The project goal was to recycle, rather than treat, benzene waste. The option of recycling benzene was chosen over treatment to minimize exposure to personnel and reduce potential future liabilities and operating costs associated with treatment.
Total benzene in waste generated was 370 tons per year. A major waste stream is a closed hydrocarbon blowdown system that collects benzene containing materials from the olefins units for direct recycling to the process. Some large water streams, representing another major benzene stream, are directly piped from process equipment to a storage tank and are fed to recovery columns to recycle and produce a clean wastewater stream. Small volume, low benzene concentration streams continue to go to the process sewer. These streams, containing less than six tons per year of benzene, are also sent to the benzene recovery columns. The benzene and other hydrocarbons recovered from all these streams are recycled to the olefins process.
Total benzene emissions to air from wastewater have been reduced by about 100 tons per year. Most of this reduction is due to recycling of benzene containing streams before they enter wastewater. Furthermore, 140 tons per year of other hydrocarbons (toluene, xylene, etc.) are recycled along with this benzene. Since most streams are recycled through a closed-loop process, benzene exposure potential to our plant personnel is greatly reduced.
Details of Reductions
Additional Information :
The initial capital cost was $50 million. The cost savings are due to reduced hazardous waste disposal and regulatory burden, but environmental and employee benefits are greater