Syngas production via combined oxy-CO2 reforming of methane over Gd2O3-modified Ni/SiO2 catalysts in a fluidized-bed reactor

In this research, Ni/SiO₂ catalyst was modified with different amount of Gd₂O₃ and characterized with temperature-programmed desorption of CO₂ (CO₂-TPD) and NH₃ (NH₃-TPD), temperature-programmed reduction with H₂ (H₂-TPR) and X-ray diffraction (XRD). It was found that Gd₂O₃-modified Ni/SiO₂ catalysts possessed higher CO₂ adsorption and activation ability due to the formation of surface carbonate species. H₂-TPR and XRD characterizations found that the strong interaction among nickel, Gd₂O₃ and SiO₂ took place, which improved the dispersion of Ni. Gd₂O₃-modified Ni/SiO₂ catalysts exhibited higher activity and stability for the combined oxy-CO₂ reforming of methane in fluidized-bed reactor. The H₂/CO ratio in produced syngas could be controlled via controlling reaction temperature and CO₂/O₂ ratio in feed.     

Experimental and numerical simulation of lignite chemical looping gasification with phosphogypsum as oxygen carrier in a fluidized bed

Phosphogypsum (PG) is a solid waste produced in the wet process of producing phosphoric acid.Lignite is a kind of promising chemical raw material.However,the high sulfur of lignite limits the utilization of lig-nite as a resource.Based on fluidized bed experiments,the optimal reaction conditions for the production syngas by lignite chemical looping gasification (CLG) with PG as oxygen carrier were studied.The study found that the optimal reaction temperature should not exceed 1123 K;the mole ratio of water vapor to lignite should be about 0.2;the mole ratio of PG oxygen carrier to lignite should be about 0.6.Meanwhile,commercial software Comsol was used to establish a fuel reaction kinetics model.Through computational fluid dynamics (CFD) numerical simulation,the process of reaction in fluidized bed were well captured.The model was based on a two-fluid model and coupled mass transfer,heat transfer and chemical reac-tions.This study showed that the fluidized bed presents a flow structure in which gas and solid coexist.There was a high temperature zone in the middle and lower parts of the fluidized bed.It could be seen from the results of the flow field simulated that the fluidized bed was beneficial to the progress of the gasification reaction.     

Syngas production by biomass gasification using Rh/CeO2/SiO2 catalysts and fluidized bed reactor

We have been developed novel catalysts for gasification of biomass with much higher energy efficiency than conventional methods (non-catalyst, dolomite, commercial steam reforming Ni catalyst). From the result of the gasification of cellulose over novel Rh/CeO₂/SiO₂ catalysts, it is found that the gasification process consists of the reforming of tar and the combustion of solid carbon. We also tested novel Rh/CeO₂/SiO₂ in the gasification with air, pyrogasification, and steam reforming of cedar wood. As a result, Rh/CeO₂/SiO₂ gave higher yield of syngas than the conventional steam reforming Ni catalyst. Furthermore, we compared the performance between single and dual bed reactors. Single bed reactor was effective in the gasification of cedar, however, it was not suitable for the gasification of rice straw since a rapid deactivation was observed. Gasification of rice straw, jute stick, baggase using the fluidized dual-bed reactor and Rh/CeO₂/SiO₂ was also investigated. Especially, the catalyst stability in the gasification of rice straw clearly was enhanced by using the fluidized dual bed reactor.     

Fluidized-Bed Bioreactor Applications for Biological Wastewater Treatment: A Review of Research and Developments

Wastewater treatment is a process that is vital to protecting both the environment and human health. At present, the most cost-effective way of treating wastewater is with biological treatment processes such as the activated sludge process, despite their long operating times. However, population increases have created a demand for more efficient means of wastewater treatment. Fluidization has been demonstrated to increase the efficiency of many processes in chemical and biochemical engineering, but it has not been widely used in large-scale wastewater treatment. At the University of Western Ontario, the circulating fluidized-bed bioreactor (CFBBR) was developed for treating wastewater. In this process, carrier particles develop a biofilm composed of bacteria and other microbes. The excellent mixing and mass transfer characteristics inherent to fluidization make this process very effective at treating both municipal and industrial wastewater. Studies of lab- and pilot-scale systems showed that the CFBBR can remove over 90% of the influent organic matter and 80% of the nitrogen, and produces less than one-third as much biological sludge as the activated sludge process. Due to its high efficiency, the CFBBR can also be used to treat wastewaters with high organic solid concentrations, which are more difficult to treat with conventional methods because they require longer residence times; the CFBBR can also be used to reduce the system size and footprint. In addition, it is much better at handling and recovering from dynamic loadings (i.e., varying influent volume and concentrations) than current systems. Overall, the CFBBR has been shown to be a very effective means of treating wastewater, and to be capable of treating larger volumes of wastewater using a smaller reactor volume and a shorter residence time. In addition, its compact design holds potential for more geographically localized and isolated wastewater treatment systems.     

