METHOD OF PURIFYING SULPHUROUS ALKALI WASTE WATER Russian patent published in 2019 - IPC B01D1/00 B01D19/00 B01D3/00 C02F1/20 C02F9/00 

FIELD: oil and gas industry.

SUBSTANCE: invention can be used in oil refining and petrochemical industries. Sulphurous alkali wastes (SAW) are fed into the middle part of stripping column 3, in which there is evaporation of ammonia, part of hydrogen sulphide, as well as water, which are discharged from the upper part of stripper column 3 successively into cooler 7 and separator 8. Condensate from separator 8 is returned to upper plate of stripping column 3 as circulating reflux, providing its operation in rectification column mode. Stripped SAW from cube of stripping column 3 is directed into recuperative heat exchanger 2, and then cooled to temperature of 25÷35 °C in water cooler 10 and directed to saturator 12 operating at pressure up to 4.5 atm, where also supplied is gaseous CO₂ with ratio of CO₂ : SAW equal to 5÷15 nm³ : 1 m³. Carbonated SAW is fed into desorption column 13 operating at pressure of 1–1.2 atm where desorption of formed H₂S takes place. Into the middle and lower part of the desorption column the CO₂ is supplied with ratio of CO₂ : SAW equal to 5÷15 nm³ : 1 m³, wherein total flow rate of CO₂ is defined by relationship with SAW in range of values 10÷30 nm³ : 1 m³ and depends on the degree of contamination of SAW with sulphides. Reheating of bottom part of desorption column 13 is carried out to temperature of not more than 60 °C due to natural heat transfer through a blind partition separating the lower part of desorption column 13 from the upper part of stripping column 3. Gaseous products are removed from the upper part of desorption column 13 and sent successively into refrigerator 16 and separator 17, where condensation of water vapor with partial dissolution of H₂S, as well as separation of formed condensate from gaseous products. Condensate from separator 17 is supplied to top plate of desorption column 13 as circulating reflux, providing its operation in rectification column mode. Gaseous products from separator 17 containing predominantly H₂S, is removed for further processing at ESP unit (elementary sulfur production).

EFFECT: disclosed invention enables deep cleaning of SAW by stripping and complex carbonization with gaseous CO₂ to residual content of ammonium nitrogen of not more than 10 mg/dm³, sulphides to a value of not more than 10 mg/dm³ and pH in range of 6,9–9 units, with initial content of ammonium nitrogen to 10,000 mg/dm³, sulphides to 20,000 mg/dm³ and pH not more than 13,5 units.

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