An investigation of reaction furnace temperatures and sulfur recovery

In a modern day sulfur recovery unit (SRU), hydrogen sulfide (H₂S) is converted to elemental sulfur using a modified Claus unit. A process simulator called TSWEET has been used to consider the Claus process. The effect of the H₂S concentration, the H₂S/CO₂ ratio, the input air flow rate, the acid gas flow of the acid gas (AG) splitter and the temperature of the acid gas feed at three different oxygen concentrations (in the air input) on the main burner temperature have been studied. Also the effects of the tail gas ratio and the catalytic bed type on the sulfur recovery were studied. The bed temperatures were optimized in order to enhance the sulfur recovery for a given acid gas feed and air input. Initially when the fraction of AG splitter flow to the main burner was increased, the temperature of the main burner increased to a maximum but then decreased sharply when the flow fraction was further increased; this was true for all three concentrations of oxygen. However, if three other parameters (the concentration of H₂S, the ratio H₂S/CO₂ and the flow rate of air) were increased, the temperature of the main burner increased monotonically. This increase had different slopes depending on the oxygen concentration in the input air. But, by increasing the temperature of the acid gas feed, the temperature of the main burner decreased. In general, the concentration of oxygen in the input air into the Claus unit had little effect on the temperature of the main burner (This is true for all parameters). The optimal catalytic bed temperature, tail gas ratio and type of catalytic bed were also determined and these conditions are a minimum temperature of 300°C, a ratio of 2.0 and a hydrolysing Claus bed.     

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.     

液硫脱气与克劳斯尾气处理

采用三氧化二铝或二氧化硅固体催化剂进行的最新实验室研究表明,H2Sx先在催化剂表面的碱性位分解为H2S,然后被吹扫气从液硫中驱除出去.由于H2S从气相返回液相的传质是一个有限的过程,从理论上讲,这预示着可利用克劳斯尾气作为吹扫气.试验还揭示,在涂有三氧化二铝的堇青石上,脱气期间尾气中约60％的H2S和SO2转化为元素硫.这预示着(例如)可在硫冷凝器管内衬入涂有三氧化二铝的堇青石管,以在脱气的同时提高总转化率.     

Modeling and simulation of non-isothermal catalytic packed bed membrane reactor for H2S decomposition

The recovery of H₂ from H₂S is an economical alternative to the Claus process in petroleum and minerals processing industries. Previous studies [React. Kinet. Catal. Lett. 62 (1997) 55; Catal. Lett. 37 (1996) 167] have demonstrated that catalytic decomposition of H₂S over bimetallic sulfide can proceed at relatively higher rates than over mono-metallic systems due to chemical synergism although conversions are still thermodynamically limited. In the present study, the performance of a catalytic membrane reactor containing a packed bed of Ru–Mo sulfide catalyst has been investigated with a view to improving H₂ yield beyond the equilibrium ceiling. A system of differential equations describing the non-isothermal reactor model has been solved to examine the effect of important hydrodynamic and transport properties on conversion. The results were obtained using a Pt-coated Nb membrane tube as the catalytic reactor enclosed in a quartz shell cylinder. Reynolds number for shell and tube side (Re^s and Re^t) as well as the modified wall Peclet number, Pe_m, dramatically affect H₂S conversions. Membrane reactor conversion rose monotonically with axial distance exceeding the equilibrium conversion by as much as eight times under some conditions.     

Selective catalytic reduction of sulfur dioxide with hydrogen to elemental sulfur over Co---Mo/Al2O3

The selective reduction of sulfur dioxide with hydrogen to elemental sulfur was studied over Co---Mo/Al₂O₃. When the feed conditions were properly optimized (SO₂/H₂ mole RATIO = 1:3), a sulfur yield of about 80% was achieved at temperatures around 300°C. The temperature is the lowest that has been reported so far for any catalyst for this reaction. The catalytic activity remained high and stable after presulfiding with 10% H₂S in hydrogen. Little influence on the catalytic activity was observed if the water content in the feed was kept below 11 vol.-%. The overall reaction consisted of two individual steps occurring on two different sites; sulfur dioxide was first hydrogenated to hydrogen sulfide on the metal sulfide phase, then followed by the Claus reaction of hydrogen sulfide with sulfur dioxide to produce elemental sulfur on the acidic sites of the alumina support.     

