Used skid-mounted DMF (Dimethylformamide) distillation system designed by KOCH to recover 14-35% DMF from wastewater. The system consists of a Distillation Column (CL-7001) with Koch-Glitsch valve trays, Feed Preheater (HE-7001), Steam Heater (HE-7002), Reboiler (HE-7003), Product Cooler (HE-7004), Column Condenser (HE-7005), Bottom Purge Cooler (HE-7006), Heat Recovery Condenser (HE-7007), Reflux Drum (TK-7002), Bottoms Pump (PU-7002), Product Pump (PU-7003), and Reflux Pump (PU-7004). Utilities consist of steam, cooling water, electricity, and instrument air.
The wastewater feed containing DMF, water, and formic acid is fed via Feed Preheater (HE-7001) and Steam Heater (HE-7002) to the Distillation Column (CL-7001) operating at atmospheric pressure. The column bottoms are circulated by pump PU-7002, through Reboiler (HE-7003) where 180 psig steam is used to generate vapors to strip water from the feed.
The formic acid in the feed forms a maximum boiling point azeotrope with the DMF and is rejected in a small purge stream from the reboiler loop. Prior to leaving the unit this purge stream is cooled in the Bottoms Purge Cooler (HE-7006) to 115°F and filtered by 3-stage dual cartridge filters. Part of the filtered purge stream is recycled to the suction of pump PU-7002 as coolant for the magnets.
A vapor side draw is taken which contains the dry DMF product. The vapor product is condensed on the shell side of feed preheater (HE-7001) and then cooled to 115°F in Product Cooler (HE-7004) using 85°F cooling water.
The vapor from the stripping section, containing steam and a small quantity of DMF, is condensed in Column Condenser (HE-7005) and subcooled to 140°F. The condensate flows by gravity to the Reflux Drum from where it is pumped by PU-7004, either returning to the column as reflux or to battery limits of the system for disposal. When the Heat Recovery Condenser (HE-7007) is in service, the vapors are first partially condensed in HE-7007 by 35% wt Propylene Glycol before passing to HE-7005 for remaining condensation and subcooling as before.
The DMF product contains less than 150 ppm water wt. The DMF concentration in the distillate product is less than 0.1% wt.