Effects of Operating Parameters on Solids Flux in a High-Density/-Flux Circulating Fluidized Bed Riser Reactor

The riser reactor of catalytic cracking of crude oil to chemicals (COTC) contains gas−solid heterogeneous structures represented by a particle cluster naturally. To more accurately describe the COTC, a dominant filtered drag model was established considering the reduction of an interphase exchange coefficient (k sg ) for particle cluster existence. With the updated filtered drag model, a modified Euler−Euler two fluid model (model A) was proposed and verified. Then, model A coupled with the 4-lump COTC reaction kinetic model and reaction enthalpy model was used to construct a new heterogeneous filtered two-fluid model (FTFM, model B). The mass fraction of the cracking products calculated by FTFM was in good agreement with those obtained in the experiment. Meanwhile, the effects of the catalytic cracking reaction on drag parameters were discussed. The results show that catalytic cracking reaction and reaction heat can lead to k sg decreasing, and mesoscale structures can be observed intuitively with the revised filtered model. The constructed model and methodology in this work can be used to accurately predict the cracking products distribution, which could decrease the designing and optimizing costs of an industrial COTC reactor.

Section: Gas−solid Flow With Model a 411 Heterogeneous Filtered Drag ...mentioning

confidence: 99%

Simulation of Crude Oil to Chemicals Based on Mesoscale Filtered Drag Subgrid Model

Wang,

et al. 2024

“…A solids storage system (including the storage tank and downcomer) is constructed in the CFB unit to offer a sufficient driving force for high solids circulation rates. Other detailed information of the experimental setup has been described in other reports. , During the experiment, gas is air derived from a compressor and solids are FCC catalysts with a particle density of 1500 kg/m 3 and a volumetric average diameter of 85 μm. Particle size distribution is summarized in Table .…”

Section: Experiments Sectionmentioning

confidence: 99%

“…The superficial gas velocity is measured by a vortex flow meter, and G s is obtained by a special designed column as shown in Figure and calculated based on eq . The detailed operating steps of the measuring process also have been shown elsewhere where Δ V is the solids-accumulating volume in the column, ρ b is the bulk density of 970 kg/m 3 , A r is the riser cross-sectional area, and Δ t is the measurement time.…”

Section: Experiments Sectionmentioning

confidence: 99%

Flow of High Solids Density Suspensions in an 18 m High Circulating Fluidized Bed

Wang

Lan

et al. 2019

Self Cite

The detailed distributions of solids holdup in an 18 m high-density circulating fluidized bed are mapped under various operating conditions with fluid catalytic cracking particles. Solids flux (G s) is as high as 1000 kg/(m2 s) when the superficial gas velocity (U g) ranges from 5 to 9 m/s and high-density operation is achieved. For axial distribution, solids holdup decreases exponentially along the riser with a solids holdup up to 0.17 at the riser exist, indicating the high-density operation has been achieved when G s > 800 kg/(m2 s). For radial distribution, a parabolic radial profile at high-density conditions also replaces the “core-annual” flow structure at low-density conditions. Particles can be accelerated to the axial height of 12 m under G s > 800 kg/(m2 s). Both increasing U g and/or decreasing G s can enhance flow development at high-density conditions. The solids-to-air ratio is almost the same at about 70 when high-density operations are achieved.

“…A gas–solid circulating fluidized bed (CFB) system, as a typical chemical reactor, has been widely applied into industrial processes such as oil catalytic cracking, Fischer–Tropsch synthesis, and coal combustion. , The most valuable area of potential applications for CFB is in coal gasification and biomass gasification for power generation, chemical production, and synthesis gas. − Recently, the CFB technology is a promising approach that allows effective gas–solid contact for emission control and chemical looping processes for carbon capture and utilization. − Based on the gas–solid flow directions, operations of a CFB reactor can be achieved either in a riser − where both the gas and solid flow upward counter to the gravity or in a downer , where both the gas and solid flow downward concurrent with the gravity. Normally, most of the reactions like the catalytic cracking and fuel combustion processes take place in the riser reactor since it provides good gas–solid contact, large throughput, proper residence time of the reaction, and flexible operating ranges.…”

Section: Introductionmentioning

confidence: 99%

Cluster Identification by a k-means Algorithm-Assisted Imaging Method in a Laboratory-Scale Circulating Fluidized Bed

Wang

Lan

Sun

et al. 2021

Self Cite

Particle clusters for FCC particles in a gas–solid circulating fluidized bed with a 12.4 m high riser and a 5 m high downer were identified from the images of the gas–solid flow by a k-means machine learning algorithm-assisted processing method. An optimal k value of 3 was determined and justified by several evaluation criteria for the k-means algorithm. The solid holdup obtained from the processed images agrees well with that from the optical fiber method. The particle cluster characteristics between the riser and downer, such as the cluster solid holdup, equivalent diameter, velocity, and frequency, were extracted from the processed images and then compared in detail for the first time. The cluster solid holdup and the cluster velocity in the riser (εcl = 0.05–0.20, V cl = 4–10 m/s) are much higher than those in the downer (εcl = 0.005–0.020, V cl = 2–5 m/s). The cluster equivalent diameter and the cluster frequency in the riser and downer are similar (d cl = 2–10 mm, f cl = 100–400 Hz). Empirical correlations of the cluster characteristics with the local flow conditions and the operating parameters in both the riser and downer are further studied.