Waste-fed heating and power plant - Wastewater treatment plant for the treatment of flue gas washing water - Case Study
The multi-step process for the treatment of the highly acidic wastewater was designed to remove wastewater constituents as purely as possible from the wastewater.
1st stage: Separation of coal dust and activated carbon powder
The acidic wastewater is filtered through a membrane filter press. Before emptying and draining, the filter residue is washed to remove acid residues. A white gypsum can be produced in the subsequent stage because of this filtration.
2nd stage: Gypsum recovery
The wastewater is adjusted to pH 2 in the gypsum precipitation stage, using lime milk and caustic soda. The dosing of the lime milk is regulated via continuous measurement of calcium and sulphate in the wastewater. The gypsum separated in the sedimentation system is dewatered via a vacuum belt filter and washed, so that 'pure' gypsum becomes available for further use.
3rd stage: Ammonia stripping and recovery
The wastewater, which is still acidic, is then alkalised to pH 11 using caustic soda. Steam stripping of ammonia from the wastewater takes place in two stripping columns during this process. The ammonia from the exhaust air is recovered and returned to the combustion process for the flue gas denitrification.
4th stage: Heavy metal precipitation
The heavy metals still contained in the wastewater are finally precipitated out of the wastewater through neutralisation and addition of precipitation agents and flocculants. The hydroxide sludge is settled in a sedimentation system and afterwards dewatered using a chamber filter press. The wastewater, from which the contaminants have been removed in this manner, is then filtered through two sand filters.
5th stage: Evaporation for salt extraction
An evaporation plant is then used to evaporate the wastewater to produce a pure saline solution. This stage was not included in EnviroChemie's scope of delivery.
Design of the wastewater treatment plant:2 m³/h