Building Blocks, TRL Krosaki Refactories

Project name : Light Weight Silica Brick from Recycled Material
By : Dr Raghunath Prasad Rana
Company : TRL Krosaki Refractories (Tata Refractories Ltd)
Location : Belapahar
Valuable contributors : Atanusuvrajit Bal, Biswajit Ghosh, Subrat Kumar Sahoo and Prosenjit Das

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When confronted with the problem of shrinking raw material sources owing to mining restrictions, TRL Krosaki Refractories decided to look within for a sustainable solution. Transforming this challenge into an opportunity to deal with another mounting problem-solid waste generated during the production of silica bricks-the company developed a revolutionary new process that would generate saleable bricks from this waste.

A major producer of basic and high alumina silica specialities, TRL Krosaki Refractories has its operations in Orissa, Gujarat, Jamshedpur and Salem in India, and in China. The company is also the only commercial manufacturer of dolomite refractories in India and caters to a large and diverse global customer base. TRL Krosaki Refractories recently found itself up against the challenge of managing solid wastes generated as a result of the silica brick production process. The waste had to be disposed of properly, adding to the production costs of silica bricks, which, in turn, meant higher market prices for customers, further adding to the company's woes.

Besides, the company was also simultaneously battling the growing problem of quartzite raw material shortages, due to mining restrictions levied by the government at various mines.

Looking within
When researching ways and means to find some productive use for solid wastes, the TRL Krosaki team, led by Dr Raghunath Prasad Rana, chanced upon a remarkable discovery. They found that a given silica polymorph could be transformed into another by way of reconstructive transformation, under the proper conditions.
Accompanied by Atanusuvrajit Bal, Biswajit Ghosh, Subrat Kumar Sahoo and Prosenjit Das, Dr Rana found that during firing, quartzite changes into tridymite at the temperature of 870 degrees C. This tridymite is further converted into cristobalite at 1,470 degrees C. The transformation kinetics for each of these reactions is governed by various factors such as silica crystal size, impurities and the quartzite source. For instance, large crystal sizes for silica and a smaller content of impurities slow down the transformation of silica. Besides, the amount of residual quartz must be low enough to avoid expansion during application.
The team worked on optimising the firing cycle, so as to avoid cracking during firing, and thereby achieving a homogeneous residual quartz level. During the production of silica bricks, close to 30 percent of the wastage is caused due to lack of necessary properties, causing the material to break and crack during the firing cycle. The rejected material had a bulk density that was lower than that of quartzite, along with lower density and low amount of residual quartz. These qualities made the waste material especially useful for production of lightweight bricks. The team then got to work, optimising the maximum amount of rejected material to 75 percent. This rejected material was combined with 25 percent fresh raw material, and blended together with the binder and pore former in the Eirich Mixer.

The moulded bricks, thus formed, are air-dried and then, later, oven-dried at a temperature of 150-200 degrees C to avoid cracking during the firing cycle. These lightweight bricks are then stacked in a single layer above the dense bricks, so as to avoid gravity loading, which may cause crack ignition and black core formation upon surface contact.

The lightweight bricks, so manufactured, satisfy customers' expectations, while also serving as an additional source of income for the company. Besides, by sidestepping expensive storage, logistics and disposal cost, TRL Krosaki Refractories was able to accrue valuable cost savings, which it passed on to its customers in the form of lower market prices.

Building the pathway to success
Developing this process was no mean feat for Dr Rana and his team, who ran into numerous roadblocks before they could come up with a perfectly functional solution.
For one, during trials, the waste material could not be mixed with the other additives due to variations in density. Further, the resultant improper mixing could lead to variations in the bricks' properties and texture. The team set about developing an inclined mixer with a high-speed rotor to overcome this problem, thereby enabling better homogeneity and distribution of both types of materials.

The low density of the waste materials meant that a higher amount of water had to be used to improve workability of the mix. This was a problem because the use of more water lowers the bricks' surface smoothness and green strength. Lower green strength implies that the bricks are more prone to breaking during processing, and can also crack during the later stages of drying due to the water vapour that escapes from the surface. These issues were overcome by streamlining the type and amount of binder used during the process.
Lastly, the traditional brick-setting pattern in the kiln was contributing to improper heat transfer and, consequently, under-fired bricks. To resolve the same, quartzite sand was added to the surface of each brick, so that the heat can easily be transferred to the bottom surface, eliminating the formation of black core. Also, the packaging of the quartzite grains and granulometry were optimised to reduce the black core and firing irregularities inside the bricks. In spite of all attempts was taken to avoid black core and lamination inside the brick but this problem was continued till July-2012 and during that time; it became a threat to receive any order from customer on this product. There was only one alternative not to do any production of such bricks. The root cause of this problem was investigated and found the binder creates such type of defects inside the brick. During drying of the bricks, the outer surface gets hardened and entraps the core moisture which on heating at high temperature forms lamination and forms reducing atmosphere to form black core. By replacement of suitable alternative binder with optimum amount was able to sort out the issues. The productivity of this type of brick has increased by using Sacmi Press and two layers of setting pattern during firing in the Tunnel Kiln. There is no more delivery failure of this kind of product after successfully improvement of this product.

Reaping rewards
TRL Krosaki's experiment with creating wealth from wastes generated rich rewards once the process was rolled out. To date, the company has saved a significant amount of money since the problem's being solved in the last financial year.
Minimising the amount of solid wastes generated from the manufacturing process helped the company to both reduce its expenditure on storing, handling and disposing the waste, while also reducing its carbon footprint. Most importantly, the company's innovative thinking has helped it to transform a challenge into an opportunity to serve its customers better, by giving them an additional, high-quality product that they can count and rely on.