Cement

in 2023, the cement industry generated around 2 27 billion tonnes of co2 equivalent (co2e) emissions, representing approximately 3 71% of the global 61 15 billion emissions (source climate trace ) cement production involves three key stages first, limestone and other raw materials are quarried and blended next, this mixture is processed and heated to high temperatures to create clinker, which may be partially replaced with calcined clay finally, the clinker is ground with gypsum and additional additives to produce the final cement product this final grinding can happen in so called integrated plants where the clinker is also produced or in independent grinding plants reminder transport emissions and emissions from raw material mining/quarrying are excluded from the cbam scope what are the main co2 emission sources in the cement industry? most emissions during cement production occur during clinker production in the kiln system, both from fuel consumption and, more significantly, from the calcination of limestone, which releases co₂ during thermal decomposition of calcium carbonate at about 900°c (calcium carbonate \[caco₃] → calcium oxide \[cao] + carbon dioxide \[co₂]) the proportion in the raw materials of carbonates other than caco3 is generally very small calcined clay calcined clay is covered by the eu cbam this material can be used as a supplementary cementitious material (scm) to partially replace clinker calcined clay production involves grinding kaolinite, then heating it to 600 800°c in a calciner, causing dehydroxylation that releases water vapor after cooling, the material undergoes final grinding the process requires thermal energy and electricity for grinding and material handling, generating emissions primarily from fuel combustion and power consumption cbam reminder other clays falling under cn code 2507 00 80 which are not calcined are also included under cbam scope but are assigned embedded emissions of zero (see the proposed reforms to the eu cbam the eu cbam covers the following production steps for calcined clay raw material preparation mixing drying calcining flue gas cleaning the diagram below shows the example of an installation producing 100,000 tonnes of calcined clay please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design inputs raw materials raw clay 120k tonnes → no ghg emissions (its chemical decomposition only releases water vapor) fuels natural gas 10m m³ → 21 5k tco2e (direct emissions) electricity grid 12k mwh → 8 5k tco2e (indirect emissions) resulting in the following direct and indirect specific embedded emissions (see) direct 0 2154 tco2e/tonne indirect 0 0856 tco2e/tonne clinker cement clinker is covered by the eu cbam the clinker production process ( pyro processing ) consists of several steps raw materials such as limestone, clay, bauxite, and iron ore, are crushed, mixed, and milled into "raw meal" under chemical control alternative raw materials such as fly ash may also be used in the raw meal the powdered meal passes through cyclone preheaters where hot exhaust gases coming from the kiln raise its temperature before entering a precalciner where limestone decomposition begins, converting calcium carbonate (caco3) to calcium oxide (cao), also known as quicklime in the rotating kiln, fuels (such as coal, petroleum coke, gas, oil and alternative fuels) heat the material to around 1,450°c, where calcium oxide reacts with silica (sio2), alumina (al2o3), and iron oxide (fe2o3) to form the silicates, aluminates and ferrites that constitute the clinker main fossil fuels used in europe are coal and petroleum coke the clinker is then rapidly cooled the actual thermal energy demand for different kiln systems and sizes is around 0 003 0 0065 tj/tonne of clinker during this process, cement kiln dust (ckd), containing partially calcined material and co2, is captured from kiln exhaust gases grey and white clinkers may be produced depending on temperature and raw material purity, though the eu cbam makes no distinction between them note the exact configuration and sequence of these production steps may vary depending on the specific installation moreover, some installations may use either wet, semi wet, dry, or semi dry processes in wet kilns, raw materials (often with high moisture content) are ground with water to form a slurry, while in dry kilns, materials are ground into powder the difference is relevant in the context of carbon emissions due to the higher energy efficiency of the dry process, which might correlate with lower carbon cement a variation on the clinker production process may be with permanent geological storage, i e , carbon capture and sequestration (ccs) where do emissions come from? this production process generates co2 emissions from limestone decomposition and the combustion of both kiln and non kiln fuels the eu cbam covers the following production steps for clinker raw material preparation grinding, milling, homogenisation fuel storage and preparation for conventional and waste derived fuels clinker production all steps for the integrated kiln system including preheating, kiln processing and clinker cooling intermediate storage storage of cement clinker under cover before export off site or used for cement grinding in the cement mill emissions control for treating releases