To capture elemental mercury (Hg0) at high temperatures in simulated syngas, Pd/Al2O3 sorbents were developed using an impregnation method. The Pd/Al2O3 sorbents with a Pd loading value of 8% exhibited high Hg0 capture activity from 200 to 270 °C. Over 90% of the mercury capture by 8Pd/Al2O3 was achieved for operating temperatures up to 270 °C. The superior performance of Pd/Al2O3 sorbents could be primarily ascribed to the formation of a Pd–Hg amalgam. H2 and CO were found to be promotional on Hg0 capture because of the reduction of PdO to Pd metal. H2S significantly inhibited Hg0 capture due to the consumption of the active palladium. HCl promoted Hg0 capture, which could be ascribed to the catalytic oxidation of Hg0 to HgCl2. H2O showed a prohibitive effect on Hg0 removal. The regeneration experiments indicated that the spent Pd/Al2O3 sorbents could be facilely revivified and reused.

•The exact region rich in K and Cl and the morphology of K- and Cl-rich particles in rice straw.•Visual evidence of K- and Cl-rich particles found gradually reducing or even disappearing during rice straw pyrolysis.•The release of K and Cl is determined by both the mobility of K and Cl and the resistance along the diffusion way.This study investigates the release and migration of potassium (K) and chlorine (Cl) in micro-spatial distribution during rice straw pyrolysis in a lab-scale reactor at temperatures from 300 °C to 900 °C. The K and Cl enrichment region and the morphology of K- and Cl-rich particles in rice straw and char obtained after pyrolysis was clearly revealed for the first time in this field of research. Scanning Electron Microscope/Energy-Dispersive Spectrometry (SEM/EDS) was used to analyze the morphology and distribution of inorganic matters in raw rice straw and water-washed rice straw, as well as the char obtained from raw rice straw pyrolysis, both upon the epidermis (outside surface) and the ground tissue (internal surface). X-ray Diffraction (XRD) was used to analyze the inorganic matters in the obtained char. The particles dispersedly distributed on the cell walls in the ground tissue were proven to be inorganic salt, rich in K and Cl. The ground tissue rather than the epidermis is the main part that decomposes and loses weight during pyrolysis. K and Cl diffuse from the ground tissue to the epidermis and they might be partly restricted to the epidermis during rice straw pyrolysis. The release of K and Cl is determined by both the mobility of K and Cl and the resistance along the diffusion way inside rice straw.

•A novel U-wall was proposed to extend heating surface area in a CFB furnace.•The solid volume fraction inside the U-wall has a U-shaped profile.•The solid vertical velocity inside the U-wall has an inverted-U-shaped profile.•A solid downward flow is found at the U-wall surface in the upper section.•There is an optimal width for the U-walls in a CFB boiler furnace.As the capacity of a circulating fluidized bed (CFB) boiler is increased, the surface area of the wing walls must be increased to maintain the heat balance in the furnace. The minimum spacing requirement between adjacent wing walls limits their total area. A novel suspended heat transfer surface is proposed to address this problem. The suspended surface is designed with a “U” shape and is referred to as U-wall. U-walls are suspended from the top of the furnace and may provide more than 25% greater heat transfer surface area. In this study, the flow of solids over U-walls in a CFB was measured using a fiber optical probe. The effects of the superficial gas velocity, the bed material inventory, and the width of the U-walls on the solid volume fraction and particle velocity were investigated. The solid volume fraction had a U-shaped profile inside the U-wall except in the upper section, where the profile had an approximate straight-line shape. Their values increased with the superficial gas velocity and the bed material inventory. The solid vertical velocity had an inverted-U-shaped profile inside the U-wall. The solids were found to flow downward at the U-wall surface in the upper section, where the velocity increased with the superficial gas velocity and the solid suspension density. The flow of solids at the U-wall surface in the middle and lower sections changed from downward to upward as the superficial gas velocity increased. In a CFB furnace, there is an optimal width for U-walls that provides the best heat absorption characteristics; larger or smaller widths are both undesirable.

