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Dongke Zhang - One of the best experts on this subject based on the ideXlab platform.
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an experimental investigation into mineral transformation Particle Agglomeration and ash deposition during combustion of zhundong lignite in a laboratory scale circulating fluidized bed
Fuel, 2019Co-Authors: Zhuo Liu, Quanhai Wang, Yuanyuan Zhang, Mingming Zhu, Zhezi Zhang, Dongke ZhangAbstract:Abstract The characteristics and mechanisms of inorganics and mineral transformation, Particle Agglomeration and ash deposition during Zhundong lignite combustion in a 0.2 t/d lab-scale circulating fluidized bed (CFB) furnace were experimentally investigated. A sample of Zhundong lignite with Particle size
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effect of coal blending on Particle Agglomeration and defluidisation during spouted bed combustion of low rank coals
Fuel Processing Technology, 2001Co-Authors: Hari B Vuthaluru, Dongke ZhangAbstract:The possibility of blending coals to alleviate Particle Agglomeration and bed defluidisation during fluidised-bed combustion (FBC) of several low-rank coals was exploited. A laboratory scale spouted bed combustor was employed to fire coal blends from two lignites with a sub-bituminous coal at ratios of 50:50 and 90:10, at temperatures ranging 800°C. Experiments showed significant improvements in FBC operation with the coal blends compared to the raw lignites. No Particle Agglomeration and bed defluidisation were evident after 15 h of operation with the blends at 800°C. Chemical analyses indicated that the formation of low temperature eutectics was suppressed by calcium aluminosilicate phases from the sub-bituminous coal, rendering the surface of ash-coated Particles dry and less sticky. This was identified as the key mechanism for the control of Particle Agglomeration and bed defluidisation in FBC, which led to extended combustion operation with the coal blends.
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effect of ca and mg bearing minerals on Particle Agglomeration defluidisation during fluidised bed combustion of a south australian lignite
Fuel Processing Technology, 2001Co-Authors: Hari B Vuthaluru, Dongke ZhangAbstract:Abstract Behaviour of calcium and magnesium during fluidised-bed combustion (FBC) of a South Australian lignite was investigated using a laboratory scale spouted bed combustion system. Combustion experiments were aimed at investigating the effectiveness of Ca- and Mg-bearing minerals (as alternative bed materials) in controlling Particle Agglomeration and bed defluidisation during FBC combustion of low-rank coals. Additional experiments performed with a Ca-treated coal investigated the role of Ca in Agglomeration and defluidisation process. Experimental results indicated that both Ca/Mg-bearing minerals and Ca-treated coal were effective to different extents in reducing bed defluidisation. Tests with calcite (as the bed material) and Ca-treated coal runs (with sand as the bed material) showed trouble free operation for 8–10 h before bed defluidisation incurred. Tests with magnesite (as the bed material) showed no Agglomeration and defluidisation tendencies for longer operating periods (∼12 h at 800°C). Mg-bearing compounds have been found to be effective in controlling defluidisation and allowed extended combustion operations. On the other hand, high levels of Ca either in coal or in bed material have been found to delay and decrease the severity of agglomerates formed.
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investigations into the control of Agglomeration and defluidisation during fluidised bed combustion of low rank coals
Fuel, 1999Co-Authors: Hari B Vuthaluru, Dongke Zhang, Temi M Linjewile, A R ManzooriAbstract:Abstract A laboratory scale spouted bed combustor was used to study the effectiveness of various control methodologies in alleviating ash-related problems such as Particle Agglomeration and bed defluidisation during fluid bed combustion of low-rank coals. The three control techniques investigated are: (i) the use of mineral additives; (ii) alternative bed materials; and (iii) pretreatment of coal. Mineral additives, including dolomite, two clays and gibbsite, were injected into the spouted bed combustor while burning a South Australian low-rank coal at 800°C. Samples of the same coal treated with Al, water washing and acid washing were also tested in the spouted bed combustor. In addition, experiments were also conducted with alternative bed materials including bauxite and calcined sillimanite. Experiments showed that the three techniques reported in this paper are effective to different extents in reducing Particle Agglomeration and defluidisation. Among the mineral additives tested, gibbsite and a clay additive rich in kaolinite and sillimanite were found to be most effective. The use of calcined sillimanite and bauxite as alternative bed materials extended the combustion time before defluidisation occurred by 7 and 10 times, respectively, compared to silica sand. While Al pretreatment and water-washing were found effective for control of Agglomeration and defluidisation, acid-washing did not improve the operation of the bed burning this particular coal. Al enrichment in ash coating of bed Particles which suppress the formation of Na and S rich eutectics was identified as the main mechanism for prevention of Agglomeration and defluidisation by these control techniques.
