Two-stage Fluidized Bed Reactor Research Articles

Microbial community dynamics in a feedback-redox controlled bioreactor process that enabled sequential selenate, nitrate and sulfate removal, and elemental selenium recovery

Oxidation reduction potential (ORP) feedback-control by ethanol-dosing was recently proved effective in facilitating a two-stage fluidized bed reactor (FBR) process to remove selenate, nitrate, and sulfate from wastewater, and recover high-purity elemental Se without the formation of carcinogenic SeS. However, further optimization requires knowledge on the relationship between microbial community composition and process performance. Here, changes of microbial communities during the reduction of selenate and nitrate in the first FBR (FBR1) under various ORP conditions (−240 to −520 mV vs. Ag/AgCl), sulfate reduction in subsquent FBR (FBR2) and sulfide oxidation in sulfide oxidation reactor (SOR) were examined. Based on 16S rRNA gene sequencing, high ORP (stage i without sulfate: >−360 mV; stage ii with sulfate: >−440 mV) and elevated sulfate at ORP ≤ −480 mV (stage iii) in FBR1 altered the microbial communities both on fluidized carrier and bulk liquor. Selenate reducers (Geoalkalibacter and Geovibrio genera) were impacted at ORP > −360 mV (stage i) or >−440 mV (stage ii), when selenate removal in FBR1 declined. However, nitrate reducers (Caenispirillum and Paracoccus genera) were not affected in the FBR1, and facilitated ~100 % nitrate removal. At ORP ≤ −480 mV, selenate reducers were readily enriched in FBR1. In the FBR2, the major sulfate reducing genera were Desulfomicrobium, Desulfovibrio and Desulfuromonas, whereas the dominant sulfide-oxidating genera in SOR were Paracoccus, Thiobacillus and Acholeplasma. This study suggested that both nitrate- and selenate-reducing communities could remain active under elevated sulfate concentrations, enabling sequential oxyanions removal and elemental Se recovery from wastewater.

Fate of fuel‑nitrogen during in situ gasification chemical looping combustion of coal

In situ gasification chemical looping combustion (iG-CLC) was a promising way to inherently sequestrate CO2. Due to the nitrogen in coal, the NOx emission was a key issue in iG-CLC. In this study, we aimed to identify the nitrogen conversion and distribution characteristics in two elementary stages of coal conversion (pyrolysis and subsequent char gasification) during the iG-CLC process in a tailor-made two-stage fluidized bed reactor. HCN was the dominant precursor of NOx in iG-CLC, almost all the NOx precursors were rapidly released during the coal pyrolysis stage, and no gaseous nitrogen pollutant was detected within the subsequent CO2-char gasification process. The generated HCN could be completely converted by the Fe-based oxygen carrier (OC) to either NO or N2. The high CO2 concentration and reducing reaction atmosphere in the fuel reactor were found to exert certain inhibitory effects on the formation of NO. Meanwhile, the operating conditions, that is, the O/fuel ratio and temperature, exhibited insignificant effects on the fate of fuel-N. Finally, the fate of nitrogen in volatiles, char, and tar of coal during iG-CLC and the potential homogeneous nitrogen conversion in the iG-CLC of coal were proposed based on the results obtained from both experiments and thermodynamic simulations.

Sulfur fate during in-situ gasification chemical looping combustion (iG-CLC) of coal

Sulfur conversion during in-situ gasification chemical looping combustion (iG-CLC) of coal is consisted by pyrolysis and char gasification. Insight into the fate of sulfur in these two processes is essential for exploring appropriate strategies for sulfur emission control, whereas in most of works the pyrolysis and gasification could not be fully identified. In this case, a two-stage fluidized bed reactor system comprising a lower and a higher reactor was used to generate in-situ and separate gases from pyrolysis and gasification in this work. Sulfurous gases including H2S, COS, CS2 and SO2 were experimentally studied under various conditions by changing operation temperature (T), O/fuel ratio (Φ) and OC reduction degree (XOC), while the solid samples were regularly collected for the characterization using different techniques. It was found that the sol-gel Fe2O3/Al2O3 was a sulfur resistant OC during the iG-CLC process, thus no formation of sulfur components in the material. The values of T and Φ have positive effect on the conversion of sulfurous gases to SO2, whereas a lower XOC value can improve the conversion of H2S. The main components from volatiles (mainly H2S and CS2) and from char (mainly COS) can be effectively converted to SO2 by the OC material. The coal ash exhibited a desulfurization function, as some sulfur contents were retained as CaSO4 during the iG-CLC tests. Finally, the fate of sulfur in coal during iG-CLC was comprehensively mapped, which would be significant for developing strategies for sulfur emission control.

