Simulation software: Refinery simplifies EPA compliance of distillation column

Simulation platform helps refinery prepare for compliance with coming EPA benzene regulations.
By Control Engineering Staff April 2, 2008

Silver Eagle Refining has solved its compliance with EPA regulations on benzene emissions, thanks in part to internal simulation studies performed to verify sizing and performance of distillation columns and air-cooled exchangers in its new isomerization and bensat units.

Silver Eagle launched this program at its Woods Cross, UT, refinery to solve implementation of mobile source air toxics (MSAT) requirements for benzene emissions. An engineering team with specialists from the company and Invensys Process Systems collaborated on implementing Simsci-Esscor PRO/II simulation software with Koch-Glitsch’s Ratefrac sizing methodology.

“The new EPA regulations are prompting refiners to rethink their processes and in doing so, they are finding that advanced simulation and modeling software can help them comply with regulations cost-effectively, while improving also their operating efficiency. By offering powerful Ratefrac column sizing functionality within our PRO/II simulation and modeling software, we provide an integrated solution that is not available from any other single supplier,” says Joseph McMullen, PRO/II product manager for Invensys.

The EPA classifies MSATs as hazardous air pollutants resulting from non-point sources. They contribute to ozone formation and possible addition of particulate matter to the environment. Targeted MSATs include benzene, 1,3-butadiene, formaldehyde, acetaldehyde, acrolein, and naphthalene. Benzene is a known carcinogen linked to leukemia. In regulations issued recently, the EPA requires that all refiners limit the annual average benzene content of reformulated and conventional gasoline to 0.62% of volume by January 1, 2011.

“We modeled our future benzene isomerization and saturation units ourselves, using SimSci-Esscor PRO/II software, but to be certain that we did it right, we contracted also with Invensys to perform the same analysis with the PRO/II software,” says Silver Eagle Refining process engineer, Joe Brown. “I was deliberately cryptic in the beginning because I didn’t want our results to skew theirs, but was comforted to see that they came up with similar results. The PRO/II software has definitely helped us verify that the changes we are making will meet the benzene regulations.”

PRO/II software, SimSci-Esscor’s steady-state simulator, helps meet the new requirements by applying the Ratefrac methodology to achieve accurate and realistic column design. The company says that module in the PRO/II software is a rigorous rate-based distillation model that is used in applications where the approach to equilibrium is limited by heat and mass transfer rates. Ratefrac allows for simulation of all types of multistage vapor-liquid columns. Through the use of a rigorous mass transfer methodology, the platform reportedly determines both a bulk and interface composition and determines height equivalent to theoretical plate (HETP) ratios in the packing and performance of trayed sections from the column configuration.

—Edited by Peter Welander, process industries editor, ,
Process & Advanced Control Monthly
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