Density-dependent separation of dry fine coal in a vibrated fluidized bed

Study on the surface wetting mechanism of bituminous coal based on the microscopic molecular structure

The chemical wet dust removal method is one of the hot methods for coal dust control, and the key to its success lies in whether the surface of coal dust can be well wetted or not. Nowadays, the wetting mechanism of the coal dust surface is understudied, limiting the further application of chemical wet dust removal. Thus, the exploration of the wetting mechanism based on the microscopic molecular structure characteristics of the coal surface provides a new solution to improve the wet dust removal efficiency. Herein, the bituminous coal collected from 3 groups of coal seams in the Pingdingshan mining area was used as the object of study to reveal the microscopic wetting mechanism. Proximate analysis, nuclear magnetic resonance carbon spectroscopy (¹³C NMR) and X-ray photoelectron spectroscopy (XPS) can well distinguish the microstructural information of the coal surface, enabling building the molecular structure models of three groups of coal. Joint contact angle experiments were conducted to explore the influencing factors between the molecular structure of coal dust and its wettability. Molecular simulation techniques, combined with indoor experiments, were used to explore the essential causes of the differences in the wetting mechanisms of bituminous coal dust. The results showed that the composition and structure of carbon and oxygen elements on the coal surface has a significant effect on the wettability of coal dust. The higher the relative content of aromatic carbon and oxygen elements, the better the wettability of the coal surface. An opposite trend occurred for the aliphatic carbon. The difference in wettability of coal surfaces mainly stems from the ability of hydrophilic functional groups on coal surfaces to form hydrogen bonds with water molecules. The aromatic hydrocarbon structure has a much greater ability to adsorb water molecules than the aliphatic hydrocarbon structure. The research results can provide scientific guidance for the design of efficient and environmentally friendly dust suppressants to realize clean coal production in mines.

Study on the Fluidization Quality Characterization Method and Process Intensification of Fine Coal Separation in a Vibrated Dense Medium Fluidized Bed

Uniform and stable bed density is the basis of efficient coal separation by a gas-solid dense medium fluidized bed. The traditional air dense medium fluidized bed (ADMFB) is a kind of bubbling bed. By introducing vibration energy, a vibrated dense medium fluidized bed (VDMFB) with uniform and stable bed density can be formed, where the bubble merger is suppressed, the gas-solid contact can is strengthened, and the fluidization quality is also improved. In this paper, the transfer process of vibration energy in a fluidized bed is studied in detail. By calculating the coherence of pressure signals induced by vibration energy and bubbles at different bed heights, the suppression effect of vibration energy on bubble merger is analyzed. The coefficient R _imp to quantitatively evaluate the improvement effect of vibration energy on the fluidization quality is proposed. The differences and incentives of density uniformity and stability in different height bed areas have been clarified under different vibration parameters and gas flow parameters. It is proposed that the optimal separation bed height area of VDMFB is about H = 40-150 mm. The separation effect of the ADMFB and the VDMFB on 1-6 mm fine coal was compared. The results show that, compared with the ADMFB, the VDMFB reduces the separation probable error, E, from 0.134 to 0.083 g/cm³, and the ash content of the clean coal is reduced from 18.83 to 14.97%. The vibration energy significantly improves the fluidization quality of the ADMFB and the separation effect of fine coal.

Particle movement and fluid behavior visualization using an optically transparent 3D-printed micro-hydrocyclone

A hydrocyclone is a macroscale separation device employed in various industries, with many advantages, including high-throughput and low operational costs. Translating these advantages to microscale has been a challenge due to the microscale fabrication limitations that can be surmounted using 3D printing technology. Additionally, it is difficult to simulate the performance of real 3D-printed micro-hydrocyclones because of turbulent eddies and the deviations from the design due to printing resolution. To address these issues, we propose a new experimental method for the direct observation of particle motion in 3D printed micro-hydrocyclones. To do so, wax 3D printing and soft lithography were used in combination to construct a transparent micro-hydrocyclone in a single block of polydimethylsiloxane. A high-speed camera and fluorescent particles were employed to obtain clear in situ images and to confirm the presence of the vortex core. To showcase the use of this method, we demonstrate that a well-designed device can achieve a 95% separation efficiency for a sample containing a mixture of (desired) stem cells and (undesired) microcarriers. Overall, we hope that the proposed method for the direct visualization of particle trajectories in micro-hydrocyclones will serve as a tool, which can be leveraged to accelerate the development of micro-hydrocyclones for biomedical applications.

