NOVELTY - Pyrolysis system (S1) comprises: (a) a pyrolysis chamber; (b) a feeding mechanism for feeding biomass into the pyrolysis chamber; (c) a heating mechanism for heating the pyrolysis chamber, where the heating mechanism produces exhaust gas; and (d) an air exclusion mechanism for excluding air from the pyrolysis chamber, and including a channel for conveying the exhaust gas from the heating mechanism to the feeding mechanism.    USE - The pyrolysis system is useful for producing liquid hydrocarbons (claimed), such as biodiesel.    ADVANTAGE - The pyrolysis system: is capable of processing pieces of various plants in larger sizes and producing liquid biofuel with high quality; and does not allow to air to enter the process.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a method (M1) for producing liquid hydrocarbons, comprising (a1) feeding biomass into a pyrolysis chamber, (b1) using a heating mechanism to heat the pyrolysis chamber, thus pyrolyzing the biomass to produce the liquid hydrocarbons, and (c1) excluding air from the pyrolysis chamber at least in part by directing the exhaust gas through at least a portion of the biomass as the biomass is fed into the pyrolysis chamber;    (2) a pyrolysis system (S2) comprising (a2) a pyrolysis chamber having an output end, (b2) an accumulation chamber for receiving char from the pyrolysis chamber, (c2) a removal mechanism for removing the char from the accumulation chamber, and (d2) an exclusion mechanism for excluding air from the pyrolysis chamber and including a sensor for sensing whether there is sufficient char in the accumulation chamber to block the output end so that a portion of the char can be removed from the accumulation chamber without allowing air to enter the pyrolysis chamber from the accumulation chamber;    (3) a method (M2) for producing liquid hydrocarbons, comprising (a3) pyrolyzing biomass in a pyrolysis chamber, thus producing the liquid hydrocarbons and char, (b3) receiving the char into an accumulation chamber via an output end of the pyrolysis chamber, and (c3) removing a portion of the char from the accumulation chamber while leaving sufficient char in the accumulation chamber in a manner that blocks air from entering the output end from the accumulation chamber;    (4) a pyrolysis system (S3) comprising the components (a), (b2) and (c2) as above per se, where the removal mechanism is adapted to actively cool the char below a temperature of spontaneous ignition;    (5) a method (M3) of producing liquid hydrocarbons, comprising (a4) pyrolyzing biomass, thus producing the liquid hydrocarbons and char, where the char is produced at a temperature above a temperature of spontaneous ignition, and (b4) actively cooling the char below the temperature of spontaneous ignition;    (6) a pyrolysis system (S4) comprising (a5) a pyrolysis chamber including a first end for receiving biomass to be pyrolyzed, and a second end from which char emerges, (b5) a heating mechanism for heating the pyrolysis chamber in a manner that maintains a thermal gradient within the pyrolysis chamber so that first vapors that are produced by the pyrolyzing near the first end are predominantly steam and so that second vapors that are produced by the pyrolyzing near the second end are predominantly hydrocarbons, (c5) a first port for collecting the first vapors, and (d5) a second port for collecting the second vapors;    (7) a method (M4) of producing liquid hydrocarbons, comprising (a6) feeding biomass into a pyrolysis chamber at a first end of the pyrolysis chamber, (b6) heating the pyrolysis chamber to pyrolyze the biomass, while maintaining a thermal gradient between the first and second ends of the pyrolysis chamber so that first vapors that are produced near the first end are predominantly steam and second vapors that are produced near the second end are predominantly hydrocarbons, (c6) collecting the first vapors from a first location in the pyrolysis chamber closer to the first end than to the second end, and (d6) collecting the second vapors from a second location in the pyrolysis chamber between the first location and the second end; and    (8) a method (M5) for producing liquid hydrocarbons, comprising (a7) harvesting plants that include seeds and stems, (b7) separating the seeds from the stems, (c7) extracting a first portion of the liquid hydrocarbons from the seeds, thus providing the first portion of the liquid hydrocarbons and a seed cake, and (d7) pyrolyzing both the stems and the seed cake, thus providing a second portion of the liquid hydrocarbons.