Effect of Prussian Blue on Organic Sulfur of Coal in Aqueous Medium

Abstract

This study is an attempt to desulfurize organic sulfur from coal samples with ferric hexacyanoferrate (II), Fe₄ [Fe(CN)₆], as the desulfurization agent. Effect of temperature, particle size and concentration of ferrocyanide ion on desulfurization from the coal samples has been investigated. The temperature and stirring time are the most important parameters for the level of desulfurization of organic sulfur. Removal of organic sulfur content increased continuously with increasing temperature from 298 to 368 K. The organic sulfur removal rate sharply increases from 10 min to 30 min stirring time. After 30 min, it reaches a value of plateau. Particle size between ?100 mesh and ?200 mesh slightly affects the amount of organic sulfur removal. Gradual increase in the concentration of ferric hexacyanoferrate (II) raised the magnitude of desulfurization, but at higher concentration, the variation is not significant.     

Effects of Impurities in Claus Feed,II. CO2

Abstract

Effects of CO₂ impurity in the range of 0–50 mol% in acid gas feed to a Claus once through process have been studied for air and pure oxygen combustion media. The process comprising a reaction furnace, three sulfur condensers and two converters is simulated. A computer program is developed. Results showed the effects on adiabatic flame temperature, heat recovery, sulfur recovery and equipment sizes using air and pure oxygen in combustion. Correlations were obtained for these effects. Adiabatic flame temperature could exceed the maximum allowable limit in furnace design when mol% CO₂ is lower than 44% pure oxygen is used. In this case, SURE double combustion technique can be applied. Net heat recovery increases by about 3%, whereas overall sulfur recovery is practically not changed. S _x and COS in tail gas exceed ambient air allowable limit whereas CS₂ is within the allowable limits, so further tail gas treatment is necessary. An increase in equipment size in the range of CO₂ studied reaches up to 34% when air is used in combustion, whereas it reaches up to 98% when oxygen is used. By replacing air with oxygen for a specified CO₂ concentration, a decrease up to 65% in equipment size is predicted.     

Adsorption of Sulfur Dioxide from Coal Combustion Gases on Natural Zeolite

In this study, better efficiency of SO₂ removal in flue gas from lignite coal combustion by adding of NZ in the gas phase was achieved. Natural zeolite was exposed to flue gas containing sulfur dioxide at varying conditions of relative humidity and temperature. It was found that the amount of sulfate on the zeolite increased with increasing relative humidity and temperature. The percents of adsorbed sulfur dioxide were 86, 74, 56, and 35, while the values of relative humidity (RH) were 75, 60, 45, and 30% for 40 minutes, respectively. The percents of adsorbed sulfur dioxide sharply increased within the first 40 min for the values of RH were 75 and 60, and after 40 min, slightly increased, then reached a plateau. In general, as increasing the RH increased the amount of sulfur dioxide adsorbed by natural zeolite. The amounts of adsorbed sulfur dioxide increased with exposure time. It increased and reached 30.2 mg/g for 40 min. After 40 min, it slightly increased and then reached a plateau. The NZ adsorbs 35.1 mg SO₂ per gram adsorbent with 75% RH at 298 K from a simulated coal combustion flue gas. The amounts of adsorbed sulfur dioxide increased with increasing temperature. The NZ adsorbs 71.5 mg SO₂ per gram adsorbent with 75% RH for 100 min exposure time from the flue gas mixture.     

