Surveying the Cement Decarbonization Landscape

In this Insight we delve into the structure of the domestic cement industry, outline the energy use in cement production, and discuss potential decarbonization technologies.

The cement industry plays a vital role in the economy as the key binding agent used in concrete. Concrete is ubiquitous—used to construct buildings, roads, runways, sewer pipelines, and energy infrastructure, for example—and cement is the second most-used material in the world after water.

The traditional and most common production process for cement is responsible for significant greenhouse gas emissions, primarily from the release of carbon dioxide (CO2) during early production steps. Some of those carbon emissions are unavoidable as part of the chemical process of making cement, so the industry is exploring new energy sources, new cement technologies, and carbon capture all while working with slow-changing construction standards.

Carbon Intensity

It is estimated that about 7% of global CO2 emissions arise from cement production. In the US, cement represents 1% - 2% of CO2 emissions according to the Department of Energy. The carbon dioxide intensity of global cement production has decreased on average, according to the DOE, by 1.3% from 2005 to 2012 and 0.3% from 2013 to 2019.

Main efforts to stem CO2 output include finding general energy efficiencies, shifting from wet to more efficient dry production, and using gas to replace some of the coal used in the production process. However, improvements are estimated to need to accelerate by a factor of more than 10 to reach global emissions targets.

There are systemwide variables and impacts to consider as well. For example, the durability of cement to mitigate or resist climate damage can provide meaningful cost-savings. In addition, some designs of buildings using cement can have insulation benefits that help reduce ongoing heating- and cooling-related emissions.

And cement roads can, depending on thicknesses, provide better fuel economy than asphalt roads and, depending on climate, provide lower ongoing maintenance benefits. It should also be noted that cementitious materials are estimated to reabsorb 15% - 17% of the atmospheric carbon that was emitted in production.

Cement Production Process

Cement is a chemical combination of calcium, silicon, aluminum, and iron. Calcium often comes from limestone or chalk, aluminum and silicon or aluminosilicate can be found in many clays, more silicon can be found in sand, and iron is from iron ore. Each of the ingredients are first crushed and then mixed well either by circulating air if dry or in a stirred slurry to make filter cake.

The filter cake is then burned in a kiln or furnace at 2,500 - 2,800 degrees F, resulting in calcium oxide (quicklime) with carbon dioxide a waste product. The calcium oxide is in the shape of small marble-like rocks called clinker, which are then finely ground to make cement powder. The fuel for kilns is often coal with natural gas or oil injected into the furnace. The carbon dioxide emitted to produce clinker is estimated at ~30% from coal, ~30% from the limestone, and ~33% from the burning of the fuels used to generate other energy in the process.

The ground clinker or raw cement powder when mixed with water and aggregate (e.g., stone) becomes concrete with the ratio determined by the application. Adding chemicals, heat, and various recycled ingredients to the concrete mix can impact the cure of the cement and the performance of the product through time.

With an understanding of the cement process, one can imagine the vast efforts and materials: mining equipment, truck and rail movements, power to crush the rocks and grind the clinker, fuel to move the material in the market, and energy to heat kiln furnaces.

Structure of the Cement Industry

The global cement market is about 4.6 billion tons/year with clinker being the source of ~70% of that total. The industry grows very slowly at approximately 1% annually.  

In the US, the industry consists of a network of 104 cement plants, 362 terminals, and thousands of distribution points. The plants vary in production capacity, types of cement, ownership, and regional distribution. Twenty-four companies own the active plants in the US, and the top 10 account for 80% of total cement capacity.

However, 96% of cement gets to market through thousands of intermediaries in the distribution chain. Roughly 30% of cement plants have a production capacity exceeding 1,000 kt/year, while 35% have capacities below 500 kt/year. Larger plants are typically newer (less than 20 years old) and have lower carbon emission profiles per ton.

Individual cement markets differ due to regional construction practices and transportation costs. Ownership is characterized by a mix of large multinational corporations, medium-sized firms, and smaller local producers. All these variations can impact decarbonization strategies as they might impact the feasibility and scalability of different approaches.

Approaches for Decarbonization

Decarbonizing the cement industry requires the adoption of technologies that can reduce emissions throughout the production process.

Efficiency. As noted earlier, the carbon dioxide intensity of global cement production has decreased slowly over many years. This is primarily via adoption of advanced control systems and reuse of process-generated heat and exhaust gases. The industry has continued to upgrade and scale up its cement kilns to modern technologies such as pre-calciners and dry- versus wet-kilns.

Alternative fuels. The cement production process is heavily reliant on fossil fuels both in general process use and within the kiln during the cooking process for clinker. Within the kiln, where coal is widely used for heat and chemical reasons, natural gas in the US has replaced about a quarter of the energy. Materials such as old tires, waste oils, or plastics can be burned to heat the kiln, but they have limitations chemically (both process and emissions) and from an energy density standpoint. Europe, with its higher cost of landfilling waste, is more advanced in its use of waste-based fuels (up to 50% in some cases).

Replacing fossil fuels in the processes outside the kiln, including pre-heating, have shown promise, and several companies are working on transitioning some or all of their power needs to electrical energy. A constraint could be capacity to handle the new industrial load. The next phase would be to assure the electricity is from renewable sources which are, of course, in demand in many applications.

