Removal of hydrogen sulfide from a steam-hydrogasifier product gas by zinc oxide sorbent: Effect of non-steam gas components

Removal of H₂S from a steam-hydrogasifier product gas was studied at 636 K and 1 atm using a commercially available zinc oxide sorbent in a packed-bed reactor. A mixture gas containing 22% CH₄, 18.7% H₂, 8.8% CO and 5.5% CO₂ (non-steam components subtotaling to 55%) balanced with steam was used to simulate the steam-hydrogasifier product gas. Sorbent particles of 150–250 μm size were used to eliminate the effect of intraparticle mass transfer limitation. Experiments were conducted to monitor H₂S breakthrough of reactor effluent stream for operation parameters such as space velocity and inlet H₂S concentration. With space velocity varied from 6000 to 8000 to 12,000 h^?1 for inlet H₂S concentration in the range of 100–800 ppmv, sulfur capture capacity of the sorbent (S_cap) for 2 ppmv H₂S breakthrough did not change notably, indicating that, for each inlet H₂S concentration tested, sorbent utilization for sulfur removal was not affected by the space velocity. Meanwhile, for each space velocity tested, S_cap increased monotonically as the inlet H₂S concentration increased from 100 to 500 to 800 ppmv, which is opposite to the result observed for the mixture gas devoid of CH₄, H₂, CO and CO₂. As the overall content of these non-steam components of the simulation gas was halved for each inlet H₂S concentration tested at 8000 h^?1 space velocity, S_cap for non-steam gas components of 27.5% content corresponded approximately to the median value of those for the non-steam gas components of 55% and 0% content, suggestive of linear dependency of S_cap upon the content of the non-steam components for the inlet H₂S concentration tested.     

H2S retention with Ca-based sorbents in a pressurized fixed-bed reactor: application to moving-bed design

The H₂S retention with Ca-based sorbents in a pressurized fixed-bed reactor (1 MPa) has been analyzed, obtaining the breakthrough curves with a dolomite and two different limestones, different particle size (+0.8-1.0, +1.25-1.6, and +1.6-2.0 mm), and both at calcining (1173 K) and non-calcining conditions (1123 K). The effect of the stoichiometric time in the breakthrough curves has been analyzed varying the bed length, the gas velocity and the sorbent fraction in the bed. From these results, the conversion and H₂S concentration profiles in the transition zone and the length of unused bed (LUB) have been determined. H₂S retention in fixed-bed until concentration close to the given by the thermodynamic equilibrium was obtained using dolomite or limestone at calcining conditions, and dolomite at non-calcining conditions. The results of H₂S retention in a fixed-bed reactor has been applied to the calculus of the minimum height of a countercurrent moving-bed reactor to obtain the maximum H₂S retention with the minimum amount of sorbent. A mathematical model was developed to predict the experimental results obtained in the fixed-bed reactor, which was also valid for the design of countercurrent moving-bed reactors for gas desulphurization.     

Microbial treatment of sour gases for the removal and oxidation of hydrogen sulphide

It has been demonstrated that the bacterium Thiobacillus denitrificans may be readily cultured aerobically and anaerobically in batch and continuous cultures on hydrogen sulphide (H₂S) gas under sulphide-limiting conditions. Under these conditions sulphide concentrations in the culture medium were less than 1 μM resulting in very low concentrations of H₂S in the reactor outlet gas. The stoichiometries of both the aerobic and anaerobic reactions were determined and stable reactor operation demonstrated for up to five months. Maximum loading of the biomass was determined to be 5.4–7.6 mmoles H₂S/h-g biomass under anaerobic conditions and 15.1–20.9 mmoles H₂S/h-g biomass under aerobic conditions. Indicators of reactor upset were determined and recovery from upset demonstrated. Heterotrophic contamination was shown to have negligible effect on reactor performance with respect to hydrogen sulphide oxidation. In fact, growth of T. denitrificans in the presence of floc-forming heterotrophs produced a hydrogen sulphide active floc with excellent settling characteristics. A case study of the application of this technology to the removal and oxidation of H₂S from biogas is presented.     

