Advanced Materials Research Vol. 508

Abstract: This paper discusses the current methods used to test electrostatic pulverised fuel meters in a laboratory environment and the precautions to be taken to ensure that meaningful results are obtained. In particular, the effect of particle attrition is discussed and results presented from a laboratory test facility at the University of Teesside.

Abstract: Dense phase pneumatic conveying is preferable over dilute phase conveying in many industries as lower transport velocities are beneficial due to reduced attrition of the particles and reduced wear. However, dense phase conveying is critically dependent on the physical properties of the materials to be conveyed. For many materials which are either erosive or fragile, they do not exhibit the physical properties required to be conveyed reliably in a low velocity, dense phase flow regime. This can be serious problem in the food, chemical and pharmaceutical industries. One satisfactory approach which has been widely applied is the use of bypass systems. Bypass pneumatic conveying systems provide the capacity of transporting some materials that are not naturally suitable for dense phase flow. Bypass pneumatic conveying systems also provide a passive capability to reduce minimum particulate transport velocities. In this study, pneumatic conveying experiments were carried out in a 79 mm diameter main pipe with a 27 mm inner diameter bypass pipe with orifice plate flute arrangement. Alumina, fly ash and sand were conveyed in the tests. High speed camera visualization was employed to study the flow regimes of bypass pneumatic transport systems and investigate the mechanism of material blockage inhibition provided by these systems. For alumina and fly ash, it was found that particulate material blockages were inhibited in bypass systems due to the air penetration into the particulate volume as a result of orifice plate airflow resistance. For the bypass pneumatic conveying of sand, the splitting of a long plug into two smaller plugs was observed. One of the primary concerns of bypass system is the wear of the bypass line. Material such as alumina is inherently abrasive by nature. For internal bypass systems, there is limited ability to monitor the state of the inner bypass tube while in operation. The particle velocity in the pipeline has been measured from the high speed video of the flow. The experimental result also showed that the conveying velocity of bypass system is much lower when compared conventional single bore pipelines. Based on the models developed for the assessment of service life of pneumatic conveying pipelines, the thickness loss of the bypass pipe has been estimated. It has been estimated that for a 3mm bypass tube wall thickness, a wear hole is created in approximately 2.5 years for a particle velocity of 3 m/s and 4 months for a particle velocity of 10 m/s.

Abstract: Bypass pneumatic conveying systems provide a passive capability to reduce conveying velocity and therefore reduce attrition and abrasion in the process of conveying many fragile and erosive particulate solids. Because of these capabilities, bypass pneumatic conveying systems have been used in coal-fired power stations for removing fly ash for the last couple of decades. In bypass systems, the differential pressure between bypass pipe and main pipe as well as the pipeline pressure drop are two of most significant parameters as differential pressure represents the aeration mechanism within the pipeline while pressure drop is an essential parameter for bypass pneumatic conveying system design. In bypass systems, these two parameters are determined not only by the turbulent mode of the gas solids two-phase flow but also by the bypass configurations. The objective of this study was to experimentally investigate the differential pressure between bypass pipe and main pipe as well as the pressure drop during the bypass pneumatic conveying of fly ash. Pneumatic conveying tests in bypass systems and a conventional pipeline were carried out in this study. The bypass pipeline was a 79 mm diameter main pipe with a 27 mm inner diameter bypass pipe with orifice plate flute arrangement. Fly ash was discharged to the system from the bottom of a positive pressure blow tank. The receiving bin was mounted on load cells for measuring the mass accumulation. In order to monitor real time behavior of the system, pressure transmitters were used to measure the gauge pressure. Differential pressure transmitters were employed in the system for measuring the pressure difference between the bypass pipe and main pipe. Differential pressure results between bypass pipe and main pipe in the process of conveying fly ash showed that the pressure before the orifice plate in the bypass pipe was higher than that in main pipe as a result of orifice plate airflow resistance. Therefore, air came into main pipe and aerated the material continuously. The differential pressure also illustrated that the particulate may go into the bypass pipe as pressure in the bypass pipe after orifice plate is lower than that in main pipe. The pipeline pressure drop results also showed that pressure drop was higher than in the conventional system when using the same operating parameters due to the increase of friction. The influences of bypass configurations on pressure drop of bypass system were also discussed.

Abstract: Over the past 50 years, a strong foundation for the professional discipline of bulk solids handling has been provided, but so far, the theories for predicting funnel-flow are still quite empirical. In most cases, only two-dimensional stress field models are applied, which overestimate the stable pipe or rathole dimensions defining the core of the funnel and lead to draw-down and live capacity determinations, which are too conservative. More recently, Roberts [ introduced a new, more realistic, hoop stress theory based on the three-dimensional stress state occurring in a rathole. To verify the validity of the new theory, the current research upon which this paper is based, involves an experimental study of rathole formation in laboratory scale model funnel-flow bins and gravity reclaim stockpiles. A two-dimensional laser line scanner is used to depict rathole profiles, while load cells and pressure sensors are applied to determine instantaneous loads and pressure conditions during filling, storage and discharge. Iron ore fines are used as the test material, with the test program including flat-bottom bins with different diameters as well as varying filling levels and outlet diameters and stockpiles with variable heights and outlet diameters. The tests demonstrate the capability of laser scanning to describe rathole profiles. In addition, the suitability of the load cells and pressure sensors to describe the relevant funnel-flow parameters is shown.

Abstract: The paper takes gas/solid two-phase flow cross-correlation measurement system as the research object, adopts the method of computer simulation to research the measuring mechanism of cross-correlation velocity. By using Monte-Carlo method, the gas/solid two-phase flow model is established; and it is used to study the multiple factors affecting the system measurement performance such as sensor geometry, the distance of two sensors along the pipeline axis, the particle size and velocity, solidification flow pattern, non-solidification flow pattern, etc.