Hari B Vuthaluru - One of the best experts on this subject based on the ideXlab platform.
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effect of coal blending on Particle Agglomeration and defluidisation during spouted bed combustion of low rank coals
Fuel Processing Technology, 2001Co-Authors: Hari B Vuthaluru, Dongke ZhangAbstract:The possibility of blending coals to alleviate Particle Agglomeration and bed defluidisation during fluidised-bed combustion (FBC) of several low-rank coals was exploited. A laboratory scale spouted bed combustor was employed to fire coal blends from two lignites with a sub-bituminous coal at ratios of 50:50 and 90:10, at temperatures ranging 800°C. Experiments showed significant improvements in FBC operation with the coal blends compared to the raw lignites. No Particle Agglomeration and bed defluidisation were evident after 15 h of operation with the blends at 800°C. Chemical analyses indicated that the formation of low temperature eutectics was suppressed by calcium aluminosilicate phases from the sub-bituminous coal, rendering the surface of ash-coated Particles dry and less sticky. This was identified as the key mechanism for the control of Particle Agglomeration and bed defluidisation in FBC, which led to extended combustion operation with the coal blends.
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effect of ca and mg bearing minerals on Particle Agglomeration defluidisation during fluidised bed combustion of a south australian lignite
Fuel Processing Technology, 2001Co-Authors: Hari B Vuthaluru, Dongke ZhangAbstract:Abstract Behaviour of calcium and magnesium during fluidised-bed combustion (FBC) of a South Australian lignite was investigated using a laboratory scale spouted bed combustion system. Combustion experiments were aimed at investigating the effectiveness of Ca- and Mg-bearing minerals (as alternative bed materials) in controlling Particle Agglomeration and bed defluidisation during FBC combustion of low-rank coals. Additional experiments performed with a Ca-treated coal investigated the role of Ca in Agglomeration and defluidisation process. Experimental results indicated that both Ca/Mg-bearing minerals and Ca-treated coal were effective to different extents in reducing bed defluidisation. Tests with calcite (as the bed material) and Ca-treated coal runs (with sand as the bed material) showed trouble free operation for 8–10 h before bed defluidisation incurred. Tests with magnesite (as the bed material) showed no Agglomeration and defluidisation tendencies for longer operating periods (∼12 h at 800°C). Mg-bearing compounds have been found to be effective in controlling defluidisation and allowed extended combustion operations. On the other hand, high levels of Ca either in coal or in bed material have been found to delay and decrease the severity of agglomerates formed.
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investigations into the control of Agglomeration and defluidisation during fluidised bed combustion of low rank coals
Fuel, 1999Co-Authors: Hari B Vuthaluru, Dongke Zhang, Temi M Linjewile, A R ManzooriAbstract:Abstract A laboratory scale spouted bed combustor was used to study the effectiveness of various control methodologies in alleviating ash-related problems such as Particle Agglomeration and bed defluidisation during fluid bed combustion of low-rank coals. The three control techniques investigated are: (i) the use of mineral additives; (ii) alternative bed materials; and (iii) pretreatment of coal. Mineral additives, including dolomite, two clays and gibbsite, were injected into the spouted bed combustor while burning a South Australian low-rank coal at 800°C. Samples of the same coal treated with Al, water washing and acid washing were also tested in the spouted bed combustor. In addition, experiments were also conducted with alternative bed materials including bauxite and calcined sillimanite. Experiments showed that the three techniques reported in this paper are effective to different extents in reducing Particle Agglomeration and defluidisation. Among the mineral additives tested, gibbsite and a clay additive rich in kaolinite and sillimanite were found to be most effective. The use of calcined sillimanite and bauxite as alternative bed materials extended the combustion time before defluidisation occurred by 7 and 10 times, respectively, compared to silica sand. While Al pretreatment and water-washing were found effective for control of Agglomeration and defluidisation, acid-washing did not improve the operation of the bed burning this particular coal. Al enrichment in ash coating of bed Particles which suppress the formation of Na and S rich eutectics was identified as the main mechanism for prevention of Agglomeration and defluidisation by these control techniques.