Numerical study of biomass gasification combined with CO2 absorption in a bubbling fluidized bed

Biomass gasification combined with CO₂ absorption-enhanced reforming (AER) in a bubbling fluidized bed (BFB) reactor is numerically studied via the multiphase particle-in-cell (MP-PIC) method featuring thermochemical and polydispersity sub-models. A novel bubble detection algorithm is proposed for efficiently characterizing bubble morphology. The effects of several crucial operating parameters on the microscale particle behaviors, mesoscale bubble dynamics, and macroscale reactor performance of the AER gasification process are analyzed. Compared with conventional gasification, AER gasification reduces the CO₂ concentration by 33.58% but elevates the H₂ concentration by 32.13%. Higher operating temperature and steam-to-biomass (S/B) ratio promote H₂ generation but deteriorate gasification performance. A lower operating pressure improves gas–solid contact efficiency and gasification performance as the increased operating pressure inhibits bubble dynamics and particle kinematics. Compared with pure sand as bed material, the mixed bed material (CaO:sand = 1:1) significantly improves gasification performance by enhancing H₂ generation and CO₂ removal.     

Manufacture of Granular Polysilicon from Trichlorosilane in a Fluidized‐Bed Reactor

Manufacturing of polysilicon by chemical vapor deposition from SiHCl₃ in a fluidized‐bed reactor was studied. The effects of reaction temperature, H₂/SiHCl₃ ratio, gas velocity, and seed particle loading were evaluated. The outlet gas composition was analyzed by gas chromatography. The physical features of the product particles were determined by scanning electron microscopy and laser particle size analyzer. Well‐grown product particles were obtained. The temperature and H₂/SiHCl₃ ratio significantly affected conversion, yield, and selectivity, which were less affected by gas velocity and seed particle loading at higher temperatures. The surface reaction kinetics determined the product yield only at lower temperatures, and thermodynamic equilibrium was approached at temperatures above 900 °C.     

Preparation and selection of Fe-Cu sorbent for COS removal in syngas

A series of iron-based sorbents prepared with iron trioxide hydrate, cupric oxide by a novel method was studied in a fixed-bed reactor for COS removal from syngas at moderate temperature. In addition, the sorbents mixed with various additives in different ratios were tested. The effects of additive type and ratio on the breakthrough capacity and desulfurization performance, as well as the influence of operating conditions on sulfidation behavior of the sorbent, were investigated. The simulate gas contained 1% COS, 5% CO₂, 20%–30% CO and 60%–70% H₂. The outlet gases from the fixed-bed reactor were automatically analyzed by on-line mass spectrometry, and the COS concentration before breakthrough can be kept steady at 1 ppmv. The result shows that the breakthrough sulfur capacity of the sorbent is as high as 25 g-S/100 g. At 700 K and space velocity of 1000 h⁻¹, the efficiency of sulfur removal and breakthrough sulfur capacity of the sorbent increase with the increase of copper oxide with an optimum value. The result shows that the species and content of additives also affect desulfurization performance of the sorbent.     

H2S optimization for lignite liquefaction

Two lignite samples, Beulah No. 3 and Big Brown No. 1, were liquefied at 420 °C using H₂ and synthesis gas to determine the optimum beneficial amount of H₂S in the batch autoclave reactor. Under the conditions employed, 50–100 psi partial pressure of H₂S, nominally 4–10 wt% of daf lignite, was optimum for both samples. Synthesis gas outperformed H₂ with and without H₂S for the liquefaction of the two coals.     