The distilled fraction (DF) from bio-oil molecular distillation can be used for the generation of aromatic hydrocarbons by cocracking with ethanol over HZSM-5. In this work, typical model compounds were selected to simulate the DF, and a modified Ga2O3/HZSM-5 was adopted to promote the aromatization reaction. Compared with unmodified HZSM-5, 15% Ga2O3/HZSM-5 could increase the yield of the oil phase from 31.5 to 39.2 wt % during cocracking of a mixture of model compounds and ethanol, with an obvious decrease in the C3–C4 gaseous hydrocarbon yield. Moreover, the total content of aromatic hydrocarbons in the oil phase was around 95%. The production of monoaromatics, especially xylenes, was favored. The influences of reaction temperature and feedstock weight hourly space velocity (WHSV), as well as the catalyst regeneration, were also investigated. On the basis of the experimental results, a reaction mechanism is proposed and the promotion of aromatic hydrocarbon generation by Ga2O3 is discussed.

•We design a space storage sampler for furnace particle sampling.•A typical “core-annular” flow structure was generated in the CFB boiler.•The biomass particle enrichment phenomenon occurs in the lower furnace space.•We report that an inhibition mechanism limit the flow of lighter biomass particles.Biomass and bed material particles have been found to exhibit significant density differences during the operation of a circulating fluidized bed boiler. Further studies are required to analyze the mixed flow characteristics of these particles in a furnace. We built a test apparatus for a cold-operation, biomass-circulating fluidized bed and designed a space-storage sampler for furnace particle sampling based on modeling theory. The current study found that adding biomass particles nearly did not affect the flow characteristic and distribution of bed material particles because of density difference. However, biomass-particle enrichment phenomenon unexpectedly occurred in the lower furnace region and at the bottom of the top furnace outlet where biomass particle concentration was extremely low. Analyses and observations revealed that downward flow near the wall can effectively carry biomass particles to the bottom of the furnace, thus leading to the enrichment of biomass particles in the lower furnace region. The inhibition mechanism of dense, inert, bed material particles also limited the flow of light biomass particles into the upper furnace region. Different kinds of biomass exhibited similar particle distribution characteristics. Light biomass particles were enriched at the bottom of the furnace, and could hardly reach the furnace outlet.

•Bio-oil was upgraded in supercritical ethanol with low ratios of ethanol to bio-oil.•C-supported catalysts gave better performance over Ru/HZSM-5.•Solvent recovery and reutilization reduced ethanol to bio-oil ratio to about 1:1.•Coke and metal particle sintering deactivated Ru/C.Supercritical upgrading of bio-oil is an effective method to upgrade bio-oil. In this paper, upgrading of bio-oil was carried out in supercritical ethanol with the aim of catalyst selection, reducing solvent consumption and catalyst stability study. Compared with Ru/HZSM-5, C-supported catalysts (Pt/C, Pd/C, and Ru/C) gave better catalytic performance. Over the C-supported catalysts, the heating value increased from 21.45 MJ/kg to about 30 MJ/kg and the pH value increased from 3.13 to about 5.5. The relative content of desired products reached as high as 80% over Ru/C. The ratio of ethanol to bio-oil was further reduced to about 1:1 by solvent recovery and reutilization. The relative content of desired products particularly that of esters increased with the recovered solvent. Catalytic stability study of Ru/C showed that the relative content of desired products decreased gradually with the number of catalyst recycle times while the consumption of hydrogen decreased mainly in the first recycle. Coke deposition and sintering of metal particles were the main reasons for the deactivation of Ru/C.

