So, addressing the carbon footprint of cement production is essential for achieving net-zero carbon dioxide (CO2) emissions by 2050, given its close ties to urbanisation and development. Countries experiencing rapid development are expected to increase their cement production, further worsening the emissions issue. While the problem is significant and comprehensive solutions may be challenging to find, collaborative efforts across cements value chain, offers promising pathways for developing emission-free methods of cement production. io consulting, as an energy project architect and systems integrator, would like to share our insights gleaned from our own research and study work conducted for cement manufacturers.
The simplified stoichiometric relationship is as follows:
CaCO3 + heat = CaO + CO2
At higher temperatures in the lower end or furnace end of the kiln, the lime (CaO) reacts with components of the raw meal i.e. silica, aluminium and iron containing materials to produce minerals in the clinker, an intermediate product of cement manufacture.
Simplified Clinker Process[5]
The clinker is then removed from the kiln to cool, ground to a fine powder, and mixed with a small fraction (about 5%) of gypsum to create the most common form of cement known as Portland cement. Masonry cement is generally the second most common form of cement. As masonry cement requires more lime than Portland cement, masonry cement generally results in additional CO2 emissions.
Carbon Sources in Cement
Typically, in a cement plant, the furnace (kiln burner), rotating kiln and preheaters are the primary sources of emissions in cement production.
Source S&P Global[6]About 30% of a cement plants’ carbon emissions come from energy related emissions such as burning fossil fuels to heat the kiln. This process of calcination contributes about 60% of CO2 emissions from a cement plant and sometimes is referred to as “process carbon” emissions. The remaining 10% of carbon emissions are from other operations including electricity used to power equipment such as raw meal crushers, dryers, mixing, cement mill and other electrical parts of the plant including illuminating the site. Such electrical related emissions are considered indirect as power is taken from the grid that may not come from a renewable source.
Innovation Pathways to Emission Abatement
There are multiple ways to lower the carbon footprint of cement at different stages of development. Initiatives are being taken in the industry that consider concrete use optimisation and employing substitute materials such as laminated wood in non-load bearing areas, to deliver carbon conscious designs, that can reduce the carbon footprint by up to 26%[7]. Startups are also pioneering green alternatives to clinker, such as Brimstone Cement[8], Biozeroc[9], Maa’va[10], and ecoLocked[11], however these solutions are undergoing testing and not yet scalable.
Replacing clinker with materials such as steel slag and fly ash, or utilising innovative mixtures like LC3[12], has the potential to reduce carbon emissions by 50% while meeting current building codes. However, the scalability of these solutions remains a challenge. Consequently, limestone-derived clinker-based cement continues to be the most prevalent and commercially feasible option for the foreseeable future.
As there are no commercially viable alternatives to clinker-based cement, CO2 emissions from calcination of limestone cannot be avoided. The current thinking in the sector is to apply carbon capture and storage to achieve net zero. Having investment access, such as the EU innovation fund, which was launched as part of the European Green Deal, has provided major cement players the opportunity to utilise technology innovation to build large scale carbon capture and storage[13].
Five main technologies are being tested to capture and purify CO2 and include oxy-fuel combustion, amine absorption, Calcium Carbonate Looping (CCL), membranes, cryogenic separation and solid sorbent. These technologies are further described below:
Second generation oxy-fuel kiln is a significant advancement in combustion technology, particularly in cement production. It utilises pure oxygen (O2) instead of ambient air, resulting in a highly concentrated CO2 stream in the flue gas, thereby improving energy efficiency and reducing emissions. Unlike its predecessor, this process does not recirculate CO2-enriched flue gas, eliminating the need for energy-intensive cooling and drying. Oxygen is directly supplied to critical areas such as the cooler inlet, calciner, and main burner. Modifications to kiln design and operation are necessary for optimal performance, including adjustments to thermal energy consumption and installation of smaller cyclones in new clinker plants to accommodate reduced gas volumes.
Oxy-fuel combustion is a potential solution for decarbonising the cement industry; oxy-fuel firing reduces the volumetric flow of flue gas, and thus facilitates easier capture of CO2 by concentrating the CO2 emissions in a smaller volume of gas. This technology requires significant modifications to existing cement production processes to implement i.e. a purpose designed oxy-kiln.
With a conventional kiln, and CO2 concentrations of 15-20% in the flue, a suitable technology is amine absorption or calcium carbonate looping. However, with oxy-fuel combustion processes, the flue at kiln outlet is much higher in CO2 concentration (up to 80%), therefore lends itself to process schemes that consider alternatives such as membrane or cryogenic separation, with PSA used as a concentrator to achieve export specification. It should be noted that post-combustion CCUS provides opportunities to decarbonise without compromising existing production but requires additional thermal input which is expensive and creates further emissions.
How can io help?
io consulting, a joint venture between Baker Hughes and McDermott, specialises in low-carbon solutions in the energy and hydrocarbons sectors. Our mission is to provide techno-economic expertise integrated with access to technology and execution know-how for early-stage projects or portfolio-level initiatives.
We offer a comprehensive range of capabilities, including reservoir due diligence, business case development, field development planning, smartFEED, and more. With over 400 completed assignments for diverse clients, our specialists bring proven skills and significant expertise to project development and execution, particularly in flue gas treatment, CO2 purification, CO2 utilisation, CO2 storage, CO2 transport and carbon sequestration, making us a perfect project integration partner for our clients.
Leveraging our parent companies’ expertise, including project close out costs and schedules, we deliver cost certainty and comprehensive support throughout the project lifecycle. With io consulting, clients benefit from the best-in-class expertise and integrated solutions for sustainable project development.
References:
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World Economic Forum “net-zero industrial tracker”, 2023
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Hannah Richie- US Geological Survey
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Michael J. Gibbs, Peter Soyka and David Conneely (ICF Incorporated). It was reviewed by Dina Kruger (USEPA). Entitled “CO2 Emissions from Cement Production”, 2000
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© thyssenkrupp Industrial Solution AG
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Nature 2033, Paul Fernell et.al
