Dow Chemical Company
This project installed double mechanical seals and seal pots on four feed pumps to a thermal treatment unit (TTU). This eliminated the perchloroethylene seal flush on the feed pumps, thereby reducing the amount of wastes being incinerated in the TTU. This saved more perch product, reduced waste generation and air emissions, and reduced post treatment costs.Originally, wastes entered the TTU through four centrifugal pumps with mechanical seal arrangements (see figure A). The pumps used perch seal flush at 0.4 gpm, which entered the waste stream for incineration. This project replaced the seal flush with double mechanical seals and seal pots (see figure B). The seal pots are filled with a neutral fluid, in this case synthetic oil. The barrier fluid recirculates through the seal by heat convection generated as the pump shaft rotates through the seal. The cooler oil in the pot is forced into the seal through the bottom line as the hot oil leaves the seal through the top line back into the pot (see figure C). The pot allows hot oil to cool before reentering the seal.
The double mechanical seal has several advantages over the single seal arrangement. The seal pot feeding the double seal is maintained at higher pressure than the pump so if either side failed, the barrier fluid would leak instead of the pumped fluid. Single seal failures allow seal flush or pumped fluids to leak
Elimination of the perchloroethylene flush reduced 4,403,000 lbs/yr of previously incinerated waste, 100 lbs/yr of hydrochloric acid and chlorine air emissions, and 450 lbs/yr of volatile organic compound discharges to water
Details of Reductions
Additional Information :
The capital cost was $33,000, operating cost is $2,000, and the net savings was $382,000.