, indicating that La2O3-ZrO2 holds more sulfur on its surface or binds it stronger. The surface properties of La2O3-ZrO2 were thus characterized with in situ DRIFTS using CO2 and CH3OH as probe molecules. The surface of La2O3-ZrO2 was suggested to have more low coordination sites than ZrO2, where sulfur is suggested to be bound and alter the reactivity of the surface oxygen.

Effect of air and oxyfuel staged combustion on oil shale fly ash formation with direct in-furnace limestone addition for sulphur retention

El-Lajjun oil shale fly ash formation and S retention during in-furnace limestone injection were investigated in this work. Staged air-firing and 27% O2/CO2 combustion was performed at 1200 °C in a vertical once through reactor. Ash samples were collected at 2.5 m far from the burner and from the conductive section of the reactor. Limestone was added with oil shale before burning in both combustion modes. Ultimate, proximate, and XRF analyses were done for all collected samples, while XRD and SEM analyses were performed for some of them. Sulphur retention in the convective section increased by 13% compared to the radiative section of the reactor. Sulphur retention in the collected ashes ranged from 22 to 32% and 35 to 45% at 2.5 m from the burner and at the candle filter, respectively. The combustion mode had a slight effect on the collected ashes chemical composition. In both combustion modes, the ash samples were enriched with lime and depleted in sulphur, which proved sulphur capture. Fly ash particles were spherical in shape with some aggregates. XRD analysis showed that the main crystalline phases formed in the produced fly ashes were the same regardless the combustion mode and environment, some differences in the relative intensities of anhydrite and lime peaks were present.

Severe Loss of Confined Sulfur in Nanoporous Carbon for Li–S Batteries under Wetting Conditions

One key aspect in the cathode chemistry of lithium–sulfur (Li–S) batteries is the firm contact between elemental sulfur and the conducting carbon host to ensure the occurrence of the reduction reaction. In this respect, we study the retention of sulfur in the model cathode material CMK-8 carbon loaded by 20 and 50 wt % in the presence of solvents of different nature (D2O, d-THF, d-toluene) using small-angle neutron scattering. Exploiting the contrast matching between carbon and these liquids, the scattering of the sulfur phase is isolated and the amount and distribution of sulfur in the pores is determined in precise and direct fashion. The chord-length distribution (CLD) analysis shows that sulfur is preserved in both meso- and micropores if D2O is used. In the case of d-THF, sulfur is found in the micropores only, whereas complete removal from the pore network occurs for wetting with d-toluene. This severe loss in the presence of solvents similar to those used in Li–S batteries (e.g., dioxolane, diglyme) is ascribed to their superior adhesion on the carbon surface and, more importantly, indicates that only a little amount of loaded sulfur is available for the electrochemical reactions.

Porous Coconut Shell Carbon Offering High Retention and Deep Lithiation of Sulfur for Lithium-Sulfur Batteries.

Retaining soluble polysulfides in the sulfur cathodes and allowing for deep redox are essential to develop high-performance lithium-sulfur batteries. The versatile textures and physicochemical characteristics of abundant biomass offer a great opportunity to prepare biochar materials that can enhance the performance of Li-S batteries in sustainable mode. Here, we exploit micro-/mesoporous coconut shell carbon (CSC) with high specific surface areas as a sulfur host for Li-S batteries. The sulfur-infiltrated CSC materials show superior discharge-charge capacity, cycling stability, and high rate capability. High discharge capacities of 1599 and 1500 mA h g-1 were achieved at current rates of 0.5 and 2.0 C, respectively. A high reversible capacity of 517 mA h g-1 was retained at 2.0 C even after 400 cycles. The results demonstrate a high retention and a deep lithiation of the CSC-confined sulfur. The success of this strategy provides insights into seeking high-performance biochar materials for Li-S batteries from abundant bioresources.

