System and method for extracting energy from agricultural waste

• US 6,824,682 B2
• Filed: 12/17/2002
• Issued: 11/30/2004
• Est. Priority Date: 12/18/2001
• Status: Active Grant

• Current Assignee: Best Biofuels LLC
• Original Assignee: Best Biofuels LLC
• Inventors: Branson, Jerrel Dale
• Primary Examiner(s): Prince, Fred G.
• Application Number:
  US10/320,744
• Publication Number:
  US 20030111410A1
• Time in Patent Office: 714 Days
• Field of Search: 210/603, 210/613, 210/259, 71/10, 71/21, 71/23, 518/700, 518/713, 518/714, 435/262, 435/262.5
• US Class Current: 210/603
• CPC Class Codes: C01B 2203/0216 containing a non-catalytic steam reforming step
• CPC Class Codes: C01B 2203/0222 containing a non-catalytic carbon dioxide reforming step
• CPC Class Codes: C01B 2203/0233 the reforming step being a steam reforming step
• CPC Class Codes: C01B 2203/0238 the reforming step being a carbon dioxide reforming step
• CPC Class Codes: C01B 2203/0283 containing a CO-shift step, i.e. a water gas shift step
• CPC Class Codes: C01B 2203/0495 the impurity being water
• CPC Class Codes: C01B 2203/06 Integration with other chemical processes
• CPC Class Codes: C01B 2203/061 Methanol production
• CPC Class Codes: C01B 2203/0883 by indirect heat exchange
• CPC Class Codes: C01B 2203/0894 Generation of steam
• CPC Class Codes: C01B 2203/1058 Nickel catalysts
• CPC Class Codes: C01B 2203/1211 Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
• CPC Class Codes: C01B 2203/1241 Natural gas or methane
• CPC Class Codes: C01B 2203/1258 Pre-treatment of the feed
• CPC Class Codes: C01B 2203/84 Energy production
• CPC Class Codes: C01B 3/34 by reaction of hydrocarbons with gasifying agents
• CPC Class Codes: C05F 17/00 Preparation of fertilisers characterised by biological or biochemical treatment steps, e.g. composting or fermentation
• CPC Class Codes: C07C 29/1518 one step being the formation of initial mixture of carbon oxides and hydrogen for synthesis
• CPC Class Codes: C07C 31/04 Methanol
• CPC Class Codes: C12M 21/12 for producing fuels or solvents C12M21/04 takes precedence; liquid carbonaceous fuels C10L1/00, solid fuels C10L5/00
• CPC Class Codes: C12M 43/02 : Bioreactors or fermenters combined with devices for liquid fuel extraction; Biorefineries
• CPC Class Codes: C12P 7/04 : acyclic
• CPC Class Codes: F24V 99/00 : Subject matter not provided for in other main groups of this subclass
• CPC Class Codes: Y02E 50/10 : Biofuels, e.g. bio-diesel
• CPC Class Codes: Y02E 50/30 : Fuel from waste, e.g. synthetic alcohol or diesel
• CPC Class Codes: Y02P 20/133 : Renewable energy sources, e.g. sunlight
• CPC Class Codes: Y02P 20/141 : Feedstock
• CPC Class Codes: Y02P 20/145 : the feedstock being materials of biological origin
• CPC Class Codes: Y02W 30/40 : Bio-organic fraction processing; Production of fertilisers from the organic fraction of waste or refuse

Abstract

The present invention relates to a process and apparatus for processing agricultural waste to make alcohol and/or biodiesel. The agricultural wastes are subjected to anaerobic digestion which produces a biogas stream containing methane, which is subsequently reformed to a syngas containing carbon monoxide and hydrogen. The syngas is converted to an alcohol which may be stored, sold, used, or fed directly to a reactor for production of biodiesel. The solids effluent from the anaerobic digester can be further utilized as slow release, organic certified fertilizer. Additionally, the wastewater from the process is acceptable for immediate reuse in agricultural operations.

Claims

1. A method for treating agricultural wastes comprising:

anaerobic digesting a mixture of at least agricultural waste and water to yield solids and a biogas including methane and carbon dioxide;

reforming the biogas including methane and carbon dioxide to a syngas including carbon monoxide and hydrogen in a steam reformation process;

converting the syngas containing carbon monoxide and hydrogen to methanol in an alcohol conversion process;

contacting at least a portion of the methanol with natural fats and/or oils in a transesterification reactor to form glycerine and methyl esters; and

separating the glycerine from the methyl ester.

