Apparatus and method for maintaining a urea solution in a liquid state for treatment of diesel exhaust

A system for keeping a solution of urea (16) in a liquid state comprising a tank (112) having a level sensing apparatus (124), inlet and outlet tubes (20,122) for supplying and withdrawing urea solution, and a plurality of non-contact heating elements (130) disposed in vertical relationship to one another. Preferably, the heating elements are infrared (IR) radiative coils encased in IR-transparent quartz tubes. In one embodiment, each heating element represents a horizontally defined heating zone (134). When the reservoir tank is full and predetermined temperature conditions are met, all of the heaters (128) are on, each heater irradiating its own horizontal zone (134). As zones are progressively emptied during consumption of the urea solution, as determined by the level sensor, each respective zone heater is deenergized. Because each horizontal zone is heated by a single heater, the solution is maintained at a substantially uniform temperature over the full depth of the tank without localized overheating.