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To gain an in-depth understanding of AAEMs (alkali and alkaline earth metals) transformation during biomass gasification, a fixed-bed reactor is built to simulate the CO 2 gasification at 500–900 °C. The influences of biomass species, gasification temperature, and particle size are examined. The results show that the AAEMs release follow a sequence of candlenut wood > wheat straw > corn stalk. The alkali metals mainly appear as water-soluble inorganic salts and the contents are more than 80%. K mainly occurs as KCl and KClO 4. At higher temperatures, K could combine with Al and Si to form K(AlSi 3)O 8. For candlenut wood, a bigger particle size is beneficial to the transformation of water-soluble K to organic K. For candlenut wood with centimeter-scale, K mainly occurs as organic K in the biochar during 600–700 °C. When the gasification is carried out at 700 °C, K concentrates at the center and its content is even higher than that on the outer surface. While for biochar samples obtained from gasification at 600 and 900 °C, the K content at the center is lower than that on the outer surface due to the continuous outward transformation of K from the central biochar. • AAEMs release follow an order of candlenut wood > wheat straw > corn stalk. • K can combine with Al and Si to form K(AlSi 3)O 8 above 900 °C. • Bigger particle is beneficial to transformation of water-soluble K to organic K. • K spatial transformation is related to its occurrence mode and diffusion rate. [ABSTRACT FROM AUTHOR]

To study the tri-combustion characteristics of coal, biomass, and oil sludge, the computational particle fluid dynamics (CPFD) method is employed to simulate the flow, heat transfer, and combustion processes in a 130 t h−1 circulating fluidized bed (CFB) boiler. The effects of blending ratio, secondary air inlet angle, and excess air coefficient are evaluated in detail. The results show that the mole fraction of SO 2 in the furnace is slightly lower than that in the cyclone separator. NO x has high mole fraction near the fuel inlet. As the biomass blending ratio rises from 30 % to 50 %, the O 2 mole fraction at the furnace outlet increases from 0.0601 to 0.0629, while CO 2 exhibits the opposite tendency. The highest and lowest NO x mole fractions at the furnace outlet are 4.1648 × 10−5 and 3.9862 × 10−5, respectively. As the blending ratio of oil sludge rises from 10 % to 20 %, the mole fraction of SO 2 at the furnace outlet increases from 3.3041 × 10−4 to 4.8952 × 10−4. The mole fraction of NO x in the furnace shows a positive correlation with the excess air coefficient, while SO 2 is on the contrary. As the jet angle increases from 15° to 30°, the NO x mole fraction at the furnace outlet decreases from 4.1696 × 10−5 to 3.9862 × 10−5. • CPFD method is employed to study the tri-combustion characteristics. • NO x shows a positive correlation with the excess air coefficient. • The co-combustion of oil sludge promotes the generation of SO 2. • Optimizing the secondary air inlet angle could reduce NO x emissions. [ABSTRACT FROM AUTHOR]

Candlenut wood with large particle size is selected to investigate the biomass gasification catalyzed by potassium. The sample pore structure, the spatial distribution of potassium, and the effects of potassium salt species on the biomass gasification with CO 2 are examined. The results show that the large particle candlenut wood exhibits obvious spatial anisotropy and that the pore structure is mainly distributed along the axial direction. Large particle candlenut wood has a more uniform distribution of potassium salts along the axial direction. Part of the potassium salt releases outward during the gasification, which reduces the potassium salt content in the sample center. The average potassium contents of sample loaded with KCl and biochar of sample loaded with KCl are 9.273% and 7.745%, respectively. The synthesis of polycyclic aromatic hydrocarbons in tar could be inhibited by potassium, which could also catalyze the gasification and methane removal reactions of biochar and facilitate the formation of CO and H 2. Compared to raw sample (28.99%), the syngas yields from the gasification of sample loaded with KCl, sample loaded with K 2 CO 3 , and sample loaded with K 2 SO 4 are 40.22%, 52.16%, and 41.72%, separately. The catalysis of potassium is closely related to its occupation of the active sites on biochar. The chemical bonds formed by potassium and biochar are repeatedly broken and formed during the gasification, which promotes the decomposition of organic matter. Compared with KCl and K 2 SO 4 , K 2 CO 3 has a better catalytic effect. • X-ray CT imager is employed to characterize the pore structure of samples. • K is more uniformly distributed along the texture direction of the biomass. • The catalytic effect of K 2 CO 3 is greater than that of KCl and K 2 SO 4. • K could catalyze biomass gasification by occupying active sites. [ABSTRACT FROM AUTHOR]

