Anhydrous ethanol distillation method and apparatus

In a distillation method for recovering anhydrous ethanol from a dilute ethanol-containing feedstock that also contains dissolved gases, wherein the feedstock is introduced into a stripping and rectification section, a concentrated ethanol stream is removed from said stripping and rectification section and is introduced into a dehydrating tower, an azeotropic agent is also introduced into said dehydrating tower, a substantially azeotropic overhead is removed from said dehydrating tower, an anhydrous ethanol product is recovered from the bottom portion of said dehydrating tower, the substantially azeotropic overhead from said dehydrating tower is condensed and separated into an upper phase rich in azeotropic agent and a lower water-rich phase, the upper phase is returned to said dehydrating tower, and the lower water-rich phase is introduced into an azeotropic agent stripping tower wherein the azeotropic agent is recovered and returned to the system;

• the improvement which comprises the steps of:
• (a) providing in said stripping and rectification section a first stage distillation tower comprising an ethanol stripping tower and a second stage distillation tower comprising a stripper-rectifier tower;
• (b) preheating and splitting the feedstock to provide a preheated larger feed stream and a preheated smaller feed stream;
• (c) degassing said preheated larger feed stream and introducing the removed gases into the lower portion of said second stage distillation tower;
• (d) introducing the degassed larger feed stream into the top portion of said first stage distillation tower;
• (e) introducing said preheated smaller feed stream into said second stage distillation tower;
• (f) maintaining a higher pressure in said first stage distillation tower than in said second stage distillation tower;
• (g) maintaining a higher pressure in said dehydrating tower than in said first stage distillation tower;
• (h) condensing steam to supply the heat required in said dehydrating tower;
• (i) supplying the heat required in said first stage distillation tower by condensing said substantially azeotropic overhead from said dehydrating tower;
• (j) removing overhead ethanol-containing vapors from said first stage distillation tower and condensing said vapors to supply the heat required in said second stage distillation tower;
• (k) introducing the condensate from step (j) into said second stage distillation tower;
• and
• (l) obtaining said concentrated ethanol stream by removing the same from the upper portion of said second stage distillation tower.

In an apparatus for recovering anhydrous ethanol from a dilute ethanol-containing feedstock including a stripping and rectification section, a dehydrating tower adapted to be operated at a higher pressure than said stripping and rectification section, an azeotropic agent stripping tower, means for introducing the dilute ethanol-containing feedstock into said stripping and rectification section, means for removing a concentrated ethanol stream from said stripping and rectification section and introducing the same into said dehydrating tower, means for introducing an azeotropic agent into said dehydrating tower, means for removing a substantially azeotropic overhead from said dehydrating tower, means for removing an anhydrous ethanol product from the bottom portion of said dehydrating tower, means for condensing said substantially azeotropic overhead, means for separating the resultant condensate into an upper phase rich in said azeotropic agent and a lower water-rich phase, means for returning said upper phase to said dehydrating tower, means for introducing said lower phase into said azeotropic agent stripping tower, and means for recovering said azeotropic agent from said azeotropic agent stripping tower and returning the same to said dehydrating tower;

• the improvement wherein:
• said stripping and rectification section comprises a first stage distillation tower comprising an ethanol stripping tower and a second stage distillation tower comprising a stripper-rectifier tower, said first stage distillation tower being adapted to be operated at a higher pressure than said second stage distillation tower;
• said apparatus further includes means for preheating said feedstock;
• means for splitting the preheated feedstock into two preheated feed streams of unequal size;
• means for further preheating the larger of said feed streams;
• means for introducing said larger feed stream into the top portion of the said first stage distillation tower;
• means for introducing the smaller of said feed streams into said second stage distillation tower;
• means for condensing steam to supply the heat required in said higher pressure dehydrating tower;
• first condenser-reboiler means connected to said first stage distillation tower;
• means for introducing said substantially azeotropic overhead from said dehydrating tower into said first condenser-reboiler means, whereby the heat required in said first stage distillation tower is supplied by condensation of said substantially azeotropic overhead from said higher pressure dehydrating tower;
• second condenser-reboiler means connected to said second stage distillation tower;
• means for removing overhead ethanol-containing vapors from the higher pressure first stage distillation tower and introducing them into said second condenser-reboiler means for supplying the heat required in said second stage distillation tower;
• means for introducing the condensate from said second condenser-reboiler means into said second stage distillation tower;
• and means for withdrawing bottoms streams from said first and second stage distillation towers;
• said means for removing a concentrated ethanol stream comprises means for withdrawing a concentrated ethanol stream from the upper portion of said second stage distillation tower;
• said means for preheating said feedstock comprises condenser-preheater means for condensing overhead vapors from said second stage distillation tower;
• means for passing said feedstock, prior to splitting thereof, in heat exchange relation through said condenser-preheater means for initially preheating said feedstock;
• and heat exchange means for further preheating said feedstock by the heat contained in a bottoms stream withdrawn from at least the first of said first and second stage distillation towers;
• and
• said means for further preheating said larger feed stream comprises heat exchange means for effecting said further preheating by the heat contained in the bottoms stream withdrawn from said first stage distillation tower.