TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The biological hydrocarbons of the second hydrocarbon stream comprise tall oil or tall oil fatty acids. The lignocellulosic material is waste and/or by-products of the wood-processing industry. The biomass is selected from municipal waste, industrial waste or by-products, agricultural waste or by-products, waste or by-products of the wood-processing industry, waste or by-products of the food industry, and/or marine plants. The biological origin of the Fischer-Tropsch paraffins comprise biomass selected from virgin and waste materials of plant, animal and/or fish origin, and the biological hydrocarbons are based on oils, fats and/or waxes of plant, animal and/or fish origin. The biological origin of the Fischer-Tropsch paraffins comprise waste or by-product(s) of the wood-processing industry.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The first hydrocarbon stream is provided by gasification of biomass feedstock to provide synthesis gas; Fischer-Tropsch reaction of the synthesis gas to provide 1C to greater than or equal to 100C paraffins; separating 1-4C paraffins, 5-20C paraffins and 21C to greater than or equal to 100C paraffins; removing the 1-4C paraffins and the 5-20C paraffins; and cracking/isomerization of the resulting 21C to greater than or equal to 100C paraffins to increase the proportion of diesel hydrocarbon 11-20C paraffins in the resulting first hydrocarbon stream. The second hydrocarbon stream is provided by hydrodeoxygenation of the biological hydrocarbon feedstock to provide a stream of saturated predominantly 15-18C paraffins and by an optional hydrodeoxygenation of the 5-20C paraffins; and non-cracking hydroisomerization of the paraffins to increase the proportion of iso-paraffins in the resulting second hydrocarbon stream. In the process, where 3-95% of the first and 5-97% of the second hydrocarbon streams are combined in a separator, in which the resulting mixed stream is fractionated into a middle distillate comprising 11-20C hydrocarbons and a light fraction comprising hydrogen and 1-4C hydrocarbons, and the middle distillate is recovered for use as diesel fuel. The process also recovered, a heavy fraction comprising 21C to greater than or equal to 100C hydrocarbons and a naphtha fraction comprising 5-10C hydrocarbons. In the process, where at least a part of the heavy fraction is re-circulated to the cracking/isomerization to be cracked and hydroisomerized to increase the amount of 11-20C hydrocarbons in the first hydrocarbon stream. The fractionation is set to provide a distillate fraction consisting of 15-18C hydrocarbons. The process is operated in connection with of a wood-processing industry and the biological feeds to the integrated process originate in or as by-products or waste of the wood-processing industry. The wood-processing industry comprises a Kraft mill producing crude tall oil and/or tall oil fatty acids. In the process, where water produced in the integrated fuel process is supplied to the wood-processing industry for purification and where sulfur freed in the fuel process is fed to the sulfur circulation of the wood-processing industry. The integrated fuel process is further integrated with a pulp and paper mill, where waste and/or by-products of the pulp and paper mill are utilized as raw materials for the fuel process and where wastes and energy from the fuel process are handled and/or utilized in unit operations of the pulp and paper mill. The fraction contains at least 25 (preferably greater than or equal to 40-80)% of 15-18C hydrocarbons. EXAMPLE - No suitable example given.