Abstract: Air drilling technology has been widely used in the oil and gas exploration, coal, geothermal, geological exploration, nuclear industry and other fields due to its high drilling rate and low cost. However, the design of the pneumatic conveying system for the mineral detritus is still largely based on empiricism. The paper was set in the background of gas drilling, mainly studied the gas-solids two-phase flow characteristics in 90 degree bent annular pipe and backward-facing step of an annular pipe, which are very important parts of air drilling. They refer to the bent part and backward-facing step of an annular channel formed by the drill pipe and the borehole wall. A detailed numerical simulation and experimental studies were carried out for the flow structure and pressure losses of gas-solid two-phase in the annular pipe of gas drilling. Since a unified theory has not been developed for the two-phase flow in annular pipe, a lot of experimental work should be conducted. In the experimental research, the paper independently designed and built an annular pipe pneumatic conveying system with 90 degree bend and backward-facing step, including designing material screw feeder, material receiving hopper, pipeline, control system, data acquisition system, and etc. As known, many parameters, such as gas velocity, diameter and density of the particle, and solids loading ratio, can influence the conveying process. How these primordial influence factors act on the pressure losses of two-phase flow in annular pipe was analyzed in this paper. In the numerical simulation research, turbulent two-phase flow calculations were performed with a commercial CFD computer code referred to as FLUENT to study the gas-solid two phase flow in the sections of backward-facing step and 90 degree bent pipe respectively by using Euler-Lagrange method. The RNG κ-ε model and stochastic tracking were involved in the calculation of turbulence dispersion of two phases. The discrete phase model was performed for the solid phase. In the end, the numerical study 3-D results were translated to 1-D results using the standard averaging transformation to compare with experimental results. Predicted results obtained for pressure drop and velocity variations in full developed flows in the cases examined are in good qualitative agreement and are not in quantitative agreement with experimental data. The deviations between the simulations and experimental data lie in the range of 20%-30%. These results suggest commercial CFD codes such as FLUENT can be used productively for investigations into gas-solid two-phase flow phenomena and as an aid in pneumatic conveying design. The studies of the two-phase flow characteristics in the paper will contribute to reliable determination of the optimal condition of pneumatic conveying in gas drilling.

Abstract: In order to be able to real-time control over the related equipments of pneumatic transportation system and to prevent plugging from happening, here a method that uses an electrical capacitance tomography system and grey correlation analysis to identify two-phase flow patterns is proposed. Firstly, the concrete steps of two-phase flow patterns identification based on this method are expounded in detail. Then the simulation experiment has been finished to prove the validity of this method. The simulation experiment results have shown that this method has higher recognition precision and faster operation speed in the two-phase flow pattern identification. This method also provides an effective means for the two-phase flow pattern on-line identification.

Abstract: The particle size analysis (PSA) by laser diffraction (LD) method can be used for monitor or control of particulate process, because it has the advantages of shorter measurement time and good repeatability, and a variety of commercial instruments is available. However particle size distribution (PSD) measured by LD method depends a great deal on not only optical detector configuration and calculation procedure but also on the system of sample loading into the measuring zone. From this fact, the validation of PSA by LD method should be done using reference particles (RP), whose size distribution is better to have a range over one decade of size, according to ISO 13320-1. For this purpose, the Association of Powder Process Industry and Engineering, Japan (APPIE) distribute the spherical barium titanate glass particles as RP of JIS Z 8900-1, whose size ranges are 1 - 10 µm (MBP 1 - 10), 3 - 30 µm (MBP 3 - 30) and 10 - 100 µm (MBP 10 - 100). This paper shows why LD method needs to check its performance by using RP, and then reports the results of the round robin test of two kinds of RP (MBP 1 - 10 and MBP 10 - 100) and silica RP candidate with 0.1 1.0 µm size measured by LD instruments, which was conducted by the Technical Group of Measurement and Control in APPIE. PSD results measured by LD instruments were almost same as each other for both RP samples. MBP 1 - 10 sample was well dispersed in water without detergent, but a few drops of detergent sometimes needed for dispersing MBP 10 - 100 sample. For MBP 1 - 10 sample, PSD by LD method was slightly smaller than that measured by scanning electro microscopy (SEM) or electro sensing zone (ESZ) methods. For MBP 10 - 100 sample, PSD by LD method agreed well with that by SEM or ESZ methods. Silica sample can be supplied to the users as the dry powder, which can be re-dispersed in water with small amount of surfactant. From the results of the round robin test using silica sample, PSD measured by LD method roughly agreed with EM method.

Abstract: The characteristics of dry ice particles produced by expanding liquid carbon dioxide and its application for surface cleaning have been studied experimentally. The production of the dry ice particles was based on the Joule-Thomson effect. The ejected dry ice particles were observed using a high-speed microscope camera. Through digital image processing, the particle size and particle velocity in the jet were analyzed. To in-situ measure the size distribution of the dry ice particles, a laser diffraction method was used. The experimental results showed that the primary dry ice particles ejected from the expansion nozzle were about 1 μm in mass median diameter. The presence of a thermally insulated tube at the outlet of the nozzle enhanced the agglomeration of the particles, whereby agglomerates of about 100 μm in mass median diameter were formed. The performance of dry ice jet for removing fine particles adhering to surfaces was also evaluated using microscopic observation. It was found that the particle removal process consists of two stagesslow removal stage and rapid removal stagethat are related to the jet temperature.