Abstract: The present invention relates to a method for operating combustion process in a furnace whereby a primary fuel and a secondary fuel are burnt, to an apparatus for injecting liquid oxygen into the furnace and also to the corresponding furnace. The method comprises at least the following steps: the primary fuel and a primary oxidizer are injected into the furnace to create a primary combustion zone, liquid oxygen is injected in as secondary oxidizer such that the secondary fuel combusts with the secondary oxidizer thereby creating a distinct secondary combustion zone. The invention makes it possible for a secondary fuel having a significantly lower calorific value than the primary fuel to be burnt completely in the furnace, such that a product to be produced in the furnace has an improved quality.

Abstract: An air distillation unit comprises an air distillation column (10) suitable for producing a nominal flow of gaseous nitrogen, the top of said column being connected to a liquid nitrogen source (8), and operates by carrying out the following steps: a flow of compressed, cooled and purified air is sent to an exchanger (11) and then to the column, a flow of gaseous nitrogen is withdrawn from the column, the level of liquid at the bottom of the column is controlled; and injection liquid (20), sent from the source to the column, is no longer sent if the required production reduces to at most the nominal production. Application to the separation of air by cryogenic distillation.