Investigation of sour gas desulfurization process by nano absorber and under magnetic field in a packed tower; experimentally and theoretically

ABSTRACT

Hydrogen sulfide is a major contaminant that is expelled into the atmosphere by chemical industry. So, the mechanism for absorption of sulfur from sour gas by carbon nano-tubes in a packed bed under a magnetic field is considered, in this paper. Therefore, empirical and theoretical studies have been done to obtain the sulfur content in the outlet gas stream. The independent variables studied in this paper include: the magnetic field (1.5 amperes), initial sulfur content (0, 0.003, 0.008, 0.013, 0.05 and 0.1?mole/m³) and gas temperature (33°C, 37°C and 40°C). The gas flow rate is (0.18, 0.2 and 0.22?m³/min). The minimum amount of hydrogen sulfide in the output stream is selected as the aim of the experiments and related conditions as optimal operating conditions. Results indicate that the sulfur oxidation curves contains an approximately linearly increasing segment when the applied field intensity increases from 90 to 160?Oe, and that the sulfur oxidation percentage is improved by nearly 5.8% when the magnetic field is increased from 90 to 400?Oe. Obtained results state the optimum flow rate and temperature for maximum desulfurization is 0.22?m³/min and 40°C, respectively. Results show, the increase in the initial concentration under the operating temperature and magnetic field increases the effective mass transfer coefficient from 2.2–8.3. In addition the effective mass flux of hydrogen sulfide removal can be extended to 5.9, in this state. Finally, the experimental results have a fairly good fit with theoretical results.     

Catalyst modification and process design considerations for the oxidation of low concentrations of hydrogen sulfide in natural gas

Low concentrations of hydrogen sulfide (H₂S) in natural gas can be selectively oxidized over an activated carbon catalyst to elemental sulfur, water and a small fraction of sulfur dioxide (SO₂). Efforts to improve catalyst performance and product sulfur quality have been made by a) modification of the catalyst composition b) removal of the heavy hydrocarbons from the feed and c) choice of reaction conditions. The use of a guard bed to absorb heavy hydrocarbons and operation at elevated pressures show positive results. A preliminary flow diagram incorporating these findings has been prepared for a small commercial unit capable of processing sour natural gas containing 1.0% H₂S.     

Hydrogen sulphide emission control by combined adsorption and catalytic combustion

The removal of low concentrations of hydrogen sulfide by adsorption and catalytic combustion has been studied. Concentration of hydrogen sulfide by adsorption from waste-gas streams is best effected by molecular sieve 13X, if the stream is dry, and by activated carbon, if the gas stream is moist.

Low-temperature catalytic oxidation of hydrogen sulphide in moist gas streams can be effected over activated carbon. The reaction appears to involve ionized hydrogen sulfide, dissolved in water condensed in the pores of the carbon.

At high temperatures, both supported platinum and palladium catalysts are found to be oxidation catalysts. Palladium is the best catalyst for methane oxidation but is partially deactivated in the presence of sulfur-containing gases. In contrast, platinum was more active for the same reaction in the presence of sulfur-containing gases.

Both metals were found to promote the oxidation of hydrogen sulfide above ca. 150°C. The power rate laws describing the kinetics of reaction were determined.     

The fate of methane in a claus plant reaction furnace

Experimental kinetic data are reported for key side reactions occurring in the front end [i. e. the reaction furnace (RF) and the waste heat boiler (WHB)] of modified Claus plants used for sulfur recovery from the sour gases evolved in the treatment of natural gas. An extensive experimental study was conducted in a high temperature tubular reactor system for two important homogenous gas‐phase reactions. Firstly, experiments were carried out to study the oxidation of hydrogen sulfide and methane mixtures in the presence of oxygen. Secondly, the reaction between methane and sulfur dioxide was investigated experimentally. These results showed that methane was much less competitive for oxygen than hydrogen sulfide. Hence, in a partially oxidizing environment of a RF, data showed that methane reacted significantly with other major sulfur containing species, as secondary reactions, to form COS and especially CS². This is highly problematic from an environmental point of view.     