to air, water or ground (for instance, emissions associated with the raw materials used for flue gas scrubbing) the diagram below shows the example of an installation producing 1,000,000 tonnes of cement clinker please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design inputs raw materials calcium carbonate (limestone) 1 5m tonnes → 660k tco2e (direct emissions) intermediate goods cement kiln dust (ckd) 80,000 tonnes > 42,000 tco2e (direct emissions) fuels other bituminous coal 90k tonnes → 219 6k tco2e (direct emissions) municipal waste (biomass fraction) 25k tonnes → 11 1k tco2e (direct emissions) residual fuel oil / heavy fuel oil 10k tonnes → 31 2k tco2 electricity grid 90k mwh → 20 5k tco2e (indirect emissions) resulting in the following direct and indirect specific embedded emissions (see) direct emissions 0 9641 tco2e/tonne indirect emissions 0 0205 tco2e/tonne cement cement production consists of grinding clinker with gypsum and other constituents such as limestone, granulated blast furnace slag (from steel production), natural or artificial pozzolanas, or calcined clay depending on the specific mix, this produces different types portland cement, blended cement (containing portland cement and other hydraulic constituents), or other hydraulic cements large cement plants produce around 4,000 tonnes of cement per day grinding occurs either in integrated facilities (where clinker is produced) or in separate grinding plants the process generates emissions from fuel used for material drying and electricity consumption the embedded emissions of the cement clinker and calcined clay (if used in the process) must be added the eu cbam covers the following production steps for cement material preparation production steps such as preheating and drying mineral additives cement production all steps, including crushing, grinding, further milling and separation by particle size cement storage, packaging and dispatch emissions control for treating releases to air, water or ground the diagram below shows the example of an installation producing 1 6m tonnes of white portland cement please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design inputs cbam good (relevant precursor) clinker 1 5m tonnes direct embedded emissions 1 2m tco₂e indirect embedded emissions 60k tco₂e intermediate goods gypsum 50k tonnes → no ghg emissions other constituents 100k tonnes → no ghg emissions electricity grid 230k mwh → 52 5k tco₂e (indirect emissions) resulting in the following direct and indirect specific embedded emissions (see) direct emissions 0 7455 tco₂e/tonne indirect emissions 0 0674 tco₂e/tonne note the diagram below does not show any fuel inputs however, emissions may also arise from fuel combustion for drying materials before they undergo the grinding process integrated cement plant an integrated cement plant is a facility that performs both clinker production and cement grinding no bubble approach the diagram below shows an integrated cement plant where clinker and cement production have been defined as separate processes the installation produces 1 95m tonnes of clinker, with 500k tonnes sold directly to market and the remainder used internally for cement grinding hence, no bubble approach would be permitted in this case for the cement production, only the embedded emissions from the clinker produced internally are attributed to the cement production process the grinding process consumes additional electricity however, the majority of cement's carbon footprint comes from the embedded emissions of the clinker production phase note that the process emissions from cement kiln dust (ckd) are also added using the standard emission factor of 0 525 tco2/tonne of dust bubble approach the diagram below shows another integrated cement plant however, since all clinker is used internally to produce cement, it is possible to define a joint production process (bubble approach) the advantage of this approach is that all inputs can be directly attributed to a single process, rather than having to monitor quantities for separate production processes aluminous cement aluminous cement is produced similarly to portland cement, but uses bauxite (aluminum rich) and limestone as raw materials instead of the typical limestone clay mix unlike portland cement production, which requires separate clinker formation and then grinding with gypsum, aluminous cement is produced in a single fusion process where the molten material is cooled and ground directly into cement as such, it is regarded as a good with no relevant precursors (simple good) under the eu cbam the eu cbam covers the following production steps for aluminous cement raw material preparation clinkering cement grinding emissions control the diagram below shows the example of an installation producing 1 6m tonnes of white portland cement please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design inputs raw materials bauxite 30k tonnes > no ghg emissions alumina 30k tonnes > no ghg emissions limestone 40k tonnes → 17 6k tco₂e (direct emissions) fuels natural gas 45m m³ → 91 8k tco₂e (direct emissions) electricity grid 20k mwh → 14 2k tco₂e (indirect emissions) resulting in the following direct and indirect specific embedded emissions (see) direct emissions 1 094 tco₂e/tonne indirect emissions 0 1426 tco₂e/tonne