Sulfation and attrition of calcium sorbent in a bubbling fluidized bed

A bubbling fluidized bed reactor was used as a desulfurization apparatus in this study. The height of the bed was 2.5 m, and the inner diameter was 9 cm. The bed materials were calcium sorbent and silica sand. The effects of the operating parameters of the flue gas desulfurization including relative humidity, temperature, superficial gas velocity, and the particle size of calcium sorbent on SO₂ removal efficiency and calcium sorbent conversion and attrition rate in the fluidized bed were investigated. It was found that the temperature effect in our system was negligible from 40 to 65°C. A higher relative humidity had a higher calcium conversion and a higher sulfur dioxide removal efficiency. Moreover, a smaller particle size of calcium sorbent had a lower calcium conversion in the cyclone but a higher sulfur dioxide removal efficiency. A lower superficial gas velocity resulted in a higher sulfur dioxide removal efficiency and a higher calcium conversion, thus, the total volume of the flue gas treated was maximum near the minimum fluidization velocity. Finally, an attrition rate model proposed in this study could predict the elutriation rate satisfactorily.     

Life cycle test of the NOXSO SO2 and NOX flue gas treatment process: Process modeling

The NOXSO process uses a regenerable sorbent that removes SO₂ and NO_X simultaneously from flue gas. The sorbent is a γ-alumina bead impregnated with sodium carbonate. The process was successfully tested at three different scales, equivalent to 0.017, 0.06, and 0.75 MW of flue gas generated from a coal-fired power plant. These test results were used to develop a mathematical model for the NOXSO fluid-bed adsorber (NOXSO Corp., Library, PA). The model predicts SO₂ and NO_X removal efficiencies as a function of process conditions and sorbent properties. The spent sorbent was successfully regenerated with either hydrogen or natural gas. The presence of steam during regeneration helps to remove the residual sulfur, but the benefit of steam diminishes when its inlet concentration exceeds 25%. A design equation for a moving-bed regenerator using natural gas as the regenerant was developed from the 0.06 MW results. The adsorber model and the regenerator design equation were used together to determine the optimum residual sulfur content of the regenerated sorbent. It was concluded that the NOXSO LCTU (0.06 MW) would operate at the minimum cycle time of sorption and regeneration if the sulfur content of the regenerated sorbent was controlled at 0.8 wt%.     

Reaction characteristics of Ca(OH)2, HCl and SO2 at low temperature in a spray dryer integrated with a fabric filter

The objective of this research was to evaluate the reaction characteristics of CaOH2, HCl and SO2 in the flue gas emitted by a laboratory incinerator. The amount of sulfur retained in the residues (including the spray dryer ash and baghouse ash) was also evaluated in this study. The experimental parameters included HCl concentration (500-2000 ppm), SO2 concentration (500-2000 ppm), relative humidity (40-80% RH), and the addition of CaCl2 (30 wt.%).The results indicated that an HCl concentration of 500-2000 ppm did not affect HCl removal efficiency in the spray dryer at 150 degrees C and 45+/-5% RH. On the other hand, increase in SO2 concentration from 500 to 2000 ppm enhanced SO2 removal at 150 degrees C and 75+/-5% RH. Moreover, increase in removal efficiency of SO2 was more obvious when the relative humidity was greater than 80%. When the flue gas contained both HCl and SO2 simultaneously, the removal efficiency of SO2 could increase from 56.7 to 90.33% at HCl concentration of 236 ppm. However, when the concentration of HCl exceeded 535 ppm, the removal efficiency of SO2 decreased with increasing concentration of HCl. The removal efficiency of SO2 could be increase to 97.7% with the addition of CaCl2.     