Desulfurization performance of iron-manganese-based sorbent for hot coal gas

A series of iron-manganese-based sorbents were prepared by co-precipitation and physical mixing method, and used for H₂S removal from hot coal gas. The sulfidation tests were carried out in a fixed-bed reactor with space velocity of 2000 h⁻¹(STP). The results show that the suitable addition of manganese oxide in iron-based sorbent can decrease H₂S and COS concentration in exit before breakthrough due to its simultaneous reaction capability with H₂S and COS. Fe₃O₄ and MnO are the initial active components in iron-manganese-based sorbent, and FeO and Fe are active components formed by reduction during sulfidation. The crystal phases of iron affect obviously their desulfurization capacity. The reducibility of sorbent changes with the content of MnO in sorbent. S7F3M and S3F7M have bigger sulfur capacities (32.68 and 32.30 gS/100 g total active component), while S5F5M has smaller sulfur capacity (21.92 gS/100 g total active component). S7F3M sorbent has stable sulfidation performance in three sulfidation-regeneration cycles and no apparent structure degradation. The sulfidation performance of iron-manganese-based sorbent is also related with its specific surface area and pore volume.     

Radial gas mixing characteristics in a downer reactor

In a downer reactor (0.1 m-I.D.x3.5 m-high), the effects of gas velocity (1.6-4.5 m/s), solids circulation rate (0–40kg/m²s) and particle size (84, 164 Μm) on the gas mixing coefficient have been determined. The radial dispersion coefficient(D _r ) decreases and the radial Peclet number (Pe_r) increases as gas velocity increases. At lower gas velocities, D_r in the bed of particles is lower than that of gas flow only, but the reverse trend is observed at higher gas velocities. Gas mixing in the reactor of smaller particle size varies significantly with gas velocity, whereas gas mixing varies smoothly in the reactor of larger particle size. At lower gas velocities, D_r increases with increasing solids circulation rate (G_s), however, D_r decreases with increasing G_s at higher gas velocities. Based on the obtained D_r values, the downer reactor is found to be a good gas-solids contacting reactor having good radial gas mixing.     

Removal of minor concentration of H2S on MDEA-modified SBA-15 for gas purification

A promising adsorbent for H₂S removal of minor concentration for gas purification was prepared by synthesizing and modifying the mesoporous molecular silica of SBA-15 with methyl-diethyl-amine (MDEA). Removal performance of minor concentration of H₂S on the adsorbent was experimentally studied in a dynamic setup. The adsorbents showed good performance in removing H₂S from gas steams. The loaded amines did not change the ordered structure of SBA-15, but enhanced its removing H₂S. The adsorbents were characterized by X-ray powder diffraction (XRD) and N₂ adsorption/desorption. Effect of the R (the loading ratio) of MDEA, effect of initial H₂S concentration and effect of moisture on removal performance of H₂S were studied respectively. With increase of the R of MDEA, the H₂S removal performance of the adsorbent was improved obviously. When R of MDEA was 0.6, the removal performance was optimum. Initial H₂S concentration had a large effect on the removal performance. Both breakthrough capacity and saturation capacity increased as the initial H₂S concentration increased. In the presence of moisture, the experimental results showed the improvement in the removal performance of H₂S. In addition, not only was the adsorbent regenerable by purging with the purified gas, but also the removal performance was stable in removal adsorption cycles.     

Effect of sulfidation/oxidative regeneration cycle on the solid structural changes of sorbent for high-temperature removal of H2S

In order to investigate the effects of sulfidation/oxidative regeneration cycle on the change of structural properties and removal capacity of sorbent, sulfidation/regeneration cycle was carried out up to 15 times in a fixed-bed reactor. The effluent gases from the fixed-bed reactor were analyzed by gas chromatography, and XRD, SEM, and liquid nitrogen physisorption method were used to characterize the reacted sorbents. The sorbent treated first sulfidation/regeneration cycle exhibited maximum specific surface area and the highest H₂S removal capacity. Hysteresis of adsorption isotherm of the regenerated sorbent reflected the growth of pores of fresh sorbent and pore size distribution confirmed this fact. Furthermore constant H₂S removal capacity was maintained up to 15 times of sulfidation/regeneration cycle.     

Hydrodenitrogenation of Quinoline Over a Dispersed Molybdenium Catalyst Using in situ Hydrogen

Hydrodenitrogenation (HDN) of quinoline using a Mo-based dispersed catalyst was studied in a batch reactor using H₂ generated in situ via the water gas shift reaction. In situ H₂ was found to be more active for HDN than externally supplied H₂. Both water and H₂S have an effect on HDN.     