Microwave-assisted pyrolysis of textile dyeing sludge using different additives

This paper investigated an auger pyrolyser under microwave (MW) irradiation for pyrolysis of textile dyeing sludge (DS). It showed that the sludge char (SC) yield decreased and the yield of non-condensable gas gradually increased with pyrolysis temperature. The condensate and oil yields reached maximum (i.e. 12.9wt% and 0.8wt%, respectively) at 650°C. Addition of CaO and Fe increased the SC yield and H2 contents, and decreased CO2 content in the non-condensable gas. The H2 content increased from 25.4v% without additives to 64.2v% with addition of 30wt% CaO at 650°C. Whereas Ca-bentonite and kaolin decreased H2 contents with the latter decreasing SC yields and increasing condensate yields. The content of C, H and N in SC decreased with temperature while S increased. CaO and Ca-bentonite were beneficial for sulfur retention and some heavy metal immobilization for microwave pyrolysis of DS. The maximum BET surface area of 123m2/g was observed for SC with addition of 20wt% kaolin, consistent with SEM observations. The main components of the pyrolysis oil were analyzed by GC–MS. High proportions of aromatic compounds were found in the pyrolysis oil from different pyrolysis temperatures. Oxygenates were mainly formed in the temperature range of 350–650°C. The content of aromatic compounds in the oil increased as temperature increased, up to 88.4% (GC–MS area) at 750°C. Heterocyclic aromatic compounds containing nitrogen accounted for 30% ∼ 50% of the pyrolysis oil. CaO, Fe, Ca-bentonite considerably reduced the aromatics content in the pyrolysis oil. The additives used in this study acted as microwave absorbers (MWAs), catalysts, sorbents and reactants in the microwave assisted pyrolysis of DS. The combined functions of these additives and unique characteristics of MW heating contributed to different product yields, and various product compositions and product properties.

Influence of pine sawdust on SO2 retention by CaO in coal slime briquette

ABSTRACTCoal slime, coal slime/CaO, and coal slime/CaO/pine sawdust were formed to make briquettes respectively. The effects of pine sawdust on the SO2 retention by CaO during coal slime briquette combustion were studied using a tube furnace. The obtained results demonstrated that porous structures were created in the briquette residue in the case of pine sawdust addition, and more sulfur retention product, CaSO4, was obtained in both outer and inner briquette residue. In addition, increasing combustion temperatures had a negative impact on SO2 reduction. In the experiments, SO2 retention efficiency achieved 48.3% when biomass and CaO were added to coal slime briquette at 850°C. It indicated that pine sawdust improved the reaction efficiency of CaO capturing SO2 in the coal slime briquette. The addition of CaO with pine sawdust is a dependable way for reliable reduction of SO2.

Mercury emissions from coal combustion in fluidized beds under oxy-fuel and air conditions: Influence of coal characteristics and O2 concentration

In this work, the fate of mercury in a bubbling fluidized bed combustor working under oxy-combustion conditions has been studied and compared with air combustion. The influence of burning three different rank coals, with sulphur content ranging from 0.65% to 5.17%, on Hg partitioning has been studied. The presence of limestone as sorbent for SO2 capture as well as the concentration of O2 at the entrance of the combustor were also evaluated.Coal rank does not have a direct influence on coal partitioning. However, sulphur content of the coal is an important parameter to describe not only the high percentage of particle-bound mercury, up to 87%, in presence of limestone but also the prevalence of Hg(0) as the main species in the gas phase when burning the lignite. The O2/CO2 ratio has little effect on Hg partitioning in experiments carried out in presence of limestone at 925°C (the optimum temperature for sorbent sulphating under oxy-combustion conditions) and little differences are found with air combustion at 850°C (the optimum temperature for sorbent sulphating under air combustion conditions).Percentage of particle-bound mercury shows a maximum at 925°C independently of the coal studied, which it is related with the maximum sulphur retention for each coal at this temperature.