Occurrence and volatilization behavior of Pb, Cd, Cr in Yima coal during fluidized-bed pyrolysis

The volatilization behavior of Pb, Cd, Cr and the influence of coexisting mineral matters were investigated during pyrolysis of Yima coal in a fluidized-bed reactor at temperatures ranging from 500 to 900 °C. The modes of occurrence of Pb, Cd, Cr in Yima raw coal and two char samples were determined using density fractionation, demineralization and sequential chemical extraction methods. Lead in Yima coal is mostly associated with mineral matter in various forms, mainly pyrite, sulfates and monosulfides. Large part of cadmium is associated with pyrite. Chromium in Yima coal is mainly associated with organic matter. Different trends are observed for various forms of trace metals during pyrolysis. Lead associated with pyrite, sulfates and carbonates, lead in water soluble and ion exchangeable forms, and cadmium associated with pyrite are all unstable under pyrolysis conditions. During Yima coal pyrolysis, the volatilities of lead and cadmium vary greatly with pyrolysis temperature, while chromium volatility in Yima raw coal only has slight changes over the temperature range (500-900 °C) studied. The volatility of Pb, Cd, Cr in demineralized Yima coal (YimaD) is much higher than that of Yima coal during pyrolysis. New thermally stable forms of Pb, Cd and Cr are formed during pyrolysis of Yima, whereas the sources of them are different. The interactions between chromium and its coexisting mineral matters in Yima coal retard its vaporization during pyrolysis.     

Computational fluid dynamics and electrostatic modeling of polymerization fluidized-bed reactors

Electrostatics plays an important role in gas-solid polymerization fluidized-bed reactors. Agglomeration of polymer particles can occur due to either electrostatic and/or thermal effects, and can lead to reactor operability problems if not properly mitigated. In this work a first-principles electrostatic model is developed and coupled with a multi-fluid computational fluid dynamic (CFD) model to understand the effect of electrostatics on the bulk polymer, polymer fines, and catalyst particles. The multi-phase CFD model for gas-solid flow is based on the kinetic theory of granular flows and the frictional theory. The electrostatic model is developed based on a fixed, size-dependent charge for each type of particle (catalyst, polymer fines and polymer). The combined CFD model is first verified using simple test cases and then applied to a pilot-plant-scale polymerization fluidized-bed reactor. The multi-phase CFD model is applied to reproduce qualitative trends in particle segregation and entrainment due to electrostatic charges observed in experiments.     

Energy Analysis of Low-Rank Coal Pre-Drying Power Generation Systems

Low-rank coal (LRC) is widely used for power generation in many regions of the world. However, due to the high moisture content of LRC, the overall efficiency of LRC-fired power plants without a pre-drying system is relatively low. Studies show that the overall efficiency can be improved by pre-drying the coal, and the fluidized bed drying technique is found to be a desirable choice because of its high drying rate, high processing capacity, and low maintenance cost. In this paper, two novel, fluidized-bed, LRC pre-drying systems were integrated into a 1000 MW LRC-fired power plant. Superheated steam and hot air were used as the fluidizing medium. Models for each component of these power generation systems were developed based on material and energy balances. The performances of these power plants were calculated under the typical operating conditions, and parametric analyses were also performed to evaluate the effect of operating parameters. The power generation efficiency is found to increase remarkably with a properly operated LRC pre-drying system.     

Structured cell simulator coupled with a fluidized bed bioreactor model to predict the adaptive mercury uptake by E. coli cells

A bi-level model is proposed by coupling a three-phase fluidized bioreactor (TPFB), used for mercury uptake from wastewaters by immobilized Escherichia coli cells, with a cellular simulator of the genetic regulatory circuit (GRC) controlling the mercuric ion reduction in the cytosol. While keeping a reasonable agreement with the experimental data from literature (free cell cultures with/without cell membrane permeabilization), the structured model advantages are coming from the prediction detailing degree [simulated 26 + 3 (cell + bulk) vs. 3 (bulk) variable dynamics] covering a wide range of input Hg²⁺ loads (0–100 mg L⁻¹), and cloned E. coli cells with various amounts of mer-plasmids (3–140 nM). The model offers the possibility to predict the inner cell mercury reduction rate (different from the apparent rate observed in the bioreactor), the bacteria metabolism adaptation to environmental changes over several cell cycles, and the effect of cloning cells to modify their behaviour under stationary or perturbed conditions.     

FLUIDIZED-BED APPARATUS FOR CRYSTAL GROWTH RATE MEASUREMENTS AND ITS TESTING WITH COPPER SULPHATE

Apparatus for measurement of crystal growth rate in a fluidized bed has been modified. The improvement consists of a new way of introducing and removing seeds, which substantially speeds up the measurement and, due to better stability of the temperature regime, leads to improved reliability of results. Growth rates of CuSO₄ · 5H₂O in aqueous solutions, measured in the original and improved apparatus, are compared and they demonstrate the advantages of the new version of the equipment.