Reactivity of Metal Oxide Sorbents for Removal of Sulfur Compounds from Coal Gases at High Temperature and Pressure

Abstract

Hot-gas desulfurization for the integrated gasification combined cycle (IGCC) process has been investigated to effectively remove hydrogen sulfide with various metal oxide sorbents at high temperatures and pressures. Metal oxide sorbents such as zinc titanate oxide, zinc ferrite oxide, copper oxide, manganese oxide, and calcium oxide were found to be promising sorbents in comparison with other removal methods such as membrane separation and reactive membrane separation. The removal reaction of H₂S from coal gas mixtures with zinc titanate oxide sorbents was conducted in a batch reactor. The main objectives of this research are to formulate promising metal oxide sorbents for removal of hydrogen sulfide from coal gas mixtures, to compare reactivity of a formulated sorbent with a sorbent supplied by the Research Triangle Institute at high temperatures and pressures, and to determine effects of concentrations of moisture contained in coal gas mixtures, and to determine effects of concentrations of moisture contained in coal gas mixtures on equilibrium absorption of H₂S into metal oxide sorbents. Promising durable metal oxide sorbents with high-sulfur-absorbing capacity were formulated by mixing active metal oxide powders with inert metal oxide powders and calcining these powder mixtures.     

锰系可再生高温脱硫剂的制备及其性能测试

煤气的高温脱硫净化是 IGCC 和 DRI 生产的瓶颈,直接影响整个过程的热效率。在50℃、pH值约为9的条件下采用硝酸锰、硝酸铝混合溶液与氨水进行共沉淀,制备了锰含量不同的脱硫剂,在固定床反应器中考察了脱硫剂的硫化及再生性能,并利用XRD、SEM、BET等手段表征了脱硫剂在硫化/再生过程中的物相和结构变化。共沉淀法制备的脱硫剂Mn/Al分散性好,在850℃高温下进行脱硫反应可以定量快速进行。脱硫硫容与脱硫剂锰含量呈正比,Mn-S/Mn-O交换原子比在0.90~0.95之间,改变空速和进口H₂S含量并不改变脱硫硫容。采用O₂浓度为3%的稀释空气在850℃下再生,再生后的硫容稳定,说明所制备的脱硫剂可用于高温可再生脱硫。     

Kinetics of removal of impurities from gases by high pressure adsorption

Among other processes, adsorption is used for the removal of hydrogen sulphide from natural gases. Hereby, competitive adsorption of the different gas components plays an important role, e.g., that of carbon dioxide. Data of equilibrium loading and adsorption kinetics are required for the design of adsorbers, filled with molecular sieve. In order to obtain these data under the prevailing operating conditions, hydrogen sulphide was removed from gas mixtures H₂S/CH₄ and H₂S/CO₂/CH₄, in a pilot plant, by adsorption on molecular sieve 5A. The equilibrium loading, the height of transfer zone, and the length of unused bed were determined from the measured breakthrough curves of H₂S. With these data, the breakthrough time and the optimum process conditions were calculated for a practical example.     

Chemoadsorption for Separation of Hydrogen Sulfide from Biogas with Iron Hydroxide and Sulfur Recovery

Hydrogen sulfide (H₂S) removal from biogas is essential to allow biogas storage in the natural gas grid. Several established methods exist, most of them making use of non-reusable substrates such as iron sponge or active carbon. Coated metallic foams provide a reusable sustainable alternative. Several iron oxides and hydroxides were tested to validate the H₂S adsorption properties before and after thermal regeneration, i.e., sulfur removal. Amorphous iron hydroxide proved to efficiently clean biogas after maximum four sulfur removal cycles and showed an almost ten times larger capacity for sulfur adsorption than crystalline hematite Fe₂O₃. Very low H₂S contents could be realized until breakthrough.     