Enhanced production of aromatics from propane with a temperature-shifting two-stage fluidized bed reactor.

A temperature-shifting two-stage fluidized bed reactor technology was used to convert propane and its intermediate products into aromatics. The first stage served for the aromatization of propane with a Ga/ZSM-5 catalyst at 570 °C. The second stage served for the alkylation of the intermediates of olefins at 300 °C. The increased yield of aromatics was attributed to the effective transformation of C2–C3 olefins as well as due to the suppression of the hydrogen transfer effect of the olefins.

Sulfur Fate during the Lignite Pyrolysis Process in a Chemical Looping Combustion Environment

Chemical-looping combustion (CLC) is a novel technology with the feature of CO2 inherent separation in which the fuel is converted via lattice oxygen (instead of gaseous oxygen) provided by the oxygen carrier that circulates between two structurally interconnected but atmosphere-isolated reactors, i.e., fuel reactor and air reactor. In the fuel reactor of in situ gasification CLC (iG-CLC), the pyrolysis and gasification products of coal are oxidized by lattice oxygen in the O2-free environment. Therefore, the characteristics of sulfur species evolution and distribution in the coal pyrolysis products are significantly different from those in the conventional combustion, gasification, and pyrolysis processes. In this study, a two-stage fluidized bed reactor was utilized to investigate the reaction between the oxygen carrier and in situ coal pyrolysis products, in which the coal and oxygen carrier particles are separately loaded in two reactors. In this way, the influence of oxygen carrier on the coal pyroly...

Conversion of methanol with C5–C6 hydrocarbons into aromatics in a two-stage fluidized bed reactor

The conversion of methanol mixed with C5–C6 hydrocarbons (including pentane, hexane, and cyclohexane) was studied in a two-stage fluidized bed reactor packed with 880g Zn/ZSM-5 catalyst at 475°C and 0.4MPa. The effect of the mixed feed on the methanol conversion, self-decomposition of methanol, coke deposition on the catalyst, aromatic yield, and the aromatic distribution was carefully studied. Methanol conversion was nearly complete and the self-decomposition of methanol can be suppressed significantly. There exhibited a positive heat coupling effect in the feeding of methanol with pentane or with cyclohexane to increase the aromatic yield or to suppress the undesirable side reactions. However, the mixed feed is unfavorable to the transformation of hexane into aromatics. Better aromatic yield in the lower temperature for the mixed feed, as compared to that for the conversion of pure C5–C6 hydrocarbons in higher temperature, validated the heat coupling effect. The result confirmed that it is feasible to use the exothermic methanol conversion to enhance the endothermic transformation of some C5–C6 hydrocarbons into aromatic, resulting in a great engineering simplification of heat supply or heat removal in high temperature operation.

Influence of various chlorine additives on the partitioning of heavy metals during low-temperature two-stage fluidized bed incineration

In this study, a pilot-scale low-temperature two-stage fluidized bed incinerator was evaluated for the control of heavy metal emissions using various chlorine (Cl) additives. Artificial waste containing heavy metals was selected to simulate municipal solid waste (MSW). Operating parameters considered included the first-stage combustion temperature, gas velocity, and different kinds of Cl additives. Results showed that the low-temperature two-stage fluidized bed reactor can be an effective system for the treatment of MSW because of its low NOx, CO, HCl, and heavy metal emissions. The NOx and HCl emissions could be decreased by 42% and 70%, respectively. Further, the results showed that heavy metal emissions were reduced by bed material adsorption and filtration in the second stage. Regarding the Cl addition, although the Cl addition would reduce the metal capture in the first-stage sand bed, but those emitted metals could be effectively captured by the filtration of second stage. No matter choose what kind of additive, metal emissions in the low-temperature two-stage system are still lower than in a traditional high-temperature one-stage system. The results also showed that metal emissions depend not only on the combustion temperature but also on the physicochemical properties of the different metal species.

