by the conveyor module heater 25 by means of the dosing valve 22 the urea solution supplied via the connecting line 7 is distributed to the supply line 32 leading from the filter 24 to the injection nozzle 29 of the catalyzer 30 and to a return line 31 leading to the urea tank 1 3 as another component the conveyor module 20 comprises a control unit 23 which can control for example the pump 21 the dosing valve 22 as well as the heating system the most important function of the conveyor module heater 25 is the defrosting of liquid in the pump 21 in frost conditions so that the conveyor module heater 25 is a pump heater in the exemplary embodiment shown the conveyor module heater 25 preferably contains a ptc heating element and can be provided for example in a housing of the pump 21 or of the conveyor module 20 in the schematic presentation of fig3 the conveyor module heater 25 seems to be provided at a considerable distance from the conveyor pump 21 this schematic presentation has been chosen for better clarity however in this respect it does not correspond with the actual conditions the conveyor module heater 25 is preferably provided close to the conveyor pump 21 and has a good thermoconducting connection with the conveyor pump 21.