NOVELTY - Producing (M1) low-ash biomass involves treating cellulosic biomass with extraction solution comprising steam and/or hot water, and starting acetic acid to produce an extract liquor containing soluble ash, hemicellulosic oligomers, acetic acid, dissolved lignin, and cellulose-rich solids; separating cellulose-rich solids to produce dewatered solids; hydrolyzing hemicellulosic oligomers to produce hemicellulosic sugars; removing and recycling a vapor stream from extract liquor to produce a concentrated extract liquor; and drying the dewatered solids to produce the low-ash biomass.    USE - For producing low-ash biomass useful for producing power and fertilizer (claimed).    ADVANTAGE - The method produces low-ash biomass that contains the same moisture content as contained in the cellulosic biomass, has higher energy density than the cellulosic biomass, has lower inorganic emissions potential compared to the cellulosic biomass; and recovers co-product including fermentable sugars, fermentation products such as ethanol, fertilizers, and lignin.    DETAILED DESCRIPTION - Producing (M1) low-ash biomass from cellulosic biomass, involves a) providing a feedstock comprising cellulosic biomass; b) providing an extraction solution comprising steam and/or hot water, and starting acetic acid; c) treating the feedstock with the 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 the cellulose-rich solids from the extract liquor, to produce dewatered solids containing cellulose and lignin; e) hydrolyzing the hemicellulosic oligomers contained in the extract liquor, under effective hydrolysis conditions, to produce hemicellulosic sugars, where the effective hydrolysis conditions release acetyl groups to generate additional acetic acid; f) removing a vapor stream comprising water and vaporized acetic acid from the extract liquor in at least one evaporation stage at a pH of less than or equal to 4.8 to produce a concentrated extract liquor comprising the hemicellulosic sugars; g) recycling at least a portion of the vapor stream from step (f), or its condensed form, back to step (b) to provide at least some of the starting acetic acid for the extraction solution and to provide heat for step (c); and h) drying the dewatered solids to produce the low-ash biomass. INDEPENDENT CLAIMS are included for the following:    (1) producing power from cellulosic biomass, involving performing step of (a)-(g) (M1); and combusting the dewatered solids, or its dried form to produce power; and    (2) producing biomass pellets from cellulosic biomass, involving performing step of (a)-(g) (M1); and pelletizing the dewatered solids, or its dried form to produce biomass pellets.