I.S. Lowndes

Characterisation of the cross sectional particle concentration distribution in horizontal dilute flow conveying—a review

Abstract This paper presents a review and analysis of the results of recent research that has been carried out on horizontal pneumatic conveying of materials in the dilute phase. An introduction to dilute phase pneumatic conveying is given. Many in-process applications require a detailed knowledge of the cross-sectional particle concentration distribution and an insight into the research carried out in that field is reviewed. Tomography and computational fluid dynamics (CFD) modelling have been identified as the available tools for achieving the aims of such a study and an overview of each is presented. Recent research has concentrated on identifying the optimum operating conditions to increase the energy efficiency of the systems and reducing pipe wear. A developing research area has been the modelling of particle behaviour within pipe systems, especially after bends. Gravitational settling in horizontal pipes, inertial behaviour in pipe bends and branches, turbulent dispersion, turbophoresis and transverse lift forces induced by particle rotation were reported to be the effects governing particle motion that ought to be accounted for by a dilute gas-particle flow model. Particle size, solids loading ratio, pipe material and bend characteristics were identified to be the controllable parameters that determine cross-sectional particle concentration distribution. The effect of secondary turbulent flows and lift forces are enhanced by wall roughness and particle–wall interactions. A new technique of swirling flow pneumatic conveying (SFPC) has been recently applied. However, numerical modelling of such flows is still at an early stage because the mutual coupling between the two phases is not well understood. The physical understanding and modelling of the cross sectional distribution of particles in dilute SFPC has been identified as a challenging area for future research.

The ventilation of an underground crushing plant

Abstract The use of compressive crushing plant such as gyratory crushers within minerals processing operations can generate large quantities of dust as large volumes of ore are tipped into the crusher feed bins. Methods to reduce these dust emissions include the retrofitting of shrouds, enclosures, local exhaust ventilation (LEV) systems and water suppression systems. The operation of these ancillary systems should be optimised to offer maximum performance. It is desirable that the future planning of such facilities include sufficient dust suppression and/or removal systems to ensure that material delivery rates are maintained and the welfare of the workforce is protected. This paper presents the results of an investigation of the tipping process through the application of computational fluid dynamic (CFD) methods and validation using data obtained from scale experiment. A 3-D computational model has been constructed using the Fluent™ modelling software to represent the ventilation regimen within an underground crushing installation. The falling ore has been represented as a granular fluid continuum falling under gravity from the bed of the dump truck. Transient streamlines are used to represent the dispersion of dust due to the updraft airflow generated by the tipping process. A parametric analysis has been performed on a model of the tipping process to investigate the influence on dust dispersion of; the orientation of the dump truck, the surrounding ventilation characteristics and the material tipping rate and volume. The CFD models predict a strong shear-induced flow in the region of the crusher during tipping and a high sensitivity to the surrounding ventilation regimen. These results indicate the need for further experimental studies to characterise the entrainment and transport of dust-laden air into the induced shear flow. An experimental rig has been designed and evaluated for the purposes of conducting validation studies and gaining further insight into this phenomenon. Results of these investigations are presented.

An investigation into the parameters affecting mass flow rate of ore material through a microwave continuous feed system

An investigation into the characteristics of a gravity-driven conveyor system for passing crushed ore through a microwave cavity has been undertaken using laboratory experiments and numerical modeling. The conveyor system consisted of a vertical hopper, a column passing through the microwave cavity and a tilting vibrating tray. For the efficacy of the microwave treatment of the ore, the residence time of the ore material in the cavity must be known so that the optimum microwave power and exposure time can be calculated, and so that the microwave field can be tuned effectively. The investigation was undertaken using a crushed copper ore from the Palabora mine, South Africa. Four different size fractions and two blends of ore were tested, and the affect of tilt angle and distance between the base of the column and the collector tray were examined. Equivalent numerical models were constructed using discrete element modeling. It was found that the numerical models can be calibrated against the experimental data, and thus can be used to predict flow characteristics, mass flow rates and microwave exposure times which are required in the design of such a conveyor system for microwave pre-treatment.

The development of a modelling strategy for the simulation of fugitive dust emissions from in-pit quarrying activities: a UK case study

Surface minerals extraction and processing operations can generate large quantities of fugitive dust that, when released in an uncontrolled manner, can cause widespread nuisance and potential health concerns for on-site personnel and surrounding communities. Typical fugitive dust emission sources may include minerals transfer points, conveyance, loading into crusher feed bins, haulage and blasting. To increase the understanding of the dispersion of fugitive dust from such activities it is necessary to develop suitable modelling strategies. The paper reports the results of a series of preliminary studies conducted using the UK Atmospheric Dispersion Modelling Software (ADMS3.1). A strategy was developed to model dust dispersion from blasting events and haul roads within a major UK limestone quarry. An analysis of the results confirmed the strong influence on the predicted dust dispersion of site-specific meteorological conditions and both the in-pit and surrounding terrain.