A two-stage reduction process for the production of high-purity ultrafine Ni particles in a micro-fluidized bed reactor

A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work. The raw ultrafine NiO particles are first pre-reduced using hydrogen at lower temperatures (340–400°C), followed by further reduction at higher temperatures (500–600°C). The self-agglomeration of Ni particles formed during low-temperature reduction decreases the sintering activity of the newly formed ultrafine Ni particles, leading to good fluidization quality, even for the subsequent high-temperature reduction process. The agglomerated Ni particles have a high Ni content (above 99wt%), a low density (0.78g/cm3) and a uniform particle size (approximately 100μm). A concept design for a novel two-stage fluidized bed reactor process used to produce high-purity Ni powder was also proposed. This approach may be extended to the synthesis of other ultrafine/nanosized metals or metal oxides through a fluidization method.

Post-treatment of secondary wastewater treatment plant effluent using a two-stage fluidized bed bioreactor system

The aim of this study was to investigate the performance of a two-stage fluidized bed reactor (FBR) system for the post-treatment of secondary wastewater treatment plant effluents (Shahrak Gharb, Tehran, Iran). The proposed treatment scheme was evaluated using pilot-scale reactors (106-L of capacity) filled with PVC as the fluidized bed (first stage) and gravel for the filtration purpose (second stage). Aluminum sulfate (30 mg/L) and chlorine (1 mg/L) were used for the coagulation and disinfection of the effluent, respectively. To monitor the performance of the FBR system, variation of several parameters (biochemical oxygen demand (BOD5), chemical oxygen demand (COD), turbidity, total phosphorous, total coliform and fecal coliform) were monitored in the effluent wastewater samples. The results showed that the proposed system could effectively reduce BOD5 and COD below 1.95 and 4.06 mg/L, respectively. Turbidity of the effluent could be achieved below 0.75 NTU, which was lower than those reported for the disinfection purpose. The total phosphorus was reduced to 0.52 mg/L, which was near the present phosphorous standard for the prevention of eutrophication process. Depending on both microorganism concentration and applied surface loading rates (5–10 m/h), about 35 to 75% and 67 to 97% of coliform were removed without and with the chlorine addition, respectively. Findings of this study clearly confirmed the efficiency of the FBR system for the post-treatment of the secondary wastewater treatment plant effluents without any solid problem during the chlorination.

Design of a two-stage fluidized bed reactor for preparation of diethyl oxalate from carbon monoxide

In this study, a two-stage fluidized bed reactor (TS-FBR) was designed as a new technology to produce diethyl oxalate (DEO) from carbon monoxide (CO) based on the catalytic coupling reaction. Computational fluid dynamics (CFD) approach was adopted to obtain the detailed flow field, the bubble behaviors in the TS-FBR, and further demonstrate the feasibility of the TS-FBR used in producing DEO from CO. Furthermore, the whole preparation process of DEO from CO using the optimum TS-FBR as the central unit is simulated using an advanced software tool, realizing the proper matching of coupling reaction and regeneration reaction. As a result, the realization of the whole preparation process is presented.

Two-stage steam gasification of waste biomass in fluidized bed at low temperature: Parametric investigations and performance optimization

Steam gasification of waste biomass has been studied in a two-stage fluidized bed reactor, which has the primary pyrolysis fluidized bed using silica sand as bed material and the secondary reforming fixed bed with catalyst. The main objectives are parametric investigation and performance improvement especially at low temperature of around 600 °C using the wood chip and the pig manure compost as feedstock. Main operating variables studied are pyrolysis temperature, catalytic temperature, steam/biomass-C ratio, space velocity and different catalyst. Reaction temperatures and steam/C ratio have important role on the gasification process. About 60 vol.% H2 (dry and N2 free) and about 2.0 Nm3/kg biomass (dry and ash free basis) can be obtained under good conditions. Compared to Ni/Al2O3, Ni/BCC (Ni-loaded brown coal char) has a better ability and a hopeful prospect for the stability with coking resistance.

