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What's in store for alternative fuels?

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World Cement,

Dr. Dominik Aufderheide & Dr.-Ing. Luigi Di Matteo, DI MATTEO Group, provide an overview of the typical problems associated with alternative fuels storage and feeding and introduce some best practice procedures.

The storage and discharge of bulk materials can be a great challenge and each process expert in cement manufacturing is aware of the typical problems associated with the operation of efficient silo and bunker systems. With the rise of alternative fuels within the cement clinkering process and the associated introduction of new problematic bulk materials with highly volatile characteristics, classic storage designs and discharge techniques are no longer adequate. This article provides an overview of the typical problems associated with AF storage and feeding and introduces some best practice procedures.

Alternative fuels

Alternative fuels (AFs) have become one of the primary energy sources for the clinkering process within cement manufacturing during the last three decades. In most cases, these substitutive fuels are derived from waste streams, and so can differ immensely throughout different regions of the world and are also quite often inconsistent.1 In European markets, the most commonly used AFs are derived either from industrial and/or municipal plastic waste (often referred to be as Refused Derived Fuel – RDF) or used tyres (Tyre Derived Fuel – TDF), while in other regions of the world, fuels derived from renewable resources, such as biomass and/or wood are more common. Whatever the exact nature of these materials, there is one major aspect which needs to be considered for each AF handling installation – the often problematic nature of bulk material characteristics in AF material streams and the impact of this on the associated handling equipment and machinery.

The fundamental difference between AF materials and other material streams in a cement plant, is not the actual difference in typical properties, such as density ρ [kg/m3], humidity h [%] or particle size distribution (PSD), but the actual volatile nature of the material composition. Even if recent advancements in the standardisation and quality control of AF has led to more homogeneous material streams, the reality in cement plants worldwide shows a different picture. A fuel mix originating from different suppliers and complex preparation procedures for a great variety of waste streams will always lead to a situation where operators cannot fully influence the quality of material within their AF burning installation.

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