English to Chinese Other Petroleum Eng/Sci

A barrel of crude oil will not always yield the desired ratio of hydrocarbons.
For example, the market may be heavy for gasoline, but light for lubricating oil.
Instead of discarding the lubricating oil, it is chemically cracked in a FCCU so that it can be turned into gasoline and other hydrocarbons with shorter changers.
Hydrocarbons can be cracked in other ways, but chemical cracking in a FCCU is the most common and efficient.

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