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LO-CAT® II process for elevated pressure refinery desulfurization

MOL Hungarian Oil & Gas Co. selected a LO-CAT® II Desulfurization System for operation at its production unit in Szeged, Hungary. The unit was custom-designed for direct treatment of sour associated and process gas streams at elevated operating pressures and relatively high CO2 partial pressures.

Recycled process gas and associated gases are collected from the oil fields around the plant and transported via a mixed-phase pipeline, followed by separation in a bank of gas-liquid separators. The associated gas is combined with the recycled processgas stream, compressed to 16–18 barg, and sent to the LO-CAT II. Several technological challenges arose during the project due to process restrictions. Excessive liquid entrainment occurred whenever sour-gas flow exceeded 60,000 normal cu m/hr, so a new, larger separator was retrofitted into the plant. As a result, gas flow up to 80,000 normal cu m/hr was achieved. After startup, it was discovered that considerable condensate was frequently introduced from the process gas and the operation of the two-phase oil-gas pipeline. The presence of excessive liquid hydrocarbons in the LO-CAT II unit caused foaming and floating sulfur. The sour-gas transfer line was modified by retrofitting a simple drainage boot to catch the condensate.

Later, a larger knockout pot replaced the original one, reducing the foaming and floating sulfur and increasing the unit’s effectiveness. The unit’s catalyst recirculation pump was replaced when the LO‑CAT II capacity exceeded the pump’s design. A new pump with the required capacity was installed and continues to operate successfully. The unit operates with a gas flow of 60,000 to 100,000 normal cu m/hr, with a sulfur load of about 50 kg/day (due to low H2S concentration in the gas). Current H2S removal efficiency is 90%, producing gas suitable for pipeline quality.

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