E. I. du Pont de Nemours & Co., Inc.
In one of our manufacturing processes we utilize phosphorus trichloride and hydrochloric acid. Phosphorus trichloride is a clear slightly yellowish highly volatile liquid. Both the liquid and the vapor forms will react readily with water (vapor or liquid) to form hydrochloric acid and a phosphorus based acid. There are six (6) independent scrubbers used to control HCL and PCL3 atmospheric emissions from storage tanks and process vessels. They are operated on a once-thru basis using either caustic or water. Their effluents are then sent to the waste treatment facility for proper disposal. Historically they were operated with excess caustic or water to ensure no atmospheric emissions. A revised operating philosophy will operate the two largest scrubbers, the HCL off gas scrubber and the PCL3 storage tanks scrubber, with their caustic supplies in series. The same amount of excess caustic will be fed to the HCL scrubber. The effluent from that scrubber will then become the primary caustic feed for the scrubber on the PCL3 storage tanks. A back up caustic supply will be provided for the PCL3 tank scrubber to ensure complete control. The PCL3 storage scrubber effluent is to be circulated to the remaining four scrubbers and gravity drain back to the PCL3 scrubber. Now there will be only one effluent stream of significantly reduced volume going to the waste treatment facility.
In addition to the series operation detailed above, the spent PCL3 scrubbing solution was being purged based on level control. This will be revised to purge based on solution density. This change insures that the maximum amount of neutralization is being done prior to discharging the solution.
Estimated waste water reduction is approximately 26.8MM pounds per year.
Details of Reductions
Additional Information :
Cost Savings will be on the order of $144M per year for waste disposal, caustic consumption, and taxes. The project is being estimated currently and payback has not been estimated. Future savings will be realized through reduced investment when facilities are installed to dispose of the aqueous liquid waste by methods other than deep well disposal.