In the present study, the NO and N2O formation characteristics during combustion of five biomass fuels (rice straw, wheat straw, corn stalk, sugarcane leaf, and eucalyptus bark) and one bituminous coal, as a comparison, were investigated in a horizontal fixed-bed reactor. It showed that there was still a considerable degree of N2O conversion for biomass fuels, although NO was formed in a much larger amount. Most of NO and N2O were formed during the devolatilization stage for biomass fuels; therefore, optimizing the supply of air and fuel during biomass combustion in actual boilers can be expected to achieve ultralow emissions of nitrogen oxides. There was no clear correlation between the NO and N2O yields and fuel N content, which indicated that the nitrogen functionality and other components, such as inherent mineral matter, present in biomass must have great influence on the nitrogen transformation during thermal processing. When rice straw was co-fired with eucalyptus bark, nonlinear behavior could be seen and the fuel N conversion to NO was largely enhanced. In the temperature range of 700–900 °C, the fuel N conversion to NO first increased and then decreased slightly, while the conversion to N2O showed a continuous decreasing trend. The fuel N conversion to NO and N2O showed a general increasing trend with the increase of the inlet oxygen concentration, and this phenomenon was more obvious at higher temperatures. The results presented in this study will help to gain some insight onto the fundamental mechanism of fuel N conversion during biomass combustion.

Biomass tends to form deposits and tends to slag during combustion. This study focused on deposits obtained from a circulating fluidized bed (CFB) in a biomass power plant. Analyses using scanning electron microscopy, energy-dispersive spectrometry, and X-ray diffraction are also included. The results indicate that the deposits are dense with a certain hardness, which resulted from the erosion of particles in the CFB. The deposits are high in K, Na, Cl, and Ca, whereas Si, Al, Mg, and S contents are relatively lower. KCl and K2SO4 are the main components of the deposits. The particles in the flue are captured by the viscous layer that was formed by the condensation of gaseous KCl and K2Ca(SO4)2 on the surface of the tubes. Moreover, deposits are formed under the effect of the adhesion and capturing processes, in alternation.

During biomass combustion, the SO2 emission would still be a problem in some cases, although the average sulfur content is relatively lower than that of coal and other fossil fuels. In this work, the characteristics of self-desulfurization during sugarcane leaf combustion in a circulating fluidized bed were experimentally investigated. First, a laboratory fixed-bed reactor was used to study how the char particles take part in the self-desulfurization process. It was observed that SO2 can be largely captured by char in the temperature range of 700–900 °C. Most of the captured sulfur was incorporated with organic char matrix rather than directly retained by inherent alkali and alkaline-earth matters in the form of inorganic salts. During char combustion, substantial amounts of the captured sulfur could be retained in the ash, which was mainly limited by the alkali and alkali-earth matters available. At higher temperatures (>800 °C), the sulfur retention reduced, mainly because the alkali and alkali-earth matters would give priority to form silicate compounds rather than the occurrence of sulfate reactions. Then, a pilot-scale circulating fluidized-bed experiment was performed to study SO2 emission behaviors during sugarcane leaf combustion. It showed that there was nearly no SO2 emission when the combustion temperature was controlled below 800 °C. The sulfur retention calculation based on ash balance showed that about 87% of fuel S was retained in fly ash. This was mainly attributed to the intense gas–solid contact within the combustor that could largely enhance the sulfur retention reactions.

This paper presents the experimental results of CaO sorption enhanced anaerobic gasification of biomass in a self-design bubbling fluidized bed reactor, aiming to investigate the influences of operation variables such as CaO to carbon mole ratio (CaO/C), H2O to carbon mole ratio (H2O/C) and reaction temperature (T) on hydrogen (H2) production. Results showed that, over the ranges examined in this study (CaO/C: 0–2; H2O/C: 1.2–2.18, T: 489–740 °C), the increase of CaO/C, H2O/C and T were all favorable for promoting the H2 production. The investigated operation variables presented different influences on the H2 production under fluidized bed conditions from those obtained in thermodynamic equilibrium analysis or fixed bed experiments. The comparison with previous studies on fluidized bed biomass gasification reveals that this method has the advantage of being capable to produce a syngas with high H2 concentration and low CO2 concentration.