Gas recycle loops in process for converting municipal solid waste into ethanol

1. A facility for converting organic materials into ethanol comprising:

a gasifier comprising one or more vessels, an inlet designed to accept solid organic materials, a steam inlet in fluid communication with a steam boiler, and a primary syngas outlet, and means for creating a primary syngas stream;

a syngas compressor comprising one or more pumps configured to raise the pressure of a compressor inlet stream comprising at least a portion of the primary syngas stream to a predefined level, thereby outputting a compressed gas stream; and

a main gas recycle loop comprising:

a gas recycle compressor comprising one or more pumps of sufficient power to circulate gas through the main gas recycle loop;

one or more alcohol synthesis reactors, comprising a catalyst, means for controlling the temperature of the catalyst, a reactor inlet in fluid communication with the syngas compressor which is configured to pass a reactor inlet stream comprising at least a portion of a combined recycle gas stream over the catalyst and to a reactor effluent stream, and a reactor outlet configured to pass the reactor effluent stream, wherein in operation the reactor effluent stream comprises unconverted syngas and a mixture of reaction products including alcohols and water;

a recycle separator configured to separate at least the majority of the reactor effluent stream into a mixed alcohol stream, the majority of which is composed of water and alcohols, and a gas recycle stream, the majority of which is composed of unconverted syngas; and

mixing means for mixing at least a portion of the gas recycle stream with at least a portion of the compressed syngas to create the combined recycle gas stream.

2. The facility of claim 1 , further comprising a purification unit comprising one or more separators in fluid communication, wherein the separators take at least a portion of the mixed alcohol stream as an input, and are configured to separate the mixed alcohol stream into a plurality of streams comprising an ethanol stream comprising primarily ethanol.

3. The facility of claim wherein the plurality of streams further comprises a water stream comprising primarily water.

4. The facility of claim 3 , wherein the recycle separator comprises a water absorption column, wherein the water used for absorption comprises at least a portion of the water stream.

5. The facility of claim 2 , wherein the plurality of streams further comprise:

a methanol stream comprising primarily methanol; and

a heavy alcohol stream comprising primarily propanol and heavier alcohols.

6. The facility of claim 1 , further comprising a purification unit comprising a separator configured to separate at least a portion of the mixed alcohol stream into a methanol-ethanol stream comprising the substantial majority of the ethanol from the mixed-alcohol stream, and a stream comprising the substantial majority of water and of alcohols heavier than ethanol from the mixed-alcohol stream.

7. The facility of claim 1 , wherein the main gas recycle loop further comprises a heat exchanger configured to transfer heat from the reactor effluent stream to a stream within the main gas recycle loop downstream of the mixing means and upstream of the one or more alcohol synthesis reactors.

8. The facility of claim 1 , further comprising control means configured to control the power of the gas recycle compressor to maintain the pressure of the reactor inlet stream near a predetermined value within the range of about 95 bar and about 155 bar.

9. The facility of claim 1 , wherein the main gas recycle loop further comprises a carbon dioxide separator configured to separate carbon dioxide from the recycle loop stream at a location downstream of the mixing means and upstream of the alcohol synthesis reactor.

10. The facility of claim 1 , wherein the catalyst is a suifidized catalyst, further comprising continuous injection means, at a location downstream of the mixing means and upstream of the alcohol synthesis reactor, for injecting a sulfiding agent, and control means to ensure that the sulfiding agent is approximately at a predetermined level within the syngas entering the alcohol synthesis reactor.

11. The facility of claim 10 , wherein said predetermined level is between about 25 to about 150 ppm on a volumetric basis.

12. The facility of claim 1 , wherein the main gas recycle loop further comprises:

a combustion turbine and generator;

means for conveying a minor portion of the gas within the main gas recycle loop to the combustion turbine, to be burned in the combustion turbine;

a generator for generating electricity from the mechanical energy of the combustion turbine.

13. The facility of claim 1 , wherein the recycle separator comprises an outlet, further comprising:

a mixed alcohol degassing separator operating at a lower pressure than the pressure of the recycle separator and taking at least a portion of the mixed alcohol stream as an input, configured to separate at least a portion of the mixed alcohol stream into a low-pressure gas recycle stream rich in unconverted syngas, and a second mixed alcohol stream rich in water and alcohols; and

means for conveying at least a portion of the mixed alcohol stream to the mixed alcohol degassing separator, said means further comprising means for decreasing the pressure of the portion of the mixed alcohol stream.

14. The facility of claim 13 , wherein the lower pressure is at least half the pressure of the pressure within the recycle separator.

15. The facility of claim 14 , wherein the lower pressure is less than about 2 bar absolute pressure.

16. The facility of claim 13 , further comprising means for conveying at least a portion of the low-pressure gas recycle stream to a mixing point upstream of the syngas compressor, thereby recycling the low-pressure gas recycle stream.

17. The facility of claim 13 , further comprising:

a heat exchanger configured to transfer heat from the mixed alcohol stream to a stream comprising at least a first portion of the water stream;

wherein the mixed alcohol degassing separator comprises a water absorption column, wherein the water used for absorption comprises at least a portion of said first portion of the water stream.

18. A method of converting organic materials into ethanol comprising:

providing the facility of claim 1 ;

feeding organic materials to the inlet;

creating a primary syngas stream;

in the syngas compressor, raising the pressure of the compressor inlet stream to the predefined level, thereby outputting a compressed gas stream; and

circulating gas within the main recycle loop.