Processes for producing low-ash biomass for combustion or pellets
View Patent ↗This invention provides processes and apparatus to convert biomass, including wood and agricultural residues, into low-ash biomass pellets for combustion, alone or in combination with another solid fuel. Some embodiments provide processes for producing low-ash biomass from cellulosic biomass, comprising providing an aqueous extraction solution with acetic acid; extracting the feedstock to produce an extract liquor containing soluble ash, hemicellulosic oligomers, acetic acid, dissolved lignin, and cellulose-rich solids; dewatering and drying the cellulose-rich, lignin-rich solids to produce a low-ash biomass; hydrolyzing the hemicellulosic oligomers to produce hemicellulosic sugars, wherein additional acetic acid is generated; removing a vapor stream comprising vaporized acetic acid from the extract; and recycling the vapor or its condensate to provide some starting acetic acid for the extraction solution. The disclosed processes can produce clean power from biomass. Co-products may include fermentable sugars, fermentation products such as ethanol, fertilizers, and lignin.
1. A process for producing low-ash biomass from cellulosic biomass, said process comprising:
(a) providing a feedstock comprising cellulosic biomass;
(b) providing an extraction solution comprising steam and/or hot water, and starting acetic acid;
(c) treating said feedstock with said extraction solution under effective extraction conditions to produce an extract liquor containing soluble ash, hemicellulosic oligomers, acetic acid, dissolved lignin, and cellulose-rich solids;
(d) separating at least a portion of said cellulose-rich solids from said extract liquor, to produce dewatered solids containing cellulose and lignin;
(e) concentrating said extract liquor in an intermediate evaporation stage at a pH of 4.8 or less to release vaporized acetic acid, and recycling at least a portion of said vaporized acetic acid derived from said intermediate evaporation stage back to said extraction solution;
(f) hydrolyzing said hemicellulosic oligomers contained in said extract liquor, under effective hydrolysis conditions, to produce hemicellulosic sugars, wherein said effective hydrolysis conditions release acetyl groups to generate additional acetic acid;
(g) removing a vapor stream comprising water and vaporized acetic acid from said extract liquor in at least one evaporation stage at a pH of 4.8 or less, to produce a concentrated extract liquor comprising said hemicellulosic sugars;
(h) recycling at least a portion of said vapor stream from step (g), or a condensed form thereof, back to step (b) to provide at least some of said starting acetic acid for said extraction solution and to provide heat for step (c); and
(i) drying said dewatered solids to produce said low-ash biomass.
2. The process of claim 1 , wherein said extraction solution comprises steam in saturated, superheated, or supersaturated form.
3. The process of claim 1 , wherein said extraction solution comprises hot water.
4. The process of claim 1 , wherein said extraction solution contains from about 0.01 wt % to about 10 wt % acetic acid.
5. The process of claim 1 , wherein said soluble ash includes one or more species selected from the group consisting of chlorine, chlorides, silica, silicates, metals, and combinations or derivatives thereof.
6. The process of claim 1 , wherein said effective hydrolysis conditions in step (f) include hydrolysis in the presence of heat and acetic acid.
7. The process of claim 1 , wherein said at least one evaporation stage in step (g) is controlled at a pH selected from about 3 to 4.8.
8. The process of claim 1 , wherein said low-ash biomass contains about the same moisture content as contained in said cellulosic biomass.
9. The process of claim 1 , wherein said low-ash biomass has higher energy density than said cellulosic biomass.
10. The process of claim 1 , wherein said low-ash biomass has lower inorganic emissions potential compared to said cellulosic biomass.
11. The process of claim 1 , said process further comprising combusting said low-ash biomass, to produce power.
12. The process of claim 11 , said process further comprising co-combusting lignin with said low-ash biomass, to produce power.
13. The process of claim 1 , said process comprising pelletizing said dewatered solids, optionally with lignin as a binder.
14. The process of claim 1 , said process comprising pelletizing said low-ash biomass, optionally with lignin as a binder.
15. The process of claim 1 , said process further comprising a step of fermenting said hemicellulosic sugars to a fermentation product.
16. The process of claim 15 , said process further comprising distilling said fermentation product to produce a purified fermentation product and a distillation bottoms stream; introducing said distillation bottoms stream to a bottoms evaporation stage, to produce residual solids; and then co-combusting at least a portion of said residual solids with said low-ash biomass, to produce power.
17. The process of claim 15 , said process further comprising distilling said fermentation product to produce a purified fermentation product and a distillation bottoms stream; introducing said distillation bottoms stream to a bottoms evaporation stage, to produce residual solids; and then recovering said residual solids as a fermentation co-product in solid, liquid, or slurry form for use as a fertilizer or fertilizer component.
18. A process for producing biomass pellets from cellulosic biomass, said process comprising:
(a) providing a feedstock comprising cellulosic biomass;
(b) providing an extraction solution comprising steam and/or hot water, and starting acetic acid;
(c) treating said feedstock with said extraction solution under effective extraction conditions to produce an extract liquor containing soluble ash, hemicellulosic oligomers, acetic acid, dissolved lignin, and cellulose-rich solids;
(d) separating at least a portion of said cellulose-rich solids from said extract liquor, to produce dewatered solids containing cellulose and lignin;
(e) concentrating said extract liquor in an intermediate evaporation stage at a pH of 4.8 or less to release vaporized acetic acid, and recycling at least a portion of said vaporized acetic acid derived from said intermediate evaporation stage back to said extraction solution;
(f) hydrolyzing said hemicellulosic oligomers contained in said extract liquor, under effective hydrolysis conditions, to produce hemicellulosic sugars, wherein said effective hydrolysis conditions release acetyl groups to generate additional acetic acid;
(g) removing a vapor stream comprising water and vaporized acetic acid from said extract liquor in at least one evaporation stage at a pH of 4.8 or less, to produce a concentrated extract liquor comprising said hemicellulosic sugars;
(h) recycling at least a portion of said vapor stream from step (g), or a condensed form thereof, back to step (b) to provide at least some of said starting acetic acid for said extraction solution and to provide heat for step (c); and
(i) pelletizing said dewatered solids, or a dried form thereof, to produce biomass pellets.