Two-Dimensional Computational Fluid Dynamics Simulation of Heat Removal in Fluidized Bed Methanation Reactors from Coke Oven Gas Using Immersed Horizontal Tubes

Accurate prediction of the bed-to-tube heat transfer coefficient (HTC) is the foundation of developing efficient fluidized bed heat exchangers, but there is still a lack of an effective prediction method. In this paper, the heat transfer mechanism around the immersed tube is revealed through the correlation analysis method. A computational fluid dynamics simulation was conducted to provide various flow field data for a gas–solid fluidized bed with an immersed tube. A correlation analysis was conducted to characterize the relationship between the local HTC and various factors. The results show that Kendall’s rank correlation coefficient (r k) between the solid phase volume fraction and HTC is less than 0.5 on the top of the tube, while the r k on the bottom side exceeds 0.9. According to the distribution characteristics of r k and the emulsion phase contacting time fraction (δe) around the tube, a theoretical model containing three different heat transfer mechanisms was developed. The threshold value for defining the dynamically changing boundaries of each heat transfer mechanism is obtained (δe = 0.88 and r k = 0.82). A comparison analysis demonstrates that the proposed model can predict the average HTC with a deviation of less than ±25% within a wide range of particle sizes (100–1000 μm).

Section: Introductionmentioning

confidence: 99%

Novel Segmental Model for Predicting Bed-to-Tube Heat Transfer Coefficient in Gas–Solid Fluidized Beds

Zheng,

Chen,

Liu

et al. 2024

“…Dense downward particle flow is a common particle flow state and is widely applied in various particle transport equipment or chemical reactors (circulating fluidized bed, silos, moving bed heat exchanger, chemical looping combustion reactor, etc.). In a downward particle flow channel, it is common to arrange internals to adjust the flow state or to serve as heat exchange tubes . Also, the installed intrusive measurement equipment can be viewed as another kind of internal.…”

Section: Introductionmentioning

confidence: 99%

“…In a downward particle flow channel, it is common to arrange internals to adjust the flow state 5 or to serve as heat exchange tubes. 6 Also, the installed intrusive measurement equipment 7 can be viewed as another kind of internal. The drag forces acting on the arranged internals when particles flow around it may result in vibration, material fatigue, or even failure of the whole internal.…”

Section: Introductionmentioning

confidence: 99%

Semiempirical Model of the Drag Force Acting on an Obstacle in Downward Dense Particle Flows as per the Flow-Around Behavior

Liu

Yang

Zhang

et al. 2023

Determination of the flow-around drag force acting on an internal when particles downwardly flow around the internal is important for the safety of internals in the downward particle flow channel. In this study, the flow behaviors of particles downwardly flowing around different obstacles were investigated and a semiempirical drag force model was proposed based on the characteristics of the flow patterns. The proposed model was validated and key coefficients were correlated using the experimental data. The results indicate that there were three featured flow zones when particles downwardly flowed around an obstacle: the flow stagnant zone (disappear for triangular/conical obstacle), the slip-shear flow zone, and the flow separation zone. The stagnant zone angle and the flow separation angle were proposed to depict transition points of three flow zones when particles flowed around a cylindrical/spherical obstacle, and the two angles were found independent of the flow condition. A drag force model as per the flow patterns was proposed. The model decomposed the drag force into the compression force, the shear force, and the confinement force. The expressions of the compression stress, the shear stress, the effective area, and the confinement force were given. The mathematical form of the proposed model was validated and key coefficients in this model were also correlated using the experimental data. The average error of the drag force model was ±7.6% while the maximum error was within ±15%.

“…The oil crisis in the 1970s accelerated the development of substitute natural gas (SNG) production via methanation. Today, a sustained effort is made to investigate the methanation technology. , Usually, the main reactions in a fluidized-bed reactor for the methanation process are as follows The first reaction is CO methanation over the catalytic metal, such as Ni, Ru, Zr, etc. The second reaction is the water–gas shift (WGS) reaction, which accompanies the methanation process and contributes to improving the methane purity .…”

Section: Introductionmentioning

confidence: 99%

Three-Dimensional Simulation of the Methanation Process in a Circulating Fluidized-Bed Reactor

Sun

Luo

Fan

2021

In the current work, a circulating fluidized-bed reactor for methanation was proposed and studied numerically. A three-dimensional (3D) model was built, and the model was validated with measurements in a lab-scale reactor. The operating behavior and influences of inlet gas velocity, mass inventory, and temperature on the performance of the circulating fluidized-bed reactor were obtained by numerical simulations. It turned out that the circulating fluidized bed can be used as a reactor for the methanation process, and products with a high fraction of CH 4 were obtained at the outlet of the reactor. Increasing the solid inventory or circulating rate was beneficial for full conversion of reactants and the high selectivity of methane. Moreover, the temperature influenced the final products, and the reversible reaction and the water−gas shift reaction played an important role with higher temperatures. Finally, this work proved the feasibility and advantage of the circulating fluidized-bed reactor for the methanation process.