Fire at the Wax Isomerization Unit of a Refinery
In a lube oil plant of a refinery, during the isomerisation of wax, the high pressure reactor ruptured, releasing gas composed by 70 % of hydrogen and 30 % of gaseous hydrocarbons (methane, ethane and others). The release gas was ignited and a fire developed in the plant area where operators and engineers were working. After the shut-down of the plant, 4 on-site firemen brigade provided to extinguish the fire. No people were injured. The fire damaged the unit and adjacent structures.The initial investigations revealed anomalies inside the temperature control system with the absence of a high temperature trip device, an inadequate cooling facilities and an inadequate operational procedures and training of the employees.
Event Date
May 22, 1994
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
The accident occurred because operating outside the design specifications. The temperature indicators on reactor had maximum readings below expected temperatures and, besides, no high temperature trips were available.Contributing causes were presence of manufacturing defects or corrosion of the reactor. The root causes are multiple, and point at one organization-related common root cause : of the incident can be summed up as follows:(1) Failure to understand the processes occurring in the reactor and the effect of an increase in temperature on the rate of exothermic reactions.(2) Inadequate cooling facilities.(3) An inadequate control system and the absence of a high temperature trip device.(4) Inadequate operational procedures and training of managers, engineers and operators.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
high pressure wax isomerization reactor
Storage/Process Medium
Design Pressure
64
Location Type
Location description
Industrial Area
Pre-event Summary
The unit affected by this event consisted in a dewaxing process aiming at lowering the pour point of an oil by catalytic isomerizing the paraffinic waxy components.The incident occurred during the activation of a platinum catalyst using refinery treat gas. The component involved was a wax isomerization reactor of the following dimension: 23 m high, 1 m diameter, wall thickness walls of 55 mm. Operating conditions: 64 barg and 430-480C.
Lessons Learned
Lessons Learned
According to the eMARS report (see references), the accident investigation identified several causes, mostly related to the inadequacy of the operational measures to early spot anomalies and to learn from them. The findings can be cluster as follows. DESIGN SHORTCOMING(1) Catalyst activation was not taken into account during the reactor design: (2) There was no automatic trip in case of trespassing of the maximal reactor temperature. NEAR MISSES which were not taken into account (1) During initial plant start-up in 1991 and catalyst activation at 400 degrees Celsius an exothermic was experienced. Its cause was identified as a hydro cracking reaction of the parafins in the treat gas, but no further action was taken; (2) In 1994 during a preliminary hot de-waxed treatment at 430 degrees Celsius, temperature indicators were seen to be out of range. No investigation was made. The settings of the temperature indicators was 410 and 450 Celsius although the instruments had a potential maximum of 1000 Celsius. All alarms were set at 405 Celsius. RISK ASSESSMENT SHORTCOMING(1) The original risk assessment did not consider the catalyst activation stage and dismissed the possibility of a runaway exothermic reaction.(2) The reactor installation was provided with an emergency shut-down control which was manually activated and required operators to respond correctly to the situation. (3) In May 1994 a new catalyst had to be activated. A temperature 430 Celsius was planned, instead of the 400 C originally used, but there was no risk assessment on this change in operating conditions. (4) During the activation stage 3 people went out onto the reactor ladders and platforms at various times, if they had been present when the reactor ruptured they would have been caught by the fire.LESSON LEARNED - ORGANISATION: A. Near misses are an important indicator of the potential for accidents. The plant organisation has to record and assess them, and act upon. B. Operation process parameters cannot be changed without performing a new (partial) risk assessment C. Management of changes is a critical tool which should be adopted. It was not in the present case. LESSON LEARNED TECHNICAL KNOWLEDGE: At the time of the accidents, very little published information on runaway exothermic in continuous reactors was available. A case report in Safety Digest of American Petroleum institute, Publication 758 Section 2 1979 Chapter 5 is similar to this incident. Also "Chemical Reaction Hazards - A Guide" Editors Barton and Rogers published by IChemEng 1993 and IChemSymposium Series No. 85 "Protection of Exothermic Reactors and Pressurised Storage Vessels" could have been used to identify the chemical process on going in the reactor. Since then, hydro cracking and thermal cracking of parafins at the temperatures experienced in this reactor are widely reported in standard text books.
Event Nature
Emergency Action
Operators shut-down the plant and shut-off the fuel supply. Four people of the company fire brigade extinguished the fire, after which a decontamination of the plant was performed
Release Substance
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event description in the European database eMARS
https://emars.jrc.ec.europa.eu/en/eMARS/accident/search?bfd=1#
(accessed December 2020)
ARIA data base
event no. 5906