Michael D. Ward - One of the best experts on this subject based on the ideXlab platform.
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dynamic behavior of Particle Agglomeration of europium oxalate during reaction crystallization in semi batch reactor
Chemical Engineering Communications, 2006Co-Authors: Taesung Jung, Michael D. WardAbstract:ABSTRACT During reaction crystallization of europium oxalate in a semi-batch reactor, a monotonical increase in the mean Particle size and corresponding reduction in the total Particle population were observed due to Particle Agglomeration occurring simultaneously with Particle nucleation and growth. However, since Particle Agglomeration was achieved via Particle aggregation and molecular growth, the mean Particle size and total Particle population in the product suspension were significantly influenced by the crystallization conditions of the feed concentration, agitation speed, and feeding time. A higher feed concentration and feeding time resulted in a larger mean Particle size and smaller total Particle population due to the higher supersaturation and longer holding time in the reactor. Meanwhile, agitation was found to exhibit a rather complicated influence on Particle Agglomeration because Particle collision and a turbulent fluid shear were both promoted at the same time. In the semi-batch reactor, ...
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crystal Agglomeration of europium oxalate in reaction crystallization using double jet semi batch reactor
Materials Research Bulletin, 2004Co-Authors: Michael D. WardAbstract:The Particle Agglomeration of europium oxalate was investigated in a double-jet semi-batch reactor over a wide range of operating variables, including the agitation speed, reactant feed rate, and reactant concentration. The size of the agglomerates was directly dictated by the Particle collision and supersaturation promoting Agglomeration and the fluid shear force inhibiting Agglomeration. Thus, with a longer feeding time and higher feed concentration for the reaction crystallization, the mean Particle size increased, while the corresponding total Particle population decreased due to the enhanced chance of Particle Agglomeration, resulting from a longer residence time and higher supersaturation in the reactor. Agitation was found to exhibit a rather complicated influence on Particle Agglomeration. Although both Particle collision and turbulent fluid shear were promoted by an increase in the mixing intensity, the crystal Agglomeration of europium oxalate was maximized at around 500 rpm of agitation speed due to an optimized balance between Particle aggregation and breakage.
Michael Fairweather - One of the best experts on this subject based on the ideXlab platform.
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large eddy simulation of Particle Agglomeration with shear breakup in turbulent channel flow
Physics of Fluids, 2018Co-Authors: Derrick O Njobuenwu, Michael FairweatherAbstract:A systematic technique is developed for studying Particle dynamics as induced by a turbulent liquid flow, in which transport, Agglomeration, and breakup are considered. An Eulerian description of the carrier phase obtained using large eddy simulation is adopted and fully coupled to a Lagrangian definition of the Particle phase using a pointwise discrete Particle simulation. An efficient hard-sphere interaction model with deterministic collision detection enhanced with an energy-balance Agglomeration model was implemented in an existing computational fluid dynamic code for turbulent multiphase flow. The breakup model adopted allows instantaneous breakup to occur once the transmitted hydrodynamic stress within an agglomerate exceeds a critical value, characterised by a fractal dimension and the size of the agglomerate. The results from the developed technique support the conclusion that the local turbulence kinetic energy, its dissipation rate, and the agglomerate fractal dimension control the kinetics of the Agglomeration and de-Agglomeration processes, and as well as defining with time the morphology of the Particles and their resultant transport. Overall, the results are credible and consistent with the expected physical behavior and with known theories.
