NOVELTY - The method comprises supplying solid fuel into a drying zone in the pyrolysis reactor, drying the solid fuel in the drying zone and removing moisture containing gases from the solid fuel, passing the dried solid fuel and the bed material horizontally from the drying zone to the pyrolysis zone arranged sequentially in horizontal direction in the pyrolysis reactor, pyrolyzing the dried solid fuel for separating pyrolysis gases from the dried solid fuel, and conducting the pyrolysis gases from the pyrolysis reactor to a condenser.    USE - The method is useful for carrying out pyrolysis of solid fuel such as wood, wood chips, saw dust, peat or any other solid biomass in an apparatus to produce pyrolysis oil (claimed).    ADVANTAGE - The method is capable of effectively, economically, easily and rapidly pyrolyzing the solid fuel thus producing the pyrolysis oil with optimum water content.    DETAILED DESCRIPTION - The method comprises supplying solid fuel into a drying zone in the pyrolysis reactor, drying the solid fuel in the drying zone and removing moisture containing gases from the solid fuel, passing the dried solid fuel and the bed material horizontally from the drying zone to the pyrolysis zone arranged sequentially in horizontal direction in the pyrolysis reactor, pyrolyzing the dried solid fuel for separating pyrolysis gases from the dried solid fuel, conducting the pyrolysis gases from the pyrolysis reactor to a condenser for producing pyrolysis oil or conducting the moisture containing gases out of the pyrolysis reactor in the drying zone, controlling moisture content of the pyrolysis oil by adjusting the drying of the solid fuel in the drying zone, analyzing the moisture content of the produced pyrolysis oil for controlling the drying of the solid fuel in the drying zone, adjusting residence time of the solid fuel in the drying zone by adjusting the movement speed of the solid fuel through drying zone, adjusting the temperature in the drying zone, adjusting the supply rate of solid fuel into the pyrolysis reactor, adjusting the removal rate of moisture containing gases from the drying zone, drying the solid fuel in the drying zone to moisture content of 4-10 wt.%, passing the bed material and the solid fuel in horizontal direction through the pyrolysis reactor, controlling temperature in the drying zone by adjusting temperature of the bed material supplied to the drying zone of the pyrolysis reactor, adjusting the drying of the solid fuel in the drying zone by adjusting the speed of the fluidizing gas fed into the drying zone, and feeding bed material to the pyrolysis process from a fluidized bed boiler consisting of bubbling fluidized bed boiler and circulating fluidized bed boiler. The pyrolysis process is carried out in connection with a fluidized bed boiler, and a heat required for the pyrolysis process is supplied partly by bed material of the fluidized bed boiler. The bed material of the fluidized bed boiler is circulated through the pyrolysis reactor and fluidized in the pyrolysis reactor by fluidizing gas. The pyrolysis gases separated from the solid fuel in the pyrolysis reactor are condensed in to liquid form as pyrolysis oil. The bed material of the fluidized bed boiler and the solid fuel are passed through the pyrolysis reactor in transverse direction in relation to the flow direction of the fluidizing gas. The fluidizing gas is fed to the pyrolysis process underneath the bed material. An INDEPENDENT CLAIM is included for a pyrolysis apparatus.    DESCRIPTION OF DRAWING(S) - The diagram shows a side view of a pyrolysis reactor.    Fluidizing nozzles (5)    Pyrolysis gas outlets (6)    Bed material outlets (12)    Moisture outlets (20)    Partition wall (24)    Bed material. (40)