Gas Flow Distribution Research Articles

Low-rank coal gasification using a bubbling fluidized bed reactor at low operating temperature

Coal gasification is one of coal utilizations that produces less CO2 emission than coal combustion. Coal gasification technology that has been used in Indonesia is generally a fixed bed gasification. Fixed bed is designed for high-rank coal and the majority of Indonesian coal is of a low-rank. Low ash and high moisture content of the Indonesian coal in a fixed bed can affect mechanical and thermal fragmentation, pressure drop, gas and particle flow distribution. The operation of gasifier may cause unstable condition. Another gasification technology is bubbling fluidized bed, which is operated above 1,200°C, so ash can melt. High operating temperature causes agglomeration and makes unstable gasification process. Therefore, in this study, low-rank coal is gasified in bubbling fluidized bed reactor at low operating temperature. The purpose of this study is to determine the optimal conditions of bubbling fluidized bed gasification. The research was conducted in bubbling fluidized bed coal gasification Process Development Unit (PDU) at Coal Utilization Technology Centre of R&D Centre of tekMIRA, Palimanan. Coal was fed continuously as many as 20 kg/hour into a gasifier then was gasified to produce gas using air as a gasifying agent and silica sand as a bed material at 850- 950°C. The produced gas from the gasification was analyzed using the Orsat Analyzer. A simulation using a ChemCAD 7.1 CC steady state was applied to validate the experiment result. From the analyzed result of yield gas composition, the produced CO and CO2 were about 10-15 wt%. Gas compositions that are close to criteria of producer gas, no agglomeration, and stable process condition during study indicate that bubbling fluidized bed gasification at low operating temperature is suitable to be applied as gasification technology for Indonesian low-rank coal.

Gas-Dynamic Stability and the Distribution of Gas Flow Rates over the Blast-Furnace Height

Abstract—The distribution of the gas flow rates over the blast-furnace height is studied. The best blast-furnace gas dynamics is determined by the range of gas-flow rates in the batch column—in particular, at the tuyere exit and in the batch-free charging zone. The velocity of the blast and the blast-furnace gas may be used to assess the stability and optimality of the gas-dynamic conditions in smelting.

РОЗРОБКА І ВПРОВАДЖЕННЯ НОВИХ ПІДХОДІВ ДО ДІАГНОСТИКИ ТА УПРАВЛІННЯ ДОМЕННОЮ ПЛАВКОЮ

The article presents a brief description of the results of blast furnace production research carried out at the Yenakiieve Iron & Steel Works and the Dneprovsky Iron & Steel Integrated Works in 2011–2019. For the conditions of transition modes of blast furnace to ensure its stability in changing the qualitative and quantitative composition of the components of the charge materials, as well as in the change of fuel additives in the blast, the complex use of information of modern means of automated control is proved: stationary thermosets and thermocouples to the lining. New approaches to the choice of rational charging programs using the principle of variable maximum ore loading along the radius of the furnace within the charging cycle for working conditions on a charge of low quality have been developed. The implementation of such a charging program over the next three years has allowed to ensure a stable and economical course of melting, and its adaptation to the technology of using pulverized coal has allowed to reduce the gas flow temperature of the peripheral zone throughout the height of the blast furnace, as well as to preserve the cooling system during the development of lining-free. Expert module of adjustment of the program of charging using the established rational ranges of change of temperature indices of gas flow distribution along the radius of the furnace under different technological conditions of blast furnace has been developed and implemented on three blast furnaces. The method of reasonable choice of location of closed air tuyeres or air tuyeres of different diameter was developed and tested using information on change of lining temperatures on height and circumference of blast furnace. The method of equalizing the raceway adiabatic flame temperature around the blast furnace circumference by creating a non-uniform flow rate of pulverized coal in the air tuyeres has been improved and implemented. The basic technological requirements for blast furnace blasting after its long stop without release of "gantry" cast iron and scraping of materials from the furnace, the use of which before and in the blast furnace blasting of the Yenakiieve Iron & Steel Works and the Dneprovsky Iron & Steel Integrated Works after a long-lasting set-up were developed economic indicators, while ensuring the preservation of refractory lining, structures and equipment.

