Distillate Stripper Process Flow Diagram

Liquid from hot separator at 11.0 barg and 272°C shall enters on Distillate Strippet on tray 10 and condensate from cold separator at 10.3 barg and 57°C shall be heated in Feed / Stripper Bottom HX to 248°C and shall feed the Stripper at tray 7. The top vapors at 9.0 barg and 159°C shall be condensed in Stripper Air Cooler – exit T = 60°C and Stripper Trim Cooler to 40°C and shall feed the reflux drum. From the reflux drum, a portion of condensate shall be sent as reflux to Stripper top tray under flow control reset by reflux drum level and the rest shall be pumped to refinery at 15 barg. The distillate from the tower bottom at 268°C & 9.5 barg, shall be pumped to be cooled to 256°C by heat exchange in Feed / Bottom HX, further cool to 177°C and sent to vacuum dryer top tray under flow control reset by level. The top of Vacuum Dryer Column at 160 mmHg is passing to vacuum system (one stage steam ejector) and the incondensable are sent to fire box of Distillate Reaction Heater. The liquid condensed in steam ejector condenser is recycle to Vacuum Dryier feed by Vacuum Pump. The dry distillate from Vacuum Dryer bottom is pumped to storage at 12.0 barg at 40°C via Vacuum Air Cooler and Vacuum Trim Cooler. Keep the Distillate Stripper top operating temperature above water dew point. Feed vaporization determines the traffic in the top of the column for a given reboiler duty. When feed vaporization is too high, the column top reflux ratio is to high thus overloading the condenser and top trays, when feed vaporization is too low, the reflux ratio is to low thus impacting separation quality. Feed preheat is commonly provided by heat exchange against stripper bottoms. When this is the case then heat recovery is normally maximized up to an economic exchanger approach temperature limit and a manual bypass provided should feed vaporization be to high – the vaporization shall not be higher than 25.0 – 30.0 wt%. H2S breakthrough it is a common issue and is caused by insufficient bottom tray vapor to liquid ratio – insufficient stripping. Most commonly caused by inadequate reboiler control schemes that control reboiler return temperature rather than bottom tray vapor/liquid equilibrium. With reboiler return temperature control schemes the reboiler effectively turns itself down as feed preheat increases or feedstock molecular weight increases. Remember when you set the ASTM D-86 specification to chose not initial / final boiling point but 5% respectively 95% (the simulators are not accurate in prediction of IBP/FBP). The feed composition to the vacuum dryer tower is largely impacted by product flash point requirements and the preferred disposal route for condensate is to recycle it back to the stripper column. This allows the vacuum dryer to provide one additional stage of stripping which reduces the amount of stripping steam required. Usually the vent gas from the vacuum system is disposed via a flame arrestor into the reactor heater fire box.