10MWth高硫石油焦化学链气化制合成气耦合硫磺回收新系统模拟研究

基于化学链气化技术依靠气固反应定向调控气化产物中H₂S和SO₂摩尔比为2的优势，将化学链气化与Claus工艺中的催化转化单元相结合，提出了高硫石油焦化学链气化制合成气和回收硫磺的新系统。针对系统核心单元，即化学链气化过程，基于Aspen Plus，开展热输入10 MW_th的高硫石油焦化学链气化过程模拟，以赤铁矿石为载氧体，水蒸气为气化介质，重点考察了氧碳比、气化温度对化学链气化过程及硫转化过程的影响。结果发现，氧碳比的增大导致合成气产率显著降低，但系统从需要外部提供能量逐渐转变为对外部放热，在氧碳比0.8669～0.9535区间内，系统可以达到热量自平衡。同时，气化温度的提高对合成气产率是有利的，在975℃时达到2.15 m³/kg，主要是由于CO体积分数随气化温度增加而增加。氧碳比和气化温度的提高都会导致H₂S浓度的降低和SO₂浓度的提高。并且研究了当H₂S和SO₂摩尔比为2的最佳工况时，氧碳比和气化温度为反相关，其中氧碳比为0.8669，气化温度为900℃时，冷煤气效率为64.09%。     

Sulfur exchange on Co---Mo/Al2O3 hydrodesulfurization catalyst using S radioisotope tracer

A commercial Co---Mo/Al₂O₃ catalyst was labeled with the radioisotope ³⁵S in hydrodesulfurization (HDS) of ³⁵S-labeled dibenzothiophene (³⁵S-DBT) in a high-pressure flow reactor at 50 kg/cm². Then, HDS of 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) or sulfur exchange of H₂S were carried out on the labeled catalyst at 50 kg/cm² and 260–360°C. The amounts of labile sulfur participating in the reaction were determined from the radioactivity of ³⁵S---H₂S released from the ³⁵S-labeled catalyst. In the HDS reactions, the amount of labile sulfur participating in the reaction decreased in the order: DBT> 4-MDBT> 4,6-DMDBT. In the sulfur exchange reaction with H₂S, the adsorption of H₂S on the catalyst reached saturation above a H₂S partial pressure of 0.36 kg/cm². It was suggested that the release of H₂S from the labile sulfur may be the rate determining step of the HDS reaction.     

Microbial removal of sulfur dioxide from a gas stream

A study of the feasibility of utilizing the Thiobacillus ferrooxidans or Desulfovibrio desulfuricans bacterium for microbial removal of sulfur dioxide from flue gases has been carried out. Sulfur dioxide may be readily reduced to H₂S by contact with sulfate-reducing microorganisms in which Desulfovibrio desulfuricans were dominant in the first stage. The H₂S was then oxidized to sulfur by the ferric sulfate in a second stage where ferrous ions were regenerated. These results were compared to microbial oxidation of SO₂ from flue gases to sulfate by Thiobacillus ferrooxidans. The mechanisms for the reduction of SO₂ to H₂S in the presence of Desulfovibrio desulfuricans and the oxidation of SO₂ to H₂SO₄ in the presence of ferric sulfate and Thiobacillus ferrooxidans are discussed. Sulfuric acid or gypsum CaSO₄ · 2H₂O are byproducts from microbial flue gas desulfurization.     

