NOVELTY - A system (1) for gasification of biomasses to produce combustible gas, comprises a fixed-bed gasifier (10) in which the biomass undergoes a controlled combustion in oxygen deficiency, to provide sufficient energy to trigger a pyrolysis process, which boils tars contained in the biomass, to release hydrocarbons and combustible gases, and thus produce a gaseous fuel; and an oxygen supply system (2) to feed/supply air enriched with oxygen into the gasifier, to promote the controlled combustion of the biomass.    USE - As a system for gasification of biomasses, to produce combustible gas (claimed) or syngas, which is supplied to electrical and thermal power-generating plants.    ADVANTAGE - The gasifier's performance is improved, in terms of quality and composition of the syngas produced from gasifier, by enriching the gasification air with oxygen, thus consequently improving the performance/yield of the electricity generator connected to the gasifier. The biomass gasification system provides an increase in the heating value of the syngas produced from the gasifier, thus increasing the electrical yield of the electrical generator. The electrical yield is maximized using same thermal power input. The greater heating value of the syngas, allows the engine of the electricity generator to work at a higher-performance torque speed and with an optimal running curve, thus reducing the maintenance interventions, and increasing the reliability of the power plant. The greater reactivity of the oxygen-enriched air, favors complete extraction of the carbon from the biomass, thus increasing the carbon yield, and reducing the amount of carbon lost in the ashes; and prevents the formation of vapors of complex organic compounds such as tars, thus increasing the purity of the syngas in terms of tar, which facilitates cleaning related to scrubbing and filtration, and reduces the pollution load of scrubbing water. The system provides reduction in investments; and widens the range of biomasses compatible with the gasification process, using biomasses with a lower heating value and a greater moisture content. The system uses the source of oxygen to provide oxygen and/or ozone gases for the treatment/regeneration of the scrubbing water in a closed circuit that provides in-line removal of the pollutants such as biological oxygen demand (BOD) and chemical oxygen demand (COD).    DETAILED DESCRIPTION - A system (1) for gasification of biomasses to produce combustible gas, comprises a fixed-bed gasifier (10) in which the biomass undergoes a controlled combustion in oxygen deficiency, to provide sufficient energy to trigger a pyrolysis process, which boils tars contained in the biomass, to release hydrocarbons and combustible gases, and thus produce a gaseous fuel; and an oxygen supply system (2) to feed/supply air enriched with oxygen into the gasifier, to promote the controlled combustion of the biomass. The oxygen supply system includes an on-site oxygen production system (20); at least one cryogenic tank (21) for storage of liquid oxygen, and a vaporizer (22) to transform the liquid oxygen into gaseous oxygen; cylinders or cylinder packs (23) in which compressed gaseous oxygen is stored; and control valves (27, 27') to control the amount of oxygen input to the gasifier. The oxygen supply system is further connected to an auxiliary water system (4), for feeding oxygen into the auxiliary water system, to remove pollutants contained in water, in the form of process residues. An INDEPENDENT CLAIM is included for a biomass gasification method to produce combustible gas, involving introducing biomass into the fixed-bed gasifier, so that the biomass undergoes a controlled combustion in oxygen deficiency, to produce a gaseous fuel; and introducing oxygen-enriched air into the gasifier, to promote the controlled combustion of the biomass.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a complete gasification system.    System for gasification of biomasses (1)    Oxygen supply system (2)    Optimization system (3)    Auxiliary water system (4)    Electric generator (5)    Power user (7)    Electrical main (8)    Fixed-bed gasifier (10)    Input nozzles of gasifier (15, 15')    Gas outlet duct (16)    On-site oxygen production system (20)    Cryogenic tank (21)    Vaporizer (22)    Cylinders in which compressed gaseous oxygen is stored (23)    Delivery lines for oxygen-enriched air (25, 25')    Control valves to control amount of oxygen input to gasifier (27, 27')    Filters (35, 36, 37)    Engine of the electrical generator (53)    Electrical panel. (56)