Online prediction of dense medium suspension density based on phase space reconstruction

In the dense medium separation process of the coal preparation plant, the fluctuation of raw coal quality and the lag of heavy media separation density adjustment often lead to the instability of clean coal quality. To solve this problem, phase space reconstruction with online data was carried out to derive a mathematical formula of working dense medium density with raw coal ash and clean coal ash produced. Then the data was trained by two ways, namely Least Square Support Vector Machine (LS-SVM) and LS-SVM based on time series. Simulation results show that the latter way can achieve a more accurate prediction of heavy medium suspension density.     

Novel method of air distributor design for enhancing bed stability and reducing impurities in gas–solid fluidized bed system

Coal plays a key role in the economic development of China. It is greatly significant to improve the efficient use of coal through high-efficiency dry separation. In this paper, a porous sponge was used to optimize the air distributor, and its fluidization characteristics were studied. Response surface methodology was used to study the collaborative optimization effects of gas velocity, separation time, and bed height on the fine coal separation. Gas velocity was the main factor which affects separation efficiency. When separation is in operation parameters, the yield and ash content were 65.48 and 10.89% as to the clean coal product and 9.24 and 80.47% as to the gangue product, respectively. Furthermore, the yield and ash content of middlings were 25.29 and 20.32%, respectively. The probable error, E, values were between 0.085 and 0.100?g/cm³. Using XRF and FTIR analysis, it was observed that the harmful elements and impurities in coal were reduced during the separation process.     

Mixing and migration rule of binary medium in vibrated dense medium fluidized bed for fine coal separation

The vibrated dense medium fluidized bed is an efficient waterless dry coal separation technology. In order to reduce the interference of the macroscopic migration of the entire bed with the coal settlement process, the material composition and diffusion behavior of the binary medium are studied. The results show that the maximum mass fraction of fine coal particles is 18% in the uniformly mixed binary medium. Bubbles and vibration are the main factors influencing the mixing process. At low vibration intensity and high gas velocity (f = 15 Hz, U_v = 15 cm/s), the fine coal particles rapidly rise and back mixing under the entrainment of a large number of bubbles. If the vibration frequency is increased to 25 Hz, the excessive kinetic energy causes the entire bed to flow circularly in the vertical direction, interfering with the normal settlement of coal. After reducing the gas velocity (f = 25 Hz, U_v = 11 cm/s), the fine coal particles in the wall region rise rapidly, which is mainly driven by the vibration, whereas the fine coal particles in the central region migrate upward at a relatively low velocity, dragged by the bubbles. The bed impact forces in the opposite directions differ slightly, which promotes the directional settlement of coal.     

Flow pattern transition and coal beneficiation in gas solid fluidized bed with novel secondary distributor

Gas solid fluidized bed (GSFB) is an effective method of dry coal separation. In this study, porous sponge was introduced into a typical gas solid fluidized bed as secondary air distribution layer (PSFB) to stabilize the fluidized bed layer. The difference between PSFB and GSFB in flow pattern transition process was studied. Compared with GSFB, the minimum gas velocity and bed density fluctuation decreased while bed expansion ratio increased in PSFB. Furthermore, the distribution of bubble phase and emulsion phase were more homogeneous in PSFB. Under the operational conditions, the results of coal preparation in a PSFB showed that the ash content of clean coal was 10.25% .The probable error (E) was 0.095?g/cm³, indicating that PSFB could provide a novel way for a good performance of dry coking coal beneficiation.     

Interaction effect of various factors and sulfur migration for pyrite recovery by vibrated fluidized bed

ABSTRACT

Gangue is a hazardous solid waste with high yield in the world. Due to higher proportion of pyrite in the gangue, pyrite recovery from gangue is significant for environmental protection. As effective recovery methods, dry separation methods have been received amount of attentions in the mineral processing field. In this study, vibrated fluidized bed was attempted to use for pyrite recovery. Vibration energy was introduced to strengthen the density segregation in the fluidized bed. The study also investigated the interaction effect of gas velocity, vibration intensity, and bed height in the vibrated fluidized bed. Moreover, sulfur migration has been studied by several advanced analytical techniques. The results showed that separation efficiency was directly related to the interaction effect among various factors. After the separation, the sulfur content of concentrates were increased to 37.31, 35.43, and 28.62% for ?6?+?3, ?3?+?1, and ?1?+?0.5?mm size fractions. The sulfur segregation’s standard deviation (S_sulfur) was beyond 0.70. In addition, elements of S and Fe accounted for higher proportion in the concentrates after the separation. The study indicated that pyrite could be effectively enriched by the vibrated fluidized bed.     

Separation of the coal-quartz mixture using tribo-electrostatic separator: Effect of surface pretreatment

The present study illustrates the effect of physical (thermal) and chemical surface treatment on the separation of the coal-quartz synthetic mixture in a tribo-electrostatic separator. The work also reports the effect of applied voltage and splitter position on the tribo-electrostatic separation of surface treated and untreated samples. Different reagents used in chemical conditioning of the synthetic mixture are kerosene, acetic acid, acetone, ethanol, phenol, toluene, and aniline. The study establishes that both chemical and heat treatment improves the tribo-electrostatic separation efficiency of coal and quartz particles. The applied voltage and splitter position affect the product grade and yield of treated and untreated samples. The ash removal and combustible separation efficiency of the synthetic mixture improved after chemical conditioning of the synthetic mixture with ethanol, acetone, acetic acid, and aniline. However, aniline treatment has produced the best separation result. It is possible to achieve 9 and 14% ash clean coal with 40% yield each from 53% ash synthetic mixture at 15 kV applied voltage after aniline and heat treatment, respectively. The ash removal and combustible separation efficiency of the tribo-electrostatic separator for the aniline and heat-treated synthetic mixture are 96, 60% and 90, 70%; respectively.     