Blast Furnace Performance Under Varying Pellet Proportion

As a promising method to strengthen the blast furnace smelting and to realize reduced fuel operation, high-proportion pellet charging has become the practice of BF ironmaking. Use of pellet gives rise to uniform bed permeability in comparison with iron ore or sinter. This leads to better gas–solid contact resulting in higher productivity at reduced coke and fuel rate. To achieve the desired gas flow distribution, the burden distribution is changed so that the rollability of pellets is encountered and furnace is maintained in stable condition. This paper discusses the effect of pellet charging proportion on working indices, gas utilization, permeability, fuel rate and production rate of blast furnace. The present work is made to understand the effect of replacing the iron ore proportionately by pellets. An attempt is made to understand the effect of increasing the pellet per cent of the burden charge on the blast furnace process parameters. The results are based on the effect observed in the blast furnace operation.

CFD to Improve the Repeatability and Accuracy of Dust Explosion Tests in the 20-liters Sphere

The experimental characterization of combustible dusts is usually associated to several uncertainty factors that rely on the physical properties of the powder and the operating conditions of the standardized tests (e.g. the ignition time, the dispersion nozzle and pressure). These parameters affect the repeatability of the flammability tests and the precision, or even the accuracy, of their results. In this regard, an explanatory study has been focused on the description of the dispersion process of a combustible dust inside a 20-liters sphere by joining two complementary approaches. At first, a Computational Fluid Dynamics simulation (CFD - Star CCM+) based on an Euler-Lagrange scheme was set according to the geometry and operating parameters that have been established for this equipment through international standards. The predictive results that were determined with this approach were compared with a Particle Image Velocimetry analysis and in-situ measurements. Explosions tests were also performed to validate our analyses. The results showed how the particle size distribution of the dust affects its dispersion trajectories inside the sphere due to the inertial effects and the drag force exerted by the fluid. Furthermore, the analysis of the velocity field and turbulence intensity reveals that the dispersion process can be divided into three different stages, each related to a different repeatability. Tests performed with the classical rebound nozzle have clearly evidenced their effect on the internal distribution of the gas flow and the segregation levels of the disperse dust. These facts suggest that the homogeneity assumption that is usually considered for the dust dispersion is obviously invalid. As a consequence, the operating conditions should be adapted to the physical properties of each combustible powder in order to improve both tests accuracy and precision. For this purpose, CFD simulations have been proven to be a useful tool to identify the most suitable conditions to perform this analysis and obtain the most conservative information about the reactivity of the dust as well

Data analysis of blast furnace gas center based on STING grid clustering

Distribution of gas flow is related to the temperature distribution in the furnace, furnace condition running, and utilization of the gas, ultimately affecting the blast furnace smelting. The research results show that the gas utilization and temperature field center shift gas share were positively correlated, and negatively correlated with the excursion of the larger and smaller gas share. After the processing of the STING grid, there are five categories. The comparison shows that the gas utilization rate is mainly determined by the non offset gas occupation rate of the temperature field center.

Pilot⁻Scale Production of Carbon Hollow Fiber Membranes from Regenerated Cellulose Precursor-Part II: Carbonization Procedure.

The simultaneous carbonization of thousands of fibers in a horizontal furnace may result in fused fibers if carbonization residuals (tars) are not removed fast enough. The optimized purge gas flow rate and a small degree angle in the furnace position may enhance the yield of high quality carbon fibers up to 97% by removing by-products. The production process for several thousand carbon fibers in a single batch is reported. The aim was developing a pilot-scale system to produce carbon membranes. Cellulose-acetate fibers were transformed into regenerated cellulose through a de-acetylation process and the fibers were carbonized in a horizontally oriented three-zone furnace. Quartz tubes and perforated stainless steel grids were used to carbonize up to 4000 (160 cm long) fibers in a single batch. The number of fused fibers could be significantly reduced by replacing the quartz tubes with perforated grids. It was further found that improved purge gas flow distribution in the furnace positioned at a 4-degree to 6-degree angle permitted residuals to flow downward into the tar collection chamber. In total, 390 spun-batches of fibers were carbonized. Each grid contained 2000–4000 individual fibers and these fibers comprised four to six spun-batches of vertically dried fibers. Gas permeation properties were investigated for the carbon fibers.

Effect of the ignition delay time on explosion severity parameters of coal dust/air mixtures

Explosion pressure and pressure rise rate are two important indicators of the severity parameters of coal dust explosion. Ignition delay time has a significant effect on the explosion severity parameters of coal dust/air mixtures. In this work, this effect was studied through a combination of experiment and numerical simulation. The 20-L spherical vessel explosion test system was used to study the severity parameters of coal dust/air mixtures at the concentration of 250 g/m3 under different ignition delay times. The results showed that both of the maximum explosion pressure and the maximum rate of pressure rise appear a trend of first increase and then decrease with the increase of ignition delay time, reaching its maximum at 60 ms. Besides, the numerical simulation was conducted to investigate the distribution and variation of gas flow, coal dust particles, and turbulence kinetic energy before ignition in detail. The simulation results were in good agreement with the previous research data, and the effect of ignition delay time on the explosion severity parameters of coal dust/air mixtures was analyzed from the aspect of mechanism.

