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ISO/TR 27922:2021 — Carbon Dioxide Capture Technologies for the Cement Industry
Focused technical review of CO₂ capture technologies integrated with cement manufacturing for deep decarbonization
ISO/TR 27922: Carbon Dioxide Capture Technologies for the Cement Industry
ISO/TR 27922:2021 provides a focused technical review of carbon dioxide capture technologies specifically applicable to the cement industry, which accounts for approximately 7-8% of global anthropogenic CO₂ emissions. Cement production presents unique challenges for CO₂ capture because approximately 60% of its emissions are process-related (from calcination of limestone: CaCO₃ → CaO + CO₂) rather than energy-related, meaning these emissions cannot be eliminated through fuel switching or efficiency improvements alone. This Technical Report systematically evaluates capture technologies that can be integrated with cement manufacturing, considering the specific constraints of cement plant operation including raw gas composition, heat recovery opportunities, and product quality preservation.
The cement industry’s emissions profile — with roughly 60% process emissions from calcination and 40% from fuel combustion — means that even a fully electrified cement plant using 100% renewable energy would still emit approximately 525 kg CO₂ per tonne of clinker from the calcination reaction alone, making post-capture essential for deep decarbonization.
The standard provides an overview of the cement manufacturing process and identifies the key integration points for CO₂ capture technologies. It covers the full range of technology readiness levels, from commercially available systems (amine scrubbing adapted for cement kiln flue gas) to pilot-stage technologies (calcium looping, oxyfuel cement kilns) and emerging concepts (electrochemical calcination, concentrated solar calcination). The specific challenges addressed include the high dust loading in cement kiln flue gas (50-100 g/Nm³), the presence of SO₂ and NOx at concentrations higher than power plant flue gas, and the critical requirement that capture processes do not compromise clinker quality or production rates.
Technology Assessment for Cement Plant Integration
ISO/TR 27922 provides a detailed comparative assessment of capture technologies for cement plants. Post-combustion amine scrubbing is the most mature option, with demonstration projects at multiple cement plants worldwide. However, the high CO₂ concentration in cement flue gas (20-30% compared to 12-15% for coal power) actually improves capture economics. Oxyfuel cement kilns represent a transformative approach where the kiln is fired with pure oxygen, producing a CO₂-rich flue gas that requires minimal purification. Calcium looping uses calcium oxide as a sorbent to capture CO₂ from cement kiln flue gas, with the spent sorbent being directly usable as cement raw material — a uniquely elegant integration.
| Capture Technology | TRL | CO₂ Avoidance Cost | Key Advantage | Key Challenge |
|---|---|---|---|---|
| Post-combustion (amine) | TRL 7-8 | $60-90/tCO₂ | Retrofit-friendly | Solvent degradation, energy |
| Oxyfuel cement kiln | TRL 5-6 | $50-70/tCO₂ | Near-pure CO₂ stream | Kiln redesign, air in-leakage |
| Calcium looping | TRL 5-6 | $40-60/tCO₂ | Sorbent = cement raw material | Sorbent deactivation, heat |
| Direct separation (LEILAC) | TRL 5-6 | $40-65/tCO₂ | Captures process emissions only | Indirect calcination heat transfer |
| Membrane separation | TRL 4-5 | $70-110/tCO₂ | Simple operation, no chemicals | Moderate selectivity, durability |
| Chilled ammonia | TRL 5-6 | $55-80/tCO₂ | Low regeneration energy | Ammonia slip, corrosion |
A critical consideration unique to cement industry CO₂ capture is the impact of SO₂ on capture solvents. Cement kiln flue gas typically contains 50-500 ppm SO₂ — 5-10 times higher than coal-fired power plant flue gas. Without upstream desulfurization, SO₂ reacts irreversibly with amine solvents, causing solvent consumption 3-5 times higher than power plant applications.
The standard emphasizes that capture technology selection must be integrated with the cement plant’s existing heat recovery network. The average cement plant generates significant waste heat from clinker cooling and kiln exhaust that can be harnessed for solvent regeneration in post-combustion capture. A detailed heat integration study can reduce the effective energy penalty of amine-based capture by 20-35% compared to standalone operation. The standard provides specific guidance on temperature levels and heat exchanger network design optimized for cement plant thermal profiles.