Evaluation of a high protein distiller's dried grains product as a protein source in practical diets for Pacific white shrimp Litopenaeus vannamei

A series of trials were conducted to evaluate the efficacy of a high protein distiller's dried grains (HPDDG) product in practical shrimp feed formulation. In the three growth trials, the basal diet (35% crude protein, 8% lipid) consisted primarily of fish meal (FM), soybean meal (SBM), whole wheat, and corn starch. In trial 1 and trial 2, test diets were produced by supplementing the basal diet with 10, 20, and 30% HPDDG as a replacement for SBM or a combination of FM and SBM, respectively. In trial 1, shrimp (0.18 initial mean weight, 10 shrimp/tank, n=5) were offered diets for six weeks. No significant differences were detected in the growth and feed conversion ratio (FCR). In trial 2, shrimp (1.24 initial mean weight, 30 shrimp/tank, n=4) were offered diets over seven weeks. Significant reductions in growth and FCR were observed when shrimp were fed with diets containing >20% HPDDG. To explore the upper inclusion limit of this product a third trial was conducted for which the basal diet was modified to contain 6, 12, 18, and 24% HPDDG. Shrimp (0.25 initial mean weight, 10 shrimp/tank, n=4) were offered diets over six weeks. Significant reduced growth and increased FCR as well as enhanced iron and copper contents of whole body were detected in treatment containing 24% HPDDG. Apparent net sulfur, calcium, iron, copper, and zinc retention were also significantly affected by different HPDDG inclusions levels. Apparent digestibility coefficients of energy, protein, and amino acid (AA) for the meal were determined using chromic oxide as an inert marker and the 70:30 replacement technique. Generally, nutrients availability of HPDDG were similar to that of FM, while significantly lower than SBM that were evaluated at the same time. Result of this study indicate that HPDDG is a good plant based ingredient and can be included up to 30% as a replacement of SBM without compromising growth of shrimp. When HPDDG was utilized to replace a combination of SBM and FM, an upper limit of 18% of the diet should be recommended in shrimp feed formulation. The growth depression observed at high levels of inclusion is not likely due to digestibility but a limitation of some nutrients (e.g. marginal amino acids). Palatability shifts or unidentified factors could also be factors influencing the negative effects at high levels (≥18% of the diet).

Microwave pyrolysis of textile dyeing sludge in a continuously operated auger reactor

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. 12.86wt% and 0.84wt%, 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 91.9m2/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 25.39vol% without catalyst to 64.17vol% with addition of 30wt% 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 60wt% water content were 0.76–2.59kWh/kg wet DS in the temperature range of 450–750°C and auger speed range of 1–9rpm. Higher pyrolysis temperature and lower auger speeds increased electricity consumptions.

Organic and inorganic sulphur compounds releases from high-pyrite coal pyrolysis in H2, N2 and CO2: Test case Chinese LZ coal

The effects of different atmospheres on the distribution of organic and inorganic sulphur compounds during high-pyrite coal pyrolysis were investigated. Sulphur compound releases were determined by atmospheric pressure-temperature programmed reduction (AP-TPR) “on-line” coupled with MS and AP-TPR “off-line” coupled with TD-GC/MS, which is a reliable technique for coal sulphur characterization. The results show that the decomposition of both organic and inorganic sulphur is different in the three applied atmospheres: H2, N2 and CO2. In H2, most sulphur from LZ coal is hydrogenated/reduced to H2S, decomposition of inorganic sulphur (pyrite and sulphates) has a great effect on the formation of H2S. It not only enhances the intensity of its m/z 34 signal but also shifts the peak maximum of its profile to a higher temperature, even without a returning to the base line. In inert N2 gas, as expected, hydrogenation of some sulphur compounds such as less-reactive di-aryl sulphur species and simple thiophenic structures are highly limited. The dominant peak of m/z 34 can also be related to the reduction of pyrite. In CO2, coal sulphur is mainly converted into SO2/SO, because CO2 is a more reactive gas and rather acts as an oxidizing agent. Decomposition of organic sulphonic acids occurs before 500°C and of sulphonics/sulphoxides after 500°C. The decomposition of sulphates and pyrite is better detectable in CO2 than in inert gas atmosphere. After 800°C char gasification in CO2 results in further decomposition of sulphur compounds and lower sulphur retention.