Characteristic gas velocity and fluidization quality evaluation of vibrated dense medium fluidized bed for fine coal separation

In order to remove incombustible impurity minerals, a vibrated dense medium fluidized bed (VDMFB) can be adopted for fine coal dry separation, while Geldart B magnetite powder can serve as the medium. The influence of vibration on characteristic gas velocity in flow pattern transition stage was experimentally investigated at a vibration amplitude range of 0.5–4?mm and frequency range of 5–35?Hz. The experimental results demonstrate that at a low frequency (f?<?10?Hz), the vibration effect results in a denser bed and a slightly smaller initial fluidization gas velocity. As the vibration frequency increases to a level similar to the bed’s natural frequency, the minimum fluidization gas velocity reduces sharply. The minimum fluidization gas velocity correlation in the VDMFB is obtained by means of theoretical deduction and experimental data fitting. Furthermore, a method is proposed for evaluating the effects of vibration on improving fluidization quality. Based on that, using the coal separation probable error $E_p?0.1$ as the evaluation index, a suitable effective operating gas velocity range for coal separation under different vibration parameters is determined. The ratio of the boundary operating gas velocity to $U_{\mathit{mfc}}$ is 0.67–2.28. Thus, a uniform and stable fluidization environment is provided for dry fine coal separation.     

Separation of flocculated ultrafine coal by enhanced gravity separator

The separation of ultrafine coal is inefficient due to the low settling velocity in centrifugal field. The feasibility of increasing particle size by flocculation to increase the separation efficiency is verified. The effect of flocculant on the size distribution of ultrafine coal was tested. The effect of flocculant dose on deash and desulfurization efficiency was studied to determine the appropriate dosage. Further, influence of the main operating parameters of the concentrator, including centrifugal force and water counter pressure on the separation performance, was studied. In addition, a comparative test was designed to verify the stability of the flocs. Results showed that the size of ultrafine coal particles could be effectively increased by the addition of flocculant, and the yield of ?0.045 µm fraction was decreased from 50% to 17% when the flocculant dosage was 10 g/t. The combustible material recovery of clean coal increased from 58% to 66%; meanwhile, the ash content reduced from 16.7% to 14.6%. In addition, combustible matter recovery and desulphurization efficiency decreased with the increase of centrifugal force, while they increased with the water counter pressure. Results of comparison tests of ultrafine coal with flocculant pretreatment and artificial coal with the same size composition showed that the latter had greater combustible recovery and desulfurization efficiency.     

Investigation on flow pattern evolution and restraint of vibration energy to bubbles in vibrated dense medium fluidized bed

Vibrated dense medium fluidized bed (VDMFB) provides a feasible and low-cost method for fine coal separation. In this study, empirical mode decomposition (EMD) was used to study the evolution of the dominant flow pattern and the restraint effect of vibration energy on the bubble in VDMFB. The internal pressure fluctuation signal of VDMFB was analyzed by EMD, and the intrinsic mode functions (IMFs) of the signal were extracted, and the corresponding relationship between the IMFs and dominant fluidization behavior was verified. The intermediate-frequency signal components (IMF-3 ~ IMF-4) and low-frequency signal components (IMF-5 ~ IMF-8) corresponded to the particle oscillation of emulsion phase and bubble behavior in the particle bed, respectively. Additionally, the energy variation of IMFs in different frequency bands was closely related to the evolution of dominant fluidization behavior. Further, the intermediate-frequency energy decreased and the low-frequency energy increased gradually along the bed height; additionally, the intersection point Tr existed between the two curves, indicating that the dominant energy controlling the flow pattern of the bed changed from vibration to bubbles. The constraint range of vibration energy on bubble behavior was defined, and the quasi-dispersed micro-bubble fluidization environment suitable for fine coal separation was identified in VDMFB, in which the steady vibration energy effectively controlled the unsteady bubble.     

Effects of fly ash fineness on the mechanical properties of concrete

The present study reviews the effects of fly ash fineness on the compressive and splitting tensile strength of the concretes. A fly ash of lignite origin with Blaine fineness of 2351?cm²/g was ground in a ball mill. As a consequence of the grinding process, fly ashes with fineness of 3849?cm²/g and 5239?cm²/g were obtained. Fly ashes with three different fineness were used instead of cement of 0%, 5%, 10%, and 15% and ten different types of concrete mixture were produced. In the concrete mixtures, the dosage of binder and water/cement ratio were fixed at 350?kg/m³ and 0.50, respectively. Slump values for the concretes were adjusted to be 100 ± 20?mm. Cubic samples were cast with edges of 100?mm. The specimens were cured in water at 20°C. At the end of curing process, compressive and splitting tensile strengths of the concrete samples were determined at 7, 28, 56, 90, 120 and 180?days. It was observed that compressive and splitting tensile strength of the concretes was affected by fineness of fly ash in short-and long-terms. It was found that compressive and tensile strength of the concretes increased as fly ash fineness increased. It was concluded that Blaine fineness value should be above 3849?cm²/g fineness of fly ash to have positive impact on mechanical properties of concrete. The effects of fly ash fineness on the compressive and splitting tensile strength of the concretes were remarkably seen in the fly ash with FAC code with fineness of 5235?cm²/g.