• Large particle size biomass is conducted for oxygen-stream gasification. • The spatial distribution of AAEMs are detected and analyzed. • X-ray CT technology is employed to interpret AAEMs catalytic gasification. • The mechanism of AAEMs catalytic gasification for large particle biomass is studied. To evaluate the effect of alkali and alkaline earth metals (AAEMs) species on the catalytic gasification of large particle-size biomass, a vertical fixed-bed reactor is conducted for candlenut wood gasification under the oxygen-stream atmosphere. The biochar samples derived from gasification are characterized by SEM, X-ray CT, BET, and FTIR. Tar and syngas are analyzed via GC–MS and GC respectively. Advanced X-ray CT technology provides beneficial visualization to assist in the interpretation of the catalytic gasification of large particle-size biomass loaded with AAEMs. The results indicate that a progressive augmentation of AAEMs content along the radial direction and end surface for all loaded samples and biochar samples, which could also be visualized from the 3D reconstruction of X-ray CT. Many large pores (40–60 μm) aligned along the grain direction collapse after the gasification and generate numerous micropores in biochar samples. 10–20 μm pores are more prominent in biochar as the biomass samples are loaded with KCl and CaCl 2. The biochar from gasification of biomass loaded with CaCl 2 has more well-developed pores, a larger specific surface area, and –OH compounds, aldehydes, ketones and carboxylic acids. The addition of AAEMs facilitates the high generation of M1 compounds (contains 1 benzene ring) in the tar and suppresses the enhancement of M4 compounds, long-chain alkanes, and other compounds. The lowest carbon conversion (57.12 %) is acquired from acid-washed sample. H 2 concentration augments but CO concentration declines by loading AAEMs. The highest H 2 concentration of 62.1 % is detected by the addition of CaCl 2. When loaded with KCl, the syngas calorific value reduces by 1.37 %, whereas loaded with NaCl, CaCl 2 , and MgCl 2 show an augmentation of 11.48 %, 10.56 %, and 2.55 %, respectively. A decrement of C n H x concentration in the syngas derived from gasification of biomass samples loaded with KCl and MgCl 2 and an increment one loaded with NaCl and CaCl 2 are acquired. [ABSTRACT FROM AUTHOR]

The separation of low-temperature coal tar (LTCT) containing solid particles by vacuum distillation is essential in various applications, such as in-situ pyrolysis. However, the separation characteristics of solid-containing LTCT using vacuum distillation have yet to be fully understood. Therefore, explorations were conducted with variations in pressure and solid particle concentration by analyzing pitch with Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The FTIR demonstrated that the organic constituents exhibit greater regularity at higher temperatures, leading to a 2 % reduction in the tightly bound cyclic OH tetramers, an intricate hydrogen bonding. The structural parameters indicate a 2 % decrease in f ar H, alongside a decline in AR from 0.332 to 0.293. This suggests that the low-pressure distillation conditions contribute to an increased retention of aromatic hydrocarbons in pitch, potentially complicating its subsequent utilization. The reduction in F from 2.273 to 2.029 signifies a shorter aliphatic chain, indicative of an intensified degradation effect. The elevated content of solid particles results in a more rigid texture of pitch in micromorphology. This study examined LTCT pitch to clarify the separation mechanism of solid-containing LTCT, offering insights into appropriate vacuum distillation conditions for LTCT separation and aiding in the effective utilization of pitch products. [Display omitted] • Analyzing pitch using FTIR and SEM reveals the LTCT vacuum distillation procedure. • Elevated distillation temperatures lead to deeper deoxygenation of the pitch. • Organic components are arranged more regularly at elevated temperatures. • Too low distillation pressure results in aromatic hydrocarbons remaining in pitch. • Increasing solids content makes the pitch harder and less friable texture. [ABSTRACT FROM AUTHOR]