TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process Details : The pre-determined value of H2 / CO is 1.8 - 2.2. The gasification stage is carried out in a temperature zone maintained above 1000degreesC..The charge is contacted with an oxidizing agent in pyrolytic conditions to produce a primary gaseous effluent in a zone in which the solid charge is fluidized and the content of oxidizing gas is maintained below 10% molar ; the gaseous effluent produced is submitted to a finishing treatment in a secondary zone at 1000 - 1500degreesC. The supply of energy to the primary zone is effected by circulation of a solid heat carrier. preferably acidified silica-alumina. The solid charge is injected by means of a fluid such as CO2 or superheated water vapor, with exclusion of N2. In the second(purification) stage, treatments include reduction of water content, reduction of dust content, extraction of CO2 and compression of the synthesis gas. The third stage of Fischer-Tropsch synthesis comprises also a stage of filtration of waxes produced and a fractionating stage to recover a hydrocarbon cut having at least 10C, with a hydrocracking stage of the latter compounds. Part of the gaseous effluents from the third and fourth stages are recycled to the gasification stage. Part of the naphtha cuts are recycled to the primary or secondary zones of the first stage.Preferred Installation Details : The installation comprises means of gasification(zones Z1, Z2), purification (zone Z3), means of conversion of the synthesis gas by a Fischer-Tropsch reactor(zone Z4), fractionation of the liquid effluent to obtain a liquid fuel and naphtha cut(zones Z5, Z6) and recycling of the naphtha to zones Z1, Z2. EXAMPLE - The example was based on an information module based on the logic Pro II from SIMSCI. Calculations were effected on a 50 tonne/hour capacity installation using biomass, and operating at 0.4MPa. The biomass consisted of sawdust and was conveyed by combustion fumes composed of N2 and CO2 into a zone Z1 with a relative humidity of 10% in the presence of water vapor at 500degreesC. The effluents from Z1 were at 800degreesC. The finishing treatment of the synthesis gas in zone Z2 converted tars and residual methane and was effected at 1300degreesC. Zone Z3 comprised zones of compression, adjustment of the H2/CO molar ratio to 2.15 and extraction of CO2(by an amine wash). Zone Z4 comprised a Fischer-Tropsch reactor , a primary fractionater giving a head gas and liquid effluents which passed to a hydrocracking reactor. Zone Z5 comprised a de-butaniser and a naphtha withdrawal column. The cumulative production of gasoil and kersosene was 6906 kg/hour, i.e. a yield of 13.8% of biomass on dry base. The molar ratio H2 / CO was 1.87 on leaving zone Z1; conversion of methane and tars in Z2 resulted in a ratio drop to 1.60, and necessitated a adjustment of the synthesis gas to a ratio of 2.15.