Oxidation of hydrogen sulfide to elementary sulfur on an activated carbon bed in the presence of iron (III) chloride aerosol

Oxidation of H₂S to elemental sulfur in a gas stream at room temperature was examined in a bed of activated carbon. The reaction was observed in the presence and absence of a ferric chloride aerosol.The H₂S concentration was in the range 500 – 2000 p.p.m., gas velocities from 4.2 – 22.5 cm/sec and aerosol concentration in the range 0.001 – 1 mg/l air.The activity of carbon as an adsorbent catalyst dropped to a relatively low value within a short time in the absence of the aerosol. The ferric chloride aerosol, which acted as another catalyst, improved the removal of H₂S to a great extent. This improvement depended on the concentration of the aerosol. Up to 98% removal was obtainable and was maintained indefinitely. These results suggest that iron chloride aerosols may be used to remove H₂S from gas streams in a dry particle bed of adsorptive material.     

Particle segregation in a spouted bed of binary mixtures of particles

Minimum spouting velocity and segregation behaviour of binary mixtures of particles differing in size have been studied. The experiments were carried out in a bed of 20 cm diameter at superficial gas velocities up to 1.3 U_ms by use of silica sand of four different particle sizes from 0.655 to 2.23 mm. An empirical equation was proposed for the minimum spouting velocity of binary mixtures. The effects of the particle size difference and the superficial gas velocity on segregation were investigated. Results showed that considerable radial segregation as well as axial segregation occurred even for high gas velocity under the condition of large particle size difference.     

Sulfur tolerance of methanol synthesis catalysts: Modelling of catalyst deactivation

A series of supported Pd and commercial Cu-based catalysts was tested for methanol synthesis activity and activity maintenance in the presence of 2 ppm H₂S in a differential fixed-bed reactor operated at 523 K and 1.5 MPa. Sulfur breakthrough curves were obtained by monitoring the H₂S concentration in both the feed and exit streams using a gas chromatograph with a flame photometric detector. A comparison of the resistance to sulfur poisoning of the various catalysts is given using a qualitative examination of activity maintenance plots as well as a mathematical model for catalyst deactivation. The rates of deactivation of the Cu-based catalysts in the absence or presence of H₂S were very similar, with 70–90% of the initial activity being lost during 300 h on stream. No H₂S breakthrough was observed with these catalysts whereas the Pd catalysts exhibited breakthroughs after short times (10–30 h) on stream. The Pd catalysts retained a much higher residual activity in the presence of H₂S than those reported for Fe, Co, Ni and Ru at much lower H₂S pressures, and Pd/SiO₂ possessed a stable, lined-out activity in 2 ppm H₂S that was near half its original activity. Problems that arise in catalyst evaluation when a single deactivation model does not apply in all cases are discussed. The Szepe-Levenspiel approach, with a modification recently proposed by Fuentes for poison-tolerant catalysts, was found to give meaningful quantification of sulfur resistance of Pd-based catalysts.     

Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H2S

Removal of Hg⁰ vapor from the simulated coal combustion flue gases with a commercial activated carbon was investigated using H₂S. This method is based on the reaction of H₂S and Hg over the adsorbents. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system in the temperature range of 80–150 °C using simulated flue gases having the composition of Hg⁰ (4.9 ppb), H₂S (0–20 ppm), SO₂ (0–487 ppm), CO₂ (10%), H₂O (0–15%), O₂ (0–5%), N₂ (balance gas). The following results were obtained: in the presence of both H₂S and SO₂, Hg removal was favored at lower temperatures (80–100 °C). At 150 °C, presence of O₂ was indispensable for Hg⁰ removal from H₂S–SO₂ flue gas system. It is suggested that the partial oxidation of H₂S with O₂ to elemental sulfur (H₂S+1/2O₂=S_ad+H₂O) and the Clause reaction (SO₂+2H₂S=3S_ad+2H₂O) may contribute to the Hg⁰ removal over activated carbon by the following reaction: S_ad+Hg=HgS. The formation of elemental sulfur on the activated carbon was confirmed by a visual observation.