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simulation of deterministic energy balance Particle Agglomeration in turbulent liquid solid flows
Physics of Fluids, 2017Co-Authors: Derrick O Njobuenwu, Michael FairweatherAbstract:An efficient technique to simulate turbulent Particle-laden flow at high mass loadings within the four-way coupled simulation regime is presented. The technique implements large-eddy simulation, discrete Particle simulation, a deterministic treatment of inter-Particle collisions, and an energy-balanced Particle Agglomeration model. The algorithm to detect inter-Particle collisions is such that the computational costs scale linearly with the number of Particles present in the computational domain. On detection of a collision, Particle Agglomeration is tested based on the pre-collision kinetic energy, restitution coefficient, and van der Waals’ interactions. The performance of the technique developed is tested by performing parametric studies on the influence of the restitution coefficient (en = 0.2, 0.4, 0.6, and 0.8), Particle size (dp = 60, 120, 200, and 316 μm), Reynolds number (Reτ = 150, 300, and 590), and Particle concentration (αp = 5.0 × 10−4, 1.0 × 10−3, and 5.0 × 10−3) on Particle-Particle interaction events (collision and Agglomeration). The results demonstrate that the collision frequency shows a linear dependency on the restitution coefficient, while the Agglomeration rate shows an inverse dependence. Collisions among smaller Particles are more frequent and efficient in forming agglomerates than those of coarser Particles. The Particle-Particle interaction events show a strong dependency on the shear Reynolds number Reτ, while increasing the Particle concentration effectively enhances Particle collision and Agglomeration whilst having only a minor influence on the Agglomeration rate. Overall, the sensitivity of the Particle-Particle interaction events to the selected simulation parameters is found to influence the population and distribution of the primary Particles and agglomerates formed.
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simulation of deterministic energy balance Particle Agglomeration in turbulent liquid solid flows
arXiv: Fluid Dynamics, 2017Co-Authors: Derrick O Njobuenwu, Michael FairweatherAbstract:An efficient technique to simulate turbulent Particle-laden flow at high mass loadings within the four-way coupled simulation regime is presented. The technique implements large eddy simulation, discrete phase simulation, a deterministic treatment of inter-Particle collisions and an energy-balanced Particle Agglomeration model. The algorithm to detect inter-Particle collisions is such that the computational costs scale linearly with the number of Particles present in the computational domain. On detection of a collision, Particle Agglomeration is tested based on the pre-collision kinetic energy, restitution coefficient and the van der Waals' interactions. The performance of the technique developed is tested by performing parametric studies of the influence the restitution coefficient $(e_{n} = 0.2, 0.4, 0.6$ and $0.8)$, Particle size ($d_p = 60, 120, 200$ and $316 \mu{m}$), fluid inertia ($Re_{\tau} = 150, 300$ and $590$) and Particle concentration ($\alpha_{p} = 5.0 \times 10^{-4}, 1.0 \times 10^{-3}$ and $5.0 \times 10^{-3}$) have on Particle-Particle interaction events (collision and Agglomeration). The results demonstrate that the collision frequency shows a linear dependency on the restitution coefficient, while the Agglomeration rate shows an inverse dependence. Collisions among smaller Particles are more frequent and efficient in forming agglomerates than those of coarser Particles. The Particle-Particle interaction events show a strong dependency on the shear Reynolds number $Re_{\tau}$, while increasing the Particle concentration effectively enhances Particle collision and Agglomeration. Overall, the sensitivity of the Particle-Particle interaction events to the selected simulation parameters is found to influence the population and distribution of the primary Particles and agglomerates formed.
Zijing Lin - One of the best experts on this subject based on the ideXlab platform.
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theoretical model for surface diffusion driven ni Particle Agglomeration in anode of solid oxide fuel cell
Journal of Power Sources, 2014Co-Authors: Sheng Gao, Zijing LinAbstract:Abstract The Agglomeration of Ni Particles in nickel–yttria stabilized zirconia (YSZ) anode is an important degradation mechanism for the solid oxide fuel cell and is widely believed to be driven by surface diffusion. This work aims to develop a quantitative model to describe the Agglomeration kinetics. The model treats the anode as a system of random packing Ni and YSZ Particles. Surface diffusion occurs between the connected Ni Particles of different sizes characterized by two representative radii, but is influenced by the YSZ network. The Fick's law for diffusion, the Gibbs–Thomson relation for vacancy concentration and the coordination number theory for percolating Ni network are employed in the mathematical derivation. The growth kinetics is expressed as an analytical function consisting of two model parameters, one for the Ni-Particle size distribution and the other for the influence of the YSZ backbone. The model is in excellent agreement with the available experiments. The influence of the YSZ backbone is further considered to obtain a model with just one fitting parameter. The one-parameter model is also in good agreement with the experiments and the fundamental physics for the Ni-Particle growth is therefore believed to be well characterized.