LEILAC: capturing CO2 in Cement Precalciners

Daniel Rennie, Calix, explains how new technology is helping plants capture emissions directly from the precalciner, paving the way towards scalable CO2 capture for the cement industry.


The adoption of the Paris Agreement, ratified by 175 countries, provided the clear objective of keeping a global temperature rise of well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to below 1.5 degrees Celsius.

In support of those ambitions, the very challenging goal of reaching carbon neutrality by 2050 has been set. These commitments are being made at a variety of levels. 127 countries, 823 cities, 101 regions, and 1,541 companies have committed to decarbonising their activities by 2050 (New Climate Institute 2021).
These commitments are being matched in the cement industry. The Climate Ambition articulated by the members of the Global Cement and Concrete Association, and 2050 Roadmap by Cembureau, and the corresponding wave of individual corporate commitments, all have ambitions for neutrality by 2050.
This is not an easy commitment to reach for the cement or lime industry - responsible for 8% of global CO2 emissions. Cement and lime provide vital services to our society, with essential products that are low cost and very efficiently produced. Since 1990, major efforts have been made to reduce emissions, including improvements to energy efficiency, use of alternative and waste fuels and clinker substitution.
However, complete decarbonisation of this industrial sector is far harder than many others, as most CO2 emissions are released directly and unavoidably from the processing of the limestone. These “process emissions” are in addition to the CO2 released from the combustion of fuels used to power the process (representing around two-thirds of a plant’s total emissions, depending on the fuel used).


To reach the corporate emissions reductions targets by 2050, these unavoidable process emissions must be addressed. The most effective means is to capture the CO2, and ensure that it does not reach the atmosphere. Called Carbon Capture Use and Storage (CCUS), this general approach to decarbonisation has been used for decades in the hydrocarbon processing and recovery industries, further developed for the power sector. This will need to be applied to the majority of cement and lime plants due to those process emissions (Cembureau 2050 Carbon Neutrality Roadmap). As noted by the 2018 IPCC report, “CCS plays a major role in decarbonizing the industry sector in the context of 1.5°C and 2°C pathways, especially in industries with higher process emissions, such as cement.”

Capturing carbon from industrial and power generation plant has not yet been widely adopted due to the efficiency and cost penalties of traditional capture technologies, and a lack of meaningful (and universally applied) cost implications for emitting CO2. However, changes are very rapidly being seen. Globally, 61 carbon pricing initiatives have been introduced covering 22% of all emissions (World Bank Group, 2021). The European Emissions Trading System (EU ETS), the largest carbon market in the world, reached a price of €56 per tonne of CO2 in 2021.

The current collective objective facing industry and government (creating incentives) is threefold: to maintain economic prosperity, meet cement and lime market demand, while dramatically lowering CO2 emissions.


The majority of initiatives to capture carbon are based, or adapted, from processes and techniques developed for the energy and chemical sectors, and are all based on separating gases. For 60 years solvents, such as amines, have been used to strip CO2 from gases (particularly in refineries and natural gas processing plants), and a lot of work has been recently undertaken to apply them to the cement sector at increasingly lower cost. Sorbents (including calcium looping), membranes, and enhancements are being actively developed to reduce the volumes and/or energy required to separate CO2 from flue gases. Other approaches, such as oxyfuel, separate gases in air, rather than at the stack. All these approaches must be developed as quickly as possible.

A new capture approach is being introduced. Calix’s new process of ‘indirect calcination’ focuses solely on the cement, lime and magnesia sectors, ensuring that the relatively pure, unavoidable, CO2 released from the limestone itself in the precalciner is not contaminated by either air or flue gases.


The LEILAC (Low Emissions Intensity Lime And Cement) projects are developing this new technology, aiming to enable the cement and lime industries to capture those unavoidable CO2 emissions emitted from the raw limestone.

The Calix process works within a normal cement plant’s process. It is based on indirect calcination, by heating the limestone via a special steel reactor within the precalciner. This unique system enables pure CO2 to be captured as it is released from the limestone, as the furnace exhaust gases are kept separate. Calcining raw meal by indirect heating (LEILAC) or by direct-heating (conventional calciner) can be done in principle with the same specific energy. The process does not involve any additional processes or chemicals, and simply involves a novel “precalciner” design (or new kiln, in the case of a lime plant).

This type of precalciner aims to use any type of fuel or heat source. This makes achieving a very efficient zero-emissions cement kiln , when using biomass rich fuels, green electricity, or hydrogen. If alternative fuels, biomass, or conventional fuels are used, any of the previously mentioned conventional carbon capture techniques can be applied to capture the combustion (heating) emissions. There would be synergies to such a combination, as the lowered energy requirements and capital of such a combined system would result in the most efficient means of achieving ‘negative emissions’ cement plants.


Supported by the European Union, the LEILAC projects are applying this new type of precalciner. Applying the technology to the cement industry carries a large number of risks – and to quickly and effectively apply this technology, the European-Australian collaboration LEILAC projects include consortiums of some of the world’s largest cement, and lime companies, as well as leading research and environmental institutions.

The LEILAC1 project involved the construction of a Pilot plant at the HeidelbergCement plant in Lixhe, Belgium. Extensive research, development and engineering was necessary to design and construct the first-of-a-kind pilot – involving the dedicated, flexible, and professional inputs from all the project’s partners, particularly the industrial users HeidelbergCement, Lhoist and CEMEX. This has enabled the construction of the pilot on time and on budget in 2019. Additionally, studies examining integration of the plant in different configurations, and confirmation of the sustainability of the process, and outreach activities have also been conducted by the other parties (Imperial, PSE, Quantis and the Carbon Trust).
Several challenges were faced in getting the system to run, particularly the burners, feed and conveying systems. These are gradually being overcome, and the system is increasingly stable.