Chemical looping combustion of lignite with the CaSO4–CoO mixed oxygen carrier

Chemical looping combustion (CLC) has well developed as a novel combustion technology for simultaneous completion of the coal combustion and CO₂ capture with a low energy penalty. Among all the oxygen carriers available, CaSO₄ has gained great attention as a promising oxygen carrier (OC) in CLC due to its high oxygen capacity and low price. But further application of CaSO₄ OC also suffers the problems of low reactivity and even deactivation due to the sulfur loss via the side reactions of CaSO₄, which should be well addressed. In this research, the CaSO₄–CoO mixed OC was prepared firstly, and experiments based on thermogravimetric analyzer coupled with Fourier transform infrared spectroscopy (TG-FTIR) were conducted to evaluate the reaction characteristics and evolution of the gaseous products during the reaction of the prepared CaSO₄–CoO mixed OC with lignite (abbreviated as YN). Both the higher reaction rate of the prepared mixed OC with YN coal and the elevated CO₂ concentration fully reflected the enhanced reactivity of the prepared mixed OC for YN coal conversion. Furthermore, the micromorphology of the solid reaction products was analyzed by the field emission scanning electron microscopy spectrometry (FESEM). Good sintering resistance of the prepared CaSO₄–CoO mixed OC during its reaction with YN was verified, which was ascribed to the temporary inert support role played by the CaSO₄ substrate. In order to further study the desulfurization ability of CoO in the mixed OC, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermodynamic simulation were used for in-depth analysis. The gaseous sulfur species released by the CaSO₄ side reactions were mainly fixed as solid CoS, Co₉S₈ and CaS, with the total content higher than 99.8%. And the sulfided OC could be completely regenerated to its original state at the oxidation stage according to the X-ray diffraction (XRD) result. Overall, the prepared CaSO₄–CoO mixed OC not only has the enhanced reactivity and good sintering resistance, but also owns the potential to control sulfur released from the CaSO₄ side reactions, which has broad application prospect to simultaneously achieve decarbonization and desulfurization in the CLC process.     

MSW landfill biogas desulfurization

Biogas utilization in MCFC systems requires a high level of gas purification in order to meet the stringent sulfur tolerance limits of both the fuel cells and the reformer catalysts. In this study, two commercial activated carbons (ACs) have been tested for H₂S removal from the biogas produced at the Montescarpino Municipal Solid Waste landfill in Genoa, Italy. The performed analyses show a low selectivity of activated carbon towards the adsorption of only sulfur species. This represents a drawback for the use of this type of system, however, the use of mixed beds of different ACs has demonstrated to be advantageous in improving the removal efficiency of H₂S. Thus, the adsorption treatments with AC can ensure the high level of gas desulfurization required for fuel cell application. Nevertheless, the low adsorption capacity observed using landfill biogas would lead to high operative costs that suggest the application of a preliminary gas-scrubbing stage.     

Modeling the effect of key cathode design parameters on the electrochemical performance of a lithium‐sulfur battery

A 1D model is developed for the Li‐S cell to predict the effect of critical cathode design parameters—carbon‐to‐sulfur (C/S) and electrolyte‐to‐sulfur (E/S) ratios in the cathode—on the electrochemical performance. Cell voltage at 60% depth of discharge corresponding to the lower voltage plateau is used as a metric for calculating the cell performance. The cathode kinetics in the lower voltage plateau is defined with a single electrochemical reaction; thus, the model has a single apparent kinetic model parameter, the cathode exchange current density (i_0,pe). The model predicts that cell voltage increases considerably with increasing carbon content until a C/S ratio of 1 is attained, whereas the enhancement in the cell voltage at higher ratios is less obvious. The model can capture the effect of the C/S ratio on the cathode kinetics by expressing the electrochemically active area in the cathode in carbon volume fraction; the C/S ratio in the cathode does not affect i_0,pe in the model. On the other hand, the electrolyte amount has a significant impact on the kinetic model parameter such that increasing electrolyte amount improves the cell voltage as a result of increasing i_0,pe. Therefore, in the model, i_0,pe needs to be defined as a function of the electrolyte volume fraction, which is known to have a crucial effect on reaction kinetics.     

Development of integrated reformer systems for syngas production

Precision Combustion, Inc. (PCI) has developed autothermal reformer (ATR) units based on its patented Microlith^® technology and demonstrated stable, coke-free operation using JP-8 consisting of up to 70 ppm_w sulfur for 1100 h with complete fuel conversion and reforming efficiency of ∼85%. The feasibility of operating ATR reformers with distillate fuels containing higher sulfur (up to 400 ppm_w) has also been demonstrated for 55 h, while producing syngas (i.e., H₂ and CO) at >80% reforming efficiency and at complete fuel conversion. Reformer test results, demonstrating water neutral operation, catalyst sulfur tolerance, removal of sulfur to <1 ppm_v, and maintenance of higher hydrocarbons to levels acceptable for fuel cell stacks, provide a measure of the ATR performance that can be expected under realistic conditions with readily available fuels. The results also give valuable insights to the system design and operation strategy for integrated power generation systems.     