Recycling of FGD gypsum to calcium carbonate and elemental sulfur using mixed sulfate-reducing bacteria with sewage digest as a carbon source

A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes sewage digest as its carbon source to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated to calcium carbonate using carbon dioxide. Employing anaerobically digested-municipal sewage sludge (AD-MSS) medium as a carbon source, SRB in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg dm⁻³ h⁻¹ (10⁹ cells)⁻¹. A chemostat with continuous addition of both AD-MSS medium and gypsum exhibited sulfate reduction rates as high as 1·3kg FGD gypsumm⁻³ day⁻¹. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO₄ dm⁻³ h⁻¹ or 6·6kg FGD gypsum m⁻³ day⁻¹. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and as high as 70% COD utilization. Calcium carbonate was recovered from the reactor effluent upon precipitation using carbon dioxide. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.     

A new approach for hydrogen production in Claus sulfur recovery process

In this study, the decomposition of hydrogen sulfide and reforming of hydrocarbons were employed for producing hydrogen. Thermolysis of H₂S in the platinum-based catalytic reactor led to the production of hydrogen and sulfur. It is observed that the presence of catalyst increased the conversion of H₂S decomposition up to 99.6%. Also, the hydrocarbon content of acid gas stream (CH₄) was converted to syngas, especially hydrogen in a catalytic reforming process. The produced hydrogen was separated using a Pd/Ag membrane. The simulation results showed that hydrogen production in a sulfur recovery unit provided a green source of energy by incinerating gasses. By hydrogen production during the process, the molar flow rate of incinerating gasses reduced from 2555 to 621?Kmol/h. Moreover, the hazardous sulfur compounds of the stack were removed, while hydrogen was produced by 256?Kmol/hr.     

Electrochemical Separation of Hydrogen Sulfide from Natural Gas

Abstract

An electrochemical process has been developed for the removal of H₂S from contaminated natural gas. Removals as high as 80.7% have been achieved from a simulated process gas (2000 ppm H₂S). H₂S is removed by reduction to the sulfide ion and hydrogen gas at the cathode. The sulfide ion migrates to the anode through a molten electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. No materials are required beyond initial electrolyte membrane installation; the H₂S is converted in one step to elemental sulfur making it an economically attractive process both from the lack of raw materials and the lack of any solvent regeneration.     

液化天然气工厂天然气净化工艺的选择

介绍了天然气中水分、硫化氢、二氧化碳、重烃、汞及氮气等杂质对LNG工厂液化的影响,以及天然气的净化工艺.根据某公司液化天然气工厂天然气来源变化,说明天然气的组成对天然气净化工艺选择的影响.     

Effect of CaSO4 Pelletization Conditions on a Novel Process for Converting SO2 to Elemental Sulfur by Reaction Cycles Involving CaSO4/CaS – Part II: Reduction of SO2 with CaS

A new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and calcium sulfate without generating secondary pollutants, developed at the University of Utah, was described in Part I of this series. In this process, sulfur dioxide is reacted with calcium sulfide to produce elemental sulfur and calcium sulfate; the latter is reduced by hydrogen to regenerate calcium sulfide. Here, in Part II, the effects of different pelletization conditions for the initial reactant calcium sulfate on the reactivity of CaS pellets produced from calcium sulfate pellets toward sulfur dioxide were studied. Experiments were performed to investigate the effects of temperature in the range 1023–1173 K, pellet size, cycle repetition, and water vapor or carbon dioxide content in the sulfur dioxide stream. The binder amount and the presence of nickel catalyst did not significantly affect the reaction rate.     

Biofiltration control of pulping odors – hydrogen sulfide: performance,macrokinetics and coexistence effects of organo‐sulfur species

