Why has the cement industry become the main battlefield of carbon reduction in China?

During the two sessions this year, Hu Shuguang, a member of the National Committee of the CPPCC and professor of Wuhan University of Technology, pointed out that the carbon emission reduction of the cement industry is directly related to the success or failure of the national "double carbon" strategy, therefore, the country will inevitably develop and introduce high standard carbon emission reduction technical requirements for cement production, and the building materials industry should actively respond.

In fact, for the cement industry to reduce carbon, the policy level has been very important. On December 21, 2021, the Ministry of Industry and Information Technology, the Ministry of Science and Technology and the Ministry of Natural Resources jointly issued the "14th Five-Year Plan" for the Development of Raw Material Industry.

According to the plan, the raw material industry is a typical "high energy consumption, high material consumption, high pollution" industry, which is the key control object of national energy conservation and emission reduction. Therefore, the green development of the raw material industry is an important part of the plan. The plan emphasizes the comprehensive implementation of energy-saving and low-carbon actions around the target node of reaching the peak of carbon and carbon neutrality.

The plan gives three numerical indicators: During the "14th Five-Year Plan" period, "the comprehensive energy consumption per ton of steel in the steel industry will be reduced by 2%, the energy consumption per unit of clinker of cement products will be reduced by 3.7%, and the carbon emissions of electrolytic aluminum will be reduced by 5%."

How can cement, alongside steel and electrolytic aluminum, become the main battlefield for carbon reduction?

If the cement industry were a country, it would rank third on the carbon emissions list, behind China and the United States. The world produces 3.5 billion tons of ordinary Portland cement each year, and each ton of cement produced emits 561-622 kilograms of carbon dioxide, and the cement industry as a whole contributes about 8% of global carbon dioxide emissions.

The world's cement looks to China. In 2020, China's cement production is about 2.4 billion tons, accounting for about 60% of the world's total, and China's cement industry's carbon emissions account for about 14% of the country's total carbon emissions. Therefore, the low-carbon transformation of the traditional cement industry is of great significance for China and the world.

1.The carbon emission of the industry is only second to that of China and the United States, and clinker production accounts for 90% of it

The above mentioned total carbon emissions from the cement industry cover the full life cycle of cement.

Cement production begins with the mining and treatment of limestone (mainly calcium carbonate), which is then mixed with clay (mainly silicate) and fed to a rotary kiln at 1450 ° C to 1500 ° C for calcination. This process emits a lot of carbon dioxide, and the bulk material left behind is mainly composed of calcium silicate, or clinker. The clinker is cooled, gypsum and auxiliary cementing materials are added, and ground into a powder, which is cement.

In the entire cement production process, the clinker production stage emits the most carbon dioxide, accounting for about 95% of the total production process, more than half of which comes from limestone calcination, and less than half from the fuel used in this process

2. Fuel carbon reduction program: from waste heat utilization to green fuel

In 2019, Lafarge announced that half of the rotary kiln fuel at a cement plant in Nigeria is biomass, mostly from agricultural waste, and the company is also working to mine more fuel from municipal solid waste.

In fact, the practice of adding solid waste such as tires, organic waste, sewage sludge and plastics to cement kilns has been around since the 1970s.

In the beginning, these practices were more about reducing costs for companies, since garbage was certainly cheaper than coal, and some local governments even paid cement companies as a way to dispose of municipal waste.

In recent years, the cement industry has actively promoted the corporate strategy of solid waste as a fuel, more calling it a social responsibility to solve plastic waste and mitigate climate change, such as the Mexico-based Cemex Group.

From the perspective of fossil energy combustion and utilization, the utilization efficiency of heat energy has improved in recent years. Producing 1 ton of clinker required 3.75 gigajou in 2000 and 3.5 gigajou in 2014, reducing energy consumption by an average of 0.5% per year. Since then, according to the International Energy Agency, the energy intensity of clinker production has stagnated at 3.4-3.5 gigajou per ton. Based on such energy consumption, the production of 10 tons of clinker is roughly equivalent to the heat energy consumed by a small household in a heating season.

The rate of decline in energy consumption is a little slow, but there are still ways to reduce carbon and increase efficiency.

One approach is waste heat recovery.

The high temperatures required for rotary kilns are maintained by the heat generated by burning fossil fuels, 44% of which is wasted. If this waste heat can be recycled and used, it can greatly save fuel and thus reduce carbon emissions. A case study in India showed that using waste heat to generate electricity increased fuel efficiency in cement plants by 5%. However, it should also be noted that the current mainstream use of waste heat is power generation, for carbon reduction, at present, the effect is very limited.

