(4e) Troubleshooting EB/SM Splitters: How a Maldistribution Analysis Can Help?

Senthil Krishnamoorthy, Sulzer Chemtech USA Inc.

Lee Ming Yang, Sulzer Singapore Pte. Ltd.

The ethylbenzene (EB) / styrene (SM) splitter (a.k.a. the EB recovery column) is the biggest column in the styrene production process. It can be considered a mega column: column diameters are often larger than 5 m, column heights are taller than 60 m, and 6 beds of structured packing are usually employed.

Generally, packed columns with large diameters are susceptible to large-scale maldistribution. For the EB/SM splitter, the low relative volatility (α-value) of the binary system, and the stringent product specifications, make the column extremely sensitive to maldistribution. Therefore, if an EB/SM splitter is exhibiting poor separation efficiency, a maldistribution evaluation is strongly recommended as part of the troubleshooting evaluation.

This paper will review the various sources of maldistribution susceptibility, which can stem from design, installation, and operational issues. Sometimes, the problem source(s) can only be exactly determined after opening up the column during plant shutdown. As the shutdown time frame is usually limited, there is only a narrow window period to both identify and resolve the source(s) of column underperformance.

Fortunately, it is possible to narrow down the possibilities prior to plant shutdown, via methodologies that encompass process, hydraulic and mechanical considerations. Some important steps include: simulation matchback to operating data, hydraulic evaluations of the column internals, and maldistribution sensitivity analysis of the column. After opening up the column, further methodologies can help to pinpoint the problem source(s). Some important steps include: visual inspection of the column internals, and liquid distributor water tests.

The troubleshooting process will be illustrated via several troubleshooting case studies. They will describe the methodologies used to identify the source(s) of column underperformance, and the subsequent corrective actions to return the column to satisfactory operations. These experiences should help engineers to perform troubleshooting in a structured manner, and allow plant owners to optimize their resources in a troubleshooting activity.