The work reported here describes the aerobic biodegradation of reduced sulfur compound mixtures in air streams by biofilters. Rates of removal of hydrogen sulfide as a sole substrate and in the presence of organo‐sulfur compounds were determined to see if there were any inhibitory effects of the organo‐sulfur compounds on the rate of hydrogen sulfide removal. Experiments were conducted in three bench‐scale biofilters packed with the mixtures of compost/perlite (4:1), hog fuel/ perlite (4:1), and compost/hog fuel/perlite (2:2:1), respectively. Hydrogen sulfide, the predominant odorous gas produced from kraft pulping processes, was used as the main pollutant (substrate). Other organo‐sulfur species (dimethyl sulfide and dimethyl disulfide), also emitted from kraft pulp mills, were used as competing (secondary) substrates in the waste gas stream. To describe rates of removal a Michaelis–Menten type kinetic equation was modified to incorporate the plug flow behavior of biofilters, and used in evaluating the pseudo‐kinetic parameters, V_max (the maximum removal rate) and K_m (the half saturation concentration), for hydrogen sulfide biodegradation, and the type of macrokinetic competition between hydrogen sulfide and the organo‐sulfur compounds. No significant differences in V _max for the three biofilters were observed. The V _max ranged between 136 and 147 g m⁻³ h ⁻¹, while the K_m varied from 44 to 59 ppmv for the three biofilters. Hydrogen sulfide elimination capacity was not affected by the presence of any of the organo‐sulfur species in all of the three biofilters, confirming earlier results that hydrogen sulfide removal in biofilters is independent of the presence of organo‐sulfur compounds mainly because of its easy biodegradability. © 1999 Society of Chemical Industry     

Removal of sulfur inorganic compounds by a biofilm of sulfate reducing and sulfide oxidizing bacteria in a down‐flow fluidized bed reactor

BACKGROUND: Biological sulfate removal is a process based on the biological sulfur cycle that consists of two steps: (1) production of sulfide by sulfate reduction; and (2) biological or physico‐chemical sulfide oxidation to elemental sulfur (S⁰). The objective of this work was to transform soluble sulfur (sulfate) into insoluble sulfur (elemental sulfur) coupling sulfate reduction and sulfide oxidation in one reactor. To accomplish this, a 2.3 L down‐flow fluidized bed reactor was used. Lactate was supplied as electron donor, sulfate and oxygen (air) were the electron acceptors. RESULTS: After 55 days of batch operation a biofilm with sulfate reducing and sulfide oxidizing activities was developed over a plastic support. Continuous operation for 90 days at a down‐flow superficial velocity of 7.7 m h^?1 and 30 °C, showed that sulfate reduction amounted to 72–77% and carbon removal to 20–31%. Under low aeration rates (2.3 L d^?1) 50% of the sulfate was transformed to elemental sulfur, when aeration increased to 5.4 L d^?1 elemental sulfur recovery was only 30% and sulfide in the effluent amounted to 27% of the sulfur fed. CONCLUSION: It was possible to obtain elemental sulfur through a coupled anaerobic/aerobic process in one reactor using lactate, sulfate and oxygen (air) as substrates. The development of a biofilm with sulfate reducing and sulfide oxidizing activities was the key of the process. Copyright © 2007 Society of Chemical Industry     

活性炭担载金属氧化物用于热煤气脱硫

以热煤气脱硫并回收单质硫为目的,考察了活性炭担载金属氧化物(M/AC)在中温范围150—250℃内,催化氧化硫化氢生成单质硫的研究。担载量1%(质量分数)的M/AC通过等体积浸渍法制得,在固定床上评价了其脱硫活性,并考察了温度、反应气氛等工艺条件对脱硫效果的影响。M/AC脱硫的活性顺序为:Mn/ACCu/ACCe/ACFe/ACCo/ACV/AC。通过DTG分析,硫化氢选择性氧化的主要产物是单质硫。M/AC上金属氧化物起主要的催化作用,催化硫化氢和氧气反应生成单质硫,生成的单质硫被吸附在活性炭的孔道中。     

微生物培养液脱H2S及副产物的性质

以氧化亚铁硫杆菌培养液和酸性Fe2（SO4）3溶液为吸收剂,采用优化的工艺条件进行了H2S的脱除实验,并对微生物培养液脱H2S后的副产物硫磺的相关性质进行了测定分析,以期为工业应用中硫磺回收工艺的设计提供参考。实验结果表明：采用微生物培养液脱H2S比单纯使用酸性Fe2（SO4）3溶液的效果好,反应进行45 min后,脱硫率仍可保持在90%以上;微生物培养液脱H2S后的副产物硫磺颗粒不溶于水,微溶于乙醇,完全溶于二硫化碳和四氯化碳,密度为1. 90 g·cm-3,熔点为121℃;该颗粒为不规则球形,在溶液中极易发生团聚现象,加入分散剂后测得平均粒径为5. 09 μm;该副产物硫磺具有亲水性,在工业应用上优于具有疏水性的升华硫和酸性Fe2（SO4）3溶液脱H2S产生的硫;该副产物硫颗粒在溶液中的沉降速度为0. 125×10-2 m·s-1。     