2. The method according to claim 1, wherein the anaerobic digesting compriss digesting concentrated agricultural waste having a solids content of greater than about 4-8% that is heated prior to digestion.

3. The method according to claim 1, wherein prior to anaerobic digestion, the agricultural waste is concentrated up to about 30% solids, the concentrated agricultural waste then is contacted with water to produce an agricultural waste stream having a solids content from about 4% to about 8%.

4. The method according to claim 1, wherein the anaerobic digesting has a retention rime of less than about 30 days.

5. The method according to claim 1, wherein the agricultural waste is comprised primarily of animal manures.

6. The method according to claim 1, wherein the biogas produced by anaerobic digestion is purified to form a cleaned biogas stream prior to reforming.

7. The method according to claim 6, wherein the biogas is purified by passing the gas through a solvent vessel to remove entrained H₂S.

8. The method according to claim 7, wherein the biogas is purified by:

separating entrained moisture from the biogas by passing the gas through an inlet separator;

compressing the separated gas in a feed gas compressor to form a compressed gas stream; and

removing hydrogen sulfide in a hydrogen sulfide absorber wherein the compressed gas stream is contacted with methyldiethanolamine to produce a cleaned biogas stream.

9. The method according to claim 1, wherein reforming the biogas comprises:

heating the biogas;

reforming the biogas by mixing the heated biogas with steam in the presence of a catalyst to form a hot syngas stream; and

cooling the hot syngas stream to form a syngas stream.

10. The method according to claim 9, wherein the syngas stream comprises about 69 mol% hydrogen, about 13 mol % carbon dioxide, and about 17 mol % carbon monoxide.

11. The method according to claim 1, wherein converting the syngas to methanol comprises:

compressing the syngas to form a hot, compressed syngas stream;

converting the hot, compressed syngas into methanol in a methanol converter to form a hot methanol stream;

cooling the hot methanol stream to form a condensed methanol stream; and

separating condensed methanol from gas in a methanol separator.

12. The method according to claim 11, wherein additional carbon dioxide is not added to convert the syngas into methanol.

13. The method according to claim 11, wherein the methanol converter is a catalytic reactor containing a catalyst selected from ZnO—

Cr₃O₃ and CuO—

ZnO—

Al₂O₃.

14. The method according to claim 1, wherein at least a portion of the solids remaining after anaerobic digestion are removed and treated to form fertilizer.

15. A system for treating agricultural waste comprising:

an anaerobic digestion apparatus to digest agricultural waste and create solids and a biogas;

a biogas reformation apparatus to reform the biogas into a syngas comprising carbon monoxide and hydrogen;

and an alcohol conversion apparatus to convert the carbon monoxide and hydrogen into methanol;

transesterification reactor to react at least part of the methanol with natural fats and/or oils to form glycerine and methyl esters; and

a separation apparatus to separate the glycerine from the methyl esters.

16. The system according to claim 15, further comprising a biogas purification system, the biogas purification system comprising:

an inlet separator to separate entrained moisture from the biogas;

a feed gas compressor to compress the separated gas and to form a compressed gas stream; and

a hydrogen suit tie absorber to remove hydrogen sulfide by contacting the compressed gas stream with methyldiethanolamine to produce a cleaned biogas scream.

17. The system according to claim 15, wherein the biogas reformation apparatus comprises:

a heater to heat the biogas;

a reformer to reform the biogas by mixing the heated biogas with steam in the presence of a catalyst to form a hot syngas stream; and

a heat exchanger to cool the hot syngas scream with compressed air to form a syngas stream and a hot air stream.

18. The system according to claim 17, wherein the biogas reformation apparatus further includes an electricity generating apparatus.

19. The system according to claim 18, wherein the electricity generating apparatus comprises:

a compressor to compress the hot air stream from the heat exchanger

a turbine engine connected to the compresseor and to an electrical generator by a common shaft;

a combustion apparatus connected to the compressor and turbine engine to provide hot compressed air to the turbine engine; and

an electrical generator connected to the turbine engine by the common shaft.

20. The system according to claim 15, further comprising a distillation unit to distill the methanol product.

21. The system according to claim 20, wherein the distillation unit comprises a two-column distillation system comprising:

a product cooler to heat the methanol with a product methanol stream;

a tapping column to remove lights, the topping column comprising a column reflux condenser, and a purge condenser; and

a refining column to produce a product methanol stream, the refining column comprising at least a refining reflux condenser.