High temperature removal of hydrogen sulfide using an N-150 sorbent

In this study, an N-150 sorbent was used as a high temperature desulfurization sorbent for the removal of hydrogen sulfide from coal gas in a fixed bed reactor. The results indicate that the N-150 sorbent could be used for H(2)S removal in the tested temperature ranges. Regeneration test also reveals that utilization of the N-150 sorbent maintains up to 85% compared to the fresh sorbent. No significant degeneration occurs on the N-150 sorbent. In addition, various concentrations of H(2)S, H(2) and CO were also considered in the performance test of the N-150 sorbent. Except for H(2)S, H(2) and CO act the important roles in the high temperature desulfurization. By increasing the H(2) concentration, the sulfur capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction. On the basis of the instrument analysis, X-ray powder diffraction determination and SEM images with EDS spectrum characterization, residual sulfur is found in the regenerated N-150 sorbent and this sulfur species is sulfate which resulted by incomplete regeneration. The sulfate formation and sintering effect are major reasons to cause activity loss in the sulfidation/regeneration cycles.     

A dual-use of DBD plasma for simultaneous NO(x) and SO(2) removal from coal-combustion flue gas

Dielectric barrier discharge (DBD) was investigated for the simultaneous removal of NO(x) and SO(2) from flue gas in a coal-combustion power plant. The DBD equipment was used in either a mode where flue gas was directed through the discharge zone (direct oxidation), or a mode where produced ozonized air was injected in the flue gas stream (indirect oxidation). Removal efficiencies of SO(2) and NO for both methods were measured and compared. Oxidation of NO is more efficient in the indirect oxidation, while oxidation of SO(2) is more efficient in the direct oxidation. Addition of NH(3), has lead to efficient removal of SO(2), due to thermal reaction, and has also enhanced NO removal due to heterogeneous reactions on the surface of ammonium salt aerosols. In the direct oxidation, concentration of CO increased significantly, while it maintained its level in the indirect oxidation.     

Catalytic effects of carbon sorbents for mercury capture

Activated carbon sorbents have the potential to be an effective means of mercury control in combustion systems. Reactions of activated carbons in flow systems with mercury and gas stream components were investigated to determine the types of chemical interactions that occur on the sorbent surface. The effects of carbon type, particle size, temperature, and reactive gases were studied. Sorption kinetics and capacities for lignite- and bituminous-based carbons were compared with those for catalytic carbons at temperatures of 107 degrees C, 150 degrees C, and 163 degrees C. In the air and baseline gas studies, the catalytic carbons exhibited far better sorption than the lignite- and bituminous-derived carbons. With the catalytic carbons, the greater sorption kinetics and capacity in an air stream or baseline gas composition compared with nitrogen provides a clear demonstration that O(2) is required in the gas stream for higher reactivities and capacities. Thus, a catalytic chemisorption mechanism predominates for the sorption of mercury at these conditions. The reaction kinetics are inversely proportional to the temperature, indicating that a preliminary physisorption step with mercury associating with a surface site is rate-determining. In synthetic flue gas streams containing HCl (50 ppm), the sorption kinetics of the catalytic carbon are slightly inferior to those of lignite-based carbon. Thus, the reaction is dominated by a different interaction, where HCl reacts with mercury on the carbon surface and the oxidation sites on the catalytic carbon apparently have no advantage. Granular and fine-particle carbons gave similar results in flue gas streams.     

Hydrogen sulfide removal from coal gas by the metal-ferrite sorbents made from the heavy metal wastewater sludge

The metal-ferrite (chromium-ferrite and zinc-ferrite) sorbents made from the heavy metal wastewater sludge have been developed for the hydrogen sulfide removal from coal gas. The high temperature absorption of hydrogen sulfide from coal gas with the metal-ferrite sorbent in a fixed bed reactor was conducted in this study. The metal-ferrite powders were the products of the ferrite process for the heavy metal wastewater treatment. The porosity analysis results show that the number of micropores of the sorbents after sulfidation and regeneration process decreases and the average pore size increases due to the acute endothermic and exothermic reactions during the sulfidation–regeneration process. The FeS, ZnS, and MnS peaks are observed on the sulfided sorbents, and the chromium extraction of the CFR6 can fulfill the emission standard of Taiwan EPA. The suitable sulfidation temperature range for chromium-ferrite sorbent is at 500–600 °C. In addition, effects of various concentrations of H₂ and CO were also conducted in the present work at different temperatures. By increasing the H₂ concentration, the sulfur sorption capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction.     

