Method of upgrading biomass, upgraded biomass, biomass water slurry and method of producing same, upgraded biomass gas, and method of gasifying biomass

A method of producing an upgraded biomass gas, comprising:

• performing upgraded treatment of cellulose based biomass with an oxygen/carbon atomic ratio of at least 0.5, in presence of water, under a pressure of at least that of saturated water vapor pressure, and at a temperature of 250 to 350° C. for a period of 5 to 120 minutes, and reducing said oxygen/carbon atomic ratio of said biomass from 0.216 to 0.38,
• separating an upgraded reactant obtained by said upgraded treatment into a solid component and a liquid component, and recovering said solid component which is an upgraded biomass with said oxygen/carbon atomic ratio of 0.216 to 0.38 whose recovered weight is at least 40% of the weight of said cellulose based biomass, and
• subjecting said recovering solid component to gasification treatment at a gasification temperature within a range from 800 to 1300° C. and a gasification pressure of 0.1 to 10 MPa, in presence of a gasifying agent comprising from 25 to 40% of a quantity of oxygen required for complete combustion, and a required quantity of steam.