Let’s build for a green future

The raw material for cement is limestone; and to manufacture the product, carbon must be removed from limestone. This adds to cement’s emission intensity. The process, known as calcination, requires very high temperatures in the kiln — up to 1,450°C — which requires fuel to burn. More than 50 per cent of the industry’s greenhouse gas footprint comes from process emissions — the reduction of limestone and the release of CO2 — and the remaining mainly from combustion in the furnace. So, “greening” this industry is tough going, but not impossible

Globally, the cement industry is known to be part of the “hard to abate” sectors. It is critical for economic growth, but has a high carbon intensity — accounting for 7 per cent of the carbon dioxide (CO2) emitted globally. Emissions are intrinsic to the manufacturing of cement. The raw material for cement is limestone; and to manufacture the product, carbon must be removed from limestone. This adds to cement’s emission intensity. The process, known as calcination, requires very high temperatures in the kiln — up to 1,450°C — which requires fuel to burn. More than 50 per cent of the industry’s greenhouse gas footprint comes from process emissions — the reduction of limestone and the release of CO2 — and the remaining mainly from combustion in the furnace. So, “greening” this industry is tough going, but not impossible.

My colleagues at the Centre for Science and Environment (CSE) have deep dived into the Indian cement industry to set a road map for the future. Our analysis shows much can be done to decarbonise India’s cement sector and if done well, the efforts could work to set right the other sectors. This is not to say that you can manufacture cement with no emissions, but you can make it as green as possible.

According to the Union environment ministry, India’s cement industry contributed 5.63 per cent of the total emissions in 2016 and 5.72 per cent in 2019. This is even as the industry is growing, as it will, with the much needed and massive investments to build the infrastructure needed for economic growth.India’s cement industry has had a head start over its global counterparts on reducing carbon intensity by doing two critical things. One, it has substituted to some extent the use of limestone with fly ash — a waste product from the burning of coal in thermal power plants — and two, it has improved its energy efficiency because it could reduce the cost of fuel. These measures, done for long to improve the cost-competitiveness of the industry, signal to what more can be done in the future. This is why consumers of cement count.

The carbon intensity of the product is partly in the type of materials used for its manufacture. We need to understand the types of cement and why this matters to saving the climate. There are broadly three types of cement — Ordinary Portland Cement (OPC), which uses limestone to make cement; Pozzolana Portland Cement (PPC), which uses fly ash to partially replace limestone; and Portland Slag Cement (PSC) in which slag, a waste product from steel plants partially, replaces limestone. The Bureau of Indian Standards (BIS) has notified standards for another category called composite cement (CC), in which fly ash and slag can substitute limestone use by as much as 60 per cent. Why does this matter?

Quite simply because the more limestone is reduced in the manufacture of cement, the less it will pollute. So, while OPC with 95 per cent limestone emits 0.84 tonnes of CO2 for each tonne of cement produced, it goes down to less than half in the case of PSC, which substitutes limestone by using waste slag by over 55 per cent. Currently, PPC, which has lower emissions, dominates with 65 per cent market share, but the country is still producing OPC—roughly 30 per cent of the total cement.

CSE’s decarbonisation roadmap for the cement sector recommends that the production of OPC should be controlled; brought down to less than 10 per cent. And there should be targets for increased share of blended cement by 2030. It also says fly ash use in PPC should be increased from the current up to 35 per cent to 45 per cent, which in turn will reduce emission intensity even as the consumption increases.

The second decarbonisation pathway — to replace fuel for combustion — has opportunities for waste management. Currently, the cement industry is mainly dependent on coal, lignite or pet coke as fuel — replacing this would bring down the emission intensity of the product. Many cement companies are today taking municipal solid waste for incineration in the kiln. But this is not happening at the scale that is possible. This is also because the quality of waste — mixed plastic and low-grade materials that cities send — are not cement-grade refuse-derived fuel (RDF). This is where the opportunity is: to take the garbage and process it so that it makes a fuel that can be used as a substitute for coal.

CSE recommends that the country should define green and low-carbon cement — that has replaced the use of limestone by over 50 per cent and displaced the use of coal by 50 per cent by using RDF or renewable energy. By doing this, India’s cement industry could halve its CO2 emissions even as it doubles its production by 2030. This green cement should get the advantage of a lowered GST. It’s a win-win strategy. But it needs everyone to contribute to this “building” of green India.

(Writer is Director General of CSE and editor of Down To Earth, an environmentalist who pushes for changes in policies, practices and mindsets)