Figuring out feeding

Sustainability has become the most important word in cement manufacturing throughout the last decade and is by far the primary decision-making factor when it comes to future investments and plant optimisations. Therefore, the substitution of fossil fuels with more sustainable energy sources is a primary goal for every player in the industry. In this context, the introduction of a circular economy for the re-use of former waste streams in the clinkerisation process is a very prominent example of one of the first fully implemented closed material chains. In regions with highly developed waste collection and sorting systems, the co-processing of Alternative Fuels and Resources (AFRs) can be introduced on the solid foundation of pre-existing fuel supply chains with various different suppliers and material sources available in a healthy market.

However, the implementation and operation of the necessary AFR feeding equipment in the cement plant can be challenging for designers and operators, this is due to the fact that the material sources used in co-processing differ immensely from conventional bulk materials typically handled in cement plants. As shown in several technical reports, the actual pre-processing of collected waste streams into an AFR source typically involves a defined sequence of processing steps, which leads to volatile material properties. For example, the bulk density and the particle size distribution (PSD) of the AFR can vary enormously over time. Furthermore, even if a biological drying of the AFR stream is involved in the pre-processing procedure, the humidity of the substitute fuel is typically unstable due to the influence of additional moisture, e.g. from storing or transport.

If an AFR handling installation is not well planned and implemented, there are typically a lot of operational problems associated with the inhomogeneous material properties, such as clogging, immense wear and tear, and low availability. In recent years, modular AFR handling procedures were established in the industry, which are based on well-proven practical scenarios from former projects. In ‘Systematic Classification and Modularisation of Handling Systems for Alternative Fuels’ the so-called Seven Stage Concept (SSC) of the Di Matteo Group is described in detail. However, even if these modular toolkits are utilised, there is still potential for misconceptions about new handling lines, especially if multiple kiln lines and/or calciners shall be fed by a single installation.

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