One strategy that looks at the source is to reduce or eliminate fossil fuel use. At home and abroad, fuel substitution and collaborative disposal technologies continue to be explored, and it is expected to achieve "zero consumption" of fossil energy in clinker production.

Lafarge, the world's cement giant, has been working to replace fossil fuels with low-carbon and carbon-neutral fuels since 2013. Carbon neutral fuels are mainly biomass, because the carbon inside the biomass will eventually be released, and the use of fuel will not add carbon to the atmosphere.

3. Carbon Capture & coagulene

The most direct way to deal with the carbon dioxide emitted by calcination of limestone is carbon capture and storage, that is, the carbon dioxide emitted is separated, or can be recycled for direct use, or can be stored deep in the formation, long-term isolation from the atmosphere, and can be converted into minerals for secondary use.

The captured carbon dioxide can be used on-site. When cement is mixed with water, sand, stone, etc., to make concrete, carbon dioxide is applied to control the appropriate reaction conditions, and calcium carbonate is generated, which is stored in the concrete without reducing the performance of the concrete. Canadian company CarbonCure has fully commercialized this technology, which is currently equipped with more than 300 cement plants, and plans to reduce carbon emissions by 500 million tons per year by 2030, which is equivalent to removing 100 million fuel trucks.

However, CarbonCure's technology requires the purification and encapsulation of carbon dioxide from exhaust gases, which is still inconvenient. Australian company Calix has invented a new kiln that could make carbon dioxide harvesting easy. In traditional kilns, raw materials and fuel are mixed together; Calix's kilns, on the other hand, are filled with ground lime and water vapor, which is heated outside the kiln, expelled from the kiln by simple condensation, turning the water vapor into water, and the rest is pure carbon dioxide, which can be captured and reused.

The European Union is so interested in Calix's technology that it has included it in its €20 million research project "Low Emissions Intensity Lime and Cement" (LEILAC).

In 2019, Heidelberg Cement began pilot trials of the technology at a cement plant in Belgium. The pilot test results successfully separated the carbon dioxide and did not increase the fuel input, with no significant negative effects on the product and production plant. According to a Calix press release, an upgraded version of the pilot plant will go into demonstration production in Hanover, Germany, in 2023, and the demonstration plant will be able to capture 20% of the carbon emissions, or 100,000 tons of CO2 per year.

In addition, academia and industry are collaborating to apply cutting-edge scientific advances to improve traditional concrete.

The University of Manchester has teamed up with the UK's Nationwide engineering company to invent graphene-reinforced concrete - Concretene. With better performance and a 30% reduction in carbon emissions, the concrete has already had its first commercial application. In October 2021, Concretene poured an entire 756 square meter floor for a ballroom in Manchester.

So, where does the raw graphene come from? Rice University has found a cheap source: used tires. Rice University has invented a flash process that can turn leftover carbon or old tire debris from the pyrolysis of old tires into mixed layers of graphene, which can be added directly to cement. While solving municipal solid waste, the carbon in the waste is fixed in the concrete.

Carbon reduction not only depends on hard science and technology, information technology can also contribute.

European cement industry giant LafargeHolcim launched the "Factory of Tomorrow" program in 2019, developing a technical information system that integrates robots, artificial intelligence, Predictive Maintenance (Predictive Maintenance), real-time monitoring of the state of the assembly line, according to the development trend of the state of the equipment and possible failure modes. Predictive maintenance planning) and other technologies are integrated organically. Eighty percent of LafargeHolcim's cement plants have been connected to this system, which is estimated to increase plant operating efficiency by 15-20 percent and reduce carbon by 10 percent.

articulation

The cement industry is a major carbon emitter and is of great significance for global carbon reduction. This paper Outlines several directions and paths for carbon reduction in the cement industry:

● Waste heat recovery and utilization, improve energy efficiency;

● Fuel substitution, such as recycling biomass fuel from waste, hydrocarbon free fuel, green electricity, etc.;

● Raw material replacement, such as fly ash instead of cement, adding graphene;

Improve production processes, such as adding carbon capture and mineralization processes, and increase the level of digitization of production lines.

While the challenge of reducing carbon emissions is enormous, the industry now has a range of tools at its disposal to do its part to mitigate the greenhouse effect through market competition and technological advances.