(157d) The Cleanest Way to Treat Spent Caustic

Spent caustic is arguably the world’s most foul industrial wastewater. It is generated in the removal of acidic contaminants from ethylene. The acid contaminants include hydrogen sulfide (H₂S) and mercaptan, which are toxic, corrosive, and extremely malodorous – and carbon dioxide. These compounds make conventional wastewater treatment tough for several reasons:

>> Toxicity to the biological wastewater treatment facility

>> High concentrations of chemical oxygen demand and total dissolved solids

>> Health, safety, and environmental concerns for people onsite

Additionally, the quantity of hydrogen sulfide and mercaptan can produce obnoxious odors that will extend far beyond the cracking facility’s fence line.

Oxidation is the best approach to treating spent caustic because the oxidized effluent is non-reactive inorganic salts and low-molecular-weight carboxylic organics. That’s why, after decades of proven, reliable use worldwide, cost-effective wet air oxidation (WAO) has become the preferred technology for treating spent caustic.

This presentation will outline the Zimpro® WAO process that Siemens has been using to produce high quality oxidized effluent from ethylene spent caustic over the past 25 years. The presentation will include a case study from one of China’s largest integrated refineries, with a crude oil processing capacity of 23 million metric tons a year. The plant produces more than 50 refining and chemical products. Among them are gasoline of different grades, diesel, jet fuel, asphalt, polypropylene plastics, and ethylene. The plant uses Zimpro WAO technology to process a spent caustic flow of 18.2 m³/hr generated from its ethylene production.

This presentation will also briefly cover the most recent technology upgrades for treating spent caustic, including the recent coupling of Zimpro WAO with advanced biological treatment technologies for a greatly simplified, end-to-end industrial water treatment solution.