Engineering Design Insights for Cement Decarbonization
ISO/TR 27922 delivers several engineering insights critical for cement industry decarbonization. First, the distinction between process emissions and energy emissions has profound implications for technology selection. Process emissions (60% of total) are inherent to the calcination chemistry and cannot be avoided — only captured. This means cement plants cannot achieve net-zero through fuel switching alone, making CO₂ capture an essential technology for the sector.
Second, the standard highlights the promising potential of calcium looping, where the spent calcium-based sorbent from the capture process (CaCO₃) can be directly fed into the cement kiln as raw material. This creates a circular material flow: limestone → CaO sorbent for capture → CaCO₃ from carbonation → kiln feed. This integration avoids the sorbent disposal problem that plagues calcium looping in power plant applications and simultaneously reduces the cement plant’s limestone quarrying requirements by 30-50%.
The LEILAC (Low Emissions Intensity Lime And Cement) technology, referenced in ISO/TR 27922, demonstrates that by indirectly heating limestone through a calciner wall, the CO₂ released from calcination remains separate from combustion gases, enabling capture of process emissions at minimal energy penalty. This approach has achieved 95% capture rates in pilot-scale demonstrations.
The standard also addresses the important question of retrofitting constraints. Many existing cement plants have space limitations that preclude adding large capture equipment. The standard provides guidance on modular capture unit design, integration with existing cooling water systems, and optimization of the plant layout to minimize additional land requirements. For plants with severe space constraints, membrane-based capture or direct separation technologies may be preferred over conventional amine scrubbing despite higher per-ton costs.
Frequently Asked Questions
Q: Why is cement production such a significant source of CO₂ emissions?
A: Cement emissions are high because: (1) the calcination reaction CaCO₃ → CaO + CO₂ releases CO₂ inherently (process emissions), (2) kiln temperatures of 1450°C require large amounts of fuel, and (3) global cement production exceeds 4 billion tonnes annually, driven by urbanization and infrastructure development.
A: Cement emissions are high because: (1) the calcination reaction CaCO₃ → CaO + CO₂ releases CO₂ inherently (process emissions), (2) kiln temperatures of 1450°C require large amounts of fuel, and (3) global cement production exceeds 4 billion tonnes annually, driven by urbanization and infrastructure development.
Q: Which CO₂ capture technology is most suitable for existing cement plants?
A: For retrofit of existing plants, post-combustion amine scrubbing is currently the most proven option. The LEILAC direct separation technology also shows promise for retrofit as it can be added to existing preheaters without major modifications to the clinker production process.
A: For retrofit of existing plants, post-combustion amine scrubbing is currently the most proven option. The LEILAC direct separation technology also shows promise for retrofit as it can be added to existing preheaters without major modifications to the clinker production process.
Q: Can captured CO₂ from cement plants be used productively?
A: Yes. Potential utilization pathways include enhanced oil recovery, production of synthetic fuels (via hydrogenation to methanol or methane), carbonation of construction products, and use in greenhouses. However, the scale of cement emissions means that storage will likely be needed for the majority of captured CO₂.
A: Yes. Potential utilization pathways include enhanced oil recovery, production of synthetic fuels (via hydrogenation to methanol or methane), carbonation of construction products, and use in greenhouses. However, the scale of cement emissions means that storage will likely be needed for the majority of captured CO₂.
Q: How does ISO/TR 27922 relate to the global cement industry’s decarbonization roadmap?
A: The standard provides the technical foundation for the capture component of cement decarbonization. It complements other strategies including clinker substitution (reducing clinker factor), alternative fuels (biomass, waste), and energy efficiency improvements, which together can reduce emissions by 30-50% but cannot eliminate process emissions.
A: The standard provides the technical foundation for the capture component of cement decarbonization. It complements other strategies including clinker substitution (reducing clinker factor), alternative fuels (biomass, waste), and energy efficiency improvements, which together can reduce emissions by 30-50% but cannot eliminate process emissions.
