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.

Industry’s Decarbonisation vision

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).

CO₂ Cement Precalciner
Calix’s Direct Separation Technology
One configuration of Calix’s Direct Separation Technology

Capturing unavoidable carbon

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, “CCUS plays a major role in decarbonising 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 plants 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.

Carbon capture

The majority of initiatives to capture carbon are based on processes and techniques developed for the energy and chemical sectors. 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 other gas separation systems are being actively developed to reduce the volumes and/or energy required to separate CO2 from flue gases. Other approaches, such as oxyfuel, seek to concentrate CO2 in the flue gas to very high levels to enhance CO2 recovery.

A very different approach has been invented and patented by Calix. Calix’s Leilac (Low Emissions Intensity Lime and Cement) Technology focuses on separating, for minimal energy or capital penalty, the CO2 coming from the raw limestone, which is responsible for about 2/3 of the total CO2 emissions of the cement and lime industries.

It is based on heating the limestone via a special steel tube – with the heat on the outside of the tube and the limestone or raw cement meal on the inside – separating “how” you heat from “what” you heat.

This unique system enables pure CO2 to be captured as it is released from the limestone, since the furnace exhaust gases are kept separate. Processing raw cement meal by indirect heating (Leilac) or by direct-heating (conventional cement or lime kiln) can be done in principle with the same specific energy. This practice 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).

The Leilac Technology aims to use any type of fuel or heat source. This makes achieving a very efficient zero-emissions cement or lime kiln possible when using biomass rich fuels, green electricity, or hydrogen.

The Leilac projects

Supported by the European Union, the Leilac projects are applying this new type of kiln. Applying the technology to the cement industry will require scale-up of the technology and close integration with a cement plant. 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 Leilac-1 project involved the construction of a Pilot Plant at the HeidelbergCement site in Lixhe, Belgium (CBR Lixhe). 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 enabled the construction of the Pilot Plant on time and within 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 optimised, particularly the burners, feed and conveying systems. These were eventually overcome, and the system went on to complete over 1500 hours of test runs on multiple feed stocks and under multiple operating conditions.

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 (conversion of limestone to lime) seen at 85%. Meal for Leilac-2 (Hannover) has been processed at up to 8tph, with consistent calcination of 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 “mini projects” are currently in train, as part of the Leilac-2 project, to optimise the throughput and calcination rates. These include alternative burner configurations, additional pre-heat, and feed distribution and product handling studies. The lime cooler is being removed, and a simpler return system is being installed, to improve throughput rates. There are several process configurations also being tested to improve per-tube throughput and calcination rates.

While these optimisation studies are underway as part of the Leilac-2 project, Leilac-1 itself has nonetheless successfully demonstrated that both limestone and raw meal can be processed; that the CO2 is successfully separated; and that (disaggregated from the entire system) the energy penalty for indirect calcination (Leilac) is not higher than for direct (conventional) calcination. Other major findings are that there was no build-up of material on the reactor’s wall; that the reactor (despite the numerous runs) experienced no significant negative operational deterioration; that there were no negative impacts on the host plant, and no impact on clinker production; and that the pilot was safe and easy to operate, with no safety incidents.

The Leilac-1 Project has been concluded and the output report – Leilac Roadmap 2050 – has been endorsed by the consortium members and European Union and released to the public https://leilac.calix.global/news/leilac-roadmap-2050/. Our thanks go to all the staff at Lixhe, service providers, and consortium members who have worked tirelessly to deliver the Leilac-1 Project successfully despite the massive challenges arising from the COVID pandemic.

Leilac-2: Towards process integration

A follow-on project – Leilac-2 – has just started, having been awarded €16m by the EU Horizon 2020 program with additional cash and in-kind industry contributions of €18m. HeidelbergCement has kindly agreed to closely integrate the demonstration plant into their operational facility in Hannover, Germany.

Leilac-2 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 and 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 material from the Leilac kiln 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 and waste) fuels.

Earlier this year, the Leilac-2 Consortium endorsed the pre FEED1 study. The criteria for passing this study were that: the demonstration plant’s design was technically viable; the operational objectives of the overall project were fulfilled; the plant’s design posed low integration risk for the main plant; and it fell within the cost constraints including budgeted CAPEX and OPEX.

The Leilac-2 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 that LEILAC-2 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 CO2 avoided of this first-of-a-kind commercial demonstration scale Leilac plant is expected to be in the region of €20-25/t CO2.

Process flow diagram
The process flow diagram for a full-scale cement plant with a Leilac tower instead of the conventional pre-heater tower.

Full Scale Leilac Precalciner

The intention with Leilac-2 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 Leilac-2 project is the first attempt at closely integrating via retrofitting the technology to a plant. In a future implementation at full scale, the Leilac process conditions (and costs) will be improved from the current Leilac-2 projection through the following steps: the use of more heat from the existing cement plant kiln gases; using the heat from the CO2; enhanced preheat; the use of unprocessed RDF2 (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 best available technology (BAT) efficiency of a modern cement plant.

On a greenfield site – when the Leilac Technology 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.

Leilac plant

A sustainable solution using precalciners

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.

Once tested and scaled up, the Leilac technology should provide a low cost option for reducing the costs of carbon capture and accelerate the decarbonisation in both the cement and lime industries, enabling society to continue to benefit from these vital products without negatively impacting the environment.

Retrofit Leilac-2 module
An impression of a retrofit Leilac-2 module alongside an existing pre-heater tower. Multiple modules (arranged flexibly, including vertically) can be used for a 100% retrofit.