Effects of the shape and inclination angle of DRI-flaps on DRI distribution in COREX melter gasifiers

Burden distribution plays a crucial role in controlling gas flow distribution and achieving the stability operation of the melter gasifier in COREX. This work presents a coupled DEM-CFD study on burden formation and gas injection of a COREX melter gasifier (MG), mainly focusing on the effects of inclination angle and shape of the DRI-flaps. A one-eighth MG was simulated and compared with the experimental results. The burdens were analysed in terms of particle segregation index and particle distribution index. It was observed that the particles were unevenly distributed in the circumferential directions. This phenomenon was further enhanced with decreasing flap inclination angles as the burden stream became wider and more separated with decreasing inclination angle. To reduce the uneven distribution of particles, flap shapes were changed. It was observed that the thickness of burden piles was proportional to the area of the flaps. The Arc-shape flap, with a medium size of cross-sectional area, was able to control the uniform distribution of DRI particle and formed a uniform pressure distribution in the circumferential direction. The study shows the importance of flaps to maintain the uniform pressure distribution in the circumferential direction of burden beds for stable operation of the melter gasifier.

The BubbleTree toolset: CFD-integrated algorithm for Lagrangian tracking and rigorous statistical analysis of bubble motion and gas fluxes for application to 3D fluidized bed simulations

Bubbling dynamics and distribution of gas flow critically influence the performance of fluidized bed reactors and must be quantified accurately for their design and performance optimization. In this study, a new toolset called the BubbleTree toolset (BT) was developed using Python and the Visualization Tool Kit (VTK) for analyzing computational fluid dynamics simulation data and performing statistical analysis of bubbling dynamics such as their volume, location, and velocity. In addition, the BT toolset provides the capability to (a) track bubbles through coalescence and splitting events and (b) compute throughflow by integrating gas fluxes through the bubble surface. The toolkit was verified using the method of manufactured solutions as well as by comparing bubbling dynamics predictions in large-scale simulations with relevant open-source software. The BT toolset also incorporates tools for rigorous statistical analysis in selected regions of interest as well as the reactor in its entirety. The BT will be integrated with MFiX CFD simulations which will enable the fundamental investigation of gas-solids flow interaction in complex reacting particulate flows, in situ estimation of bubbling (and cluster) dynamics dependent sub-grid models and performance optimization of fluidized bed reactors using CFD-simulations.

Experimental and numerical study of flow in expanded metal plate for water electrolysis applications

Polymer electrolyte membrane water electrolysis (PEMEC) is a high-yield technique for hydrogen generation from renewable energy. One challenge for commercialisation of the technology is a low-cost and highly efficient flow plate. Flow plates are one of the most expensive parts of an electrolysis system, therefore a thorough study on alternative flow plate manufacturing methods pays off. Expanded metals have low manufacturing cost. Even though they are being used in different industries from electrochemistry to ventilation and air conditioning systems, there is little information available on their fluid flow behaviour. In this paper, the distribution of gas and liquid flow in expanded metal is analysed. Expanded metal flow resistance properties such as porosity, permeability and inertial resistance for two different sizes in both horizontal and vertical directions are determined. Alongside the experiments, two different computational fluid dynamic (CFD) simulations of flow in the experimental setup and the structure of the expanded metal was done.

Application Study on Three-Bed Regenerative Thermal Oxidizers to Treat Volatile Organic Compounds

Organic solvents with different volatilities are widely used in various processes and generate air and water pollution problems. One of the popular treatment processes for volatile organic compounds (VOCs) is regenerative thermal oxidation for the high destruction and removal efficiency. In this paper, the authors presents a project case dealing with VOCs, the waste gas with triethylamine and N-butylamine is disposed by a three-bed RTO treatment process. Two novel strategies were used in this project compared with the conventional RTO systems. Firstly, heat storage materials are saddle-shaped honeycomb, which could reform the distribution of waste gas flow in the saddle area and improve the efficiency of heat exchange. Secondly, the control mode of quick-opening valve is exhaust temperature control method instead of the time interval. The operation data shows that more than 99% of destruction and removal efficiency of VOC is obtained with slightly-level natural gas consumption. This research could provide a practical basis for the design of a RTO system.

