Chemical plants spend from 50 to 70 percent of their energy in "separations," which are usually distillation steps required to separate a raw material into various products. An energy-efficient Purdue University method rearranges the distillation sequence needed to separate crude petroleum into products.
In the case of petroleum, four distillation columns are needed to separate raw crude into five separate components - naphtha, kerosene, diesel fuel, gas oil, and heavy residue. Some of these components are later used to make gasoline.
"Separations are a huge part of what chemical plants do," said Rakesh Agrawal, professor of Chemical Engineering. "Improving efficiency by only a few percentage points translates into major savings. For every 100 barrels of oil distilled, nearly two barrels go into supplying energy for distillation. That's a lot of oil."
Crude petroleum is fed into the system, heated, and vaporized. Vapor rises up the first column, and the product is collected in a condenser at the top. The process is repeated in additional columns, with the number of columns depending on how many components are to be separated.
But the distillation is more energy efficient depending on the order in which the columns are operated.
Doctoral student Vishesh Shah created a computer algorithm that identifies all of the possible sequences and then determines which require the least heat and energy. The Purdue researchers used their new technique to determine there are nearly 6,000 possible sequences for the four columns used in petroleum distillation.
The researchers also determined that 70 of the new sequences identified have potential to consume less energy than the sequence now used by industry. Those 70 sequences range from being 6 to 48 percent more energy efficient than the method currently in use.
"However, just because a particular sequence would be more energy efficient doesn't mean it would be practical for industry to implement," Agrawal said. "There are a lot of challenges. Some are easy to build and just involve trivial retrofitting, and some are more difficult. So we'll need to work with companies and refinery experts to determine which sequences could be built."
Purdue has filed a patent application for the new crude distillation sequences.