Using fly ash and bauxite residue would help cement firms reduce their carbon intensity further, says the firm.
Metals major Vedanta which is the largest aluminium producer in India has invited partnerships from cement producers for using its voluminous by-products fly ash and bauxite residue for manufacturing low-cost low-carbon cement.
In a national workshop conducted with global industry experts, the company made a case for using fly ash (a by-product in thermal power generation) and bauxite residue (a by-product of producing alumina from bauxite) in cement manufacturing. India is the second largest producer and consumer of cement.
Data analysed by think tank Alliance for an Energy Efficient Economy (AEEE) shows that in 2018-2019, India had an annual cement consumption of 337 million tons and this is expected to increase up to 550 million tons by 2025. Though the per-capita consumption of cement in India is 240 kg, well below the global consumption of 530 kg.
According to International Energy Agency, the global cement industry accounts for around 7% of total global CO2 emissions. In India, the industry is responsible for 8% of the total national emissions. These emissions are a product of electricity usage, combustion of fossil fuel (coal, gas etc. for energy use), and the conversion process of limestone into lime (process emissions), which accounts for 13%, 31%, and 56% respectively.
The CO2 emission intensity of the Indian cement industry in 2018 was 576 kg CO2/ton of cement produced whereas the global average is 634 kgCO2/ton of cement produced. Key strategies being used currently to cut carbon emissions in cement production include improving energy efficiency, switching to lower-carbon fuels, promoting material efficiency (to reduce the clinker-to-cement ratio and total demand) and advancing process and technology innovations such as CCS (carbon capture and sequestration/storage).
The use of circular economy principals (like use of SCMs, utilisation of construction and demolition waste through technologies like “SmartCrusher”) is one significant method to cut down emissions.
Fly ash can partially replace cement in concrete (or be used to produce blended cement), significantly improving durability and workability of cement. With a 30 – 33% blending ratio, fly ash can help save 270 kg of carbon emissions for every tonne of cement produced.
Bauxite residue can be added to the raw mix in clinker manufacturing to replace virgin bauxite, improving its hydraulic properties and strength. Owing to high concentration of iron oxide and alumina, bauxite residue is a better substitute for laterite, used in clinker manufacturing. Moreover, the residual caustic in bauxite residue helps in controlling the emission of sulphur when used directly, making it a better fit for the purpose.
Both fly ash and bauxite residue being industrial wastes themselves, come with significant cost and energy advantages as well.
Vedanta Aluminium’s technical workshop was attended by over a hundred executives from the cement industry and featured globally renowned experts in this domain – Mr. Shreesh Khadilkar, ex-Director of Quality and Product Development at one of India’s leading cement producers, and Mr. Robin De Beer, a concrete technologist from South Africa with 40+ years of experience in gainful utilization of fly ash in concrete.
Mr. Rahul Sharma, CEO, Vedanta Aluminium Business, said that industries must develop waste-to-wealth value-chains to truly become sustainable and hoped that the Indian cement producers would come forth to work together on this innovative solution mutually beneficial for the industry and environment.
“Good quality fly ash can help reduce water demand, lower heat of hydration and significantly enhance workability of concrete, resulting in long-term strength and durability,” said Mr. Robin De Beer.
Mr. Shreesh Khadilkar added, “Bauxite residue has multiple advantages in cement manufacturing, such as lower silica relative to laterite/bauxite, higher alkali content and fine particles, which reduces grinding cost. It also improves hydraulic properties of cement. Indian cement industry should leverage this innovative opportunity to reap benefits of quality and sustainability.”
In FY21, Vedanta Aluminium supplied over 3 lakh metric tonnes of fly ash to various cement plants in India. Since February 2021, the company has also supplied over 30,000 metric tonnes of bauxite residue to cement manufacturers. The company is also supplying fly ash free of cost to local brick making MSMEs in its catchment.
In the same period, the firm also supplied nearly 4 lakh metric tonnes of ash to brick manufacturers. Ash bricks are not only lighter and stronger than traditional clay bricks, but play a crucial role in preserving nutrient-rich topsoil from being used as the raw material. This amounts to estimated savings of 1.9 metric tonnes of topsoil for every tonne of ash brick manufactured.
Besides, ash brick manufacturing is an eco-efficient process, contrary to the energy-intensive process of producing clay bricks in brick kilns that result in substantial greenhouse gas emissions. For every tonne of ash bricks manufactured, an estimated 5900 kg of carbon dioxide equivalent emissions is avoided.
To promote the use of fly ash bricks in building construction, NTPC, India’s largest integrated power producer, has set up fly ash brick manufacturing plants at its coal-based thermal power plants. These bricks are being utilized in plants as well as township construction activities exclusively. On average, 60 million fly ash bricks are being manufactured annually by NTPC.