SULFUR RECOVERY WITH REDUCED EMISSIONS, LOW CAPITAL INVESTMENT AND HYDROGEN CO-PRODUCTION

The main disadvantage of the Claus process is that by introducing air as oxidant a large volume of tail gas is produced. This must be treated to reduce atmospheric emissions of sulfur-containing gases. The costs of the tail-gas unit are a significant fraction of the total capital and operating costs for sulfur recovery. A new process uses thermal decomposition of hydrogen sulfide in the presence of carbon dioxide instead of air oxidation. The products of this reaction are hydrogen, carbon monoxide, elemental sulfur, water vapor and carbonyl sulfide. Carbonyl sulfide is easily converted to H₂S and C0₂ by liquid- or vapor-phase hydrolysis. Unreacted H₂S and C0₂ are recovered by absorption and recycled to the reactor. Since no air is introduced, there is no tail gas and the tail-gas unit is eliminated, giving a substantial reduction in capital investment. The concentrations of sulfur-containing gases in the product streams depend only on the operation of the absorber and stripper units and can be controlled to very low levels by increasing stripper boil-up. Process operating costs depend on the level of sulfur recovery required and can also be much lower than those of the modified Claus Process.

The process chemistry depends on a shift in the equilibrium of H₂S decomposition caused by reaction of hydrogen with C0₂ by the reverse of the water-gas-shift reaction. Catalysts for this chemistry have been identified. Reactor conversion is further improved by rapid cooling of the reactor effluent gas. Other aspects of process design and operation confer further advantages with respect to the Claus process; however, the process equipment used is similar to that used in a Claus plant. Retrofit of existing plant to the new technology can therefore be considered.     

Sulfur poisoning in the nickel catalyzed gasification of activated carbon in hydrogen

The effect of hydrogen sulfide on the catalytic activity of nickel has been investigated in the hydrogasification of activated carbon. The low-temperature gasification activity in the range of 400–700° C was seriously suppressed when hydrogen sulfide was added to the hydrogen stream. The carbon conversion in this temperature region was approx. 75,50,20 and 0 % for hydrogen sulfide concentration of 0,20,50 and 100 ppm. respectively. A similar deactivation was observed even in pure hydrogen if the catalyst had been previously treated with hydrogen sulfide. On the other hand, the retardation effect was much smaller in the temperature region higher than 900° C. and the original activity was easily reproduced when the catalyst was exposed to pure hydrogen. The sulfur problems in the catalytic gasification of activated carbon are discussed in connection with the gasification of coal.     

活性炭的改性条件及其对硫化氢吸附性能的影响

以工业活性炭为载体制备改性活性炭,对比研究了未改性活性炭,NaOH、Na2CO3、Fe(NO3)3、Cu(Ac)2改性活性炭及挂膜硫氧化细菌后活性炭在相同条件下对硫化氢穿透时间及吸附容量的影响。结果表明：在相同控制条件下,NaOH改性活性炭明显优于其它改性剂;不同梯度改性剂条件下,20% NaOH改性活性炭对硫化氢的吸附效果最好,吸附穿透容量为78.25 mg/g,穿透时间可以达到2000 min以上;不同改性剂挂膜硫氧化细菌后对硫化氢均有一定的处理效果,其中对已达到饱和吸附的NaOH改性活性炭挂膜后的再生效果可以达到100%以上,说明挂膜硫氧化细菌活性炭对硫化氢的处理具有很好的效果。     

