What Is Sour Water?
Sour water is any water stream that contains H2S, CO2, or NH3 (ammonia). Gas plants typically don’t require sour water treatment because the volumes are small enough to be discharged to a plant sewer or removed by a tank truck.
Refineries are a whole different story. Sources of sour water in refineries include dissolved water in the feedstock, condensate from stripping steam, process wash water, vacuum ejector condensate, and egress into equipment from any exchanger tube leaks or condensate in contact with a sour stream. The typical units in a refinery that produce sour water are:
- Crude Distillation Unit (CDU)
- Vacuum Distillation Unit (VDU)
- Hydrodesulfurization Units (HDU)
- Fluid Catalytic Cracking Unit (FCC)
- Residue Desulfurization Unit (RDU)
H2S is present in crude and is also produced in desulfurization units. Ammonia (NH3) is produced from hydrogenation and catalytic unit feeds that contain nitrogen. NH3 and H2S in reactor effluent will form salts that settle out in the equipment when cooled. Wash water is injected upstream of coolers and condensers to remove the soluble salts. The resulting sour water must be treated before reuse or discharge to wastewater treatment.
Sour water throughout a refinery is collected into a sour water system. Combined sour water is stabilized in a large tank that is usually designed with a three-day holding capacity. Hydrocarbons that separate in the tank are skimmed off and sent to the slop oil system for processing. The sour water is sent to a sour water stripping unit to remove H2S and NH3. Stripped water can be used in other equipment like a Desalter or sent to the plant wastewater treatment facility.