Clinker replacement. Reducing the amount of clinker can be achieved by replacing the virgin cement binder with alternative materials with lower CO2 emissions. They include industrial waste products such as fly ash from burning coal, ground bottle glass, and slag from manufacturing iron, in addition to naturally occurring materials such as volcanic ash, calcined clays and limestone.

Those alternative materials are typically cheaper than clinker, which is a plus, though each has chemical limitations. All are viable, however, as long as the final products’ characteristics meet an acknowledged cement product performance standard.

The DOE has estimated that further efficiency gains, alternative fuels, and clinker substitutions could abate ~30% of emissions by the early 2030s and ~40% by 2050 and require $3B - $8B of investment.

Additional Approaches

Further decarbonization efforts face more questions on cost and scalability and could mean a significant increase in cement prices, but there is a lot of experimentation across the industry.

Carbon capture with permanent storage or sequestration (CCS) is an approach that many industrial and utility facilities are considering, with cement being no exception. Carbon capture methods include pre-combustion capture, post-combustion capture, and oxy-fuel combustion. Expectations are the technology could become more commercialized in the late 2020s and will likely need both private and government support to fund investment with billions of dollars.

Several CCS hubs have been defined in the U.S. wherein there is a combination of both CO2 sources and potential underground storage options available. This opportunity could develop for cement facilities in those areas, though it is estimated that carbon capture could add $30-$40/ton to cement’s average price of $120/ton.

Alternatively, carbon capture and utilization (CCU) is another path to reduce atmospheric carbon. CCU technologies could capture carbon dioxide emitted during the cement production process and convert it into valuable products. Those end products could include fuels, alcohol, certain plastics, soap, and even meat-substitutes.

Injecting CO2 into cement and concrete is another application getting some attention. In this use the carbon matrix in the final product can replace the metal rebar in some concrete applications and may actually be stronger, albeit with an extended curing time.

There is some experimentation with hydrogen as a fuel for clinker production—up to 20% of coal can be used without equipment modification. Hydrogen, when compressed, has a higher energy density by weight than coal, so it could be an interesting modification in cement production as well as many other industrial processes such as integrated steelmaking. But hydrogen is expensive and can have significant carbon-emission aspects in its production.

Most hydrogen is currently produced from natural gas with a process that itself releases carbon dioxide. Carbon capture developments will also then apply to hydrogen production from natural gas as will renewable energy supply for hydrogen produced from water.

Six Challenges for New Production Methods

Transitions can bring challenges. Here are six for the cement industry beyond the technology uncertainty of new production methods suggested earlier.

Building codes. The market lacks uniform standards to define low-carbon materials. The current cement standards will have to be expanded to include new blends and materials, much like with various steels.

The sector has a 10- to 20-year adoption cycle to update building code standards and customer use familiarity, so every year could see some regional progress phasing in new rules. Some ‘new’ cements, too, require different construction techniques, some of which include onsite heating or drying. More pre-fab and modular housing—where production is centralized in a controlled area and currently represents 10-15% of cement use—could be an adjunct approach.

Procurement. The current procurement model of shorter-term government demand contracts does not attract longer-term capital at required scale for cement plants that last 30 - 50 years. That said, governments across the US purchase ~50% of cement, which could help support decarbonization policy. We are seeing some jurisdictions move towards future mandating of lower carbon cement in some applications.

Carbon taxes. Phasing in carbon taxes and carbon-emission tariffs in the EU and many other international jurisdictions will likely impact trade patterns and international prices for cement. Because the US is a net importer of cement, perhaps the US market will benefit from cement tons diverted from taxing regions. However, if a general US carbon tax of $100/ton was adopted simply to compete internationally in other products, the price of cement could rise by 50% - 75% as estimated by the DOE.

Plant sizes. Smaller cement plants have fewer output tons over which to spread cost recovery for carbon capture equipment. Others may not be located near where captured CO2 can be utilized or stored. These characteristics may be particularly true internationally where many facilities are older, smaller, and operate with varied equipment (e.g., wet kilns vs. more carbon-efficient dry kilns).

Local pushback. Projects may lack support from local communities and the public. And CCUs could face pushback due to environmental and safety concerns as well as the impact of accompanying pipeline and storage infrastructure. Significant expenditure on additional equipment will tend to drive up the price of cement as well. The DOE estimates a price increase of 20% - 40% to accommodate CCS costs.  

Fuel costs. Cement has a relatively low value-to-weight ratio, so it gets expensive quickly when it is shipped longer distances. While this protects the market for cement plants, it also means that smaller plants have less of a market opportunity to absorb the cost of new equipment or a newer, larger facility.

Conclusion

The cement industry faces significant challenges in its journey toward complete decarbonization, though some associations are working to achieve the goal by 2050. As an integral part of the economy, the industry overall—and particularly overseas—will continue to leverage material efficiencies, alternative fuels, and clinker replacement approaches while also investigating carbon capture utilization and storage technologies, and alternative materials and binders. Policy here and abroad (e.g., in material requirements and carbon taxes) could matter significantly for the industry.

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