Microbial reduction of sulfur dioxide and nitric oxide

Two process concepts have been developed for a microbial contribution to the problem of flue gas desulfurization and NO_x removal. We have demonstrated that the sulfate-reducing bacterium Desulfovibrio desulfuricans can be grown in a mixed culture with fermentative heterotrophs in a medium in which glucose served as the only carbon source. Beneficial cross-feeding resulted in vigorous growth of D. desulfuricans, which used SO₂(g) as a terminal electron acceptor, with complete reduction of SO₂ to H₂S in 1–2 s of contact time. We have proposed that the concentrated SO₂ stream, obtained from regeneration of the sorbent in regenerable processes for flue gas desulfurization, could be split with two-thirds of the SO₂ reduced to H₂S by contact with a culture of sulfate-reducing bacteria. The resulting H₂S could then be combined with the remaining SO₂ and used as feed to a Claus reactor to produce elemental sulfur. However, the use of glucose as an electron donor in microbial SO₂ reducing cultures would be prohibitively expensive. Therefore, if microbial reduction of SO₂ is to be economically viable, less expensive electron donors must be found. Consequently, we have evaluated the use of municipal sewage sludge and elemental hydrogen as carbon and/or energy sources for SO₂ reducing cultures. Heat and alkali pretreated sewage sludge has been successfully used as a carbon and energy source to support SO₂ reduction in a continuous, anaerobic mixed culture containing D. desulfuricans. The culture operated for nine months with complete reduction of SO₂ and H₂S. Another sulfate-reducing bacterium, Desulfotomaculum orientis, has also been grown in batch cultures on a feed of SO₂, H₂ and CO₂. Complete reduction of SO₂ to H₂S was observed with gas-liquid contact times of 1–2 s. We have also demonstrated that the facultative anaerobe and chemoautotroph, Thiobacillus denitrificans, can be cultured anoxically in batch reactors using NO(g) as a terminal electron acceptor with reduction to elemental nitrogen. We have proposed that the concentrated stream of NO_x, as obtained from certain regenerable processes for flue gas desulfurization and NO_x removal, could be converted to elemental nitrogen for disposal by contact with a culture T. denitrificans. Two heterotrophic bacteria have also been identified which may be grown in batch cultures with succinate or heat and alkali pretreated sewage sludge as carbon and energy sources and NO as a terminal electron acceptor. These are Paracoccus denitrificans and Pseudomonas denitrificans.     

Catalytic synthesis of methanethiol from hydrogen sulfide and carbon monoxide over vanadium-based catalysts

The direct synthesis of methanethiol, CH₃SH, from CO and H₂S was investigated using sulfided vanadium catalysts based on TiO₂ and Al₂O₃. These catalysts yield high activity and selectivity to methanethiol at an optimized temperature of 615 K. Carbonyl sulfide and hydrogen are predominant products below 615 K, whereas above this temperature methane becomes the preferred product. Methanethiol is formed by hydrogenation of COS, via surface thioformic acid and methylthiolate intermediates. Water produced in this reaction step is rapidly converted into CO₂ and H₂S by COS hydrolysis.

Titania was found to be a good catalyst for methanethiol formation. The effect of vanadium addition was to increase CO and H₂S conversion at the expense of methanethiol selectivity. High activities and selectivities to methanethiol were obtained using a sulfided vanadium catalyst supported on Al₂O₃. The TiO₂, V₂O₅/TiO₂ and V₂O₅/Al₂O₃ catalysts have been characterized by temperature programmed sulfidation (TPS). TPS profiles suggest a role of V₂O₅ in the sulfur exchange reactions taking place in the reaction network of H₂S and CO.     

Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts

The interactions of H₂ and H₂S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H₂ and H₂S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H₂ and H₂S were enhanced, but the adsorption energy of H₂ increased more than that of H₂S, indicating that the adsorption of H₂S became less favorable compared with H₂ on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst.     

Preparation of Ru metal nanoparticles in mesoporous materials: influence of sulfur on the hydrogenating activity

Hydrogenating catalysts were prepared by inserting Ru into the pores of mesoporous Al-MCM-41 materials by selective adsorption of [Ru(NH₃)₆]³⁺. Ru/support catalysts were obtained after reduction with H₂. The activities of these catalysts in hydrogenation reactions were compared to those of Ru/HY and Ru/SiO₂. The catalytic properties in the absence of sulfur were tested in benzene hydrogenation, and the intrinsic activities of all the catalysts (either supported on mesoporous materials or on zeolites) were identical. It was concluded from this result that the dispersion of the Ru metallic phase was similar for all these catalysts. These samples were tested in the tetralin hydrogenation in pure H₂ and in the presence of H₂S (330 ppm of H₂S in H₂). They were found to be much less active than the zeolite-supported catalysts in the presence of H₂S. It is proposed that the lower activity of the catalysts supported on mesoporous materials is either due to their milder acidity, as evidenced by NH₃-TPD, cumene cracking and pyridine desorption experiments, or to the localization of the Ru nanoparticles on alumina islands.     

