METHOD OF PURIFYING SULPHUR-ALKALINE SEWAGE WATERS Russian patent published in 2020 - IPC B01D1/00 B01D3/00 C02F9/00 C02F9/08 

FIELD: oil, gas and coke-chemical industries.

SUBSTANCE: present invention relates to methods of cleaning sulphurous-alkaline process effluent from oil refining and petrochemical industries. Method includes sulphur-alkaline sewage waters (SASW) supply to the middle part of the stripping column, on the contact devices of which due to heat supplied through the remote boiler, there is evaporation of ammonia, part of hydrogen sulphide, as well as water, which are further discharged from the upper part of the stripping column sequentially into the refrigerator and separator. There is condensation of water vapour and partial dissolution of ammonia and hydrogen sulphide in it, as well as separation of formed condensate from gaseous products. Condensate from the separator is returned to the upper plate of the stripping column as circulating reflux, thus ensuring its operation in the rectification column mode. Gaseous products, which are a mixture of ammonia and hydrogen sulphide, are discharged from the plant. Stripped SASW from bubble column bottom is directed to recuperative heat exchanger, where it is cooled by heating of SASW column entering into stripping column, is additionally cooled to temperature of 25÷35 °C in water cooler and is directed to preliminary high-efficiency mixer, where also gaseous CO₂ is supplied at ratio of CO₂ : SASW equal to 5÷15 nm³ : 1 m³. Obtained mixture is fed into the saturator at increased pressure up to 4.5 atm. Ion-molecule equilibrium is established in the saturator, the pH of the averaged state decreases to values less than 7.5 units. and molecular H₂S is formed. Carbonated SASW is supplied to desorption column operated at low pressure of 1÷1.2 atm, on mass exchange devices of which there is desorption of formed H₂S, and for replenishment of natural losses of CO₂ from SASW solution and maintaining intensity of carbonisation process to lower part of desorption column, supply CO₂ with ratio of CO₂ : SASW is equal to 5÷15 nm³ : 1 m³. Total flow rate of CO₂ is determined by ratio with SASW in range of values 10÷30 nm³ : 1 m³ and depends on degree of contamination of high-altitude sulphides. Gaseous products, mainly consisting of H₂S, are discharged from the upper part of the desorption column and can then be processed for elementary sulphur production. Bottom product, which is an SASW with residual content of ammonium sulphides and nitrogen, is directed to the middle part of the additional stripping column, where due to heat supplied through the external boiler, there is evaporation of residual amounts of NH₃, CO₂, H₂S, as well as water, which are further discharged from the upper part of the stripper column successively into the cooler and separator. There is condensation of water vapour with partial dissolution of NH₃, CO₂, H₂S, as well as separation of formed condensate from gaseous products. Condensate from the separator is returned to the upper plate of the additional stripping column as circulating reflux, thus ensuring its operation in the rectification column mode. Gaseous products, which are a mixture of CO₂, H₂S and insignificant admixture of NH₃, are directed to the lower part of the desorption column in order to reuse CO₂ as a carbonising agent. Stripped bottom product, which is a cleaned SASW, is directed into a recuperative heat exchanger, where it is cooled by heating of the carbonised SASW entering the stripping column, is additionally cooled in a water cooler and can be directed to a biological treatment unit for purification from phenols and oil products.

EFFECT: technical result: deep purification of an SASW 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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