SIEMENS Energy has announced it will supply a wet air oxidation ethylene spent caustic treatment system to Qatar Petrochemical Company (Qapco) as part of an ethylene plant expansion.

The Siemens Zimpro wet air oxidation (WAO) system will be part of Qapco’s facility in Mesaieed Industrial City, Qatar, and provide the Qatari company with more efficient wastewater treatment while eliminating noxious spent caustic sulphide odours. The facility is expected to go operational in December, 2013.

Qapco is expanding its ethylene cracking unit from a current capacity of 720,000 tonnes per year to a new capacity of 900,000 tonnes per year. The Siemens scope of supply encompasses a Zimpro wet air oxidation system as well as a complete power management system for this project. The WAO will destroy odorous sulphide pollutants and generate a biodegradable effluent that can be discharged to conventional biological wastewater treatment. Zimpro wet air oxidation has been widely accepted as the preferred technology for safe and reliable treatment of spent caustic wastewater generated in ethylene plants. There have been nearly 40 systems installed for this application over the past 20 years.

Wet oxidation is the oxidation of soluble or suspended components in an aqueous environment using oxygen as the oxidising agent. When air is used as the source of oxygen, the process is referred to as wet air oxidation (WAO). The system will oxidise odorous reduced sulphur compounds such as sulphides and mercaptides, and will also break down complex organic contaminants, such as phenols, to either carbon dioxide and water, or biodegradable organic materials.