Though distillation column is designed and installed as per some sophisticated mathematical calculations and computer software model it not so easy while operating it in the field. Operation of distillation column ultimately works by the hands of the distillation operator. Even tons of books explain how to design the distillation column and at last the erected column works based on the operators and engineers in the field. Based on the experience and knowledge of distillation operation of senior personals could help but in course of time due to the shift of manpower the knowledge may shatter for particular operation and control of distillation column.
The following are some of major problems arise during running distillation column in a chemical plant.
• Instrument devices and control systems problems
• column internal valves and packing damages
• Startup and shutdown operation problems
• Re-boiler and condenser fouling and inefficiency
• Foaming, entarinment, flooding problems
• Column tray, weir and down comer layout
Up on main failure cases the column operation is disturbed or adjusted based on startup and shut down operation practices some of the hint for start up and shut down of distillation would come as given below which are established by experience.
How to start a ideal distillation column:
• After commissioning the column it is pressure tested to find out the leaks at fitting and joints.
• Than the column is flushed with nitrogen the operation is called as line blowing.
• The column is purged out to remove the oxygen content and then cooling system is started.
• All vent and drains are kept in loop control systems.
• Reboilers is filled with feed mixture till the level glass mark, heating media such as steam is introduced to heat the mixture and produce the vapors till they reach the condenser.
• Reflux valve is opened to maintain the top temperature and pressure drop in column.Feed is introduced proportional to the vapors produced in the column.
• Finally column is operated at constant reflux till the pressure and temperature indicator show the designed process values.
• Feed flow rate is increased to the designed value and all controls valves are switched from manual mode to auto mode.
How to shut down a ideal distillation column:
• Flow rates of the feed is reduced with controlling the reflux flow rate proportionally.
• Heating system is stopped first following cooling system which is working until vapor produced in the bottom of the column.
• Than feed to stop with reflux valve open which will make the entire vapor to condense and collected in the reflux drum and bottom of distillation column.
• All the liquid is than drained out from the column and reflux drum Bring the column to room temperature by flush out with inert nitrogen.
• Flush out the off gas valve to remove the remaining vapor mixtures to the flare Finally the column should be check for oxygen level and opened to atmosphere for maintenance.