天然气生物脱硫技术研究进展

天然气作为绿色、高效的优质清洁能源,在我国能源结构中所占比例日益增加。因为天然气中含有一定量的有毒有害气体硫化氢,所以天然气在使用之前就需要脱除其中的硫化氢气体。生物脱硫是利用微生物脱除气体和废水中的含硫化合物,具有操作条件温和、能量消耗低、环境污染小、脱硫效率高、副产生物硫黄等优势。因此,天然气生物脱硫技术已成为天然气净化研究的热点之一。本文首先介绍了天然气中硫化氢气体的主要来源,回顾了工业上广泛应用的天然气脱硫技术（克劳斯法脱硫和络合铁法脱硫）;随后阐述了生物脱硫的主要菌种以及脱硫机理,并重点介绍了天然气生物脱硫技术的典型工艺（Bio-SR脱硫和Shell-Paques脱硫）和新型工艺 （嗜盐嗜碱生物脱硫）;最后指出了天然气生物脱硫技术的发展方向。     

H2S adsorption/oxidation on unmodified activated carbons: importance of prehumidification

Three microporous activated carbons supplied by Norit^® (of peat and bituminous coal origin) were used in this study as hydrogen sulfide adsorbents. Their surface properties were evaluated by means of nitrogen adsorption, Boehm titration, potentiometric titration, and thermal analysis. The results show that the carbons significantly differ in their pore structure and surface chemistry. This is reflected in their hydrogen sulfide breakthrough capacity. The breakthrough capacity is underestimated when not enough water is adsorbed on the carbon surface. The performance follows the expectations after extensive humidification of the sorbents’ surfaces. Moderately low pH in the acidic range of coal-based carbon, Vapure 612, promotes the oxidation of H₂S to sulfur oxides which is important from the point of view of water regeneration. The high pH of peat-based carbon, RB 4, results in H₂S oxidation to elemental sulfur.     

Electrochemical polishing of hydrogen sulfide from coal synthesis gas

An advanced process has been developed for the separation of H₂S from coal gasification product streams through an electrochemical membrane. This technology is developed for use in coal gasification facilities providing fuel for cogeneration coal fired electrical power facilities and molten carbonate fuel cell (MCFC) electrical power facilities. H₂S is removed from the syn-gas by reduction to the sulfide ion and hydrogen gas at the cathode. The sulfide ion migrates to the anode through a molten salt electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. The syn-gas is enriched with the hydrogen. Order of magnitude reductions in H₂S have been repeatedly recorded (100 ppm to 10 ppm H₂S) on a single pass through the cell. This process allows removal of H₂S without cooling the gas stream and with negligible pressure loss through the separator. Since there are no absorbents used, there is no absorption/regeneration step as with conventional technology. Elemental sulfur is produced as a byproduct directly, so there is no need for a Claus process for sulfur recovery. This makes the process economically attractive since it is much less equipment intensive than conventional technology.     

New effective catalysts based on mesoporous nanofibrous carbon for selective oxidation of hydrogen sulfide

The systems based on granular mesoporous nanofibrous carbonaceous (NFC) materials synthesized by decomposition of hydrocarbons over nickel-containing catalysts are promising catalysts for selective oxidation of hydrogen sulfide. Sample series of nanofibrous carbon with three main types of their fiber structures and different contents of metal catalysts inherited from the catalysts for their synthesis were studied in this reaction. The correlation between NFC structure and its activity and selectivity in hydrogen sulfide oxidation was determined. The metal inherited from the initial catalysts for the synthesis of NFC influences the activity and selectivity of the resulting carbon catalysts. A particular influence is observed in the case of the catalyst withdrawn from the synthesis reactor at the stage of stationary operation of the metal catalyst (low specific carbon yields per unit weight of the catalyst). The presence of the metal phase results in an increase in the carbon catalyst activity and in a decrease in the selectivity to sulfur. NFC samples with the highest activity and selectivity are nanotubes and those with graphite planes perpendicular to the axis of the fibers. Carbon nanotubes have high selectivity, while samples obtained on copper–nickel catalysts also possess high activity. The promising NFC catalysts provide high conversion and selectivity (almost independent of the molar oxygen/hydrogen sulfide ratio) when a large excess of oxygen is contained in the reaction mixture.