ICR looks at the impact of various methods such as use of alternative fuel and raw materials, tackling the emissions issue and encouraging carbon capture in a bid to make green cement and progress towards Net Zero goals.

The analytical journey is long past its prime when it comes to diagnosing the emission problem pertaining to cement and concrete. There is no denying the fact that the problem is too big.
If concrete was a country, it would be the biggest production centre as all other commodities put together will not even come close to the 30 billion tonnes of concrete that the world produces every year. If cement was a country, it would be the third highest emitter of CO2 in the world. But the efforts have been to find an approach that would force corporations to either limit and progressively reduce over time the impact on the environment through a slew of measures directed at reducing the carbon footprint of cement.
The chart attached shows the distribution of the CO2 emission based on the processing steps for making cement from limestone.

United efforts
The last five years has seen acceleration in the efforts towards finding significant pathways for reducing carbon footprint in cement production around the world. The progress on substantial reduction has been positive with concentration in the following areas:

• Focus on Calcination Emission: Reducing clinkering by adding alternative materials that can replace clinker
• Focus on Fossil Fuel Emission: Efficiency improvement in a number of areas that reduce the use of fossil fuels per unit of cement output, together with the use of alternative fuel.
  Under the first category, we see a rise in the use of fly ash from the coal-based power plants that replace clinker during grinding and the percentage increase in the last five years on this count would be around 2 per cent (31 per cent moving to 33 per cent with the balance being clinker). Alternatively, the use of blast furnace slag has seen a rise of 5 per cent (50 per cent moving to 55 per cent with the balance being clinker). Both of these actions have taken the total CO2 emission to 860 kg per tonne for some of the best operating plants of the world.
  The challenges for the future in this regard is that fly ash will remain a constantly depleting resource as all fresh investments into coal fired power plants are scrutinised and it is most likely that the current generation of fly ash will not move up in the coming years. This poses some challenges for the future as the emission pathways that consider use of fly ash as a potential lever for replacing clinker would have to find new pathways as a countermeasure. The use of blast furnace slag also has the same problem brewing at large as steel production is slated for overall sustainability improvement measures, which ordains reduced output of blast furnace slag as a definitive measure.

Tackling the emissions issue
This leaves the focus on alternative use of other non-fossil fuels for producing cement, where the actual progress is almost entirely hinged on renewable sources producing electricity that would be used for clinkerisation as well as for grinding. While the latter has progressed well, the former is still at a stage where a handful of cement units have signed up for the alternative technology in kilns.
Most of the technologies so far have progressed little towards solving the real issue of emission stemming from the clinkerisation process itself, as the molecular structure change from limestone to clinker involves generation of CO2 quite inevitably. The solutions therefore looked at ways of capturing carbon from the emission process, somewhat similar to the photo-synthesis process in plants as Professor Dr Aldo Seinfeld from ETH Zürich has shown. However, the progress is still at a laboratory scale and to find an economic solution will still take some time. For example, most cement kilns today produce close to 2.5 million tonnes of clinker and the sizing is only moving up, which means the amount of CO2 generation from these kilns per year would be close to 2 million tonnes. To get CO2 capturing systems to scale up to these levels would need many years.

Putting carbon to good use
The question is how can we help to scale up the capacity to sequester and store carbon from the emissions from cement kilns? The problem needs to be approached scientifically to make the process economical, which is where the current focus is. But more than the laboratories where this progress is well grounded, we need the cement corporations to set aside funds for investments that need to be made for all future kilns that have the provisions for carbon capture.
The next question is to look at how the stored carbon can be put to use in production of concrete? This requires more than the usual scientific research, as the supply chain of concrete making must factor in ways and means of finding pathways for using stored carbon in the concrete making. The Economist reports that companies like CarbonCure, a Canadian firm, are doing this. They have fitted equipment, which injects CO2 into ready-mixed concrete to more than 400 plants around the world. Its system has been used to construct buildings that include a new campus in Arlington, Virginia, for Amazon, an online retailer (and also a shareholder in CarbonCure), and an assembly plant for electric vehicles, for General Motors in Spring Hill, Tennessee.

Piloting new technologies
One of the other areas of focus has been to find an alternative route to clinkerisation that is based on electricity.
Calix, based in Sydney, Australia, is working on an electrically powered system, which heats the limestone indirectly, from the outside of the kiln rather than the inside. That enables pure CO2 to be captured without having to clean up combustion gases from fuel burnt inside the kiln—so, if the electricity itself came from green sources, the resulting cement would be completely green.
A pilot plant using this technology has run successfully as part of a European Union research project on a site in Belgium operated by Heidelberg Cement, a German firm that is one of the world’s biggest cement-makers. A larger demonstration plant is due to open in 2023, in Hanover, to help scale up the technology.
Almost all of this would need sacrifice from many stakeholders, as the cost of making cement and concrete will rise as investments have to be made in new technology. Bill Gates’ book, ‘How to Avoid a Climate Disaster,’ projected an increase of the cement making cost from the current $125 per tonne to a range of $219 to $300 if the CO2 emissions have to be taken care of for achieving Net Zero. However, the price of cement is already much above $125 per tonne even without factoring any of the carbon capture and sequestration measures, so the real rise could be much more.
A community of stakeholders, starting with the corporation making cement, the community near the cement kilns, the customers, the suppliers and the government, all have a role to play to find a solution how this increase in costs would have to be borne and distributed. Carbon taxes have always been the time-tested path to decarbonisation. Stringent use of taxes as a potent tool has seen better progress, especially in Europe, where some serious progress has happened. Recycling of cement from the demolition waste is one great example.
The best example of coordination and collaboration is captured in the initiatives of the world’s largest kiln near Wuhan, where one would witness how the city municipality came forward to proactively recycle the entire city municipal waste into the kiln of the cement unit situated on the Yangtze river. The waste is transported by barges and through a pipeline taken directly into the cement kiln. Such collaboration could replace the hard stand of putting penalties, which after all could be regressive at times.

-Procyon Mukherjee