A Theoretical And Experimental Investigation Of Coke Gasification In A Batch Reactor

A computer model has been developed to simulate the char-gasification process occurring in the gasification component of a crossflow coal gasifier. This process corresponds to the batch gasification process in a combustion pot. Temperature and concentration profiles along the gasifier were obtained by solving the material and energy balances. In order to obtain the data necessary for evaluating and improving the computer model, an experimental system was developed to obtain data for the char-gasification process in the combustion pot. The results show that the gasification rate strongly depends on the air flow rate and that the reactivity of the char has a strong effect on the output gas composition. The results from the computer model were compared with available literature data on the fixed-bed gasifier and the experimental data obtained from this study, and were found to be in good agreement. A sensitivity analysis was performed on the input parameters (heat transfer coefficient, void fraction, particle diameter, and reactivity factor coefficients) of the computer model. The results show the importance of the input parameters in predicting the desired gas composition and total process time

Substitutional Si impurities in monolayer hexagonal boron nitride

We report the first observation of substitutional silicon atoms in single-layer hexagonal boron nitride (h-BN) using aberration corrected scanning transmission electron microscopy (STEM). The medium angle annular dark field (MAADF) images reveal silicon atoms exclusively filling boron vacancies. This structure is stable enough under electron beam for repeated imaging. Density functional theory (DFT) is used to study the energetics, structure and properties of the experimentally observed structure. The formation energies of all possible charge states of the different silicon substitutions (Si$_\mathrm{B}$, Si$_\mathrm{N}$ and Si$_\mathrm{{BN}}$) are calculated. The results reveal Si$_\mathrm{B}^{+1}$ as the most stable substitutional configuration. In this case, silicon atom elevates by 0.66{\AA} out of the lattice with unoccupied defect levels in the electronic band gap above the Fermi level. The formation energy shows a slightly exothermic process. Our results unequivocally show that heteroatoms can be incorporated into the h-BN lattice opening way for applications ranging from single-atom catalysis to atomically precise magnetic structures

Transient Characterization of Type B Particles in a Transport Riser

Simple and rapid dynamic tests were used to evaluate fluid dynamic behavior of granular materials in the transport regime. Particles with densities ranging from 189 to 2,500 kg/m3 and Sauter mean size from 61 to 812 μm were tested in a 0.305 m diameter, 15.5 m height circulating fluidized bed (CFB) riser. The transient tests involved the abrupt stoppage of solids flow for each granular material over a wide range gas flow rates. The riser emptying time was linearly related to the Froude number in each of three different operating regimes. The flow structure along the height of the riser followed a distinct pattern as tracked through incremental pressures. These results are discussed to better understand the transformations that take place when operating over various regimes. During the transients the particle size distribution was measured. The effects of pressure, particle size, and density on test performance are also presented