War Strategies to Guarantee Peace Time in a Primary Fractionator

The 21st Ethylene Producers Conference
2010 AIChE Spring Meeting
AIChE Spring Meeting and Global Congress on Process Safety
March 24, 2010 - 8:00pm
Braskem is a Brazilian petrochemicals manufacturer, producing monomers, resins and chemicals specialties. Its ethylene capacity is 2,500 Kty, distributed in four Olefins plants, all based on naphtha steam cracking. This paper reports a high rate of fouling in the Primary Fractionator, resulting in a severe capacity loss and an imminent plant shutdown. The main functions of Primary Fractionator Tower is to separate the LFO (Light Fuel Oil) fraction from HFO (Heavy Fuel Oil) and to cool the mixture effluent from TLE's, with the recovered heat used in other parts of the plant. The top section of this tower contains 16 single-pass trays. In 2002, during the last revamp, the Primary Fractionator Tower trays were replaced. The new trays were designed with small fixed valves to improve the separation capacity. A lot of process troubles and bad feed specification contributed to a continuous and high rate of fouling in the system. The high capacity trays did not have a good fouling tolerance. Their small openings plugged, causing premature flooding, high tower pressure drop (more than double of normal value), abrupt and severe tower bottom level reductions during furnace switches, separation efficiency reduction, high concentration of heavy components in the pygas, and difficulties to control quench oil viscosity. Even the most optimistic prognostics did not show the possibility to keep this plant in operation, even with low feed rate, until the next planed turnaround. By the middle of 2006, the production loss became unacceptable. A brainstorm session adopted the concept of removing the deposits in the Primary Fractionator lower trays using hydroblasting during plant operation. The exact location of the flow restriction in the tower was determined from the gamma scan. In order to prevent a similar issue, the Primary Fractionator Tower trays were replaced again in the following turnaround (middle of 2008). The new trays have larger openings and therefore a better fouling resistance. Beside this, the plant no longer cracks process condensate, and some process improvements were implemented.
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