LOCOS PW: Produced water treatment

TECHNOLOGY OF HETEROGENEOUS-CATALYTIC OXIDATIVE REMOVAL OF FORMATION WATER FROM HYDROGEN SULFIDE (“LOCOS PW” process)

Application area

Oxidation of toxic sulfides and hydrosulfides contained in produced water by air to less harmful – thiosulfate, hydrosulfate and sodium sulfate in the presence of KSM-X catalyst at 60÷80°C and a pressure of 0.5 MPa.

Concentration of sulfide sulfur in produced water may be up to 1000 mg/dm3 (0.1% wt.). After treatment residual content of sulfide sulfur (hydrogen sulfide) in produced water is not more than 10.0 mg/dm3 (0.001 wt.%).

Technology description

Principal technological scheme of heterogeneous catalytic process of produced water treatment with KSM catalyst:

Produced water separated from oil and mechanical impurities accumulates in tank D-101. Further it is pumped by P-101A/B into heat exchanger E‑101, where it is heated to 60÷80°C, and then supplied through distributor to the bottom of reactor R‑101. Before entering reactor R-101 produced water is mixed with air under 0.8 MPa pressure.

This mixture goes co-currently upward from the bottom of R-101 through the densely loaded layer of KSM-X catalyst, on the surface of which oxidation of toxic, corrosive hydrosulfides into inert odorless sodium hydrosulfate and thiosulfate proceeds in a continuous-flow mode by reactions (1) and (2):

H₂S + 2NaHS + 4O₂ → NaHSO₄ + NaHS₂O₃ + H₂O (1)
9NaSH + 10O₂ → 4Na₂S₂O₃ + NaHSO₄ + 4Н₂O (2)

Treated produced water with the exhausted air from the top of reactor R-101 are fed to degasser D-102. Produced water from the bottom of degasser flows into cooler E-102 and then sent out of battery limits. Exhaust air from the top of D-102 is sent to the furnace for combustion.

When E-101 is packed with sand and oil, hot neutralized formation water is supplied from the bottom of the E-102 separator to the E-101 tank. In this case, sand is drained from the bottom of the E-101 tank, and oil is removed from the upper pocket along the phase separation level.

Advantages

Technology effectively and sustainably operates in a wide range of hydrogen sulfide 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. 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.