Refineries are caught in between the dwindling availability of sweet crude feedstocks, which is forcing facilities to process sourer crudes, and the trend toward more stringent limits on petroleum products' contaminant levels. This situation implies two things might happen to refineries as time goes by: they'll incur higher operating costs and produce larger amounts of waste by-products.
However, researchers at the Rowan University department of chemical engineering believe they've not only cottoned onto a way to help refineries retrofit their sour water systems to tolerate the increasingly sour crudes coming their way -- they also think their proposed solution will cut down waste production and help refineries save more than a few nickels and dimes.
Their work appears in the April issue of the periodical Chemical Engineering and Processing: Process Intensification.
In their case study of an unnamed refinery in northeast USA, the researchers looked at a facility with a sour-crude feedstock capacity of about 195,000 barrels per day. The refinery currently generates about 292 gallons of sour water daily.
An "engineering clinic" at the refinery saw the researchers come up with a tailored proposal based on intensifying the use of water: reusing water where possible, measuring and then tweaking contaminant loads, combining streams where it makes sense to do that, and manipulating inlet and outlet flow-rates. Their concept, should it be adopted by the refinery following feasibility studies, will involve about 2.8 miles of repiping at the refinery. The changes would cost $248,000, they said.
The researchers say their proposed changes to the refinery's sour water network should cut the annual volume of sour water generated to about 279,000 cubic meters from about 581,000 cubic meters. It should also reduce the annual consumption of freshwater by 83%, and slash the network's annual energy use and annual carbon dioxide emissions by 54% each.
They estimate that the sour water network's annual operating costs will decrease by 54% (by $10,525) as well, thanks to a reduced need for pumping. Reduced flowrates would produce a roughly $686,000 reduction in operating costs associated with consumables. Further annual operating cost savings, amounting to about $676,000, could also be expected at the refinery's sour water stripper. This is because the stripper, which is where contaminants are removed from sour water to produce less-contaminated water earmarked for re-use, would use less heat under the researchers' proposed plan.
The researchers said a similar boost to a refinery's operations could be done for systems handling the removal of other contaminant types, such as benzene.
They believe their approach to improving a refinery's sour water network, which they describe as a heuristic method, can deliver good results and avoid the need for intricate preparatory studies and analyses.
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