Abstract: An air pollution control system using a novel control system is disclosed. The control system is particularly useful with a gas conditioning tower ("GCT") which uses a spray from a two-fluid nozzle to cool hot process gases prior to flowing to an electrostatic precipitator. A first control loop, employing, for example, a temperature feedback control system, is used during normal operation of the system, and an override control loop is used to protect the electrostatic precipitator from overheated gases which may be diverted in the case of a plant upset. The override control loop adjusts the spray based on a calculation of the spray characteristics needed to meet the new GCT conditioning requirements. In another aspect the present invention relates to a method and apparatus for optmizing the spray from a two-fluid nozzle used in a GCT. In particular, the spray droplets are made larger when possible, thereby reducing the energy usage of the system.