Value added product, classified fly ash

September 2020
Value added product, classified fly ash

Dirk India Pvt Ltd (Unit of Ambuja Cement Limited) is in the business of classification of fly ash and manufacturing PPC by the method of intermixing. Fly ash is being classified by centrifugal cyclone separators to various micron size constitutes to different grades of fly ash known as Pozzocrete. This Pozzocrete is sold under various brand names of P100, P63 and P60 depending upon particle size of fly ash. P100 (Microfine Fly Ash) is basically used for High Performance Concrete starting from M60 and above and Pozzocrete P63 grade of concrete is used for M40 to M60 and P60 is used for normal grade of concrete. Coarse material known as P10 is now used in making bricks and blocks as well as partial replacement of sand. Presently, P100 and P63 had been extensively used by Builders and RMC Industries for their large and small projects including infrastructure projects. The possibility of using P10 (less than Blaine 150 m2/Kg) had been studied by grinding the coarse fly ash to the desired Blaine. The same has also been tried in lab ball mill to achieve different fineness and its Lime Reactivity Testing have been checked and lab scale PPC have been prepared by the method of inter-mixing to see the performance in cement and concrete. At the same time, ground fly ash and classified fly ash of identical Blaine have been compared to see their relative properties in their performance both in mortar and concrete.

1.0 History
Over the years there has been a growing demand for finer, more accurately sized and Quality Assured particulate-materials to meet the material specifications of industry. To some extent this has been due to a better understanding of the function that the complete particle size distribution of a material and not just some aspect of it contributes to the performance of a powder when applied to a particular process. The ash - produced Pulverised fuel ash( fly ash) / by product - quality varies widely dependant on fuel source and quality variations on plant design, combustion and dust collection processes, plant engineering and plant operational practice International Standards for Cement Replacement Materials dictate that chemical, physical and particle size characteristics should be controlled. These characteristics are not a part of all the Pulverised fuel ash produced by coal fired power stations. Hence it becomes necessary to Process the Pulverised fuel ash by using the technology that produces the product that confirms stringent requirements laid out by various international standards. The high performance concrete includes all those types of concrete with special requirements such workability, pump ability, high flow and higher retention in fresh state and high strength and high durability in Solid state. Classified fly ash has very high potential to produce all these types of Concrete effectively. At the same time one needs to ensure right Particle size as well as Particle size distribution which can only be achieved by state of art classification systems similar to one of those installed at Dirk India private Limited. By choosing right type of fly ash one can precise+ly produce High Volume fly ash mixes (Fly ash % above 40%) event at Low grade and normal grade concrete as well as normal replacement levels for High early strength mixes.

2.0 Objective
As the Processed Pulverised fuel ash needs to undergo a process which will not change the geometry of the tiny particles as the shape, which is spherical, plays very important role in the concrete. This ensures that the chemistry of the ash is not changed. Apart from this the ash needs to be processed in large volumes and at minimum cost and also in environmental friendly manner. Our long experience lead us to Mechanical Air Classifier which met all the requirements of processing the fly ash.

2.1 Description of the Equipment (Classifier) Mechanical Air Classifier works on the principle that wherever relative motion exists between a particle and a surrounding fluid, the fluid will exert a drag force on the particle. If the individual particle was falling under the influence of gravity in still air, it would accelerate until it reached a constant velocity which is known as the Terminal Settling Velocity. This occurs when the drag force exerted by the air balances the gravitational force exerted on the particle. This velocity rises the air thus the smaller particles of lower terminal settling velocity is entrained and carried upwards. Since the difference in terminal settling velocity between particles in the sub sieve range (fine powders) becomes so small, then a simple gravitational system becomes impractical. To overcome these limitations it is necessary to increase the gravitational force in this way the air velocity necessary for the entrainment of a given particle is increased, the difference between particles magnified and high efficiency classification becomes possible in a relatively small space.

Figure no 1: Typical Cross Section of a High Efficiency Side Draft DIRK Classifier.

In practice this is achieved by causing the carrying air and particles to follow a curved path which spiral inwards to a concentric discharge point. In this way forces of several hundred gravities may be generated