Sulfur Retention Research Articles

Effect of Additive on the SO2 Removal from Flue Gas by Activated Coke

The objective of this work was to use coal as the raw material to prepare activated coke (AC) catalysts of industrial-scale size for SO2 removal from flue gas and to find the optimal additives and preparation methods. Results showed that activated coke with metal loaded was a suitable method, and that the activated coke catalysts, prepared by loading with CoCl2 or CaCO3 and finally calcining at 700°C, exhibited the best desulfurizing property with a sulfur retention of about 98.6mg-SO2/1g-AC at a reaction temperature of 80°C. Also, the effects of H2O content in the flue gas, reaction temperature and space velocity on the desulfurizing property were investigated to determine optimum operating conditions. An H2O content of about 10% was appropriate for catalysts in this work. In the temperature range 70∼110°C, the catalyst showed good performance for SO2 removal and was gradually deactivated at temperatures above 110°C. Space velocity exhibited an optimal value of 800 h-1. The kinetic behavior varied with space velocity and the desulfurizing property was controlled by adsorption at space velocities below 800 h-1, and controlled by catalytic reaction at space velocities above 800 h-1.

Numerical analysis of particle clustering effects on desulphurization and NO emission in a circulating fluidized bed combustor

Desulphurization by a calcium oxide particle cluster and an isolated calcium oxide particle in a circulating fluidized bed (CFB) combustor was numerically analyzed. The gas flow field, the sulphur retention and the nitrogen oxide emission of the cluster were predicted. Computed results showed that the SO 2 capture rate by a calcium oxide particle in the cluster is less than that of the isolated calcium oxide particle out of the cluster. The captured SO 2 and NO emissions decrease with the decrease of the cluster porosity. The maximum SO 2 capture rate by the cluster is at a temperature between 1025 and 1055 K, whereas more NO emissions were found with the increase of the gas temperature. The sulphur removal and the NO emission increase with the increase of the inlet gas velocity.

High unique diversity of sulfate‐reducing prokaryotes characterized in a depth gradient in an acidic fen

The dissimilatory reduction of sulfate contributes to the retention of sulfur in acidic mineratrophic peatlands. Novel sulfate-reducing prokaryotes (SRPs) colonize these low-sulfate fens. This study assessed the community structures of SRPs in a depth gradient (0-50 cm) in a fen, located in the Fichtelgebirge (Spruce Mountains), Germany. Detection of SRPs with multiplex (terminal-) restriction fragment length polymorphism analysis of amplified dissimilatory (bi)sulfite reductase genes (dsrAB) separated three subgroups derived from (i) the upper 5 and 10 cm, (ii) 15-25 cm, and (iii) 30-50 cm depth. Biogeochemical parameters measured in the soil solution from July 2001 to July 2004 documented that the upper 5-10 cm were exposed to drying and oxygenation prior to sampling. Periodic oxygenation reached a maximum depth of 25 cm in the water-saturated fen and was concomitant with relative high concentrations of nitrate (120 microM) and sulfate (up to 310 microM). The fen soil was permanently anoxic below 30 cm depth with average concentrations of sulfate below 40 microM and maximum concentrations of methane. Cloning of dsrAB PCR products from 5, 20 and 40 cm depth yielded a total of 84 unique dsrAB restriction patterns. Partial sequencing of 61 distinct clones resulted in 59 unique partial protein sequences that mainly clustered with DsrA sequences of uncultivated sulfate reducers. Syntrophobacter fumaroxidans- and Syntrophobacter wolinii-related bacteria appeared to be present only in 40 cm depth. Differences in the SRP community structures suggested that SRPs present in the upper fen soil have to tolerate O(2) and even drying, whereas SRPs present in deep anoxic zones may act as syntrophic fermentors in cooperation with H(2)-utilizing methanogens.