Image Recognition of Coal and Coal Gangue Using a Convolutional Neural Network and Transfer Learning

Recognizing and distinguishing coal and gangue are essential in engineering, such as in coal-fired power plants. This paper employed a convolutional neural network (CNN) to recognize coal and gangue images and help segregate coal and gangue. A typical workflow for CNN image recognition is presented as well as a strategy for updating the model parameters. Based on a powerful trained image recognition model, VGG16, the idea of transfer learning was introduced to build a custom CNN model to solve the problems of massive trainable parameters and limited computing power linked to the building of a brand-new model from scratch. Two hundred and forty coal and gangue images were collected in a database, including 100 training images and 20 validation images for each material. A recognition accuracy of 82.5% was obtained for the validation images, which demonstrated a decent performance of our model. According to the analysis of parameter updating in the training process, a principal constraint for obtaining a higher recognition accuracy mainly resided in a shortage of training samples. This model was also used to identify photos from a washing plant stockpiles, which verified its capability of dealing with field pictures. CNN combined with the transfer learning method we used can provide fast and robust coal/gangue distinction that does not require harsh data support and equipment support. This method will exhibit brighter prospects in engineering if the target image database (as with the coal and gangue images in this study) can be further enlarged.

A 3D-printed mini-hydrocyclone for high throughput particle separation: application to primary harvesting of microalgae

The separation of micro-sized particles in a continuous flow is crucial part of many industrial processes, from biopharmaceutical manufacturing to water treatment. Conventional separation techniques such as centrifugation and membrane filtration are largely limited by factors such as clogging, processing time and operation efficiency. Microfluidic based techniques have been gaining great attention in recent years as efficient and powerful approaches for particle-liquid separation. Yet the production of such systems using standard micro-fabrication techniques is proven to be tedious, costly and have cumbersome user interfaces, which all render commercialization difficult. Here, we demonstrate the design, fabrication and evaluation based on CFD simulation as well as experimentation of 3D-printed miniaturized hydrocyclones with smaller cut-size for high-throughput particle/cell sorting. The characteristics of the mini-cyclones were numerically investigated using computational fluid dynamics (CFD) techniques previously revealing that reduction in the size of the cyclone results in smaller cut-size of the particles. To showcase its utility, high-throughput algae harvesting from the medium with low energy input is demonstrated for the marine microalgae Tetraselmis suecica. Final microalgal biomass concentration was increased by 7.13 times in 11 minutes of operation time using our designed hydrocyclone (HC-1). We expect that this elegant approach can surmount the shortcomings of other microfluidic technologies such as clogging, low-throughput, cost and difficulty in operation. By moving away from production of planar microfluidic systems using conventional microfabrication techniques and embracing 3D-printing technology for construction of discrete elements, we envision 3D-printed mini-cyclones can be part of a library of standardized active and passive microfluidic components, suitable for particle-liquid separation.

The application of pneumatic jigging in the recovery of metallic fraction from shredded printed wiring boards

Waste electrical and electronic equipment (WEEE) is one of the fastest growing waste streams worldwide with volumes increasing by 40% each year. WEEE has attracted increasing concern worldwide due to its high metal content and the potential environmental threat which results from uncontrolled recycling practices. Innovative physical separation techniques for WEEE recycling are preferential compared with chemical methods because of the reduction of energy and chemical consumption as well as potential environmental threats. Pneumatic jigging is a dry separation process capable of achieving good separation of coarse material within a very narrow density range, which makes it suitable as a pretreatment process for WEEE recycling. The work presented in this paper investigates the potential application of pneumatic jigging in metal recovery from WEEE. A pilot scale pneumatic jig has been developed by University of Nottingham Ningbo to separate shredded printed wiring boards into two streams: a light fraction (mainly non-metallic fraction consisting of glass fiber, fluffs, and plastic pieces) and dense fraction (metallic fraction). The novelty of work presented in this paper is the application of a dry separation technique in WEEE recycling for metal recovery. Compared with conventional wet separation processes involved in WEEE recycling industry, dry separation has the advantage of zero secondary pollution. The results of this experimental program show pneumatic jigging to be an effective and environmental friendly technique as a pretreatment process for the recovery of the metallic fraction from shredded WEEE.