LOCOS SA: Sulfur-alkaline waste water treatment
TECHNOLOGY OF HETEROGENEOUS-CATALYTIC OXIDATIVE TREATMENT OF SULFUR-ALKALINE WASTE WATER («LOCOS SA» process)
The technology relates to the field of treatment of sulphurous-alkaline wastewater from oil refineries and petrochemical enterprises from inorganic sulfides.
Oxidation of toxic, corrosive sulfides, hydrosulfides and mercaptides contained in sulfur-alkaline waste water by air oxygen to inert, odorless hydrosulfate and sodium thiosulfate, to disulfides and alkylthiosulfonates, in the presence of KSM-X catalyst at 60÷90°C and pressure of 0.5-0.7 MPa.
Concentration of sulfide sulfur in sulfur-alkaline waste water may be up to 50000 mg/dm3 (5.0 wt%), and mercaptide sulfur – up to 0.2÷8.0 wt%. After treatment the residual content of sulfide and mercaptide sulfur in sulfur-alkaline waste does not exceed 50.0 mg/dm3 (0.005 wt%).
Schematic diagram of the treatment of the SA:
Sulfur-alkaline waste water from different plants separated from oil products and mechanical impurities are mixed in tank D-101, pumped by P-101A/B to heat exchanger E-101, where they are heated up to 60÷90°C and supplied to the top of reactor R-101 which is filled with KSM catalyst. Air is supplied through a distributor to the bottom of reactor with pressure of 0,6÷0,8 MPa. The pressure at the top of reactor R-101 is maintained at 0.5 MPa. Oxidation of hydrogen sulfide, sodium sulfide and mercaptide proceeds in a countercurrent mode according to the following reactions:
9NaSH + 10O2 → 4Na2S2O3 + NaHSO4 + 4Н2О (1)
9Na2S + 9O2 + 4Н2О→ 4Na2S2O3 + Na2SO4 + 8NaOH (2)
2RSNa + 0,5 O2 + H2O → RSSR + 2NaOH (3)
RSSR + O2 → RSО2SR (4)
Treated sulfur-alkaline waste water are removed from the bottom of reactor, cooled in E-102 and further directed for neutralization and biological treatment for additional purification from organic impurities. Exhaust air from the top of R-101 is fed to the furnace for combustion.
Technology effectively and sustainably operates in a wide range of sulfide and mercaptide sulfur concentrations, does not require large consumption of heat and reagents, carbon steel units are used in the process.
KSM-X catalyst having high mechanical strength and chemical resistance to acids and alkalis allows reducing temperature and volume of the reactor.
No need for periodical or continuous catalyst feeding with expensive variable valence metal compounds. This prevents cobalt phthalocyanines and derivatives, as well as salts of other heavy metals getting into wastewater.
Guaranteed service life of KSM-X catalyst is 8 years. During operation, catalyst does not require additional regeneration since it runs in parallel with reaction of sulfur compounds oxidation.