A pilot plant technical assessment of an advanced in-duct desulphurisation process

In-duct sorbent injection (DSI) is a well-known, low-cost desulphurisation technology handicapped by its moderate SO(2) removal capacity. Fortunately, there are some technical options for increasing the desulphurisation efficiency without eliminating its inherent advantages. In this experimental study, several improvement design options like the recirculation of reactivated sorbent, the pre-collection of the fly ash and the use of seawater for humidification have been analysed using an extensive parametric testing programme. The effect of the main operating variables directly related to the desulphurisation efficiency has been also tested following a fractional factorial design. These variables were the Ca/S ratio, the approach to the adiabatic saturation temperature and the recirculation ratio of the partially converted sorbent. Other important questions like the use of a high-BET-area lime and the impact of the DSI process on an ESP have been also included in this experimental assessment.More than 50 experimental tests were carried out in a 3-MWe equivalent pilot plant to assess the different improvement options for in-duct sorbent injection. The results of this study allow us to extract practical conclusions about the devices, equipment and operating conditions as a function of the target SO(2) efficiency, and even enable us to provide an economic assessment. Using the proposed improvement options to process a flue gas with 400-1000ppm of SO(2) concentration, a 90% sulphur removal with a lime utilisation of 45% was achieved.     

Sorption of As(V) from aqueous solution using acid modified carbon black

The sorption performance of a modified carbon black was explored with respect to arsenic removal following batch equilibrium technique. Modification was accomplished by refluxing the commercial carbon black with an acid mixture comprising HNO(3) and H(2)SO(4). Modification resulted in the substantial changes to the inherent properties like surface chemistry and morphology of the commercial carbon black to explore its potential as sorbent. The suspension pH as well as the point of zero charge (pH(pzc)) of the material was found to be highly acidic. The material showed excellent sorption performance for the removal of arsenic from a synthetic aqueous solution. It removed approximately 93% arsenic from a 50mg/L solution at equilibration time. The modified carbon black is capable of removing arsenic in a relatively broad pH range of 3-6, invariably in the acidic region. Both pseudo-first-order and second-order kinetics were applied to search for the best fitted kinetic model to the sorption results. The sorption process is best described by the pseudo-second-order kinetic. It has also been found that intra-particle diffusion is the rate-controlling step for the initial phases of the reaction. Modelling of the equilibrium data with Freundlich and Langmuir isotherms revealed that the correlation coefficient is more satisfactory with the Langmuir model although Freundlich model predicted a good sorption process. The sorption performance has been found to be strongly dependent on the solution pH with a maximum display at pH of 5.0. The temperature has a positive effect on sorption increasing the extent of removal with temperature up to the optimum temperature. The sorption process has been found to be spontaneous and endothermic in nature, and proceeds with the increase in randomness at the solid-solution interface. The spent sorbent was desorbed with various acidic and basic extracting solutions with KOH demonstrating the best result ( approximately 85% desorption).     

Aqueous and vapor phase mercury sorption by inorganic oxide materials functionalized with thiols and poly-thiols

