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Direct-heated Fast-quenched Thermal Desorption (DFTD) process
- Contaminated soil, at up to 30 Tonnes per hour, enters the rotary dryer and is gently heated to around 450°C to evaporate the hydrocarbon contaminants.
- The clean soil is then removed from the process, via a separation breach with an airlock valve, cooled and re-hydrated in the soil cooler, ready for beneficial reuse as clean fill.
- Meanwhile, the contaminant vapours are ducted from the separation breach into the conversion stage of the plant where they are heated to over 1000°C, destroying the hydrocarbon contaminants and leaving CO2 and water vapour.
- The gas stream is then quench-cooled to around 200°C in < 100ms to stop contaminants such as dioxins or furans from forming in the off gas.
- Heat captured in the gas cooling stage is used to preheat air fed to the desorber and conversion stages, increasing energy efficiency.
- A filter baghouse is used to remove dust particles from the gas stream, which are then combined with the clean product soil.
- An acid gas wet scrubber is used to remove any acid gases such as HCl or H2SO4 through neutralisation with NaOH.
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