Within the current configuration, CBR’s Lixhe cement meal has been processed at up to 8tph and briefly at 10 tph, with extents of calcination seen at 85%. Lhoist’s Hermalle limestone has been calcined at 70–78%. Meal Hannover has been processed at up to 8tph, with consistent calcination at 91% at 5tph. Calix reactors have obtained 98+% calcination results on pure limestone, using an optimised particle size distribution (PSD). In all runs, separation of CO2 was undertaken (>95% purity) directly from the reactor and before any clean up steps, with no air ingress or loss of containment.

A number of steps are currently in train to improve the throughput and calcination rates. These include improvements to the natural gas burners used, enabling the furnace to reach its design capacity; the installation of a 3 stage cyclone pre-heat unit, currently underway, aiming to increase the usable length of reactor for calcination – further improving throughput and calcination rates and reflecting integration with a host plant. The Lime cooler is being removed, and a simpler return system is installed, to improve throughput rates. There are several process configurations also being tested to improve per-tube throughput and calcination rates.

Outside of such optimisation, the project has successfully demonstrated that both limestone and raw meal can be processed; that the CO2 is successfully separated; and that (disaggregated from the entire system) energy penalty for indirect calcination (LEILAC) is not higher than direct (conventional) calcination. Other major findings are that there has been no build-up of material on the reactor’s wall; that the reactor (despite the numerous runs) is exhibiting no significant negative operational deterioration; that there have been no negative impacts on the host plant, and no impact on clinker production; and that the pilot is safe and easy to operate, with no safety incidents.

Thanks go to all the staff at Lixhe, service providers, and consortium members tirelessly working despite the massive challenges arising from the pandemic.


A follow-on project – LEILAC2 – has just started, having been awarded €16m funding by the EU Horizon 2020 program with additional industry contribution. HeidelbergCement has kindly agreed to closely integrate the Demonstration plant into their operational plant in Hannover, Germany.

LEILAC2 will build a Demonstration Plant that aims to separate around 100,000 tonnes per year of CO2, in a scalable module. The consortium, comprising Calix, HeidelbergCement, Cimpor, Lhoist, CEMEX, IKN, Certh, Polimi, BGR, GSB, Engie Laborelec, Port of Rotterdam aims to also demonstrate the overall efficiency of the technology, as the reactor will be integrated into the kiln line in a kind of second preheater string configuration, where the calcined material is directly fed to the existing rotary kiln and the impact on clinker quality as well as the energy-efficiency can be demonstrated. The demonstration plant will also aim to show the applicability of less carbon intensive heat sources for the required calcination heat, i.e. the use of electricity and alternative (biomass rich) fuels.

Earlier this year, the LEILAC2 Consortium endorsed the pre-FEED study. The criteria for passing this study were that: the Demonstration Plant’s design is technically viable; fulfilment of the operational objectives of the overall project; the plant's design poses low integration risks for the main plant; it is within the cost constraints including CAPEX and OPEX of the budget.

The LEILAC2 plant is a first-of-a-kind retrofit. The CAPEX is expected to be around €16m. Further design, work and testing is required – but should the design work as planned - current estimates suggest the LEILAC2 may separate CO2 at a cost of around €10/t CO2 extra OPEX (above the host plant’s operating costs). This excludes compression costs and CAPEX retrofit depreciation costs (including foundations, installation, structure), etc., which are expected to be in the region of an additional €10-€15/t CO2. (Compression costs will change greatly depending on what happens to the CO2)
Therefore, total costs of this first-of-a-kind LEILAC carbon capture plant is expected to be in the region of €20-25/t CO2.


The intention with LEILAC2 is to start forming a robust, replicable module that can be simply scaled to capture 100% of a cement plant’s process emissions (at any scale).

The LEILAC2 project is the first attempt at retrofitting the technology to a plant. At full scale, the LEILAC process conditions (and costs) will be improved from the current LEILAC2 projection through the following of steps in a future implementation, including: the use of the kiln gases; using the heat from the CO2; enhanced preheat; the use of unprocessed RDF (reducing capture costs to €4/t CO2); locating the reactors closer to the tower; skin loss reduction through module placement; and increasing the levels of insulation.

A full scale retrofit, depending upon the site in question and capital required to recover and utilise the heat, is expected to be close to BAT efficiency.

On a greenfield site - when this type of precalciner is part of the planned installation – there is the opportunity for simpler integration, and minimal additional capital costs as a large proportion of the technology’s costs are for foundations, structure, and installation.


Every possible decarbonisation option needs to be urgently developed and deployed. In order to reach the required emission reductions by 2050, carbon capture will need to be applied to a vast majority of cement and lime kilns, and every technology option developed.

Once tested and scaled up, the LEILAC technology should provide an option for reducing the costs of carbon capture and accelerate the deployment in both industries using this new type of precalciner – enabling society to continue to benefit from these vital product without negatively impacting the environment.

Featured in WorldCement Magazine from August 2021 :

Project Gallery

LEILAC1 pilot, sitting to the right of the precalciner at Lixhe
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An impression of a retrofit LEILAC module alongside an existing precalciner
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One configuration of Calix's Direct Separation Technology
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Example of a Process Flow for a complete Retrofit
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