Refineries’ Processes, Products a Volatile Mix : Safety: ‘Cracking’ equipment brings chemicals, open flame together. More than 110 people have been killed in U.S. oil plant accidents in the past seven years.
The explosion and fire that devastated Texaco’s Wilmington refinery Thursday night was neither unusual nor likely to be the last.
More than 110 people have been killed in oil and petrochemical refineries in Southern California and across the United States during the past seven years. The American Petroleum Institute reported that between 1985 and 1989, refineries reported 66 serious accidents involving substantial property damage and loss of life.
Whenever volatile liquids and gases are in close proximity to flames--as is the case at refineries--there is always a chance of an accident despite the efforts of the petroleum industry and government watchdog agencies to make safety a priority.
Such was the case Thursday night at the Texaco refinery. Although the cause of the inferno is still under investigation, Los Angeles Fire Department investigators are focusing their attention on a possible leak in a high-pressure feed line within the refinery’s “cracking unit,” a tower of boilers, heaters and piping at the heart of the refining process.
Refining industry officials say the cracking unit “cracks” oil by heating it and then breaking it down chemically so that it can be distilled into everyday products--gasoline, diesel fuel and jet fuel.
Despite Thursday’s explosion and fire, it is still unclear the extent of hazards posed to surrounding communities by even more powerful fires, explosions or gas leaks in Texaco’s cracking unit.
City Fire Department officials said the firm has yet to prepare a state-required “risk management prevention program”--or RMPP--for its oil cracking equipment.
Such a program is required by the state for all businesses handling acutely hazardous material. An RMPP typically includes a seismic analysis, a hazard and operability study, and an analysis of the hazards posed to surrounding neighborhoods. Maps showing the possible direction of a toxic plume are also required.
Texaco spokeswoman Kelly McAndrew said the firm has not prepared such a plan, adding that “right now the attention is being focused on handling this incident. Once it is over, they will be addressing when they will prepare the RMPP.”
City Fire Battalion Chief Lawrence Krokes said Friday that fire officials have not pressed for an RMPP because the department has placed a higher priority on other hazardous threats--ranging from power plants to paint factories.
“It’s very difficult to do them all at one time,” Krokes said.
The cracking unit that caught fire Thursday night is common to all refineries, including the 28 in California. The unit that burned was a two-stage hydrocracker, which uses hydrogen gas to enhance the cracking process.
During the cracking process, crude oil is mixed with hydrogen vapor. The mixture is heated to 550-750 degrees, pressurized and moved through pipes to a first-stage reactor, a cylindrical vessel made of steel up to six inches thick.
Inside the reactor, the crude passes over a catalyst--typically a compound of sulfur with cobalt, molybdenum or nickel plus alumina--which enhances the cracking process. At this stage, about half of the crude has been cracked into gasoline-range material.
The mixture is moved to a hydrogen separator, where it is cooled and liquefied before moving to a fractionator, a unit that distills it into a variety of products--gasoline, jet fuel or gas oil.
Fire officials and environmentalists said Friday that they were also concerned that hydrogen sulfide gas, a byproduct of the refining process, was released during the fire. The colorless gas, which has a strong odor of rotten eggs, can be life threatening under certain circumstances. It can result in convulsions, dizziness, even coma.
But authorities said that concentrations during the Texaco explosion and fire were never high enough to pose a danger.
The South Coast Air Quality Management District said that concentrations of the gas did not appear to exceed one part of gas per million parts of air during the duration of the fire.
State guidelines call for an evacuation when concentrations reach 10 p.p.m. However, hydrogen sulfide can be smelled at concentrations as low as 8 parts of gas per billion parts of air, AQMD spokeswoman Claudia Keith said.
How Oil Is Refined
The investigation of the Texaco refinery fire is focusing on the hydrocracker, a simplified version of which is shown below. It is at the very heart of the the refining process. It heats up the thick crude oil and breaks it down chemically so that it can be distilled into everyday products such as gasoline and diesel and jet fuel. 1. Crude oil is mixed with hydrogen vapor in the heater and brought to a temperature of 550 to 750 degrees Fahrenheit. Under pressure of 1,200 to 2,000 pounds per square inch, it is dispatched to the first stage reactor. 2. As it passes through the catalyst in the first stage reactor, 40% to 50% of the crude oil is broken down into a range of gasoline-like materials. 3. Next the crude oil and gasoline-type material are run through a hydrogen separator, cooled and liquefied. The hydrogen is recycled to the original feed line. 4. The liquid is sent to the fractionator and distilled until the desired product--gasoline, jet fuel or gas oil, for example--is obtained, depending on the temperature used. 5. The leftover, known as fractionator bottoms, are again mixed with a hydrogen steam and sent to the second-stage reactor, which operates under higher temperatures. Like the output of the first-stage reactor, the second stage-product is separated from the hydrogen and sent to the fractionator.