Enhancing sulphur self-retention by building-in CaO in straw–bitumen pellets

Combined straw–bitumen pellets have been proposed as an alternative fuel. An interesting finding is the potentiality of straw ash constituents to retain sulphur as bitumen that has relatively high sulphur content. The aim of the present work is to enhance sulphur self-retention to directly meet the environmental regulations by building-in CaO in the pellet instead of feeding sorbent separately. CaO powder has been mixed with the pellet constituents during production processes. An experimental study has been carried out to investigate the effectiveness of built-in CaO to retain sulphur. Two experimental facilities have been utilized. A fluidized bed combustor of 100 mm ID is used to perform batch tests, whereas a pre-pilot scale combustor of 300 mm ID is used for continuous operation. The obtained results demonstrate that building-in CaO is a very efficient technique for retaining sulphur. A major portion of sulphur is retained within the pellet throughout the entire burning period, in particular, during char burning stage. After being a completely burned pellet the remaining ashes work as a very efficient sorbent within the combustor. Typically, at built-in Ca/S = 0.75, SO 2 is reduced to about 65 ppm corresponding to 96% sulphur retention efficiency.

Nutrient retention capabilities of Nile tilapia ( Oreochromis niloticus) fed bio-regenerative life support system (BLSS) waste residues

Nile tilapia were evaluated as a bio-regenerative sub-process for reducing solid waste potentially encountered in bio-regenerative life support systems. Ten juvenile Nile tilapia (mean weight = 2.05 g) were stocked into triplicate aquaria and fed one of seven experimental diets consisting of vegetable, bacterial, or food waste for a period of seven weeks. Weight gain (g), specific growth rate (mg/d), and daily consumption (g) was significantly higher ( p < 0.05) in the control group (13.80, 281.60, and 47.49, respectively) followed by the wheat bran/wheat germ group (4.25, 86.87, and 24.24). Carbon and crude lipid retention was significantly higher ( p < 0.001) in fish fed the control diet (37.99 and 68.54, respectively) followed by fish fed the wheat bran/wheat germ diet (23.19 and 63.67, respectively). Nitrogen, sulfur, and crude protein retention was significantly higher ( p < 0.001) in fish fed the wheat bran/wheat germ group (40.73, 98.65, and 40.75, respectively) followed by fish fed the control diet (23.68, 21.89, and 23.68, respectively). A general loss of minerals was observed among all groups. Strong associations were observed between crude lipid retention and sulfur retention ( r 2 = 0.94), crude lipid retention and carbon retention ( r 2 = 0.92), WG and fiber content of dietary treatments ( r 2 = 0.92), WG and carbon retention and ( r 2 = 0.88), WG and lysine content of waste residues ( r 2 = 0.86), crude protein retention and carbon retention ( r 2 = 0.84), sulfur retention and crude protein retention ( r 2 = 0.84), and total sulfur amino acid (TSAA) content of residues and WG ( r 2 = 0.81). Weaker associations existed between WG and crude lipid retention ( r 2 = 0.77), crude fiber content and carbon retention ( r 2 = 0.76), and WG and methionine content of waste residues ( r 2 = 0.75). Additional research is needed to improve the nutritional quality of fibrous residues as a means to improve tilapia’s ability to utilize these residues as a food source in bio-regenerative support systems.

A New Flue Gas Activation Process for SO2 Removal with Activated Coke in Coal Power Plant

The overall objectives of this study were to use waste flue gas as the activation gas to produce desulfurizers with industrial-scale size, to find the appropriate activated coke and the optimal preparation method, and to determine the operating conditions for the activated coke preparation. The effects of H2O, CO2 and O2 contents in the flue gas were investigated to determine the optimal operating conditions. The results showed that the higher the content of carbon, volatile and calcium oxide (THC) in a coal was, the better the Brunsuer-Emmett-Teller (BET) surface area and the pore volume are due to the increased activating temperature and decreased particle size. The activated coke, loaded with coal tar and finally activated with the flue gas at 800°C, exhibited the best desulfurizing performance with a sulfur retention of about 101 mg-SO2/g-activated coke at a reaction temperature of 100°C. The mechanism for SO2 removal by activated coke shows that the BET surface area, pore volume and THC have a significant influence on SO2 removal efficiency.

