Sheng Su

Influence of different demineralization treatments on physicochemical structure and thermal degradation of biomass.

To study the catalytic role of alkali and alkaline earth metallic species and eliminate their negative impact during biomass thermal utilization, different leaching methods have been applied in numerous experiments. Thus it is necessary to investigate the potential influence on biomass physicochemical structure using different agents. Rice straw was selected to study the demineralization impact on physicochemical structure and pyrolysis characteristics. It is shown that strong acid leaching exhibited higher removal efficiency of minerals, but it introduced more notable impact on physicochemical structure of biomass comparing to water and weak acid leaching. Different leaching methods give chance to study catalysis characteristics of intrinsic metals on biomass thermal reaction. Contrast to alkaline earth metals especially Ca hindering thermal decomposition, alkali metals promoted this reaction obviously. In addition, comparing to physicochemical structure changes created by leaching process, the influence of removal of minerals played the dominant role in biomass thermal behavior.

Effects of inherent alkali and alkaline earth metallic species on biomass pyrolysis at different temperatures

This work aimed to investigate effects of inherent alkali and alkaline earth metallic species (AAEMs) on biomass pyrolysis at different temperatures. The yield of CO, H2 and C2H4 was increased and that of CO2 was suppressed with increasing temperature. Increasing temperature could also promote depolymerization and aromatization reactions of active tars, forming heavier polycyclic aromatic hydrocarbons, leading to decrease of tar yields and species diversity. Diverse performance of inherent AAEMs at different temperatures significantly affected the distribution of pyrolysis products. The presence of inherent AAEMs promoted water-gas shift reaction, and enhanced the yield of H2 and CO2. Additionally, inherent AAEMs not only promoted breakage and decarboxylation/decarbonylation reaction of thermally labile hetero atoms of the tar but also enhanced thermal decomposing of heavier aromatics. Inherent AAEMs could also significantly enhance the decomposition of levoglucosan, and alkaline earth metals showed greater effect than alkali metals.

Catalytic oxidation of Hg0 by MnOx–CeO2/γ-Al2O3 catalyst at low temperatures

MnOx-CeO2/γ-Al2O3 (MnCe) selective catalytic reduction (SCR) catalysts prepared by sol-gel method were employed for low-temperature Hg(0) oxidation on a fixed-bed experimental setup. BET, XRD and XPS were used to characterize the catalysts. MnCe catalysts exhibited high Hg(0) oxidation activity at low temperatures (100-250 °C) under the simulated flue gas (O2, CO2, NO, SO2, HCl, H2O and balanced with N2). Only a small decrease in mercury oxidation was observed in the presence of 1200 ppm SO2, which proved that the addition of Ce helped resist SO2 poisoning. An enhancing effect of NO was observed due to the formation of multi-activity NOx species. The presence of HCl alone had excellent Hg(0) oxidation ability, while 10 ppm HCl plus 5% O2 further increased Hg(0) oxidation efficiency to 100%. Hg(0) oxidation on the MnCe catalyst surface followed the Langmiur-Hinshelwood mechanism, where reactions took place between the adsorbed active species and adsorbed Hg(0) to form Hg(2+). NH3 competed with Hg(0) for active sites on the catalyst surface, hence inhibiting Hg(0) oxidation. This study shows the feasibility of a single-step process integrating low-temperature SCR and Hg(0) oxidation from the coal combustion flue gas.

Vaporization of heavy metals during thermal treatment of model solid waste in a fluidized bed incinerator

This paper investigated the volatilization behavior of heavy metals during thermal treatment of model solid waste in a fluidized bed reactor. Four metal chlorides (Cd, Pb, Cu and Zn) were chosen as metal sources. The influence of redox conditions, water and mineral matrice on heavy metal volatilization was investigated. In general, Cd shows significant vaporization especially when HCl was injected, while Cu and Pb vaporize moderately and Zn vaporization is negligible. Increasing oxygen concentration can lower heavy metal vaporization. Heavy metal interactions with the mineral matter can result in the formation of stable metallic species thus playing a negative effect on their behavior. However, HCl can promote the heavy metal release by preventing the formation of stable metallic species. The chemical sorption (either physical or chemical) inside the pores, coupled with the internal diffusion of gaseous metal species, may also control the vaporization process. With SO(2) injected, Cd and Pb show a higher volatility as a result of SO(2) reducing characteristics. From the analysis, the subsequent order of heavy metal volatility can be found: Cd>Cu≥Pb≫Zn.

Kinetic models comparison for steam gasification of coal/biomass blend chars

The non-isothermal thermogravimetric method (TGA) was applied to different chars produced from lignite (LN), sawdust (SD) and their blends at the different mass ratios in order to investigate their thermal reactivity under steam atmosphere. Through TGA analysis, it was determined that the most prominent interaction between sawdust and lignite occurred at the mass ratio of sawdust/lignite as 1:4, but with further dose of more sawdust into its blends with lignite, the positive interaction deteriorated due to the agglomeration and deactivation of the alkali mineral involved in sawdust at high steam gasification temperature. Through systematic comparison, it could be observed that the random pore model was the most suitable among the three gas-solid reaction models adopted in this research. Finally, rational kinetic parameters were reached from these gas-solid reaction models, which provided a basis for design and operation of the realistic system of co-gasification of lignite and sawdust in this research.

Kinetic vaporization of heavy metals during fluidized bed thermal treatment of municipal solid waste.

