Chevron Chemical Company
Chevron Chemical Company operates an ethylene unit at its Cedar Bayou plant in Baytown. A by-product of the cracking process in this unit is coke, which gets carried over from the furnaces into the gasoline fractionator, and into the bottom stream (quench oil). It is removed from the quench oil via filtration. The filters are cleaned weekly. They are first flushed with a wash oil to remove heavy hydrocarbons, which are recycled to the process. The remaining coke sludge becomes a process waste. The coke was characteristically hazardous due to benzene. Because the conditions at which the gasoline fractionator is operated should prohibit benzene from being in the coke sludge, Chevron Technical and Operations personnel investigated the source of the benzene in an effort to remove it. It was discovered that the wash oil being used was off-specification heavy aromatic distillate (HAD), another by-product of the process. During startup of the hydrogenated pyrolysis gas (HPG) unit, the product streams, including HAD are not within specifications.
The solution to the problem was to make a procedural change. On start up of the HPG unit, the HAD is now recirculated back to the gasoline fractionator until it is within specifications. The wash oil tank is now filled with on-spec HAD, and the waste no longer tests (TCLP) positive for benzene.
This process produced 146 tons of hazardous waste in 1994. As a result of this change, the waste is no longer classified as a hazardous waste.
Details of Reductions
Additional Information :
Since the material is now handled as a Class 1 nonhazardous waste Chevron saves an estimated $160,000 a year in disposal and regulatory costs.