The lance of a burner includes a body that defines a first duct with first nozzles for injecting a liquid fuel and a second duct with second nozzles for injecting a gaseous fuel. Outlets of the first nozzles are spaced apart from outlets of the second nozzles. The body includes a third duct with third and fourth nozzles for injecting air. The third nozzles surround an axis of the first nozzles and the fourth nozzles surround an axis of the second nozzles.