Cerium–manganese mixed oxides for high temperature H 2S removal and activity comparisons with V–Mn, Zn–Mn, Fe–Mn sorbents

High temperature H 2S sorption activities of cerium–manganese mixed oxide sorbents containing different molar ratios of Ce/Mn and pure CeO 2, prepared by the complexation technique, were investigated in a fixed bed flow reactor. Sulfur retention capacity and the H 2S sorption rate of CeO 2 were significantly enhanced by the incorporation of Mn into the sorbent. Cerium–manganese mixed oxide having a Ce/Mn ratio of 1/3 showed very high sorption rate. Another advantageous feature of this sorbent was its excellent regeneration properties. No deactivation of this sorbent was observed after 10 successive sulfidation–regeneration cycles. Also about 90% of the retained sulfur was converted to elemental sulfur instead of SO 2, during regeneration step. The H 2S sorption rate constant observed at 600 °C with the Ce1–Mn3 mixed oxide sorbent was also found to be much higher than the corresponding values for Zn–Mn, V–Mn and Fe–Mn mixed oxide sorbents prepared in this study.

Kinetics of H2S Sorption on Manganese Oxide and Mn-Fe-Cu Mixed Oxide Prepared by the Complexation Technique

Hydrogen sulfide sorption activities of manganese oxide and Mn-Fe-Cu mixed oxide sorbents were examined in a fixed bed reactor. Sulfur retention capacity of Mn-O sorbent was found to be quite high at 600 °C both in the absence and presence of hydrogen gas (0.17 and 0.14 g S/g sorbent, respectively). This sorbent has a high porosity and a relatively high surface area. Best regeneration temperature of this sorbent was found as 700 °C, with a gas stream containing 6% oxygen in nitrogen. Mn-Fe-Cu mixed oxide sorbent had a lower sulfur retention capacity (0.07 g S/g sorbent). However, both of these sorbents gave quite high initial sorption rate constants, resulting very sharp breakthrough curves. Deactivation model was shown to give good agreement with the experimental H2S breakthrough curves.

The Effects of Ca-Based Sorbents on Sulfur Retention in Bottom Ash from Grate-Fired Annual Biomass

Approaches to reduce sulfur emissions during combustion by using in situ sorbent additives have proven to be nominally successful in reducing SO2 emissions from coal-fired boilers. Concerning sulfur release from biomass combustion, however, relatively little work has been published. Accordingly, the objective of the current research was to investigate sulfur-binding sorbent additives that can be mixed with annual biomass fuels to obtain an increased retention of sulfur in the bottom ash. To do so, laboratory-scale experiments were performed with five annual biomass fuels and five Ca-based sorbent additives, using various sorbent/fuel contact arrangements and stoichiometries, in the temperature range of 800−1100 °C. From the relevant practical findings from the lab-scale experiments, additional demonstrations were made with wheat straw and added limestone using a large-scale fixed bed reactor (FBR).The retention of a given element in the ash was quantified by the difference according to a simple mass balan...

Oxide melt solution calorimetry of sulfides: Enthalpy of formation of sphalerite, galena, greenockite, and hawleyite

Oxidative drop solution calorimetry is being developed as a general method for sulfide thermochemistry. The samples are dropped from room temperature into molten 3Na 2 O·4MoO 3 solvent at 975 K, with oxygen bubbling through the melt to ensure rapid and complete conversion of sulfide to dissolved sulfate. Complete dissolution of sulfides and retention of sulfur in the solvent is documented by furnace tests and visual observation, consistent determination of enthalpy of drop solution, and comparison with previous data for the heat of formation of ZnS, PbS, and CdS. Enthalpies of formation (kJ/mol) from the elements (Δ H f 0 ) are determined for sphalerite (ZnS) (−206.53 ± 4.03 kJ/mol), galena (PbS) (−98.12 ± 4.37 kJ/mol), greenockite (hexagonal CdS) (−148.79 ± 4.13 kJ/mol), and hawleyite (cubic CdS) (−147.65 ± 4.28 kJ/mol). Thus, hawleyite appears to be energetically very similar to greenockite but possibly slightly metastable by about 1 kJ/mol. The results confirm that oxidative drop solution calorimetry in molten sodium molybdate is a viable method for sulfide thermochemistry. It will be most useful for sulfides with moderate heats of oxidation (e.g., the Fe-S, Co-S, and Ni-S systems), and should be applicable to ternary compounds, e.g., the Fe-Ni-S and Ni-Co-S systems, and systems showing large homogeneity ranges, as well as to other chalcogenides and pnictides.