Mathematical Modeling and Mechanism of VUV Photodegradation of H2S in the Absence of O2

The existence of H2S has limited the biogas energy promotion. The traditional photodegradation of H2S is usually conducted in the presence of O2, yet this is unsuitable for biogas desulfurization which should be avoided. Therefore, the ultraviolet degradation of H2S in the absence of O2 was investigated for the first time in the present study from a mathematical point of view. Light wavelength and intensity applied were 185 nm and 2.16 × 10−12 Einstein/cm2·s, respectively. Firstly, the mathematical model of H2S photodegradation was established with MATLAB software, including the gas flow distribution model and radiation model of photoreactor, kinetics model, mass balance model, and calculation model of the degradation rate. Then, the influence of the initial H2S concentration and gas retention time on the photodegradation rate were studied, for verification of the mathematical model. Results indicated that the photodegradation rate decreased with the increase in initial H2S concentration, and the maximum photodegradation rate reached 62.8% under initial concentration of 3 mg/m3. In addition, the photodegradation rate of H2S increased with the increase in retention time. The experimental results were in good accordance with the modeling results, indicating the feasibility of the mathematical model to simulate the photodegradation of H2S. Finally, the intermediate products were simulated and results showed that the main photodegradation products were found to be H2 and elemental S, and concentrations of the two main products were close and agreed well with the reaction stoichiometric coefficients. Moreover, the concentration of free radicals of H• and SH• was rather low.

Research on the Influence of Furnace Structure on Copper Cooling Stave Life

Abstract In this paper, a blast furnace gas flow distribution model with variable furnace structure was founded based on CFD (computational fluid dynamics) theory, and the gas velocity distribution near the surface of the copper staves in different areas of the BF is calculated under different conditions of variational structure parameters like Bosh angle, shaft angle, and the newly proposed “equivalent Bosh angle.” Based on the calculation, the influence rule of the BF structure on the service life of copper stave and the corresponding operation measures were obtained. The result shows that the increase of the Bosh angle and the decrease of the shaft angle will incur increasing of the gas flow velocity near the surface of the copper staves, which is harmful to the cooling stave life; the variation of the equivalent Bosh angle has a most significant influence on the cooling stave life, and the increase of the equivalent Bosh angle will cause a sharp increase of the gas flow velocity, which will damage the copper staves seriously; adopting long tuyeres and minishing the equivalent Bosh angle will reduce the washing action of the gas flow and ensure the stability of slag hanging to achieve a long service life of copper staves.

Analysis of Temperature and Gas Flow Distribution in Chamber with Wafer Batch

ABSTRACTWafer temperature distribution and gas flow inside a tube of a chemical vapor deposition chamber, which is a semiconductor fabrication equipment, were analyzed. The control volume was assumed to be a two-dimensional space, and calculation program was developed based on a MATLAB code. The program is divided into two parts – heat transfer and gas flow analyses. The results of the calculation and the temperature test agreed well with each other. Heat loss was observed at both ends of the wafer batch, and gas convection momentum was not enough for the flow to invade into the wafer spacing. Thus, the flow rate and the temperature of the wafer needed to be increased to make the film thickness uniform. To increase the wafer temperature, the radiation adiabatic pedestal was considered. Low emissivity made the pedestal almost adiabatic, which increased the temperature of the wafer batch. To increase the flow rate in the wafer spacing, the eccentric wafer batch was proposed.

Transient Interaction Between Reduction and Slagging Reactions of Wustite in Simulated Cohesive Zone of Blast Furnace

The blast furnace cohesive zone plays an important role in the gas flow distribution and heat-transfer efficiency. Previous work mainly employed temperature-based indices to evaluate and predict the shape and thickness of the cohesive zone, whereas the internal reactions and related effects on the softening and melting properties of a complex burden are ignored. In this study, an innovative index, namely, shrinkage rate (SR), is first proposed to directly estimate the shrinkage behavior of wustite (FeO)-packed bed inside a simulated cohesive zone. The index is applied as the temperature increases to elucidate the transient interaction between reduction and slagging reactions. Results show that the thermally induced slagging reaction causes the packed bed to shrink at lower temperature, and the SR doubles when compounds with low melting temperature are generated by adding a reasonable concentration of CaO or SiO2. The reduction reaction becomes the driving force during the shrinkage of the packed bed between 1173 K and 1273 K when CO is introduced in the mixture gas. Then, the dominating factors for further shrinkage include slagging, reduction, or both factors. These factors vary with respect to the added compounds or temperature.