Stability of lanthanum oxide-based H2S sorbents in realistic fuel processor/fuel cell operation

We report that lanthana-based sulfur sorbents are an excellent choice as once-through chemical filters for the removal of trace amounts of H₂S and COS from any fuel gas at temperatures matching those of solid oxide fuel cells. We have examined sorbents based on lanthana and Pr-doped lanthana with up to 30 at.% praseodymium, having high desulfurization efficiency, as measured by their ability to remove H₂S from simulated reformate gas streams to below 50 ppbv with corresponding sulfur capacity exceeding 50 mg S g_sorbent⁻¹ at 800 °C. Intermittent sorbent operation with air-rich boiler exhaust-type gas mixtures and with frequent shutdowns and restarts is possible without formation of lanthanide oxycarbonate phases. Upon restart, desulfurization continues from where it left at the end of the previous cycle. These findings are important for practical applications of these sorbents as sulfur polishing units of fuel gases in the presence of small or large amounts of water vapor, and with the regular shutdown/start-up operation practiced in fuel processors/fuel cell systems, both stationary and mobile, and of any size/scale.     

Glass fiber entrapped sorbent for reformates desulfurization for logistic PEM fuel cell power systems

Glass fiber entrapped ZnO/SiO₂ sorbent (GFES) was developed to remove sulfur species (mainly hydrogen sulfide, H₂S) from reformates for logistic PEM fuel cell power systems. Due to the use of microfibrous media and nanosized ZnO grains on highly porous SiO₂ support, GFES demonstrated excellent desulfurization performance and potential to miniaturize the desulfurization reactors. In the thin bed test, GFES (2.5 mm bed thickness) attained a breakthrough time of 540 min with up to 75% ZnO utilization at 1 ppm breakthrough. At equivalent ZnO loading, GFES yielded a breakthrough time twice as long as the ZnO/SiO₂ sorbent; at equivalent bed volume, GFES provided a three times longer breakthrough time (with 67% reduction in ZnO loading) than packed beds of 1–2 mm commercial extrudates. GFES is highly regenerable compared with the commercial extrudates, and can easily be regenerated in situ in air at 500 °C. During 50 regeneration/desulfurization cycles, GFES maintained its desulfurization performance and structural integrity. A composite bed consisting of a packed bed of large extrudates followed by a polishing layer of GFES demonstrated a great extension in gas life and overall bed utilization. This approach synergistically combines the high volume loading of packed beds with the overall contacting efficiency of small particulates.     

Emissions estimation for lignite-fired power plants in Turkey

The major gaseous emissions (e.g. sulfur dioxides, nitrogen oxides, carbon dioxide, and carbon monoxide), some various organic emissions (e.g. benzene, toluene and xylenes) and some trace metals (e.g. arsenic, cobalt, chromium, manganese and nickel) generated from lignite-fired power plants in Turkey are estimated. The estimations are made separately for each one of the thirteen plants that produced electricity in 2007, because the lignite-fired thermal plants in Turkey are installed near the regions where the lignite is mined, and characteristics and composition of lignite used in each power plant are quite different from a region to another. Emission factors methodology is used for the estimations. The emission factors obtained from well-known literature are then modified depending on local moisture content of lignite. Emission rates and specific emissions (per MWh) of the pollutants from the plants having no electrostatic precipitators and flue -gas desulfurization systems are found to be higher than emissions from the plants having electrostatic precipitators and flue -gas desulfurization systems. Finally a projection for the future emissions due to lignite-based power plants is given. Predicted demand for the increasing generation capacity based on the lignite-fired thermal power plant, from 2008 to 2017 is around 30%.     

