Incineration Units for Waste Containing Halogens or Sulphur
During combustion of halogenated wastes, typically chlorine or fluor, at temperatures above 1100°C and sufficient oxygen in the flue gas, HCl and traces of Cl2 respectively HF are formed. Accordingly, during combustion of sulphur-containing wastes, SO2 and small amounts of SO3 are formed.
These impurities have to be removed from the flue gas. This is usually achieved by a scrubber using aqueous sodium hydroxide or soda solution. In order to cool down the flue gas to a temperature suitable for a scrubber made of FRP, it will be first cooled in a spray or submerged quench system. Depending on the HCl concentration in the fluegas and the resulting HCl dewpoint, HCl aerosols will be formed in this cooling step if the quench temperature is too low. In this case, an aerosol removal system is required in addition.
The undesired formation of Cl2 or SO3 respectively is minimised by combustion process optimisation.
Steam generation is the common way of heat recovery for these kind of incinerators. However as the flue gas is cooled down slowly in a steam boiler, dioxins can be formed by the so called De-Novo synthesis. Therefore, a DeDioxine catalyst has to be used in such systems.
At a higher halogene content in the waste, a HCl-recovery step prior to the flue gas treatment may be feasible. Please refer to chapter 'Acid Production from Incineration'