Connect With Us:

Louisiana Refinery Accident Database

Valero (1238), Meraux

LDEQ Accident Report

Pollutants Released

Accident Classified As: Reportable Quantity

Cause of Problem: Equipment Design

Incident occurred following Hurricane Isaac at the North Flare during start up of the Hydrocracker unit. Valero has determined the cause to be the system design of the Hydrocracker/Hydrotreater Unit. Under normal operations, gases produced in the Hydrocracking/Hydrotreating Reactors, including H2S, are completely stripped out by steam in the Ore-Fractionator Stripper and sent to amine contractors for treatment; they do not pass into the Fractionator and on to the Fractionator Overheard Receiver. Consequently, the Fractionator Overhead Receiver was not designed with gas handling capabilities. Manual venting to the flare is the only available method of controlling an increase in pressure caused by gas carryover from the Pre-Fractionator Stripper. The design deficiency becomes apparent during unit start up because gases are produced prior to the ability to introduce stripping steam to the Pre-Fractionator Stripper. Stripping steam cannot be introduced until the unit is at the proper operating temperature. Operational experience has shown that even once stripping steam can be introduced, its use is limited at the low charge rates during a start up because excess steam causes erratic flows in the heater passes and delays the completion of the start up. A contributing factor in this event was that De-Asphalted Oil (DAO), a higher sulfur content feed, was introduced to the Hydrotreater prior to reaching adequate stripping steam rates in the Pre-Fractionator Stripper.

Discharge Preventable - No

Valero followed written startup procedures, which were based on unit design and sound engineering judgement. Valero has concluded that the Hydrocracker/Hydrotreater unit cannot be started up as currently designed without venting some H2S-containing gas to the flare.

Notes/Remedial Actions

Valero will engineer and install a "start-up vent" that will direct the gases vented from the Fractionator Overhead Receiver to be collected by the refinery's HiJet, treated for H2S removal, and used in the refinery fuel gas system. Valero will also revise the Hydrocracker/Hydrotreater startup procedure to delay the introduction of DAO into the Hydrotreater feed until adequate stripping steam rates have been established. According to the LDEQ's list of reportable quantities, the reportable quantity for sulfur dioxide is 500 pounds.