In situ and downstream sulfidation reactivity of PbO and ZnO during pyrolysis and hydrogenation of a high–sulfur lignite

Economical valorization of low quality, high sulfur feedstocks is an important challenge. Most of the valorization processes start from pyrolysis, with a significant amount of evolution of sulfur containing compounds. This study addresses in situ and downstream sulfur capture ability of lead oxide (PbO) in comparison to zinc oxide (ZnO) during the pyrolysis of high–sulfur Tuncbilek lignite. In order to assess the role of hydrogen in sulfur capture, hydrogenation experiments were also performed. Sulfidation reaction thermodynamics of PbO and ZnO was compared to most commonly used metal oxides for sulfur capture i.e., FeO, MnO, and CaO. The equilibrium conversions indicated superior performance of PbO and ZnO towards sulfidation reactions at high temperatures. Thermodynamic superiority of PbO sulfidation encouraged us to investigate the PbO as a new sulfur sorbent for hot gas desulfurization. The experimental verification of the high temperature sulfidation ability of PbO and ZnO was performed using high–sulfur Tuncbilek lignite under semibatch conditions. The final compounds formed after each process were observed by X-ray diffractometer (XRD) and Diffuse Reflectance Infrared Fourier Transformation Spectroscopy (DRIFTS). Experiments revealed that PbO can be promising candidate as hot gas sulfur trap during pyrolysis and hydrogenation processes, while ZnO can hold up sulfur only in the presence of hydrogen. Furthermore, both PbO and ZnO show the superior sulfur capture performance in the presence of hydrogen when they were used as adsorbents located after the reactor (downstream) at ambient conditions.     

Removal of elemental mercury from simulated flue gas by a novel composite sulfurized activated carbon

Gas-phase elemental mercury (Hg°) removal by composite sulfurized activated carbon (CSAC) was studied under simulated flue gas conditions. The results showed that the CSAC, which was impregnated activated carbon (AC) with aqueous-phase sodium sulfide (Na₂S) and followed with vapor-phase elemental sulfur (S°), had 1.5 times higher removal capacity than AC impregnated with single S°. This study further investigated the effect of individual flue gas components on the performance of CSAC. Fixed-bed experiments showed that SO₂ and NO had no obvious impact on Hg° removal by CSAC, while the presence of O₂ (up to 9%) increased the removal capacity up by 25%.     

Oxidative Desulfurization of Tufanbeyli Coal by Hydrogen Peroxide Solution

Abstract

It is becoming popular to use fossil fuels efficiently since the necessary energy is mostly supplied from fossil fuels. Altough there are high lignite reservoirs, high sulfur content limits the efficient use of them. In this article, we aimed to convert combustible sulfur in coal to non-combustible sulfate form in the ash by oxidizing it with a hydrogen peroxide solution. The parameters affecting the sulfur conversion were determined to be: hydrogen peroxide concentration, reaction time, mean particle size at constant room temperature and shaking rate. The maximum desulfurization efficiency reached was 74% of the original combustible sulfur with 15% (w/w) hydrogen peroxide solution, 12 hours of reaction time, and 0.25 mm mean particle size.     

A high energy density lithium/sulfur–oxygen hybrid battery

In this paper we introduce a lithium/sulfur–oxygen (Li/S–O₂) hybrid cell that is able to operate either in an air or in an environment without air. In the cell, the cathode is a sulfur–carbon composite electrode containing appropriate amount of sulfur. In the air, the cathode first functions as an air electrode that catalyzes the reduction of oxygen into lithium peroxide (Li₂O₂). Upon the end of oxygen reduction, sulfur starts to discharge like a normal Li/S cell. In the absence of oxygen or air, sulfur alone serves as the active cathode material. That is, sulfur is first reduced to form a soluble polysulfide (Li₂S_x, x ≥ 4) that subsequently discharges into Li₂S through a series of disproportionations and reductions. In general, the Li/S–O₂ hybrid cell presents two distinct discharge voltage plateaus, i.e., one at ～2.7 V attributing to the reduction of oxygen and the other one at ～2.3 V attributing to the reduction of sulfur. Since the final discharge products of oxygen and sulfur are insoluble in the organic electrolyte, it is shown that the overall specific capacity of Li/S–O₂ hybrid cell is determined by the carbon composite electrode, and that the specific capacity varies with the discharge current rate and electrode composition. In this work, we show that a composite electrode composed by weight of 70% M-30 activated carbon, 22% sulfur and 8% polytetrafluoroethylene (PTFE) has a specific capacity of 857 mAh g^?1 vs. M-30 activated carbon at 0.2 mA cm^?2 in comparison with 650 mAh g^?1 of the control electrode consisting of 92% M-30 and 8% PTFE. In addition, the self-discharge of the Li/S–O₂ hybrid cell is expected to be substantially lower when compared with the Li/S cell since oxygen can easily oxidize the soluble polysulfide into insoluble sulfur.     

