NOVELTY - The method comprises introducing a feed material to be subjected to gasification into a dual fluidized bed gasifier (10) comprising a pyrolyzer (20) connected with a combustor (30) such that a circulation stream comprising a heat transfer material is continuously circulated between the pyrolyzer, in which the temperature of the circulation stream is reduced, and the combustor, in which the temperature of the circulation stream is increased, where the combustor increases the temperature of the circulation stream via combustion of char with the circulation stream and a supplemental fuel (8).    USE - The method is useful for gasifying (claimed) carbonaceous materials for a production of synthesis gas that is useful in a Fischer-Tropsch synthesis of hydrocarbons, production of power, production of non-Fischer-Tropsch chemicals/fuels, where the carbonaceous materials are shredded bark, wood chips, sawdust, sewage sludge, municipal solid waste, refuse derived fuel and a variety of other carbonaceous materials.    ADVANTAGE - The method is capable of controlling a gasification temperature via the use of supplemental fuel to the combustor of the gasifier so as to provide an appropriate synthesis gas for a desired downstream application, and to reduce an amount of an undesired product such as methane and/or tars in the gasifier product gas, and reducing environmental emissions.    DETAILED DESCRIPTION - The method comprises introducing a feed material to be subjected to gasification into a dual fluidized bed gasifier (10) comprising a pyrolyzer (20) fluidly connected with a combustor (30) such that a circulation stream comprising a heat transfer material is continuously circulated between the pyrolyzer, in which the temperature of the circulation stream is reduced, and the combustor, in which the temperature of the circulation stream is increased, where the pyrolyzer converts a portion of the feed material into a gasifier product gas comprising hydrogen and carbon monoxide, and the combustor increases the temperature of the circulation stream via combustion of char with the circulation stream and a supplemental fuel (8). The supplemental fuel is: introduced into the combustor separately from the circulation stream; directly introduced into the combustor; combined with the circulation stream prior to introduction into the combustor; combined with the circulation stream upstream of the pyrolyzer; and introduced into the pyrolyzer. The supplemental fuel comprises a dryer vent gas stream comprising volatile organic compounds. The drying step further comprises utilizing a portion of the heat from a flue gas produced in the combustor to dry the feed material. The subjecting step comprises scrubbing tar from the gasifier product gas with an absorption liquid to provide a tar-reduced product gas and a spent scrubbing liquid comprising tar and utilizing a portion of the spent scrubbing liquid as supplemental fuel to the combustor. The absorption liquid is aqueous or oil-based. The portion of the product upgrading tailgas is introduced as supplemental fuel for the combustor and the feed material for the pyrolyzer. The gasifier product gas comprises a molar ratio of hydrogen to carbon monoxide. The method further comprises: producing the supplemental fuel upstream of the dual fluidized bed gasifier; drying a portion of the feed material to reduce the moisture content prior to introduction into the pyrolyzer, where the drying produces a dryer vent gas comprising volatile organic compounds; scrubbing the volatile organic compounds from the dryer vent gas; utilizing the volatile organic compound-reduced dryer vent gas from a scrubber as the supplemental fuel; producing the supplemental fuel downstream from the dual fluidized bed gasifier; subjecting a portion of the gasifier product gas to tar removal and utilizing a portion of the removed tar as the supplemental fuel to the combustor; introducing a portion of the spent scrubbing liquid to the pyrolyzer to produce additional synthesis gas; utilizing a portion of the gasifier product gas to produce power and in a catalytic operation downstream of the dual fluidized bed gasifier; subjecting a portion of the gasifier product gas to Fischer-Tropsch synthesis for producing Fischer-Tropsch hydrocarbons and a Fischer-Tropsch tailgas; utilizing a portion of the Fischer-Tropsch tailgas as supplemental fuel; utilizing a portion of the Fischer-Tropsch tailgas as the feed material; separating a spent catalyst material comprising Fischer-Tropsch catalyst and Fischer-Tropsch hydrocarbon products and introducing a portion of the spent catalyst material to the dual fluidized bed gasifier; utilizing a portion of the spent catalyst material as the supplemental fuel for the combustor and the feed material for the pyrolyzer; subjecting a portion of the Fischer-Tropsch hydrocarbons to product upgrading, where product upgrading produces a product upgrading tailgas; introducing a portion of the product upgrading tailgas to the dual fluidized bed gasifier; obtaining a desired molar ratio by adjusting an amount of the supplemental fuel; adjusting the amount of the supplemental fuel to alter an amount of methane in the gasifier product gas; reducing the amount of tar in the gasifier product gas by increasing the temperature of the circulation stream introduced into the pyrolyzer by increasing the amount of the supplemental fuel introduced into the combustor; producing a product consisting of Fischer-Tropsch hydrocarbons, power and non-Fischer-Tropsch chemicals; performing VSA and PSA for producing a tailgas consisting of a VSA tailgas and a PSA tailgas; introducing a portion of the tailgas to the dual fluidized bed gasifier; from the portion of the gasifier product gas downstream of the dual fluidized bed gasifier; utilizing a portion of a hydrocarbon-containing fluid produced downstream of the dual fluidized bed gasifier as the supplemental fuel for the combustor; introducing the supplemental fuel into the combustor without directly contacting a refractory with the supplemental fuel prior to combination of the supplemental fuel with the contents of the combustor; and operating the gasifier at a lower pressure during turndown such that a velocity of the gasifier product gas exiting the pyrolyzer is constant during turndown and production. The portion of the at least one tailgas is introduced as the supplemental fuel for the combustor and the feed material for the pyrolyzer. The supplemental fuel is primarily liquid, primarily solid or primarily gaseous. The supplemental fuel comprises primarily a low pressure gas. An INDEPENDENT CLAIM is included for a dual fluidized bed gasification system.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a gasification system.    Supplemental fuel (8)    Dual fluidized bed gasifier (10)    Pyrolyzer (20)    Combustor (30)    Downstream processing unit. (55)