Global hydrodynamic of hybrid external loop airlift reactor: Experiments and CFD modelling

In this study, the mixing and mass transfer of air-water system were characterized in hybrid external loop airlift reactor using the computational fluid dynamics (CFD). This hybrid configuration involves the advantages of both airlift and torus reactors. To predict the flow in hybrid geometry, an Eulerian-Eulerian approach has been adopted with per-phase interaction of the standard k–ε turbulence model. To simplify the solution, the bubbles were considered to have approximately the same size. The global flow characteristics were experimentally determined by a conductimetric method. Gassing-out method was applied to determine gas-liquid mass transfer coefficients. The findings highlighted a uniform gas flow distribution in the riser tube, despite the riser included two different sections. It was noticed that beyond the superficial gas velocity, 0.0253 m/s, the fine rotational bubbles were dragged away by the liquid recirculation in the downcomer section. The STD k–ε turbulence model with per-phase effect, estimated correctly the hydrodynamic of homogenous and transition regimes except for high superficial gas velocity, Ug = 0.0703 m/s. For superficial gas velocities ranging from 0.0253 to 0.0703 m/s, there was a good agreement between simulated and experimental values; the error was less than 6%. Optimal conception of this hybrid geometry and its industrial scale use need further research and testing.

Improvement of two-phase flow distribution in the header of a plate-fin heat exchanger

The two-phase (liquid and gas) flow distribution in the header of a plate-fin heat exchanger was experimentally investigated. Small mass fractions of the liquid phase in the liquefaction process of natural gas were considered in this study. The liquid and gas flow velocity were measured using optical methods such as PIV/PTV/LIF. The flow maldistribution of liquid and gas flows was quantified and addressing this problem by attaching a porous baffle or modifying the inlet nozzle configuration was studied. The results showed that a vane swirler with a diffuser enhanced the flow distribution of both the liquid and gas phases fluid.

Liquid distribution model based on a volume cell for a column with structured packing under permanent tilt and roll motions

An improved liquid distribution model based on a volume cell (LDMvc) was proposed to predict the liquid load distribution in a packed column under offshore conditions. The LDMvc contained four tuning parameters. The LDMvc is an improvement of the existing intersection-based LDM since the number of model tuning parameters is reduced to four through a sophisticated flow split algorithm, and a gas flow distribution model can be associated with the LDMvc. Two experimental columns with inner diameters of 0.133 m and 0.4 m were packed with Mellapak 500X-like elements for a 1.4 m bed height and Mellapak 250X-like elements for a 4 m bed height, respectively. The 4 m bed height column was built on a sloshing machine to simulate ship movement. The liquid distribution inside the columns was measured using an electrical resistance tomography (ERT) system. The offshore conditions were a permanent tilt ranging from 2 to 6° and a roll motion with three amplitude-period pairs. The LDMvc, after tuning with the experimental data, reliably predicted the liquid load distribution in the packed columns under different tilts and roll motions.

Introduction of a New Baffle-Plate Concept to Control the Gas Flow Behavior in a Large Volume PECVD Chamber

Achieving a reasonable homogeneity of the coating deposition rate within a low-pressure plasma process is a challenge, especially in large volume chambers. The local gas flow behavior is one key parameter in the coating deposition. Basically, with the exception of the product geometry and the electrode design, there are two main influences on the gas flow distribution inside a large volume chamber: 1) gas feed-in system and 2) gas exhaustion system. This work focuses on the gas exhaustion system with the aim to reduce its influence on the gas flow behavior inside a large plasma coater. In this sense, a solution with a perforated plate, named “Baffle-Plate”, is created. Thereby relevant construction parameters are identified and investigated to understand their influence in respect to the homogeneity of the gas exhaustion. Number of holes, hole diameter, distance of the Baffle-Plate to the top of the chamber, gas flow and chamber volume are evaluated parameters. Computational fluid dynamics (CFD) simulations are used as a tool to determine velocity and pressure distribution inside the PECVD-chamber and, consequently, to evaluate the layout parameters of the Baffle-Plate. Additionally, practical coating experiments with and without the Baffle-Plate installed are performed. The results show a correlation between the gas flow distribution and the homogeneity of the coating deposition rate. With these results construction guidelines have been formulated. Hence in future developments correct technical layouts of the Baffle-Plate can be applied, easily.