Search

In this paper, we propose and analyse pressure-correction schemes based on marker and cell (MAC) method for the linear Stokes–Biot system with a fixed interface. The implicit backward Euler scheme for the time discretization is used, whereas the coupling terms are treated explicitly. These schemes are computationally efficient in that we only solve two decoupled problems. And for Stokes equations, we solve one vector-valued elliptic equation and one scalar-value Poisson equation per time step. These methods have optimal order without the incompressibility constraint of the Stokes system. We prove rigorously that they are unconditionally stable and present the numerical experiments to show their performance. [ABSTRACT FROM AUTHOR]

In this study, a two-section pyrolysis reactor was used for the pyrolysis of corn straw at 550°C. The pyrolysis of corn straw was performed in the first section, while a biochar sample (untreated biochar, acid-washed biochar, or biochar loaded with NaCl, KCl, MgCl2, or CaCl2) was placed in the second section. The effects of the biochar and the metal salts it contained on corn straw pyrolysis were researched. The results showed that acid-washing pretreatment removed most of the metal ions (99.1% of K, 95.2% of Ca, 94.3% of Na, and 95.3% of Mg) in biochar. As the amount of acid-washed biochar added raised from 0 to 3 g, the bio-oil yield declined from 51.2% to 45.3%, the gas yield raised from 21.9% to 27.1%, and volume fraction of CO and H2 increased from 33.5% and 10.8% to 35.6% and 13.1% respectively. In addition, the acid-washed biochar promoted the decomposition of acid substances in the pyrolysis volatiles and the formation of phenolic substances. After loading with various metal salts in biochar, the bio-oil yield is further reduced while gas yield is further increased. Among the metal salts, KCl exhibited the strongest effects on the enrichment of phenolics and decomposition of acids. In addition, MgCl2 clearly promoted CO formation. The results in this study confirm that both biochar and its constituent metal ions play important roles in the secondary cracking of pyrolysis volatiles, and thus biochar has potential for application as a catalyst in biomass pyrolysis. [ABSTRACT FROM AUTHOR]

CeO2-coated SiO2 composite particles with Core-shell structure were successfully prepared, and the dispersion behavior in water was investigated under different pH values, ion-surfactant types and contents by means of Zeta potential and absorbance. Potential energy between particles in suspension was precisely evaluated via DLVO theory, by which the dispersion mechanism of SiO2/CeO2 core-shell composite particles was analyzed, combined with adsorption isotherms and infrared (IR) spectra measurements. The results showed that Zeta potential had a quite coherence with dispersion stability which was greatly affected by pH value, surfactant types and contents. The particles retained dispersion balance by adjusting pH value of suspension to increase electrostatic repulsion energy between particles, and the dispersion stability of suspension was preferable under pH value being 10 around. The adsorption of composite particles was physical adsorption, maximum amount of which reached 31.7 mg/g for CTAB and 19.23 mg/g for SDBS in certain range of concentration. The adding of surfactant SDBS proper dosage improved dispersion behavior greatly, and the adsorption layer of SDBS weakened the Van der Waals attractive energy dramatically and enhanced the absolute value of Zeta potential meanwhile, therefore, heightening of the electrostatic repulsion energy, then, leading to the improvement of dispersion stability of suspension. For the dispersion stability of suspension, SDBS was preferable to CTAB. [ABSTRACT FROM PUBLISHER]

Torrefaction is a promising pretreatment for upgrading biomass. Biomass pellets have been widely used in heating and power plants, but the pellets torrefaction has not been fully studied. The torrefaction performance of raw biomass samples and molded pellets of those biomass samples were compared in this study. The torrefaction was performed using a horizontal sliding tube furnace with different torrefaction severities (210°C, 240°C, 270°C, and 300°C; 15 min, 30 min, and 45 min). Three key results were obtained from this work. (i) The temperature and residence time had an obvious influence on biomass torrefaction performance. Compared to the untreated samples (rice husk particles, rice husk pellets, pine wood sawdust, and pine wood pellets), the oxygen content of the samples torrefied under the most severe torrefaction conditions (300°C and 45 min) decreased by 43.1%, 27.4%, 34.2%, and 25.3%, respectively. In contrast, the high heating value and hydrophobicity of the torrefied samples increased. (ii) The biomass source had important effects on the torrefaction results. Under the same torrefaction conditions, the mass yields and energy yields were highest for pine wood sawdust, followed by rice husk particles, pine wood pellets, and rice husk pellets. This is related to the composition and thermal decomposition of the different biomass samples. (iii) The loose raw biomass released more volatiles during torrefaction compared to biomass pellets, which were limited by heat and mass transfer, leading to complete thermal decomposition of hemicellulose and other components. Overall, the torrefaction performance of biomass varied with the temperature and residence time, and torrefaction had a greater effect on the raw biomass than on the biomass pellets. [ABSTRACT FROM AUTHOR]