Mechanism of Woody Biomass Pyrolysis and Gasification in a Fluidized Bed of Porous Alumina Particles

To understand the mechanism of steam gasification of woody biomass, pyrolysis and gasification were carried out at 773 and 973 K on porous γ-alumina in a two-stage fluidized bed reactor. Significant amounts of volatiles, including gas and tarry materials, were formed upon devolatilization, but the tar was mostly captured by the alumina. The tar captured on the alumina was subsequently reformed with the steam to H2 and CO. However, little of the char was gasified under the present conditions. CO and water molecules penetrated into the large pores of the char, allowing the water−gas shift reaction to occur on the active sites on the surface of the char. Although the char itself was not gasified at these relatively low temperatures, it played an important role in the water−gas shift reaction.

Gaseous catalytic hydrogenation of nitrobenzene to aniline in a two-stage fluidized bed reactor

Gaseous hydrogenation of nitrobenzene over a Cu/SiO 2 catalyst has been studied in a two-stage and in a single-stage fluidized bed reactor, at 513–553 K and atmospheric pressure. The placement of the second perforated plate in the fluidized bed reactor inhibits the backmixing of gases and solids and consequently increases the local molar ratio of hydrogen to nitrobenzene in the second stage. Thus, the conversion of nitrobenzene and the selectivity of aniline production and the stable life of the catalyst are significantly increased in the two-stage fluidized bed reactor, as compared with those in the single-stage one. A comparison of the coke formation and the burning characteristics of cokes in different reactors has also been presented. It suggests the simple catalyst regeneration for the two-stage fluidized bed technology. This work provides an effective method to produce aniline with higher purity.

Enhanced degradation of chlorinated ethylenes in groundwater from a paint contaminated site by two-stage fluidized-bed reactor

Groundwater, used in this study, contaminated predominantly with aromatic compounds, was biologically treated in a fluidized-bed reactor (FBR) with immobilized cells. The aromatics were completely decomposed, while cis-1,2-dichloroethylene ( cis-DCE) and trichloroethylene (TCE) were decomposed only approximately 20% and 5%, respectively. In these studies a significant improvement of the decomposition efficiency for chlorinated ethylenes was achieved by utilizing cometabolism. Methanol (MeOH) and toluene were used as the substrate in the case of one-stage reactor (Single Reactor). MeOH (187 mg l −1) increased the decomposition efficiency up to 40% and 60% for cis-DCE and TCE, respectively, while toluene (20 mg l −1) increased the decomposition efficiency of cis-DCE to 92% and the decomposition efficiency of TCE to 76%. In the case of two-stage reactor system (Reactor 1 and Reactor 2), MeOH and methane (CH 4) were used as the substrate. In this system, cells grown on MeOH or CH 4 in the Reactor 1 were continuously fed into Reactor 2 and groundwater was fed into Reactor 2 only. When MeOH (384 mg l −1 d −1) was used as substrate the decomposition efficiency of cis-DCE and TCE were 60% and 70%, respectively. Similar decomposition efficiency was observed for a small amount of CH 4 (19.3 mg l −1 d −1).

Production of hydrogen and carbon nanotubes from methane decomposition in a two-stage fluidized bed reactor

Methane decomposition over a Ni/Cu/Al 2O 3 catalyst is studied in a two-stage fluidized bed reactor. Low temperature is adopted in the lower stage and high temperature in the upper stage. This allows the fluidized catalysts to decompose methane with high activity in the high temperature condition; then the carbon produced will diffuse effectively to form carbon nanotubes (CNTs) in both low and high temperature regions. Thus the catalytic cycle of carbon production and carbon diffusion in micro scale can be tailored by a macroscopic method, which permits the catalyst to have high activity and high thermal stability even at 1123 K for hydrogen production for long times. Such controlled temperature condition also provides an increased thermal driving force for the nucleation of CNTs and hence favors the graphitization of CNTs, characterized by high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and XRD. Multistage operation with different temperatures in a fluidized bed reactor is an effective way to meet the both requirements of hydrogen production and preparation of CNTs with relatively perfect microstructures.