The objective of the study is the development of sorbents where the sorption sites are highly accessible for the capture of mercury from aqueous and vapor streams. Only a small fraction of the equilibrium capacity is utilized for a sorbent in applications involving short residence times (e.g., vapor phase capture of mercury from coal-fired power plant flue gases). So, dynamic capacity rather than equilibrium capacity is more relevant for these kinds of situations. Rapid sorption rates and higher dynamic capacity can be achieved by increasing the accessibility of active sites and decreasing the diffusional resistance to mass transport for the adsorbing species. This requires the use of open structured sorbent materials and attachment of functional groups on the external surface area of supports. The strong interaction of sulfur containing ligands (e.g., thiol) with mercury makes them suitable candidates for immobilization on these types of materials. In this study, inorganic oxide supports like alumina and silica are functionalized with thiol moieties like mercapto silane, cysteine and poly-cysteine for capturing mercury from aqueous and vapor phase. Aqueous phase Hg (II) sorption studies with cysteine/poly-cysteine functionalized silica showed that high dynamic capacity can be achieved by attaching active sites (thiol) on the external area of supports. Vapor phase Hg capture studies with thiol-functionalized mesoporous silica (Hg⁰ concentration = 3.37 mg/m³ with N₂ as the carrier, gas temperature = 70 ^°C) yielded a capacity of 143 g Hg/g for the sorbent. Although the sulfur content for the sorbent was low (0.80 wt. %) the molar ratio of Hg captured to sulfur was comparatively high (2.86×10^–3) pointing to the high accessibility of sulfur sites.     

Leaching of APC residues from secondary Pb metallurgy using single extraction tests: the mineralogical and the geochemical approach

Two air-pollution-control (APC) residues--one from flue gas cooling with alkaline water and one from deionized water cooling--from secondary lead metallurgy were submitted to two different standardized short-term leaching protocols: US EPA toxicity characteristic leaching procedure (TCLP) and static leaching according to Czech/European norm EN 12457-2. The experimental procedure was coupled with detailed mineralogical investigation of the solid material (SEM, XRPD) and speciation-solubility calculations using the PHREEQC-2 geochemical code. Both types of residues were considered as hazardous materials exhibiting substantial leaching of Pb (up to 7130 mg/l) and other inorganic contaminants. However, the APC residue produced by flue gas cooling with alkaline water (sample B) exhibits more favourable leaching and environmental characteristics than that produced by simple deionised water cooling (sample A). At pH < 5, primary caracolite (Na3Pb2(SO4)3Cl) and potassium lead chloride (KCl.2PbCl2) are completely or partially dissolved and transformed to residual anglesite (PbSO4), cotunnite (PbCl2) and laurionite (Pb(OH)Cl). At pH 5-6, anglesite is still the principal residual product, whereas at pH > 6, phosgenite (PbCl2.PbCO3) became the dominant secondary phase. The results are consistent with the mineralogical and geochemical studies focused on acidic forest soils highly polluted by smelter emissions, where anglesite, as a unique Pb-bearing phase, has been detected. From the technological point of view, the mixing of APC residue with alkaline water, followed by an increase in the suspension pH and equilibration with atmospheric CO2, may be used to ensure the precipitation of less soluble Pb carbonates, which are more easily recycled in the Pb recovery process in the metallurgical plant.     

Simultaneous desulfurization and denitrification by microwave reactor with ammonium bicarbonate and zeolite

Microwave reactor with ammonium bicarbonate (NH(4)HCO(3)) and zeolite was set up to study the simultaneous removal of sulfur dioxide (SO(2)) and nitrogen oxides (NO(x)) from flue gas. The results showed that the microwave reactor filled with NH(4)HCO(3) and zeolite could reduce SO(2) to sulfur with the best desulfurization efficiency of 99.1% and reduce NO(x) to nitrogen with the best NO(x) purifying efficiency of 86.5%. Microwave desulfurization and denitrification effect of the experiment using ammonium bicarbonate and zeolite together is much higher than that using ammonium bicarbonate or zeolite only. NO(x) concentration has little effect on denitrification but has no influence on desulfurization, SO(2) concentration has no effect on denitrification. The optimal microwave power and empty bed residence time (EBRT) on simultaneous desulfurization and dentrification are 211-280 W and 0.315 s, respectively. The mechanism for microwave reduced desulfurization and denitrification can be described as the microwave-induced catalytic reduction reaction between SO(2), NO(x) and ammonium bicarbonate with zeolite being the catalyst and microwave absorbent.     

