In this project, dust suppression systems using ultra fine water mist technology, were used for suppressing the respirable dust. A new water mist based venturi system was developed for the purpose of suppressing respirable dust. This unit is powered by compressed air and water using an ultrasonic nozzle (MAL 1300 B1) embedded in the venturi body. These ultrasonic nozzles are capable of producing ultra fine water mist with droplet sizes ranging from 1 to 100 microns. As a result of the small droplet sizes, these particles collide more effectively with respirable dust particles, facilitating the reduction of respirable dust concentration. In order to optimise design configurations for optimum spray coverage and spray distances, several design assemblies were considered, namely, standard body rear fit, standard body front fit, shortened body rear fit, shortened body front fit, shortened body rear fit with extension of 1-40mm, and shortened body rear fit with extensions of 2-50mm and 3 -65mm. In our experimental design, two different ultrasonic nozzles were used, namely MAL-1300-B1 and MAD-1131-B1. The air pressure, air volume, water pressure, water flow rate, air induction velocity and air induction volume were varied and the water mist velocity and spray distance were monitored to determine the best optimal values. Further relative positioning of the nozzle within the venturi system was varied to minimise water droplets hitting the venturi body. After rigorous laboratory tests, the results indicated that the nozzle MAL-1300-B1 performed better than the MAD-1131-B1, and 70 mm (diameter) x 143 mm (length) venturi was capable of producing an optimum spray coverage and spray distance over 10 m. Further tests showed that a combination of air supply at 6 bar and water at 4 bar produced the optimum water mist thrust with inducted air velocity over 8 m/s. Water consumption for these nozzles was about 2 L/min in for a single unit. These optimised parameters were then considered for use in underground field trials. Two underground coal mines were considered for the field trials; one in Central Queensland (Moranbah North mine) and the other one in New South Wales (Metropolitan mine). Prior to carrying out the field trials with the ultra fine water mist technology in the underground mines, 3D Computational Fluid Dynamics (CFD) modelling was undertaken to gain a better understanding of the air flow and the dust flow and to further optimise the direction of the venturi system at these mines.For the CFD models, a longwall face with a cutting height of 3.5m was simulated based on the field dimensions. The full scale simulated longwall face comprised 103 supports, a shearer, Armoured Face Conveyer (AFC), BSL, and MG. The model geometry and mesh were created using the built in mesh tool features of the ANSYS13 design modeler. The model was meshed using the tetrahedron elements. A total of 1.8 million elements were used for construction of model. The base model results of the simulated longwall ventilation were calibrated and validated with the field data.The model results indicated relatively higher air velocity at the MG corner due to the presence of BSL, AFC transfer point and AFC motor. The respirable dust flow behaviour was investigated with various dust generation sources such as, intake air, stage loader and supports movements.Results indicated the dust particle flow pattern was closely associated with air flow patterns for respirable dust; predominantly respirable dust followed the air stream.Additional 3D CFD models were constructed by considering the longwall dust particles from various sources including MG chocks and BSL. The numerical modelling results demonstrated that much of the respirable dust particles generated from MG chock movements and BSL would disperse onto the longwall face ventilation, contributing significantly to dust levels in the longwall face. To optimise the position of the water mist venturi units on the
PDF
download
878987797
028-85220240
