The electrofragmentation process, developed and marketed by the SELFRAG (HISER partner), uses high voltage pulse power generators, which converts a continuous flow of electricity into pulses by storing the electricity in banks of capacitors and spark gaps.
The process produces highly energetic electrical pulses (150 - 750 J/pulse) with a very fast voltage ramp-up time (<500 ns). These pulses causes electrical breakdowns, which happens when a material is neither conductive enough to allow electricity to flow through, nor resistive enough to fully inhibit the flow of electricity. Consequently, tiny plasma channels are formed through the feed material passing between the electrodes. These discharge channels generates very strong shockwaves that are responsible for the majority of feed fragmentation by high voltage processing. Lightning and conventional blasting using explosives are similar to the SELFRAG electrical discharge and fragmentation process. The high selectivity of the process arises from the way the electricity and shockwaves interact with electrical and acoustic properties of the material. The resulting selective breakage allow full liberation of clean intact components from the feed material without overgrinding.
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| Plasma channel along natural grain boundaries |
Conventional crushing damaging aggregates |
The application to various construction and demolition waste streams shows the benefits of the process for a real recycling potential (full recovery) compared to the current practice of down-cycling. Concrete is after water the second most used material in the world. To recover intact embedded aggregates, sand, clean metallic armor, and cementitious paste is important to close material cycles. Tests on various types of concrete were previously performed at SELFRAG pilot plant. Rounded and angular aggregates, and included metals were liberated intact.
Example of fully liberated clean concrete components after SELFRAG process
Current test results indicate very low specific energy inputs to be sufficient to liberate included concrete components. The reuse of these have been tested and proven in several projects, indicating similar and in some cases better dynamic performances than with new aggregates. Current SELFRAG pilot plant can treat 3 tph continuous throughputs. Different other construction waste streams are currently under investigation, such as concrete waste with adhered gypsum and brick waste with adhered mortar or gypsum.