Analysis of corrosion residues by WDXRF

In this article, a methodology for the wavelength dispersive X-ray fluorescence analysis of corrosion residues is described. Corrosion residues are generally composed of elements that are, total or partially, in a reduced state. Therefore, to prepare fused beads to be measured by wavelength dispersive X-ray fluorescence, it is necessary to oxidize species and to avoid any analyte loss, as sulfur, which is present in residues composition. The combination of an oxidizing agent (LiNO3) and a flux (Li2B4O7 + LiBO2), at a mass ratio residue : oxidizing agent : flux of 1:5:12, is demonstrated to be suitable for the quantitative retention of sulfur in the sample preparation. The addition of silica to the mixture (residue : oxidizing agent : flux) for the formation of homogeneous fused beads is also studied. The optimal parameters for the sample preparation are as follows: A temperature of 600 °C for 15 min for the oxidation process and a fusion temperature of 950 °C for fused beads preparation. The quantitative retention of sulfur in the entire process was validated by an independent method, combustion and infrared detection, and analyzation reference materials. Moreover, minor and major elements (Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, S, and Ti) present in corrosion residues were simultaneously measured with low uncertainty. Copyright © 2017 John Wiley & Sons, Ltd.

Effect of flue gas components on the adsorption of sulfur oxides on CaO(1 0 0)

Due to the prevalence of coal combustion technologies utilizing calcium-based materials, it is important to understand the varied reactions between the flue gas species and these calcium-based materials. Of particular importance is the reaction between sulfur oxides (SO2 or SO3) and calcium oxide (CaO), which plays an important role in sulfur retention on fly ash during oxy-coal combustion or carbon capture with calcium looping. To better understand these reactions, density functional theory (DFT) calculations were performed investigating SOx binding to CaO surfaces functionalized by other flue gas components. Analyses of the energetic, geometric and electronic nature of the modeled systems were conducted. Generally, the most stable conformation on the surface is in the form of either a sulfite- or sulfate-like structure. Water can have an effect on sulfur binding by introducing other favorable intermediate conformations, while carbon dioxide could negatively impact adsorption by weakening sulfur-surface bonds.

In situ gasification Chemical-Looping Combustion of coal using limestone as oxygen carrier precursor and sulphur sorbent

In-situ Gasification Chemical-Looping Combustion (iG-CLC) burning coal is achieving a great interest due to the possibility of using low cost oxygen carriers such as CaSO4. The Limestone Chemical Looping Combustion process (LCL-C™) registered by Alstom Power Inc. proposes the use of a continuous CaCO3 feeding together with coal to produce CaSO4 as an oxygen carrier via sulphur retention. The operation is similar to what happens in a circulating fluidized bed boiler burning coal. In the present research work, the study of thermodynamic equilibrium limitations together with mass and enthalpy balances have been carried out for a CLC system in order to investigate whether the LCL-C™ process is a promising and energy efficient option to carry out the coal combustion with CO2 capture and in-situ desulphurisation. So, no limitations were found to transfer the required oxygen from air to fuel using sulphated limestone as oxygen carrier for whatever coal used. The selection of a suitable oxygen carrier to fuel ratio mainly depends on the sulphur content of the coal used. In addition, no drawback referred to thermal integration in the system has been detected. Thus, operation at 950°C in the fuel reactor to avoid SO2 release via side reactions, and 1050°C in the air reactor is feasible. Likewise, experimental tests have been performed in a thermogravimetric analyser to evaluate the capability of a limestone to be sulphated and to transfer oxygen. A value of the oxygen transport capacity of about 16.7wt.% was obtained. This value is four times higher than that of others typical inexpensive oxygen carriers published in literature.