Resistance to sulfur poisoning of hot gas cleaning catalysts for the removal of tar from the pyrolysis of cedar wood

In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H₂S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO₂/SiO₂ using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H₂S. Steam reforming Ni catalyst was effective for the tar removal without H₂S addition, however, the addition of H₂S deactivated drastically. In contrast, Rh/CeO₂/SiO₂ exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H₂S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO₂/SiO₂, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis.     

Selective oxidation of H2S to elemental sulfur over chromium oxide catalysts

CrO_x and CrO_x supported on SiO₂ have been found to be active for the selective oxidation of hydrogen sulfide to elemental sulfur. The catalysts show maximum sulfur yield at a stoichiometric ratio of O₂/H₂S, 0.5. Amorphous Cr₂O₃ exhibits higher yield of sulfur and has stronger resistance against water than supported Cr/SiO₂, especially at low temperatures. At high temperatures above 300°C, the sulfur yield over the supported catalyst becomes similar to amorphous Cr₂O₃ because the Claus reaction occurring on the silica support removes SO₂ to increase the sulfur yield. Active sites are the amorphous monochromate species that can be detected as a strong temperature programmed reduction (TPR) peak at 470°C. Catalytic activity can be correlated with the amount of labile lattice oxygen and the strength of Cr–O bonding. The reaction proceeds via the redox mechanism with participation of lattice oxygen.     

锆基双金属氧化物催化剂硫中毒的研究

在工业二氧化碳加氢制甲醇过程中,硫化氢气体的引入将对该过程中使用的催化剂活性及稳定性带来负面的影响。基于此,采用微反应合成法成功制备了InZrO_x和ZnZrO_x锆基催化剂,并研究了在二氧化碳加氢反应中,硫化氢气体对锆基催化剂的结构性质及其催化性能的影响规律。结果表明,在T=573 K、p=3.0 MPa和GHSV=18 000 mL/(g_cat·h)条件下,仅通入二氧化碳/氢气反应气时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择性分别为7.2%、9.3%和93%、92%。在二氧化碳/氢气原料气中通入体积分数为5×10^-3硫化氢气体时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择性都降为0,这主要是因为硫化氢气体占据了氧空位,导致锆基双金属氧化物催化剂硫中毒失活。当停止通硫化氢气体时,InZrO_x和ZnZrO_x催化剂的二氧化碳转化率和甲醇选择...     

PASSIVATION OF MERCURY CONTAMINANTS IN PROCESS SYSTEMS

Mercury contamination from gas and condensate can cause concerns in the safe operation of LNG plants, LPG plants and naphtha crackers. The mercury contamination is tenacious and it is difficult to decontaminate the systems by clean gas or condensate purging. We have demonstrated in the laboratory that the systems contaminated with mercury, both from gas and liquids condensate, can be passivated effectively. The most effective passivation procedure is to discontinue the normal processing, remove the hydrocarbon from the system, inject H₂S gas into the system for adsorption and then flow with air, both at atmospheric pressure and room temperature. Because of its effectiveness, simplicity, and mild condition this process lends itself to held applications in the plants and storage tanks. The process could be implemented safely by handling H₂S carefully, injecting H₂S slowly and stopping H₂S injection as soon as the H₂S could be detected at the exit of the system.

The procedure involves three chemical steps. The H₂S is adsorbed on the Hg and then reacts with O₂ to form nascent sulfur [S], Finally, [S] reacts with Hg to form innocuous HgS. This procedure appears to be effective for all types of Hg compounds, including the organic mercury in the condensate.     

Development of sulfur tolerant catalysts for the synthesis of high quality transportation fuels

