Control method for adjusting the individual air/fuel ratios of the individual burners of a furnace with several burners

The control method is intended to reduce substantially the time needed at start-up to reach the optimum air/fuel ratio of all the burners of a furnace whose flue gases cannot be analysed separately for each burner. If there is an oxygen excess in the flue gas larger than a specified value (O2 1), the amount of air supplied to the burners is first reduced simultaneously for all burners, until the point of carbon monoxide formation (CO 1) is reached for a burner. The amount of air supplied to the remaining burners is reduced further simultaneously, until the point of carbon monoxide formation (CO 1) is reached again. If the O2 concentration in the flue gas has dropped far enough to fall below the specified value (O2 1), the amount of air supplied to the burners is reduced step by step for all burners one after the other. When the point of carbon monoxide formation (CO 1) has been reached, and the last step has thereupon been reversed, the size of the increments of the air reduction is reduced to a minimum. The air/fuel ratio is thus adjusted for all burners so that it is operated with a slight excess of air with respect to the point of carbon monoxide formation (CO 1).