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 SO₂ concentration first rises, then declines along the traveling grate and reaches the peak near the midpoint of the grate. The fluctuation of the SO₂ 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.     

Sulfur-doped shaddock peel–derived hard carbons for enhanced surface capacity and kinetics of lithium-ion storage

Sulfur doping has been regarded an energetic route to optimize the lithium storage properties of carbon-based electrode materials. In this work, sulfur-doped shaddock peel–derived hard carbon is successfully prepared by a KOH- and C₂H₅NS-assisted pyrolysis procedure. It is demonstrated that sulfur doping has strong effect on surface activation and graphitization enhancement, which results in the significant enhancement of the surface adsorption capacity and reaction kinetics of the hard carbon materials. When employed as a lithium ion batteries (LIBs) anode, the as-obtained hard carbon demonstrates excellent cycling and rate properties, presenting a great specific capacity of 738 mAhg⁻¹ at 50 mAg⁻¹ after 200 cycles, as well as 491 mAhg⁻¹ at 200 mAg⁻¹ after 300 cycles. Even at 1000 and 2000 mAg⁻¹, the hard carbon provides a large rate capacity of 283 and 179 mAhg⁻¹, respectively. Besides, it is revealed that the Li⁺ storage process is determined by the surface-induced pseudocapacitive process, whose capacitive proportion reach 60% at 0.5 mVs⁻¹. This work suggests that the low cost and eco-friendly sulfur-doped shaddock peel–derived hard carbon is a very prospective LIB anode material.     

Combustion Characteristics of 24 Lignite Samples

Abstract

In this study, the combustion characteristics such as thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTGA), burning profile, ignition temperature, and peak temperature were analyzed for 24 lignite samples from different areas of Turkey. The samples were heated up to 900°C at a constant rate of 10°C/min in a 5 mL/min flow of dry air. The burning profiles of the samples studied, combined with proximate, sulfur analysis and calorimetry results, contribute to a clearer identification of lignite samples' structure and a better understanding of the coalification process. The lignite samples have been tested with particle size of 0–0.05 mm. Ignition temperatures of the samples have been determined from their burning profiles.     

Electrochemical properties of lithium sulfur cells using PEO polymer electrolytes prepared under three different mixing conditions

Lithium sulfur cells were prepared by composing with sulfur cathode (PEO)₆LiBF₄ polymer electrolyte and lithium anode. (PEO)₆LiBF₄ polymer electrolyte was prepared under three different mixing conditions: stirred polymer electrolyte (SPE), ball-milled polymer electrolyte (BPE) and ball-milled polymer electrolyte with 10 wt%Al₂O₃ (BCPE). The effects of ball milling and additive were investigated by discharge test according to depth of discharge. The initial discharge capacity of lithium sulfur cell using BCPE was 1670 mAh g⁻¹-sulfur, which was better than those of SPE and BPE, and approximately equal to the theoretical capacity. The cycle performance of Li/(PEO)₆LiBF₄/S cell was remarkably improved by the addition of Al₂O_3.     

Biodesulfurization of Cayirhan Lignites

In this study, the lignite was improved oxidizing sulfur compounds by Thiobacillus thiooxidans and Thiobacillus ferrooxidans bacteria. Experiments in the batch reactors have been carried out 20% aqueous suspension of coal samples. Sugar beet molasses was used as the bacterial substrate. The maximum removal of combustible sulfur was obtained as 78.2% under the following conditions; addition 5% of T. thiooxidans and 5% T. ferrooxidans into coal suspension, 0.2 g molasses/g coal change, pH value of 3, at shaking rate of 70 rpm and at 40°C for 5 days.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.