Cement, a crucial material for construction globally, is heavily dependent on coal for energy — which accounts for approximately 90% of the energy requirements of cement plants worldwide.
While coal is not a direct ingredient in cement, it plays a dual role in its production — both as the primary energy source for kiln firing, and as a supplier of fly ash, a pozzolanic material that directly replaces clinker in cement blends.
Coal’s dual role in cement production
Though not a direct ingredient, coal is indispensable to cement — from the heat that drives the kiln to the ash that replaces its most carbon-intensive component.
Energy source
Coal is combusted to generate the intense heat required to fire the kilns that produce cement. Roughly 450 grams of coal are needed to produce 900 grams of cement — making coal the single most important energy input in cement manufacturing globally.
Fly ash — a pozzolanic substitute
Fly ash, the fine powdery residue produced when coal is burned, is a pozzolan — it reacts with water to form a cement-like material. Fly ash is used as a direct substitute for Ordinary Portland Cement (OPC), reducing clinker content, energy use, and CO₂ emissions per tonne of cement produced.
How is cement made?
Cement production is a five-stage process in which coal plays a central role — both as the fuel that drives the kiln and as a source of fly ash that can reduce the clinker content of the final product.
Raw material preparation
Raw materials such as limestone, clay, and sand are quarried, crushed, and mixed together in precise proportions to form the raw meal for kiln feed.
Kiln firing
The raw meal is fed into a rotary kiln and heated using pulverised coal to temperatures of approximately 1,450°C. At this temperature, the calcium carbonate in limestone decomposes and reacts to form clinker.
Clinker formation
The high-temperature chemical reactions produce small, dark grey nodules called clinker — the essential intermediate product that determines cement's binding properties.
Cooling and grinding
Clinker is rapidly cooled, then ground with a small amount of gypsum (and optionally fly ash, slag, or other supplementary cementitious materials) to produce the final cement powder.
Distribution
The finished cement is stored in silos and then packed into bags or loaded into bulk tankers for distribution to construction sites, ready-mix plants, and precast facilities.
Applications for concrete
Concrete finds extensive use in construction applications — buildings, bridges, and roads. As global infrastructure projects increase, particularly in developing countries dependent on coal, consumption of coal-fuelled cement remains vital.
Looking ahead to 2050, global demand for cement is projected to exceed 4.01 billion tonnes. This projection holds even with moderating demand in economies like China, where rationalisation of excess cement production capacity is underway.
Fly ash in cement and concrete not only mitigates climate change by lowering the clinker-to-cement ratio — it also increases concrete durability, extending the service life of reinforced concrete structures and reducing the long-term impact of cement production.
By adopting innovative solutions such as using waste coal fly ash as a substitute for kiln-based cement production, the cement industry can significantly contribute to global efforts towards achieving a greener and more sustainable future.
China National
Building Materials.
Innovation in the cement sector extends beyond the use of fly ash. China National Building Materials (CNBM) has led the charge in pioneering advancements in this industry. A key breakthrough is their development of a new dry-process technology for cement production — more energy-efficient and environmentally friendly than traditional wet-process production.
CNBM’s innovative approach includes utilising municipal waste from the Beijing area as a fuel source, with coal as the primary heat source. The ash produced is retained and used as a crucial ingredient in clinker production.
Furthermore, CNBM has ventured into creating high-performance building materials — including plasterboard, ceramics, and carbon fibres derived from coal — highlighting their commitment to sustainability and efficiency in the cement industry.