Challenge

Chinese Petroleum Corporation (CPC) in Taiwan, Republic of China, needed to treat spent caustic liquor from different sources at various refineries.

Spent caustic liquors typically come from the scrubbing of cracked gas with aqueous sodium hydroxide. In oil refining, the liquors emanate from caustic washing, which is practiced to improve the quality of the product and to aid in the refining process.

Spent caustic streams are generally a significant odor source, as well as being disruptive to the operation of a biotreatment facility.

Solution

Sulfides and mercaptans in the spent caustic streams are oxidized to sulfates, and a substantial portion of other organic constituents such as phenols, oils and polymers are removed by using Zimpro® wet air oxidation systems at each site.

In the wet air oxidation process, liquors are pumped to system pressure, mixed with compressed air, and brought to oxidation temperature. In the reactor, the oxidation is autothermal and destroys complex organics or reduces them to biodegradable forms or to carbon dioxide and water.

At CPC's Kaohsiung Refinery, three wet air oxidation units were each designed to treat 25 gallons per minute of spent caustic liquor. At the Lin Yuan Petroleum Plant, two wet air oxidation units were each designed to treat 16.7 gallons per minute of spent caustic, and three units were sent to the Talin Refinery, each designed to treat 5.3 gallons per minute of spent caustic.

Results

The wet air oxidation systems have all been performing well. At all locations, the wet air oxidation effluent is biodegradable.