Patent ID: 8597431

Claim:
A method for pre-treating biomass, comprising: steaming biomass in a steaming bin; processing the steamed biomass in a first pressurized pretreatment reactor which contains the biomass, acid and liquids, wherein the process disperses sugars in the biomass to the liquids, wherein the processing of the steamed biomass is performed under pressure in the first pretreatment reactor removing at least some portion of the liquids with the sugars from the processed biomass to generate substantial solids; feeding the substantial solids to a second pressurized pretreatment reactor while maintaining the substantial solids under pressure from the first pretreatment reactor to the second pressurized pretreatment reactor; processing the substantial solids in the second pretreatment reactor at a pH level in a range of 1.3 to 2.0 pH and under pressure; applying a rapid pressure drop to the substantial solids in the second pretreatment reactor or as the processed biomass flows from the second pretreatment reactor, wherein the rapid pressure drop opens up a cellulosic structure of the substantial solids; and sending the substantial solids with opened cellulosic structure to at least one of a saccharification process and a fermentation process for ethanol processing.