Methods for optimization of distillation column for reduction of energy consumption

A method for separating ethylene from a hydrocarbon feed, the method comprising:

• supplying a hydrocarbon feed to a fractional distillation column;
• separating ethylene in liquid and vapor phases from the hydrocarbon feed within the fractional distillation column;
• extracting a first ethylene fraction from the hydrocarbon feed, the first ethylene fraction extracted in a liquid phase, and having an ethylene content of 99.95 wt. % or greater;
• extracting a second ethylene fraction from fractional distillation column, the second ethylene fraction extracted in a vapor phase and having an ethylene content of 99.90 wt. % or greater;
• and
• discharging a vent stream from the fractional distillation column to a condenser, the vent stream being discharged in vapor phase and including an ethylene content less than 99.90 wt. %;
• wherein extracting the second ethylene fraction reduces a heat duty on the condenser such that energy consumption of the fractional distillation column due to reduction of the heat duty on the condenser is reduced by at least approximately 5%.

A system for separation of ethylene from a cracked hydrocarbon feed, the system comprising:

• a fractional distillation column comprising:
• an inlet positioned to receive the cracked hydrocarbon feed;
• a plurality of outlets, each of the plurality of outlets being positioned along the fractional distillation column at one of a plurality of levels and comprising:
• a first outlet positioned at a first level of the plurality of levels, the first outlet configured to extract a first ethylene fraction in a liquid phase from the cracked hydrocarbon feed, wherein the first ethylene fraction has a first ethylene content;
• a second outlet positioned at a second level of the plurality of levels, the second distillation outlet configured to extract a second ethylene fraction in a vapor phase from the cracked hydrocarbon feed, wherein the second ethylene fraction has a second ethylene content;
• and
• a third outlet, the third distillation outlet configured to extract a third ethylene fraction in a vapor phase from the cracked hydrocarbon feed, wherein the third ethylene fraction has a third ethylene content, the third ethylene content being of a lower ethylene content than the first ethylene fraction and the second ethylene fraction;
• a condenser in communication with the third outlet and configured to condense at least a portion of the third ethylene fraction and return a liquid recycled stream including ethylene to the fractional distillation column;
• and
• a reboiler connected to the fractional distillation column and configured to receive a stream of constituent materials of the hydrocarbon feed remaining after separation of ethylene therefrom;
• wherein extracting the second ethylene fraction in the vapor phase from fractional distillation column reduces a volume of the third ethylene fraction discharged to the condenser such that energy consumption resulting from operation of one or more of the condenser to which the third ethylene fraction is supplied or the reboiler is reduced by approximately 0.5 MW to approximately 4.0 MW.

A method for recovery of ethylene, the method comprising:

• supplying a cracked hydrocarbon feed to a fractional distillation column;
• separating a first ethylene fraction from the cracked hydrocarbon feed, the first ethylene fraction being a liquid phase and having an ethylene content of 99.95 wt. % ethylene or greater;
• separating a second ethylene fraction from the cracked hydrocarbon feed, the second ethylene fraction being in a vapor phase and having an ethylene content of 99.90 wt. % ethylene;
• separating a third ethylene fraction from the cracked hydrocarbon feed, the third ethylene fraction being in vapor phase and having a third ethylene content that is different from the first and second ethylene contents;
• wherein separating the first ethylene fraction in liquid phase and the second ethylene fractions and third ethylene fraction in vapor phases with different ethylene contents from the cracked hydrocarbon feed reduces energy consumption of the fractional distillation column by about 5% or greater.