The benefits of co-processing

The use of alternative fuels, or in other words co-processing, is the combination of simultaneous material recycling and energy recovery from waste in a thermal process. This substitutes natural mineral resources and fossil fuels, such as coal and petroleum products. Within a cement kiln, waste fuels are co-processed utilising the heat value derived from the waste fuel to substitute fossil fuels and incorporating the ash as a partial replacement of the raw materials, leaving no waste residue.

In addition to providing sound and sustainable solutions for waste streams and strengthening the circular economy, the use of secondary materials in cement kilns is key for society to reduce its CO₂ emissions and support the vision of a carbon neutral Europe by 2050.

Moreover, through co-processing, the cement sector provides a safe and affordable disposal route for national authorities and other industries by transforming the waste and by-products into alternative resources for cement production. It is worth highlighting that air emissions would not be any lower if cement kilns solely relied on fossil fuels. This is because the air emissions are primarily influenced by the natural raw material input, which constitutes approximately 85% of the total material input, compared to the 15% contributed by fuels. Air emissions vary regardless of the type of fuel used.

Both biomass and non-biomass waste fuels are derived from intermediary waste treatment processes. These processes collect and process different waste streams to produce the final fuel, adhering to the specifications agreed by the authorities for use in cement kilns.

Optimising this waste-to-energy capacity has the advantage of reducing the need for additional investment in new waste-to-energy infrastructure. Furthermore, EU member states could save around €12.2 billion by leveraging the existing capacity in the EU cement industry. This saving is equivalent to the investment required for the construction of new waste-to-energy incinerators. Co-processing proves a more efficient waste management solution than landfilling or incineration. It shows that the cement industry is a net consumer of waste and therefore is at the heart of the circular economy.

The clinker process is highly energy efficient. For example, a notable portion of waste heat is recovered by drying the raw materials and fuels in integrated grinding mills. The high energy efficiency, the use of alternative fuels and using renewable energy sources has made the cement industry a success story in reducing both costs and carbon footprint. According to the technical report ‘Evaluation of the energy performance of cement kilns in the context of co-processing’ by the European Cement Research Academy, energy efficiency in cement kilns varies between 70 – 80%, depending on the raw materials’ moisture content.

Overview and achievements of alternative fuels in cement industry

The use of alternative fuels (AF) as a resource in the European cement industry began over 30 years ago, in 1990. Since then, the AF usage rate has been steadily increasing every year, reaching 53% as the average rate in the EU-27 in 2021. Currently, several cement plants operate at a very high rate (90 – 100%) of AF substation, and the trend suggests more cement plants will achieve this level. Typical alternative fuels currently used in the EU cement industry include: solid recovered fuel (SRF)/refused derived fuel (RDF), end-of-life tyres, animal meal, sewage sludge, wood/paper/pulp waste, sawdust, and more.

The average AF rate of 53% in the EU-27 includes 20% of biomass waste which is particularly important as it is considered carbon neutral in the EU-Emissions Trading Scheme, meaning its CO₂ emissions are accounted for as neutral. The biomass waste used in the cement industry derives from a variety of streams and includes for instance the biomass fraction in refuse derived fuels (RDF), end-of-life tyres, sawdust from related industries or processing, animal meals, agricultural waste or wood waste. In 2021 alone, approximately 23 million t CO₂ emissions were avoided through the use of alternative fuels in the EU cement industry, which is equivalent to the CO₂ emissions produced by 15 million cars. In terms of quantities, the EU cement industry used approximately 36 million t of secondary materials, such as waste and by-products in the overall cement manufacturing process. Of this, around 13 million t were used specifically as alternative fuels in the clinker production process.

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