Multi-stage scrubbing system and method for ethanol vent streams

1. A multi-stage scrubbing method for improving the yield of ethanol during ethanol production from corn comprising:

producing a vent stream from the fermentation of corn mash during ethanol production, the vent stream consisting essentially of carbon dioxide, ethanol and volatile organic compounds;

directing the vent stream into a pre-scrubber system comprising a pre-scrubber column;

pre-scrubbing and cooling the vent stream with a cooled pre-scrubber fluid distributed by countercurrent flow by a fluid distributor to produce a cooled pre-scrubbed vent stream;

directing the cooled pre-scrubbed vent stream from the pre-scrubber system into a main scrubber system comprising a column having a fluid flow capacity that is less than the pre-scrubber column, the main scrubber system being fluidly coupled in series to the pre-scrubber system;

recirculating at least a portion of a fluid discharge stream from the pre-scrubber system back into the pre-scrubber system through the fluid distributor;

scrubbing the pre-scrubbed vent stream with a main scrubber fluid; and

recirculating at least a portion of a fluid discharge stream from the main scrubber system into the pre-scrubber system through the fluid distributor,

wherein said multi-stage scrubbing method improves the yield of ethanol from the ethanol production process by about 1.5%.

2. The multi-stage scrubbing method of claim 1 wherein said pre-scrubber:

system includes a first outlet for discharging said pre-scrubbed vent stream and a second outlet for discharging said discharge stream of pre-scrubber fluid.

3. The multi-stage scrubbing method of claim 1 further comprising discharging a discharge stream of scrubber fluid through an outlet in said main scrubber system and recirculating at least a portion of the discharge stream of scrubber fluid to the pre-scrubber system through the fluid distributor.

4. The multi-stage scrubbing method of claim 3 wherein the pre-scrubber fluid is a mixture of the discharge streams from the pre-scrubber system and the main scrubber system.

5. The multi-stage scrubbing method of claim 4 , further comprising cooling the pre-scrubber fluid by a heat exchanger prior to pre-scrubbing the vent stream.

6. The multi-stage scrubbing method of claim 5 further comprising directing a first portion of the discharge stream of pre-scrubber fluid to a distillation system and recirculating a second portion of the discharge stream of pre-scrubber fluid to the pre-scrubber system through the fluid distributor.

7. The multi-stage scrubbing method of claim 6 further comprising directing a first portion of the discharge stream of scrubber fluid to a slurry tank and recirculating a second portion of the discharge stream of scrubber fluid to the pre-scrubber system through the fluid distributor.

8. The multi-stage scrubbing method of claim 3 wherein the pre-scrubber system includes an inlet in fluid communication with an outlet of a fermentation vessel for receiving the vent stream.

9. The multi-stage scrubbing method of claim 3 , further comprising transferring the pre-scrubbed vent stream to the main scrubber system by a blower operably coupled between the first outlet of the pre-scrubber system and the inlet of the main scrubber system.

10. A multi-stage scrubbing method for improving the yield of ethanol during an ethanol production process comprising:

producing a vent stream from the fermentation of corn mash during ethanol production, the vent stream consisting essentially of carbon dioxide, ethanol and volatile organic compounds;

directing the vent stream into a first scrubber system comprising a first scrubber column;

allowing the vent stream to migrate up the first scrubber column;

scrubbing and cooling the vent stream by distributing a cooled first scrubber fluid by countercurrent flow to wash and cool said vent stream to produce a cooled pre-scrubbed vent stream;

directing the cooled pre-scrubbed vent stream from the first scrubber column into a second scrubber system comprising a second scrubber column, said second scrubber column having a fluid flow capacity that is less than the first scrubber column; and

scrubbing the pre-scrubbed vent stream with a second scrubber fluid,

wherein said multi-stage scrubbing method improves the yield of ethanol from the ethanol production process by about 1.5%.

11. The multi-stage scrubbing method of claim 10 , further comprising collecting a fluid discharge stream from the first scrubber system and recirculating at least a portion of the fluid discharge stream back into the first scrubber system.

12. The multi-stage scrubbing method of claim 11 , further comprising collecting a fluid discharge stream from the second scrubber system and recirculating at least a portion of the fluid discharge stream from the second scrubber system into the first scrubber system.

13. The multi-stage scrubbing method of claim 12 wherein the first scrubber fluid is a mixture of the fluid discharge streams from the first and second scrubber systems.

14. The multi-stage scrubbing method of claim 13 wherein a first portion of the fluid discharge stream from the first scrubber system is directed to a distillation system and a second portion of the fluid discharge stream from the first scrubber system is recirculated into the first scrubber system.

15. The multi-stage scrubbing method of claim 14 wherein a first portion of the fluid discharge stream from the second scrubber system is directed to a slurry tank and a second portion of the fluid discharge stream from the second scrubber system is recirculated into the first scrubber system.

16. The multi-stage scrubbing system of claim 13 , further comprising providing a first pump and a first control valve for controllably recirculating the fluid discharge stream from the first scrubber system.

17. The multi-stage scrubbing system of claim 16 , further comprising providing a second pump and a second control valve for controllably recirculating the fluid discharge stream from the second scrubber system.

18. The multi-stage scrubbing method of claim 13 , the cooled first scrubber fluid is cooled in a heat exchanger.