Microwave-enhanced roasting of copper sulfide concentrate in the presence of CaCO 3

The microwave irradiation is used to the oxidative roasting of copper sulfide concentrate in the presence of CaCO 3 with the aim of eliminating sulfur dioxide emissions and accelerating roasting process. The calcine obtained is leached with NH 3–(NH 4) 2CO 3 solution for the recovery of copper. It is shown that the copper extractions from the calcine roasted with microwave heating are as high as 90–96.6%, while those with conventional heating are only 71–77.4%. The sulfur retention is greater than 96% for both the microwave and conventional heating. The reaction rates of the roasting process increased 3.97–17.15 times when using microwaves instead of conventional heating. The phase changes and reaction mechanism of the roasting process are also investigated with X-ray diffraction and thermal analysis.

PbS nanocrystal synthesis in Pb-containing silicate glasses

We describe a synthesis of PbS nanocrystals in glasses, involving 150keV sulfur implantation into Pb-containing silicate glasses at peak concentrations up to 3.6at.% and postannealing around the glass transition temperature (500–600°C). The PbS nanocrystals, whose growth is evidenced by transmission electron microscopy, display intense photoluminescence (PL) in the 1–1.5μm wavelength range. Besides bypassing the sulfur retention problem occurring in traditional glass fusion techniques, our method improves control over nucleation and growth. The latter is demonstrated by the impact on the PbS nanocrystal PL properties of progressively replacing CaO by ZnO in a S-implanted Pb glass.

Adsorption of Hydrogen Sulfide onto Activated Carbon Fibers: Effect of Pore Structure and Surface Chemistry

To understand the nature of H2S adsorption onto carbon surfaces under dry and anoxic conditions, the effects of carbon pore structure and surface chemistry were studied using activated carbon fibers (ACFs) with different pore structures and surface areas. Surface pretreatments, including oxidation and heattreatment, were conducted before adsorption/desorption tests in a fixed-bed reactor. Raw ACFs with higher surface area showed greater adsorption and retention of sulfur, and heat treatment further enhanced adsorption and retention of sulfur. The retained amount of hydrogen sulfide correlated well with the amount of basic functional groups on the carbon surface, while the desorbed amount reflected the effect of pore structure. Temperature-programmed desorption (TPD) and thermal gravimetric analysis (TGA) showed that the retained sulfurous compounds were strongly bonded to the carbon surface. In addition, surface chemistry of the sorbent might determine the predominant form of adsorbate on the surface.

Application of artificial neural networks for the prediction of sulfur polycyclic aromatic compounds retention indices

Quantitative models for structure–retention relationships have been developed for the retention indices of polycyclic aromatic sulfur heterocyclic compounds (PASHs). Six nonlinear models for predicting linear temperature programmed gas chromatographic retention characteristics on a Bpx5 (%5 phenyl) stationary phase. The developed predictive models relate molecular structure of each PASH compound to its experimental retention index.

