Modification of rotary air preheater toward achieving extended life-span utilizing porous media approach: A case study

Author(s):  
Hamed Hajebzadeh ◽  
Abdulhamid NM Ansari

The main goal of this study is to achieve the extended operating life of the rotary regenerative air pre-heater (Ljungström) of Bandar Abbas power plant by modifying operational parameters by decreasing the corrosion. To achieve this goal, a three-dimensional CFD simulation of the Ljungström is carried out, utilizing the thermal non-equilibrium porous media model. Temperatures are validated against measured data from the power plant with a maximum relative error of 5.54% on the Celsius scale, and mass flow rates are validated with a maximum relative error of −5.25%. The effect of the Ljungström key parameters including the rotational speed, cold layer material, inlet air/flue gas temperature, and mass flow rate, are analyzed in presence of leakages and neglecting it, using porous media approach. The leakage effect is investigated considering radial and axial/peripheral clearances. Finally, a simulation is performed by applying feasible improved parameters extracted from the above analyses considering the effect of all parameters together in presence of leakages, which shows a 6.14% improvement in the Ljungström effectiveness, reducing the total leakage to about one-third of the actual model and eliminating any corrosion.

2021 ◽  
Vol 261 ◽  
pp. 01006
Author(s):  
Boxu Zhang ◽  
Qi Li ◽  
Shilong Ding ◽  
Bowen Lv

The air preheater of coal-fired units has the problem of ash blocking. Combining the working principle and ash blocking mechanism, FLUENT uses the porous media model to simulate the air preheater, and the corresponding mass flow rate at different speeds or air side inlets is obtained. The temperature results are compared and analyzed, and a reasonable air preheater is used to reduce ash clogging.


2020 ◽  
Vol 165 ◽  
pp. 01006
Author(s):  
Yiquan Guo ◽  
Junying Zhang

In this paper, a collision model between atomized droplets of agglomeration solution and particles is established. On this basis, the effects of flue gas temperature, atomized droplet diameter and other factors on the particle agglomeration process are studied. In addition, the evaporation model of agglomeration solution in the flue of a power plant is established for the coal-fired unit of power plant. Through CFD software, the variation of flow field velocity, temperature and pressure in the flue is simulated to determine whether the chemical agglomeration technology has negative impact on the actual operating conditions of the power plant. The simulation results show that the velocity and pressure of the flow field in the flue have no obvious change after the agglomerating agent is injected. Besides, the temperature drop of about 7°C. The droplets evaporate completely at a distance of 7-8 m after spraying. The evaporation time of droplets is within 1.6 s.


2020 ◽  
Vol 307 ◽  
pp. 01050
Author(s):  
Karima SELLAMI ◽  
M’barek FEDDAOUI ◽  
Nabila LABSI ◽  
M’hand OUBELLA ◽  
Youb Khaled BENKAHLA

The paper deals with numerical study of drying process of porous media of sand during the evaporation of a liquid saturated porous layer within parallel vertical channel. The liquid and air streams are modeled as two coupled laminar boundary layers incorporating non-Darcian models of the inertia and boundary effects. The governing equations and the associated boundary conditions are discretized by means of the finite volume method implemented on a staggered mesh and the velocity-pressure coupling is processed by the SIMPLER algorithm. The influences of the inlet mass flow of the drying gas, porous layer thickness and the porosity on the drying process are analyzed. Results show that the drying rate of the porous media is improved by the reduction of the porosity and porous layer thickness a large drying rate is obtained with high inlet mass flow and high inlet gas temperature.


2017 ◽  
Author(s):  
E. Rogdakis ◽  
P. Bitsikas ◽  
G. Dogkas

In the present work, a three dimensional (3D) Computational Fluid Dynamics (CFD) analysis is applied to a designed small compact regenerator with specific porosity and wire diameter. The regenerator was studied as a part of a Stirling Engine designed in a simple way. The gas temperature along the regenerator followed an approximately linear profile, while the metal temperature showed a small deviation during the engine cycle. The heat transfer coefficient between the gas and the matrix of the regenerator, along with the associate heat transferred were also derived. The heat exchanged in the regenerator is significantly higher to the respective heat in the engine’s heater and cooler. Additionally, the pressure drop and the related energy dissipation are studied. Their variation is largely dependent on both mass flow-rate and working gas velocity. The friction factor coefficient for the designed regenerator is correlated with Reynolds number and an equation of two variables is derived. Finally, the results of the CFD simulation are compared to those produced by a one-dimensional numerical model. These results include gas mass, mass flow-rate and Reynolds number, as well as the heat transferred between the gas and the regenerator matrix. Except for the case of the exchanged heat, the deviation between the two approaches is very small.


2021 ◽  
pp. 281-281
Author(s):  
Kamyar Mohammadpour ◽  
Ali Alkhalaf ◽  
Ali Chitsazan ◽  
Eckehard Specht

Understanding the flow pattern of the gas jets in packed beds can have considerable significance in improving reactor design and process optimization. This study researches the fuel diffusion in the radial direction and the flame length in a packed bed of a Parallel Flow Regenerative (PFR) Shaft kiln. This kiln is characterized that the fuel is injected vertically in the packed bed using a lot of lances in the cross-section while the combustion air is distributed continuously. Such a large, packed bed has to be approximated as a porous media. This assumption is used to model the reactive flow in the kilns. Using a box with 700 spheres of 52 mm spheres in Body-Centered Cube (B.C.C.) arrangement the local concentrations of injected nitrogen in airflow were measured. The measured values match approximately with those calculated with the Porous Media Model (PMM). The studied parameters are the number of burners and burner arrangements. The radial mixing of fuel and air in a packed bed is relatively bad. Therefore, a lot of burners are needed for better temperature homogenization in the cross-section.


2020 ◽  
Vol 10 (4) ◽  
pp. 471-477
Author(s):  
Merin Loukrakpam ◽  
Ch. Lison Singh ◽  
Madhuchhanda Choudhury

Background:: In recent years, there has been a high demand for executing digital signal processing and machine learning applications on energy-constrained devices. Squaring is a vital arithmetic operation used in such applications. Hence, improving the energy efficiency of squaring is crucial. Objective:: In this paper, a novel approximation method based on piecewise linear segmentation of the square function is proposed. Methods: Two-segment, four-segment and eight-segment accurate and energy-efficient 32-bit approximate designs for squaring were implemented using this method. The proposed 2-segment approximate squaring hardware showed 12.5% maximum relative error and delivered up to 55.6% energy saving when compared with state-of-the-art approximate multipliers used for squaring. Results: The proposed 4-segment hardware achieved a maximum relative error of 3.13% with up to 46.5% energy saving. Conclusion:: The proposed 8-segment design emerged as the most accurate squaring hardware with a maximum relative error of 0.78%. The comparison also revealed that the 8-segment design is the most efficient design in terms of error-area-delay-power product.


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