The Rhone-Poulenc Houston plant produces various grades of Sulfuric Acid, some of which are saturated in sulfur trioxide (SO3) to the point that they fume continuously in atmospheric storage tanks. The plant had a vent scrubber on its storage tanks but the water (3 to 5 gpm) used to scrub the vent gases was very acidic and required 0.5 to 1.0 tons caustic per day to neutralize it before discharge into the plant treatment system.
A new system was designed with waste minimization and cost reductions in mind. It utilizes surplus equipment from Rhone- Poulenc's Seattle, Washington plant that was shutdown in 1991. The Investment Recovery Department published a booklet of all equipment that was available. Houston plant personnel quickly acquired a Carpenter 20 tower, acid pumps and a small 1,200 gallon tank. These components evolved into a new scrubber system that utilizes circulating sulfuric acid as the scrubbing fluid. The new system completely eliminates the acidic water as well as neutralization costs. Additionally, 0.5 to 1.0 tons sulfuric acid are produced daily.
The amount of sodium sulfate discharged to Buffalo Bayou was reduced by 400 tons per year.
Details of Reductions
Additional Information :
The annual savings of this project are $99,000 and the payback period is 1.6 years. The caustic cost was reduced by $82,000 per year and the recovered sulfuric acid is worth $17,000 per year. The project cost $160,000.