An investigation into unpaved road emissions from a UK surface limestone quarry using cylindrical adhesive pad collectors and image analysis

Demand for increased aggregates extraction combined with ongoing pressure to adhere to existing and future environmental regulatory requirements requires sustained research and investigation into associated particulate emissions. Open pit quarries commonly operate ‘blast and haul’ extraction methods, implying that any increase in production will lead to increases in quarry traffic and hence unpaved haul road particulate emissions. This paper presents an analysis and discussion of experimental data collected during a roadside particulate emission sampling study conducted within a major UK limestone quarry. The particulate samples were collected using a total of six cylindrical adhesive pad type collectors located symmetrically, at equally spaced intervals upwind and downwind of an unpaved truck haul road. A total of three sampling studies were conducted, each representing approximately 1 hour of road activity and between 6 and 8 vehicle passes. The first two sampling periods were conducted on an initially unwetted haul road. The third sampling period was conducted following road wetting by a bowser. The surface characteristics of the haul road surface were obtained by the collection of a series of swept surface material samples. An analysis of these samples collected prior to and during each of the sampling periods established the surface moisture and silt content of the unpaved road surface. Weather data were obtained using a permanently sited metrological station located on a hill above the quarry, together with a portable weather station located upwind of the haul road to providing accurate localized data. The dust samples collected on the adhesive pads were sized using an image analysis (IA) based method. The IA method employed advanced image enhancement functions to characterize the captured particulates in terms of total count, captured mass, particle aspect ratio and size distribution. These characteristics were compared for each collector sample over each of the three sampling periods. The study concluded that the IA method was able to provide a useful and consistent range of sample characteristics, although the limit of the resolution of the sizing of the particulates sampled was found to be approximately 5 μm. It was found that there was minimal variation in the sampled particulate size distribution and aspect ratio up to a collection distance of 29 m from the roadside in the downwind direction. A clear attenuation in the capture of particles was identified in terms of particle count and total captured mass reporting to measured upwind background levels at 29 m from source. The directionality of the particulate concentrations collected on the pads was found to vary significantly. It was concluded that IA offers a viable method for the analysis of samples collected from cylindrical adhesive pad collectors.

A Review of Primary Mine Ventilation System Optimization

Within the mining industry, a safe and economical mine ventilation system is an essential component of all underground mines. In recent years, research scientists and engineers have explored operations research methods to assist in the design and safe operation of primary mine ventilation systems. The main objective of these studies is to develop algorithms to identify the primary mine ventilation systems that minimize the fan power costs, including their working performance. The principal task is to identify the number, location, and duty of fans and regulators for installation within a defined ventilation network to distribute the required fresh airflow at minimum cost. The successful implementation of these methods may produce a computational design tool to aid mine planning and ventilation engineers. This paper presents a review of the results of a series of recent research studies that have explored the use of mathematical methods to determine the optimum design of primary mine ventilation systems relative to fan power costs.

Dust dispersion from haul roads in complex terrain: the case of a mineral reclamation site located in Sardinia (Italy)

In recent years, there has been significant research effort to investigate the use of plume dispersion models to assess the environmental impact of fugitive dust emissions from surface mining operations. In particular, the results of these studies have identified challenges to the use of traditional Gaussian plume dispersion models to satisfactorily reproduce fugitive dust dispersion and deposition experienced from low elevation release heights within complex topography. This paper presents a discussion of the results of a preliminary series of modelling studies that have employed the UK-Atmospheric Dispersion Modelling System (ADMS) model to investigate the dust dispersion and deposition from a former mining site currently undergoing remediation. The remediation site is located within a valley in south-western Sardinia that may be considered an aerodynamically complex terrain. A series of field measurement surveys were conducted along the length of an unpaved surface haul truck roadway to measure the PM2.5 and PM10 dust fractions within the emitted plumes. To investigate the potential effects that the surrounding topography may have on the atmospheric dispersion and deposition experienced a series of UK-ADMS dispersion models were solved for a range of meteorological stability conditions typical of the area under investigation. A preliminary analysis of the results of these simulations concludes that there was a strong influence of the surrounding terrain on the dispersion and deposition phenomena predicted.

The application of genetic algorithms to optimise the performance of a mine ventilation network: the influence of coding method and population size

This paper presents an application of genetic algorithms (GAs) to the solution of a real-world optimisation problem. The proposed GA method investigates the optimisation of a mine ventilation system to minimise the operational fan power costs by the determination of the most effective combination of the fan operational duties and locations. The paper examines the influence that both the encoding method and the population size have on the performance of the GA. The relative performance of the GA produced by the use of two different encoding methods (a binary and a hybrid code) and various solution population sizes is assessed by performing a two way ANOVA analysis. It is concluded that the genetic algorithm approach offers both an effective and efficient optimisation method in the selection and evaluation of the cost-effective solutions in the planning and operation of mine ventilation systems.

Review of experimental methods to determine spontaneous combustion susceptibility of coal – Indian context

Abstract This paper presents a critical review of the different techniques developed to investigate the susceptibility of coal to spontaneous combustion and fire. These methods may be sub-classified into the two following areas: (1) Basic coal characterisation studies (chemical constituents) and their influence on spontaneous combustion susceptibility. (2) Test methods to assess the susceptibility of a coal sample to spontaneous combustion. This is followed by a critical literature review that summarises previous research with special emphasis given to Indian coals.

Modelling of auxiliary ventilation systems

Abstract In subsurface excavations, auxiliary ventilation systems are an important and integrated component of the overall ventilation scheme. Without adequate auxiliary ventilation, it is impossible to provide sufficient air to working faces, regardless of the quantity or quality of air in the main airways. Extended development headings are typically ventilated using fan and duct systems, which either force or exhaust air through the duct. The optimum design of such systems can be complex, depending on factors such as duct resistance, leakage and diameter, fan selection and spacing, and shock losses. This paper describes the development and application of a comprehensive design process for auxiliary ventilation systems. Included is a summary of published theory and literature, a description of software development, information and results from detailed field measurements, and a description of the application of the software to the design of an actual extended auxiliary fan and duct system.