Heavy metals volatilization during thermal treatment of model solid waste was theoretically and experimentally investigated in a fluidized bed reactor. Lead, cadmium, zinc and copper, the most four conventional heavy metals were investigated. Particle temperature model and metal diffusion model were established to simulate the volatilization of CdCl(2) evaporation and investigate the possible influencing factors. The diffusion coefficient, porosity and particle size had significant effects on metal volatilization. The higher diffusion coefficient and porosity resulted in the higher metal evaporation. The influence of redox conditions, HCl, water and mineral matrice were also investigated experimentally. The metal volatilization can be promoted by the injection of HCl, while oxygen played a negative role. The diffusion process of heavy metals within particles also had a significant influence on kinetics of their vaporization. The interaction between heavy metals and mineral matter can decrease metal evaporation amount by forming stable metallic species.

Removal of elemental mercury from coal combustion flue gas by bentonite-chitosan and their modifier

Abstract Adsorption experiments of vapor-phase elemental mercury were carried out using modified bentonite-chitosan in a laboratory-scale fixed-bed reactor. VM3000 online mercury analyzer was applied to detect the inlet and outlet mercury (Hg 0 ) concentrations. The characterizations of the sorbents were analyzed using the methods such as nitrogen (N 2 ) adsorption/desorption, scanning electron microscopy (SEM), and Fourier transform infra-red spectroscopy (FT-IR). It was observed that the porosity and specific surface area decreased after modification. The FT-IR spectra demonstrated that the iodine was found in the inner layer of bentonite and the chemical reactions of iodine and sulfuric acid with the amide of chitosan occurred. The tests in the fixed-bed reactor showed that the bentonite-supported chitosan exhibited lower mercury capture than raw bentonite, which indicated that the mechanism of gas phase mercury removal was different from that of ionic state mercury in liquid. In general, the iodine-modified sorbents demonstrated higher mercury capture efficiency than raw sorbents and the iodine-modified bentonite showed the best one. Mercury removal efficiency of bentonite supported by chitosan sorbents could be promoted from 85 to 100% when added appropriate amount of H 2 SO 4 , while that of iodine- and sulfuric acid-modified bentonite exhibited opposite tendency because of their absolutely different physicochemical properties.

Physical and chemical characterization of ashes from a municipal solid waste incinerator in China.

In this study we analyzed the characteristics of bottom and fly ashes from a municipal solid waste incinerator in China. The physical properties of particle size distribution and morphology were evaluated. At the chemical level, the chemical composition, heavy metal leaching behavior and BCR sequential extraction procedure (the Community Bureau of Reference, now the European Union ‘Measurement and Testing Programme’) were determined. The main mineralogical crystalline phases in raw and leached bottom and fly ashes were also identified. For the bottom ashes, the concentration of heavy metals showed a slight decrease with an increase in particle size, and most of the heavy metal concentrations in fly ashes were higher than those in bottom ashes. The results of the toxicity characteristic leaching procedure indicated that, among the metals, the concentrations of lead (Pb) and copper (Cu) in fly ash leachate exceeded thresholds, while the concentrations of studied heavy metals in bottom ash leachate were all below the regulatory limit. The BCR results indicated that more easily mobilized forms (acid exchangeable) were predominant for cadmium and zinc; in contrast, the largest amount of Pb, Cu and manganese were associated with iron/manganese oxide, organic matter/sulfide fractions, or were residual.

Fe3 xCuxO4 as highly active heterogeneous Fenton-like catalysts toward elemental mercury removal

A series of novel spinel Fe3-xCuxO4 (0<x<0.71) composites, synthesized by chemical co-precipitation method, are proposed synthesized to use as highly active heterogeneous Fenton-like catalysts to remove elemental mercury (Hg0) from the simulated flue gases. Inductively coupled plasma-Atomic emission spectrometry (ICP-AES), X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, and X-ray photoelectron spectrometer (XPS) were used to characterize the catalysts. The catalysts were confirmed the presence of the redox pairs Fesurf2+/Fesurf3+ and Cusurf+/Cusurf2+ on the surface of the cubic structure. The performance of heterogeneous Fenton-like reactions for Hg0 removal was evaluated in a lab-scale bubbling reactor at the solution temperature of 50°C. The systematic studies on the effects of different catalysts, H2O2 concentration and solution pH values on Hg0 removal efficiencies were performed. The recycling of the Fe3-xCuxO4 catalysts in Fenton-like solution is stable and Hg0 removal efficiency remain above 90% after 3 cycles. The active hydroxyl radical (OH) generated during heterogeneous Fenton-like reactions was confirmed through electron spin resonance (ESR) spin-trapping technique. The Hg0 removal mechanism has been discussed based on the experimental and analytical results.

Effects of reaction conditions on the emission behaviors of arsenic, cadmium and lead during sewage sludge pyrolysis

Sewage sludge is an important class of bioresources whose energy content could be exploited using pyrolysis technology. However, some harmful trace elements in sewage sludge can escape easily to the gas phase during pyrolysis, increasing the potential of carcinogenic material emissions to the atmosphere. This study investigates emission characteristics of arsenic, cadmium and lead under different pyrolysis conditions for three different sewage sludge samples. The increased temperature (within 723-1123K) significantly promoted the cadmium and lead emissions, but its influence on arsenic emission was not pronounced. The releasing rate order of the three trace elements is volatile arsenic compounds>cadmium>lead in the beginning of pyrolysis. Fast heating rates promoted the emission of trace elements for the sludge containing the highest amount of ash, but exhibited an opposite effect for other studied samples. Overall, the high ash sludge released the least trace elements almost under all reaction conditions.