Secondary Capture of Chlorine and Sulfur during Thermal Conversion of Biomass

In larger combustion facilities, secondary reactions between char and chlorine and sulfur may be important. In this work, the interactions of chlorine and sulfur with biomass char during thermal conversion have been experimentally investigated. A laboratory-scale fixed-bed reactor was applied to study the capture of HCl and SO2 by biomass char in the temperature range of 400−950 °C. The observed reaction rate was sufficient for significant recapture of HCl and SO2 to occur under conditions typical for fixed-bed combustors. A maximum in the chlorine and sulfur retention existed at ∼600 °C. Relatively high amounts of chlorine and sulfur could be retained in the char samples over the entire temperature range, compared to the inherent chlorine and sulfur content in the biomass. Spectroscopic and chemical analyses revealed that HCl was mainly captured by the inherent metal species, whereas SO2 was mainly captured by the organic matrix. As a result, the maximum chlorine retention was dictated by the inherent metal content of the biomass. Combustion of the chlorine- and sulfur-laden char samples resulted in high retention values of chlorine and sulfur in the ash at temperatures up to 600 and 800 °C, respectively. At higher combustion temperatures, chlorine and sulfur was gradually released to the gas phase, because of evaporation of KCl and dissociation of sulfates. A larger fixed-bed reactor was applied to simulate the combustion process that occurs in industrial-scale grate-fired boilers. Combustion of wheat straw samples in the large fixed-bed reactor confirmed that higher retention values of both chlorine and sulfur could be obtained, compared to the smaller laboratory reactor, presumably because of secondary capture.

Mn−Cu and Mn−Cu−V Mixed-Oxide Regenerable Sorbents for Hot Gas Desulfurization

Porous Mn−Cu and Mn−Cu−V mixed-oxide sorbents prepared by the complexation technique were tested for high-temperature removal of H2S in the presence of hydrogen gas. Sorption experiments carried out at 627 °C in a fixed-bed reactor showed higher reactivity and also higher sulfur retention capacity (over 0.15 g of S/g of sorbent) for the Mn−Cu mixed oxide than for the Mn−Cu−V mixed oxide. Successive sulfidation−regeneration cycles demonstrated that the Mn−Cu mixed oxide was also more stable than Mn−Cu−V, maintaining its activity and about 90% of its sulfur retention capacity at the end of five cycles. Although formation of some MnSO4 was observed during regeneration at 700 °C with a gas mixture containing 6% oxygen in nitrogen, this did not cause significant reduction in the activity of this mixed-oxide sorbent. It was also shown that a previously proposed deactivation model gave good predictions of the experimental breakthrough curves obtained with these sorbents.

Selective Removal of Hydrogen Sulfide from Gaseous Streams Using a Zinc-Based Sorbent

A sorbent that was developed by Phillips Petroleum Company, now ConocoPhillips Company, has demonstrated very high and stable reactivity under numerous fixed-bed testing regimes in simulated gases. This sorbent, under the tradename of Z-Sorb III, has been determined to be suitable for sulfur removal applications in a wide range of temperatures (250−650 °C), pressures (2−20 atm), and gas space velocities (3500−10 000 h-1). The suitability of the system has been evaluated according to the following criteria: operational conditions (temperature, pressure), sulfur retention, sulfur capacity, side reactions, mechanical stability, and regeneration features. The execution of the experimental work program has been conducted in a high-temperature, high-pressure bench-scale plant that operates with synthetic gases. The influence of fuel gas components, temperature, pressure, gas hourly space velocity, gas type, and cyclic testing on sulfur sorption has been studied.

Spectroscopic study on sorption of hydrogen sulfide by means of red soil

This paper reports the results of the characterization of red soils in relation to the sorption of H 2S from coal gas at 500 °C by spectroscopic techniques in order to provide more information on red soils’ structural change both before and after reaction. In addition, by-products analysis has also been studied using Fourier transform infrared (FTIR) spectroscopy. Before and after the experiments the red soils were characterized with X-ray powder diffraction (XRPD), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and FTIR spectroscopy. XRPD results indicate that iron oxide species disappear from the original to reacted red soil. EDS analysis shows that a significant amount of sulfur is present in the reacted red soil, which is in agreement with the results of the elemental analysis and the calculated value based on breakthrough curve. XPS regression fitting results further indicate that sulfur retention may be associated with the iron oxides. S 2p XPS fittings point out that the major sulfur species present in the reacted red soil are composed of S −2, elemental sulfur, polysulfide, sulfite and sulfate. Additionally, the binding energy of iron shifts to a lower position for the reacted red soil, which indicates that iron oxides in the original red soil have been converted into iron sulfide. Appreciable amounts of the by-products CO 2, SO 2 and COS are detected by on-line FTIR spectroscopy during the initial and later stages of the sorption process. The formation of CO 2 is related to the water-shift reaction, and SO 2 is probably attributable to the reaction of organic matters and H 2S. The concentration of COS is quantified by GC/FPD and found it to be about 350 ppm, which is close to the equilibrium concentration of the reaction of inlet CO and H 2S at a temperature of 500 °C.