In this paper, results concerning the development of sulfur tolerant catalysts for Fischer–Tropsch synthesis (FTS), C₂₊ alcohol synthesis, methanol and/or DME synthesis are presented. In the FTS reaction on Fe using H₂-rich syngas such as the biomass-derived syngas, the composition of catalyst pretreatment gas and the addition of MnO on Fe had strong impacts on its sulfur resistance as well as activity. Especially the Fe/MnO catalyst pretreated with CO showed a much lower deactivation rate and a higher FTS activity than an Fe/Cu/K catalyst in the presence of H₂S. For C₂₊ alcohol synthesis a novel preparation method was developed for a highly active MoS₂-based catalyst that is well known as the sulfur tolerant catalyst. Besides some metal sulfides were found to show higher CO hydrogenation activities than MoS₂. In particular, both Rh and Pd sulfides were active and selective for the methanol synthesis. Modified Pd sulfide catalyst, i.e. sulfided Ca/Pd/SiO₂, showed an activity that was about 60% of that of a Cu/ZnO/Al₂O₃ catalyst in the absence of H₂S. This catalyst preserved 35% of the initial activity even in the presence of H₂S. The sulfided Ca/Pd/SiO₂ mixed with γ-Al₂O₃ was also available for in situ DME synthesis in the presence of H₂S.     

Aspen Plus模拟高浓度H2S/CO2酸性气的选择性分离

以煤制氢尾气中的高浓度酸性气体H₂S和CO₂为对象,以聚乙二醇二甲醚（NHD）为吸收剂,使用PC-SAFT状态方程拟合了酸性气体CO₂和H₂S在聚乙二醇二甲醚（NHD）溶剂中溶解参数,运用Aspen Plus流程模拟软件,构建两级吸收分离工艺,实现H₂S和CO₂的高效分离,H₂S浓度由30%提升至98.7%,CO₂含量由55%提升至99.4%。由此,可以通过高效分离酸性气H₂S和CO₂,并以提浓后再资源化利用的方式实现酸性气的污染控制。     

化学链燃烧中H2S对NiFe2O4氧载体活性的影响机理

采用密度泛函理论方法研究H₂S与NiFe₂O₄（001）完整表面和氧缺陷表面的相互作用机理。结果表明,H₂S在NiFe₂O₄氧载体表面Ni原子位的吸附能比其在Fe原子位的吸附能大。氧缺陷的形成会使H₂S在氧载体表面金属原子位的吸附能增大,并且Ni原子位吸附H₂S的吸附能增加更为明显。因而,NiFe₂O₄氧载体表面的Ni原子位是H₂S的主要吸附位。同时采用热力学方法进一步研究含H₂S的合成气与NiFe₂O₄氧载体之间的反应,发现H₂S与氧载体的反应产物与氧载体的还原程度密切相关。由于铁氧化物的深度还原过程受到热力学限制,H₂S与NiFe₂O₄氧载体反应的主要产物为Ni₃S₂。密度泛函理论方法与热力学方法研究结果均表明H₂S倾向于与NiFe₂O₄氧载体中Ni发生相互作用,这将对NiFe₂O₄氧载体的反应性能产生不利影响。     

SIMULTANEOUS ABSORPTION OF H2S AND CO2 INTO A SOLUTION OF SODIUM CARBONATE

The simultaneous absorption of H₂S and CO₂ has been studied both experimentally and theoretically. A model has been developed which predicts the absorption rates of H₂S and CO₂ into a sodium carbonate solution. The absorption rates are calculated according to the two-film theory. In the liquid film, the finite rate of the CO₂ reaction was considered. Otherwise, in the liquid film as well as in the liquid bulk, equilibrium conditions for all reactions were assumed. Absorption experiments were performed on a packed column using a counter-flow strategy. In the experiments the influence of the initial carbonate concentration, the gas flow rate and the temperature on the removal efficiencies of H₂S and CO₂ and the selectivity of H₂S were investigated. It is desirable to absorb the H₂S but not the CO₂. The agreement between the absorption model and the experimental results from the absorber tower was satisfactory. The mass transfer coefficients were determined by fitting the experimental data to the model with respect to the H₂S and CO₂ content in the outgoing gas. The H₂S content was used to determine the gas side mass transfer coefficient and the CO₂ content was used to determine the liquid side mass transfer coefficient, The effective contact area of mass transfer was taken from published data. With a constant packing height, both the experiments and the model indicated that high carbonate concentration benefits the removal efficiency of H₂S. Higher gas flow rate also benefits the selectivity for H₂S. However, the removal efficiency will decrease. At higher temperatures the selectivity and the removal efficiency of H₂S decreased. Under the conditions investigated, the absorption of H₂S was essentially controlled by gas-side mass transfer and the absorption of CO₂ was controlled by liquid-side mass transfer