3-D full-loop simulation of an industrial-scale circulating fluidized-bed boiler

Shape Effect of the Riser Cross Section on the Full-Loop Hydrodynamics of a Three-Dimensional Circulating Fluidized Bed

In this work, numerical simulation is carried out in a three-dimensional full-loop pilot-scale circulating fluidized bed to explore the shape effect of the riser cross section on the typical flow characteristics of the bed via the multiphase particle-in-cell (MP-PIC) method. The gas and solid phases are modeled with the large eddy simulation and Newton's law of motion in the Eulerian and Lagrangian frameworks, respectively. The proposed model has been well validated with experimental data, followed by evaluating the typical core-annulus structure and the nonuniformity of the solid phase distributed along the radial and axial directions of the riser. Then, the particle-scale information of the solid phase distributed in different parts of the system is explored. The results demonstrate that (i) the square riser gives rise to a higher solid inventory in the standpipe owing to the stronger circulation intensity; (ii) the thickness of the solid back-mixing layer reduces along the riser height; the solid back-mixing tends to concentrate in the four corners, while it is not obvious near the sidewalls of the square riser; and (iii) nonuniform distribution of the particle-scale information of the solid phase (e.g., mass, flux, drag force, and slip velocity) can be observed. The square riser gives rise to comparatively more uniform axial mass distribution, a larger rising solid flux, larger horizontal transportation velocity between the core and annulus regions, and a larger horizontal dispersion coefficient in the riser, as compared with the corresponding ones in the circular riser.

Progress in coal chemical technologies of China

China’s unique energy reserve structure abundant in coal and scarce in crude oil and natural gas has promoted heavy investment on the research and development of clean coal chemical technologies during last two decades, which has turned China into a heartland for demonstrating, developing, and commercializing virtually every aspect of new coal chemical process technologies. Consequently, breakthroughs in coal gasification, indirect and direct coal-to-liquid (CTL) processes, and methanol-to-olefins (MTO) technologies are catching attention worldwide. Gasification technology for syngas production is the key to high plant availability and economic success for most coal chemical projects. During the past 20 years, both international and Chinese gasifier vendors have reaped great successes in licensing their technologies in the domestic market. Notably, the local vendors have been investing heavily on inventing and improving their technologies to suit the specific requirement of gasifying a variety of coals. The opposed multinozzle gasification technology from East China University of Science and Technology was taken as an example to demonstrate the recent development in this field. The coal chemical industry in China has witnessed several notable achievements in chemical engineering progress, namely CTL (indirect and direct) and MTO. Comprehensive reviews on topics such as catalysis, kinetics, and reactor design and process integration will be provided by leading scientists in related fields with firsthand information to showcase the contributions of Chinese researchers to chemical engineering science and technology.

Energy-minimization multiscale based mesoscale modeling and applications in gas-fluidized catalytic reactors

Gas-solid fluidization is intrinsically dynamic and manifests mesoscale structures spanning a wide range of length and timescales. When involved with reactions, more complex phenomena emerge and thus pose bigger challenges for modeling. As the mesoscale is critical to understand multiphase reactive flows, which the conventional two-fluid model without mesoscale modeling may be inadequate to resolve even using extremely fine grids, this review attempts to demonstrate that the energy-minimization multiscale (EMMS) model could be a starting point to develop such mesoscale modeling. Then, the EMMS-based mesoscale modeling with emphasis on formulation of drag coefficients for different fluidization regimes, modification of mass transfer coefficient, and other extensions are discussed in an attempt to resolve the emerging challenges. Its applications with examples of development of novel fluid catalytic cracking and methanol-to-olefins processes prove that the mesoscale modeling plays a remarkable role in improving the predictions in hydrodynamic behaviors and overall reaction rate. However, the product content primarily depends on the chemical kinetic model itself, suggesting the necessity of an effective coupling between chemical kinetics and flow characteristics. The mesoscale modeling can be believed to accelerate the traditional experimental-based scale-up process with much lower cost in the future.