Helical sorbent for fast sorption and desorption in solid-phase microextraction-gas chromatographic analysis

A new technique for solid-phase microextraction (SPME) of analytes using a helical solid sorbent followed by thermal desorption into a gas chromatographic injector is reported. The main factors that affect the mass transport of analytes in sorption and thermal desorption process using a poly(dimethylsiloxane) (PDMS) helical sorbent are described. The sorption and thermal desorption were achieved in a few seconds, being very close by the theoretical prediction. Both processes were very fast by the reduction of the thickness of boundary layer between sorbent and gaseous sample as a result of a turbulent rotational flow of the headspace air on the surface of sorbent, which is generated by the helical configuration of the sorbent. The thermal desorption was also reduced by improving heat transfer into a thin boundary layer and by increasing the temperature of the heat transporter (carrier gas). The sorption and desorption with PDMS helical sorbent were compared with those of the PDMS silica rod. The extraction time was as much as 15 times faster with the PDMS helical sorbent than with the PDMS silica rod. The desorption with the PDMS helical sorbent was very fast, giving narrow peaks without tailing and a high efficiency of separation in comparison with PDMS silica rod.     

Simultaneous removal of SO2 and NO by wet scrubbing using aqueous chlorine dioxide solution

The present study attempts to generate chlorine dioxide (ClO(2)) gas continuously by chlorate-chloride process and to utilize it further to clean up SO(2) and NO(x) gases simultaneously from the flue gas in the lab-scale bubbling reactor. Experiments were carried out to examine the effect of various operating parameters like input SO(2) concentration, input NO concentration, pH of the reaction medium, and ClO(2) feeding rate on the SO(2) and NO(x) removal efficiencies at 45 degrees C. Complete oxidation of NO into NO(2) occurred on passing sufficient ClO(2) gas into the scrubbing solution. SO(2) removal efficiency of about 100% and NO(x) removal efficiency of 66-72% were achieved under optimized conditions. NO(x) removal efficiency decreased slightly with increasing pH and NO concentration. Input SO(2) concentration had marginal catalytic effect on NO(2) absorption. No improvement in the NO(x) removal efficiency was observed on passing excess of chlorine dioxide in the scrubbing solution.     

Production of a new wastewater treatment coagulant from fly ash with concomitant flue gas scrubbing

The research focused on the production of a complex wastewater coagulant containing polymeric sulfates of aluminum and iron from fly ash. At the same time, SO(2) in the simulated flu gas was removed by absorption in a fly ash slurry and oxidized with sodium chlorate. Extraction efficiency of iron and aluminum oxides from fly ash was affected greatly by reaction temperature and time. The extraction efficiency increases as temperature increases. Removal efficiency of SO(2) was influenced by temperature, SO(2) feed concentration and feed gas dispersing method. The produced complex coagulant containing both polymeric ferric sulfate (PFS) and polymeric aluminum sulfate (PAS) was proven to be effective in removing total suspended solids (TSS) and turbidity in wastewater. The complex coagulant is more effective than conventional iron and aluminum sulfates in turbidity removal.     

Ni-Cr-Mo-Nb超音速火焰喷涂层在模拟烟气中的热腐蚀行为

选用适量的Ni,Cr,Mo和Nb的配比,在20钢表面超音速火焰喷涂了Ni-Cr-Mo-Nb合金层,以期提高其耐蚀性。采用XRD,SEM/EDS技术对Ni-Cr-Mo-Nb合金层及其高温腐蚀产物成分、形貌进行了分析;对Ni-Cr-Mo-Nb合金层涂覆75%Na_2SO_4+25%NaCl(质量分数)混合熔盐后于600,650℃烟气中的热腐蚀行为进行了研究。结果表明:Ni-Cr-Mo-Nb合金层结构致密,孔隙率低;Ni-Cr-Mo-Nb合金层在涂覆75%Na2SO4+25%Na Cl盐膜后的烟气中600,650℃时先增重后失重,其腐蚀产物分为2层,外层富含Ni,内层富含Cr且S含量较高,具有良好的耐蚀性能。     

