(48f) Upgrading a Super-Fractionator C4-Splitter with 4-Pass High Performance Trays

The column is located in an integrated C4-Plant at Evonik Degussa's site in Marl, Germany. Its key function is the sharp separation of light C4-olefins from heavier C4s. The column was originally equipped with a high number of conventional 4-pass valve trays, installed at a tray spacing as low as 300 mm. The throughput and especially the production rate of the desired distillate product were limited by excess carryover of heavier C4s into the distillate. Following growing demand, a capacity increase by higher feed flow rate to the column and / or higher overhead product recovery was planned. Distillate purity had to remain at established values and the revamp had to be performed during a planned 3 week plant shutdown.

The paper covers all essential steps of the revamp.

First, the problem definition via process simulation, column scan and detailed review of existing trays is outlined. Bottlenecks in the existing tray design were revealed.

In the second part, the design procedure for high capacity 4-pass truncated downcomer trays at low tray spacing is outlined.

The safe exchange of more than 160 metric tons of tray material during a three weeks plant shutdown was made possible by a combination of hardware designed for easy installation, extensive pre-assembly of tray elements before the shutdown and carefully planned installation work.

A comparison of column performance before and after the revamp is given. Before the revamp, the column was run at maximum capacity at most times, and frequent operator action was required to keep the distillate within specification. The new trays give a twofold advantage: hydraulic capacity has been increased by more than 15%, while the reflux ratio could be significantly reduced. This apparent improvement in tray efficiency results in a further capacity increase. The column now runs stable at 20% higher capacity, requires less operator action and the products are in specification.