NOVELTY - A hydrogen system (10) comprises reformer (12), in which vaporized hydrocarbon fuel is reformed to yield reformate gas having hydrogen and a hydrogen consumer (40) arranged in fluid communication such that gas can be fed to consumer, where consumer consumes part of hydrogen produced by reformer. The system further has offgas burner (35) in fluid communication with consumer and first heat exchanger (21), in which offgas burner, when in use, remaining reformate gas in offgas from consumer is combusted, producing exhaust gas which is passed through exchanger; air pump (30); and water pump.    USE - As hydrogen system (claimed); as APU system.    ADVANTAGE - The system achieves a more efficient start-up procedure. The system allows generation of electric energy with or without utilization of produced heat energy. The system can be arranged such that a quicker start-up procedure can be carried out.    DETAILED DESCRIPTION - A hydrogen system (10) comprises a reformer (12), in which vaporized hydrocarbon fuel is reformed to yield a reformate gas containing hydrogen and a hydrogen consumer (40), where reformer and consumer are arranged in fluid communication such that reformate gas can be fed to consumer, where consumer, when in use, consumes at least a part of the hydrogen produced by the reformer. The hydrogen system further contains an offgas burner (35) which is arranged such that it is in fluid communication with the hydrogen consumer and a first heat exchanger (21), in which offgas burner, when in use, remaining reformate gas in offgas from the hydrogen consumer is combusted, producing exhaust gas which is passed through the first heat exchanger; at least one air pump (30) which is arranged such that it is in fluid communication with the reformer and the offgas burner, where the at least one air pump, when in use, supplies air to the reformer and offgas burner; and a water pump which is arranged such that it is in fluid communication with the first heat exchanger. The system further comprises a third heat exchanger (23) arranged such that, when in use, heat energy from the offgas burner can be used to heat the air flow from the air pump to the reformer; a second heat exchanger through which, when in use, the reformate gas from the reformer and the steam from the first heat exchanger and/or air from the air pump flows such that the heat energy contained in the reformate gas flow can be used to heat up the steam and/or air flow, thereby reducing the temperature of the reformate gas; a water shift reactor through which, when in use, the reformate gas flows so that carbon monoxide produced in the reformer is used to produce hydrogen and carbon dioxide. The reformer is provided with mixing space (14) and a reforming space (15). The mixing space comprises a vaporizer (16) for the vaporization of a liquid hydrocarbon fuel, a combined inlet or separate inlets (19) for supply of air and steam, and a glow plug (17) for the ignition of the mixture of hydrocarbon vapor and air during the warm-up period of the hydrogen system. The reforming space comprises a catalyst (18) and an outlet (20) for the products from the reformer. The fuel cell is a HT-proton exchange membrane (PEM) fuel cell. The hydrogen consumer comprises a PEM fuel cell or HT-PEM fuel cell. INDEPENDENT CLAIMS are included for the following:    (1) offgas burner comprising a housing with at least one inlet for air and a combustible offgas, and an outlet for exhaust gas from the offgas burner, where the offgas burner is provided with a glow plug for ignition of the combustible offgas; and    (2) method for starting up hydrogen system comprising a reformer for the production of hydrogen from a liquid hydrocarbon fuel, where the reformer is provided with mixing space and a reforming space; a hydrogen consumer arranged in fluid communication with the reformer; offgas burner for burning off reformate gas, where the off-gas burner is provided with a glow plug; and at least one air pump supplying air to the offgas burner and the reformer; a first heat exchanger arranged in fluid communication with the offgas burner such that offgas from the offgas burner can be passed through the first heat exchanger; a water pump arranged in fluid communication with the first heat exchanger such that water can be passed through the first heat exchanger, where fluid communication is provided between the first heat exchanger and the reformer for steam produced in the first heat exchanger, involving: passing the liquid hydrocarbon fuel through vaporizer and mixing the resulting hydrocarbon vapor with air in the mixing space; turning on the glow plug when the hydrocarbon fuel vaporizer has reached a predetermined temperature and thereby starting a combustion of the mixture of hydrocarbon vapor and air; continue the combustion process until the reformer catalyst inlet temperature has reached a predefined value after the combustion process is terminated by turning off the fuel supply and the glow plug; cooling down the mixing space in which the combustion process has taken place, until a predetermined temperature has been reached where self-ignition of the mixture of hydrocarbon vapor and air will not take place; turning on the glow plug in the offgas burner and the supply of liquid hydrocarbon fuel to the reformer, so that the reformer starts producing a reformate gas by catalytic partial oxidation (CPO); passing the reformate gas to the offgas burner, where the reformate gas is burned off producing heat which is used to preheat the air being fed to the reformer, where the preheating takes place in a third heat exchanger; turning on the water pump when the temperature of the first heat exchanger reaches a predetermined temperature, preferably at least 100 degrees C, so that heat energy contained in the exhaust from the offgas burner is used to produce steam; and feeding the reformer with the mixture of steam and air so that a steam reforming process starts, gradually increasing the amount of steam being fed into the reformer such that the steam reforming process gradually is converted to auto thermal reforming (ATR).    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of hydrogen system.    Hydrogen system (10)    Reformer (12)    Mixing space (14)    Reformer space (15)    Vaporizer (16)    Glow plug (17)    Catalyst (18, 36)    Inlet for air and air/steam mixture (19)    Outlet of the reformer (20)    First heat exchanger (21)    Third heat exchanger (23)    Air pump (30)    Offgas burner (35)    Outlet of burner (39)    Hydrogen consumer (40)    Inlet of the hydrogen consumer (48)    Outlet (49)    Fluid line to the vaporizer (50)    Fluid line which feeds the reformate gas from the reformer to a hydrogen consumer (62)    Fluid line connected to the inlet (64)    Control unit. (100)