NTPC ties up with cement companies to supply fly ash

NTPC Ltd, India’s largest power producer, has started to collaborate with cement manufacturers across the country to supply fly ash. It is part of NTPC’s endeavour to achieve 100 per cent utilisation of fly ash produced during power generation. The power producer is leveraging Indian Railways’ sprawling network to transport fly ash in an economical and environment friendly manner.

What is fly ash?

In India, coal is a major source of fuel for power generation. In the process of electricity generation, large quantities of fly ash get produced and becomes available as a byproduct. It is a fine powder resulting from the combustion of powdered coal - transported by the flue gases of the boiler and collected in the Electrostatic Precipitators (ESP).

Fly ash produced in modern power stations of India is of good quality as it contains low sulphur  and very low unburnt carbon. In order to make fly ash available for various applications, most of the new thermal power stations have set up dry fly ash evacuation and storage systems.

Fly ash consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium and sulfur are also present to a lesser degree. When used as a mineral admixture in concrete, fly ash is classified as either Class C or Class F ash based on its chemical composition. 

Class C ashes are generally derived from sub-bituminous coals and consist primarily of calcium alumino-sulfate glass, as well as quartz, tricalcium aluminate, and free lime (CaO). Class C ash is also referred to as high calcium fly ash because it typically contains more than 20 per cent CaO.

Class F ashes are typically derived from bituminous and anthracite coals and consist primarily of an alumino-silicate glass, with quartz, mullite, and magnetite also present. Class F, or low calcium fly ash has less than 10 per cent CaO.

The unique spherical shape and particle size distribution of fly ash make it a good mineral filler in hot mix asphalt (HMA) applications and improves the fluidity of flowable fill and grout. The consistency and abundance of fly ash in many areas present unique opportunities for use in structural fills and other highway applications.

Different modes of fly ash utilisation include:

• Building materials

• Mine filling

• Road and pavement construction

• Cement blending

• Agriculture/soil amendment

• Concrete and mortar

• Lightweight aggregate

• Manufacture of asbestos products

• Embankment/land development

• Floor and wall tiles

• Refractory bricks/tiles

• Paint industry

• Domestic scouring powder.

Environmental benefits of fly ash utilisation 

Fly ash utilisation has significant environmental benefits. They are: 

1) Increasing the life of concrete roads and structures by improving concrete durability.

2) Net reduction in energy use and greenhouse gas and other adverse air emissions when fly ash is used to replace or displace manufactured cement. 

3) Reduction in the amount of coal combustion products that must be disposed of in landfills. 

4) Conservation of other natural resources and materials.

Fly ash utilisation by NTPC

NTPC is India’s largest power utility with an installed capacity of 62.9 GW (including JVs), plans to become a 130 GW company by 2032. It was established in 1975. NTPC became a Maharatna company in May 2010. 

NTPC Group has 70 power stations comprising 24 coal, seven combined cycle gas/liquid fuel, one hydro, 13 renewables along with 25 subsidiary & JV power stations. The group has over 20 GW of capacity under construction, including 5 GW of renewable energy projects.

NTPC Rihand in Uttar Pradesh recently transported 3,834 metric tonnes (MT) of conditioned fly ash in 59 BOXN wagons to Dalmia Cement (Bharat) Ltd.’s plant at Nagaon in Assam. 

Earlier, the rail rakes of conditioned fly ash were dispatched to ACC plants in Tikaria (Uttar Pradesh), Kymore (Madhya Pradesh) and Ropar (Punjab).

During the financial year 2019-20, almost 44.33 million tonnes of fly ash was utilised for various productive purposes. NTPC produces approximately 65 million tonnes of ash annually, out of which 80 per cent (approximately 52 million tonnes) is fly ash. 

Presently, about 73 per cent of total ash is being utilised for production of cement and fly ash bricks, road embankment construction, mine filling, low-lying land development, and ash dyke raising.

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