Division BAT 23: In order to prevent or reduce the amount of sulphides discharged to waste water treatment from the spent caustic scrubber liquor originating from the removal of acid gases from the cracked gases, BAT is to use one or a combination of the techniques given below.
United Kingdom
| Technique | Description | Applicability | |
|---|---|---|---|
| a. | Use of low-sulphur raw materials in the cracker feed | Use of raw materials that have a low sulphur content or have been desulphurised | Applicability may be restricted by a need for sulphur doping to reduce coke build-up |
| b. | Maximisation of the use of amine scrubbing for the removal of acid gases | The scrubbing of the cracked gases with a regenerative (amine) solvent to remove acid gases, mainly H2S, to reduce the load on the downstream caustic scrubber | Not applicable if the lower olefin cracker is located far away from an SRU. Applicability for existing plants may be restricted by the capacity of the SRU |
| c. | Oxidation | Oxidation of sulphides present in the spent scrubbing liquor to sulphates, e.g. using air at elevated pressure and temperature (i.e. wet air oxidation) or an oxidising agent such as hydrogen peroxide | Generally applicable |