An Investigation into the Flow Mechanism of Gas-Solids Flow of Fine and Dusty Powders

Abstract

Bulk solids handling of fine powders finds place in a wide variety of industries, such as mineral processing, coal-fired thermal power plants, petrochemical, food, and pharmaceutical. These industries require handling and conveying of various products such as pulverized coal & iron ore used in the blast furnace of steelmaking industries, fly-ash produced in thermal power plants and essential consumable products such as flour and powdered spices, etc used in food processing industries. Designing of such systems using simulation tools such as EDEM, provides a valuable platform. Although EDEM is well established in the areas where the particle size is large (i.e. from 10 mm to 0.5 mm) it has not been utilized in the area of fine powders (i.e. from 300 μm to 0.5 μm). In this work, an attempt has been made to simulate fundamental behavior of fine powders and validate it against experimentally obtained results. Apart from handling equipment, design of a pneumatic conveying system is also a challenging task. The minimum amount of air required per unit weight of the material to avoid blockage in the line changes with the characteristics of the material to be conveyed. Therefore, it is a common practice to first generate the pneumatic conveying characteristic (PCC) in an experimental test rig. For the same purpose, a pilot plant was developed under an industrial research project sponsored by the National Thermal Power Corporation (NTPC) entitled “On Developing Reliable Scale-up Procedures and Design Optimization for Pneumatic Fly Ash Conveying Systems for 500/800/1000 MW Units”. For the purpose of measurement of air flow rate required for conveying, various orifice flow meters were designed, fabricated, installed and calibrated. The equipment developed were found to be working properly. National Thermal Power Corporation (NTPC) has experienced that in cases of rainy season/winter/high relative humidity condition with no air-drying plant installed downstream to the transport air compressor in the Ash Handling Plants in Coal-Fired Thermal Power Plants, there were cases of water droplets (dew formation) in the air stream (especially towards the end of pipeline). Thus, a case study was carried out. It was found out that for avoiding this problem, the installation of air-drying equipment is a must.