Выражение встречается в следующем контексте:

Ethylene plant solid wastes

The following material may be produced in the Ethylene Plant:

Pyrolysis tar from Quench Tower, and DOX Unit
Spent catalysts and desiccants

The pyrolysis tar must be periodically removed from the bottom of the quench tower and the DOX unit performax coalescer. Normally, the majority of this material will leave the unit with the heavy gasoline residue.

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