Pruning particle size to perfect the pyroprocess

Particle size minimisation of waste-derived fuels has seen much discussion and development in recent years. Such initiatives primarily stem from the ongoing struggle to diminish fossil fuel usage while ensuring the constancy and stability of the kiln process. This quandary is particularly apparent in main burners, where finer solid recovered fuel (SRF) particles can be challenging to incorporate, despite the fact that modern calciners routinely accept coarser fragments and achieve 100% fuel replacement.

Widely recognised shredder brands deliver efficient solutions for consistently reducing SRF particles to the 20 – 30 mm sizes typically used in main burners. Some cement plants have managed to achieve substantial substitution levels using this particle size at the main burner, usually with a backup of alternative fuels such as solvents. However, over the past year, N+P has conducted trials at various European kilns using milled material of 100% < 5 mm size to achieve near-total thermal substitution at the main burner. Simultaneously, similar materials have been used in multiple injection feed systems like vertical shaft kilns for lime production, underscoring the importance of particle size and flowability.

While N+P does not manufacture particle size reduction equipment, the company has a vested interest in this area due to their numerous projects requiring smaller particles. Accordingly, the company has invested in several techniques to enhance SRF milling, which is now yielding promising outcomes.

Pulverised alternative fuel (PAF)

A significant breakthrough has been the company’s capacity to produce milled material, potentially as fine as 90% < 2 mm, boasting excellent flowability properties. This so-called ‘Pulverised Alternative Fuel’, or PAF, provides a compelling solution for industries seeking fuel sources with superior properties.

Reducing SRF to under 5 mm presents certain process challenges. SRF tends to become fibrous and woolly as it is downsized, making it difficult to handle and store. Furthermore, the material’s tendency to clog and adhere together can cause blockages in feeding and storage equipment.

Moreover, downsizing SRF often results in significantly reduced throughput, as the material must be cut repeatedly. Consequently, the density of smaller SRF can drop below 80 kg/m3, causing additional issues with feed system capacities and pneumatic transport requirements.

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Read the article online at: https://www.worldcement.com/special-reports/21082023/pruning-particle-size-to-perfect-the-pyroprocess/