Patterns of nitrogen and sulfur accumulation and retention in ombrotrophic bogs, eastern Canada

AbstractNitrogen (N) and sulfur (S) play important roles in peatlands, through their influence on plant production and peat decomposition rates and on redox reactions, respectively, and peatlands contain substantial stores of these two elements. Using peat N and S concentrations and dry bulk density and 210Pb dating, we determined the rates of N and S accumulation over the past 150 years in hummock and hollow profiles from 23 ombrotrophic bogs in eastern Canada. Concentrations of N and S averaged 0.80% and 0.18%, respectively, generally increased with depth in the profile and there was a weak but significant correlation between N and S concentrations. Rates of N and S accumulation over the past 50–150 years ranged from 0.5 to 4.8 g N m−2 yr−1 and from 0.1 to 0.9 g S m−2 yr−1. There were significant but weak correlations between C, N and S accumulation rates over 50‐, 100‐ and 150‐year periods. Over the last 50 years, rates of S accumulation showed little differentiation between hummocks and hollows, whereas the pattern for N accumulation was more variable (hummock minus hollow rate ranged from −1 to +1.5 g N m−2 yr−1), with hummocks generally having a larger N accumulation rate, correlated with the rate of carbon (C) accumulation. There was a modest but significant positive correlation between 50‐year rates of N accumulation and wet atmospheric deposition of N measured between 1990 and 1996, with accumulation rates about four times that of wet deposition. The difference between deposition and accumulation of N is attributed to organic N deposition, dry deposition and N2 fixation. A weaker, but still significant, correlation was observed between 50‐year S accumulation and 1990–1996 wet atmospheric S deposition, with about 75% of the deposited S accumulating in the peat. A laboratory experiment with peat cores exposed to varying water table position and simulated N and S deposition, showed that on average 87% and 98% of the deposited NH4+ and NO3−, respectively, and 58% of the deposited S were retained in the vegetation and unsaturated zone of the cores, supporting the results from the field study.

Microarray and functional gene analyses of sulfate-reducing prokaryotes in low-sulfate, acidic fens reveal cooccurrence of recognized genera and novel lineages.

Low-sulfate, acidic (approximately pH 4) fens in the Lehstenbach catchment in the Fichtelgebirge mountains in Germany are unusual habitats for sulfate-reducing prokaryotes (SRPs) that have been postulated to facilitate the retention of sulfur and protons in these ecosystems. Despite the low in situ availability of sulfate (concentration in the soil solution, 20 to 200 microM) and the acidic conditions (soil and soil solution pHs, approximately 4 and 5, respectively), the upper peat layers of the soils from two fens (Schlöppnerbrunnen I and II) of this catchment displayed significant sulfate-reducing capacities. 16S rRNA gene-based oligonucleotide microarray analyses revealed stable diversity patterns for recognized SRPs in the upper 30 cm of both fens. Members of the family "Syntrophobacteraceae" were detected in both fens, while signals specific for the genus Desulfomonile were observed only in soils from Schlöppnerbrunnen I. These results were confirmed and extended by comparative analyses of environmentally retrieved 16S rRNA and dissimilatory (bi)sulfite reductase (dsrAB) gene sequences; dsrAB sequences from Desulfobacca-like SRPs, which were not identified by microarray analysis, were obtained from both fens. Hypotheses concerning the ecophysiological role of these three SRP groups in the fens were formulated based on the known physiological properties of their cultured relatives. In addition to these recognized SRP lineages, six novel dsrAB types that were phylogenetically unrelated to all known SRPs were detected in the fens. These dsrAB sequences had no features indicative of pseudogenes and likely represent novel, deeply branching, sulfate- or sulfite-reducing prokaryotes that are specialized colonists of low-sulfate habitats.