Urea supply system for a waste gas cleaning catalyst and heating insert suitable therefor

A urea supply system for a waste gas cleaning catalyst of an internal combustion engine, comprising:

• a urea tank for storing of urea solution;
• a connection line that connects the urea tank with a waste gas cleaning catalyst;
• a pump to pump urea solution via the connection line from the urea tank to the catalyst;
• a heating insert for the defrosting of frozen urea solution, the heating insert comprising at least one PTC-heating element arranged in a metal housing and a plastic casing surrounding the metal housing
• a return line that branches off the connection line and extends to the urea tank, said return line being configured and arranged in such a manner that, during operation, the urea solution discharging from the return line prevents forming an air gap between the heating insert and the frozen urea solution to be defrosted;
• and
• a defrosting vessel disposed in the urea tank, the connecting line being connected to the defrosting vessel in which a portion of the frozen urea solution in the system can be defrosted by means of the single heating insert, the portion sufficing for starting of the catalyst, and wherein the return line leads to the defrosting vessel, the defrosting vessel further including an overflow opening through which urea solution can flow from the defrosting vessel into the surrounding urea tank.