DPM Simulations of A-Type FCC Particles’ Fast Fluidization by Use of Structure-Dependent Nonlinear Drag Force

Nonlinear drag force has been a research frontier in complex gas-solid systems. The literature has reported that the commonly-used drag correlations often overestimate drag force and, thus, cause unrealistic homogeneous flow structures in gas-solid fluidized beds of fine particles. For solving this problem, the structure-dependent drag model, derived from energy-minimization multi-scale approach, is used in discrete simulations of fluid catalytic cracking particles in a small riser. The gas phase is dealt with by computational fluid dynamics. Particles are considered as a discrete phase and described by Newton’s second law of motion. Gas-particle phases are coupled according to Newton’s third law of motion. Simulations show that use of structure-dependent drag model results in drag reduction, the effect of which is not so apparent as that in simulations of the two fluid model. The particle clustering tendency, however, is more distinct and leads to more heterogeneous flow structures in riser flow with a much greater amplitude of outlet solid flux fluctuations. Moreover, the behaviors of particle and gas back-mixing can be captured in the present simulations, which was supported by past simulations and experimental data. The simulation time resolution is discussed. The spring constant can be artificially brought down for safe setting of larger time step when modelling the collision process between fine particles with a higher calculation load. To appropriately mimic the continuous decay of van der Waals force may, however, need a much smaller time step. There is also an obvious effect of space resolution on simulations. When using a grid size smaller than 3 times the particle diameter, the simulated clusters turn extraordinarily large, and the effect of gas-solid back-mixing turns insignificant.

Novel Multiplicity and Stability Criteria for Non-Isothermal Fixed-Bed Reactors

With the increasing need to utilize carbon dioxide, fixed-bed reactors for catalytic hydrogenation will become a decisive element for modern chemicals and energy carrier production. In this context, the resilience and flexibility to changing operating conditions become major objectives for the design and operation of real industrial-scale reactors. Therefore steady-state multiplicity and stability are essential measures, but so far, their quantification is primarily accessible for ideal reactor concepts with zero or infinite back-mixing. Based on a continuous stirred tank reactor cascade modeling approach, this work derives novel criteria for stability, multiplicity, and uniqueness applicable to real reactors with finite back-mixing. Furthermore, the connection to other reactor features such as runaway and parametric sensitivity is demonstrated and exemplified for CO2 methanation under realistic conditions. The new criteria indicate that thermo-kinetic multiplicities induced by back-mixing remain relevant even for high Bodenstein numbers. In consequence, generally accepted back-mixing criteria (e.g., Mears’ criterion) appear insufficient for real non-isothermal reactors. The criteria derived in this work are applicable to any exothermic reaction and reactors at any scale. Ignoring uniqueness and multiplicity would disregard a broad operating range and thus a substantial potential for reactor resilience and flexibility.

Discussion on product oil on-line back mixing technology based on a product oil pipeline

The mixed oil treatment of Product oil is an important task of pipeline enterprises. The paperconcluded that the on-line back mixing technology was feasible, compared treatment methods from the perspective of safety and economic benefits. TheProduct oil pipeline is taken as the research object in this paper, studied the concentration distribution of mixed Product oil and amount of mixed Product oilunder operation and shutdown condition, and brief studied Product oil On-line back mixing technology. Combined with the demand and pipeline length, the mixing test is determined at CD station and CQ station. The operation process as follow: First, Product oilsamples areextracted from the pipeline. Second, the index parameters are detected after the oil samples are mixed with different proportions, and obtaining the blending potential under the theoretical situation, the result show that the mixing potential of gasoline is greater than that of diesel. Third, the field test do with arbitrarily mixed oil download scheme, which study two mixed oil surfaces. The required fund of dealing with the mixed oil is obtained combined with the download amount of mixed oil.Finally, comparing with the funds of the previous contaminated treatment methods, it is concluded that the On-line Back Mixing technology has great advantages in both safety and economic benefits.