Kinetics of gas-liquid reaction between NO and Co(NH3)6(2+)

Wet ammonia desulphurization process can be retrofitted for combined removal of SO2 and NO from the flue gas by adding soluble cobalt(II) salts into the aqueous ammonia solutions. The Co(NH3)6(2+) formed by ammonia binding with Co2+ is the active constituent of scrubbing NO from the flue gas streams. A stirred vessel with a plane gas-liquid interface was used to measure the chemical absorption rates of nitric oxide into the Co(NH3)6(2+) solution under anaerobic and aerobic conditions separately. The experiments manifest that the nitric oxide absorption reaction can be regarded as instantaneous when nitric oxide concentration levels are parts per million ranges. The gas-liquid reaction becomes gas film controlling as Co(NH3)6(2+) concentration exceeds 0.02 mol/l. The NO absorption rate is proportional to the nitric oxide inlet concentration. Oxygen in the gas phase is favorable to the absorption of nitric oxide. But it is of little significance to increase the oxygen concentration above 5.2%. The NO absorption rate decreases with temperature. The kinetic equation of NO absorption into the Co(NH3)6(2+) solution under aerobic condition can be written as.     

Multi-pollutants simultaneous removal from flue gas

The multi-stage humidifier semi-dry flue gas cleaning technology, the CRS plasma flue gas cleaning technology and oxidative additive flue gas cleaning technology were investigated for multi-pollutants removal. The semi-dry flue gas cleaning technology using multistage humidifier and additive can improve oxidation and absorption, and it can achieve high multi-pollutants removal efficiency. The CRS discharge can produce many OH radicals that promote NO oxidation. Combining NaOH absorption can achieve high deSO2 and deNOx efficiencies. It is very fit of the reconstruction of primary wet flue gas desulfurization (WFGD). In addition, Using NaClO2 as additive in the absorbent of WFGD can obtain very high removal efficiency of SO2 and NOx.     

中温干法烟气脱硫反应器中脱硫剂颗粒磨耗过程的数值模拟

针对循环流化床中温干法烟气脱硫技术中存在的由于脱硫剂颗粒磨耗而引起钙利用率偏低的问题,在多流体模型的基础上,采用能够描述颗粒尺度分布变化过程的直接积分矩方法,对脱硫剂颗粒在中温干法烟气脱硫反应器内的流动扩散以及磨耗情况进行数值模拟,获得颗粒尺度分布随时间的变化过程。结果表明,直接积分矩法-多流体模型能够有效地模拟脱硫剂颗粒在反应器内的流动扩散以及磨耗破碎过程,对于循环流化床中温干法烟气脱硫技术的完善具有重要的意义。     

Evaluation of various additives on the preparation of rice husk ash (RHA)/CaO-based sorbent for flue gas desulfurization (FGD) at low temperature

This paper examines the effectiveness of 10 additives toward improving SO2 sorption capacities (SSC) of rice husk ash (RHA)/lime (CaO) sorbent. The additives examined are NaOH, CaCl2, LiCl, NaHCO3, NaBr, BaCl2, KOH, K2HPO4, FeCl3 and MgCl2. Most of the additives tested increased the SSC of RHA/CaO sorbent, whereby NaOH gave highest SSC (30mg SO2/g sorbent) at optimum concentration (0.25mol/l) compared to other additives examined. The SSC of RHA/CaO sorbent prepared with NaOH addition was also increases from 17.2 to 39.5mg SO2/g sorbent as the water vapor increases from 0% RH to 80% RH. This is probably due to the fact that most of additives tested act as deliquescent material, and its existence increases the amount of water collected on the surface of the sorbent, which played an important role in the reaction between the dry-type sorbent and SO2. Although most of the additives were shown to have positive effect on the SSC of the RHA/CaO sorbent, some were found to have negative or insignificant effect. Thus, this study demonstrates that proper selection of additives can improve the SSC of RHA/CaO sorbent significantly.