NOVELTY - A gas (3) is heated (4) and vaporizes a subsequently-introduced liquid (5). Further heat supplied (8), vaporizes a second liquid introduction (9) downstream. The mixture enters the reaction chamber (1). Each vaporization may be partial.    USE - A means of preheating, atomizing, mixing, vaporizing and further heating of liquids introduced sequentially into a gas flow. To prepare for steam reforming of liquids, especially diesel, containing long chain hydrocarbons. The disclosure refers to a solid oxide fuel cell (SOFC) system in US 5686196-A, indicating e.g. reforming of diesel to hydrogen for use in an electric vehicle.    ADVANTAGE - The method vaporizes and further heats the diesel and steam for partial oxidative- or autothermal reforming, avoiding conditions which would cause solids to deposit. Mixing is thorough. Using the multi-stage arrangement, 400degreesC can be reached without forming high-boiling residues. Thus contamination and blockage are avoided. The interested reader may care to consult 19955892-A1 where the same corporate author reveals a related reformer reactor with design for long catalyst life and high yield.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for plant carrying out the reforming process. This includes appropriate pipework and two heat exchangers (4, 8) followed by mixing nozzles (6, 10) introducing the liquids (5, 9). Preferred features: Heat (12) added before introduction into the reaction chamber is sufficient for vaporization of all liquids, and to reach the reforming temperature. Heating the gas, takes it above the boiling temperature of the first liquid introduction. Heat addition after the second liquid introduction, brings the mixture above the boiling temperature of the second introduction (9). Second and third introductions include atomization. The gas is air and/or steam. The first liquid (5) is a hydrocarbon (especially diesel) which is liquid at normal temperatures. The second liquid is water. In the plant, there is a further heat exchanger (12) near the second mixing nozzle. The mixing nozzles each have a constriction and a duct supplying the liquid. A plate heat exchanger (4, 8, 12) construction is used.    DESCRIPTION OF DRAWING(S) - The pretreatment system is presented in a block schematic diagram. The disclosure also contains a more detailed cross section of region II of this diagram.    reaction chamber (1)    gas (3)    plate heat exchangers (4, 8, 12)    subsequently-introduced liquid (5)    mixing nozzles (6, 10)    second liquid introduction (9)